Publication Summary

Mercury concentrations were assessed in 185 fish and 60 sediment samples collected from 18 lakes and two rivers across Washington State.

Largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieu) were chosen as the target species due to their wide distribution, predatory nature, and known tendency to bioaccumulate mercury. Mercury concentrations in fish tissue were found to vary widely among waterbodies and individual fish, but were positively correlated with fish age.

Mercury levels in fish are compared to human health consumption criterion. Mercury levels in sediment are compared to available North American Sediment Quality Values.

During 2001 and 2002, the Washington State Department of Ecology conducted a screening survey for mercury concentrations in fish tissue and sediments from selected lakes and rivers across Washington State. The project was conducted in support of the goals of the Washington State Mercury Chemical Action Plan to continually reduce the use and release of anthropogenic mercury, and to minimize human exposure to mercury (Peele 2003).

This project follows two earlier studies in Washington State, in which elevated mercury levels were identified in fish tissue collected from Lake Whatcom (Serdar et al. 1999; 2001).

In this current study, concentrations of total mercury and percent lipids were measured in edible muscle from 185 bass, collected from 18 lakes and two rivers. Largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieu) were chosen as the target species due to their wide distribution, predatory nature, and known tendency to bioaccumulate mercury in muscle.

Sediment samples also were collected and analyzed for total mercury and total organic carbon. Water quality measurements were made to evaluate selected parameters which may affect the methylation of mercury.

Mercury concentrations found in tissue varied widely among waterbodies and individual fish within the same waterbody. Mercury levels in sediment also varied widely among waterbodies, with the highest concentrations occurring in western Washington.

Mercury concentrations in tissue were shown to have a strong correlation with fish age, weight, and length. Only one of the 185 fish collected contained a mercury concentration (1280 µg/Kg ww) which exceeded the National Toxics Rule criterion of 825 µg/Kg ww. However, 23% of the fish collected contained mercury concentrations at or above the revised EPA Fish Tissue Residual Criterion (TRC) for methylmercury of 300 µg/Kg ww. Additionally, 51% of the fish collected were found to contain mercury concentrations at or above a draft Washington State Department of Health (DOH) Interim Fish Tissue Criterion of 150 µg/Kg ww.

Average tissue mercury concentrations exceeded the TRC in 35% of the waterbodies sampled and exceeded the DOH Interim Fish Criterion in 70% of the waterbodies sampled.

Link to EIM data for User Study ID PAND0001