重金属污染农田安全利用:进展与展望

我国耕地土壤污染面积广,污染情况复杂,农产品重金属超标问题已经关系到国计民生。常用的物理化学修复方法成本高,不适用于大面积的中低污染农田。植物提取修复方法成本低,环境友好,但修复时间长,推广困难。总的来讲,基于重金属移除的诸技术在解决农田重金属污染方面还没有太大优势。相较而言,农田安全利用在不移除或缓慢移除土壤重金属的条件下,以生产安全农产品为目标,具有更加坚实的现实意义和推广价值。种植低吸收农作物是安全利用的重要措施,基因工程手段在低吸收农作物品种筛选中具有巨大的潜力,但其可能带来的生态环境风险使得这些通过基因工程得到的低吸收作物的田间种植面临着巨大挑战。土壤添加剂可以改变土壤重金属形态,降低重金属的生物有效性,但会对土壤质量产生影响。微生物尤其是土著微生物的利用越发受到关注,改变微生物的生存环境与基因工程手段能够强化微生物的钝化效果。施肥、水分管理、间作等农艺措施也能改变土壤重金属的形态,抑制作物对重金属的吸收。未来以加强推广为目的,多种技术手段的联合应用是重金属污染农田安全利用的重要发展方向,其中以生物技术为核心的利用模式具有十分重要的意义。

Safe utilization of farmland contaminated with heavy metals in China: Progress and outlook

Farmland heavy metal pollution is now a serious problem in China. Food heavy metal contents in some agricultural regions exceed the national limits and threaten human health and the development of economy and society. Meanwhile, farmland resources are very limited in China. Therefore, farmland heavy metal pollution needs to be resolved urgently. Among available remediation tools, the physical or chemical ones are costly and are not suitable for the slightly/moderately contaminated farmland at a large scale. The phytoextraction method is cost-effective and environmentally friendly, but requires a long time. Overall, techniques aiming at heavy metal removal have limitations in solving heavy metal pollution in farmland. Safe utilization is to produce safe agricultural products, without removing the heavy metal content in soil purposefully. Safe utilization of heavy metal contaminated farmland is preferable for China at this stage. Cultivation of low-accumulation crops is an important option for the safe utilization scheme. A number of low-accumulation cultivars of grain crops and vegetables have been screened out in China. Genetic engineering has potential in breeding of low-metal-accumulation crops. Soil additives such as clay minerals, organic wastes and biochar can inhibit heavy metal uptake of crops by immobilization of heavy metals in soil, via ion-exchange, precipitation, etc. However, use of soil additives may impact soil qualities by changing soil structure, loss of nutrition and secondary pollution. Some microorganisms showing strongly resistant to heavy metals have already been used to inhibit the heavy metal uptake of crops. Genetically modified microbes possessing stronger immobilization ability should be paid more attention. Furthermore, agronomic strategies including fertilization, water management, and intercropping can transform the heavy metal forms in soil and influence the heavy metal uptake by crops. However, the crop yield and quality like nutrient content can also be influenced by the safe utilization measures. Efforts should be made to get a balance between low accumulation of heavy metals and crop yield and qualities. In the future, researches may focus on the integration of various remediation techniques for the large-scale field implementation.