| Microplastics refer to plastic fragments with a particle size of less than 5 mm and is now attracting attention as a new type of pollutant that affects the global marine ecological environment.In addition to its own contaminants,it also has the effect of enriching and migrating typical pollutants.Some of the contaminants they carried will cause direct poisoning to marine organisms,and can be transported and enriched along the food chain.Therefore,microplastics not only affects coastal tourism,but also threatens the safety and quality of marine food and even human health.As a new research field,how to separate and analyze microplastics from the marine environment and study their characteristics of complex pollution is an urgent problem to be solved in microplastics contamination research.In this study,the surface water samples collected from sandy beaches,sediments and trawls were used to establish different sampling and separation systems,and achieved high efficiency and high recovery rate of the flotation separation of microplastics according to the differences in the samples.The basic flotation separation method was improved.According to the microplastic material and density characteristics,different suspension solution systems were screened to establish different pretreatment and separation techniques for relative density microplastic samples.This separation method was applied to typical sea area of Qingdao respectively.A large number of microplastics were detected and classification statistics was made according to their morphological characteristics.According to the size classification,microplastics with a particle size of less than 1 mm accounted for the largest proportion,reaching 57.9%,by the shape classification,the representative shapes such as fibers,film,granules were mainly observed,and the fibers and granule types were dominant,accounting for more than 90% of the total.According to the material classification,surface water trawling samples detected polyethylene terephthalate(PET),polystyrene(PS),polyethylene(PE)and high density polyethylene(HDPE),polypropylene(PP).Microplastics have unique physical and chemical properties such as large surface area,strong hydrophobicity,and complex surfaces.These properties of microplastics enhance their ability to adsorb contaminants in the environment.In this study,we studied the adsorption characteristics of heavy metals on microplastics in laboratory simulation experiment and field experiments.We demonstrated that five types of microplastics,polyvinyl chloride(PVC),polypropylene(PP),polyethylene(PE),polyamides(PA)and polyformaldehyde(POM)adsorb three heavy metals,lead(Pb),copper(Cu)and cadmium(Cd)in the indoor simulating solution.We found that compared with PA,PE and POM,heavy metals showed higher adsorption on PVC and PP particles.With the increase of adsorption time and ion concentration,the adsorption of heavy metals by microplastics increases.At the same time,the specific surface area and adsorptivity of microplastics increase with the decrease of particle size,and the adsorption of three heavy metals increases.In Pb,Cu,and Cd coexisting solution systems,microplastics of four materials(PVC,PP,PE,and PA)selectively adsorbed three heavy metals.In field experiments,the adsorption rates of heavy metals and their concentrations in seawater vary significantly between different microplastic types and different locations.The adsorption capacities of Pb and Mn for PP and PVC are closely related to the metal concentration in seawater.In the experiment,the microstructure of the surface of the particles before and after adsorption was observed by using a scanning electron microscope.It was found that during the adsorption experiment,the surface morphology of the microplastics undergoes a rough-smooth-rough changing process,and the materials are different.The surface of microplastics is quite different,which may also be the reason for the different adsorption of different heavy metal elements by the microplastic particles. |
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