Migration, transformation of arsenic, and pollution controlling strategies in paddy soil-rice system: A comprehensive review

Selenium-carrageenan modulates arsenic bioaccessibility in simulated gastrointestinal bio-fluids: Dual mechanisms of gastric promotion and intestinal inhibition

Inorganic arsenic (As) exposure via oral ingestion poses significant carcinogenic risks, with bioaccessibility in the gastrointestinal tract critical for risk assessment. Selenium (Se), an essential micronutrient, exhibits paradoxical effects on As toxicity, yet its mechanistic role in modulating As bioavailability during digestion remains poorly understood. This study investigates the dual-phase impact of selenated carrageenan (Se-car), a cost-effective organic Se supplement, on As bioaccessibility using an in vitro simulated digestion model. Results show that Se-car (50 g/L) enhances total As, As(III), and As(V) bioaccessibility by 22.28 %, 20.00 %, and 22.53 % during gastric digestion (pH 1.5, 1 h), driven by competitive adsorption of Se-car's anionic groups on hematite surfaces, proton dissociation, and pepsin-mediated reductive dissolution. Conversely, in intestinal digestion (pH 6.5, 8 h), Se-car suppresses total As, As(III), and As(V) bioaccessibility release by 8.51 %, 9.08 %, and 4.71 % through molecular entanglement, enzyme encapsulation, and reduced Fe(II) solubility. Elevated NaCl concentrations (0.01-1 M) synergistically inhibit As release by 7.28 % (gastric) and 2.47 % (intestinal), attributable to ionic shielding-induced Se-car chain contraction. Mechanistic insights indicate gastricization relies on acidic dissolution and Se-car-pepsin interactions, while intestinal inhibition stems from Se-car-trypsin binding and surface passivation. Health risk assessments demonstrate Se-car exacerbates gastric-phase THQ values of As (children: 5.20 → 16.97) but mitigates intestinal-phase risks (children: 9.14 → 3.99). This work elucidates pH- and ionic strength-dependent Se-car behaviors, offering novel insights for optimizing dietary Se interventions in As-endemic regions. The dual-phase regulatory mechanism highlights the importance of digestive-phase-specific risk management and provides a foundation for developing polysaccharide-based As antagonists targeting complex gastrointestinal environments.

Biooxidation of Arsenopyrite by Acidithiobacillus ferriphilus QBS 3 Exhibits Arsenic Resistance Under Extremely Acidic Bioleaching Conditions

As arsenopyrite is a typical arsenic-bearing sulfide ore, the biooxidation process of arsenopyrite is of great significance for the extraction of gold from arsenic-bearing gold ores and the generation of arsenic-bearing acid mine drainage. During the biooxidation of arsenopyrite, a large amount of arsenic is produced, which inhibits the growth and metabolism of microorganisms and thus affects the extraction of gold from arsenic-bearing gold ores. Therefore, the screening and enrichment of microorganisms with high arsenic resistance have become important aspects in the study of arsenopyrite biooxidation. As described in this paper, through arsenic acclimation, the maximum arsenic tolerance concentration of Acidithiobacillus ferriphilus QBS 3 isolated from arsenic-containing acid mine drainage was increased to 80 mM As(Ⅲ) and 100 mM As(V). Microorganisms with high arsenic resistance showed better bioleaching performance for arsenopyrite. After 18 days of bioleaching, the leaching rate of arsenopyrite reached 100% at a pulp concentration of 0.5%, and after 30 days of bioleaching, the leaching rate of arsenopyrite was 79.96% at a pulp concentration of 1%. Currently, research on arsenopyrite mainly focuses on the control and optimization of environmental conditions, but there have been few studies on the biooxidation process of arsenopyrite at the protein and gene levels. Therefore, combining the results of a one-month bioleaching experiment on arsenopyrite by A. ferriphilus QBS 3 and the analysis of arsenic resistance genes, a bioleaching model of arsenopyrite was constructed, which laid an experimental basis and theoretical foundation for improving the gold recovery rate from refractory arsenic-bearing ores and exploring the arsenic resistance mechanism of microorganisms during the arsenopyrite leaching process.

Rainwater-Derived Reactive Oxygen Species Diminish Environmental Risk from Arsenic in Paddy Rice Systems

It has been previously observed that rainwater input into paddy rice soils reduced the level of grain-borne arsenic, and it is hypothesized that a Fenton-like reaction triggered by interaction between rainwater-borne hydrogen peroxide and ferrous iron in paddy soils is responsible for microbially mediated impediment of As uptake by rice plants. However, this hypothesis remains untested. This study tested the hypothesis through mesocosm experiments, confirming that rainwater-borne hydrogen peroxide triggered hydroxyl radical (•OH) generation, elevating soil redox potential, and oxidizing arsenite to less phytoavailable arsenate in soil porewater, thereby reducing As uptake by rice and As accumulation in rice grain. Comparison between two crops of rice cultivation with different fluxes of rainwater-borne hydrogen peroxide confirms that seasonal rainfall variation has an impact on accumulation of rice grain-borne arsenic, with paddy soil receiving more rainfall having a lower arsenic concentration in the rice grain compared to that receiving less rainfall. Using China's major rice-producing region as an example, it is demonstrated that spatial variation in rainfall regime could impact the geographical distribution of rice grain-borne As at a national scale. The findings have implications for the assessment and management of the environmental risk from arsenic-contaminated rice grains.

Mitigating arsenic accumulation in rice plant in paddy soil: influence of persulphate and ferrous application

Rice cultivation under flooded conditions usually leads to a high accumulation of arsenic (As) in grains. Sulphur and iron played vital roles in affecting the bioavailability of As in the soil-rice system. Herein, using pot experiments, we investigated the effects of persulphate (PS) and ferrous (Fe2+) on the transfer and accumulation of As in the soil-rice system under flooded conditions. The concentration of As and Fe in soil porewater declined with continuous flooding. Persulphate/ferrous addition significantly inhibited the formation of iron plaque and the transfer of As to the aboveground tissues of rice. The total As, dimethylarsinicacid (DMA), As (III), and As (V) in grains significantly decreased by 49∼75%, 60∼89%, 20∼24%, and 35∼36%, respectively, by persulphate/ferrous application. Furthermore, a decrease of As in husk, leaf, and, stem was also found in persulphate and ferrous treatment. To some degree, the Fe2+ can facilitate the decreased efficiency of As accumulation and translocation in rice tissue. The present study's results demonstrated that applying persulphate/Fe2+ could effectively alleviate the excessive accumulation of As in rice grains in the soil-rice system under flooding conditions.

Recent Advances in Transcriptome Analysis Within the Realm of Low Arsenic Rice Breeding

Arsenic (As), a toxic element, is widely distributed in soil and irrigation water. Rice (Oryza sativa L.), the staple food in Southern China, exhibits a greater propensity for As uptake compared to other crops. Arsenic pollution in paddy fields not only impairs rice growth but also poses a serious threat to food security and human health. Nevertheless, the molecular mechanism underlying the response to As toxicity has not been completely revealed until now. Transcriptome analysis represents a powerful tool for revealing the mechanisms conferring phenotype formation and is widely employed in crop breeding. Consequently, this review focuses on the recent advances in transcriptome analysis within the realm of low As breeding in rice. It particularly highlights the applications of transcriptome analysis in identifying genes responsive to As toxicity, revealing gene interaction regulatory modules and analyzing secondary metabolite biosynthesis pathways. Furthermore, the molecular mechanisms underlying rice As tolerance are updated, and the recent outcomes in low As breeding are summarized. Finally, the challenges associated with applying transcriptome analysis to low-As breeding are deliberated upon, and future research directions are envisioned, with the aim of providing references to expedite high-yield and low-arsenic breeding in rice.