Cytotoxicity evaluation of organophosphorus flame retardants using electrochemical biosensors and elucidation of associated toxic mechanisms.

ABSTRACT

In recent years, organophosphorus flame retardants (OPFRs) have been widely used as substitutes for brominated flame retardants with excellent properties, and their initial toxicological effects on the water ecosystem and human health have gradually emerged. However, to date, research on the cytotoxicity and health risks of OPFRs is still limited. Therefore, this study aims to systematically explore the cytotoxic effects and toxic mechanisms of OPFRs on cells. Human liver cancer (HepG2) cells were adopted as an ideal model for toxicity evaluation due to their rapid growth and metabolism. This study proposes a sensitive electrochemical cell-based sensor constructed on a graphitized multi-walled carbon nanotube/ionic liquid/gold nanoparticle-modified electrode. The sensor was used to detect the cytotoxicity of tri(2-butylxyethyl) phosphate (TBEP), tributyl phosphate (TnBP), triphenyl phosphate (TPhP), tri(1,3-dichloro-2-propyl) phosphate (TDCIPP), tri(2-chloropropyl) phosphate (TCPP) and tri(2-chloroethyl) phosphate (TCEP) in the liquid medium, providing insight into their toxicity in water environments. The half-maximal inhibitory concentration (IC50) of TBEP, TnBP, TPhP, TDCIPP, TCPP and TCEP on HepG2 cells were 179.4, 194.9, 219.8, 339.4, 511.8 and 859.0 µM, respectively. Additionally, the cytotoxic mechanism of six OPFRs was discussed from the perspective of oxidative stress and apoptosis, and four indexes were correlated with toxicity. Furthermore, transcriptome sequencing was conducted, followed by a thorough analysis of the obtained sequencing results. This analysis demonstrated a significant enrichment of the p53 and PPAR pathways, both of which are closely associated with oxidative stress and apoptosis. This study presents a simplified and efficient technique for conducting in vitro toxicity studies on organophosphorus flame retardants in a water environment. Moreover, it establishes a scientific foundation for further investigation into the mechanisms of cytotoxicity associated with these compounds.