Durban - Proving a clear link between a chemical and health damage can be tricky at the best of times.
At what dose does the chemical become poisonous? One drop, or two?
What if the harmful effect of the chemical lies dormant for a while and only shows up 10 or 20 years later?
What if the chemical damages our genes in some way, so that the harm only becomes obvious in our children or grandchildren?
And in this modern world of ours, where people can be exposed to hundreds of chemicals (or mixtures of many chemicals), how is it possible to isolate which chemicals might be causing a problem?
To complicate the picture further, a healthy 70kg adult might not suffer any damage from a chemical dose which is highly toxic in a developing foetus or new-born baby.
From a cold, scientific perspective, the simplest way of getting answers to such complex questions might be to conduct experiments in a laboratory, but it would be completely unacceptable to turn people into the human equivalent of guinea pigs or lab rats by injecting them with chemicals and then chopping them up to look for clues.
Faced with some of these dilemmas, several researchers have turned to nature and the animal world in the search for the answers and early warning bells.
One of these warning bells rang very loudly in the early 1950s in the city of Minamata, Japan, with the frenzied behaviour of cats, crows and fish.
The cats developed convulsions which came to be known as “cat-dancing disease”.
Crows fell from the sky, seaweed no longer grew on the seabed and fish floated belly-up on the surface of the sea.
The first evidence of sickness in humans turned up about five years later and was eventually linked to severely polluted mercury wastewater from the Chisso Corporation chemical factory.
Since then, there have been numerous cases of disease and sickness in wildlife from around the world linked to endocrine-disrupting chemicals (EDCs).
One well-known case is the pesticide poisoning of Lake Apopka in Florida, US, where male and female alligators developed a wide variety of problems.
Male alligators ended up with smaller, malformed penises and researchers also found abnormalities of the ovaries in females.
In Bothnian Bay in Sweden, there was a 60 percent drop in the number of pregnancies in seals exposed to polychlorinated biphenyls.
Smaller testicles and lower testosterone levels were found in polar bears exposed to several toxic chemicals in Greenland.
Closer to home, South African researchers have found sexual deformities in fish and animals in a nature reserve outside Pretoria.
Other researchers also found chickens in Limpopo province with DDT pesticide levels up to 700 times higher than chickens living in areas which were not sprayed with DDT for malaria control.
In Canada, scientists noted significant homosexual behaviour patterns in birds exposed to methylmercury. These birds also had altered levels of testosterone and estradiol hormones.
There has also been consistent evidence from several parts of the world of fish changing sex from male to female (and vice versa) in rivers polluted by paper mills or sewage treatment works.
The UN report notes that unlike humans, the brains of fish are not permanently sexualised during early development and they remain highly susceptible to the effects of hormones throughout their lives. As a result fish were vulnerable to skewed sex ratios when exposed to EDCs in polluted rivers and laboratory experiments.
The report says some of the most convincing evidence of sexual disruption by EDCs has been gathered from fish studies.
“This research has focused on the steroid oestrogens and there is now unequivocal evidence from a wealth of laboratory-based studies demonstrating their capacity to feminise fish.”
German researchers also did EDC laboratory experiments which led to a phenomenon known as “super-feminisation” in snails.
Although their experiments were contested by some researchers, the German group found that super-females developed extra sex organs, enlarged sex glands and gross deformities of the oviduct after being exposed to the chemical bisphenol A.
In their summary report on EDCs, the 16 UN scientific experts note that the wide range of feminising and demasculinising disorders in wildlife were consistent with some of the symptoms seen in human populations.
They say it is important to take notice of the parallels between the disorders in humans and those seen in wildlife.
“Genital malformations, lowered semen quality and altered sex hormone levels seen in male fish in urban areas and amphibians in agricultural areas appear to mirror those observed in human populations in similar environments and may reflect common causes.
“The apparent similarities between diseases and disorders reported in humans and in various wildlife populations are not surprising, given that there is often considerable overlap between their environments and food chains as well as in their physiology.”
Disturbingly, the researchers warn that some EDCs produce effects that can cross the generations.
“This means that the increase in disease rates that we are seeing today could in part be due to exposures of our grandparents to EDCs, and these effects could increase over each generation.”
They also voice concern about the inadequacy of chemical testing methods and caution that doses declared “safe” are mostly calculated and not actually tested.
“Close to 800 chemicals are known or suspected to be capable of interfering with hormone receptors, hormone synthesis or hormone conversion,” the researchers say.
“However, only a small fraction of these chemicals have been investigated in tests capable of identifying overt endocrine effects in intact organs.
“The vast majority of chemicals in current commercial use have not been tested at all… Despite substantial advances in our understanding of EDCs, uncertainties and knowledge gaps still exist that are too important to ignore.”
Despite the fact that EDCs were a global threat, there was still a major lack of data from Africa and other developing countries.
“It is also critical that we move beyond the piecemeal one chemical at a time, one disease at a time, one dose approach being used by scientists studying animal models, humans or wildlife.” - The Mercury