At its meeting held on October 26-29, 2010, the committee reviewed the TSDs on ethyl mercaptan, methyl mercaptan, phenyl mercaptan, and tert-octyl mercaptan. Presentations of the TSDs were made by Mark Follansbee, of Syracuse Research Corporation.

Ethyl Mercaptan

The following is excerpted from the Executive Summary of the TSD:

Ethyl mercaptan depresses the central nervous system and affects the respiratory center, similar to hydrogen sulfide, producing death by respiratory paralysis…. AEGL-1 values were based on a NOEL for irritation in rabbits exposed to 10 ppm for 20 minutes.… AEGL-2 values for ethyl mercaptan were based upon a 3-fold reduction in the AEGL-3 values.… AEGL-3 values were based on a calculated LC01 (2250 ppm) in mice exposed to ethyl mercaptan for 4 hours.

A revised document should be submitted to the committee for review.

AEGL-Specific Comments

AEGL-1

Page 16, line 33 (also page 7, Table S 1, and Appendix B): The POD for AEGL-1 is identified as 10 ppm, which is characterized as a NOEL for irritation in rabbits exposed for 20 min. Just prior to that (page 16, lines 28-29), this effect is characterized as “no significant effect”. However, the description of the experimental results (page 13, lines 26-28) described effects at 10 ppm without characterizing their significance (e.g., author’s statement to that effect). Additional information is needed to characterize these findings as a NOEL rather than a LOAEL.

Page 19, Table 9: The AEGL-1 values are higher by a factor of 2 than the occupational exposure limits shown. Some discussion in the text would be appropriate to clarify why the general population exposure is being set higher than an occupational exposure limit.

NIOSH (1978) derived sufficient quantitative information from the Katz and Talbert (1930) publication to either set or support the recommended exposure limit (REL) values. Review these references, the case report and the human experimental data to determine if an exposure-response estimate, even a rough one, can be identified to either derive an AEGL-1 based on human data or to support the values derived from animal data.

AEGL-2

Page 17, line 13: The authors report that animal data were not available for deriving AEGL-2 values. Reassess the cited literature, in particular, Fairchild and Stokinger (1958), Zieve et al. (1974), and Shibata (1966a,b) to determine whether data are sufficient to either derive values or support default values rather than rely on the default procedure. If distinct levels of exposure (which are given) cannot be equated with distinct occurrence of the effects sufficiently for AEGL value derivation or support, perhaps they can provide at least some indication of AEGL-2 effects, information that may also be helpful to the end user.

Pages 1, line 26, to Page 12, line 21: The Fairchild and Stokinger (1958) paper may have data for exposure groups that did not experience mortality; these data, if available, might be useful to identify, as a minimum, AEGL-2 effects and possibly exposure-response relationships. For instance, page 11, lines 36-39, describes clinical signs from a study on mice, and page 12, lines 5-8, describes clinical signs from a study on rats.

Page 12, line 26 to page 13, line 13: The Zieve et al. (1974) study of 15-min exposures in rats describes central nervous system (CNS) effects that would be relevant to escape impairment. Please consider using these data in deriving AEGL-2 values. See also the comment on the Shibata study below.

Page 13, lines 21-25: The Shibata (1966b) study in rabbits describes changes in respiratory parameters for a short exposure period (1,000 ppm for 20 min). These effects may have AEGL-2 consequences for asthmatics and others with compromised respiratory systems. If ese data are otherwise acceptable, AEGL-2 values might be derived except for 4-h and 8-h time periods; alternatively, the data might be supportive of the values derived using the default procedure. Please consider these data in deriving AEGL-2 values.

AEGL-3

Page 18. lines 4-6: Regarding the selection of the data from mice as the POD for AEGL-3, it could also be noted (perhaps parenthetically) here that the mouse was the more sensitive species. This could be more fully stated in lines 10-12 when used to justify the interspecies UF of 3, with perhaps a cross-reference to Section 4.5.

Page 18, Section 7.3: The values proposed for AEGL-3 10- and 30-min values are about a factor of 4 higher than that used in Shibata (1966a). This factor is noted on page 18, lines 20-23. Elsewhere, and several times, it is emphasized that ethyl mercaptan has a steep concentration-response curve; that is, the distance between no effects and very serious effects is a relatively small increment in concentration. Derivation of the AEGL-3 values is from the 4-h lethality data time-scaled via the standard procedure. Greater confidence in the degree of conservatism of the values for short exposure periods could be provided by noting that the results of the Zieve et al. (1974) study (30,000 ppm for 15 min, no coma and loss of righting reflex) provide additional support for the protective nature of the AEGL-3 values.

Other Comments

The authors can be complimented for their excellent and critical review of the literature, their analysis of the data, and their establishment of scientifically defensible AEGLs.

Page 6, lines 36-39 and lines 43-46: “(a 4 hour exposure to 2600 ppm caused 40% lethality in mice, the 4-h mouse LC50 value was 2770 ppm and at 3573 ppm for 4 hours 100% of mice died; the 4-h rat LC01 value was 3808 ppm and the 4-h rat LC50 value was 4740 ppm).” This information is useful information for the derivation of the AEGL-2 and -3 values, but this parenthetical is out of place in an Executive Summary. A brief summary of these data would be good, but is not necessary. This level of detail is not appropriate for an Executive Summary. The parenthetical should be deleted or summarized.

Page 6, line 41, to page 7, line 19: This paragraph simply repeats the derivation of the AEGL-3 values from the text of the document (page 18, lines 3-31). Readers are not looking for this kind of information in an executive summary. This paragraph should be revised to summarize the information that was essential to derive the AEGL-3 values.

Page 8, Table 1: Given the data in the table, the calculated saturated vapor concentration is about 58%, indicating great potential to generate toxic concentrations very quickly in an emergency. This potential should be discussed in the TSD.

Pages 8-10, Section 2.2.1: This section discusses very small numbers (such as 0.00026 and 0.00076 ppm). The authors should consider the use of scientific notation to make comparisons easier.

Page 14, lines 38-39: “It was hypothesized that oxidation converted the thiol to the sulfide and then to the sulfone.” Although it is evident from the context what the specific components of the metabolic pathway are, the term “sulfide” can be ambiguous. Verify that Snow (1957) used the specific phrasing shown, or revise the sentence to be more specific.

Page 15, line 12: The phrase “caused an increased reduction in the mitochondria ” is ambiguous. What was increased, and compared with what? Consider alternative phrasing to clarify.

Page 15, Section 4.3: Insert the Comparative Toxicity of the Mercaptans table from the tert-octyl mercaptan TSD. This table is very useful for comparing relative potency across the different mecaptan compounds.

Page 16, lines 34-37: The POD for AEGL-1 is direct irritation. UFs of 3 for both intra- and interspecies are justified based on common mechanism of action and effects that do not vary greatly (PK and PD factors), and are supported by the fact that higher values would result in AEGL-1 values at odds with information from human exposures. The following wording change is recommended: “Uncertainty factors of 3 each were applied to account for interspecies and intraspecies variability because direct-acting irritation is not expected to differ substantially between species or between individuals. These values are considered sufficient”

Page 17, lines 21-23, and page 18, lines 7-10: “(a 4 hour exposure to 2600 ppm caused 40% lethality in mice, the 4-h mouse LC50 value was 2770 ppm and at 3573 ppm for 4 hours 100% of mice died; the 4-h rat LC01 value was 3808 ppm and the 4-h rat LC50 value was 4740 ppm).” To improve readability, consider replacing the material in the parenthetical with a reference to Table 4, “Mortality of Mice and Rats Exposed to Ethyl Mercaptan for 4 Hours,” on page 12.

Page 18, lines 17-19: “The 4-hour rat LC50 value for ethyl mercaptan was 4740 ppm (Fairchild and Stokinger 1958), whereas, the 4-hour LC50 value for hydrogen sulfide was 444 ppm (Tansy et al. 1981).]” Replace the material in square brackets with a cross-reference to Section 4.3., the comparative toxicity table.

Page 18, lines 24-30: This information repeats what is detailed in Section 4.6. Either replace with a reference to Section 4.6. (e.g., “Time-scaling was done as described in Section 4.6.”) or delete Section 4.6. Having both is redundant.

Page 19, line 13: “NIOSH (1996) REL is a 15-min TWA exposure that should not be exceeded at any time during a workday.” A definition of “REL” was not apparent on cursory review of the NIOSH IDLH Web site. A better source would be the NIOSH Pocket Guide to Chemical Hazards online at http://www.cdc.gov/niosh/npg/pgintrod.html. The REL is defined at the Exposure Limits link.

Page 21, lines 37-38: Van Doorn et al. is cited as the source for determining the level of distinct odor awareness, but the reference is to an unpublished report with no other source information. As cited, this reference is of limited use: Now that the 2009 version of this report has been published, the citation should be updated to Ruijten et al. (2009) (see below in Comment References for the full citation).

Page 29, Appendix D: Does this plot include the Zieve et al. (1974) data? If not, please revise the plot. In addition, a subtitle or footnote should be added saying that the decimal is lost on this log-scale plot.

Comment References

  • Fairchild, E.J., and H.E. Stokinger. 1958. Toxicologic studies on organic sulfur compounds. I. Acute toxicity of some aliphatic and aromatic thiols (mercaptans). Am. Ind. Hyg. Assoc. J. 19(3):171-189. [PubMed: 13559131]

  • Katz, S.H., and E.J. Talbert. 1930. Intensities of Odors and Irritating Effects of Warning Agents for Inflammable and Poisonous Gases. U.S. Department of Commerce, Bureau of Mines Technical Paper 480. Washington DC: U.S. Government Printing Office.

  • NIOSH (National Institute for Occupational Safety and Health). 1978. Occupational Exposure to n-Alkane Monothiols, Cyclohexanethiol, and Benzenethiol. Criteria for a Recommended Standard DHEW (NIOSH) 78-213. U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, Cincinnati, OH.

  • NIOSH (National Institute for Occupational Safety and Health). 1996. Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH): NIOSH Chemical Listing and Documentation of Revised IDLH Values (as of 3/1/95)-Ethyl Mercaptan. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. August 1996 [online]. Available: http://www​.cdc.gov/niosh/idlh/75081.html [accessed Dec. 13, 2010].

  • NIOSH (National Institute for Occupational Safety and Health). 2005. NIOSH Pocket Guide to Chemical Hazards. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Cincinnati, OH. September 2005 [online]. Available: http://www​.cdc.gov/niosh/npg/ [accessed Dec. 13, 2010].

  • Ruijten, M.W.M.M., R.van Doorn, and A.P. van Harreveld. 2009. Assessment of Odour Annoyance in Chemical Emergency Management. RIVM Report 609200001/2009. RIVM (National institute for Public Health and the Environment), Bilthoven, The Netherlands: [online]. Available: http://www​.rivm.nl/bibliotheek​/rapporten/609200001.pdf [accessed Dec.13, 2010].

  • Shibata, Y. 1966. a. Studies on the influence of ethyl mercaptan upon the living body: III. Inhalation experiment of ethyl mercaptan gas in the human body [in Japanese]. Shikoku Acta Med. 22:844-850.

  • Shibata, Y. 1966. b. Studies on the influence of ethyl mercaptan upon the living body: II. On the respiratory function and clinical findings in rabbits which inhaled ethyl mercaptan gas [in Japanese]. Shikoku Acta Med. 12:136-145.

  • Snow, G.A. 1957. The metabolism of compounds related to ethanethiol. Biochem J. 65(1):77-82. [PMC free article: PMC1199830] [PubMed: 13403874]

  • Tansy, M.F., F.M. Kendall, J. Fantasia, W.E. Landin, R. Oberly, and W. Sherman. 1981. Acute and subchronic toxicity studies of rats exposed to vapors of methyl mercaptan and other reduced-sulfur compounds. J. Toxicol. Environ. Health 8(1-2):71-88. [PubMed: 7328716]

  • Van Doorn, R., M.W. Ruijten, and T. Van Harreveld. 2002. Guidance for the Application of Odor in Chemical Emergency Response, Version 2.1, August 29, 2002. Presented at the NAC/AEGL Meeting, September 2002, Washington, DC.

  • Zieve, L., W.M. Doizaki, and F.J. Zieve. 1974. Synergism between mercaptans and ammonia or fatty acids in the production of coma: A possible role for mercaptans in the pathogenesis of hepatic coma. J. Lab. Clin. Med. 83(1):16-28. [PubMed: 4808653]

Methyl Mercaptan

The following is excerpted from the Executive Summary of the TSD:

Data were insufficient for derivation of AEGL-1 values for methyl mercaptan…. AEGL-2 values were based on shallow breathing and hypoactivity in mice exposed to 258 ppm methyl mercaptan for 6 hours…. AEGL-3 values were based on the calculated LC01 (430 ppm) for rats exposed for four hours.

A revised document should be submitted to the committee for review

AEGL-Specific Comments

AEGL-1

The committee agrees that data are insufficient at this time for the derivation of AEGL-1 values for methyl mercaptan.

AEGL-2

Page 8, line 12 to Page 9, line 2: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is not uncommon in humans and is more prevalent among African-Americans. The case report described mentions that the affected individual was G6PD deficient. If there is reason to suspect that this condition was contributory to the outcome, assess whether the intraspecies UF of 3 is sufficient to protect more sensitive individuals.

AEGL-3

The committee approves the derivation of AEGL-3 values for methyl mercaptan.

Other Comments

The authors can be complimented for their excellent and critical review of the literature, analysis of the data and establishment to scientifically defensible AEGLs. A number of revisions have been made to this document in response to previous reviews. The authors have responded to these comments adequately.

If all the mercaptans are combined into a single document or published in a single volume, the document should include some discussion about their relative toxicities.

Page 15, lines 12-15: Nephrotoxicity, specifically a disturbance of glomerular filtration, could also explain the effects noted here and should be included in this sentence.

Phenyl Mercaptan

The following is excerpted from the Executive Summary of the TSD:

Phenyl mercaptan depresses the central nervous system and affects the respiratory center, similar to hydrogen sulfide, producing death by respiratory paralysis…. AEGL-1 values are not recommended for phenyl mercaptan due to insufficient data. No robust data consistent with the definition of AEGL-2 were available. Therefore, the AEGL-2 values for phenyl mercaptan were based upon a 3-fold reduction in the AEGL-3 values…. AEGL-3 values were based on a calculated LC01 (10.3 ppm) in rats exposed to phenyl mercaptan for 4 hours.

A revised document should be submitted to the committee for review.

AEGL-Specific Comments

AEGL-1

The authors should reconsider whether sufficient data exist to set AEGL-1 values. Both the ACGIH TLV and the National Institute for Occupational Safety and Health (NIOSH) REL are set at 0.1 ppm (a value below the derived AEGL-2 values). The documentation of these values (the primary sources) should be reviewed to determine whether the data used would be adequate to derive AEGL-1 values. The NIOSH authors appear to have found sufficient information in Katz and Talbert (1930) to set or at least support an exposure standard. This study is also cited in the phenyl mercaptan document on page 8, lines 12-20. The Katz and Talbert publication should be reviewed in conjunction with the NIOSH criteria document to determine whether quantitative exposure-response data are present that are adequate to derive AEGL-1 and/or AEGL-2 values or to support values otherwise derived. If not, a discussion needs to be added to Section 8.2 Comparison with Other Standards and Guidelines (page 17), particularly because headache and dizziness have been reported in humans, as well as ocular, throat, and nasal irritation and some clinical signs in animals.

AEGL-2

Based on the 8-h TWA values used to control chronic occupational exposures listed in Section 8.2., the AEGL-2 values should be reassessed. These recommendations have been applied for many years without reports of adverse effects due to exposure at these levels. Although the current ACGIH value is slightly more than half the AEGL-2 value, until 2004 it was the same as the current Dutch maximum accepted concentration (MAC) value, which is almost three times the AEGL-2 value. Note also that these TWAs permit excursions above the average value: “Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a work day, and under no circumstances should they exceed 5 times the TLV-TWA, provided that the TLV-TWA is not exceeded.”

Although the statement is made that there were no animal data for derivation of AEGL-2 values (page 15, lines 14-15), several studies reported effects at exposure concentrations that did not cause lethality and that therefore might be useful for deriving AEGL-2 values. These studies are on (1) page 9, lines 38-41 and 44-46; (2) page 10, Table 3, first entry and lines 14-17 and 20-21; and (3) page 10, lines 31-32, and page 11, lines 1-2.

The Fairchild and Stokinger paper, items 1 and 2, should be reviewed to ensure that distinct levels of exposure (which are given) are not associated with distinct occurrence of these effects—the phrasing used in the TSD allows the opposite inference, especially given the entry in Table 3. Note that item 3, the Stauffer Chemical Company study, does cite specifics. If these data are indeed not adequate for deriving AEGL values, a more detailed explanation should be provided.

AEGL-3

The committee approves the derivation of AEGL-3 values for phenyl mercaptan.

Other Comments

Page 6, line 22, to Page 7, line 4: The Executive Summary discussion of AEGL-3 repeats the text from page 16 on derivation of the AEGL-3. The Executive Summary should briefly summarize the information essential to derive the AEGL-3 values, not repeat it verbatim.

Page 8, Table 1: Given the molecular weight and vapor pressure listed here, insert the calculated saturated vapor concentration (SVC): 1,316 ppm (5,930 mg/m3).

Page 13-14, Section 4.3, Structure-Activity Relationships: Insert the Comparative Toxicity of the Mercaptans table from the tert-octyl mercaptan document.

Page 14, lines 18-19: “data suggest that mice and rats are of similar sensitivity with regard to lethality from inhalation.” The data presented by Fairchild and Stokinger (1958) in their Table III on page 181 of the paper may be less supportive than this statement suggests. The 48-h LC50 values are reasonably close, but comparing the time to death values in the table would support a conclusion that mice were more sensitive, at least to the onset of effects and death, even if the ultimate result (the 15-day LC50) was similar. Consider a change in phrasing to capture this distinction.

Page 15, line 17: “is considered appropriate given the extremely steep concentration-response curve.” Is the slope more steep than those for other similar chemicals (e.g., tert-octyl mercaptan)? Either delete “extremely” or provide some justification for this statement.

Page 16, lines 15-19: Replace with a cross-reference to Section 4.3.

Comment References

  • Fairchild, E.J., and H.E. Stokinger. 1958. Toxicologic studies on organic sulfur compounds. I. Acute toxicity of some aliphatic and aromatic thiols (mercaptans). Am. Ind. Hyg. Assoc. J. 19(3):171-189. [PubMed: 13559131]

  • Katz, S.H., and E.J. Talbert. 1930. Intensities of Odors and Irritating Effects of Warning Agents for Inflammable and Poisonous Gases. U.S. Department of Commerce, Bureau of Mines Technical Paper 480. Washington DC: U.S. Government Printing Office.

  • NIOSH (National Institute for Occupational Safety and Health). 1978. Occupational Exposure to n-Alkane Monothiols, Cyclohexanethiol, and Benzenethiol. Criteria for a Recommended Standard DHEW (NIOSH) 78-213. U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, Cincinnati, OH.

  • Stauffer Chemical Company. 1969. Acute Inhalation LC50Study of Thiophenol in Male and Female Rats with Cover Letter Dated 05/06/94. Submitted by Zeneca Specialties to U.S. Environmental Protection Agency, Washington, DC. Document No. 86940000970. Microfiche No. OTS0557380.

Tert-octyl Mercaptan

The following is excerpted from the Executive Summary of the TSD:

Data were insufficient for derivation of AEGL-1 values for tert-octyl mercaptan. Therefore, AEGL-1 values are not recommended. In the absence of appropriate chemical-specific data, the AEGL-3 values were divided by 3 to derive AEGL-2 values for tert-octyl mercaptan…. A 4-hour BMCL05 value of 11.5 ppm calculated from combined female rat data (Atochem 1982) was used as the point-of-departure (POD) for AEGL-3 values. This is considered a threshold for lethality calculated from the most sensitive test animals (females).

A revised document should be returned to the committee for review.

AEGL-Specific Comments

The authors are complimented for their analysis of the data and establishment of scientifically defensible AEGL values, considering the sparse database.

AEGL -1

The authors should investigate the sources used by Hazardous Substances Data Base (2006), which states in the Introduction (page 9, lines 5-7) that tert-octyl mercaptan “is moderately irritating to the eyes, and may cause headache, nausea, vomiting, and central nervous system effects, resulting in dizziness, convulsions, unconsciousness, and respiratory depression.” If dose and time of exposure are extractable from those sources, they should be evaluated for the derivation of AEGL-1 values.

AEGL-2

The committee approves the derivation of AEGL-2 values for tert-octyl mercaptan.

AEGL-3

The committee approves the derivation of AEGL-3 values for tert-octyl mercaptan.

Other Comments

Studies that focus on nonlethal effects are not available for some chemicals, and a database derivation of AEGL-2 values cannot be developed. The default procedure of dividing the AEGL-3 values is used in these cases, including for tert-octyl mercaptan. This procedure, however, provides no information on the types of disabling and/or escape-impairing effects that may be of concern to the end user. Another source of data may sometimes be available, however, and should be considered. Lethality studies frequently have exposure groups that have no deaths but have signs of toxicity from which they recover during the observation period and show no gross abnormalities at necropsy. These data are typically reported, and should be explored to determine their suitability either for deriving AEGL-2 values or for supporting the values obtained through the default procedure. Page 17, lines 13-18, of this TSD is a good example of the latter. A conceptually similar approach may also be useful in identifying AEGL-1 effects and deriving data-based values. This comment is offered as an observation; it is not meant to cause change in AEGL values derived for tert-octyl mercaptan. Discussion is invited to improve the AEGL development process.

Page 7, lines 14-20: This information is useful for the derivation of the AEGL-2 and -3 values, but this parenthetical is out of place in an executive summary. The first sentence of this paragraph captures the essence; a second sentence could elaborate and provide some summary data, but detailing the studies’ results here is not appropriate for an executive summary.

Page 7, Lines 22-46: This paragraph repeats the derivation of the AEGL-3 values from the text of the document. It is not the kind of information expected by those who read an executive summary. This paragraph should briefly summarize the information that was essential to derive the AEGL-3 values

Page 10, Lines 28-35: “Clinical signs included respiratory stimulation, followed by CNS stimulation initially characterized by a ‘threshold effect’ consisting of localized minimal convulsive movements in the form of repeated facial and ear twitches. Propulsive and retropulsive thrusts of the trunk were also observed, followed by circumscribed clonic convulsions limited to the forebody and forelimbs, resulting in a sitting position while pawing in the air. This was followed by generalized clonic seizures of fore- and hind-limbs causing a loss of upright position. Exophthalmus with conjunctival congestion and salivation accompanied the seizures. Muscle relaxation, irregular labored breathing, and coma preceded death.” It is not clear from the wording whether all exposure groups experienced the described respiratory and CNS effects. Please explicitly state if all or some of the exposure groups experienced these effects. If review of data indicates that some exposure groups did not experience symptoms, consider whether this information could be used to establish AEGL-2 values (the effects reported exceed AEGL-1). See also the first paragraph above under ‘Other Comments’.

Page 10, Table 2: Are the “Seizures observed within 45 min-1.5 h; average of 2 mild seizures” the “threshold effect” mentioned in line 29? If so, this concentration should be included in the text.

Page 11, lines 9-10: “Clinical signs were noted in females at 29 ppm and above and included seizing the wire mesh bottom….” What was the concentration in males? Please include this concentration in the document or state if the concentration was not noted for males.

Page 11, lines 9-13: Since female mortality was reported at two concentrations of less than 29 ppm, were there no clinical signs noted in the animals that died? The current phrasing leads to the inference that the animals died without warning.

Page 12, line 20-21: “Clinical signs included convulsions, with females affected more frequently and with greater severity than males.” Were clinical signs noted in all exposure groups given in lines 14-15? If not, please clarify for which exposure groups the clinical signs were observed.

Page 15, Table 7: The table titled Comparative Toxicity of Mercaptans is very useful. This table should be included in the Structure-Activity Relationship section of each mercaptan document for which it provides information, in particular ethyl-, methyl-, and phenylmercaptan documents discussed during the October 27-30 meeting.

Page 17, lines 13-18: “The AEGL-2 values are considered protective. No effects (clinical signs or mortality) were noted in male and female rats exposed to 7 ppm tert-octyl mercaptan for 4 hours (Atochem 1982). Using the 7 ppm concentration as a POD and applying time scaling and uncertainty factors as proposed, yields 10- and 30-minute values of 1.4 ppm, a 1-h value of 1.1 ppm, a 4-hour value of 0.70 ppm, and an 8-hour value of 0.35 ppm, values slightly higher than the proposed AEGL-2 values.” This discussion is instructive, but could provide more useful information on potential AEGL-2 effects. Rewording the second sentence of this paragraph as follows would indicate both the not-necessarily-lethal clinical signs of concern as well as their proximity to lethal concentrations: “An exposure of 7 ppm for 4 h produced no observable effects in either male or female rats, whereas an exposure of 12 ppm for 4 h produced both clinical effects (tremors and clonic convulsions in all exposed animals) as well as 10% mortality in female rats (Atochem 1982).” This statement does not change the POD, or the AEGL-2 values but does provide information to the end user beyond the values themselves

Comment References

  • Atochem (Atochem North America, Inc). 1982. Initial Submission: Final Report on a Study to Establish an LC50 Concentration of t-Octyl Mercaptan in Adult Sprague-Dawley Rats of Both Sexes (Final) with Attachments and Letter. Submitted to U.S. Environmental Protection Agency, Washington, DC. Microfiche No. OTS0534952.

  • HSDB (Hazardous Substances Data Bank). 2006. t-Octyl Mercaptan (CASRN 141-59-3). TOXNET, Specialized Information Services, U.S. National Library of Medicine, Bethesda, MD: [online]. Available: http://toxnet​.nlm.nih​.gov/cgi-bin/sis/htmlgen?HSDB [accessed Feb. 27, 2008].