Lower IQs seen in Mexican girls living near manganese mines.
Riojas-Rodriguez, H, R Solis-Vivanco, A Schilmann, S Montes, S Rodriguez, C Rios and Y Rodriguez-Agudelo. 2010. Intellectual function in Mexican children environmentally exposed to manganese living in a mining area. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.0901229.
Higher levels of manganese in hair and blood are associated with lower IQ in children, especially girls, who live near a manganese processing site, finds a study of Mexican children. The children scored lower on a suite of intelligence tests than their counterparts who lived well away from the mining operations.
The children's exposures were high because they live so close to the mining operation. In this case, the median hair levels measured in the children who lived within a kilometer of the manganese processing facility were about 20 times higher than hair levels in those who lived far away – 80 kilometers – from the industrial site.
Despite being an essential element, high levels of manganese may cause cognitive and intellectual deficits, especially if exposure occurs during childhood. Few studies have examined the impact of airborne manganese on children's intelligence.
Manganese is emitted during industrial processes and gasoline/diesel combustion. For people, contact is primarily through diet and breathing.
Breathing manganese is especially dangerous because it can enter the lungs and directly expose the brain. Manganese is a neurotoxin, which means it is harmful to developing nerves and brain.
Researchers in Mexico studied 79 exposed children ages 7 to 11 who live in a community less than one kilometer from a manganese processing plant. An unexposed group of 93 who live in communities more than 80 kilometers from the manganese facility were also studied. Blood and hair samples were analyzed for manganese content. Verbal skills, performance IQ scores and total IQ were assessed and measured through questionnaires and established IQ tests.
Exposed children had significantly higher levels of manganese in their hair and blood when compared to the unexposed children. Median levels in hair and blood in those living near the plant were 12.6 micrograms per gram (μg/g) and 9.5 micrograms per liter (μg/L) compared to 0.6 μg/g and 8.0 μg/L in the non-exposed group.
IQ scores were also significantly lower in the children living near the manganese mine when compared to the control group. Levels of manganese in hair was found to be associated with decreased intelligence after controlling for other risk factors including maternal education and lead levels. The association between levels of manganese in hair was greatest in younger girls and minimal for the boys at any age.
The results of this study suggest that industries emitting manganese near residential areas develop strategies to minimize environmental exposures, particularly to children who live nearby.
