Abundance and distribution of tire and road wear particles in the Seine River, France.

Tire and road wear particles (TRWP) are formed at the frictional interface between tires and the road surface. Tire tread and road pavement materials are denser than water but can be washed from the road surface into receiving water bodies, ultimately depositing into sediment, soil, or other media depending on the receiving environment. However, the paucity of mass-based measurements has limited the knowledge on the nature and extent of environmental concentrations necessary for environmental risk assessment of TRWP. Surface water and sediment samples were collected from the Seine River, France to characterize TRWP concentration. Sample locations were established upstream, within, and downstream of a major metropolitan area (Paris); downstream of smaller urban areas; adjacent to undeveloped land; and near the confluence of the estuary. Surface water and sediment were collected from the left and right banks at each of the eight locations, including two duplicates, for a total of 18 samples. Additionally, three sediment traps were deployed near the mouth of the river to quantify the flux of TRWP to sediment. Retained solids and sediment samples were analyzed using a modified pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) method that minimized the matrix interferences in the samples thus improving the current ISO Technical Specification ISO/TS 21396 : 2017 for TRWP mass concentration by Py-GC/MS. TRWP concentration was alternatively estimated by separating the sediment into the <1.9 g cm-3 fraction and analyzing for tread-derived zinc content. TRWP concentrations estimated by zinc method were significantly higher than results from the modified Py-GC/MS method. TRWP and total zinc concentrations show a decreasing trend from available historical data.

Accelerated aging of tire and road wear particles by elevated temperature, artificial sunlight and mechanical stress - A laboratory study on particle properties, extractables and leachables.

Tire and road wear particles (TRWP) are generated in large quantity by automobile traffic on roads but their way of degradation in the environment is largely unclear. Laboratory experiments were performed on the effect of elevated temperature (simulating 2-3 years), sunlight exposure (simulating 0.5 years) and mechanical stress on the physical properties and chemical composition of TRWP and of cryo-milled tire tread (CMTT). No significant effects were observed of the applied mechanical stress on mean properties of pristine particles. After sunlight exposure up to 40 % in mass were lost from the TRWP, likely due to the loss of mineral incrustations from their surface. The chemical composition of TRWP and CMTT was characterized by determining 27 compounds, antioxidants (phenylene diamines), vulcanization agents (benzothiazoles and guanidines) and their transformation products (TPs). Extractables of TRWP (580-850 µg/g) were dominated by TPs, namely benzothiazolesulfonic acid (BTSA). CMTT showed much higher amounts of extractables (4600 µg/g) which were dominated by parent chemicals such as N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (6-PPD), diphenylguanidine (DPG) and mercaptobenzothiazole (MBT). Sunlight exposure affected the amount of extractables more strongly than elevated temperature, for TRWP (-45 % vs -20 %) and CMTT (-80 % vs -25 %) and provoked a clear shift from parent compounds to their TPs. After sunlight exposure extractables of TRWP were dominated by BTSA and DPG. Sunlight exposure drastically reduced the 6-PPD amount extracted from both, TRWP and CMTT (-93 %, -98 %), while its quinone (6-PPDQ) increased by around 1 % of the 6-PPD decrease, only. For many TPs, concentration in leachates were higher than in extracts, indicating ongoing transformation of their parent compounds during leaching. These results highlight that abiotic aging of TRWP leads to strong changes in their chemical composition which affect their particle properties and are of relevance for the environmental exposure to tire-related chemicals.

Abiotic oxidative transformation of 6-PPD and 6-PPD quinone from tires and occurrence of their products in snow from urban roads and in municipal wastewater.

The antiozonant N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6-PPD) is added to tires to increase their lifetime and is emitted with tire and road wear particles into the environment. Recently, one of its transformation products (TPs), 6-PPD quinone (6-PPDQ), has gained attention due to its toxicity towards coho salmon. In this study, the abiotic oxidative transformation of 6-PPD is investigated by a series of ozonation experiments in the lab followed by analysis of TPs using liquid chromatography-high resolution-mass spectrometry (LC-HRMS). A total of 38 TPs were detected and tentatively identified, which were formed either directly from 6-PPD or via 6-PPDQ as intermediate. A suspect screening by LC-HRMS showed 32 of these TPs to occur in snow collected from urban roads as surrogate of road-runoff, where 6-PPDQ, 4-aminodiphenylamine (4-ADPA), TP 213, and TP 249 were the most prominent besides 6-PPD. More than 90% of the total load of 6-PPD and its TPs was found in the particulate fraction of snow. Thus, retaining the particulate fraction of road runoff before its discharge into surface water would substantially reduce the emission of 6-PPD and many of its TPs. Some TPs prevailed in the water phase of the snow due to their higher polarity. A total of 13 TPs were detected by suspect screening in the dissolved phase of a wastewater treatment plant (WWTP) influent. Their total load was markedly enhanced during a day of snowmelt (approx. 1100 g/d) and rainfall (approx. 2000 g/d) compared to dry weather (approx. 190 g/d). 6-PPD and 6-PPDQ contributed to less than 1% to this total load in the water phase (estimated concentrations of max 0.1 µg/L). The elimination of the estimated total loads of 6-PPD related TPs from the water phase in WWTP ranged from 22 to 67% depending on weather conditions. Eventually TP 249, 4-ADPA and TP 259_2 dominated in WWTP effluent (estimated concentration from 0.5 up to 2 µg/L). Thus TP 249 and TP 259_2 are, likely, the most specific and stable TPs of 6-PPD to be determined in the environment.

Comprehensive characterization of tire and road wear particles in highway tunnel road dust by use of size and density fractionation.

Tire and road wear particles (TRWPs) are a major component of non-exhaust traffic emissions, but knowledge about their physico-chemical properties is limited. Road dust of a highway tunnel was fractionated by size and density, and fractions were analyzed for TRWPs, metals, seven tire tread indicator chemicals (benzothiazoles, 6-PPD and DPG) and effects in in-vitro bioassays. TRWP content in tunnel dust was very high (11-12%). The peak of the TRWP mass distribution was in the size fraction 20-50 µm, with 31-36% of the total TRWP mass and a content of up to 260 mg/g. The mass of organic tire constituents peaked in the smallest analyzed size fractions (<20 µm) with 35-55% of their total mass. They also peaked in the density fraction 1.3-1.7 g/cm³, indicating a lower TRWP density and a higher contribution of TP to TRWP (approx. 75%) than expected. Video-based shape analysis and SEM showed elongated particles, likely TRWPs, to be present in those size and density fractions ascribed to TRWPs by chemical analysis. But also irregular heteroagglomerates could be found. Solvent extracts of size and density fractions induced effects in bioassays indicative of the activation of the arylhydrocarbon receptor (AhR-CALUX) and the adaptive response to oxidative stress (AREc32). Similar comprehensive characterization of road dust from other sites may be needed to decide on whether TRWPs occurring in high concentrations in tunnel dust are suited as representative test materials for analytical purposes and TRWP fate studies.