Publication Summary

Mercury concentrations were measured in 60 individual fish and 32 composite samples as part of the third year of long-term monitoring of mercury in fish tissues across Washington State. Previous Department of Ecology studies identified elevated mercury levels leading to fish consumption advisories.

A total of 73% of individuals and 28% of composites sampled had mercury concentrations higher than the EPA′s recommended water quality criterion of 300 ppb. A single four-year-old female bass from Lake Ozette contained a concentration of 1800 ppb. This sample was the highest mercury concentration recorded in a largemouth bass during the first three years of this long-term study.

This report presents results from the third year of a long-term monitoring effort by the Washington State Department of Ecology to measure mercury trends in resident freshwater fish tissue. Six sites per year for five years (30 sites total) are assessed to characterize trends over time (temporal trends).

In 2007, 60 individual largemouth bass and 32 composite samples representing eight species were analyzed from Deer Lake, Lake Fazon, Lower Goose Lake, Lake Ozette, Lake Samish, and Lake St. Clair. Water and sediment samples were also collected to evaluate selected parameters that may influence mercury uptake in fish tissues.

Seventy-three percent of individuals and 28% of composites sampled exceeded the Environmental Protection Agency′s recommended water quality criterion of 300 ppb. A single four-year-old female bass from Lake Ozette contained a mercury concentration of 1800 ppb. This sample was one of seven exceeding the National Toxics Rule human health criterion of 825 ppb. This sample had the highest concentration recorded in a largemouth bass during the first three years of this long-term monitoring study.

A temporal analysis was performed for three lakes (Deer, Fazon, and Samish) sampled in 2001-2002 and again in 2007. Time between sampling events ranged from 58-72 months. Results from Deer Lake estimated a 15% decrease in mercury concentrations for fish at a given length. Estimated changes in concentration were small at Samish and Fazon Lakes.

Mercury concentrations in standard-sized bass from the first three years of the project were compared through a t-test to determine if concentrations from eastern and western Washington differed. The test showed a significant difference between the two areas with a higher average concentration among western Washington waterbodies (294 ppb to 126 ppb).

Link to EIM data for User Study ID HgFish07