Screening p-Phenylenediamine Antioxidants, Their Transformation Products, and Industrial Chemical Additives in Crumb Rubber and Elastomeric Consumer Products

Abstract

Recently, roadway releases of N,N′-substituted p-phenylenediamine (PPD) antioxidants and their transformation products (TPs) received significant attention due to the highly toxic 6PPD-quinone. However, the occurrence of PPDs and TPs in recycled tire rubber products remains uncharacterized. Here, we analyzed tire wear particles (TWPs), recycled rubber doormats, and turf-field crumb rubbers for seven PPD antioxidants, five PPD-quinones (PPDQs), and five other 6PPD TPs using liquid chromatography-tandem mass spectrometry. PPD antioxidants, PPDQs, and other TPs were present in all samples with chemical profiles dominated by 6PPD, DTPD, DPPD, and their corresponding PPDQs. Interestingly, the individual [PPDQ]/[PPD] and [TP]/[PPD] ratios significantly increased as total concentrations of the PPD-derived chemical decreased, indicating that TPs (including PPDQs) dominated the PPD-derived compounds with increased environmental weathering. Furthermore, we quantified 15 other industrial rubber additives (including bonding agents, vulcanization accelerators, benzotriazole and benzothiazole derivatives, and diphenylamine antioxidants), observing that PPD-derived chemical concentrations were 0.5−6 times higher than these often-studied additives. We also screened various other elastomeric consumer products, consistently detecting PPD-derived compounds in lab stoppers, sneaker soles, and rubber garden hose samples. These data emphasize that PPD antioxidants, PPDQs, and related TPs are important, previously overlooked contaminant classes in tire rubbers and elastomeric consumer products.

Transformation Products of Tire Rubber Antioxidant 6PPD in Heterogeneous Gas-Phase Ozonation: Identification and Environmental Occurrence

“…For 1,3-DMBA (a small aliphatic amine), although its high abundance in TWPs correlates well with its high environmental occurrence, we still note that there are potential sources of 1,3-DMBA other than as a 6PPD TP. 65 For example, it is reported as a potent stimulant used in dietary supplements. 66,67 TP 274/6PPDQ and TP 282b/6PPDQ peak area ratios were increased to 68 and 40 in roadway runoff versus 19 and 3 in TWP leachate, respectively (Figure 4d).…”

Establishing an In Vitro Model to Assess the Toxicity of 6PPD-Quinone and Other Tire Wear Transformation Products

“…Substituted para-phenylenediamines (PPDs), such as 6PPD, are a prominent class of synthetic antioxidants used in many commercial and industrial products, including tire rubber, to inhibit oxidation and corrosive reactions. 6PPD comprises ∼1% of tire rubber mass, and measured PPD additive concentrations exceed 25 μg/g in tire wear particles (TWPs) . Several PPDs present in crumb rubbers and consumer products are considered high production volume chemicals; in 2020, 6PPD production was 200,000 tons in China alone .…”

“…6PPD comprises ∼1% of tire rubber mass, and measured PPD additive concentrations exceed 25 μg/g in tire wear particles (TWPs) . Several PPDs present in crumb rubbers and consumer products are considered high production volume chemicals; in 2020, 6PPD production was 200,000 tons in China alone . Amino antioxidants including PPDs and their quinoid transformation products are now being recognized as pervasive environmental pollutants present in most environmental matrices including air, dust, water, and snow. − …”

“…7 Several PPDs present in crumb rubbers and consumer products are considered high production volume chemicals; 7 in 2020, 6PPD production was 200,000 tons in China alone. 7 Amino antioxidants including PPDs and their quinoid transformation products are now being recognized as pervasive environmental pollutants present in most environmental matrices including air, dust, water, and snow. 8−11 Induction of 6PPDQ mortality in aquatic species at concentrations measured in receiving waters (<2.85 μg/L) 12 has only been demonstrated in select teleost fish belonging to the Salmoninae family (coho salmon; rainbow trout, O. mykiss; brook trout, Salvelinus fontinalis; white spotted char, S. leucomaenis).…”

H/D Exchange Coupled with 2H-labeled Stable Isotope-Assisted Metabolomics Discover Transformation Products of Contaminants of Emerging Concern

“…Additionally, it should be noted that HRMS-based NTA is blind to stereochemistry and often regiochemistry, with metabolites isomers being included. Thus, accurate annotations should be done with references. − …”