Biological monitoring of Soil pollution caused by two different Zinc species using earthworms

Abstract

Zinc oxide nanoparticles (ZnO-NPs) are frequently employed in both commercial and agricultural sectors. Consequently, it is imperative to evaluate their impact on the soil ecosystem to ensure their safe and sustainable utilization in the long term. Earthworms are often used as a first indicator of soil pollution to monitor various pollutants. Nevertheless, there are unavoidable impediments that emerge during monitoring contamination in practical situations. To address the challenges, the study used soil bioindicator earthworm species Eudrilus eugeniae as an experimental model to evaluate the effects of two zinc species (ZnO-NPs and ZnCl2) on survival, reproduction, neuro-biomarkers, avoidance behavior, and their accumulation. The highest avoidance percentage was recorded 27.5% for ZnO-NP exposure and 37.5% for ZnCl2 exposure at 750 mg kg-1. ZnCl2 exposure decreased juvenile production by 3.00 ± 1.73 compared to 4.67 ± 1.15 for ZnO-NPs. At 750 mg kg−1, soils containing ZnCl2 (63.3%) had worse survival than those with ZnO-NPs (53.3%) administered, likely due to higher Zn ion. The bioaccumulation of nanoparticles and zinc ions adversely affect earthworm reproduction by reacting unfavourably with the neurotoxic marker AChE. Nevertheless, earthworms exposed to ZnCl2 had less Zn build-up in their gastrointestinal tracts than those exposed to NPs. The present work contradicts the finding that ZnO-NPs have hazardous effects on soil organisms. Instead, the study found that the toxicity of ZnCl2 was higher than that of ZnO-NPs. This difference in toxicity may be attributed to the ionic forms of Zn rather than its size. The study is valuable for ensuring the secure and sustainable application of ZnO-NPs.