Environmental Exposure to Lead and Children's Intelligence at the Age of Seven Years

TLDR

Lead exposure in early childhood is linked to delayed neuropsychological development, yet longitudinal evidence on persistence into later childhood is limited. The study aimed to determine whether lead‑related IQ deficits persist at age seven by measuring IQ in 494 children from the Port Pirie lead‑smelting community. Lead exposure was quantified through serial blood lead measurements taken from mothers antenatally and at delivery and from children at birth, 6 months, 15 months, 2 years, and annually thereafter, alongside systematic collection of developmental covariates. After adjusting for multiple covariates, higher postnatal blood lead concentrations (15 months–4 years) were associated with a 4–5 point (≈4–5 %) reduction in IQ at age seven, confirming that low‑level lead exposure during early childhood remains inversely linked to neuropsychological development.

Abstract

Exposure to lead in early childhood is thought to result in delayed neuropsychological development. As yet there is little longitudinal evidence to establish whether these effects persist into later childhood.We measured IQ scores in 494 seven-year-old children from the lead-smelting community of Port Pirie, Australia, in whom developmental deficits associated with elevated blood lead concentrations had already been reported at the ages of two and four years. Exposure to lead was estimated from the lead concentrations in maternal blood samples drawn antenatally and at delivery and from blood samples drawn from the children at birth (umbilical-cord blood), at the ages of 6 and 15 months and 2 years, and annually thereafter. Data relating to known covariates of child development were collected systematically for each child throughout the first seven years of life.We found inverse relations between IQ at the age of seven years and both antenatal and postnatal blood lead concentrations. After adjustment by multiple regression for sex, parents' level of education, maternal age at delivery, parents' smoking status, socioeconomic status, quality of the home environment, maternal IQ, birth weight, birth order, feeding method (breast, bottle, or both), duration of breast-feeding, and whether the child's natural parents were living together, the relation with lead exposure was still evident for postnatal blood samples, particularly within the age range of 15 months to 4 years. For an increase in blood lead concentration from 10 micrograms per deciliter (0.48 mumol per liter) to 30 micrograms per deciliter (1.45 mumol per liter), expressed as the average of the concentrations at 15 months and 2, 3, and 4 years, the estimated reduction in the IQ of the children was in the range of 4.4 points (95 percent confidence interval, 2.2 to 6.6) to 5.3 points (95 percent confidence interval, 2.8 to 7.8). This reduction represents an approximate deficit in IQ of 4 to 5 percent.Low-level exposure to lead during early childhood is inversely associated with neuropsychological development through the first seven years of life.