By Peter Montague
The chemical industry received some extraordinarily bad news in early June. Science magazine published a new study showing that some combinations of hormone-disrupting chemicals are much more powerful than any of the individual chemicals by themselves.
Science magazine is the conservative voice of mainstream science in the US. Until this article, Science had largely ignored the possibility that industrial chemicals may be interfering with hormones in wildlife and humans.
The new study shows that combinations of two or three common pesticides, at low levels that might be found in the environment, are up to 1600 times as powerful as any of the individual pesticides by themselves. The study showed that one chemical, chlordane, which has no ability to disrupt hormones by itself, nevertheless greatly magnifies the ability of other chemicals to disrupt hormones.
If these findings are confirmed by follow-up studies, it could profoundly affect the way chemicals are viewed, tested for toxicity and regulated because combinations of chemicals will have to be considered. The environmental protection apparatus of the US and, indeed, the world, is presently based on studies of individual chemicals acting alone.
Hormones are particularly important during growth and development. About 100 different hormones have now been identified, and they control growth, development and behaviour in all vertebrates, including humans.
Since 1991, studies have shown that at least 50 synthetic (human-created) industrial chemicals can interfere with hormones and disrupt normal growth and development in birds, fish, mammals, reptiles, amphibians and humans. Many of the 50 hormone-disrupting chemicals are commonly found in detergents, plastics and pesticides.
In response to these studies, the chemical industry has asserted that low-level environmental exposures are not powerful enough to affect humans. The new study published in Science shows that the chemical industry's position is not likely to hold up under scrutiny.
The editors of Science evidently considered the new study so important that they simultaneously published two articles commenting on the findings. Furthermore, in the same issue, they published a flattering review of the recent book on hormone-disrupting chemicals, Our Stolen Future.
Even the editors of the New York Times considered the new study important enough to report on it in a straightforward manner. In March and April the Times had published a series of biased and inaccurate articles by Gina Kolata, who said the theory that industrial chemicals might interfere with hormones had been "refuted by careful studies", none of which she cited or described.
When scientists wrote letters to the editor, seeking to restore balance after Kolata's reporting, the Times refused to publish any of their letters. One group of scientists finally grew so frustrated that they took the highly unusual step of purchasing ad space in the Times to complain about Kolata's inaccuracies and bias.
The idea that common industrial chemicals may be interfering with the hormones of wildlife and humans has far-reaching implications. If it is true, it means that the chemical industry as we know it is a threat to all life on earth. How can we learn whether this is true?
Chemicals with vastly different molecular structures have proven to be hormone disrupters. This means that a chemical's ability to disrupt hormones cannot be discovered simply by examining a diagram of the molecule.
Therefore thousands of chemicals will need to be tested individually for their ability to disrupt hormones. A thorough battery of tests has not yet been devised, and there are now 70,000 chemicals currently in commercial use, with about 1000 new ones added each year. The prospect of testing the toxicity of this number of chemicals, even one at a time, is daunting.
The new study in Science makes the enormous problem of individually testing 70,000 chemicals seem small by comparison. If scientists have to study combinations of chemicals, their job is vastly increased. For example, to test just the commonest 1000 toxic chemicals in unique combinations of three would require at least 166 million different experiments (and this disregards the need to study varying doses). Even if each experiment took just one hour to complete and 100 laboratories worked round the clock seven days a week, testing all possible unique three-way combinations of 1000 chemicals would still take over 180 years.
This is not the first evidence that some combinations of chemicals are more powerful than any of their individual chemicals. Earlier this year researchers at the Duke University Medical Center published a study of three chemicals to which US soldiers were exposed during the Gulf War. None of the three chemicals, by itself, caused nerve damage in laboratory animals, but together the three chemicals showed powerful nerve-damaging effects — effects so strong that the researchers concluded that they may have found the cause of "Gulf War Syndrome", which plagues at least 30,000 US veterans of that war.
Even earlier, studies had shown that exposure to radiation enhances the toxicity of certain chemicals, and that tobacco smoke and asbestos enhance each other's toxicity. However, the US never tests chemical combinations to assess dangers.
For example, the National Research Council recently studied the problem of doing "risk assessments" for combinations of chemicals. The NRC concluded that simply adding up the individual toxicities was the way to handle combinations. NRC said this approach would underestimate the toxicity of combinations of chemicals no more than 10-fold.
The new study in Science throws the NRC's conclusion into a cocked hat. Combinations of two and three pesticides turn out to be anywhere from 160 to 1600 times as powerful as any of the individual pesticides. Risk assessments that assume chemical combinations are only 10 times as powerful as the individual chemicals may underestimate the dangers 100-fold or more.
Most importantly, one chemical (chlordane) by itself showed no hormone-disrupting effects, yet it magnified the hormone-disrupting power of other chemicals. This means that we must identify, and protect ourselves against, even very weak hormone-disrupting chemicals because they may not be so weak when combined with other common chemicals.
It is hard to imagine a practical, manageable testing program that can sort through these problems and produce reliable, comprehensive results in less than a century. By that time, if damage is being done now, as many scientists believe is the case, it will be far too late.
[From Rachel's Environment & Health Weekly.]