Car and truck tire wear particles in complex environmental samples – A quantitative comparison with “traditional” microplastic polymer mass loads

Tire wear particles (TWP) are assumed to be the most dominant source of environmental microplastics (MP). Besides rubber components around 60% of tires are additives such as filling material and various chemicals added for vulcanization. The inevitably released TWP in daily traffic are therefore considered a threat to the ecosystem. Nevertheless, published studies on MP mass loads often exclude elastomers. Data concerning composition and concentrations of TWP compared to prominent "traditional" MP polymers, such as polyethylene, polypropylene, poly(ethylene terephthalate) and poly(vinyl chloride), are missing. Identification and quantification of TWP was implemented in an existing pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) method for MP determination. An approach to differentiate between car and truck tire wear and to quantify their respective mass loads is presented. Complex environmental samples such as road dust, fresh water and marine sediments, blue mussels, and marine salts were partly retrospectively analyzed using Py-GC/MS. The results showed ratios of car to truck tire wear up to 16 to 1 and underline the dominance of car compared to truck tire wear mass loads in all analyzed samples. Even though some retrospective data sets might be affected by suboptimal density separation conditions (NaBr, ρ = 1.5 g/cm), TWP concentrations in road dust clearly exceeded those of "traditional" MP (Ø 5 g TWP vs 0.3 g MP per kg road dust (dry weight). Samples included in this study, which were archived further away from TWP sources such as roads, reflected decreasing TWP concentrations (Ø 24 μg TWP vs. 107 μg MP per kg sediment (dry weight); Ø 126 μg TWP vs. 378 μg MP per kg marine salt) or were no longer present (blue mussels), while "traditional" polymers were still ubiquitously distributed.