Evidence shows that the majority of aquatic field microplastics (MPs) could be microfibers (MFs) which can be originated directly from massive sources such as textile production and shedding from garments, agricultural textiles and clothes washing. In addition, wear and tear of tyres (TRWPs) emerges as a stealthy major source of micro and nanoplastics, commonly under-sampled/detected in the field. In order to compile the current knowledge in regards to these two major MPs sources, concentrations of concern in aquatic environments, their distribution, bulk emission rates and water mitigation strategies were systematically reviewed. Most of the aquatic field studies presented MFs values above 50%. MPs concentrations varied from 0.3 to 8925 particles m⁻³ in lakes, from 0.69 to 8.7 × 10⁶ particles m⁻³ in streams and rivers, from 0.16 to 192000 particles m⁻³ estuaries, and from 0 to 4600 particles m⁻³ in the ocean. Textiles at every stage of production, use and disposal are the major source of synthetic MFs to water. Laundry estimates showed an averaged release up to 279972 tons year⁻¹ (high washing frequency) from which 123000 tons would annually flow through untreated effluents to rivers, streams, lakes or directly to the ocean. TRWPs in the aquatic environments showed concentrations up to 179 mg L⁻¹ (SPM) in runoff river sediments and up to 480 mg g⁻¹ in highway runoff sediments. Even though average TRWR emission is of 0.95 kg year⁻¹ per capita (10 nm- 500 μm) there is a general scarcity of information about their aquatic environmental levels probably due to no-availability or inadequate methods of detection. The revision of strategies to mitigate the delivering of MFs and TRWP into water streams illustrated the importance of domestic laundry retention devices, Waste Water Treatment Plants (WWTP) with at least a secondary treatment and stormwater and road-runoff collectors quality improvement devices.

The weathering and contaminant transport behavior of both primary (PMPs) and secondary microplastics (SMPs) are interrelated to their original physiochemical features and variations within the environment. This study examines the influence of PMPs' intrinsic characteristics (polymer structure and crystallinity) and SMPs' extrinsic features (surface oxidation and external sediments attachment) on the photodegradation kinetics, and subsequently Pb(II) and Zn(II) uptake from stormwater. For this purpose, high density polyethylene (HDPE) and low density polyethylene (LDPE) with different degrees of crystallinities were produced as PMPs, and their photodegradation behaviors were compared with original polymers. Furthermore, the SMPs generated by abrasion and surface oxidation of PMPs and the virgin PMPs underwent accelerated photodegradation, and the changes of their crystallinity, surface chemistry, and morphology were examined. Scanning electron microscopy (SEM) imaging and X-ray photoelectron (XPS) studies revealed the formation of cracks and different oxidized functionalities on MPs surface due to UV photodegradation. The vinyl and carbonyl indices calculated using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy demonstrated an elevated photodegradation rate for SMPs compared to the PMPs. Moreover, the Differential Scanning Colorimetry (DSC) demonstrated an increasing percentage of crystallinity in all MPs due to the photodegradation. The percent crystallinity of HDPE pellets increased after photodegradation from 49.8 to 62.6 and it increased from 17.2 to 38.9 for LDPE pellets respectively. The greater level of increase in crystallinity for LDPE in comparison to HDPE upon photodegradation was referred to as LDPE's greater amorphous content and branched structure. A greater level of metal uptake was obtained for photodegraded LDPE pellets as 2526 μg/m² for Pb(II) and 2028 μg/m² for Zn(II) respectively.

Microplastics (MPs) are an emerging pollutant and a worldwide issue. A wide variety of MPs and tyre wear particles (TWPs) are entering and spreading in the environment. TWPs can reach waterbodies through runoff, where main contributing particulate matter comes from impervious areas. In this paper, TWPs and other types of MPs that were transported with the runoff of a high populated-impervious urban area were characterised. Briefly, MPs were sampled from sediments in a stormwater detention reservoir (SDR) used for flood control of a catchment area of ∼36 km², of which 73% was impervious. The sampled SDR is located in São Paulo, the most populated city in South America. TWPs were the most common type of MPs in this SDR, accounting for 53% of the total MPs; followed by fragments (30%), fibres (9%), films (4%) and pellets (4%). In particular, MPs in the size range 0.1 mm–0.5 mm were mostly TWPs. Such a profile of MPs in the SDR is unlike what is reported in environmental compartments elsewhere. TWPs were found at levels of 2160 units/(kg sediment·km² of impervious area) and 87.8 units/(kg sediment·km street length); MP and TWP loadings are introduced here for the first time. The annual flux of MPs and TWPs were 7.8 × 10¹¹ and 4.1 × 10¹¹ units/(km²·year), respectively, and TWP emissions varied from 43.3 to 205.5 kg/day. SDRs can be sites to intercept MP pollution in urban areas. This study suggests that future research on MP monitoring in urban areas and design should consider both imperviousness and street length as important factors to normalize TWP contribution to urban pollution.

Microplastics are a pollutant of growing concern, capable of harming aquatic organisms and entering the food web. While freshwater microplastic research has expanded in recent years, much remains unknown regarding the sources and delivery pathways of microplastics in these environments. This review aims to address the scientific literature regarding the spatial and temporal factors affecting global freshwater microplastic distributions and abundances. A total of 75 papers, published through June 2021 and containing an earliest publication date of October 2014, was identified by a Web of Science database search. Microplastic spatial distributions are heavily influenced by anthropogenic factors, with higher concentrations reported in regions characterized by urban land cover, high population density, and wastewater treatment plant effluent. Spatial distributions may also be affected by physical watershed characteristics such as slope and elevation (positive and negative correlations with microplastic concentrations, respectively), although few studies address these factors. Temporal variables of influence include precipitation and stormwater runoff (positive correlations) and water flow/discharge (negative correlations). Despite these overarching trends, variations in study results may be due to differing scales or contributing area delineations. Thus, more rigorous and standardized spatial analytical methods are needed. Future research could simultaneously evaluate both spatial and temporal factors and incorporate finer temporal resolutions into sampling campaigns.

The deployment of aqueous film forming foams (AFFF) used for firefighting during emergencies and training often releases per- and polyfluoroalkyl substances (PFAS) into the environment. In October 2018, first responders in Providence, RI, USA applied an AFFF during a fuel spill. Due to the proximity of the incident to the upper reaches of Narragansett Bay (NB), an unknown quantity of gasoline and AFFF entered the estuary via surface runoff and stormwater drains. Water samples near the spill were collected approximately 15 h after the incident and analyzed for 24 PFAS. Minor increases in measured PFAS concentrations were observed relative to pre- and post-spill samples at monitoring sites near the incident, except 6:2-fluorotelomer sulfonate (6:2-FTS) that peaked post-spill (max 311 ng/L). After performing the total oxidizable precursor (TOP) assay on water samples and the AFFF concentrate, significant increases in perfluorocarboxylic acids (PFCAs) were observed. One compound, 6:2 fluorotelomer mercaptoalkylamido sulfonate (6:2-FTSAS), was identified as a major component of the AFFF used. Peak areas of 6:2-FTSAS and the degradation product 6:2-FTSAS-sulfoxide corresponded to observed increases in the TOP assay results and were useful as tracers of AFFF in surrounding waters. Elevated levels of PFAS at the time of sampling were limited to a confined area of the Providence River due to river flow and tidal action. Observed concentrations were also compared to hydrodynamic model results, and results confirmed rapid dissipation of AFFF components with distance from the spill. However, modeled results did not capture possible secondary releases of AFFF from local municipal stormwater and sewer infrastructure, as observational data suggest. The multiple lines of evidence of PFAS present in surface waters permitted a better assessment of the potential environmental impacts from products such as AFFF for which the chemical composition is largely unknown.

Wastewater and stormwater are both considered as critical pathways contributing microplastics (MPs) to the aquatic environment. However, there is little information in the literature about the potential influence of constructed wetlands (CWs), a commonly used wastewater and stormwater treatment system. This study was conducted to investigate the abundance and distribution of MPs in water and sediment at five CWs with different influent sources, namely stormwater and wastewater. The MP abundance in the water samples ranged between 0.4 ± 0.3 and 3.8 ± 2.3 MP/L at the inlet and from 0.1 ± 0.0 to 1.3 ± 1.0 MP/L at the outlet. In the sediment, abundance of MPs was generally higher at the inlet, ranging from 736 ± 335 to 3480 ± 4330 MP/kg dry sediment and decreased to between 19.0 ± 16.4 and 1060 ± 326 MP/kg dry sediment at the outlet. Although no significant differences were observed in sediment cores at different depth across the five CWs, more MPs were recorded in silt compared to sandy sediment which indicated sediment grain size could be an environmental factor contributing to the distribution of MPs. Polyethylene terephthalate (PET) fibres were the dominant polymer type found in the water samples while polyethylene (PE) and polypropylene (PP) fragments were predominantly recorded in the sediment. While the size of MPs in water varied across the studied CWs, between 51% and 64% of MPs in the sediment were smaller than 300 μm, which raises concerns about the bioavailability of MPs to a wider range of wetland biota and their potential ecotoxicological effects. This study shows that CWs can not only retain MPs in the treated water, but also become sinks accumulating MPs over time.

Recently, increasing attention has been paid to antibiotic resistance genes (ARGs) in urban stormwater runoff. However, there were little data on the diversity and distribution of ARGs associated with road sediments transported in runoff. The investigation of ARGs diversity showed that sulfonamide resistance genes (sul2 and sul3) occupied 61.7%–82.3% of total ARGs in runoff. The analysis of ARGs distribution in particulate matter (PM) implied that both tetQ and trbC existed mainly in PM with size of 150–300 μm, but other ARGs and mobile genetic elements (MGEs) were dominant in PM with size <75 μm. The discussion of potential hosts indicated that target genes (ermF, blaOXA1/blaOXA30, ermC, qnrA, sul2, tnpA-01, intI2, tetW, intI1, sul3, trbC) had the strongest subordinate relationship with Proteobacteria at phylum level and Enterobacter at genus level. The effect evaluation of ARGs distribution suggested that 13 kinds of ARGs were positively correlated with Pr/PS and Zeta potential, resulting in the more ARGs in PM with smaller size (<75 μm).

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 are continuously released into the terrestrial environment from sources where they are used and produced. These microplastics accumulate in soils, sediments, and freshwater bodies, and some are conveyed via wind and water to the oceans. The concentration gradient between terrestrial inland and coastal regions, the factors that influence the concentration, and the fundamental transport processes that could dynamically affect the distribution of microplastics are unclear. We analyzed microplastic concentration reported in 196 studies from 49 countries or territories from all continents and found that microplastic concentrations in soils or sediments and surface water could vary by up to eight orders of magnitude. Mean microplastic concentrations in inland locations such as glacier (191 n L⁻¹) and urban stormwater (55 n L⁻¹) were up to two orders of magnitude greater than the concentrations in rivers (0.63 n L⁻¹) that convey microplastics from inland locations to water bodies in terrestrial boundary such as estuaries (0.15 n L⁻¹). However, only 20% of studies reported microplastics below 20 μm, indicating the concentration in these systems can change with the improvement of microplastic detection technology. Analysis of data from laboratory studies reveals that biodegradation can also reduce the concentration and size of deposited microplastics in the terrestrial environment. Fiber percentage was higher in the sediments in the coastal areas than the sediments in inland water bodies, indicating fibers are preferentially transported to the terrestrial boundary. Finally, we provide theoretical frameworks to predict microplastics transport and identify potential hotspots where microplastics may accumulate.

Microplastic pollution has received considerable attention in marine systems, but recent work shows substantial plastic pollution also occurs in freshwater ecosystems. Most freshwater research has focused on large rivers and lakes, but small streams are the primary interface between land, where plastic is used, and drainage networks. We examined variation in the amount and form of plastic occurring in small streams spanning an urbanisation gradient. All streams contained microplastics with concentrations similar to that found in larger systems (up to 303 particles m−3 in water and 80 particles kg−1 in sediment). The most abundant types were fragments and small particles (63–500 μm). Chemical types of plastic were quite variable and often not predictable based on size, form and colour. Variation in microplastic abundance across streams was high, but only partially explained by catchment scale parameters. There was no relationship between human population density or combined stormwater overflows and microplastic abundance. Residential land cover was related to microplastic abundance, but explanatory power was low. Our results suggest local-scale factors may be more important than catchment-scale processes in determining microplastic pollution in small streams.