Mercury Fact Sheet

Mercury & The Columbia: Should I Be Concerned?

April 11, 2024

In the 2009 State of the River Report, the U.S. Environmental Protection Agency (EPA) identified mercury as one of the four classes of toxic contaminants of the greatest concern in the Columbia River Basin, alongside polychlorinated biphenyls (PCBs), dichloro-diphenyl-trichloroethane (DDT), and polybrominated flame retardants (PBDEs). While the Columbia is burdened with too much toxic pollution and all kinds of chemical pollutants, mercury contamination is one of the primary drivers of fish advisories and concerns around consuming Columbia River fish.


Mercury is a naturally occurring element that is persistent (doesn’t break down easily), bioaccumulative (builds up over time), and toxic. It enters the environment from both natural sources and human activities and is harmful to human health and environmental ecosystems. Mercury can harm neurological, developmental, and reproductive systems in both people and animals.


Mercury contamination can come from multiple sources including both natural and  industrial sources. Mercury can enter the Columbia through direct releases from industrial sources (e.g. incinerators, cement plants), coal-fired power plants, mining, improper disposal of items that have mercury (e.g. transformers, thermostats, fluorescent bulbs) or from atmospheric deposition and runoff. Coal burning power plants are one of the primary sources of mercury air emissions.

When coal is burned mercury is released into the atmosphere, where it can travel long distances. That mercury can then enter the Columbia River as it is deposited through snow or rain. The EPA State of the River Report states that “based on available data, atmospheric deposition appears to be the major pathway for mercury loading to the Columbia River Basin.” When mercury settles to the bottom of the river, bacteria convert it into methylmercury, a more toxic and bioavailable form of mercury. Increased bioavailability means that much more of the toxic mercury can be absorbed into an organism.


Mercury can harm the central nervous system, developmental systems, and the immune system. In humans, the very young are more sensitive than adults. Exposure is particularly dangerous for babies and fetuses where high exposure can lead to lifelong learning and behavioral problems. Methylmercury, the highly toxic form of mercury that accumulates in fish, can biomagnify so predators or species higher up the food chain will have much higher levels than the surrounding water or species near the bottom of the food chain. The most common pathway for mercury exposure to humans is from eating fish contaminated with methylmercury.


Mercury pollution is one of the top drivers of fish advisories in the Columbia River. And studies on Columbia River lamprey show concentrations high enough to threaten the recovery and survival of the species. The primary source of mercury in the Columbia River Basin is atmospheric deposition. This includes air emissions from sources that are inside the basin as well as global sources of mercury that are transported in the atmosphere from facilities as far away as Asia and Europe. The EPA estimated that total mercury deposits in the Columbia River Basin is 11,500 pounds per year. A whopping 84% of that mercury comes from global sources, but regional sources can still have big local impacts.


You can learn more about the concerns with mercury and other toxic contaminants and consuming Columbia River fish by reading our fish consumption fact sheet.  Because mercury is persistent and bioaccumulative it can accumulate in the flesh of Columbia River fish, and there is no way to reduce mercury through cooking or preparations. Due to the amount of fish consumed, tribal people face a disproportionate risk from eating Columbia River fish. While in some places fish advisories suggest limiting consumption to reduce risk, fish advisories unfairly shift the burden to tribal people who must then make choices between exposure to toxic contaminants, socio-economic impacts, and cultural practices.


Community-based participatory science projects like the Crayfish Mercury Project are helping to increase monitoring and understanding of the distribution of mercury throughout the Columbia Basin.

Other studies like those by Yakama Nation and USGS will increase understanding of the impacts of mercury contamination on the Columbia River, and helpful resources like the NRDC Mercury in Fish Guide can help you make decisions to limit personal mercury exposure.