ArticlesEnvironmental exposure to polychlorinated biphenyls and quality of the home environment: effects on psychodevelopment in early childhood
Introduction
Both endogenous and exogenous factors and their interactions regulate human child development. Among the endogenous factors, genetic and biochemical induction and modulation are predominant, whereas psychosocial and physicochemical factors and their interactions are important exogenous determinants of general development or psychodevelopment of the human infant.
As for the psychosocial dimension many different individual aspects of the child environment have received attention in developmental studies.1 However, the isolated study of such variables underestimates the contribution of the many interacting environmental components for development. Therefore, more comprehensive constructs for a quantitative description of relevant features of home environments have been developed. A prominent instrument in this respect is the Home Observation for Measurement of the Environment (HOME).2 We have used the score to compare the developmental effects of the quality of the home environment with those of early chemical exposure.
Among the exogenous factors affecting early neurobehavioural child development is the exposure to chemicals in utero or during the early stages of brain development.3 Some environmental chemicals, such as inorganic lead or organic mercury, have received attention in this respect, including the polychlorinated biphenyls (PCBs). PCBs are persistent environmental contaminants consisting of up to 209 individual congeners. PCBs and their metabolites cross the placenta, exposing the vulnerable fetus to PCBs circulating in maternal blood. After birth the infant is additionally exposed to relatively high PCB concentrations in human milk. Among a broad spectrum of biological effects, developmental neurotoxicity seems to be a prominent feature of these chemical mixtures, as can be judged from findings in animals and human beings.4
Evidence of neurodevelopmental effects of prenatal or early postnatal PCB exposure in human beings at environmental exposure levels is largely based on findings from four sets of cohort studies.5, 6, 7, 8, 9, 10 Although all of these studies did report some adverse effects of early PCB exposure on neurological or cognitive development, they are not fully consistent with regard to confounding, spectrum, persistence of effects, or the biological matrix in which PCBs were reported most predictive for later developmental effects.11
Previous reports describing neurodevelopmental effects of environmental chemicals have typically concentrated on exposure-response effects in isolation, and have treated other factors of developmental impact merely as confounders. We have compared the independent effects of early PCB-exposure and the home environment from the age of 7–42 months. Part of the findings at 7 months has already been reported;12 they are covered again in a modified manner here, to allow for direct comparisons with the observations made at the later ages.
Section snippets
Study population
We recruited 171 healthy mother-infant pairs between October, 1993, and May, 1995, from the obstetrical wards of three Düsseldorf hospitals. Three advanced medical students were involved in the recruitment process. Criteria for inclusion were: principal agreement of the mother, first and second born babies delivered at term (weeks 37–42 of pregnancy) from native German families; an Apgar score at 5 minutes of at least 78; and no serious illnesses or complications during pregnancy and delivery.
Results
From recruitment until 42 months of age the sample size dropped from an initial 171 to 116. 126 mothers from the initial 171 provided milk samples at 2 weeks and 91 of these remained in the study until final testing at 42 months. Despite this attrition the sample structure changed only marginally. No significant difference from recruitment to testing at 42 months was detected for PCB concentrations, sex, birthweight, gestational/maternal age, neonatal condition, parental education, maternal
Discussion
Despite considerable attrition of the cohort during the study period, mainly due to loss of interest, moving away from Düsseldorf, or some cases of initially unidentified congenital disorders, we observed a strong positive effect of the home environment as assessed by the HOME scale for psychodevelopment. With increasing age the degree of association between HOME and mental or motor development increased, an observation which is consistent with published evidence.22 This effect might reflect
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