# A Systematic Review on Earthworms in Soil Bioremediation
## 3 Results
### Combined Vermierendiation for Organic Pollution  
In this chapter, ten articles were analysed, six of which were reworked, as shown in Figure 5.  
[PERSON] et al. [148] studied the efficiency of the co-application of _E. fetida_ and _Lolium pereenne_ in agriculture topsoil contaminated in a laboratory test with anthracene, a model compound for PAHs. Earthworms alone reduced the amount of contamination by 40%, while plants gave significantly higher results (81%, S + P). However, as seen in Figure 5, earthworm-assisted phytoremediation gives the best results, decreasing 92% (S + E + P) of the anthracene in the soil. Figure 4: Combined vermierendiation for inorganic pollution. Xenobiotic reduction percentage (blue bars) and initial concentration (red dash) for each treatment. Treatments (yellow labels) legend: S (substrate), E (earthworm), 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: 4, in order of comparison, [PERSON] et al., 2022 [138]; [PERSON] et al., 2021 [139], [PERSON] et al., 2022 [144]; [PERSON] et al., 2022 [147]). This research article reported that ryegrass and _E. fetida_ have a mutualistic relationship. The plant presence was beneficial in contaminated treatments for the earthworm survival rate, which was statistically more relevant than in the S + E treatment. The excavation activity of these organisms raised soil porosity and aeration, favouring plant dry biomass in general; specifically, the root extension demonstrated a significant increase with or without contamination. Also, [PERSON] et al. [149] investigated the effect of joint application of bio-techniques, using plant (_Pennisetum clandestinum_) and earthworm (_E. andrei_) versus hydrocarbon contamination. The substrate employed was a compost obtained after six months of aerobic composting process of hydrocarbon-contaminated waste food industry sludge and shredded plant material. The bioassay results with plants and earthworms are reported in Figure 5. In the S + P treatment, a significant TPH reduction of 9.3% was observed, which becomes superior (15.2%) in the joint treatment (S + E + P). The reduction observed in the combined treatment may be due to the transfer of TPHs in the earthworm body to the plant's rhizosphere, where these pollutants were degraded in the best way [150]. Another recent study conducted in Italy [151] used the earthworm-plant strategy as a restoration technique. This combined process was tested on soil taken from the national priority site of Brescia-Caffaro, which is over-limit contaminated by polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and polychlorinated biphenyl (PCBs). The study found that plants and earthworms had a weak bioremediation effect compared to treatments with only soil; moreover, in this case, earthworms and plant interaction seems to reduce the positive impact of each other alone. These negative results may be related to the low bioavailability of PCDD/Fs and PCB, the insufficient experiment length and the number of _E. fetida_ individuals. Furthermore, due to their excavation activity, earthworms may contribute to a higher contaminant concentration in percolated water; accordingly, attention must be paid to the fate of these pollutants under field conditions. The purpose of [PERSON] et al. [152] was to investigate the effect of _L. terrestris_ (at 5 and 10 earthworms kg\({}^{-1}\) soil, E1 and E2, respectively in Figure 5) and a consortium of three bacteria (_Corynebacterium_ sp., _Sphingobacterium gobiese_ and _Kocuria flava_) on the percentage removal of chlorpyrifos insecticide from the soil. The bacteria consortium alone (S + M) showed the highest effect on the reduction percentage (73.83%), followed by their combination with a high density of earthworms (71.22%, S + E2 + M).