Records of the environmental occurrence of organothiophosphate esters (OTPEs), which are used as flame retardants and food and industrial additives, are unavailable. In this study, we discovered three OTPEs, namely O,O,O-tris(2,4-di-tert-butylphenyl) phosphorothioate (AO168═S), O-butyl O-(butyl-methylphenyl) O-(di-butylphenyl) phosphorothioate (BBMDBPt)/O,O-bis(dibutylphenyl) O-methyl phosphorothioate (BDBPMPt), and O-butyl O-ethyl O-hydrogen phosphorothioate (BEHPt), in the surface water of the Yangtze River Basin by applying a characteristic phosphorothioate fragment-directed high-resolution mass spectrometry method. Among the 17 water samples tested, the detection frequencies of AO168═S and BEHPt were 100% and that of BBMDBPt/BDBPMPt was 29%. The mean concentration of AO168═S was 56.9 ng/L (30.5-148 ng/L), and semi-quantitative analysis revealed that the mean concentrations of BEHPt and BBMDBPt/BDBPMPt were 17.2 ng/L (5.5-65.4 ng/L) and 0.8 ng/L (<the limit of quantification, LOQ, to 6.3 ng/L), respectively. Twelve organophosphate esters were also detected, of which the highest mean concentration was found for tris(2,4-di-tert-butylphenyl) phosphate (AO168═O, 366 ng/L), followed by triphenyl phosphate (84.3 ng/L), triethyl phosphate (19.3 ng/L), and tributyl phosphate (15.7 ng/L). The Spearman's correlation coefficient between AO168═S and AO168═O was 0.547 (p < 0.05), suggesting that AO168═S commonly transforms into AO168═O or that these chemicals have a similar source and behavior in the environment. Future studies are warranted to assess the potential toxicity, environmental behavior, and health risks posed by OTPEs.
Keywords: O-butyl O-(butyl-methylphenyl) O-(di-butylphenyl) phosphorothioate/O,O-bis(dibutylphenyl) O-methyl phosphorothioate; O-butyl O-ethyl O-hydrogen phosphorothioate; data-independent acquisition; organothiophosphate esters; source water; tris(2,4-di-tert-butylphenyl) phosphorothioate.