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Abstract for RACB88036

Reproductive Toxicity of a Chemical Mixture in CD-1 Swiss Mice

Report Date: Report Date: November 1990


The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.

The potential reproductive toxicity of a mixture of 25 chemicals (MIX), formulated to simulate ground water supplies near hazardous waste dumps, was evaluated in CD-1 (Swiss) mice using the Reproductive Assessment by Continuous Breeding Protocol (RACB). Male and female mice were exposed to MIX in the drinking water at concentrations of 1%. 5%, and 10% of a technically-achievable stock solution. During 14 weeks of cohabitation in Task 2, with continuous access to MIX- containing drinking water, there was no effect on the ability of the F0 animals to produce litters. However, the number of live female pups per litter. and the total number of live pups per litter, was significantly depressed in the 5% and 10% group, and in the 10% group, respectively, compared to controls. Correspondingly, the sex ratio of pups born alive (males/total) was increased at 5% and 10% MIX. At necropsy, no significant effects of treatment with 10% MIX were noted for vaginal cytology, testes weight, or testicular sperm count. No other effects of MIX on reproduction and fertility were observed in Task 2. Exposure to MIX produced few signs of generalized toxicity in the F0 animals. Body weight and feed consumption for male and female F0 animals were generally unaffected by treatment, and there were no distinctive treatment-related clinical signs. Water consumption (g/kg/day) was significantly depressed in the 5% and 10% MIX groups throughout Task 2.

Task 4, a trial to determine the fertility and reproductive competence of the second generation (F1 animals), was conducted with the final offspring of all groups. The number of live female pups per litter and the adjusted live pup weight in the 10% MIX group were significantly depressed below control values. At necropsy. relative seminal vesicle weight was elevated in all three MlX-treated groups, but not in a dose-related manner. In addition, epididymal sperm concentration was significantly reduced at 1% and 10% MIX, and was reduced, but not significantly, at 5% MIX. Testicular spermatid head count exhibited a decreasing trend and was significantly depressed compared to controls at 10% MIX. For 5% and 10% MIX, a significant increase in the proportion of days the females exhibited no cycle or an unclear estrous cycle was observed.

F1 male body weights were significantly depressed in all three MIX-treated groups, and F1 female body weights were significantly depressed in the 10% dose group compared to controls at age 74+10 days of age, the day of selection for Task 4, but the decrease did not persist throughout Task 4. There was no significant effect of MIX treatment on feed consumption by F1 animals. Water consumption (g/kg/day) in F1 mice was significantly depressed at 5% and 10% MIX. There was no significant effect of MIX treatment on the body weight of F1 animals at necropsy. Relative kidney plus adrenal weight was significantly elevated for both males and females in the 5% and 10% groups. Histopathologic evaluation of tissues from F1 animals revealed an increased incidence and severity of acute to chronic inflammation in the livers of female mice in the 5% and 10% MIX groups, and an increased incidence of nephropathy in the kidneys of both sexes, particularly at the 10% MIX dose level.

Reproductive toxicity, observed as a 10% to 17% reduction in the number of female pups per litter at 5% or 10% MIX, and a 10% reduction in the total number of pups per litter at 10% MIX, was observed. For the F1 animals, an MTD of 5% MIX was determined, based on a persistent reduction in water consumption, relative kidney plus adrenal weight, and liver histopathology. Decreased sperm concentration and an increase in unclear estrous cycles did not significantly alter fertility. However, a decrease in the number of female pups per litter and adjusted live pup weight at 10% MIX indicated reproductive / developmental effects at that dose.

In summary, a "cocktail" of 25 chemicals commonly found in contaminated ground water supplies was administered to CD-1 mice. In the presence of low doses of many known reproductive and developmental toxicants, including cadmium, mercury, lead, chloroform, and methylene chloride, relatively mild reproductive effects of MIX administration were observed in the reproductive evaluation of both F0 mice and their offspring. regardless, evidence of reproductive toxicity was observed at the high dose of MIX in both generations, with the female embryo/fetus emerging as a target of toxicity.