PLANT TOXICITY AND PLANT UPTAKE OF FLUOROBENZOATE AND BROMIDE WATER TRACERS

The plant toxicity and plant uptake of pentafluorobenzoate (PFBA); 2,6 -difluorobenzoate (2,6-DFBA); 3,4-difluorobenzoate (3,4-DFBA); and KBr were determined in greenhouse experiments. The germination of 11 diff erent crop species was not inhibited by the fluorobenzoates at concent rations below 250 mg L-1 and KBr at concentrations below 500 mg L-1. A lfalfa (Medicago sativa L.), barley (Hordeum vulgare L.), and canola w ere planted in sealed pots in which different concentrations of the tr acers were maintained in the soil solution, The threshold for plant gr owth inhibition by the fluorobenzoates was between 50 and 125 mg L-1; KBr did not inhibit growth even at 1000 mg L-1. At the no-growth-effec t level of 50 mg L-1, 0.1 to 55 % of the added fluorobenzoates or Br w as recovered from the tissue of seedling alfalfa, barley, or canola. A s much as 65% of the added fluorobenzoates was not recovered; the fluo robenzoates were presumably degraded in the soil or metabolized follow ing plant uptake. All of the added Br was recovered. The greatest mass loss was observed for 3,4-DFBA (the isomer with the highest negative- log acid dissociation constant); otherwise there was no correlation of plant response with fluorobenzoate properties, The results show that fluorobenzoates and Br can be readily taken up by growing plants, and that fluorobenzoate mass losses may occur when plants are present.