3.2.1.1. Death

No studies were located regarding death in humans and/or animals after inhalation exposure to atrazine.

3.2.1.2. Systemic Effects

No studies were located regarding systemic effects in humans or animals after inhalation exposure to atrazine.

3.2.1.3. Immunological and Lymphoreticular Effects

Altered immunological parameters have been observed in male Fischer-344 (F344) rats receiving a single 30 mg/kg intratracheal dose of atrazine (Hurbankova et al. 1996). One week after exposure, statistically significant changes included increased number of aveolar macrophages; decreased percent of active phagocytes; increased lactate dehydrogenase in bronchoalveolar lavage and serum; decreased percent of monocytes in blood; increased lactate dehydrogenase in serum; and increased acid phosphate in serum. Three months after exposure, the percent of active phagocytes and acid phosphatase levels in serum were still statistically significantly altered.

3.2.1.4. Neurological Effects

No studies were located regarding neurological effects in humans and/or animals after inhalation exposure to atrazine.

3.2.1.5. Reproductive Effects

Results of a survey of farm couples in Ontario, Canada, to assess reproductive effects of pesticides indicated an association between atrazine use in the yard with an increase in preterm delivery (Arbuckle et al. 2001; Savitz et al. 1997). Other results from this survey of Ontario farm couples indicated that atrazine was not associated with any decrease in fecundity as a result of effects on spermatogenesis (Curtis et al. 1999). In these cohort studies, it is probable that the application of atrazine involved both dermal and inhalation exposure. The men performed most of the farm activities that involved pesticide use; most of the women were indirectly exposed, possibly through contact with contaminated clothing or by consuming contaminated drinking water.

A survey of 1,898 farm couples living year-round on farms in Ontario, Canada, assessed reproductive effects of pesticides by comparing the pregnancies in which the men used pesticides during the 3 months prior to conception, to the referent group, which consisted of pregnancies in which the men had no farming or chemical activity in the 3 months prior to conception (Savitz et al. 1997). The use of atrazine as a yard herbicide, but not the use as a crop herbicide, was significantly associated with an increase in preterm delivery after adjusting for mother’s age, education, income, occupation, ethnicity, use of tobacco and caffeine during pregnancy, primary language, and month of conception (OR=4.9, 95% CI=1.6–15; OR=2.4, 95% CI=0.8–7.0, respectively). There was no significant association with crop herbicide activity and yard herbicide activity using atrazine with miscarriage (pregnancy loss before 20 weeks of gestation) (adjusted OR=1.5, 95% CI=0.9–2.4 and OR=1.2, 95% CI=0.6–2.3, respectively). The risk of small for gestational age deliveries was not increased in relation to pesticide exposure and sex ratio was not altered. Farm activities, pesticide use, and pregnancy outcome were self-reported, no specific exposure levels were available, and other pesticides were used during the period when atrazine was used; therefore, it was not possible to make a definite correlation between observed effects and atrazine exposure.

A related study of Ontario farm couples analyzed the effect of pesticide exposure on the risk of spontaneous abortion (Arbuckle et al. 2001). Exposures were considered separately for preconception (3 months before and up to 1 month of conception) and postconception (first trimester) and for early (<12 weeks) and late (12–19 weeks) spontaneous abortions. Pesticides were divided into use classes, chemical family, and active ingredient categories, and were considered separately. A total of 2,110 women provided information on 3,936 pregnancies, including 395 spontaneous abortions. The occurrence of spontaneous abortion was self-reported. The women were asked to recall how many weeks pregnant they were at the time of the incidence as well as other information considered in the study, including demographic and lifestyle information, pesticides currently and historically used on the farm and around the home, medical history, and complete reproductive history. The majority of pesticide application was done by the men; only 20% of the women reported direct handling of the pesticides. There was no significant increase in risk of early (<12 weeks) or late (12–19 weeks) spontaneous abortion (OR=1.3, 95% CI=0.8–2.0 and OR=1.1, 95% CI=0.7–1.9, respectively) in women who were exposed to atrazine prior to conception. Post-conception exposures served as the referent in assessing the importance of the timing of exposure to the risk of spontaneous abortion. Women age 35 and older who were exposed to triazines preconception had 3 times the risk of spontaneous abortion (OR=2.7, 95% CI=1.1–6.9) compared to women of the same age who were not exposed. There was no observed increased risk of spontaneous abortion associated with postconception exposure to atrazine.

Another study of 1,048 Ontario farm couples, reporting 2,012 pregnancies, was conducted during 1991–1992 to assess the influence of pesticide exposure on time to pregnancy (Curtis et al. 1999). Pesticide exposure was defined as pesticide use on the farm during the month of trying to conceive or at any time during the prior 2 months (the time in which spermatogenesis may have been affected). The study only included women who planned and became pregnant. A number of confounders were controlled for, including age when trying to conceive, ethnicity, smoking, caffeine consumption, alcohol use, diseases or drugs that may affect fertility, working at a hazardous job off the farm, recent full-term pregnancies, breastfeeding, method of contraception discontinued when beginning to attempt pregnancy, body mass index, and gestational age at pregnancy diagnosis. Atrazine was not associated with any decrease in fecundity; the adjusted odds ratios were 1.06 (95% CI=0.64–1.74) and 0.97 (95% CI=0.79–1.17) for women directly exposed to atrazine and women without direct exposure (indirect male exposure), respectively.

No studies were located regarding reproductive effects in animals after inhalation exposure to atrazine.

3.2.1.6. Developmental Effects

The results of a survey of 1,898 farm couples living year-round on farms in Ontario, Canada, designed to assess reproductive effects of pesticides, indicated that the sex ratio was not altered and the risk of small for gestational age deliveries was not increased in relation to pesticide exposure (atrazine exposure level not available) (Savitz et al. 1997). It is probable that the pesticide application resulted in both dermal and inhalation exposure.

No studies were located regarding developmental effects in animals after inhalation exposure to atrazine.

3.2.1.7. Cancer

A retrospective cohort study was conducted to investigate the mortality of workers from two triazine manufacturing plants located in Alabama (major products are agricultural chemicals including triazines) and Louisiana (major products are triazine herbicides) from 1960 to 1986 (Sathiakumar et al. 1996). Vital status of the cohort was ascertained as of January 1, 1987 from records obtained from the two plants, the Social Security Administration, the Department of Motor Vehicles, and the National Death Index. Based on job information of workers from both plants, including period of employment, job title, and work area, a subgroup of 4,917 male workers was identified as having definite/probable (n=2,683) or possible (n=2,234) triazine exposure. Overall, there were 220 deaths observed compared to 253 expected according to U.S. mortality rates (standardized mortality ratio [SMR]=87; 95% CI=75–99). Deaths from cancer were also similar to U.S. rates (SMR=106; 95% CI=76–142). Of those with definite or probable triazine exposure, the SMR (385; 95% CI=79–1124) was elevated for non-Hodgkin’s lymphoma (3 deaths observed versus 0.78 expected); however, two of the three observed deaths were males with <1 year of definite triazine-related work. Limitations of this study include young age of cohort, short duration of follow-up (median of 16 years), and the lack of control for exposure to other pesticides.

Several case-control studies were located regarding cancer incidence and exposure of humans to atrazine or to triazine herbicides in general. Although the exposure route was not specified in these studies, it is probable that inhalation (e.g., application of atrazine), dermal (e.g., handling and use of atrazine), and perhaps even oral (e.g., due to groundwater contamination) exposure occurred. Although limitations of these studies include lack of specific exposure data, recall error, small number of exposed cases and controls, and exposure to other chemicals, these studies nevertheless provide some suggestive evidence of an association between atrazine and some forms of cancer in humans.

An ecological study that assessed the correlation of the amount of atrazine (in pounds) used in 58 California counties to the incidence rates of each of several cancer types (non-Hodgkin’s lymphoma, leukemia, soft-tissue sarcoma, brain cancer, prostate cancer, and testicular cancer) found a correlation between atrazine use and some cancers in certain ethnic groups (Mills 1998). The correlation coefficients for brain and testis cancers and leukemia in Hispanic males were r=0.54, r=0.41, and r=0.40, respectively; although the 95% CI was not reported, the study author noted that the confidence interval included zero. Hispanic females had positive correlations for non-Hodgkin’s lymphoma (r=0.12) and leukemia (r=0.27); the 95% confidence intervals included zero. For prostate cancer in black males, the correlation coefficient was r=0.67 (95% CI=0.01–0.92). Limitations of this study include that no individual exposure data were available, no latency period was allowed for between potential exposure and cancer diagnosis, and there was possible exposure to a number of other pesticides.

Data from 173 adult (≥30 years of age) white men in Iowa with histologically diagnosed multiple myeloma during 1981–1984 and 650 age- and vital-status-matched white male controls were analyzed to determine the association between general farming activities and use on the farm of 24 animal insecticides, 34 crop insecticides, 38 herbicides (including atrazine), and 16 fungicides and the risk of multiple myeloma (Brown et al. 1993). Cases were identified through the Iowa Health Registry. Information on pesticide use was obtained through questionnaires and interviews, and included the first and last year the pesticide was used, whether the subject personally handled, mixed, or applied the pesticide, and whether protective equipment was used. Risks for multiple myeloma were not increased significantly for farmers who personally handled, mixed, or applied atrazine (number of cases=12; number of controls=74; OR=0.8, 95% CI=0.4–1.6).

Another case-control study of multiple myeloma and triazine use (atrazine exposure level not identified) in Iowa was conducted by Burnmeister (1990). Cases were ascertained from the State Health Registry of Iowa for males with histologically confirmed multiple myeloma who were diagnosed in 1982–1984. Information was gathered through personal interviews with farmers (n=175) and male controls who were matched for age group, vital status, and year of death (for deceased cases). A non-significant (p>0.05) increased OR of 1.29 (95% CI not reported) was found.

Results from a population-based case-control study of 201 white men (≥21 years old) in 66 counties in eastern Nebraska who had histologically confirmed non-Hodgkin’s lymphoma indicated that there was an association between atrazine use and non-Hodgkin’s lymphoma (Weisenburger 1990). Cases were identified through the University of Nebraska Lymphoma Study Group Registry and area hospitals and physicians. Controls (n=725) were selected from the same 66 counties and were matched for age, sex, race, and vital status. Based on data obtained from telephone interviews of cases and controls, it was determined that there was an elevated risk of non-Hodgkin’s lymphoma associated with atrazine use (OR=1.4, 95% CI=0.8–2.2). The risk for non-Hodgkin’s lymphoma increased with duration of atrazine use (OR=0.9, 0.8, 2.0, and 2.0 for use 1–5, 6–15, 16–20, and 21+ years, respectively.

A population-based case-control study was conducted in Iowa and Minnesota to determine the association between pesticide exposure (including atrazine) and leukemia (Brown et al. 1990). Cases of histologically confirmed leukemia, diagnosed in 1981–1984, were identified through review of records from the Iowa State Health Registry and Minnesota hospitals and pathology labs. Cases in four large Minnesota cities with little farming activity (Minneapolis, St. Paul, Duluth, and Rochester) were excluded from the study. Interviews were conducted with 578 white male farmers with leukemia (aged ≥30 years) and 1,245 white male controls who were matched for age, vital status, and state of residence to obtain data on medical history, farming practices, and pesticide use. The risk of leukemia for farmers who mixed, applied, or handled triazines (OR=1.1; 95%CI=0.8–1.5; number of cases=67; number of controls=172) or atrazine (OR=1.0; 95% CI=0.6–1.5; number of cases=38, number of controls=108) was not significantly increased.

Cantor et al. (1992) conducted a similar population-based case-control study in Iowa and Minnesota to determine whether there was an association between non-Hodgkin’s lymphoma and exposure to pesticides, including atrazine. Histologically confirmed non-Hodgkin’s lymphoma cases diagnosed during the period of 1980–1983 of white male farmers aged 30 or older were ascertained through the Iowa State Health Registry and Minnesota hospitals and pathology labs. Patients who resided in four large cities in Minnesota (Minneapolis, St. Paul, Duluth, and Rochester) at the time of diagnosis were excluded. Data were obtained through interviews of 622 farmers with non-Hodgkin’s lymphoma and 1,245 white male controls (same control group as in the Brown et al. 1990 study above) who were matched for age, vital status, and state of residence. The interviews included questions on medical history, occupational and farming practices, and pesticide use. There was no significant increase in the risk of non-Hodgkin’s lymphoma for farmers who mixed, applied, or handled triazines (OR=1.2; 95% CI=0.8–1.6; number of cases=64; number of controls=133) or atrazine (OR=1.2; 95% CI=0.9–1.8; number of cases=59; number of controls=108).

Risks of soft tissue carcinoma, Hodgkin’s disease, and non-Hodgkin’s lymphoma associated with herbicide exposure were investigated by Hoar et al. (1986). Although the study was designed to determine the association of phenoxyacetic acids with these types of cancers, exposure to triazines (but not specifically atrazine) was also considered. White male residents of Kansas with histologically confirmed soft tissue carcinoma (n=133), Hodgkin’s disease (n=132), and non-Hodgkin’s lymphoma (n=170) were identified from the University of Kansas Data Service. Cases were ≥21 years old and were diagnosed in 1976–1982. Interviews gathering detailed information on farming practices, including frequency and duration of herbicide use, were conducted with cases or their next-of-kin as well as with 948 white male controls matched for age and vital status. In addition, pesticide suppliers for 110 cases were surveyed to corroborate self-reported pesticide use. Following adjustment for age, no increased risk of soft tissue carcinoma (OR=0.9; 95% CI=0.5–1.6) or Hodgkin’s disease (OR=0.9; 95% CI=0.5–1.5) was associated with herbicide use. An odds ratio of 2.5 (95% CI=1.2–5.4) was found for non-Hodgkin’s lymphoma and exposure to triazines and other herbicides (number of cases=14; number of controls=43). After adjusting for phenoxyacetic acids or uracils, the odds ratio was reduced to 2.2 (95% CI=0.4–9.1; number of cases=3; number of controls=11).

The relationship between herbicide (neither triazine nor atrazine exposure was specified) use on farms in 66 eastern Nebraska counties and non-Hodgkin’s lymphoma was investigated by Zahm et al. (1990). Telephone interviews were conducted with 201 white males (age ≥21 years) with histologically confirmed non-Hodgkin’s lymphoma (diagnosed in 1983–1986) and 831 white male controls matched for age and vital status. Herbicide use was associated with an increased risk (OR=1.3; 95% CI=0.8–2.0) of non-Hodgkin’s lymphoma (attributed by the study authors mainly to the handling of phenoxyacetic acids).

Zahm et al. (1993a) performed a combined analysis of data gathered from three previous case-control studies of atrazine exposure and non-Hodgkin’s lymphoma: one in eastern Nebraska (Zahm et al. 1990), one in Kansas (Hoar et al. 1986), and one in Iowa-Minnesota (Cantor et al. 1992) (see above for descriptions of each of these studies). The age-adjusted ORs for farmers using atrazine were 1.4 (95% CI=0.8–2.5; 29 cases, 69 controls) for Nebraska, 1.2 (95% CI=0.8–1.8; 52 cases, 90 controls) for Iowa, 1.4 (95% CI=0.9–2.2; 36 cases, 53 controls) for Minnesota, and 2.7 (95% CI=1.2–5.9; 13 cases, 37 controls) for Kansas. In all states combined, 130 cases and 249 controls reported atrazine farm use; the age- and state-adjusted odds ratio was 1.4 (95% CI=1.1–1.8); the age-adjusted only odds ratio was 1.5 (95% CI=1.1–1.9). The risk of diffuse type non-Hodgkin’s lymphoma was higher (age- and state-adjusted OR=1.6; 95% CI=1.1–2.2) than follicular type non-Hodgkin’s lymphoma (age- and state-adjusted OR=1.3; 95% CI=0.9–1.9). Contrary to expectations, the risk of non-Hodgkin’s lymphoma in all states combined were greater among farmers who used atrazine but did not personally handle it in their practices (OR=1.6, 95% CI=1.0–2.4) than among those who did personally handle atrazine (OR=1.4, 95% CI=1.0–1.8). Adjustment for use of 2,4-dichlorophenoxyacetic acid (2,4-D) and organophosphate insecticide resulted in a large decrease of the OR for farmers in Nebraska (OR=0.7; 95% CI=0.3–1.3), a slight decrease for farmers in Minnesota (OR=1.3; 95% CI=0.8–2.2) and Kansas (OR=1.9, 95% CI=0.8–4.5), and an increase in Iowa (OR=1.6; 95% CI=0.9–2.9); the age-, state-, and 2–4-D and organophosphate insecticide use-adjusted odds ratios for all states combined was 1.2 (95% CI=0.9–1.7). For farmers in Nebraska with long-term exposure to atrazine, the age-adjusted odds ratios were 2.7 (5 cases, 8 controls) and 2.5 (7 cases, 11 controls) for 16–20 years and ≥21 years of use, respectively. However, adjustment for 2,4-D and organophosphate insecticide use decreased the odds ratios to 0.6 and 0.8 for farmers with 16–20 and ≥21 years of atrazine use, respectively. The only odds ratio that did not fall below unity was for farmers who used atrazine for more than 21 days/year; the age-adjusted odds ratio was 3.1 and the age- and 2,4-D and organophosphate use-adjusted odds ratio was 1.4; however, this frequency category only included one case and one control.

A population-based case-control study was conducted to determine the association between atrazine exposure and the risk of non-Hodgkin’s lymphoma in women who lived or worked on farms in 66 counties of eastern Nebraska (Zahm et al. 1993b). Cases were identified from the University of Nebraska Lymphoma Study Group and area hospitals. White women (age ≥21 years) with histologically confirmed cases of non-Hodgkin’s lymphoma (or their next-of-kin) and white female controls (matched for county of residence, race, vital status, and age) were interviewed to determine medical history, pesticide use, application method, use of protective equipment, and how often the pesticides were personally handled. Interviews were completed for 134 of 206 cases and 707 of 824 controls. The OR for women living on a farm where atrazine was used was 1.4 (95% CI=0.6–3.0) with 11 cases and 31 controls. For women who reported having personally used atrazine, the OR was 2.2 (95% CI=0.1–31.5, one case and two controls). Very few women examined in this study reported personally handling pesticides; indirect exposure (e.g., handling pesticide-contaminated clothing or through contaminated drinking water) to atrazine was more likely.

The association between colon cancer and triazine use was explored by Hoar et al. (1985) in a case-control study of Kansas farmers. Information on pesticide exposure was gathered via interviews with 57 histologically confirmed colon cancer cases (identified in 1976–1982) and 948 controls. Only 2 cases and 43 controls had confirmed triazine exposure (atrazine exposure not specified). An association between colon cancer and triazine exposure was not found in this study (OR=1.4; 95% CI=0.2–7.9).

Exposure of Italian female farmers to the chemical class, triazines (atrazine exposure not specified), was associated with a significant increased risk for ovarian neoplasms in a case-control study conducted by Donna et al. (1989). The women lived in an Italian province where triazine herbicides were used in farming practices. Cases were women with epithelial ovarian cancer diagnosed during the period of 1980–1985 identified from 18 area hospitals. Interviews with 65 cases and 126 female age-matched controls provided data on herbicide use, farming activity, and reproductive factors. Subjects were then classified by the authors as having definite, possible, or no exposure to herbicides. The odds ratios, adjusted for age, number of live births, and use of oral contraceptives, were 2.7 (90% CI 1.0–6.9) for those ‘definitely’ exposed (7 cases and 7 controls) and 1.8 (90% CI 0.9–3.5) for those ‘possibly’ exposed (14 cases and 20 controls).

Donna et al. (1984) conducted a hospital-based study of 60 women in Piedmont, Italy who were diagnosed between 1974 and 1980 with histologically confirmed primary mesothelial ovarian tumors. Personal interviews were conducted with cases and 127 controls diagnosed with other types of cancer to determine residence and occupational history as well as herbicide exposure (categorized as definite, probable, or no herbicide exposure). Although no data were provided specifically for atrazine or triazines, there was an increased risk of ovarian cancer with herbicide use (OR=4.4, 95% CI=1.9–16) based on 8 cases and no controls with ‘definite’ herbicide exposure and 10 cases and 14 controls with ‘probable’ herbicide exposure.

The overall evidence from epidemiological studies indicates that there is a slightly increased risk of non-Hodgkin’s lymphoma among farmers exposed to atrazine. There is also suggestive evidence of weak associations between triazine/atrazine exposure and the increased risk of prostate, breast, and ovarian cancers. Significant increases in the risk of other forms of cancer (i.e., multiple myeloma, leukemia, soft tissue sarcoma/carcinoma, and Hodgkin’s disease) were not found after exposure to atrazine or triazines.

No studies were located regarding cancer in animals after inhalation exposure to atrazine.

3.2.2.1. Death

The available information on the lethality of atrazine in humans is limited to a case report of a man intentionally ingesting 500 mL weed killer containing 100 g of atrazine, 25 g of aminotriazole, 25 g of ethylene glycol, and 0.15 g of formaldehyde (Pommery et al. 1993); the approximate amount of atrazine ingested was 1,429 mg/kg. The man exhibited coma, circulatory collapse, metabolic acidosis, and gastric bleeding, and died 3 days later. The study authors stated that some of the symptoms displayed by the patient upon hospital admission (metabolic acidosis and large anion gap) indicated that ethylene glycol was an important toxicant. Ethylene glycol was present in the blood (300 mg/L), and formic and oxalic acids were detected in the urine. The study authors also speculated that aminotriazole and possibly formaldehyde, as well as atrazine, may have contributed to the symptoms and ultimate outcome of the case.

Atrazine has a low acute toxicity in laboratory animals. Exposure of pregnant Charles River rats to 700 mg/kg/day atrazine in the commercial product, Aatrex, throughout gestation resulted in 78% mortality; the cause of death was not determined (Infurna et al. 1988). Acute oral LD₅₀ values for adult male and female rats of 1,471 and 1,212 mg/kg (Ugazio et al. 1991b) and 737 and 672 mg/kg (Gaines and Linder 1986), respectively, have been reported. An LD₅₀ of 2,310 mg/kg was reported for young (weanling) male rats (Gaines and Linder 1986), indicating a lower sensitivity to atrazine than adult rats. A significant increase in mortality was observed in female Sprague-Dawley rats exposed to 39 or 71 mg/kg/day atrazine for up to 24 months (EPA 1986; Wetzel et al. 1994); mortality was not affected in similarly exposed female F344 rats (Wetzel et al. 1994). Survival was statistically decreased in female mice receiving 247 or 483 mg/kg/day atrazine in the diet for ≥91 weeks; similar exposure of male mice did not affect mortality (EPA 1987b; Stevens et al. 1999).

Cattle that consumed an unknown quantity of spilled Aatrex (containing 76% atrazine) became ill and one became recumbent and died within 8 hours (Jowett et al. 1986). Necropsy results revealed edematous lungs and a froth in the trachea. Six other cattle died within 3 days after exhibiting anorexia, salivation, tenesmus, stiff gait, and weakness.

3.2.2.2. Systemic Effects

No studies were located regarding systemic effects in humans after oral exposure to atrazine. The highest NOAEL values and all LOAEL values from each reliable study for the systemic effects of atrazine in each species and duration category are recorded in Table 3-1 and plotted in Figure 3-1. These studies are discussed below.

Respiratory Effects. No animal studies were located that evaluated respiratory function. Mice gavaged with a single dose of 875 mg/kg atrazine (Fournier et al. 1992), sheep that consumed hay sprayed with atrazine (approximately 47 mg atrazine/kg body weight/day) for 25 days (Johnson et al. 1972), and pigs treated with 2 mg/kg/day atrazine in the feed for 19 days (Ćurić et al. 1999) had no gross or histopathological lesions of the lungs. Chronic exposure of male and female rats to up to 52 and 71 mg/kg/day atrazine, respectively, in the diet also had no gross or histopathological lung lesions (EPA 1984f, 1987d).

Cardiovascular Effects. Alterations in electrocardiograph measures and heart pathology were observed in dogs exposed to about 34 mg/kg/day in the diet for 52 weeks (EPA 1987f). Observed electrocardiographic changes consisted of slight to moderate increases in heart rate (primarily in males), moderate decreases in P-II values in both sexes, moderate decreases in PR values, slight decreases in QT values, atrial premature complexes in one female, and atrial fibrillation in both sexes. Gross postmortem examination revealed moderate to severe dilatation of right and/or left atria in the majority of animals, and some dogs had fluid-filled pericardium and enlarged heart. Atrophy and myolysis of atrial myocardium and edema of the heart were also observed in these dogs. No cardiac abnormalities were observed at 5 mg/kg/day. These cardiac effects are supported by the finding of degeneration of a small number of myocardial fibers in pigs exposed to 2 mg/kg/day atrazine in the feed for 19 days (Ćurić et al. 1999); no clinical manifestations were apparent. Female and male mice exposed to atrazine in the diet at ≥247 and 386 mg/kg/day, respectively, had an increased incidence of cardiac thrombi (EPA 1987b). In contrast, no histopathological alterations were observed in male and female rats exposed to up to 52 and 71 mg/kg/day atrazine, respectively, in the diet for 12–24 months (EPA 1984f, 1986, 1987d) or in sheep consuming hay sprayed with atrazine (approximately 47 mg atrazine/kg body weight/day) for 27 days (Johnson et al. 1972).

Table 3-1

Levels of Significant Exposure to Atrazine - Oral.

Figure 3-1

Levels of Significant Exposure to Atrazine - Oral.

Gastrointestinal Effects. No histological alterations were observed in the gastrointestinal tracts of rats exposed to 52–71 mg/kg/day for 12–24 months (EPA 1984f, 1986, 1987d) or in sheep exposed to approximately 47 mg atrazine/kg body weight/day for 25 days (Johnson et al. 1972).

Hematological Effects. Although some animal studies have reported hematological effects, the results have been inconsistent across studies. Decreases in erythrocyte, hemoglobin, and hematocrit levels and increases in mean platelet levels were observed in female rats exposed to 71 mg/kg/day atrazine in the diet for 12–24 months (EPA 1984f, 1986, 1987d). No effects were observed in female rats exposed to 35 mg/kg/day or in male rats exposed to doses up to 52 mg/kg/day. Decreases in erythrocyte and hemoglobin levels and increases in platelet counts were also seen in dogs exposed to about 34 mg/kg/day atrazine for 52 weeks (EPA 1987f); however, the study authors considered these changes to be secondary to decreased body weight. Reductions in mean erythroid parameters were noted in mice administered atrazine in the diet at >194 mg/kg/day (males) or 483 mg/kg/day (females); these alterations, however, did not correlate with any other hematological changes, and the authors suggest that they were secondarily related to decreased body weight and/or food and water consumption (EPA 1987b). No alterations in erythrocyte or platelet parameters were observed in rats exposed to 75 mg/kg/day atrazine in the diet for 3 months (Dési 1983), rats exposed to 9.8–43.1 mg/kg/day atrazine in the diet for 6 months (Suschetet et al. 1974), or sheep exposed to approximately 47 mg/kg/day atrazine in the diet for 25 days (Johnson et al. 1972).

A decrease in total white blood cell counts was observed in male and female rats exposed to 43 and 10 mg/kg/day atrazine, respectively, in the diet for 6 months; white blood cell levels were increased in female rats exposed to 71 mg/kg/day atrazine in the diet for 12 months (EPA 1984f, 1987d). No alterations in white blood cell levels were observed in male rats exposed to 52 mg/kg/day for 12 months (EPA 1984f, 1987d) or in sheep consuming hay sprayed with atrazine for 25 days (Johnson et al. 1972).

Musculoskeletal Effects. No histopathological changes were noted in skeletal muscle of male or female rats exposed to up to 52 or 71 mg/kg/day atrazine, respectively, in the diet for 12 months (EPA 1984f, 1986, 1987d) or dogs exposed to up to 34 mg/kg/day atrazine in the diet for 52 weeks (EPA 1987f).

Hepatic Effects. The available data suggest that the liver is a target of atrazine toxicity with apparent species differences in sensitivity and, therefore, in the extent of damage. Of the tested animal species, the pig appears to be the most sensitive species. Intermediate-duration exposure of pigs to 2 mg/kg/day resulted in a 350% increase in serum γ-glutamyltransferase activity and mild histopathological changes, including chronic interstitial inflammation, lymphocyte and eosinophil infiltration, and narrowing and irregular forms of bile canaliculi (Gojmerac et al. 1995). Ćurić et al. (1999) found similar histopathological changes in the livers of pigs exposed to 2 mg/kg/day for 19 days.

Alterations in clinical chemistry parameters and liver weight have been observed in rats, although strain differences have been observed. In Wistar rats receiving gavage doses of atrazine in gum arabic for up to 14 days (Santa Maria et al. 1987), dose-related increases in serum total lipids, alkaline phosphatase activity, and alanine aminotransferase activity were observed at 100 mg/kg/day. Decreases in serum glucose levels and subcellular changes including proliferation and degeneration of the smooth endoplasmic reticulum, lipid accumulation, mitochondrial malformation, and alteration of bile canaliculi were observed at 200 mg/kg/day. Significantly decreased relative liver weight was observed at 400 mg/kg/day; the decreased relative liver weight may be reflective of the decreased body weight also observed in these animals. Significant decreases in serum glucose, calcium, total triglyceride, and globulin (males only) levels, and an increase in albumin/globulin ratios (males only) were observed in male and female CD rats exposed to 52 or 71 mg/kg/day, respectively, in the diet for 12–24 months (EPA 1984f, 1986, 1987d). Significantly decreased liver weight and liver/brain weight ratio were also observed in males at 12 months); no hepatic effects were observed at 26 and 35 mg/kg/day for males and females, respectively (EPA 1984f, 1986, 1987d). Liver effects (increased relative liver weights) have also been observed in Sprague-Dawley and Donryu rats receiving gavage dose of 50 mg/kg/day, but not 5 mg/kg/day, for 28 days (Aso et al. 2000); no histological alterations were observed. No liver effects were observed in similarly exposed F344 rats (Aso et al. 2000). An increase in relative liver weight was also observed in male dogs exposed to 34 mg/kg/day atrazine in the diet for 52 weeks; no alterations in clinical chemistry parameters were observed. This study identified a NOAEL of 5 mg/kg/day. No liver effects were observed in mice receiving a single dose of up to 875 mg/kg atrazine (as the commercial product Aatrex) (Fournier et al. 1992) or sheep exposed to 47 mg/kg/day atrazine in the diet for 25 days (Johnson et al. 1972).

Renal Effects. Kidney effects have been observed in rats and pigs, but not in mice, sheep, or dogs. In male Wistar rats administered atrazine via gavage at 100 mg/kg/day or higher for 14 days, increases in urinary sodium, potassium, chloride, and protein levels, and serum lactate dehydrogenase and γ-hydroxybutyrate dehydrogenase activities (considered by the study authors to be of renal, not hepatic, origin) were observed (Santa Maria et al. 1986); this study did not identify a NOAEL. Exposure of male rats to 52 mg/kg/day atrazine in the diet for 12 months resulted in decreased kidney weight and kidney to brain weight ratios, decreased specific gravity and increased volume of urine, and increased incidence of pelvic calculi in the kidney; females exposed to 71 mg/kg/day had only increased relative kidney weight (EPA 1984f, 1986, 1987d). In this study, no renal effects were observed at 26 (males) or 35 (females) mg/kg/day. No significant alterations in kidney weight, gross pathology, or histopathology were observed in female Sprague-Dawley, F344, and Donryu rats gavaged with up to 50 mg/kg/day for 28 days (Aso et al. 2000). The rat data suggest that males may be more sensitive to the renal toxicity of atrazine than females.

Subacute glomerulitis and degeneration and desquamation of the proximal tubules were observed in female pigs receiving 2 mg/kg/day atrazine in the diet for 19 days (Ćurić et al. 1999). Female mice administered atrazine in the diet at 483 mg/kg/day for ≥91 weeks had a slight, but statistically significant, decrease in mean absolute kidney weight; however, the authors indicate that this did not correlate with any significant gross or microscopic pathology (EPA 1987b). No renal effects were observed in mice administered single gavage doses of up to 875 mg/kg/day atrazine (kidney weight and gross pathology examined) (Fournier et al. 1992), in sheep receiving gavage doses of 50 mg/kg/day for 28 days (gross and histopathology examined) (Johnson et al. 1972), or in dogs administered up to 71 mg/kg/day atrazine in the diet for 52 weeks (gross and histopathology examined) (EPA 1987f).

Endocrine Effects. Several mild to moderate endocrine effects have been observed in laboratory animals following atrazine administration, the majority of which are related to reproductive effects (see Section 3.2.2.5). The endocrine effects consisted of alterations in gland weight, histological damage in some endocrine glands, and alterations in hormone levels. A number of studies have found pituitary effects. Increased pituitary weight, hyperemia and hypertrophy, and impaired testosterone metabolism were observed in male Fischer rats administered 12 mg/kg/day atrazine by gavage for 7 days (Babic-Gojmerac et al. 1989). The levels of three testosterone metabolites (5α-androstane-3α,17β-diol, 5α-dihydrotestosterone, and androstene-3,17-dione) were decreased in the anterior pituitary, suggesting impaired metabolism of testosterone. No effects on the pituitary gland were observed at 6 mg/kg/day (Babic-Gomerac et al. 1989). Atrazine exposures of 50 mg/kg/day administered by gavage for 3 days significantly reduced serum (p<0.008) and intratesticular (p<0.005) levels of testosterone in juvenile male Sprague-Dawley rats. Given the same dose for 27 days, serum and testicular levels of testosterone were also significantly reduced (p<0.0002 and p<0.0003, respectively) (Friedmann 2002). Peripubertal Sprague-Dawley rats administered atrazine by gavage from postnatal day 22 to 47 at doses of 100 and 200 mg/kg/day had significantly reduced (p<0.05) serum and interstitial fluid testosterone concentrations (Trentacoste et al. 2001). A decrease in body weight gain was also observed in these rats. To assess whether the alterations in testosterone were directly related to atrazine or were secondary to the decreased food intake. Vehicle-gavaged rats were fed amounts of feed equivalent to that consumed by the atrazine-exposed rats. Decreases in serum testosterone concentration, androgen-dependent organ weights, and serum luteinizing hormone levels were found in the food-restricted controls.

Increased pituitary weights were observed in male rats gavaged with 120 mg/kg/day for 7 days, and then were observed for 14 days (Šimić et al. 1994). Female CD rats exposed to 71 mg/kg/day atrazine in the diet for 12 months had an increased incidence of enlarged pituitaries (EPA 1984f, 1987d). No pituitary effects were observed in the male rats. No histological alterations were observed in the pituitary of dogs exposed to 34 mg/kg/day atrazine in the diet for 52 weeks (EPA 1987f).

Possibly related to the effects on the pituitary are alterations in a number of pituitary-related and controlled hormones. Ovariectomized Long-Evans rats implanted with estrogen-filled silastic capsules (which standardizes the estrogen levels and eliminates the ovary’s influence on the pituitary) and administered 50 mg/kg/day atrazine or higher for 3 days had increased levels of pituitary prolactin and decreased serum prolactin levels (Cooper et al. 2000). The decrease in serum prolactin levels was also observed in similarly treated Long-Evan rats administered a single dose of 300 mg/kg/day (Cooper et al. 2000). In parallel studies, Sprague-Dawley rats treated in an identical manner and administered 300 mg/kg/day for 3 days had no increases in pituitary prolactin levels, but did have decreased serum prolactin levels (Cooper et al. 2000); a single dose of 300 mg/kg/day did not result in alterations in prolactin levels. Long-Evans and Sprague-Dawley rats treated similarly with 75–300 mg/kg/day for 21 days had increased pituitary prolactin, and the Long-Evans rats also had decreased serum luteinizing hormone and prolactin (Cooper et al. 2000). A significant increase in serum prolactin levels was observed in Sprague-Dawley rats exposed to 39 mg/kg/day atrazine in the diet for 9 months, but no alterations were observed after 12, 18, or 24 months of exposure (Wetzel et al. 1994). No alterations in serum prolactin levels were observed in female F344 similarly exposed to up to 45 mg/kg/day for 24 months (Wetzel et al. 1994). Wistar rat dams that received 25 mg/kg/day atrazine on lactation days 1–4 had decreased prolactin release in response to pup suckling (Stoker et al. 1999).

In the studies of ovariectomized rats supplemented with estrogen (via an implanted silastic capsule), decreases in serum luteinizing hormone levels were observed at 300 mg/kg/day in Long Evans rats receiving a single dose (Cooper et al. 2000), 50 mg/kg/day in Long Evans rats receiving daily doses for 3 days (Cooper et al. 2000), 75 mg/kg/day in Long Evans rats receiving 21 doses of atrazine (Cooper et al. 2000), and 150 mg/kg/day in Sprague-Dawley rats exposed to atrazine for 21 days (Cooper et al. 2000). In ovariectomized Long Evans rats supplemented with estrogen and gonadotropin releasing hormone, a 3-day exposure to atrazine resulted in higher blood luteinizing hormone levels than in atrazine-exposed rats not receiving gonadotropin releasing hormone (Cooper et al. 2000), suggesting that atrazine disrupts neuroendocrine regulation.

The alterations in pituitary hormones result in changes in peripheral gland hormone levels. As discussed in the Reproductive Effects section, significant increases and decreases in plasma estradiol and progesterone levels have been observed in rats following acute, intermediate, or chronic duration exposure to atrazine (Cooper et al. 1996b; Cummings et al. 2000b; Eldridge et al. 1994a; Wetzel et al. 1994).

Several studies have examined the adrenal glands following oral exposure to atrazine, and most studies did not find adverse effects. No alterations in adrenal weight and/or histopathology were observed in mice receiving a single gavage dose of 875 mg/kg/day (Fournier et al. 1992), Sprague-Dawley, F344, and Donryu rats administered 50 mg/kg/day for 28 days (Aso et al. 2000), F0, F1, and F2 albino rats exposed to up to 31 mg/kg/day atrazine in the diet (EPA 1987e), sheep exposed to up to 47 mg/kg/day atrazine for 25 days in the diet (Johnson et al. 1972), pigs that received 2 mg/kg/day in the diet for 19 days (Ćurić et al. 1999), or dogs exposed to 34 mg/kg/day atrazine in the diet for 52 weeks (EPA 1987f). Increases in adrenal weights were observed in female Sprague-Dawley and F344 rats administered by gavage 100 mg/kg/day atrazine (Eldridge et al. 1994a) and in female rats, but not males, exposed to 71 mg/kg/day atrazine in the diet for 12 months (EPA 1984f, 1987d).

The thyroid may also be a target of atrazine toxicity. It is not known whether the thyroid changes are direct results of atrazine toxicity or indirect results via atrazine effects on the regulation of pituitary hormones. A significant increase in relative thyroid weight was reported in Wistar rats dosed with 139 mg/kg/day atrazine by gavage for 3 weeks (Vos et al. 1983); because a decrease in body weight gain was also observed at this dosage, it is difficult to determine whether the increased thyroid weight was due to a direct effect of atrazine or was reflective of the decreased body weight. A decrease in serum triiodothyronine levels were observed in rats receiving gavage doses of 240 mg/kg/day atrazine for 6–12 days (Kornilovskaya et al. 1996). Histological damage to thyrocytes (decreased diameter, decreased cell height, increased), increased thyroid follicle size, and desquamation of the epithelium of the follicular cavity were also observed in these rats. No histological effects on the thyroid were reported in rats exposed to 71 mg/kg/day atrazine in the diet for 12 months (EPA 1984f, 1987d) and no alterations in thyroid stimulating hormone levels were observed in Long-Evans and Sprague-Dawley rats receiving gavage doses of atrazine for 1, 3, or 21 days (Cooper et al. 2000). No histopathological changes were seen in the thyroid and no clinical signs were observed in female cross-bred pigs administered 2 mg/kg/day atrazine in the feed for 19 days (Ćurić et al. 1999). There was no alteration in thyroid stimulating hormone levels observed in Wistar rats administered atrazine by gavage for 19 days (postnatal days 22–41) with doses of 0, 50, 100, or 200 mg/kg/day (Laws et al. 2000).

Dermal Effects. Information on the dermal toxicity of atrazine is limited to two studies that found no gross or histological abnormalities in the skin of male and female rats administered up to 52.0 and 71 mg/kg/day technical atrazine, respectively, in the diet for 12–24 months (EPA 1984f, 1986, 1987d) or in dogs that received up to about 34 mg/kg/day technical atrazine in the feed for 52 weeks (EPA 1987f).

Ocular Effects. No treatment-related ocular effects were noted in male and female rats administered up to 52 and 71 mg/kg/day technical atrazine, respectively, in the diet for 12–24 months (EPA 1984f, 1986, 1987d), in male and female mice that received up to 386 and 483 mg/kg/day technical atrazine, respectively, in the diet for ≥91 weeks (EPA 1987b), or in dogs that received up to about 34 mg/kg/day technical atrazine in the feed for 52 weeks (EPA 1987f).

Body Weight Effects. Many rat studies involving acute, intermediate, or chronic exposure to atrazine in the diet or by gavage showed mild to severe weight loss (Cantemir et al. 1997; Cooper et al. 2000; Cummings et al. 2000b; Eldridge et al. 1994a, 1999a; EPA 1984f, 1986, 1987d; Infurna et al. 1988; Peruzović et al. 1995; Pintér et al. 1990; Santa Maria et al. 1987; Šimić et al. 1994; Stevens et al. 1999; Suschetet et al. 1974; Tennant et al. 1994b; Wetzel et al. 1994). Some of these studies noted corresponding reductions in food intake (Infurna et al. 1988; Suschetet et al. 1974), and recovery following cessation of atrazine administration was noted in one study (Peruzović et al. 1995). One study in mice showed no weight loss after a single dose of up to 875 mg/kg (Fournier et al. 1992). Mice exposed to atrazine in the diet for ≥91 weeks had reduced mean body weight and percent body weight gain at ≥38 mg/kg/day (males) and ≥48 mg/kg/day (females) (EPA 1987b; Stevens et al. 1999). Mean food and water consumption was also decreased in male and female mice at ≥194 and ≥247 mg/kg/day, respectively (EPA 1987b). Rabbits exposed to 75 mg/kg/day atrazine by gavage experienced severe food intake reduction and weight loss (Infurna et al. 1988). A 1-year diet study in dogs showed that terminal body weights were 19 and 14% less than controls in males and females, respectively, exposed to 34 mg/kg/day atrazine and body weight gain was reduced by 17 and 14%, respectively (EPA 1987f). Food intake was also decreased in these dogs by a similar amount as body weight decreased (EPA 1987f).

Metabolic Effects. No studies were located regarding metabolic effects in humans or animals following oral exposure to atrazine.

3.2.2.3. Immunological and Lymphoreticular Effects

No studies were located regarding immunological and lymphoreticular effects in humans after oral exposure to atrazine.

Líšková et al. (2000) performed a variety of tests to assess the immunotoxicity of atrazine in Balb/c and C57B1/10 mice. In the plaque-forming cell assay, which tests humoral immunity by determining the integrity of three immune cells, macrophages, T cells, and B cells, administration of 100 mg/kg/day atrazine in corn oil by gavage for 10 days resulted in a 16 and 25% decrease in the number of IgM plaque-forming cells per million splenic cells as compared to saline and oil controls, respectively. Other immunological effects observed in this group of mice included a decrease in spleen cellularity and a decrease in relative thymus weight. No significant alterations were observed in politeal lymph node activation in the graft versus host and host versus graft reactions, which were used to assess the potential of atrazine to induce autoimmune disease, or the delayed-type hypersensitivity reaction. No immunological effects were observed at 20 mg/kg/day.

Female Wistar rats treated with 15 mg/kg/day atrazine for 3 weeks had decreased lymphocyte counts (Vos et al. 1983). Exposure to 139 mg/kg/day also produced increased thyroid and mesenteric lymph node weights and decreased thymus weights (Vos et al. 1983); no increases in histological abnormalities were seen. Lymphoid depletion in the lymphoid follicles of prescapular and mesenteric lymph nodes, accompanied by infiltration of eosinophilic granulocytes, was seen in female cross-bred pigs administered 2 mg/kg/day atrazine in the feed for 19 days (Ćurić et al. 1999). Lymphoid depletion was also seen in the lymph nodes of the white pulp of the spleen.

3.2.2.4. Neurological Effects

No studies were located regarding neurological effects in humans after oral exposure to atrazine.

Sixty and 90 minutes after a single oral dose of 100 mg/kg atrazine was administered to Wistar rats, the spontaneous cerebellar activity (spontaneous firing rate of Purkinje cells) was reduced to 50 and 80%, respectively, of control values (Podda et al. 1997). The evoked spike activity of Purkinje cells following stimulation of the radial nerve was almost completely abolished in atrazine-treated rats, and the amplitude of the cerebellar potentials of N2 (expression of the mossy fibers input) and CF (expression of the climbing fibers input) were reduced by 58 and 75%, respectively, 30 minutes after atrazine administration (Podda et al. 1997). Six days of oral exposure to Ceazine herbicide (used to deliver 220 mg/kg/day atrazine) resulted in decreased brain monoamine oxidase activity in Wistar rats (Bainova et al. 1979). All cerebellar activities recovered fully in 1.5–2 hours. Rats treated with up to 75 mg/kg/day atrazine in the diet for 3 months showed no differences from controls in running time to the goal (food) or number of errors in behavioral maze studies (Dési 1983).

3.2.2.5. Reproductive Effects

No studies were located regarding reproductive effects in humans after oral exposure to atrazine.

Much of the research on the reproductive toxicity of atrazine has focused on the disruption of the endocrine system and its effect on estrus cyclicity. Peruzović et al. (1995) monitored estrus cyclicity in F344 rats before, during, and after atrazine exposure, which consisted of gavage administration of 120 mg/kg atrazine (purified by recrystallization) every 48 hours for a total of 6 doses. Atrazine exposure did not affect duration or frequency distribution of the individual phases of estrus. In contrast, F344 rats exposed to 120 mg/kg/day for 7 consecutive days showed a significant decrease in the percent of females with regular ovarian cycling, an increase in the average length of diestrus (10.5 days compared to 2 days in controls), and an increase in the average number of days between treatment cessation and the first proestrus (6.2 days compared to 2.2 days in controls) (Šimić et al. 1994). Gavage dosing of 300 mg/kg/day for 3 days resulted in pseudopregnancy (defined as maintaining diestrus for ≥12 days and having elevated serum progesterone levels) in Long Evans rats; this dose also blocked the appearance of subsequent proestrus and ovulation (Cooper et al. 2000). No effect on estrus cyclicity was observed at 150 mg/kg/day. The acute data suggest that both dose and duration of exposure may be important in the atrazine-induced disruption of the estrus cycle in rats.

The intermediate-duration studies that examined atrazine-induced alterations in the estrus cycle support the findings of the acute-duration studies that the threshold of toxicity appears to be dose- and duration-related; the rat data also suggest strain differences. No statistically significant alterations in estrus cycle were observed in Sprague-Dawley, F344, or Donryu rats administered via gavage 50 mg/kg/day atrazine for 28 days (Aso et al. 2000). This study has low statistical power because of the small number of animals tested (6/group/strain). Persistent estrus was observed in one of the six F344 rats exposed to 50 mg/kg/day, one of six Donryu rats exposed to 5 mg/kg/day, and one of six Donryu rats exposed to 50 mg/kg/day. At a similar exposure duration (21 days), alterations in the estrus cycle were observed in Long-Evans and Sprague-Dawley rats administered 150 or 300 mg/kg/day atrazine via gavage (Cooper et al. 1996b). The alterations consisted of a significant increase in the percentage of days in vaginal diestrus and a significant decrease in the percentage of days in vaginal estrus (not seen in Sprague-Dawley rats dosed with 150 mg/kg/day). A study by Eldridge et al. (1994a) also investigated possible strain differences among rats exposed to atrazine for <30 days. Altered estrus cyclicity was observed at 100 mg/kg/day (lowest dose tested) in Sprague-Dawley rats and 300 mg/kg/day in F344 rats administered atrazine by gavage for 14–21 days. A long-term exposure study by Wetzel et al. (1994) identified a no effect level of 45 mg/kg/day in F344 rats following intermediate- or chronic-duration exposure. A no-effect level for estrus cycle alterations was not identified for Sprague-Dawley rats. Studies with Sprague-Dawley rats showed that as the rats aged, the effect of atrazine on the estrus cycle changed (Eldridge et al. 1999a). During the first couple of weeks of exposure to 33 mg/kg/day atrazine in the diet, an increase in diestrus was observed with no effect on the number of days in estrus. After 13–14 weeks of exposure, there was a shift in the atrazine-affected estrus cycle; the number of days in diestrus decreased and the number of days in estrus increased. This is supported by the findings of the Wetzel et al. (1994) study that significant increases in the percentage of time in estrus was seen in Sprague-Dawley rats exposed to 7 mg/kg/day atrazine in the diet for 1, 9, and 18 months, but not after 24 months of exposure.

The alterations in estrus cycle length most likely resulted from alterations in reproductive hormones. However, consistent alterations in reproductive hormone levels have not been observed across studies. In general, increases in plasma estradiol levels were associated with increases in percentage of days in estrus and increases in plasma progesterone levels were associated with increases in percentage of days in diestrus. A significant increase in plasma estradiol levels was observed in Sprague-Dawley rats exposed to 150 mg/kg/day atrazine via gavage for 14–23 days (Eldridge et al. 1994a). However, a decrease in plasma estradiol and an increase in plasma progesterone levels were observed at 300 mg/kg/day. The study authors suggested that this may reflect a diminished ability of rats in the 300 mg/kg/day group to develop mature ovarian follicles. An increase in estradiol levels was also observed in Sprague-Dawley rats exposed to 7 mg/kg/day atrazine for 3 months, but not after 1, 9, 12, 15, 18, or 24 months (Wetzel et al. 1994). In the similarly exposed F344 rats, no alterations in estradiol levels were found, and progesterone levels were not significantly altered in either strain. In the Cooper et al. (1996b) study, significant increases in plasma progesterone levels were observed in Long Evans and Sprague-Dawley rats administered 150 mg/kg/day for 21 days. Other associated effects that have been observed include decreased ovarian and/or uterine weight in rats (Eldridge et al. 1994a), and absence of corpora lutea and well-developed ovarian follicles in Long Evans rats that went into diestrus immediately after exposure initiation (Cooper et al. 1996b). Atrazine did not affect ovulation or number of ova in rats that did cycle (Cooper et al. 1996b, 2000).

Several studies have been conducted by a single group of investigators who examined the effects of atrazine ingestion in pigs (Ćurić et al. 1999; Gojmerac et al. 1996, 1999). Pigs with observed normal estrus cycles were given 0 or 2 mg/kg body weight/day atrazine in the feed for 19 days of the estrus cycle (Gojmerac et al. 1996). The last day of treatment corresponded to day (−3) of the beginning of the next expected estrus cycle. Blood samples drawn thrice daily (at 3-hour intervals beginning at approximately 9:00 a.m.) during the first 5 days after treatment cessation showed that serum estradiol and progesterone levels were significantly altered. Estradiol levels at day (−2) of estrus were normally high and increased slightly to day (−1), then declined precipitously to day 0 and remained low during estrus. Progesterone levels during this time were normally very low from day (−2) to day 0, then gradually increased through day 2. In atrazine-treated pigs, estradiol levels were approximately 45% of normal at estrus day (−2) and remained at that level through expected estrus day 2. Progesterone levels were severely elevated (approximately 16 times normal) at estrus day (−2) and increased 3-fold to estrus day 2. These changes in hormone levels were accompanied by a short-term delay in estrus onset. Histological examination of the ovaries showed multiple ovarian follicular cysts in various stages of development or regression, persisting corpus luteum, and cystic degeneration of secondary follicles in all treated pigs. Ćurić et al. (1999) exposed pigs to atrazine in a similar manner to the above study and examined the thoracic and abdominal contents grossly and microscopically 9 days after treatment cessation. Again, multiple ovarian follicular cysts in various stages of development or regression, persisting corpus luteum, and cystic degeneration of secondary follicles were seen, as well as a small number of atretic follicles and normal primary and secondary follicles. The uterus was in diestrus (uterine rest) instead of in estrus.

In a similar study, groups of nine female Swedish Landrace/Large Yorkshire cross pigs (6–7-month-old gilts) were administered 0 or 1 mg/kg/day atrazine in the feed for 19 days beginning with the onset of estrus (day 0) (Gojmerac et al. 1999). Blood samples were drawn 3 times daily at 3-hour intervals on the 5 days immediately following the final day of atrazine administration (this corresponded to the expected day of the next estrus [day 0] and 2 days before [days −1 and −2] and 2 days [days 1 and 2] after the expected estrus). Serum 17β-estradiol (E₂) concentrations in the blood samples were determined, and histopathological examination of the uterus was performed. E₂ concentrations were statistically significantly different (p<0.001) from controls on all 5 days measured. In controls, E₂ concentrations were high on days −2 and −1, then dropped on day 0 (beginning of estrus) and remained low on days 1 and 2. In treated animals, E₂ concentrations were lower than controls on days −2 and −1, and higher than controls on days 0 through 2. Treated pigs failed to exhibit overt signs of estrus onset and uterine histopathology indicated a state of uterine rest (diestrus) at the end of the observation period. A slight, but steady increase of E₂ hormone level was seen in the treated animals on day 24 of the estrus cycle (day 2). The study authors suggested that the balance of the E₂ hormone level was being gradually restored, which is the pattern that would be anticipated if the animals were about to go into estrus. Similar results were seen after administration of 0 or 2 mg/kg/day atrazine (Gojmerac et al. 1996). An intermediate-duration oral MRL of 0.003 mg/kg/day was calculated based on the LOAEL of 1 mg/kg/day in the Gojmerac et al. (1999) study.

Two studies examined the effect of atrazine on fertility. A decrease in the number of sperm positive females was seen when atrazine-exposed male and female F344 rats were mated (Šimić et al. 1994). No effect was seen when exposed males were mated with unexposed females and only a slight effect (82% sperm positive versus 100% in controls) was seen when exposed females were mated with unexposed males. No significant alterations in fertility were observed in a 2-generation rat study in which male and female Charles River albino rats were fed 27 mg/kg/day atrazine for at least 10 weeks prior to mating (EPA 1987e).

The highest NOAEL and all reliable LOAEL values for reproductive effects are recorded in Table 3-1 and plotted in Figure 3-1.

3.2.2.6. Developmental Effects

A study was conducted to assess the relationship between herbicides in the drinking water supply and intrauterine growth retardation (IUGR) (Munger et al. 1997). A survey of 856 municipal drinking water supplies in Iowa found that, in 1986–1987, the Rathbun water system contained persistently elevated levels of triazine herbicides, including atrazine; the mean level of atrazine was 2.2 μg/L compared to 0.6 μg/L in other Iowa surface water supplies. Alachlor, cyanazine, metolachlor, and 2,4-D were more frequently detected in the Rathburn water supply. A comparison of rates of low birth weight, prematurity, and IUGR in live singleton births by women in 13 communities served by the affected water system to rates in other communities of similar size in the same Iowa counties during the period of 1984–1990 showed that there was a greater risk of IUGR (relative risk=1.8; 95% CI=1.2–2.6) for the Rathbun-served communities. Multiple linear regression analyses showed that levels of atrazine (regression coefficient of 1.8, R²=0.19) as well as metolachlor (regression coefficient of 8.2, R²=0.16), cyanizine (regression coefficient of 2.05, R²=0.15), and chloroform (regression coefficient of 0.17, R²=0.12) were significant predictors of community IUGR rates in the exposed populations. Several potential confounders were controlled for in the regression analysis, including maternal smoking, mothers who received poor prenatal care, and socioeconomic variables (e.g., median income, women in the workforce, and women with a high school or greater education); however, the confounding factors were measured on an ecological, rather than an individual, level. Atrazine had the best fit (R²) in the regression model, but effects of other herbicides, which are intercorrelated, could not be ruled out. The study authors determined that there was no strong causal relationship between any single water contaminant and the risk of IUGR due, in part, to the limited ability to control for confounding factors related to source of drinking water and risk of IUGR.

The rate of birth defects was also evaluated in the Rathbun-served Iowa communities compared to other Iowa communities of similar size (Munger et al. 1992b). Birth defects were identified from the Iowa Birth Defects Registry for babies born in 1983–1989. There were excesses of cardiac defects (relative risk [RR]=3.38, 95% CI=2.07–5.48), limb reduction defects (RR=3.24, 95% CI=1.35–7.35), urogenital defects (RR=2.96, 95% CI=1.67–5.19), and all birth defects combined (RR=2.51, 95% CI=1.85–3.41) in the Rathbun communities. No significant excess of other birth defects was reported for the Rathbun communities, including cleft palate, hypertrophic pyloric stenosis, congenital dislocation of the hip, or foot deformities.

Developmental effects have been observed following pregestational, gestational, and lactational exposure of rat dams to atrazine. The observed effects included postimplantation losses, decreases in fetal body weight, incomplete ossification, neurodevelopmental effects, and impaired development of the reproductive system. In the offspring of Sprague-Dawley rats administered 70 mg/kg/day atrazine by gavage on gestational days 6–15, incomplete ossification of the skull, hyoid bone, teeth, forepaw metacarpals, and hindpaw distal phalanges were observed (Infurna et al. 1988). In a parallel study, pregnant rabbits administered 75 mg/kg/day atrazine on gestational days 7–19 had increased resorptions/litter and postimplantation losses/litter and decreased live fetuses/litter (Infurna et al. 1988). Decreased fetal body weights and nonossification of forepaw metacarpals and middle phalanges, hindpaw talus and middle phalanges, and patella were observed in the rabbit offspring. Severe maternal toxicity was also observed in the rabbits exposed to 75 mg/kg/day. No developmental effects were observed at 5 mg/kg/day. Holtzman rats exposed to 100 mg/kg/day, but not 50 mg/kg/day, atrazine on gestational days 1–8 also had increased postimplantation losses, as well as decreased serum luteinizing hormone and progesterone (Cummings et al. 2000b). Postimplantation losses were not seen at the same dose levels in Sprague-Dawley, Long-Evans, or F344 rats, although serum luteinizing hormone was decreased at 100–200 mg/kg/day (Cummings et al. 2000b). Some differences were noted between groups of rats exposed to atrazine during the afternoon (prior to the diurnal prolactin surge) and those exposed in the early morning (prior to the nocturnal prolactin surge). Narotsky et al. (2001) evaluated atrazine-induced full-litter resorption susceptibility in rats for different periods of gestation (during and after the luteinizing hormone-dependent period). Sprague-Dawley, F344, and Long Evans rats were administered 0, 25, 50, 100, 200, or 300 mg/kg/day atrazine by gavage on gestation days 6 through 10. The rats were allowed to deliver, and the number of implantation sites was recorded. F344 rats administered atrazine exhibited dose-related incidences of full-litter resorption (63, 80, and 100% at 100, 200, and 300 mg/kg/day, respectively). F344 rats exposed to 200 mg/kg atrazine that maintained their litters had increased prenatal loss, decreased litter size, and reduced pup weights (Narotsky et al. 2001).

No developmental effects were noted in a 2-generation study in which Charles River albino rats were exposed to 31 mg/kg/day atrazine in the diet (EPA 1987e). No alterations in the number of pups per litter or weaning weight of pups were observed in the offspring of four rats (strain not specified) exposed to up to 113 mg/kg/day atrazine in the diet on gestational days 1–21 (Peters and Cook 1973).

Studies by Peruzović et al. (1995) and Stoker et al. (1999, 2000) examined the effect of pregestational or lactational exposure to atrazine on the development of the nervous and reproductive systems. In the Peruzović et al. (1995) study, female Fischer rats were administered via gavage 0 or 120 mg/kg purified atrazine every 48 hours for 12 days. Four weeks after the cessation of treatment, rats were mated with untreated males and allowed to carry to term and deliver pups. Litter size, pup weight, and pup survival were not statistically different between control and treated groups. At 70 days of age, the offspring were tested for spontaneous activity by recording ambulatory activity in 4 time blocks of 15-minutes each. Avoidance response was tested at 72 days of age and extinction response was tested at 73 days of age. Mild neurobehavioral effects were observed and differences were noted between male and female offspring. Female offspring of atrazine-treated dams had a statistically significant (p<0.05) higher spontaneous activity level than the female offspring of control dams during the first 15 minute block; no differences were seen between groups of male offspring. In the avoidance conditioning trials, male offspring of treated dams had statistically significant (p<0.05) shorter latency times and increased number of avoidances, compared to control offspring. Conversely, female offspring of atrazine-treated dams had longer latency times and decreased number of avoidances, compared to controls, but without statistical significance. No statistical differences between treated and control groups were seen in the extinction tests (Peruzović et al. 1995).

Adult male offspring of Wistar rat dams administered up to 50 mg/kg/day atrazine on lactational days 1–4 had increased incidence and severity of inflammation of the lateral prostate, increased myeloperoxidase levels in the prostate, and increased total DNA in the prostate (Stoker et al. 1999). These effects are hypothesized to be indirect effects mediated by a lack of prolactin release in the dam in response to pup suckling; this hypothesis was supported in this study by the elimination of increased prostate inflammation in the offspring in response to co-administration of prolactin with atrazine to the dams. The level of myeloperoxidase, a lysosomal enzyme found primarily in neutrophils and macrophages, was used as an indication of the severity of inflammation. Histological examination also found increases in the incidence of focal luminal polymorphonuclear inflammation and focal interstitial mononuclear inflammation in lateral prostates at 120 days of age in the 25 and 50 mg/kg groups. Offspring of rat dams receiving atrazine on lactational days 6–9 had only statistically insignificant increases in prostate inflammation, and offspring of dams receiving atrazine on lactational days 11–14 had no increase in prostate inflammation (Stoker et al. 1999).

Male rats exposed to 50 mg/kg/day atrazine or higher on postnatal days 23–53 had decreased ventral prostate weights and delayed preputial separation, which is a marker of male puberty in the rat (Stoker et al. 2000). Dose-related increases in serum estrone and estradiol concentrations and serum triiodothyronine were only significant in rats exposed to 200 mg/kg/day. No histopathological changes were seen in the thyroid and only mild hypospermia was seen in some high-dose rats, which may be a result of delayed puberty.

Studies by Laws et al. (2000) and Ashby et al. (2002) investigated the effect of peripubertal exposure to atrazine on the reproductive development of female rats. Female Wistar rats exposed to 50, but not 25, mg/kg/day atrazine from 20 to 41 days of age had delayed vaginal opening, which is a marker of female puberty in the rat (Laws et al. 2000). The age of the first 4–5-day estrus cycle after vaginal opening was also delayed; estrus cycles were normal within 3–4 weeks after cessation of atrazine exposure (Laws et al. 2000).

Ashby et al. (2002) administered atrazine to female Wistar and Sprague-Dawley rats at doses of 10, 20, 30, and 100 mg/kg/day on postnatal days 21–46. Delayed uterine growth was observed in female Wistar rats exposed to 100 mg/kg/day of atrazine at postnatal days 30 and 33, but was normal by postnatal day 43. Uterine weights in Sprague-Dawley rats were unaffected by day 46 (Ashby et al. 2002). Vaginal opening was significantly delayed in Sprague-Dawley rats exposed to atrazine at 30 and 100 mg/kg/day and in Wistar rats at 100 mg/kg/day by postnatal day 46 (Ashby et al. 2002).

3.2.2.7. Cancer

An ecological study in Ontario, Canada, that examined the association of atrazine in the drinking water supply with cancer incidence rates found a positive association between atrazine levels and stomach cancer (p=0.046 and p=0.242 for males and females, respectively) (Van Leeuwen et al. 1999). For men, this corresponded to an observed increase of 0.6 cases of stomach cancer per 100,000 person-years at risk for each 100 ng/L increase in atrazine levels in drinking water. For women, for each 50 ng/L increase in atrazine levels in drinking water, there was an observed increase of 1.0 stomach cancer cases per 100,000 person-years at risk. Statistically significant (p≤0.04) negative associations were noted between atrazine levels and colon cancer in males and females; it was not ascertained what may have caused this result. There were no statistically significant associations between atrazine exposure and ovarian cancer or non-Hodgkin’s lymphoma in females. In males, there was a negative association between atrazine exposure and non-Hodgkin’s lymphoma, but the association was not statistically significant (p=0.075). Data were collected and analyzed for ecodistricts; no individual data were used or provided. The average atrazine contamination level was 162.74 ng/L (range of 50–649 ng/L) and potential confounding variables, including alcohol consumption, smoking, education level, income, and occupational exposures, were considered.

An association between exposure to triazines and breast cancer incidence rates in women was found in an ecological study conducted in 120 Kentucky counties (Kettles et al. 1997). Two-year age-adjusted breast cancer rates for 1991–1992 and 1993–1994 were calculated from state registry data. Although atrazine levels were unavailable, it is likely that much of the triazine exposure was due to atrazine since it is the most widely used herbicide in Kentucky. Triazine exposure data were generated using estimated exposures based on water contamination (the mean triazine level in groundwater was 0.11±0.19 μg/L), county corn crop production (in acres), and county pesticide use. Based on these data, the Kentucky counties were classified as having low, medium, or high exposure levels. Confounding variables, including age, race, income, and education level, were controlled for. Breast cancer risk based on 1993–1994 breast cancer rates was significantly increased in women in counties having medium (OR=1.14; 95% CI=1.08–1.19) and high (OR=1.2; 95% CI=1.13–1.28) triazine exposure levels.

Another ecological study was conducted in Kentucky (120 counties) to examine the association between atrazine in the drinking water and incidence of breast and ovarian cancers (Hopenhayn-Rich et al. 2002) in 1993–1997. Data were obtained from state records on ovarian and breast cancer age-adjusted incidence rates, amount of atrazine in drinking water (mean concentration in all 120 counties ranged from 0.21 to 1.39 μg/L), pounds of atrazine sold, and acres of corn planted. No significant association was found between atrazine exposure and the incidence of breast or ovarian cancer in Kentucky women. The race- and education-adjusted rate ratios for women with the highest atrazine exposure were 0.96 (95% CI=0.92–1.01) and 0.85 (95% CI=0.73–0.98), respectively. Similar results were found when acres of corn planted and atrazine sales by geographic location were used as surrogates for atrazine exposure.

A number of animal studies have examined the carcinogenic potential of atrazine in animals. In F344/LATI rats administered atrazine via the diet, significant increases in the number of rats with malignant tumors and total benign mammary gland tumors were observed in male rats exposed to 65 mg/kg/day (Pintér et al. 1990). However, no significant increase was seen in any specific tumor type. It is likely that the mammary tumors were an effect of increased survival of treated rats rather than dietary atrazine administration. Thakur et al. (1998) noted that six of eight high-dose mammary tumors appeared after the last control died at week 111 and that the increase in mammary tumors in treated male rats was not significant when adjusted for survival. Female rats receiving a dietary level of 65 mg/kg/day had statistically significant increased incidences of leukemia/lymphoma (22/51 versus 12/44 in controls) and uterine adenocarcinoma (13/45 versus 6/45 in controls). The overall proportion of benign and malignant uterine tumors in treated females was similar to controls (16/45, 19/52, and 17/45 for 0, 32, and 65 mg/kg/day, respectively). In addition, it was pointed out that the female leukemia/lymphoma data should not have been combined because these two cancer types are of different origins in Fischer rats; when the tumor types were separated, there was no longer a significant trend in treated rats (Thakur et al. 1998). Another study of Fischer rats found no significant increases in the incidences of mammary or pituitary tumors after two years of dietary exposure to doses as high as 45 mg/kg/day (Wetzel et al. 1994).

In contrast, several studies have found increases in tumor incidences in female Sprague-Dawley rats. Three of these studies were submitted to EPA as confidential business information and are not publicly available; reviews of these studies were published by Stevens et al. (1994, 1999). As reported by Stevens et al. (1994, 1999), two of these studies found significant increases in the incidence of mammary fibroadenomas in female Sprague-Dawley rats exposed to 71–80 mg/kg/day via the diet for 106 weeks or a lifetime; no significant alterations were found at 35 mg/kg/day and lower. The third study, a two-generation study, did not find significant alterations in the incidence of mammary tumors in F2 females after 2 years of exposure to ≤40 mg/kg/day in the diet. Additionally, one study found an increase in mammary adenocarcinomas following 106 weeks of dietary exposure to ≥5 mg/kg/day. An increase in interstitial cell tumors were observed in the testes of Sprague-Dawley rats following lifetime exposure to 52 mg/kg/day in the diet; this was attributed to increased survival in this group. Wetzel et al. (1994) found similar results in female Sprague-Dawley rats. In this study, statistically significant increases in earlier onset of mammary and pituitary tumors were observed in animals killed or dying during the first 54 weeks of exposure to 39 mg/kg/day; these effects were not noted in rats exposed to 7 mg/kg/day (Stevens et al. 1999; Wetzel et al. 1994). No significant alterations in the incidence of mammary or pituitary tumors were found between weeks 55 and 105. There were no significant increases in malignancies in any treatment group for the entire study period (0–105 weeks), likely due to age-related increases in tumors in the controls. Mammary and pituitary tumors appeared earlier in rats treated with atrazine, apparently due to the mechanism of reproductive senescence in Sprague-Dawley rats (see Sections 3.5.2 and 3.5.3).

Another unpublished study discussed by Stevens et al. (1999) compared the carcinogenicity of atrazine in ovariectomized and intact female Sprague-Dawley rats exposed to atrazine in the diet for 2 years. Significantly increased mortality was noted in intact rats at 32 mg/kg/day, but mortality was not significantly affected in ovariectomized rats at the same exposure level. Intact rats had increased incidences of mammary carcinomas at 4 and 32 mg/kg/day (but not at 2 or 6 mg/kg/day) and mammary fibroadenomas at ≥4 mg/kg/day. No mammary tumors were found in any treated ovariectomized rats.

Two unpublished studies of male and female CD-1 mice reviewed by Stevens et al. (1999), did not find significant increases in the incidence of neoplastic changes in males exposed to 386 mg/kg/day or females exposed to 483 mg/kg/day in the diet for ≥91 weeks. Similarly, no significant alterations in tumor incidences were observed in mice administered by 22 mg/kg/day atrazine by gavage in a 0.5% gelatin vehicle from 7 days old until 4 weeks old and then in the diet with no vehicle for 18 months (Innes et al. 1969).

The available oral carcinogenicity data in animals suggest that high doses atrazine in the diet result in an increased incidence and earlier onset of mammary tumors in female Sprague-Dawley rats as compared to age-matched controls; however, these effects are not found in similarly exposed female Fischer 344 rats or CD-1 mice.

CEL values from each reliable study in each species and duration category are recorded in Table 3-1 and plotted in Figure 3-1.

3.2.3.1. Death

No studies regarding death in humans following dermal exposure to atrazine were located.

The acute (14-day) dermal LD₅₀ in rats has been reported to be >2,500 mg/kg/day (Gaines and Linder 1986).

3.2.3.2. Systemic Effects

No studies were located regarding respiratory, cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, endocrine, ocular, and body weight effects in humans and/or animals after dermal exposure to atrazine.

Dermal Effects. A 40-year-old white male farmer developed blisters on his hands and forearms one afternoon after having applied atrazine to crops in the morning using a spray rig and cleaning the plugged nozzles several times with his hands (Schlicher and Beat 1972). By 14 hours later, both hands and forearms had painful erythematous eruptions with blistering and swelling. The diagnosis was acute contact dermatitis, and treatment resulted in complete recovery. The farmer had also applied a second herbicide (Bladex=2-[4-chloro-6-ethylamino-s-triazin-2-ylamino]-2-methylpropionitrile) in the same afternoon; therefore, the exact cause of the dermatitis was not discernable.

3.2.3.3. Immunological and Lymphoreticular Effects

No studies were located regarding immunological and lymphoreticular effects in humans and/or animals after dermal exposure to atrazine.

3.2.3.4. Neurological Effects

No studies were located regarding neurological effects in humans and/or animals after dermal exposure to atrazine.

3.2.3.5. Reproductive Effects

Results of a survey of farm couples in Ontario, Canada, to assess reproductive effects of pesticides indicated weak to moderate associations between atrazine use on crops and in the yard with an increase in preterm delivery and with miscarriage (Arbuckle et al. 2001; Savitz et al. 1997). Other results from this survey of Ontario farm couples indicated that atrazine was not associated with any decrease in fecundity as a result of effects on spermatogenesis (Curtis et al. 1999). In these cohort studies, it is probable that the application of atrazine involved both inhalation and dermal exposure; most of the women were indirectly exposed, possibly through contact with contaminated clothes or contaminated drinking water (for additional study details, see Section 3.2.1.5 Inhalation Reproductive Effects).

No studies were located regarding reproductive effects in animals after dermal exposure to atrazine.

3.2.3.6. Developmental Effects

The results of a survey of 1,898 farm couples living year-round on farms in Ontario, Canada, designed to assess reproductive effects of pesticides, indicated that the sex ratio was not altered and the risk of small for gestational age deliveries was not increased in relation to pesticide exposure (atrazine exposure level not available) (Savitz et al. 1997). It is probable that the pesticide application resulted in both dermal and inhalation exposure.

No studies were located regarding developmental effects in animals after dermal exposure to atrazine.

3.2.3.7. Cancer

Several studies were located regarding cancer incidence and exposure of humans to atrazine. Although the exposure route was not specified in these studies, it is probable that dermal (e.g., handling and use of atrazine), inhalation (e.g., application of atrazine), and perhaps even oral (e.g., due to groundwater contamination) exposure occurred. These population-based case-control studies found some suggestive evidence of positive associations between atrazine use and brain, testes, and prostate cancers (Mills 1998), leukemia (Mills 1998), and non-Hodgkin’s lymphoma (Mills 1998; Weisenburger 1990; Zahm et al. 1993b). Limitations of these studies included small sample sizes, lack of specific exposure data, and exposure to chemicals other than atrazine. Further details on these studies can be found in Section 3.2.1.7.

No studies were located regarding cancer in animals after dermal exposure to atrazine.

3.4.1.1. Inhalation Exposure

No studies were located that measured absorption or monitored metabolites in excreta of humans or animals exposed to atrazine only via the respiratory route. The only available inhalation toxicity studies involved exposure to very large atrazine particles (30–70 μm) (Catenacci et al. 1990, 1993), which made it unlikely that any significant amount of atrazine reached the lungs.

3.4.1.2. Oral Exposure

Absorption of atrazine in humans following oral exposure was indicated in a single case report of a 38-year-old man who died of progressive organ failure and shock 3 days after ingesting 500 mL of a weedkiller that contained 100 g atrazine, 25 g of aminotriazole, 25 g of ethylene glycol, and 0.15 g of formaldehyde (Pommery et al. 1993). At autopsy, atrazine was detected in the kidney, small intestine, lung, liver, pancreas, muscle, heart, and plasma.

In rats gavaged with a single dose of 30 mg/kg [¹⁴C]-atrazine in aqueous solution, radioactivity levels in plasma peaked 8–10 hours postdosing (Timchalk et al. 1990). The absorption of radioactivity (K_a) was described as a first-order process and was used to calculate an absorption half-life of 2.6 hours. Approximately 66% of the administered radioactivity was excreted in the urine over a 72-hour monitoring period. About half of this amount appeared in the urine within the first 12 hours after dosing, and an additional 20% was detected within the next 12 hours. Over the 72-hour monitoring period, about 18% of the administered radioactivity was detected in the feces, suggesting that total absorption amounted to 82% of the administered does (100% minus 18% in the feces). In a similar study, Meli et al. (1992) administered a singe dose of 50 mg/kg of atrazine in dimethylsulfoxide (DMSO) and recovered approximately 37% of the administered dose in the urine over a 96-hour period. Most of the dose was absorbed within the first 24 hours. The reason for the apparent discrepancy in the amounts absorbed (as determined only by urinary excretion) between the two studies is unknown, but it is possible that the different vehicles may have played a role.

3.4.1.3. Dermal Exposure

Data regarding dermal exposure to atrazine in humans indicate that limited absorption occurs. Buchholz et al. (1999) applied dermal patches containing ring-radiolabeled atrazine mixed with the commercial atrazine product Aatrex to the forearms of 10 healthy male subjects for 24 hours. Unabsorbed radioactivity and the radioactivity excreted in urine and feces were measured for the 7-day period including and following the application. Quantitative data presented for three subjects indicate that 91–94% of the applied dose was not absorbed. Only 0.3–5.1% of the applied dose was absorbed as monitored by the radioactivity recovered in the urine and feces. An in vitro study using human skin samples exposed to [¹⁴C]-atrazine found that approximately 16.4% was absorbed in a 24-hour period, and that most of the absorbed atrazine (12% of the applied dose) remained in the skin (Ademola et al. 1993). Less than 5% progressed through the skin and into receptor fluid. Dermal absorption of atrazine in humans has also been indicated by occupational studies that found atrazine and its metabolites in the urine of workers exposed primarily via dermal contact (Catanacci et al. 1990, 1993).

A single study in rats compared the dermal absorption of [¹⁴C]-atrazine in young and adult rats (Hall et al. 1988) by measuring the fractional skin penetration (radioactivity in the body, skin, and excreta divided by the total radioactivity recovered in the body, skin, excreta, and unabsorbed atrazine on the application blister). The fractional skin penetration values indicated slightly higher absorption in young rats (3.2–9.6%) than in adult rats (2.8–7.7%), and decreased percent absorption with increasing atrazine dose. It is unclear what caused the difference in absorption between young and adult rats; skin thickness was almost identical in the two groups and, therefore, was not a factor. No data are available on the transport mechanism of atrazine in skin. Dermal absorption may be limited by saturation of the transport mechanism or by physical/chemical restrictions and interactions; this hypothesis is supported by an in vitro study showing a percentage decrease in metabolite formation with increasing atrazine dose to human skin samples (Ademola et al. 1993).

3.4.2.1. Inhalation Exposure

No studies were located regarding distribution of atrazine after inhalation exposure in humans or animals.

3.4.2.2. Oral Exposure

Data on distribution of atrazine in humans after oral exposure were limited to a single case report of a 38-year-old man who died of progressive organ failure and shock 3 days after ingesting 500 mL of a weedkiller that contained 100 g atrazine, 25 g of aminotriazole, 25 g of ethylene glycol, and 0.15 g of formaldehyde (Pommery et al. 1993). At autopsy, atrazine was detected in the kidney, small intestine, lung, liver, pancreas, muscle, heart, and plasma. The highest concentration was found in the kidney and the lowest concentration was found in the heart.

In male Fischer rats that received a single dose of 30 mg/kg [¹⁴C]-atrazine by gavage, plasma levels of radioactivity peaked at 8–10 hours postdosing and the rate of clearance was apparently first-order with a half-life of 10.8–11.2 hours (Timchalk et al. 1990). Radioactivity was also determined for the whole skin and for the rest of the carcass and found to be 1.5 and 4%, respectively, of the administered dose.

In rats administered about 1.5 or 17.7 mg/kg [¹⁴C]-atrazine by gavage, the majority of the radioactivity was recovered in the urine (65.5%) and feces (20.3%) over the course of 8 days (Bakke et al. 1972). The whole carcass contained 15.8% of the radioactivity 3 days after exposure, and radioactivity was detected in liver, brain, heart, lung, kidney, digestive tract, omental fat, and skeletal muscle on days 2, 4, and 8. Fate and skeletal muscle had the lowest amount of radioactivity, whereas the liver and kidney had the highest amounts. In all of the organs monitored, the levels of radioactivity decreased over time.

3.4.2.3. Dermal Exposure

No studies were located regarding distribution of atrazine after dermal exposure in humans or animals.

3.4.4.1. Inhalation Exposure

No studies were located regarding the elimination and excretion of atrazine following inhalation exposure in humans or animals.

3.4.4.2. Oral Exposure

No studies were located regarding the elimination and excretion of atrazine following oral exposure in humans.

Male F344 rats administered 30 mg/kg of [¹⁴C]-atrazine by gavage eliminated 93% of the administered radioactivity within 72 hours (Timchalk et al. 1990). The primary route of excretion was in urine (67%); 36 and 21% of the administered radioactivity was eliminated in the 0–12- and 12–24-hour postexposure intervals, respectively. Fecal excretion accounted for 18% of the administered radioactivity. The elimination of atrazine from plasma followed first-order kinetics and the elimination half-life was calculated to be 10.8 hours (Timchalk et al. 1990). In rats that received a single dose of 50 mg/kg atrazine by gavage, atrazine and its metabolites were present in urine 24 hours postexposure and at 48 hours at a fraction of the 24-hour level (Meli et al. 1992).

3.4.4.3. Dermal Exposure

Doses of 0.167 mg (6.45 μCi) or 1.98 mg (24.7 μCi) of [¹⁴C]-atrazine were applied to 25 cm² of the forearm of healthy males for 24 hours (Buchholz et al. 1999). Urinary excretion varied widely, accounting for 72, 30, and 3.5% of radioactivity absorbed by one low-dose and two high-dose individuals, respectively. Fecal excretion also varied, accounting for 11.5, 4.2, and 0%, respectively, of the absorbed radioactivity.

Urine was collected from six male workers at an atrazine production plant for 24 hours during and after an 8-hour workshift and analyzed for atrazine and atrazine metabolites (Catenacci et al. 1993). Fifty percent of the atrazine-related compound detected in the urine during the 24-hour period was excreted in the first 8 hours. A related study that measured only atrazine found that urinary levels were highest during and immediately after workshifts; levels 12 hours after the end of the workshift were one-tenth of the levels during the workshift (Catenacci et al. 1990).

3.4.4.4. Other Routes of Exposure

Lu et al. (1997b) examined the atrazine levels in the saliva of rats continuously infused with atrazine through a cannula in the femoral vein. Salivary rates were stimulated and controlled with intravenous injections of pilocarpine. Salivary and plasma levels of atrazine were simultaneously monitored over 200–300 minutes. Salivary atrazine levels remained relatively constant over a range of salivary flow rates, and the salivary/plasma concentration ratio remained fairly constant with changing salivary flow rates and plasma atrazine concentrations. The salivary atrazine concentration was found to be highly correlated with the plasma atrazine concentration.

Biomarkers of Exposure and Effect

Exposure. Atrazine is primarily excreted in the urine as dealkylated metabolites and mercapturic acid derivatives (Bakke et al. 1972; Buchholz et al. 1999; Catenacci et al. 1993; Gojmerac and Kniewald 1989; Meli et al. 1992; Timchalk et al. 1990), which can be detected in urine at levels as low as 1 μg/L (Ikonen et al. 1988). Atrazine and its metabolites can also be detected in blood and tissues at levels as low as 14.25 ng/g (Pommery et al. 1993). The detection of atrazine in urine or tissues may be a specific biomarker for atrazine exposure, but <2% of atrazine is excreted in the urine unchanged (Buchholz et al. 1999; Catenacci et al. 1993). The detection of atrazine metabolites is not necessarily specific for atrazine exposure, but may indicate exposure to other triazine herbicides such as cyprazine, simazine, or propazine (Bradway and Moseman 1982; Hanioka et al. 1999; Larsen and Bakke 1975). There is no quantitative relationship between exposure levels and levels of atrazine or metabolites found in the body or in urine (Lucas et al. 1993). Additional studies are needed to establish a relationship between exposure level and urinary concentration of atrazine metabolites.

Effect. The primary target organs of atrazine are the female reproductive system and the liver. The reproductive effects in animals included altered estrus cyclicity or anestrus (Cooper et al. 1996b, 2000; Ćurić et al. 1999; Eldridge et al. 1994a, 1999a; Gojmerac et al. 1996, 1999; Šimić et al. 1994; Wetzel et al. 1994), altered serum and/or pituitary hormone levels (Cooper et al. 1996b; Eldridge et al. 1994a; Gojmerac et al. 1996, 1999), reduced fecundity (Šimić et al. 1994), ), increased litter resorption (Narotsky et al. 2001), decreased ovarian and uterine weights (Ashby et al. 2002; Eldridge et al. 1994a), and ovarian histopathology (Ćurić et al. 1999; Gojmerac et al. 1996). The hepatic effects seen following atrazine exposure were increased serum lipids and liver enzymes (Gojmerac et al. 1995; Morichetti et al. 1992; Radovcic et al. 1978; Santa Maria et al. 1987; Wurth et al. 1982), liver histopathology (Ćurić et al. 1999; Gojmerac et al. 1995), changes in liver weight (Aso et al. 2000; EPA 1984f, 1987d, 1987f), and changes in trigycerides and globulin levels (EPA 1984f, 1987d). While all of these effects may be useful biomarkers to indicate possible atrazine exposure, none are specific for atrazine. Additionally, it is unclear which, if any, of the above reproductive effects may occur in humans following atrazine exposure. Development of additional, more sensitive biomarkers that are specific for atrazine effects would be useful in monitoring populations at high risk. This may need to be done in tandem with the determination of the interaction of atrazine, if any, with the hypothalamus in humans and the elucidation of the mechanism of that interaction.

Absorption, Distribution, Metabolism, and Excretion. The absorption, distribution, metabolism, and excretion of atrazine has been investigated in humans and animals. The only available inhalation toxicity studies in humans involved occupational exposure to very large atrazine particles (30–70 μm) (Catenacci et al. 1990, 1993), which made it unlikely that any significant amount of atrazine reached the lungs. Evidence of absorption following oral exposure was provided by a single case report of a man who ingested a weedkiller containing atrazine and other chemicals; atrazine was detected in the plasma and several organs at autopsy (Pommery et al. 1993). Absorption of atrazine following dermal exposure has been evidenced by the presence of atrazine and its metabolites in urine of people exposed to radiolabelled Aatrex (a commercial product containing atrazine) via a forearm patch (Buchholz et al. 1999), and in urine of workers exposed primarily via dermal contact (Catenacci et al. 1990, 1993). An in vitro study using human skin samples also indicated that limited absorption (16.4% in 24 hours) occurs through the skin (Ademola et al. 1993). Further evidence of absorption following oral (Meli et al. 1992; Timchalk et al. 1990) and dermal (Hall et al. 1988) exposure to atrazine has been provided by animal studies showing the presence of atrazine and its metabolites in the plasma, urine, and/or feces. Absorption following gavage administration has been described as a first-order process with an absorption half-life of 2.6 hours (Timchalk et al. 1990), with 37–57% of the administered dose recovered in the urine and 14% in the feces (Meli et al. 1992; Timchalk et al. 1990). Animal studies to determine the absorption efficiency of inhaled atrazine would be useful for determining the risk to occupationally exposed individuals.

Data on distribution of atrazine in humans after oral exposure was limited to a single case report of a 38-year-old man who died of progressive organ failure and shock 3 days after ingesting 500 mL of a weedkiller that contained 100 g atrazine, 25 g of aminotriazole, 25 g of ethylene glycol, and 0.15 g of formaldehyde (Pommery et al. 1993). At autopsy, atrazine was detected in the kidney, small intestine, lung, liver, pancreas, muscle, heart, and plasma. Radioactivity was detected in the plasma, whole skin, and carcass of rats gavaged with 30 mg/kg [C¹⁴]-atrazine (Timchalk et al. 1990), and in the liver, brain, heart, lung, kidney, digestive tract, omental fat, and skeletal muscle of rats gavaged with up to 17.7 mg/kg [C¹⁴]-atrazine (Bakke et al. 1972). Animal studies to determine the distribution following inhalation and dermal exposure to atrazine would be useful for evaluating the exposure and risk of occupationally exposed individuals.

Atrazine is extensively and rapidly metabolized as indicated by plasma levels of atrazine and the relative amounts of metabolites and parent compound in the urine within 8–24 hours after exposure. Plasma levels of ¹⁴C from radiolabeled atrazine have been shown to peak at 8–10 hours postexposure in rats, and the rate of clearance half-life has been calculated to be 10.8–11.2 hours (Timchalk et al. 1990). In urine, unchanged atrazine has been detected, but comprised <2% of all atrazine-related compounds after dermal exposure in humans (Buchholz et al. 1999; Catenacci et al. 1993) or oral exposure in rats (Meli et al. 1992). In humans, 50% of all urinary atrazine metabolites were excreted within 8 hours and 100% within 24 hours (Catenacci et al. 1993). In rats, approximately 57% of the radioactivity from administered [¹⁴C]-atrazine was excreted in the urine within 24 hours (Timchalk et al. 1990), and urinary atrazine metabolites decreased to 1/30 or less of the 24-hour level by 48 hours postexposure (Meli et al. 1992).

Atrazine is primarily metabolized in humans via dealkylation, probably followed by glutathione conjugation and conversion to mercapturic acids. This is apparently true regardless of route of exposure (Buchholz et a. 1999; Catenacci et al. 1993; Meli et al. 1992; Timchalk et al. 1990). In vitro studies using microsomal preparations from liver and other tissues of humans and animals have indicated that dealkylation of atrazine is mediated by cytochrome P-450 enzymes (CYPs) (Adams et al. 1990; Ademola et al. 1993; Croce et al. 1996; Hanioka et al. 1998a, 1999; Lang et al. 1996, 1997; Meli et al. 1992; Venkatesh et al. 1992). In humans, the primary CYP responsible for phase I metabolism is probably CYP1A2 (Lang et al. 1997), and in rats, CYPs 2B1 and 2C11 have been implicated as the primary metabolic enzymes (Hanioka et al. 1998a). Available data indicate that phase II metabolism of atrazine proceeds through glutathione conjugation and mercapturic acid formation (Adams et al. 1990; Egaas et al. 1995). Additional studies examining the enzymes responsible for phase I and phase II metabolism and the ratio of products would be useful.

Specific data on elimination and excretion of atrazine by any route were limited. However, the primary route of excretion appears to be in urine, as indicated by the detection of urinary atrazine and its metabolites in a number of species exposed via oral and dermal routes (Bakke et al. 1972; Buchholz et al. 1999; Catenacci et al. 1990, 1993; Meli et al. 1992; Timchalk et al. 1990). Fecal excretion was a minor route (Buchholz et al. 1999; Timchalk et al. 1990). No data were located regarding enterohepatic circulation and biliary secretion or excretion of atrazine in breast milk. Studies to determine whether enterohepatic circulation occurs and the extent to which it occurs, and studies examining the release of atrazine and its metabolites in breast milk would be helpful in better defining exposure.

Comparative Toxicokinetics. Available data indicate that atrazine is readily absorbed through the intestinal tract (Meli et al. 1992; Pommery et al. 1993; Timchalk et al. 1990) and that limited absorption occurs through the skin (Ademola et al. 1993; Buchholz et al. 1999; Catenacci et al. 1990, 1993; Hall et al. 1988) in humans and animals. Studies examining absorption following inhalation exposure in humans (occupational exposure) and animals would be useful.

Atrazine was detected in the kidney, small intestine, lung, liver, pancreas, muscle, heart, and plasma of a man who ingested weedkiller containing atrazine (Pommery et al. 1993). Radioactivity was detected in the liver, brain, heart, lung, kidney, digestive tract, omental fat, and skeletal muscle of rats gavaged with [C¹⁴]-atrazine (Bakke et al. 1972). Additional studies to determine the relative distribution of atrazine and its metabolites in internal organs after inhalation, oral, and dermal exposure to atrazine would be useful. Studies to determine if atrazine crosses the placenta in pregnant animals would also be useful.

While atrazine metabolites have been shown to be qualitatively similar across species, quantitative differences and differences in rate of formation and ratio of products have been observed (Adams et al. 1990; Hanioka et al. 1999; Lang et al. 1996). Inter- and intra-species and age and sex differences in glutathione S-transferase (GST) activity have also been seen (Egaas et al. 1995). Additional studies examining potential sex- and age-related differences between and within species would be useful.

Only 0.3–4.4% of an applied dose of [C¹⁴]-atrazine was recovered in urine and 0.0–0.7% in feces of people exposed dermally via an arm patch (Buchholz et al. 1999). No studies were located regarding excretion in humans after oral exposure to atrazine. In rats exposed orally to [C¹⁴]-atrazine, 57% of the administered radioactivity was excreted in the urine and only 14% in the feces (Timchalk et al. 1990). Additional studies on routes of elimination of atrazine following exposures of animals by the inhalation, oral, and dermal routes would be useful.

Methods for Reducing Toxic Effects. Oral absorption of atrazine can be reduced with gastric lavage, activated charcoal, sodium sulfate, and cathartics (Ellenhorn and Barceloux 1988; Haddad and Winchester 1990); however, animal studies indicate that gastrointestinal absorption of atrazine is fairly rapid (absorption half-life of 2.6 hours) (Timchalk et al. 1990) and thus, these measures would need to be employed soon after exposure. Dermal absorption of atrazine can be reduced by removing contaminated clothing and thoroughly washing the exposed skin with a mild soap (Ellenhorn and Barceloux 1988; Haddad and Winchester 1990). Additional data regarding interference with gastrointestinal absorption would be useful.

Since animal studies indicate that atrazine is rapidly metabolized and cleared from the body, methods for reducing body burden are not expected to be especially effective in reducing human exposures.

The primary effect of atrazine in rats is disruption of estrus cyclicity, which is mediated through an alteration of the gonadal-hypothalamic-pituitary axis. Differences in reproductive physiology between rats and humans make it unlikely that this mechanism would occur in humans. However, similar effects are seen in pigs and the mechanism has not been elucidated. Additionally, it is not known whether atrazine or its metabolites are responsible for these effects. Studies in pigs and other animals (except rats) to elucidate the mechanism for the reproductive effects of atrazine may be useful for developing methods that can interfere with these effects.

Children’s Susceptibility. A single cohort study of farm couples in Canada indicated that atrazine exposure may be associated with increased preterm delivery and miscarriage (Arbuckle et al. 2001; Savitz et al. 1997), and an ecological study indicated that atrazine levels in drinking water were positively associated with decreased intrauterine growth rates and increased birth defects in the respective communities (Munger et al. 1992b, 1997). Additional epidemiological studies examining these associations may be useful.

Developmental effects have been observed following pregestational, gestational, and lactational exposure of rat dams to atrazine. The observed effects included postimplantation losses (Infurna et al. 1988), decreases in fetal body weight (Infurna et al. 1988), incomplete ossification (Infurna et al. 1988), neurodevelopmental effects (Peruzović et al. 1995), and impaired development of the reproductive system (Stoker et al. 1999). A neurodevelopmental toxicity study is needed to verify and further characterize the Peruzović et al. (1995) results.

There are no studies that indicate that metabolism of atrazine differs between children and adults. The primary pathway by which atrazine is metabolized is dealkylation to yield the mono- and/or didealkylated atrazine derivatives. A study by Lang et al. (1997) indicated that CYP1A2, CYP2C19, and CYP1A1 may be the major CYP enzymes for atrazine, but that other forms, including CYP2A6, CYP2C9, and CYP2B6, are likely to be major contributors, especially in individuals with low levels of CYP2C19 or CYP1A2. While CYP2C19 and CYP1A2 are not present in appreciable levels in human fetal liver, their activities increase to adult levels by 4–6 months of age (Leeder and Kearns 1997; Ratenasavanh et al. 1991; Sonnier and Cresteil 1998). GST activity, involved in phase II metabolism of atrazine, generally reaches adult levels by 6–18 months of age (Leeder and Kearns 1997). Studies examining the metabolic differences between children and adults may be useful. Studies to determine if atrazine or its metabolites cross the placenta of animals and enter the developing fetus and if they are present in breast milk would also be very useful.

Child health data needs relating to exposure are discussed in Section 6.8.1 Identification of Data Needs: Exposures of Children.