Carbon isotope fractionation patterns distinguish the transformation mechanisms for tris(1-chloro-2-propyl) phosphate (TCPP): Hydrolysis, photolysis, and natural pyrite-activated persulfate degradation.

In this study, carbon isotope analysis was employed to investigate hydrolysis and natural pyrite-activated persulfate (NP/PDS) degradation of TCPP. EPR and radical quenching experiments revealed that •OH and SO4•⁻ were the dominant reactive oxygen species. The XPS, XRD, and FTIR results indicated Fe(Ⅱ) served as the primary active site, generating •OH and SO4•⁻. For acidic and neutral hydrolysis, the apparent kinetic isotope effects (13C-AKIE = 1.031 ± 0.004 and 1.030 ± 0.004, respectively) were consistent with the intrinsic KIE associated with C-O bond cleavage (1.00-1.03), suggesting that C-O bond cleavage was the initial rate-limiting step. In contrast, negligible carbon isotope fractionation during alkaline hydrolysis indicated that P-O bond cleavage was the initial rate-limiting step. For degradation in the NP/PDS, the observed 13C-AKIEs were 1.009 ± 0.001, 1.004 ± 0.000, and 1.005 ± 0.001, respectively. These values were inconsistent with intrinsic KIEs expected for C-H (1.01-1.03) and C-Cl (1.02-1.03) bond cleavage but corresponded to the lower end of the intrinsic KIEs range for C-O bond cleavage, indicating that P-O bond cleavage was the initial rate-limiting step. Overall, this study demonstrates isotope analysis is a powerful tool for identifying the geochemical mechanisms of OPFRs in contaminated fields.