Dioxins in Fish and Shellfish

Posted: 12-Aug-2004; Updated: 07-Sep-2004

Dioxins are highly toxic byproducts of industrial processes. Like many other contaminants found in fish, these chemicals are slow to break down and they accumulate in the bottom sediments of streams, rivers, lakes and coastal areas. Dioxins can build up in the fatty tissues of fish and other animals, and in high enough concentrations pose serious health risks to people who frequently eat contaminated fish. Based on the available data on contaminants in fish, Environmental Defense recommends limiting consumption of farmed or Atlantic salmon partly because of their elevated dioxin levels. View full chart.

What Are Dioxins and Where Do They Come From?

Polychlorinated dibenzo-p-dioxins (or simply dioxins) and polychlorinated dibenzofurans (or simply furans) are two closely related families of hazardous compounds. Like PCBs, "dioxins" and "furans" are general terms that refer to a mixture of individual dioxin and furan compounds. The most dangerous (and the most studied) of these dioxin compounds is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin).

Small amounts of dioxins are produced naturally during forest fires and volcanic eruptions. However, the majority of dioxins and furans in the environment are an unwanted result of human industrial processes, such as the production of certain herbicides and disinfectants, waste incineration, and chlorine bleaching of pulp at paper mills. Improved pollution controls and changes in manufacturing processes have in some instances reduced releases of dioxins to the environment.

What Are the Health Risks Associated With Consuming Dioxin-Contaminated Fish?

Based on studies done on laboratory animals, exposure to dioxins and furans is known to cause a variety of cancers and can harm the immune system. Effects on reproductive, endocrine, circulatory and nervous systems have also been observed. TCDD (the most hazardous of the dioxin compounds) exhibits the highest cancer potency of any chemical ever studied in animals.

In humans, where epidemiological evidence must be relied on, the link between dioxins and cancer is less certain. Some studies have shown a direct relationship between dioxin exposure and increased cancer risk, whereas others have not. This suggestive evidence in humans, combined with the clear results of animal testing, has led EPA to classify dioxin as a "probable human carcinogen."

The most common and well-documented acute effect of dioxin exposure on human health is chloracne, a severe skin rash characterized by acne like lesions. Studies also show dioxin exposure causes other effects in humans, including other types of skin diseases and changes in the blood levels of reproductive hormones and of enzymes involved in liver function.

How Can I Reduce the Risks of Eating Seafood Contaminated With Dioxins?

Dioxins build up in fish and animal fat, and therefore proper cooking methods can help reduce your exposure:

• Before cooking, remove the skin, fat (found along the back, sides and belly), internal organs, tomalley of lobster and the mustard of crabs, where toxins are likely to accumulate.
• When cooking, be sure to let the fat drain away and avoid or reduce fish drippings.
• Serve less fried fish; frying seals in chemical pollutants that might be in the fish's fat.
• On the other hand, grilling or broiling allows fat to drain away.
• For smoked fish, it is best to fillet the fish and remove the skin before the fish is smoked.

What Fish Should I Avoid?

Fish low in contaminants are an important part of a healthy diet. That's why Environmental Defense recommends limiting consumption of farmed or Atlantic salmon in part because of their elevated dioxin levels.

View full chart.

Where Can I Get More Information on Dioxins?

Scorecard.org Chemical Profile - Dioxins
EPA Chemical Fact Sheet - Dioxins
FDA: Questions and Answers on Dioxins
Agency for Toxic Substances and Disease Registry: Dioxins Fact Sheet

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