TRACER CHARACTERISTICS OF BRILLIANT BLUE FCF

Dyes are widely used to stain the travel paths of water and solutes in soils. Brilliant Blue FCF (C.I. Food Blue 2) is a valuable dye tracer for visualizing water Bow patterns. Because this dye is nontoxic, it is particularly suited for field use. Depending on pH, the dye is either neutral or dissociates to a mono- or bivalent anion. The water solubility is 200 kg m(-3). In this study, properties of the dye that characterize the adsorbing behavior in soil were determined. Batch adsorption experiments were carried out in the laboratory, and a field experiment was conducted to compare the mobility of Brilliant Blue FCF with that of I- and Br-. The batch studies gave distribution coefficients K-d Of 0.19, 3.00, and 5.78 dm(3) kg(-1) for three different soils. The results of the batch studies suggest that the dye forms ion pairs with Ca2+. The field experiment showed that the dye is retarded compared with the conservative tracer Br-. A comparison between Brilliant Blue FCF and I- analyzed with the iodide-starch method resulted in a relative retardation of 1.2 Brilliant Blue FCF compared with I-.