As(V) reduction mediated by microorganisms might be an essential process in resisting As toxicity since As(V) is the major species in the landfill. LSZ has been considered as a trigger of all types of microbial activity inside a landfill site. This research investigated the microbial As(V)-reducing behavior in LSZ. The results revealed that higher As(V)-reduction efficiency in higher As(V) content-stress LSZ scenario. The corresponding microbial diversity also varied with the As(V) content. The microbial community structure was related to arrA and arsC distribution, which encode respiratory As(V) reductase and cytoplasmic As(V) reductase, respectively. The landfill As bio-reduction pathways were modeled, as well as the As functional gene distribution among different As(V) contents at different landfill stages. The C, N, and S metabolic processes generally affected the As(V)-resistance genes distribution. Thiosulfate oxidation, denitrification, and dissimilatory nitrate reduction positively affected arsC, while dissimilatory sulfate reduction and methanogenesis trended to play a negative role. This research provides new insight into As(V) bio-reduction inside a landfill site in terms of functional genes distribution and correlation with nutrient elements metabolic processes.

High-arsenic wastewater derived from the metallurgical industry of nonferrous minerals is one of the most dangerous arsenic (As) sources that usually follow the emission of massive hazardous arsenic-bearing wastes. Considering the properties of red mud (RM), we propose an alternative and environmentally friendly method for the efficient remediation of high-arsenic wastewater using RM through formation of AlAsO₄@silicate precipitate, aiming at ''zero-emission of hazardous solid waste''. The results show nearly 100% of arsenic could be stepwisely removed from high-arsenic wastewater and reduce the arsenic concentration from 6100 mg/L to 40 μg/L using RM at room temperature. The highest arsenic removal capacity of RM reaches 101.5 mg/g at a RM-to-wastewater ratio of 40 g/L due to the superior arsenic adsorption and the co-precipitation of arsenate and Al³⁺ to form insoluble aluminum arsenate. The silicate shell of arsenic-loaded RM created at an alkaline condition acts as an arsenic stabilizer, resulting in a leached arsenic concentration of 1.2 mg/L in TCLP tests. RM acts as a highly effective arsenic remover and stabilizer for the disposal of high-arsenic wastewater. It shows great potential for the remediation of wastewater containing heavy metals with varying concentrations to produce clean water available for industrial purpose.

Salinity stress affects aquatic microalgal growth and their physiological responses have been studied extensively. However, arsenic (As) accumulation and biotransformation by freshwater phytoplankton under a salinity gradient have never been addressed. This study reports a distinctive pattern of As uptake, accumulation, and biotransformation by four axenic freshwater phytoplankton species, i.e., Scenedesmus acutus, Closterium aciculare, Staurastrum paradoxum, and Pediastrum duplex. Phytoplankton cells were incubated in sterilised C medium modified with varying salinity levels (0–5‰) in association with arsenate and phosphate concentrations. The biotransformation of arsenate (i.e., As(V)) to arsenite (As(III)) and to further methylated species decreased with increasing salinity in the culture medium whereas As accumulation increased. Among the four strains, only S. acutus and S. paradoxum converted As(V) to As(III), with no detected methylated species. In contrast, C. aciculare and P. duplex biotransformed As(V) to As(III) and further to methyl arsenic species, such as DMAA. S. acutus and S. paradoxum exhibited higher accumulation tendency than the other two species. S. paradoxum showed the lowest As reduction rate (i.e., As(V) to As(III)) compared to other species, although, without significant variations. The morphological changes were observed in phytoplankton cells in response to increased salinity stress. Moreover, As(V) concentrations in the culture medium significantly decreased by day 7–14. Thus, this study presents a conceptual model of the As biotransformation pattern by axenic freshwater phytoplankton.

Nano-silica as an important part of soil is an ideal carrier of passivator material. In this paper, nano-silica was modified by silane coupling agent containing mercapto group and iron (II) salt to afford an organic-inorganic hybrid containing –S-Fe-S functional group (coded as RNS-SFe) on the surface of nano-silica. Results demonstrate that the RNS-SFe nanoparticle has network-like spheroidal shape and a primary particle size is about 18.0 nm. The RNS-SFe hybrid as a potential immobilization agent for heavy metal in soil shows excellent performance for the remediation of the contaminated soil. Specifically, with a dosage of 3.0% (mass ratio) in the soil, it can immobilize bioavailable Pb, Cd, and As by 97.1%, 85.0%, and 80.1%, respectively. Namely, the RNS-SFe hybrid can transform the bioavailable Pb, Cd, and As into insoluble mercapto metal compounds (–S-Pb-S- and –S-Cd-S-) and less soluble iron arsenate (Fe₃(AsO₄)₂, FeAsO₄) precipitate on the surface of nano-silica particle, thereby reducing the toxicity and mobility of the toxic contaminant fractions. In the meantime, the immobilized products of the Pb, Cd and As fractions have good resistance against acid leaching. These results are contributive to the application of RNS-SFe for the remediation of multi-heavy metal-contaminated soils in field.

This study examined arsenite [As(III)], arsenate [As(V)] and fluoride (F⁻) removal potential of bone char produced from sheep (Ovis aries) bone waste. Pyrolysis conditions tested were in the 500 °C–900 °C range, for a holding time of 1 or 2 h, with or without N₂ gas purging. Previous bone char studies mainly focused on either low or high temperature range with limited information provided on As(III) removal. This study aims to address these gaps and provide insights into the effect of pyrolysis conditions on bone char sorption capacity. A range of advanced chemical analyses were employed to track the change in bone char properties. As pyrolysis temperature and holding time increased, the resulting pH, surface charge, surface roughness, crystallinity, pore size and CEC all increased, accompanied by a decrease in the acidic functional groups and surface area. Pyrolysis temperature was a key parameter, showing improvement in the removal of both As(III) and As(V) as pyrolysis temperature was increased, while As(V) removal was higher than As(III) removal overall. F⁻ removal displayed an inverse relationship with increasing pyrolysis temperature. Bone char prepared at 500 °C released significantly more dissolved organic carbon (DOC) then those prepared at a higher temperature. The bone protein is believed to be a major factor. The predominant removal mechanisms for As were surface complexation, precipitation and interaction with nitrogenous functional groups. Whereas F⁻ removal was mainly influenced by interaction with oxygen functional groups and electrostatic interaction. This study recommends that the bone char pyrolysis temperature used for As and F⁻ removal are 900 °C and 650 °C, respectively.

Ubiquitous contamination of microplastics and arsenic in soil ecosystems can induce many health issues to nontarget soil organisms, and will also cause many potential threats to the gut bacterial communities of soil fauna. However, the changes in the gut bacterial communities of soil fauna after exposure to both microplastics and arsenic remain unknown. In this study, the toxicity and effects on the gut microbiota of earthworm Metaphire californica caused by the combined exposure of microplastics and arsenic were examined by using arsenic species analysis and high throughput sequencing of gut microbiota. Results showed that total arsenic and arsenic species in the earthworm gut and body tissues after exposure to combination of microplastics with arsenate (As(V)) were significantly different from that treated with As(V) alone. Microplastics lessened the accumulation of total arsenic and the transformation rate of As(V) to arsenite (As(III)). Microplastics alleviated the effect of arsenic on the gut microbiota possibly via adsorbing/binding As(V) and lowering arsenic bioavailability, thus prevented the reduction of As(V) and accumulation of total arsenic in the gut which resulted in a lower toxicity on the earthworm. The study broadens our understanding of the ecotoxicity of microplastics with other pollutants on the soil animals and on their gut microbiota.

Arsenic (As) is a metalloid element that is ubiquitous in the marine environment and its contamination has received worldwide attention due to its potential toxicity. Arsenic can induce multiple adverse effects, such as lipid metabolism disorder, immune system dysfunction, oxidative stress and carcinogenesis, in animals. Inorganic arsenic includes two chemical forms, arsenite (As (III)) and arsenate (As (V)), in natural environment. As (V) is the dominant form in natural waters. In the present study, metabolomic and proteomic alterations were investigated in juvenile rockfish Sebastes schlegelii exposed to environmentally relevant concentrations of As (V) for 14 d. The analysis of iTRAQ-based proteomics combined with untargeted NMR-based metabolomics indicated apparent toxicological effects induced by As (V) in juvenile rockfish. In details, the metabolites, including lactate, alanine, ATP, inosine and phosphocholine were significantly altered in As-treated groups. Proteomic responses suggested that As (V) could not only affected energy and primary metabolisms and signal transduction, but also influenced cytoskeleton structure in juvenile rockfish. This work suggested that the combined proteomic and metabolomic approach could shed light on the toxicological effects of pollutants in rockfish S. schlegelii.

The effects of arsenic (As), cadmium (Cd) and zinc (Zn) on each other's uptake and oxidative stress in As-hyperaccumulator Pteris vittata were investigated. P. vittata plants were exposed to 50 μM As, Cd and/or Zn for 15 d in 0.2-strength Hoagland solution. When applied alone, P. vittata accumulated 185 mg kg⁻¹ As, 164 mg kg⁻¹ Cd and 327 mg kg⁻¹ Zn in the fronds. While Cd and Zn did not impact each other's uptake, As affected Cd and Zn uptake. Whereas As decreased Zn uptake, Zn affected As speciation in P. vittata fronds, with more arsenate (AsV) than arsenite (AsIII) being present. At 50 μM As, 75 μM Zn increased As accumulation in P. vittata fronds by 10 folds to 2363 mg kg⁻¹ compared to 50 μM Zn. Although AsV was the predominant As species in all tissues, Cd enhanced AsIII levels in the fronds but increased AsV in the roots. Co-exposure of Cd + Zn elevated oxidative stress basing on thiobarbituric acid reactive substances, H₂O₂ content, Evans blue dye uptake, membrane injury index and reactive oxygen species (ROS) relative to single metal. By lowering Cd and Zn concentrations in P. vittata fronds, As reduced the associated stress comparative to Cd or Zn treatment. The results enhance our understanding of the mechanisms underlying the interactions between As, Cd and Zn in As-hyperaccumulator P. vittata.

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) is an arsenic-containing compound widely used as a feed additive in poultry industries. ROX excreted in chicken manure can be transformed by microbes to different arsenic species in the environment. To date, most of the studies on microbial transformation of ROX have focused on anaerobic microorganisms. Here, we isolated a pure cultured aerobic ROX-transforming bacterial strain, CZ-1, from an arsenic-contaminated paddy soil. On the basis of 16S rRNA gene sequence, strain CZ-1 was classified as a member of the genus Enterobacter. During ROX biotransformation by strain CZ-1, five metabolites including arsenate (As[V]), arsenite (As[III]), N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA) and a novel sulfur-containing arsenic species (AsC₉H₁₃N₂O₆S) were detected and identified based on high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), HPLC-ICP-MS/electrospray ionization mass spectrometry (ESI-MS) and HPLC-electrospray ionization hybrid quadrupole time-of-flight mass spectrometry (ESI-qTOF-MS) analyses. N-AHPAA and 3-AHPAA were the main products, and 3-AHPAA could also be transformed to N-AHPAA. Based on the results, we propose a novel ROX biotransformation pathway by Enterobacter. sp CZ-1, in which the nitro group of ROX is first reduced to amino group (3-AHPAA) and then acetylated to N-AHPAA.

Inhibition of reductive transformation of arsenic (As) in flooded paddy soils is of fundamental importance for mitigating As transfer into food chain. Anaerobic arsenite (As(III)) oxidizers maintain As in less mobile fraction under nitrate-reducing conditions. In this study, we explored the dynamic profile of As speciation in porewater and As distribution among the pools of differential bioavailability in soil solid phase with and without nitrate treatment. In parallel, the abundance and diversity of As(III) oxidase gene (aioA) in flooded paddy soil with nitrate amendment was examined by quantitative PCR and aioA gene clone library. Furthermore, the impact of nitrate on As accumulation and speciation in rice seedlings was unraveled. With nitrate addition (25 mmol NO₃⁻ kg⁻¹ soil), porewater As(III) was maintained at a consistently negligible concentration in the flooded paddy soil and the reductive dissolution of As-bearing Fe oxides/hydroxides was significantly restrained. Specifically, nitrate amendment kept 81% of total soil As in the nonlabile fraction with arsenate (As(V)) dominating after 30 days of flooding, compared to only 61% in the unamended control. Nitrate treatment induced 4-fold higher abundance of aioA gene, which belonged to domains of bacteria and archaea under the classes α-Proteobacteria (6%), ß-Proteobacteria (90%), ɣ-Proteobacteria (2%), and Thermoprotei (2%). By nitrate addition, As accumulation in rice seedlings was decreased by 85% with simultaneously elevated As(V) ratio in rice plant relative to control after 22 days of growth under flooded conditions. These results highlight that nitrate application can serve an efficient method to inhibit reductive dissolution of As in flooded paddy soils, and hence diminish As uptake by rice under anaerobic growing conditions.