## 4 Discussion  
Mortality data showed a significant effect in the highest GLY concentration (8 mg/kg) in the non-amended soil (Figure 1). The corresponding LC\({}_{10}\), LC\({}_{20}\), and LC\({}_{50}\) were 5.54 mg/kg, 7.067 mg/kg, and greater than 8 mg/kg (Table 1). This means that, as the concentrations of GLY were increased, deleterious effects on the survival of the earthworms also increased. These results are in conformity with those of [PERSON] and [PERSON] [28] who observed significant mortality after a 96-h exposure of the earthworm _Nsukkadrilus mbae_ to GLY and reported an LC\({}_{50}\) of 10.40 mg GLY/kg soil (i.e., LC\({}_{50}\) > 8 mg/kg). Others have reported variable findings depending on the duration of exposure and the glyphosate-based product assessed. [PERSON] et al. [32] reported 71% mortality in _E. fetida_ exposed to 50,000 mg GLY/kg for 7 days. [PERSON] et al. [33] reported an LC\({}_{10}\) and an LC\({}_{50}\) of 0.496 (0.389-0.527) and 26.804 (23.437-27.821) g/m\({}^{2}\), respectively, after 21 days exposure of the earthworms _Lumbricus terrestris_ to GLY. After 72-h filter paper contact exposures of _Eisenia anderi_ to Roundup FG and Mon 8750, [PERSON] et al. [34] reported glyphosate LC\({}_{50}\) values of 66.0 (54.6-82.1) ug GLY/cm and 293.9 (254.0-339.8) ug GLY/cm, respectively. As for biochar amendment, no significant mortality was experienced in all biochar-amended treatments (Figure 1). Our survival data suggest that in the presence of biochar, regardless of the amendment rate, GLY toxicity was significantly reduced as evidenced by the lack of mortality and failure to compute LC\({}_{10}\), LC\({}_{20}\), and LC\({}_{50}\) values (Table 1). This is an indication that biochar was able to alleviate the toxicity of this herbicide. Biochar has been shown to improve survival rates in the manner reported in our study. [PERSON] et al. [35] observed no earthworm death in 5% biochar-amended soil after 28 days of exposure of _E. fetida_ to fenoxprop-ethyl. [PERSON] et al. [20] found that _E. fetida_ exposed to imidalcoprid in 10% biochar-amended soils experienced significant improvement in survival rate. These authors already reported similar findings after exposing the potworm _Enchytraeus albidus_ to silver nanoparticles in soils amended with 10% biochar for 21 days [17]. It is worth noting that depending on the toxicant and the concentration range, biochar has its limitations in improving survival rates. For instance, [PERSON] et al. [17] reported finding no difference in the mortality of _E. albidus_ between a 10% biochar-amended substrate and a non-amended control, after exposure to imidalcoprid for 21 days. The literature shows that such limitation can depend on the origin of the biochar itself. [PERSON] et al. [23] assessed the effects of different rates of application of biochar alone on earthworms. These authors used a poultry litter biochar and a pine chip biochar and found 100% mortality in 68 and 90 Mg (metric ton)/ha using the poultry litter biochar. At these same amendment rates, the pine chip biochar showed no difference in mortality with the non-amended control. Our biomass results, as in the case of survival, showed significant effects in the highest GLY concentration in the absence of biochar (Figure 2). It is only in the non-amended soil that an EC\({}_{10}\) and an EC\({}_{20}\) for biomass can be computed (Table 2). These results indicate that higher concentrations of GLY exerted greater negative effects on the biomass of the earthworms. Several studies have demonstrated that _E. fetida_ and _E. Andrei_ exposed to GLY lose a variable amount of weight [32; 36; 37; 34]. On the contrary, [PERSON] et al. [39] reported no significant differences in _E. fetida_ biomass after 7, 14, and 21 days of exposure to 60.7 mg GLY/kg. [PERSON] et al. [7] also reported no significant difference in the weight of _E. fetida_ exposed for up to 40 days to twice the recommended amount of GLY in Roundup (Monsanto, St. Louis, MO, USA, 48% formula).