EVALUATION OF FLUOROBENZOATE TRACERS IN SURFACE SOILS

The availability of several conservative, noninteracting tracers is de sirable for the study of water movement in porous media. Recent studie s have identified a family of fluorinated benzoic acid derivatives as having transport properties similar to Br-. The transport properties o f 2,6-difluorobenzoate (2,6-DFBA), 2,5-difluorobenzoate (2,5-DFBA), 3, 4-difluorobenzoate (3,4-DFBA), 3,5-difluorobenzoate (3,5-DFBA), o-(tri fluoromethyl)benzoate (o-TFMBA), m-(trifluoromethyl)benzoate (m-TFMBA) , and pentafluorobenzoate (PFBA) were compared to Br in two neutral pH , high organic soils from Iowa. Batch equilibrium studies and column t ransport studies showed that 2,6-DFBA, PFBA, and o-TFMBA have transpor t properties very similar to Br-, although their behavior may deviate slightly as the organic carbon and clay fractions of the soil increase . 2,5-DFBA is retarded less and dispersed slightly more than the above tracers in these soils, but may be a useful tracer since it is still conservative. The other fluorobenzoates showed greater degrees of inte raction with the soil matrix and were not conservative precluding thei r use as acceptable tracers. Plant growth studies using corn (Zea mays L.) and soybean (Glycine max [L] Merr.) showed significantly (P = 0.0 5) decreased growth for treatments using 3,4-DFBA and 3,5-DFBA, preclu ding their use in agronomic settings. Given the variation shown here a nd in earlier studies, the transport behavior of any of the fluorobenz oates should be evaluated prior to use in new environments.