Characterization of mercury species in brown and white rice (Oryza sativa L.) grown in water-saving paddies

In China, total Hg (HgT) and methylmercury (MeHg) were quantified in rice grain grown in three sites using water-saving rice cultivation methods, and in one Hg-contaminated site, where rice was grown under flooded conditions. Polished white rice concentrations of HgT (water-saving: 3.3 ± 1.6 ng/g; flooded: 110 ± 9.2 ng/g) and MeHg (water-saving 1.3 ± 0.56 ng/g; flooded: 12 ± 2.4 ng/g) were positively correlated with root-soil HgT and MeHg contents (HgT: r2 = 0.97, MeHg: r2 = 0.87, p < 0.05 for both), which suggested a portion of Hg species in rice grain was derived from the soil, and translocation of Hg species from soil to rice grain was independent of irrigation practices and Hg levels, although other factors may be important. Concentrations of HgT and other trace elements were significantly higher in unmilled brown rice (p < 0.05), while MeHg content was similar (p > 0.20), indicating MeHg infiltrated the endosperm (i.e., white rice) more efficiently than inorganic Hg(II).

► First time that HgT and MeHg were characterized in both brown and white rice.
► MeHg translocation into the endosperm was more efficient than inorganic Hg(II).
► In this respect, MeHg behaved like dimethylarsinic acid and organic Se species.
► In white rice, HgT and MeHg were positively correlated with soil HgT and MeHg.
► Uptake rates of HgT and MeHg were independent of irrigation methods and Hg content.