Biological monitoring of soil pollution caused by two different zinc species using earthworms.

Abstract

Zinc oxide nanoparticles (ZnO-NPs) are commonly used in both commercial and agricultural sectors. As a result, ZnO-NPs are extensively discharged into soil ecosystems, creating a significant environmental issue. Therefore, it is crucial to assess their influence on the soil ecology to ensure its secure and enduring utilization in the future. The exact degree of toxicity associated with ZnO-NPs and their ionic form is still uncertain. To address the challenges, the study used the soil bioindicator earthworm species Eudrilus eugeniae as an experimental model to evaluate the effects of two zinc species (ZnO-NPs and ZnCl2) at 100, 250, 500, and 750mgkg-1 and control (0mgkg-1) in garden soil over 28days. The investigation alsoexamined the impact ofexposure on survival, reproduction, neuro-biomarker, avoidance behavior, and accumulation. The highest avoidance rates were 27.5% for ZnO-NP and 37.5% for ZnCl2 at 750mgkg-1. ZnCl2 treatment reduced juvenile production by 3.73 ± 1.73, while ZnO-NPs showed 4.67 ± 1.15. At 750mgkg-1, soils with ZnCl2 (63.3%) demonstrated lower survival rates than those with ZnO-NPs (53.3%), likely because of higher Zn ion levels. After 28days of exposure, ZnCl2 (536.32 ± 11molmin-1) activated AChE enzymes more than ZnO-NPs (497.7 ± 59molmin-1) at the same dose, compared to control (145.88 ± 28 to 149.41 ± 23molmin-1). Nanoparticles and zinc ions bioaccumulated and reacted negatively with the neurotoxic marker AChE, affecting earthworm reproduction and behavior. However, earthworms exposed to ZnCl2 exhibited less intestinal Zn than those exposed to NPs. The present work contradicts the finding that ZnO-NPs have hazardous effects on soil organisms. The results indicate that earthworm E. eugeniae may significantly affect soil metal uptake from metallic nanoparticles (NPs). This may help design NP soil pollution mitigation strategies.The study offers valuable information for establishing a relationship between the environmental toxicity of ZnO-NPs and soil ecosystems.