Microplastics In Sedimentation Environments

Since the 1980 s,the ingestion and entanglement of marine debris by marine organism have attracted mass attention by academia.With the increase in the amount of the world's total plastics production,plastic patches in the oceanic gyres gradually formed,including the Great Pacfic Garbage Patch.Marine debris will fragment into smaller pieces,the so-called microplastics,that have a diameter of less than 5 mm and are widely distributed in populated estuaries,coastal waters,sediments and biota,and even in extreme marine environments.This thesis investigated microplastic distribution in sediments from a megacity located in coastal zones,subaquous surface sediments and sediment cores from the Changjiang Estuary,and sediments from the deep sea and hadal trenches,including the deepest place on Earth,the Mariana Trench,to illustrate the spatialtemporal distribution and characterization of microplastics in various sedimentation environments.This study investigated the transport mechanism of microplastics from land to the deep sea.Priliminary risk assessment of microplastics in sediments was conducted based on microplastic data acquired with valid and reasonable proxies,thus the risk of microplastics was assessed and the framework for risk assessment of microplastics was developed.A recent risk assessment framework named Aggregate Exposure Pathway was also introduced and applied in integrating data for assessing the ecological risk of microplastics.The thesis also summarized sampling guidelines for microplastics collected from various sedimentation environments and analytical methods in the laboratory.Considering the fact that microplastic data obtained across the world cannot be directly compared due to differentiated sampling and analytical methods researchers applied,this study designed tablets and capsules with known amount,size and shape of plastic polymers,distributed across 34 microplastic laborotaries,and conducted interlaboratory study to quantify the variance and performance among various microplastic laboratories.Main conclusions of this thesis are as follows:1.Two types of standard microplastic pills were designed with known polymer numbers,polymer types,shapes and colors in the form of tablets and capsules.Standard microplastic particles were applied in the interlaboratory study(ILS)of microplastics among 34 microplastic laboratories to illustrate performance of each laboratory and quantify the variance of microplastic analytical methods for the same kind of microplastics.The same batch of microplastic tablets were distributed to microplastic laboratories without knowing the polymer type or number of particles in the tablets.All the laboratories were able to report the polymer type in different kinds of microplastic tablets.The RSD of the number of reported particles varied from 29-78%.2.Sediments from river channels and tidal flats in a mega city,Shanghai,were polluted by microplastics.The microplastic abundance for six riverbed sites was on average 802 items/kg dry sediment.Microplastic abundance in rivers near densely populated areas was one to two orders of magnitude greater than in the tidal flat in rural areas of Shanghai.Moreover,features of microplastics in rivers were different from those in the tidal flat.White spheres composed the majority of microplastics in all river samples,while fibers and fragments outnumbered spheres in the tidal flat.Our study corroborates with other similar studies that the main source of microplastics is river input at the estuary.3.Microplastic concentration from subaquous surface sediments in the Changjiang Estuary varied from 20 to 340 items/kg dry weight.It was found that the concentration of microplastics was the highest on the southeast coast of Shanghai.The distribution pattern of microplastics may be affected by the Changjiang diluted water in summer.Rayon,polyester,and acrylic were the most abundant types of microplastics identified using ?-FT-IR,indicating that the main source of microplastics in the Changjiang Estuary was from washing clothes(the primary source).4.In subaquous sediment core samples from the Changjiang Estuary,microplastics were not detected below a depth of 90 cm with maximum counts occurring in the top 16 cm.The maximum value was found at the top part of the core with nine particles at 4–16 cm depth(180 n/kg).Given the massive change in plastic production and usage in China this record shows,we suggest that the age of sediment at 84 cm lies around the 1950 s.This study shows that multiple dating approaches can provide high resolution dating framework in recent hundred years of age determination,and firstly proposed that microplastics may be a promising dating technique.5.Microplastics found in sediments in the three deepest hadal trenches show that microplastics are already accumulating at the bottom of deepest corners on the planet,with an average abundance of 71.1 items/kg dry weight sediment.Our study provides essential baseline data on microplastic pollution in hadal environments(down to 10,890 m),which confirms that microplastics have reached full-ocean depth.The potential cascading processes that transport microplastics to hadal trenches provides an answer to the question how microplastics are transported from sea surface to seafloor.6.Risk assessment of microplastics in river sediments in Shanghai was conducted based on monomer toxicity of polymers.Among all the seven sites,one site had greater environmental risk than other sites.Meanwhile,a recently proposed Aggregate Exposure Pathway(AEP)framework was applied to microplastic pollution based on data acquired and integrated in estuaries,coasts and the deep sea in this study.Knowledge gap of AEP framework for microplastics was illustrated.