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Facts About Illinois' Methylmercury Advisory

A statewide methylmercury advisory is in place for all Illinois water bodies. Women who are or could become pregnant, women who are nursing, and children less than 15 years of age should limit their consumption of predatory fish to one meal per week. Additionally, site-specific advisories are issued for water bodies when further restrictions (1 meal/month or do not eat) are warranted to protect these sensitive groups, restrictions are needed to protect the entire population, or advisories for non-predatory fish are warranted. Water bodies with site-specific advisories can be found on the Illinois Department of Public Health’s current fish advisory map.

Why has Illinois issued a statewide methylmercury advisory?

The advisory has been issued due to the prevalence of methylmercury in predatory fish collected throughout Illinois. Because mercury primarily enters aquatic environments through atmospheric deposition, all Illinois water bodies are susceptible to contamination. Thus, the advisory includes all public and private water bodies, including those not monitored by the state.

Why does the statewide methylmercury advisory only apply to women and children?

Predatory fish contain methylmercury at levels that may impair the neurodevelopment of embryos, fetuses, and children. Though these levels are not harmful to adults, mothers may pass methylmercury to their child during pregnancy or when nursing and cause harm. Thus, the statewide advisory also applies to women who are or could become pregnant, and women who are nursing.

Why is the statewide methylmercury advisory only for predatory species?

Low levels of methylmercury accumulate into small fish due to contributions from the water and their diet. Predatory species that consume these smaller fish can accumulate much higher methylmercury levels over time. This is especially true for larger or long-lived predatory species. Predatory species for Illinois include largemouth bass, smallmouth bass, spotted bass, striped bass, white bass, walleye, sauger, flathead catfish, all species of gar, muskellunge, northern pike, all species of trout and salmon, and associated hybrids.

How does methylmercury get into bodies of water in Illinois?

Mercury occurs naturally in rocks and soils. It is primarily released into the environment through air pollution associated with mining, coal combustion, and the production of metals and cement. Once emitted, mercury can travel thousands of miles in the atmosphere before being deposited into water bodies. In aquatic environments microorganisms can transform mercury into methylmercury, a form that accumulates in fish and is more easily absorbed by humans when ingested.

Why do some Illinois water bodies have site-specific methylmercury advisories?

Site-specific advisories are issued for water bodies that are known to contain fish with methylmercury levels beyond the statewide advisory levels. The amount of methylmercury in fish is primarily dependent on the amount of mercury deposited into a water body, and the chemical and physical attributes of the water body that promote methylmercury production. Some regions of Illinois tend to have fish with greater methylmercury contamination, though it is unclear why.

What are the potential health effects for people who eat fish contaminated with methylmercury?

Methylmercury can damage the developing nervous systems of fetuses and children, resulting in adverse outcomes, such as lower IQ, slowed motor function, and incoordination. At higher exposures methylmercury can affect the central nervous system of adults, resulting in memory loss, slurred speech, and poor muscle control. The potential for health effects is dependent on the methylmercury content in fish, how often the fish are eaten, and over what period of time.

Is methylmercury stored in the human body for long periods of time?

Once ingested, methylmercury is absorbed through the gastrointestinal tract into the bloodstream where it is rapidly carried to other parts of the body. It takes about 50 days for half of the mercury that has entered the body to be removed. The remaining mercury is slowly removed from the body over several months, mainly in feces.

How can I reduce my exposure to methylmercury in fish?

Methylmercury accumulates in the muscle of fish and cannot be reduced by trimming, skinning, or cooking your meal. You can reduce your mercury intake by avoiding large fish, choosing non-predatory fish (e.g., bluegill), and following the statewide and site-specific methylmercury advisories.

Are fish I buy from the grocery store contaminated with methylmercury?

Fish purchased from grocery stores and restaurants contain methylmercury. The U.S. Food and Drug Administration advises that women who are or could become pregnant, women who are nursing, and children less than 12 years of age not eat shark, swordfish, king mackerel, and tilefish due to high methylmercury levels. Other purchased fish, such as catfish, salmon, tilapia, and canned light tuna, contain lower levels of methylmercury.

Should I be concerned about swimming in bodies of water due to mercury contamination?

Advisories are issued due to high levels of methylmercury in fish, not water. Methylmercury levels in water can be hundreds or thousands of times lower than the levels in fish tissue. Swimming poses a low risk of methylmercury exposure.

What is being done to reduce the amount of mercury entering the environment?

In 2012 the U.S. Environmental Protection Agency (USEPA) finalized the Mercury and Air Toxics Standards. The rule requires coal and oil-fired power plants to meet technology-based emissions standards for mercury and other hazardous air pollutants. The USEPA estimates that by 2017, mercury emissions from power plants were reduced by 86%. However, mercury emissions in other countries remain high and will continue to contribute to methylmercury levels in Illinois water bodies.