Objectives Retrospective assessment of environmental pesticide exposure is challenging. Exposure measurements or information on crop-specific pesticide use are often lacking historically. We applied expert assessment to reconstruct historical pesticide use patterns in the Netherlands, and evaluated reliability and accuracy of this procedure.

Methods For six main crops in the Netherlands, two experts per crop individually rated the probability (percentage of farmers applying) and frequency of use of authorised active ingredients between 1961 and 2005 per 5-year period. Inter-rater agreement was investigated by the percentage overall agreement and weighted Cohen's κ's (κ_w)_. Experts’ ratings were compared with self-reported pesticide use from recent farmer surveys to determine accuracy of the ratings.

Results Inter-rater agreement on the probability of use varied between crops (κ_w 0.25 to 0.69), as well as agreement on the frequency of use (κ_w 0.32 to 0.64). Inter-rater agreement was marginally higher for herbicides and fungicides than insecticides. Comparisons with survey data indicated fair to good accuracy of the experts’ ratings for the probability (κ_w 0.48 to 0.65) and frequency of use (κ_w 0.38 to 0.68). For all crops except fruit, the specificity of the experts’ ratings was higher than the sensitivity.

Conclusions Overall inter-rater agreement between experts was fair to good and experts’ ratings were reasonably accurate. Results of this study indicate that expert assessment can be used to derive information on historical pesticide use, which is essential for epidemiological studies evaluating the effect of (past) environmental exposure to pesticides on health.