Eating fish by candlelight

Fresh caught Minnesota walleye. Predator fish like walleye and pike contain the highest concentrations of mercury.

Minnesota waters have a problem with a not-so-common sense solution. Based on monitoring data collected around the state, the Minnesota Pollution Control Agency (MPCA) has determined that 1613 of our lakes and river-stretches are contaminated by mercury, a neurotoxin that works its way up the food chain, putting people and anything else that likes to eat fish at risk. Unlike other pollutants, however, mercury affects lakes throughout the state, even in pristine locations like the Boundary Waters that are far away from development, industry and other human intrusions. So how is the mercury ending up in our water?It turns out that 99% of the mercury in Minnesota’s lakes and streams comes from atmospheric deposition, the process by which pollutants and particulates that end up in the atmosphere settle back down onto the earth’s surface. According to the MPCA, 70% of atmospheric mercury deposition is due to human activities, such as energy production, and the remaining 30% is from natural sources, such as volcanoes. Since the air travels where it may throughout our state, this means that mercury from the atmosphere is just as likely to reach a lake in the Boundary Waters as one in the Twin Cities metro area, though differences in geography, water chemistry, and food webs mean that some lakes suffer more from the effects of this mercury pollution than others. This also means that keeping mercury out of our lakes is a lot harder than, say, building a few hundred raingardens or improving technology at a wastewater treatment plant.

The MPCA has set a goal of ensuring that mercury concentrations in top predator fish – walleye and pike – caught anywhere in the state are less than 0.2 ppm, a level which would allow even children and pregnant women to safely eat Minnesota-caught fish once a week throughout the year. Because mercury bioaccumulates as it climbs the food chain, achieving this standard for walleye and pike will also guarantee that mercury levels are low enough for smaller fish, as well as other aquatic animals.

The good news is that through an array of voluntary, regulatory, incentive-based and educational tools that involve local governments, state agencies and businesses, Minnesota has reduced its mercury emissions by 70% in the last 13 years. Additionally, the U.S. Environmental Protection Agency estimates that mercury emissions in the U.S. decreased 45% between 1990 and 1999, and that since then, additional reductions have been achieved through more rigorous standards for coal combustion and a ban on the use of mercury in interior and exterior paints. Best of all, an analysis of air concentrations from around the world showed a 20% decrease in mercury between 1990 and 2000 (Slemr et al. 2003).

The bad news is that even with all the progress we have made, we haven’t quite reached our goal yet.  Nearly all of the reductions we have made in mercury emissions in Minnesota since 1990 are product-related or due to changes in incineration and waste-combustion facilities. As of 2000, the top six sources of mercury emissions in Minnesota were coal (46% of emissions), taconite processing (21%), volatilization from disposed products (7%), petroleum (5%), municipal solid waste combustion (5%), and smelters that recycle cars and appliances (5%). Meanwhile, emissions from coal-burning power plants and taconite processing, now our two biggest sources, actually increased slightly between 1990 and 2000.

Currently, no cost-effective mercury reduction technologies exist for taconite-processing operations, but the MPCA and the Minnesota Department of Natural Resources are working with the industry to identify and fund the development of future control technologies. There is still vast potential, however, to reduce the amount of mercury emissions coming from coal-fired power plants.

To begin with, several power plants have made changes in their procedures or stopped using coal all together. Minnesota Power now uses lower-mercury coal in all of its operations and Xcel Energy converted its High Bridge plant in St. Paul and Riverside plant in Minneapolis to natural gas and upgraded the pollution-control equipment at a third, metro-area plant. Together, these changes equate to a 16% reduction in utility emissions in the state. Further reductions in mercury will likely happen as more power companies upgrade their existing equipment or switch to other forms of energy.

In summary, federal, state and local government, businesses and the energy industry have all stepped up to the plate, often at considerable expense, to reduce mercury and other emissions. What about the rest of us? About half of the electricity used in Minnesota comes from coal, which means that cutting back further on mercury emissions could be as easy as turning off a light. Buying energy efficient appliances and unplugging household electronics when they aren’t in use might seem like insignificant actions, but simple acts like these might ultimately make the difference between healthy and unhealthy lakes in Minnesota. It turns out Minnesota fish really do taste better when eaten by candlelight.

For more details on mercury in Minnesota’s waters, visit the MPCA’s Statewide Mercury TMDL page.

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