Dioxin. The mere word has become synonymous with environmental disaster in the United States. And yet, in many parts of the world, the highly toxic chemical is treated differently. ``Everyone regards it as dangerous - the difference arises when it comes down to determining safe exposures,'' says Dr. Walter Rogan, chief of the epidemiology branch of the National Institute of Environmental Health Sciences.
US standards are among the most conservative in the world. But some policymakers are now moving to ease the guidelines, prompting a storm of criticism.
Yesterday's report by a university researcher that significant levels of dioxin were found in the breast milk of American women underscores the controversial nature of the dioxin debate.
Dioxin accumulation in body tissues has been known for some time. Dioxins, like DDT and polychlorinated biphenyls (PCBs), are fat-soluable. Rather than breaking down once inside the body, the chemicals accumulate in fat and stay there. Mother's milk is more than 3 percent fat and is often used as an indicator of the concentration of such chemicals inside the body.
But researchers worry that dioxin in breast milk could injure infants, who might absorb a disproportionately large amount of the chemical during their first year of life.
Dioxins are produced as an unwanted byproduct from a variety of chemical and combustion processes. Traces of the chemical have been found in pesticides, incinerator ash, paper napkins, and disposable diapers. Exposure in the course of daily life - through breathing contaminated air, drinking contaminated water, and physical contact with materials - is generally quite low. But in some circumstances, such as with soldiers in Vietnam who were exposed to the herbicide Agent Orange, doses can be extremely high.
``We're finding that the US is typical of the industrialized countries which are careless with dioxin,'' says Arnold Schecter, professor of preventative medicine at the State University of New York at Binghamton and author of the study. Dr. Schecter, presenting his data at a press conference hosted by the Environmental Defense Fund, compared the US to other industrialized countries as well as countries in the developing world where dioxins are less prevalent.
In general, he found the level of dioxin in mother's milk significantly higher in the industrialized nations. The exception, he says, is South Vietnam, where the broad use of Agent Orange occurred. More significant is that the levels of dioxin absorbed by infants are likely to exceed the levels considered safe under current federal guidelines.
The United Nations' World Health Organization is conducting its own research on dioxin in mother's milk, focusing on Western Europe. The UN is concerned because it has promoted reliance on mother's milk in the developing world.
Concern about dioxin has mushroomed in the last decade. Part of the reason, say scientists, is the rapidly developing technology that allows the measurement of faint traces of dioxins.
``As time goes by, we're finding more and more sources of dioxins,'' says Donald Barnes, a dioxin specialist with the Environmental Protection Agency. But many of these sources are minuscule.
When scientists do identify a problem, it creates a huge stir. Earlier this year the agency stumbled onto dioxin in wood pulp products.
During a nationwide survey, the agency noticed an unusually high level of dioxin in fish taken from waters downstream from paper plants. This has prompted a full-scale study of paper products and the manufacturing processes that are involved.
There's no single rule for what amount of dioxin is permitted to be released into the atmosphere or carried in a particular product. Instead, the EPA has dealt with problems as they have arisen.
Part of the problem is that nobody's quite sure what the long-term impact of dioxin is on human health. Studies have shown that the chemical, even in extremely small doses, can cause cancer and other health problems in laboratory animals.
But scientists disagree about what this means for humans. It is against this background that policymakers have sought to establish what they consider safe levels of dioxin.
The US subscribes to one of the most stringent standards in the world. In a 1985 risk assessment, the EPA estimated that exposure to one six-thousandth of a picogram (a trillionth of a gram) of dioxin per kilogram of body weight over a 70-year lifetime creates a 1-in-1-million risk of cancer. Other countries allow for much larger accumulations.
Part of the reason for the difference has to do with the way various nations assess suspected carcinogens. Many countries have established a ``threshold'' for exposure that assumes the human body can absorb a considerable amount of dioxin without ill effects.
The US may soon move to ease its standard as well. In a draft report leaked to the press earlier this month, a group of policymakers inside EPA suggested sharply reducing the estimate of dioxin's cancer-causing potential. The report prompted criticism from some scientists who said it was too early to downgrade the danger. But others say it is high time the US adopted an approach more in line with other industrialized nations.