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Lead contamination in soil has become a worldwide threat on food security and human health. To assess the Pb bioavailability and evaluate the safe use of low Pb polluted soil for food production, the speciation of Pb in 19 types of paddy soil were investigated by chemical extraction and X-ray absorption near-edge structure (XANES), and the uptake and accumulation characteristics of Pb in different soil-rice systems were investigated. Moreover, an empirical model was established to predict the content of Pb in rice grain, and field validation was conduct to evaluate model performance. Results showed that the proportion of available Pb in different soil satisfied normal distribution N (0.47, 0.23). Pb(CH 3 COO) 2 , GSH-Pb, PbO, PbHPO 4 and Pb 3 (PO 4) 2 performed well in characterizing the speciation of Pb in different rhizosphere soils, and PbHPO 4 accounted for more than 70%. The exceedance of Pb in grain in CK, 0.5X and 1X treatment were 10.5%, 36.1% and 42.1%, respectively, and the accumulation of Pb in grain was significantly related with Pb content in root. Carbonate and organic bound Pb in rhizosphere soil were two major Pb species that influenced the accumulation of Pb in rice. Moreover, content of total Pb, clay and SOM performed well in predicting the Pb content in grain, both for pot and field samples. Above all, our predicting model worked well in evaluating Pb accumulation in rice grain among low polluted paddy farmland (Total Pb < 300 mg/kg). Image 1 • Edible Pb content was positively related to the carbonate and organic bounded Pb in rhizosphere soil. • The specific speciation of Pb in different rhizosphere soils was clarified using XANES. • The content of total Pb, clay and SOM performed well in predicting the Pb content in rice grain. • Our model worked well in evaluating Pb content in rice grain among low polluted farmland. [ABSTRACT FROM AUTHOR]

Arsenic (As) has been recognized as one of the most toxic metalloids present in the surface soil contaminating food chain and posing threat to human life. Sulfur (S) fertilizer is often supplied in paddy soil for rice growth, but its impact on As mobility and related bacteria remains poorly understood. In this study, a pot experiment was set up with two different types of sulfur treatments (element sulfur and Na 2 SO 4) to evaluate the effect of sulfur fertilizers on As speciation in porewater, As fractions in soil, As accumulation in rice plants. Besides, rhizosphere bacterial composition and functional genes that might influence As mobility were also studied. The results revealed that the addition of 150 mg/kg Na 2 SO 4 decreased As(III) and As(V) concentrations in soil porewater at maturation stage by 77% and 64%, respectively. With the same sulfur content, Na 2 SO 4 was more effective than element sulfur. The addition of sulfur fertilizers promoted rice growth and reduced As accumulation in shoots, further reduced As translocation from root to above-ground parts by 39–59%. The addition of sulfur fertilizers had little effect on genes involved in As metabolism. However, the relative abundance of Fe(III) and sulfate reduction related genera increased with the addition of 150 mg/kg Na 2 SO 4 , consistent with the increase of Fe(III) reducing bacteria Geobacteraceae and sulfate reducing gene dsrA. The phenomenon likely influenced the decrease of As concentrations in soil porewater and rice uptake. The outcomes indicate that promoting Fe- and S- reducing bacteria in the rhizosphere by sulfur fertilizers may be one way to reduce As risk in the soil-rice system. Image 1 • Addition of sulfur fertilizers decreased As(III) in soil solution and reduced the mobility of As. • Addition of sulfur fertilizers decreased As accumulation in rice shoots. • Application of Na 2 SO 4 increased the relative abundance of Fe(III) and sulfate reducing related bacteria. • Application of Na 2 SO 4 did not affect the relative abundance of as functional genes significantly. Sulfur fertilizers decreases As bioavailability likely via increasing the rhizospheric Fe(III) and sulfate reducing bacteria. [ABSTRACT FROM AUTHOR]