The mercury cycle and fish in the adirondack lakes.

LAKES i s t o r i c a l l y high concen­ t r a t i o n s of mercury (Hg) in fish h a v e b e e n a t t r i b ­ uted to point sources of mercury generally as­ sociated wi th industrial discharge (1-3). In recent years, there has been renewed inter­ est in the transport and fate of mercury in the environ­ ment because of 'widespread reports of elevated concen­ trations of mercury in fish caught in remote lakes {4-8). Mercury in fish occurs almost entirely as methylmercury in muscle tissue (5, 9), where it is associated with protein sulfhydryl groups [10, 11). Ingestion of fish muscle is an important exposure pathway of mercury to humans . Methylmercury is highly toxic; it is thought to inhibit enzyme activity in the cerebellum, which is re­ sponsible for neuron growth in early developmental stages. Chronic exposure to organomercurials can result in mental retardation (12). As a result, the U.S. Food and Drug Administrat ion (FDA) has set an Action Level of 1 μg/g (wet weight) for concentration of mercury in fish. Fish containing concentrations of mercury above this level are considered to be hazardous for human consumpt ion and cannot be sold in interstate com­ merce. Canada and several U.S. states have developed consumpt ion advisories of 0.5 μg/g for mercury in fish. In the 1980s, the number of fish consumption adviso­ ries increased in several states and the province of On­ tario. More recently, the number of advisories has in­ creased because of the imposition of a blanket advisory covering more than 11,000 lakes in Michigan. This trend is probably the result not of an increase in the numbers of fish wi th elevated mercury, but of increased monitoring and awareness of the problem.