Illinois Department of Natural Resources

Q: Why has Illinois issued a statewide methyl mercury advisory?

A: The Illinois Fish Contaminant Monitoring Program (IFCMP)* has issued a statewide advisory for predator species in Illinois waters. The change is based on the latest scientific findings of recent studies that have documented impaired fetal development and a consistent pattern of methyl mercury levels detected in predator species throughout the state. The advisory has been established to protect the most sensitive populations including pregnant or nursing women, women of child-bearing age, and children <15 years of age.

*IFCMP includes staff from the Departments’ of Agriculture, IEPA, DNR, IDPH, and Nuclear Safety

Q: Has the concentration of mercury increased in Illinois predator sport fish?
A: No. Methyl mercury levels detected in predator sport fish have remained relatively consistent; the advisory has been issued based on the results of recent scientific studies indicating that methyl mercury is more toxic than previously thought. Based on the study results, the guidelines that were used to establish the Illinois fish advisories have been lowered for methyl mercury.

Q: Why is the statewide methyl mercury advisory only for predator species?

A:Mercury is very persistent in the environment. Small organisms absorb mercury from water and sediment and the organisms are eaten by smaller fish. Predator fish eat the smaller fish and methyl mercury is accumulated up the food chain so the larger fish have the highest amounts of methyl mercury stored in their bodies. Predator species for Illinois include all species of black bass (largemouth, smallmouth, and spotted), striped bass, white bass, hybrid bass, walleye, sauger, saugeye, flathead catfish, muskellunge, and northern pike.

Q: Is mercury stored in the human body for long periods of time?
A: When methyl mercury is ingested, approximately 95% is absorbed through the gastrointestinal tract into the bloodstream and it is rapidly carried to other parts of the body. The half-life for methyl mercury in the body is approximately 70 days. It is slowly excreted from the body over several months, mainly in feces.

Q: Why is there a special methyl mercury advisory for pregnant or nursing women, women of child-bearing age, and children <15 years of age?

A. These are the populations at highest risk for adverse health effects. This is due to the greater sensitivity of the developing nervous system of infants and children.

Q: How does methyl mercury get into water bodies in Illinois?
A: Mercury is a metal that occurs naturally in small amounts in the environment. It also is thought to come from burning coal or trash, as well as from industry. Mercury gets into lakes and rivers several ways, including rain and runoff. When conditions are right in the water, certain kinds of bacteria change inorganic mercury into methyl mercury. Methyl mercury is stored in the muscle of fish that eat mercury-contaminated food or live in mercury-contaminated water.

Q: What are the potential health effects for people who eat fish contaminated with methyl?

A: At low doses, methyl mercury can harm the developing nervous system in a fetus and children. At high doses, methyl mercury can affect the central nervous system (triggering such health problems as memory loss and slurred speech), kidney damage and failure, and gastrointestinal damage. The health affect is dependent on the amount of methyl mercury in the fish and how much is consumed over a period of time. Based on the concentrations detected in predator sport fish in Illinois, it is unlikely that individuals would experience health effects associated with high doses.

Q: What about the fish I buy in the grocery store - do I have to be concerned that they may be contaminated with mercury?

A: Fish such as shark, swordfish, king mackerel, and tilefish contain high levels of methyl mercury. The FDA is advising pregnant women, women of child-bearing age, and children not to eat these fish. The FDA advisory acknowledges that seafood can be an important part of a balanced diet for pregnant women and those of child-bearing age who may become pregnant. FDA advises these women to select a variety of other kinds of fish including shellfish, canned fish (including tuna), smaller ocean fish or farm-raised fish. These women can safely eat 12 ounces per week of cooked fish. A typical serving size of fish is from 3 to 6 ounces.

Q: Why has Illinois issued a statewide methyl mercury advisory based on a new standard, but at the same time lowered the advisory for Cedar Lake and Lake Kinkaid? Has the concentration of mercury decreased in these lakes and in the sport fish?

A:The concentration of methyl mercury in predator sport fish in Cedar and KinkaidLakes has not changed significantly. A new approach for issuing fish advisories for methyl mercury in Illinois has changed significantly. Prior to this year’s fish advisory, advisories for methyl mercury were based solely on protecting sensitive populations and there were only two categories: “do not eat” and “unrestricted”. The new approach for issuing fish advisories for methyl mercury has resulted in five categories (similar to the PCB approach) and the added categories include advisories for sensitive populations as well as men (>15 years) and women beyond child-bearing age.

Q:   Should I be concerned about children swimming in water bodies in Illinois based on mercury contamination?

A:   No. The amount of contact or incidental consumption you would experience while swimming in waters contaminated with mercury is insignificant.

Q:   Why is there a Special Mercury Advisory for some water bodies in the state?

A:  Laboratory results from predator sport fish in some water bodies (Ohio River, Campus Lake, Cedar Lake, and Kinkaid Lake) have shown higher contamination than what has typically been found in other water bodies. Based on these higher concentrations of methyl mercury, a more restrictive advisory is necessary to protect public health.

Q : Why are there so many new advisories based on PCBs this year?

A:The IFCMP is a source of federal funds that paid for the analyses of fish samples was reduced in 1992 and 1993, and disappeared from 1994-1996. Therefore, there is a fairly large gap in the database used by the IFCMP to determine the need for advisories. Beginning in 1997, state funds became available to pay for the fish analyses, and the IFCMP began filling in the data gaps. Since in most cases two consecutive samples are needed to add, change, or remove an advisory, it wasn t until 1999 that changes could start to occur in the advisory list. A large number of waters that were identified as needing a second sampling from 1997-1999 had the required follow-up sampling completed last year, which is why there are 21 new bodies of water listed for PCB contamination, and a major revision of the advisory for the Rock River this year.

Q:What actions are being taken to reduce man-made sources of mercury into the environment?

A:There are several actions being taken, at the national, regional, state, and local level. At the national level, USEPA is developing Maximum Achievable Control Technology (MACT) standards for air pollution sources that emit mercury, which should be released soon. It is also working on regulations or guidance on air pollution controls to limit the amount of mercury emitted from coal-burning power plants, which have been identified as significant sources of airborne mercury. At the regional level, the US-Canadian Binational Toxics Strategy has developed numerous approaches for voluntary reductions in mercury releases to the environment, some of which are already being implemented in the Great Lakes basin (ex., fluorescent bulb recycling programs, mercury thermometer exchange programs). At the state level, the IEPA has formed a mercury workgroup to research sources of mercury release to the air in Illinois, and to identify opportunities for mercury reductions through regulations and air permits (these efforts will require the final release of the MACT standards before they can be implemented). The IEPA has also obtained a grant from the USEPA' s Great Lakes National Program Office to investigate ways to decrease the use of mercury in hospitals, which has resulted so far in a pilot program for mercury thermometer exchanges at two hospitals. At a more local level, there are a few fluorescent lamp recycling programs in existence (a listing can be found at, and elemental mercury and mercury-containing products can be turned in at Household Hazardous Waste collections sponsored by IEPA each year.


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