In vitro reproductive toxicity of polychlorinated biphenyls: Effects on oocyte maturation and developmental competence in cattle

Polychlorinated biphenyls (PCBs) are one of the most persistent and widespr ead group of endocrine disrupting compounds in the ecosystem. High concentr ations of these substances are known to be present in sewage sludge from in dustrial, agricultural, and domestic origin that is spread in increasing am ounts on arable land and pasture as fertilizer and is found in water, repre senting an increasing risk for the reproductive health of farm animals. Obj ective of this study was to determine the impact of PCBs on maturation and developmental competence of cattle oocytes. Since PCBs are a family of 209 molecules present in the environ ment as a mixture, Aroclor-12 54, a pool o f more than 60 congeners, was used in these experiments as its composition is considered to be environmentally relevant. Cumulus-oocytes complexes wer e exposed during IVM to serial concentrations of Aroclor-1254 (between 1 mu g/ml and 0.0001 mug/ml) and compared with control groups. Aroclor decreased the percentage of oocytes that reached metaphase ii stage after 24 hr, at doses as law as 0.01 mug/ml. Groups treated with 0.001 mug/ml or above, sho wed an impaired fertilization rate and a dramatic increase of polyspermy. M oreover, exposure during maturation resulted in a reduced proportion of ooc ytes that cleaved and developed until blastocyst stage although no differen ces in embryo cell numbers were observed. The present study indicates that very low PCBs concentrations are sufficient to disrupt bovine oocyte matura tion, its fertilization, and developmental competence. These results also p rovide a set of reference data for the assessment of the risk posed by thes e substances to animal reproductive health, though further work wi II be ne cessary to equate in vitro doses to in vive exposures. (C) 2001 Wiley-Liss, Inc.