Nitrate of mercury was used in the early production of felt used to make hats. However, the general public is primarily exposed to the organic form, methylmercury, through the consumption of fish. At highest risk from mercury exposure are fetuses, infants, and children. Mercury is also toxic to most wildlife including loons, otter, and mink which rely on fish as a significant part of their diet. These animals are often more susceptible to exposure than humans because of their relative size and consistency of fish in their diets.
Adults can suffer adverse effects from exposure to elemental mercury .
As mercury enters the environment from human or natural sources, it may readily be converted, by microorganisms, into the highly toxic organic form, methylmercury. Although some mercury is found naturally cycling, in the environment, the human contributions of mercury have steadily increased since the Industrial Revolution, upsetting this natural balance. For the northern hemisphere, atmospheric levels of mercury have increased two to five fold, in the past 150 years. Combined sources from the State of Michigan, annually release in excess of 15,000 lbs of mercury each year. Some of the largest contributors of mercury are the burning of fossil fuels, particularly coal, by utility companies and from the incineration of municipal and medical wastes.