Abstract
Representing the staple crop for half of the world population, rice can accumulate high levels of cadmium (Cd) in its grain, posing concerns on food safety. Different soil amendments have been proposed to decrease Cd accumulation in rice grain by either decreasing soil Cd availability, introducing competitive ions on Cd uptake, or down-regulating the expression of transporters for Cd uptake. However, the effectiveness of soil amendments applied alone or in combinations needs to be tested under field conditions. Here, we present results of field trials with two rice cultivars differing in Cd accumulation grown at three field sites in southern China in two years, to investigate the effects of two Mn-containing soil amendments (MnO2, Mn-loaded biochar (MB)), Si fertilizer (Si), limestone, and K2SO4, as well as interactions among MnO2, Si, and limestone on decreasing Cd accumulation in rice grain. We found that single applications of MnO2 or MB to acidic soils low in Mn decreased grain Cd concentrations by 44–53 % or 78–82 %, respectively, over two years without decrease in performance. These effects were comparable to or greater than those induced by limestone liming alone (45–62 %). Strong interactions between MnO2 and limestone resulting from their influence on soil extractable Cd and Mn led to non-additive effects on lowering grain Cd. MB addition minimized grain Cd concentrations, primarily by increasing extractable and dissolved Mn concentrations, but also by decreasing Cd extractability in soil. In comparison, Si and K2SO4 amendments affected grain Cd levels only weakly. We conclude that the amendments that decrease labile Cd and increase labile Mn in soils are most effective at reducing Cd accumulation in rice grain, thus contributing to food safety.
Highlights
Cadmium (Cd) accumulation in rice grain poses a serious threat to food safety and human health in many rice-growing regions of the world
Cadmium concentrations in brown rice of both XWX and Shenyou 957 (SY) cultivars are shown in Fig. 2 for all treatments in the four field trials
With respect to the Chinese maximum permissible value of 200 μg/kg Cd in rice, only the cultivar SY grown on Mn-loaded biochar (MB) amended soil met the food safety limit, in all trials consistently
Summary
Cadmium (Cd) accumulation in rice grain poses a serious threat to food safety and human health in many rice-growing regions of the world. In some of the contami nated areas, intake of Cd from consumption of rice by the local pop ulations has exceeded the tolerable intake limit recommended by the FAO/WHO (Chen et al, 2018a, 2018b, 2018c; Wang et al, 2019), posing serious threat to human health (Wang et al, 2019). Cd is mainly weakly bound to negatively charged surfaces or oxygen groups of min erals and organic matter in oxic soils (Loganathan et al, 2012), e.g., when the rice fields are drained. Strong Cd binding to reduced inorganic and organic sulfur-containing groups can be estab lished, e.g., during flooding of paddy soils (Fulda et al, 2013; Furuya et al, 2016). Cd mobility in oxic soils is controlled by adsorption to
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