Role of soil texture and earthworm casts on the restoration of soil enzyme activities after exposure to an organophosphorus insecticide.

Pesticides exert important effects on the soil fauna and health. However, little is known about the interactions of soil, microorganisms and earthworms in the presence of pesticides and about their respective roles in the soil biological activity. The aim of this study was to evaluate the effect of the soil type on enzyme activities, measured in bulk soil and in casts of two earthworm species, after exposure to the organophosphorus pesticide parathion. To this aim, two endogeic earthworm species (Apporectodea caliginosa and Allolobophora chlorotica) were cross-acclimated in two different soil textures (each representing the most favorable soil environment for that species). Enzyme activities were measured as a soil quality indicator in samples of bulk soil (collected at day 4 and day 7 of exposure to parathion) and in earthworm casts (collected at day 7). A short exposure (4 days) to parathion significantly (ANOVA, p < 0.001) inhibited carboxylesterases (25–43 % of inhibition) and alkaline phosphatase (∼23 % of inhibition). At day 7 of exposure, parathion impact on the overall soil enzyme activities mainly depended on the soil texture. Indeed, activity inhibition was higher (ANOVA, p < 0.001) in silt-clay soil (decrease by 37 %) than in silt-loamy soil (decrease by ∼18 %). Conversely, parathion effect was not influenced by earthworm presence/absence and earthworm species. However, after soil exposure to parathion, earthworms (both species) improved enzyme activity restoration in their casts. • Parathion exposure induced a decrease in bulk soil enzyme activities. • Bulk soil enzyme activity changes were influenced by the soil type. • After parathion exposure, soil enzyme activities were restored in earthworm casts. • Earthworm species did not influence enzyme activities in control and polluted soils. [ABSTRACT FROM AUTHOR]