General discussion, conclusions

Abstract

We studied the relationships between prenatal exposure to PCBs and postnatal exposure to PCBs and dioxins on the one hand, and the neurological and cognitive development at 42 months on the other. In order to be able to detect small negative effects of PCB and dioxin exposure, we followed a large group of children (n=418) at low risk of developmental deficit from birth. For each mother/infant pair, a wide range of social, obstetrical, nutritional, and perinatal conditions was recorded and in the statistical analyses, if necessary, adjustments were made for differences. Breast milk not only is a source of toxic substances such as PCBs and dioxins, but it also contains components that are considered to be essential for optimal child development. In order to solve this controversy, the early type of feeding was explored in addition to the effects of lactational exposure to PCBs and dioxins. We found a beneficial effect of breast-feeding on neurological development at 42 months and at nine years of age. Our findings are in accordance with several other studies which have also shown a positive relationship between breast-feeding and brain development 1-6. Furthermore, in the present study no effects of lactational exposure to PCBs and dioxins could be detected, although plasma PCB levels of breast-fed 42-month-olds were 4½ times as high as those among formula-fed children. In all, despite the contamination of human milk with PCBs and dioxins, breast-feeding is the most optimal feeding method during the first period of life. Prenatal exposure to PCBs was negatively associated with cognitive abilities at 42 months, but not with neurological development at that age. Both the cognitive and the neurological development are parameters of brain integrity. But they reflect different functions of the brain and they are assessed in a basically different manner. Cognitive tests, including the Kaufman Assessment Battery for Children, measure children's abilities in a quantitative way, whereas the neurological examination measures functioning in a qualitative fashion. More importantly, in our age group the neurological examination might not have enough discriminating power to discern differences in motor behaviour due to perinatal exposure to PCBs and dioxins. At 42 months the so called 'higher' functions, that is the more complex motor skills which are cortically mediated, have not yet developed 7. Long-term follow-up and similar research in areas where the environmental PCB and/or dioxin exposure is