A critical review on the occurrence and distribution of the uranium- and thorium-decay nuclides and their effect on the quality of groundwater.

Journal Article (Review;Journal Article)

This critical review presents the key factors that control the occurrence of natural elements from the uranium- and thorium-decay series, also known as naturally occurring radioactive materials (NORM), including uranium, radium, radon, lead, polonium, and their isotopes in groundwater resources. Given their toxicity and radiation, elevated levels of these nuclides in drinking water pose human health risks, and therefore understanding the occurrence, sources, and factors that control the mobilization of these nuclides from aquifer rocks is critical for better groundwater management and human health protection. The concentrations of these nuclides in groundwater are a function of the groundwater residence time relative to the decay rates of the nuclides, as well as the net balance between nuclides mobilization (dissolution, desorption, recoil) and retention (adsorption, precipitation). This paper explores the factors that control this balance, including the relationships between the elemental chemistry (e.g., solubility and speciation), lithological and hydrogeological factors, groundwater geochemistry (e.g., redox state, pH, ionic strength, ion-pairs availability), and their combined effects and interactions. The various chemical properties of each of the nuclides results in different likelihoods for co-occurrence. For example, the primordial 238 U, 222 Rn, and, in cases of high colloid concentrations also 210 Po, are all more likely to be found in oxic groundwater. In contrast, in reducing aquifers, Ra nuclides, 210 Pb, and in absence of high colloid concentrations, 210 Po, are more mobile and frequently occur in groundwater. In highly permeable sandstone aquifers that lack sufficient adsorption sites, Ra is often enriched, even in low salinity and oxic groundwater. This paper also highlights the isotope distributions, including those of relatively long-lived nuclides (238 U/235 U) with abundances that depend on geochemical conditions (e.g., fractionation induced from redox processes), as well as shorter-lived nuclides (234 U/238 U, 228 Ra/226 Ra, 224 Ra/228 Ra, 210 Pb/222 Rn, 210 Po/210 Pb) that are strongly influenced by physical (recoil), lithological, and geochemical factors. Special attention is paid in evaluating the ability to use these isotope variations to elucidate the sources of these nuclides in groundwater, mechanisms of their mobilization from the rock matrix (e.g., recoil, ion-exchange), and retention into secondary mineral phases and ion-exchange sites.

Full Text

Duke Authors

Cited Authors

  • Vengosh, A; Coyte, RM; Podgorski, J; Johnson, TM

Published Date

  • February 2022

Published In

Volume / Issue

  • 808 /

Start / End Page

  • 151914 -

PubMed ID

  • 34856287

Electronic International Standard Serial Number (EISSN)

  • 1879-1026

International Standard Serial Number (ISSN)

  • 0048-9697

Digital Object Identifier (DOI)

  • 10.1016/j.scitotenv.2021.151914

Language

  • eng