Science Center Objects

Mercury is a potent neurotoxin that can affect the human nervous system. Eating fish contaminated with mercury can cause serious harm to people and wildlife.


Mercury is a potent neurotoxin that can accumulate in fish to levels of concern for human health and the health of fish-eating wildlife. Mercury contamination of fish is the primary reason for issuing fish consumption advisories, which exist in every State in the Nation. Much of the mercury in the environment originates from combustion of coal and can travel long distances in the atmosphere before being deposited on the land surface. As a result, mercury can bioaccumulate in fish in areas with no obvious source of mercury pollution.1

Mercury is the leading cause of impairment in the Nation's estuaries and lakes and was cited in nearly 80 percent of all reported fish-consumption advisories.2 The geographic extent of mercury advisories covers more than 10 million acres of lakes and more than 400,000 stream miles.3 

The fact sheet Mercury Contamination of Aquatic Ecosystems answers many of the basic questions about mercury. For a deeper dive into the topic, download the USGS Circular 1395, highlighted below. 



  • Highly toxic to the nervous system
  • Persistent in the environment
  • Bioaccumulates (higher concentrations in tissues of aquatic plants and animals than in water)
  • Biomagnifies (higher concentrations at increasingly higher levels in the food chain)
  • Numerous chemical forms in air, water, sediment, and biota



Mercury contamination is global and affects many waters that have no obvious mercury source. This is because mercury emissions generally disperse widely in the atmosphere before being deposited to the earth's surface. Mercury is emitted by natural sources, such as volcanoes, geothermal springs, geologic deposits, and the ocean. Human-related sources primarily include coal combustion, waste incineration, industrial uses, and mining. During the last 150 years, human activities have more than doubled natural amounts of mercury in the atmosphere.4

In matural waters, inorganic mercury is generally not a health concern. The real issue is methylmercury, an organic form that is highly toxic to the nervous system. Methylmercury is produced from inorganic mercury by methylation, a microbial process that is controlled by certain bacteria and enhanced by chemical and environmental variables, such as the presence of organic matter and oxygen. More than 95 percent of all         mercury in fish is methylmercury, and this form of mercury biomagnifies to high concentrations at the top of food chains.5





U.S. Environmental Protection Agency