Evidence for negative effects of ZnO nanoparticles on leaf litter decomposition in freshwater ecosystems

We investigated the negative effects of ZnO nanoparticles (NPs) on ecosystem function by focusing on the process of leaf litter decomposition in an aquatic ecosystem. In an indoor microcosm experiment, the influence of 3 different sizes (30, 90 and 200 nm) of ZnO NPs at 100 mg L−1 concentration on Populus nigra L. leaf litter decomposition was determined. Exposure to ZnO NPs significantly inhibited the leaf litter decomposition and a strong inhibitory effect occurred on day 10, 17, and 27 in the 90, 30, and 200 nm ZnO microcosms, respectively. After 46 days' exposure of leaf litter, the highest decomposition rate was found in the control microcosms (0.47 m−1), followed by the 200 nm ZnO microcosms (0.37 m−1), the ZnSO4 microcosms (0.36 m−1), the 30 nm ZnO microcosms (0.28 m−1), and 90 nm ZnO microcosms (0.25 m−1), respectively. A significant decrease of the microbial biomass and enzyme activities (acid phosphatase, cellobiohydrolase, N-acetylglucosaminidase, polyphenol oxidase, and peroxidase) was observed in the ZnO NP exposure microcosms. ZnO NPs caused damage to the mycelium of aquatic hyphomycete and altered the composition of the fungal community associated with litter decomposition. In conclusion, the study expanded our understanding of ZnO NP toxicity on decomposition systems in freshwater ecosystems and highlighted the importance of using litter decomposition processes in NPs ecotoxicity assessments.