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June 8, 2020

Using recently developed and sensitive laboratory methods, the USGS has documented where the radionuclides lead-210 and polonium-210 occur in principal aquifers of the U.S. used for drinking-water supply, reports a new study.

Ingestion of low levels of naturally occurring radionuclides in drinking water has been linked to increased cancer risk, but until now, information on where lead-210 and polonium-210 occur in U.S. groundwater and at what levels has been lacking. With the gradual improvement of laboratory techniques, by 2010 low-level measurement of lead-210 and polonium-210 in groundwater had become possible, and the USGS National Water Quality Program set out to characterize occurrence of these two radionuclides in 19 principal aquifers across the contiguous 48 states.

Although there are no drinking-water standards for lead-210 and polonium-210, the Environmental Protection Agency has determined that values of 1.0 picoCuries per liter of water for lead-210 and of 0.7 picoCuries per liter for polonium-210 are associated with a lifetime cancer risk of 5 in 100,000; these values were used as benchmarks in the study. Curies are a measure of radionuclide activity (radioactivity), which is analogous to a concentration.

Monitoring and removal of lead-210 and polonium-210 from groundwater can be expensive, so knowing where high activities of these radionuclides are likely to occur in groundwater could aid water-supply managers and public-health officials to prioritize and optimize monitoring and drinking water treatment programs. The researchers determined characteristics of groundwater and associated aquifer rocks and sediments that were related to activities of lead-210 and polonium-210, based on results from untreated filtered samples of groundwater collected from more than 1,200 public-supply wells. For example, high activities of lead-210—that is, exceeding the benchmark—most frequently occurred in aquifers with uranium-rich rocks and high dissolved radon-222 concentrations, especially in the Appalachian Piedmont crystalline rock aquifers. In confined Coastal Plain aquifers, high polonium-210 activities occurred frequently in samples with high pH, low dissolved oxygen concentration, and sodium concentrations much greater than chloride concentrations.

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