MERCURY POLLUTION OF FISH IN WISCONSIN LAKES: A DETAILED FISH TISSUE ANALYSIS

A Briefing Report from the
State Environmental Leadership Program
and Clean Wisconsin

September 2004

OVERVIEW

Game fish in Wisconsin’s lakes have higher-than-safe levels of the neurotoxin mercury, posing a health risk to anglers and others who consume the fish. A detailed analysis of fish tissue data from 601 lakes in Wisconsin shows that, even though mercury pollution from coal-fired power plants is a problem for anglers on a statewide basis, the fish in some Wisconsin lakes are considerably more mercury-laden than are those in other lakes in the state.

THE SCIENCE OF MERCUY LEVELS

The EPA has established a reference dose – a so-called “safe” daily dose of mercury – of just 0.1 micrograms of methylmercury per kilogram of body weight per day. This dose represents the amount of methylmercury that EPA believes can be ingested on a daily basis over the course of a lifetime without adverse health effects, based on current scientific knowledge. In 2000, the National Academy of Sciences affirmed that EPA’s reference dose “is a scientifically justifiable level for the protection of public health.”

According to EPA, the average U.S. woman weighs 143 pounds, and an average meal of fish is six ounces (cooked). Based on EPA’s reference dose, the “safe” limit of methylmercury in fish for U.S. women of average weight who eat two average meals of fish per week is 0.13 ppm. A woman who is pregnant, plans to become pregnant, or is nursing and eats fish with methylmercury levels that exceed 0.13 ppm may expose her baby to unsafe levels of methylmercury.

The Center for Disease Control and Prevention (CDC) conducted a recent study that for the first time measured mercury levels in the blood of women and children across the country and found that about one in six – nearly 16 percent – women of childbearing age have mercury levels above what is considered safe by the EPA. This translates to 4.7 million women of childbearing age nationwide with potentially unsafe levels of mercury and approximately 630,000 newborns in the nation who are at risk of neurological and developmental health impacts each year. Schober, S.E. et al. “Blood Mercury Levels on US Children and Women of Childbearing Age, 1999-2000.” 2003. JAMA Vol.289, No13 (April 2, 2003): 1667-1674.

Based on surveys of fish consumption, the National Academy of Sciences National Research Council estimated in 2000 that 60,000 newborns each year may be at risk for adverse neurological effects from in utero exposure to mercury. “The population at highest risk is the children of women who consumed large amounts of fish and seafood during pregnancy. The committee concludes that the risk to that population is likely to be sufficient to result in an increase in the number of children who have to struggle to keep up in school and who might require remedial classes or special education.” National Academy of Sciences. Toxicologic effects of methylmercury. Washington DC: National Research Council. 2000

.WORST LAKES IN WISCONSIN FOR MERCURY LEVELS IN FISH

How do Wisconsin’s lakes stack up when it comes to mercury pollution?

To answer that question, the State Environmental Leadership Program and Clean Wisconsin requested and received fish tissue testing data for mercury levels generated by Wisconsin’s Department of Natural Resources. Fish of a variety of species have been collected from 601 lakes and rivers and tested for mercury by the WDNR between 1985 and 2002.

SELP then analyzed the mercury level data for several popular gamefish species – walleye, largemouth bass, smallmouth bass, northern pike - and ranked the Wisconsin lakes and rivers in order of average mercury concentration across these fish species. Waters where less than 3 fish of these species were tested were dropped from the analysis to guard against misleading results due to small sample size.

Using this conservative methodology, the 10 worst mercury-polluted lakes in Wisconsin were as follows:

The full list of lakes analyzed also included the following:

THE SOURCE OF WISCONSIN LAKE MERCURY POLLUTION

What is the source of most of the mercury found in the fish in Wisconsin’s lakes?

Pollution from coal-fired power plants is the chief contributor of mercury pollution to the waters of Wisconsin. Mercury pollution is a primary reason why the Wisconsin Department of Natural Resources has issued a fish advisory for all Wisconsin lakes and rivers.

The Environmental Protections Agency (EPA) could nearly wipe out mercury pollution in Wisconsin, but it is not taking steps to do so. The Agency has proposed a regulation requiring a 70 percent reduction in mercury from coal-burning power plants by 2018 with a trading scheme that would allow utilities to buy their way out of making some or all of those reductions. Environmental groups have pointed out that the existing Clean Air Act requires the maximum achievable reductions of mercury – a 90 percent reduction of mercury emissions from coal plants by 2008 – and does not allow for the trading scheme. Anglers and others concerned about the pollution of Wisconsin’s lakes would be well advised to support efforts to curb the mercury pollution to the maximum extent possible – and as quickly as possible.