Ecological Risk Assessment of Heavy Metals in Industrial Land and Farmland Soils of Tianjin with Toxicity Characteristic Leaching Procedure

Toxicity characteristic leaching procedure (TCLP) is a currently recognized method by the USA for evaluation of heavy metal pollution in soils, by extracting the effective state of heavy metals in soils to evaluate the degree of heavy metal pollution and ecological risk of the pollution area. In this study, the TCLP method was used for extracting the effective state of heavy metals in industrial land and farmland in Tianjin. The total heavy metals and the effective state of heavy metals were measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Atomic Fluorescence Spectrometry (AFS), respectively. Single Pollution Index and Comprehensive Pollution Index were used for the ecological risk assessment of heavy metal. Results show that Zn is the primary pollutant, which comes from galvanizing and metal products factories, and electroplating plants. Secondary to Zn pollution is the Pb and Cu pollution but no pollution of Cd. Pb and Zn may have the same source or alternatively Pb is associated with Zn. Most of the soil is safe with heavy metal pollution rates of less than 30%, but the farmland is slightly polluted by Zn. Total heavy metals is the main influence for the effective state of heavy metal. When Zn concentration is more than the environmental quality standard limits (300 mg/kg) and Pb concentration is more than 80 mg/kg, effective states of Zn and Pb show a positive correlation with total metals. Therefore, TCLP method can be used to quantify the total and effective state of heavy metals in soil.