A cross-sectional study of water arsenic exposure and intellectual function in adolescence in Araihazar, Bangladesh

Abstract

Background: Exposure to inorganic arsenic (As) from drinking water is associated with modest deficits in intellectual function in young children; it is unclear whether deficits occur during adolescence, when key brain functions are more fully developed.

Objectives: We sought to determine the degree to which As exposure is associated with adolescent intelligence, and the contributory roles of lead, cadmium, manganese and selenium.

Methods: We recruited a cross-section of 726 14-16 year olds (mean age = 14.8 years) whose mothers are participants in the Bangladesh Health Effects of Arsenic Longitudinal Study (HEALS), and whose household well water As levels, which varied widely, were well characterized. Using a culturally modified version of the WISC-IV, we examined raw Full Scale scores, and Verbal Comprehension, Perceptual Reasoning, Working Memory and Processing Speed Indices. Blood levels of As (BAs), Mn, Pb, Cd and Se were assessed at the time of the visit, as was creatinine-adjusted urinary As (UAs/Cr).

Results: Linear regression analyses revealed that BAs was significantly negatively associated with all WISC-IV scores except for Perceptual Reasoning. With UAs/Cr as the exposure variable, we observed significantly negative associations for all WISC-IV scores. Except for Se, blood levels of other metals, were also associated with lower WISC-IV scores. Controlling for covariates, doubling BAs, or UAs/Cr, was associated with a mean decrement (95% CI) of 3.3 (1.1, 5.5), or 3.0 (1.2, 4.5) points, respectively, in raw Full scale scores with a sample mean of 177.6 (SD = 36.8). Confirmatory analyses using Bayesian Kernel Machine Regression, which identifies important mixture members, supported these findings; the primary contributor of the mixture was BAs, followed by BCd.

Conclusions: Our data indicate that the adverse consequences of As exposure on neurodevelopment observed in other cross-sectional studies of younger children are also apparent during adolescence. They also implicate Cd as a neurotoxic element that deserves more attention.

Keywords: Adolescence; Arsenic exposure; Cognitive test scores; Intellectual function; Metal mixtures.

Figure 1.

The relationships between quartiles of WAs and UAs and adjusted WISC-IV full scale raw scores. Scores were adjusted for child’s years 8.2 (−14.5, of education, head circumference, maternal intelligence, paternal education and home construction wall type. The mean difference in Full Scale scores between the highest and lowest quartiles of BAs was −8.2 (−14.5, −1.8); for WM the corresponding difference was smaller but still significant [ −1.5 (−2.7, −0.4)].

Figure 2.

Metal-specific effect estimates of the mixture on Full Scale raw score of adolescents in Araihazar, Bangladesh estimated by Bayesian Kernel Machine Regression (BKMR). Model adjusted for child’s sex, years of education, head circumference, maternal intelligence, paternal education, and type of home construction (wall materials). Single predictor associations and 95% confidence bands for each metal with other metals fixed at the median. Estimate represents the predicted standardized Full Scale raw score. All metal concentrations (μg /L) were log transformed. mUAscr = mother’s urinary arsenic at HEALS baseline.

Figure 3.

Joint effect of the mixture on Full Scale raw score of adolescents in Araihazar, Bangladesh estimated by Bayesian Kernel Machine Regression (BKMR). Model adjusted for child’s sex, years of education, head circumference, maternal intelligence, paternal education, and type of home construction (wall materials). Overall effect of the mixture (estimates and 95% credible intervals), comparing Full Scale raw score when all exposures are at a particular quantile to the median. Estimate represents the predicted standardized Full Scale raw score. All metal concentrations (BAs, BMn, BPb, BCd, BSe, mUAscr (μg /g)) were log transformed.