Zinc protoporphyrin levels, blood lead levels and neurocognitive deficits in Andean children with chronic lead exposure

Objectives: To investigate the relationship between blood lead (PbB), zinc protoporphyrin (ZPP) levels and performance on a test of auditory memory in Andean children and adolescents with chronic lead (Pb) exposure. Design and methods: PbB and ZPP levels were measured in blood samples from 166 participants (aged 6–16 yrs.) exposed to Pb in a local ceramic glazing cottage industry in Ecuadorian villages. PbB levels and ZPP/heme ratios were analyzed in relation to performance on the Digit Span subtest of the Wechsler IV intelligence scale, a test of auditory memory. Results: Mean PbB level for the study group was 18.0 μg/dL (S.D.: 15.1; range: 3.0–86.0), and the mean ZPP/heme ratio was 105.7 μmol/mol (S.D.: 100.9; range: 36.0–592.0). There was no significant difference in PbB and ZPP levels between the 84 females and the 82 males. The mean Digit Span scale score (DS SS) for the study group was 6.81 (S.D.: 2.95; range: 1.0–17.0), which is below the average score of 10 for the test, with the females performing significantly better than males (t = 2.435; p = 0.01). Regression analyses revealed statistically significant inverse associations between DS SS and PbB level (r = 0.251, p = 0.001), and between DS SS and ZPP/heme ratio (r = 0.246, p = 0.001). Conclusion: Elevated PbB levels, representing acute exposure, and ZPP levels, reflecting chronic Pb exposure in this cohort of Andean inhabitants were associated with poor performance on a test of auditory memory, suggesting that the children and adolescents in the study area have neurocognitive deficits that may affect learning.