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.

BTEX and PAH contributions to Lake Kinneret water: a seasonal-based study of volatile and semi-volatile anthropogenic pollutants in freshwater sources.

Benzene , toluene, ethylbenzene, and xylenes (BTEX) BTEX molecules are toxic components, ubiquitous in the environment, often found in concentrations- a few orders of magnitude higher than the well-studied PAHs levels. This fact is demonstrated in either crude oil, fuels, water, and air samples. BTEX studies focus mainly on the airborne levels of these molecules, while their waterborne presence is understudied. In this study, BTEX levels were assessed at Lake Kinneret, Israel. As a result, 0-1.5 ppb of BTEX was recorded in five stations (2021-2022). Elevated BTEX levels (3-10 ppb) were recorded at the northern rivers nourishing this lake, implying the existence of remote polluting sources. Transect air samplings of BTEX conducted at the lake next to the bathing season of 2021 revealed airborne BTEX levels between 0.8 and 10 µg/m3, peaking up close to the bathing season, yet inconsistent with the BTEX water level trend. Lake water samples collected next to Tiberias city outfalls following the "Carmel" rainstorm showed elevated concentrations of BTEX up to 35 ppb and PAHs up to 0.47 ppb with an urban isotopic signal. The remote station's PAHs levels were less than one order of magnitude, with a distinct rural isotopic signal. Additionally, a human-specific microbial marker revealed increased sewer contributions at some of the urbansites. The results of this study show that a wide area dispersion of low atmospheric BTEX levels exists in the lake's perimeter. The dispersion rate is most likely influenced by season-based factors, e.g., motors and biomass fires. The unstudied waterborne BTEX levels in this lake are influenced by rivers, city runoff, and other yet unknown factors that may contribute to the sedimentation of these components. This process may result in a chronic pollution state. Despite the BTEX's medium-low solubility and high volatility, its under-evaluated waterborne transportation may lead to high toxic levels following bioaccumulation.

The atmospheric microplastics deposition contributes to microplastic pollution in urban waters.

Identifying and understanding the potential sources delivering microplastics into the urban water environment is imperative for microplastic pollution control. However, how atmospheric deposition contributes to microplastic pollution in the urban water environment is unclear. Therefore, this study investigated the contribution of atmospheric deposition to microplastic pollution in urban waters based on the analysis of the atmospheric deposition characteristics in the urban area. The results showed that microplastic deposition fluxes during wet weather and dry weather varied from 1.1 × 103±0.06×103 to 3.5 × 103±0.3 × 103 particles/m2/day and 0.91×103±0.09×103 to 1.6 × 103±0.1 × 103 particles/m2/day, respectively. The microplastics deposition flux showed moderate to strong correlations to atmospheric particulate matter concentrations, especially the PM2.5 concentration (R2 = 0.76-0.93), suggesting the regularly monitored PM2.5 concentration might be served as an indicator for microplastics deposition flux estimation. The deposited microplastics were mainly transparent fragments with an average size of 51-67 µm. Polyethylene and polypropylene were the most abundant plastic polymer, followed by polyethylene terephthalate and polyamide. The comparison of microplastics collected during different weather conditions suggested that rain events could increase microplastics deposition fluxes when air quality conditions are similar. Particularly, rains promoted the deposition of fibrous microplastics as well as smaller microplastics. The estimated daily microplastics deposition in the whole city region suggested more microplastics were deposited in summer and winter. The total quantity of microplastics deposited in the urban environment could reach 1.7-12 times of those discharged from treated wastewater. Among them, 10% would directly deposit to urban waters in the studied city region, while the others may also enter the urban waters through runoff. The results of this study highlighted that the atmospheric microplastics deposition is an important source for microplastics, especially smaller ones, to enter the urban waters, which could not be ignored during microplastics pollution control.

Assessing the genotoxic potential of freshwater sediments after extensive rain events - Lessons learned from a case study in an effluent-dominated river in Germany.

Wastewater treatment plant effluents and releases from rainwater overflow basins can contribute to the input of genotoxic micropollutants in aquatic ecosystems. Predominantly lipophilic genotoxic compounds tend to sorb to particulate matter, making sediment a source and a sink of pollution. Therefore, the present study aims to investigate the genotoxic potential of freshwater sediments (i) during the dry period and (ii) after extensive rain events by collecting sediment samples in one small anthropogenically impacted river in Germany up- and downstream of the local wastewater treatment plant. The Micronucleus and Ames fluctuation assays with Salmonella typhimurium strains TA98, TA100, YG1041, and YG1042 were used to assess the genotoxic potential of organic sediment extracts. For evaluation of possible genotoxicity drivers, target analysis for 168 chemical compounds was performed. No clastogenic effects were observed, while the genotoxic potential was observed at all sampling sites primarily driven by polycyclic aromatic hydrocarbons, nitroarenes, aromatic amines, and polycyclic heteroarenes. Freshwater sediments' genotoxic potential increased after extensive rain events due to sediment perturbation and the rainwater overflow basin release. In the present study, the rainwater overflow basin was a significant source for particle-bound pollutants from untreated wastewater, suggesting its role as a possible source of genotoxic potential. The present study showed high sensitivity and applicability of the bacterial Salmonella typhimurium strains YG1041 and YG1042 to organic sediment extracts to assess the different classes of genotoxic compounds. A combination of effect-based methods and a chemical analysis was shown as a suitable tool for a genotoxic assessment of freshwater sediments.

Rare earth elements in surface specific urban runoff in Northern Beijing.

Rare earth elements (REEs) have been increasingly diffused to the environment through mining activities and the extensive use in modern commodities, vehicular activities, coal burning and various environmental and agricultural applications. Studies of REEs in urban environments are limited with no data on REEs in urban runoff. To investigate the concentration and distribution of REEs, a total of 150 runoff samples were collected from trafficked areas, rooftops and residential parking lots in a moderate to densely populated area in Beijing, China. The runoff samples were separated into dissolved and particulate phases and analyzed by ICP-MS. The REEs were mainly (>80%) found in the runoff particulate material. The sum of REEs (ΣREE) total concentrations in urban stormwater runoff samples ranged from 0.16 to 185 µg/l. The observed mean total concentration of ΣREE in the runoff samples were 3-14 folds higher and dissolved fractions 1.5 to 6 times higher than published concentrations for recipients such as sewage channels and rivers. The distribution of REEs in runoff was dominated by light REE. Cluster analysis and Pearson's correlations revealed a strong association between the individual REEs pointing to a similar source. Higher Ce concentrations compared to other REEs indicated strong influence from traffic emission particulates. The La/Sm (5.90-8.05), La/Ce (0.53-0.58) and Ce/Yb (31.0-42.7) ratios pointed to REE sources from traffic emissions and coal burning thus defining an urban fingerprint.

Evaluating the Capability of Grass Swale for the Rainfall Runoff Reduction from an Urban Parking Lot, Seoul, Korea.

This field study elaborates the role of grass swale in the management of stormwater in an urban parking lot. Grass swale was constructed by using different vegetations and local soil media in the parking lot of Mapu-gu Seoul, Korea. In this study, rainfall runoff was first retained in soil and the vegetation layers of the grass swale, and then infiltrated rainwater was collected with the help of underground perforated pipe, and passed to an underground storage trench. In this way, grass swale detained a large amount of rainwater for a longer period of time and delayed peak discharge. In this field study, various real storm events were monitored and the research results were analyzed to evaluate the performance of grass swale for managing rainfall runoff in an urban area. From the analysis of field experiments, grass swale showed the significant rainfall runoff retention in different rain events. Grass swale markedly reduced total rainfall runoff volume and peak flow during the small storm events of intensity about 30 mm/h. From the analysis, on average rainfall runoff retention from the grass swale was found around 40 to 75% during the various small rain events. From the results, we can say that grass swale is a stormwater mitigation practice which can help avoid flash flooding problems in urban areas.

Role of rain intensity and soil colloids in the retention of surfactant-stabilized silver nanoparticles in soil.

Undisturbed outdoor lysimeters containing arable loamy sand soil were used to examine the influence of either heavy rain events (high frequency of high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP). In addition, the AgNP-soil associations within the Ap horizon were analyzed by means of particle-size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis-detection and inductively coupled plasma mass spectrometer (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the Ap horizon, which was attributed to the high pore water flow velocities and to the mobilization of AgNP-soil colloid associations. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil. In particular, water-dispersible colloids (WDC) in the size range of 0.45-0.1 µm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids (mainly composed of Al, Fe, Si, and organic matter). These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homo-aggregated, and small AgNP probably due to dissolution.