The highest levels ever of DDT in breast milk have been measured in mothers living in malaria-stricken villages in South Africa. The values lie well over the limits set by the World Health Organization. DDT has been used for many years in South Africa, sprayed indoors to fight malaria. It works, but it exposes the inhabitants to other risks not yet fully known.
"To our ears, spraying DDT inside people's homes sounds absurd. But it is one of the most effective agents against malaria. And by only spraying adult mosquitoes in the vicinity of people, the risk of developing resistance in mosquitoes decreases, " says Henrik Kylin, environmental chemist and professor at Water and Environmental Studies, Linköping. Together with South African researchers and doctors, he is collaborating on a project to map the effects of DDT on the population.
"We know a lot about how DDT affects nature and animals, but the effects on people's health are not as well studied, especially concerning long-term exposure."
"Based on the argument that "malaria is worse than DDT," people accept this spray treatment programme. The purpose of our project is to study the side effects, thereby creating a better basis for decisions."
In a newly published article, the researchers report on a study of DDT levels in breast milk from nursing mothers in four villages, of which three are afflicted by malaria. DDT has been used continuously in these three villages for more than 60 years. The spray treatment takes place a couple of times a year and is carried out by specially trained and equipped staff.
The levels proved to be unacceptably high in the villages sprayed. They were well over (100 times greater) the highest daily dosage recommended by WHO. In once case they measured the highest known level of DDT in breast milk ever, more than 300 times higher than the level allowed in cow's milk.
DDT has been associated with diagnoses such as breast cancer, diabetes, impaired sperm quality, spontaneous abortions, and neurological disorders in children. In the region where the measurements were carried out, malformed genitalia among boys was significantly more common in areas treated with DDT compared with untreated areas.
"DDT contains oestrogen-like substances; we know that the breakdown products from DDT counteract male sexual development," Kylin says. Based on breast milk samples, it was estimated that boys ingest somewhat more DDT than girls, with the exception of first-born children. This could depend on the fact that the fat content of breast milk is higher if a boy is nursing. First-born children, however, get the highest levels, depending -- as Kylin explains -- on the mother's higher stored levels of DDT at her first birth.
What surprised the researchers more was the large differences between the treated villages. Despite apparently similar conditions, the measured DDT levels were twice as high in one treated village compared with one of the others. A whole range of factors may come into play here, such as procedures in connection with treatment, the condition of the walls, ventilation, people's behaviour and cleaning habits. Identifying these factors, the researchers write, could contribute to decreasing exposure, thereby also the risk for both mothers and children.
"Unfortunately the smallest children are exposed to the highest DDT levels; they are also extra sensitive to chemical influence," Kylin says.
He also emphasizes the staff operating the spray treatments as an overlooked risk group requiring further study.
As things stand today, there is no real alternative to DDT in these malaria-stricken areas. "Mosquito-proof netting has successfully been tested in a few places, but doesn't work everywhere," Kylin says.
He is convinced that research could have come farther in finding alternatives for DDT if malaria were a widespread illness in rich countries.
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