| As a new addition to the list of global threats,plastic marine debris(PMD)has now joined the ranks of climate change,ozone depletion and ocean acidification.Microplastic(<5 mm,MP)has been the subject of intensifying investigation.Due to its physical and chemical properties,the negative impacts of MP on marine ecosystem are far more than it from large plastic debris.MP not only could pose physical impacts via ingestion,but also provide an exposure pathway of toxic pollutants(inherent and extern toxics)to the respective organisms.Furthermore,MP facilitating the spread of alien species and potential pathogens endangers the marine environment.Nevertheless,MP contamination and its ecological impacts have not been systematically investigated.Although China was thought to be one of the top PMD generating countries,MP research is still in the start-up phase.Depending on variant coastal environmental compartments,the ecological risk of MP is different.Special attention should be paid to esturies which are recognized worldwidely as hot spots of MP pollution and closely related to human activities.The background data of the composition and concentration of MP in the coastal environments of China is extremely scarce.Based on this,this thesis aims to:1)discover the contamination levels,characteristics and potential origins of MP in the selective estuaries,beaches and biotas of the Southern China,2)develop a safety,easy,scalable method of extracting and identification MP in coastal marine snow samples for exploring the potential transfer mechanism of MP from marine surface waters.(1)Based on the source-sink design,suspended MP in the surface water of the Yangtze Estuary and East China Sea was firstly evaluated.Plastic items were widely distributed in the study areas.The MP densities were 4137.3 ± 2461.5 and 0.167 ±0.138 n/m~3,respectively,in the estuarine and the sea samples.Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment.The size of plastic particles ranges from 0.51 mm to 6.29 mm.MP(0.5-5 mm)constituted more than 90%by number of items.The most frequent geometries were fibres,followed by granules and films.Plastic spherules occurred sparsely.(2)To clarify the influence of human activities(e.g.Population,urban development)and the extreme meteorological events on MP occurrence,this study was to quantify the accumulation of MPs suspending in the subsurface waters of three urban estuaries(Jiaojinag,Oujiang and Minjiang Estuary).MPs were detected in all the samples,with a total of 1009 plastic particles.The maximum abundance(1245.8±531.5 n/m~3)of MP was in post-typhoon Minjiang,followed by afore-typhoon Minjiang(1170.8±953.1n/m~3),Jiaojiang(955.6±848.7 n/m~3)and Oujiang(680.0±284.6 n/m~3).Plastic lengths ranged from 0.5 mm to 10.6 mm.Plastic particles(0.5-2 mm)occupied more than 70%of total plastics by number.Fibers and granules were the primary shapes,with no pellets found.Colored MP was the majority.Polypropylene and polyethylene were the prevalent Polymer matrix of MP analyzed.Economic structures in urban estuaries influenced on MP contamination levels.Although the MP density in Minjiang showed an increasing trend during the storm,typhoon didn’t influence the suspended MP concentration significantly.Multidimensional scaling analysis showed that MP density within five size-fractions,three plastic shapes and four color types didn’t vary before and after typhoon.(3)A total number of 587.0 items(42.3 g)was detected on six tourism beaches around the South China Sea.The averaged density was 97.5±157.4 n/m2(0-636 n/m2)and 7.0±12.1 g/m2(0-44.4 g/m2).Spatial discrepancies in the amounts of plastics were correlated to the river inputs,local human activities and managements.Small plastics(1-20 mm)accounted for 63.4%of plastic debris quantified by number and 25%by weight.An exponential damping relationship between the size and amount of plastic debris was determined.Polypropylene(59.7%)and polyethylene(31.9%)were the most common polymer compositions in the selected samples.Vast amounts of plastic remain in beaches after beach cleaning,which would be a potential source of marine MP.(4)The study of contamination by microscopic anthropogenic litter(MAL,0.5-5 mm)in terrestrial ecosystems is beneficial to the construct not well understood.MAL from the gastrointestinal tracts of 17 terrestrial birds was identified and categorized under a stereo microscope based on its physical properties and melting tests.In total,364 items were identified as MAL,ranging in size from 0.5 to 8.5 mm.Natural fibers,plastic fibers and fragmented plastics represented,respectively,37.4%(136 items),54.9%(200 items)and 7.7%(28 items)of total litter items.The decline in the proportion of natural fibers from the esophagus to stomach and intestine suggested that they may be digestible,which may disperse and adsorb chemical pollutants differently from MP and may pose an even greater risk.(5)The ocean surface habitat is not the ultimate fate of floating MP.The removal mechanism of MP from the surface wasters is not still clear.We present a new dual density separation method employing sodium iodide extraction followed by methanol precipitation,specifically designed for MP isolation and identification in natural marine snow samples.Residual organic matter which can cause interference in downstream Raman spectroscopic analyses was eliminated by employing a 15%hydrogen peroxide(H2O2)digestion step,which caused neglig:ible chemical modifications to the polymer samples.Extensive precautions such as combusted glassware,a microfiltration air hood,and incorporation of process blank samples ensured that airborne MP contamination was avoided.A total of 60 microscopic particles from 48L marine snow samples collected at coasts were confirmed as plastics and/or substances containing typical plastic manufacturing additives.This study firstly presented evidence that PMD can be incorporated in the natural marine snow and represents a mechanism for transporting MP to the sea floor.Generally,this thesis firstly presents the occurrence,distribution,abundance and characteristics MP in various environmental compartments in some key estuaries of China.In ad,dition,this study supplemented the knowledge gap on the evaluation of MP ingestion by terrestrial biomass.To explore the fate of MP in surface waters,we developed a new method and certified marine snow is the benthic-pelagic coupling mechanism of MP in the oceans.This study is of great significance in understanding the spatial distribution,migration path and environmental fate of MP in offshore environments,and provide reference data for the MP pollution control and the establishment of ecological risk assessment frame. |
