贵州铅锌冶炼区农田土壤镉铅有效性评价与预测模型研究

摘要

Distribution of different metal pools and soil-solution partitioning models are able to provide information on different available fractions of heavy metals and their leaching capacity, thus are crucial for risk assessment and remediation practices. 30 historically contaminated arable soils with a wide range of soil properties and contaminated status were collected from Pb and Zn mining areas in Bijie City of Guizhou Province. 5 typical-type soils without apparent contamination (clean soils) were collected from Guizhou Province and were artificially spiked with CdSO4 or Pb(NO3)2 to form single-contaminated soils with different Pb/Cd concentrations. After aging for 3 months, chemically reactive metal pools, operationally defined by 0.43 mol/L HNO3, 0.1 mol/L HCl and 0.005 mol/L DTPA, and directly available metal pool, defined by 0.01 mol/L CaCl2 extraction, were determined to assess Cd and Pb contamination and to establish soil-solution partitioning models by using extended-Freundlich type equations. Chemical extraction was selected to best indicate total metal contents in soils. Factors affecting soil-solution partitioning were discussed. Results indicated that the ratio of directly available Cd and Pb pools to their total contents in historically contaminated soils were 4 and 223 times, respectively, lower than those in artificially-spiked soils. However, total reactive metal pools in historically contaminated soils were larger than those in these artificially-spiked soils and posed a great potential risk for agricultural production and human health vie food chain. Freundlich type equations perfectly described the relationships between total metal content and reactive metal pool. 0.43 mol/L HNO3 extraction was selected to best predict total metal content in arable soils and the percentage of variation explained reached up to 99% and was able to replace the total metal content to indicate soil contamination. pH dependent Freundlich type equations were also able to accurately predict directly available Cd (R2=0.90) and Pb (R2=0.81) concentrations. Total reactive Cd pool controlled Cd concentration in soil solution. Soil pH was always the most important factor affecting Cd and Pb bioavailability, but soil organic matter and available phosphorus should also be considered to improve model prediction of directly available Pb pool.%农田土壤重金属的不同活性库分布和土壤-溶液分配模型能够提供重金属的生物有效性和浸出能力等信息,因而在风险评价和修复实践中非常重要.本研究采集毕节铅锌冶炼区30个历史污染农田土壤,同时在贵州省范围内采集5种类型背景土壤制成不同浓度Pb/Cd单一污染土壤;经3个月老化,分别测定由0.43 mol/L HNO3、0.1 mol/L HCl和0.005 mol/L DTPA提取态表征的重金属反应活性库以及由0.01 mol/L CaCl2提取态表征的直接有效库;分析铅锌冶炼区农田土壤Cd、Pb不同有效库的分布特征,建立土壤-溶液分配模型,并讨论土壤理化性质的影响.结果表明:历史污染土壤中Cd和Pb的直接有效库占全量比例分别比人工污染土壤低4倍和223倍,然而历史污染土壤Cd和Pb的反应活性库(0.43 mol/L HNO3提取态)占全量比例要高于相应人工污染土壤中的比例.拓展Freundlich形式吸附方程能够准确描述各提取态表征的Cd和Pb活性库与土壤全量Cd和Pb的关系,尤其0.43 mol/L HNO3提取方法能够克服土壤理化性质对土壤Cd和Pb提取的影响而与总量建立极显著的相关关系.pH依附性Freundlich吸附方程准确描述了Cd和Pb的总反应活性库分别与土壤溶液Cd和Pb的关系,对于Pb而言,还要考虑土壤有机质和有效磷的影响.本研究可为矿区农田土壤重金属污染评价、修复以及农田有效态标准的推导提供参考.