Unveiling a Large Fraction of Masked Tire Additives in Roadside Plants: Field Evidence for Gastrointestinal Digestion-Driven Dietary Risks

Widespread tire wear emissions introduce substantial tire additives (TAs) into terrestrial ecosystems; however, the real-world occurrence and environmental risk of TAs accumulated in plants remain poorly understood. Here, all 20 target TAs were detected in 100% of roadside soil samples from southeastern China, while only 16 of these were identified in paired plants with lower detection frequency (38%–100%) due to their metabolic masking as conjugates. Using an in vitro gastrointestinal model, we demonstrated that these conjugates were efficiently converted back to parent compounds during digestion, greatly increasing the concentrations of 16 persistent TAs by 2.7–22.3-fold and enabling the detection of the 4 previously undetected TAs. Gastric acidity and intestinal enzymes promoted the deconjugation of TA conjugates during gastrointestinal digestion, significantly elevating the bioaccessibility of plant-sourced TAs and the associated dietary risks. Our findings uncover the prevalence of conjugated TAs in field vegetation impacted by vehicular traffic, underscoring the critical need to incorporate plant conjugation and digestive deconjugation into future risk assessment frameworks.