The uncertainty of sampling has been estimated based on three independent pesticide residue databases. The results of in vivo studies (residues in 120-300 crop units taken from individual fields, composite samples taken from commercially treated crops, and from supervised residue trials) reflect the situations expectable under practical conditions. In addition, computer modelling from the database of residues in primary samples was applied to simulate the likely distribution of pesticide residues in samples of various sizes with large number of iterations. The results of the modelling indicated that obtaining reliable and accurate estimate requires large number of samples. The confidence intervals for the sampling uncertainty decreased with the number of replicate samples taken from one lot and the number of lots sampled. The estimated relative ranges of sampling uncertainty are independent from the relative standard deviation of the measurand in the sampled commodity. The sampling uncertainties calculated from three different types of pesticide residue datasets with different methods were statistically not different. The applicability of the modelling methods applied has been validated. The supervised trial database was used for estimation of typical sampling uncertainties because it was much larger than that of commercially treated fields. To account for the higher variability expectable under practical conditions and the potential serious consequences of underestimating the sampling uncertainty, the upper confidence limits of the uncertainties are recommended for practical use. The typical uncertainties were determined for 22 different crop groups. These values can be used for the calculation of action limits in a decision making process for verifying the performance objectives of producers and planning risk based early warning monitoring programmes. Inclusion of the typical sampling uncertainties in the combined uncertainty for testing compliance of agricultural products with specification before placing them on the market will reduce the trade dispute cases.

Estimation of uncertainty of sampling for determination of pesticide residues in plant commodities

248th National Meeting (2014)

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