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The consumption of agricultural products grown on paddy soils contaminated with toxic element has a detrimental effect on human health. However, the processes and mechanisms of iron (Fe) mineral-associated arsenic (As) availability and As reactivity in different paddy soil profiles are not well understood. In this study, the fractions, immobilization, and release risk of As in eleven soil profiles from the Changzhutan urban agglomeration in China were investigated; these studied soils were markedly contaminated with As. Sequential extraction experiments were used to analyze fractions of As and Fe oxide minerals, and kinetic experiments were used to characterize the reactivity of Fe oxide minerals. The results showed that concentrations of total As and As fractions had a downward trend with depth, but the average proportions of As fractions only showed relatively small changes, which implied that the decrease in the total As concentrations influenced the changes in fraction concentrations along the sampling depth. Moreover, we found that easily reducible Fe (Fe ox1 ) mainly controlled the reductive dissolution of the Fe oxides, which suggest that the reductive dissolution process could potentially release As during the flooded period of rice production. In addition, a high proportion of As was specifically absorbed As (As-F2) (average 20.4%) in paddy soils, higher than that in other soils. The total organic carbon (TOC) content had a positive correlation with the amount of non-specifically bound As (As-F1) (R = 0.56), which means that TOC was one factor that affected the As extractability in the As-F1. Consequently, high inputs of organic fertilizers may elevate the release of As and accelerate the diffusion of As. Graphical abstract.

Samples of moss (Haplocladium microphyllum) were collected at different elevations on a mountain and four representative sites in Guiyang City, and the concentrations of metal(loid)s were determined by ICP-MS. The altitudinal deposition of soil-originated metals differed from that of anthropogenic metal(loid)s. The concentrations of soil-related elements decreased with elevation, indicating that these elements tend to deposit at lower elevations and their impact on the higher elevations is less. The concentrations of anthropogenic elements varied only slightly with elevation, indicating that the atmospheric deposition of these elements did not vary largely with elevation. The results of this study showed that the mosses at different locations may serve to indicate a vertical gradient of atmospheric metal(loid) deposition.

Cd and As are difficult to co-remediate in co-contaminated soils. In this study, remediation materials comprising large-grained and nano-sized biochar (BC), ferrihydrite (FH), and complexes thereof were added to Cd- and As-contaminated soil. The uptake of Cd and As by pak choi (Brassica chinensis L.) was then evaluated using a pot experiment and the Cd and As concentrations of the soil pore water and leaching water were measured. The Cd and As concentrations of the pore and leaching water were slightly increased with the addition of BC, and decreased with addition of FH and the biochar–ferrihydrite complex (BC-FH). However, nano-sized BC (BC N), FH (FH N), and BC-FH (BC–FH N) had little influence on the decreases in Cd and As of the two monitored water types. Large-grained remediation materials, rather than nanomaterials, decreased the Cd and As concentrations of the two monitored water types. Nonetheless, nanomaterial treatments more effectively decreased the Cd and As concentrations in plants by an average of >10% relative to the large-grained treatments. The DLVO theory analysis suggested that BC N , FH N , and BC-FH N , immobilized in the topsoil, adsorbed heavy metals in the rhizosphere soil. The remainder of the nano-sized materials was dispersed in the rhizosphere soil pores, shielding the uptake of Cd and As by the roots. Although the doses of nanomaterials used in this study were less than one-fortieth of those of the large-grained materials, changes in the plant rhizosphere microenvironment caused by the nanomaterials decreased the risk of toxicity transfer from the soil to the plants. [Display omitted] • Large-grained materials reduced Cd and As concentrations of pore/leaching water. • Nano-sized materials reduced Cd and As uptakes of pak choi. • Nano-sized materials reduced Cd and As uptakes by changing soil pore environment. [ABSTRACT FROM AUTHOR]