The truth about pollution and penises is somewhat different. Scientists are concerned about the effects of certain pollutants that appear to mimic female hormones, and thus could inhibit the development of male sexual organs, but they are a very long way from proving that penises are getting smaller. They are also nowhere near demonstrating that dumping man-made chemicals in the sea is whittling away at other aspects of male sexuality - as the advertisement also suggested.
Greenpeace was right to say that sperm counts have fallen significantly and that other disorders of the male reproductive system, such as testicular cancer, are on the increase. But scientists are only beginning to work their way through the long list of possible causes that could account for this.
Once again, this most aggressive of pressure groups has used a certain licence - let us call it lobbyist's licence - with scientific cause and effect, and experience shows it won't be the last time. The question is: how often can Greenpeace cry wolf?
The claim about penis size originates with a study of a group of 2,000 Taiwanese people who had been poisoned in 1978-79 by eating rice contaminated with PCBs, a toxic and environmentally persistent class of pollutants. Scientists have monitored the children born to the women in this group, looking for signs of congenital abnormality, and among the many medical measurements they have taken in the course of the study were the penis lengths of boys at different ages.
In 1993, they published research suggesting that the penises of boys aged between 11 and 14 (but not younger than 10) were shorter by a centimetre or so than those of boys in the general population. They also found that girls in the group were on average nearly three centimetres shorter in height than other girls.
The implication is that PCBs in the mothers caused a hormonal imbalance that affected the development of their babies. So there you are then: "Scientists have shown that the same chemicals that we dump into our seas are causing willies to shrink in size."
Well no. It is not so simple as that. First, the doses of PCBs that the mothers of these boys received were colossal - the most conservative estimate is that they were several hundred times higher than anyone in this country is likely to come across through environmental contamination. Second, we do not dump PCBs into the sea. Production of these chemicals stopped here in 1986 and Britain is engaged in attempts to destroy its existing stocks, but not by sea dumping.
The claim made in the advertisement simply cannot be sustained. Greenpeace has been here before. Last year it published pictures of a child with a grotesquely swollen head, supposedly a victim of Soviet nuclear tests in Kazakhstan.
While it is true that radiation exposure can cause a wide range of horrible medical conditions, hydrocephalus, or water on the brain, is not one of them. The Advertising Standards Authority ordered the advertisement to be withdrawn - but not before the campaign had raised pounds 70,000 in donations.
So Greenpeace takes the odd liberty - does it matter? After all, it was only an advertisement, and who believes them? Surely what counts is that the environmental lobby keeps going?
What is at stake here is credibility. It is perhaps ironic that Greenpeace's scientific reputation is actually higher than those of the government- funded scientists who do much of the work on which the activists base their claims. According to a Mori poll, less than half of the British public said it had a ''great deal'' or even a ''fair amount'' of trust in what scientists working in either industry or for the government said about environmental issues. Yet nearly three out of four said they trusted scientists working for environmental groups.
Richard Sharpe, a world authority on male sexual disorders at the Medical Research Council's Reproductive Biology Unit in Edinburgh, falls into the category of government-funded scientist. He has done more than most to identify the potential problem of the oestro-genic pollutants that Greenpeace is concerned about. He believes that last week's advertisement is a serious distortion that could backfire on the environmental movement.
''I support the spirit of Greenpeace and other environmental pressure groups," he says. "But in the long run they do themselves a disservice when they stray from the facts. People get desensitised when things don't turn out to be true.''
Dr Sharpe and his colleagues believe a range of environmental chemicals - from dangerous PCBs to "surfactants" found in soap - may affect development of the male reproductive system. But the research is far from reaching any definite conclusions on cause and effect.
A crucial issue for them is how much of a pollutant is likely to reach the public. This is critical in determining the amount of risk it poses. Dr Sharpe says that for this reason alone the Taiwan study says next to nothing about what these pollutants may be doing to the British population.
To illustrate, he points to the case of recent fears over the use of clingfilm to wrap cheese. Certain chemicals in clingfilm (chemicals that have since been removed by the manufacturers) were known to cause congenital problems in laboratory animals when given in high enough doses. When it was found that these chemicals could leach from clingfilm into fatty foods such as cheese, there was public alarm.
But when Dr Sharpe and others calculated how much it would take to cause any ill-effect, they found that a person would have to eat five rolls of clingfilm to run a serious risk. In short, dose levels are all-important.
Another problem with environmental chemicals revolves around the concept of "natural". These days, when the worst excesses of nature - from deadly infections to mass famine - are at a safe distance from most of us, the word ''natural'' has become a byword for goodness. Yet some of the most toxic chemicals are natural. Vitamin A, for instance, is natural and indeed essential for life, but if pregnant women take it in large enough doses, as they can through anti-acne drugs for instance, it can be one of the most powerful causes of congenital abnormalities.
The moral here is that when it comes to biology, chemicals often have a threshold dose below which they are harmless or even beneficial. Above the threshold they can become increasingly harmful. Greenpeace, however, rarely accepts the principle of threshold levels for pollutants, arguing that any level of an unnatural substance is not to be tolerated.
Recently the organisation mounted a campaign against polychlorinated paraffins, chemicals which are used in a wide range of applications, often as substitutes for the more dangerous PCBs that are now banned. An analysis of foods commissioned by Greenpeace found that chlorinated paraffins were ''known carcinogens'' and could be found in everyday products ranging from mackerel to cow's milk.
The problem with this was that there is no scientific evidence that these chemicals cause cancer in humans and, furthermore, the amounts found in the foods analysed by Greenpeace were measured in parts per billion, which is at the very limit of what modern science can detect, never mind establishing its effects.
There are other examples: last year, for instance, Nirex, the Government's nuclear waste body, was able to gloat over half a dozen errors that Greenpeace committed in its assessment of the risks of an underground repository at Sellafield. Among other things the environmentalists said the site was on a major earthquake fault, a claim that was demonstrably untrue. And in the debate over the Thorp nuclear reprocessing plant at Sellafield, Greenpeace said the long-term effects of the plant would kill 600 people, but again its calculations were shown to be seriously at fault.
Fred Pearce, author of Green Warriors, a book on the environmental movement, says that Greenpeace's science has improved over the years but it still employs its lobbyist's licence. ''These days I think they are better than many groups by at least having some science to back up their claims. They want to use science, but sometimes they push it too hard and go over the top.''
None the less, many scientists continue to respect Greenpeace's aims. Richard Sharpe is one; another is John Sumpter of Brunel University. He is phlegmatic about the willy ad: ''The place it oversteps the mark is by saying 'scientists have shown that
Most people would probably agree, but there has to be a limit. Unless it is careful, Greenpeace will soon find the public as sceptical about its scientific claims as it is about the Government's.Reuse content