Examining magnetic susceptibility as a proxy for microplastic pollution in granulometric fractions of road dust: A case study in Warsaw, Poland

The main objective was to assess the contamination of road dust (RD) with microplastics (MPs) and plasticizers and to investigate whether magnetic susceptibility (χ) can indicate MP pollution. The study employed laser direct infrared (LDIR) imaging with a quantum cascade laser (QCL), magnetic susceptibility measurement using the MFK1-FA Kappabridge, and gas chromatography-mass spectrometry (GC-MS). RD collected in Warsaw was divided into the fractions: 0.8 mm (1-0.8 mm), 0.6 mm (0.8-0.6 mm), 0.4 mm (0.6-0.4 mm), 0.2 mm (0.4-0.2 mm), and <0.2 mm. MP analysis revealed materials such as polypropylene and rubber, with the highest number of MPs (51,660 particles) in the <0.2 mm. RD was analyzed for bisphenol A and phthalic acid esters, with the highest concentrations of DEHP and DBP in the <0.2 mm fraction. χ were highest in the fraction <0.2. Strong correlations were found between χ and DEHP (0.78), DBP (0.96), and BPA (0.89) for WAW2 and between χ and MPs (0.97) for WAW4. Strong correlations were also observed for the 0.2 mm and <0.2 mm fractions between χ and DBP. The main conclusion is that χ strongly correlates with DEHP and DBP in the <0.2 mm fraction and with MPs in the 0.2 mm fraction. This study is novel due to the limited research on using χ as a screening method for MP pollution, making it a promising, cost-effective tool for pollution monitoring. The results could support the development of simplified monitoring tools, helping to assess human exposure risks and improve environmental management strategies.