PCBs are a family of 209 chemical compounds, each of which consists of two benzene rings and 1 to 10 chlorine atoms. Their long-term stability and dispersion into the environment and the food chain have caused concern about their impact on humans and the environment. Native American communities are believed to be at particularly high risk of such exposure since they typically are more dependent than other populations on local fish and game as a food source. We have evidence for a significant excess in incidence and prevalence of hypothyroidism among Mohawks, particularly older women, as compared to other populations. The goal of the current project is to compare serum PCB concentrations to indicators of thyroid function in controls and patients with demonstrated thyroid dysfunction. Studies on experimental animals (rats) have shown significant depression of circulating levels of T4 and moderate reductions in levels of T3 after exposure to PCBs. We are conducting a retrospective observational case-control study. The participants are Mohawk women 30 years of age and older. Controls are participants in an ongoing environmental epidemiology study, whose thyroid hormone tests show a normal function. Our study aims to investigate the association between long-term exposure to PCBs and acquired hypothyroidism, to identify the critical exposure routes and to develop and apply toxic equivalents for thyroid disease for the various PCB congeners. PCB exposure is assessed by ultra-trace, congener-specific determination in blood specimen using GC/ECD. The study is currently ongoing. We have analyzed 46 samples of cases and 75 samples of controls.

        Key words: PCB congeners, hypothyroidism, women, Mohawk Nation