Abundance, composition and fluxes of plastic debris and other macrolitter in urban runoff in a suburban catchment of Greater Paris

Litter in French urban areas - Part 2: transport dynamic and fluxes in stormwater

Urban areas constitute a major hotspot of litter, including plastic litter, that stormwater can wash off towards waterways. However, few studies quantified and characterized litter densities in urban areas and fluxes transported by stormwater networks. Moreover, little information is available on litter transport dynamics in stormwater, and on the factors driving this transport. This study aims at characterizing and quantifying litter amounts transported by stormwater of two nested French urban catchments (total surface area of 105 ha). Litter densities relative to land uses and rain events were investigated in the same catchments as in a compagnon paper (Ledieu et al., 2024). The present study explores the impact of rain events on the transport of urban litter in stormwater. Litter collection and characterization combined with a capture/recapture experiment using tagged litter placed in stormwater inlets show total litter fluxes of 29 kg/year, in which 14 kg/year are plastics, exported at the stormwater outlet. These fluxes confirm that stormwater runoff is a considerable pathway from urban surfaces to waterways, especially regarding small plastic litter (< 2.5 cm). Item transport dynamic is however not linear and only 0.3% of the urban litter appear remobilized. Litter transport dynamics depends on several factors (urban litter densities, hydrometeorological parameters, item composition and morphologies, and stormwater management systems) that should be considered in global models.

Macrolitter and microplastics along the East Pacific coasts - A homemade problem needing local solutions

The East Pacific (EP) region, especially the central and southern EP, has been fairly less studied than other world's regions with respect to marine litter pollution. This comprehensive literature review (257 peer-reviewed publications) showed that both macrolitter (mostly plastics) and microplastics tend to accumulate on EP shorelines. Moreover, they were also reported in all the other compartments investigated: sea surface, water column, seafloor and 'others'. Mostly local, land-based sources (e.g., tourism, poor waste management) were identified across the region, especially at continental sites from low and mid latitudes. Some sea-based sources (e.g., fisheries, long-distance drifting) were also identified at high latitudes and on oceanic islands, likely enhanced by the oceanographic dynamics of the EP that affect transport of floating litter. Our results suggest that effective solutions to the problem require local and preventive strategies to significantly reduce the levels of litter along the EP coasts.

Wind- and rain-driven macroplastic mobilization and transport on land

Wind and rain are considered main drivers for mobilization and transport of macroplastics on land, yet there is a lack of empirical data that quantifies this. We present lab experiment results on land-based macroplastic mobilization and transport. We placed four types of macroplastics on terrains with varying surface roughness and slope angles, and exposed them to changing wind speeds and rain intensities. In general, we find that the mobilization probability and transport velocity of macroplastics strongly depend on the combination of the terrain characteristics and material properties. At Beaufort 3, 100% of the plastic bags were mobilized, whereas for the other plastic types less than 50% were mobilized. We found 1.4 (grass) to 5 times (paved surface) higher mobilization probabilities on land than assumed by existing plastic transport models. Macroplastic transport velocities were positively correlated with wind speed, but not with rain intensity. This suggests that macroplastics are not transported on land by rain unless surface runoff develops that can bring the macroplastics afloat. Macroplastic transport velocities were, driven by wind, 1.9 and, driven by rain, 4.9 times faster on paved surfaces than on grass. This study enhances our understanding of land-based macroplastic transport and provides an empirical basis for models.

Monthly variation and transport of microplastics from the Soan River into the Indus River

The presence of plastic and microplastic pollution in freshwater systems receives extensive concerns for its accumulative trend and potential ecological impacts. This is the first annual study that investigated the monthly profile of plastic pollution in the mouth of the Soan River. Plastic pollutants comprising microplastic content up to 91.7 % were abundantly found during different seasons around the year, ranging from 132.7 items/m3 to 641.3 items/m3. The average abundance of plastics was significantly higher in August (641.3 ± 23.7 items/m3) than in other months. Overall, fibers, large microplastics (L-MPs), and transparent items were dominant by shape (57.7 %), size (61.9 %), and color (24.6 %), respectively. The highest average number of fibers (374.3/m3) and L-MPs (396 items/m3) were recorded during May and remained higher in the surface water from December to May. Fragments (432.3/m3) and S-MPs were observed higher (362.3 items/m3) during the peak rainy month of the summer monsoon season (August). Variations in the abundance and morphotypes were seemingly not only influenced by the seasonal change but also might be due to hydromorphological characteristics of the river, especially riverbed morphology, and the flow of the water. Only 5.2 % of the total items found were identified using μ-FTIR (micro-Fourier Transformed Infrared Spectroscope) which consisted of 70.7 % plastic items. Spectroscopy revealed that polyethylene terephthalate was an abundantly found polymer that largely prevailed in the form of fibers, followed by polypropylene and polyethylene. Most of the fragments, foams, and films were composed of polypropylene, polystyrene, and rayon respectively. Being an urban river, the polymeric profile demonstrated that anthropogenic activities had a significant impact on polluting the river. These findings are a very important source to understand the profile of plastic pollution in the Soan River and also a significant reference for policy-making in controlling plastic pollution among the riverine networks.

Measuring sediment loads and particle size distribution in road runoff: Implications for sediment removal by stormwater control measures

Road runoff contributes an array of pollutants which degrade the quality of receiving waters. Sediment conveyed in runoff results in loss of habitat and loss of reservoir capacity, among other undesirable impacts. To select and design stormwater control measures (SCMs), the sediment particle size distribution (PSD) is needed to quantify the required hydraulic retention time for particle settling and to understand what other treatment processes (e.g., filtration) are needed to meet sediment removal targets. A two-year field monitoring study was undertaken across the state of Ohio, USA, to evaluate the PSD of sediment in runoff at twelve roads. The highest TSS concentrations were observed on interstate highways (highest annual average daily traffic [AADT]) and minor arterials (low AADT), suggesting factors beyond AADT, such as antecedent dry period, rainfall intensity, and windborne dust and particulates, contribute to the varied sediment characteristics in runoff. The median TSS load across all samples collected was 2.7 kg/ha per storm event, while annual TSS loads for the monitoring sites varied from 98 kg/(ha·yr) to 519 kg/(ha·yr), with a mean value of 271 kg/(ha·yr). Particle size distributions varied across the monitoring sites, with mean and median d50 of 48.6 μm and 52.5 μm, respectively. Interstate highways (highest AADT) had significantly finer PSDs than other functional classes, while roads in low density residential areas had coarser PSDs than other land uses. Observed differences in PSD across road characteristics may guide SCM selection; dry detention basins and wet ponds/wetlands were predicted to provide effective removal across a variety of PSDs, while TSS reductions provided by hydrodynamic separators and high-flow media filters (which effectively remove larger particles) may be maximized in areas with coarser PSDs (e.g., roads surrounded by low density residential areas studied herein).

Citizen scientists study beach litter along 12,000 km of the East Pacific coast: A baseline for the International Plastic Treaty

Anthropogenic Marine Litter (AML) accumulating on beaches causes damage to coastal ecosystems and high costs to local communities. Volunteers sampled AML on 130 beaches along the central and southern East Pacific coasts, with AML densities ranging from 0.46 to 2.26 items m-2 in the different countries. AML composition was dominated by plastics and cigarette butts, the latter especially in Mexico and Chile. The accumulation of AML in the upper zones of the beaches and substantial proportions of cigarette butts, glass and metal pointed mainly to local sources. Statistical modelling of litter sources on continental beaches revealed that tourism, access and related infrastructure (e.g. parking lots) best explained AML densities, while plastic densities were also influenced by the distance from river mouths and national Gross Domestic Product. Large-scale monitoring can be a useful tool to evaluate the effectiveness of public policies that should primarily focus on land sources.

Macro-, meso- and microplastic abundance in sandy beaches and factors influencing their distribution in an SW Atlantic resort

The present study recorded the abundance of plastic debris in marine sediments of tourist beaches in the Southwest Atlantic (Argentina). We aimed to determine the abundance of macro-, meso- and microplastics in different beaches, considering different anthropogenic and natural factors. Generalized Linear Mixed Models (GLMMs) were performed and the explanatory factors were: Beach Morphology; Grain Size; Recreational Use Level; Continental Water Discharge, Location, Distance Urban Centre and Season. The Continental Water Discharge was the factor responsible for the highest abundance of plastic debris on the beach surface. Beaches with fine granulometry, between groins, with high to very high intensity of recreational use, tend to accumulate and/or retain greater amounts of plastic debris. The seasonal factor influences the abundance of plastic waste in the central zone between the pre-summer and post-summer seasons, despite the cleaning effect of the city goverment. In beaches with greater anthropogenic pressure, the influence of this factor on the abundance of litter is altered.

Exploring factors driving macroplastic emissions of Mahiga Creek, Cebu, Philippines to the estuary

Rivers function as a pathway for plastic pollution to enter the marine environment. This study presents one of the first field estimates of macroplastic emissions from the Mahiga Creek into its estuary. Thirty-minute plastic counting surveys were conducted for 31 days with the use of videos and a collecting trawl. The captured plastics were classified according to the OSPAR marine litter manual. The three main categories were crisp packets (27.96 %), small bags (27.08 %), and plastic/polystyrene pieces (2.5-50 cm) (18.35 %). Intraday and daily changes in plastic flux values were compared. Plastic flux comparisons between holidays and regular days were also done. No relationship between plastic flux and discharge was found on days without rainfall (r = 0.0237). However, a significant increase in plastic flux was observed during rainfall events. The findings in this study present an insight into different factors that may affect macroplastic emissions in the Philippines.

Amsterdam urban water system as entry point of river plastic pollution

Accumulation of plastic litter in aquatic environments negatively impacts ecosystems and human livelihood. Urban areas are assumed to be the main source of plastic pollution in these environments because of high anthropogenic activity. Yet, the drivers of plastic emissions, abundance, and retention within these systems and subsequent transport to river systems are poorly understood. In this study, we demonstrate that urban water systems function as major contributors to river plastic pollution, and explore the potential driving factors contributing to the transport dynamics. Monthly visual counting of floating litter at six outlets of the Amsterdam water system results in an estimated 2.7 million items entering the closely connected IJ river annually, ranking it among the most polluting systems measured in the Netherlands and Europe. Subsequent analyses of environmental drivers (including rainfall, sunlight, wind speed, and tidal regimes) and litter flux showed very weak and insignificant correlations (r = [Formula: see text]0.19-0.16), implying additional investigation of potential drivers is required. High-frequency observations at various locations within the urban water system and advanced monitoring using novel technologies could be explored to harmonize and automate monitoring. Once litter type and abundance are well-defined with a clear origin, communication of the results with local communities and stakeholders could help co-develop solutions and stimulate behavioral change geared to reduce plastic pollution in urban environments.

Abundance and composition of anthropogenic macrolitter and natural debris in road runoff in Ohio, USA

Urban stormwater conveys dissolved pollutants, micropollutants, particulate matter, natural debris, and anthropogenic macrodebris to receiving waters. Though it is widely recognized that anthropogenic macrodebris mobilized by stormwater contributes to global pollution management issues (e.g., ocean garbage patches), these materials often are not the focus of stormwater sampling campaigns. Furthermore, macrodebris can cause clogging of sewer systems, exacerbating flooding and public health hazards. Due to their engineered structures draining directly connected impervious areas (e.g., catch basins, inlets, and pipes), roads present a unique opportunity to mitigate the conveyance of macrodebris in stormwater. To optimize control measures, data are needed to understand expected volume and mass of macrodebris in road runoff. To address this gap in knowledge, a field monitoring study was conducted in Ohio (USA) to quantify the mass, volume, and moisture content of macrodebris transported by road runoff. Designed to filter macrodebris (i.e., material with diameter greater than 5 mm) while maintaining drainage, purpose-built inserts were deployed in catch basins at eleven geographically diverse locations across the state. Macrodebris samples were collected from the inserts every 11.6 days (mean) over a two-year monitoring period. Volume and mass of total and categorical (i.e., vegetation, cigarettes, plastic, glass, metal, wood, fabric, gravel, and paper) debris were characterized. Mean total macrodebris volume and mass were 4.62 L and 0.49 kg per sampling window, corresponding to mean volumetric and mass loading rates of 8.56 L/ha/day and 0.79 kg/ha/day, respectively. Natural debris (e.g., vegetation) was the primary contributor to macrodebris (mean 80.3% (i.e., 3.94 L of the mean 4.66 L total sample volume) and 79.7% (i.e., 0.42 kg of the mean 0.53 kg total sample mass) of total volume and mass, respectively), and exhibited seasonal peaks in autumn due to leaf drop. Road functional class (i.e., interstate, principal arterial, and minor arterial routes), land use, and development density significantly impacted macrodebris generation, with increased total and categorical macrodebris along urbanized interstate highways near commercial and residential areas. Macrodebris moisture content was highly variable (ranging from 1.5 to 440%; mean 78.5%), indicating additional management (e.g., drying, solidification) may be required prior to landfilling. Results of this study inform macrodebris mitigation strategies and required maintenance frequencies for pre-treatment devices for other stormwater control measures treating road runoff, including catch basin inserts and hydrodynamic separators, among others.

Land use and COVID-19 lockdowns influence debris composition and abundance in stormwater drains

Stormwater drains act as a pathway for anthropogenic debris from land to sea, particularly in urbanised estuaries where impervious surfaces expedite the process. Debris type and abundance in stormwater drains may vary due to land use and human activity, and knowledge of this variation is necessary to manage the growing threat of debris. Surveys of stormwater debris can inform targeted reduction and remediation efforts by intercepting and identifying pollutants near their source. We surveyed replicate stormwater gross pollutant traps across four land use zones (city centre, shopping centre, transportation hub, industrial precinct) before and during COVID-19 measures to assess the effects of changing human activities. Gross pollutant traps were installed in 120 drains in Greater Melbourne, Australia, and citizen scientists trained by Tangaroa Blue Foundation weighed and classified debris at 6-week intervals between October 2019 and October 2020. Four survey cycles were conducted before lockdowns were implemented, then another four during lockdowns. COVID-19 lockdowns and patterns of debris type and abundance across land use revealed how changes in human activity might impact the flow of debris. Cigarette butts were the most abundant macro debris (>5 mm) item in every survey cycle, regardless of lockdowns. Industrial land use zones had the lowest macro debris counts but contained over 90 % of the micro debris (1-5 mm). The amount of total macro debris decreased during lockdowns, however the most abundant and problematic debris items such as cigarettes and single-use plastics did not decrease as much as might be expected from the concomitant reductions in human activity. Occupational health and safety items, such as masks and gloves, increased (144 %) during COVID-19 lockdowns. Micro debris counts did not change in industrial zones during lockdowns, suggesting that workplace interventions may be necessary to reduce this debris leakage. Tracing the pathway of debris from source to sea can inform reduction and long-term management strategies.

Amount, composition and sources of macrolitter from a highly frequented roadway

Many researches mention the need to identify the land-based sources of riverine macrolitter but few field data on litter amount, composition and sources are available in the scientific literature. Describing macrolitter hotspot dynamics would actually allow a better estimation of fluxes in the receiving environments and a better identification of the more appropriate mitigation strategies. This study provides new insights in roadway macrolitter production rates, typologies and input sources (i.e. deliberate or accidental). The macrolitter from an 800 m portion of a highly frequented roadway (around 90,000 vehicles per day) was collected during almost one year. Typologies were defined using the OSPAR/TGML classification. Results show high annual loads of macrolitter (42.8 kg/yr/ha), suggesting significant contributions of the road runoff to the litter fluxes in urban stormwater. Over the course of a year, 88.5 kg of debris were collected, including 53.2 kg (60%) of plastic debris. In total, 36,439 items were characterized, of which 84% were plastics. The macrodebris collected present a low diversity of components with Top 10 items accounting for 92% by count and a majority of small and lightweight items like plastic fragments (31%) or cigarette butts (18%). Input sources were estimated for 43% of the mass collected in which 37.2% were deliberately littered and 62.8% were accidental leaks, illustrating a major contribution of uncovered trucks and unsecured loads. The accumulation rates show a linear correlation with the road traffic. Such data are of prime interest since they enable to determine the potential contribution of road traffic to plastic fluxes to the environment.

Macrolitter dataset from a highly frequented roadway in Nantes, France

Land-based sources of riverine macrolitter are now recognized as a major concern, but few field data on litter amount, composition and sources are available. This is especially the case for macrolitter hotspots like high frequented roadways that could generate large amount of macrolitter potentially reaching rivers. This dataset provides macrolitter amount and composition over one year from a retention pond collecting stormwater and carried macrolitter from a 800 m portion of a highly frequented roadway (around 90,000 vehicles per day). The typology of macrolitter was defined using the TSG-ML/OSPAR classifications. A total of 36,439 items in which 84% of plastics were individually counted, classified and weighted by category for a total mass of 88.5 kg (60% of plastics). Raw data are available in Mendeley Data (DOI:10.17632/t6ryv6crjd.4). Top 10 items represent 92% by count of the total with plastic fragments (31%), cigarette butts (18%), EPS fragments (17%) or foam packaging (11%) as most common items. Top 10 items represent 72% by mass of the total with plastic fragments (24%) and Cardboard (13%) as most common items, followed by foam packaging (6%), wood fragments (6%), industrial plastic sheets (5%), rubber fragments (4%) and EPS fragments (4%). More than 94% of plastic items are below 1.9 g/item. This dataset is related to the research paper Amount, composition and sources of macrolitter from a highly frequented roadway.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Riverine litter in a small urban river in Marseille, France: Plastic load and management challenges

Small urban rivers are thought to be major sources of riverine litter, especially macroplastics, into the ocean. In well-developed countries, waste management infrastructures and recovery systems are sometimes implemented to prevent their emission into the sea meeting environmental and economic goals. The Huveaune River in Marseille, South of France, is a typical case study showing a non-negligible and uncontrolled leakage of riverine litter remains, despite all recovery systems implemented. Giant bar screens are settled over the river to collect riverine litter from the whole water column before water is released into the Sea. In this paper, screened material was characterized during a dry, wet and heavy rainfall period and annual macroplastic mass flows were estimated. The plastic fraction represented 83% by count of the 3147 items sorted and counted. Mass flow of plastic debris ranged between 1.1 and 5.8 mt/yr (equivalent to 2.1-11.4 g/cap/yr), in which 0.4-2.1 mt/yr (equivalent to 0.8-4.1 g/cap/yr) are bypassed to the sea during heavy rainfall periods. Giant bar screens across the Huveaune River prevent 65% of the mass flow to reach the sea annually, but 35% remain uncontrolled. When compared to the Seine River and other European Rivers, macroplastic leakage into the ocean per capita may range between 1 and 10 g/cap/yr. This suggests that end-of-pipe solutions are not enough and further supports urgent regulations of the plastic production on local to global scales to tackle the plastic pollution at its source.

Microplastic and microfiber fluxes in the Seine River: Flood events versus dry periods

Studies on the influence of hydrodynamic conditions on anthropogenic microfiber (MF) and microplastic (MP) distributions in freshwater environments are sparse. In this study, we evaluated the influence of urbanisation gradient on the spatial variability of MFs and MPs. Temporal variability was also assessed by comparing the concentrations and fluxes of MFs and MPs under low flow conditions with those during the January-February 2018 flood event. For each period, Seine river water was collected upstream and downstream of Greater Paris and filtered through an 80 μm net at three different sampling sites. MFs were counted using a stereomicroscope, while MPs were analysed using micro-Fourier transform infrared spectroscopy coupled with siMPle analysis software. The highest concentrations of MFs and MPs were reported at the furthest downstream sites during both periods. However, high water flowrates and urbanisation gradient did not significantly impact MF and MP concentrations, sizes, or polymer distributions. The median MF and MP concentrations were 2.6 and 15.5 items/L and their interquartile ranges were 1.6 and 4.9 items/L (n = 10), respectively, illustrating relatively stable concentrations in spite of the urbanisation gradient and variations in the flowrate. In contrast to the concentration, size, and polymer distribution characteristics, MP mass fluxes were strongly affected by river flow. MF and MP fluxes show increases in the number and mass of particles from upstream to downstream. The downstream site presents high MP mass fluxes, which range between 924 and 1675 tonnes/year. These results may indicate significant MP inputs from the Paris Megacity through wastewater treatment plant effluents and untreated stormwater. The January-February 2018 flood event, which represented 14.5% of the year (in terms of time), contributed 40% of the yearly MP mass fluxes. Thus, flood events contribute strongly to MP fluxes.

Plastic Pollution, Waste Management Issues, and Circular Economy Opportunities in Rural Communities

Rural areas are exposed to severe environmental pollution issues fed by industrial and agricultural activities combined with poor waste and sanitation management practices, struggling to achieve the United Nations’ Sustainable Development Goals (SDGs) in line with Agenda 2030. Rural communities are examined through a “dual approach” as both contributors and receivers of plastic pollution leakage into the natural environment (through the air–water–soil–biota nexus). Despite the emerging trend of plastic pollution research, in this paper, we identify few studies investigating rural communities. Therefore, proxy analysis of peer-reviewed literature is required to outline the significant gaps related to plastic pollution and plastic waste management issues in rural regions. This work focuses on key stages such as (i) plastic pollution effects on rural communities, (ii) plastic pollution generated by rural communities, (iii) the development of a rural waste management sector in low- and middle-income countries in line with the SDGs, and (iv) circular economy opportunities to reduce plastic pollution in rural areas. We conclude that rural communities must be involved in both future plastic pollution and circular economy research to help decision makers reduce environmental and public health threats, and to catalyze circular initiatives in rural areas around the world, including less developed communities.

Transport process and source contribution of nitrogen in stormwater runoff from urban catchments

Nitrogen in urban stormwater has been widely studied, and effective management of nitrogen pollution is critical for improving urban stormwater and receiving water quality. This requires an in-depth understanding of the transport process and source contribution to both dissolved and particulate nitrogen in stormwater from urban catchments. In this study, 123 stormwater runoff samples were collected from an urban catchment during different rainfall events. Dissolved and particulate nitrogen concentrations in roof runoff, road runoff, and sewer flow were analyzed. The concentration of dissolved nitrogen was higher in roof runoff than in road runoff and sewer flow. However, the concentration of particulate nitrogen was lower in roof runoff than in road runoff and sewer flow. Isotopic analysis and Bayesian mixing models showed that road runoff was the largest source contributor of both nitrate and particulate organic nitrogen (PON) in sewer flow discharged from the study catchment. In addition, road runoff contributed the majority of PON associated with coarse particles (>105 μm), whereas PON associated with fine particles (<105 μm) was primarily washed-off of sewer sediments. The results provided several suggestions for the management of nitrogen pollution in urban catchments. This study could help to fully understand the transport and sources of nitrogen pollution in urban stormwater and provide recommendations to the government for implementing appropriate stormwater management strategies to minimize stormwater pollution.

Microplastics and microfibers in urban runoff from a suburban catchment of Greater Paris

Microplastics (MPs) and microfibers (MFs) in stormwater have been poorly investigated. Data on their intra and inter rain events variability over time are still sparse. For the first time, the variability of microlitter concentrations in stormwater has been studied. MF and MP concentrations were investigated in stormwater runoff at the outlet of the suburban catchment at Sucy-en-Brie (a suburb of Paris, France), during four rain events. Median MF and MP concentrations were 1.9 and 29 items/L, with an interquartile range of 2.3 and 36 items/L, respectively (N = 18). A different pattern was observed between MFs and MPs. While no relationship or trends were observed for MFs, the highest MP concentrations were observed before the flow rate peak of the rain events. This could indicate a difference in the behaviour between MFs and MPs. We estimated the median MP mass concentration to be 56 μg/L with an interquartile range of 194 μg/L, whereas the mass concentration of macroplastics was estimated to be 31 μg/L with an interquartile range of 22 μg/L at the same sampling site, in a previous study. For this sampling site, MPs and macroplastics have the same order of magnitude. This study may have strong implications on microplastic assessment in urban waters.