Chemical mapping of tire and road wear particles for single particle analysis

Michael Kovochich; Monty Liong; Jillian A Parker; Su Cheun Oh; Jessica P Lee; Luan Xi; Marisa L Kreider; Kenneth M Unice

doi:10.1016/j.scitotenv.2020.144085

Chemical mapping of tire and road wear particles for single particle analysis

Sci Total Environ. 2021 Feb 25:757:144085. doi: 10.1016/j.scitotenv.2020.144085. Epub 2020 Nov 26.

Authors

Michael Kovochich¹, Monty Liong², Jillian A Parker³, Su Cheun Oh⁴, Jessica P Lee², Luan Xi⁴, Marisa L Kreider⁵, Kenneth M Unice⁶

Affiliations

¹ Cardno ChemRisk, 30 North LaSalle Street Suite 3910, Chicago, IL 60602-2590, United States of America.
² Exponent, 149 Commonwealth Drive, Menlo Park, CA 94025, United States of America.
³ Cardno ChemRisk, 65 Enterprise Drive Suite 150, Aliso Viejo, CA 92656, United States of America.
⁴ Exponent, Unit 802-803, 12 Science Park West Avenue, Shatin, New Territories, Hong Kong.
⁵ Cardno ChemRisk, 20 Stanwix Street Suite 505, Pittsburgh, PA 15222, United States of America.
⁶ Cardno ChemRisk, 20 Stanwix Street Suite 505, Pittsburgh, PA 15222, United States of America. Electronic address: Ken.Unice@cardno.com.

PMID: 33333431
DOI: 10.1016/j.scitotenv.2020.144085

Abstract

Tire and road wear particles (TRWP), which are comprised of polymer-containing tread with pavement encrustations, are generated from friction between the tire and the road. Similar to environmentally dispersed microplastic particles (MP), the fate of TRWP depends on both the mass concentration as well as individual particle characteristics, such as particle diameter and density. The identification of an individual TRWP in environmental samples has been limited by inherent characteristics of black particles, which interfere with the spectroscopic techniques most often used in MP research. The purpose of this research was to apply suitable analytical techniques, including scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping, to characterize the specific physical and chemical properties of individual TRWP. Detailed elemental and organic surface maps were generated for numerous samples including bulk tread material, cryogenically milled tire tread particles, and TRWP generated from two separate road simulator methods. Key physical and chemical characteristics of TRWP for single particle identification included (1) elongated/round shape with variable amounts of mineral encrustation, (2) elemental surface characteristics including co-localization of (S + Zn/Na) ± (Si, K, Mg, Ca, and Al), and (3) co-localization of organic surface markers, such as C₆H₅⁺ and C₇H₇⁺. Comparisons of TRWP with other polymeric (polystyrene) and non-polymeric (carbon black) particle types demonstrated that a combination of physical and chemical markers is necessary to identify TRWP. Addition of a density separation step to the single particle analysis techniques allowed for the determination of average primary TRWP particle size (34 μm by number distribution and 49 μm by volume distribution) and aspect ratio (65% of TRWP with an aspect ratio > 1.5). The use of chemical mapping techniques, such as SEM/EDX and/or ToF-SIMS mapping as demonstrated herein, can support future research efforts that aim to identify complex MP.

Keywords: Chemical mapping; EDX; Microplastic; Single particle analysis; Tire and road wear particle; ToF-SIMS.