Evaluation of Fluorobenzoate Tracers in Surface Soils

Abstract

AbstractThe availability of several conservative, noninteracting tracers is desirable for the study of water movement in porous media. Recent studies have identified a family of fluorinated benzoic acid derivatives as having transport properties similar to Br. The transport properties of 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‐(trifluoromethyl)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 transport studies showed that 2,6‐DFBA, PFBA, and o‐TFMBA have transport 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 interaction with the soil matrix and were not conservative precluding their use as acceptable tracers. Plant growth studies using corn (Zea mays L.) and soybean (Glycine max [L] Merr.) showed significantly (P = 0.05) decreased growth for treatments using 3,4‐DFBA and 3,5‐DFBA, precluding their use in agronomic settings. Given the variation shown here and in earlier studies, the transport behavior of any of the fluorobenzoates should be evaluated prior to use in new environments.