Inverse association of intellectual function with very low blood lead but not with manganese exposure in Italian adolescents

BackgroundPediatric lead (Pb) exposure impacts cognitive function and behavior and co-exposure to manganese (Mn) may enhance neurotoxicity.ObjectivesTo assess cognitive and behavioral function in adolescents with environmental exposure to Pb and Mn.MethodsIn this cross sectional study, cognitive function and behavior were examined in healthy adolescents with environmental exposure to metals. The Wechsler Intelligence Scale for Children (WISC) and the Conners-Wells’ Adolescent Self-Report Scale Long Form (CASS:L) were used to assess cognitive and behavioral function, respectively. ALAD polymorphisms rs1800435 and rs1139488 were measured as potential modifiers.ResultsWe examined 299 adolescents (49.2% females) aged 11–14 years. Blood lead (BPb) averaged 1.71 μg/dL (median 1.5, range 0.44–10.2), mean Blood Manganese (BMn) was 11.1 μg/dL (median 10.9, range 4.00–24.1). Average total IQ was 106.3 (verbal IQ=102, performance IQ=109.3). According to a multiple regression model considering the effect of other covariates, a reduction of about 2.4 IQ points resulted from a two-fold increase of BPb. The Benchmark Level of BPb associated with a loss of 1 IQ-point (BML01) was 0.19 μg/dL, with a lower 95% confidence limit (BMLL01) of 0.11 μg/dL. A very weak correlation resulted between BPb and the ADHD-like behavior (Kendall's tau rank correlation=0.074, p=0.07). No influence of ALAD genotype was observed on any outcome. Manganese was not associated with cognitive and behavioral outcomes, nor was there any interaction with lead.ConclusionsThese findings demonstrate that very low level of lead exposure has a significant negative impact on cognitive function in adolescent children. Being an essential micro-nutrient, manganese may not cause cognitive effects at these low exposure levels.

► We examined 299 children exposed to Pb and Mn from industrial ferroalloy emission.
► BPb averaged 1.71 μg/dL (median 1.5) and was inversely related to the IQ scores.
► The Benchmark of BPb was 0.19 μg/dL, and the lower 95% confidence limit 0.11 μg/dL.
► No Mn×Pb interaction and no separate effect of Mn on the IQ scores was observed.
► This study shows cognitive effects of lead at the lowest exposure level.