Little information is available on the effects of nano-α-Fe2O3 on arsenic (As) metabolism of algae and potential associated carbon (C) storage in As-contaminated water with dissolved organic phosphorus (DOP) as a phosphorus (P) source. In this study, Microcystis aeruginosa (M. aeruginosa) was used to investigate impacts of nano-α-Fe2O3 on cell growth and As metabolism of algae under a phytate (PA) environment as well as potential associated C storage. Results showed that nano-α-Fe2O3 had a subtle influence on algal cell growth in a PA environment. Herein, algal cell density (OD680) and chlorophyll a (Chla) were inhibited at elevated nano-α-Fe2O3 levels, which simultaneously limited the decrease of Yield. As suggested, the complexation of PA with nano-α-Fe2O3 could alleviate the negative influence on algal cell growth. Furthermore, the elevated nano-α-Fe2O3 increased As methylation in the PA environment due to higher monomethylarsenic (MMA) and dimethylarsenic (DMA) concentrations in the test media. Additionally, microcystins (MCs) in the media changed consistently with UV254, both of which were relatively lower at 10.0 mg·L-1 nano-α-Fe2O3. Enhanced As(V) methylation of algal cells was found to simultaneously reduce the release risk of As(III) and MC while increasing dissolved organic carbon (DOC) content in media, suggesting unfavorable C storage. Three-dimensional fluorescence analysis revealed that the main DOC constituent was the tryptophan-like component in aromatic proteins. Correlation analysis showed that decreases in pH and the zeta potential and an increase in Chla may lead to metabolic As improvements in M. aeruginosa. The obtained findings highlight the need for greater focus on the potential risks of DOP combined with nano-α-Fe2O3 on algal blooms as well as the biogeochemical cycling processes of As and C storage in As-contaminated water with DOP as the P source.

Rice is an important food crop that is susceptible to arsenic (As) contamination under paddy soil conditions depending on As uptake characteristics of the rice genotypes. Here we unveiled the significance of eighteen (fine and coarse) rice genotypes against As accumulation/tolerance, morphological and physiological response, and antioxidant enzymes-enabled defense pathways. Arsenic significantly affected rice plant morphological and physiological attributes, with relatively more impacts on fine compared to coarse genotypes. Grain, shoot, and root As uptake were lower in fine genotypes (0.002, 0.020, and 0.032 mg pot^-1 DW, respectively) than that of coarse (0.031, 0.60, and 1.2 mg pot^-1 DW, respectively). Various biochemical (pigment contents, hydrogen peroxide, lipid peroxidation) and defense (antioxidant enzymes) plant parameters indicated that the fine genotypes, notably Kainat and Basmati-385, possessed the highest As tolerance. Arsenic-induced risk indices exhibited greater hazard quotient (up to 1.47) and carcinogenic risk (up to 0.0066) for coarse genotypes compared to the fine ones, with the greatest risk for KSK-282. This study elaborates the pivotal role of genotypic variation among rice plants in As accumulation, which is crucial for mitigating the associated human health risk. Further research is required on molecular aspects, e.g., genetic sequencing, to examine rice genotypes variation in defense mechanisms to As contamination.

Continuous flooding has been widely used in paddy field to decrease the accumulation of heavy metal(loid)s by rice due to their decreased solubility and bioavailability of most heavy metal(loid)s under water flooding condition. A field experiment with six drainage treatments during grain-filling stage was performed to investigate the influence of different water flooding conditions on availability of cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As), and mercury (Hg) and their accumulation by rice in alkaline paddy soil. The results showed at the end of experiment, the availability of Cd and Pb in soil with continuous flooding for above 25 days after full heading significantly decreased compared with draining immediately after full heading of rice. But some increase of the As availability in soil with different water regimes was observed at 15 days after beginning of experiment where the As availability was below its detection limit. Meanwhile, the concentrations of Cd and Cr both in rice grains and straws were decreased evidently with prolonged flooding at rice filling stage. The concentrations of Pb and Hg in grain were all below the detection limit, but increased in straw with draining 15 days later compared with draining immediately after full heading of rice. However, water regimes during grain-filling stage had little effect on As uptake by rice in alkaline paddy soil. Moreover, this study also discovered that organic matter may played a critical role in controlling availability of heavy metal(loid)s in alkaline soil. This work demonstrated that at alkaline paddy soil, maintaining water flooding until 5 days before harvest in rice grain-filling stage was an effective method to improve rice safety without decreasing yields in paddy field polluted with Cd, Cr, and As, but careful consideration is required for Pb and Hg.