| With the quick development of urbanization, industrialization and agricultural modernization, agriculture soil pollution of city suburbs has become more and more serious and cause a potential threat to ecological environment quality and human health. In order to reveal the concentration levels and pollution characteristics of pollutants in the vegetable fields from Xianyang suburbs, the four typical vegetable fields (i.e. Dongzhangcun, Guoun, Caojiazhai and Baxingtan) from the suburbs of Xianyang City were selected and a total of 140 vegetable soil samples were collected. The physiochemical properties of soil were analyzed by using pH Meter, Conductivity Meter, Carbonate Analyzer, Muffle Furnace, Lase Size Analyzer and Magnetic Susceptibility Meter. These physiochemical parameters included pH values, electro-conductivity (EC), carbonate concentration, loss on ignition (LOI), size composition, low frequency susceptibility (XLF), high frequency susceptibility (XHF) and frequency dependent susceptibility (XFD).The concentration and speciation of heavy metals (e.g. Co, Cr, Cu, Cd, Mn, Ni, V, Zn, As and Hg) in vegetable soil digested by the mixed solution of HNO3-HF-HCIO4 and extracted by the modified BCR sequential extraction procedure were measured by using Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). The concentration of 6 phthalic acid esters (PAEs) which have been classified as priority pollutants by United State Environmental Protection Agency was analyzed by using High Performance Liquid Chromatography (HPLC). According to the experiment data obtained, the concentration level, distribution properties, environmental sources, correlation with physiochemical parameters, speciation, pollution level and potential risk of these pollutants were studied. This paper has drawn the following conclusions:1) Physiochemical analysis results showed that the pH values of soil ranged from 6.98 to 8.25 with a mean of 7.61, which indicating a neutral and alkaline soil. The mean of electro-conductivity of soil was 468.26 μS/cm and the values in vegetable soil from Baxingtan was higher than 1000 μS/cm. The results of magnetic parameters analysis showed that the mean values of high frequency susceptibility and low frequency susceptibility were 88.64×10-8 m3/kg and 83.52×10-8 m/kg; The average of frequency dependent susceptibility was 5.7%. The average concentration of CaCO3 was 42.63 g/kg which belonged to grade three. The mean concentration of LOI was 48.41 g/kg which reached to grade one. The results of soil size analysis showed that soil particulate was dominated by silt (54.45%), clay and sand were 32.45% and 13.04%.2) The results of statistic analysis showed that the mean concentration of Cd, Co, Cu, Mn, Pb, Zn and Hg in soil was higher than Shaanxi Soil Background Values. The coefficient of variation and dispersion of Cd, Pb, Zn and Hg was larger, indicating that they were affected by human activities. And the average concentration of Cd and Zn in soil was also higher than the standard limitation values of China Soil Environment Quality Standard (GB 15618-1995) and the concentration level of other agricultural soil in China. The concentration of 6 individual PAE was in the range of no detected to 6313.35 μg/kg whit the significant difference in 4 vegetable fields. The averagely total concentration of 6 PAEs was 632.10 μg/kg and belonged to a moderate level through comparison with other research results.3) The results of correlations between PAEs pollutants and physicochemical properties showed that there were not significant correlations. There were siginificantly positive correlations between pH and Cd, Cu and Pb in different degrees and negative correlations between pH and Mn, V. High frequency susceptibility and low frequency susceptibility presented siginificantly positive correlations with nine elements except Co and Zn and susceptibility took on the significantly positive correlations with Cr, Mn, Ni, V and As. There were positive correlation between LOI and Cr, Cu, Mn, Hg, Ni and V. Soil CaCO3 presented a significant positive correlation with Cd, while showed the significantly negative correlations with Cr, Mn, Ni, V and As. Sand presented the significant negative correlations with Cr, Cu, Mn, Ni, V and As, while those elements presented the siginificantly positive correlations with slit and clay.4) Correlation analysis, principal component analysis and cluster analysis were employed to explore the source of pollutants. The results indicated natural source and anthropogenic source were the mainly source of the pollutants. Five heavy metals (Ni, V, Cr, As and Mn), which were mainly affected by parent material, belonged to natural source, while other pollutants were more human activities-affected. The factors affected by human activities could be divided into four small factors as well:Cd, Pb, Cu and Hg were regarded as traffic factor; DnBP and DEHP derived from the application of mulching film in agricultural production; the sources of DnOP and Co may be in connection with urbanization and building decotation materials; DMP, Zn, BBP and DEP maybe come from industrial production.5) Based on the Shaanxi Soil Element Background Value, the assessment results of Geoaccumulation pollution index indicated that the average values of Igeo for Cu, Cr, Mn, Ni, V and As were less than 1, indicating a practically uncontaminated level. Co, Pb, Zn and Hg were in a slight contamination level. Cd was in a middle pollution level. The mean of Nemerow indexes (P) was 7.28 and the value in 87.86% of soil samples were in a heavily contaminated level. According to the standard limitation values of China Soil Environment Quality Standard (GB 15618-1995), the average of Igeo for all (except Cd in a slight contamination level) elements was less than 1, which belonging to a practically uncontaminated level. The mean of Nemerow Indexes of vegetable field was 1.07 which indicating a caution level to mild contamination level. All of the concentrations of six PAEs compounds don’t exceed admisistrative standard of New York; the concentrations of the other four compounds (except DMP and DnBP) don’t exceed the control standard of New York.6) Speciation of heavy metals was analyzed and results showed that the movability order of heavy metals was Mn≈Pb> Co> Cd> Ni> V> Zn≈Cu> Cr. Among of them, the movability percentage of Pb, Co, Mn and Cd was higher than 50%, presenting a higher risk. Pb was mainly in oxidizable fraction, Co and Mn were mainly in reducible fraction, Cd was mainly in acid extractable fraction and reducible fraction. The results of Potential Ecological Risk Index based on Shaanxi Soil Background Values showed that the potential risk of Cd (Eri= 266.67) and Hg (Eri=181.17) arrived at high risk level, other heavy metals belonged to a low risk level, and the total Potential Ecological Risk (RI= 490.86) of the study area was at a very high risk level. The results of Potential Ecological Risk Index based on the standard limitation values of China Soil Environment Quality Standard (GB 15618-1995) showed that Cd (Eri= 40.00) reached to a moderate risk and other elements were at a low risk level. The totally potential risk (RI= 53.87) reveled a low Risk Revel. Risk analysis of PAEs showed that there was no remidation measures to apply. However, DnBP in 5% of samples and DEHP in 3% of samples exceed the Environmental risk level. |
PDF Full Text Request