Metals are a diverse group of elements that can occur naturally in water or be contributed to water from human activities. Some of these elements are required in very small (trace) amounts by things that live in water, but at higher concentrations they can be toxic. Some metals are toxic to living things in any amount, like mercury. Metals do not degrade, but they can change form and move between water and sediments in aquatic systems.
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A metal that is toxic and extremely persistent in the environment