麦玉轮作区农田土壤重金属调查及评价

Investigation and evaluation of soil heavy metals in a wheat-maize cropping system in upland China

为全面了解旱地两熟区典型轮作制农田土壤重金属污染和风险状况,通过采集150个耕层土壤样品调查分析了我国高利用强度下麦玉轮作农田土壤重金属含量(Ni、Cr、Cu、Cd、Zn、Pb、Hg、As),并采用单因子污染指数(Pi)、内梅罗综合污染指数(PN)、富集因子(EF)和生态风险评价(RI)4项指标进行土壤污染评价。结果表明:PN和RI指数表明,旱地两熟区土壤整体为清洁状态。As(29.04±9.21 mg·kg^(-1))、Cd(0.15±0.14 mg·kg^(-1))、Pb(17.84±18.10 mg·kg^(-1))含量高于全国土壤背景值,除As处于轻微污染外,其他重金属均未达到污染水平。不同区域间,云南地区的重金属含量高于其他区域,处于较低潜在生态风险,但逼近中等生态风险警戒。相关性、主成分和聚类分析结果进一步发现,土壤污染主要来源于成土母岩和人为活动,其中Ni、Cr、Cu、Cd和Zn含量受成土母岩影响更大,而Pb、Hg和As含量受人为活动影响更大。研究表明,农田土壤重金属含量在成土母岩的基底含量基础上通过人为活动进一步积累。

The purpose of this study was to conduct a targeted investigation and systematic evaluation of soil heavy metal pollution in 150 fields in a regional scale wheat-maize cropping system in upland China. Soil pollution by eight heavy metal elements(Ni, Cr, Cu, Cd, Zn,Pb, Hg and As)was evaluated using the single factor pollution index(Pi), Nemerow comprehensive pollution index(PN), enrichment factor(EF), and ecological risk assessment(RI). The results showed that the overall soil pollution status of the wheat-maize cropping system is clean based on PN and RI. The As(29.04±9.21 mg·kg^(-1)), Cd(0.15±0.14 mg·kg^(-1)), and Pb(17.84±18.10 mg·kg^(-1))contents were higher than the national soil background values. The soils were not classified as polluted by the heavy metals, except for As, which had a slightly polluted status. Among different regions, the soil heavy metal content in the Yunnan area was higher than that in other areas, which posed a low potential ecological risk and was close to the medium ecological risk warning. The correlation, principal component analysis, and cluster analysis results showed that the soil heavy metals mainly originated from the soil parent materials and human activities. Ni, Cr, Cu,Cd, and Zn were more affected by soil parent materials, whereas Pb, Hg, and As were more affected by human activities. Pb and Hg originated from the application of mineral fertilizers, whereas As originated from the use of organic fertilizers and chemical fertilizers and the human activities of coal combustion and atmospheric deposition. In summary, the concentration and pollution risk characteristics of the eight heavy metals in the study area varied. The heavy metals in farmland soil originated from the soil-forming parent rock and further accumulated owing to human activities.