Livestock waste-mediated biosynthesis of stable bactericidal silver nanoparticles and their chronic toxicity evaluation in fish using biomarkers

Silver nanoparticles (Ag-NPs) are contaminants of emerging concern. However, limited work has been done on chronic toxicity of Ag-NPs to fish using biomarkers. The present study elucidates the extracellular synthesis of non-agglomerated Ag-NPs using processing waste of sheep and swine by dispensing with additional capping agents and their characterisation, and toxicity evaluation on the physiological stress response of Pangasianodon hypophthalmus using biomarkers. Spectrophotometry, FTIR, DLS and HR-TM were employed for characterisation of Ag-NPs. Antioxidant, metabolic and acetylcholinesterase (AChE) enzyme activities were assayed using standard methods for chronic toxicity analysis of Ag-NPs to fish. Characterisation results showed a spherical shape of AgNPs with predominant size frequency between 5-20, 21-30 followed by 31-50 and 51-100 nm, capping by biomolecules, absorption at 400-410 nm with zeta potential of -27 and -32 mV. Sheep waste-derived Ag-NPs showed high bactericidal properties against fish pathogens. An enhancement in antioxidant and metabolic enzyme activities and inhibition of AChE activity were observed with increased sub-lethal ammonia concentration and temperature. Biosynthesis of Ag-NPs can be undertaken using animal wastes for their potential application in environment and health management of aquaculture based on characterisation, capping, bactericidal activity, biomarkers and physiological responses in fish.