Mercury occurs naturally in the earth’s crust, is ubiquitous in the environment, and is a component of freshwater and marine fish and mammals. Human industrial activities such as coal burning contribute to the global distribution of mercury in the environment. Global mercury emissions have increased since the 1700s. Currently, known man-made emissions of mercury roughly equal known natural emissions. Mercury has many chemical forms that occur naturally in the environment. From a public health standpoint, methyl mercury is the most important.
Alaskans are exposed to methylmercury primarily from ingestion of fish and marine mammals. Methylmercury concentrations in the most frequently consumed fish (e.g., salmon, cod, halibut, pollock, sole, and herring) are very low, consistently below 0.2 ?g/g [parts per million, ppm, wet weight (all tissue concentrations are wet weight unless noted otherwise)]. This is one-fifth of the Food and Drug Administration (FDA) action level for commercial sale of seafood of 1 ppm. Alaska salmon average 0.05 ppm of methylmercury. Similarly for marine mammals, except for some beluga whale tissues, average methylmercury concentrations are below 0.2 ppm. Bowhead whale tissues (e.g., muscle, blubber, epidermis, liver and kidney) contain very low methylmercury concentrations (<0.02 ppm). Older fish and marine mammals that are higher on the food chain have higher concentrations of methylmercury.