Compositions,Identification And Sources Of Macroplastic Debris And Microplastics In Coastal Environments

Coastal zone is the area where sea and land meet.It is affected by both human activities and natural factors such as tidal and currents,which makes it easy to accumulate a large amount of plastic debris and microplastic pollutants.Macroplastics accumulated on the beaches for a long time are easily broken into small plastics or microplastics through environmental effects such as light,wind,and waves.The microplastics formed after fragmentation have smaller sizes and incomplete surface characteristics,hence makes it difficult to identify their sources.At present,most studies that related to microplastics focus on types,abundances,distributions and ecological risks.The identification of microplastics sources is mainly determined by morphology and components with few direct or indirect evidences.Hence,this study takes the Sanggou Bay beaches in the Yellow Sea and the Dongchu island in Rongcheng City,Shandong Province as the research sites.Based on literature review and field investigation,methods to identify the sources of microplastics were summarized,and a technical methods system for microplastics sources identification was established.By investigating the colors,types,morphologies and components of macroplastic debris and microplastics from different sources,a searchable inventory of macroplastic debris and microplastics was established.Based on above,the sources of macroplastic debris and microplastics in Sanggou Bay beaches were identified.Finally,through the simulation of the fragmentation of macroplastics in the beach environment,the variation characteristics of different types and effect factors of microplastics formation were explored,the formation processes of secondary microplastics in coastal environment was examined by simulation.The main results of this study are as follows:(1)Through literature collection and field investigations,a series of methods for identifying macroplastic debris and microplastics characteristics,such as: visualization,microscopy,morphology,component,functional group and particle size,were summarized.Visualization and microscopic methods mainly identify the color and size of macroplastic debris and microplastics.Morphology method identifies the microstructure of microplastic surfaces,such as cracks and bulges.Component method identifies polymer components of macroplastic and microplastics.Functional group method is combined with the component method to identify the functional group changes on the polymer surfaces.The particle size method compares the morphological and component characteristics of different sizes of macroplastic debris and microplastics,and to identify the sources of microplastics.(2)Based on the site investigation in Sanggou Bay and Dongchu island,macroplastic debris from mariculture activities,daily life,recreation and agricultural activities were collected and classified according to their source,use,shapes,colors,polymer components and possible fractured microplastics.A searchable inventory of macroplastic debris and microplastics sources was listed,with photos of each type of macroplastic debris attached for intuitive comparison.Camera is used to obtain photos of various types of macroplastic debris being broken into microplastics,which proves that macroplastic debris in the environment can be broken into microplastics.(3)Through the investigation of the macroplastic debris and microplastics in the beaches of Sanggou Bay,based on the established inventory and microplastic sources identification methods system,part of the microplastics in Sanggou Bay beaches were identified as polyethylene float,polystyrene foam buoy,polyurethane sponge,polyethylene fiber fishing rope,and polypropylene film rope which were derived from mariculture activities.(4)During the processes of macroplastic debris breaking into microplastics,UV irradiation may cause discoloration,deformation,thinning and brittleness of microplastic surface.Functional groups such as-OH,C=O and C-O appeared on the polymer surfaces,indicating the oxidation inside the microplastic polymers.With the increasing of weathering periods,the surface roughness of the polymers increased,and the folds and cracks on the polymer surfaces gradually appeared,presenting a bumpy state.After sand physical abrasion,the thinner and brittle plastics broke up into microplastics.By collecting and oberseving the secondary microplastics fragmented by the crushing of polypropylene woven bags and polypropylene film ropes,the results show that the abundances of microplastics increase with the extension of weathering time,while the sizes decrease gradually.In this study,through the combination of technical methods system and sources inventory for identification of macroplastic debris and microplastics sources,the sources of macroplastic debris and microplastics in Sanggou Bay beaches are identified,which provide new ideas and methods for identification of microplastic sources in the environment,and provide scientific methods and basis for the sources control of microplastics.