Use of a Deuterated Internal Standard with Pyrolysis-GC/MS Dimeric Marker Analysis to Quantify Tire Tread Particles in the Environment

Abstract

Pyrolysis(pyr)-GC/MS analysis of characteristic thermal decomposition fragments has been previously used for qualitative fingerprinting of organic sources in environmental samples. A quantitative pyr-GC/MS method based on characteristic tire polymer pyrolysis products was developed for tread particle quantification in environmental matrices including soil, sediment, and air. The feasibility of quantitative pyr-GC/MS analysis of tread was confirmed in a method evaluation study using artificial soil spiked with known amounts of cryogenically generated tread. Tread concentration determined by blinded analyses was highly correlated (r2 ≥ 0.88) with the known tread spike concentration. Two critical refinements to the initial pyrolysis protocol were identified including use of an internal standard and quantification by the dimeric markers vinylcyclohexene and dipentene, which have good specificity for rubber polymer with no other appreciable environmental sources. A novel use of deuterated internal standards of similar polymeric structure was developed to correct the variable analyte recovery caused by sample size, matrix effects, and ion source variability. The resultant quantitative pyr-GC/MS protocol is reliable and transferable between laboratories.

Comparison of Tire and Road Wear Particle Concentrations in Sediment for Watersheds in France, Japan, and the United States by Quantitative Pyrolysis GC/MS Analysis

“…15,17,19−21 In the case of the org-Zn marker, 22 recent research has shown that the dichloromethane extraction does not reliably exclude inorganic ZnO from partitioning from tread polymer into the solvent. 23 Inorganic Zn, while found in tread polymer, is also found in deicing salts, combustion exhaust, galvanized metal in automobiles, road barriers, fuel, oil, and brake linings, all of which can contribute to road runoff. 10,24−26 In one detailed study of an urban highway site with average daily traffic count of 150 000 vehicles, total zinc was found to be present primarily in the dissolved phase, 27 further suggesting that zinc-related markers are unlikely to be reliable markers for TRWP in the environment, despite the relatively high content of Zn in tread polymer (about 1%).…”

“…5 Recently, a marker using pyrolysis products of tread polymers was developed for quantifying TRWP in environmental media. 23,28,29 In pyrolysis analysis, a sample is thermally decomposed under high temperature, and the characteristic fragments of tread polymers are quantified by a mass selective detector, such as gas chromatography−mass spectroscopy (GC/MS). This marker offers high specificity to tread, and stability in the environment due to high abundance of tread polymer in TRWP, which means that the marker will remain a component of TRWP during environmental transport; these characteristics were limited with previous markers used to measure tread in sediment.…”

“…39,40 Total polymer concentration was converted to tread polymer concentration assuming a 15% market average styrene content for SBR+BR used in tread. 23,29 Additionally, polymer fractions of 44, 45, and 50% were assumed for SBR, NR, and SBR+BR +NR, respectively. 23 TRWP concentration was calculated from the tread polymer content using a 1:1 ratio observed for the ratio of the mass of mineral encrustations to the mass of tread polymer.…”

“…23,29 Additionally, polymer fractions of 44, 45, and 50% were assumed for SBR, NR, and SBR+BR +NR, respectively. 23 TRWP concentration was calculated from the tread polymer content using a 1:1 ratio observed for the ratio of the mass of mineral encrustations to the mass of tread polymer. 5 The method detection limit for TRWP in soil and sediment is 28 μg/g d.w. 23 QA/QC.…”

“…42 The ANOVA analyses were performed after log e transformation to meet the homogeneity of variance assumption of the test. Previously reported field duplicate sediment samples at two locations 23 were averaged before statistical analysis for inclusion in this analysis.…”