DDT EXPOSURE AND HUMAN HEALTH IMPACT IN MEXICO .

Lizbeth López-Carrillo 1, Mariano E. Cebrián-García 2, Luisa Torres-Sánchez 1.

1 Mexico National Institute of Public Health.
2 Center of Research and Advanced Studies.

The insecticide dichlorodiphenyltrichloroethane (DDT) was extensively used in Mexico to control malaria, with an annual decreasing trend of use from 9,000 tons to 2,000 tons during the period of 1971 to 1991. Later in 1997, its production and use were banned.

Levels of p,p´dichlorodiphenyldichloroethane (p,p´-DDE), the main metabolite of DDT, have been detected in more than 90% of human biological samples in Mexico . In 1999, p,p´-DDE serum levels in women of childbearing age residents of Morelos, a southern state, were as high as those observed twenty years ago among inhabitants of agricultural areas in the state of California, U S.A. Levels of p,p´-DDE in human adipose tissue and maternal milk have also been documented throughout the country. The consumption of salted pork meat and fish was specifically linked to those levels.

Breastfeeding is an important pathway of p,p´-DDE elimination. In Mexican lactating women we estimated that 17 months of accumulated lactancy are needed to eliminate half of the p,p´-DDE body burden levels. It was also estimated that at least 6% of lactating newborns in Mexico City are exposed to DDT via maternal milk at levels resulting in intakes above the acceptable daily intake recommended by international organizations, thus it is expected that in tropical areas, a higher proportion of children are exposed to non-acceptable levels of DDT.

The association of DDT exposure with the risk of breast cancer, premature birth, spontaneous abortion and children neurodevelopment respectively, have been epidemiologically evaluated in Mexico . No clear effect of DDE on breast cancer risk was identified in Mexican women. However, a borderline increased risk of 1.67 (I.C 95% 0.84-3.31) for preterm birth was detected in exposed pregnant women. Preliminary results from an ongoing perinatal prospective cohort study suggest a positive association between DDE levels and motor development impairment in children at three months of age. Additional findings also show a potential increased risk for spontaneous abortion due to the exposure to other organochlorine pesticides.

Long time has been invested to confirm in humans the devastating effects of DDT that were previously observed in wildlife. Notwithstanding that DDT production and use has been banned in Mexico, many further years will be needed for Mexicans to eliminate its metabolites from their bodies. Multidisciplinary research approaches are needed to avoid delays in the decision making process and reduce unnecessary human exposures.

Keywords: Pesticides, DDT, Human Health , Mexico, Persistent Organic Pollutants.