Di(2-ethylhexyl) adipate: Condensation of the Carcinogenesis Bioassay Technical Report.

Di(2-ethylhexyl) adipate [bis(2-ethylhexyl) adipate, DEHA, octyl adipate, dioctyl adipate, DOA, CAS No. 103-23-1], a plasticizer added to vinyl plastics to give low temperature flexibility, is dispersed (not bound) in the polymer chain matrix. Approved by the U.S. Food and Drug Administration for use in plastics that may contact nonfatty, nonalcoholic foods (not to exceed 24% by weight of the plastic polymer), DEHA has wide use in vinyl packaging ifim for refrigerated and frozen food products. Other products containing DEHA include electric wire insulation, garden hoses, vinyl coated fabrics for automotive and upholstery use, synthetic rubber, base oils for hydraulic fluids, and, among others, polyvinyl tubing for hemodialysis. For these uses 44 million pounds were produced in 1978. DEHA was selected as a representative of the adipate class of plasticizers, because it is structurally related to di(2-ethylhexyl) phthalate, because human exposure is widespread, and because no carcinogenesis studies had been done. Testing was initiated by the Carcinogenesis Testing Program, National Cancer Institute (now part of the National Institute of Environmental Health Sciences/National Toxicology Program).

Di(2-ethylhexyl) Adipate: Condensation of the Carcinogenesis Bioassay Technical Report* Di(2-ethylhexyl) adipate [bis (2-ethylhexyl) adipate, DEHA, octyl adipate, dioctyl adipate, DOA, CAS No. 103-23-1], a plasticizer added to vinyl plastics to give low temperature flexibility, is dispersed (not bound) in the polymer chain matrix. Approved by the U.S. Food and Drug Administration for use in plastics that may contact nonfatty, nonalcoholic foods (not to exceed 24% by weight of the plastic polymer), DEHA has wide use in vinyl packaging ifim for refrigerated and frozen food products. Other products containing DEHA include electric wire insulation, garden hoses, vinyl coated fabrics for automotive and upholstery use, synthetic rubber, base oils for hydraulic fluids, and, among others, polyvinyl tubing for hemodialysis. For these uses 44 million pounds were produced in 1978.
DEHA was selected as a representative of the All animals that died during the study or that were killed at the end of the exposure period were subjected to a gross necropsy and a complete histopathological examination. Statistical analyses comparing survival and numbers of animals with specific site tumors were done with trend tests and pairwise comparisons (1)(2)(3)(4). The study design conformed to the NCI Guidelines for carcinogen bioassay (5).

Results
Mean body weights of high dose male and female rats and treated male and female mice were lower than the corresponding controls. Survival was comparable among all groups of mice and male rats; survival in the female control rats was reduced relative to the treated groups (29/50 control, 39/50 low dose, 44/50 high dose).
The number of DEHA-treated rats with specific site tumors did not differ significantly from those found in controls. Table 1 lists those primary tumors occuring in at least three animals of any one group.
Liver tumors occurred with significantly higher frequencies in treated male and female mice than in controls ( Table 2). Other specific site tumors were not significantly increased in treated mice when compared to controls (Table 3).

Discussion
In male rats the positive dose-related trend (p = 0.010) and the statistically significant (p <0.05) increase in interstitial cell testicular tumors in the  gSignificant dose-related trend for males and females (p < 0'.005). Significant negative trends were obtained for male rats with adrenal gland pheochromocytomas (p < 0.05) and for female rats with adrenal cortical adenomas (p < 0.05) and with mammary gland fibroadenomas (p = 0.001).
Hepatocellular carcinomas were increased in both low and high dose female mice; hepatocellular adenomas or carcinomas combined occurred in high dose mice of either sex and in low dose female mice at incidences that were dose related and significantly higher than those in the controls. The time to observation of hepatocellular adenomas or carcinomas in the dosed female mice, but not in dosed male mice, was significantly shorter than the time to observation ofthese tumors in the controls. Because the increase in liver tumors in males reflects only an increase in adenomas for the high dose group and because the time to observation of tumors in dosed groups as compared with the control group was not significantly different, the association ofliver tumors in the males with administration of di(2-ethylhexyl) adipate is not considered conclusive.
Hepatocellular adenoma compressed the adjacent liver tissue. Cells in the adenoma were large. Cytoplasm of the cells was acidophilic or vacuolated and nuclei were hyperchromatic. Hepatocellular carcinoma involved a part or an entire lobe of the liver. The lobular architecture was distorted and cell plates were two or more cells thick, forming trabeculae. Cellular pleomorphism was apparent. The nuclei had coarse chromatin, and the nucleoli were prominent. Both normal and abnormal mitotic figures were numerous. Areas of necrosis and mineralization were common in the large tumors.
Hepatocellular carcinoma metastasized to the lung in 14 male mice (control, 5; low dose, 4; high dose, 5) and in 11 female mice (low dose, 6; high dose, 5). In all cases, the primary liver tumors were of the trabecular type. The other sites of metastases were the kidney, adrenal, and lymph nodes in dosed female mice.
Negative trends were calculated for male (p = 0.010) and for female (p = 0.001) mice with lymphomas; the number of mice in each treated group with lymphoma was significantly less (p < 0.05) than the corresponding controls. This interesting phenomenon of decreases in leukemias/lymphomas concomitant with increases in hepatocellular neoplasms is receiving considerable research attention from the National Toxicology Program (6).
In conclusion and under the conditions of this bioassay, di(2-ethylhexyl) adipate was not carcinogenic for F344 rats of either sex. Di(2-ethylhexyl) adipate was carcinogenic for female B6C3F1 mice causing increased numbers of female mice with hepatocellular carcinomas, and was probably carcinogenic for male B6C3F1 mice, causing increased numbers of male mice with hepatocellular adenomas as well as inducing increased numbers of male mice with combined hepatocellular adenomas or carcinomas (10).