Removal and fate of microplastics in permeable pavements: An experimental layer-by-layer analysis.

The increasing prevalence of microplastics (MP) in urban environments has raised concerns over their negative effects on ecosystems and human health. Stormwater runoff, and road dust and sediment, act as major vectors of these pollutants into natural water bodies. Sustainable urban drainage systems, such as permeable pavements, are considered as potential tools to retain particulate pollutants. This research evaluates at laboratory scale the efficiency of permeable interlocking concrete pavements (PICP) and porous concrete pavements (PCP) for controlling microplastics, including tire wear particles (TWP) which constitute a large fraction of microplastics in urban environments, simulating surface pollution accumulation and Mediterranean rainfall conditions. Microplastic levels in road dust and sediments and stormwater runoff inputs were 4762 ± 974 MP/kg (dry weight) and 23.90 ± 17.40 MP/L. In infiltrated effluents, microplastic levels ranged from 2.20 ± 0.61 to 5.17 ± 1.05 MP/L; while tire wear particle levels ranged between 0.28 ± 0.28 and 3.30 ± 0.89 TWP/L. Distribution of microplastics within the layers of PICP and PCP were also studied and quantified. Microplastics tend to accumulate on the pavements surface and in geotextile layers, allowing microplastic retention efficiencies from 89 % to 99.6 %. Small sized (< 0.1 mm) fragment shaped microplastics are the most common in effluent samples. The results indicate that permeable pavements are a powerful tool to capture microplastics and tire wear particles, especially by surface and geotextile layers. The study aims to shed light on the complex mobilisation mechanisms of microplastics, providing valuable insights for addressing the growing environmental concern of microplastic pollution in urban areas.

ArcDrain: A GIS Add-In for Automated Determination of Surface Runoff in Urban Catchments.

Surface runoff determination in urban areas is crucial to facilitate ex ante water planning, especially in the context of climate and land cover changes, which are increasing the frequency of floods, due to a combination of violent storms and increased imperviousness. To this end, the spatial identification of urban areas prone to runoff accumulation is essential, to guarantee effective water management in the future. Under these premises, this work sought to produce a tool for automated determination of urban surface runoff using a geographic information systems (GIS). This tool, which was designed as an ArcGIS add-in called ArcDrain, consists of the discretization of urban areas into subcatchments and the subsequent application of the rational method for runoff depth estimation. The formulation of this method directly depends on land cover type and soil permeability, thereby enabling the identification of areas with a low infiltration capacity. ArcDrain was tested using the city of Santander (northern Spain) as a case study. The results achieved demonstrated the accuracy of the tool for detecting high runoff rates and how the inclusion of mitigation measures in the form of sustainable drainage systems (SuDS) and green infrastructure (GI) can help reduce flood hazards in critical zones.

Influence of rainfall intensity and pollution build-up levels on water quality and quantity response of permeable pavements.

Permeable pavements are part of stormwater management practices known as sustainable urban drainage systems (SUDS). This study describes the influence of several environmental variables, such as the rainfall regime or the pollution build-up level, on the hydraulic and water quality performance of permeable pavements. Four infiltrometers with different configurations of pavement layers were used to study the influence of two rainfall regimes (Atlantic and Mediterranean) and two rainfall intensities (0.5 and 2.2mm/min). The influence of the progressive pollution build-up level was studied by dry sprinkling of road deposited sediments collected with a mechanical street sweeper with a dose of 5g/m2/d. The results show that permeable pavements retained a significant rainwater volume and improved the infiltrated water quality in terms of suspended solids, organic matter and nutrients when compared to the corresponding surface runoff potentially generated from an impervious pavement. The volume of rainwater retained inside them varied between 16 and 66% depending on the variables studied. The water infiltrated from permeable pavements subjected to a Mediterranean rainfall regime contained, in general, higher concentrations of organic matter (22 to 89mg Chemical Oxygen Demand/l) and nutrients (0.6 to 2.1mg Total Nitrogen/l and 0.05 to 0.45mg Total Phosphorus/l) than those under Atlantic regime. However, the latter infiltrated higher loadings in terms of mass. Nitrogen was the substance that infiltrated the most, reaching a 25% of the total mass of nitrogen deposited on the pavements surface. The concentration and mass loading in infiltrated water increased as the pollution build-up level did. The leachability of nutrients and organic matter was greater for high rainfall intensities. The results suggest that it is essential to carry out an adequate cleaning in dry conditions, especially when high intensity rainfall events are foreseen, because of its greater capacity to mobilize pollutants.

Characterization of wash-off from urban impervious surfaces and SuDS design criteria for source control under semi-arid conditions.

Knowledge about pollutant wash-off from urban impervious surfaces is a key feature for developing effective management strategies. Accordingly, further information is required about urban areas under semi-arid climate conditions at the sub-catchment scale. This is important for designing source control systems for pollution. In this study, a characterization of pollutant wash-off has been performed over sixteen months, at the sub-catchment scale for urban roads as impervious surfaces. The study was conducted in Valencia, Spain, a city with a Mediterranean climate. The results show high event mean concentrations for suspended solids (98mg/l), organic matter (142mgCOD/l, 25mgBOD5/l), nutrients (3.7mgTN/l, 0.4mgTP/l), and metals (0.23, 0.32, 0.62 and 0.17mg/l for Cu, Ni, Pb, and Zn, respectively). The results of the runoff characterization highlight the need to control this pollution at its source, separately from wastewater because of their different characteristics. The wash-off, defined in terms of mobilized mass (g/m2) fits well with both process-based and statistical models, with the runoff volume and rainfall depth being the main explanatory variables. Based on these results and using information collected from hydrographs and pollutographs, an approach for sizing sustainable urban drainage systems (SuDS), focusing on water quality and quantity variables, has been proposed. By setting a concentration-based target (TSS discharged to receiving waters <35mg/l), the results indicate that for a SuDS type detention basin (DB), an off-line configuration performs better than an on-line configuration. The resulting design criterion, expressed as SuDS volume per unit catchment area, assuming a DB type SuDS, varies between 7 and 10l/m2.

Analysis of monitoring programmes and their suitability for ecotoxicological risk assessment in four Spanish basins.

Data from four Spanish basin management authorities were analysed. Chemical and biological data from four Spanish basin management authorities were analysed, focusing on three consecutive years. Aims were to i) determine the chemicals most likely responsible for the environmental toxicological risk in the four Spanish basins and ii) investigate the relationships between toxicological risk and biological status in these catchments. The toxicological risk of chemicals was evaluated using the toxic unit (TU) concept. With these data we considered if the potential risk properly reflects the risk to the community or, alternatively, if new criteria should be developed to improve risk assessment. Data study revealed inadequacies in processing and monitoring that should be improved (e.g., site coincidence for chemical and biological sampling). Analysis of the chemical data revealed high potential toxicological risk in the majority of sampling points, to which metals were the main contributors to this risk. However, clear relationships between biological quality and chemical risk were found only in one river. Further investigation of metal toxicity may be necessary, and future analyses are necessary to accurately estimate the risk to the environment.