Temporal dynamic of anthropogenic fibers in a tropical river-estuarine system☆
Graphical abstract
Introduction
Plastic pollution in the aquatic environment is a worldwide issue that affect both the marine and the freshwater environments. Plastic in the aquatic environment are categorized according to their size. Macroplastic refers to plastic items larger than 5 mm while microplastic to items comprised between 1 μm and 5 mm length size (Barnes et al., 2009; Gigault et al., 2018; Hartmann et al., 2019; Frias and Nash, 2019). Microplastic are composed of fragments, fibers, pellets and microbeads originated from both primary and secondary manufacturing.
Among microplastic, fibers are the most prevalent ones observed in the natural environment (Browne et al., 2011) and micropollution fibers are more and more of concern. Anthropogenic fibers, as we defined in Lahens et al. (2018) refer to the synthetic fibers from petrochemical origin (i.e. polyester, polyamide, polypropylene, etc.), to the artificial fibers from artificial cellulose or silk (i.e. viscose, rayon) and to the natural fibers (i.e. cotton, wool), all used in textile and apparel industries. The synthetic fibers are released to the aquatic environment mainly by the use of synthetic polymers in textile and garment industry (e.g. 98 million tons of polyester fibers in 2018, Textile Exchange, 2018), by nets and other materials like geotextile. Synthetic fibers and artificial fibers are found in all aquatic compartments: lake, river, estuary, sea an ocean, atmospheric fallout (see reviews of Cesa et al., 2019; Gago et al., 2018; Blettler et al., 2018) and can be transferred through freshwater and marine foodwebs and have implications to human health (see review Carbery et al., 2018; Blettler et al., 2018). Their concentrations in seawater (e.g. ND - 450 items m−3; Gago et al., 2018) are in the same range as in most riverine waters (e.g. 5–398 items m−3; Dris et al., 2018 and reference within) but their dominant polymer's type differ between environment. Polypropylene (PP) fibers were found the most common in the marine environment (Gago et al., 2018) while polyethylene terephthalate PET (Dris et al., 2018) and polyester (Lahens et al., 2018) were the dominant one in rivers, pointing out the different sources of fibers to the environment. These features evidenced then the need to better understand the sources, the fate and dynamic of synthetic fibers from river to sea.
Despite the possibility that the South East Asian countries are among the ones emitting the most plastic to the ocean (Jambeck et al., 2015), the majority of plastic assessment's studies in freshwater environments were conducted in Europe, North America and more recently in China (see review Blettler et al., 2018), pointing out a clear lack of data in South East Asia. Vietnam is the third top garment exporters in the world after China and Bangladesh (International Trade Administration, 2016). There are about 6000 textile and apparel manufacturing companies, employing 2.5 million workers, which 60% of them are located in the Southern part of the country (International Trade Administration, 2016). In the Saigon River and its canals, crossing the megacity Ho Chi Minh City (HCMC; 8.4 million inhabitants (GSO, 2017)) in Southern Vietnam, tremendous concentrations of anthropogenic fibers were measured (e.g.172–519 items L−1 Lahens et al., 2018) in the dense and urbanized part of the River. Their synthetic origin, with 70% of them being made of polyester, evidenced that textile and apparel industry are the main sources of fibers in this River and that, associated to poor wastewater treatment, it impacts the quality of the River (Lahens et al., 2018). In line with the previous study, the main objective of the present study is to characterize the temporal variation at an annual scale of the anthropogenic fibers in the surface water of the Saigon River, a tropical river-estuarine environment characterized by two contrasted seasons (e.g. rainy and dry) and by tidal influence. We hypothesized that the contrasted seasons via the rainfall, the change of water discharge and the intrusion of the salinity front will strongly influence the concentrations of anthropogenic fibers in the river. We examined the impact of (i) the season via the rainfall, (ii) the monthly water discharges and (iii) the water's physico chemical conditions on the seasonal dynamic of fibers. We also aim to quantify the emission of fibers by the Saigon River to the coastal zone. Accordingly, we set up a monthly monitoring survey during eighteen months in the surface water of the Saigon River at a sampling site located in the dense urban zone.
Section snippets
The Saigon River Estuary system
The Saigon River Estuary system (250 km long; 4717 km2), located in Southern Vietnam, originates from South Eastern Cambodia, forms the Dau Tieng Reservoir (120–270 km2; 470-1680 million m3), flows through the economic capital city of HCMC, confluences with the Dong Nai River (470 km long) and then flows into the Can Gio mangrove and the South China Sea (Fig. 1). The Saigon River is under a tropical monsoon climate with a rainy season lasting from May to November and a dry season from December
Results
Over the year and half monthly sampling, a total of 1055 anthropogenic fibers were observed and measured. The fiber's concentrations vary through the year, with a minimum of concentrations of 22 items L−1 observed in July 2017 and a maximum of 251 items L−1 observed in August 2016 (Fig. 2). The difference between the two duplicates ranged from 2% to 65% with a mean and a median of 25%, showing that anthropogenic fiber's concentrations can be both well-homogenized and not well-homogenized in the
Variation of anthropogenic fiber's concentrations and size
The range of anthropogenic fiber's concentrations measured during this survey is lower than previously observed by Lahens et al. (2018) at the same sampling site in April 2016 (172–519 items L−1) but much higher than concentrations reported in most rivers like in the Seine River (0.005–0.398 items L−1; Dris et al., 2018), the Yangtze River (1.9 items L−1; Wang et al., 2017), the Hanjiang River (2.3 items L−1; Wang et al., 2017; the Antua River (0.02–0.071 items L−1; Rodrigues et al., 2018) for
Conclusions
The dynamic of anthropogenic fibers in the surface waters of this tropical river-estuarine environment was independent of the seasonal variability of rainfall, water discharges, saline intrusion and others abiotic factors (e.g. TSS concentrations, pH, O2) of the river. We suggested that their fate might rely mostly on both their sinking properties in the water column under contrasted estuarine water current velocities and on the sources. Efforts should be continued on those topics to better
CRediT authorship contribution statement
Emilie Strady: Conceptualization, Methodology, Investigation, Resources, Writing - original draft, Writing - review & editing. Thuy-Chung Kieu-Le: Conceptualization, Methodology, Investigation, Resources, Writing - original draft, Writing - review & editing. Johnny Gasperi: Conceptualization, Methodology, Writing - original draft, Writing - review & editing. Bruno Tassin: Conceptualization, Methodology, Writing - original draft, Writing - review & editing.
Declaration of competing interest
We declare that we don't have any conflicts of interest with no one considering this study.
Acknowledgements
This study has been conducted under the framework of CARE-RESCIF initiative. The authors would like to thank the student Nguyen Van Thoai for his help during sampling and laboratory analysis. This study was funded by CNRS-INSU EC2CO-Ecodyn grants, France and Vietnam National University Ho Chi Minh City (VNU-HCM) under grant number C2018-20-17.
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This paper has been recommended for acceptance by Maria Cristina Fossi.