Scientists probing hormone-disrupting chemicals say politicians should not wait until it is too late to act. Robert Allen reports. As health workers, mothers and baby milk manufacturers debate the controversial findings of a Ministry of Agriculture Fisheries and Food study that found chemicals in infant formula milk, one of the scientists working on the threat to human health from hormone-disrupting synthetic compounds believes it is nearly time to start taking political action.

Physician Carlos Sonnenschein argues that "we should wait a little bit longer" until more evidence is gathered but after that politicians should act. "I personally believe it will neither be very efficient nor effective to wait until all the evidence is in. There are hundreds of thousands of compounds. We cannot study them one by one and when all of them are in say 'I told you so'. This would take decades. Therefore at some point political authorities will have to take decisions."

The MAFF survey (on 59 samples of 15 brands of powdered baby milk) found levels of phthalates - synthetic compounds which soften plastic - insufficient to damage human fertility, according to Richard Sharpe, who led the research, Yet the average levels in formula milk exceed EU precautionary limits and are close to levels known to cause reproductive problems in wildlife. The concern arises because toxological information on the estrogenic effects of phthalates is only available for a fraction of the known phthalate compounds used in industry. Scientists believe phthalates leach from plastic packaging and are absorbed in fatty foods.

Sonnenschein has, with his colleague Ana Soto, been at the forefront of scientific research into hormone-disrupting chemicals since 1987 when they both discovered, during a controlled experiment on cell growth at their laboratory in Tufts Medical School in Boston, United States, that something estrogenic was contaminating their blood serum samples. After two years of painstaking detective work they found the culprit - a synthetic chemical called p-nonylphenol which was leaching from seemingly benign plastic test tubes.

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Sonnenschein and Soto quickly learned that p-nonylphenol is one a family of synthetic chemicals known as alkyphenol polyethoxylates - used by manufacturers to stabilise and strengthen plastics such as polystrene and PVC. The plastic test tubes used by Sonnenschein and Soto were made from polystrene to which some manufacturers add nonylphenols. Alkylphenols have been implicated as environmental estrogens - man-made chemicals capable of mimicking the sex hormone estrogen. In 1990 there were more than 600 million alkyphenol polyethoxylates in use globally.

This discovery set the pair on a new course of research - into synthetic chemicals. They teamed up with two Spanish researchers and began to learn of other hormone-disrupting synthetic chemicals, significantly Bisphenol-A, which they found in the saliva of dental patients and in the plastic lining of food cans.

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Aware that many in the scientific community believe that phytoestrogens (found in plants and vegetation) can also disrupt hormones in wildlife, Sonnenschein and Soto have begun research to determine the impact on humans from the man made kind. "We can take human blood, and probably in the future human fat, extract everything that is there and separate three components - man-made estrogens, ovarian estrogens and phyto estrogens and we can make a nice micro-study," says Soto, explaining that they can then determine, for example, whether the incidence of undescended testicles "correlate with environmental estrogens, ovarian estrogens or phytoestrogens".

But Sonnenschein and Soto are more concerned about the synergistic effect of hormone-disrupting chemicals - that the estrogen problem is the result of a combination of chemicals. "We combined ten chemicals at one tenth of the active dose and we found a cumulative effect; we started removing one at a time and we realised we still had activity by the time we had removed four or five; now we are trying to understand what is the relationship among them. Apparently at low doses they act in an additive synergistic way," Soto explains. She says that they are being very careful with their research because "it seems now that we get more than the sum but we are not convinced because the study is not finished".

So is there a problem? While Sonnenschein is sure, Soto can't say. "I am a member of the [US] National Academy of Sciences committee that is reviewing data in an attempt to find out whether or not there is a problem so I cannot tell you. We're bound to keep cool. I can only talk about my research. Ana Sota cannot think as a citizen for a while. I can't talk about policy. I can tell you we have no idea what is the relative risk of natural [phyto] estrogens versus environmental estrogens."

But she adds with the same caution as her partner: "You cannot even start with anything unless you change the approach. You can't check everything under the sun. If you start doing what has been done with breast cancer you can keep doing this until the cows come home and you won't find anything because humans are not bound to a small area."

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Individual exposures and environmental backgrounds differ for every person, she explains.