中国土壤54项指标的地球化学背景与基准研究

The study of geochemical background and baseline for 54 chemical indicators in Chinese soil

1999—2021年,中国地质调查局组织实施的土地质量地球化学调查共获得670321件表层组合土壤样品(0~20 cm)和167746件深层组合土壤样品(150~180 cm),覆盖面积约266.5万km^(2),囊括我国人口集中区和大部分耕地。对相关土壤样品均按统一标准分析了54项化学指标(Ag、As、Au、B、Ba、Be、Bi、Br、Cd、Ce、Cl、Co、Cr、Cu、F、Ga、Ge、Hg、I、La、Li、Mn、Mo、N、Nb、Ni、P、Pb、Rb、S、Sb、Sc、Se、Sn、Sr、Th、Ti、Tl、U、V、W、Y、Zn、Zr、SiO_(2)、Al_(2)O_(3)、TFe_(2)O_(3)、MgO、CaO、Na_(2)O、K_(2)O、pH、全碳和有机碳)。本文利用这些数据讨论了中国土壤54项指标的地球化学背景值、基准值及其上下限的划定方法和基本特征,并对我国耕地土壤背景与现行环境、养分等相关标准中各种阈值进行了对比。结果显示:在全国尺度上,各项指标表层与深层Spearman相关系数均高于0.50,表明表层土壤中大部分指标都继承了深层土壤的含量与分布特征。54项指标中仅C_(org)、TC、N、S、Se、Hg、Br、Cd和P等指标背景值相对基准值发生了较大变化。我国耕地土壤中,Cd的农用地污染风险筛选值在背景范围内,Hg、As、Pb和Cr的筛选值则高于背景上限值。由于许多指标的空间分布存在着巨大的差异,在全国范围内划定一个统一的背景值并不利于土壤资源的精细化管理和保护,因此有必要在全国尺度地球化学背景与基准的基础上建立区域尺度地球化学背景与基准,为政府部门合理制定相关土壤环境质量的标准和保护法规提供依据。

The Geochemical Survey of Land Quality conducted by the China Geological Survey from 1999 to 2021 collected 670321 composite surface soil samples(0-20 cm)and 167746 composite deep soil samples(150180 cm)across approximately 2.665 million km^(2),covering most densely populated areas and farmland in China.Each composite sample underwent analysis for 54 chemical indicators using a standardized method(Ag,As,Au,B,Ba,Be,Bi,Br,Cd,Ce,Cl,Co,Cr,Cu,F,Ga,Ge,Hg,I,La,Li,Mn,Mo,N,Nb,Ni,P,Pb,Rb,S,Sb,Sc,Se,Sn,Sr,Th,Ti,Tl,U,V,W,Y,Zn,Zr,SiO_(2),Al_(2)O_(3),TFe_(2)O_(3),MgO,CaO,Na_(2)O,K_(2)O,pH,total carbon and organic carbon).This study examines the methodologies and fundamental characteristics of establishing geochemical background values,baseline values,and their upper and lower threshold limits for the 54 soil indicators in China.Additionally,it compares various thresholds of the background of cultivated soil with existing environmental and nutrientrelated standards.The findings reveal that,on a national scale,most surface soil indicators exhibit content and distribution patterns inherited from deep soil,with notable changes observed only in the background values of specific indicators such as organic carbon,total carbon,N,S,Se,Hg,Br,Cd,and P.Spearman correlation coefficients for each indicator in both surface and deep soil consistently exceeded 0.50.Across the entire cultivated land in the country,only the upper limit of Cd background exceeds the risk screening value for soil contamination of agricultural land,while the upper limits of Hg,As,Pb,and Cr backgrounds were all lower than their respective risk screening values.Due to significant spatial distribution differences in many indicators,a simplistic national-scale background delineation is insufficient for refined soil resource management.Hence,the establishment of geochemical background/baseline at different scales based on national data is crucial to inform government regulations and standards for soil environmental quality management.