## 3 Results and Discussion
### Dissipation of Pesticide Residues in the Biomixtures  
Regarding to the non-colonized biomixtures by _E. fetida_ (-E), after 12 weeks of incubation, the amount of pesticide residues dissipated in the CO biomixture was between 1.7 and 3.9 fold higher than in CP, except for oxyfluorfen, which showed similar dissipation in both biomixtures (Figure 4). In the CO biomixture, the dissipation of imidalcoprid, tebuconazole and oxyfluorfen residues was similar and ranged from 45.7% to 55.3%, while 100% of diuron was dissipated. By contrast, in CP,  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline
**Biomixure\({}^{\,\bullet}\)** & \multicolumn{3}{c}{**pH**} & \multicolumn{3}{c}{**EC dS m\({}^{-1}\)**} & \multicolumn{3}{c}{**TOC g kg\({}^{-1}\)**} & \multicolumn{3}{c}{**WSC g kg\({}^{-1}\)**} & \multicolumn{3}{c}{**N g kg\({}^{-1}\)**} \\ \hline  & & **I** & **F** &  
the percentage of dissipation ranged from 11.8% to 58.8% and followed the trend tebuconazole \(<\) imidacloprid \(<\) oxyfluorfen \(<\) diuron. As indicated above, the CO biomixture had Dhase activity levels higher than the CP biomixture (Figure 3) and, therefore, it is biologically more active, enhancing the dissipation of the pesticides. In addition, the CO biomixture has vermicompost, which contains a relative high abundance of microorganisms than the peat, but also, like compost, has higher richness of xenobiotic-degraders that can degrade these pesticides to less toxic compounds [25; 45; 46]. The colonization of these biomixtures by _E. fetida_ (+E) did not significantly (\(p>0.05\)) affect the dissipation of imidacloprid and tebuconazole residues. Neither was the dissipation of diuron residues affected in the CO biomixture, but it increased in CP. By contrast, the presence of _E. fetida_ (+E) enhanced the dissipation of oxyfluorfen residues 1.4 fold in both biomixtures (Figure 4). It is well known that earthworms can stimulate the pesticide degradation in soils and organic wastes [15; 47], through different interdependent mechanisms: (i) release of pesticide-detoxifying enzymes in their gastrointestinal tract [48], (ii) stimulating the growth and activity of microorganisms by increasing their contact with pesticide residues [12], and (iii) secretion of mucus, which would improve the nitrogen concentration in the substratum, enhancing the growth of degrading microorganisms [16]. This last mechanism could explain the higher dissipation of diuron observed in CP+E biomixture regarding to CP\(-\)E (\(-\)E). As shown in Table 2, the presence of earthworms increased the concentration of N in both biomixtures, CP and CO. This increase may have favored the activity of diuron degrading microorganisms already in the biomixtures, more noticeable for CP biomixture with lower N content. In a previous study  
Figure 4: Relative concentration (C/C\({}_{\text{O}}\times 100\)) of residues (colored bars) and dissipated percentage (white bars) of diuron, imidacloprid, tebuconazole and oxyfluorfen in the CP and CO biomixtures, treated (+E) or not (\(-\)E) with _E. fetida_ after 12 weeks of vermicomposting. Error bars represent the mean standard error. For each pesticide residue, means followed by the same letter do not significantly differ (\(p<0.05\)). of our research group, it was demonstrated that diuron degradation was enhanced in biomixtures added with indigenous microorganisms previously exposed to diuron residues [5]. In the case of oxyfluorfen, it is a persistent and hydrophobic (Log Kow 4.7) pesticide that renders to be adsorbed in the organic matter of the biomixture. Since earthworms ingest these organic particles, it might explain the reduction of oxyfluorfen residues in the biomixtures with earthworms. As neither the extraction of pesticide residues in earthworms nor the detection of metabolites were carried out, we cannot elucidate if oxyfluorfen degradation occurred in the digestive tract of the earthworms. Imidacloprid ant tebuconazole dissipation was not enhanced in the presence of earthworms, which might attend to different reasons.