Teratologic evaluation of hexabrominated naphthalenes in C57BL/6N mice

Hexabrominated naphthalenes (HBNs) have been identified as contaminants in the commercial PBB mixture, Firemaster. Similarities between polyhalogenated naphthalenes and polyhalogenated biphenyls, dibenzofurans, and dibenzo-p-dioxins with regards to structure and capacity to elicit certain toxicological responses in laboratory animals have previously been evaluated. In this study, teratogenicity and embryo/fetal toxicity, which have been associated with maternal exposure to other toxic polyhalogenated aromatics, was characterized for a synthetic mixture of HBNs in C57BL/6N mice. Pregnant adult mice were treated on gestation Days 6 through 15 with 0.5, 1.0, 2.5, 5.0, 7.5, and 10.0 mg HBN/kg body wt/day and sacrificed on gestation Day 18. Maternal toxicity as evidenced by decreased body weight gain or actual weight loss was observed at 7.5 and 10.0 mg/kg/day. Maternal liver-to-body weight ratios were increased relative to controls at all exposure levels. Dose-related increases were recorded in fetal mortality at 5.0, 7.5, and 10.0 mg/kg/day, and in the incidence of various teratogenic effects at all dose levels. Kidney lesions, best described as apparent hydronephrosis, were the most sensitive fetal abnormality observed, followed by a reduction in the size of lymphatic organs (thymus and spleen), cleft palate, subcutaneous edema, sternebral anomalies, and delayed cranial ossification. HBNs are concluded to be potent fetotoxic and teratogenic agents producing similar effects to TCDD and other toxic polyhalogenated aromatic hydrocarbons.