Ecotoxicity assessment for environmental risk and consideration for assessing the impact of silver nanoparticles on...

Silver nanoparticles (AgNPs) are found in a range of commercial products due to their proven antibacterial properties. The unused silver nanoparticles (AgNPs) may make its way into the soil via biosolids that come from wastewater treatment or the effluent that comes from industrialisation processes, where it could be harmful to the organism that live in terrestrial ecosystems. In addition, silver ions are one of the most toxic forms of heavy metal released from dissolved silver nitrate (AgNO₃) and AgNPs through dissolution or oxidation. The study examined the effect of engineered AgNPs, and AgNO₃ on earthworms which are one of the most important bioindicator for determining toxicity in soil environment. Epigeic earthworm, Eudrilus eugeniae was exposed to soils spiked with equivalent concentrations of AgNPs or AgNO₃ at 0, 10, 100, and 200 mg kg^-1 in soil for 56 days of experiments. The survival and growth rate was recorded at 7^th, 14^th, 21^st, 28^th days and accumulation of Ag in earthworm tissue at 14^th and 28^th days, antioxidant enzymes at 28^th days and reproduction at 56^th days of experiment. Further, a short-term exposure of AgNPs and AgNO₃ was conducted to observe avoidance behaviour after 48 h of exposure. The result indicated that survivability was relatively low on exposure of AgNO₃ (83.3%) than AgNPs (86.7%) in 200 mg kg^-1 spiked soils, besides the growth was inhibited in both AgNPs (3.68%) and AgNO₃ (3.25%) at 28^th days. The uptake of Ag from AgNO₃ in the earthworm tissue was slightly higher than uptake of Ag from AgNPs and it showed concentration-dependent inhibitory effects on reproduction. In AgNO₃ spiked soil, a high level of the Malondialdehyde (MDA) based lipid peroxidation and increased activity of antioxidant enzyme catalase (CAT) was observed than AgNPs spiked soil. Similarly, glutathione (GSH), a cofactor for GPx and GST enzymes, was lower in AgNO₃-spiked soil than in AgNPs-spiked soil. In terms of avoidance behaviour, there was no discernible difference between the distribution of earthworms in AgNPs and AgNO₃ after 48 h. The study found E. eugeniae exhibits concentration-dependent alterations in its competence to survive, antioxidant enzymes, and reproduction. AgNO₃ was found to be more sensitive than AgNPs in the study. The research investigates the effect of AgNPs on earthworms in the soil ecosystem since this understanding is crucial for a comprehensive evaluation of AgNPs' environmental consequences.