Size effect of polystyrene microplastics on sorption of phenanthrene and nitrobenzene.

Microplastics can have strong sorption capacity for many contaminants, thus greatly influencing the fate, transport and bioavailability of those contaminants in the environment. However, the effect of particle size on contaminant sorption by microplastics is still poorly understood. This study investigated the sorption of phenanthrene and nitrobenzene to micron-, submicron- and nano- sized polystyrene microplastics of 170 µm, 102 µm, 50 µm, 30 µm, 800 nm, 235 nm or 50 nm. All phenanthrene sorption isotherms and most nitrobenzene sorption isotherms were linear because of the strong sorption capacity of microplastics and the hydrophobic partitioning. The log Kd values ranged between 3.07-4.20 and 1.58-3.14 log (L/kg) for phenanthrene and nitrobenzene, respectively. The log Kd values of phenanthrene and nitrobenzene both increased with decreasing particle size for micron-sized polystyrenes (micro-polystyrene) and submicron-sized polystyrenes (submicro-polystyrene). However, in comparison with 235 nm submicro-polystyrene, the log Kd values of 50 nm nano-polystyrene were significantly lower for phenanthrene and comparable for nitrobenzene because its aggregation greatly reduced the effective surface area accessible for sorption. The results improved our understanding of the fate and risks of microplastics associated with the two typical organic contaminants in the micrometer to nanometer scale.

Phytotoxicity of microplastics to the floating plant Spirodela polyrhiza (L.): Plant functional traits and metabolomics.

Freshwater ecosystems are gradually becoming sinks for terrestrial microplastics (MPs), posing a potential ecological risk. Although the effects of MPs on plankton and aquatic animals in freshwater ecosystems have been given increasing attention, the toxicity of MPs to the metabolism of aquatic plants remains unclear. Here, the model aquatic plant Spirodela polyrhiza (L.) Schleid. (S. polyrhiza) was exposed to polyvinyl chloride (PVC; 0, 10, 100 and 1000 mg/L) MPs, and changes in the plant functional traits and physiological metabolism were monitored. The results showed that the high dose of PVC MPs decreased the adventitious root elongation ratio by 41.68% and leaf multiplication ratio by 61.03% of S. polyrhiza, and resulted in the decrease in anthocyanin and nitrogen contents to 63.45% and 84.21% of the control group, respectively. Moreover, the widely targeted metabolomics analysis results showed 37 differential metabolites in the low-dose treatment and 119 differential metabolites in the high-dose treatment. PVC MPs interfered with organic matter accumulation by affecting carbon metabolism, nitrogen metabolism, amino acid metabolism and lipid metabolism, and S. polyrhiza resists PVC MP stress by regulating the synthesis and metabolism of secondary metabolites. PVC MPs had concentration-related toxicological effects on plant functional traits, inhibited plant growth and reproduction, affected plant nutrient metabolism, and exhibited profound effects on the nitrogen fate of aquatic plant habitats. Overall, we systematically summarized the metabolic response mechanisms of aquatic plants to PVC MP stress, providing a new perspective for studying the effects of MPs on plant trait function and ecological risks.

Spatiotemporal dynamics of suspended particulate matter in the Yellow River Estuary, China during the past two decades based on time-series Landsat and Sentinel-2 data.

Twenty-two years of suspended particulate matter (SPM) concentrations in the Yellow River estuary and adjacent sea, China were derived from 532 Landsat and Sentinel 2A/B satellite images. Optimal SPM retrieval model was selected by comparing five state-of-art models using 79 in-situ datasets and recalibrated to ensure consistency among multiple-sensor-derived SPM concentrations. SPM in the estuary, in South Bohai Bay, and Laizhou Bay exhibited distinct temporal variations. 73% and 52% of the interannual and monthly SPM variations near the river mouth were explained by riverine water and sediment discharge, showing impact of the operation of the Xiaolangdi Reservoir and Water-Sediment Regulation Scheme. Land area accretion and erosion in river delta are associated with SPM variation. Riverine impacts on SPM rapidly declined off-shore because of the rapid deposition of the coarse-grain sediment. Ocean current and wind-wave forces explained high concentrations and intra-annual variations of SPM in the South Bohai Bay and Laizhou Bay.

Microbial community structure of different electrode materials in constructed wetland incorporating microbial fuel cell.

The microbial fuel cell coupled with constructed wetland (CW-MFC) microcosms were operated under fed-batch mode for evaluating the effect of electrode materials on bioelectricity generation and microbial community composition. Experimental results indicated that the bioenergy output in CW-MFC increased with the substrate concentration; maximum average voltage (177mV) was observed in CW-MFC with carbon fiber felt (CFF). In addition, the four different materials resulted in the formation of significantly different microbial community distribution around the anode electrode. The relative abundance of Proteobacteria in CFF and foamed nickel (FN) was significantly higher than that in stainless steel mesh (SSM) and graphite rod (GR) samples. Notably, the findings indicate that CW-MFC utilizing FN anode electrode could apparently improve relative abundance of Dechloromonas, which has been regarded as a denitrifying and phosphate accumulating microorganism.