Where do heavy metals come from?

Toxic metals can present in industrial, municipal, and urban runoff, which can be harmful to humans and aquatic life. Increased urbanization and industrialization are to blame for an increased level of trace metals, especially heavy metals, in our waterways.

The heavy metals linked most often to human poisoning are lead, mercury, arsenic and cadmium. Other heavy metals, including copper, copper, and chromium, are actually required by the body in small amounts, but can also be toxic in larger doses. There are over 50 elements that can be classified as heavy metals, 17 of which are considered to be both very toxic and relatively accessible. Toxicity levels depend on the type of metal, its biological role, and the type of organisms that are exposed to it.

Heavy metals in the environment are caused by air emissions from coal-burning plants, smelters, and other industrial facilities; waste incinerators; process wastes from mining and industry; and lead in household plumbing and old house paints. Industry is not totally to blame, as heavy metals can sometimes enter the environment through natural processes. For example, in some parts of the U.S., naturally occurring geologic deposits of arsenic can dissolve into groundwater, potentially resulting in unsafe levels of this heavy metal in drinking water supplies in the area. Once released to the environment, metals can remain for decades or centuries, increasing the likelihood of human exposure.

In addition to drinking water, we can be exposed to heavy metals through inhalation of air pollutants, exposure to contaminated soils or industrial waste, or consumption of contaminated food. Because of contaminated water, food sources such as vegetables, grains, fruits, fish and shellfish can also become contaminated by accumulating metals from the very soil and water it grows from.

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