| Polycyclic aromatic hydrocarbons (PAHs) are mainly important persistent organic pollutants (POPs) and have serious impacts on environment. Current researchs were lacked the reports of the distribution, sorption and degradation of PAHs in urban forests. This study focused on PAHs distribution in space, sorption process and the decomposition by fprest soil and known microorganisms in two evergreen broad-leaved forests at Maofeng mountain and Baiyun mountain. The concentrations of PAHs, SOC, pH, TN and SOM in two soil depths were investigated by field monitoring or used laboratory simulation to explore their spatial dynamics. The main results were list as follow:(1) The concentrations of PAHs in the soil (0-20cm) of Maofeng mountain were higher than that in the soil layer (20-60cm). The concentration of naphthalene was highest among the16PAHs in the soil (at the depth of0-20and20-60cm). And its concentration in the soil layer (20-60cm) was accounted for30%in the total mass of PAHs. This distribution characteristic in Baiyun mountain was similar with Maofeng mountain, which the surface layer was higher than lower soil layer. Furthermore, the mass percentage would decrease with the increasement of benzene rings in PAHs. In the lower soil layer, mass percentage of fewer benzene rings in PAHs increased, but decreased in PAHs with many benzene rings. The concentrations of PAHs in the soil of Maofeng mountain were higer than these in Baiyun mountain. Moreover, the concentration of total PAHs in two soil layers (0-20and20-60cm) of Maofeng mountain and Baiyun mountain were123.5,30.10,95.62and14.80μg·g-1. In different sampling sites, the correlations among PAHs with the same benzene rings were significant(P<0.01).(2) The correlations between PAHs and soil organic carbon and total nitrogen were positive (P<0.01). Furthermore, the correlations of PAHs with cation exchange capacity, silt concentration, dehydrogenase activity were also significantly positive. But there was no significant correlation between PAHs and sand concentration, clay particle concentration, poly phenol oxidase(P<0.01). (3) The dynamic sorption of PAHs indicated that adsorption equilibrium achieved after48h, and the concentration of PAHs in the liquid phase would stay stably. When the equilibrium achieved, the concentration of PAHs in liquid phase decreased, and sharply within the24h. The sorption process fitted well with the classical models of dynamic adsorption. The coefficients of association were0.316-0.936,0.603-0.858and0.532-0.898for sorption models of phenanthrene, anthracene and benzo[a]pyrene. Generally, pseudo-second order kinetics best fitted the sorption process of PAHs between soil and water. The intra-particle diffusion model was better than pseudo-first order kinetics. The constant of adsorption rate (K) in pseudo-second order kinetics indicated that the order of K was benzo[a]pyrene> phenanthrene>anthracene. It was just contrast with pseudo-first order kinetics. But in the intra-particle diffusion model, the constant of pore diffusion rate was phenanthrene>anthracene> benzo[a]pyrene.(4) The adsorption coefficient (KF) of phenanthrene, anthracene and benzo[a]pyrene in adsorption isotherm were0.7952,1.4381and1.211. Phenanthrenehad higher KF, so it had stronger soil sorption than anthracene. Models of Freundlich adsorption isotherm and Langmuir monolayer adsorption fitted well with the data of sorption, and the coefficients of association (R2) were above0.95. Monolayer adsorption qualities of phenanthrene, anthracene and benzo[a]pyrene were6.15×104,3.53×10-6and0.25×10-7mmol·g-1.(5) It was confirmed that the forest soil and6selected microorganisms had the capacity of PAHs degradation in soil culture medium. The concentrations of phenanthrene, anthracene and benzo[a]pyrene decreased9.6-32.6%,2.2-35.2%and0.6-19%, respectively. Moreover, the degradation rate of benzo[a]pyrene was lower than phenanthrene and anthracene. And there would be have difference with different PAHs and microorganisms. |
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