Predicting the bioremediation potential of earthworms of different ecotypes through a multi-biomarker approach.

Earthworms are attracting the attention of bioremediation research because of their short-term impact on pollutant fate. However, earthworm-assisted bioremediation largely depends on the earthworm sensitivity to target pollutants and its metabolic capacity to break down contaminants. The most studied species in soil bioremediation has been Eisenia fetida, which inhabits the soil surface feeding on decomposing organic residues. Therefore, its bioremediation potential may be limited to organic matter-rich topsoil. We compared the detoxification potential against organophosphate (OP) pesticides of three earthworm species representative of the main ecotypes: epigeic, anecic, and endogeic. Selected biomarkers of pesticide detoxification (esterases, cytochrome P450-dependent monooxygenase, and glutathione S-transferase) and oxidative homeostasis (total antioxidant capacity, glutathione levels, and glutathione reductase [GR] and catalase activities) were measured in the muscle wall and gastrointestinal tract of E. fetida (epigeic), Lumbricus terrestris (anecic) and Aporrectodea caliginosa (endogeic). Our results show that L. terrestris was the most suitable species to bioremediate OP-contaminated soil for the following reasons: 1) Gut carboxylesterase (CbE) activity of L. terrestris was higher than that of E. fetida, whereas muscle CbE activity was more sensitivity to OP inhibition than that of E. fetida, which means a high capacity to inactivate the toxic oxon metabolites of OPs. 2) Muscle and gut phosphotriesterase activities were significantly higher in L. terrestris than in the other species. 3) Enzymatic (catalase and GR) and molecular mechanisms of free radical inactivation (glutathione) were 3- to 4-fold higher in L. terrestris concerning E. fetida and A. caliginosa, which reveals a higher potential to keep the cellular oxidative homeostasis against reactive metabolites formed during OP metabolism. Together with biological and ecological traits, these toxicological traits suggest L. terrestris a better candidate for soil bioremediation than epigeic earthworms.

Exploring the potential enzymatic bioremediation of vermicompost through pesticide-detoxifying carboxylesterases.

Vermicompost is a known biofertilizer of potential use in soil bioremediation. This study was undertaken to explore the capacity of grape marc-derived vermicompost to inactivate methyl carbamate (MC) and organophosphorus (OP) pesticides via exploring the carboxylesterase (CE) activity level and its response to pesticide exposure. We first optimized the method for enzyme activity assay comparing the CE activity in two contrasting homogenization procedures (30-min mixing and mortar grinding). Thereafter, we assessed the sensitivity of the enzyme by both in vitro and vermicompost incubation trials with selected pesticides. The main findings can be summarized as follows: i) grinding the vermicompost in water (2% w/v) yielded maximum enzyme activity; ii) at concentrations around 10-4 M, highly toxic oxygen-analog metabolites of OPs strongly inhibited the CE activity (76-93% inhibition), but MC did not inhibit the enzyme activity; iii) liquid vermicompost was able to degrade chlorpyrifos and inactivate its highly toxic metabolite chlorpyrifos-oxon. Our results suggest that liquid vermicompost is the most appropriate preparation to increase the enzymatic potential of vermicompost in pesticide-contaminated soils.

Biochar increases pesticide-detoxifying carboxylesterases along earthworm burrows.

Herein, we examined whether synergistic effects of earthworms (Lumbricus terrestris) and pine needle-derived biochar result in biochar-coated burrows with enhanced carboxylesterase (CE) activity (a pesticide-detoxifying enzyme). Biochar was placed at the top of soil columns at two doses (2.5 and 5% w/w dry mass), with an additional biochar-free treatment as control. Carboxylesterase and dehydrogenase activities were measured in the burrow walls sampled at three depths (0-4, 8-12, and 18-22 cm). Biochar was recovered from these samples to confirm its vertical transport and enzymatic activation. We tested whether biochar protected CE activity against desiccation stress of burrow wall samples. Likewise, the role of earthworm mucus in stabilizing CE onto biochar surface was also investigated by measuring the enzyme activity in fresh biochar particles previously incubated in the presence of earthworm mucus and purified esterase. Finally, we checked for the sensitivity of biochar-bound CE activity against selected organophosphorus pesticides. The main results were: i) co-application of earthworms and biochar caused a significant increase of CE activity in the first 12 cm of the soil column, ii) recovered biochar particles displayed CE activity which was significantly higher in the particles collected from the bottom of columns, iii) soil desiccation decreased the enzymatic activity, although such effect depended on biochar treatment and column depth (22-77% inhibition). Nevertheless, CE activity still was higher in the samples from the 5%-biochar treatment than activity in control and 2.5%-biochar treatments, iv) earthworm mucus favored the retention of CE onto the biochar surface, and v) the activity of biochar-bound CE was sensitive to inhibition by chlorpyrifos-oxon. These results suggest that the joint application of L. terrestris and biochar may be a suitable vermiremediation strategy to inactivate OP pesticides.