| From the late 1980s, polycyclic aromatic hydrocarbons (PAHs) have been widely studied in environmental investigations as typical hydrophobic organic pollutants. Sorption to organic matter is the key process that controls the toxicity, transport, and degradation of non-polar organic compounds, such as PAHs, in soils.One property that sets BC apart from other types of organic matter is its very high capacity for sorbing organic compounds. The past decade has seen a growing awareness of the importance of natural BCs, which are ubiquitous in the environment, in controlling the fate and behaviour of organic pollutants. The addition of BC to soil would therefore be expected to enhance the sorption properties of the soil and, hence, has a strong influence on the fate and behaviour of non-polar organic compounds present in, or added to, that soil. Given that BC is a much stronger sorbent for neutral organic compounds than other forms of organic matter present in most soils, and that BC is ubiquitous in the environment, it should be expected that BC naturally present in soil would play an influential role in overall soil sorption properties.In the current study,9 representative soils were collected from 7 provinces across a climatic gradient ranging from south (22°N) to north (48°N) in eastern China. The gradient will have partially determined the characteristics of these soils, therefore, their types and properties varied widely. The objectives of the present research were: (1) to study the detailed sorption isotherms of phenanthrene (a three-ring polycyclic aromatic hydrocarbon) in 9 soils with various physical and chemical properties, (2) to investigate the predominant soil factors controlling the sorption behavior of phenanthrene, and (3) to investigate the effects of added BC on the adsorption of phenanthrene by the selected soils. (4) to investigate the influence of BC amendment over time on the extractability of phenanthrene and, using PLFAs profiles, to evaluate the subsequently changes in the microbial community in two different soils. A subsidiary aim was to promote awareness of the environmental behavior of BC and the environmental benefits of using BC in environmental remediation. The main experiments and conclusions are as follows:Sorption isotherms for a hydrophobic solute probe, phenanthrene, were determined in 9 Chinese soils. They were sampled along a climatic gradient, and amended, or not, with charcoal (0.2%,0.5%, and 1%), a form of black carbon (BC). Within the concentration range of added phenanthrene (0.2-0.8 mg I-1), most of the adsorption isotherms of the unamended soils were non-linear. The Freundlich equation and the Dual Reactive Domain Model (DRDM) model closely fitted the data, indicating that phenanthrene sorption in these soils was site-specific and capacity-limited adsorption in a condensed organic domain. Correlations between the Freundlich model capacity factor (KF) and soil physico-chemical properties showed that the total soil organic C (TOC) concentrations, cation exchange capacities, silt contents and specific surface area had a cumulative effect on phenanthrene sorption, indicating that organic and inorganic components interacted in this process. The results also indicated that humic acid carbon (HAC) concentration may be a further relevant factor that should be considered.The soils covered a wide range of physical and chemical properties, in particular organic C. It was found that the organic carbon-normalized distribution coefficients (KOC) were in a large range of variation. Therefore, Koc values may be poor predictive parameters for phenanthrene sorption by soils. Addition of BC not only enhanced the sorption of phenanthrene but also altered the sorptive characteristics of the soils studied.The selected seven zonal soils showed different desorption hysteresis as shown by the hysteresis index (HI) values. The HI value was positively related to the black carbon content and the specific surface area of soils. The presence of black carbon in soil would enhance the adsorption/desorption hysteresis.Biodegradation processes and changes in microbial community structure were investigated in black carbon (BC) amended soils in a laboratory experiment using two soils (black soil and red soil). We applied different percentages of charcoal as BC (0%,0.5% and 1% by weight) to soils treated with 100 mg kg-1 of phenanthrene. Soil samples were collected at different incubation times (0,7,15,30,60,120 d). The amounts of extracted phenanthrene increased substantially in each soil as the BC concentration increased from 0 to 1%. For example, after 120 d incubation time, extractable phenanthrene concentrations increased from 2.94 to 26.35 mg kg-1 and 0.66 to 34.88 mg kg-1 in the black soil and red soil between BC concentrations of 0 and 1%, respectively. A similar trend was observed at each incubation time in both soils. The amendment with BC caused a marked decrease in the dissipation (ascribed to mainly degradation and/or sequestration) of phenanthrene residues from soil.There were significant changes in the PLFA pattern in phenanthrene-spiked soils with time but BC had little effect on the microbial community structure of phenanthrene-spiked soils, as indicated by principal component analysis (PCA) of the PLFA signatures. The bacterial PLFAs were more sensitive to phenanthrene than fungi and actinobacteria, so that the latter two groups appeared to be mainly responsible for phenanthrene degradation in soil.
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