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That DDT builds up in our environment, kills marine life, and thins the eggshells of songbirds are lurid facts. But its effects on the human body have long been debated. The mantra of the international community these past few years has been that DDT’s life-saving powers have far outweighed limited evidence of long-term health consequences. The World Health Organization classifies the compound as only “moderately hazardous,” innocuous enough for the 2001 Stockholm Convention to ban 12 persistent organic compounds, while making an exception of DDT usage for malaria control. It was also deemed harmless enough in 2006 for the World Health Organization and the USAID to endorse spraying it directly into people’s homes, a method known as Indoor Residual Spraying (IRS), in order to reduce rates of malaria infection. Usage has gone up around the world since then with at least 3,950 tons used for mosquito control in Africa and Asia in 2007, according to a report by the United Nations Environment Programme.
But a recent report published in the Environmental Health Perspectives reveals a growing body of research that links DDT to breast cancer, diabetes, infertility, and impaired brain development in children and warns of the consequences to children exposed in utero and through breast milk. Early studies on indoor spraying, of which there are only a few, show far higher concentrations of DDT in the blood than have ever been found in populations exposed through agricultural spraying. The long-term health effects of such unprecedentedly high concentrations are unknown.
In May, several UN agencies including the WHO announced funding for malaria-fighting alternatives to DDT and set a deadline to wean the world off the pesticide by 2020. It’s a victory on all sides fighting for global public health, but the questions raised by the report, known as the Pine River Statement, remain. Here, lead author Brenda Eskenazi, a UC Berkeley professor of epidemiology and maternal and child health, talks to SEEDMAGAZINE.COM’s Elizabeth Cline about balancing the short-term benefits against the long-term risks of DDT, and what’s standing in the way of clear answers and solid research of the health risks of indoor spraying.
SEED: The literature on the health effects of DDT has been raked over for decades without clear results, so why did it occur to your group to review it again?
Brenda Eskenazi: Well, there had been a number of policy decisions like the President’s Malaria Initiative, and USAID and WHO’s endorsement of DDT use for malaria control, and yet there hadn’t been any review of literature since 2005. I was quite surprised to find that when I did a quick PubMed search, there had been 500 papers published in this past five years. I felt that we really needed to review the literature to find out what has happened since all these policies [and] decisions were made.
SEED: Why has it been so difficult to determine the long-term health effects of DDT?
BE: To be honest, most of the research has been done on animals. Studies that have been done with humans have measured DDE, which is a by-product of DDT, in the blood of people usually some period of time after they’ve been exposed—maybe years, maybe decades after they’ve been exposed. There was a recent study using blood that had been stored from the 1950s and 60s, closer to the time that DDT had been used in the United States, and they found that women with higher levels of exposure and women who had been exposed before the age of 14 had a five-fold increased risk for breast cancer. That’s the kind of study that couldn’t be readily done because the exposure levels need to be measured years and years before the disease is manifested.
SEED: How much of the new literature is on the health consequences of indoor residual spraying?
BE: There are really only a handful of papers—or even less—that have been published on the health consequences [of] populations where DDT is being used in the way it’s being used now with indoor residual spraying. I want to emphasize that. There have been hardly any studies done on the effects of indoor residual spraying.
SEED: So what do those few studies tell us?
BE: The studies that were done indicated levels of exposure that were incredibly high, higher than what we would have seen in the United States even when we were using DDT. Probably the most interesting study was from South Africa where they showed that men who live in the huts that have been sprayed with DDT have a dose-related decrease in semen quality that are pretty profound.
SEED: What kinds of long-term health problems can we expect?
BE: I don’t really know. I can’t predict, but I can say that if the studies that I read hold true we may see higher rates of diabetes; we may see higher rates of breast cancer; we may see higher rates of male infertility. We may see poor neurodevelopment in children. We may also see more spontaneous abortions.
SEED: In the report you mention a number of unknown factors that could combine in vulnerable populations to make indoor spraying more of a threat.
BE: : Yes. There might be more sub-populations [susceptible to health problems related to indoor spraying] either because of genetics, or other types of disease like HIV. And we know that the people coming from malaria-endemic areas where DDT is being used also happen to be the populations who have the highest rates of HIV. We are also concerned about the fact that DDT accumulates in breast milk and that breast milk is the major source of food for infants in this community. And we don’t really know what the levels of exposure are then to the developing infants.
SEED: In your opinion, why hasn’t more of an effort been made to study the health effects of indoor spraying?
BE: I think in some cases people don’t have the money to do that kind of research in the places where these populations are being sprayed. They may not have the big, academic facilities to do that kind of research. Some of the only research [on indoor residual spraying] has come out of South Africa, which does have some infrastructure to do that.
SEED: How do we balance the malaria-fighting benefits of DDT with this information about long-term health?
BE: It’s a very complicated. There are people who are responsible scientists and policy makers who believe that DDT is the only way in certain areas to control malaria. I’m not an entomologist; I can’t make decisions like that. Entomologists could make the decision if there’s mosquito resistance, or given the ecological framework that mosquitoes are living in, what would be the best [way] to control it. As an epidemiologist I can address what the literature says around health consequences. I just want to emphasize that [all the authors of the report] care deeply about the health of children and future generations, and we wouldn’t want children dying of malaria, but we need to weigh the costs and benefits of all of it. It’s not a simple, easy decision. My purpose as a professor of maternal and child health is to not only protect the health of children living right now, but the children of the future. We need to be concerned about the fact that the half-life of DDT and DDT-related compounds are something like four to 10 years, so what we use today is going to be exposing populations for years to come.
Originally published June 11, 2009