The Increase in the Arsenic Concentration in Brown Rice Due to High Temperature during the Ripening Period and Its Reduction by Silicate Material Treatment

We investigated the effect of temperature during the ripening period on the rice yield and arsenic (As) concentration in brown rice, using temperature gradient chambers (TGCs). Rice grown in Wagner pots (1/5000a) was placed in three TGCs (each TGC was set at four temperature levels: ambient, mildly-high temperature, moderately-high temperature, and super-high temperature) from one week after heading until harvest. In the TGCs, a range of mean air temperatures was observed in the range of 2 °C above the ambient temperature. There was a significant negative correlation between the brown rice yield and the air and soil temperatures, and the increase in air and soil temperatures resulted in a decrease in the yield. The reduction in yield was significantly mitigated by the application of calcium silicate. The concentration of As in the brown rice was significantly positively correlated with the air and soil temperature, and the concentration of As increased with increasing air and soil temperatures. When calcium silicate was applied, the concentration of As in brown rice was significantly lower at all temperature ranges, and its application was effective in reducing the arsenic concentration even at high temperatures. These results suggest that the application of silicate material may help mitigate the decrease in yield and the increasing As concentration in brown rice even under high-temperature conditions

Simultaneous decrease of arsenic and cadmium in rice (<i>Oryza sativa</i> L.) plants cultivated under submerged field conditions by the application of iron-bearing materials

<p>The Codex Alimentarius Commission has recently adopted maximum levels for inorganic arsenic (As; in 2014) and total cadmium (Cd; in 2006) in polished rice grains to maintain food safety and to decrease the risk to human health. As rice is a staple crop in Japan and monsoon Asian countries, reducing concentrations of As and Cd in rice is an urgent matter. In flooded conditions, Cd concentration in soil solution decreases whereas As concentration increases. Therefore, we aimed to evaluate the efficiency of iron-bearing materials to decrease As concentration in soil solution and rice (<i>Oryza sativa</i> L.) grain under submerged cultivation, while also considering Cd concentration. In experiments conducted in paddy fields in six regions, As concentrations in the soil solution during the cultivation period decreased in the following order: control (REF) > steel converter furnace slag (SCS) > non-crystalline iron hydroxide (FH) > zero-valent iron (ZVI). The concentrations of As in brown rice were in the same order, with ZVI achieving particularly strong reduction. Cadmium concentrations were low, probably owing to submerged cultivation conditions. Application of iron-bearing materials slightly and insignificantly reduced the yields of brown rice and straw. Application of these materials did not have a significant negative impact on the quality of rice. Our data indicate that the application of iron-bearing materials effectively reduces As concentrations in soil solution and rice grains without negative effects on yield and quality, with a particularly powerful effect of ZVI which is possibly explained by arsenic sulfide formation.</p