Effects of nanoplastic exposure routes on leaf decomposition in streams.

Polystyrene nanoparticles (PS NPs) released from plastic products have been demonstrated to pose a threat to leaf litter decomposition in streams. Given the multitrophic systems of species interactions, the effects of PS NPs through different exposure routes on ecosystem functioning remain unclear. Especially dietary exposure, a frequently overlooked pathway leading to toxicity, deserves more attention. A microcosm experiment was conducted in this study to assess the effects of waterborne and dietary exposure to PS NPs on the litter-based food chain involving leaves, microbial decomposers, and detritivores (river snails). Compared to waterborne contamination, dietary contamination resulted in lower microbial enzyme activities and a significantly higher decrease in the lipid content of leaves. For river snails, their antioxidant activity was significantly increased by 20.21%-69.93%, and their leaf consumption rate was significantly reduced by 16.60% through the dietary route due to the lower lipid content of leaves. Besides, the significantly decreased nutritional quality of river snails would negatively influence their palatability to predators. The findings of this study indicate that dietary exposure to PS NPs significantly impacts microbial and detritivore activities, thus affecting their functions in the detritus food chain as well as nutrient cycling.

Response of a simulated aquatic fungal community to nanoplastics exposure and functional consequence on leaf decomposition.

Nanoplastics pose a potential threat to a wide variety of aquatic organisms. Despite the awareness of this existing hazard, the impact of nanoplastics on natural fungal communities remains a research gap. In this study, five dominant fungi species, isolated from a stream ecosystem, were used to explore the effects of different nano-polystyrene (nano-PS) particles concentrations on a simulated fungal community. Specifically, the evaluation was conducted regarding the fungal growth, reproductivity, structural composition, and ecological function in leaf litter decomposition. A 15-day exposure experiment showed that 100 µg/L nano-PS significantly reduced the microcosm pH. The extracellular enzyme activities of ß-glucosidase, leucine-aminopeptidase, and peroxidase were significantly promoted by nano-PS exposure for 5 days or 15 days. Total sporulation rate significantly decreased after the 15-day exposure to 1 and 100 µg/L nano-PS and significantly increased under 10 µg/L nano-PS. In contrast, nano-PS concentrations had no effects on fungal biomass. In addition, the reduced relative abundance of Geotrichum candidum lowered its contribution to leaf decomposition, resulting in a decreased litter decomposition rate of a 24.5-27.9 % after exposure. This suggests that 1-100 µg/L nano-PS inhibited leaf decomposition by inhibiting fungal reproduction and reducing the contribution of specific fungal species. In addition, the findings highlight the importance of exploring the potential mechanisms of the interaction between nanoplastics and fungal species.

Polystyrene size-dependent impacts on microbial decomposers and nutrient cycling in streams.

The particle size of plastic is one of the most important factors influencing its ecotoxicity, but we are unclear about the effect of polystyrene (PS) particle size on microbial decomposers and consequent nutrient cycling in streams. Here, using microcosm experiments, we assessed how three PS sizes (50 nm, 1 µm, and 20 µm) influenced the process and consequences of leaf litter decomposition. Under acute exposure to 1 µm and 20 µm PS, fungal biomass significantly decreased, but microbial biomass significantly increased, indicating compensations may work between fungi and other microbial decomposers. After chronic exposure to 50 nm and 1 µm PS, the leaf decomposition rate decreased by 19.27 % and 15.22 %, respectively, due to the reduced microbial enzyme activity, fungal diversity, and dominance of Anguillospora. As a result, the regeneration of nutrients, especially phosphorus, was significantly depressed, which might influence the primary productivity of streams. Therefore, our results suggest that nanoscale PS has a greater impact on microbial activity, thus affecting their functioning in leaf litter decomposition and consequent nutrient cycling. The findings provide a data support for the risk assessment of plastic pollution in freshwater systems.