TRI-FLUOROBENZOATES 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 trace rs. In this study, four previously untested trifluorobenzoates (TFBA) and two tetrafluorobenzoates (TEFBA) were examined for their suitabili ty as water tracers in saturated and unsaturated environments. Negativ e log acid dissociation constants (pK(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 frac tion soils. An algorithm was developed for calculating a linear partit ion coefficient (K(D)) for each FBA isomer based on pK(a), soil organi c C, pH, and an average organic C-based partition coefficient for prot onated 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 co nditions yielded breakthrough curves for TFBA and TEFBA isomers that w ere indistinguishable from Br-. The results presented herein suggest t hat all 16 ring-substituted FBAs can serve as nonreactive water tracer s.