中国粮食主产区耕地土壤重金属时空变化与污染源分析

土壤重金属污染威胁着农田生态系统安全和人类健康.基于2000年以来中国五大粮食主产区3 006个耕地样点的土壤重金属实测数据和20世纪80年代的土壤重金属历史数据,采用单因子指数法评估了粮食主产区耕地土壤重金属的污染现状和变化趋势,并基于地累积指数,结合区位环境污染探讨了其污染来源.结果表明,中国粮食主产区耕地土壤重金属点位超标率为21.49%,整体以轻度污染为主,其中轻度、中度和重度污染比重分别13.97%、2.50%和5.02%.四川盆地、长江中游及江淮地区、黄淮海平原、松嫩平原和三江平原的耕地点位超标率分别为43.55%、30.64%、12.22%、9.35%和1.67%,南方耕地污染重于北方.主要污染物为Cd、Ni、Cu、Zn、Hg,超标率分别为17.39%、8.41%、4.04%、2.84%、2.56%.自20世纪80年代以来,耕地土壤重金属含量呈增加趋势,整体上点位超标率增加了14.91%,其中Cd、Ni、Cu、Zn和Hg的污染比重分别增加了16.07%、4.56%、3.68%、2.24%和1.96%.除三江平原外,其他4个粮食主产区耕地土壤重金属点位超标比重增加趋势显著,且南方地区的Cd、Ni和Cu重金属超标比重变化量高于北方,而Hg和Cr增速低于北方.Cd、Hg以人为污染源为主,其他6种重金属以自然污染源为主,但Pb、Zn和Cu约有20.00%的点位受人为活动的影响.矿业、工业、污灌水是主要的污染源,除污灌水来源北方重于南方外,其余污染来源均是南方污染重于北方,污染物种类也多于北方.

Spatial-Temporal Trends and Pollution Source Analysis for Heavy Metal Contamination of Cultivated Soils in Five Major Grain Producing Regions of China

Heavy metal pollution of farmland soils in China has been identified as a threat to ecosystem safety and human health. A total of 3006 soil samples were analyzed from arable lands in five grain producing regions of China, which included data from published studies from 2000 up to now. An additional 656 historical samples were derived from the 1980s by a digitizing grained point sites map (Cd, Pb, As, Ni, Cu, Zn, Cr, and Hg) from the PRC Atlas of Soil Environmental Background Values. A GIS-based approach and single factor index method were employed to identify the current status and spatial distribution of heavy metal (Cd, Pb, As, Ni, Cu, Zn, Cr, and Hg) contamination in agricultural soils, and these were then compared with historical data to explore contamination trends over time. Then, based on the I_geo method and the effects of the surrounding environment on contamination rates, pollution sources were analyzed. Results showed that 21.49% of the agricultural soil samples exceeded the environmental quality standard set by the Ministry of Environmental Protection. The proportions of slight, moderate, and severe pollution were 13.97%, 2.50%, and 5.02%, respectively. Pollution is more extensive in the south compared with the north. Exceedance percentages in the Sichuan Basin (SC), Yangtze River Middle Plain and Jianghuai Plain (CJ), Huang-Huai-Hai Plain (HHH), Songnen Plain (SN), and Sanjiang Plain (SJ), were 43.55%, 30.64%, 12.22%, 9.35%, and 1.67%, respectively. The main pollutants were Cd, Ni, Cu, Zn, and Hg, with exceedance percentages of 17.39%, 8.41%, 4.04%, 2.84%, and 2.56%, respectively. Since the 1980s, heavy metal pollution has increased by 14.91%. The proportion of Cd, Ni, Cu, Zn, and Hg increased by 16.07%, 4.56%, 3.68%, 2.24%, and 1.96%, respectively. Except for SJ, exceedance percentages in cultivated land increased significantly, while the exceedance percentages of Cd, Ni, and Cu in the southern areas were higher than for the northern areas-although the growth rate of Hg and Cr in the south was lower than that in the north. The main sources of Cd and Hg were anthropogenic pollution, while the other six heavy metals were from predominantly natural sources. However, about 20.00% of Pb, Zn, and Cu were affected by anthropogenic activities. Mining, industry, and sewage water were the main sources of pollution. In addition to the larger impact of sewage irrigation in the north, other sources of pollution showed greater influence in the south. Mining mainly caused pollution by Cd, Hg, Ni, Cr, and Cu, while excessive levels of Cd, Ni, Cu, Zn, and Hg was the signature of industrial pollution. Irrigation with sewage effluent causes excessive Cd, Ni, and Zn. Results from this study provide valuable information for agricultural soil management and food safety in China.