Pollution Characteristics And Source Apportionment Based On PMF Of Soil Heavy Metals In Cropland Near A Contaminated Site

Soil is not only an important part of the ecosystem, but also a main base of the agricultural production. With the unreasonable development of the economy and society, soil pollution is becoming more and more serious, especially for the soil heavy metals. Identifying the sources of the heavy metals is the basic requirement for the pollution abatement in cropland.This paper focused on the cropland near the lead battery plants contaminated site in Zhejiang Province. The concentrations of the heavy metals (Cd、Pb、As、Hg、Zn、Cu、 Cr、Ni、Co、Mn) and other elements (Al、P、S、K) in104topsoil samples were measured. The enrichment characteristic and potential ecological risk of soil heavy metals were analysed based on the local soil background concentration and environmental quality standard for soils. The distribution characteristics of the speciations for soil Cd and Pb were analysed using the sequential extraction procedure (GB/T25282-2010) in40soil samples. The spatial distribution of soil heavy metals were studied by geostatistics. Furthermore, the positive matrix factorization (PMF) receptor model was employed to apportion the sources of heavy metals. The results showed that:(1) Results showed that accumulated phenomenon of heavy metals had been universal existed in the study area, indicating that human activities have been played a role in adding these elements to the topsoils. The average concentration of soil Cd was0.33mg kg-1, Cd concentrations in35.58%of the topsoil samples exceeded the Type II limit (Cd>0.30mg kg-1) set by Chinese environmental quality standard for soils, with the enrichment factor was1.92. Therefore, soil Cd accumulation was the most serious. The average concentration of soil Pb was35.91mg kg-1, Pb concentrations in46.15%of the topsoil samples exceeded the local soil background concentration. The average concentration of soil As was16.25mg kg-1, As concentrations in95.19%of the topsoil samples showed the accumulated phenomenon in the topsoil. The average concentrations of soil Zn, Cr were114.87、77.85mg kg-1respectively, higher than the local soil background concentration. For soil Cu、Ni、Hg, their concentrations were close to their corresponding local soil background concentration.(2) The analysis of the speciations for soil heavy metals indicated that, soil Cd gave priority to the mild acido-soluble fraction (42.35%), followed by the reducible fraction (40.91%), the average content of the residual fraction and the oxidisable fraction were low (11.78%、4.97%, respectively). The average content of the water-soluble fraction was very low, the value was0.003mg kg-1. The distribution of the speciations for soil Pb showed a different characteristic when compared with soil Cd. Soil Pb gave priority to the reducible fraction (54.89%), followed by the residual fraction (32.62%), the average content of the oxidisable fraction and the mild acido-soluble fraction were low (8.99%、3.50%, respectively). The average content of the water-soluble fraction was also very low, the value was0.21mgkg-1.(3) The potential ecological risk of soil heavy metals was analysed. The results indicated that61.54%of soil samples existed ecological hazard of Cd, indicating high pollution of soil Cd. There were also22.12%of soil samples with moderate ecological risk of Hg. According to the average value of potential ecological risk index, the degree of potential ecological risk of soil heavy metals was as the follows:Cd> Hg> As>> Pb> Cu> Ni> Cr> Zn. The average value of the comprehensive ecological risk index was137.24, there were21soil samples with moderate ecological risk (150≤RI<300), and4soil samples with strong ecological risk. The highest value of RIs was825.29, showed the very strong ecological risk. Therefore, soil Cd which demonstrated a higher environmental risk should be given priority attention in the agricultural production.(4) The spatial distribution of soil Pb and Cd were studied by geostatistic. Soil Cd and Pb concentrations showed an obvious decreasing trend as the distance from the battery plants increases. The high value area of soil As was mainly located at east, while the high value area of soil Hg was mainly located at northeast far from the plants. The concentrations of soil Zn and Cu had similar and unconspicuous spatial distribution patterns. The spatial distribution of soil Cr and Ni were relatively homogeneous.(5) Furthermore, the PMF receptor model was applied to apportion the sources of soil heavy metals, and three sources were obtained combined with the the discussion above. The sources were soil parent materials, agricultural chemical inputs, lead battery plants. The concentration of Ni and Cr appeared to be controlled by the soil parent materials, the natural source contributed56.67%、58.09%respectively for soil Ni and Cr. While Zn and Cu were mainly associated with the agricultural chemical inputs, with this source contributed46.39%、47.93%respectively for soil Zn and Cu. Additionally, Cd、Pb were mainly from the lead battery plants, with65.92%、55.37%respectively from the plants. Furthermore, the fitted parameters by PMF were discussed; this research indicated that PMF combining with geostatistics was a useful tool for source identification and apportionment.