Superfund Research Program

Consequences of Arsenic and Manganese Exposure on Children

Project Leader: Joseph H. Graziano
Grant Number: P42ES010349
Funding Period: 2000-2017

Project-Specific Links

Final Progress Reports

Year:   2016  2010  2005 

Chronic exposure to arsenic (As) and manganese (Mn) has been taking place in Bangladesh for more than three decades due to the consumption of groundwater that is naturally elevated in both elements.  Dr. Graziano’s lab recently reported findings from a cross-sectional study of 10 year-old children in Bangladesh that found an adverse association between As exposure and cognitive function in children.  Since Mn is also known to be neurotoxic, they subsequently conducted an additional study of 10 year-olds to test the hypothesis that water-borne Mn exposure might also be neurotoxic in children. 

The original study of As in 201 ten year-olds included 54 children using wells with low As concentrations, i.e., ≤ 10 μg/L.  In subsequent field work, Graziano’s team recruited 88 additional children drinking from wells comparably low in As and reported on associations between water Mn and intellectual function in children in the combined sample of 142 children.

The mean water Mn concentration was 795 μg/L, with a range of 4 to 3908 μg/L; by comparison, the World Health Organization (WHO) maximal contaminant level is 500 μg/L.  By design, the range of water As concentrations was narrow (0.1 to 10 μg/L), with a mean of 3.0 μg/L. 

Linear regression analyses, which predict raw test scores from the socio-demographic features retained in the final “core” model, as expected, revealed better scores among children who:  1) had more educated mothers; 2) lived in more adequate dwellings; 3) had access to television; 4) were taller; and 5) had a larger head circumference (data not shown).  Collectively, these factors explained 25.0%, 24.1%, and 17.7% of the variances in Full Scale, Performance, and Verbal raw scores, respectively.

Prior to adjustment for sociodemographic factors, water Mn was significantly associated with Full Scale, Performance, and Verbal raw scores, explaining 10%, 10%, and 4%, respectively, of the variances in scores.  After adjusting for sociodemographic factors, water Mn concentration remained significantly and negatively associated with all three scores, explaining incremental portions of the variances in Full, Performance and Verbal scores.

The addition of water As to these regression models failed to change the pattern of associations between intellectual function and sociodemographic variables, or between intellectual function and water Mn.  Given the extremely low levels of water As, water As was not significantly associated with intellectual function.  Similarly, associations between water Mn and intellectual function scores were unchanged when we adjusted for both urinary As and urinary creatinine.

In order to examine the dose-response relationship between water Mn and intellectual function, Graziano’s team subsequently stratified children into four approximately equal-sized groups, based on well water Mn.  After adjustment for other factors that influence child intelligence, children in Groups 1 and 4 were significantly different for Full Scale, Performance, and Verbal scores. Compared to Group 1, children in Groups 2 and 3 had lower, albeit not significantly so, Full Scale and Performance Scores. Verbal score comparisons between children in Groups 2 and 3 and those in Group 1 were in the expected direction but did not approach significance.