铅锌矿区不同土地利用类型铅污染特征及其影响因素

Pb Pollution Characteristics and Their Affecting Factors in Different Land Use Types in Lead-Zinc Mining Zone

矿区周围土壤的重金属含量和形态分配特征是了解矿区土壤污染状况的重要前提,找到其影响因素是关键。研究以陕西凤县银洞梁铅锌矿区不同土地利用类型土壤为研究对象,基于欧共体提出的BCR三步法,研究了该矿区不同土地利用类型土壤中Pb的化学形态及影响因素。结果表明:该矿区不同土地利用类型土壤总Pb的含量差异显著,其中农地(410.1mg/kg)>林地(315.9mg/kg)≈草地(313.6mg/kg);且不论何种土地利用类型,土壤中的Pb形态均以铁锰氧化物结合态为主,其次是酸交换态、残渣态、有机硫化物结合态;矿区土壤中各形态Pb含量存在明显的空间分异,草地与林地土壤中的总Pb含量差异不显著,但草地土壤中的酸交换态Pb的含量和分配系数占比要显著大于林地;土壤中Pb的含量和形态分配各受土壤理化性质的影响,铅总量主要受砂粒和黏粒的影响,酸交换态仅与总量和土壤含水量有关;铁锰氧化结合态与总量和pH值相关;有机硫化物结合态和残渣态与总量、有机质以及当地气候因素有关。总体而言,不同耕作方式、管理制度及矿山开采引起的人类活动对Pb的污染特征产生了重要影响。其中农地土壤中的Pb具有更高的潜在生物有效性,当处于还原条件下时,这些土壤可能存在重金属Pb的潜在危害。

Soil pollution by heavy metals was characterized in the mine tailing and surrounding farmland,woodland and grassland in an old Pb-Zn mining zone of Baoji.Thirty-eight soil samples were taken and the total Pb concentrations of soil samples were determined by acid digestion,and the chemical fractionation of Pb was analyzed with the modified BCR sequential extraction method.In the present study,it was found that the characteristics of soil Pb accumulation in different land use types were significant different,the contents of soil Pb decreased in the order：farmland（410.1 mg/kg）〉woodland（315.9 mg/kg）≈ grassland（313.6 mg/kg）.At the same time,the results of sequential extraction showed that the most of Pb in soils was associated with Fe-Mn oxides faction,followed by acid-exchangeable faction and organic-sulfide faction,and residual faction was rather low.Additionally,the spatial distribution characteristics of total Pb concentration and fractions were significant different in three land use types.The soil total Pb concentration of woodland was no significant difference from that of the grassland,while the average percentage of acid-exchangeablefraction of the grassland was significantly higher than that of the woodland.Meanwhile,the total Pb concentration and speciation characteristics were influenced by soil physical and chemical properties as well as land use types.There were positive correlations between soil Pb accumulation,sand particles,and pH in farmland and woodland,which were related to the anthropogenic activities such as mining and transport of metal ores.There were negative correlations between the contents of total Pb and sand particles in the grassland.There were positive correlations among the total Pb,clay particles,and Fe-Mn oxides fraction.It was related to mine soils and superficial geochemical forms.In general,the anthropogenic activities such as mining,cultivation practices and management aprroaches had the important impact on the Pb pollution characteristics in soils of the mining area.