Abstract
Triphenyl phosphate (TPHP) is one of the most highly utilized organophosphorus flame retardants, and has been frequently detected in various environmental matrices, including soil. So far, limited information is known regarding the potential toxicity of TPHP to the earthworm-soil ecosystem. We investigated the metabolism of TPHP and the perturbation of the endogenous metabolome in the earthworm, Perionyx excavatus, using gas chromatography mass spectrometry (GC-MS) and liquid chromatography quadrupole time-of-flight (LC-QTOF)-based untargeted metabolomics approach after acute exposure to TPHP for one and two days through a filter paper contact test, as well as after chronic exposure for 28 days in a soil microcosm experiment. TPHP showed low bioaccumulation potential in the earthworm-soil ecosystem at concentrations of 10 mg/kg and 50 mg/kg. Identified phase I metabolites include diphenyl phosphate, mono-hydroxylated and di-hydroxylated TPHP. Two groups of phase II metabolites, thiol conjugates (including mercaptolactic acid, cysteine, cysteinylglycine, and mercaptoethanol conjugates) and glucoside conjugates (including glucoside, glucoside-phosphate, and C14H19O10P conjugates), were putatively identified. Only acute TPHP exposure caused significant perturbations of the endogenous metabolome in earthworms, featuring fluctuations in amino acids, glucose, inosine and phospholipids. These results reveal novel phase II metabolism and toxicity of TPHP in P. excavatus.
Highlights
Flame retardants are commonly added to manufactured materials, such as textiles and plastics, to inhibit the spread of fire
Triphenyl phosphate (TPHP) metabolites and endogenous metabolites of earthworm were comprehensively profiled by using multi-platform techniques combing liquid chromatography - quadrupole time-of-flight (LC-QTOF) tandem mass spectrometry and gas chromatography - mass spectrometry (GC-MS) analyses
Su et al.[28] revealed that TPHP maintained its concentration in aqueous solution at pH 7–11 in the dark for 35 days, it is likely that TPHP did not degrade in the soil pore water
Summary
Flame retardants are commonly added to manufactured materials, such as textiles and plastics, to inhibit the spread of fire. Triphenyl phosphate (TPHP) is one of the most highly utilized organophosphorus flame retardants, with usage volume reaching 4500–22700 tons in the United States as of 20062. Recent studies revealed that TPHP possesses endocrine disrupting properties[13,14,15,16,17], and can induce developmental toxicity in fish, including neurotoxicity[18] and cardiotoxicity[3] In rats, it can cause serum hypertriglyceridemia by inhibiting specific liver carboxylesterases[19]. By analyzing significantly differentiated metabolites and their related pathways, metabolomics provides the opportunity to potentially gain insights on novel toxicity targets for xenobiotics This saves time and resources compared with using multiple targeted assays in traditional toxicology studies, and allows discovery of novel biomarkers[23]. Various biotransformation products of TPHP were identified and perturbations of certain metabolic pathways caused by TPHP exposure were proposed
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