Aim: To determine whether early lead exposure at levels below 10 microg/dL has an impact on educational and behavioural outcomes at school.
Methods: Venous samples were taken from a subgroup of the Avon Longitudinal Study of Parents and Children (ALSPAC) attending a research clinic at 30 months of age (n=582), and lead levels were measured by atomic absorption spectrometry. Developmental, behavioural and standardized educational outcomes (SATs) were collected on these children at 7-8 years. In the analysis, blood lead concentration was investigated as both a continuous covariate and as a categorical variable.
Results: 488 cases (84%) had complete data on confounders and outcomes. After adjustment for confounders and using a log dose-response model for lead concentration, blood lead levels showed significant associations with reading, writing and spelling grades on SATs, and antisocial behaviour. A doubling in lead concentration was associated with a 0.3 point (95% CI -0.5, -0.1) decline in SATs grades. Treating lead levels categorically, with the reference group 0-2 microg/dL, no effects on outcomes were apparent between 2-5 microg/dL, but levels between 5-10 microg/dL were associated with a reduction in scores for reading (OR 0.51, p=0.006) and writing (OR 0.49, p=0.003). Lead levels >10 microg/dL were also associated with increased scores for antisocial behaviour (OR 2.9, p=0.040) and hyperactivity (OR 2.82, p=0.034).
Conclusions: Exposure to lead early in childhood has effects on subsequent educational attainment, even at blood levels below 10 microg/dL . These data suggest that the threshold for clinical concern should be reduced to 5 microg/dL.