Spatial distribution and historical trend of microplastic pollution in sediments from enclosed bays of South Korea.

Seafloor sediments are an important sink for microplastics (MPs), and the vertical profile of MP accumulation in a sediment core represents historical pollution trends. In this study, MP (20-5000 µm) pollution in surface sediments of urban, aquaculture, and environmental preservation sites in South Korea was evaluated, and the historical trend was investigated using age-dated core sediments from the urban and aquaculture sites. The abundance of MPs ranked in the order of urban, aquaculture, and environmental preservation sites. Polymer types were more diverse at the urban site compared to other sites, and expanded polystyrene was dominant in the aquaculture site. An increase in MP pollution and polymer types was observed from bottom to top of cores, and historical trends of MP pollution reflect local influences. Our results indicate that the characteristics of MPs are determined by human activities, and MP pollution should be addressed according to the characteristics of each site.

Fragmentation of nano- and microplastics from virgin- and additive-containing polypropylene by accelerated photooxidation.

Plastic is ubiquitous in the environment, where it gradually weathers and fragments into nanoplastics (NPs) and microplastics (MPs); however, the weathering process and fragmentation rate are poorly understood. In this study, we quantitatively determined the abundances and size distributions of NPs and MPs produced from virgin polypropylene (PP) and additive-containing PP (PPa) sheets via photooxidation with water in a simulated sunlight chamber followed by vortexing. The fragmentation rate of PP and PPa were approximately 1.1 × 108 particles/cm2 and 1.0 × 108 particles/cm2, respectively, during 176 days of exposure in the chamber (corresponding to 2.7 years of exposure in an outdoor environment in the Republic of Korea). However, quadratic regression analysis of the relationship between total particles produced and exposure duration revealed that the PP fragmentation rate was faster than the PPa fragmentation rate after a sunlight exposure duration equivalent to 2.7 years. Furthermore, the mechanical stress of vortexing after photooxidation played an important role in the production of MPs; it had a smaller role in the production of NPs. The sizes of fragmented particles produced by photooxidation and mechanical stress followed a power law distribution, with a scaling exponent of α = 2.87 ± 0.15, which was similar to a three-dimensional fragmentation pattern. This study provides valuable insights into the weathering and fragmentation processes of plastics. Further studies on the environmental fate and impact of NP and MP production from plastic weathering and fragmentation, as well as the potential influence of plastic additives on these processes.

Effects of wastewater effluent-borne nutrients on phytoplankton off the coast of Jeju Island.

The spatiotemporal distributions of nutrients in coastal waters surrounding eight wastewater treatment plants (WWTPs) in four seasons were investigated to determine the effects of WWTP effluents on seawater off Jeju Island, Korea. The highest concentrations of nutrients were observed in the outlets of WWTPs with relatively high ammonium concentrations among dissolved inorganic nitrogen (DIN). The reduced DIN (NO2- and NH4+)/total DIN ratios are used as a potential short-term index for marine environmental conditions. In seawater surrounding the WWTPs, relatively low nutrient concentrations were observed in spring and fall, due to enhanced biological production, which is closely linked to decreased N/P ratios. Because the highest WWTP effluent fluxes of ammonium in this study were similar to the fluxes of nutrients from submarine groundwater discharge, diffusion from bottom sediments, and discharge from land-based fish farm wastewater, WWTP effluent-derived nutrients are potentially important in oligotrophic environments and can be readily utilized by phytoplankton.

The fragmentation of nano- and microplastic particles from thermoplastics accelerated by simulated-sunlight-mediated photooxidation.

The plastic debris that washes ashore and litters the shoreline often undergoes weathering under sunlight exposure, such that it fragments to form nanoplastics and microplastics, but the fragmentation rate for many thermoplastics is unknown. In this study, three major thermoplastics were exposed to simulated sunlight in an accelerated weathering chamber to evaluate the speed of photooxidation-induced fragmentation. The initiation of photooxidation-induced fragmentation extrapolated from the accelerated weathering chamber to real sunlight exposure in South Korea followed the order of PS (< 1 year) > PP (< 2 years) > LDPE (> 3 years). The surface cracks created by photooxidation were not directly reflected in the initiation of fragmentation of thermoplastics. The initiation of fragmentation was faster in PS than other polymers, but the total abundance of particles produced, and increasing ratio (exposure/non-exposure) were comparable or lower than those of PP. The increasing ratio pattern between nanoplastics and small microplastics of PP differed noticeably from other polymers. The initiation of nanoplastic and small-microplastic fragmentation determined in this study will be useful for the further estimation of secondary microplastic production by weathering and thus for decision-making regarding methods for the timely removal of plastic litter in the environment.

Underwater hidden microplastic hotspots: Historical ocean dumping sites.

Three ocean dumping sites located in the Yellow Sea (YS) and East Sea (ES) of South Korea have accumulated terrestrial waste from 1988 to 2015. Most of this waste comprised industrial wastewater and sewage sludge, which are sources of microplastics. In this study, we investigated the spatiotemporal distribution and characteristics of microplastics in surface and core sediments of the YS, South Sea (SS) and ES, including at dumping sites (YDP and EDP). The mean abundance of microplastics in surface sediments was ranked in order of EDP (59,457 ± 49,130 particles/kg d.w.), ES (5,047 ± 9,404 particles/kg d.w.), YDP (3,965 ± 3,213 particles/kg d.w.), SS (314 ± 488 particles/kg d.w.) and YS (288 ± 400 particles/kg d.w.). EDP and YDP showed about 14- and 12-fold higher microplastic abundances, and more diverse polymer compositions, than the ES and YS, respectively. The historical trend of microplastic pollution in age-dated core sediments from EDP and YDP aligned well with the amount of historical ocean dumping. As the level of ocean dumping has gradually reduced since 2006, and was finally banned in 2015, the microplastic abundance decreased accordingly. Interestingly, spherical polystyrene (PS) primary microplastic was the dominant type in EDP sediments (78%) and other surface sediments in the ES (52%). More than 60 million tons of sewage and wastewater sludge were dumped at EDP, and extremely high abundances of up to 130,000 particles/kg d.w. were observed in EDP surface sediments. PS primary microplastics were continuously present in the EDP and ES sediment cores in the dumping period and are suspected to have originated from industrial wastewater sludge. The particle transportation model results showed that PS was dispersed throughout the ES during ocean dumping. In addition, deep circulation can contribute to the dispersion of particles after sinking. These results indicate that ocean dumping sites represent an underwater hotspot and source of microplastics in seafloor sediments.

A comparison of spectroscopic analysis methods for microplastics: Manual, semi-automated, and automated Fourier transform infrared and Raman techniques.

This study was conducted to establish the best practice for microplastic analysis by reducing the time demand and human bias and comparing the characteristics of µ-FTIR and Raman techniques. A manual analysis, semi-automated method, and fully automatic identification method were compared. Fully automated identification took the shortest time to analyze a whole filter paper (Ø25 mm), but its false positive identification rate was 80 ± 15%. The semi-automated analysis using spectrum profiling was suitable for all aspects of microplastic analysis. It was less time consuming than the manual analysis (manual: 6.1 ± 0.8 h, semi-automated: 4.0 ± 0.6 h), and 22 ± 12% more microplastic particles were detected using the semi-automated method compared to the manual analysis due to the reduction in false negative results. Raman microscopy was suitable for small microplastic (>5 µm) identification, although the Raman analysis took nine times longer than the semi-automated analysis.

Prevalence of small high-density microplastics in the continental shelf and deep sea waters of East Asia.

Microplastics are widely distributed throughout aquatic environments. Information about the vertical distribution and fate of microplastics in seawater remains limited. To elucidate the vertical distribution of microplastics, three to six vertical water column layers were sampled based on the thermocline depth, from which the vertical distribution and characteristics of microplastics larger than 20 µm were investigated in continental shelf and deep-sea waters around South Korea. In addition, microplastics incorporated into marine aggregates (aggregated fraction) were investigated to determine the contribution of aggregates to vertical transport of microplastics. The abundance of microplastics was in the range of 15-9,400 particles/m3. No consistent trend was observed in the overall vertical profiles. The size, shape and polymer compositions of microplastics at each station were generally comparable throughout the water column. Unexpectedly, high-density (HD; > 1.02 g/cm3) polymers accounted for an average of 73% of total microplastics. As polymer density increased, the proportion of microplastics less than 100 µm in size increased. HD polymers also accounted for 68% of the aerosol samples collected together with water samples. Due to the relatively high proportion of HD polymers in far-offshore waters, high-density solution should be used to extract microplastics, even from surface seawaters. The aggregated fraction accounted for 0-28.6% (average, 3.4%) of total microplastics. Marine aggregates are considered an important mechanism of transport for microplastics less dense than seawater to the deep-water column, but they showed lower proportions than expected in continental shelf and deep-sea waters around South Korea.

Ecological risk assessment of microplastics in coastal, shelf, and deep sea waters with a consideration of environmentally relevant size and shape.

This study assessed the ecological risk posed by microplastics in surface and subsurface seawaters in coastal, continental shelf, and deep-sea areas of South Korea. The target microplastics for risk assessment were specified as only non-spherical type microplastics in the size range 20-300 µm, because this type was predominantly observed in our study areas, and adverse biological effects have previously been reported. Exposure data for non-spherical microplastics were obtained from a previous study or were measured for microplastics of sizes down to 20 µm. A predicted no-effect concentration (PNEC) of 12 particles/L was derived by employing a species sensitivity distribution approach. Then the results were compared to the in situ observed concentrations at each site. The detected microplastic concentrations did not exceed the derived PNEC, i.e., the current pollution levels of fragment and fiber microplastics in the size range 20-300 µm would not pose a significant threat to the marine ecosystem in South Korea. However, predictions are that microplastic pollution will increase to 50-fold by 2100 at the current rates, and in this scenario, the microplastic concentration is expected to far exceed the derived PNEC values for marine ecosystems. It is therefore urgent to take precautionary actions to prevent a further increase in microplastic concentrations in these environments.

Rapid Production of Micro- and Nanoplastics by Fragmentation of Expanded Polystyrene Exposed to Sunlight.

Expanded polystyrene (EPS) is a common plastic marine debris found in oceans worldwide. The unique "foamed" structure of EPS, which is composed of thin layers, is more vulnerable to fragmentation than bulk plastics. However, the production rate of micro- and nanoplastics by the fragmentation of EPS following sunlight exposure remains largely unknown. Here, we determined the fragmentation rate and weight loss of EPS in an outdoor weathering experiment that ran for 24 months. It took only 1 month for the weight of an EPS box to decline by 5% due to photodegradation, and approximately 6.7 × 107 micro- and nanoparticles/cm2 could be produced at a latitude of 34 °N. These results indicate that macro EPS debris can continually produce a massive number of particles within a relatively short exposure duration. The findings provide useful information to inform policymakers how rapidly to remove "likely fragmented" plastic litter from the environment.

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.

An interlaboratory comparison exercise for the determination of microplastics in standard sample bottles.

An interlaboratory comparison exercise was conducted to assess the consistency of microplastic quantification across several laboratories. The test samples were prepared by mixing one liter seawater free of plastics, microplastics made from polypropylene, high- and low-density polyethylene, and artificial particles in two plastic bottles, and analyzed concurrently in 12 experienced laboratories around the world. The minimum requirements to quantify microplastics were examined by comparing actual numbers of microplastics in these sample bottles with numbers measured in each laboratory. The uncertainty was due to pervasive errors derived from inaccuracies in measuring sizes and/or misidentification of microplastics, including both false recognition and overlooking. The size distribution of microplastics should be smoothed using a running mean with a length of >0.5 mm to reduce uncertainty to less than ±20%. The number of microplastics <1 mm was underestimated by 20% even when using the best practice for measuring microplastics in laboratories.

Spatiotemporal distribution and annual load of microplastics in the Nakdong River, South Korea.

Although rivers represent an important pathway for the transport of microplastics to the oceans, research on riverine microplastics is limited compared to the marine environment. Hence, we investigated the spatiotemporal distribution of microplastics in the Nakdong River down to 20 µm in size and characterized them using Fourier transform infrared spectroscopy in surface and mid waters and sediment. The mean (±standard deviation) abundance of microplastic in the Nakdong River was in the range of 293 ±â€¯83 (upstream, February 2017) to 4760 ±â€¯5242 (downstream, August 2017) particles/m3 in water, and 1970 ±â€¯62 particles/kg in sediment. The abundance of microplastics was about three times higher in surface than mid waters in the downstream area. Polypropylene and polyester accounted for 41.8% and 23.1% of microplastics in the water, respectively, whereas about 50% in the sediment was composed of polypropylene and polyethylene. Microplastics smaller than 300 µm in size accounted for 74% in the water and 81% in sediment, and the distribution peaked in the 50-150 µm size range. Based on these results, we estimated the annual load of microplastics carried by the Nakdong River in 2017 to be 5.4-11 trillion by number and 53.3-118 tons by weight. The proportions of the total load transported through surface water and the water column were 8% and 92%, respectively. In addition, the microplastic load was concentrated in the wet season, which makes up 71% in number and 81% in weight. These results indicate that it is necessary to reflect seasonal variation and sample both in the surface water and water column to estimate microplastic transport. Without considering these factors, the annual load of microplastics may be overestimated or underestimated.

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.

Formation of microplastics by polychaetes (Marphysa sanguinea) inhabiting expanded polystyrene marine debris.

Fragmentation of large plastic debris into smaller particles results in increasing microplastic concentrations in the marine environment. In plastic debris fragmentation processes, the influence of biological factors remains largely unknown. This study investigated the fragmentation of expanded polystyrene (EPS) debris by polychaetes (Marphysa sanguinea) living on the debris. A large number of EPS particles (131 ±â€¯131 particles/individual, 0.2-3.8 mm in length) were found in the digestive tracts of burrowing polychaetes living on EPS debris. To confirm the formation of microplastics by polychaetes and identify the quantity and morphology of produced microplastics, polychaetes were exposed to EPS blocks in filtered seawater under laboratory conditions. Polychaetes burrowed into the blocks and created numerous EPS microplastic particles, indicating that a single polychaete can produce hundreds of thousands of microplastic particles per year. These results reveal the potential role of marine organisms as microplastic producers in the marine environment.

Abundance, composition, and distribution of microplastics larger than 20 µm in sand beaches of South Korea.

To support microplastic management, the abundance, composition, and spatial distribution of microplastics on a national scale must be known. Hence, we studied the baseline level of microplastic pollution at 20 sandy beaches along the South Korean coast. All microplastic particles extracted from the sand samples were identified down to 20 µm in size using Fourier transform infrared spectroscopy. The abundances of large microplastics (L-MPs; 1-5 mm) and small microplastics (S-MPs; 0.02-1 mm) were in the range of 0-2088 n/m2 and 1400-62800 n/m2, respectively. Maximum microplastic abundance was in the size range of 100-150 µm, and particles smaller than 300 µm accounted for 81% of the total abundance. Expanded polystyrene (EPS) accounted for 95% of L-MPs, whereas S-MPs were predominantly composed of polyethylene (49%) and polypropylene (38%). The spatial distribution of L-MPs, excluding EPS, was significantly related to population, precipitation, proximity to a river mouth and abundance of macroplastic debris on beach. However, there were no relationships between S-MPs and other environmental and source-related factors, except for macroplastic debris and L-MPs excluding EPS. These results imply that S-MPs are mainly produced on beaches by weathering, whereas L-MPs other than EPS are mainly introduced from land-based sources and are also partly produced on beaches.

Widespread detection of a brominated flame retardant, hexabromocyclododecane, in expanded polystyrene marine debris and microplastics from South Korea and the Asia-Pacific coastal region.

The role of marine plastic debris and microplastics as a carrier of hazardous chemicals in the marine environment is an emerging issue. This study investigated expanded polystyrene (EPS, commonly known as styrofoam) debris, which is a common marine debris item worldwide, and its additive chemical, hexabromocyclododecane (HBCD). To obtain a better understanding of chemical dispersion via EPS pollution in the marine environment, intensive monitoring of HBCD levels in EPS debris and microplastics was conducted in South Korea, where EPS is the predominant marine debris originate mainly from fishing and aquaculture buoys. At the same time, EPS debris were collected from 12 other countries in the Asia-Pacific region, and HBCD concentrations were measured. HBCD was detected extensively in EPS buoy debris and EPS microplastics stranded along the Korean coasts, which might be related to the detection of a quantity of HBCD in non-flame-retardant EPS bead (raw material). The wide detection of the flame retardant in sea-floating buoys, and the recycling of high-HBCD-containing EPS waste inside large buoys highlight the need for proper guidelines for the production and use of EPS raw materials, and the recycling of EPS waste. HBCD was also abundantly detected in EPS debris collected from the Asia-Pacific coastal region, indicating that HBCD contamination via EPS debris is a common environmental issue worldwide. Suspected tsunami debris from Alaskan beaches indicated that EPS debris has the potential for long-range transport in the ocean, accompanying the movement of hazardous chemicals. The results of this study indicate that EPS debris can be a source of HBCD in marine environments and marine food web.

Combined Effects of UV Exposure Duration and Mechanical Abrasion on Microplastic Fragmentation by Polymer Type.

It is important to understand the fragmentation processes and mechanisms of plastic litter to predict microplastic production in the marine environment. In this study, accelerated weathering experiments were performed in the laboratory, with ultraviolet (UV) exposure for up to 12 months followed by mechanical abrasion (MA) with sand for 2 months. Fragmentation of low-density polyethylene (PE), polypropylene (PP), and expanded polystyrene (EPS) was evaluated under conditions that simulated a beach environment. PE and PP were minimally fragmented by MA without photooxidation by UV (8.7 ± 2.5 and 10.7 ± 0.7 particles/pellet, respectively). The rate of fragmentation by UV exposure duration increased more for PP than PE. A 12-month UV exposure and 2-month MA of PP and PE produced 6084 ± 1061 and 20 ± 8.3 particles/pellet, respectively. EPS pellets were susceptible to MA alone (4220 ± 33 particles/pellet), while the combination of 6 months of UV exposure followed by 2 months of MA produced 12,152 ± 3276 particles/pellet. The number of fragmented polymer particles produced by UV exposure and mechanical abrasion increased with decreasing size in all polymer types. The size-normalized abundance of the fragmented PE, PP, and EPS particles according to particle size after UV exposure and MA was predictable. Up to 76.5% of the initial EPS volume was unaccounted for in the final volume of pellet produced particle fragments, indicating that a large proportion of the particles had fragmented into undetectable submicron particles.

Benzotriazole-type ultraviolet stabilizers and antioxidants in plastic marine debris and their new products.

Ultraviolet stabilizers (UVSs) and antioxidants are the most widely used additives in plastics to enhance the lifetime of polymeric materials. There is growing interest in the roles of plastic marine debris and microplastics as source or vector of toxic substances to marine environment and organisms. However, there is limited information available on plastic associated chemicals, particularly additive chemicals. Therefore, to evaluate their extent of exposure from plastics to the marine environment, we determined UVSs and antioxidants in plastic debris (n=29) collected from beaches along with their corresponding new plastic products in markets (n=27) belonging to food, fisheries, and general use. Antioxidants were present at higher concentrations than UVSs in both plastic debris and new plastics, indicative of their high use over UVSs. Irganox 1076 and Irganox 1010 were more commonly used than other chemicals investigated. The irregular use with high concentration of additive chemicals was observed in short-term use plastic products. Except for Irganox 1076 and UV 326, most antioxidants and UVSs were relatively high in new plastics compared to corresponding plastic marine debris, implying their potential leaching or degradation during use or after disposal. The present study provides quantitative information about additive chemicals contained in plastic marine debris and their new products. These results could be useful for better understanding of environmental exposure to hazardous chemicals through plastic pollution.

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.