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Cadmium in soils and groundwater: A review
Citation:
Kubier, A., Richard T. Wilkin, AND T. Pichler. Cadmium in soils and groundwater: A review. APPLIED GEOCHEMISTRY. Elsevier Science Ltd, New York, NY, 108:104388, (2019). https://doi.org/10.1016/j.apgeochem.2019.104388
Impact/Purpose:
Cadmium (Cd) is a non-essential trace element that is widely distributed in the environment. Both geogenic and anthropogenic sources can elevate Cd concentrations in soils and groundwater. Elevated Cd doses are carcinogenic to humans. In aqueous solutions, Cd generally occurs as the divalent Cd2+ ion. The transport and fate of Cd in groundwater environments depends on geochemical parameters such as pH, redox conditions, and the presence of ligand-forming species such as dissolved carbonate, chloride, sulfate, and organic species. The goal of this study was to present a broad overview of the origin and concentration of Cd in groundwater and its reaction pathways in aquatic environments. To gain an overview on the hydrochemical behavior of Cd, cases of Cd pollution in soil and groundwater and studies investigating Cd release were compiled. The work is of interest to the international environmental community, including EPA’s regional, program, and local partners.
Description:
Cadmium (Cd) is a non-essential trace element that is widely distributed in the environment. Both geogenic and anthropogenic sources can elevate Cd concentrations in soils and groundwater. Elevated Cd doses are carcinogenic to humans. Inhalation and dietary intake are the most significant routes of Cd exposure. The first well-investigated case of Cd-induced disease occurred in Japan in the 20th century, where mining activities caused Cd pollution of paddy fields and drinking water. The WHO Guidelines for Drinking-Water Quality recommend a maximum contamination level for Cd of 3 µg/L. Important anthropogenic Cd sources include mining, atmospheric deposition of combustion emissions, and the use of Cd-containing fertilizers. Apart from direct pollution, Cd can also accumulate and biomagnify in the marine food web. Due to high marine primary production, organic-rich sediments, such as black shales, can have elevated Cd concentrations, primarily in the sulfidic fraction. Cadmium is also incorporated into carbonates and phosphorites resulting in elevated geogenic Cd concentrations in associated rock types. The crustal average Cd content is 0.2 mg/kg. In soils, Cd occurs at concentrations of 0.01 to 1 mg/kg with a worldwide mean of 0.36 mg/kg. Weathering of parent materials leads to Cd concentrations up to 5 µg/L in soil water and up to 1 µg/L in groundwater. In aqueous solutions, Cd generally occurs as the divalent Cd2+ ion. It is mobilized mainly in oxic and acidic conditions. Cadmium sorption is enhanced by the presence of high amounts of clays and other solid-phase sorbents and its mobility is further influenced by pH, the redox state, and ionic strength of the solution. However, Cd can remain in solution as water-soluble complexes with anions and dissolved organic matter while sorption and precipitation decrease the aqueous concentrations of other heavy metals. As a consequence, Cd is one of the most mobile heavy metals in the environment. The elevated mobilization potential is the reason for Cd release from soil into groundwater. The goal of this study was to present a broad overview of the origin and concentration of Cd in groundwater, and its reaction pathways in aquatic environments. To gain an overview on the hydrochemical behavior of Cd, cases of Cd pollution in soil and groundwater, studies investigating Cd release, and information about the legal framework were compiled.
