西北地区重金属元素累积现状及典型地区成因分析

Accumulation Status of Heavy Metals in Northwest China and Analysis of Causes in Typical Areas

2004年以来,西北地区累计完成1∶25万土地质量地球化学调查面积为29.07万km^(2)。采用以X射线荧光光谱法(XRF)、原子荧光光谱法(AFS)和电感耦合等离子体质谱法(ICP-MS/AES)等测试方法,获得共计66006件表层土壤中的Cd、Hg、As、Pb、Cr、Cu、Ni、Zn等8种重金属含量。笔者运用地累积指数、单项污染指数和内梅罗综合指数等方法,对西北地区表层土壤重金属含量及其累积现状进行综合分析;在此基础之上,讨论了白银、拉脊山等典型地区重金属累积的原因。结果表明:①西北地区土壤中Cd、Hg、As、Pb、Cr、Cu、Ni、Zn的单项污染指数中无污染均在99.26%以上,表明区内土壤总体未受重金属污染,整体情况良好。②西北地区土壤重金属筛选值以上点位以地质累积为主,达到52.7%,其中仅4个点位的As达到管制值,说明在自然条件下,土壤中的重金属含量较难达到管制值,生态风险低。由人为因素引起的筛选值以上点位主要分布在白银、潼关、西安等地区,大于管制值的点则集中分布在白银和潼关。③建议深入开展西北干旱区土壤重金属生物有效性研究,进一步优化重金属在不同背景下的管制值和筛选值。

Since 2004,a total of 290700 km 2 of 1∶250000 land quality geochemical survey has been completed in Northwest China.The contents of eight heavy metals elements such as cadmium,mercury,arsenic,lead,chromium,copper,nickel and zinc in 66006 topsoils have been obtained by X-ray fluorescence spectrometry(XRF),atomic fluorescence spectrometry(AFS)and inductively coupled plasma mass spectrometry(ICP-MS/AES).The content and accumulation of heavy metals in topsoil in Northwest China were analyzed by using the methods of Geo-accumulation index,single factor index and Nemerow multi-factor index.On this basis,the causes of heavy metal accumulation in typical areas such as Baiyin and Laji mountain are discussed.The results show that:①the single pollution indexes of cadmium,mercury,arsenic,lead,chromium,copper,nickel and zinc in the soil are more than 99.26%,indicating that the soil in Northwest China is not polluted by heavy metals and they are as a whole in good condition.②The sites above the screening value of soil heavy metals in Northwest China are up to 52.7%and dominated by geological accumulation,which only four sites reach the control value.It shows that,the content of heavy metals in soil is very difficult to reach the control value under natural conditions and pose low-risk threat to ecosystem health.The sites above the screening value caused by human factors are mainly distributed in Baiyin,Tongguan,Xi'an and other areas,and the points greater than the control value are concentrated in Baiyin and Tongguan.③It is recommended to carry out in-depth research,especially the bioavailability of soil heavy metals in the arid area of Northwest China,so as to further optimize the control value and screening value of heavy metals under different backgrounds.