Profiling the Vertical Transport of Microplastics in the West Pacific Ocean and the East Indian Ocean with a Novel in Situ Filtration Technique.

A new technique involving large-volume (10 m3) samples of seawater was used to determine the abundance of microplastics (MPs) in the water column in the West Pacific Ocean and the East Indian Ocean. Compared to the conventional sampling methods based on smaller volumes of water, the new data yielded abundance values for the deep-water column that were at least 1-2 orders of magnitude lower. The data suggested that limited bulk volumes currently used for surface sampling are insufficient to obtain accurate estimates of MP abundance in deep water. Size distribution data indicated that the lateral movement of MPs into the water column contributed to their movement from the surface to the bottom. This study provides a reliable dataset for the water column to enable a better understanding of the transport and fate of plastic contamination in the deep-ocean ecosystem.

Consistent Transport of Terrestrial Microplastics to the Ocean through Atmosphere.

Although atmospheric transport and deposition could be an important pathway of terrestrial pollutants to the ocean, little information concerning the presence and distribution of these suspended atmospheric microplastics in marine air is available. We investigated, for the first time, the occurrence and distribution of suspended atmospheric microplastics (SAMPs) in the west Pacific Ocean. In this study, the spatial distribution, morphological appearance, and chemical composition of suspended atmospheric microplastics were studied through continuous sampling during a cruise. SAMPs abundance ranged from 0 to 1.37 n/m3, the median of 0.01 n/m3. Fiber, fragment, and granule SAMPs quantitively constituted 60%, 31%, and 8% of all MPs, respectively. Interestingly, plastic microbeads with numerical proportion of 5% were also observed. A high suspended atmospheric microplastics abundance was found in the coastal area (0.13 ± 0.24 n/m3), while there was less amount detected in the pelagic area (0.01 ± 0.01 n/m3). The amount of suspended atmospheric microplastics collected during the daytime (0.45 ± 0.46 n/m3) was twice the amount collected at night (0.22 ± 0.19 n/m3), on average. Our observations provide field-based evidence that suspended atmospheric microplastics are an important source of microplastics pollution in the ocean, especially the pollution caused by textile microfibers.

Dynamic signatures of microplastic distribution across the water column of Yangtze River Estuary: Complicated implication of tidal effects.

Riverine microplastic (MP) discharge into the ocean contributes greatly to global MP contamination, yet our understanding of this process remains primitive. To deepen our interpretation of the dynamic MP variation throughout the estuarine water columns, we sampled at Xuliujing, the saltwater intrusion node of the Yangtze River Estuary, over the course of ebb and flood tides in four seasons (July and October 2017, January and May 2018 respectively). We observed that the collision of downstream and upstream currents contributed to the high MP concentration and that the mean MP abundance fluctuated with the tide. A model of microplastics residual net flux (MPRF-MODEL), taking the seasonal abundance and vertical distribution of MP along with current velocity into consideration, was developed to predict the net flux of MP throughout the full water columns. 2154 ± 359.7 t/year of MP was estimated to flow into the East China Sea via the River in 2017-2018. Our study suggests that riverine MP flux can be overestimated due to reciprocating current carried MP from the estuary. Using the tidal and seasonal variation in MP distribution, we calculated the tide impact factor index (TIFI) for the Yangtze River Estuary to be between 38.11% and 58.05%. In summary, this study provides a baseline of MP flux research in the Yangtze River for similar tidal-controlled rivers and a contextual understanding of how to appropriately sample and accurately estimate in a dynamic estuary system. The redistribution of microplastics may be impacted by complex tide processes. Although not observed in this study, it may merit investigation.

Efficient transport of atmospheric microplastics onto the continent via the East Asian summer monsoon.

The presence of microplastics (MPs) in the atmosphere is a global concern because of its environmental and health impacts; however, the monsoonal transport of atmospheric MPs has not yet been investigated. To fully understand the effect of the monsoon on atmospheric MP transport, we conducted a study along the southeast coast of China during the East Asian summer monsoon (EASM). We found that the EASM transports atmospheric MPs back onto the continent at a flux of up to 212.977-213.433 kg/EASM/year. The backward trajectory and wind field results indicate that the EASM provides an effective MP transport pathway from Vietnam, the Philippines, and Malaysia to southeastern China. This suggests that only some of the airborne MPs over the ocean enter the marine ecosystem. The average abundance of atmospheric MPs over the sampling area was 0.39 items/100 m3 (0.39 ± 0.43 items/100 m3) during the EASM season, with high variability among the sampling sites. This study improves our understanding of the impact of the EASM on atmospheric MP transport, which can help quantify the contributions of atmospheric MPs to marine or terrestrial ecosystems.

To what extent are we really free from airborne microplastics?

Quality assurance and quality control (QA&QC) procedures are vital for ensuring data reliability, but little is known about the use of such procedures in reducing airborne microplastic (MP) contamination. To address this issue, we tried to determine the efficiency of two common methods (washing and ashing experimental glassware) for removing airborne MPs and identified airborne contamination during MP analytical procedure. The results showed the removal efficiencies of washing and ashing were an average of 88%-98% and 100%, respectively, indicating that both methods could eliminate most of the spiked airborne MPs with no significant difference noted between the two methods. Although rigorous measures were taken to prevent contamination from ambient air, trace amounts of airborne MPs were still detected, which is an issue that has not been adequately investigated in previous studies. All of the procedural contaminants detected in this study were fibrous. Approximately 88% of these fibers were cotton-like (cotton, cellulose, and cellophane) fibers, and 13% of them were plastic. Surprisingly, cotton-like fibers and MPs had a similar size distribution, suggesting that they may have undergone a similar weathering process. In the end, to cope with inevitable airborne contamination, several measures were proposed for further research. Such measures will provide the necessary methodological assistance for accurate quantification of MP pollution in the field.

Terrestrial plants as a potential temporary sink of atmospheric microplastics during transport.

Atmospheric transport is an important pathway by which terrestrial microplastics (MPs, with sizes less than 5 mm) can move long distances to remote areas. However, little is known about the environmental behaviors of atmospheric MPs during movement. To address this issue, deposits of MPs on the leaves of plants were studied in two regions, with abundance ranging from 0.07 n/cm2 (pieces per area of leaves) to 0.19 n/cm2. The attached substances were mainly natural materials, but 28% of the total substances were plastics. There was a similar physical-chemical composition of the attached MPs in the two regions suggesting a similar origin. Leaves, regardless of plant species, can indiscriminately retain atmospheric MPs. About 0.13 trillion pieces of MPs are estimated to be attached to leaf surfaces in the top 11 green countries. Leaves of terrestrial plants could be a temporal sink and a source of MPs pollution to remote areas. This is not fully recognized and merits further study.

Elucidating the vertical transport of microplastics in the water column: A review of sampling methodologies and distributions.

There have been numerous studies that have investigated floating microplastics (MPs) in surface water, yet little data are currently available regarding the vertical distribution in the water column. This lack constrains our ability to comprehensively assess the ecological effects of MPs and develop further policy controls. In this study, we reviewed current progress of sampling methodologies, the distribution patterns, and the physiochemical properties of MPs throughout the water column. Three sampling protocols were identified in this study: bulk, net and submersible pump/in-situ sampling. In different regions, the vertical patterns of MPs in the water column varied with depth, which is possibly related to the morphological characteristics, polymeric densities, and biofouling of the MPs. The results of this review revealed that fibrous and fragmented MPs comprised over 90% of the total MPs by quantity, of which fibrous MPs constituted the majority (43%-100%). In addition, polyethylene terephthalate, polyamide, polyethylene, polyvinyl chloride, and polypropylene have been widely identified in previous studies. To minimize the impact caused by various sampling protocols, the use of a volume gradient trail experiment and a unified mesh size of 60-100 µm for the initial concentration are recommended according to the results of this review. Given the limited knowledge regarding the vertical transport of MPs in the water column, harmonized sampling methods should first be developed. The mechanisms of this process can be separately considered for different water bodies, such as freshwater systems, coastal waters, and pelagic zones. The presence of these anthropogenic pollutants in the water column poses a threat to the largest but most vulnerable habitats of life on earth, and hence they merit further investigation.

Atmospheric microplastic over the South China Sea and East Indian Ocean: abundance, distribution and source.

At present, microplastic (MP) is pervasive globally and has a regional difference. Recent studies have identified MP in the terrestrial atmospheric environment. However, the connection between terrigenous atmospheric MP emissions and impacts over the ocean is not well known. Here, we present the distribution of atmospheric MP abundance over the ocean based on a transoceanic survey conducted across 21 sampling transects from the Pearl River Estuary (PRE) to the South China Sea (SCS) and then to the East Indian Ocean (EIO). The abundance of atmospheric MP over the PRE (4.2 ± 2.5 items/100 m3) was significantly higher than that over the EIO (0.4 ± 0.6 items/100 m3). However, the abundance of atmospheric MP in the SCS (0.8 ± 1.3 items/100 m3) was not significantly different from the EIO and PRE. This result revealed that MP undergoes long-range transport, more than 1000 km away, through the atmosphere, but atmospheric MP transmission as the main source of oceanic MP based on transoceanic studies is not a plausible assumption. Furthermore, backward trajectory model analysis of 21 sampling transects preliminary showed the potential sources of atmospheric MP over the PRE, SCS, and EIO.

Global inventory of atmospheric fibrous microplastics input into the ocean: An implication from the indoor origin.

Atmospheric transport could be a significant pathway for inland microplastics (MPs, with size＜5 mm) to the ocean in addition to catchment runoff and coastal discharge. However, atmospheric input of MPs to the ocean is rarely quantified. To address this issue, transport of atmospheric MPs from source to sink was studied in the Asia-Pacific region during nine cruises from October 2018 to September 2019. Both deposited atmospheric MPs (DAMPs) and suspended atmospheric MPs (SAMPs) were collected, ranging from 23.04 n/(m2·d) to 67.54 n/(m2·d), and 0 to 1.37 n/m3, respectively. Size composition revealed that atmospheric deposition of MPs originating in terrestrial regions seems inadequate and insufficient to quantify the atmospheric input to the ocean. In addition, combined with aerodynamic modelling, for the first time, we estimated that 7.64-33.76 t of fibrous atmospheric MPs was globally generated in 2018, which is 3 % and 31 % of riverine input MPs of The Yangtze River and The Pearl River in terms of mid-point mass, respectively. The increasing load of ingestible plastics from sea air could have a far-reaching impact on marine ecosystem.

Accurate quantification and transport estimation of suspended atmospheric microplastics in megacities: Implications for human health.

Although atmospheric microplastics have been found to be ubiquitous even on untraversed mountains and have potential impacts on human health, little information concerning their sampling methodology and transport is currently available. Until a realistic quantification of suspended atmospheric microplastics (SAMPs) is obtained, however, any potential health risk assessment for this pollutant will be open to criticism for using an ambiguous dataset. To address this knowledge gap, in May 2019 a trial experiment was performed to explore the potential relationship between sampling volume and SAMP abundance. A significant logarithmic regression between SAMP abundance and the sampling volume of filtrated air was found and the sufficient volume of filtrated air for accurate SAMP quantification was recommended. Investigation results indicated that fibrous and fragment-shaped SAMPs comprised 91% of all of the identified synthetic particles. Interestingly, for the first time, plastic microbeads were also observed in the collected air, constituting 9% of the all of the SAMPs by quantity. Spectral analysis revealed that these SAMPs consisted of polyethylene terephthalate (PET), epoxy resin (EP), polyethylene (PE), alkyd resin (ALK), rayon (RY), polypropylene (PP), polyamide (PA), and polystyrene (PS). PET, EP, PE, and ALK constituted the majority (90%) of all of the polymer types, with quantitative percentages of 51%, 19%, 12%, and 8%, respectively. Based on our numerical modeling simulation, the approximate transport flux of SAMPs during June in Shanghai was estimated, ranging from 9.94 × 104 n/(m·d) to 6.52 × 105 n/(m·d), with a mean of 3.00 ±â€¯1.58 × 105 n/(m·d). The goal of our study was to provide an essential methodological aid for the accurate determination of SAMPs in the environment and a better understanding of terrestrial microplastic transport in megacities.

A novel method enabling the accurate quantification of microplastics in the water column of deep ocean.

Little information concerning microplastic (MP) pollution in the deep ocean is currently available, and a huge gap exists between sampling methodology and obtaining an authentic dataset. Verified sampling methodology is a fundamental step in the accurate determination of MP pollution in the pelagic environment, of which sample volume is a crucial factor. To address this methodological challenge, in situ filtration technology, a novel sampling method for microplastics in the water column, was proposed and investigated. On 27 April 2019, we took the East China Sea as a typical example in order to determine the relationship between sample volume and MP abundance. Analysis indicated that the filtrated volume has an impact on MP quantification and significant exponential regression between the sample volume and MPs was observed. This investigation indicated that a small volume sample could easily lead to MP overestimation, with at least 8 m3 water required to obtain reliable data.