# A Systematic Review on Earthworms in Soil Bioremediation
## 3 Results
### Alone Inorganic Vermiremediation
Other papers not shown in the radar graph used _E. fetida_ to remedy organic sludge waste [90; 91; 92; 93], obtaining ecologically stabilised products rich in nutrients and with PTEs concentrations below the imposed limits. _Lumichrieus terrestris_, although studied in only one [94] among the twelve articles considered in this subchapter, achieved the greatest reduction percentages compared to the other earthworms for all the metals studied. The authors applied vermiremediation on seven soils collected near welder and auto mechanic workshops with different starting PTEs concentrations. Despite variability in contaminations, _L. terrestris_ has shown itself to be particularly efficient, with reduction averages always higher than 80% for all studied metals except for Zn (69%). Averaging the reduction percentages due to earthworms' presence (comparing the PTEs concentrations in the same soils without or with earthworms) from all the soils analysed, the authors found that Pb was the element that best lends itself to vermiremediation with _L. terrestris_. Data reported by [PERSON] et al. [94] also deal with _Eudrilus eugeniae_ and, comparing its remediation capacity with _L. terrestris_, finds it even more efficient. Both [PERSON] et al. 2022 and 2020 [83; 95] evaluated the vermiremediative power of _E. eugeniae_ by applying these earthworms to cotton textile sludge (CTS1, CTS2). Regarding Cd, the most newsworthy result was found in the CTS2 matrix; in fact, starting from a high initial concentration (59.03 mg kg\({}^{-1}\)), a reduction of 70.96% was obtained. Also, in CTS1, earthworms restored the substrate from Cd (84.73%), although the level of contamination was low. More interesting results were found in CTS1 relating to Cr, Pb and Zn. However, the Cr, Zn and Cu removal efficiency was higher in the mixtures CTS2 and CD in a 1:1 or 2:1 ratio. The primary industrial source of Cr pollution comes from the leather industries because this metal is widely used as a tanning agent [96]. The tannery sludge substrate used in the experiment conducted by [PERSON] et al. [97] contains high concentrations of Cr (711.6 mg kg\({}^{-1}\)). In the pure matrix, _E. eugeniae_ effectively reduced the amount of that PTE by 63.95%, while in the mixture with 50% CD, the reduction reached 89.45%, starting from a lower initial concentration (467.2 mg kg\({}^{-1}\)). Aerobic composite, in the absence of earthworms, showed very low and even negative reduction values, indicating the fundamental role of _E. eugeniae_ in this work. The remediation capacity of the epigeic earthworm _Perionyx excavatus_ was studied in the article by [PERSON] et al. [98] on a substrate composed of sludge from paper mill wastewater added with CD in various proportions. The authors measured that earthworms improve the remediation of all PTEs studied (linear regression analysis showed a positive correlation in earthworm treatments). More satisfactory results were obtained when the contaminated matrix was mixed with 50% CD; in this treatment, the health parameters of earthworms (biomass, fertility and histopathological changes) were significantly better, and vermieremediation caused a significant decrease in the level of elements in the following order: Pb (56%) > Cr (46%) > Cu (42%) and Cd (27%).