Mercury is an element that is found naturally in the environment and is typically found in substances like rocks and coal. We use mercury for many products, like fluorescent light bulbs, thermometers, and batteries. Since mercury is a simple element it persists in the environment and changes into different forms as it cycles through the environment. However, since the beginning of the industrial age, mercury emissions have increased as a result of burning fossil fuels and other industrial processes. Increases are also due to releases from burning municipal and hospital wastes.

Figure 1

In accordance with the law of gravity, "what goes up must come down." Mercury that is released by combustion processes falls soon after it is released from a stack or it contributes to a global pool of mercury in the atmosphere. The Electric Power Research Institute and the Minnesota Pollution Control Agency calculate that up to 10% of mercury released is deposited within 100 kilometers (about 62 miles) of a power plant, 50% is deposited within 1000 kilometers (about 621 miles), and the rest is transported regionally and globally.¹ Air concentrations depend on three criterion: the total mercury emission rate, the height of the smoke stack that emits mercury, and the exit velocity of the smoke plume from the source. Mercury dispersion modeling by the EPA for all sources of mercury shows similar distribution patterns.²

Mercury falls from the atmosphere in its inorganic form within precipitation. The form of mercury emitted affects how it is transported and deposited. One form is particulate mercury. Particulate mercury is dry deposition--particles of mercury that falls out directly, like debris after a fireworks display. The second is ionic, divalent mercury, a gas that undergoes changes in the atmosphere and binds to water vapor which eventually falls within rain or snow. The third is elemental mercury, which remains in the atmosphere indefinitely. This elemental mercury can undergo a chemical reaction at any time in the atmosphere. After that reaction it can then fall with rain or snow also.²

Once in an aquatic system, the inorganic mercury reacts with organic materials and turns into its organic form. The organic form, methylmercury, becomes available for metabolic uptake in organisms, like fish and mammals. This process will be explained in more detail later in this report.

Figure 2

As the fourth largest source of mercury emissions from power plants nationwide, Indiana has a serious problem concerning mercury. While it is impossible to determine the exact source of each molecule of mercury deposited in a lake or stream, this report focuses on lakes selected for their proximity to coal-fired power plants and is strong evidence that these plants are major contributors to mercury contamination. These conclusions are based on mercury emissions source locations, weather patterns, and air deposition estimates.

Table 1
DIRTY DOZEN:
STATES WITH HIGHEST MERCURY EMISSIONS FROM POWER PLANTS
Source: U.S. Environmental Protection Agency, 1997 1994 Estimates: U.S. Department of Commerce, November 1997; and EPA's Fish Consumption Advisory Database, 1996-97

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