Experts from Universities of Pretoria and North West form part of an international group reviewing DDT/malaria impact
Posted on 05 May 2009
Experts find health impacts likely due to DDT exposure, express caution regarding the use of DDT in malaria control, and urge a renewed and accelerated search for safer malaria control methods
An international panel of health and toxicological scientists who convened to review recent studies on the link between DDT and human health; expressed concern that the current practice of spraying the pesticide indoors to fight malaria is leading to unprecedented – and insufficiently monitored – levels of exposure to it.
The consensus statement emerged from a March 2008 conference jointly organized by the Pine River Superfund Citizen Task Force, the Center for Responsible Leadership and the Public Affairs Institute of Alma College in the USA. More than 200 participants attended the conference, which was held near the site in St. Louis, Michigan where a chemical plant leached massive levels of DDT into the Pine River. In 1983, the area was named a Superfund site by the U.S. Environmental Protection Agency. The St Louis conference was attended by Prof. Tiaan de Jager and Prof. Riana Bornman of the University of Pretoria and Prof. Henk Bouwman of the North-West University. They presented the results and insights of individual and collaborative research done in South Africa and Mexico on the effects of DDT in humans and the environment.
Following the publication of a review of nearly 500 epidemiological studies, in the May 2009 issue of the journal Environmental Health Perspectives, the researchers developed a consensus statement calling for increased efforts to reduce exposure to DDT, to understand the health effects of exposure to DDT, and to develop alternatives to using DDT so that other methods could ultimately be relied upon for malaria control. Examples of safer measures to control malaria include the use of alternative insecticides, bed nets, management of standing water, and the rapid diagnosis and treatment of malaria cases. Some of these are already done in South Africa.
The researchers noted that the majority of studies on DDT have thus far focused on the impact on wildlife and the environment. Moreover, most of the studies on DDT and human health were done in developed countries where the pesticide was banned in the 1970s, the researchers said. Of the studies published on human health, almost all have dealt with populations exposed to low, background levels of DDT. Nevertheless, some of those studies have suggested links between DDT and cancer risk, diabetes, developmental problems in fetuses and in children, and decreased fertility.
"Any studies conducted up to now on the human health effects from DDT exposure may not be relevant to the populations currently exposed to the pesticide through indoor residual spraying," said Brenda Eskenazi, professor of epidemiology and maternal and child health at the School of Public Health, UC Berkeley, who has published research on the negative impact of DDT exposure to a child's neurodevelopment.
Although DDT has been largely abandoned as an agricultural pesticide worldwide, it has continued to be used since the 1940s to combat malaria in South Africa and elsewhere. Its use to combat malaria was endorsed in 2006 by the World Health Organization (WHO). According to WHO, in 2006 alone there were 247 million cases of and 880,000 deaths from malaria. Most of the deaths were of young children in Africa.
"DDT is now used in countries where many of the people are malnourished, poor and possibly suffering from immune-compromising diseases such as AIDS, bilharzias and hepatitis, which may increase their susceptibility to effects from chemical exposures"; said co-author Jonathan Chevrier, University California, Berkeley post-doctoral researcher in epidemiology and in environmental health sciences.
In regions where malaria is endemic, the organochlorine pesticide is sprayed on the inside walls and under rafters of homes in malaria areas of Mpumalanga, Limpopo and KwaZulu-Natal, thereby repelling and killing the mosquitoes that spread the disease. This is being done despite a paucity of data on the human health impacts of DDT exposure at such high levels in currently exposed populations, according to the experts from fields ranging from environmental health to cancer biology.
"We have to put our concerns in the context of people dying of malaria," said lead author of the EHP article Brenda Eskenazi. "We know DDT can save lives by repelling and killing disease-spreading mosquitoes. But evidence suggests that people living in areas where DDT is used are exposed to very high levels of the pesticide. The only published studies on health effects conducted in these populations have shown profound effects on male fertility. Clearly, more research is needed on the health of populations where indoor residual spraying is occurring, but in the meantime DDT should ideally be the last resort against malaria rather than the first line of defense."
DDT has been banned for agricultural use in South Africa since 1976. To date, more than 160 countries, including South Africa, have signed the Stockholm Convention on Persistent Organic Pollutants (called POPs), an international treaty banning DDT and 11 other persistent organic pollutants. DDT is allowed however, for the control of malaria by countries that need it. South Africa played a major role during the negotiations for the Stockholm Convention regarding the continued use of DDT in malaria control and the need for alternatives. In cases where DDT must be used, the Stockholm Convention requires an implementation and management plan to minimize human exposure to the pesticide and the latter’s release into the environment.
South Africa is one of the very few developing countries boasting past and current research efforts regarding environmental and health effects of DDT used in malaria control. The malaria control programme in South Africa is effectively protecting 5-6 million people through the application of pesticides inside houses and other structures, using DDT and other insecticides. The researchers observed a general lack of compliance with safety measures, such as control workers not wearing protective clothing and not complying with other safety requirements, which indicates an urgent need for retraining, monitoring, and awareness raising.
According to Prof. Tiaan de Jager from the School of Health Systems & Public Health at the University of Pretoria, the extremely high DDT exposure levels found in young men living in a malaria area in South Africa are reason for concern. He found significantly higher DDT exposure levels in men living in houses sprayed with DDT compared to those living in houses that were not sprayed. De Jager and Bornman also confirmed effects of DDT on male reproductive health, including seminal parameters, hormones levels and DNA damage. Prof. De Jager is collaborating with other scientists at the University of Pretoria, working on safer alternatives to DDT. He urged that “while we are still dependent on DDT for malaria control, we need to train and educate the pesticide spray workers and the affected communities to limit exposure to these harmful chemicals. Communities are often exposed to complex mixtures of chemicals, many of them endocrine disruptors”.
Prof. Henk Bouwman added that research needs to look at how DDT and alternative insecticides is taken up by inhabitants. His research has shown that DDT in breast milk is most likely derived from contact with the chemical inside and around the sprayed houses, rather than through food as was previously assumed. Levels of DDT in breast milk are very high and exceed all known health criteria, contributing significantly towards levels of DDT in breastfeeding babies. Levels of DDT in the environment, birds and fish are also of concern and may have negative effects on reproduction. He added, “We should not look at DDT alone, but also at the presence of the alternative malaria control insecticides and other pollutants that can complicate and add to health and environmental impacts”.
The South African researchers strongly urge the need for an accelerated drive to look at better, robust and safer ways of controlling malaria, without compromising the health of the people and the environment.