Toxicological effects, bioaccumulation, and metabolic pathways of tricresyl phosphate in Scenedesmus obliquus

In this study, Scenedesmus obliquus (S. obliquus) has been employed as a model organism to investigate the bioaccumulation, metabolism, and toxicity mechanisms of tricresyl phosphate (TCP). The results indicated that S. obliquus enhanced TCP degradation in water by 97 % after 14 days. The bioaccumulation factor of tricresyl phosphate in S. obliquus were calculated to be 8. When exposed to a high concentration of TCP (160 μmol/L), the algal growth rate was initially negative at 24 h, but gradually recovered over time. By 96 h, the inhibition rate was 64.74 % and the EC₅₀ values was determined to be 86.41 μmol/L. Prolonged exposure to TCP substantially inhibited photosynthesis in S. obliquus, as indicated by a significant reduction in chlorophyll content. The addition of humic acid (HA), a representative substance of dissolved organic matter, exacerbated TCP toxicity by increasing ROS production, indicating a synergistic effect between HA and TCP. Conversely, a mixed nitrogen source reduced TCP toxicity. Four TCP metabolites were identified, resulting from hydroxylation, ketonization, hydrolysis, and ester bond cleavage. ECOSAR analysis revealed that these metabolites exhibit lower toxicity compared to TCP. These findings indicate that metabolic transformations within the algae may mitigate TCP toxicity, whereas HA significantly exacerbates TCP-induced oxidative stress. This study offers novel insights into the ecological risks of TCP in aquatic environments, especially in the presence of natural organic matter.