Estimation of the annual flow and stock of marine debris in South Korea for management purposes

Phthalates contamination in sediments: A review of sources, influencing factors, benthic toxicity, and removal strategies

Sediments provide habitat and food for benthos, and phthalates (PAEs) have been detected in numerous river and marine sediments as a widely used plastic additive. PAEs in sediments is not only toxic to benthos, but also poses a threat to pelagic fish and human health through the food chain, so it is essential to comprehensively assess the contamination of sediments with PAEs. This paper presents a critical evaluation of PAEs in sediments, which is embodied in the analysis of the sources of PAEs in sediments from multiple perspectives. Biological production is indispensable, while artificial synthesis is the most dominant, thus the focus was on analyzing the industrial and commercial sources of synthetic PAEs. In addition, since the content of PAEs in sediments varies, some factors affecting the content of PAEs in sediments are summarized, such as the properties of PAEs, the properties of plastics, and environmental factors (sediments properties and hydrodynamic conditions). As endocrine disruptors, PAEs can produce toxicity to its direct contacts. Therefore, the effects of PAEs on benthos immunity, endocrinology, reproduction, development, and metabolism were comprehensively analyzed. In addition, we found that reciprocal inhibition and activation of the systems lead to genotoxicity and apoptosis. Finally, the paper discusses the feasible measures to control PAEs in wastewater and leachate from the perspective of source control, and summarizes the in-situ treatment measures for PAEs contamination in sediments. This paper provides a comprehensive review of PAEs contamination in sediments, toxic effects and removal strategies, and provides an important reference for reducing the contamination and toxicity of PAEs to benthos.

Expanded Polystyrene-Debris-Induced Genotoxic Effect in Littoral Organisms

Expanded polystyrene (EPS) is a major component of plastic debris in the environment, including coastal and littoral zones. EPS is widely used in various industries including fish farming and aquaculture, which poses a serious potential threat not only to cultured hydrobionts but also to all living organisms, including humans. This paper presents the results of experimental studies on the effects of EPS (0.024 m2/L) on marine mollusks Mytilus trossulus and Tegula rustica, which are typical inhabitants of the upper littoral of Peter the Great Bay (Sea of Japan), belonging to different systematic groups and differing in the type of nutrition. The results of biochemical marker analysis showed the development of oxidative stress processes. Thus, increasing malondialdehyde content relative to control values was registered in the digestive glands of M. trossulus and T. rustica. In the cells of the digestive glands of M. trossulus, integral antioxidant activity decreased more than 1.5 times compared with that of the control. The change in the concentration of protein carbonyls was unchanged in M. trossulus, whereas in T. rustica, there was a 1.5-fold increase. EPS exposure also resulted in significant DNA damage in the studied mollusks-the damage level increased 2.5-fold in M. trossulus and 1.5-fold in T. rustica relative to the control, indicating the genotoxic potential of EPS litters.

River export of macro- and microplastics to seas by sources worldwide

Seas are polluted with macro- (>5 mm) and microplastics (<5 mm). However, few studies account for both types when modeling water quality, thus limiting our understanding of the origin (e.g., basins) and sources of plastics. In this work, we model riverine macro- and microplastic exports to seas to identify their main sources in over ten thousand basins. We estimate that rivers export approximately 0.5 million tons of plastics per year worldwide. Microplastics are dominant in almost 40% of the basins in Europe, North America and Oceania, because of sewage effluents. Approximately 80% of the global population live in river basins where macroplastics are dominant because of mismanaged solid waste. These basins include many African and Asian rivers. In 10% of the basins, macro- and microplastics in seas (as mass) are equally important because of high sewage effluents and mismanaged solid waste production. Our results could be useful to prioritize reduction policies for plastics.

Factors in enhancing environmental governance for marine plastic litter abatement in Manila, the Philippines: A combined structural equation modeling and DPSIR framework

This empirical study examines the factors enhancing environmental governance for marine plastic litter abatement in Manila, the Philippines. We use a combined covariance-based hybrid structural equation modeling (SEM) and DPSIR framework, with data collected via an online survey from 456 barangays in Manila, the Philippines. The survey was processed and analyzed using a combined model, validated through interviews and focused group discussions. With Higher-Order Model good internal consistency (0.917) and achieved measures of CFI (0.992), RMSEA (0.036), and SRMR (0.019), the findings revealed that environmental governance (COVID-19 waste), community participation, socio-economic factors, and solution measures have positively affected marine plastic litter (MPL) abatement. Notwithstanding, environmental governance (SWM policies and guidelines) has a negative impact on MPL abatement. There is, however, no link between waste infrastructure and MPL abatement. The findings provide significant perspectives in Manila to enhance environmental governance for MPL abatement. This paper presents policy-actions implications drawn from DPSIR-SEM.

Physical and anthropogenic drivers shaping the spatial distribution of microplastics in the marine sediments of Chilean fjords

Several studies have focused on the presence and distribution of microplastics within the water column of coastal waters, but the dynamics of these particles in sediments have received little attention. Here we examine the concentrations and characteristics of microplastics in sediment samples collected from 35 stations within the Inner Sea of Chiloé, Chilean Patagonia. Current velocity, grain size, intensity of salmon farming activities, and human population density were all evaluated as factors potentially explaining concentrations and distribution of microplastic particles within these sediments. Microplastics were detected in all samples, with the highest abundance represented by fibers (88%), fragments (10%) and films (2%). Across the sampled sites, microplastic concentrations averaged 72.2 ± 32.4 (SD) items per kg dw (dry weight) sediment, with the principal polymers identified as polyethylene terephthalate (PET), acrylic, polypropylene (PP) and polyurethane (PUR). Approximately 40% of the variability in distribution and abundance of microplastics was explained by current velocity combined with proximity and intensity of local salmon production activities. SYNOPSIS: Marine currents and aquaculture intensity explain abundance and dynamics of microplastics in marine sediments.

MARIDA: A benchmark for Marine Debris detection from Sentinel-2 remote sensing data

Currently, a significant amount of research is focused on detecting Marine Debris and assessing its spectral behaviour via remote sensing, ultimately aiming at new operational monitoring solutions. Here, we introduce a Marine Debris Archive (MARIDA), as a benchmark dataset for developing and evaluating Machine Learning (ML) algorithms capable of detecting Marine Debris. MARIDA is the first dataset based on the multispectral Sentinel-2 (S2) satellite data, which distinguishes Marine Debris from various marine features that co-exist, including Sargassum macroalgae, Ships, Natural Organic Material, Waves, Wakes, Foam, dissimilar water types (i.e., Clear, Turbid Water, Sediment-Laden Water, Shallow Water), and Clouds. We provide annotations (georeferenced polygons/ pixels) from verified plastic debris events in several geographical regions globally, during different seasons, years and sea state conditions. A detailed spectral and statistical analysis of the MARIDA dataset is presented along with well-established ML baselines for weakly supervised semantic segmentation and multi-label classification tasks. MARIDA is an open-access dataset which enables the research community to explore the spectral behaviour of certain floating materials, sea state features and water types, to develop and evaluate Marine Debris detection solutions based on artificial intelligence and deep learning architectures, as well as satellite pre-processing pipelines.

Study on the Propeller Rope Cutter Concerning Transient Torsional Vibration Due to Cutting Action

Nowadays, damage to ships due to marine debris at sea is increasingly reported. Specifically, a piece of rope or fishing net can wrap around the propeller shaft, stopping it from rotating. Although various efforts have been made, there are still numerous practical challenges. A rope cutter system, which was designed to cut suspended objects wrapped around the propeller shaft, offers a great advantage in protecting the propulsion system. Since the cutting action produces the transient torsional vibration, the connecting bolts should be stable and sufficiently rigid under normal conditions. However, in the event of an encounter with an object that is too hard to cut, the bolts must be broken so that the rope cutter is released. Those kinds of objects may not be long enough to wrap around the shaft, such as a piece of wood. Therefore, this research presents the novelty in maintaining the safety of the propulsion system installed with a rope cutter. In this study, a method for obtaining the maximum diameter of the connecting bolt as a safety device is described, and the torques required to cut ropes of various thicknesses were determined based on actual measurements. Finally, a series of experiments in the laboratory-scale and shipboard test on an actual ship show that the rope cutter does not significantly reduce the ship’s power performance or increase the structural vibration.

Mathematical modeling of microplastic abundance, distribution, and transport in water environments: A review

Microplastic pollution in marine and riverine environments is a threat not only for the aquatic ecosystem itself but also for human activity and life. Although there are reviews regarding microplastic debris in environments, most of them focus on the studies on their type, occurrence, and distribution. Only a limited number of these studies focus on the modeling methods, usually concentrating on particular aspects, such as settling or bioaccumulation. In this paper, physically-based existing microplastics modeling studies are classified and reviewed according to the environment, modeling methodology, and input-output relationships. Considering the strengths and weaknesses of all modeling methodologies, it is deduced that more reliable results are obtained using hybrid methods, especially the coupling of hydrodynamic and process-based models, and hydrodynamics and statistical models. The significance of having much more consideration and knowledge on the microplastics' physical properties and the environmental processes affecting their fate and transport in the aquatic environments is revealed for future research. It has also been recommended that a standardized method for data calibration, validation, and verification is necessary to be able to compare the modeling results with field investigations more efficiently than it is currently.

Anthropogenic fibres in white clams, Meretrix lyrata, cultivated downstream a developing megacity, Ho Chi Minh City, Viet Nam

Anthropogenic fibres are an emerging pollutant worldwide. The Can Gio mangrove area is located downstream of the Saigon River, and is characterised by high level of anthropogenic fibres originating from domestic and industrial textile and apparel manufacturing. In this area, biota is thus subjected to a high potential risk of anthropogenic fibre contamination. This study aims to characterise the accumulation of anthropogenic fibres in different tissues, i.e. gills, digestive systems, and remaining tissues, of white clams (Meretrix lyrata) cultivated in the Can Gio beach sand, during a seven-month sampling period. The results showed an average concentration of 3.6 ± 2.1 fibres individual^-1 or 2.7 ± 2.4 fibres g^-1 ww. Higher fibre accumulation was observed in remaining tissues than in gills and digestive systems, and no temporal variation was observed in all clam tissues. The intake of fibres by humans consuming clams was estimated to be 324 fibres inhabitant^-1 yr^-1.

Standing stock and mass balance of marine litter in the Seto Inland Sea, Japan

The basin of Seto Inland Sea has a population of 31 million people. The standing stock and mass balance of marine litter in this area was estimated using rapid assessment for beach litter, questionnaire surveys on removed amounts of marine litter, and existing data. The mass balance of marine litter was explained by using a single box model, assuming complete mixing and uniform density. If the standing stock of drifting and beach litter combined was 3400 tons, the inflow of litter from rivers was 3000 tons/year, generation of litter at sea was 1200 tons/year, and inflow from the open sea was 300 tons/year. The amount of marine litter removed from the beach and sea surface was 1400 tons/year, outflow to the open sea was 2400 tons/year, and deposition on the sea bottom was 700 tons/year.

Evaluating the fate of hexabromocyclododecanes in the coastal environment: Fugacity analysis using field data

Abundant use of plastic materials has increased the amount of microplastics (MPs) and related hazardous chemicals in the marine environment. Hexabromocyclododecanes (HBCDs), brominated flame retardants added to expanded polystyrene (EPS), have been detected in biotic and abiotic samples. In this study, the partition constants of HBCDs between plastics and seawater (K_Psw) were determined. Fugacities of HBCDs in EPS, seawater, sediment, and mussels were obtained to determine the directions of the diffusive flux. The fugacities in EPS (f_EPS) were greater than those in seawater (f_sw), sediment (f_sed), and mussels (f_swmussel-EPS and f_mussel-rock) by three orders of magnitude, indicating that EPS plastics are a significant source of HBCDs. The f_mussel-rock of α-HBCD in rock mussels was greater than f_sw by factors of 1.7, whereas the f_mussel-rock of γ-HBCD was smaller than f_sw by factors of 16, indicating the bioisomerization from γ-to α-HBCD. The relatively constant concentration ratio of β-HBCD to the total HBCDs indicated that β-HBCD is a sufficient tracer for determining the diffusive flux. The f_sed values of HBCDs were greater than f_sw by factors of 17-28, implying a probable advective vertical flow of HBCDs from the EPS plastics, which requires further investigation.

A comparative study of deep learning-based network model and conventional method to assess beach debris standing-stock

The conventional survey of marine debris standing-stock has various drawbacks such as high cost and inaccuracy because the total amount of debris in the whole beach is inferred using the results of the manual investigation in selected narrow areas. To overcome the disadvantages, an automatic detection method using a deep learning-based network model was developed to detect and quantify the beach debris. The network model developed in this study classified items with a precision of 0.87 (87%) mAP and showed <5% error compared to actual survey. This study is the first fieldwork in Korea that shows the difference between automatic and conventional methods to predict the beach debris standing-stock. The results provide essential information for the development of effective beach debris management systems and policies.

Economic Valuation of Reducing Submerged Marine Debris in South Korea

Submerged marine debris (SMD) scattered between sea level and the bottom of the sea damages the habitats of marine life and threatens its growth in South Korea. The collection of SMD is more difficult and expensive than that of coastal and floating debris. The government is trying to achieve a 33% reduction in SMD by 2023 by expanding its collection, which requires huge additional investments and additional information about the economic value or benefits of the reduction. This article seeks to conduct an economic valuation of the reduction by employing contingent valuation (CV), which asks people to indicate their willingness to pay (WTP) for the reduction. A dichotomous choice CV survey was undertaken with 1000 households by a professional survey firm through person-to-person interviews during July 2019. Overall, people understood the CV questions well and reported the WTP responses for a hypothetical market successfully created with CV. Although 37.9% of interviewees stated zero WTP, the average of the yearly household WTP was estimated as 5523 Korean won (KRW) (USD 4.92). This value ensures statistical significance. The population’s WTP for the reduction would be KRW 110.30 billion (USD 99.75 million) per year over the next five years. It was found that the reduction is socially beneficial since the value was greater than the costs involved in the reduction.

Microplastics on beaches along the eastern Gulf of Thailand - A preliminary study

Several studies have shown the ubiquitousness of microplastics across ecosystems worldwide including significant amounts in beach sand. In Thailand, however, there is a lack of studies about the microplastic pollution of beaches. This study aimed to quantify microplastics at the high-tide line of 21 beaches along the eastern Gulf of Thailand. Observed amounts ranged from 420 to >200,000 counts/kg. Anthropogenic and environmental factors affect distribution and amount of microplastics. Tide-dominated beaches and beach sections protected by beachrocks exhibit higher microplastic amounts due to lesser hydrodynamics. While human activities have a visible impact, in some cases environmental factors seem to predominate. Despite effective protection efforts led by the government and NGOs, our study shows that the substantial microplastic pollution of beach sand requires a proper management system with appropriate laws and regulations, and a public awareness campaign to reduce effects of microplastics on organisms and their ecosystems.

A close relationship between microplastic contamination and coastal area use pattern

Human activity is thought to affect the abundance and contamination characteristics of microplastics (MPs) in the environment, which may in turn affect aquatic species. However, few studies have examined the impact of coastal area use pattern on characteristics of MPs in coastal regions. In this study, we investigated MP contamination of abiotic matrices (seawater and sediment) and biotic matrices (bivalves and polychaetes) in three coastal regions characterized by different types of human activity, covering urban, aquafarm, and rural areas. MP abundance was higher in sediment from the urban site than in that from the rural site, but similar to that from the aquafarm site. In the abiotic matrices, different MP polymer compositions were observed among the three sites. Diverse polymers were found in marine matrices from the urban site, implying diverse MP sources in highly populated and industrialized areas. Polystyrene was more abundant in the aquafarm site, reflecting the wide use of expanded polystyrene aquaculture buoys. Polypropylene was more abundant at the rural site, probably due to the use of polypropylene ropes and nets in fishing activity. MP accumulation profiles in marine invertebrates showed trends similar to those exhibited by abiotic matrices, reflecting coastal area use patterns. These results indicate that marine MPs are generated from both land- and marine-based sources, and that the abiotic and biotic marine matrices reflect the MP characteristics.

Estimating a regional budget of marine plastic litter in order to advise on marine management measures

Using simple models, coupled with parameters extracted from published studies, the annual inputs of macro and micro plastics to the Scottish Atlantic Coast and the Scottish North Sea Coast regions are estimated. Two estimates of land-based sources are used, scaled by catchment area population size. The oceanic supply of floating plastic is estimated for wind-driven and general circulation sources. Minimum, typical and maximum values are computed to examine the magnitude of uncertainties. Direct inputs from fishing and the flux of macroplastic onto the seabed are also included. The modelled estimates reveal the importance of local litter sources to Scottish coastal regions, and hence local management actions can be effective. Estimates provide a scale against which removal efforts may be compared, and provide input data for future more complex modelling. Recommendations for research to improve the preliminary estimates are provided. Methods presented here may be useful elsewhere.

Rapid assessment of marine debris in coastal areas using a visual scoring indicator

Information regarding the spatial distribution and standing stock of marine debris in coastal areas is a prerequisite for efficient cleanup and management. We conducted a rapid assessment of marine debris on the coasts of South Korea using a visual scoring indicator. The indicator consisted of a table and photographs representing nine pollution levels that were quantitatively tested. Locations at every 10 km were selected along the natural coastline for a total of 382 locations, and a length of 100 m at each location was assessed. Approximately 40 participants were trained and assessed the pollution levels using a smartphone application. The surveys were conducted four times in 2017, in April, June, August, and October. The total amount of marine debris stock in the natural coastal areas was estimated to be approximately 17 thousand tons. It suggests that approximately 60% of the marine debris can be cleaned from 10% of the coastline.

Abundance and characteristics of microplastics in market bivalves from South Korea

Microplastic contamination in marine organisms is a growing environmental issue with implications for seafood safety. Among marine organisms, shellfish are considered to be an important route of human exposure to microplastics because they filter a large volume of seawater while feeding and, thus, accumulate microplastics from seawater; furthermore, they are consumed whole, without gut removal. In this study, a market survey was carried out to understand microplastic contamination in domestic bivalves sold in fishery markets in three major cities of South Korea. Four popular bivalve species, oyster (Crassostrea gigas), mussel (Mytilus edulis), Manila clam (Tapes philippinarum) and scallop (Patinopecten yessoensis), were selected as monitoring species, which together account for 79-84% of total shellfish consumption in Korea. The mean concentration of microplastics in these four species was 0.15 ± 0.20 n/g and 0.97 ± 0.74 n/individual. Fragments and particles smaller than 300 μm were dominant shape and size, accounting for 76% and 65% of total microplastics, respectively. Polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyester were the major polymer types. Interestingly, differing polymer compositions were observed according to the culture methods and habitat characteristics of each species. PS was found in high proportions in oysters and mussels cultured in the upper layer of the water column, while the proportions decreased and those of polyester increased in Manila clams and scallops that were cultured in intertidal sediments or the middle and bottom layers of the water column. The annual dietary intake of microplastics by the Korean population via shellfish consumption was estimated as 212 n/person·year. Our results suggested that microplastic pollution is widespread in commercial bivalves and we recommend a systematic and integrative market-basket survey to clarify the current status of human exposure to microplastics.

Occurrence of microplastics in municipal sewage treatment plants: a review

Municipal sewage treatment plants (STPs) are thought to be important point sources of microplastics in freshwater systems and many peer-reviewed articles have been published on this issue since mid-2010s. In this review, we summarize existing literature on the occurrence of microplastics in STPs and experimental methods used for isolation and identification of microplastics. The number concentrations of microplastics in STP influents were 15.1-640 L-1 , whereas those in the STP effluents were highly variable and ranged from not detectable to 65 L-1 . For most of cases, conventional STPs are removing microplastics very effectively. Fragments and fibers are dominant shapes of microplastics. Thermoplastics (polyethylene and polypropylene) and polyester are the predominant materials recovered. Although further research is needed, size distribution of microplastics in STPs is likely to follow a power law, implying that different studies using different size cutoffs may be compared after establishing a power law relationship.

Collected marine litter - A growing waste challenge

Marine litter, in particular plastic debris, poses a serious threat to marine life, human health and the economy. In order to reduce its impact, marine litter collections such as beach clean-ups are frequently conducted. This paper presents a systematic review of temporal developments, geographical distribution, quantities and waste treatment pathways of collected marine litter. Results from over 130 studies and projects highlight the worldwide increase in collection efforts. Many of these are in wealthy countries that do not primarily contribute to the problem. Over 250 thousand tonnes, have already been removed, but there is little or no information available regarding how this waste is treated or used post collection. This paper highlights the need for a whole-system quantitative assessment for the collection and waste treatment of marine litter, and identifies the challenges associated with utilising this waste in the future.

Releasing of hexabromocyclododecanes from expanded polystyrenes in seawater -field and laboratory experiments

Expanded polystyrene (EPS) is a major component of marine debris globally. Recently, hazardous hexabromocyclododecanes (HBCDDs) were detected in EPS buoys used for aquaculture farming. Subsequently, enrichment of HBCDDs was found in nearby marine sediments and mussels growing on EPS buoys. It was suspected that EPS buoys and their debris might be sources of HBCDDs. To confirm this, the release of HBCDDs from EPS spherules detached from a buoy to seawater was investigated under field (open sea surface and closed outdoor chambers with sun exposure and in the dark) and laboratory (particle-size) conditions. In all exposure groups, initial rapid leaching of HBCDDs was followed by slow desorption over time. Abundant release of HBCDDs was observed from EPS spherules exposed to the open sea surface (natural) and on exposure to sunlight irradiation or in the dark in controlled saline water. Water leaching and UV-light/temperature along with possibly biodegradation were responsible for about 37% and 12% of HBCDDs flux, respectively. Crumbled EPS particles (≤1 mm) in samples deployed on the sea surface for 6 months showed a high degree of weathering. This implies that surface erosion and further fragmentation of EPS via environmental weathering could enhance the leaching of HBCDDs from the surface of EPS. Overall, in the marine environment, HBCDDs could be released to a great extent from EPS products and their debris due to the cumulative effects of the movement of large volumes of water (dilution), biodegradation, UV-light/temperature, wave action (shaking), salinity and further fragmentation of EPS spherules.

Navigational threats by derelict fishing gear to navy ships in the Korean seas

This study assessed the impact of derelict fishing gear (DFG) on navigation. The Republic of Korea's navy (ROKN) recorded every case of approximately 170 naval ships associated with propeller entanglement by DFG from January 2010 to December 2015. The frequency of cases was 2.3 per ship and 397.7 (±37.5) per year. The amount of DFG disentangled was 0.025tons per ship and 10.0 (±1.7) tons per year. The frequency temporally decreased whereas the amount increased over these six years. To disentangle propellers, 3.1 divers were needed on average per case. Propeller entanglement occurred in all local seas and some of these areas showed increases over time. Our study highlights that the impact of DFG on navigational threats has been persistent and ubiquitous and can potentially be reduced by preventing DFG in fishing areas, with a focus on improved management by fishermen and government and with more efficient retrieval of DFG.

Styrofoam Debris as a Source of Hazardous Additives for Marine Organisms

There is growing concern over plastic debris and their fragments as a carrier for hazardous substances in marine ecosystem. The present study was conducted to provide field evidence for the transfer of plastic-associated chemicals to marine organisms. Hexabromocyclododecanes (HBCDs), brominated flame retardants, were recently detected in expanded polystyrene (styrofoam) marine debris. We hypothesized that if styrofoam debris acts as a source of the additives in the marine environment, organisms inhabiting such debris might be directly influenced by them. Here we investigated the characteristics of HBCD accumulation by mussels inhabiting styrofoam. For comparison, mussels inhabiting different substrates, such as high-density polyethylene (HDPE), metal, and rock, were also studied. The high HBCD levels up to 5160 ng/g lipid weight and the γ-HBCD dominated isomeric profiles in mussels inhabiting styrofoam strongly supports the transfer of HBCDs from styrofoam substrate to mussels. Furthermore, microsized styrofoam particles were identified inside mussels, probably originating from their substrates.

Estimation of the Environmental Load of High- and Low-Density Polyethylene From South Korea Using a Mass Balance Approach

The accumulation of marine plastic debris is one of the main emerging environmental issues of the twenty first century. Numerous studies in recent decades have reported the level of plastic particles on the beaches and in oceans worldwide. However, it is still unclear how much plastic debris remains in the marine environment because the sampling methods for identifying and quantifying plastics from the environment have not been standardized; moreover, the methods are not guaranteed to find all of the plastics that do remain. The level of identified marine plastic debris may explain only the small portion of remaining plastics. To perform a quantitative estimation of remaining plastics, a mass balance analysis was performed for high- and low-density PE within the borders of South Korea during 1995-2012. Disposal methods such as incineration, land disposal, and recycling accounted for only approximately 40 % of PE use, whereas 60 % remained unaccounted for. The total unaccounted mass of high- and low-density PE to the marine environment during the evaluation period was 28 million tons. The corresponding contribution to marine plastic debris would be approximately 25,000 tons and 70 g km(-2) of the world oceans assuming that the fraction entering the marine environment is 0.001 and that the degradation half-life is 50 years in seawater. Because the observed concentrations of plastics worldwide were much lower than the range expected by extrapolation from this mass balance study, it is considered that there probably is still a huge mass of unidentified plastic debris. Further research is therefore needed to fill this gap between the mass balance approximation and the identified marine plastics including a better estimation of the mass flux to the marine environment.

Distribution and Size Relationships of Plastic Marine Debris on Beaches in South Korea

The characteristics of the distribution of plastic marine debris were determined on 12 beaches in South Korea in 2013 and 2014. The abundances of large micro- (1-5 mm), meso- (5-25 mm), and macroplastics (>25 mm) were 880.4, 37.7, and 1.0 particles/m(2), respectively. Styrofoam was the most abundant debris type for large microplastics and mesoplastics (99.1 and 90.9 %, respectively). Fiber (including fabric) was the most abundant of the macroplastics (54.7 %). There were no statistical differences in the mean numbers and weights of plastic debris among three beach groups from west, south, and east coasts. No significant differences were detected between the abundances of beached plastics in high strandline and backshore for all three size groups. Spearman's rank correlation was used to determine the relationships between the three debris size classes. The abundance of large microplastics was strongly correlated with that of mesoplastics for most material types, which suggests that the contamination level of large microplastics can be estimated from that of mesoplastics. As surveying of smaller particles is more labor intensive, the surveying of mesoplastics with a 5-mm sieve is an efficient and useful way to determine "hot-spots" on beaches contaminated with large microplastics.