According to new research that analysed 146 samples of breast milk, the pesticide DDT and related Persistent Organic Pollutants are still being found in humans. Despite a ban on its use, these chemicals continue to linger in our food supply - particularly in dairy products, seafood, cattle and poultry.
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SYDNEY: Despite an international treaty banning its use, the pesticide DDT is still turning up in humans, confirming a continued presence in our food chain, new research suggests.
The bulk of Persistent Organic Pollutants (POPs) found in 146 human milk samples belonged to the DDT family of chemicals, a health researcher said, speaking at the CleanUp 2011 conference in Adelaide today.
POPs are chemical substances that persist in the environment long after their original use, enter and accumulate in the food web, and could pose adverse affects to human health and the environment.
"Finding them in human milk indicates that these pollutants are still present in food chain, which means that they're highly persistent and have a slow decline rate," said Tze Wai Wong, an environmental epidemiologist at The Chinese University of Hong Kong.
"Or, worse still," he added, "they are still being used in some countries in food production- neither of which is good news for consumers."
Controversial history
DDT was first synthesised in the 1870s and later exploited for its insecticidal properties. It was used with great effect during WWII to control the spread of diseases like malaria and typhus, and following the war, was used as an agricultural insecticide.
Concerns eventually surfaced, however, about what the chemical substance was doing to the environment, and later, to human health.
The U.S. banned DDT in 1972. Australia followed suit 15 years later in 1987 and an international ban became effective in 2004 under the Stockholm Convention on Persistent Organic Pollutants.
However, DDT continues to be the most produced and widely used POP listed in the treaty, and is still permitted for disease control under guidelines recommended by the World Health Organisation.
Contaminated food sources
"DDT was only one type of contaminant that we found," said Wong. "There were also dioxins, other organochlorines and banned pesticides that were once widely used in agriculture."
The human uptake of dioxins and POPs is mostly from contaminated food products that originate from places with heavily polluted soil and water, said Wong, and they can also enter the body through contaminated air.
Apart from previous use of toxic pesticides, he said factors such as diet and waste disposal influence how widespread the problem will become in a given community, especially if those disposal methods result in marine and soil contamination.
"We suspect that high concentrations of DDT will be found in communities which consume large amounts of seafood, dairy products, cattle and poultry, as animals tend to bioconcentrate these toxins," he added.
DDT metabolite present in everyone?
It is not surprising that DDE - the metabolite of DDT - was found in samples of breast milk, commented Jochen Mueller, a toxicologist at the University of Queensland.
"It is common scientific knowledge that every person in Australia and around the world has measurable levels of DDE in their blood," he said, "because DDE is everywhere and we take it in with our food and even in small quantities through breathing."
Mueller said the levels have come down significantly since the chemicals were banned, as people reduced their usage.
But to bring the levels down even further may be much harder, because they are very persistent in sediments and soils, which can find their way back to the surface when top-covers are perturbed.
Long-lasting impacts
"In some environments they can have a half-life of 10 to 20 years or even longer, so the chemicals that we released in the 1950s to 1970s are still there," said Mueller. "We're still seeing their residues."
Wong said his research is turning up pollutants that were present in the human environment decades ago.
"Its persistence shows that we need to be cautious about what we are doing now," said Wong, "because the effects of today's pollutants on health are not likely to be felt until some decades later."
