Influence Of Dissolved Organic Matter On Environmental Behavior And Plant Uptake Of Polycyclic Aromatic Hydrocarbons (Phenanthrene) In Soils

Polycyclic aromatic hydrocarbons (PAHs) are a unique class of pollutants which are constituted by hundreds of individual substances. These compounds contain two or more fused aromatic rings made up of carbon and hydrogen atoms. The behaviors and fates of PAHs in the environment are of increasing concern, due to their carcinogenic, mutagenic and tumorigenic properties of certain of them. Dissolved organic matter (DOM) is ubiquitous in soil and aqueous environment, and is one of the most active chemical components in terrestrial and water ecosystem. It has been found that DOM has great effect on the solubility, adsorption-desorption equilibrium, biodegradation and translocation of organic pollutants in soil and water. Increasing attention has been paid on the study of the influence of DOM on environmental behavior of PAHs, especially in soil-plant ecosystem. The study of the relationship about DOM and PAHs can help us to prevent and control contaminating plant, surface water and groundwater by PAHs, and enhance bioremediation in soils contaminated by PAHs. Consequently, this study was carded out to explore the influence of DOM derived from sewage sludge, pig manure and green manure on the environmental behavior of PAHs and mechanisms.Batch experiments were conducted to investigate effect of dissolved organic matter (DOM) on the adsorption and desorption behavior ofPhenanthrene (Phe) in a soil-water system. It was found that the three natural DOM derived from pig manure (PM), sewage sludge (SS), and green manure (GM) and a surfactant Tween reduced sorption of Phenanthrene significantly onto the tested soils. Within the selected concentration range of the Phenanthrene and DOM in this study, the sorption quantity has minus-linear correlativity with the concentration of DOM(r_PM=-0.9888^**,r_SS=-0.9826^**, r_Tween-80=-0.9743^**, r_GM=-0.9905^**). The sorption inhibition of Phenanthrene caused by DOM of GM origin was more significant than that of SS origin and GM origin for the same soils. Phenanthrene sorption isotherm could be described well by the Freundlich equation. It implied that Phenanthrene behavior in some DOM-rich farmland could be altered.Soil enzymes play an important role in circles of carbon, nitrogen and phosphorus, which are concerned with metabolic processes in soil system, such as soil occurrence and development, fertility formation in soil, nutrition material transformation, organic matter decomposing, and contaminations degradation and so on. Soil enzyme activity can reflect intensities and directions of many bio-chemical processes, and is affected by those lots of environmental factors are physical, chemical, biological ingredient and so on. PAHs' toxicity and carcinogenic characteristics have been paid attention to human attaches gradually. In this experiment Phenanthrene is selected as a representative pollution of PAHs. The dynamic changes of soil enzyme activities were researched under condition of phenanthrene and Dissolved Organic Matter (DOM) exposure. The results showed that pollutant had different action on 3 kinds of enzyme activity. In the first 8 days of incuabtion, the phenanthrene inhibited the activity of the soil dehydrogenase activities significantly, and recovered quickly after 16d; the activity of the soil urease activities significantly inhibited in the first day after add Phe; but the activity of soil polyphenol oxidase were activated after add Phe in the soil. The DOM had favorable to enhance the activity of biochemical process in soil; and to reduce the soil ecological environmental influence by outside contaminants.Pot experiment with wheat was studied to explore DOM effect on the wheat uptake Phe. Results showed that Phe inhibited plant growth by 10.0%～45.8%. The inhibition increased in the presence of DOM and Tween-80. Wheat can assimilated and transit Phe from the soil, with the growth of wheat, the concentrations of Phe in roots and shoots decreased gradually, DOM and wheat Tween promote the assimilated of Phe, and bioconcentration factor more than to deal with a single large Phe; tillering in wheat from the root to shoot part of the transshipment capacity is the highest period in the four wheat fertility period. Polluted by Phe can increased the pH of soil which higher than controls, DOM and Tween-80 further increased pH, suggesting that H⁺-Phe contransport system was involved in the uptake of Phe by wheat.