Abstract:
Urban road dust (URD) is a complex matrix of geogenic and anthropogenic particles, posing
significant ecotoxicological and human health risks. It contains heavy metals (Ba, Cd, Co, Cr, Cu,
Mo, Ni, Pd, Zn, etc.), polycyclic aromatic hydrocarbons (PAHs), phthalates and microplastics,
originating from vehicular emissions, industrial activities, pavement abrasion and atmospheric
deposition. This study collected road dust and slag samples from five locations representing
conventional roads and without tramlines, highways with high traffic, residential areas and a
waste slag heap from a ferrochromium industry in Wroclaw, Poland. Acute toxicity of the road
samples was assessed using Daphnia magna (LC50) which indicates the concentration of a
pollutant that causes 50% mortality in tested population. Although a few studies have examined
magnetic susceptibility (χ) and its spatial and seasonal variations in URD, no study has
investigated the association between toxicity and χ. This study was conducted to determine
whether the χ can be used as a tool for toxicity assessment. According to the results, both the
highest χ and the highest LC50 were detected in road dust samples from the same high-traffic
highway, despite the sample containing significantly low concentrations of typical magnetic
metals such as Fe, Ni and Co. This may be due to nanoscale magnetite (Fe₃O₄) generated from
brake and tire wear, which contributes to high χ while its minimal mass fraction can lead to
underestimation of total Fe content in bulk chemical analysis. Pearson’s correlation analysis
revealed no statistically significant correlation between LC50 and χ (r = 0.24, p = 0.697). The
former industrial slag heap, was characterized by the highest concentrations of Cr, Sb and Hg
compared to other sites, likely originating from ferrochromium slag, explaining its high toxicity
despite low magnetic susceptibility. The road with tramlines showed the elevated levels of Fe, Cd,
Cu and Ni, and the presence of these metals was possibly caused by wear of tram rails, in addition
to traffic-derived emissions. These findings indicate that magnetic susceptibility is not a
supporting tool for interpreting the toxicity in URD, while highlighting the significance of heavy
metals and organic pollutants (ex: poly aromatic hydrocarbons, phthalates, microplastics, etc.).
