Horizontal and Vertical Distribution of Microplastics in Korean Coastal Waters.

This is the first survey to investigate the vertical distribution and composition of microplastics >20 µm at the surface (0-0.2 m; bulk sample) and in the water column (3-58 m depth; pump) of six semi-enclosed bays and two nearshore areas of South Korea. The average microplastic abundance of 41 stations at all sampling depths was 871 particles/m3, and the microplastic abundance near urban areas (1051 particles/m3) was significantly higher than that near rural areas (560 particles/m3). Although the average microplastic abundances in the midcolumn (423 particles/m3) and bottom water (394 particles/m3) were approximately 4 times lower than that of surface water (1736 particles/m3), microplastics prevailed throughout the water column in concentrations of 10-2000 particles/m3. The average sizes of fragment and fiber type microplastics were 197 and 752 µm, respectively. Although the polymer composition differed by depth depending on the particle size and density, polypropylene and polyethylene predominated throughout the water column regardless of their low density and particle size. Finally, the middle and bottom water samples contained higher abundances of microplastics than predicted by a model based on physical mixing, indicating that biological interactions also influence the downward movement of low-density microplastics.

Quantification of ocean microplastic fragmentation processes in the Sea of Japan using a combination of field observations and numerical particle tracking model experiments.

This study estimated the fragmentation rate of microplastics (MiPs) in the Sea of Japan by analyzing MiP size over time following their generation from macroplastics (MaPs). A 5-year particle-tracking model was used to simulate the MaP and MiP motions driven by ocean currents, Stokes drift, the windage of MaPs, beaching, re-drifting, the conversion process from MaPs to MiPs, and the removal of MiPs from the upper ocean. MiP sizes decreased downstream in the Tsushima Current flowing northeastward. The highest correlation between MiP size and elapsed time occurred in the simulation where MiP fragmentation also occurred in the ocean, at 20 % of the rate on beaches. The apparent fragmentation rate in nature was estimated to approximately 1.0 mm/100 days. This study demonstrated that incorporating spatiotemporal information from the simulation into observed size results could further our understanding of fragmentation of MiPs degraded in marine environments.

Reduction scenarios of plastic waste emission guided by the probability distribution model to avoid additional ocean plastic pollution by 2050s.

Marine plastic pollution is progressing worldwide and will become increasingly serious if plastic waste emissions continue at the current rate or increase with economic growth. Here, we report a particle tracking-based probability distribution model for predicting the abundances of marine macroplastics and microplastics, which undergo generation, transport, and removal processes in the world's upper ocean, under various scenarios of future land-to-sea plastic waste emissions. To achieve the Osaka Blue Ocean Vision, which aims to reduce additional pollution by marine plastic litter to zero by 2050, plastic waste emission in ∼2035 should be reduced by at least 32 % relative to 2019. It is necessary to take stringent measures such as 'system change scenario' or 'improve waste management scenario' proposed in previous studies to reduce the marine plastic pollution by 2050.

A particle tracking model approach to determine the dispersal of riverine plastic debris released into the Indian Ocean.

Although the Indian Ocean receives a large amount of land-based plastic waste, the studies on pathways of riverine plastic debris are limited to date. Therefore, a particle tracking model that included ocean surface currents, horizontal diffusion, Stokes drift, windage, and beaching/re-drifting processes was developed to reproduce the behavior of riverine plastic debris in the Indian Ocean. The modeled particles were released in the model domain based on riverine plastic debris database. The maximum abundance of beached particles occurred during the southwesterly monsoon season, particularly in the Bay of Bengal. The particles released from the rivers were trapped in the northern Indian Ocean unless both Stokes drift and windage were excluded from transportation velocity. These results suggest that the riverine plastic debris was trapped in the northern Indian Ocean until it fragmented into less buoyant small microplastics drifting in the subsurface layer, free from windage and Stokes drift at increasing depths.

Quantification of litter in cities using a smartphone application and citizen science in conjunction with deep learning-based image processing.

Cities are a major source of litter pollution. Determination of the abundance and composition of plastic litter in cities is imperative for effective pollution management, environmental protection, and sustainable urban development. Therefore, here, a multidisciplinary approach to quantify and classify the abundance of litter in urban environments is proposed. In the present study, litter data collection was integrated via the Pirika smartphone application and conducted image analysis based on deep learning. Pirika was launched in May 2018 and, to date, has collected approximately one million images. Visual classification revealed that the most common types of litter were cans, plastic bags, plastic bottles, cigarette butts, cigarette boxes, and sanitary masks, in that order. The top six categories accounted for approximately 80 % of the total, whereas the top three categories accounted for more than 60 % of the total imaged litter. A deep-learning image processing algorithm was developed to automatically identify the top six litter categories. Both precision and recall derived from the model were higher than 75 %, enabling proper litter categorization. The quantity of litter derived from automated image processing was also plotted on a map using location data acquired concurrently with the images by the smartphone application. Conclusively, this study demonstrates that citizen science supported by smartphone applications and deep learning-based image processing can enable the visualization, quantification, and characterization of street litter in cities.

Open dumping site as a point source of microplastics and plastic additives: A case study in Thailand.

Microplastics (MPs) and plastic additive chemicals are emerging pollutants of great concerns around the world. Open dumping sites can be important sources of those pollutants in emerging countries, but little is known about their occurrence, distribution, transport pathway, and remediation approach. This study aimed to obtain the comprehensive dataset on plastic pollution in an open dumping site in Thailand, including (1) the polymer types and organic/inorganic plastic additives in plastic garbage, (2) horizontal distribution of MPs and plastic additives in the surface soil, (3) the effects of soil-capping treatment, and (4) the vertical transport. First, thirty-two plastic garbage collected from the dumping site were analyzed, and a total of 40 organic chemicals (mean: 1400,000 ng/g dw) and 7 heavy metals (mean: 2,030,000 ng/g dw) were identified. The burdens stored in the dumping site were estimated to reach to 3.3-18 tons for organic additives and 4.9-26 tons for heavy metals. In the surface soil analysis, 13 types of polymers in MPs, 20 elements, and 37 organic plastic additives were detected. The pollution levels were significantly higher near the dumping site than at control sites, indicating that the open dumping site is a point source of MPs and plastic additives. Interestingly, a significantly positive correlation was found between the concentrations of MPs and organic additives in soil. This suggests that MPs act as carriers of plastic-derived chemicals. Soil-capping treatment (including removal of some trash) drastically mitigated the contaminant levels in the surface soil, indicating this treatment is one of the effective approaches to control the horizontal distribution of MPs and plastic additives. However, soil core analyzes implied that the vertical transport is still continued even after soil-capping treatment. Our findings provided the comprehensive dataset to support for understanding plastic pollution in the open dumping site.

Possible sink of missing ocean plastic: Accumulation patterns in reef-building corals in the Gulf of Thailand.

Individual coral polyps contain three distinct components-the surface mucus layer, tissue, and skeleton; each component may exhibit varying extent of microplastic (MP) accumulation and serve as a short- or long-term repository for these pollutants. However, the literature on MP accumulation in wild corals, particularly with respect to the different components, is limited. In this study, we investigated the adhesion and accumulation of MPs in four coral species, including both large (Lobophyllia sp. and Platygyra sinensis) and small (Pocillopora cf. damicornis and Porites lutea) polyp corals collected from Si Chang Island in the upper Gulf of Thailand. The results revealed that MP accumulation varied significantly among the four coral species and their components. Specifically, P. cf. damicornis exhibited the highest degree of accumulation (2.28 ± 0.34 particles g-1 w.w.) [Tukey's honestly significant difference (HSD) test, p < 0.05], particularly in their skeleton (52.63 %) and with a notable presence of high-density MPs (Fisher's extract test, p < 0.05). The most common MP morphotype was fragment, accounting for 75.29 % of the total MPs found in the coral. Notably, the majority of MPs were black, white, or blue, accounting for 36.20 %, 15.52 %, and 11.49 % of the samples, respectively. The predominant size range of MP particles was 101-200 µm. Nylon, polyacetylene, and polyethylene terephthalate (PET) were the prevalent polymer types, accounting for 20.11 %, 14.37 %, and 9.77 % of the identified samples, respectively. In the large polyp corals, while MP shapes, colors, and sizes exhibited consistent patterns, remarkable differences were noted in the polymer types across the three components. The findings of this study improve the understanding of MP accumulation and its fate in coral reef ecosystems, underscoring the need for further investigation into MP-accumulation patterns in reef-building corals worldwide.

Small microplastic ingestion by the calanoid Centropages furcatus in the Gulf of Thailand.

Microplastics could be ingested by many organisms, including zooplankton, involving bioaccumulation and biomagnification mechanisms a cross food webs. The information about microplastic ingestion by zooplankton keeps increasing worldwide. However, it is still limited for particle sizes under 300 µm (small microplastics, SMPs) and in areas such as Southeast Asia, which is considered one of the hotspots for plastic debris. This study aimed to characterize the size, shape, and polymer types of the SMPs ingested by the copepod Centropages furcatus in Si Chang Island (upper Gulf of Thailand). The study spans offshore and coastal waters, with data collected across wet, intermediate, and dry seasons. Using a semi-automated technique for micro-FTIR (Fourier-transform infrared) scanning spectroscopy for particle analysis, we found ingested SMPs in all samples. A total of 750 individuals of the calanoid Centropages furcatus were analyzed, finding 309 plastic particles and an average ingestion value of 0.41 ± 0.13 particles ind-1, one of the highest recorded values. All the particles were fragments, with a predominant size under 50 µm, and polymer types as Polypropylene (PP, 71 %), followed by Ethylene-Propylene-Diene-Monomer (EPDM, 16 %) and Polyethylene (PE, 7 %). Up to 470.2 particles m-3 were estimated to be retained by this calanoid species and potentially available for trophic transfer. The effect of rainfall on SMPs ingestion was inconclusive, with a non-significant observed tendency to higher ingestion values near the coastal area than offshore area, suggesting a decrease in particle exposure due to the runoff effect. Nevertheless, future studies should increase the frequency of surveys to arrive at better conclusions.

Influence of monsoon seasonality and tidal cycle on microplastics presence and distribution in the Upper Gulf of Thailand.

Southeast Asian countries are recognized as significant contributors to the discharge of abundant plastic waste into the ocean. In this study, we conducted neuston net surveys on Si Chang Island of the Gulf of Thailand, a coral reef conservation area, to determine the presence of microplastic (MP) pollution. The survey, conducted during the wet (southwesterly monsoon), transition, and dry seasons (northeasterly monsoon), revealed that the MP abundance was in the range of 0.02-42.46 particles m-3. The precipitation, wind, and current direction induced by monsoons influenced the abundance and distribution of MP, presenting a significant seasonality. The cluster analysis for colors and polymer types of MPs suggested that the origin of plastic particles is diverse. Based on our results, a proposal for the generation, sources, and pathways for MPs in the Gulf of Thailand is presented: 1) plastic wastes exposed to strong UV light during the dry season get fragmented around the river, and 2) heavy rains wash away the particles during the wet season. This proposal is applicable to tropical regions, including the Gulf of Thailand. Therefore, this paper concluded that ocean currents induced by monsoons and the unique climate, resulting in the generation of MPs on land, increase MP presence and distribution in the ocean surrounding Southeast Asia countries. Furthermore, coral reef ecosystems can be particularly threatened by MPs in these areas. So, an increase in MP monitoring on coral ecosystems from Thailand and the world is highly recommended.

Abundance and potential sources of floating polystyrene foam macro- and microplastics around Japan.

Polystyrene foam is widely used due to its lightweight, impact resistance, and excellent thermal insulation properties. Meanwhile, weak adhesion between beads in polystyrene foam leads to fragmentation, generating a substantial amount of microplastics (<5 mm). Such polystyrene foam debris littered on beaches diminishes the aesthetic value of coastal areas, negatively impacting tourism. Due to its density lower than other plastics, polystyrene foam macroplastics float on the sea surface and, thus, they are significantly influenced by wind drag during oceanic transport. In contrast, polystyrene foam microplastics drifting beneath the sea surface are carried mostly by ocean currents. These properties of polystyrene foam macroplastics and microplastics hinder the elucidation of their transport, distribution, and fate in nature, despite their potential to adversely impact marine ecosystems. To elucidate the generation, transport, and fragmentation processes of polystyrene foam ocean plastics, we conducted concurrent visual observations and surface net towing from seven training vessels around Japan during 2014-2020. Overall, the abundances of polystyrene foam ocean plastics were higher in the Sea of Japan than in the North Pacific south of Japan. The average abundances of polystyrene foam microplastics and macroplastics were 0.33 pieces/m3 and 0.45 pieces/km, respectively, over the entire sea area around Japan. In the Sea of Japan, the peak abundances of polystyrene foam macroplastics occurred in upstream of the Tsushima Current, while the peak for microplastics occurred downstream, suggesting that continuous fragmentation occurred during transport between the two peaks. Backward-in-time particle tracking model experiments suggested that the sources of polystyrene foam macroplastics observed in the Sea of Japan included aquaculture buoys and styrene debris beached around the Tsushima Strait. The present study demonstrated that reducing the release of polystyrene foam aquaculture floats will likely diminish the abundance of ocean plastics in the Sea of Japan.

Estimation of the age of polyethylene microplastics collected from oceans: Application to the western North Pacific Ocean.

The knowledge of microplastic (MP) age could aid the deduction of the origin and fate of a fragment carried by ocean currents over long time periods and distances. The present study developed a novel method to estimate the age of MPs (i.e., UV radiation exposure time) using the oxidation level of polyethylene (i.e., carbonyl index) from infrared spectrometry, ultraviolet erythemal radiation (UVER) data, and ambient seawater temperatures. Accelerated and outdoor exposure experiments were conducted to establish relationships among the temporally integrated UVER, ambient temperature, and carbonyl index. Thereafter, the age of MPs was computed, with Miyakojima Island serving as the reference location. The estimated ages of MPs collected from the western North Pacific Ocean ranged from 1 to 3 years, and those MPs from nearshore waters ranged from 0 to 5 years.

Comparative evaluation of the carbonyl index of microplastics around the Japan coast.

The carbonyl index (CI) of polyethylene and polypropylene microplastics (MPs) (2950 particles) collected in coastal waters around Japan was investigated. The CI of MPs was calculated by the specified area under band technique. The mean MP CI in all samples (regardless of shape and color) was 0.69 ± 0.34 and 0.70 ± 0.34 for polyethylene and polypropylene, respectively, and there was no significant difference in the color or shape of the MPs. The polyethylene, white, and fragment MPs CI was negatively (p < 0.05) correlated with the major length of the MPs. Large MPs with relatively little deterioration were distributed along the west coast of the Sea of Japan, whereas small MPs were distributed along the east coast. Our findings of this gradual change in the deterioration of MPs, based on geographical distribution, are in accordance with literature CI-size and MP degradation hypotheses.

Zooplankton as a suitable tool for microplastic research.

In recent years, significant efforts have been dedicated to measuring and comprehending the impact of microplastics (MPs) in the ocean. Despite harmonization guidelines for MPs research, discrepancies persist in the applied methodologies and future challenges, mostly for the smaller fractions (< 100 µm). Whether intentional or accidental, ingesting plastic particles by zooplankton can lead to incorporating this pollutant into aquatic food chains. Therefore, zooplankton can serve as a suitable proxy tool for assessing the presence of plastic particles in ocean waters. However, reliable information is essential for conducting experimental laboratory studies on the impact of MPs ingestion by zooplankton organisms. Using zooplankton as a research tool for MPs offers numerous advantages, including similar sampling methodologies and study techniques as MPs and particle data integration over space and time. The scientific community can gain novel perspectives by merging zooplankton studies with MPs research. This review explores key aspects of using zooplankton as a tool for MPs research in water samples, encompassing various views such as particles ingestion in natural environments, particle quantification in zooplankton samples (past and future), ecotoxicological and toxicology model studies. By leveraging the potential of zooplankton research, advancements can be made in developing innovative techniques for MPs analysis.

Polymer types and additive concentrations in single-use plastic products collected from Indonesia, Japan, Myanmar, and Thailand.

Marine debris comprising single-use plastic products (SUPs) is ubiquitous in Asian coastal waters, but there is little information on the types of polymers and the concentrations of plastic additives such waste products contain. In this study, 413 SUPs randomly collected from 4 Asian countries between 2020 and 2021 were analyzed to obtain specific polymer and organic additive profiles. Polyethylene (PE), coupled with external polymers, was prominent in the inside of the SUPs, whereas polypropylene (PP) and polyethylene terephthalate (PET) were prevalent in both the insides and outsides of the SUPs. The use of different polymers in the insides and outsides of PE SUPs implies specific and complicated recycling systems are required to maintain the purity of the products. Phthalate plasticizers including dimethyl phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DiBP), dibutyl phthalate (DBP), and di(2-ethylhexyl) phthalate (DEHP), and the antioxidant butylated hydroxytoluene (BHT) were prevalent in the SUPs (n = 68). High concentrations of DEHP were detected in PE bags from Myanmar (820,000 ng/g) and Indonesia (420,000 ng/g), which were an order of magnitude greater than the concentrations in PE bags collected in Japan. SUPs containing high concentrations of organic additives may be the primary source of harmful chemicals in the environment, and should be responsible for their ubiquitous distribution in ecosystems.

Drones for litter monitoring on coasts and rivers: suitable flight altitude and image resolution.

Multirotor drones can be efficiently used to monitor macro-litter in coastal and riverine environments. Litter on beaches, dunes and riverbanks, along with floating litter on coastal and river waters, can be spotted and mapped from aerial drone images. Items detection and classification are prone to image resolution, which is expressed in terms of Ground Sampling Distance (GSD). The GSD is determined by drone flight altitude and camera properties. This paper investigates what is a suitable GSD value for litter survey. Drone flight altitude and camera setup should be chosen to obtain a GSD between 0.5 cm/px and 1.25 cm/px. Within this range, the lowest GSD allows litter categorization and classification, whereas the highest value should be adopted for a coarser litter census. In the vision of drawing up a global protocol for drone-based litter surveys, this work sets the ground for homogenizing data collection and litter assessments.

Quantification of toxic metals derived from macroplastic litter on Ookushi Beach, Japan.

The potential risk of toxic metals that could leach into a beach environment from plastic litter washed ashore on Ookushi Beach, Goto Islands, Japan was estimated by balloon aerial photography, in situ beach surveys, and leaching experiments in conjunction with a Fickian diffusion model analysis. Chromium (Cr), cadmium (Cd), tin (Sn), antimony (Sb), and lead (Pb) were detected in plastic litter collected during the beach surveys. Polyvinyl chloride (PVC) fishing floats contained the highest quantity of Pb. Balloon aerial photography in conjunction with a beach survey gave an estimated mass of Pb derived from plastic litter of 313 ± 247 g. Lead leaching experiments on collected PVC floats showed that Pb in the plastic litter could leach into surrounding water on the actual beach, and that plastic litter may act as a "transport vector" of toxic metals to the beach environment. Using the experimental data, the total mass of Pb that could leach from PVC plastic litter over a year onto Ookushi Beach was estimated as 0.6 ± 0.6 g/year, suggesting that toxic metals derived from plastic beach litter are a potential "pathway" to contamination of the beach environment due to their accumulation in beach soil over time.

The fate of missing ocean plastics: Are they just a marine environmental problem?

The fate of mismanaged plastic waste released into oceans (ocean plastics) remains a topic of debate, where the mass imbalance between the leakage and abundance in the world's oceans appears paradoxical. In the present study, a budget for ocean plastic mass was estimated based on a combination of numerical particle tracking and linear mass-balance models, both validated using a worldwide ocean plastic dataset. Integrating the time series of worldwide macroplastic emission from both rivers and the fisheries industry over the period 1961-2017 yielded a total mass of 25.3 million metric tonnes (MMT). Macro- and microplastics currently floating in the oceans, and microplastics on beaches, each account for 3-4% of the ocean plastics emitted worldwide to date. Overall, 23.4% of ocean plastics were macroplastics on beaches. Meanwhile, 66.7% of ocean plastics were heavier than seawater or microplastics removed from the upper ocean and beaches, which are difficult to monitor under current observation frameworks adopted worldwide. However, the present study on ocean plastics suggested that the whole ocean plastics accounted for only 4.7% of mismanaged plastic waste (542.2 MMT) generated between the 1960s and today.

Mesh selectivity of neuston nets for microplastics.

Two neuston nets, mesh opening 1.00 mm and 0.333 mm, were towed in parallel. The 0.333 mm net collected more microplastics of longest length ≤2.00 mm than the 1.00 mm net. Mesh selection curve of the 1.00 mm mesh net for microplastics was estimated with the SELECT analysis by comparison of size distributions of microplastics collected by the two nets. Selection curve of the 0.333 mm mesh net, often used as a standard mesh size for microplastic net sampling, was also estimated on the assumption of geometrical similarity between microplastic size and mesh opening for a given retention probability. Approximately 60% amount of microplastics (0.4-1.0 mm) in net sampling with the 0.333 mm net passed through the mesh and was thus unaccounted for. The 0.333 mm net can retain at most 1.5% of microplastics ≤0.4 mm entering the net, and rarely retained microplastics ≤0.3 mm.

Microplastics on plankton samples: Multiple digestion techniques assessment based on weight, size, and FTIR spectroscopy analyses.

Digestion protocols are needed to determine microplastics abundance and features. This study assessed the organic matter (OM) digestion efficiency on plankton samples and the MPs' weight, size, and polymer changes under different digestion techniques. For this, 2-step (KOH and H2O2 + Fe2+) and 3-step (2-step and enzymes) digestion techniques were assessed under different duration and temperature conditions. The results obtained for OM digestion with 2-step and 3-step techniques were satisfactory. Weight changes were registered for polyethylene terephthalate (PET), polystyrene foam, polyvinyl chloride, and polycarbonate with 2-step digestion, but with inconsistent values. Significant size changes were registered only for PET applying 2-step digestion techniques at 60 °C. Using 40 °C for 72 h prevailed all polymers from size changes. Polyethylene weathered MPs were also preserved, including an enzymatic step. Polymer fingerprints were not affected by any digestion technique. Based on these results, any method applying high temperatures will damage MPs.

Abundance of non-conservative microplastics in the upper ocean from 1957 to 2066.

Laboratory-based studies have suggested that marine organisms can be harmed by ingesting microplastics. However, unless the current and future microplastic abundance in the ocean environment is quantified, these experimental studies could be criticized for using an unrealistic density or sparsity of microplastics. Here we show the secular variations of pelagic microplastic abundance in the Pacific Ocean from 1957 to 2066, based on a combination of numerical modeling and transoceanic surveys conducted meridionally from Antarctica to Japan. Marine plastic pollution is an ongoing concern especially in the North Pacific, and pelagic microplastics are regarded as non-conservative matter due to the removal processes that operate in the upper ocean. The results of our numerical model incorporating removal processes on a 3-year timescale suggested that the weight concentrations of pelagic microplastics around the subtropical convergence zone would increase approximately twofold (fourfold) by 2030 (2060) from the present condition.