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International audience; Wastewater-treatment plants (WWTPs) are considered significant point sources of microplastics (MiP) in the receiving waters; MiP release is poorly estimated in developing countries. MiP abundance, recovery efficiency and daily load to receiving waters were explored in treatment stage facilities of four WWTPs in Vietnam, located in Ho Chi Minh City, Thu Dau Mot, and Da Lat. MiP abundance varied from 1860 items m −3 to 125,000 items m −3 in influents and between 140 items m −3 and 813 items m −3 in the final effluents. The MiP-removal efficiency was the highest in the Da Lat wastewatertreatment plant (DL WWTP), a tertiary treatment plant using trickling filters followed by aerated lagoon and maturation ponds for BOD and nitrogen removals. The lowest MiPremoval efficiency was observed in Binh Hung wastewater-treatment plant (BH WWTP), a combined sewer system using conventional activated sludge processes as secondary treatment. The total daily MiP load to the receiving environment varied from 1,840,000 items d −1 at the DL WWTP to 77,127,000 items d −1 at the BH WWTP. Change in MiP abundance, morphology, and removal efficiency were discussed after each stage of the treatment process for the four WWTPs.

International audience; 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 .

Microplastic fibres are the most abundant microplastics in waterways worldwide. The settling of fibres is distinct from other particles because of their aspect ratio and shape. In this paper, we test the hypothesis that length, curliness, and settling orientation control the settling velocity of microplastic fibres in a suite of laboratory experiments. Using a Particle Tracking Velocimetry method, we measured the settling velocity of 683 polyester microplastic fibres of 1 to 4 mm in length. Experimental findings support our hypothesis that for microplastic fibre longer than 1 mm, changing settling orientation from horizontal to vertical can increase 1.7 times the settling velocity. Fibre curliness can significantly reduce the settling velocity, where a curly fibre 1.3 times longer than a straight fibre can settle 1.75 times slower. In contrast, short microplastic fibres (less than 1 mm) mostly settle horizontally, and their settling velocity is unaffected by curliness. The drag force exerting on settling microplastic fibres was analysed, and the sphere-equivalent diameter was found to be a good representation of microplastic fibre size to predict the drag coefficient. Measured settling velocity ranges between 0.1 and 0.55 mm/s and exhibits a slight increase with the increasing length of the fibres. This low-velocity range raises concerns that microplastic fibres can favour biological flocculation, form clustered aggregates with microorganisms, feed aquatic organisms and cause bioaccumulation at higher trophic levels.

International audience; River plastic pollution is an environmental challenge of growing concern. However, there are still many unknowns related to the principal drivers of river plastic transport. Floating aquatic vegetation, such as water hyacinths, have been found to aggregate and carry large amounts of plastic debris in tropical river systems. Monitoring the entrapment of plastics in hyacinths is therefore crucial to answer the relevant scientific and societal questions. Longterm monitoring efforts are yet to be designed and implemented at large scale and various field measuring techniques can be applied. Here, we present a field guide on available methods that can be upscaled in space and time, to characterize macroplastic entrapment within floating vegetation. Five measurement techniques commonly used in plastic and vegetation monitoring were applied to the Saigon river, Vietnam. These included physical sampling, Unmanned Aerial Vehicle imagery, bridge imagery, visual counting, and satellite imagery. We compare these techniques based on their suitability to derive metrics of interest, their relevancy at different spatiotemporal scales and their benefits and drawbacks. This field guide can be used by practitioners and researchers to design future monitoring campaigns and to assess the suitability of each method to investigate specific aspects of macroplastic and floating vegetation interactions.

International audience; Microplastics in atmospheric fallouts from a developing megacity influenced by a tropical monsoon climate were investigated during a year. Three sites were selected according to the surrounding population density, the land use and occupation. The microplastic deposition fluxes varied between of 71–917 items m−2 d−1, for an observation size range of 300–5000 μm. Fibers predominated while fragments were observed occasionally. Unexpectedly, contrary to available scientific literature, deposition fluxes did not vary temporally with rainfall and wind intensity or direction, showing no effect of the tropical climate. Variations were observed between sites and were attributed to their environmental characteristics: population density and occupation space. The median length of fibers also differed between sites and could be related to in-situ fragmentation processes due to occupation space (solid waste treatment facility). Those first results from tropical climate region are showing interesting insights and are opening new perspectives on the understanding of microplastics fate from atmospheric fallouts.

In aquatic environments, assessment of microplastic concentrations is increasing worldwide but environments from developing countries remain under-evaluated. Due to disparities of facilities, financial resources and human resources between countries, protocols of sampling, analysis and observations used in developed countries cannot be fully adapted in developing ones, and required specific adaptations. In Viet Nam, an adapted methodology was developed and commonly adopted by local researchers to implement a microplastic monitoring in sediments and surface waters of 21 environments (rivers, lakes, bays, beaches) of eight cities or provinces. Microplastic concentrations in surface waters varied from 0.35 to 2522 items m-3, with the lowest concentrations recorded in the bays and the highest in the rivers. Fibers dominated over fragments in most environments (from 47% to 97%). The microplastic concentrations were related to the anthropogenic pressure on the environment, pointing out the necessity in a near future to identify the local sources of microplastics.

Excess of plastic debris in the environment is a worldwide problem. The origin of the plastic sources is partly land-based, the function of rivers as transportation pathways for plastics is an emerging research field. However, the transportation dynamics of macroplastic in river systems are still poorly understood(Blettler et al., 2018; Schmidt et al., 2017). By studying the interaction of riverine plastic transport and water plants, the transport dynamics can be better understood, which might help with the mitigation of the environmental plastic debris problem. A field study based in the Saigon river, Vietnam, found a correlation between macroplastic(>5 cm) abundance and organic material, where no other correlations were found(van Emmerik et al., 2019). We hypothesize that water hyacinths have an important role in the spatiotemporal dynamics of riverine macroplastic transport. The organic material in this river was predominantly identified as water hyacinths, an invasive plant common in Southeast Asia. In this study, we developed a method using image analysis, to detect macro plastics and floating vegetation(lab-grown water hyacinths). Image analysis in combination with drone technology creates opportunities to collect field data, with already promising results(Geraeds et al., 2019). We analyzed the images, to obtain an approximation of the amount of plastic and vegetation, visible from the surface. We subsequently use this data to evaluate the relationship between plastic abundance and vegetation in rivers. The method developed in this study can be used to collect data in the field. Targeted observations of plastic entrapment in water hyacinths may shed additional light on the potential of using water hyacinths as a proxy for riverine macroplastic transport dynamics. ReferencesM. C. Blettler, E. Abrial, F. R. Khan, N. Sivri, and L. A. Espinola. Freshwater plastic pollution:Recognizing research biases and identifying knowledge gaps. Water research, 143:416-424, 2018.M. Geraeds, T. van Emmerik, R. de Vries, and M. S. bin Ab Razak. Riverine plastic litter monitoring using unmanned aerial vehicles (uavs). Remote Sensing, 11(17):2045, 2019.C. Schmidt, T. Krauth, and S.Wagner. Export of plastic debris by rivers into the sea. Environmental science & technology, 51(21):12246-12253, 2017.T. van Emmerik, E. Strady, T.-C. Kieu-Le, L. Nguyen, and N. Gratoit. Seasonality of riverine macroplastic transport. Nature Scientific Reports, 2019.

Marine plastic pollution is an increasing environmental threat. Although it is assumed that most marine plastics are transported from land to the ocean through rivers, only limited data on riverine plastic transport exists. Recently, new methods have been introduced to characterize riverine plastics consistently through time and space. For example, combining visual counting observations and plastic debris sampling can provide order of magnitude estimations of plastic transport through a river. In this paper, we present findings from multi-season measurement campaign in the Saigon River, Vietnam. For the first time, we demonstrate that macroplastic transport exhibits strong temporal variation. The monthly averaged plastic transport changes up to a factor five within the measurement period. As it is unclear what drives the variation in plastic transport, relations between rainfall, river discharge, presence of organic material and plastic transport have been explored. Furthermore, we present new findings on the cross-sectional and vertical distribution of riverine plastic transport. With this paper we present new insights in the origin and fate of riverine plastic transport, emphasizing the severity of the emerging thread of plastic pollution on riverine ecosystems.

International audience; Anthropogenic fibers, gathering synthetic fibers, artificial fibers and natural fibers are ubiquitous in the natural environment. Tremendous concentrations of anthropogenic fibers were previously measured in the tropical Saigon River (Vietnam), i.e. a river impacted by textile and apparel industries. In the present study, we want to examine the role of contrasted seasonal variation (e.g., dry and rainy seasons), via the rainfall and monthly water discharges, and of water's physico-chemical conditions on the concentrations of anthropogenic fibers in the surface water. The one year and half monthly survey evidenced that concentrations of anthropogenic fibers varied from 22 to 251 items L-1 and their variations were not related to rainfall, water discharge or abiotic factors. However, their color and length distribution varied monthly suggesting variations in sources and sinks. Based on the 2017 survey, we estimated an annual emission of anthropogenic fibers from the river to the downstream coastal zone of 115e164 × 10 12 items yr-1.

International audience; Both macroplastic and microplastic contamination levels were assessed for the first time in a tropical river estuary system, i.e. the Saigon River, that traverses a developing South East Asian megacity, i.e. Ho Chi Minh City, Vietnam. The analysis of floating debris collected daily on the Nhieu Loc - Thi Nghe canal by the municipal waste management service shows that the plastic mass percentage represents 11-43%, and the land-based plastic debris entering the river was estimated from 0.96 to 19.91 g inhabitant-1d-1, namely 350 to 7270 g inhabitant-1yr-1. Microplastics were assessed in the Saigon River and in four urban canals by sampling bulk water for anthropogenic fiber analysis and 300 μm mesh size plankton net exposition for fragment analysis. Fibers and fragments are highly concentrated in this system, respectively 172,000 to 519,000 items m-3and 10 to 223 items m-3. They were found in various colors and shapes with smallest size and surface classes being predominant. The macroplastics and fragments were mainly made of polyethylene and polypropylene while the anthropogenic fibers were mainly made of polyester. The relation between macroplastic and microplastic concentrations, waste management, population density and water treatment are further discussed.