Numerous compounds in the environment interfere with normal endocrine function in humans and other animals. These compounds, which include heavy metals, a wide variety of anthropogenic organic compounds, steroids and steroid-mimicking compounds, are collectively termed endocrine disrupting compounds (EDCs). Over the past 20 years, research on the impacts of EDC exposure has identified a range of effects on growth, development, and reproduction in humans and wildlife.
Most studies of EDC effects on wildlife have focused on vertebrates. Findings of reduced reproductive success in amphibians, reptiles, birds, and mammals resulting from environmental exposure to EDCs have generated considerable alarm (e.g., Colborn et al. 1996). Though less attention has been focused on invertebrates, it is clear that a wide variety of compounds introduced into the environment by humans can alter normal endocrine function in numerous taxa, affecting growth, development, and reproduction. Most widely noted in this regard has been impairment of the molt cycle in crustaceans due to insecticide exposure. Among mollusks, induction of imposex and intersex in gastropods exposed to tributyltin has been widely studied. Fewer studies have addressed effects of EDC exposure on bivalve mollusks, but there is evidence from several species that a range of compounds can affect sex determination, gonadal and gamete development, egg and sperm viability and function, and larval development. Intergenerational effects, in which exposure of one generation to EDCs reduces the survival of larvae in the next generation, have also been observed.
Viewed in the context of conservation and restoration of bivalve populations already at historic low levels and facing multiple stressors (e.g., Chesapeake Bay oyster populations), environmental pollutants which reduce the reproductive success of individuals can have very pronounced effects on population dynamics. For instance, on oyster reefs where recruitment is intermittent or provided primarily by stocking with hatchery-produced juveniles, exposure to compounds which result in early maturation as females and/or reduce sperm function can lead to reduced fertilization success in the population. Unfortunately, there are large gaps in our knowledge about inputs and fates of EDCs in Chesapeake Bay, and about the impacts these pollutants have on bivalves at the individual, population, and ecosystem levels.
We identify several areas in which critical information is needed to effectively evaluate the magnitude of EDC impacts on bivalves in Chesapeake Bay. Specifically, we recommend seven priority research and development needs: (1) development of an integrated database and communications structure, (2) identification of the major effects and modes of action by EDCs in native bivalves, (3) linkage of effects on individuals at specific stages in the life cycle to population and ecosystem models to evaluate larger-scale impacts of exposure, (4) identification in bivalves of biomarkers indicative of field exposure to EDCs, (5) monitoring of potential EDC source areas, (6) in situ field exposure studies, and (7) evaluation of EDC effects on bivalves exposed to multiple stresses characteristic of many Bay habitats.