Abstract

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 standardised educational outcomes (Standard Assessment Tests, SATs) were collected on these children at age 7-8 years. In the analysis, blood lead concentration was investigated both as 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 to -0.1) decline in SATs grades. Treating lead levels categorically, with the reference group 0-2 microg/dl, no effects on outcomes were apparent at 2-5 microg/dl, but levels of 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.