Fluorescent Tracers for Dispersion Measurements

Laboratory tests on the behavior of the fluorescent dyes rhodamine B, Pontacyl Brilliant Pink B, and fluorescein in surface waters of variable quality indicate that Pontacyl Brilliant Pink B is the most suitable quantitative tracer. Pontacyl Brilliant Pink B and fluorescein demonstrate no physical adsorption on suspended solids indigenous to San Francisco Bay, whereas rhodamine B exhibits quite significant adsorption. The photochemical decay rate of Pontacyl Brilliant Pink B is 1/2 that of rhodamine B and 1/25th that of fluorescein. The use of fluorescein must be restricted to short-term studies in waters of only the highest quality, due to both its exceedingly high photochemical decay rate and natural background levels. Background levels of rhodamine B and Pontacyl Brilliant Pink B are sufficiently low, though significant, to permit their use as tracers in San Francisco Bay. The cost of Pontacyl Brilliant Pink B is appreciably higher than rhodamine B, but its use in most applications is believed justified for attainment of meaningful results from tracer studies.