Harmful effect of nanoparticles on the functions of freshwater ecosystems: Insight into nanoZnO-polluted stream

ZnO nanoparticle toxicity on aquatic organisms has been extensively studied, but its concentration-and time-dependent effects on ecosystem functioning are remain uncertain. Here we assessed the harmful effects of nano-ZnO (10, 100, 1000 mg L^-1) on the stream functioning by using a microcosm system simulating poplar leaf decomposition for 50 days. The 100 mg L^-1 ZnO nanoparticles had significantly and stably inhibitory effect on the litter decomposition during the exposure period. The inhibition was not detected in the 10 mg L^-1 treatment until 43 d. In contrast, the significant and continuous inhibition started to disappear from 43 d in the 1000 mg L^-1 treatment. The varied consequences on litter decomposition might be directly affected by the different ZnO nanoparticle homogeneity of the different treatments. ZnO nanoparticles led to significant decreases in pH value of the decomposition environment, which had significant and positive relationships to the activities of dehydrogenase, glycine-aminopeptidase, N-acetylglucosaminidase, and acid phosphatase. Besides, 10 and 1000 mg L^-1 ZnO nanoparticles led to lower fungal diversity, which was negatively related to the variability of decomposition. In conclusion, fungal decomposers showed different responses to the different concentrations of ZnO nanoparticle, and ultimately affected the stability of ecosystem functions.