许昌市街道灰尘重金属含量及其粒径效应

Concentrations and particle size effect of heavy metals in the street dust of Xuchang City

对许昌市街道灰尘样品进行了重金属含量和粒度测试,研究了重金属在各粒径上的富集规律及其原因。结果表明:许昌市街道灰尘主要以粉砂为主(平均为57.62%),砂粒次之(平均值为25.18%),粘粒含量最少(平均值为17.21%)。街道灰尘中Cr、Cu、Zn、Pb、Mn、Ni和Co含量范围分别为60.9—277.4μg?g^(-1)、15.5—116.4μg?g^(-1)、76.5—398.7μg?g^(-1)、25.1—63.7μg?g^(-1)、356—519μg?g^(-1)、9.0—25.6μg?g^(-1)和7.9—10.4μg?g^(-1),平均值分别为96.8±42.7μg?g^(-1)、35.4±23.8μg?g^(-1)、145.3±67.2μg?g^(-1)、41.9±10.4μg?g^(-1)、408±35.7μg?g^(-1)、18.5±4.1μg?g^(-1)和9.0±0.7μg?g^(-1)。Zn、Pb、Cu和Cr的平均值均高于土壤背景值,分别为背景值的2.42倍、2.14倍、1.80倍和1.52倍,污染较重。而Mn、Ni和Co值富集程度较低,污染较轻。研究发现,Cu、Pb、Zn和Cr与50—100μm粗粉砂相关性显著,Mn和Ni与10—50μm细粉砂相关性较高,但其含量并未随着粒径的进一步减小而增强;而Co与<10μm的粘粒组分相关性较强,其粒径效应明显。街道灰尘中不同重金属含量粒径效应的不同可能与重金属的吸附作用和同晶替换作用的相对强弱有关。

Background aim and scope Street dust is an important pathway for pollution material in the urban environment. Street dust often becomes a sink for both industrial and residential pollutants, including waste incineration residues, vehicle exhaust emissions, and products of tire wear, metallic fragments, fossil fuel combustion emissions and garden soil. Among the pollutants in street dust, heavy metals are often more severe than others. Heavy metal elements are often not decomposed by microorganisms and may become enriched through the food chain, affecting human health, especially that of children and elderly people. Moreover, heavy metals have more affinity to establish metallic bonds with ferrous material, which leads to enhancement of the magnetic susceptibility of street dust. Many studies have reported excellent relationships between magnetic susceptibility and the levels of some heavy metals in street dust or industrial/urban soils, this relationship forms the basis for the use of magnetic methods in pollution studies. Therefore, magnetic susceptibility characteristics of street dust can be used to refl ect a city＇s heavy metal pollution. Furthermore, heavy metal enrichment regularity in street dust research has important signifi cance. Along with the remarkably fast development of the economy and urbanization of China, environmental pollution is becoming a more serious problem in many cities. Xuchang City is one core city of the Central Megalopolis of China; industrial pollution and vehicle exhaust emissions have aggravated the city＇s pollution in recent years, especially the particulate matter pollution. At present particle size effect of heavy metal of Xuchang City street dust has not been reported. This present research studied the Xuchang City street dust particle size and heavy metals concentration. Our main aims are to analyze the particle size and heavy metal concentration and to identify the relationships between them. The results may provide useful information for the establishment of control policies and environmental risk assessment of street dust in China. Materials and methods Particle size and heavy metals in street dust samples of Xuchang City were analyzed. The enrichment regularity of heavy metals in different partical size and the reason of it were discussed. Twenty two street dust samples were collected around Xuchang. Street dust samples were collected by ground sweeping with a polyethylene scoop and a brush, and then the sample was put into a pocketsized sealable plastic bag. All samples were air-dried in the laboratory for more than 24 hours, and then passed through a 1-mm sieve to remove leaves, refuse and small stones before measurement in the laboratory. All sieved samples were fi nely ground, passed through a 200 mesh sieve and pressed into a tablet. Particle sizes of samples were determined using Mastersizer 2000 Laser Particle Sizer. Heavy metal concentrations of samples were determined using a PANalytical PW2403/00 X-ray fl uorescence（XRF） analyzer. Blank samples and the China national reference materials GSD-9 were used for accuracy control; the analytical accuracy was better than 10%. Results The results showed that street dust was dominated by silt（average = 57.62%）, followed by sand（average = 25.18%）, and clay（average = 17.20%）. Cr, Cu, Zn, Pb, Mn, Ni, and Co content in street dust ranged 60.9 — 277.4 μg·g^（-1）, 15.5 — 116.4 μg·g^（-1）, 76.5 — 398.7 μg·g^（-1）, 25.1 — 63.7 μg·g^（-1）, 356 — 519 μg·g^（-1）, 9.0 — 25.6 μg·g^（-1）, and 7.9 — 10.4 μg·g^（-1）, with an average value of 96.8 ± 42.7 μg·g^（-1）, 35.4 ± 23.8 μg·g^（-1）, 145.3 ± 67.2 μg·g^（-1）, 41.9 ± 10.4 μg·g^（-1）, 408 ± 35.7 μg·g^（-1）, 18.5 ± 4.1 μg·g^（-1）, and 9.0 ± 0.7 μg·g^（-1）, respectively. The average values of Zn, Pb, Cu, and Cr were 2.42, 2.14, 1.80, and 1.52 times higher than that of soil background values, indicating heavy pollution of these metals. Discussion The enrichment degree of Mn, Ni, and Co was relatively low. The results showed that the concentrations of Cu, Pb, Zn, and Cr were relatively strong positive with coarse silt, while Mn and Ni were relatively strong positive with fine silt. But these heavy metals content did not further increase with decreasing particle size. The concentrations of Co were relatively strong positive with clay, and the particle size effect of it was obvious. The differences in particle size effect of different heavy metals may be related with the relative strength of adsorption and isomorphous replacement. Conclusions Xuchang City street dust was dominated by silt, followed by sand and clay. The average values of Zn, Pb, Cu, and Cr were 2.42, 2.14, 1.80, and 1.52 times higher than soil background values, indicating heavy pollution of these metals. Cu, Pb, Zn, and Cr were relatively strong positive with coarse silt, while Mn and Ni were relatively strong positive with fine silt. Co was relatively strong positive with clay. Recommendations and perspectives Initial data and useful information for establishing relevant pollution-control guidelines are provided.