First Identification of Toxic Cyclotriphosphazenes as New Pollutants Prevailing in Various Urban Environments: A Class of Widely Used Flame Retardant Electrolyte Additives in Lithium-Ion Batteries

Cyclotriphosphazenes (CTPs) are widely used as flame retardant electrolyte additives in lithium-ion batteries. However, their environmental occurrence, levels, and risks have until now remained unexplored. To address this gap, this study screened, identified, and prioritized six CTPs in dust samples from various urban environments, including e-waste recycling plants, residential households, underground parking lots, and outdoor roads. Notably, all six CTPs were detected in the samples, with hexaphenoxycyclotriphosphazene (HPCTP) being identified as the most predominant congener. The total concentrations of six CTPs in dust from e-waste recycling plants ranged from 24.0 to 1790 ng/g (median of 150 ng/g), which were significantly higher than those from residential houses (median of 50.5 ng/g) and other urban environments. Different composition profiles of CTPs were observed between indoor and outdoor environments, indicating that multiple sources or variations in environmental behaviors influenced contamination levels. Exposure assessments revealed that e-waste recycling workers ingested more CTPs than did the general population. Among the newly identified CTPs, HPCTP emerged as a significant pollutant owing to its abundance, ubiquity, persistence, mobility, and toxicity. Overall, this study is the first to report the occurrence of CTPs in the environment. Our findings point to the emerging concern regarding CTPs as extensively used yet insufficiently evaluated chemicals.