Effects of environmental and anthropogenic factors on the distribution and abundance of microplastics in freshwater ecosystems.

Although microplastics are emerging marine pollutants that have recently attracted increasing attention, it is still difficult to identify their sources. This study reviewed 6487 articles to determine current research trends and found 237 effective concentration points after sorting, which were distributed in four regions and related to freshwater ecosystems. Results found that 15 environmental variables represented natural and anthropogenic environmental characteristics, of which seven environmental variables were selected for experimental modelling. Random forest models fitted sample data, thus facilitating the identification of regional microplastics distribution. The global random forest model had random forest importance scores (RFISs) for gross domestic product, population, and the proportion of agricultural land use were 15.76 %, 15.64 %, and 14.74 %, respectively; these indicate that human activities significantly affected the global distribution of microplastics. In Asia, agriculture and urban activities are the main sources of microplastics, with an RFIS of 11.58 % and 12.24 % for the proportion of agricultural and urban land use, respectively. Activities in urban areas were determined to be the main influencing factors in North America, with an RFIS of 13.92 % for the proportion of urban land use. Agricultural activities were the main influencing factors in Europe, with RFISs for the proportion of agricultural land use of 16.90 %. Our results indicate that region-specific policies are required to control microplastics in different regions, with soil composition being a latency factor that affects microplastics' distribution.

Higher toxicity induced by co-exposure of polystyrene microplastics and chloramphenicol to Microcystis aeruginosa: Experimental study and molecular dynamics simulation.

Antibiotics and microplastics (MPs) inevitably coexist in natural waters, but their combined effect on aquatic organisms is still ambiguous. This study investigated the individual and combined toxicity of chloramphenicol (CAP) and micro-polystyrene (mPS) particles to Microcystis aeruginosa by physiological biomarkers, related gene expression, and molecular dynamics simulation. The results indicated that both individual and joint treatments threatened algal growth, while combined toxicity was higher than the former. Photosynthetic pigments and gene expression were inhibited by single CAP and mPS exposure, but CAP dominated and aggravated photosynthetic toxicity in combined exposure. Additionally, mPS damaged cell membranes and induced oxidative stress, which might further facilitate the entry of CAP into cells during co-exposure. The synergistic effect of CAP and mPS might be explained by the common photosynthetic toxicity target of CAP and mPS as well as oxidative stress. Furthermore, the molecular dynamics simulation revealed that CAP altered conformations of photosynthetic assembly protein YCF48 and SOD enzyme, and competed for functional sites of SOD, thus disturbing photosynthesis and antioxidant systems. These findings provide useful insights into the combined toxicity mechanism of antibiotics and MPs as well as highlight the importance of co-pollutant toxicity in the aquatic environment.

Comparative effects of polystyrene nanoplastics with different surface charge on seedling establishment of Chinese cabbage (Brassica rapa L.).

Micro- and nano-plastics are common emerging pollutants of great interest. However, the impacts of them on terrestrial plants were still poorly understood. In this study, comparative effects of exposure of polystyrene nanoplastics (PS) and amino-modified polystyrene nanoplastics (PS-NH2) on Chinese cabbage (Brassica rapa L.) plants at different growth stages were investigated. Hydroponically cultured seedlings were exposed to PS and PS-NH2 at 0, 1, 10, and 100 mg/L at skotomorphogenesis stage for 48 h, photomorphogenesis stage for 18 h, and the whole stage, respectively. Results showed that both PS and PS-NH2 had no discernible effect on radicle elongation at the skotomorphogenesis stage whereas significantly (P < 0.05) reduced photosynthetic pigment contents in varying degrees (18.06%-28.52%, 22.46%-36.86%) at the photomorphogenesis stage and the whole stage. Moreover, there was no significant difference between PS treatments and control except the 26.52% decline of chlorophyll a content at 1 mg/L at photomorphogenesis, while PS-NH2 significantly (P < 0.05) decreased photosynthetic pigment contents except the chlorophyll b content at 10 mg/L at photomorphogenesis. The content of chlorophyll a decreased by 26.68% for the PS-NH2-treated group and 22.46% for the PS-treated group at 1 mg/L during the whole stage. Results manifested that less negatively charged PS-NH2 seemed to show more severe phytotoxicity both at the photomorphogenesis stage and the whole stage. Notably, the surface charge of nano-plastics and the integrity of seedling establishment could be the main factors impacting the above difference. These findings are expected to improve our understanding of the effects of PSNPs on crop plants.

Microcystis aeruginosa's exposure to an antagonism of nanoplastics and MWCNTs: The disorders in cellular and metabolic processes.

Nanoplastics and carbon nanotubes (CNTs) is one of the emerging environmental contaminants and a widely used engineering nanomaterial, and their biological toxicity has been frequently studied. However, there has been no research on the combined exposure of these two totally different shape nanoparticles. To explore their potential threat to freshwater ecosystems, Microcystis aeruginosa (M. aeruginosa) was exposed to concentration gradients of polystyrene nanoplastics (Nano-PS) and multi-walled carbon nanotubes (MWCNTs). The physiological analysis and whole-transcriptome sequencing were integrated to certify the cytotoxicity. As the physiological results showed, the low concentration (5 mg/L) of these two nanoparticles showed a stimulation on the growth (6.49%-12.2%) and photosynthesis (0-7.6%), and the coexposure was slightly higher than individuals. However, other concentrations showed inhibitory effect, especially at high concentration (50 mg/L), and all physical signs and electron microscope images showed obvious cytotoxicity. Compared with the individuals, the coexposure showed an antagonistic effect induced by the heterogeneous agglomeration which decreased the surface toxicity and the contact with algae of nanomaterials. Transcriptome results showed that coexposure treatment had the fewest differential genes, and the primary effects embodied in the disturbances of cellular and metabolic processes which were superior to the individuals. In the 50 mg/L Nano-PS, the translation process was significantly disordered, and MWCNTs could disrupted the photosynthesis, multiple metabolism processes, membrane transport, and translation. These findings demonstrated the aquatic toxic mechanism from cellular and metabolic processes of Nano-PS and MWCNTs for M. aeruginosa and provided valuable data for environmental risk assessment of them.