Acute and chronic toxicity of nickel oxide nanoparticles to Daphnia magna: The influence of algal enrichment

•Acute toxicity of nNiO on Daphnia magna increased in a time and dose-dependent manner.•Exposure to nNiO at sub-lethal concentration (< 1 mg/L) significantly affected daphnia's fecundity.•Dietary is the main exposure route by which nanoparticles are absorbed by the daphnid.•Toxicity was enhanced when algae were enriched with nNiO before daphnia ingestion.

Among the emerging literature addressing the biological effects of nickel oxide nanoparticles (nNiO), very little information exists, particularly on aquatic organisms. And the extensive application of nNiO may result in their bio-transfer in a food chain through various routes in a freshwater ecosystem. In this study, the potential effects of nNiO on the water flea, Daphnia magna, were examined with 48-h acute toxicity tests and 21-day chronic assays. In addition, three exposure experiments representing different uptaking mechanisms (aqueous, environmental and dietary exposures) were performed. The acute test indicated that the 48-h LC50 was 36.79 (26.14-56.72) mg/L and the toxicity increased in a time and dose dependent manner. Meanwhile, the chronic test demonstrated that reproduction was a more sensitive indicator of toxicity than mortality and the adult growth. The LOEC of 0.1 mg/L was obtained by the offspring number at first brood. There was a significant difference between the groups exposed through aqueous and dietary treatments (p < 0.05). Compared to the aqueous exposure, animal survival rates in environmental and dietary exposure groups decreased to 43.3% and 6.7% at 1 mg/L, respectively. Meanwhile, the proportion of animals that survived at 10 mg/L decreased to 23% and 10% for the environmental and dietary exposures, respectively. Dietary exposure group showed the lowest proportion of surviving individuals, indicating that ingestion of food (i.e. algae) contaminated by nanoparticles could be the efficient route for uptake of nNiO.