# A Systematic Review on Earthworms in Soil Bioremediation
## 3 Results
### Alloobe Organic Vermieremediation  
Regarding vermieremediation for organic xenobiotics, it was found that many species were used only for one contaminant; instead, _E. fetida, Amythhas robustus_ and the combination of _Dravida modesta + Lumpito mauriti_ have been tested for different types of pollutants (Figure 3). Six articles [99; 100; 101; 102; 103; 104] of the seventeen deal with alone vermieremediation versus organic contaminants and were not included in Figure 3 due to the absence of explicit reduction values; however, they are discussed below. Several authors examined the vermieremediation efficiency and the tolerance of different earthworm species in substrates contaminated by TPHs. Figure 3: Alone organic vermieremediation. Reduction percentages were averages of the same contaminant and earthworm species collected from different articles (Number of articles: 11). The reduction values reported for the NA series refer to the test in the absence of earthworms. [PERSON] et al. [105] investigated the bioremediation of crude oil at two concentrations (45.2 and 62.4 mg kg\({}^{-1}\)) using _Allopophora calignosa_, a common species found in Egypt. These endogeic organisms consume large quantities of soil during burrowing; this feeding way might increase the contact of soil particles with the worm gut and result in more TPHs degradation. At the end of the study, the authors found that TPHs concentrations followed a time- and dose-dependent pattern and significantly decreased by 54.9% and 71% in soil samples at 45.2 and 62.4 mg kg\({}^{-1}\), respectively. The maximum reduction was observed at the highest TPHs concentration, highlighting that _A. calignosa_ had a good remedial capacity for these contaminants. Despite this, some changes in worms' metabolic and haematological parameters were observed. In a recent study, [PERSON] et al. [101] evaluated _E. fetida_'s tolerance to pyrene, a very soil-persistent PAH. Authors have chosen this earthworm for its ability to survive in highly contaminated soils; it is also known that _E. fetida_ promotes the degradation of crude oil in soils thanks to its ability to stimulate and synergise with other beneficial microorganisms [64]. For this purpose, three different soil conditions were utilised to cultivate the earthworms: sterilised, unsterilised and soil mixed with CD. The worst pyrene degradation was recorded in sterilised soil (23.2%), while the best was in soil supplemented with CD (31.2%). This information indicates that sterilised soil inhibited pyrene decomposition due to the absence of indigenous pyrene-degrading microbes, emphasising the crucial symbiotic relationships between soil biota and earthworm enzymes. Furthermore, the study demonstrated that _E. fetida_ is extremely resistant and can live and thrive in PAHs-contaminated environments, although survival rates followed a dose- and time-dependent trend. The PAHs soil restoration ability of _E. fetida_ was also studied by [PERSON] et al. [106]. The contaminants used in this experiment were Acenaphthylene (AcPY), Benzo(e)pyrene (BeP) and Benzo(ghi)perylene (BP), which differ in their structural configurations. The data showed that the PAHs vermiremediation in soil was 100% efficient; the authors [106] suggested that these contaminants were degraded into various metabolite states. In particular, _E. fetida_ accelerates the successful removal of PAHs, leading to their removal and disappearance [65]. Earthworms release soil-bound organic contaminants and prevent new binding; in this way, PAHs are more easily available for degrading microorganisms [107]. [PERSON] et al. [108] experimented with vermiremediation using _E. fetida_ and _Amynthus morrisi_, alone or in combination in a precomposed matrix artificially contaminated with TPHs; the incorporation of both species was performed to assess a synergistic effect. _A. morrisi_ is an epi-endogeic earthworm that lives on the soil-litter interface and produces large amounts of cast, improving soil proprieties.