Bachelor Thesis

Arsenic in red rice of Camargue

Anne Eberle (07/2014-10/2015)

Support: Britta Planer-Friedrich, Gunter Ilgen, Jörg Schaller

Rice is known to accumulate more arsenic in its grains than other cereals. Literature values, however, showed particularly high concentrations in French rice from the Camargue region. Commercially purchased brown, red, and black rice as well as water, pore water and soil samples were analyzed for their total arsenic content and speciation to elucidate the origin. Irrigation water (1.9 µg/L), water on the field (2.8 µg/L) and soil (8.6 mg/kg) did not reveal any obvious contamination, but compared to irrigation water arsenic was enriched in pore water (56 µg/L). The high arsenic content in French rice compared to literature values from other countries and own analyses of Italian and Thai rice was confirmed. In addition, total arsenic concentrations in brown rice (296 µg/kg) were significantly different from red (452 µg/kg) and black rice (440 µg/kg), which indicates different enrichment of arsenic in different varieties. Speciation analysis showed that arsenite dominates in brown and arsenate in black rice while red rice contains equal shares of both arsenite and arsenate. This could possibly indicate differences in the occurrence of transporters for silicic acid and phosphate transporters. Furthermore, French rice has a different speciation than Italian rice. After polishing a red rice sample the white grains still contained more arsenic than originally brown grains, so the bran alone does not explain the higher accumulation of arsenic. All in all, not just environmental factors but also genetic differences between the rice colors as well as between French rice and rice from other countries seem to contribute substantially to the accumulation of arsenic in French rice.