North Carolina State University researchers estimate that thousands of North Carolina residents and more than 1 million residents in the southeast have high levels of manganese in their well water. Manganese is found naturally in soil, but studies have linked long-term exposure to health problems, including cancer and heart defects.
NC State associate professor of crop and soil sciences Matt Polizzotto said water with manganese levels above accepted water quality standards could have a distinct taste or might stain clothing.
"There are some signs that you can look for," Polizzotto said. "Brown or black stains on your dishwasher or any kind of discoloration of clothes can be indicative. ... And then also sometimes you can get kind of black materials that are accumulating in pipes."
Polizzotto said residents who suspect their wells have high manganese levels should have them tested. But he says the contamination is not an immediate health threat.
"The concentrations of manganese that are observed are not anything that's going to harm someone right away," he said. "With natural contaminates, it often takes a long time of exposure before concentrations accumulate to cause these health impacts."
Polizzotto added that stains in clothing and dishwashers don't necessarily indicate manganese levels high enough to cause health problems.
Researchers suspect the geology of the Piedmont region, which extends through central North Carolina, South Carolina, Virginia, and Georgia, makes wells in the area prone to manganese contamination.
NC State Ph.D. student Elizabeth Gillispie was lead author of the paper, published in the journal Environmental Science and Technology. She said as bedrock breaks down, manganese gets concentrated in a geological layer known as the saprolite − between the bedrock and the soil layer near the water table.
North Carolina saprolite is extra porous, allowing more manganese to seep into the well water. Researchers used census data about well locations as well as groundwater monitoring data to make their estimates.
In addition to more well testing, the researchers recommend digging new wells deeper into the earth − farther from the manganese-laden saprolite.