Accumulation of copper and cadmium in soil–rice systems in terrace and lowland paddies of the Red River basin, Vietnam: the possible regulatory role of silicon

Rice production in floodplain deltas is currently vulnerable to climate change and contamination from anthropogenic activities. The relocation of rice production to upland regions could be an option for increasing the sustainability of rice production. Our study evaluated the spatial patterning of heavy metals, i.e., copper (Cu) and cadmium (Cd), in rice along a topogradient from terrace to lowland areas in the Red River basin. The dataset obtained from the analysis of 61 farm sites throughout the whole basin indicated a large discrepancy in the Cu and Cd contents in rice grains from terrace and lowland paddies. While Cu and Cd were not found in most of the rice grain samples from the terrace paddies, the median Cu and Cd contents of the lowland paddy rice were 1.895 and 0.033 mg kg −1 , respectively. Assessing the relationship of Cu and Cd in the soil–rice system to soil properties revealed possible correlations between soil available silicon (Si) and the Cu and Cd contents in rice grain. The enrichment of Si in rice plants likely reduces the translocation of Cu and Cd from soil to grain. Therefore, management of the Si supply, particularly in lowland paddies, should be highlighted as a way to reduce dietary intake of Cu and Cd.