Mercury FAQs

An advisory is just a warning...it is not a law. You will not go to jail for eating fish out of a particular stream or lake, and no one can stop you from fishing or eating the fish. A fish consumption advisory is a very conservative estimate of how much fish you can eat without any adverse health effects.

Most people can safely eat at least some if not all of the fish they catch. Advisories vary and it is important to read each one carefully, as many include only certain species of fish. Pregnant and nursing women and children under the age of 7 are most sensitive to the effects of mercury. Some advisories apply ONLY to sensitive groups, while others apply to the general population.

If you occasionally eat fish from an advisory area, it is very unlikely that you will get sick. Even in advisory areas, the mercury levels found in fish are well below what normally causes adverse health effects. If fish from an advisory area is a primary part of your diet, you should follow the advisory consumption levels, especially of the predatory species like bowfin and largemouth bass. However, if you have eaten fish from an advisory area, especially if you are pregnant or nursing, and are concerned about your health you may want to speak with a health care provider.

Fish consumption advisories are directed towards sports and subsistence fishermen. Commercial fishermen are not prohibited from fishing in advisory areas. Bowfin and freshwater drum are two commercial species that are often targeted in advisories. Consumers are advised to buy fish only from reputable sources and to question grocers/suppliers as to the location of the catch and follow the species-specific language in the advisories.

Symptoms of mercury poisoning usually begin with numbness and tingling in the fingers and toes, irritability, tremors. High-level, long-term exposure can lead to memory loss, vision loss, hearing loss, psychosis, birth defects, and death. All forms of mercury affect the central nervous system. High levels of elemental, inorganic, or organic mercury can permanently damage the brain, kidneys, and developing fetuses. Organic forms of mercury, which are found in the edible parts of fish, are the most toxic.

If you experience any of the described symptoms or other neurological problems, you should see a doctor. Even if you do not experience any symptoms and are concerned about mercury contamination, you may ask your doctor to take a sample of your hair or blood and test it for mercury levels.

All mercury advisories apply only to fish consumption, so you will not be exposed to mercury by swimming in a mercury advisory area. Swimming advisories are posted for several water bodies in Louisiana, so it is important to check with either LDEQ or the Louisiana Department of Health (LDH) to get a list of the most recent swimming advisories. Swimming advisories are issued due to high levels of fecal coliform or other chemicals, not mercury.

Mercury advisories on a water body should not affect your desire to enjoy a day of fishing. The fish are largely unaffected by the mercury in their tissues and will continue to give you the challenge and fun of trying to catch them. In areas where mercury concentrations are a concern for eating you can always practice catch and release. But as described above you can generally still safely eat some of the fish you catch, provided you follow the consumption advisory recommendations. 

Mercury, a naturally occurring element, is mined by humans and used in numerous household products, dental fillings, industrial processes, and is also a trace element in fossil fuels (primarily coal). Although there are many potential sources, the greatest anthropogenic source of mercury in water appears to be emissions from coal fired electric plants. Natural sources of mercury contamination include volcanic activity. Mercury released into the air can travel long distances and then be deposited into streams and lakes through atmospheric deposition (fall-out), making it nearly impossible to pinpoint sources of contamination. Mercury is also released into water and air by some industrial processes, waste incineration, and improper disposal of mercury-containing products. All sources of mercury emissions are being evaluated and reduced or eliminated where possible.

Unfortunately, you can't get rid of mercury. Mercury is an element and can exist in several forms (elemental, inorganic compounds, organic compounds), but it does not degrade. Soil, sludge, and other solid waste contaminated with mercury can be removed and disposed of elsewhere, such as in an approved hazardous waste landfill, but it will never be gone. In order to reduce the risk of further mercury contamination mercury use has been or is in the process of being phased out of certain products. Things like batteries, children's light-up shoes, fluorescent lights, mercury vapor lights and other products are among the items where the use of mercury has been eliminated or significantly reduced. The ongoing development of LED lights will further aid in the reduction of mercury use in lighting. Industrial permit limits are becoming more stringent, and better control technology is being developed. As a result, mercury discharges into streams and lakes have been greatly reduced in the past few decades.

In 1992, data from fish tissue sampling on the Ouachita River resulted in issuance of a fish consumption advisory by the Louisiana Department of Health (LDH) and the Louisiana Department of Environmental Quality (LDEQ). The advisory consisted of two recommendations: First, pregnant or nursing women and children under seven years of age should not consume any bass, and should limit consumption of other species to two meals per month. Second, non-pregnant women, men, and children over seven years of age should limit consumption of bass from the Ouachita to two meals per month. There is no limit on the consumption of other species by this second population. In addition to the LDH/LDEQ advisory, the U.S. Fish and Wildlife Service (USFWS) strongly recommends that no fish or raccoons taken on either Upper Ouachita or D'Arbonne National Wildlife Refuges be consumed. The USFWS used different fish samples, analytical techniques and risk assessment methodologies.

Since that time, extensive work has been done to determine the scope of mercury contamination in Louisiana. This has involved two separate studies, first on 12 North Louisiana lakes, and second a statewide study originally designed for a three-year span which will be continued as funding permits. Results of these two studies as well as additional information on the effects of mercury on humans and wildlife are presented here.

The Louisiana Department of Health (LDH) and LDEQ coordinate in the assessment of data for health risks and jointly issue advisories if warranted. The Louisiana Department of Wildlife and Fisheries and the Louisiana Department of Agriculture and Forestry are also apprised of the situation and allowed to comment. LDH and LDEQ use a limited meals approach in establishing health advisories. The two lead agencies will consider issuing a health advisory limiting fish consumption for pregnant or breast feeding women and children under seven for locations and species where the average concentration of mercury exceeds 0.23 parts per million (ppm) in fish and shellfish. At average concentrations exceeding 0.7 ppm, the agencies will recommend limited meals or no consumption for pregnant or breast feeding women and children under seven and limited consumption for the general population. In addition, LDH considers other types of information when making advisory decisions. These considerations include, but are not limited to, information on sensitive subpopulations and local fish consumption practices that can affect exposure, the number of samples within a species, and the size and number of fish collected. The Food and Drug Administration (FDA) uses a maximum allowable level of 1.0 ppm, which was established to protect consumers at mercury concentrations 10 times lower than the lowest levels associated with the initial adverse effects of mercury.

Adverse effects on the nervous system, particular in developing fetuses and young children among whom effects can be permanent, is of primary concern with mercury contamination. Paresthesia, which consists of numbness and tingling of lips, fingers and toes, is generally the first symptom of mercury poisoning. Continued exposure results in stumbling, slurred speech, constricted visual fields, and impaired hearing. In extreme cases tremors and jerks can occur, followed by coma and death.

It is important to note that both the mercury concentrations found thus far in Louisiana and the alert levels used by FDA and LDH/LDEQ are well below those found to cause mercury poisoning due to consumption of contaminated fish. Two notable mercury poisoning cases occurred in the 1960's in which over 100 persons were killed or became ill as a result of eating contaminated fish almost daily over an extended period of time (Foulke, 1994). These episodes took place in Minimata and Nigata, Japan. In each case, industrial discharges of mercury were routed to bays where fish were obtained for local consumption. Average mercury concentrations in fish tissue from both areas ranged from 9-24 ppm, with some fish having concentrations of up to 40 ppm. By comparison, the highest average concentration found to date in Louisiana was 0.984 ppm for king mackerel collected south-southwest of Grand Isle. The highest single sample concentration of 4.04 ppm was found in a largemouth bass from the Ouachita River. Therefore, the lowest average concentration found in Japan was over nine times higher than the highest reported average for Louisiana. For individual samples, the highest concentration in Japan was over 10 times higher than the highest individual sample reported in Louisiana. This illustrates both the highly protective nature of FDA and LDH/LDEQ alert levels and the significantly lower mercury concentrations found in Louisiana and the United States. There have been no cases similar to the Japanese episode reported in the United States.

Besides posing a human health risk, elevated levels of mercury in fish can also have ecologically significant effects, such as affecting reproduction in fish and wildlife. Although fish can generally excrete inorganic mercury, methylmercury crosses biological barriers more readily and is not readily excreted nor sequestered in a form less harmful to the fish. Because of the ease with which methylmercury crosses biological barriers, embryonic fish are at much higher risk of mortality than adults even at mercury concentrations 1% to 10% lower than concentrations associated with adult mortality in fish. Due to biomagnification, predatory fish at or near the top of aquatic food chains and larger, older fish tend to have the highest concentration of mercury and, therefore, pose the greatest risk to human consumption.

Among terrestrial wildlife, top predators of the aquatic food chain tend to have the highest concentrations of mercury. Such species include raccoons, mink, otters, cougar and fish-eating birds such as eagles, ospreys and great blue herons. Effects on terrestrial wildlife are similar to those of aquatic organisms and range from adverse effects on growth and reproduction to behavioral effects and mortality.

LDEQ has been testing fish for mercury throughout the state since 1992. Initial sampling centered on north Louisiana water bodies and lakes because the problem was first identified by Arkansas in the Ouachita River. A North Louisiana Twelve-Lakes Study was conducted in 1993 as a follow-up to the initial Ouachita River study. A total of 15 largemouth bass from each lake were tested for mercury in fillets. The twelve lakes covered by the study are listed below along with the average concentration for each lake (Table 1.).

Table 1: Average concentration of mercury (ppm) in largemouth bass fillet samples from twelve North Louisiana lakes sampled in 1993.

No advisories were issued following the North Louisiana Twelve-Lakes Study; however, five of the lakes were scheduled for resampling as part of a statewide study conducted in conjunction with the United States Geological Survey (USGS). These included D'Arbonne Lake, Cheniere Brake, Cross Lake, Toledo Bend and Caddo Lake. Although mercury concentrations in fish tissue from Caddo Lake were found to be below the 0.5 ppm trigger level for resampling, additional sampling was recommended because Texas had issued an advisory for their side of the lake. Resampling of those lakes with average concentrations greater than 0.5 ppm did not confirm the presence of high levels of mercury, and no advisories were issued.

Following the Twelve-Lakes Study, LDEQ and the USGS began a statewide mercury contaminants study in early 1994 to sample approximately 33 new sites per year over a three-year period. At the completion of the first three years, LDEQ elected to continue the study on its own in an effort to more fully characterize the extent of health risks due to mercury. Targeted species for the statewide study include largemouth bass, channel catfish, blue catfish, crappie and bowfin. Substitutes included sunfish, freshwater drum, gar, striped bass, white bass, and buffalo. Composites consisting of at least three fish of the same species were collected for each sample, with generally five to 12 samples at each water body or sample site. The initial study was discontinued in approximately 2009 due to changes in budget priorities. However, the sampling program was restarted in 2014, with the same general sampling protocols.

As of June 2023, statewide sampling of fish continues with approximately 60 water bodies typically sampled each year. To date, over 300 sites have been sampled as part of the statewide study. Water bodies currently under advisories are being resampled as scheduling allows. Water bodies without advisories but with slightly elevated concentrations of mercury in fish are also being resampled as time permits. New water bodies not previously sampled are occasionally added as they are identified. Data from the mercury fish tissue sampling program can be found through the LDEQ online data access tool, LEAU Web Portal.

Based on sampling conducted by LDEQ and upon risk assessment work provided by the Louisiana Department of Health, there are currently 50 separate fish consumption advisories due to mercury. Because some advisory statements include more than one named water body there are currently 97 named Louisiana water bodies under an advisory. The presence of an advisory on any water body does not necessarily indicate that no one should eat any of the fish. Rather, it means that some precautions should be taken regarding the type of fish consumed or the segment of the population you are in (for example pregnant or not; adult or child under 7). Details on each of these advisories can be found on LDEQ's fish consumption and swimming advisory web page. Interested persons may also call the Louisiana Department of Health (LDH) hotline at 1-888-293-7020 or the LDEQ at 1-866-896-5337.

Possible sources of mercury in Louisiana and the nation are many and varied. Ambient concentrations of mercury have increased significantly since the beginning of the industrial revolution. One study on Minnesota and Wisconsin lakes found that annual mercury deposition increased from 3.7 µg/m2 prior to 1850 to 12.5 µg/m2 in modern times. In addition, they found that mercury deposition rates were similar among widely scattered lakes indicating regional or global sources. These lakes were relatively undisturbed and had no known direct sources of mercury. Other reports have confirmed these results, indicating that anthropogenic sources are increasing the level of mercury contamination in the environment.

As a result of the proliferation of mercury in the environment, many of the fish people consume, including ocean caught species such as tuna, swordfish and shark purchased at local stores, are contaminated with low levels of mercury. Much of this is due to the fact that mercury is present in coal used at electrical power plants and is used in many products such as thermometers, fluorescent and mercury vapor lights, and electrical switches which may eventually be incinerated or placed in landfills. Mercury in these materials is released to the atmosphere as a gas by coal burning, trash incineration or direct volatilization. In a process similar to acid rain, the mercury is later deposited on the earth's surface through atmospheric deposition.

Other sources of mercury emissions to the atmosphere include chloralkali plants, which use mercury cathodes to generate chlorine and alkali from brine using electricity; hazardous waste incinerators; and pulp and paper mills. In addition to these regional and global sources of mercury, potential localized sources of mercury, both natural and anthropogenic, are known to occur. These include, but are not limited to, mercury leaching or vaporization from bedrock; active and inactive mercury mines; metal processors; natural gas meters containing mercury; and past use of mercury as a fungicide or pesticide. A complete list of mercury uses and sources is beyond the scope of this summary.

Paper mills, waste incinerators, and chloralkali plants that are major sources under LDEQ's Air Toxics rule are required to report mercury emissions under the Toxics Emissions Data Inventory (TEDI). Results from the past five years indicate that, with the exception of chloralkali plants, the other facilities generally report mercury emissions of less than 100 lbs. per year. One chloralkali plant is part of a major source facility and emits approximately one ton per year. The second chloralkali plant is not a major source facility and does not report mercury emissions; however, other reports indicate emissions of less than one ton per year. Electrical power plants are currently exempt from LDEQ's Air Toxics rule but not other Air Quality regulations, and are not required to report mercury or any other emissions as part of the TEDI. In addition, power plants generally do not have any type of pollution abatement systems for mercury. EPA is currently in the process of preparing a report on mercury emissions from power plants and other sources. Results of this study will be provided in future summaries. LDEQ's Air Analysis Section does not currently monitor ambient air for mercury. However, if funding can be obtained mercury monitoring may be incorporated in order to support LDEQ's research on mercury in fish.

Fortunately, due to the nature of mercury's bioaccumulation contamination levels of fish in Louisiana are generally below those considered harmful to humans. This is evidenced by the fact that despite the widespread testing done in Louisiana, and the application of even more protective fish consumption advisories than some other states, we currently have a limited number of advisories for mercury. In addition, these advisories usually permit at least limited consumption of most fish by most people. This fact is often overlooked when a new fish consumption advisory is first issued by the Louisiana Department of Health (LDH) and LDEQ and then publicized by the media. LDH and LDEQ will consider issuing additional fish consumption advisories due to mercury as the statewide mercury survey continues.

To summarize, it is unfortunate that mercury has become, over many years, all too common in Louisiana's and the world's environment; this includes our air, soil, sediments and water. However, even those water bodies currently under advisory in Louisiana are still capable of supporting sport fishing and fish consumption, provided some precautions are taken.

For more information regarding mercury and other fish consumption advisories contact the LDH hotline at 1-888-293-7020, or call the LDEQ at 1-866-896-5337 or email to Water Planning and Assessment Division. 

Anthropogenic - environmental contaminants released by human activities.

Bioaccumulation - the rate and means by which a substance is incorporated and concentrated in an organism.

Biomagnification - process by which contaminants are accumulated to higher concentrations in predatory species due to consumption of many smaller organisms with lower concentrations of the contaminant. Bioaccumulated contaminants are frequently biomagnified as one moves up the food chain to higher predators, including humans.

Inorganic mercury - the commonly known elemental form of mercury, Hg 0, found as a silvery liquid or vapor, or the mercuric ion, Hg(II). Liquid inorganic mercury is not absorbed during digestion, but the vapor is absorbed by the lungs. Neither form is readily bioaccumulated by fish, humans or other organisms.

Methylmercury - mercury that has been converted by bacteria or other processes into an organic (containing carbon) compound, CH3Hg-. Methylmercury is the only form of mercury that can be readily bioaccumulated by fish, humans and other organisms; therefore, essentially all mercury found in fish is methylmercury.

TEDI - Toxics Emissions Data Inventory - a data base containing actual toxic air pollutants emissions as listed in LAC 33:III.Chapter 51. Major sources of toxic air pollutants are required to report these emissions annually.