Biochemical- and neuro-toxicity of silver nanoparticle and silver nitrate in soil to Aporrectodea calginosa earthworms

Abstract

Silver nanoparticles (AgNPs) are now widely used in many industry applications. Because there are no regulations on discharge limits, improper discharge of waste from these industries can lead to environmental contamination and damage to ecosystem organisms. In this study Aporrectodea caliginosa earthworms were exposed to 0 (control), 0.3, 3, 30, 300 mg/kg Ag as AgNPs and 0, 0.03, 0.3, 3, 10 mg/kg of Ag as AgNO₃ in soil for 4 weeks and select biochemical and neurotoxicity studies were conducted weekly. The lipid peroxidation (measured using thiobarbituric acid reactive substances; TBARS) and activities of antioxidant enzymes (catalase, glutathione peroxidase, superoxide dismutase, glutathione S transferase, lipid peroxidation), and nerve conduction velocity (NCV) of the medial giant fibers (MGF) using a novel non-invasive electrophysiological technique were measured in earthworms weekly. The TBARS and antioxidant enzyme activities were elevated by both AgNO₃ and AgNPs and this was most evident in earthworms at 4 weeks >3 > 2 > 1. In neurotoxicity studies, MGF NCV progressively decreased in A. caliginosa exposed to both AgNPs and AgNO₃. The findings highlight oxidative stress and neurotoxic effects of Ag compounds on earthworms and the importance of government authorities to have legislations in place to prevent excessive soil contamination by AgNPs produced by the expanding nanotechnology industries.