Occurrence and Geochemistry of Lead-210 and Polonium-210 Radionuclides in Public-Drinking-Water Supplies from Principal Aquifers of the United States

Abstract

On the basis of lifetime cancer risks, lead-210 (210Pb) and polonium-210 (210Po) ≥ 1.0 and 0.7 pCi/L (picocuries per liter), respectively, in drinking-water supplies may pose human-health concerns. 210Pb and 210Po were detected at concentrations greater than these thresholds at 3.7 and 1.5%, respectively, of filtered untreated groundwater samples from 1263 public-supply wells in 19 principal aquifers across the United States. Nationally, 72% of samples with radon-222 (222Rn) concentrations > 4000 pCi/L had 210Pb ≥ 1.0 pCi/L. 210Pb is mobilized by alpha recoil associated with the decay of 222Rn and short-lived progeny. 210Pb concentrations ≥ 1.0 pCi/L occurred most frequently where acidic groundwaters inhibited 210Pb readsorption (felsic-crystalline rocks) and where reducing alkaline conditions favored dissolution of iron–manganese- (Fe–Mn-) oxyhydroxides (which adsorb 210Pb) and formation of lead–carbonate complexes (enhancing lead (Pb) mobility). 210Po concentrations ≥ 0.7 pCi/L occurred almost exclusively in confined Coastal Plain aquifers where old (low percent-modern carbon-14) groundwaters were reducing, with high pH (>7.5) and high sodium/chloride (Na/Cl) ratios resulting from cation exchange. In high-pH environments, aqueous polonium (Po) is poorly sorbed, occurring as dihydrogen polonate (H2PoO3(aq)) or, under strongly reducing conditions, as a hydrogen-polonide anion (HPo–). Fe–Mn- and sulfate-reduction and cation-exchange processes may mobilize polonium from mineral surfaces. Po2+ occurrence in low-to-neutral-pH waters is attenuated by adsorption.

Machine-Learning Predictions of High Arsenic and High Manganese at Drinking Water Depths of the Glacial Aquifer System, Northern Continental United States

“…Potential sulfide concentrations for reducing samples were computed using measured aqueous iron concentration (assumed Fe +2 ) in equilibrium with pyrite or mackinawite. 109 Eh and pe are equivalent electrochemical descriptions of redox potential for a system in equilibrium. 110 However, waters at low temperature rarely achieve redox equilibrium, 111 so no single value of Eh or pe can be used to represent the redox state.…”

Freshwater salinization syndrome: from emerging global problem to managing risks

“…Geology is also important for the occurrence of various metals as well (Wright and Belitz 2010;Izbicki et al 2015;McClain et al 2019), except for the cosmogenic/fallout radionuclides (Gellis et al 2020). In public drinking water wells across the USA, lead-210 and polonium-210 radionuclides contaminate aquifers used for drinking water (Szabo et al 2020). The radionuclides Pb-210 and Po-210 do not co-occur in groundwater despite both being derived from Rn-222 due to control by decay rates and interactions with various aquifer materials such as the association of Pb-210 with felsic crystalline rocks, whereas Po-210 presence is dictated by reducing conditions and high pH (Szabo et al 2020).…”

A preliminary study of rapid measurements of aqueous 210Po by accelerator mass spectrometry

“…Most recently, Szabo et al showed elevated levels of 210 Po (≥26 mBq L −1 ) in some drinking water supplies with groundwater source across the United States. 23 Thus, a rapid analytical technique of 210 Po in water would be beneficial for routine screening and health risk safeguard. At present, the most common method for 210 Po measurements is alpha spectrometry, 2 which involves the electrodeposition of 210 Po onto a silver disc in the standard protocol.…”