From the Road to the Field: Decoding Chemical Transformation in Aging Tire and Artificial Turf Crumb Rubber

Increasing tire use worldwide raises concerns about the health impact of rubber-derived chemicals. Of particular concern is the aging of these chemicals, which may lead to the formation of unknown, potentially harmful transformation products. Existing studies have not comprehensively assessed different aging mechanisms and their impact on rubber-derived chemicals from tires from various sources. To address current knowledge gaps, we exposed two tire and one artificial turf samples to outdoor and accelerated artificial photoaging, in dry and wet conditions over 12 weeks. Extracts underwent targeted quantitation, suspect, and nontarget screening via liquid chromatography-mass spectrometry followed by temporal trend analysis and molecular networking. Results indicate that accelerated photoaging and contact with water result in faster transformation/degradation rates. Temporal trend analysis prioritized 572 potential transformation products, including 37 proposed aging markers such as 1-phenylguanidine, which can guide future studies. Molecular networking revealed 180 potential 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ)-related features, including two bioavailable compounds previously reported as para phenylbenzene diamines. We tentatively identified eight TMQ-related aging markers, including novel reaction products between TMQ and other rubber-derived chemicals. Our analysis highlights the complexity of tire and turf crumb rubber aging and the need for further investigation of rubber-derived chemicals and their transformation products.