Estimating past residential exposure to respiratory irritant pesticides in Valais, Switzerland: A crop exposure matrix informed by a Delphi expert survey

• Identification of respiratory irritant pesticides commonly used in Valais • Two-stage experts Delphi-survey the application of 11 pesticides between 2018-2023 • A Crop-Exposure Matrix for organic and non-organic vines and fruit orchards • Copper, sulphur, and folpet had the highest modelled exposure • Very strong correlation between exposure scores (median 0.98 [IQR 0.52 to 0.99]) : Long-term pesticide exposure data are often lacking. In this study, we developed a Crop Exposure Matrix (CEM) for respiratory irritant pesticides used in Valais, Switzerland, and applied it to a sample of schoolchildren to estimate their pesticide exposure at household level. : First, we identified respiratory irritant pesticides used on vines, apples, apricots, and pears cultivation. Using a two-stage Delphi survey, we collected and validated expert-estimated data on the probability and frequency of use of 11 pesticides (six fungicides, two insecticides and three herbicides) between 2018 and 2023. Second, we modelled retrospective pesticide exposure scores of 272 children in five buffers (50 m to 1 km) around their residence and compared their intensities and correlations between the scores. : Ten experts participated in the first survey and five in the second. Median confidence and agreement in the reported data was between 80–90%. Vineyards dominated land use around children’s residences. The modelled exposure scores to the fungicides sulphur, folpet, and copper were the highest, with medians of 6.2, 4.7, and 3.3 times the total surface area covered by vines and fruit orchards, compared to less than one for the other pesticides. The median correlation coefficient between the exposure scores was 0.98 (IQR 0.52 to 0.99). : Our results illustrate the potential of CEMs to estimate long term exposure to frequently used conventional (e.g. folpet) and organic (e.g. copper, sulphur) pesticides which are difficult to measure using direct exposure assessment methods. We provide important methodological insights on collecting expert-estimated pesticide use data in Switzerland and lay the ground for future CEMs which can be used to evaluate the human and environmental health risks of pesticides in Switzerland.