An environmentally relevant mixture of organochlorines, their metabolites and effects on preimplantation development of porcine embryos

Environmental exposure of human populations to organochlorines is still widespread despite several international regulations banning or restricting their use. This study tested the hypothesis that an environmentally relevant complex mixture of organochlorines comprising polychlorinated biphenyls (PCBs), technical chlordane, dichlorodiphenyldichloroethylene and 12 other components is toxic for porcine embryos (at relative concentrations of 1-10000-fold the environmental organochlorine levels of contamination or 4.2 microg/l total PCBs). We also tested the embryotoxicity of a metabolised organochlorine mixture (relative concentrations of 0.9, 1.8, 2.7, 3.6 and 4.5 microg/l hydroxy-PCBs (OH-PCBs)) obtained by extracting plasma samples from sows treated with the native mixture. Embryos produced in vitro were exposed to either the organochlorine mixture or the metabolised extract for 9 days. The organochlorine mixture reduced embryonic development at the 10000x concentration (relative concentration of 42 mg/l PCBs; p=0.05). The organochlorine mixture also reduced the mean number of blastomeres per expanded blastocyst in a dose-dependent manner (p=0.038) but did not induce blastomere apoptosis (p>0.05). In contrast, the metabolised extract did not affect development or blastomere number at the concentrations tested, although the highest level of this mixture (4.5 microg/l OH-PCBs) was still very low (i.e. similar to the 1x concentration of the organochlorine mixture, which also did not alter embryo parameters). These data lead to the conclusion that while high concentrations of the native organochlorine mixture are toxic for porcine embryos, concentrations of either the native or the metabolised mixture that bear some relevance to exposure of human populations in the Arctic were without observable effect.