Academic journal article Environmental Health Perspectives

Intellectual Function in Mexican Children Living in a Mining Area and Environmentally Exposed to Manganese

Academic journal article Environmental Health Perspectives

Intellectual Function in Mexican Children Living in a Mining Area and Environmentally Exposed to Manganese

Article excerpt

BACKGROUND: Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children.

OBJECTIVE: This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children.

METHODS: Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure.

RESULTS: Exposed children had significantly higher median values for MnH (12.6 [micro]g/g) and MnB (9.5 [micro]g/L) than did nonexposed children (0.6 [micro]g/g and 8.0 [micro]g/L, respectively). MnH was inversely associated with Verbal IQ [[beta] = -0.29; 95% confidence interval (CI), -0.51 to -0.08], Performance IQ ([beta] = -0.08; 95% CI, -0.32 to 0.16), and Total Scale IQ ([beta] = -0.20; 95% CI, -0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants.

CONCLUSIONS: The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.

Key WORDS: children, environmental exposure, IQ, manganese, neurotoxicity. Environ Health Perspect 118:1465-1470 (2010). doi:10.1289/ehp.0901229 [Online 1 June 2010]


Manganese (Mn) is an essential element. It actively participates in important enzymatic reactions for cellular function (Gwiazda et al. 2007). Nevertheless, continuous exposure to high concentrations of this metal, mainly by inhalation (Dorman et al. 2006a), may produce alterations in the central nervous system.

Few studies have examined the effect of Mn on neurobehavioral functions in nonoccupationally exposed populations. Those studies did not report evident clinical effects; however, this does not preclude the existence of important cognitive deficits identified by detailed neuropsychological assessment (Mergler et al. 1999; Rodriguez-Agudelo et al. 2006).

Children are considered a vulnerable population, prone to cognitive alterations and long-term neurodevelopmental impairment due to neurotoxic agents (Erikson et al. 2007; Grandjean and Landrigan 2006; Weiss 2000). Lead (Pb), for example, is a confirmed neurotoxicant, and its detrimental effect on IQ has been the outcome most often studied (Needleman 2006; Weiss 2000). Because it is known that Mn exposure mainly affects the basal ganglia (Reaney et al. 2006) and frontal cortex (Schneider et al. 2009), cognitive and intellectual functions in children may be affected. A cross-sectional study performed in China demonstrated that 11- to 13-year-old children exposed to drinking water containing 0.24-0.36 mg/L Mn scored significantly lower in tests that evaluate manual skills, attention span, visual memory, and tracking than did a control group of children exposed to water with 0.03-0.04 mg/L Mn (He et al. 1994); most of the test scores correlated negatively with hair Mn (MnH). Wasserman et al. (2006) reported the results of a cross-sectional study on intellectual function in 10-year-old children exposed to Mn from drinking water in Bangladesh. Water Mn was associated with reduced Total, Verbal, and Performance IQ raw scores in a dose--response manner. …

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