DDT Risk Assessments: Response.

Donald Roberts contends that organizations such as the World Wildlife Fund (WWF) failed in efforts to eliminate DDT under the recently negotiated persistent organic pollutants (POPs) treaty.

To the contrary, the WWF strongly supports the treaty's language on DDT. Throughout the negotiations, the WWF recognized that DDT should not be banned immediately and that uncertainties about the cost and effectiveness of alternatives required flexibility in treaty language (1,2). Reflecting this, the new treaty proclaims ultimate elimination of DDT as a goal while establishing a mechanism for reducing reliance on DDT and promoting alternatives (3). As a result of the treaty, new funds are being provided by the Global Environment Facility to develop malaria control programs that reduce use of DDT.

Roberts has been an outspoken defender of DDT. He has prolifically and passionately downplayed the toxicologic risks of DDT while emphasizing its effectiveness for malaria control (4-6). He frequently argues that external political pressures drive poorer nations to abandon DDT, thereby endangering millions of the world's most impoverished people.

Malaria-endemic countries have had ample scientific justification for seeking alternatives. For example, in the mid-1990s, Mexican public health researchers expressed concern about high human exposures to DDT as a result of malaria control operations (7,8). Mexico has since eliminated DDT while successfully combating malaria. South Africa also sought to reduce use of DDT in the mid-1990s because of concern about elevated levels in mothers' milk (9). One species of mosquito was resistant to alternative sprays, so South Africa resumed using DDT. South Africa concluded that the hazards from malaria outweigh those associated with DDT exposure. South Africa's experience underscores the importance of the flexibility provided by the POPs treaty.

Brazil and India offer important lessons about limits to DDT's effectiveness. During the late 1980s and early 1990s, malaria rates in Brazil went up even as spraying of houses with DDT increased, but dropped after Brazil shifted strategies (10). With assistance from the World Bank, India is reducing its reliance on DDT. The main rural malaria vector (responsible for 65% of India's malaria) is resistant to DDT (11). Indian researchers found elevated levels of DDT in buffalo milk, soil, water, and human blood where DDT had been sprayed to control malaria (12,13).

The ATSDR's 2000 update of its toxicologic profile for DDT/DDE (14) reflects major concerns raised by the WWF and other environmental and public health groups during the POPs negotiations. In contrast to the previous profile published in the early 1990s, the update contains a large section, "Health Effects in Wildlife Potentially Relevant to Human Health," reminding readers that animals are sentinels for health effects in humans. A new section captioned "Children's Susceptibility" reiterates a central message from the U.S. National Academy of Sciences' landmark 1993 report on pesticides in the diets of infants and children (15): children are not little adults, but may be uniquely susceptible and exposed to pesticides.

The data in the toxicologic profile support the logic of the POPs treaty: DDT can be valuable for controlling malaria, but it is prudent to reduce human exposures. Recent studies on humans, too late to be included in the toxicologic profile, further support such caution. For example, Longnecker et al. (16) found ,that DDE concentrations in mothers are associated with increased risk of pre-term delivery and lowered birth weight.

Roberts takes EHP's contributors to task for their "one-sided" references to DDT's risks and their failures to account for DDT's benefits. Roberts' encomium to DDT is itself one-sided. Why expose humans to hazards from DDT when less risky strategies might be employed? The POPs treaty encourages development of alternatives and provides a new funding mechanism to support malaria control.

REFERENCES AND NOTES

(1.) Liroff RA. Commentary: Reduction and elimination of DDT should proceed slowly. Br Med J 321:1404-1405 (2000).

(2.) Liroff RA. Beyond the DDT controversy: a search for common ground. Presented at the 66th Annual Meeting, American Mosquito Control Association, 13 March 2000, Atlantic City, NJ.

(3.) United Nations Environment Programme. Text of the Stockholm Convention on Persistent Organic Pollutants for Adoption by the Conference of Plenipotentiaries. UNEP/POPS/CONF/2. Available: http://irptc.unep.ch/pops/POPS_Inc/dipcon/meetingdocs/conf2/en/conf-2e.pdf [cited 3 July 2001].

(4.) Roberts DR, Manguin S, Mouchet J. DOT house spraying and re-emerging malaria. Lancet 356:330-332 (2000)

(5.) The DDT question. Lancet 356:1189-1191 (2000).

(6.) Roberts DR. DDT and the global threat of re-emerging malaria. Pesticide Safety News 2(4):4-5 (1999).

(7.) Lopez-Carrillo L, Torres-Arreola L, Torres-Sanchez L, Espinosa-Torres F, Jimenez C, Cebrian M, Waliszewski S, Saldate O. Is DDT use a public health problem in Mexico? Environ Health Perspect 104:584-588 (1996).

(8.) Waliszewski SM, Pardio Sedas VGT, Chantiri JN, Infanzon RM, Rivera J. Organochlorine pesticide residues in human breast milk from tropical areas in Mexico. Bull Environ Contam Toxicol 57:22-28 (1996).

(9.) Bouwman H. Malaria control and the paradox of DDT. Africa--Environment and Wildlife 8:54-56 (2000).

(10.) Gusmao R. The control of malaria in Brazil. Presented at the International Workshop on the Contextual Determinants of Malaria, 14-18 May 2000, Lausanne, Switzerland.

(11.) Sharma VP. Current scenario of malaria in India. Parassitologia 41:349-353 (1989).

(12.) Battu RS, Singh PP, Joia DS, Kalra RL. Contamination of bovine milk from indoor use of DDT and HCH in malaria control programmes. Sci Total Environ 86:281-287 (1989).

(13.) Dua VK, Pant CS, Sharma VP. Determination of levels of HCH and DDT in soil, water and whole blood from bioenvironmental and insecticide-sprayed areas of malaria control. Indian J Malarialogy 33:7-15 (1996).

(14.) ATSDR. Toxicological profile for DDT/DDD/DDE (update; released for public comment). Atlanta, GA:Agency for Toxic Substances and Disease Registry, 2000.

(15.) National Research Council. Pesticides in the Diets of Infants and Children. Washington, DC:National Academy Press, 1993.

(16.) Longnecker MP, Klepaboff MA, Brock JA, Zhou H. DDE is associated with increased risk of preterm delivery and small-for-gestational-age birthweight in humans. Organohalogen Compounds 48:161-162 (2000).

Richard A. Liroff
Alternatives to DDT Project
World Wildlife Fund
Washington, D.C.
E-mail: [e-mail]