The Effects of Forest Litter and Waterlogging on the Ecotoxicity of Soils Strongly Enriched in Arsenic in a Historical Mining Site

Profile Distributions of Potentially Toxic Metal(loid)s in Soils of the Middle Odra Floodplain (SW Poland)

Floodplain soils are often contaminated with potentially toxic elements of geogenic and anthropogenic origin. This also applies to a valley of the Odra river, which in its upper reach flows through areas of historical and contemporary mining and heavy industry. This study examined the distribution of typically anthropogenic metal(loid)s, i.e., Pb, Zn, Cu, As and Cd, and geogenic metals, i.e., Mn and Fe, in soil profiles of the middle Odra valley, and analyzed factors that determine their concentrations. Thirteen soil profiles, located inter the embankment area and outside the embankments, were examined. Most of profiles indicated stratification typical for alluvial soils. Topsoil layers in the inter-embankment zone showed considerable enrichment in Pb, Zn and Cd, and to a lesser extent in Cu and As. Low soil pH is an important factor of environmental risk; therefore, acidic soils definitely require liming. The soils located out of embankments did not show any considerable enrichment in the elements examined. Based on significant correlations between the concentrations of metal(loid)s in deep soil layers and soil texture, the values of local geochemical background were derived. Outliers, particularly in the case of As, were explained by possible redistribution under reducing conditions.

Antimony release and volatilization from rice paddy soils: Field and microcosm study

The fate of antimony (Sb) in submerged soils and the impact of common agricultural practices (e.g., manuring) on Sb release and volatilization is understudied. We investigated porewater Sb release and volatilization in the field and laboratory for three rice paddy soils. In the field study, the porewater Sb concentration (up to 107.1 μg L^-1) was associated with iron (Fe) at two sites, and with pH, Fe, manganese (Mn), and sulfate (SO₄^2-) at one site. The surface water Sb concentrations (up to 495.3 ± 113.7 μg L^-1) were up to 99 times higher than the regulatory values indicating a potential risk to aquaculture and rice agriculture. For the first time, volatile Sb was detected in rice paddy fields using a validated quantitative method (18.1 ± 5.2 to 217.9 ± 160.7 mg ha^-1 y^-1). We also investigated the influence of two common rice agriculture practices (flooding and manuring) on Sb release and volatilization in a 56-day microcosm experiment using the same soils from the field campaign. Flooding induced an immediate, but temporary, Sb release into the porewater that declined with SO₄^2-, indicating that SO₄^2- reduction may reduce porewater Sb concentrations. A secondary Sb release, corresponding to Fe reduction in the porewater, was observed in some of the microcosms. Our results suggest flooding-induced Sb release into rice paddy porewaters is temporary but relevant. Manuring the soils did not impact the porewater Sb concentration but did enhance Sb volatilization. Volatile Sb (159.6 ± 108.4 to 2237.5 ± 679.7 ng kg^-1 y^-1) was detected in most of the treatments and was correlated with the surface water Sb concentration. Our study indicates that Sb volatilization could be occurring at the soil-water interface or directly in the surface water and highlights that future works should investigate this potentially relevant mechanism.

Does Soil Drying in a Lab Affect Arsenic Speciation in Strongly Contaminated Soils?

This study examined the changes in extractability and fractionation of arsenic (As) that can be caused by the drying of strongly polluted anoxic soil samples. Two untreated and manure-amended soils were incubated for 7 and 21 days in flooded conditions. Thereafter, As water- and 1M NH4NO3-extractability and As fractionation in a 5-step sequential extraction according to Wenzel were examined in fresh, oven-dried and air-dried samples. Soil treatment with manure considerably affected the results of the sequential extraction. Air-drying caused a significant decrease in As extractability with 1M NH4NO3 and in As concentrations in the F1 fraction. The highest reduction of extractability (30–41%) was found in manure-treated soils. Oven-drying resulted in a smaller reduction (5–34%) of As extractability. These effects were explained by opposing processes of As mobilization and immobilization. Sequential extraction did not allow for balancing As redistribution due to drying, as As loss from the F1 fraction was smaller than the confidence intervals in the other fractions. The results showed that for the precise determination of As extractability in anoxic soils, fresh samples should be analyzed. However, oven-dried samples may be used for a rough assessment of environmental risk, as the order of magnitude of easily soluble As did not change due to drying.

Advances in As contamination and adsorption in soil for effective management

Arsenic (As) is a heavy metal that causes widespread contamination and toxicity in the soil environment. This article reviewed the levels of As contamination in soils worldwide, and evaluated how soil properties (pH, clay mineral, organic matter, texture) and environmental conditions (ionic strength, anions, bacteria) affected the adsorption of As species on soils. The application of the adsorption isotherm models for estimating the adsorption capacities of As(III) and As(V) on soils was assessed. The results indicated that As concentrations in contaminated soil varying significantly from 1 mg/kg to 116,000 mg/kg, with the highest concentrations being reported in Mexico with mining being the dominating source. Regarding the controlling factors of As adsorption, soil pH, clay mineral and texture had demonstrated the most significant impacts. Both Langmuir and Freundlich isotherm models can be well fitted with As(III) and As(V) adsorption on soils. The Langmuir adsorption capacity varied in the range of 22-42400 mg/kg for As(V), which is greater than 45-8901 mg/kg for As(III). The research findings have enhanced our knowledge of As contamination in soil and its underlying controls, which are critical for the effective management and remediation of As-contaminated soil.