添加保水剂和栽种黑麦草对土壤不同形态铅转化的影响

Effects of water-retaining agents and ryegrass on the transformation of Pb into different forms in soil

为了探讨保水剂进入土壤后是否影响重金属的存在形态及其减少植物对重金属吸收的原因,首先通过电镜技术对保水剂(聚丙烯酸钠)吸附重金属铅的行为从表面结构和元素组成上进行了表征确认,并在了解其对铅吸附能力的基础上,采用保水剂和黑麦草进行盆栽试验。试验设4个处理(保水剂0%、保水剂0.2%、黑麦草、保水剂0.2%+黑麦草),试验结束后,对土壤不同形态的铅和黑麦草植株地上部的铅含量进行测定。结果显示,保水剂对重金属铅具有较强的吸附能力,其吸附方式以螯合作用和络合作用为主,通过离子交换方式吸附的量很少。单独添加保水剂可促进土壤中易溶性铅向难溶性铅转化,有助于土壤铅的钝化;单独栽种黑麦草促进难溶性铅向易溶性铅的转化,对土壤铅具有活化作用。保水剂和黑麦草的双重作用可导致大量残渣态铅的溶解释放,但释放的铅率先被保水剂吸附,从而使黑麦草体内的铅含量降低。

Heavy metal（HM）pollution in soil is an important environmental problem with respect to food security. Water-retaining agents（WRAs）have recently been used to remediate heavy metal contaminated soil. However, the mechanisms of HM remediation using WRAs have not been well documented. The purpose of this study was to investigate the effects of WRAs on the distribution and morphology of lead（Pb）in soil and to identify the possible mechanisms associated with reduced Pb uptake by plants. To achieve this, Pb-loaded WRAs were characterized using scanning electron microscopy（SEM）to confirm the elemental distribution of Pb on WRAs. A pot experiment with ryegrass（Lolium perenne L.）（0% WRA, 0.2% WRA, ryegrass, and 0.2% WRA ＋ ryegrass）was then carried out to determine Pb uptake and accumulation in aboveground plant tissues. The results indicated that WRAs have good Pb sorption capacity. Pb was mainly immobilized by chelation and complexation with WRAs, and to a considerably lower extent by ion exchange. The pot experiment revealed that soil Pb tends to be mobilized by plant roots, while WRAs can immobilize Pb by transforming it to less soluble species. The combined effects of WRAs and ryegrass roots can induce the release of residual Pb in soil, but much of the released Pb can be quickly sorbed by WRAs. This contributes to a reduction in Pb content in aboveground plant tissues.