Volume 8, Issue 3 (March 2011)
A Fluorescent Tracer Method for Evaluating Spray Transport and Fate of Field and Laboratory Spray Applications
Field and laboratory testing spray nozzles and application systems use spray collectors to assess where the spray deposits once it leaves the spray system. Tracer materials, such as oil and water soluble fluorescent dyes, can be mixed into spray solutions in small amounts with minimal impact on the solution physical properties and atomization characteristics of the nozzle or spray system. Depending on the dye and recovery methods used, detection levels may range from g/ha down to the parts per trillion making them practical for use in studies where these ranges may occur, such as drift studies that measure in-swath and downwind deposition. Exposed samples can be quickly processed, typically using non-toxic solvents such as purified water or ethyl alcohol. This quick, inexpensive processing allows users the flexibility to plan studies requiring large numbers of samples. Spray formulations using these dyes at specific rates are used as the basis for establishing a set of standard concentrations which are used to relate fluorescence to dye concentration. Laboratory evaluations of tracer deposition compare the fluorescence of processed samples with the fluorescence from a set of reference samples with known dye concentrations allowing users to calculate the actual amount of dye in the sample and thus concentration on the sample being processed. This work will present the step by step process of converting dye concentrations from known and unknown samples to deposition measurements. A downloadable Microsoft Excel® spreadsheet will be made available to allow users to replicate these techniques. This technique effectively allows these tracer materials to provide a direct measure of the amount of active ingredient and/or spray mixture that deposits on sampling surfaces of interest.