Comparison of grain cadmium and arsenic concentration between main and ratoon crop in rice ratooning system.

Rice ratooning system is becoming increasingly important for food security in China, however, information on grain cadmium (Cd) and arsenic (As) levels is lacking. We collected grain samples of main crop (MC) and ratoon crop (RC) from five sites, where the same eleven varieties were planted, and determined the Cd and As concentration in brown rice. Results showed that differences in grain Cd level between MC and RC were inconsistent across experimental sites, although the average value was comparable. In contrast, the grain As level was significantly higher in MC than in RC by 99.8% on average, which was consistent across all sites. Moreover, there was a significant positive correlation in grain Cd concentration between RC and MC. Overall, RC-produced rice is safer than MC with dramatically lower As concentration, and planting rice varieties with low Cd accumulation capacity is important for production of safe rice in rice ratooning system.