Sprinklers Reduce Arsenic In Rice

Compared with continuous flooding, watering rice fields with sprinklers results in rice contaminated with far less arsenic, according to researchers in Sardinia, Italy (Environ. Sci. Technol., DOI: 10.1021/es300636d). Rice usually grows in perpetually flooded fields. In countries in Southeast Asia where groundwater is contaminated with arsenic, the toxic metal accumulates in rice grains. Gavino Sanna of the University of Sassari and his colleagues knew that oxidation states of inorganic arsenic species vary in toxicity: As(III) compounds are more toxic than As(V) species. In floodwater, which has low oxygen content, Sanna says As(III) species are more soluble. And aerobic conditions favor the formation of As(V) species. He reasoned that aerating water via sprinkling should reduce the likelihood that arsenic—in particular the more toxic As(III)—would accumulate in rice grains. The researchers grew 37 genotypes of rice and tested the total arsenic concentrations. In rice grown in a continuously flooded field, arsenic concentrations ranged from 95 to 235 µg per kg. Arsenic levels were much lower in rice grown in sprinkled fields: between 1.3 and 5.1 µg per kg. What’s more, sprinkling required only half as much water.