Amendment of sulfate with Se into soils further reduces methylmercury accumulation in rice

Abstract

Purpose Both selenium (Se) and sulfate could largely affect methylmercury (MeHg) dynamics and phytoavailability in soil-rice systems, while their combined effects are less understood. Here, we aimed at exploring the potential effects of sulfate on MeHg accumulation in rice in the presence of Se. Materials and methods Rice was cultivated in inorganic Hgspiked soils amended with Se only (selenite/selenate, BSe treatments^) or Se and sulfate (BSe + Sulfate treatments^). Soil parameters (e.g., pH and redox potential (Eh)), MeHg concentrations in soils, as well as MeHg or Se accumulation in rice plants were quantified during the rice growth period. Results and discussion Soil MeHg concentrations were generally comparable between Se + Sulfate and Se treatments. However, MeHg uptake by rice plants in Se + Sulfate treatments was 9-31 % lower than those in Se treatments, possibly due to the increased soil pH and formation of iron sulfides, which may reduce MeHg phytoavailability under sulfate amendment. Furthermore, sulfate input enhanced Se accumulation in root (especially in the presence of selenate), which could be responsible for the increased MeHg distribution in root and thus lower MeHg distribution in grain. Consequently, the reduced plant uptake of MeHg together with the decreased MeHg distribution in grain resulted in decline of grain MeHg concentrations in Se + Sulfate treatments (8-31 % lower compared to Se treatments). Conclusions Our results suggest that sulfate input with Se could further reduce MeHg accumulation in rice, which improved mechanistic understanding of MeHg behaviors in soilrice systems.

A quantitative review of the effects of Se application on the reduction of Hg concentration in plant: a meta-analysis

“…Meta-analysis showed that both Se(VI) and Se(IV) can significantly reduce Hg concentration in plants ( Figure 4 ), which is consistent with most research results ( Wang et al., 2016a ; Wang et al., 2016b ; Wang et al., 2016c ; Tang et al., 2017 ). In addition, meta-analysis also showed that Se(VI) application can reduce the concentrations of Hg more than Se(IV) in plants ( Figure 4 ).…”

Nanoactivated Carbon Reduces Mercury Mobility and Uptake by Oryza sativa L: Mechanistic Investigation Using Spectroscopic and Microscopic Techniques

“…However, such methods have limited application to productive agricultural soil due to high cost, and the degradation of soil physical, chemical, and biological properties that can result from remediation . Recent studies have shown that immobilization is a better approach to manage the risk of bioavailable Hg in paddy soil. − Selenium compounds, , elemental sulfur, and sulfate have been shown to immobilize Hg when used as a soil amendment although their application beyond laboratory scale is limited. The lack of any proven, reliable, and high-efficiency immobilization technology remains a key barrier for the use of such technology to manage the risk of Hg in productive farmlands.…”

Mercury and Sulfur Redox Cycling Affect Methylmercury Levels in Rice Paddy Soils across a Contamination Gradient

“…Therefore, S-regulated Hg transformation in agricultural fields (e.g., paddy soils) requires more attention. To date, limited studies have examined S input-influenced Hg transformation in paddy soils, with both promotion and inhibition of Hg II methylation reported. − Most of these studies were based on bulk Hg concentration measurements, with little investigation of the precise transformation processes of Hg. Moreover, S species with different valent states determine the redox cycling of S and, thus, influence Hg transformation .…”