|Other Abstract||Micro-nanoplastics (the general name of microplastics and nano-plastics) have been widely concerned as a new type of pollutants, and have become a research hotspot in the field of ecological and environmental. In recent years, scientists at home and abroad have carried out a lot of research and made some progress on the environmental distribution, source investigation, behavior transmission and ecotoxicology of micro-nanoplastics, but there are still two key problems that have not been solved. First, the micro-nanoplastic model for effect evaluation is lack of authenticity. Many studies use polystyrene (PS) spherical particles to substitute micro-nanoplastics, but the surface shape of micro-nanoplastics in the natural environment is irregular, and the surface properties, interaction with biomolecules and toxicological effects are different due to different plastic materials. Therefore, the experimental results obtained from PS spherical particles should not be regarded as a general conclusion applicable to all plastic materials. Second, there is a lack of high sensitivity tracing methods for micro-nanoplastics. At present, a lot of work has been done on micro-nanoplastics from the aspects of imaging analysis, spectral identification and mass spectrometry detection. However, there are some problems in the detection of micro-nanoplastics by these methods, such as low sensitivity, poor resistance to environmental background interference, unsuitable for the analysis of nano plastics, and so on. The development of highly sensitive nano-plastic tracing methods is still in a bottleneck. In order to solve the above problems, the preparation method of "realistic" micro-nanoplastics based on mechanical fragmentation and the method of labeling micro-nanoplastics based on swelling were developed. The iridium (Ir) labeled micro-nanoplastics were applied to the distribution in mice and the sediment resuspension model. It was concluded that the distribution of micro-nanoplastics in mice was particle size dependent and the micro-nanoplastics in the natural environment had adsorption and sedimentation behavior. The ultra-hydrophobic enrichment imaging study of micro-nanoplastics marked with Nile red was carried out, which preliminarily verified the feasibility of rapid imaging detection of micro-nanoplastics and improved the sensitivity of micro-nanoplastics detection. The details are as follows:
(1) A method for the preparation and labeling of "realistic" micro-nanoplastics based on mechanical crushing has been developed.
By simulating the formation process of micro-nanoplastics in natural environment, 200 nm, 900 nm and 2500 nm micro-nanoplastics (PET200, PET900 and PET2500) were prepared from PET mineral water bottles sold in the market. The dense ring coordination compounds of platinum group element Ir were used as markers to label micro-nanoplastics based on the swelling characteristics of polymers, and three kinds of labeled micro-nanoplastics, including PET200-Ir, PET900-Ir and PET2500-Ir, were obtained. The labeling and digestion methods were optimized. The labeling concentration was 0.5 mg/mL, the labeling ratio was 6:1, the labeling time was 12 h, and the digestion time was 10 h and the digestion temperature was 100 ℃. Through the simulated leakage experiments in environment and biological media, it was found that the leakage of PET-Ir in other matrices was less than 3% except 5% in fetal bovine serum matrix, indicating that this labeling method has the potential of labeling in vivo. The preparation method in this study achieves the truth of the formation process (physical wear) and the physical and chemical properties of the material (derived from real daily plastics), and the labeling method has the advantage of anti-background interference, which is an important progress in the preparation of micro-nanoplastic models. It lays a foundation for the follow-up application research of biological and environmental distribution.
(2) Study on the distribution of nanoplastics in mice.
The distribution of PET200-Ir and PET900-Ir nanoplastics in mice was studied by intravenous injection and intragastric administration, with the aqueous dispersion of Ir marker as control. It was found that under the condition of intravenous injection, the liver was the main organ of nano-plastic accumulation and the distribution behavior of nano-plastic was particle size-dependent. The accumulation rate and clearance rate of PET200 were faster than that of PET900. The aqueous dispersions of Ir and nanoplastic with two kinds of particle size were not detected in other tissues except gastrointestinal tract, which may be due to the influence of gastrointestinal barrier. This study explores the feasibility of the application of "realistic" micro-nanoplastics in organisms, and shows the particle size dependence of the behavior of nano-plastics in organisms, which can provide a reference for the toxicological study of "realistic" nano-plastics.
(3) Study on the distribution of micro-nanoplastics in the resuspension model of coastal sediments.
Sediment resuspension is a common physical phenomenon in the intertidal zone. Based on the sediment resuspension model, this study explored the effect of oscillation time on the vertical distribution of micro-nanoplastics and the detection of the vertical distribution of micro-nanoplastics. The results show that with the increase of oscillation time, the concentration of micro-nanoplastics in the supernatant decreases and the concentration of micro-nanoplastics in sediment increases, which accords with the sedimentation behavior driven by adsorption. 45.3% of the micro-nanoplastics are concentrated in the sediment layer with a depth of 1.4~1.8 cm, which is 3.6 times of the adjacent water layer and 5.5 times of the adjacent sediment layer, indicating that the micro-nanoplastics are easy to be distributed in the top layer of the sediment and the bottom of the water body. This study illustrates the feasibility of applying "realistic" micro-nanoplastics to environmental behavior research, and explores the effects of sediment disturbance and interaction with natural materials on the settlement of micro-nanoplastics. It is revealed that the benthos living on the sediment surface may be more susceptible to micro-nanoplastic pollution in the coastal environment where sediment resuspension exists.
(4) Fluorescence detection of micro-nanoplastics in real samples by super hydrophobic enrichment.
Based on the current situation that the field of vision of imaging detection is small, the distribution area of samples on the carrier substrate is large, and the particles are sparse, it is difficult to locate the particles accurately and quickly, which leads to the low efficiency of analysis. There is an urgent need to expand the concentration detection range of imaging analysis. Superhydrophobic enrichment is an effective enrichment method for imaging detection, which is suitable for the detection of small volume, small particle size and low concentration particle samples. In this study, a super-hydrophobic enrichment method was developed, which can reduce the diameter of 10 mL samples on glass slides to 0.1 mm, which promotes the detection of low concentration samples. At the same time, the superhydrophobic enrichment combined with fluorescence labeling method tried to solve the problem of fluorescence background interference, and carried out the enrichment detection of low concentration unlabeled micro-nanoplastic samples. The lowest detectable concentration of PET900 in seawater and pure water samples was as low as 6.7× 10-5 mg/ml, and the lowest detectable concentrations of PET200 and PET2500 in pure water samples were 3.4×10-5 mg/mL and 5.7×10-5 mg/mL, respectively. This study reduces the detection limit of fluorescence imaging nanoplastics, significantly improves the detection efficiency and detection sensitivity, thus providing a methodological reference for the detection of micro-nanoplastics in real environment.|