How Environmental Pollution
Impairs Brain Development
—
and How to Protect the Brains
of the Next Generation
Manganese in water drains brains
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7 January 2015. Manganese contamination of drinking water can stain the laundry and result in an unpleasant taste, although thought to be of doubtful health significance. As late as 2011, the World Health Organization (WHO) decided to discontinue its guideline for maximal manganese in drinking water (400 µg/L, an excessive level). Because “this health-based value is well above concentrations of manganese normally found in drinking water, it is not considered necessary to derive a formal guideline value,” WHO concluded. New research suggests that this decision needs urgent revision.
Researchers from the University of Montreal examined 375 Quebec children aged 6-13 years and measured manganese in home tap water and the children’s hair. After adjustment for other factors affecting children’s neurodevelopment, manganese concentrations on both water and hair showed strong negative associations with the children’s scores on memory and attention tests. Children exposed to the highest 20% of water manganese concentrations had a decline of 8% in memory function compared to children exposed to the lowest levels of manganese. These findings suggest that chemical brain drain can result from manganese exposures at concentrations commonly encountered worldwide – much below the (former) WHO concentration limit.
The study adds important support to existing evidence that manganese contamination of drinking water is a health hazard. Other new research further adds to the concern. Two newly published studies from Brazil also showed signs of neurotoxic effects in school children from communities close to a polluting ferromanganese plant. One report focused on behavioral problems and found that girls in particular had greater problems with inattention at higher manganese exposures. The second study relied on neuropsychological tests and reported IQ deficits and other adverse findings in highly exposed children. Manganese is already considered a chemical brain drainer. The new data show adverse effects at elevated manganese concentrations that commonly occur worldwide, whether from industrial pollution or leaching from soil minerals. Inexpensive methods are available to remove manganese from the water. No matter the WHO inaction, developing brains must be protected against manganese toxicity.
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Children born from a mother with a higher blood level of manganese in their later period of the pregnancy have a neurodevelopmental delay compared with the infants born from a medium level of blood manganese. Neurotoxicity of manganese was well established in the adults with high level of occupational or environmental exposure. However, there are few studies on the potential neurotoxicity of manganese in the population with low level of exposure. Furthermore, there are no reports on the infants with their in utero environment with manganese.
Researchers in Korea have studied the Bayley Scale of Infant Development six months after birth in relation to the level of maternal blood manganese level at the time of pregnancy. Both MDI and PDI, which represents the cognitive and motor development of infants, were lower in infants born from both very high and low level of blood manganese, which was manifested as an inverted U-shaped dose-response relation in a birth cohort. The highest score was set between 24 and 28 ug/L for both MDI and PDI. (Chung et al., 2015)
Nonlinearity of the relationship between maternal blood manganese level and the neurodevelopment of the infants may represent the essentiality of manganese in the neurodevelopment, which is also evident in the previous reports on the relationship between birth weight and maternal manganese level (Zota et al., 2009; Eum et al., 2013). In addition, maternal blood level of manganese rises after second trimester, reaching its maximum at term.
Does it imply that there is an “optimal” level of manganese for the pregnant women? Is it needed for the women with either higher or lower blood level of manganese to supplement or reduce blood level for the women in their pregnancy? Even though the association is evident and consistent, maternal blood level may not represent the level of exposure to the fetus. There is good enough reason to avoid high exposure to manganese, either environmental or occupational, during pregnancy. Supplement of manganese or monitoring blood manganese for the pregnant women, however, may not be rationalized solely based on the maternal blood manganese level except when it is extremely low or when the mother has a problem in the metabolism of metals.