Generation of nano- and micro-sized organic pollutant emulsions in simulated road runoff

A wide range of organic pollutants (OPs) are emitted from the road and traffic environment and transported with road runoff to receiving waters. To provide an understanding of the transport routes of OPs in the environment, an investigation was carried out with the aim to determine whether OPs are transported with nano- and microparticles in the form of emulsions. Tests were performed on simulated road runoff, using laboratory prepared mixtures of ultrapure water and specific polycyclic aromatic hydrocarbons (PAHs), alkylphenols (APs) and their ethoxylates (APEOs), phthalates, diesel oil (aliphatic hydrocarbons), with and without addition of humic acid (HA) and iron (Fe) colloids. The samples were analysed directly after mixing and after a few days of stabilisation for particle size distribution (PSD) and concentrations of particles in the size range 10 nm–100 μm, and zeta potential > \ub1 500 mV. Further, after long-term storage to achieve stabilisation, selected samples were investigated for the PSD and particle concentrations in the ranges 10 nm–2 μm, to determine whether stable emulsions had formed. The following simulation mixtures, both mixed and stabilised, were identified as potential emulsions: diesel, APs and APEOs, diesel with APs and APEOS, phthalates, and a mixture of all OPs with and without colloids. Measurements with the Zetasizer and Nanosight instruments imply that the majority of particles in the samples were found in the nano-range of 30–660 nm respectively, and a smaller portion of particles < 28% also measured with Coulter Counter were found to be micro-sized. Higher concentrations of the smallest nanoparticles were found in the mixture of all OPs without colloids added, than in the OP mixture with colloids added. The results indicate that the addition of colloids favours the formation of larger micro-sized emulsions that may break down with time into nano-sized particles. In the mixed samples, the number of micro-sized particles decreased, while the number of nanoparticles increased; this process may also occur in road runoff transportation systems during heavy rain events. This is the first study to indicate that emulsions of OPs may be formed in road runoff, and that emulsions may act as carriers of OPs in urban stormwater

Alternative sorption filter materials effectively remove non-particulate organic pollutants from stormwater

Urban runoff contains a mixture of both particulate and non-particulate organic pollutants (OPs). Hydrophobic OPs such as higher petroleum hydrocarbons, phthalates, and polycyclic organic hydrocarbons (PAHs) are not exclusively bound to particles, but also present in runoff in colloidal and truly dissolved forms. These hydrophobic compounds can also form nano- and microsized emulsions that may carry pollutants in stormwater. Hence, it is of great importance to develop treatment technologies such as sorption filters that can remove non-particulate OPs from contaminated stormwater. A pilot plant using column bed-filters of sand as a pre-filter, in combination with granulated activated carbon, Sphagnum peat or Pinus sylvestris bark, was used to investigate the removal of non-particulate OPs from urban stormwater. Samples from the filter effluents were collected weekly; during or after rain events; and during stress tests when incoming water was spiked with contaminated sediment and petrol or diesel. All sorption filters showed efficient reduction of aliphatic diesel hydrocarbons C16–C35, benzene, and the PAHs phenanthrene, fluoranthene, and pyrene during most of the operation time, which was 18\ua0months. During the stress test events, all sorption filters showed 100% reduction of PAH-16, petrol and diesel aliphatics C5–C35. All sorption filters released DOC and nanoparticles, which may explain some of the transportation of OPs through the filter beds. The recommendation is to use a combination of sand pre-filtration and all the studied sorption materials in stormwater filters in series, to achieve effective removal of different types of OPs. It is also important to improve the hydraulic conditions to obtain sufficient water flows through the filters

Hydrodynamic modelling of traffic-related microplastics discharged with stormwater into the G\uf6ta River in Sweden

Microplastics (MP) are transported from land-based sources from rivers to marine waters. However, there is currently little knowledge about MP fate from land sources to marine waters. Traffic is estimated to be one of the largest sources of MP; hence, stormwater is expected to be an important transportation route of MP to marine waters. The aim of this study was to investigate the effect of the size and density of tyre wear particles in road run-off on their fate in the Gota River in Sweden using hydrodynamic modelling. The model of the stretch of Gota River, Sweden\u27s largest river, passing through Gothenburg (Sweden\u27s second largest city) and out to the sea, was set up using MIKE 3 FM software. Literature data were used to define the MP characteristics: concentrations in stormwater, prevalent particle sizes, density of MP commonly occurring in road run-off and settling velocities. Results show that higher concentrations of MP are found on the south side of the river, compared with the north side, due to higher annual average daily traffic loads along the south side of the river. The mixing processes in the river and the MP concentrations were generally influenced by the vertical water density gradient caused by saline water from the Kattegat strait. While most MP with higher density and larger size settle in the river, smaller MP with density close to 1.0 g/cm(3) do not settle in the river and therefore reach the Kattegat strait and the marine environments. Further research is needed to describe the fate and transport of microplastics in the stormwater system, including treatment facilities, i.e. biofouling, aggregation, degradation and/or further fragmentation and settling

Organic pollutants, nano- and microparticles in street sweeping road dust and washwater

Road areas are pollution hotspots where many metals, organic pollutants (OPs) and nano/microparticles accumulate before being transported to receiving waters. Particles on roads originate from e.g. road, tyre and vehicle wear, winter road maintenance, soil erosion, and deposition. Street sweeping has the potential to be an effective and affordable practice to reduce the occurrence of road dust, and thereby the subsequent spreading of pollutants, but there is currently little knowledge regarding its effectiveness. In this paper we investigate the potential of street sweeping to reduce the amounts of OPs and nano/microparticles reaching stormwater, in a case study sampling road dust and washwater from a street sweeping machine, road dust before and after sweeping, and stormwater. The compound groups generally found in the highest concentrations in all matrices were aliphatics C5–C35\ua0>\ua0phthalates\ua0>\ua0aromatics C8–C35\ua0>\ua0PAH-16. The concentrations of aliphatics C16–C35\ua0and PAHs in washwater were extremely high at\ua0≤\ua053,000\ua0\ub5g/L and\ua0≤\ua0120\ua0\ub5g/L, respectively, and the highest concentrations were found after a 3-month winter break in sweeping. In general, fewer aliphatic and aromatic petroleum hydrocarbons and PAHs were detected in road dust samples than in washwater. The relative composition of the specific PAH-16 suggests tyre wear, vehicle exhausts, brake linings, motor oils and road surface wear as possible sources. The study indicates that many of the hydrophobic compounds quantified in washwater are attached to small particles or truly dissolved. The washwater contains a wide range of small particles, including nanoparticles in sizes from just below 1\ua0nm up to 300\ua0nm, with nanoparticles in the size range 25–300\ua0nm present in the highest concentrations. The results also indicated agglomeration of nanoparticles in the washwater. The street sweeping collected a large amount of fine particles and associated pollutants, leading to the conclusion that washwater from street sweeping needs to be treated before disposal

Traffic-related microplastic particles, metals, and organic pollutants in an urban area under reconstruction

In urban environments, particularly areas under reconstruction, metals, organic pollutants (OP), and microplastics (MP), are released in large amounts due to heavy traffic. Road runoff, a major transport route for urban pollutants, contributes significantly to a deteriorated water quality in receiving waters. This study was conducted in Gothenburg, Sweden, and is unique because it simultaneously investigates the occurrence of OP, metals, and MP on roads and in stormwater from an urban area under reconstruction. Correlations between the various pollutants were also explored. The study was carried out by collecting washwater and sweepsand generated from street sweeping, road surface sampling, and flow-proportional stormwater sampling on several occasions. The liquid and solid samples were analyzed for metals, polycyclic aromatic hydrocarbons (PAH), oxy-PAH, aliphatics, aromatics, phthalates, and MP. The occurrence of OP was also analyzed with a non-target screening method of selected samples. Microplastics, i.e. plastic fragments/fibers, paint fragments, tire wear particles (TWP) and bitumen, were analyzed with a method based on density separation with sodium iodide and identification with a stereo microscope, melt-tests, and tactile identification. MP concentrations amounted to 1500 particles/L in stormwater, 51,000 particles/L in washwater, and 2.6 7 106 particles/kg dw in sweepsand. In stormwater, washwater and sweepsand, MP ≥20 μm were found to be dominated by TWP (38%, 83% and 78%, respectively). The results confirm traffic as an important source to MP, OP, and metal emissions. Concentrations exceeding water and sediment quality guidelines for metals (e.g. Cu and Zn), PAH, phthalates, and aliphatic hydrocarbons in the C16–C35 fraction were found in most samples. The results show that the street sweeper collects large amounts of polluted materials and thereby prevents further spread of the pollutants to the receiving stormwater

Adsorbents for the removal of contaminants from stormwater

Contaminated urban runoff is a major cause of concern for water quality and aquatic ecosystems worldwide. Recent research shows that stormwater often contains metals and emerging organic contaminants at levels exceeding environmental quality standards. To comply with quality guidelines for receiving waters, stormwater treatment is considered to be critical. Filtration of stormwater through an adsorptive material is one of the most promising techniques for removal of particulate, colloidal and dissolved pollutants. The aim of this research was to use laboratory-based experiments to determine the removal capacity of selected sorbents for organic pollutants and metals found in stormwater. The ideal sorbent should be efficient in removing pollutants, inexpensive, abundant and easily accessible. A variety of materials, including minerals, wood- and bark-based media, were subjected to batch tests. By comparing the capacity of a range of sorbents under identical laboratory conditions, the most promising sorbent can be identified.The study revealed that cellulose and minerals adsorbed organic pollutants to a negligible degree. However, these materials may serve as efficient adsorbents of metals because of their potential to attract cations. Sawdust and bark efficiently and promptly sorbed organic compounds, whereas their capacity for metals was found to be low. Activated carbon produced from sewage sludge exhibited substantially higher adsorption capacity for organic pollutants than the wood- and bark-based media tested

Sources and fluxes of organic contaminants in urban runoff

Urban runoff quality is recognized as one of the most significant pressures on aquatic ecosystems worldwide. Research into pollutants in urban runoff has traditionally focused on nutrients, suspended solids and metals and consequently knowledge of anthropogenic organic pollutants is limited. The aim of this research was to investigate the occurrence and identify the sources of certain selected organic contaminants in urban runoff, and to evaluate tools for predicting the fluxes of these pollutants in urban catchment areas. Alkylphenols and phthalates were selected for further study since they are used in large quantities and emissionsof these compounds are likely to end up in urban runoff.The occurrence of alkylphenols and phthalates was investigated in urban snow, stormwater and sediment. In general, 4-nonylphenol showed high concentrations and detection frequencies compared to most other alkylphenols. Among the phthalates, diisononyl phthalate (DINP) was detected at the highest concentrations in all matrices, followed by diisodecyl phthalate (DIDP) and di(2-ethylhexyl) phthalate (DEHP). Nonylphenol, octylphenol and DEHP were repeatedly detected in stormwater and snow at concentrations exceeding the European water quality standards. This suggests that measures to reduce the discharge of anthropogenic substances to urban areas are necessary to achieve good water status. Substance flow analysis (SFA) was used to map the sources and quantify the loads of phthalates and nonylphenols in urban catchment areas. The calculated loads of thecontaminants were in agreement with measured loads in a studied catchment area and SFA was thus considered efficient for identifying the most important sources of phthalates and nonylphenols. The emission factors used in the calculation of the pollutant loads were also used in a process-based stormwater quality model for predicting nonylphenol and phthalate concentrations in runoff. The model revealed low predictive power; the simulatedconcentrations were generally one magnitude higher than the measured concentrations. In future studies, it is recommended to link the outcomes from the SFA to a fate model. This integrated model would provide a holistic overview of the sources and sinks of pollutants in urban catchment areas and could be used to evaluate both source control and end-of-pipe mitigation practices

Phthalates and Nonylphenols in Stormwater: A Substance Flow Analysis

The occurrence of several phthalates and nonylphenol in water environments is highly undesiredbecause of their negative effects on aquatic organisms. The objectives of this study were to identifyemission sources of phthalates, nonylphenol and its ethoxylates (NP/EOs) in urban stormwater, and toquantify the substance fluxes from the source to the stormwater system, using the methodology ofsubstance flow analysis (SFA). The flow analysis showed that phthalates are mainly emitted fromvehicles and coated roofing material, whereas the major NP/EOs sources are vehicles and concrete. It wasestimated that approximately 5.5 kg of four selected phthalates and more than 400 g of NP/EOs areemitted annually to stormwater in the studied area. The SFA approach presented in this study could beapplied in urban catchments of various character to estimate fluxes of unwanted water contaminants

Adsorbents for the removal of contaminants from stormwater

Contaminated urban runoff is a major cause of concern for water quality and aquatic ecosystems worldwide. Recent research shows that stormwater often contains metals and emerging organic contaminants at levels exceeding environmental quality standards. To comply with quality guidelines for receiving waters, stormwater treatment is considered to be critical. Filtration of stormwater through an adsorptive material is one of the most promising techniques for removal of particulate, colloidal and dissolved pollutants. The aim of this research was to use laboratory-based experiments to determine the removal capacity of selected sorbents for organic pollutants and metals found in stormwater. The ideal sorbent should be efficient in removing pollutants, inexpensive, abundant and easily accessible. A variety of materials, including minerals, wood- and bark-based media, were subjected to batch tests. By comparing the capacity of a range of sorbents under identical laboratory conditions, the most promising sorbent can be identified.The study revealed that cellulose and minerals adsorbed organic pollutants to a negligible degree. However, these materials may serve as efficient adsorbents of metals because of their potential to attract cations. Sawdust and bark efficiently and promptly sorbed organic compounds, whereas their capacity for metals was found to be low. Activated carbon produced from sewage sludge exhibited substantially higher adsorption capacity for organic pollutants than the wood- and bark-based media tested

Phthalates and Nonylphenols in Stormwater: A Substance Flow Analysis

The occurrence of several phthalates and nonylphenol in water environments is highly undesiredbecause of their negative effects on aquatic organisms. The objectives of this study were to identifyemission sources of phthalates, nonylphenol and its ethoxylates (NP/EOs) in urban stormwater, and toquantify the substance fluxes from the source to the stormwater system, using the methodology ofsubstance flow analysis (SFA). The flow analysis showed that phthalates are mainly emitted fromvehicles and coated roofing material, whereas the major NP/EOs sources are vehicles and concrete. It wasestimated that approximately 5.5 kg of four selected phthalates and more than 400 g of NP/EOs areemitted annually to stormwater in the studied area. The SFA approach presented in this study could beapplied in urban catchments of various character to estimate fluxes of unwanted water contaminants