Evaluation of the studies on decline of pesticide residues.

A specifically designed field trial was carried out in an apple orchard by applying Reldan 50 EC (active ingredient, chlorpyrifos-methyl) according to registered uses in Hungary to study the variability of results derived from supervised field trials. Two types of composite samples (A, size 24; and C, size 12) were taken at days 0, 3, 7, 10, and 14 after application to study the uncertainty of estimated residue values derived from supervised trials. In the case of type A the sampling officer selected the fruits from the specified quadrant of the tree, whereas for type C the fruits were taken from the vicinity of the marked position at consecutive sampling times. An evaluation model applying various formulas for the linearization of the decline curves of pesticide residues was applied, which enabled using the statistics of linear regression for calculating the best fit and confidence intervals for the experimental data. The results indicated that the uncertainty of sampling contributed approximately 84-90% of the combined uncertainty of the results (24-30%). In the decline studies performed simultaneously on the same field, the estimated time required to decrease the initial concentration to half ranged from 0.64 to 4.7 days. Despite the fact that the sample size of type C is half that of type A, both sampling methods provided similar results.