Role and possible mechanisms of earthworm Eisenia fetida in the elimination of microcystin-LR in soil

A better understanding of microcystin elimination in soil will boost the development of effective strategies to mitigate associated contamination. This study addressed the role and mechanism by which earthworm Eisenia fetida take part in the elimination of microcystin-LR (MC-LR) in soil. The degradation kinetics of MC-LR exhibited good fits with the availability-adjusted first-order kinetic model ( R 2  > 0.97), where >71% of the toxin was rapidly eliminated within the initial eight days ( t 1/2  = 2.34–3.07 days). E . fetida significantly accelerated MC-LR elimination, with a less t 1/2 of 1.09–1.12 days; however, E . fetida did not further improve the final elimination efficiencies on Day 29 (82.59–93.57% with E . fetida vs . 82.96–92.34% without E . fetida ). In soil, E . fetida accelerated MC-LR elimination mainly via biodegradation arising from elevated total organic carbon, enhanced enzyme activities (urease and sucrase) and ameliorations of bacterial bioactivity, diversity and abundance. Indigenous bacteria of Methylophilus and Methylovorus , as well as earthworm-derived Flavobacterium , were considered as potential bacterial degraders for MC-LR. These findings elaborate on the variations in soil properties and soil bacterial community structure and diversity that occurs during MC-LR elimination and lay a foundation for controlling MC-LR contamination in the soil environment.