Effect of humic acid on the toxicity of bare and capped ZnO nanoparticles on bacteria, algal and crustacean systems

•Nanoparticles were prepared by chemical coprecipitation method.•Humic acid capping affected the hydrodynamic size and stability of the particles.•Adsorption of humic acid affected the toxicity of the particles.

Zinc oxide nanoparticles are one of the most extensively used nanoparticles in various commercial products. Depending on the purpose, the particles are coated with various agents including poly vinyl pyrrolidone, poly vinyl alcohol, ethylene glycol etc. As the particles are heavily used, the chance of the particles to get run off into the environment is very high. The study explains the difference in toxicity of bare and capped zinc oxide nanoparticles under various environmental conditions including humic acid and visible light against bacterial, algal and crustacean system. Staphylococcus aureus and Pseudomonas aeruginosa were used as model system for bacterial toxicity testing. Plate counting assay was employed for assessing the toxicity against bacteria. Chlorella pyrenoidsa was used for studying toxicity against algal system, which was evaluated using the chlorophyll estimation assay. Daphnia sp. was used for studying the toxicity in crustacean system. The particles had the ability to adsorb humic acid which further affected the stability of the particle. The study concludes that the presence of environmental factors including humic acid affects the toxicological nature of ZnO NPs.