Research On Pollution Character, Spatial Distribution And Ecological Risk Of Contaminated Flow From Soil-water Interfaces In Suburb

Contaminated flow from soil-water interfaces is a special form of non-point pollution source. Under erosion of rainfall or snow melt, chemical reactions as diffusion, dispersion, desorption, dissociation and multiple processes resulted in the entrance of soil pollutants into surface runoff and the special effluent occurred including multiple pollutants such as heavy metals, persistent organic pollutants, nitrogen and phosphorus. The suburb area, as a typical transitional zone between city and country, is a multifunctional and complex ecosystem with high level agricultural producing, complex land use structure. Due to the interaction of city and country, the suburb area is one of highly human activities zone and affected by urbanization,industrialization and country development. So taking the Xiqing area of Tianjin suburb as a research object, pollution characters of heavy metals and PAH, spatial distribution and pollution sources have been discussed in this work through information collection, extensive systematic investigation and analysis. Based on the geostatistical method, the spatial variability and spatial distribution of heavy metal and PAHs were analyzed in the paper. In addition, ecological risk method was designed by Monte-Carlo model and assessed the risk of contaminated flow from soil-water interfaces of the study area. The main findings as follows:(1) Based on the extensive investigation and analysis, pollution characters of heavy metals and PAHs of contaminated flow from soil-water interfaces of the study area were discovered.The concentrations of Cr, Ni, Cd and Zn in the contaminated flow from soil-water interfaces were in lognormal distribution. The concentration of Cu, As and Pb were in skew distribution. The coefficients of variation of heavy metals were almost big, which indicated that the degrees of scatter of havy metal datum were greater and the concentrations of heavy metal varied greatly. There were significant relationships between heavy metals except As. The results of principal component analysis revealed that three components could be chosen to represent the data set. The first factor include Cr, Ni and Zn, the second factor include Pb and Hg, while As was strongly related to the third componentPAHs with 3-ring, 4-ring and 5-ring numbers were dominated in the contaminated flow from soil-water interfaces of study area, the contribution of which were quantified as 36.49%,26.34% and 27.85%, respectively. Except PAHs with high-ring, the concentrations of PAHs with low-ring, median-ring and total PAHs were in lognormal distribution. The coefficients of variation of each PAHs were almost big. The relationships between fourteen PAHs and total PAHs were significant except for Dba and Inp. The relationships of Flu, Pyr, BaA and Chr to total PAHs were the strongest, which belongs to PAHs with 4-ring. At confidence levels of 0.01, the relationships coefficients were 0.90,0.84, 0.87 and 0.89 respectively.PAHs sources of contaminated flow from soil-water interfaces of study area were examined using principal component analysis, ration method and typical source of triangle plot. The results of principal component analysis revealed that five components could be chosen to represent the data set. The first factor mainly includes PAHs with high-ring, which reveals the synthetical contribution by traffic exhausts and coal combust, ion source. The second factor mainly includes PAHs with low-ring, which represents the process of atmospheric deposition. The third factor reflected the effect of Flu,Phe and Pyr and shows the typical character of combustion source. The forth factor include Acy and Inp, which reflected the straw combustion and petrolic source. In the end, Dba was especially reflected by the fifth component.Phe/Ant ratio showed that incomplete combustion was the primary source of PAHs. All Flu/Pyr ration was bigger than 1.0 in the study area, which inferred that coal combustion and biomass burning were the main sources. Bar/Chr ration was bigger than 0.5 in some of the samples, which concluded that the primary source of these samples was combustion source. Some Bar/Chr ration was 0.25-0.35 reflected that mixed source of petroleum and combustion. Few Bar/Chr ration was lower than 0.25 that indicated petroleum source.The analysis result of typical source of triangle plot included that combustion process was the primary source that contains coal combustion, straw burning, high-temperature combustion of engine, oil combustion and biomass burning. It was clear that low-ring, median-ring and high-ring PAHs did not dominate total PAH burden. The results showed that PAHs in the samples were not come from the single source and may be affected by the joint of multiple pollution sources.(2) Based on geostatistical technique, spatial variability and distribution of heavy metal and PAHs were analyzed.The results showed that the spatial structures of seven heavy metals were isotropy and the ranges were 4040-7404 meters. As and Cd were strong spatial relationship in a small scale and it was median spatial heterogeneity of Zn, Ni, Cr. Except As, other heavy metals obvious showed nugget effect. Semivariogram of As, Zn, Cr, Pb and Cu could be fitted well with spherical model. And semivariogram of Ni and Cd could be fitted well with exponential model. The spatial structure of Cu and Pb were obvious spatial trend, kriging with trend was used to estimate spatial distribution.The spatial structures of low-ring and high-ring PAHs were isotropy and semivariogram could be fitted well with spherical model. Result form geostatistical analysis demonstrated that low-ring PAHs have a weak spatial heterogeneity, high-ring PAHs have a median spatial heterogeneity and median-ring PAHs have no spatial heterogeneity. Ordinary kriging was used to estimate spatial distribution of low-ring and high-ring PAHs. IDW was used to estimate spatial distribution of median-ring PAHs. Overlay analysis was used to attain spatial distribution of total PAH.(3) Based on probability density function and Monte-carlo model, ecological risk method was constructed to assess the ecological risk of heavy metal and PAHs in study area.The results showed that the ecological risk probability of Cu, Cd and Pb were 80.75%, 43.09% and 16.49%, respectively. Based on Rapant index, the results of ecological risk assessment showed that 50.3% of study area was in degree of none or low ecological risk, 13.75% of study area was in degree of moderate ecological risk and 13.61% of study area was in degree of high ecological risk.The potential ecological risk of Phe,Ant,Pyr,BkF and Bghip was low, which had small harm to ecosystem. The potential ecological risk of Nap,Ncy,BbF,Bap existed and could harm to ecosystem. By contrast, the potential of Ace,Fl,Flu,BaA,Chr,DahA was high and the probability harm to ecosystem was also high. For total PAH, the risk probability of 90% was higher than ERL or ESQVL and the risk probability of 11.21% was higher than ERM or ISQVH.