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 is helpful in preventing 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 its 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 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 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, 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 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, 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, 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:
o Batteries,
o Electrical switches,
o Thermometers,
o Fluorescent light bulbs,
o Municipal incinerator
ash placed in landfills, and
o Application of sewage
sludge to cropland.
Aquatic environment 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 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:
o Largemouth bass,
o Freshwater drum,
o Gar,
o Pike, and
o Walleye
o King mackerel,
o Shark, and
o Swordfish
may contain methyl mercury levels 1 to 10 million times greater
than those found in the surrounding water.
Eating fish that contain methyl mercury can damage the brain and
other parts of the nervous system. The greatest health risk from methyl mercury
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
methyl mercury 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 methyl mercury
may include:
o Tingling of the skin,
o Loss of coordination,
o Visual and hearing
impairment, and
o Slurred speech.
Infants and children exposed to very high levels of methyl
mercury 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, and
- 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 varies with:
- Species,
- Age,
- Size,
- Fat content,
- Diet, and
- Surface water concentrations.
Larger, older fish will generally have higher levels of PCBs
than 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 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, and
- Liver
and may increase the risk of cancer.
DDT, DDE, and DDD
DDT is a chlorinated pesticide once widely used to control
insects on agricultural 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 builds 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 may 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
agricultural crops, lawns, 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 U.S. 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, and
- 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 Unites States Department of Agriculture canceled
all agricultural uses of dieldrin in the United States. It was still used to
control termites until 1987. Then, the EPA banned it in the U.S. for all uses. Aldrin
and 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 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, 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 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, and the
- 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 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.