Industrial effluents often contain metallic compounds. For example, Halifax, a small city in eastern Canada, discharged into its harbor during the 1990s about thirty-three tons of zinc and thirty-one tons of lead per year, with
Garbage strewn across a sandy area. (S. Barnett, United States Environmental Protection Agency. Reproduced by permission.)
dinoflagellate single-celled aquatic organism effluent discharge, typically wastewater—treated or untreated—that flows out of a treatment plant, sewer, or industrial outfall; generally refers to wastes discharged into surface waters
Coral grows a new layer each year, much as a tree adds a new ring each year. Scientists analyzing layers of Bermudan coral have discovered an environmental record dating back to the mid-i8oos. Marine pollution can be measured across the Industrial Revolution. Marine levels of lead have dropped dramatically since the phaseout of leaded gasoline but levels of lead in the Atlantic are still double their preindustrial concentrations.
organochlorine chemical containing carbon and chlorine lesser amounts of copper and other metals. These metals are held in the sediment in a relatively inert form, but if stirred up into the water column, they become oxygenated and toxic. Tin is another common pollutant in harbors. It occurs as tributyltin (TBT), which is used as a component of antifouling paints on the undersides of ships. When taken up by shellfish, it accumulates in their tissues and has proved toxic to the shellfish and to organisms that consume them. The United States began to phase out TBT in 1988, and it will be banned internationally beginning in 2008.
Industry also produces organic compounds such as polychlorinated biphenyls (PCBs) and various pesticides. These accumulate in the fatty tissue of plants and animals low in the food chain, and as they pass through the food web to larger and long-lived animals, there is an increase in concentration of the substances in their fat, a process known as bioaccumulation. The St. Lawrence River, which drains the Great Lakes, has accumulated large amounts of organochlorines, which have amassed in the tissues of Beluga whales. During the 1990s, the level of this pollution was much reduced, and the whales have been protected from hunting, but their population fails to increase. Many animals have tumors and disease. There is mounting evidence that chronic exposure to contaminants causes suppression of the immune responses of marine mammals. Similar problems have occurred with seals in the Baltic Sea.
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