Presence, partitioning, and toxicity of lithium-ion battery-derived cyclotriphosphazenes in aquatic environment

Cyclotriphosphazenes (CTPs) have been widely used as flame retardant electrolyte additives in the manufacturing of lithium-ion batteries (LIBs). However, their environmental occurrence, behaviors, and toxic effects have not been well explored. This study analyzed six CTPs in surface water and sediment samples collected surrounding a LIB manufacturing park. All target CTPs were detected in surface water samples, displaying the detection frequencies of 10-90 %. Phosphonitrilicchloridetrimer (HCCTP; 55 ng/L) exhibited the highest mean water concentration, followed by ethoxy(pentafluoro)cyclotriphosphazene (EPFCTP; 29 ng/L) and hexafluorocyclotriphosphazene (HFCTP; 24 ng/L). Detection frequencies of CTPs in sediment were in the range of 19-95 %. EPFCTP (mean 24 ng/g dw) and hexaphenoxycyclotriphosphazene (HPCTP; 20 ng/g dw) were the predominant CTPs in sediment. HPCTP (3.5 ± 0.61) displayed the highest mean log K_oc value, which was followed by phosphonitrilicchloridetrimer (HCCTP; 3.2 ± 0.69), EPFCTP (2.8 ± 0.60), and HFCTP (2.6 ± 0.43). In addition, a high-throughput phenotypic screening assay was used to evaluate the toxic effects of CTPs on Caenorhabditis elegans. Target CTPs showed different effects on the four phenotypic parameters (i.e., length, movement, survival, and fecundity) of Caenorhabditis elegans, and HCCTP was the most toxic CTP at the exposure levels of 50-500 μM. To our awareness, this study provides the first evidence on the environmental behaviors and toxic effects of CTPs. These findings are critical for the development of strategies to mitigate the release and toxic impact of CTPs derived from the LIB manufacturing.