Manganese in drinking water: higher doses may hamper intellectual function.Manganese manganese (măng`gənēs, măn`–) [Lat.,=magnet], metallic chemical element; symbol Mn; at. no. 25; at. wt. 54.938; m.p. about 1,244°C;; b.p. about 1,962°C;; sp. gr. 7.2 to 7. is an essential nutrient An essential nutrient is a nutrient required for normal body functioning that cannot be synthesized by the body and must be obtained from a dietary source. Some categories of essential nutrient include vitamins, dietary minerals, essential fatty acids, and essential amino acids. for humans, but its excessive consumption can cause adverse health impacts. Past studies have linked inhalation of excessive manganese to neurotoxicity neurotoxicity /neu·ro·tox·ic·i·ty/ (noor?o-tok-sis´it-e) the quality of exerting a destructive or poisonous effect upon nerve tissue. in adults. Now a group of U.S. researchers suggests that ingesting high doses of manganese in drinking water drinking water
supply of water available to animals for drinking supplied via nipples, in troughs, dams, ponds and larger natural water sources; an insufficient supply leads to dehydration; it can be the source of infection, e.g. leptospirosis, salmonellosis, or of poisoning, e.g. can hamper intellectual function in children [EHP EHP
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2. electric horsepower 114:124-129]. These effects were seen most strongly on scales that measure performance aspects of intellectual function.
The same group had earlier observed a negative impact of water arsenic on intellectual function among children in Araihazar, Bangladesh. Though the manganese concentration in the water these children drank was much higher than its arsenic content, the independent impact of manganese on intellectual function could not be verified. The present study included 142 10-year-old children (including 54 children from the earlier study) who consumed well water with average concentrations of 793 micrograms per liter ([micro]g/L) manganese and 3 [micro]g/L arsenic.
The children's intellectual function was assessed on six tests (similarities, digit span, picture completion, coding, block design, and mazes) drawn from the Wechsler Intelligence Scale for Children Wechsler intelligence scale for children
A standardized intelligence test that is used for assessing children from 5 to 15 years old. , Version III. Results were summed to create Verbal, Performance, and Full-Scale raw scores. These tests were chosen as they could be applied to Bangladesh's rural context with minimal alteration. The results showed that manganese concentration had a significant negative dose-response association with all three raw scores.
The researchers found that children in exposure groups 1 (manganese lower than 200 [micro]g/L) and 4 (manganese higher than 1,000 [micro]g/L) differed significantly from one another for Verbal, Performance, and Full-Scale raw scores. Compared to group 1, children in exposure groups 2 (manganese between 200 [micro]g/L and 500 [micro]g/L) and 3 (manganese between 500 [micro]g/L and 1,000 [micro]g/L) had lower Full-Scale and Performance scores, but the differences were not statistically significant. Verbal scores of the children in groups 2 and 3 also did not differ significantly from those in group 1. Due to the lack of measures of intelligence standardized for use in Bangladesh, the team could not calculate IQ points lost.
Though the children's waterborne manganese intake was lower than the highest safe daily dose (6 milligrams per day) estimated by the U.S. Institute of Medicine, the authors write that additional dietary exposure could have pushed the total daily dose above this value. Moreover, bioavailability bioavailability /bio·avail·a·bil·i·ty/ (bi?o-ah-val?ah-bil´i-te) the degree to which a drug or other substance becomes available to the target tissue after administration.
n. of manganese from food is very low, while it is high from drinking water. This could have contributed to neurotoxicity seen in children drinking water with higher amounts of manganese.
The authors point out that their findings are relevant in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. as well. Data collected by the U.S. Geological Survey The term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information.
A geological survey have shown that about 6% of domestic wells contain manganese concentrations higher than 300 [micro]g/L. Based on these data and their study results in Bangladesh, the researchers suggest that some U.S. children may be at risk for manganese-induced neurotoxicity.