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Excess chromium (Cr) and arsenic (As) coexist in soil such as chromated copper arsenate (CCA) contaminated sites, leading to high risks of pollution. Fe-biochar with adjustable redox activity offers the possibility of simultaneous stabilization of Cr and As. Here, a series of Fe-biochar with distinct Fe/C structure were rationally produced for the remediation of Cr and As contaminated soil (BCX-Fe, X represented the biomass/Fe ratio). Adsorption tests showed that maximal adsorption of BC5-Fe for Cr(VI) and As(III) reached 73.7 and 81.3 mg/g. A 90-day soil remediation experiment indicated that the introduction of 3% (w/w) Fe-biochar reduced the leaching state of Cr(VI) by 93.8-99.7% and As by 75.2-95.6%. Under simulated groundwater erosion for 10 years and acid rain leaching for 7.5 years, the release levels of Cr(VI) and As in the BC5-Fe remediated soil could meet the groundwater class IV standard in China (Cr(VI)<0.1 mg/L, As<0.05 mg/L). Accelerated aging tests demonstrated that BC5-Fe had long-term Cr and As stabilization ability. The quenching experiment, EPR, and XPS suggested that the corrosion products of Fe dominated the adsorption and redox reactions, while the O groups acted as electron transfer stations and constituted redox microcirculation in the synchronous uptake of Cr/As. Based on these insights, we believe that our study will provide meaningful information about the application potential of Fe-biochar for the heavy metal contaminated soil remediation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Copper oxide nanoparticles (CuO NPs) are widely used as fungicides in agriculture. Arsenic (As) is a ubiquitous contaminant in paddy soil. The present study was focused on the adsorption behavior of CuO NPs with regard to As as well as the characteristics of the microbial community changes in As-contaminated soil-rice systems in response to CuO NPs. The study found that CuO NPs could be a temporary sink of As in soil; a high dose of CuO NPs promoted the release of As from crystalline iron oxide, which increased the As content in the liquid phase. The study also found that the As bioavailability changed significantly when the dose of CuO NPs was higher than 50 mg kg -1 in the soil-rice system. The addition of 100 mg kg -1 CuO NPs increased the microbial diversity and the abundance of genes involved in As cycling, decreased the abundance of Fe(III)-reducing bacteria and sulfate-reducing genes, and decreased As accumulation in grains. Treatment with 500 mg kg -1 CuO NPs increased the abundance of Fe(III)-reducing bacteria and sulfate-reducing genes, decreased Fe plaques, and increased As accumulation in rice. The adverse effects of CuO NPs on crops and associated risks need to be considered carefully.

Lead (Pb) and arsenic (As) exist in soil with different ionic forms, and it is difficult to immobilize simultaneously Pb and As in soil. The objective of this study is to determine the effects of water management including flooding (FL), alternate wetting and drying (AWD) and dry farming (DF) combined with addition of phosphate (P) on the accumulation of Pb and As in rice. Our results showed that Pb accumulated in root during vegetative stage, and most of As in root was transported to the above ground parts during the reproductive stage. Pb was evenly distributed in grains, and As was mostly accumulated in bran and aleurone layer. Water management had a reverse effect on the accumulation of Pb and As in rice. However, the effects of P on arid soil environment and Pb, As accumulation in rice were stronger than that in flooded soil. Application of P under AWD treatment could maintain a similar quantity of Fe plaque with flooding, decrease the availability of Pb in rhizosphere soil, reduce Pb and As accumulation in root, and result in the reduction of Pb and As accumulation in grains by 86% and 66% respectively. Besides, our study also found that flooding or AWD during vegetative stage facilitated the formation of iron plaque. In conclusion, AWD combined with P application could maintain a relatively lower concentrations of Pb and As in grains., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Copper oxide nanoparticles (CuO NPs) are widely used as a fungicide in agriculture. The application of CuO NPs in agriculture affects the growth of rice and metal accumulation in rice. However, the mechanism of CuO NPs on arsenic (As) accumulation in rice remains unclear. In this study, a hydroponic culture was produced to investigate the mechanism of the effect of 50 and 100 mg L−1 CuO NPs on As accumulation in rice. Our results showed that CuO NPs decreased As(III/V) accumulation in the roots and shoots by adsorbing As(III/V), oxidizing of As(III) on the surface, and thickening the root cell wall. The addition of CuO NPs regulated the expression of the OsNIP1;1, OsHAC1;1, and OsHAC4 genes, which decreased As(III) transport and promoted As(V) reduction in the roots. Moreover, when CuO NPs were co-exposed to As, a negative correlation between the concentration of Cu and As in rice was also found in our study. However, CuO NPs significantly increased Cu accumulation in rice and constrained the rice growth. In conclusion, CuO NPs might be a promising way to decrease As accumulation in rice, but the negative effects such as growth inhibition should be further considered. Therefore, the application of CuO NPs in rice plants should take a more restrained approach. [ABSTRACT FROM AUTHOR]