In vitro transformation assessment of organophosphate esters (OPEs) via electrochemistry and rat liver S9 and their toxicological evaluation

Organophosphate esters (OPEs) can be biodegraded through phase Ⅰ process in liver by cytochrome P450 enzymes and cause adverse effects to target organs. This study examined the transformation of three OPEs using electrochemistry (EC) and rat liver S9 system to compare the distinctions between the two systems concerning their transformation products (TPs) formed. The toxic effects of OPEs and the primary TPs include endocrine disruption, genotoxicity and dioxin-like potential were further investigated across a range of exposure concentrations that do not induce significant cytotoxicity. OPEs were transformed in both EC and S9 with the degradation degree followed as tris(4-isopropylphenyl) phosphate (T4IPPP)> tris(2-butoxyethyl) phosphate (TBOEP)> tris(1,3-dichloro-2-propyl) phosphate (TDCIPP). Compared with S9 system, the transformation of OPEs in EC method was relatively slower. Bis(butoxyethyl) phosphate (BBOEP), hydroxyethyl phosphate triester (BBOEHEP) and bis(2-butoxyethyl) 2-(3-hydroxybutoxy) ethyl phosphate triester (3-OH-TBOEP) were the most abundant TPs of TBOEP, while bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) was the only TPs of TDCIPP detected in EC and S9 system. Concerning the toxic effects, OPEs declined the cell viability significantly in H4ⅡE, A549 and U2OS cells in time- and concentration- specific relationship. However, no significant cytotoxic effect occurred after exposure to the TPs up to 1000 μM. TDCIPP showed significant antagonistic activities against ERα and AR with IC10 value of 42.4 and 0.301 μM, respectively. BBOEHEP and BDCIPP also exhibited ERα agonistic activity and antagonistic AR activity, which was lower than that of their respective parent compounds. Furthermore, OPEs and their TPs caused significant micronucleus formation in the absence or presence of S9 fraction compared to the solvent control. Taken together, TDCIPP pose considerable risks to humans and the environment considering the limited transform capability and strong toxic effects.