Benthic (bottom-dwelling) invertebrates may face exposure to mercury released directly from sediments. They may also release mercury bound in the sediment by direct ingestion, having thus entered the food chain, mercury bioaccumulates as bottom-dwellers are consumed by others.

Toxic methylmercury can inflict increasing levels of harm upon species near the top of the aquatic food chain. These likely victims include: predatory fish such as ocean swordfish; fish-eating birds such as loons, cormorants, pelicans, ospreys, and eagles; and humans.

We can be certain of the harm resulting from methylmercury contamination of fish, even if the exact degree of risk is yet uncertain. Reasonable preventive actions that will safeguard humans from methylmercury poisoning should also protect birds that eat freshwater fish. Controlled feeding studies suggest that the methylmercury threshold dose for adverse effects to wildlife is the same or higher than for humans.

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