According to a new study published in the journal Environmental Science & Technology, when compared with continuously flooding rice fields, watering fields with sprinklers results in rice with around one-fiftieth as much arsenic. Rice usually grows in perpetually flooded fields. In countries in Southeast Asia such as Bangladesh, where groundwater is contaminated with arsenic, the toxic metal accumulates enough in rice grains that it can harm peoples health. Gavino Sanna at the University of Sassari and his colleagues thought that the extra air in sprinkler water could change the oxidation state of the dissolved arsenic. Oxidation states of inorganic arsenic species vary in toxicity: As(III) compounds are much more toxic than As(V) species, explains Sanna. In flood water, which has lower oxygen content, Sanna says, As(III) species become more soluble. And aerobic conditions favour the formation of As(V) species, he adds. He reasoned that aerating water via sprinkling should reduce the likelihood that the more toxic arsenic would accumulate in rice kernels. In their study in Sardinia, the researchers grew 37 species of rice in two fields and tested their total arsenic concentrations. In one field, which the researchers continuously flooded, arsenic concentrations ranged from 95 to 235 µg per kg. In the other field, which they watered with sprinklers, the levels were much lower: between 1.3 and 5.1 µg per kg. Whats more, the researchers note, sprinkling required only half as much water. Sanna says their work is only just starting. Now we are chasing a dream, he says, that worldwide there are no more deaths from food arsenicosis.
Chemical & Engineering News, 13 July 2012 ;http://pubs.acs.org/cen/news ;