Toxicological significance of non-, mono- and di-ortho-substituted polychlorinated biphenyls in oysters from Galveston and Tampa Bays

Abstract: Concentrations of non-ortho (77, 126, and 169), mono-ortho (105 and 118) and di-ortho (128 and 138) -substituted PCB congeners were measured in oysters from Galveston and Tampa bays, and reported toxic equivalent factors were used to assess their toxicity. Most of the relative toxicity encountered in the oysters analyzed during this study was due to the presence of planar non-ortho-PCBs (53.8-94.3%), particularly congener 126. In contrast, the contribution of di-ortho-substituted PCB congeners to the total relative toxicity of the samples was negligible (<1%). On average, the contribution of each of these non-, mono-, and di-ortho-substituted PCB congeners to the total toxicity encountered in oysters from Galveston and Tampa bays were 126 > 118 greater than or equal to 169 greater than or equal to 105 > 77 >> 138 > 128 and 126 > 118 > 169 greater than or equal to 77 > 105 >> 138 > 128, respectively. Based on the reported lower clearance rates of non-ortho- and mono-ortho-substituted PCB congeners compared to other congeners within the same chlorination level, contaminated oysters that are depurated in clean environments will lower their total PCB concentrations, but their original toxicity may not be proportionally reduced.