A CONTROVERSIAL look at the health effects of chemical environmental pollution has just been published - Our Stolen Future by Theo Colburn, J.P. Myers and D. Dumanoski (Little, Brown and Co, 1996). The authors argue the world is polluted everywhere with long lasting chemicals that mimic human hormones and that have insidpious and serious effects, mainly on the human reproduction system (recent studies report that male sperm counts have halved over the last 50 years).
In other words, the future of our species might be compromised. However, the evidence, although indicative, falls well short of proving the case, and the authors admit this. Nevertheless, the argument is strong enough to merit serious investigation.
Hormones are natural chemicals in the body that regulate growth, body chemistry, reproduction and the functioning of our organs. They are secreted in minute concentration (parts per million) into the bloodstream by various glands and they travel to their tissue destination where they exert their influence.
For example, the thyroid gland (in the neck) secretes a hormone called thyroxine, which regulates our general rate of metabolism and also has a profound effect on the rate of change of the infantile to the adult form. The main male sex hormone is testosterone (produced in the testes), and the main female sex hormone is estradiol (produced in the ovaries). Both are important in controlling sexual development and characteristics. A deficiency or excess of any of the hormones upsets the chemical equilibrium of the body and can play havoc with normal development and with general health.
Since 1940, the world has seen an explosion of synthetic chemical use - plastics, herbicides, insecticides, wood preservatives, paints, etc. In 1992, 1,700 billion lb of carbon based synthetic chemicals were manufactured globally. There are about 100,000 synthetic chemicals on the market and 1,000 new ones are introduced each year. In the United States, nine lb of pesticides are used per capita per year.
BEFORE a synthetic chemical is released to the public market it is tested for possible repercussions on human health. Prior to the 1940s these tests concentrated on acute poisonous effects - does exposure to the chemical make you ill, or kill you? Since the 1940s, the safety tests have concentrated almost exclusively on the potential of chemicals to cause cancer in those exposed to them, and birth defects in babies born to exposed mothers.
This is fine as far as it goes, but, according to this book, it doesn't go far enough. The authors claim many synthetic chemicals mimic natural hormone action and can therefore interfere with normal hormonal regulation of the body. New synthetic chemicals are not being checked for this.
The authors describe the work of biologist Frederick von Saal to illustrate the exquisite sensitivity of living organisms, especially during development, even to the tiniest variation in natural hormone levels. Von Saal correlated the adult behaviour and characteristics of individual male and female mice from the same litter, with the physical location they had in the mother's womb.
About one in six female mice are carried in the womb, sandwiched between two brothers. These females are thus exposed to more male testosterone during development than sisters who lie between sisters, but only about one part per billion more. Von Saal noted that such females behaved more aggressively as adults than their sisters, came into puberty later, had less heat and were less attractive to males. Similarly, males carried in the womb between females developed somewhat differently to males carried between males.
Problems associated with ingestion of synthetic chemicals that have hormone mimicking action are well illustrated by the diethylstilbesterol (DES) story. DES acts like estrogen (a female sex hormone) and was synthesised in 1938. It was administered to women in a widespread fashion, mainly to treat problems in pregnancy.
No birth defects were noticed following its use, and anyway it was believed chemicals ingested by the mother did not cross the placental barrier to the fetus. However, years later, problems were noticed during the development of children of mothers who had taken DES. Girls were more prone to develop vaginal cancer. It was also reported that boys had reproductive problems such as abnormal sperm and undescended testicles, but the evidence is not conclusive here.
DES showed the body can mistake a synthetic chemical for a hormone. The insecticide DDT also mimics female sex hormones when ingested. Of 51 synthetic chemicals that are loose in the environment, and that are known hormone disrupters, over half are long lived, i.e., they do not readily break down to harmless chemicals in the environment.
Other known hormone disrupters are nonylphenol, dioxins and phthalates. Nonylphenol is added to polystyrene and plastics to make them stable and pliable. Industrial detergents also contain chemicals that can break down to nonylphenol. Nonylphenol can leach in low concentrations from plastics and has been shown to be an estrogen mimic. Dioxin is another longlasting chemical that is generated by burning certain plastics and fossil fuels. Phthalates are used in plastics, paints, inks and adhesives.
WE have been ingesting these chemicals from the food chain at low levels for a long time. The blood of most persons contains PCBs, DDT, dioxins, and so on, at a concentration of parts per billion or trillion. Are such levels sufficiently high to affect the developing fetus in the mother's womb? Also, many of these chemicals concentrate in body fat and are secreted in a more concentrated form in mother's milk. Will nursing mothers pass on a problem to the infant? The big question in the book is - have we compromised the reproductive future of our children?
These chemicals have been in the environment for 50 years. If they have any effect one would predict that it would be transgenerational and mainly affect sexual reproductive function. Is there any evidence for such effects? Yes. Three studies have shown a decline in sperm counts by up to 50 per cent over the last 50 years. Testicular cancer rates have increased (threefold in Denmark) over the same period, and there are reports of increased rates of undescended testicles in England and Wales for the period 1962-82.
Rates of ectopic pregnancies have increased. Also, since 1940, rates of breast cancer have increased by 1 per cent a year. As a general principle, risk of breast cancer is linked to lifelong exposure to estrogen.
So what do we make of all this? First of all there is no need to panic. The evidence in this matter is far from conclusive. This is clear from the book, even though the authors naturally have a vested interest in making the case as plausibly as possible. I therefore conclude that the real strength of the case is considerably less than it seems. But the human sperm count data is worrying - but other studies have found no decline in counts.
But the evidence is sufficiently strong to stimulate serious notice. From now on synthetic chemicals should be tested for their hormone mimicking capacity. Intensive studies should be carried out to further test this book's hypothesis.
In the meantime, the extra stress caused by worrying about the matter in the absence of firmer evidence would probably cause more harm than any effects the chemicals might have.