Heavy metals and contaminants
Vermicomposting facilities often receive sewage from both domestic and industrial sources that might be contaminated by medicines and heavy metals. These contaminants may be detrimental to earthworm growth, survival and reproduction. Earthworms are able to accumulate a number of metals in their body (Morgan, 2011). However, earthworms do not act like plant accumulators. It was shown that Zn and Cu uptake was counter-balanced by excretion while Cd and Pb had low excretion and could thus accumulate more easily (Spurgeon et al., 1999). It has been hypothezised that heavy metal accumulation in earthworms depends on bioavailable heavy metals in the substrate. It was suggested to lower heavy metal bioavailability through pH modification or additives (Li et al., 2010).
Feed safety
Rats fed on 10% earthworm meal showed no signs of morbidity, mortality, or deteriorated health parameters. No effects were observed on their reproduction or lactation. Only their gonads were found to be heavier. It was concluded that earthworm meal could be safely used in animal feeding (Ibanez et al., 1993).
Coelomic fluid of Eisenia fetida
The coelomic fluid of earthworms moistens their skin and allows them to move in the ground. In Eisenia fetida, the foul-smelling yellow coelomic fluid is excreted when the worms are stressed, and it plays a role of deterrent for predators (Musyoka et al., 2019). The coelomic fluid of Eisenia fetida was found to be safe for 42 species of invertebrates (larvae and aquatic adults) but it was toxic to vertebrates, including fish (11 species), toad tadpoles (Bufo japonicus formosus), reptiles (lizard Japanula polygonata, soft shelled turtle Trionyx japonicus), birds (Japanese quail) and mammals (mouse and rat). The toxicity occurs at low levels (0.2-2%) and within 10 to 225 min depending on the species. This toxicity can be alleviated by heating the coelomic fluid, hence the necessity of blanching the earthworms (Kobayashi et al., 2001).