WHO collaborative breast feeding study. I. Organochlorine contaminants in individual samples of Swedish human milk, 1978--1979.

Individual samples of human milk collected in Uppsala at 3 months post-partum (18 samples) or 6 months post-partum (23 samples) were analysed for chlorinated insecticides and polychlorinated biphenyls (PCBs) by gas chromatography. The mean levels of the organochlorine compounds in the 3- and 6-month groups were similar. The mean content of DDE, the major metabolite of DDT, in all the samples was 54 micrograms/kg fresh weight (1.3 mg/kg on a fat basis) with a range of 8.4--220 micrograms/kg (0.49--3.0 mg/kg fat). The results confirm that the decline since 1967 in the levels of DDT and its metabolites in Swedish human milk reported by other authors is continuing. The levels of dieldrin and beta-hexachlorocyclohexane found are lower than those reported earlier in Sweden, whereas the levels of hexachlorobenzene are about the same. On the other hand, the levels of PCBs (mean 64 micrograms/kg, range 15--150 micrograms/kg, fresh weight, equivalent to 1.6 mg/kg, range 0.84--2.9 mg/kg, on a fat basis) are higher than those reported earlier in Swedish human milk. Although the calculated intake of the DDT complex (DDT + DDE + DDD) by some of the suckling infants exceeds the acceptable daily intake proposed by a FAO/WHO expert group, it does not constitute a reason for recommending any restrictions on breast feeding--for nutritional, immunological and other reasons it should be encouraged.