Dislodgeable foliar residues are lognormally distributed for agricultural re-entry studies

The Agricultural Reentry Task Force (ARTF) conducted a study to determine if dislodgeable foliar residues (DFR) are either normally or lognormally distributed. This is important because the data are used with worker exposure data, which generally appear to be lognormally distributed, to calculate transfer coefficients that will be used to assess farm worker re-entry exposure. Two chemicals were used for this study. Carbaryl, a moderately water-soluble chemical, was applied to cabbage at a rate of 2.0 lbs active ingredient/acre (lb ai/A), while methomyl, a highly water soluble chemical, was applied to cabbage at a rate of 0.9 lb ai/A. The residues were dislodged following an ARTF standardized procedure of collecting leaf punches and shaking in a solution of 0.01% Aerosol OT 75. A total of 28 samples were analyzed for each chemical. The mean+/-SD residue of the carbaryl samples was higher than that for methomyl (511+/-196 and 170+/-71 mug per sample, respectively). However, several types of statistical analyses of the data indicated that, for both chemicals, the residues are lognormally distributed.