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Comparatively few field experiments have been conducted to monitor the long-term effects of Si fertilizer amendments on the mitigation of Cd and As accumulation in rice grains. A 4-year field trial (eight growing seasons) was established in paddy fields to investigate the effects of different Si fertilizers on the mitigation of Cd and As uptake in rice cultivars. Cultivars for the spring and summer growing seasons were chosen based on their local popularity to investigate the effect of Si fertilizers on different cultivars. Average Cd concentrations in spring rice grains (0.020 ± 0.006 mg/kg) were much lower than those in summer rice grains (0.416 ± 0.370 mg/kg) regardless of rice cultivar. Spring rice grains contained slightly higher average As concentrations (0.43 ± 0.07 mg/kg) than summer rice grains (0.30 ± 0.09 mg/kg). Silicon fertilizers, except sodium silicate, significantly decreased grain Cd concentrations. Calcium silicate fertilizer substantially decreased grain Cd, by up to 55.1 ± 17.6%, and to a greater extent than that in response to Si-potash fertilizer, by up to 26.4 ± 7.9%, probably because of competition between Cd and Ca for Ca transport channels. Slow-release Si fertilizer resulted in the greatest decrease in grain Cd concentration (69.0% ± 8.6%). Slow-release fertilizer may provide a longer-term Si source and higher efficiency of use for rice than readily soluble Si. Silicon fertilizers substantially reduced Cd, but not As, concentrations in summer rice grains for a long term (eight growing seasons). Calcium silicate fertilizer reduced grain Cd concentrations more significantly than potassium silicate fertilizer. Calcium silicate fertilizer exhibited higher efficacy of Cd reduction in grains regardless of rice cultivar or growing season. Slow-release Si fertilizer showed superior ability for Cd mitigation than that of soluble Si fertilizers.

Nitrate pollution is an important cause of eutrophication and ecological disruption. Recently, element sulfur-based denitrification (ESDeN) has attracted increasing attention because of its non-carbon source dependence, low sludge yield, and cost-effectiveness. Although the denitrification performance of sulfur autotrophic denitrifying bacteria at different temperatures has been widely studied, there are still many unknown factors about the adaptability and the shaping of microbial community. In this study, we comprehensively understood the shaping of ESDeN microbial communities under different temperature conditions. Results revealed that microbial communities cultivated at temperatures ranging from 10 °C to 35 °C could be classified as high-temperature (35 °C), middle-temperature (30, 25 and 20 °C), and low-temperature (15 and 10 °C) communities. Dissolved oxygen in water was an important factor that, in combination with temperature, shaped microbial community structure. According to network analysis, the composition of keystone taxa was different for the three groups of communities. Some bacteria that did not have sulfur compound oxidation function were identified as the "keystone species". The abundances of carbon, nitrogen, and sulfur metabolism of the three microbial communities were significantly changed, which was reflected in that the high-temperature and middle-temperature communities were dominated by dark oxidation of sulfur compounds and dark sulfide oxidation, while the low-temperature community was dominated by chemoheterotrophy and aerobic chemoheterotrophy. The fact that the number of microorganisms with dark oxidation of sulfur compounds capacity was quite higher than that of microorganisms with dark sulfur oxidation capacity suggested that the sulfur bioavailability at different temperatures, especially low temperature, was the main challenge for the development of efficient ESDeN process. This study provided a biological basis for developing a high-efficiency ESDeN process to cope with temperature changes in different seasons or regions.

The co-contamination with cadmium (Cd) and arsenic (As) in the paddy soil is the most seriously combined pollution of toxic elements in China, and it is rather difficult to decrease bioavailable Cd and As levels in soil because of the opposite ionic forms of bioavailable Cd (cation) and As (anion). This study explored the optimal conditions of Eh and pH in different soils for simultaneous decrease of Cd and As bioavailabilities in the soil-rice system through soil culture and rice pot experiments under water management strategies. The results showed that near neutral soil pH (7.0) were eventually observed under long-term flooding conditions. Under unflooded conditions, soil pH is the dominant factor influencing bioavailabilities of Cd and As, while under flooded conditions, Eh becomes the most important factor. Pot experiments showed that flooding significantly reduced the Cd concentration in rice grains from 54.5% to 95.5%, but concomitantly increased rice As concentration substantially (214%–302%). By evaluating the trade-off value between the bioavailabilities of Cd and As in the soil, the minimal trade-off value was obtained when the soil Eh was −130 mV and the pH was 6.8.

Arsenic (As) is a well-known human carcinogen, and rice consumption is the main way Chinese people are exposed to As. In this study, 14 kinds of paddy soils were collected from the main rice-producing areas in China. The results showed that rice roots and leaves accumulated more As than stems and grains in the following sequence: Asroot > Asleaf > Asstem > Asgrain. The accumulation of As by rice grains mainly depends on the total As and bioavailable As (0.43 mol/L HNO3 extractable As), which explained 32.2% and 22.2% of the variation in the grain As, respectively. In addition, soil pH, organic matter (OM) and clay contents were the major factors affecting grain As, explaining 13.1%, 7.9% and 5.3% of the variation, respectively. An effective prediction model was established via multiple linear regression as Asgrain = 0.024 BAs - 0.225 pH + 0.013 OM + 0.648 EC - 0.320 TN - 0.088 TP - 0.002 AS + 2.157 (R2 = 0.68, P

The relationship of toxic elements (As, Cd, Cr) and trace elements (Cu, Se, Ni, Zn, Mn) in rice bran and corresponding polished rice is not well known. A total of 446 rice grains were collected from paddy fields distributed across China, and the concentrations of 8 elements in rice bran and their corresponding polished rice were measured. The levels of As, Cd, Cr, and Se have a good linear relationship between rice bran and polished rice (R 2: .79, .97, .82, .99, respectively; all p, Arsenic accumulation in rice reduced the levels of essential mineral nutrients (Mn, Ni, and Se). Improving nutrient elements by fertilization could decrease the accumulation of some toxic elements.

The application of current soil quality standards based on total arsenic (As) fails to assess the ecological risks of soil arsenic or to ensure the safety of crops and foods. In this study, bioavailable arsenic instead of total arsenic was applied to improve predictive models for arsenic transfer from soil to wheat (Triticum turgidum L.). The stepwise multiple-linear regression analysis showed that bioavailable arsenic and amorphous iron oxides (FeOX) were the two most important factors contributing to arsenic accumulation in wheat grain, with the explained percentage of variation being up to 82%. Compared with the bioavailable arsenic extracted by NH4H2PO4, bioavailable arsenic extracted by HNO3 from soils generated better predictions of the amount of arsenic in grain. The best reliable model was log[Asgrain] = 0.917 log[HNO3-As] - 0.452 log[FeOX] - 1.507 (R2 = 0.82, P