Underground drinking water sources in parts of the U.S. and three Asian countries may not be as safe as previously thought due to high levels of manganese, especially at shallow depths, according to a study led by a researcher at the University of California, Riverside.
Of the four regions, the Glacial Aquifer had the fewest contaminated wells.
While groundwater can be contaminated with a number of heavy metals, more emphasis has been placed on assessing the levels of arsenic than manganese, although the latter also poses a threat to human health.
Although the WHO suggests a health-based limit of 400 ppb, manganese is not listed as a contaminant on the EPA’s National Primary Drinking Water Regulations, and therefore the levels are not monitored or enforced.
In the current study, the researchers collected and analyzed chemical data from 16,000 wells in the Glacial Aquifer, the Ganges-Brahmaputra-Mehta Basin in Bangladesh, the Mekong Delta in Cambodia, and the Yangtze River Basin of China.
When accounting for both metals at levels suggested by the WHO, the percentage of contaminated wells across all depths increased as follows: Glacial Aquifer (U.S): 9.3 percent contaminated when considering arsenic only; increased to 16.4 percent when considering arsenic and manganese.
Ganges-Brahmaputra-Mehta Basin (Bangladesh): 44.5 percent contaminated when considering arsenic only; increased to 70 percent when considering arsenic and manganese.
“However, due to increasing knowledge on the detrimental impact of manganese on human health, particularly on children, manganese levels in these sources should be monitored more closely and governments should consider introducing manganese drinking water standards.
The title of the paper is “Depth stratification leads to distinct zones of manganese and arsenic contaminated groundwater.” In addition to Ying, UC Riverside contributors include: Michael V. Schaefer, a postdoctoral researcher and Jun Li, an associate professor of statistics.
Co-contributors include Scott Fendorf, a professor of soil biogeochemistry at Stanford University, and Alicea Cock‐Esteb, program manager at Aquaya Institute.