Separation And Identification Method Of Nanoplastics In Environmental Water

Plastic products or microplastic particles can continuously fragment into nanoplastics in environments.These small particles are more likely to carry organic pollutants into organisms and cause harm.Previously,there is still a need of separation and identification methods for nanoplastics.Feasible analysis protocols are important basis to understand environmental nanoplastics.Therefore,according to the analysis process of nanoplastics,we focused on separation,enrichment,and identification steps,selected urban river water as the environmental medium,and took the ecological risk assessment of micro-and nanoplastics as the guide.We put forward a feasible scheme for the separation and identification of nanoplastics in environmental water with the goal of"Combination of Images and Spectra",aiming to reveal the difficulties and the interaction among analysis steps,accelerate the establishment of analysis methods.The main contents and conclusions of the study are as follows:(1)According to the analysis process of environmental water samples,the separation efficiency of commonly-used membrane filtration method on nanoplastics were analyzed.Filtration can remove large-sized impurities and microplastics,reducing their interference with the analysis of nanoplastics.The results showed that the removal rates of microplastics of different shapes can be affected by the structures of filters.Among them,nylon membrane(double-layer pore type)had the highest removal rate of fibers(99.2%),and polycarbonate membrane(single-layer pore type)had the highest removal rate of fragments(80.8%).The pore size of the filter membrane can affect the removal rate of microplastics and the retention/loss rate of nanoplastics.Filter with 1?m in pore size removed microplastics but also retained88.5%of the nanoplastics with the filter.The verification results of environmental water samples showed that the use of 20?m pore size filter membrane removed microplastics with the highest concentration at 9.4/L in a short filtration time,while retaining more nanoplastics in the filtrate for further analysis.(2)Pre-filtered river water samples were used to explore new methods to enrich and separate nanoplastics.Ultracentrifugation method was developed to enrich and separate low-concentration(10~8–10~9 particles/L)fragmented polystyrene nanoplastics spikes in river water.In addition,a method was developed to quantify the concentration of nanoplastics using UV-vis spectroscopy with a detection limit of7.24×10~8 particles/L.After ultracentrifugation and enrichment separation,the spikes in the river water were successfully separated and enriched into a 1 m L of liquid,and the concentration was about 50 times higher than the original sample with a relatively high recovery rate at 87.1%.After verification with scanning electron microscopy and enhanced dark-field microscope-hyperspectral imaging technology(HSI),the morphology and composition of the spikes remained unchanged.The results showed that the ultracentrifugation method is an efficient,mild,and non-destructive method for nanoplastics.The method was developed on environmentally-relevant nanoplastics,hence,it is potential to be applied to other types of environmental water samples.In order to locate the nanoplastics in water samples,the staining effects of NVOC2-Q-rhodamine-5-PEG3-azide were tested on plastic particles.Among them,polyvinyl chloride(1478.866/4095 a.u.)and polyethylene terephthalate(894.865/4095 a.u.)had obvious fluorescence increase.They are considered more difficult to be stained with Nile Red.Staining method can realize the localization of nanoplastics under the fluorescence microscope.(3)The nanoplastic samples after enrichment,separation or staining process should be prepared on the substrate for component confirmation.The effects were compared for alumina filter,glass slide,quartz,and mica on micro-Raman spectroscopy,atomic force microscopy-Raman spectroscopy,and atomic force infrared spectroscopy.The confirmation of polymer types also relies on the library to match the spectra with reference spectra.However,commercial libraries suffer from low hit quality index(HQI)when matching aged plastics and natural celluloses.Characteristic band method and a custom spectral library were established to improve the HQI and screen out natural celluloses.The results showed that the characteristic peak at 1105 cm^-1 could be used as a criterion to quickly identify natural cellulose.The HQI can be improved by adding spectra of local products to the library.In addition,this study also established a new method to identify nanoplastic fragments in river water using HSI technology.The effects of different solvents on particle spectra were compared.HSI technology can quickly obtain the composition,number,and morphological features of particles in dark field.The results shows that the spectra of the same type of nanoplastics dispersed in ultrapure water and surfactant Tween 20were obviously different,so the influence of solvent on the spectra of nanoplastics should be considered when establishing the HSI reference spectral library.Environmentally-relevant nanoplastic spikes in fragment shape and low-concentration were prepared as the research object,ultracentrifugation method was first established and used to separate and enrich these spikes in river water samples.The spiked nanoplastics were successfully enriched to 50 times higher than the original concentration.Enhanced dark-field microscope-hyperspectral imaging technology and the corresponding reference library were developed to identify and confirm the composition of the separated nanoplastics.After the study on environmentally-relevant nanoplastic spikes in water samples,we established a new feasible protocol which can be connected with the analysis process of microplastics to separate,enrich,and identify nanoplastics based on the goal of"Combination of Images and Spectra".This thesis advanced the research on the separation and identification methodology of nanoplastics.However,there are still bottlenecks and challenges in the analysis of nanoplastics,and the research on the analysis methods needs to be continued in the future.