EVALUATION OF THE EFFECTS OF DIOXIN AND PCBS ON FUNDULUS-HETEROCLITUSPOPULATIONS USING A MODELING APPROACH

The U.S. Environmental Protection Agency (EPA) is reevaluating the ris ks associated with 2,3,7,8-tetrachlorodibenzo-p-dioxin and related chl orinated hydrocarbons (CHCs). Most information currently available con cerning CHC toxic action and biological effects focuses on the respons es of individual organisms, as opposed to the potential impacts of CHC s on populations, communities, or ecosystems. In support of EPA's reev aluation, survivorship and reproduction data from two previous studies involving the estuarine fish, Fundulus heteroclitus (Linnaeus), expos ed as adults to either dioxin or polychlorinated biphenyls (PCBs), wer e interpreted at the population level using a stage-classified model o f F. heteroclitus population dynamics. The studies differed with respe ct to the route of exposure of the parental stock: dietary exposure to dioxin in the laboratory and natural exposure to PCBs at the New Bedf ord Harbor, Massachusetts marine Superfund site. The CHC effects docum ented 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 populatio n-level effect. In both cases, a negative relationship was observed be tween CHC dose (quantified as dioxin whole-body burden and liver burde n of non-ortho- and mono-ortho-substituted PCB congeners) and populati on growth rate. The dose-response relationships developed in this stud y provide useful information for assessing the ecological risks of CHC s to estuarine fish populations.