Selenium translocation in the soil-rice system in the Enshi seleniferous area, Central China.

Abstract

Rice is an important source of selenium (Se) exposure; however, the transformation and translocation of Se in the soil-rice system remain poorly understood. Here, we investigated the speciation of Se in Se-rich soils from Enshi, Central China and assessed which Se species is bioavailable for rice grown in Enshi. Extremely high Se concentrations (0.85 to 11.46\u202fmg/kg) were observed in the soils. The soil Se fractions, which include water-soluble Se (0.2 to 3.4%), ligand-exchangeable Se (4.5 to 15.0%), organically bound Se (57.8 to 80.0%) and residual Se (6.1 to 32.9%), are largely controlled by soil organic matter (SOM) levels. Decomposition of SOM promotes the transformation of organically bound Se to water-soluble Se and ligand-exchangeable Se, thereby increasing the bioavailability of Se. The bioaccumulation factors (BAFs) of Se decrease in the following order: roots (0.84\u202f±\u202f0.30)\u202f>\u202fbran (0.33\u202f±\u202f0.17)\u202f>\u202fleaves (0.18\u202f±\u202f0.09)\u202f>\u202fpolished rice (0.14\u202f±\u202f0.07)\u202f>\u202fstems (0.12\u202f±\u202f0.07)\u202f>\u202fhusks (0.11\u202f±\u202f0.07). Selenium levels in rice plants are affected by multiple soil Se fractions in the soil. Water-soluble, ligand-exchangeable and organically bound Se fractions are the major sources of Se in rice tissues.