Effects of an iron-silicon material, a synthetic zeolite and an alkaline clay on vegetable uptake of As and Cd from a polluted agricultural soil and proposed remediation mechanisms

Abstract

Economic and highly effective methods of in situ remediation of Cd and As polluted farmland in mining areas are urgently needed. Pot experiments with Brassica chinensis L. were carried out to determine the effects of three soil amendments [a novel iron-silicon material (ISM), a synthetic zeolite (SZ) and an alkaline clay (AC)] on vegetable uptake of As and Cd. SEM-EDS and XRD analyses were used to investigate the remediation mechanisms involved. Amendment with ISM significantly reduced the concentrations of As and Cd in edible parts of B. chinensis (by 84-94 % and 38-87 %, respectively), to levels that met food safety regulations and was much lower than those achieved by SZ and AC. ISM also significantly increased fresh biomass by 169-1412 % and 436-731 % in two consecutive growing seasons, while SZ and AC did not significantly affect vegetable growth. Correlation analysis suggested that it was the mitigating effects of ISM on soil acidity and on As and Cd toxicity, rather than nutrient amelioration, that contributed to the improvement in plant growth. SEM-EDS analysis showed that ISM contained far more Ca, Fe and Mn than did SZ or AC, and XRD analysis showed that in the ISM these elements were primarily in the form of silicates, oxides and phosphates that had high capacities for chemisorption of metal(loid)s. After incubation with solutions containing 800 mg L AsO or Cd, ISM bound distinctly higher levels of As (6.18 % in relative mass percent by EDS analysis) and Cd (7.21 % in relative mass percent by EDS analysis) compared to SZ and AC. XRD analysis also showed that ISM facilitated the precipitation of Cd as silicates, phosphates and hydroxides, and that arsenate combined with Fe, Al, Ca and Mg to form insoluble arsenate compounds. These precipitation mechanisms were much more active in ISM than in SZ or AC. Due to the greater pH elevation caused by the abundant calcium silicate, chemisorption and precipitation mechanisms in ISM treatments could be further enhanced. That heavy metal(loid)s fixation mechanisms of ISM ensure the remediation more irreversible and more resilient to environmental changes. With appropriate application rate and proper nutrients supplement, the readily available and economic ISM is a very promising amendment for safe crop production on multi-metal(loids) polluted soils.

Biogenic hydroxyapatite synthesis by Bacillus subtilis: An efficient passivator for the reduction of cadmium contamination in agricultural soil

“…[ 38,39 ] In addition, it can help slow down the release of P fertilizer to increase its utilization efficiency in soil. [ 40 ]…”

“…[38,39] In addition, it can help slow down the release of P fertilizer to increase its utilization efficiency in soil. [40] The addition of hydroxyapatite can fix Cd in soil because of the similarity of the crystal structure and ion radius of Ca 2+ in hydroxyapatite with those of some cations, such as Cd 2+ , Pb 2+ , Zn 2+ , and Ni 2+ , allows them to exchange with Ca 2+ in the hydroxyapatite lattice [41] and form more stable phosphate through surface adsorption and cation exchange. [27] When the obligate adsorption of ions occurs on the hydroxyapatite surface, the ions form chemical bonds on the hydroxyapatite surface, which can transfer the charge of the ions themselves to the hydroxyapatite surface, thus affecting its surface charge.…”

Remediation of Arsenic and Cadmium Co-Contaminated Soil: A Review

“…However, achieving collaborative remediation of both As and Cd through these methods remains challenging [24]. Few plant species can hyperaccumulate both As and Cd, and suitable amendments for simultaneously immobilizing these two elements are limited by various factors [25][26][27].…”

Approaches to the development of environmental standards for the content of petroleum hydrocarbons and Pb, Cr, Cu, Ni in soils of Greatest Caucasus

“…This is due to the influence of HMs on the binding of humic acids and their transformation into humates (Zybalov & Popkova, 2018). Many studies report a decrease in soil microbial activity and microbial biomass, inhibition of organic matter mineralization, and changes in the structure of the microbial community after HMs are introduced into the soil (Bai et al, 2021;Chu, 2018;Guo et al, 2017;He et al, 2016;Yao et al, 2017) TM ions have been shown to bind to cellular components such as DNA and proteins, causing DNA damage and conformational changes and may exhibit carcinogenic and genotoxic properties (Malar et al, 2014).…”