How the variability issue was uncovered: the history of the UK residue variability findings

As a result of routine monitoring data on carrots generated in the 1990s in dicating MRL exceedances, further studies showed that residues of organopho sphorus compounds in individual roots could vary up to 25 times the levels found in composite samples. Additional work found that this phenomenon also extended to other crops including apples, peaches and celery. Variability (defined as the highest residue level found in any one crop item divided by the level found in a composite sample from the same batch) of up to 34 tim es mean values was found in one batch of plums. Conventional deterministic methods used in consumer assessments were likely to give gross overestimate s of short-term exposure because of the assumptions employed. This led to t he development of probabilistic models which made the best use of all avail able information and was capable of indicating percentages of consumers tha t could exceed relevant toxicological end points. This indicated that there was unlikely to be serious health effects as a result of ingesting these r esidues and has subsequently proved to be a useful aid to regulatory decisi on making.