盐渍化条件下污灌区土壤重金属的释放特征

Release of heavy metals from soils under the different salinity levels in the wastewater-irrigated area of Tianjin City

以受盐渍化和重金属双重胁迫的天津污灌区土壤为研究对象,通过径流实验和淋溶实验,探讨盐渍化土壤重金属的释放特征及对水质安全的影响.研究的盐分种类为污灌区土壤盐渍化进程中的主要盐分Na Cl,设置的盐度梯度为7个,添加质量分数为0(CK)~5%,污染土壤中Cd、Pb和Hg含量分别为2.21、234.1和0.601 mg·kg^(-1).结果表明,(1)不同盐度处理下产流所需时间为(51'25″±15″),盐度对径流产流时间影响不显著;(2)随着Na Cl盐度梯度的提高,土壤径流和淋溶液中Cd、Pb和Hg的累计释放量均显著上升.Cd累计释放量从CK的53.40μg·kg^(-1)(径流)和55.63μg·kg^(-1)(淋溶)分别提高到5%Na Cl盐度处理的122.56μg·kg^(-1)(径流)和135.79μg·kg^(-1)(淋溶),Pb的累计释放量从CK的168.30μg·kg^(-1)(径流)和94.44μg·kg^(-1)(淋溶)分别提高到5%Na Cl盐度处理的340.68μg·kg^(-1)(径流)和201.93μg·kg^(-1)(淋溶),Hg的累计释放量从CK的39.66μg·kg^(-1)(径流)和9.60μg·kg^(-1)(淋溶)分别提高到5%Na Cl处理的89.37μg·kg^(-1)(径流)和11.97μg·kg^(-1)(淋溶).同时,径流及淋溶液中可溶态重金属含量显著上升,颗粒态含量有所下降,其所占比例也显著下降.Cl-含量与重金属累计释放量之间关系可以用线性或对数模型拟合.(3)高盐度处理下径流和淋出液中Cd浓度超过地下水水质Ⅲ类标准,对环境及地下水存在一定威胁;径流和淋溶前期Pb浓度超过Ⅲ类标准;径流和淋溶过程中Hg浓度均超过Ⅲ类标准,风险较高.本研究结果表明高强度降雨强度下污染农田土壤重金属释放风险不可忽视.

This study was designed to understand the release characteristics of Cd,Pb and Hg from soil in the wastewater-irrigated area of Tianjin City,and to assess its risk to groundwater contamination under different salinity level（ 0 ~ 5%） by using simulated rainfall tests and leaching experiments. The amounts of metals in tested soil were 2.21 mg·kg-1 for Cd,234.1 mg·kg-1 for Pb and 0.601 mg·kg-1 for Hg,respectively. The results showed that,（1）Runoffs generated at（ 51＇25″±15″） after simulated rainfall tests started,which were irrelevant to soil salinity levels.（2）As Na Cl spiked into soil,contents of heavy metals in runoffs/leachates markedly increased,from 53.40（ runoffs）/55.63（ leachates） μg·kg-1 at CK to 122.56/135.79 μg·kg-1 at 5% Na Cltreatment for Cd,from 168.30/94.44 μg·kg-1 to 340. 68/201. 93 μg·kg-1 for Pb,and from 39. 66/9. 60 μg·kg-1 to 89. 37/11. 97 μg·kg-1 for Hg,respectively. It was also found that the dissolved metal in the runoffs/leachates significantly increased,while the particulate metal distinctly decreased with the increasing soil salinity levels. Besides,quantitative release amounts of heavy metals from soils in the runoffs/leachates as functions of Cl-contents in soils could be simulated by the linear or logarithm model.（3）Concentrations of Cd in the runoffs/leachates under the high soil salinity levels（ 2% and5%）,concentrations of Pb in the early stage of experiments under all studied soil salinity levels,and concentrations of Hg under all studied soil salinity levels were comparatively high,more than Groundwater Quality Standard for Class Ⅲ,which may cause a high risk to groundwater through rainfall.