Although the brain continues developing in the postnatal period, epidemiological studies on the effects of postnatal exposure to neurotoxic POPs through breast-feeding remain mostly inconclusive. Failure to detect associations between postnatal exposure and health outcomes may stem from the limitations of commonly employed approaches to assess lactational exposure. The aim of the present study was to assess whether lactational exposure to polychlorinated biphenyl-153 (PCB-153), dichlorodiphenyldichloroethylene (DDE), or hexachlorobenzene (HCB) as estimated with a physiologically based pharmacokinetic (PBPK) model, is associated with decrements in mental and psychomotor development scores of the Bayley Scales of Infant Development (BSID) test in children aged around 14-months of a subsample (N=1175) of the Spanish INMA birth cohort, and to compare this with the effects of prenatal exposure. Although in the present study population PCB-153, DDE and HCB exposure increased within the first months of postnatal life, no associations were found between different periods of postnatal exposure to these compounds and mental or psychomotor scores. Increasing prenatal PCB-153 concentrations were associated with worse mental and psychomotor scores, although significance was only reached for psychomotor development (β [95%CI]=-1.36 [-2.61, -0.11]). Indeed, the association between exposure and effects observed during prenatal life weakened gradually across periods of postnatal life. Results of the present study suggest that, although breastfeeding increases children's blood persistent organic pollutants (POPs) levels during postnatal life, deleterious effects of PCB-153 on neuropsychological development are mainly attributable to prenatal exposure.
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