Effects and Mechanisms of Copper Oxide Nanoparticles with Regard to Arsenic Availability in Soil–Rice Systems: Adsorption Behavior and Microbial Response

Abstract

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.

Mobilization of Colloid- and Nanoparticle-Bound Arsenic in Contaminated Paddy Soils during Reduction and Reoxidation

“…This association is noteworthy because colloid- and nanoparticle-bound As are expected to be highly mobile and quite stable over significant distances, ,, enhancing its movement from As-contaminated paddy soils to an adjacent aquifer and surface water. , In addition to the As transport, the association of As with colloid- and nanoparticle OM–Fe may impact arsenic bioavailability in soil–rice systems by bypassing adsorption on immobile solids, , such as iron plaques that are dominated by Fe (oxyhydr)­oxides . Previous studies have demonstrated that the introduction of engineered nanoparticles to rice paddy soils altered As bioavailability and its accumulation in rice . However, the role of those naturally occurring Fe–OM–As colloids and nanoparticles in rice As uptake, translocation, and accumulation remains unknown.…”

“…64 Previous studies have demonstrated that the introduction of engineered nanoparticles to rice paddy soils altered As bioavailability and its accumulation in rice. 31 However, the role of those naturally occurring Fe−OM−As colloids and nanoparticles in rice As uptake, translocation, and accumulation remains unknown. Soil drainage, which is typically performed toward the end of tillering to control excessive rice tillering and 1−2 weeks before harvest, will cause rapid coagulation of As-bearing colloids and a decrease of total As.…”

“…They often occur as Fe (oxy)­hydroxide or/and Fe-containing clay minerals , and strongly associate with soil organic matter (OM) . Arsenite and arsenate, which are two dominant As species in paddy soil porewaters, have strong affiliation with Fe-rich colloids and nanoparticles as suggested by previous studies in artificial systems. − The binding of As to OM via Fe-bridging and association with colloidal Fe-(oxy)­hydroxides are well-accepted to underpin the formation of Fe-OM-As colloids. − These associations can enhance As mobility in soil environments by bypassing adsorption on immobile solids, , thereby it may increase arsenic availability in soil–rice systems and facilitate its long-distance transport to the adjacent aquifer and surface water. ,, However, current As characterization in paddy soil porewaters mainly focuses on the chemical speciation that passes through 0.45 or 0.22 μm membrane filters, which fails to distinguish particle-bound As from truly dissolved species. Although limited, several studies have reported linkages between Fe and As in porewater colloids in flooded paddy fields using filter membranes with a variety of molecular weight cutoffs, the so-called sequential ultrafiltration. , Yet, this method suffers from artifacts due to coagulation and a low size resolution of the obtained fractions, impeding an in-depth characterization of colloids and nanoparticles .…”

“…25−29 The binding of As to OM via Fe-bridging and association with colloidal of Fe-OM-As colloids. 25−29 These associations can enhance As mobility in soil environments by bypassing adsorption on immobile solids, 6,30 thereby it may increase arsenic availability in soil−rice systems 31 and facilitate its long-distance transport to the adjacent aquifer and surface water. 6,32,33 However, current As characterization in paddy soil porewaters mainly focuses on the chemical speciation that passes through 0.45 or 0.22 μm membrane filters, which fails to distinguish particlebound As from truly dissolved species.…”

Microbial community composition in the rhizosphere of Pteris vittata and its effects on arsenic phytoremediation under a natural arsenic contamination gradient

“…Microorganisms are mainly involved in arsenic metabolism and biological transformation in soil through their functional genes related to arsenic cycling ( Abou-Shanab et al, 2022 ). The arsenic metabolism mediated by microbial functional genes, including arsenic redox ( aoxR , arxA , aioAB , and arsJ ), reduction ( arsC , gstB , and arrAB ), methylation and demethylation ( arsI and arsM ), and efflux ( arsP , arsK , and arsB ), is a determinant of arsenic bioavailability in soil and an important step of global arsenic geochemical cycling ( Zhu et al, 2017 ; Chen et al, 2020 ) that has been extensively reviewed ( Zhu et al, 2017 ; Wu et al, 2022a ). To explore these key functional genes, Zhao et al (2018) developed a high-throughput qPCR chip (AsChip) containing 81 primer sets targeting 19 arsenic-related genes, aiming to comprehensively detect those genes linked to the microbial cycling of arsenic.…”