A Mixture of Dioxins, Furans, and Non-ortho PCBs Based upon Consensus Toxic Equivalency Factors Produces Dioxin-Like Reproductive Effects

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Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD; dioxin) and related polyhalogenated aromatic hydrocarbons (PHAHs) alter the reproductive development of laboratory animals. Therefore, we exposed animals to a mixture of dioxins, furans, and polychlorinated biphenyls (PCBs) that included TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzofuran (1-PeCDF), 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF), octachlorodibenzofuran (OCDF), 3,3′,4,4′-tetrachlorobiphenyl (PCB77), 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), and 3,3′,4,4′,5,5′-hexachlorobiphenyl (PCB169). The mixture composition approximated the relative abundance of these compounds in foodstuff (L. S. Birnbaum and M. J. DeVito, 1995, Toxicology Vol. 105, pp. 391–401). Following the work of Gray et al. with TCDD (1997, Toxicology and Applied Pharmacology Vol. 146, pp. 11–20), we exposed time-pregnant dams on gestation day (GD) 15 at doses up to 1.0 μg TCDD toxic equivalency (TEQ)/kg and the development of offspring was monitored. This mixture significantly increased the time to puberty in both male and female offspring. At postnatal day (PND) 32 seminal vesicle weights were decreased; however, only ventral prostate weight was affected at PND 49 and no effects were seen at PND 63. In female offspring, the mixture caused dose-dependent increases in the incidence of vaginal thread. Ethoxyresorufin-O-deethylase (EROD) activity was higher than with TCDD the comparable TEQ exposure. Based on the slightly lowered responsiveness to the mixture, we used 2.0 μg TEQ/kg to examine reproductive effects. This dose elicited the responses observed with 1.0 μg TCDD/kg. Results indicate that the mixture causes a similar spectrum of effects seen with TCDD and the slightly lowered degree of response based on administered dose appears to be due to decreased transfer of mixture components to the offspring. Thus, the use of the WHO consensus TEFs (M. Van den Berg et al., 1998, Environ. Health Perspec. 106, 775–792) reasonably predicts the developmental toxicity of this mixture of dioxin-like PHAHs.

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