Research On Detection Method Of Microplastics In The Marine

Microplastics are an emerging contaminant for marine environmental,which have attracted increasing attention in worldwide.Plastic particles with a particle size of less than 5 mm are generally defined as microplastics,mainly derived from leaked raw materials in the plastic manufacturing industry,fragments formed by the fragmentation of large plastics through physical,chemical or biological processes,and additives of plastic microbead in various daily products.Due to their similar size to low-trophic plankton,microplastics are easily ingested by marine organisms,and can threaten higher nutritional organisms and even human health through the food chain.Most of the current research has focused on the abundance of microplastics in the environment.However,the abundance of microplastics in the environment are easily overestimated or underestimated,due to the limitations of analytical methods and instruments.This research focuses on the identification and quantitative analysis of microplastics and the qualitative analysis of microplastics and nanoplastics.The main contents and results are as follows:1.Fluorescent quantitative analysis of microplastics in the environmentA new fluorescent staining method for quantification of microplastics was developed based on thermal expansion and contraction.Dye molecules can enter inside the microplastics at high temperature when macromolecular chain is loosened.When it is decreased to the room temperature,loose structure is transformed into dense one and dye molecules are encapsulated into the microplastics.Four different types of microplastics(polyethylene,polystyrene,polyvinyl chloride and polyethylene terephthalate)were stained with three different types of dyes(nile red,fluorescein isophosphate and safranine T),respectively.The staining temperature is 25?,50?,75?,and the staining time is 10 min,20 min,and 30 min,respectively.Scanning electron microscope(SEM),thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FTIR),and Raman spectroscopy were applied to characterize microplastics before and after staining.The results indicate that PE,PS,PVC and PET stained with three dyes have excellent fluorescence intensity after heating.Most of them show the best fluorescence signal at50?for 30 min.The results of SEM,TGA and DSC demonstrate that the microstructure of the microplastics stained for 30 min at the highest experimental temperature of 75?has no obvious damage,and the four microplastics have brilliant thermal stability in the temperature range below 100?.The results of FTIR and Raman spectrum show that the analysis of the chemical composition of microplastics is not interfered by dye molecules.Furthermore,this method has been successfully applied to the quantification of microplastics in marine biological samples.The results show that there are about 54 particle s/g(dry weight)microplastics in the Sipunculus nudus.2.The qualitative study of microplastics and nanoplastics in aquatic environmentsA method based on surface-enhanced Raman spectroscopy(SERS),which uses silver colloid as the active substrate,was developed for the qualitative analysis of microplastics and nanoplastics in aquatic environments.Plastic particles with 100 nm,500 nm and 10?m and different plastic types(polystyrene(PS),polyethylene(PE)and polypropylene(PP))were tested in different environments(pure water and seawater).The condition of different tests including the volume ratio of sample to silver colloid,the concentrations of Na Cl,and the concentrations of the samples,were assessed for the Raman enhancement efficiency of microplastics and nanoplastics(PS,PE and PP)in pure water and seawater.The microstructure and particle size of silver colloid and nanoplastics were characterized by transmission electron microscopy(TEM)and dynamic light scattering(DLS).The results show that the Raman signals of microplastics and nanoplastics in pure water and seawater both show brilliant enhancement efficiency.Among them,the 100 nm and 500 nm PS have the optimal SERS signals when the volume ratio of the sample solution to the silver colloid is 1:1and the Na Cl concentration is 0.25 mol/L.Especially for 500 nm PS sphere,its enhancement factor can reach 4×10~4.The SERS-based detection method overcomes the limitations of microplastics and nanoplastics in liquids and enables detection of 100 nm plastics as low as 40?g/mL.