About 20% of untreated water samples from public, private, and monitoring wells across the United States contain at least one trace element, such as arsenic, manganese, and uranium, at levels of potential health concern, according to a U.S. Geological Survey (USGS) research report released last year.
The report, Trace-Elements and Radon in Groundwater Across the United States, 1992–2003, says that these trace elements in groundwater exceed human health benchmarks at a rate that outpaces most other groundwater contaminants, such as nitrate, pesticides, and volatile organic compounds, a USGS news release says.
Even though these contaminants are removed from public drinking water before consumption, trace elements could be present in private wells and pose a risk to human health, explained Joe Ayotte, USGS hydrologist and the report’s lead author, in the release.
The trace elements found in groundwater that most frequently exceeded U.S. Environmental Protection Agency (EPA) health benchmarks were arsenic in 7% of wells, uranium in 4% of wells, and manganese in 12% of wells. “Radon, a product of the decay of natural uranium, also exceeded its proposed EPA maximum contaminant level in 65% of wells tested,” the release says.
The study also found that climate and land use are important factors in trace element distribution. For example, dry areas and agricultural areas had higher concentrations of trace elements in groundwater than did humid regions or urban areas, the release says.
Geology and geochemistry of water samples helped predict the occurrence of trace elements in groundwater. For example, anoxic and slightly alkaline samples commonly contained arsenic and molybdenum, the release says.
The report also notes that the effects of trace element mixtures could cause further health concerns. About 10% of wells that exceeded human health benchmarks contained two or more trace elements each exceeding health benchmarks. “Contaminants can act together to be more toxic than each individual contaminant,” the release says.
Findings were based on more than 5000 samples collected throughout the United States between 1992 and 2003. The study evaluated samples for 23 different trace elements and radon, the report’s abstract says. For more information, see http://water.usgs.gov/nawqa/trace/pubs/sir2011-5059.