HCH isomers, endosulfan, malathion, chlorpyrifos, and methyl-parathion were monitored in human milk samples from Bhopal, Madhya Pradesh. The endosulfan concentrations were highest and exceeded the S-HCH, chlorpyrifos, and malathion concentrations by 3.5-, 1.5-, and 8.4-fold, respectively. Through breast milk, infants consumed 8.6 times more endosulfan and 4.1 times more malathion than the average daily intake levels recommended by the World Health Organization. A correlation analysis (r values) between mothers' age and the content of the chemicals accumulated in breast milk indicated a substantial degree of correlation for malathion (r–0.5). The other chemicals showed low to negligible correlation with donor age.

The larvae and adults of Aedes aegypti were tested for the potential to develop resistance to the synthetic pyrethroid, deltamethrin, alone or a combination of deltamethrin with the synergist, piperonyl butoxide (PBO). Although continuous larval selection for 40 generations resulted in 703-fold resistance, the resistance ratio in the adults was only 1.3. Similarly, adult selections with deltamethrin showed a resistance ratio of less than four after 40 generations, indicating differential response to deltamethrin selection in the two developmental stages of the insect. When the susceptible larvae were subjected to selection pressure of deltamethrin and PBO in the ratio of 1:5 for 20 generations, the speed of selection for deltamethrin resistance slowed down by 60%. The F24 larvae obtained from the strain selected with deltamethrin alone were further subjected to selection pressure with synergized deltamethrin, which resulted in 89% reversal in deltamethrin resistance in just one generation. However, long-term selection with the insecticide-synergist combination returned resistance close to original levels in 15 generations. The data indicate the involvement of cytochrome P450-dependent detoxification as the primary mechanism of development of resistance to deltamethrin in the larvae. Implications of the results on the management of larval and adult stages of Ae. aegypti are discussed.

This exhibit represents part of the work of the Department of Zoology in the past 5 years, and others who have contributed to it are F. Matsumura, Z. H. Abedi, T. Kimura, P. G. Fast, J. G. Towgood, J. N. Telford and N. H. Khan.The work with the mosquito Aedes aegypti has involved study of 8 susceptible strains. The mechanism of DDT-resistance has been found to be associated with its detoxication by an enzymic process of dehydrochlorination to DDE; the amount of DDE produced has been found to be directly proportional to the resistance level, both by experiments with larvae in vivo and with larval homogenates incubated with DDT and glutathione in vitro. A secondary resistance mechanism in American strains has been a very pronounced secretion and excretion of peritrophic membrane by the larvae.

Among the organochlorine pesticides, DDT and HCH excel in their broad spectrum toxicity and residual activity. However, developed countries have banned the usage of DDT since 1975, due to its inherent chemical stability, persistence, high liposolubility and bioaccumulation. Despite these undesirable properties, developing countries still use these insecticides primarly due to cost-benefit efficacy and broad spectrum toxicity. Also, it has been shown that both DDT and HCH have significantly shorter half lives in tropical environments than in temperate zones (Sleicher and Hoperaft, 1984, Samuel et al., 1988, Nair et al., 1992.In India, DDT and HCH contribute more than 70 percent of the total pesticide consumption. Hence, it becomes imperative to ascertain the extent of contamination in man. The aim of the present study was to assess the levels of DDT and HCH in breast milk, maternal serum and cord serum from mothers and their infants; to examine a possible correlation between them and finally to compare the extent of transfer of these chemicals by primigravidae and multigravidae donors to the newborn. Comparative data concerning all these parameters is lacking from the developing countries. MATERIALS AND METHODSSamples of maternal blood, breast milk and cord blood from 25 mothers (23.4 ± 1.085 years of age with range of 18-40 years) and their newborn from Irwin Hospital, Delhi constituted the study group. Donors were unemployed, non-smokers, on a vegetarian diet, belonging to a lower socio-economic class but healthy with no major illness in the recent past. Twelve donors were primigravidae while the remaining were multigravide.

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