Learning Disabilities in Children: Significance of Low‐Level Lead‐Exposure and Confounding Factors

Abstract

The hypothesis that low-level lead absorption is a risk factor for learning disabilities in school children was examined in the municipality of Aarhus, Denmark. During 1982-1983, a total of 1,302 children in the first grade (54% of the eligible population) delivered shed deciduous teeth. The lead concentration in the circumpulpal dentin was used as an indicator of the cumulated lead absorption, and 200 cases (high-lead) and controls (low-lead) were selected, and matched for socioeconomic group and gender. The parents were interviewed regarding the child's development and past medical history. Possible confounders were identified and controlled for in a logistic multivariate model. The influence of lead absorption became statistically significant only after exclusion of the children with proven medical risk factors, thereby the adjusted odds ratio in the weighted analysis was changed from 2.2 to 4.3. Thus, in a Scandinavian low-level lead-polluted area, lead absorption appears to be a risk factor for learning disabilities.

Investigation of Environmental Lead Contamination Caused by Thermo-Electric Power Plants

“…Also, increasing lead levels have been documented in permanent teeth with increasing age. 29 The results obtained in this study were obtained in a way specified in the literature, and the values were found to be higher than the values obtained by Aladag et al, 30 who have investigated the lead amount in deciduous teeth. In their study carried out in Leinigerwerk Thermal Power Plant, Bunzl et al 8 took soil samples from 0.4, 0.8, 1.4, 2.7 and 5.2 km away from the power plant; collected fly ash samples from electrostatic collectors at 4 different time for 2 years; and analyzed them.…”

Behavioral effects of lead: commonalities between experimental and epidemiologic data.

“…(34,38,49) studies in children. Effects have been (63) observed at blood lead levels similar to those (28,40) in children; a no observable effect level has (28) not been identified in either children or ani- (18) mals. Research in the last decade has often included analyses to identify the behavioral (59) processes underlying the observed lead- (54) induced behavioral deficits (75).…”

“…A measure of global failure that has been linked to increased lead burden is academic failure and the need for special education. In the Danish study, Lyngbye et al (40) found an increased need for special education, especially verbal, in first-graders as a function of increased lead body burden. In a follow-up of the 1979 Boston cross-sectional study, Bellinger et al (28) assessed school performance in sixth-graders as a function of their first-grade tooth lead levels.…”

Lessons from a Danish Study on Neuropsychological Impairment Related to Lead Exposure

“…Thus, the highlead group also had a higher proportion of children needing special education in school (22). This result would tend to confirm the significance of the test results.…”

“…This result would tend to confirm the significance of the test results. Again in this case, children with medical risk factors more frequently required special education, despite their low dentin lead levels; this confounding effect was controlled by restriction in the analysis (22).…”