Publication Summary

Mercury concentrations were measured in 85 individual fish and 30 composite fish samples as part of the second year of long-term monitoring of mercury in fish tissues across the state. Previous Ecology studies identified elevated mercury levels leading to fish consumption advisories.

A total of 17% of individuals and 3% of composites sampled exceeded the EPA recommended water quality criterion of 300 ppb. Largemouth bass and northern pikeminnow were the only species exceeding EPA criterion. A single nine-year-old female bass from Mason Lake contained a mercury concentration of 952 ppb. This was the only sample exceeding the National Toxics Rule (NTR) criterion of 825 ppb.

This report presents results from the second year of a long-term monitoring effort by the Washington State Department of Ecology to measure mercury trends in fish tissue. The primary goal of this project is to monitor mercury levels in edible tissue from freshwater fish at six sites per year for five years (30 sites total) to characterize temporal trends.

In 2006, 85 individual fish and 30 fish composite samples, representing 10 species, were analyzed from seven lakes in Washington: American Lake, Mason Lake, Lake Meridian, Moses Lake, Newman Lake, Offut Lake, and Lake Sammamish. Water and sediment samples were collected to evaluate selected parameters that may influence mercury loading in tissues.

A total of 17% of individuals and 3% of composites sampled exceeded the U.S. Environmental Protection Agency (EPA) recommended water quality criterion of 300 ppb. Largemouth bass and northern pikeminnow were the only species exceeding EPA criterion. A single nine-year-old female bass from Mason Lake contained a mercury concentration of 952 ppb. This was the only sample exceeding the National Toxics Rule (NTR) criterion of 825 ppb.

Dissolved organic carbon (DOC), total organic carbon (TOC), pH, temperature, and percent anoxic water had the most significant correlations with mercury concentrations in individual bass.

A temporal analysis was performed for four lakes (Newman, Meridian, Long, and Moses) sampled in 2003 and again in either the 2005 or 2006 mercury trends report. Time between sampling events ranged from 49-59 months, and results estimated decreases in log10 tissue concentrations of 13-31%.

Link to EIM data for User Study ID HgFish06