Metal pollution in coastal environments

Metals are naturally occurring elements that become contaminants when human activity raises their environmental concentration above natural levels. Metals can be released from industrial processes and wash into estuaries and marshes. When marshes were being filled in for development in years past, industrial wastes were a common component of the ‘fill’. Landfills sited in marshes frequently held household materials such as old paint cans and other cans made of metal, as well as remnants of paint with pigments usually composed of metal compounds. Metals such as mercury, cadmium, lead, and copper from industrial sources are common contaminants of salt marshes and estuaries.

Copper is used in copper pipes, boat anti-fouling paints, and CCA (chromated copper arsenate) treated wood used in bulkheads and pilings. While copper does not generally pose risks to human health, it is extremely toxic to marine algae and invertebrates, and is even used as an algicide. Lead, commonly used as a gasoline additive in the past, enters waters in run-off from road surfaces during rainfall. While leaded gasoline is no longer used in the U.S., lead does not break down and remains in the environment. Some otherwise fairly pristine marshes, such as that in Tuckerton, New Jersey, have elevated lead levels in sediments, resulting from decades of hunting ducks with lead shot.

Knowing the chemical form of a metal is necessary for understanding its fate in the environment and uptake by organisms. Metals do not reach high concentrations in water, but rather bind (adsorb) to sediment particles. Smaller particles have more surface area for binding metals. Because there is more surface area in the fine particles (silt and clay) in estuaries and marshes than in larger particles (such as sand), contaminant levels in estuarine and marsh sediments will be higher. Metals may bind to sulfur, forming sulfides in marsh sediments, making it less available for uptake into living things.

caption Sign posted by the New Jersey Department of Environmental Protection warning that blue claw crabs are contaminated.

Mercury is a particular problem because it is very toxic and can be converted to an organic form, methylmercury, by bacteria in bottom-level sediments. Methylmercury is taken up by organisms more rapidly and is much more toxic than inorganic mercury; it is particularly toxic to the nervous system. The severity of mercury toxicity was recognized in the late 1950s and 1960s because of an environmental tragedy in Minamata, Japan, where hundreds of individuals suffered from mercury poisoning. A local factory discharged mercury into Minamata Bay, from which the community caught and ate fish that had accumulated high amounts of methylmercury. Major neurological and developmental defects occurred in the residents of Minamata, a condition now called “Minamata Disease.” This disaster served as a “wake up call” to the rest of the world.

Berry’s Creek Marsh, in the Hackensack Meadowlands of New Jersey, also has extremely high concentrations of mercury in its sediments as a result of industrial activities. Fortunately for local residents, the mercury has not become methylated and has not accumulated to such high levels in local fish. The explanation is that there is so much sulfide in the sediments as a result of years of accumulating wastes from sewage treatment plants, that the mercury is tightly bound to sulfide and not available for the bacteria to methylate. Nevertheless, the mercury levels in the fish are above safe levels, and warnings are posted that people should not consume fish or crabs from the waters in the Hackensack Meadowlands.

Further Reading

Glossary

Citation

Weis, J. (2006). Metal pollution in coastal environments. Retrieved from http://www.eoearth.org/view/article/154582

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