Occurrence, cross-media transport, and ecological risks of tire-derived contaminants 6PPD and 6PPD-quinone in Jiuzhaigou World Natural Heritage Site, China

Ecotourism is rapidly expanding worldwide, yet vehicle-derived emerging contaminants remain under-explored and poorly managed in protected areas. This study investigated the occurrence, cross-media transport, and ecological risks of the tire antioxidant N -(1,3-dimethylbutyl)- N’ -phenyl- p -phenylenediamine (6PPD), its oxidation product 6PPD-quinone (6PPD-Q), and three vehicle-related metals (Zn, Cu, and Pb) in the Jiuzhaigou World Natural Heritage Site. Jiuzhaigou is a subalpine watershed characterized by intensive shuttle-bus traffic and close road-water connectivity. Based on a summer sampling campaign during the peak tourist and wet seasons, 6PPD in road dust reached urban-comparable levels, whereas 6PPD-Q accumulation was lower than in highly urbanized settings. A clear cross-media concentration gradient was observed, with concentrations decreasing from road dust to roadside soil, sediment, and surface water. While 6PPD was ubiquitously detected across all sampled media, 6PPD-Q was confined to solid media and remained undetected in surface waters. This distinct partitioning, coupled with an increasing ratio of 6PPD/6PPD-Q from road dust to soils and sediments, indicates limited downstream enrichment of 6PPD-Q during short-range transport in this mountainous setting. Risk assessments revealed minimal to low risks in surface waters, whereas 6PPD-Q in road dust and roadside soils and Zn in road dust represented potential ecological risk hotspots. These findings demonstrate that intensive tourist traffic can generate localized near-road contaminant pressures comparable to those in urban environments, underscoring the need to manage road-water interfaces for both legacy and emerging pollutants in ecotourism destinations.