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Microorganisms dominated speciation of arsenic (As) play an important role in the biogeochemical cycling of As. In the study, species transformation of arsenite [As(III)] and As(III) influx and efflux across the cell membranes of Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 cells were studied using a cellular lysis plus chromatographic separation method and further the in-situ X-ray absorption near edge structure (XANES) analysis. The results indicated that As(III) can enter into fungal cells and that a portion of the As(III) can be exuded out of cells. For both As sequestrated into fungal cytoplasm and As adsorbtion onto cell walls, As(III) was found to be the dominated form of As. XANES analysis showed that As(III) accounted for 58.4%, 59.5%, and 73.0% of the total As in the cells of T . asperellum SM-12F1, P . janthinellum SM-12F4, and F . oxysporum CZ-8F1, respectively. Among these fungal strains, however, there were obvious differences in the relative proportions of arsenate [As(V)], monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). For T . asperellum SM-12F1, the proportion (%) of MMA was 31.1%, and no As(V) or DMA was detected. For F . oxysporum CZ-8F1, the proportions of As(V) and MMA were 15.8% and 8.8%, respectively, but no DMA was observed. As(V), MMA, and DMA accounted for 4.2%, 29.5%, and 8.1%, respectively, of the P . janthinellum SM-12F4 cells. Some of the intracellular As(III) can be oxidated and methylated by these fungal strains and yield As(V), MMA, and DMA as products. [ABSTRACT FROM AUTHOR]

Abstract: Bioremediation of arsenic (As)-contaminated soil using microorganisms has been a focus of research because it is environment friendly and cost-effective. The As-resistant fungi Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 were exposed to 50mgl−1 of As(V), and the biotransformation of As and the concomitant variance of Eh and pH in the media were studied. Fresh weights of all three isolates increased and then decreased depended on cultivation period. After cultivation for 2 or 3days, the As(V) added to the media had been completely changed into As(III), whilst As(V) was predominate in fungal cells with concomitantly little As(III) during cultivation. After 15days, little monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) besides of As(V) and As(III) were found in the cells of T. asperellum SM-12F1, and the total As content was the highest in cells of P. janthinellum SM-12F4 (about 41.5μg) according to the quantitative analysis of As speciation in cultures. Moreover, when cultivation period reached 3days, the Eh and pH in the media of T. asperellum SM-12F1 (312.5mV and 4.8), P. janthinellum SM-12F4 (411.1mV and 4.2), and F. oxysporum CZ-8F1 (269.4mV and 4.8) might not responsible for the reduction of As(V) based on the previous study. Therefore, it is speculated that import/export, reduction, and methylation of As are conducted in fungal cells. Future studies investigating the biochemical behaviour of fungi responding to As are needed to gain a better understanding of bioremediation of As-contaminated soils. [Copyright &y& Elsevier]

Although specific soil properties controlling the arsenic (As) aging process have been studied extensively, few investigations have attempted to determine how soil types influence As bioavailability and fractionations in soils. Nine types of soil were selected from typical grain producing areas in China, and the bioavailability and fractionations of As during aging were measured. Results showed that available As in all soils rapidly decreased in the first 30 days and slowly declined thereafter. In spiked soils, As easily became less available and less toxic in low pH soils compared to high pH soils, demonstrating the importance of soil pH on As availability. Results from fitting kinetic equations revealed that the pseudo-second-order model described the As aging processes well in all soils ( R 2 = 0.945–0.999, P < 0.01, SE = 0.09–4.25), implying that the mechanism for As aging combined adsorption, external diffusion, and internal diffusion. Fe oxides were more important than Al oxides for determining the As aging rate (| k |). Based on these results, we are the first to propose the approximate aging equilibrium time ( T ) for As, which was mainly influenced by soil clay content. The shortest time for approximate stabilization of As aging was 28 d in latosol soils (LS), while the longest approximate equilibrium time was 169 d in cinnamon soils (CS). Individual soil properties controlling the variation in different As fractionations further confirmed that the influences of soil types on As aging were the result of the combined effects of soil properties and a time-consuming redistribution process. [ABSTRACT FROM AUTHOR]

The simultaneous mitigation of toxic arsenic (As) and cadmium (Cd) in rice grain remains a global challenge. The over-accumulation of husk dimethylarsinic acid (DMAs) induces the rice straight-head disease, which threatens rice production worldwide. In this study, we investigated various soil ridge height treatments with Eh ranging from − 225–87 mV and pH ranging from 6.3 to 4.1. Soil ridge cultivation can maintain grain As and Cd at low levels for slightly co-contaminated paddy soils, especially when the ridge height is 11 cm (Eh of 43 mV and pH of 4.6), where grain inorganic As decreased—at maximum—by 48% and DMAs by 55%. Grain Cd (0.14 mg kg−1) increased but was still below the limit (0.2 mg kg−1) in China, and the cost of ridging is acceptable. There were definite correlations among porewater As, Cd, Fe, S, and Mn contents across various Eh and pH values. Soil ridge cultivation significantly (P < 0.05) diminished the copy number of As-reducing (harboring arsC and arrA), As-methylating (harboring arsM), and sulfate-reducing (harboring dsrA) bacteria. Moreover, soil ridge cultivation shifted the arsM -harboring microbiota. In response to ridge height increase, the abundance of the bacterial biomarker phylum Euryachaeota declined and the families Halorubrum and Planctomyces were gradually replaced by Sandaracinus in paddy soil. [Display omitted] • Soil ridge cultivation as an old agronomic measure practiced 2000 years ago. • Soil Eh and pH varying in a large range was set up by various ridge heights. • 11 cm ridge height helps to simultaneously control grain As and Cd at a low level. • Soil ridge cultivation reduced grain DMAs by inhibiting soil As methylation. • The abundance and composition of arsM -harboring microbiota shifted after ridging. [ABSTRACT FROM AUTHOR]

Agricultural planning via substitution with crops of low arsenic (As) accumulation can efficiently reduce the dietary exposure from As to human health through food chain. In this study, in total 157 crop cultivars, including rice, vegetable and maize, were used and their risk of As accumulation in edible parts was studied via pot and field experiments. When soil As level was 56.7 mg kg−1, equivalent to a level of slight contamination, inorganic As (iAs) in rice grain ranged from 0.44 to 0.61 mg kg−1 Fresh weight (FW), which was 2.2–3.0 times higher than its limit in China (0.2 mg kg−1). When soil As enhanced to 156.2 mg kg−1 (moderate contamination), mater convolvulus and crown daisy had the over-limit risk of As accumulation in their edible parts. Green tender, pakchoi cabbage, rape and amaranth emerged with the over-limit risk of As, when soil As reached 238.3 mg kg−1 (severe contamination). Comparatively, maize and tuber or fruit vegetables had the lower levels of As in their edible parts and sweet potato, peanut, pepper and potato had less variation of As accumulation among cultivars of the same crop. A recommended list was provided for preferable food crops under different contamination level of As in soils. Switching paddy soil into upland soils and planting in priority with tuber or fruit vegetables and maize are encouraged. Agricultural planning resulted in significant decreases for the target hazard quotient (THQ) and target cancer risk (TCR) of iAs via dietary exposure to the residents near the realgar mine in Shimen County of China. [Display omitted] • 7-year field experiments were conducted by employing 157 cultivars or varieties of food crops. • Arsenic accumulation in food crops under different degree of soil contamination was investigated. • Food crops in priority with tuber or fruit vegetables and maize was strongly suggested. • Agricultural planning resulted in significant decrease in human dietary exposure to As. [ABSTRACT FROM AUTHOR]

Soil management and cultivar selection are two strategies to reduce the accumulation risk of heavy metals in crops. However, it is still an open question which of these two strategies is more efficient for the safe utilization of contaminated soil. In this study, the available bio-concentration factors (aBCF) of arsenic (As) and cadmium (Cd) among 39 maize cultivars were determined through a field experiment. The effect of soil management was mimicked by choosing diverse sampling sites having different soil available contents of As and Cd. The aBCF of As and Cd in grain ranged from 0.02 to 0.13 and 1.17 to 42.2, respectively. The accumulation ability of As and Cd was classified among different maize cultivars. Soil pH and total As controlled the level of available As in soils, while soil pH dominated available Cd in soil. A soil pH of 6.5 was recommended to simultaneously minimize soil available As and Cd by managing soil conditions. The quantitative effects of cultivar and soil management on grain As and Cd were expressed as Q [Grain As] = 0.746 Q [Cultivar]-0.126 Q [pH]+0.276 Q [As available ] (R2 = 0.648, P = 1.00 × 10−37) and Q [Grain Cd] = 0.913 Q [Cultivar]-0.192 Q [pH]+0.071 Q [SOC] (R2 = 0.782, P = 1.00 × 10−37), respectively. Cultivar selection contributed stronger than soil management to decrease the As and Cd levels in maize grains. A feasible method to seek for a more efficient strategy was proposed for the safe utilization of contaminated soil. [Display omitted] • 39 maize cultivars used to reflect the effects of cultivar on As/Cd accumulation. • Difference in soil available As/Cd well mimicked the effect of soil management. • Maize cultivars were classified based on their accumulation abilities of As/Cd. • Maize cultivar contributes stronger than soil management in this case study. • A method seeking for a more efficient strategy for safe utilization of contaminated soil was proposed. [ABSTRACT FROM AUTHOR]