Characteristics And Heavy Metal Contamination Of Urban And Suburban Soils In Hangzhou City

Urban and suburban soils, created and/or modified in the process of urbanization, are complex and heterogeneous in their structure and composition. The urban and suburban soils are affected greatly by human activity. In contract to natural soils, human activity is the predominant active agent in the modification of these soils. There is a higher probability of historic anthropogenic contamination in the urban and suburban soils than in undeveloped area. The extent of anthropogenic influence on soil characteristics depends on both current and previous land use in most urban areas. Comprehensive study of these human-modified urban and suburban soils is much needed for urban and suburban soil management and land use decision. Hangzhou city is an attractive socio-econimic center of Zhejiang province, China. Due to the rapid growth of human and industrial population, the environmental quality of surface soils in the city has been seriously affected. Most of the land in this area was intensively used for different purpose including residence, industry, agriculture, commerce, and tourist. Soil properties were continuously being altered However, no systemic study of characteristics and heavy metal accumulation of the urban and suburban soils has attempted in the city. Therefore, this study was conducted to examine physical and chemical properties, and heavy metal contamination of the urban and suburban soils under different land uses in the city. A total of thirty-two urban and suburban soils and two background (control) soils were sampled from the Hangzhou city for characterizing particle composition, bulk density, organic matter, available K (Nl^OAc-extractable), available N (alkaline hydrolysable N), Olsen-P (NaHCO3 extractable), population of organisms, and total concentrations and fractions of eight heavy metals (Cd, Co, Cr, Cu, Ni, Pb, Zn, Mo and Mn). The principal component analysis was employed for relations among the heavy metals.From suburban zone to center of the city, sand, gravel,soil clay content, organic matter,48pH, total P, and Olsen-P tended to increase.Population and species of organisms varied with land use. Data indicate that the urban and suburban soils in the city were anthropogenically contaminated by heavy metals to a great extent. Lead was the metals most enhanced with about 65 times as the concentration in the background soils. The degree of heavy metal contamination was in the order of suburban industrial zone > urban commercial zone> tourist zone, residential and education zone, and suburban agricultural zone. Mean concentrations of all heavy metals except for Co were the lowest in the suburban agricultural soils, and those were the highest in the suburban industrial soils with exception of Pb. The comprehensive environmental quality of the soils decreased in the order of suburban agricultural zone > tourist zone, residential and education zone > urban commercial zone > suburban industrial zone.An optimized European Community Bureau of Reference three-step sequential extraction procedure was applied to heavy metal fractionation of the soils. Four operationally defined fractions were identified: acid extractable, reducible, oxidizable and residual. More than 60% of Cd, Co, Cr and Ni was associated with residual fraction and reflects relative low. Of the four remaining heavy metals that are considered to be high release potential, copper was dominantly associated with oxidizable fraction followed by reducible fraction. Lead was primarily associated with the reducible fraction with a mean of 65%. Zinc and Mn had only one-third of their total concentrations in the residual fraction, but one-third in the reducible and one-fifth in the acid extractable, which is susceptible to release.It was suggested that monitoring heavy metals of the urban and suburban soils should be as a routine content for city environmental monitor.