城市植物叶面尘粒径和几种重金属(Cu、Zn、Cr、Cd、Pb、Ni)的分布特征

为研究城市植物叶面尘粒径及重金属元素(Cu、Zn、Cr、Cd、Pb、Ni)的分布规律和污染特征,以西安市不同功能区大叶女贞(Ligus-trum lucidum)和小叶女贞(Ligustrum quihoui)叶面尘为研究对象,用激光粒度分析仪测定叶面尘的粒径分布,用原子吸收分光光度计测定叶面尘重金属质量比,并探讨了叶面尘重金属的可能来源。结果表明,大叶女贞和小叶女贞叶面尘粒径小于50μm。前者叶面尘粒径累积曲线呈双峰分布,平均粒径和粒径峰值从大到小为相对清洁区、工业区、居住文教区、交通枢纽区、商业区;后者呈单峰分布,平均粒径和粒径峰值由大到小为工业区、居住文教区、交通枢纽区、商业区和相对清洁区。不同功能区叶面尘中Cu、Zn、Cr、Cd、Pb、Ni有明显的富集,其质量比分别为(325.5±72.6)mg/kg、(3 965.6±1 112.9)mg/kg、(349.2±149.3)mg/kg、(35.3±6.8)mg/kg、(1 182.0±355.1)mg/kg、(324.1±129.5)mg/kg,为陕西省土壤背景值的7.9～20.8、29.7～77.9、2.6～11.1、262.8～489.4、26.4～71.8和6.9～18.9倍。不同功能区2物种叶面尘各重金属质量比差异显著(p<0.001),物种间差异不显著(p>0.05)。叶面尘中Zn、Pb、Ni、Cr的质量比以工业区最高,Cu、Cd以交通枢纽区最高,其次为商业区,居住文教区和相对清洁区负荷最低。研究认为,叶面降尘中的重金属可能来自外源输入。

Distribution features of particle size and heavy metal elements in foliage-captured dust

This paper takes as its target to reveal the distribution features of particle size and heavy metal elements(Cu,Zn,Cr,Cd,Pb,Ni) in foliage-captured dust,by using the foliar dust samples of Ligustrum lucidum and Ligustrum quihoui collected from different areas of Xi’an,including its industrial area (IA),commercial and service area(CSA),heavy-traffic area(HTA),residential and educational area(REA) and comparatively pollution-free area(CPFA).Size distribution of the collected samples was determined with a laser particle size analyzer,while the concentrations of heavy metals in the samples were measured with an atomic absorption spectrophotometer.We have also discussed the likely sources of the heavy metals in the dust.The particulate size of the foliar dust proves to be less than 50 μm,and PM10(particulate matter with aerodynamic diameter less than 10 μm) makes up between 13.8% and 63.1% of the particles.There exist two peak values of the foliar dust for Ligustrum lucidum,with its mean and peak values of the dust size being highest in CPFA,and followed by IA,REA,HTA and CSA.For Ligustrum quihoui,however,the size distribution of the foliar dust proves to be normal,with its mean and peak value in the increasing order of CPFA,CSA,HTA,REA,IA.Heavy metals are significantly enriched in foliar dust,with its mean concentrations being(325.5±72.6) mg/kg for Cu,(3 965.6±1 112.9) mg/kg for Zn,(349.2±149.3) mg/kg for Cr,(35.3±6.8) mg/kg for Cd,(1 182.0±355.1) mg/kg for Pb,(324.1±129.5) mg/kg for Ni.Significant differences are found in heavy metals among different urban areas.By contrast,Cu,Zn,Cr,Cd,Pb and Ni concentrations in foliar dust prove no significant difference between Ligustrum lucidum and Ligustrum quihoui.The results of our investigation suggest that the contents of Zn,Pb,Ni and Cr in the foliar dust are the highest in IA with the greatest values observed in HTA for Cu and Cd.However,the contamination of heavy metals proves relatively minor in REA and CPFA.More fine dust particles are found with heavy metals accumulated in the leaves of the two plants.Heavy metals in foliar dust exceed those in background soil in Shaanxi to a factor of 7.9-20.8,29.7-77.9,2.6-11.1,26.4-71.8,6.9-18.9 and 262.8-489.4 for Cu,Zn,Cr, Pb,Ni and Cd,respectively,indicating that the foliar heavy metal dusts are likely to be caused by the industrial pollution,vehicle emission,and/or other anthropogenic sources.The proportion of heavy metal particles in the foliar dust proves to be mutually correlated,revealing the fact that the foliar dust indeed originated from the extraneous source.