New evidence on dioxin's health effects


New evidence of dioxin's ability to cause cancer in humans has come to light just as environmental justice activists across the US are planning a major campaign to attack dioxin at its sources. The dioxin campaign puts the grassroots environmental community squarely "in the face" of the biggest polluters in the nation, and it creates a "line in the sand" — a challenge to the old conservative wing of the environmental community, which to some extent has made its peace with the dioxin polluters.

"We know that we are up against huge corporate power, but tackling the misuse of corporate power is what the 21st century is going to be about", says Ellen Connett, one of the leaders of the new campaign, and editor of the indispensable weekly, Waste Not.

A new study published in December found a dose-dependent increase in risk of cancer and heart disease among a group of 1189 workers at a pesticide manufacturing plant in Hamburg, Germany, who were exposed to dioxins during the period 1952 to 1984. The study group included every worker employed for three months or longer at the plant from 1952 until it shut down in 1984. The workers were followed through the end of 1992.

Exposure to dioxins was evaluated to see if dioxins were related to particular causes of death. Deaths among the pesticide workers were compared to deaths among a control group consisting of 2528 non-dioxin-exposed workers at a gas supply company located in the same region of Germany.

The pesticide workers had produced phenoxy herbicides (examples: 2,4-D, 2,4,5-T and silvex), chlorophenols and other herbicides and insecticides known to be contaminated with dioxins and furans. Dioxins and furans are a family of 210 unwanted by-products (75 dioxins and 135 furans) from certain chemical reactions in the production of phenoxy herbicides. Dioxins may be produced by other chemical reactions as well, including metal smelting and the incineration of solid and medical wastes. TCDD is the most toxic of the dioxin family.

The study found, among dioxin-exposed workers, an increase in all deaths, an increase in cancer deaths and an increase in deaths due to ischaemic [narrowing of the arteries] heart disease, compared to same-aged individuals in the control group. The disease-related deaths increased with the dose of dioxin to which the workers were exposed.

The study found that pesticide workers with the highest dioxin exposures faced more than three times the risk of dying from cancer and 2.5 times the risk of dying from ischaemic heart disease, compared to workers of similar ages from a nearby gas plant.

The study grouped the 1189 workers according to their degree of dioxin exposure. Dioxin exposure was calculated by measuring dioxin in the blood of 190 workers, or 16% of the exposed group. As the authors themselves say, "The major strength of the present study is the availability of a quantitative measure of exposure, which allows a direct estimate of dose-response relations".

The study evaluated several factors that could have biased the results. For example, they ruled out possible bias due to smoking because the group of pesticide workers and the control group both contained about the same proportion of smokers.

They evaluated and discussed possible effects due to exposures to chemicals besides dioxins. They could not rule out possible bias from exposure of the pesticide workers to cancer-causing chemicals besides dioxins.

The authors conclude that the results of this study "support the hypothesis of a dose-related effect of PCDD/F [dioxins and furans] on cancer and ischaemic heart disease mortality".

The finding of elevated cancer deaths among dioxin-exposed workers is not a new finding. Three previous studies have reported cancer increases among dioxin-exposed workers.

However, this new study is particularly interesting because it is based on actual measurements of dioxin levels in the blood. Previous studies have estimated dioxin exposures instead of measuring them. Finding greater numbers of cancers associated with larger doses of dioxin provides strong evidence of a cause-and-effect relationship between dioxin exposure and cancer in humans.

The finding of increased heart disease among dioxin-exposed workers is somewhat more surprising. Previous studies of this effect have been inconclusive; some studies of dioxin-exposed populations have reported increased heart disease, and other studies have reported no such increases. However, these previous studies have not been able to establish a dose-response relationship, as the present study has done.

In studies of people exposed to dioxin after a chemical accident at a Hoffman-LaRoche pesticide factory in Seveso, Italy, in 1976, it was noted that excessive numbers of people died of heart attacks. The authors of the Seveso study attributed these deaths to "stress from the accident". Now there is reason to ask whether these Seveso deaths were possibly caused, not by stress, but by exposure to dioxins released during the accident.
[From Rachel's Environment & Health Weekly.]