New Evidence of Rubber-Derived Quinones in Water, Air, and Soil

Abstract

p-Phenylenediamines (PPDs) have been extensively used in the rubber industry and found to be pervasive in various environmental compartments for decades, while their transformation products and associated ecological and human health risks remain largely unknown. Herein, we developed and implemented a mass spectrometry-based platform combined with self-synthesized standards for the investigation of rubber-derived quinones formed from PPD antioxidants. Our results demonstrated that five quinones are ubiquitously present in urban runoff, roadside soils, and air particles. All of the identified sources are closely related to mankind's activities. Among the identified quinones, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone has been recently found to be highly toxic, causing acute mortality of coho salmon in the Pacific Northwest. Ultrahigh-performance liquid chromatography coupled with triple quadrupole mass spectrometry was then applied for quantification of the five quinones and their corresponding PPD antioxidants. The results revealed interesting distinct distribution and concentration patterns of PPD-derived quinones in different environmental matrices. Daily intake rates of these quinones in a compact city of Hong Kong were estimated to be varied from 1.08 ng/(kg·day) for adults to 7.30 ng/(kg·day) for children, which were higher than the exposure levels of their parent compounds. Considering the prevalence of the use of rubber products, the outcome of this study strongly suggests for additional toxicological studies to investigate potential ecological and human health risks of the newly discovered quinones.

Keywords: 6PPD-quinone; human health; p-phenylenediamines; rubber-derived quinones.

Figure 1

Extracted ion chromatograms and MS/MS spectra of [M + H]⁺ ions of 6PPD-quinone (a), IPPD-quinone (b), CPPD-quinone (c), DPPD-quinone (d), and DTPD-quinone (e) using UHPLC Orbitrap MS analysis.

Figure 2

Total concentration and composition profiles of PPDs and PPD-Qs in multiple environmental media. Concentrations are given in picogram per cubic meter for air particles (AP), nanogram per gram for roadside soils (RS), and microgram per liter for runoff water (RW).

Figure 3

Daily intake rates of PPD antioxidants and PPD-Qs via dermal absorption, oral ingestion of roadside soils, and inhalation of outdoor air for adults and children in Hong Kong. The error bars represent the median with a 95% confidence interval of each contaminant.