Runoff to the Abyss: A Large-Scale Investigation of the Occurrence, Transport, and Risk-Driven Prioritization of...

Vulcanization accelerators (VAs) are essential additives widely used in rubber production, especially for tire rubber. However, their environmental occurrence, migration, and risk in sediments on a large geographical scale remain poorly understood. In this study, we conducted the first large-scale geographical investigation of eight VA classes in sediments from multiple hydrologically connected water bodies spanning urban rivers, estuaries, coastal areas, the deep sea, and the open ocean. Five of the eight classes of VAs were detected across the studied areas, demonstrating the ubiquity of these anthropogenic chemicals. Thiazoles were the predominant class, followed by thioureas and guanidines. A total of 34 of the 43 traditional and emerging VAs were detected, with most nonthiazole VAs being reported in sediments for the first time. Total sedimentary VA concentrations declined along a gradient: urban river (median: 188 ng/g) > estuary (81.8 ng/g) > coast (53.5 ng/g) > deep sea (12.0 ng/g) > open ocean (7.49 ng/g). Riverine export fluxes indicate a significant input of these anthropogenic chemicals via particle-mediated transport from terrestrial sources into the coastal ocean. We developed a novel framework that combines multidimensional substance hazards and environmental occurrence indices to prioritize the identified chemicals and assess the risks of surface-deposited VAs in aquatic environments. Fourteen VAs posed medium to high risks in urban rivers and were identified as high-priority VAs of concern. These findings underscore the urgent need for regular monitoring and risk assessment of these ubiquitous but understudied rubber chemicals.