Evaluation of the effects of dioxin and PCBs onFundulus heteroclituspopulations using a modeling approach

The U.S. Environmental Protection Agency (EPA) is reevaluating the risks associated with 2,3,7,8-tetrachlorodibenzo-p-dioxin and related chlorinated hydrocarbons (CHCs). Most information currently available concerning CHC toxic action and biological effects focuses on the responses of individual organisms, as opposed to the potential impacts of CHCs on populations, communities, or ecosystems. In support of EPA's reevaluation, survivorship and reproduction data from two previous studies involving the estuarine fish, Fundulus heteroclitus (Linnaeus), exposed as adults to either dioxin or polychlorinated biphenyls (PCBs), were interpreted at the population level using a stage-classified model of F. heteroclitus population dynamics. The studies differed with respect to the route of exposure of the parental stock: dietary exposure to dioxin in the laboratory and natural exposure to PCBs at the New Bedford Harbor, Massachusetts marine Superfund site. The CHC effects documented in these studies were used to modify fertility and survivorship in the population model. The finite population multiplication (growth) rate, estimated using the model, was used as the measure of population-level effect. In both cases, a negative relationship was observed between CHC dose (quantified as dioxin whole-body burden and liver burden of non-ortho- and mono-ortho-substituted PCB congeners) and population growth rate. The dose-response relationships developed in this study provide useful information for assessing the ecological risks of CHCs to estuarine fish populations.