First Insight into the Formation of In Vivo Transformation Products of 2-Ethylhexyl diphenyl phosphate in Zebrafish and Prediction of Their Potential Toxicities

As a frequently detected organophosphorus flame retardant in the environment, 2-ethylhexyl diphenyl phosphate (EHDPHP) is vulnerable to biotransformation, while the trans-formation mechanisms and potential toxicities of its transformation products remain unclear. In the present study, in vivo trans-formation products of EHDPHP in exposed zebrafish for 21d were analyzed by suspect screening and identified by mass spectrometry. Fifteen metabolites were identified, including 10 phase I and 5 phase II products with monohydroxylated products being primary, among which 5-OH-EHDPHP was the most predominant. Two sulfation products and one terminal desaturation metabolite of EHDPHP were reported for the first time. A density functional calculation coupled with molecular docking disclosed that the specific conformation of EHDPHP docked in the protein pockets favored the primary formation of 5-OH-EHDPHP, which was fortified to be a more suitable biomarker of EHDPHP exposure. The in vitro tests suggested that EHDPHP transformation took place not only in liver but also in intestine, where gut microbes played an important role. Due to lack of standards, in silico toxicity prediction combined with molecula r docking indicated that several metabolites potentially cause higher toxicities t h a n EHDPHP. The results provide deep insight into the potential health risks due to specific in vivo transformation of EHDPHP.

Automated summary

In this study, the in vivo transformation products of 2-ethylhexyl diphenyl phosphate (EHDPHP) in exposed zebrafish were analyzed, and 15 metabolites were identified, including both phase I and phase II products. The primary metabolite was 5-OH-EHDPHP. The study also reported new sulfation products and a terminal desaturation metabolite of EHDPHP. In vitro tests showed that EHDPHP transformation occurred not only in the liver but also in the intestine, with gut microbes playing an important role. The toxicity of several metabolites was predicted to be higher than that of EHDPHP.