MRL calculations based on both intra- and inter-trial residue variability

Methods for calculating maximum residue levels or, at least, high percentile values (e.g. 95th percentile) to support the estimation have been developed in recent years. A mathematical equation is proposed that, for a set of supervised pesticide residue trials on a crop, expresses the incidence of residues as a function of residue concentration in the food commodity. Each residue concentration is expressed as a population reflecting its intra-trial variability. The equation is then the sum of these sub-populations to represent the set of trials, a population of sub-populations (POSP). The equation is formulated so that the area under the curve precisely equals the number of trials. Calculation of a residue concentration corresponding to a percentage of the area under the curve produces the required percentile. Results are generally consistent with the current OECD method calculation. The POSP calculation will be a useful tool in estimating maximum residue levels, where the first choice, other matters being acceptable, would be a value between the 95th and 99th percentiles. Replicate data are directly accommodated in the calculation. The POSP calculator can answer such questions as: what percentile corresponds to the highest residue (HR) in the residue data set?