# A Systematic Review on Earthworms in Soil Bioremediation
## 3 Results
### Combined Vermierendiation for Co-Contamination Pollution  
Unfortunately, cross-contamination with inorganic and organic xenobiotics of several environmental matrices is a widespread and dangerous condition that needs to be studied in depth. [PERSON] et al. [166] conducted an in-depth study on natural soil contaminated by PTEs (Cd, Cr, Pb and Ni) and organic compounds (Dieldrin and Benzo(x)pyrene). Ecotoxicological tests were first conducted on this matrix to understand the applicability of the proposed bioremediation techniques, which were then applied, i.e., vermierendiation (with earthworms _E. ftida_), phytoremediation (using _Medicago sativa_) and bioaugmentation (_Burkholderia xenovorans LB400_ and _Paenibacillus_ sp. _Burkholderia xenovorans LB400_ strain). These techniques were applied individually and in all possible combinations (double or triple) in situ. From integrating the ecotoxicological endpoints and the chemical characterisation of the substrate after the twelve-month treatment, the authors measured the better remediations in combined treatments and, above all, in the triple application (\(\mathrm{E+P+M}\)) for all the contaminants studied. More important reduction percentages were found for Dieldrin (50-78%), followed by PTEs (maximum reduction for Cd, Cr, Pb and Ni of 35%, 39%, 33%  
Figure 5: Combined vermierendiation for organic pollution. Xenobiotic reduction percentage (pink bars) and initial concentration (blue dash) for each treatment. Treatments (yellow labels) legend: S (substrate), E (earthworm), P (plant), M (microorganisms), O (other treatment). When progressive numbers appear on the label, different substrates (i.e., S1, S2, etc.) or experimental designs (i.e., E1, E2, etc.) were tested. The square brackets show the bibliographic references of the articles taken into consideration (Number of articles: 6, in order of comparison, [PERSON] et al., 2018 [148]; [PERSON] et al., 2023 [149]; [PERSON] et al., 2020 [152]; [PERSON] et al., 2020 [153]; [PERSON] et al., 2022 [162]; [PERSON] et al., 2019 [164]). and 37%, respectively) and, finally, to a lesser extent for the PAH Benzo(\(\alpha\))pyrene (maximum reduction of 28%). The E + P + M combination proved to be the winning strategy, showing results with less variability. Another study that considers co-remediation techniques on soil always contaminated by an organochlorine insecticide (landane) and Cr is that of [PERSON] et al. [167]. In this work, several bioremediation approaches (vermineremediation with _E.__etida_, phytoremediation with _Brassica napus_ and Bioaugmentation with _Streptomyces_ sp. _M7_, _Streptomyces_ sp. _M5_, _Streptomyces_ sp. _A5_ and _Amyclatopsis tucumanensis_ strain) were tested alone or in combination on two natural soils that differed mainly in organic matter content (OM): 1% (unamended soil; U) and 2.6% (amended soil; A). Regarding the organic contaminant, it has been noted that this was generally less degraded in soil A, where it has been less bioavailable for biodegradation due to its links with organic substances and probably because the microorganisms prefer to consume the OM rather than the pesticide. On the other hand, regardless of the concentrations tested (100 and 300 mg kg\({}^{-1}\)), OM decreased the toxicity of hexavalent chromium, reducing it to Cr (III). The authors [167] observed how combining _E.__etida_ or _B.__nupus_ with the consortium of actinomycetes gave better results in reducing both studied xenobiotics. Still, the highest efficiency was found if the three bioremediation techniques were combined. The same soils (U and A) and contaminants (landane and Cr) were employed by [PERSON] et al. [168] to evaluate the remediation capacity of nano remediation techniques with nZVI alone or in aid of the combined previously discussed (E + P + M + nZVI).