DDT linked with birth defects

October 29, 2009

Growing body of research suggests that pesticide used for indoor malaria control carries health risks
Source: WHO\TDR\S.Lindsay

New evidence on the health effects of DDT, a chemical used in routine malaria control, has emerged in South Africa. Women living in villages sprayed with the pesticide between 1995 and 2003 had a 33% higher risk of giving birth to boys with urogenital birth defects compared with unexposed women, according to the findings of a study published in the British Journal of Urology International.

“Monitoring the impact of indoor residual spraying on human and environmental health is imperative if DDT is being used, especially as climate change raises concerns about the global spread of malaria,” write the authors, Riana Bornman, of the University of South Africa in Pretoria, and colleagues.

Unemployed women ran an even greater risk of giving birth to boys with the malformation, they say. For these women the risk rose to 41%, which the authors presume is because they spend more time indoors and so get exposed to the chemical more often and for longer periods.

The authors stress that people who could be at risk should be educated about how they can protect themselves from excessive exposure to the chemical “as a matter of urgency”.

Few researchers have looked at the health effects of DDT when used inside people’s homes to kill the mosquitoes that transmit malaria, says Henk van den Berg from Wageningen University in The Netherlands. This makes the findings important, he adds, especially because the use of DDT for malaria control in Sub-Saharan Africa is growing.

DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) has long been a controversial chemical. It can persist in the environment for up to 12 years and was used worldwide to control disease and eradicate crop pests until the 1970s, when scientists raised concerns about toxicity to humans and wildlife. Under the Stockholm Convention, an international treaty governing the use of the most dangerous persistent organic pollutants, its use is still permitted for mosquito control in some malarious areas. But experts are keeping a close eye on reported impacts of this strategy on health.

A recent review of epidemiological studies published in the past few years has suggested that exposure to DDT and its main breakdown product, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), may be associated with breast cancer, diabetes, reduced semen quality, spontaneous abortion, and impaired neurodevelopment in children.

In some districts of Limpopo province in South Africa, villages have been sprayed with DDT every year since 1966 to prevent malaria. Bornman and colleagues set out to examine what effect this has had on children born to mothers living in these areas. They assessed for urogenital birth defects all babies born between 2004 and 2006 in hospitals of one district in Limpopo. Using questionnaires they also found out whether the mothers had ever lived in villages included in the spraying programme, and collected information about other factors known to cause birth defects such as drinking alcohol, smoking, and marrying family members.

Their analysis revealed that women who had lived in a sprayed village at some point in their lives gave birth to 264 boys with urogenital birth defects, compared with 93 boys born to women who had always lived in unsprayed villages. The difference was statistically significant. Very few women included in the study smoked tobacco or drank alcohol, say the authors, so this has probably not affected the number of birth defects.

Although the findings suggest a link, they do not prove that exposure to DDT is the direct cause of the urogenital malformations. People living in the region have a history of interfamilial marriage, explain the authors. But as urogenital birth defects are not a reported outcome of this practice among other ethnic groups, it is unlikely that hereditary factors alone are behind the findings, they add.

Brenda Eskenazi, from the University of California, Berkeley, says that the link needs to be confirmed with studies that include a measure of the amount of pesticide to which these people have been exposed.

But the findings from this part of South Africa, where people are likely exposed to high levels of the chemical, are troubling, according to Eskenazi. In the end, decisions on use of DDT come down to carefully weighing up the evidence of toxicity against the risk of malaria, she notes.

“The adverse health effects of DDT are much more difficult to measure than the benefits of DDT in malaria control,” explains van den Berg. In spite of this they should be monitored as part of indoor spraying programmes, he suggests.

The signs of toxicity shown by this study highlight the importance of using several different anti-malaria measures in control strategies, says van den Berg. He believes that such integrated programmes can work better while being ecologically sound. “Policy support for integrated vector management will reduce the reliance on DDT.”
Reference and links


1. Bornman R, de Jager C, Worku Z, Farian P, Reif S. DDT and urogenital malformations in newborn boys in a malarial area. British Journal of Urology International 2009. doi: 10.1111/j.1464-410X.2009.09003.x
World Health Organization information about residual indoor spraying to control malaria
Stockholm Convention on Persistent Organic Pollutants information about DDT

Article at: http://www.eht-forum.org/news.html?fileId=news091029030111&from=home&id=0

Research on how health risks in use of DDT?
DDT is banned for most of its initial use since the 70s, why would one need to continue making use of it?

Here some excerpts from Wikipedia:

Vietnam is an example of a country that has seen a continued decline in malaria cases after switching in 1991 from a poorly funded DDT-based campaign to a program based on prompt treatment, bednets, and the use of pyrethroid group insecticides. Deaths from malaria dropped by 97%.

In Mexico, the use of a range of effective and affordable chemical and non-chemical strategies against malaria has been so successful that the Mexican DDT manufacturing plant ceased production voluntarily, due to lack of demand. Furthermore, while the increased numbers of malaria victims since DDT usage fell out of favor would, at first glance, suggest a 1:1 correlation, many other factors are known to have contributed to the rise in cases.

However, a study in Thailand found the cost per malaria case prevented of DDT spraying ($1.87 US) to be 21% greater than the cost per case prevented of lambdacyhalothrin-treated nets ($1.54 US), at very least casting some doubt on the unexamined assumption that DDT was the most cost-effective measure to use in all cases. The director of Mexico's malaria control program finds similar results, declaring that it is 25% cheaper for Mexico to spray a house with synthetic pyrethroids than with DDT.

However, another study in South Africa found generally lower costs for DDT spraying than for impregnated nets.

A more comprehensive approach to measuring cost-effectiveness or efficacy of malarial control would not only measure the cost in dollars of the project, as well as the number of people saved, but would also take into account the negative aspects of insecticide use on human health and ecological damage. One preliminary study regarding the effect of DDT found that it is likely the detriment to human health approaches or exceeds the beneficial reductions in malarial cases, except perhaps in malarial epidemic situations. It is similar to the earlier mentioned study regarding estimated theoretical infant mortality caused by DDT and subject to the criticism also mentioned earlier.