By Peter Montague
Several new studies have implicated chlorinated chemicals in human disease, including breast cancer and tooth decay. Chlorine chemistry is the premier example of humans adopting a new technology without thinking about the consequences.
Breast cancer
A recent study in Denmark reveals a relationship between breast cancer and the chlorinated pesticide dieldrin. The prospective study examined blood taken in 1976 from 7712 women enrolled in the Copenhagen City Heart Study. In the following 17 years, 268 of the women developed breast cancer.
The blood samples drawn in 1976 were analysed in 1993 for 46 chlorinated chemicals, including 28 individual PCBs [polychlorinated biphenyls] and 18 other chlorinated compounds such as DDT, mirex, aldrin, dieldrin and others. Of the compounds studied, only dieldrin was significantly elevated in the blood of women who developed breast cancer.
In Denmark, about 14% of all women (one in seven) develop breast cancer, and the incidence of the disease has more than doubled in the past 30 years.
Most of the identified "risk factors" for breast cancer indicate that oestrogen (female sex hormone) in a woman's blood plays an important role in the disease. The major known risk factors for breast cancer are commencement of menstruation at an early age, late menopause, not having any children, late conception of the first child and hormone-replacement treatment after menopause. All tend to increase a woman's lifetime exposure to oestrogens circulating in the blood.
The authors of the Copenhagen study conclude, "These findings support the hypothesis that exposure to xeno-oestrogens may increase the risk of breast cancer". Xeno-oestrogens are industrial chemicals (such as pesticides) that can mimic oestrogen in the human body.
Dioxin
For several years, US and European health authorities have been hinting that the public is being exposed to levels of dioxin that are probably causing harm in sensitive people. Now the federal Agency for Toxic Substances and Disease Registry (ATSDR) has confirmed the bad news.
The term "dioxin" encompasses 219 different toxic chlorinated chemicals, all with similar characteristics but different potencies.
Because some dioxins are more toxic than others, scientists have established a way of comparing the toxicities and the quantities of various mixtures of dioxins. The technique is called TEQ, or toxic equivalents. The TEQ system takes into account the variations in toxicity, expressing toxicity in terms of the most toxic dioxin, which is TCDD.
Dioxin is a highly toxic, unwanted byproduct of many industrial processes, including incineration of municipal, medical and hazardous wastes; metal smelting; the burning of fossil fuels; and the manufacture of many pesticides and other chemicals. We are all exposed to dioxin through our diets, mainly by eating fish, meat, and milk products. Vegetarians get much less than the average, but they do not get zero because dioxin falls out of the air onto vegetation.
Last December, the ATSDR in Atlanta published the long-awaited Toxicological Profile for Chlorinated Dibenzo-p-dioxins. The report had been circulating in draft form since 1991.
In the final report, ATSDR establishes a "minimum risk level" (MRL) for chronic (long-term) exposure to dioxin. An MRL is the amount of total dioxins (expressed as TEQs) that ATSDR believes people can take in day after day without suffering adverse health effects.
ATSDR's official MRL for chronic (long-term) exposure to dioxin is one picogram (one trillionth of a gram) of dioxin TEQ per kilogram of body weight per day. The new ATSDR report says that the average exposure of US citizens is three to six times higher than this.
Shortly after ATSDR released the report, a new study was published showing that some people have defective teeth as a result of exposure to current background levels of dioxin. The new study was conducted by dentists in Finland who have been studying dioxin for a decade.
In the early 1980s, these dentists noticed that many children had poorly developed molars — discoloured and soft. The normal hard enamel coating was partially missing, making the teeth subject to decay. The researchers hypothesised that the children were being exposed to some toxin early in life which was interfering with normal development of their teeth.
Noting that Chinese children born to mothers who were accidentally exposed to high levels of dioxin showed tooth problems similar to those in Finnish children, the Finnish dentists began exposing rats to low levels of dioxin. They found that they could produce the same kind of tooth defects in the rats.
Further research by the same scientists found that the children with the worst teeth were born to mothers with the highest levels of dioxin in their breast milk, thus establishing a dose-response relationship.
The Finnish researchers' findings "are very exciting in a scientific sense — and very concerning in a public-health sense — because they demonstrate effects from [dioxin] exposures at background levels", says Linda Birnbaum, a well-known dioxin researcher with the US Environmental Protection Agency.
[From Rachel's Environment & Health Weekly. Like Â鶹´«Ã½ Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]