Dioxin danger worse than expected

For three years, the US Environmental Protection Agency (EPA) has been reassessing the toxicity of dioxin and other dioxin-like chemicals, including dibenzofurans and some PCBs (polychlorinated biphenyls).

PCBs are industrial chemicals now banned in the US because of widespread environmental damage. Dioxins and furans are unwanted by-products of many industrial operations including incineration, tyre burning, combustion of coal and oil, manufacture of paper and some pesticides and metal smelting. Dioxins and furans are created when chlorine combines with other chemicals at high temperatures.

In 1990, the paper and chlorine industries campaigned to force EPA to undertake a thorough review of dioxin science. The reassessment has not turned out the way those industries hoped it would. We have obtained two drafts of the EPA's summary report of its dioxin reassessment, titled “Chapter 9. Risk Characterization of Dioxin and Related Compounds”, dated March 7, and May 2, 1994. Some conclusions of the May 2 draft were reported in the New York Times on May 11. What follows here is based entirely on the EPA's May 2 draft.

EPA has identified 30 dioxin-like chemicals (7 true dioxins, 10 furans, and 13 PCBs) that have dioxin-like characteristics. EPA's draft report describes the toxicity of all these 30 chemicals taken together; in this discussion we refer to them as simply dioxin.

EPA has concluded that:

* For non-cancer effects, such as damage to the reproductive, endocrine and immune systems, in birds, fish and mammals, including humans, dioxin is much more toxic than previously believed;

The agency says, “Indeed, these compounds are extremely potent in producing a variety of effects in experimental animals based on traditional toxicology studies at levels hundreds or thousands of times lower than most chemicals of environmental interest”. And: “... humans are likely to respond with a plethora of effects from exposure to dioxin and related compounds”.

* Dioxin's most powerful effects are on the reproductive system, the endocrine (hormone) system and the immune system. Most sensitive of all are newborn infants and foetuses exposed in the womb. Dioxin exposure of mammals (including humans) shortly before or shortly after birth is most likely to impair intellectual development and the immune system.

* Some of dioxin's powerful effects are observable in humans at dioxin exposure levels already occurring in the US population. EPA says, “Some of the effects of dioxin and related compounds have been observed in laboratory animals and humans at or near levels to which people in the general population are exposed.” Average levels of dioxin already present in the bodies of average Americans -- or levels not more than 10 times as high as average levels -- seem to be capable of damaging the immune system, reducing sex hormones in the bloodstream of men, interfering with glucose metabolism (a condition suggestive of diabetes) and causing other negative changes in health and well being.

The average amount of dioxin in Americans is 9 nanograms per kilogram (ng/kg) of body weight; a nanogram is a billionth of a gram. Sex hormones are diminished in men with 13 ng/kg; altered glucose tolerance has been observed in humans with 14 ng/kg; decreased growth is observable in humans having 47 ng/kg; endometriosis is produced in monkeys having 27 ng/kg.
Within the general public, some people are receiving lower than average doses of dioxin and others are receiving higher than average doses. EPA says, “Some more highly exposed members of the population may be at risk for a number of adverse effects including developmental toxicity, reduced reproductive capacity in males based on decreased sperm counts, higher probability of experiencing endometriosis in women, reduced ability to withstand immunological challenge, and others”.

* Dioxin's cancer effects are worse than previously thought. EPA now says flatly that dioxin is “likely to present a cancer hazard to humans”. Dioxin “probably increases cancer mortality of several types” in humans, EPA says.

EPA's best estimate is that existing levels of dioxin in the US population may be sufficient to cause cancer in somewhere between one in 10,000 people and one 1000 people during a lifetime (70 years). Since there are 250 million Americans, EPA is saying that existing dioxin levels may be causing somewhere between 25,000 and 250,000 cancers in a lifetime (70 years), or 350 to 3500 new cancers each year.

If EPA's estimate of the dioxin cancer hazard is correct, an individual's lifetime probability of getting cancer from dioxin in the US falls in the range of 1 in 1700 to 1 in 3300. This is the same risk you would get from 300 to 600 chest x-rays.

Dioxins are produced in very small quantities, if at all, by nature. EPA says, “... the presence of dioxin-like compounds in the environment occurs primarily as a result of industrial practices”.
EPA identifies four major sources of dioxin in the environment:

1. Combustion and incineration sources. This category includes incineration of municipal solid waste, sewage sludge, hospital wastes and hazardous wastes; metallurgical operations, such as high-temperature steel production, smelting and scrap metal recovery furnaces; and the burning of coal, wood, petroleum products and used tyres for power or energy generation.
2. Chemical manufacturing/processing sources. Dioxins and dioxin-like compounds are created by the manufacture of chlorine and such chlorinated compounds as chlorinated phenols, PCBs, phenoxy herbicides (2,4,5-T, 2,4-D and 11 others), chlorinated benzenes, chlorinated aliphatic compounds, chlorinated catalysts, and halogenated diphenyl ethers. Although manufacture of many chlorinated phenols and PCBs, ceased in the US around 1980, use and disposal are continuing both inside and outside the US. Large quantities of PCBs are in “storage” in leaking land fills; another billion pounds of PCBs (about 1/3 of all PCBs ever manufactured) simply cannot be accounted for.
3. Industrial/municipal processes: Dioxin-like compounds are created during chlorination of naturally occurring phenolic compounds, such as those in wood pulp. Chlorine bleaching in the manufacture of bleached pulp and paper has resulted in dioxins in paper products as well as in liquid and solid wastes from this industry.
4. Reservoir sources: Dioxin degrades very slowly once it is released into the environment. Therefore past releases of dioxin have accumulated in various “reservoirs”, such as soils, sediments, organic matter, and waste disposal sites. When dioxins move from these reservoirs they can become “new sources” of dioxin for a particular locale.
   

All together, these sources emit some 14 kilograms of total dioxins each year in the US. But the amount of dioxins falling on the surface of the US each year is estimated to be between 20 and 50 kg. Obviously some important sources of dioxin have not yet been identified. Dioxins may be arriving from other countries, carried on the wind. EPA simply doesn't know.

Dioxins fall out of the atmosphere onto the land and water and are then incorporated into the food chain, or they are discharged directly into waterways and incorporated into food chains. They tend to concentrate as they move upward in the food chain; over 90% of the dioxins in our bodies enter with our food. The major sources of dioxin to humans are meat, fish and dairy products, though inhalation may be important near some emission sources, such as some incinerators.