MERCURY IN SENTINEL BIOTA AS INDICATORS OF ATMOSPHERIC MERCURY DEPOSITION AT NATIONAL ESTUARINE RESEARCH RESERVE SITES FROM MAINE TO FLORIDA

Marine fish are the main route of exposure of Americans to mercury. It is generally believed that atmospheric deposition is the main route of delivery of mercury to the coastal environment. Wet deposition of mercury monitored by the Mercury Deposition Network MDN) shows a gradient of increasing flux from Maine to south Florida along the eastern seaboard. We are determining if there is a positive relationship between mercury deposition and mercury concentrations in estuarine biota from Maine to North Florida along a gradient of increasing mercury deposition.

We are testing two related hypotheses: 1. The latitudinal gradient in mercury concentrations in sentinel organisms parallels the latitudinal gradient in atmospheric mercury deposition, supporting the concept that recent atmospheric deposition of mercury determines mercury bioaccumulation. Samples have come from sites in National Estuarine Research Reserves (NERR) along the Atlantic Seaboard. This would support efforts to reduce atmospheric mercury emissions as a means to limit the detrimental effects of mercury in the coastal environment. 2. Shallow marsh habitats are critical sites of mercury methylation and bioaccumulation. It is hypothesized that sites from upstream regions of estuarine tidal creeks will display higher mercury concentrations in biota because of reduced flushing and dilution of generated methylmercury than in downstream, more open water locations.

Initial results for oysters support the first hypothesis, Samples from the north Florida NERR displayed total mercury concentrations approximately twice that of more northerly sites (mean 0.205 µg g^-1 dry weight in Florida, 0.145 µg g^-1 dry weight in North Carolina, and 0.089 µg g^-1 dry weight in Maryland). The second hypothesis is also supported. Mercury in oysters at the head of tidal creeks in Florida were 75% higher than downstream sites near open water (0.262 µg g^-1 dry weight versus 0.148 µg g^-1 dry weight).

Analyses of Fundulus are underway as are methylmercury analyses oysters.