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The chemical juggernaut
Man-made chemicals pervade and support every aspect of modern living. But are they also 'elixirs of death' the symbol of our own destruction, as forecast by Rachel Carson in Silent Spring?. The question is discussed here by Deborah Cadbury, author of a new study into the Feminization of Nature.
The chemical industry is one of the commercial success stories of the 20th century. There are now over 100,000 man-made chemicals in every day use. Many more new compounds are created each year. According to some estimates, the chemical industry has become such a powerful force in the global economy, sales of synthetic chemicals and products derived from them constitutes well in excess of a third of the world's gross national product.
Photo : Chris Stowers/Panos Pictures
New evidence has shown that some chemicals found in plastics, pesticides and industrial products, are weakly oestrogenic, modifying the action of the female hormone; others can affect the male hormone, the androgens, or anti-androgens; others are thought to target different hormone systems, such as the thyroid and adrenal glands. More frightening still, these are chemicals which we may be eating, drinking, breathing, and bathing in. They are chemicals which no human infant escapes, sometimes even from before birth. Scientists have measured some of them in our own body tissues: our saliva, blood, breast milk and fat.
Increasingly, scientists are questioning the impact of these background levels of chemicals on human health. Research from an entirely different field first sparked the debate. In the late 1980's, Professor Niels Skakkebaek, a specialist in male reproductive health at Copenhagen University Hospital, was becoming concerned at the rising incidence of testicular cancer.
"In Denmark we now have 300 per cent more testicular cancer than we had 50 years ago," he observes. "The average increase in Western countries is 2-4 per cent per year over several decades, making this now the commonest cancer in young men."
His team also found some evidence of increases in abnormalities in the male organs of baby boys: testicular non descent and hypospadias. More worrying, the Copenhagen team uncovered a startling decline in human sperm counts. Analysing over 60 studies world-wide, the data suggested sperm counts had fallen by as much as 50 per cent in the last 50 years.
Working with Dr Richard Sharpe, from the MRC's Edinburgh Reproductive Biology Labs, in 1993, Professor Niels Skakkebaek went on to propose a remarkable hypothesis. They found oestrogen could play a more important role in the development of the male reproductive tract than was previously thought. By altering the extraordinarily delicate balance of hormonal cues necessary for healthy development, excessive oestrogen exposure may affect when the testes descend, masculinisation of the reproductive tract, the development of the urethra and even determine sperm out-put in later life. By affecting cell division, it could even create abnormalities that would predispose to testicular cancer later in life. Was it possible, they asked, that widespread exposure to oestrogenic chemicals could affect the development of baby boys in the womb?
Animal studies have confirmed the plausibility of their hypothesis. Rats exposed to trace quantities of the oestrogenic chemicals, bisphenol A, octyl phenol and butyl benzyl phthalate, while in the womb had more than a 10 per cent reduction in sperm counts and testis size as adults. Accidental human exposures also revealed the same pattern of reproductive disorders. However, Sharpe and Skakkebaek point out that an increase in oestrogen exposure in the last 50 years can also arise in other ways, such as through alterations in life-style and diet and the case against chemicals is not yet proven.
In fact, although the sharp rise in testicular cancer in the West is not in dispute, scientists cannot yet agree on whether sperm counts have fallen. Dramatic declines in sperm counts have been reported in Denmark, France, Britain, Finland and Belgium, but not in New York and some other parts of America. These studies have highlighted the complexity of the issue. In the words of one British Government report, while oestrogen hypothesis must now be regarded as 'plausible,' proof is likely to be 'elusive'.
Similar concerns arise in studies of breast cancer in women. This distressing disease has increased dramatically during the last 50 years, from one in 20 to approximately one in 12 in Britain and one in nine in America. Scientists are suspicious that oestrogenic chemicals may play a role for several reasons.
Firstly, breast cells are primed to respond to oestrogens and there are many oestrogen receptors in breast tissue. So if oestrogenic chemicals can act as 'pass keys' and fit the receptor just like the women's natural oestrogen, oestradiol, it is at least plausible they could exert effects. It is widely accepted that a woman's life-time exposure to oestrogens is an important risk factor for breast cancer.
Secondly, many man-made chemical oestrogen mimics appear to target fatty tissue such as breast tissue and can be stored there, sometimes for years. Indeed, studies show that compounds, such as DDT and certain PCBs may reach levels 200 to 300 times higher in fatty tissue in the breast, than in blood: levels that are much higher than circulating levels of the natural hormone oestradiol.
Thirdly, it can be shown in the laboratory that some breast cancer cell lines will only grow in the presence of oestrogens; this is used as a test of the potency of a chemical.
Despite such clues, studies on those with breast cancer are not clear cut. Professor Mary Wolff at the Mount Sinai School of Medicine in New York was one of the first to investigate a possible relationship between DDT and breast cancer. In a study of 58 women with breast cancer matched to the same number of controls she found those with the highest 10 per cent of exposure to DDT had about a four fold risk of breast cancer. But not all studies have revealed such a link, say critics such as Professor Stephen Safe from Texas A & M university.
Wolff and others agree that there are still a great many unknowns and argue that the relationship between the chemicals and breast cancer may not be simple. Breast tissue may be exposed to a cocktail of different chemicals and attempts to link increased risk of breast cancer to individual chemicals could be of limited value. What is more the timing of the dose may be more important than the amount. All of these factors make the epidemiology hard to assess.
Animal studies have also linked chemical exposure to another serious disease that is on the increase: prostate cancer. Professor Frederick Vom Saal at the University of Missouri has found that prenatal exposure to the synthetic oestrogen, diethylstilbestrol, can permanently sensitize organs such as the prostate glands in a developing foetus, predisposing to prostate disease later in life. Scientists have even linked exposure to PCBs and other persistent contaminants to immune problems, learning and behavioural difficulties. Is it possible, asks Dr Theo Colborn of the World Wildlife Fund, Washington, that whole societies are being subtly and insidiously undermined by chemical exposure?
Photo : Mark Edwards/Still Pictures
So are these chemicals the 'elixirs of death,' the symbol of our own destruction, forecast so eloquently by Rachel Carson in Silent Spring? Or is this little more than man's inventiveness being one step ahead of safety: a matter which can be easily remedied with a few regulations?
Despite a world-wide debate, the significance of the new findings for human health are still are not known. For some, given the usefulness and pervasiveness of the chemicals it would be irresponsible to ban them until we have further data. For others, given what we know now, it would be irresponsible not to ban them. This situation calls for an international treaty, argues Dr Theo Colborn and her colleagues. Just as governments united to deal with ozone depleting chemicals in the Montreal Protocol of 1987, a similar worldwide treaty is needed to control the use of the persistent hormonally active chemicals.
As with many complex environmental issues science can highlight trends, but cannot provide black and white answers. This could be the ultimate scientific cul de sac. For the longer we wait to gather the evidence, the harder it may become to put things right. "In the long term game called evolution there are unpredictable winners and losers," warns Professor Carlos Sonnenschein at Tufts University, Boston. "It would not be too clever for humans to inadvertently load the dice against their own chances."
Deborah Cadbury is an award winning producer and journalist for the science strand Horizon, BBC TV. Her new book, The Feminization of Nature, (Hamish Hamilton £20.00 hb, followed by Penguin paperback later this year), tells the alarming story of hormone disrupting chemicals and their possible effects on wildlife and human health.
Killing pests - and people
"Evidence indicates that hundreds of millions of farm workers, farm households and consumers are probably exposed to dangerous levels of pesticides."
That is the conclusion of a study by a research team from the Washington-based World Resources Institute, led by Robert Repetto and Sanjay Baliga, into the health consequences of the $30 billion pesticide industry.
The report found that while the bulk of the spending takes place in the United States, Western Europe and Japan, nearly half of the active ingredients by weight are used in developing countries ?much of these being the older, cheaper and more dangerous pesticides such as DDT and other persistent organochlorines.
In 1995, over 70,000 tons of organochlorine pesticides were applied in developing and former socialist countries.
It is not only farm workers who are affected, as biological studies show. "The presence of persistent bioaccumulative pesticide residues in foods, body tissues and human breast milk indicates that consumers far removed from agricultural operations can also be significantly exposed."
While studies found that 10 to 30 per cent of farm workers in Latin America showed damage to their neuro-muscular system as a result of pesticide poisoning, only 10-15 per cent of pesticides reach their target on the farm. The rest is dispersed through air, soil and water, some of it only over many years.
Some of this gets into animal dairy products, for example, so that in parts of Mexico and Argentina, most butter and cheese contains pesticide residues. Research among Canadian Inuit people found contaminated fish and marine mammals were affecting breast milk and depressing the immune system in babies, laying them open to infections, including meningitis and inner ear infection.
>Research also shows that many organochlorine, organophosphate, carbamate and metallic pesticides affect the immune system of animals and humans, exposing farmers to cancers. Pesticides are also associated with other health disorders, including infectious diseases which may or may not be associated with alterations in the immune system.
"There is reason to be especially concerned about the immunosuppressive effects of pesticides on exposed populations in the developing countries" where people are much more vulnerable to infectious and parasitic diseases and where many people have weakened immunological defences, the report says.
It calls on the World Health Organization to take a lead in epidemiological research in such regions, and on the pesticide companies to ensure the safety of their products and join in health research.
It also calls on governments to expand their health research, regulatory controls, training in safe pesticide use and development of integrated pest management. And it suggests this could be funded by a small levy by agricultural ministries on each kilogram of active ingredients used.
Pesticides and the Immune System: the Public Health Risks. WRI, 1996. WRI Publications, PO Box 4852, Hampden Station, Baltimore, MD 21211, USA. Tel: 1-800-822-0504 or 4120-516-6963 for Visa or MasterCard orders.
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