Dosage relationships associated with DDT in milk

Abstract

Separate reports imply that DDT is more toxic to infant rats if they receive it via their mothers' milk rather than via stomach tube. Therefore, the effect of DDT in milk was reinvestigated, and the study was expanded to include dosage-response measurements. The results were consistent with earlier findings that young rats are no more susceptible than adults to poisoning by DDT and may be more resistant, depending on circumstances. A comparison of isomers and potential metabolites in technical DDT and in tissues indicated either lack of absorption or rapid excretion of o,p′-isomers, resistance of the blood-brain barrier to o,p′-DDT, and the increase of DDD and DDE through metabolism. The concentration of DDT in the brains and whole bodies of pups from dams dosed at 200 mg/kg/day was higher than would be predicted by extrapolation from lower dosages, suggesting relative inability of the dams to metabolize and eliminate the compound at a dosage fatal to some of them. However, the highest brain level for a pup that died following dosing of its mother was 44 ppm, compared to 83 ppm (the highest level for a surviving pup of the same kind) and compared to 132–177 ppm (the range for pups killed by DDT administered to them by stomach tube). A slight deficiency of weight gain and significantly less stomach contents of pups of mothers treated at 200 mg/kg/day indicated their relative failure to feed although their mothers produced adequate milk. Based on the concentration of DDT in rat milk and on the amount of DDT measured in litters fed exactly 24 hr, it was calculated that rats secreted milk at the rate of 26.6 and 34.5 ml/dam/day when DDT was administered ip and op, respectively. Based on the analyses of litters, the dams secreted into their milk 12.6 to 30.2% of the DDT administered to them, the mean being 24.6% in those receiving the compound from their diet at an average rate of 32.4 mg/kg/day. The concentration of DDT in the milk of rats receiving DDT at a dietary level of 200 ppm was far higher than any level reported for human milk. Infants are in no danger from DDT in their mothers' milk unless the dosage of the mother is one that approaches, or perhaps reaches, a level toxic to her.