Effects Of Earthworms And Earthworm Casts On Degradation Of Phenanthrene In The Artificially Contaminated Soil By Bacteria (Pseudomonas Putida)

Polycyclic Aromatic Hydrocarbons (PAHs) constitute a group of priority pollutants which are ubiquitous in the environment, especially present at high concentrations in the soils on many industrial sites. Phenanthrene is a polycyclic aromatic hydrocarbon (PAH) with three aromatic rings, which can be derived from coal tar. It is widely existing in the environment as a product of incomplete combustion of fossil fuels and wood and has been identified in ambient air, surface and drinking water, and in soils, even in foods. Phenanthrene is absorbed following oral and dermal exposure. Phenanthrene induces mutation, aberrance and carcinogen of fish and other animals, but no human data were available that addressed the toxicity of phenanthrene. Phenanthrene has the special structure K-region and Bay-region which can induce carcinogens. Therefore, it has been chosen as a model compound for studies on PAHs. It is valuable to understand the fate of phenanthrene in soils in the study of biodegradation, also can be beneficial to other environment contaminate of PAHs.Earthworms, as one of animals having the largest biomass, play a major role in soil functioning as soft ecological engineers. Recently, many researches demonstrated that earthworms have great potentials to remediate contaminated soils as well, mostly on their effects on soil physiological, chemical and biological functioning. Therefore, earthworms have capability to improve the remediation of organic pollutants in soils. However, there were few reports concerned about influence of earthworms when they used to remove contaminants in soil.This research monitored effects of earthworms and earthworm casts on the degradation of phenanthrene in artificially contaminated soil by bac through the microcosm experiments. The main results were shown below:1) A 30 days' incubation experiment was conducted to investigate the effect of earthworm on the bacteria (Pseudomonas putida) degradation of phenanthrene in a mimicked phenanthrene contaminated red soil. The red soil was spiked with 50, 100 and 150 mg·kg^-1 phenanthrene. Contaminated red soil was then treated with earthworm (E), bacteria (B), and earthworms-bacteria (BE), respectively. Meanwhile, the contaminated red soil without any further treatment was set as the control (CK) for comparison purpose. For the soil spiked with 50 mg.kg^-1 phenanthrene, these treatments showed significant difference in the dissipation rates of soil phenanthrene, and the rates were of the following sequence: BE＞B＞E＞CK. The dissipation rates of phenanthrene increased as the soil phenanthrene levels increased. In the soil receiving 150 mg.kg^-1 phenanthrene, the dissipation rate was 98.86% for BE, being significantly higher than those for CK and E. Moreover, as the soil phenanthrene levels increased, the dioxygenase activities were almost unchanged for B but were significantly increased for BE. This experiment indicated that both earthworm bioaccumulation of phenanthrene and earthworm-promoted bacteria biodegradation of phenanthrene should be responsible for the dissipation enhancement of soil phenanthrene.2) The results showed that treatments with cattle manure only or with earthworm casts only both could decrease the concentration of phenanthrene in soil and earthworm casts' effect was superior to cattle manure. Moreover, the addition of earthworm casts or cattle manure in treatments with bacteria could significantly stimulate the degradation of phenanthrene in soil by bacteria (the degradation vicinity was 98-99%, which was higher than all the other treatments) and casts' effect had no difference with manure's. In order to make sure the dynamic process in soil, we observed treatments with 100 mg kg^-1 phenanthrene concentration by collecting soils every four days in 20 days totally. The date demonstrated that degradation of phenanthrene in soil mainly occurred in the first 8 days and the vicinity decreased with time varying. Combined with dynamic dioxygenase activity of bac, in the beginning and middle of incubation, dioxygenase activity in treatments with bac and casts was higher than treatments with bacteria only, which indicated that casts' addition could stimulate dioxygenase activity of bacteria, but this effect decreased with time varying dioxygenase activity of bac in treatments with cattle manure was confused.3) In this experiment, both earthworms and earthworm casts could help degrade phenanthrene in soil and stimulate bacteria's degradation of phenanthrene as well. But earthworm cast's effect was superior to earthworms.