Biochemical response and vermiremediation assessment of three earthworm species (Alma millsoni, Eudrilus eugeniae and Libyodrilus violaceus) in soil contaminated with a glyphosate-based herbicide

The global use of glyphosate-based herbicides (GBHs) and release of glyphosate residues in soil environment have over the years been a major concern. In this study, we aim to evaluate the biochemical response and vermiremediation potential of three indigenous earthworm species; namely Alma millsoni, Eudrilus eugeniae and Libyodrilus violaceus in GBH treated soils. Study design: Three weed plants (Tridax procumbense, Ludwigia pasturis and Pannicum maximum) were transplanted into 140 plastic pots and 20 adult individual earthworms of each species were later introduced into 60 pots. In total, each earthworm species treatments representing 20 pots and 20 pots without earthworm were sprayed with 115.49 mL/m2 (equivalent to 83.2 g a.i/m2) of Roundup® Alphée. The remaining 60 pots with earthworm species were left unsprayed. Activities of glutathione-S-transferase (GST), lactate dehydrogenase (LDH), metallothionine (MT), acetylcholinesterase (AChE), antioxidant defense system and lipid peroxidation (MDA) were monitored at the 1st, 2nd, 4th, 6th and 8th weeks Post Herbicide Application (PHA) using standard methods. Glyphosate residues in the soil and earthworm species were quantified with a High-Performance Liquid Chromatography (HPLC) with fluorescence detector. Bioaccumulation Factor (BAF) was also calculated. Results: Higher activities of GST and LDH and reduction in MT activities were observed in the three earthworm species exposed to GBH compared to the unexposed while AChE activity was insensitive to the herbicide. The antioxidant defence system was able to protect E. eugeniae and L. violaceus against oxidative stress. The presence of earthworms reduced glyphosate residues in the soil. E. eugeniae and L. violaceus were bioaccumalators and biomagnifiers of glyphosate as indicated by the BAF (> 1) obtained after 8th week PHA. Relationships exist between glyphosate BAF in E. eugeniae and L. violaceus and exposure duration as well as between glyphosate residues in tissues of the earthworm species and their biochemical parameters. Conclusions: Alterations in the enzymatic activities and antioxidant defence of the earthworm species could be an index for GBH contaminated soil monitoring and assessment; both E. eugeniae and L. violaceus showed potential to vermiremediate soils contaminated with GBH