模拟降雨条件下典型土壤汞淋溶风险研究

Effect of simulated rain on leaching behavior of mercury from 22 typical soils and key influence factors identification

采集全国22种典型土壤,通过室内土柱试验,探讨雨水(p H 5.6)作用下污染土壤Hg(外源添加2mg/kg)的淋溶和释放特征,并对影响土壤Hg淋溶特性的因子进行分析.结果表明,22种土壤Hg的释放过程大致分为3类,第1类包括黑土?黑钙土?草毡土?水稻土?暗棕壤?福州黄壤?黄泥土?栗钙土,这8种土壤在整个淋溶过程中淋出液Hg浓度极低,未超过地下水III级标准(1μg/L).第2类包括广西红壤?贵州黄壤?棕壤?灰钙土?黄绵土等5种土壤,淋溶前期(2~3L)Hg含量较低,到淋溶中期含量显著上升,随后出现下降,到淋溶末期(5~6L)淋溶液Hg含量降低到III级标准以下.第3类土壤包括砖红壤?黄棕壤?紫色土?褐土?赤红壤?潮土?盐碱土?江西红壤?棕漠土等9种土壤,淋溶过程呈现2个阶段,当淋溶体积在4L之内,淋出液中Hg浓度较高,且变化比较剧烈,对环境及地下水威胁较大,超出4L后,Hg释放速率明显变缓,浓度降低到III级标准以下.模拟降雨条件下22种土壤Hg的释放率为0.33%~5.95%,最高的是贵州黄壤,最低是吉林黑土,平均为1.55%.逐步回归分析的结果表明,土壤有机质(OM)?p H及土壤汞含量(THg)对降雨作用下土壤Hg累计释放量(q)有重要作用,三者累计的决定系数为0.5865,回归方程为lnq=1.8+0.62ln THg-0.109p H-0.918ln

The leaching characteristics of mercury(2mg/kg Hg spiked in soil)and their influencing factors in22Chinesesoils under simulated rain(pH5.6)through soil column experiments were investigated in this study.The results indicatedthat the Hg release process of the studied soils could be divided into3classes.Firstly,concentrations of Hg in soilleachates from class1during leaching process was very low,and less than Groundwater Quality Standard for Class III(1μg/L),which included black soil from Jilin,chernozem from Jilin,felty soil from Tibet,paddy soil from Hunan,dark-brown soil from Jilin,yellow soil from Fujian,yellow soil from Jiangsu,chestnut soil from Inner Mongolia.Secondly,Hg in soil leachates from class2were comparatively low,less than Groundwater Quality Standard for Class IIIin the early of leaching process(2~3L),then it increased significantly at the middle of leaching process,and decreasedfrom5~15μg/L down to below Groundwater Quality Standard for Class III at the end of leaching process(5~6L),whichincluded red soil from Guangxi,yellow soil from Guizhou,brown soil from Liaoning,sierozem from Gansu and loessalsoil from Shanxi.Thirdly,The release mechanism of Hg in soils of class3appears to be consisted of two phases involvingthe initial rapid process(leachate are less than4L)followed by a slow continuous process(leachate exceeds4L),whichincluded the other9soils(latosol from Henan,yellow-brown soil from Jiangsu,purple soil from Chongqing,cinnamon soilfrom Hebei,latosolic red soil from Guangxi,fluvo-aquic soil from Tianjin,salt-affected soil from Jilin,red soil fromJiangxi,brown desert soil from Xinjiang).It was also found that the cumulative release rates of Hg from studied soils were accounted for0.33%(yellow soil from Guizhou)-5.95%(black soil from Jilin),on an average of1.55%.Stepwisemultiple regression analysis showed that release of Hg from soils might be related to soil organic matter(OM),pH,andsoil total Hg(THg)(lnq=1.8+0.62lnTHg-0.109pH-0.918lnOM)These3factors could describe58.65%of the variability inHg release from soils.