# A Systematic Review on Earthworms in Soil Bioremediation
## 3 Results
### Combined Vermierendiation for Inorganic Pollution  
Recently, the scientific community's attention has grown on combining different bioremediation techniques to obtain better restoration results. Phytoremediation is a technique widely used in soil restoration from PTEs; however, it has limitations, such as low biomass of accumulator plants and poor bioavailability of these contaminants in soil [125]. The co-application of other biological techniques, such as vermierendiation, can enhance the efficacy of phytoremediation. Due to their life activity and ingestion processes, earthworms improve the soil's physical, chemical and biological fertility, creating an ideal environment for plant fitness and enhancing its phytoremediation power [126, 127]. Moreover, earthworms augment the bioavailability of metals in the soil and influence pH and dissolved organic carbon [128]. Nine articles were discussed regarding the use of vermierendiation together with other bioremediation techniques with respect to inorganic contaminants, four of which were reworked, as shown in Figure 4.  
In a microcosm experiment, [PERSON] et al. [129] evaluated the influence of two species of earthworms (_E. fetida_ and _Amvthas aspergillus_) on the growth and metal accumulation of _Brassica campestris_. The substrate consists of an agricultural topsoil artificially contaminated with three different Pb concentrations (100, 500 and 1000 mg kg\({}^{-1}\)). Different ecological earthworm species may have dissimilar effects on the cycle of PTEs and soil proprieties. Indeed, this study showed that _E. fetida_ had a superior impact on cation exchange capacity, tissue accumulation and availability of Pb, while _A. aspergillus_ affects more soil C and N contents. At the end of the trial, soil bioavailable Pb was generally higher in the treatments with earthworms, independently from the species used. Although the presence of _E. fetida_ and _A. aspergillus_ increases the bioavailable Pb and, therefore, its potential toxicity towards plants, they improve the physicochemical properties of the soil, bypassing the adverse effects. In fact, _B. campestris_ subjected at the higher Pb level with the presence of earthworms, significantly increasing some parameters such as aboveground fresh biomass, leaf area and chlorophyll concentration. At the same plant biomass condition, a higher Pb concentration was observed in treatments with _A. aspergillus_; however, _E. fetida_ enhanced the aboveground biomass production, leading to a higher accumulation of this metal in the plant. Earthworm activity favours Pb accumulation and concentration; nevertheless, the translocation factor (ratio between xenobiotic concentration in aboveground and root plant tissues) indicates that the metal remains at the root level, so _B. campestris_ is not a good hyperaccumulator. The addition of organic amendments is suitable for bioremediation processes as it improves the soil's physical, chemical and biological properties by supplying nutrients and organic matter; consequently, these increase the survival and growth performance of the organisms involved in the restoration. [PERSON] et al. [130] tested the vermiremediation (_E. fetida_) and phytoremediation (_Spinacea oleracea_), alone or combined, with or without the addition of cow and buffalo dung. An artificial soil was prepared for the tests and contaminated with Pb, Cd and Cr. Cow dung is known for extending the phytoremediation potential of plant species by supplying the necessary plant nutrients [131]. Furthermore, CD creates favourable habitats for earthworms, improving parameters such as growth rate, body weight and reproduction compared to buffalo dung, which has a reduced content of organic matter. In general, the presence of _E. fetida_ in soil reduced or mitigated the effect of PTEs on _S. oleracea_.