DIFFERENTIAL TOXICITY OF 3 POLYCHLORINATED BIPHENYL CONGENERS IN DEVELOPING SEA-URCHIN EMBRYOS

The relationship between body burden and toxicity of three individual polychlorinated biphenyl (PCB) congeners in developing sea urchin embr yos was investigated to evaluate the validity of current predictive mo dels of PCB toxicity in an invertebrate system. Body burdens of radiol abeled PCB congeners (IUPAC 47, 77, and 153) accumulated from seawater were used to determine median effective concentrations (EC50s) for de velopmental and cytogenetic effects following a 72-h exposure. Congene r 47, a di-ortho-substituted tetrachlorobiphenyl, was found to be at l east four times more toxic than congener 77, a non-ortho-substituted ( coplanar) tetrachlorobiphenyl, with EC50s of 47 and >218 mmol/kg, resp ectively, using an embryo development assay. This result contradicts t he structure-activity prediction of the mammalian-based toxic equivale nts (TEQs) approach, demonstrating the need for an ecotoxicologic mode l. Congener 153, a di-ortho-substituted hexachlorobiphenyl, was virtua lly nontoxic in terms of developmental effects at the highest dose (10 2 mmol/kg) achievable at its limit of water solubility. Cytogenetic an alysis was a more sensitive method for assessing toxicity than the emb ryo development assay. Dose-response relationships were established wi th mitotic activity being the most sensitive endpoint because the PCBs appeared to inhibit mitosis. At the highest doses, complete mitotic a rrest was observed. Congener 77 was found to be at least two times mor e toxic (EC50 = 30 mmol/kg) than congener 153 (EC50 = 67 mmol/kg) but not as toxic as congener 47 (EC50 < 16 mmol/kg) using mitotic activity as the endpoint for toxicity. Thus, the developmental and cytogenetic endpoints ranked the toxicity of the congeners similarly, but establi shed different EC50s.