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.

Accumulation and potential health risks of cadmium, lead and arsenic in vegetables grown near mining sites in Northern Vietnam.

The effect of environmental pollution on the safety of vegetable crops is a serious global public health issue. This study was conducted to assess heavy metal concentrations in soil, irrigation water, and 21 local vegetable species collected from four sites near mining activities and one control site in Northern Vietnam. Soils from vegetable fields in the mining areas were contaminated with cadmium (Cd), lead (Pb), and arsenic (As), while irrigation water was contaminated with Pb. Average concentrations of Pb and As in fresh vegetable samples collected at the four mining sites exceeded maximum levels (MLs) set by international food standards for Pb (70.6 % of vegetable samples) and As (44.1 % of vegetable samples), while average Cd concentrations in vegetables at all sites were below the MLs of 0.2. The average total target hazard quotient (TTHQ) across all vegetable species sampled was higher than the safety threshold of 1.0, indicating a health risk. Based on the weight of evidence, we find that cultivation of vegetables in the studied mining sites is an important risk contributor for local residents' health.