Are PCBs the major neurotoxicant in Great Lakes salmon?

Epidemiological studies have demonstrated an association between consumption, by women, of contaminated Great Lakes salmon and deficits in cognitive performance in the children of these women. Although significant statistical associations between polychlorinated biphenyl (PCB) body burdens and these negative outcomes suggest that PCBs may be responsible, the fetus and neonate are also exposed to other fish-borne neurotoxicants. In this manuscript we present data from two developmental studies that support the hypothesis that PCBs may serve either as a marker for other contaminants that are responsible for the observed effects, or that other contaminants present in the fish interact synergistically with the PCBs to produce the observed neurotoxicity. In the first study we demonstrated that exposure of rats to diets containing lyophilized Great Lakes salmon, resulting in exposure to as little as 13.9 micrograms/(kg small middle dotday) of total PCBs, induced significant reductions in regional brain dopamine (DA) concentrations. In the second study, we demonstrated that exposure of rats to the ortho-substituted PCB congener (2,4,2', 4'-tetrachloro- biphenyl) at 1, 10 or 20 mg/(kg small middle dotday) also induced significant reductions in DA concentrations in the same brain regions although only at the two highest doses-levels at least 100-fold higher than seen in the first study. On the basis of these developmental neurochemical studies we suggest that the reported cognitive deficits in children exposed in utero and during lactation to fish-borne contaminants may be due either to contaminants other than PCBs or to complex interactions between PCBs and other neurotoxicants present in the fish.