Publication Summary

Mercury concentrations were measured in 60 individual bass and 30 composite samples representing six other species as part of the fourth year of long-term monitoring of mercury in fish tissues across Washington State. Previous Department of Ecology (Ecology) studies identified elevated mercury levels leading to fish consumption advisories.

Consistent with previous Ecology mercury fish tissue reports, mercury concentrations were generally related to fish age and size within a particular waterbody. Bass had higher concentrations than other species analyzed. Thirty percent of individual bass tested did not meet EPA′s recommended water quality criterion of 300 ppb. All composite samples met (were below) this threshold.

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

In 2008, 60 individual bass and 30 composite samples representing 6 additional species were analyzed from 6 lakes: Goodwin, Horsethief, Leland, Loomis, McIntosh, and Nahwatzel. Water and sediment samples were also collected to evaluate selected parameters that may influence mercury uptake in fish tissue.

Consistent with previous Ecology mercury fish tissue reports, mercury concentrations were generally related to fish age and size within a particular waterbody. Bass had higher concentrations than other species analyzed. Thirty percent of individual bass tested did not meet the EPA′s recommended water quality criterion of 300 ppb. All composite samples (met) were below this threshold.

Spearman Rank and Pearson correlation matrices were used to examine relationships between water and sediment variables to standard-sized bass concentrations over the first 4 years of monitoring, 2005-08. Environmental variables displaying the strongest relationships with fish tissue concentrations were sediment mercury concentration (+), pH (-), and alkalinity (-).

Consistent with earlier findings, eastern Washington bass have lower mercury concentrations than bass in western Washington. The average mercury concentration in a standard-size fish (356 mm) from western Washington (335 ppb) is significantly higher than a standard-size fish from eastern Washington (139 ppb).