Effects Of Earthworms And Earthworm Casts On Degradation Of Phenanthrene In The Artificially Contaminated Soil By White-Rot Fungi, P.chrysosporium

Polycyclic Romatic Hydrocarbons (PAHs) are one of the organic pollutants in ourenvironment. Their presence is a result of industrial, accidental, or deliberate releasefollowed by the incomplete combustion of organic material. One of the most efficient/safeways of removal of such pollutants in soil is biodegradation by microorganisms.Earthworms, as one of the most important animals, play a major role in soilfunctioning as soil ecological engineers. However, there were few reports concerned aboutinfluence of earthworms and their casts to foreign microorganisms when they used toremove contaminants in soil. In order to figure out the effect of earthworm and their castson the degradation of Phenanthrene in artificially contaminated soil by whit-rot fungi,P.chrysosporium. We monitored the phenanthrene concentration in earthworm tissue andsoil exposed to the contaminants for 30days at dark condition. The earthworms'experiments contain 4 treatments: (1) white-rot fungi only; (2) inoculations of white-rotfungi and worms; (3) worms only; (4) no fungi and worms, control; and the earthwormcasts' experiments contain 6 treatments: (1) whit-rot fungi only; (2) inoculations ofwhite-rot fungi and casts; (3) inoculations of white-rot fungi and cattle manure; (4) castsonly; (5) cattle manure only; (6) no fungi and worms, control. The objective was toinvestigate the effects of earthworms on the removal of phenanthrene in the presence ofwhite-rot fungi.1. The earthworms' experiments(1) The microcosm experiments showed that all the treatments, except treatment withinoculations of white-rot fungi and worms, were significantly different between threecontaminated concentrations (initial concentration of 50 mg kg^-1, 100 mg kg^-1,150 mg kg^-1).In the treatment with earthworms only, the average removal of phenanthrene was 14.3%(initial concentration of 50 mg kg^-1), 6.3% (initial concentration of 100 mg kg^-1) and 4.8%(initial concentration of 150 mg kg^-1) higher than control treatment respectively. Moreover,earthworms had the ability to stimulate the degradation of phenanthrene by white-rot fungi. Average phenanthrene removal in treatment with inoculations of fungi and earthworms was25.1% (initial concentration of 50 mg kg^-1), 14.5 % (initial concentration of 100 mg kg^-1)and 10.5% (initial concentration of 150 mg kg^-1) higher than control treatment respectively.At last, in the contaminated concentration with 100 mg kg^-1, concentration of phenanthrenein all treatments decreased. Treatment with earthworms only and treatment withinoculations of white-rot fungi and worms were significantly superior to other treatmentsand their peak degradation velocity was observed at the first 8 days.(2) The results also showed that, in treatment inoculations of fungi and earthworms,activities of LiP and MnP were higher than the treatment with white-rot fungi only, whichindicated that the synergistic effect between earthworms and white-rot fungi might increasedegradation of phenanthrene in soil by stimulate extracellular ligninolytic enzymes' activityof white-rot fungi.2. The earthworm casts' experiments(1) We observed that earthworm casts and cattle manure both can stimulatephenanthrene's degradation in soils and earthworm casts' effect was significantly superiorto that of cattle manure. Average phenanthrene removal by earthworm casts and white-rotfungi compared with control was 27.5% (initial concentration of 50 mg kg^-1), 15.3% (initialconcentration of 100 mg kg^-1) and 10.8% (initial concentration of 150 mg kg^-1) highrespectively. Comparably, removal of phenanthrene by cattle manure in soil was 5.5%(initial concentration of 50 mg kg^-1), 7.0% (initial concentration of 100 mg kg^-1) and 2.8%(initial concentration of 150 mg kg^-1) higher than control.(2) The results also showed that, in the treatment added with both white-rot fungi andearthworm casts, activities of LiP and MnP were higher than the treatment only added withwhite-rot fungi, which indicated that the synergistic effect between earthworm casts andwhite-rot fungi might increase degradation of phenanthrene in soil by stimulate enzymeactivity.3. We could concluded from the experiments mentioned above that white-rot fungihave high degradation capability; earthworms and earthworm casts could stimulate thedegradation of phenanthrene by fungi; the synergistic effects between earthworms andfungi, earthworm casts and white-rot fungi have great potentials and application future inthe biodegradation area of contaminated soil.Finally, we discussed the main reasons for the earthworms and earthworm casts'capability to stimulate the degradation of phenanthrene by white-rot fungi. (Including facilitating diffusion of microorganisms, allowing active growth of microbial population,enhancing soil carbon source quality and nutrient bioavailability, improving soil aerationand structure)...