Tri‐ and Tetrafluorobenzoates as Nonreactive Tracers in Soil and Groundwater

Several fluorinated derivatives of benzoic acid (fluorobenzoate, FBA) have proven their usefulness as nonreactive soil and groundwater tracers. In this study, four previously untested trifluorobenzoates (TFBA) and two tetrafluorobenzoates (TEFBA) were examined for their suitability as water tracers in saturated and unsaturated environments. Negative log acid dissociation constants (p K a ) determined by base titration ranged from 2.71 to 3.54 at 298 K. Some sorption of FBAs was observed in batch equilibration experiments with lower pH, high organic C fraction soils. An algorithm was developed for calculating a linear partition coefficient ( K D ) for each FBA isomer based on p K a , soil organic C, pH, and an average organic C‐based partition coefficient for protonated FBA (K* OC ). K* OC was estimated to be 18 200 ± 6 300 L kg −1 when total FBA solution concentration is less than 5 mg L −1 . Column mobility experiments in sandy media under saturated and unsaturated conditions yielded breakthrough curves for TFBA and TEFBA isomers that were indistinguishable from Br − . The results presented herein suggest that all 16 ring‐substituted FBAs can serve as nonreactive water tracers.