Solar and Storage Degradations of Oil- and Water-Soluble Fluorescent Dyes

The assessment of spray deposit efficiency is an important aspect in pesticide application technology research. Since fluorescent tracer dyes serve as useful markers for evaluating spray deposits in many spray application investigations, it is necessary to study the stability and degradation of the fluorescent deposits during storage and exposure to solar radiation before using them under field conditions. Therefore, this study was carried out to evaluate the degradation characteristics of spray deposits prepared with two fluorescent dyes (oil-soluble Yellow 131SC (R), and water-soluble.Pyranine 10G (R)), due to the solar radiation and duration of sample storage. Using dye solutions, droplet deposits were prepared by dispensing known amount of dye solution onto artificial targets (plastic cards). The deposits were exposed to solar radiation from 0 to 3 h and later were analyzed by fluorometry for dye degradation assessment. During the storage study, dye droplets were dispensed onto the targets; the targets were placed in re-sealable plastic bags, and stored at about 4 degrees C for 0 to 8 weeks. The samples were analyzed for percent dye recovery after: 1, 2, 4, 6, and 8 weeks of storage. The oil-soluble dye deposits photodegraded 20% when exposed to cumulative radiation of 0.52 MJ/m(2) during 10-min solar exposure but only 8% during 8 weeks of storage. The water-soluble dye was stable during storage. Moreover, its maximum photodegradation was 3% to 4% when exposed to cumulative radiation of 0.35 to 0.50 MJ/m(2) within 10-min solar exposure.