Characterizing chemical transformation of organophosphorus compounds by C-13 and H-2 stable isotope analysis

Continuous and excessive use of organophosphorus compounds (OPs) has led to environmental contaminations which raise public concerns. This study investigates the isotope fractionation patterns of OPs in the aquatic environment dependence upon hydrolysis, photolysis and radical oxidation processes. The hydrolysis of parathion (EP) and methyl parathion (MP) resulted in significant carbon fractionation at lower pH (pH 2-7, epsilon(C) = -6.9 similar to -6.0 parts per thousand for EP, -10.5 similar to -9.9 parts per thousand for MP) but no detectable carbon fractionation at higher pH (pH 12). Hydrogen fractionation was not observed during any of the hydrolysis experiments. These results indicate that compound specific isotope analysis (CSIA) allows distinction of two different pH-dependent pathways of hydrolysis. Carbon and hydrogen isotope fractionation were determined during UV/H2O2 photolysis of EP and tris(2-chloroethyl) phosphate (TCEP). The constant delta H-2 values determined during the OH radical reaction of EP suggested that the rate-limiting step proceeded through oxidative attack by OH radical on the P=S bond. The significant H isotope enrichment suggested that OH radical oxidation of TCEP was caused by an H-abstraction during the UV/H2O2 processes (epsilon(H) = -56 +/- 3 parts per thousand). Fenton reactionwas conducted to validate the H isotope enrichment of TCEP associated with radical oxidation, which yielded epsilon(H) of -34 +/- 5 parts per thousand. Transformation products of OPs during photodegradation were identified using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). This study highlights that the carbon and hydrogen fractionation patterns have the potential to elucidate the transformation of OPs in the environment. (C) 2017 Elsevier B.V. All rights reserved.