Heavy Metals Pollution And Ecological Risk Assessment Of Urban Soil

Urban soil is an important component of urban ecosystems. Human activities shtrongly changed physics and chemistry of the urban nature soil and exacerbated the soil's contamination, resulting in a series of ecological and environmental effects. Due to the rapid growth of population and industrial activity, the urban soils have been seriously polluted with heavy meatal, which resulted in a series of environmental problems. The objectives of this study were to the conditions of the heavy metal contamination in urban soil, the main carrier of heavy metal in soil and ecological risk assessment1. Results showed that selected urban topsoils were heavily polluted by heavy metal. The content of Pb ranged from 48.4 to 2273.6mg/kg with a mean content of 257.0 mg/kg. The content of Cr ranged from 51.1 to 460.1 mg/kg with a mean content of 104.2mg/kg. The content of Mn ranged from 330.3 to 1197.2mg/kg, with a mean content of 538.6mg/kg. The content of Zn ranged from 162.3 to 569.9mg/kg with a mean conten of 364.2mg/kg. The content of Cu ranged from 47.1 to 278.9mg/kg with a mean content of 111.3mg/kg.In Hangzhou city, the heavy metal content strongly varied greatly. The content of Pb ranged from 31.9 to 344.5mg/kg with a mean content ofl 34.1 mg/kg. The content of Cr ranged from 29.3 to 119.6mg/kg with a mean content of 63.3mg/kg. The content of Mn ranged from398.6 to 1042.0mg/kg with a mean content of 572.2mg/kg. The content of Zn ranged from106.7 to 873.1mg/kg with a mean content of 282.9mg/kg. The content of Cu ranged from 35.1 to 177.3mg/kg with a mean content of 93.0mg/kg. Pb and Zn varied greatly in range, CV are 55% and 55%, secondly Cu and Cr, CV are 44% and 35%, and the last Mn and Cd, CV are 25% and 22%2. The magnetic material in urban topsoils was extracted by magnet in combination with the ultrasonic dispersion. The relationship between magnetic fraction content with the soil magnetic susceptibilities was analysed. The results showed: magnetic material content had a highly significantly correlation with soil magnetic susceptibilities. The mineral component are made up of Quartz(SiO₂), Hematite (α-Fe₂O₃ ), Magnetite ( Fe₃O₄ ) and Kaoline(Al2Si205(0H)4)c3. The concentration analysis of heavy metals showed that heavy metal enriched on agnetic material. The enrichment factor in Luoyang city ranged from 3.3 to 15.8, and the enriching order follows in Fe>Cr>Cu>Mn>Pb>Zn, the factor of Fe is the largest and the factor of Zn is the smallest. In Hangzhou city, the enrichment factor ranged from 2.9 to 20.1, and the enriching order follows in Fe>Cr>Mn=Cu>Zn>Pb, the factor of Fe is the largest and the factor of Pb is the smallest. At the same time, the heavy metal content between magnetic and non-magnetic part of the soil is significantly positively correlated and the correlation factor of Mn, Zn, Pb, Cr and Cu are 0.778, 0.839, 0.937, 0.858 and 0.880 respectively in Luoyang city. The correlation factor of Mn, Zn, Pb, Cr and Cu are 0.802, 0.816, 0.913, 0.963 and 0.789 respectively in Hangzhou city.4. Using TCLP procedure, ecological risk of heavy metal in urban topsoils was evaluated. Results indicted that the heavy metals contents extracted by two reagents are significantly related to the total contents. The extracted content increases with an increaseing of total content. The content extracted by the EDTA reagents is generally higher than the content of the TCLP extracting. Compared with the TCLP international standards, we found that the heavy metals extracted by TCLP in urban topsoils of Hangzhou city and Luoyang city are higher than the limit Cd and Pb pollution are the most severest, followed by Zn. All of the Cu content of the soil are less than the limit. In Luoyang city , for Cd, 80% of tolal samples had higher than the international standard(0.5mg/kg), for Zn, 30% of the samples had higher than the international standard(25mg/kg) and for Pb, all of the samples had higher than the international standard(5mg/kg) , in the same way, In Hangzhou city , for Cd, 75% of total samples had higher than the limit (0.5mg/kg), for Zn, 40% higher the international standard(25mg/kg) and all of the Pb higher the international standard(5mg/kg). Compared with soil environmental quality standard, the TCLP procedure will be more effective on the environmental risks of soil heavy metal pollution and the impact on people's health, which is concerned about the hazards of heavy metals effective ingredients.