Speciation of arsenite and arsenate in rice grain – Verification of nitric acid based extraction method and mass sample survey

Arsenite and arsenate speciation was performed in 121 commercially purchased samples of 12 rice types to understand their relative relevance in rice grain. General effectiveness of a recently developed extraction protocol based on 0.28 M nitric acid at 95 °C was verified by checking the recovery of total grain arsenic and by comparing arsenic speciation in NIST-CRM-1568a, NMIJ-CRM-7503a and IMEP-107 with certificated and literature values. The arsenic speciation highlights the predominance of arsenite in 115 and dimethylarsinic acid in six samples and common minor components including arsenate, monomethylarsonic acid and two unknown arsenical species. Our data also indicate potential influences of other trace elements on As speciation in rice grain. Averagely, arsenite accounts for 90% of inorganic grain arsenic regardless of geographic origin, rice type, grain size, cultural practice and polish treatment. The high arsenite predominance indicates an elevated toxic effect of arsenic in rice than is perceived to date.

► General validation of 0.28 M HNO3 at 95 °C extraction for arsenic speciation in rice grains.
► Either arsenite or dimethylarsinic acid predominates in rice grains.
► Monomethylarsonic acid and two unknown arsenic are usually minor components in rice grains.
► Predominance of arsenite averagely 90% of inorganic arsenic in grains.
► Trace elements may potentially influence arsenic speciation in rice grains.