Developmental toxicity of 2-chlorodibenzofuran in cultured post-implantation rat embryos.

The developmental toxicity of 2-chlorodibenzofuran (2-MCDF), a contaminant in tap water, was examined by using post-implantation rat embryo culture with or without a metabolic activation system. 3-Chlorodibenzofuran (3-MCDF) and dibenzofuran (DF) were examined for comparison. Rat embryos at day 9 of gestation were cultured for 48 hr in the presence of the test chemicals (0, 30, 100, 300 or 1000 mum). 2-MCDF inhibited embryonic growth and increased morphological abnormalities of the embryos at 1000 mum in either the presence or absence of the metabolic activation system. The chief abnormalities were unclosed posterior neuropore and coelomic haemorrhage. Similar effects were observed in the embryos treated with 3-MCDF or DF. Dosing of 2-MCDF at maternotoxic levels to pregnant rats from days 9 to 11 of gestation, however, had no effect on the embryo-foetal development in vivo. It was concluded from these results that 2-MCDF had weak-inactive teratogenicity and that there was little risk to human embryos at the concentrations in tap water. It appeared that the embryotoxicity of 2-MCDF was caused by the dibenzofuran structure through mechanisms independent of DNA damage and the Ah receptor.