General Information on the Risk of Eating Fish-Seafood and Aquatic Life

Table of Contents

Benefits and Risks of Eating Fish and Crabs

Fish and shellfish are healthy foods. They are high in proteinand low in saturated fat. They have nutrients that are important for propergrowth and development. Studies show that omega-3 fatty acids in fish mayreduce the risk of heart disease and stroke. Many doctors suggest that eatingone to two fish meals each week is helpful in preventing heart disease.

Fish and shellfish can also store contaminants from the water orfrom the food they eat. These contaminants may get to levels that can beharmful to people who eat fish or shellfish.

Learn more about consumption advisories


Consumption advisories arenot intended to discourage people from eating fish or shellfish. They areintended to help people make informed decisions about the safety of their fishand shellfish based on its water body source.


Fish and shellfishconsumption advisories recommend consumption guidelines based on potential healthrisks. People should also use these guidelines to choose fish and shellfishspecies and water bodies with lower levels of contaminants.

Fish Consumption by Children and Pregnant Women

The US Food and Drug Administration (FDA) recommends that:

  • Young children and
  • Women who are pregnant or breastfeeding

should eat 2-3 servings each week of fish with lower mercurylevels. Recent reports show that the nutritional value of fish is highlybeneficial for the growth and development of infants and children.

The most common fish with lower mercury are:

  • Salmon,
  • Tuna (light canned),
  • Tilapia,
  • Cod,
  • Pollock, and
  • Catfish.

Fish types to avoid include:

  • Shark,
  • Swordfish,
  • King mackerel, and
  • Tilefish from the Gulf of Mexico.

Please see the FDA’s “Fish: What Pregnant Women and ParentsShould Know” for moreinformation.

DSHS Fish Consumption Guides and Documents

Contaminants of Concern

Mercury is a naturally occurring element. It is spread in theenvironment through natural processes and human activities. Mercury is releasedinto the air when rocks erode, soils decompose, and volcanoes erupt. However,70% of the total annual mercury releases to the environment are from humanactivities.

Most mercury releases in the air happen when people burn fossilfuels or incinerate solid waste. Other sources of environmental mercury include:

  • Mining,
  • Smelting,
  • Chlor-alkali and cement production, and
  • Other industrial processes that use mercury.

Mercury is also released into waters from:

  • Pulp and paper mills,
  • Leather tanning,
  • Electroplating,
  • Chemical manufacturing, and
  • Wastewater treatment facilities.

Airborne mercury is an indirect source of mercury, reachingsurface waters and soils through precipitation. Mercury can also enter waterwhen lakes or rivers are disturbed. This happens with flooding or dredging, forexample.

Sources of mercury in soil include:

  • Fertilizers,
  • Fungicides,
  • Solid waste, like:

o   Batteries,

o   Electrical switches,

o   Thermometers,

o   Fluorescent light bulbs,

o   Municipal incineratorash placed in landfills, and

o   Application of sewagesludge to cropland.

Aquatic environment microorganisms convert inorganic mercury tomethyl mercury. Acidic waters with high levels of organic matter make thischemical change more likely.

Methyl mercury accumulates in fish and is passed up the foodchain:

1.     Small fish eat methyl mercury in insects and microscopic animals,

2.     Larger fish then eat methyl mercury in the smaller fish, and,finally,

3.     People eat methyl mercury when they eat larger fish.

Fish at the top of the aquatic food chain, such as:

  • Freshwater fishes,

o   Largemouth bass,

o   Freshwater drum,

o   Gar,

o   Pike, and

o   Walleye

  • Marine fishes such as:

o   King mackerel,

o   Shark, and

o   Swordfish

may contain methyl mercury levels 1 to 10 million times greaterthan those found in the surrounding water.

Eating fish that contain methyl mercury can damage the brain andother parts of the nervous system. The greatest health risk from methyl mercurymay be to an unborn baby. The unborn baby has a higher risk of irreversiblenervous system damage from mercury.

Unborn babies, infants, and children are more sensitive tomethyl mercury than adults. This is because the brain and other parts of thenervous system are not completely developed.

Symptoms of prolonged exposure to high levels of methyl mercurymay include:

o   Tingling of the skin,

o   Loss of coordination,

o   Visual and hearingimpairment, and

o   Slurred speech.

Infants and children exposed to very high levels of methylmercury may have neurological symptoms like those of cerebral palsy. Most ofthe neurological developmental effects of low-level exposure to methyl mercuryare subtle.

Polychlorinated Biphenyls (PCBs)

PCBs are man-made substances. They used to be used once usedcommercially in electrical transformers, carbonless copy papers, cutting oils,and hydraulic fluids. PCBs may also enter the environment through many otherindustrial and commercial uses. In 1979, The United States EnvironmentalProtection Agency (EPA) banned the manufacture of PCBs in the United States. TheEPA did not require getting rid of PCB-containing materials still in use at thetime of the ban. So, some materials are still in use today.

The United States’ biggest source of environmental PCBs today isfrom ongoing use, storage, and disposal of products in landfills. It is alsofrom improper disposal of products that have PCBs.

PCBs also may be released from sediments moved by flooding,dredging, etc. We have found PCBs in:

  • Soil,
  • Ground and surface water,
  • Air,
  • Sediment,
  • Plants, and
  • Animals in all regions of the world.

PCBs break down very slowly in the environment. They accumulatein the fatty tissue, skin, and internal organs of fish and other animals.Levels of PCBs in fish may be 2,000 to 1,000,000 times greater than levels inthe surrounding water.

PCB levels in fish varies with:

  • Species,
  • Age,
  • Size,
  • Fat content,
  • Diet, and
  • Surface water concentrations.

Larger, older fish will generally have higher levels of PCBsthan smaller, younger fish. Fatty fish such as:

  • Carp,
  • Buffalo,
  • Catfish, and
  • Spotted seatrout

may contain higher levels of PCBs than lean fish.

Examples of lean fish include:

  • Largemouth bass,
  • Walleye,
  • Crappie, and
  • Red drum.

PCBs may cause infants of women who have eaten many contaminatedfish to have lower birth weights, delayed physical development, and learningdifficulties. PCBs may affect the:

  • Immune system,
  • Reproductive organs,
  • Skin,
  • Stomach,
  • Thyroid,
  • Kidney, and
  • Liver

and may increase the risk of cancer.



DDT is a chlorinated pesticide once widely used to controlinsects on agricultural crops and insects that carry diseases such as malariaand typhus. The EPA banned it in 1972.

DDT is in the United States’ environment because of past use asan insecticide and from waste sites. However, DDT continues to enter the environmentbecause it is used in many places worldwide.

DDT and its break down products, DDE and DDD, are long-livedchemicals that builds in the fatty tissue, skin, and internal organs of fishand other animals. So, DDT, DDE, and DDD levels can be much higher in fishtissue than in water or soil. Eating fish that contain DDT or its break downproducts may damage the nervous system, affect reproductive and liver function,and may increase the risk of cancer.


Chlordane is a man-made pesticide used in the United States from1948 to 1988.

  • Before 1978, people used chlordane as a pesticide onagricultural crops, lawns, gardens, and as a fumigating agent.
  • Between 1978 and 1983, the EPA phased out above-ground uses ofchlordane.
  • From 1983 until 1988, chlordane’s only approved use in theUnited States was for termite control.
  • In 1988, because of human health concerns, the EPA banned alluses of chlordane in the United States.

Chlordane breaks down very slowly in the environment. It alsoaccumulates in the fatty tissue, skin, and internal organs of fish and otheranimals.

Chlordane also remains in our food supply. This is because its widespreaduse on agricultural crops in the 1960s and 1970s contaminated agriculturalsoil. Chlordane can harm the nervous system, digestive system, endocrinesystem, and liver. Even at doses that cause no anatomical damage, Chlordane maycause behavioral disorders in infants exposed before birth or while nursing. Chlordanemay also cause cancer.


Toxaphene, introduced in 1947, was probably the most heavilyused pesticide in the United States during the 1970s.

Toxaphene was primarily used in the southern United States tocontrol insect pests on cotton and other crops. Toxaphene was also used to controlinsect pests on livestock and to kill unwanted fish in lakes.

The EPA banned toxaphene in the U.S. for most uses in 1982. From1982 until 1990,  toxaphene was approvedonly for use on livestock and for insect control emergencies. The EPA bannedall uses of toxaphene in the United States in 1990.

Toxaphene enters surface waters through:

  • Soil runoff,
  • Direct application as a pesticide,
  • Wastewater release from manufacturing facilities, and
  • Disposal of waste pesticides.

Toxaphene is a long-lived chemical in the environment. It accumulatesin fatty tissue, skin, and internal organs of fish and other animals. You mayhave degenerative changes to the liver, kidney, and nervous system if you eatfish that has toxaphene. Toxaphene may also cause cancer.

Aldrin and Dieldrin

Dieldrin is a pesticide that is also a break-down product of thechlorinated pesticide aldrin. Dieldrin was widely used as a pesticide on corn,cotton, and citrus crops between 1950 and 1974. Dieldrin was also used to controllocusts, mosquitoes, and termites.

In 1970, the Unites States Department of Agriculture canceledall agricultural uses of dieldrin in the United States. It was still used tocontrol termites until 1987. Then, the EPA banned it in the U.S. for all uses. Aldrinand dieldrin are no longer produced in the United States.

Dieldrin enters the environment through:

  • Past uses and
  • Accidental spills or leaks from storage containers at disposalsites.

Once dieldrin is in the environment, it attaches to soil andlake or river sediments. It breaks down very slowly. Dieldrin in theenvironment for a long time. It accumulates in the fatty tissue, skin, andinternal organs of fish and other animals. Your immune system may be lesseffective if you eat fish that has dieldrin. It may also:

  • Increase infant mortality,
  • Reduce reproductive success,
  • Cause birth defects,
  • Damage kidneys, and
  • May cause cancer.

Chlorinated Dibenzodioxins and Dibenzofurans (Dioxin)

Dioxins are formed from:

  • Unintentional by-products of many industrial processes,
  • Incomplete combustion, and
  • Various chemical production processes.

Dioxins are also natural products of forest fires and some othernatural processes. These sources are small compared to dioxins produced byhuman activity.

Human activities that produce dioxins include:

  • Combustion of fossil fuels and wood,
  • Municipal and industrial waste,
  • Bleaching process in pulp and paper production, and the
  • Manufacture of some chlorinated chemicals.

We have found dioxins all around the world in soil, surfacewater, lake and river sediments, and plant and animal tissue.

Dioxins last for a long time in the environment. They easilybuild up in fish and other animal tissues. Levels of dioxins found in fish andother animal tissues may be hundreds to thousands of times greater than levelsin surrounding waters or sediments.

You may get chloracne, a severe skin disease with acne-likelesions on the body if you eat fish that has dioxins. Dioxins may also causeother skin rashes, skin discoloration, and excessive body hair. Dioxins mayalso cause liver damage, weight loss, reproductive damage, and birth defects.Dioxins may weaken the immune system, disrupt the endocrine system, and mayincrease the risk of cancer in humans.

Volatile Organic Compounds (VOCs)

VOCs are used to make many products, especially plastics and solvents. Generally, these compounds do not accumulate in fish and animals. VOCs are usually found in fish at the same levels as those in the surrounding waters. Most VOC contamination is due to a direct discharge of these compounds to surface waters. Eating fish containing VOCs may cause cancer in animals and humans. 

Sources of Information

General Fish Consumption Guidance for Texas Waters

  • Eat smaller, younger fish. These fish generally contain lower levels of contaminants than larger, older fish.
  • Remove skin, dark muscle tissue, and fat from fish. This practice reduces the risk of exposure to many organic contaminants, including PCBs, pesticides, and dioxins that readily accumulate in the fatty tissues.
  • Fish internal organs may contain high levels of contaminants and should not be eaten.
  • Eat fish from a variety of water bodies to reduce risk of exposure to any one contaminant or group of contaminants.
  • Follow the DSHS safe eating guidelines for water bodies listed in this booklet. Eating a few fish meals from any area of concern probably has little or no human health risk, but eating contaminated fish frequently and regularly over a long period of time poses potential human health risks.
  • The DSHS recommends that people eat some commercially caught fish or that they substitute other sources of lean protein (i.e. chicken, venison, or soy products) for recreationally caught fish.