The labile fractions of metals and arsenic in mining‐impacted soils are explained by soil properties and metal source characteristics

Abstract

Isotopically exchangeable metals in soil, also termed labile metals, are reversibly bound to soil surface and are a better index of the environmental risk of the metals than are their total concentrations. In this study, labile fractions of potentially toxic elements were surveyed in metal mining‐impacted soils of Mexico to test the relative importance of soil properties (pH, effective cation exchange capacity, organic matter, etc.) or attributes of the mines (ore type and lithology, metal mineralogy, etc.) on the fractions of labile elements. Mining waste‐impacted soils, corresponding uncontaminated soils and mining waste were collected around 11 metal mines in Mexico presenting contrasting ore types. Pseudo‐total concentrations and labile fractions of Cd, Ni, Zn, Pb, Cu, and As were determined by aqua regia digestion and isotope dilution, respectively. Pseudo‐total concentrations of these elements ranked: waste > contaminated soil > uncontaminated soils, and Zn and As dominated the concentrations of toxic elements. The labile fractions (% of total) in the soils ranked, with median values in brackets, Pb (22) > Cd (18) > Cu(15) > Ni∼Zn(13) > As(9). The labile fractions of waste samples were slightly higher than those of soil samples suggesting either a high weathering of mining wastes or the stabilization of heavy metals by soil. Stepwise multiple regression showed that soil properties rather than source attributes primarily explained the %E of most elements, except for Zn and As for which the ore lithology was the dominant factor. This study showed that earlier generic models explain metal lability adequately in mining waste‐impacted soils.

The effect of soil properties on zinc lability and solubility in soils of Ethiopia – an isotopic dilution study

“…In principle, E-value determination is based on the premise that an added isotope is reversibly adsorbed and is in a dynamic equilibrium between the solid and solution phases (Hamon et al, 2008;Young et al, 2005). Therefore, the reliability of the determined E value rests on an accurate measurement of the distribution coefficient of the added 70 Zn (Kd Lab ) and Zn concentration in the soil solution Zn Soln (Eq.…”

“…However, these approaches cannot fully characterize both the quantity of potentially available Zn in the soil solid phase and its intensity in the soil solution phase -both of which contribute to the phyto-availability of Zn over the course of a growing season. Isotopic dilution assays may provide a more mechanistically based characterization of the geochemically reactive fraction of Zn in soils which buffers the free ion activity in the soil solution phase (Guzman-Rangel et al, 2020;Hamon et al, 2008;Young et al, 2005). This approach has been extensively used to study contaminated soils (Degryse et al, 2011;Izquierdo et al, 2013;Mossa et al, 2020;Nolan et al, 2005), but its application to Zn in agricultural soils generally, and especially in the soils of SSA countries, is very limited.…”

Validating the Use of a Toxicity Database for Prediction of Plant Cover and Biodiversity in Multi‐Metal Mining‐Impacted Soils

“…The concentration of relevant metals in the TILL‐4 samples are shown in Supplemental Data, Table S4. Additional soil properties including the determination of labile metal and As concentrations were measured with previously described methods (Guzmán‐Rangel et al 2018, 2020).…”

“…In steps V and VI, metal concentrations were expressed as labile metal (M lab , mg kg −1 ). Estimation of M lab was according to the average value of labile fractions (%E) determined in uncontaminated and contaminated soil samples, with no significant difference ( p > 0.05) in %E between both, collected at the same locations except for the newly visited Xichú location for which the median %E from 32 different soil samples (16 uncontaminated soils and 16 corresponding contaminated soils) was applied (Guzmán‐Rangel et al 2020). Labile fractions used for each metal and location are provided in Supplemental Data, Table S2.…”

Zinc lability and solubility in soils of Ethiopia – an isotopic dilution study

“…However, these approaches cannot fully characterise both the 'quantity' of potentially available Zn in the soil solid phase and its 'intensity' in the soil solution phase-both of which contribute to the phyto-availability of Zn over the course of a growing season. Isotopic dilution assays may provide a 50 more mechanistically-based characterization of the geochemically reactive fraction of Zn in soils which buffers the free ion activity in the soil solution phase (Guzman-Rangel et al, 2020;Hamon et al, 2008;Young et al, 2005). This approach has been extensively used to study contaminated soils (Degryse et al, 2011;Izquierdo et al, 2013;Mossa et al, 2020;Nolan et al, 2005) but its application to Zn in agricultural soils generally, and especially in the soils of SSA countries, is very limited.…”