lib.mainmenu_1

 
 

Effects

There is mounting evidence that prenatal exposure to PCBs induces adverse developmental effects in humans, specifically, but not limited to,neurobehavioral alterations in newborn and children exposed during gestation and/or via breast milk.
In the various cohorts studied, some common findings of neurodevelopmental effects have been reported, other affected end points have not beenthe same in all studies. This is not unexpected given the different degrees of control for confounders and the different measures of exposureused. Moreover, apparent inconsistencies between studies may reflect not only limitations in study design, but also problems inherent indetecting neurobehavioral deficits at exposure levels near the threshold for effects. Effects associated with PCB exposure included abnormalreflexes and more motor immaturity in newborns, altered PDI scores at 12 years of age, and alterations in memory functions at 7 months of ageand at 4 years of age and in cognitive abilities at 42 months using the Kaufman Assessment Battery for Children. It must be kept in mind,however, that in all of these studies, there is a possibility that other lipophilic compounds may have contributed to the observed effects. Itis expected that children from these prospective studies continue to be monitored in order to assess the impact of these subtle neurobehavioralalterations as they grow older and their potential implications at a population level.
Studies in animals support the findings in humans. Studies in rodents have provided valuable information, but monkeys, whether exposed duringgestation and/or during infancy, have proved to be much more very sensitive to PCBs and some structurallyrelated chemicals. Investigatorsshould continue efforts to develop an operant test battery that measures a variety of functions that can be validated for use in rodents,monkeys, and humans and that can be applied in epidemiological studies. Studies with single congeners are valuable in that they provideinformation on possible mechanisms of action, but people, specifically nursing infants, are exposed to a mixture of PCB congeners in the milk.Some studies in humans have suggested that gestational exposure to PCBs and other chemicals can affect the thyroid hormone system in infants.These observations have been extensively corroborated in experimental animals.

The generally negative results of in vitro and in vivo animal studies indicate that commercial PCB mixtures are not likely to pose a genotoxicthreat to humans.
An increased percentage of chromosomal aberrations was reported in a study in which workers were exposed to PCBs for over 10 years. However,there was simultaneous exposure to benzene, which is known to cause genotoxic effects in humans. A different study reported a slight increase inthe incidence of sister chromatid exchanges in 12 men exposed to PCBs following a fire in an electric station. It is quite possible, that toxicchlorinated dioxins and/or furans were generated during the fire. Studies with Aroclor 1254 in human lymphocytes in vitro gave conflictingresults.
Available pharmacokinetic data do not suggest routespecific target organs. Aroclor 1254 was not mutagenic in Salmonella.

 


Structure formula of 2,2',3,4,5,6'-Hexachlorobiphenyl


3D structure of 2,2',3,4,5,6'-Hexachlorobiphenyl