Assessment of Fraction and Mobility of Arsenic in Soil Near the Mine Waste Dam

Applicability of Brassica juncea as a bioindicator for As contamination in soil near the abandoned mine area

Soil monitoring in abandoned mine areas is important from the perspective of ecological and human health risk. Arsenic (As) is a predominant metalloid contaminant in abandoned mine area and its behavior has been influenced by various soil characteristics. Bioindicator can be a useful tool in terms of testing the extent to which they are uptaken by plants bioavailability. Eighteen soils near the mine tailings dam were collected to investigate the effect of As contamination on As absorption by Brassica juncea. The pH range of the experimental soils was between 4.90 and 8.55, and the total As concentrations were between 34 mg kg-1 and 3017 mg kg-1. The bioavailability of As was evaluated by Olsen method, and B. juncea was cultivated in eighteen soils for 3 weeks. Principal component analysis, correlation, and multiple regression analysis were performed to estimate a significant factor affecting As uptake by B. juncea. All statistical results indicated that As bioavailability in soil is the main factor affecting As uptake in root and shoot of B. juncea. Although translocation process, the amount of As in shoot was exponentially explained by As bioavailability in soil. This result suggests that the contamination and bioavailability of As can be confirmed only by analyzing the shoot of B. juncea, which is be easily found in environmental ecosystem, and implies the applicability of B. juncea as a bioindicator for the monitoring of As contamination and its behavior in soil ecosystem.

In-situ physical and chemical remediation of Cd and Pb contaminated mine soils cultivated with Chinese cabbage: A three-year field study

Soils pollution with heavy metals (HMs) is a serious concern due to their toxic effects on crop yield, crop quality, soil environment, and human health. In the current study, four stabilizers of calcium carbonate (CC), dolomite (DL), zeolite (ZL), and steel slag (SS) were applied to cadmium (Cd) and lead (Pb)-contaminated soils as in-situ chemical remediation techniques along with in-situ physical remediation techniques i.e. soil covering (SC) and soil dilution (SD) under real field conditions. For three years, Chinese cabbage (Brassica rapa L.) was grown on the amended fields to examine how the amendments impacted Cd and Pb uptake in plants. The stabilization efficiency of SS, CC, and SC were 75.7 %, 66.0 %, and 71.1 %, respectively, for Cd, and 55.6 %, 55.6 %, and 70.0 %, respectively, for Pb. Results indicated that stabilizer soil amendments significantly decreased the exchangeable (F1) and carbonates bound (F2) fractions of both Cd and Pb. For instance, F1 fraction of Cd decreased from 10.2 (control) to 1.8-2.9 % (with stabilizers). The stabilizers increased Chinese cabbage dry weight by 11.4-22.5 % and decreased Cd and Pb uptake by 67.4 % and 24 %, respectively. The results demonstrated that in-situ chemical remediation technique showed promising results and maintained its efficiency for more than 130 weeks. Current study indicated that chemical remediation of Cd and Pb contaminated soil is more effective and last longer than physical remediation.

Occurrence, source identification and ecological risk assessment of heavy metals in water and sediments of Uchalli lake - Ramsar site, Pakistan

Uchalli Lake is an internationally significant Ramsar site that needs protection for supporting migratory birds. The current study aimed to assess wetland health by examining water and sediments utilizing total and labile heavy metals concentration, pollution indices, ecological risk assessment, water recharge and pollution induction sources through isotope tracer techniques. Al concentration in water was of serious concern as it was 440 times higher than the maximum acceptable concentration of Environmental Quality Standard of the UK for aquatic life in saline waters. Labile concentration predicted very severe enrichment of Cd, Pb, and moderate enrichment of Cu. Modified ecological risk index predicted very high ecological risk in sediments. The δ 18O, δ2H and D-excess values indicate that the lake was mainly recharged by local meteoric water. Enriched values of δ 18O and δ2H suggest a high evaporation of lake water, making lake sediments more enriched with metals. Isotopic and D-excess values of groundwater suggest a quick rainwater recharge to groundwater around the Uchalli Lake. Nitrates isotopes indicate that the rainwater runoff is main source of induction of fertilizers, pesticides and soil bonded metals in the lake system. The lake is recharged by rainwater runoff, from catchment areas, that erode the soil particles and agricultural residual waste dumped in the lake.

Co application of biofertilizer and zinc oxide nanoparticles upregulate protective mechanism culminating improved arsenic resistance in maize

During this study, the bioremediation potential of zinc-oxide nanoparticles (ZnO-NPs) and PGPR mixed biofertilizer (BF) on maize plants under induced arsenic (As) stress of 50 ppm and 100 ppm was investigated. The treated plants showed increased As resistance to mitigate the adverse effects of stress by enhancing fresh and dry biomass, relative water content, protein content, soluble sugars, proline content, enzymatic antioxidant defense mechanisms including activities of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), and malondialdehyde (MDA) content. In the pot experiment, the parameters studied have shown that the integrated treatments of ZnO-NPs and BF cause a notable enhancement in relative water content 43%-50% and plant biomass. Moreover, the same treatment showed a marked upregulation in enzymes activity (APX, SOD, APX, and CAT) which oxidized the cell-damaging ROS, produced in response to As stress. Likewise, the combined treatment showed a maximum reduction in MDA content 46%-57% and electrolyte leakage in As treated plants as compared to stressed plants. On the other hand, total soluble sugar 114%-170% and total protein content 117%-241% escalated. SEM analysis revealed marked damage reduction in the treated cells caused by arsenic toxicity. Thus, the use of BF comprised of rhizobacteria along with ZnO-NPs could be a very effective bio source for improving maize plant growth under As stress. In in silico study, As mediated network of proteins showed positive and negative regulation of As activity that leads to stress generation for housekeeping genome.

Evaluation of arsenic mineralogy and geochemistry in gold mine-impacted matrices: Speciation, transformation, and potential associated risks

The risk of arsenic (As) contamination from gold mining is a long-term environmental concern for mines worldwide. Researchers have mainly focused on As contamination induced by tailings, however, less attention has been paid mineralogically to differentiate the fate of As among different As-bearing matrices. This paper presents a detailed study of the mineralogical and morphological features of three typical As-bearing matrices (waste rock, ores, and tailings) using bulk chemical, microscopic and spectroscopic analyses, and reveals the geochemical behavior of As in those matrices. Results from mineral composition identified by RoqSCAN revealed that the matrices were dominated by quartz, k-feldspar, albite, muscovite, and clay minerals, with subordinate ankerite, chlorite, smectite, hematite, arsenopyrite, pyrrhotite, apatite, pyrite, halite, and calcite. The sequential extraction scheme indicated that As in waste rock, ores and tailings was mainly hosted in arsenopyrite. Microscopic analysis observed that waste rock was significantly different from the ores and tailings in terms of mineralogical and morphological characteristics. For waste rock, from arsenopyrite to hematite, As content decreased from 46.12 wt% to 3.54 wt%. However, arsenopyrite presented as unweathered euhedral crystals or slight fragmentation in ores and tailings and a narrower oxidation rims than that of waste rock. The leaching test of SPLP showed that the highest As leaching was found in waste rock (0.246 mg/L) which was significantly higher than those in ores (0.080 mg/L) and tailings (0.148 mg/L). The As in waste rock displayed weaker geochemical stability than in ores and tailings, as supported by mineralogy analysis. Health risk assessment suggested waste rock had a higher health risk for both adults and children compared with ores and tailings. These findings reaffirm that understanding of As fate among different source materials is paramount for securing humans from As hazards. More must be done to decelerate the continuous oxidation of waste rock, thus mitigating As release into nature.

Effect of bioavailable arsenic fractions on the collembolan community in an old abandoned mine waste

Mine waste from abandoned mines poses a risk to soil ecosystems due to the dispersion of arsenic (As) in the mine waste to the nearby soil environment. Because the bioavailability of As varies depending on the As chemical fraction and exposure conditions, chemical assessment of As fractions in soil around mine waste is essential to understand their impact on soil ecosystem. Here, six sites around the mine waste were selected for investigating toxic effects of As-contaminant soil on Collembola community. To measure the As chemical fraction in soil and bioavailability, Wenzel sequential extraction employed. Meanwhile, the collembolans that live in each sampling site were identified at the species level, and the characteristics and composition of the collembola community were investigated. The mobility fraction (F1 + F2 + F3; MF) was related to the risk to the collembolan community, and the adverse impact of high MF appeared to lead to a decrease in abundance, richness, and Shannon index. According to non-metric multidimensional scaling analysis, F1, F2, F3, and pH were shown as the significant factor explaining the NMDS space. Especially, the sampling site with the highest concentration of F3 showed statistically different species composition from the other sites. In the case of As-contaminated soil around the old mine waste, the toxic effects of the remaining F3 in soil, as well as that of F1 and F2, should be fully considered. This study suggested that collembolan community could be used for understanding the impact of bioavailable As fraction in the old abandoned mine area.

Evaluation of Two Amendments (Biochar and Acid Mine Drainage Sludge) on Arsenic Contaminated Soil Using Chemical, Biological, and Ecological Assessments

Various types of organic and inorganic materials are widely examined and applied into the arsenic (As) contaminated soil to stabilize As bioavailability and to enhance soil quality as an amendment. This study deals with two types of amendments: biochar for organic amendment and acid mine drainage sludge (AMDS) for inorganic amendment. Each amendment was applied in two types of As contaminated soils: one showed low contaminated concentration and acid property and the other showed high contaminated concentration and alkali property. In order to comprehensively evaluate the effect of amendments on As contaminated soil, chemical (As bioavailability), biological phytotoxicity (Lactuca sativa), soil respiration activity, dehydrogenase activity, urease activity, ß-glucosidase activity, and acid/alkali phosphomonoesterase activity, an ecological (total bacterial cells and total metagenomics DNA at the phylum level) assessment was conducted. Both amendments increased soil pH and dissolved organic carbon (DOC), which changes the bioavailability of As. In reducing phytotoxicity to As, the AMDS was the most effective regardless of soil types. Although soil enzyme activity results were not consistent with amendments types and soil types, bacterial diversity was increased after amendment application in acid soil. In acid soil, the results of principal component analysis represented that AMDS contributes to improve soil quality through the reduction in As bioavailability and the correction of soil pH from acidic to neutral condition, despite the increases in DOC. However, soil DOC had a negative effect on As bioavailability, phytotoxicity and some enzyme activity in alkali soil. Taken together, it is necessary to comprehensively evaluate the interaction of chemical, biological, and ecological properties according to soil pH in the decision-making stages for the selection of appropriate soil restoration material.

Effect of Soil Characteristics on Arsenic Accumulation in Phytolith of Gramineae (Phragmites japonica) and Fern (Thelypteris palustris) Near the Gilgok Gold Mine

In South Korea, most metal mines were abandoned and caused contamination for more than 30 years. Even the soil is highly contaminated with trace elements, plants still grow in the area and can affect the contamination. Phytolith is amorphous silica in the plant body. Phytolith is resistant to decomposition, and the stabilization of carbon, nutrients, and toxic substances accumulated in the phytolith is being studied. In this study, the Gilgok gold mine, which is contaminated with arsenic was selected as the research site. We selected Phragmites japonica and Thelypteris palustris as targets for the analysis of arsenic accumulation in plants and phytolith. Plants accumulate more phytolith at the riverside. The higher water content of soil increased the Arsenic (As) concentration in the frond of the T. palustris. Soil available silicon (Si) did not affect phytolith accumulation but increased As accumulation in the plant and phytolith. The research result showed that P. japonica and T. palustris have the ability to accumulate As in phytolith and the accumulation can be changed with soil characteristics and plant species. This As accumulation in phytolith can affect plant tolerance in contaminated areas and change the As availability in the soil. The result of the research can be used as a database to build a sustainable environment.