不同大气沉降区Pb化学形态及风险评估

Chemical Speciation and Risk Assessment of Pb in Different Pb Sedimentation Area

环境介质中重金属Pb的毒性不仅与其含量有关,更多地取决于其生物有效性,Pb在介质中的赋存形态是衡量其环境效应的关键参数。土壤是大气降尘的最终归宿,大气降尘已经成为土壤Pb的重要输入途径之一,需要结合大气降尘比较不同降尘区降尘与土壤中重金属形态分布特征,将土壤和降尘中的Pb活性进行形态分级,评估大气降尘和土壤中的Pb形态分布,揭示不同大气沉降区Pb的毒性及可能产生的环境效应,为明晰不同区域Pb沉降特点,科学进行生态风险评价提供理论依据。调研了大气Pb高沉降区(济源豫光金铅冶炼厂周边)、低沉降区(郑州西北郊区农田)的土壤及大气降尘中Pb污染状况,并采用修正的BCR提取法对土壤和大气降尘中Pb的化学形态进行了分析和风险评估。结果表明,大气Pb低沉降区的土壤中及降尘中Pb平均质量分数分别为(7.67±0.20)mg?kg-1和(76.47±0.73)mg?kg-1;大气Pb高沉降区土壤及降尘中Pb平均质量分数分别为(102.91±0.45)mg?kg-1和(630.16±0.28)mg?kg-1,均显著高于大气Pb低沉降区。大气Pb低沉降区的土壤中Pb主要以残渣态形式存在,其比例为61.17%,其次是可还原态,为31.73%,弱酸态为1.44%,可氧化态为5.67%,处于低风险等级范围内;而降尘中Pb大多以可还原态形式存在,其比例为62.38%,其次是残渣态,为19.60%,弱酸态为11.54%,可氧化态为6.48%,处于中等风险范围内,。大气Pb高沉降区的土壤和降尘中Pb均以可还原态为主,其中土壤中Pb的可还原态占比为75.82%,降尘中Pb的可还原态为37.00%;土壤中Pb的弱酸态占比为5.12%,可氧化态为9.83%,残渣态为9.23%,处于低风险等级;降尘中Pb的弱酸态占比为26.47%,可氧化态为28.71%、残渣态为7.82%,处于中等风险等级。大气Pb低沉降区土壤及降尘的风险评估指数(RAC)值分别为1.44%、1.54%,而大气Pb高沉降区分别为5.12%、26.47%,前者显著低于后者,表明大气Pb高沉降区土壤及降尘中Pb具有更高的生物活性。

The toxicity of Pb in environmental media is not only related to its content,but also depends more on its bioavailability.The presence of Pb in media is a key parameter to measure its environmental effects.Soil is the final destination of atmospheric dustfall.Atmospheric dustfall has become one of the most important input ways for soil Pb.It is necessary to compare dustfall in different dustfall areas with heavy metal form distribution characteristics in soil in combination with atmospheric dustfall,and to classify the Pb activity in soil and dustfall.Evaluate the distribution of atmospheric dust and Pb in the soil,reveal the toxicity of Pb in different atmospheric deposition areas and possible environmental effects,and provide theoretical basis for clarifying the characteristics of Pb settlement in different regions and scientifically conducting ecological risk assessment.The status of Pb pollution in soil and atmospheric dust in high Pb sedimentation areas(around the Jiyuan Yuguang gold-lead smelter)and low sedimentation areas(fields in the northwestern suburbs of Zhengzhou)was investigated.The modified BCR method was used to analyze and risk assess the chemical form of Pb in soil and atmospheric dust.The results showed that mass fraction of Pb in soil and atmospheric dust in low Pb sedimentation area was(7.67±0.20)mg·kg^-1 and(76.47±0.73)mg·kg^-1.Pb mass fraction in soil and atmospheric dust in high Pb sedimentation area was(102.91±0.45)mg·kg^-1 and(630.16±0.28)mg·kg^-1.Pb in the soil with low Pb concentration in the atmosphere was mainly in the form of residue state,with a ratio of 61.17%,followed by a reducible state of 31.73%,the weak acid state of 1.44%,and the oxidation state of 5.67%,which was in a low-risk range;while the Pb in atmospheric dust was mostly in the form of reducible state,with a ratio of 62.38%,followed by the residue state of 19.60%,the weak acid state of 11.54%,and the oxidizable state of 6.48%,which was in a moderate risk range.The Pb in high Pb sedimentation area was mainly in the reducible state,with the ratio of 75.82%in the soil and of 37.00%in atmospheric dust.The weak acid,oxidizable state and residual state ratio of Pb in soil was 5.12%,9.83%and 9.23%,respectively,which was in a low-risk grade.The weak acid state,oxidizable state and residue state ratio of Pb in atmospheric dust was 26.47%,28.71%and 7.82%,respectively,which was in a moderate risk grade.The risk assessment index(RAC)values for soil and atmospheric dust in low Pb sedimentation areas were 1.44%and 11.54%,while in the high Pb sedimentation areas were 5.12%and 26.47%,respectively,which indicated that the Pb in soil and dust in high Pb sedimentation areas had higher biological activity.