Abstract
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 × 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.
Highlights
In high-density traffic areas, microplastics (MP) (Knight et al, 2020), metals (Huber et al, 2016; Kabir et al, 2014), polycyclic aromatic hydrocarbons (PAH), and other organic pollutants (OP) (Markiewicz et al, 2017) are emitted in large amounts
The high concentrations of MP, tire wear particles (TWP), metals, PAH, alkylated PAH, aliphatics >C16–C35, and phthalates found in the washwater and sweepsand indicate that street sweeping may be an effective measure to reduce the spread of TWP and pollutants
Similar results were found by Pramanik et al (2020), who did not analyze TWP, but found that MP were present in all stormwater samples and that microfibers were most frequently found among the analyzed MP (50%)
Summary
In high-density traffic areas, microplastics (MP) (Knight et al, 2020), metals (Huber et al, 2016; Kabir et al, 2014), polycyclic aromatic hydrocarbons (PAH), and other organic pollutants (OP) (Markiewicz et al, 2017) are emitted in large amounts. Microplastics are generally defined as solid particles insoluble in water, within the size range 1–5000 μm, and composed of synthetic polymers with thermoplastic or thermoset properties. Due to their chemical and physical properties, tire wear particles (TWP) are often included in the microplastic definition (Andrady, 2011; GESAMP, 2016; Verschoor et al, 2016). Similar to the release of MP, the release of metals depends on driving behavior (i.e. speed, use of brakes, start-stop), traffic intensity, surface structure, and road maintenance (Müller et al, 2020)
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