Purpose

This study aimed to elucidate how soil type governs the dissipation and biological effects of three widely used neonicotinoid insecticides (imidacloprid, thiamethoxam, and clothianidin) on key microbial functions linked to soil health. We evaluated whether contrasting soils differ in their sensitivity and resilience to pesticide exposure.

Methods

Microcosm experiments were conducted using two representative Araucanian agricultural soils of Chile: an organic matter–rich Andisol (Freire series) and a clay-rich Inceptisol (Chufquen series). Soils were treated with recommended (1×) and elevated (10×) doses and incubated for 30 days. Enzymatic activities, bacterial abundance (16 S rRNA), nitrogen fixation potential (nifH), nitrification potential, inorganic nitrogen dynamics, and pesticide dissipation were monitored.

Results

Neonicotinoid effects were strongly soil-dependent. The Andisol showed higher functional sensitivity, with marked inhibition of urease, dehydrogenase, and nitrification shortly after application. In contrast, the Inceptisol exhibited greater microbial stability and resilience, likely related to higher clay-mediated adsorption. Across both soils, effects were mostly transient, with recovery of microbial functions despite persistent residues. Dissipation patterns also varied between soils and compounds.

Conclusions

This study provides novel evidence that neonicotinoid effects on enzymatic and molecular indicators have not been previously evaluated in an integrated manner in Araucanian soils of Chile. Soil type is a key determinant of pesticide fate and impact. Although short-term disturbances occur, microbial communities show resilience; however, the persistence of certain compounds highlights the need to consider potential accumulation and effects on non-target organisms.