Superfund Research Program
Manganese Exposure via Drinking Water and Children's Intellectual Function
Health, earth, and social scientists from the Columbia University SBRP are conducting collaborative, multi-disciplinary studies in Araihazar, Bangladesh to examine the dose relationships between arsenic (As) drinking water and health outcomes. In the course of this work, they made an unexpected discovery about the impact of manganese (Mn) exposure to children.
In a recent cross-sectional study of 10 year-old children in Bangladesh, Dr. Joseph Graziano, Program Directory of the Columbia University SBRP, found that drinking water arsenic concentration is significantly and adversely associated with child intelligence in a dose-response manner. That study also indicated that well water manganese was adversely associated with children’s intellectual functioning. However, it was unclear whether or not water manganese had an association with intellectual functioning that was independent of arsenic.
The Columbia University researchers have now completed a follow-on study to test the hypothesis that manganese might have an independent adverse effect on cognitive function. They recruited families drinking from wells with low arsenic concentrations (ranging from 0.1 to 10 μg As/L; mean concentration: 3.0 μg As/L), but with manganese concentrations ranging from 4 to 3908 μg Mn/L (mean concentration: 795 μg Mn/L). Children and their mothers came to the field clinic, where the children participated in assessments described below and received a medical examination by a study physician. Weight, height, and head circumference were measured. In addition, children provided spot urine specimens for the measurement of urinary arsenic and creatinine, and were asked to provide a blood sample for the measurement of blood manganese, blood arsenic, blood lead and hemoglobin concentrations. Information on family demographics (parental education, occupation, housing type, etc.) was obtained from the baseline interview of parents during their enrollment in the cohort study. Information on the primary source of drinking water was obtained from the child’s mother. Parents were asked their age, education, and occupation; whether their home included a television; and the birth order of their children. As an additional surrogate for social class, the type of roofing on the well-owner’s home was recorded as thatched, tin, or cement and subsequently ranked on a scale (thatched: lowest, cement: highest). All families participating in the study continue to receive primary medical care at a Columbia University field clinic.
The children's intellectual function was assessed using a culturally modified version of the Wechsler Intelligence Scale for Children, version III (WISC-III), which provides a Total Score, a Verbal Score, and a Performance Score. Because the WISC-III has not been standardized (i.e., "normed") in Bangladesh, which would require testing of many thousands of children across the country, Dr. Graziano's team could report only raw exam scores, not traditional IQ scores. Maternal intelligence was assessed with Raven’s Standard Progressive Matrices, a nonverbal test relatively free of cultural influences.
This study was specifically designed to examine possible effects of water manganese in the absence of confounding by water arsenic. The results indicate that exposure to manganese in drinking water is associated with neurotoxic effects in children. After adjustment for sociodemographic covariates, water manganese was associated with reduced Full Scale, Performance, and Verbal raw scores, in a dose-response fashion. This study examined 10 year-old children, and does not address the question of whether the observed deficits can be detected earlier in life.
These findings led Dr. Graziano to ask whether manganese exposure from drinking water might be a concern in the United States. He learned that while breast milk contains between 3 and 10 μg Mn/L, infant formulas have been reported to contain as much as 50 to 300 μg Mn /L. In addition, data from the National Water-Quality Assessment Program of the U.S. Geological Survey (USGS) indicate that approximately 6% of domestic wells in the United States contain more than 300 μg/L. Based on the results of the present study and the USGS findings, Dr. Graziano and his colleagues believe that exposure to manganese from drinking water may pose a surprisingly widespread risk of neurotoxicity in children.
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To learn more about this research, please refer to the following sources:
- Wasserman GA, Liu X, Parvez F, Ahsan H, Levy D, Factor-Litvak P, Kline JK, van Geen AF, Slavkovich VN, Lolacono NJ, Cheng Z, Zheng Y, Graziano JH. 2006. Water manganese exposure and children's intellectual function in Araihazar, Bangladesh. Environ Health Perspect 114(1):124-129. PMID:16393669
- Wasserman GA, Liu X, Parvez F, Ahsan H, Factor-Litvak P, van Geen AF, Slavkovich VN, Lolacono NJ, Cheng Z, Hussain A, Momotaj H, Graziano JH. 2004. Water arsenic exposure and children's intellectual function in Araihazar, Bangladesh. Environ Health Perspect 112(13):1329-1333. PMID:15345348 PMCID:PMC1247525
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