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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 protein and low in saturated fat. They have nutrients that are important for proper growth and development. Studies show that omega-3 fatty acids in fish may reduce the risk of heart disease and stroke. Many doctors suggest that eating one to two fish meals each week helps prevent heart disease.

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

Learn more about consumption advisories. 

Consumption advisories are not intended to discourage people from eating fish or shellfish. They are intended to help people make informed decisions about the safety of their fish and shellfish based on their water body source.

Fish and shellfish consumption advisories recommend consumption guidelines based on potential health risks. People should also use these guidelines to choose fish and shellfish species and water bodies with lower levels of contaminants.

Fish Consumption by Children and Pregnant Women

The U.S. 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 mercury levels. Recent reports show that the nutritional value of fish is highly beneficial for the growth and development of infants and children.

The most common fish with lower mercury are:

  • Salmon
  • Tuna (light canned)
  • Tilapia
  • Cod
  • Pollock
  • Catfish

Fish types to avoid include:

  • Shark
  • Swordfish
  • King mackerel
  • Tilefish from the Gulf of Mexico

View the FDA’s “Fish: What Pregnant Women and Parents Should Know” for more information.

DSHS Fish Consumption Guides and Documents

Contaminants of Concern

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

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

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

Mercury is also released into waters from:

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

Airborne mercury is an indirect source of mercury, reaching surface waters and soils through precipitation. Mercury can also enter water when lakes or rivers are disturbed. This happens with flooding or dredging, for example.

Sources of mercury in soil include:

  • Fertilizers
  • Fungicides
  • Solid waste, like:
    • Batteries
    • Electrical switches
    • Thermometers
    • Fluorescent light bulbs
    • Municipal incinerator ash placed in landfills
    •  Application of sewage sludge to cropland

In aquatic environments, microorganisms convert inorganic mercury to methyl mercury. Acidic waters with high levels of organic matter make this chemical change more likely.

Methyl mercury accumulates in fish and is passed up the food chain:

  1. Small fish eat methylmercury in insects and microscopic animals.
  2. Larger fish then eat methyl mercury in the smaller fish.
  3. People eat methylmercury when they eat larger fish.

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

  • Freshwater fishes such as:
    • Largemouth bass
    • Freshwater drum
    • Gar
    • Pike
    • Walleye
       
  • Marine fishes such as:
    • King mackerel
    • Shark
    • Swordfish

These fishes may contain methylmercury levels 1 to 10 million times greater than those found in the surrounding water.

Eating fish that contain methylmercury can damage the brain and other parts of the nervous system. The greatest health risk from methylmercury may be to an unborn baby. The unborn baby has a higher risk of irreversible nervous system damage from mercury.

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

Symptoms of prolonged exposure to high levels of methylmercury may include:

  • Tingling of the skin
  • Loss of coordination
  • Visual and hearing impairment
  • Slurred speech

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

Polychlorinated Biphenyls (PCBs)

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

The United States’ biggest source of environmental PCBs today is from ongoing use, storage, and disposal of products in landfills. It is also from 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
  • Animals in all regions of the world

PCBs break down very slowly in the environment. They accumulate in 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 in the surrounding water.

PCB levels in fish vary with:

  • Species
  • Age
  • Size
  • Fat content
  • Diet
  • Surface water concentrations

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

  • Carp
  • Buffalo
  • Catfish
  • Spotted seatrout

These fish may contain higher levels of PCBs than lean fish.

Examples of lean fish include:

  • Largemouth bass
  • Walleye
  • Crappie
  • Red drum

PCBs may cause infants of women who have eaten many contaminated fish to have lower birth weights, delayed physical development, and learning difficulties. PCBs may affect the:

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

PCBs may increase the risk of cancer.

DDT, DDE, and DDD

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

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

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

Chlordane

Chlordane is a man-made pesticide used in the United States from 1948 to 1988.

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

Chlordane breaks down very slowly in the environment. It also accumulates in the fatty tissue, skin, and internal organs of fish and other animals.

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

Toxaphene

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

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

The EPA banned toxaphene in the United States for most uses in 1982. From 1982 until 1990, toxaphene was approved only for use on livestock and for insect control emergencies. The EPA banned all 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
  • Disposal of waste pesticides

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

Aldrin and Dieldrin

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

In 1970, the United States Department of Agriculture canceled all agricultural uses in the United States for all uses. Aldrin and dieldrin are no longer produced in the United States.

Dieldrin enters the environment through:

  • Past uses
  • Accidental spills or leaks from storage containers at disposal sites

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

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

Chlorinated Dibenzodioxins and Dibenzofurans (Dioxin)

Dioxins are formed from:

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

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

Human activities that produce dioxins include:

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

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

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

You may get chloracne, a severe skin disease with acne-like lesions on the body if you eat fish that has dioxins. Dioxins may also cause other skin rashes, skin discoloration, and excessive body hair. Dioxins may also cause liver damage, weight loss, reproductive damage, and birth defects. Dioxins may weaken the immune system, disrupt the endocrine system, and may increase 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 the 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 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.
Seafood and Aquatic Life Group

Seafood and Aquatic Life Group