Analyzing the EPA report on dioxin


October 04, 1994|By Dr. Genevieve Matanoski | Dr. Genevieve Matanoski,Medical Tribune News Service

Recently in Washington, the Environmental Protection Agency released a 2,000-page draft report on the chemical compound dioxin. The report concludes that exposure to dioxin may be dangerous, and could cause cancer in humans.

But does dioxin pose a significant threat to most people? How are we exposed to the chemical? What other risks does it represent? Is it possible to limit our exposure to dioxin? For the answers to these questions, I consulted with my colleague, Dr. Thomas Sutter, an assistant professor in the department of environmental health sciences at the Johns Hopkins School of ++ Public Health.

Q: What is dioxin?

A: Dioxin is the most potent member of a larger class of more than 200 related chemical compounds, including PCBs (once widely used in industry, but now banned). It is an accidental and unwanted byproduct of certain commercial processes, including the manufacture of pesticides and insulating materials, municipal and hospital waste incineration, and bleaching of paper with chlorinated compounds. There are natural sources of dioxins, too, including volcanic eruptions and forest fires.

Q: How are people exposed to the chemical?

A: A major source of human exposure to dioxin is through the food chain. After emission from incinerator smokestacks and other industrial sources, dioxin binds to airborne particulates, such as dust.

As the particulates fall back to earth, landing on plants, farmland, lakes and rivers, they are ingested by animals and fish. Once ingested, they lodge in the animal's fatty tissue.

Q: How do they cause cancer?

A: The process is not completely understood. Unlike most suspected carcinogenic agents, dioxin does not damage the DNA (the hereditary material in cells) and cause mutations. Instead, it acts by triggering chemical receptors on the surface of the cells. This makes it hard to study the effect in humans, because individuals may respond differently to the same amount of dioxin. They also may have different exposures.

Q: Does the EPA report call for specific action?

A: The report still is in draft form. The purpose of the release is to provide scientists, industry officials, environmentalists and the public a response period.

The report summarizes research findings and estimates the risk, but does not recommend regulations. It focuses on sources of dioxin that may be controlled to reduce exposure. It is estimated that less than half of the sources of dioxin are known.

Actually, by some observations, levels of these chemicals in the environment may have decreased in the past 10 years. The paper industry, through the use of new bleaching methods, has dramatically reduced its dioxin output from pounds to ounces. The production of PCBs has been banned. And the bird population, whose egg shells were thinned, perhaps by chlorinated pesticides, apparently is on the increase.

Q: Is there any realistic way of assessing my risk?

A: The estimates of risk state that there may be one cancer caused by dioxin in 1,000 to 10,000 people exposed to the chemical. This number is based on mathematical models, which deliberately overestimate the risk. At the other end of the scale, the risk actually could be zero. Again, some people may be more at risk than others.

Q: If the report cites the food chain as a source of dioxin, should diet changes be advocated?

A: The best approach to control is to reduce the output of dioxin into the environment. Major sources of the chemical continue to be identified, and steps are being taken to curtail the production and release of dioxin. Individuals should continue to maintain a recommended healthy diet, since most dioxin intake is very low or non-existent.

Q: What about breastfeeding?

A: Dioxin may pass from the mother's fat to breast milk, and research is continuing in this regard. However, the advantages of breastfeeding far outweigh any concern about possible traces of dioxin that may be transferred from mother to child.

Dr. Matanoski is a physician and epidemiologist at the Johns Hopkins School of Hygiene and Public Health.

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