Arsenic and cadmium concentrations in brown rice can be controlled by understanding the impacts of weekly water contributions before and after heading

ABSTRACT Arsenic (As) and cadmium (Cd) are harmful to humans, and their concentrations in rice are affected by the water management strategies used in paddy fields. Water management, however, is considered a burden for farmers, and thus an efficient strategy by which to decrease As and Cd concentrations in brown rice is desired. The purpose of this study was to estimate the effects of water management on the total As and Cd concentrations in brown rice during the 3 weeks before and after heading on a weekly basis. Moreover, the study aimed to determine the differences in this effect among soil types and cultivars. Pot cultivation experiments of rice were conducted by applying two levels of weekly flooding or draining to an L12 orthogonal table, and their effects each week on the As and Cd concentrations in brown rice were identified. Redox potentials of soils decreased during flooding and increased during draining, but the decrease during flooding in Andosols was slower than that in Fluvisols. For the plants growing in Fluvisols, the total As and Cd concentrations in the brown rice increased and decreased with flooding, respectively, and an opposite trend was observed with draining. In the Japonica varieties ‘Koshihikari’ and ‘Hitomebore,’ water management during the first week from 0 to 2 days after heading had the greatest impact on As and Cd concentrations. However, in the Indica variety ‘Takanari,’ the weeks that most affected the As and Cd concentrations were the second and first week from the day after heading, respectively. In the Andosols, the Cd concentration was changed by water management as in the Fluvisols, but the same was not found for the As. This suggests that the effect of water management on the As concentration in brown rice could be nullified by the Andosols ability to absorb As. However, it was also possible that the effect of water management could not be detected due to the low As concentration of the Andosols. These results provide insights that will help to efficiently reduce As and Cd concentrations using information on the rice variety and soil type.