The use of DDT and PCBs in the United States was banned in the 1970s, but these chemicals persist for many years. Other contaminants enter our waters every day. Some flow directly from industrial and municipal waste dischargers, while others come from polluted runoff in urban and agricultural areas. Still other contaminants are carried through the air, landing in lakes and streams far from the factories and other facilities that produced them. In cases like this, the sediment may serve as a contaminant reservoir or source of contamination.
Experts believe that contaminated sediments are a widespread and serious problem.
Areas of concern are found on the Atlantic and Pacific coasts, in the Gulf of Mexico and the Great Lakes, and along inland waterways. Contaminated sediments affect small creatures such as worms, crustaceans, and insect larvae that inhabit the bottom of a water body in what is known as the benthic environment . Some kinds of toxic sediments kill benthic organisms, reducing the food available to larger animals such as fish. Some contaminants in the sediment are taken up by benthic organisms in a process called bioaccumulation . When larger animals feed on these contaminated organisms, the toxins are taken into their bodies, moving up the food chain in increasing concentrations in a process known as biomagnification .