Unravelling the detoxification trail of potential toxic heavy metals: an insight into heavy metal auditing and ecological health upon valorisation by Lampito mauritii and Eudrilus eugeniae

Evidence on prospective remediation of municipal solid waste contaminated with toxic heavy metals by Eudrilus eugeniae (Eu) and Lampito mauritii (L) is very scarce and yet to be explored. In this study, heavy metal detoxification potential of E. eugeniae and L. mauritii in municipal solid waste (MSW) + cowdung (CD) (3:1)-based feedstocks were investigated against Eisenia fetida (E) (a well-known vermi-remediator) and aerobic composting. Excellent reduction (70.01-93.04%) of potentially toxic heavy metals (PTHMs) (Pb, Cr, Cd and Zn) were evident in both E. eugeniae and L. mauritii employed treatments. Moreover, the results on heavy metal budget quotient clearly demonstrated the unique detoxification route undertaken by E. eugeniae and L. mauritii via humic composite facilitated chelation over the nominal bioaccumulation pathway. The principal component analysis (PCA) confirmed the strong negative correlation between the heavy metal (HM) level in earthworm gut and MSW substrate, whereas a strong positive correlation between humic substances and HM remediation. Furthermore, analysis of ecological health parameters indicated substantial reduction of environmental risk and guaranteed negligible risk of PTHM if utilized as manure. Moreover, significant increment in total N content (3.2-3.8-fold), available P (4-5.9-fold), exchangeable K (3.66-fourfold) and enzyme activity along with significant reduction of TOC (~ 87%) confirmed E. eugeniae and L. mauritii could effectively stabilize MSW. Thus, the metal-binding potential of humic substances produced by earthworms during the detoxification of municipal solid waste (MSW), coupled with a metal budget analysis, has offered valuable insights into the usage of E. eugeniae and L. mauritii as effective contenders for sanitizing heavy metal-laden MSW.