## 4 Discussion
### Mycoremediation of TCE in Soil  
To the best of our knowledge, all the prior research carried out on TCE degradation by fungi has been performed using liquid broth. Therefore, this work is unique because neither _P. ostreatus_ nor _P. erygii_ or any other ligninolytic fungi have been assessed for their ability to degrade TCE in soil. The characteristics of the soil may have had an influence on fungal development as well as on the fate of the contaminant. One of the most important parameters that influences the fate of TCE is the presence of organic matter (O.M.). If this content is high enough it facilitates the adsorption of higher concentrations of the pollutant. In addition, a high O.M. supports a greater population of autochthonous microbiota which will compete for space and nutrients with the allochthonous fungi. The O.M. content of the soil used in this investigation was \(3.1\pm 0.2\%\), which supported a population of autochthonous microbiota that was estimated by the analysis of the activity of three enzymes: hydrolase, dehydrogenase, and urease. Microbial decomposing activity was determined through the activity of hydrolase, which provides a good estimate of total microbial activity [33], as well as dehydrogenase, another indicator of the general activity of the microbial community in soil [35]. Finally, urease activity was used to estimate the hydrolysis of the urea present in soil. The activity of the three enzymes indicated that the initial soil showed appreciable microbial activity; it was therefore evident that _P. ostreatus_ and _P. erygii_ had strong competition from the autochthonous microbiota. Under these conditions, the two fungi were able to completely remove the TCE after 4 weeks of incubation and clearly demonstrated a faster removal of TCE when compared with the control soil. The speed of removal by the two fungi and the control soil was similar after the first week of incubation. At this stage, the fungi were in the initial stages of growth and the colonization of the soil had not been completed. Hence, the removal of TCE was mainly biologically mediated by the activity of the autochthonous microbiota in addition to the abiotic transformation which might occur via two different pathways: one performed by elimination, yielding 1,1-dichloroethene, and the other via hydrolysis producing acetate [41]. TCE produces negative effects on the Actinobacteria population in soil, with activity such as nitrogen transformation. However, the negative impact of TCE on the fungal population is either very low or may even enhance fungal development in the long term [6]. This research demonstrates the greater degradation of TCE obtained by the two mycoremediation treatments with respect to natural attenuation (the control). Furthermore, the greater removal of TCE, and the higher slope shown in Figure 4 between the first and second week of incubation clearly indicate the important role of both _Pleurotus_ species in TCE removal. During this period, the removal speeds of TCE were 2.82, 7.05, and 8.24 mg TCE kg\({}^{-1}\) day\({}^{-1}\) for the control, _P. ostreatus_, and _P. eryngii_, respectively. This time also represented the incubation period when TCE removal was at its greatest, with both mycoremediation treatments achieving levels of TCE removal greater than 70%. By contrast, during the final two weeks of incubation, the removal of TCE was reduced, with an increment of only 6.3% observed in the control treatment when compared with week 2. However, during the same period, the two test mycoremediation treatments were once again more efficient than the control, removing 26.8% and 18.7% of TCE for _P. ostreatus_ and _P. eryngii_, respectively. Therefore, the use of mycoremediation for the removal of TCE in soil offers clear advantages with respect to autochthonous soil microbiota. The rate of TCE removal in soil by the two _Pleurotus_ species was comparable to that of anaerobic degradation by bacteria in soil that ranged between 60% and 99%, as summarized by [PERSON] et al. [17].