采用浇灌方式施用甲酸钙消减当季叶菜镉污染

Reducing cadmium pollution in present-season leafy vegetable by calcium formate application through irrigation

中轻度Cd污染农业土壤修复多采用以pH调控为主的钝化措施,但在pH中性土壤中综合效果不佳。本研究提出在蔬菜生长时期用甲酸钙溶液强化根际土壤交换态Cd向碳酸盐结态Cd的转化,在基本不改变土壤pH的情况下,阻控蔬菜对pH中性土壤Cd的吸收。室内模拟实验表明,低浓度甲酸钙(1.3~3.9 g·L^(-1))可以促使土壤交换态Cd转化为水溶态Cd;24 h内甲酸根生物降解后,土壤碱度有所提高,但pH变化不大,利于土壤交换态Cd转化为水溶态Cd后继续转化为生物有效性相对更低的碳酸盐结合态Cd。采用全Cd含量为1.03 mg·kg^(-1)、pH为7.3的棕壤开展油菜盆栽实验,结果显示,在油菜生长中后期2次以灌溉形式按76、152或228 mg·kg^(-1)土的剂量添加甲酸钙后,收获时油菜Cd含量分别比对照组减少31.6%、32.7%和39.4%,但不同处理土壤pH变化很小;在第二茬盆栽实验中,不同处理油菜Cd含量差异消失。甲酸钙阻控当季蔬菜吸收土壤Cd的作用主要归因于其对土壤交换态Cd向碳酸盐结合态Cd转化的促进作用,但土壤交换性阳离子组成与含量、铁锰氧化物和有机质等因素对甲酸钙阻控效果的影响还有待进一步研究。

Soil pH control-based approaches are often adopted for remediation of Cd-lightly and moderately contaminated agricultural soils, but their overall effects are generally not good in pH- circumneutral soils. In this study, enhancing the conversion from exchangeable Cd to carbonate- bounded Cd in rhizosphere soil with little soil pH change by calcium formate solution irrigation during vegetable growth period was proposed for reducing Cd uptake by vegetable from pH-circ- umneutral soil. The laboratory experiment showed that low-concentration calcium formate （1.3- 3.9 g · L-1） promoted the dissolution of exchangeable Cd. Meanwhile, soil alkalinity increased with little pH change after formate biodegradation within 24 hours, favoring further conversion of the dissolved Cd into less bioavailable carbonate-bounded Cd. The results from the subsequent pot experiment with brown soil （total Cd 1.03 mg · kg^-1, pH 7.3） planted with cole showed that ad- dition of calcium formate at 76, 152 or 228 mg · kg^-1 soil through irrigation twice in the middle and late growing period decreased Cd level in the edible part of cole by 31.6%, 32.7% and 39.4%, respectively, while soil pH changed among different treatments uptake by present-season disappeared leafy vegetab little compared with the control. Such differences in the subsequent cropping season. The reduction of Cd le by calcium formate application is attributed to its en- hanced conversion of exchangeable Cd into carbonate-bounded Cd in soil. Nevertheless, its effec- tiveness needs to be further assessed tion and content of soil exchangeable with consideration of impacting factors such as the composi- cations, soil iron-manganese oxides and organic matter.