Chemical contaminants accumulate in salt marshes that receive surface-water runoff and/or direct discharges of waste materials. Among the most toxic are halogenated hydrocarbons, which include many insecticides, herbicides, and industrial chemicals. When accumulated in the tissues of salt marsh animals a wide range of disorders can result, for example, immunosuppression, reproductive abnormalities, and cancer.
Petroleum hydrocarbons pollute harbors and remnant salt marshes following oil spills, urban runoff, and influxes of industrial effluent and municipal waste. Once they move into anoxic sediments, they can persist for decades, reducing primary production, altering benthic food webs, and accumulating in bird tissues. Polycyclic aromatic hydrocarbons have additional carcinogenic and muta-genic potential for aquatic organisms.
Heavy metals are also toxic to aquatic organisms and can impair feeding, respiration, physiological and neurological function, and reproduction, as well as promote tissue degeneration and increase rates of genetic mutation. Mercury is especially problematic because it is methylated in the anoxic soils of salt marshes and is then able to bioaccumulate in food chains.
Salt marsh plants in urban areas take up, accumulate, and release heavy metals. Judith Weis and others have found lowered benthic diversity and impaired fish behavior in contaminated sites. Fish are slower to catch prey and less able to avoid predators where heavy metals contaminate their habitat.
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