Effects of nanoplastic exposure routes on leaf decomposition in streams

Summary As the use of copper oxide nanoparticles (nanoCuO) in consumer products grows, aquatic ecosystems are likely to receive increasing amounts of these nanomaterials. Dissolved organic matter (DOM) may interact with nanoparticles and reduce their reactive surface area, which, in turn, can influence the impact of nanoCuO on organisms and ecological processes. We conducted a microcosm experiment to investigate the impacts of three size classes of nanoCuO (12, 50 and 80 nm mean diameter of the primary particles; five levels up to 400 mg L−1) and humic acid (three levels up to 100 mg L−1), as a major component of DOM, on microbial decomposers and leaf decomposition as an important ecosystem process in forest streams. Exposure to nanoCuO for 20 days reduced decomposition rate and fungal and bacterial biomass, fungal sporulation and spore diversity associated with the decomposing leaves. The effects were stronger as nanoparticle size decreased and the specific surface area increased. More dissolved ionic copper was released from the small nanoparticles, suggesting that Cu2+ could have played a role in the observed size‐dependent toxicity of nanoCuO. Bacteria appeared to be more sensitive to nanoCuO than fungi since nanoparticles reduced the biomass of bacteria at lower concentrations than that of fungi (EC20 was 22 times lower for small and medium‐sized nanoparticles, and five times lower for large particles). However, fungal sporulation was the variable most sensitive to nanoCuO exposure (EC20 = 0.2 mg L−1 for the small nanoparticles). Microbial activity on the decomposing leaves was also inhibited by exposure to humic acid alone. However, humic acid also mitigated the adverse effects of the small and medium‐sized nanoCuO on both the microbial decomposers and leaf decomposition. Overall, our microcosm experiment indicates that nanoCuO toxicity to microbial decomposers and leaf decomposition depends on particle size and the presence of DOM. This highlights the importance of considering environmental context and the specific properties of particles to assess toxicity of nanomaterials in stream ecosystems.

The effects of plastic pollution on marine organisms is of growing concern. The hydrophobic surface of plastics adsorbs organic contaminants and can alter the rate of chemical uptake in fishes. Per-fluorinated organic chemicals such as Perfluorooctanoic acid (PFOA) are highly hydrophobic toxic chemicals that adsorb to hydrophobic surfaces. We hypothesized that the presence of nano-sized plastic particles adsorbs PFOA and alter both the physical-chemical properties of the plastics and also enhance PFOA uptake into organisms. Using radiolabelled 14C-PFOA, we measured direct unidirectional uptake of PFOA in juvenile Pacific Oysters (Magallana gigas) at different (0.025, 0.50, and 0.100mg/L) concentrations, for different exposure periods (1, 2, 4, and 6h) and investigated whether varying concentrations (0.1, 0.5, 1mg/L) of either 500nm or 20nm polystyrene nanoparticles (PS-NPs) differentially altered the uptake rate of PFOA. Our results demonstrate that PFOA adsorbs to the surface of PS-NPs, altering PS-NP behaviour in solution and significantly increases the rate of uptake of PFOA in exposed Pacific oysters. PFOA uptake at 0.1mg/L was increased 2.3-fold in the presence of 1mg/L 500nm PS-NP and 3.2-fold in the presence of 1mg/L 20nm PS-NP. In a separate study to examine if PS NPs potentiate the biochemical response to PFOA, both 500 and 20nm PS-NP at 100mg/L increased the 1mg/L PFOA-induced oxidative stress by 2.5-fold and 3-fold respectively. These findings demonstrate that nanoplastics as co-contaminants in marine systems are able to adsorb PFOA and significantly potentiate its uptake and toxicity.

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

Nitrogen (N)‐fixing Acacia species are often aggressive invaders outside their native range. When invading native riparian temperate forests, they can decrease tree species diversity, alter the quality of litter inputs to streams and increase water N concentration. Although the effects of riparian tree species diversity and nutrient enrichment on litter decomposition and associated microbial decomposers have been widely studied, their individual and combined effects remain poorly understood, especially in streams flowing through forests invaded by Acacia species. Here, we assessed the effects of litter diversity (species evenness) and water N concentration on the decomposition of native and Acacia litter, and the activity and community structure of associated microbial decomposers. Litter of Castanea sativa (C) and Acacia melanoxylon (A) was enclosed in fine‐mesh bags in a total of five litter evenness treatments (100%C, 75%C + 25%A, 50%C + 50%A, 25%C + 75%A and 100%A), and immersed in a stream flowing through a native forest (native stream) and a stream flowing through a forest invaded by Acacia species (invaded stream). Litter decomposition rates and microbial decomposer activity differed among litter evenness treatments, generally decreasing as the proportion of A. melanoxylon increased. When considered individually, C. sativa litter decomposition and associated microbial activity did not differ among treatments. For A. melanoxylon, decomposition rates did not differ among treatments, whereas microbial activity was generally lower in treatments with higher or even proportions of C. sativa. Litter diversity had (small) antagonistic effects on litter decomposition in streams. However, litter treatments affected by diversity (species evenness) effects differed between streams, suggesting that effects can be modulated by water N concentration. Litter decomposition rates and microbial decomposer activity were higher in the invaded than in the native stream, probably as a consequence of the higher water N concentration in the former stream. However, the magnitude of the effects was small owing to the fact that water N concentration was still in the oligothrophic range in the invaded stream. Overall, our results suggest that the increasing proportion of N‐fixing Acacia species in invaded deciduous riparian forests will affect litter decomposition rates and microbial decomposer activity, and alter aquatic hyphomycete community structure, most probably as a result of decreases in the diversity and quality of litter inputs to streams, and increases in water N concentration. However, the magnitude of the effects resulting from decreases in litter input diversity and quality (due to increases in Acacia contribution) into invaded streams will probably be larger than those resulting from increases in water N concentration, thus overall litter decomposition will decrease. These impacts will possibly alter nutrient cycles in aquatic food webs that depend on riparian detritus, with implications for stream functioning.

Polystyrene nanoparticles (PS NPs) are biocompatible and low toxic material to biological systems. In this mind, PS NPs are widely used as a model for studying the interaction between nanoparticles and cells. Even PS NPs showed low toxicity, they could affect to some cellular responses. In this study, we investigated the influence of PS NPs on the epidermal growth factor (EGF)-response in the A431 human epithelial carcinoma cell line. The results showed that PS NPs interfered with the normal EGF-response of A431 cells in a dose-dependent manner. In addition, EGF significantly increased the uptake of PS NPs in A431 cells. Localization studies of PS NPs and EGF receptor (EGFR) indicated that changes in the EGF-response of A431 cells are related to the interaction between PS NPs and the EGF-EGFR complexes. The viability of cells exposed to PS NPs or combination of PS NPs and EGF decreased due to PS NPs induced cell death. The results also suggested that without EGF, PS NPs internalized in the cells cause cell death by necrosis, whereas EGF enhances the uptake ratio of PS NPs, and PS NPs in the cytoplasm together with EGF-EGFR complexes may inhibit receptors recycling, leading to apoptosis. This finding could be useful for the safe and effective use of nanoparticles in clinical applications.

Nanoplastic pollution inhibits stream leaf decomposition through modulating microbial metabolic activity and fungal community structure

Nanoscale plastic particles are widely found in the terrestrial environment and being increasingly studied in recent years. However, the knowledge of their translocation and accumulation mechanism controlled by nanoplastic characterizations in plant tissues is limited, especially in plant cells. Here, 20 mg L-1 polystyrene nanoparticles (PS NPs) with different sizes and amino/carboxy groups were employed to investigate the internalization process in wheat roots and cells. From the results, we found that the uptake of small-size PS NPs in the root tissues was increased compared to that of large-size ones, but no PS NPs were observed in the vascular cylinder. Similar results were observed in their cellular uptake process. Besides, the cell wall could block the entry of large-size PS NPs while the cell membrane could not. The -NH2 group on the PS NPs surface could benefit their tissular/cellular translocation compared to the -COOH group. The internalization of PS NPs was controlled by both particle size and surface functional group, and the size should be the primary factor. Our findings offer important information for understanding the PS NPs behaviors in plant tissues, especially at the cellular level, and assessing their potential risk to food safety, quality, and agricultural sustainability.

Polystyrene nanoparticles trigger the activation of p38 MAPK and apoptosis via inducing oxidative stress in zebrafish and macrophage cells.

It has been widely reported that shredders play an important role in leaf decomposition, especially in continental temperate streams. However, the paucity of shredders in many oceanic island streams leads to a greater contribution of microbes to litter decomposition in these streams. In this study, we investigated the importance of shredder presence and density (three levels) and leaf litter identity (Alnus glutinosa, Clethra arborea and Acacia melanoxylon) on leaf litter decomposition in one stream located in the Azores Archipelago. Coarse and fine mesh bags were used to allow natural colonisation of leaf litter by benthic macroinvertebrates or to exclude macroinvertebrates respectively. Treatments with one and three shredders were accomplished by enclosing one or three shredders in the fine mesh bags. Rates of litter decomposition differed significantly among shredder density treatments only for A. glutinosa and C. arborea. Decomposition rates were significantly faster for the natural within-stream shredder density treatment than for other shredder treatments. Shredder density differed significantly among litter species, being higher in A. glutinosa than in C. arborea and A. melanoxylon. The results indicate that when shredders are present at high densities in oceanic island streams they can substantially contribute to the decomposition of high-quality leaf litter, whereas the decomposition of hard leaf litter is mostly performed by the microbial community.

Intraspecific variability in leaf traits strongly affects alder leaf decomposition in a stream

Effects of acidification on leaf decomposition in streams were studied in four second-order streams in the Great Smoky Mountains National Park. The streams ranged in pH from 4.5 to 6.4 at baseflow. Mass loss of leaves incubated in mesh bags placed in pools in each stream was measured periodically over 15 wk beginning in late August. Measurements were also made of C, N, P, and Al in leaves, microbial biomass (adenosine triphosphate [ATP]) and respiration rate and bacterial production (thymidine uptake) associated with leaves, and the number and biomass of macroinvertebrates in leaf bags. Rates of leaf mass loss were significantly lower in streams with pH ≤5.7 compared with a stream with pH 6.4. Although rate of leaf mass loss among the streams varied directly with pH, differences between streams with pH values between 4.5 and 5.7 were not significant. Microbial ATP and respiration rates and bacterial production rates followed the same pattern as leaf mass loss rate, i.e., low for more acidic streams and highest in the stream with the highest pH. Accumulation of aluminum by the leaf-microbe complex was also greatest in the most acidic streams. The number and biomass of macroinvertebrate shredders found in leaf bags was lowest at the highest pH site and therefore cannot account for the higher rate of leaf mass loss found at this site. Our results suggest that the lower rate of leaf decomposition in the more acidic streams is due largely to low rates of microbial activity.

Polystyrene nanoparticles are emerging as contaminants in freshwater environments, posing potential risks to amphibians exposed to extended periods of water contamination. Using tadpoles as a model, this study aimed to evaluate the toxicity of PS NPs. Pyrolysis-gas chromatography-tandem mass spectrometry (Py-GCMS) analysis revealed a concentration-dependent increase in polystyrene nanoparticles (PS NPs) levels in tadpoles with escalating exposure concentrations. Following exposure to 100 nm fluorescent microspheres, fluorescence was observed in the intestines and gills, peaking at 48 hours. Histopathological analysis identified degenerative necrosis and inflammation in the liver, along with atrophic necrosis of glomeruli and tubules in the kidneys. These results indicate a discernible impact of PS NPs on antioxidant levels, including reduced superoxide dismutase and catalase activities, elevated glutathione content, and increased malondialdehyde levels. Electron microscopy observations revealed the infiltration of PS NPs into Kupffer's cells and hepatocytes, leading to visible lesions such as nuclear condensation and mitochondrial disruption. The primary objective of this research was to elucidate the adverse effects of prolonged PS NPs exposure on amphibians.

Long-term toxicity of surface-charged polystyrene nanoplastics to marine planktonic species Dunaliella tertiolecta and Artemia franciscana

Uptake, tissue distribution, and toxicity of polystyrene nanoparticles in developing zebrafish (Danio rerio)

Nanoplastics affect moulting and faecal pellet sinking in Antarctic krill (Euphausia superba) juveniles