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3) Ecological study
Dorner et al. (2002) investigated association of exposure to
dichlorodiphenyltrichloroethane (DDT) via breast milk with
mental capacities of students born in 1984-85 in 11 countries
participating in PISA (Programme for International Student
Assessment) in the framework of PISA 2000 study. German backward
children of the same age were also studied similarly. The mental
capacity of the 15 year-old students was inversely correlated
with the total DDT level in mothers' milk (p = 0.001).
Significant inverse correlation between the mental capacities
was also observed for 15 year-old children from 10 countries in
3 continents as well as from 14 states in Germany (p < 0.001).
Furthermore, the percentage of mentally retarded children in
Germany and total breast milk DDT level in 1984-85 showed
significant positive correlation (p < 0.001). These data
suggested detrimental effects of DDT on brain development of
children and mental capacities in their later life.
[Discussion and conclusions]
Follow-up observations in cohort studies in five countries
covered a period from a few months of age to schooling age in
investigation of association of neurobehavioral indexes with
chemical exposure. New cohort studies have started more recently
in three regions of the world.
Studies on severely exposed populations showed adverse effects
of prenatal exposure on nerve development of children. Lai et
al. (2002) reported partial recovery of such effects by aging. A
yusho study in Taiwan was the only cohort study conducted in
Asia.
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