The Aging Of Plastic Fragments And Residual Characteristics Of Plastic Additives In The Beach Environment

Due to improper management and other reasons,plastic waste can leak into the environment,where it is subject to various complex internal and external factors that can lead to weathering,fragmentation,and degradation.Concurrently,the formation of secondary pollutants such as microplastics and plastic additives can occur,thereby creating greater potential hazards and risks.However,there is currently a lack of in-depth research on the weathering characteristics of plastics and the evolution of plastic additives in the environment.Small plastic fragments in the environment are products of the fragmentation of larger plastic waste and serve as a bridge between large plastic waste and environmental micro-and nanoplastics.In this dissertation,beaches,estuaries,and lakes are selected as the primary investigation areas,with plastic fragments as the main research objects.By analyzing the weathering morphology of plastics and the residual characteristics of plastic additives,a weathering evaluation system of plastic fragments is constructed to elucidate the relationship between plastic weathering and additive residues.Furthermore,the pollution characteristics of secondary products of plastic in the environmental matrix are tracked.The main research results and conclusions of this dissertation are as follows:（1）A survey was conducted on plastic fragments at 11 coastal,estuarine,and lake areas in China.Results showed that 55.4%of the 5,013 samples had different types of cracks on the plastic surface.Based on the texture of the cracks,four main types of crack patterns were identified,including linear（37.3%）,curved（4.8%）,net（27.6%）,and unclassified（30.4%）patterns,along with 10 subtypes,leading to the establishment of a crack classification and symbol representation system.Additionally,the rationality and regularity of the classification method were validated using two-dimensional spectrum analysis.Through correlation analysis between crack and carbonyl index,key morphological parameters,such as line density,were selected to characterize the degree of cracks,and a methodology system for plastic weathering feature evaluation was established.The practicality and rationality of the methodology system were demonstrated through its application at two sites with distinct climates in Dalian and Haikou,which laid the foundation for the study of global weathering of plastic fragments.（2）Building upon this,a comprehensive evaluation system for plastic weathering was constructed based on parameters such as profile features,surface crack line density,surface lost,and texture index,which was further applied to the comparative analysis of 1379 samples from China and Norway.Thirteen beach sites worldwide were compared to analyze plastic fragments.The results showed that the line density of Norwegian samples（1.43 mm/mm²）was significantly lower than that of Chinese samples（8.43 mm/mm²）,and the degrees of line density（R₁-R₂）was also significantly lower than that of Chinese samples（R₂-R₃）.The surface lost of Chinese plastic fragments（10%）was significantly higher than that of Norway（7%）.However,there were no significant differences in shape descriptors and texture index between the Chinese and Norwegian beach samples.Correlation analysis with climate factors revealed that the degree of plastic weathering increases with environmental factors such as temperature,rainfall,and wind speed.（3）To further explore the relationship between the residual characteristics and weathering degree of additives in environmental plastic fragments,the residual amounts of 26 subtypes of additives from four types were analyzed in 819 plastic fragments collected from coastal areas in China.The results showed that phthalate esters（PAEs）plasticizers had the highest detection rate（99.8%）among all categories of additives,followed by antioxidants（48.7%）,while the detection rates of ultraviolet stabilizers and flame retardants were the lowest（<5%）.The residual concentration of PAEs was the highest,ranging from 19.6 to 123.6μg/g,followed by antioxidants with a residual concentration of 0.3-11.7μg/g.The correlation analysis results showed that the residual concentration of PAEs had a significant correlation with the size and line density of plastic fragments.This indicated that the release rate of additives during the weathering and fragmentation process of plastic in the environment increases with the degree of the fragmentation of the plastic.（4）In order to investigate the fate and distribution of secondary products formed during plastic weathering in the environment,microplastics and plastic additives were analyzed in surface water and sediment samples near Yangtze estuary.The results showed that polyester fibers were the main type of microplastics in surface water（58.2%）and sediment（61.0%）,with abundance ranging from 0.1-19.5 items/L and 0-1366.7 items/kg dw,respectively.The significant difference in abundance between fiber and fragment microplastics indicated their different sources.The former mainly originates from point source pollution discharge of domestic sewage and industrial wastewater,which is not completely consistent with the process and characteristics of fragment microplastics generated by fragmentation.The total concentrations of PAEs and polybrominated diphenyl ethers（PBDEs）in sediment samples ranged from 35.9-36225.2 ng/g and 3.9-253.0 ng/g,respectively.The correlation and principal component analysis results showed that the main source of additives in sediment was related to the leakage of chemical additives in small plastic fragments and microplastics.In addition,the total organic carbon content and sediment grain size slightly affected the spatial distribution of additives in sediment.（5）Based on the above work,a research scheme and implementation process for investigating the sampling to indoor analysis of environmental plastic fragments was proposed,which is based on a multidimensional and multiparameter weathering parameters evaluation system.The scheme and process are mainly divided into two parts:morphology parameter and chemical index measurement experiments and investigation ideas,providing parameters and indicators for specific experimental purposes.Through a large amount of field data,the relationship between macroplastics and micro/nano plastics was established,and the relationship between plastic weathering degree and microplastics and plastic additives was elucidated.This is conducive to explaining the lifecycle,sources,fate,and toxicity evaluation of microplastics in the real natural environment and controlling the environmental release and input of microplastics from the source.Finally,it is proposed that investigating and studying the weathering of environmental plastics is of great scientific significance for revealing the existence level and migration law of plastic waste in the environment,predicting its degradation cycle,and providing important theoretical basis and technical support for the full life cycle management,risk assessment,and global governance of plastic pollution.This dissertation focused on the weathering and fragmentation of environmental plastics,and proposed an index system and workflow to evaluate the degree of plastic weathering through field surveys and indoor analysis.The residual characteristics and their interrelationships of plastic additives during environmental plastic weathering were revealed.The research in this dissertation provided scientific basis and technical methods for the degradation cycle and ecological risk assessment of environmental plastic waste.