Farmers (used to be)
                  •   Conservative  
                  •   Stable: career and residency
                  •   Knowledgeable
                  •   Well-informed (by extension workers)
                  •   Fond of their work
                      So what’s the problem when we want 
                      to study their agricultural exposure? 
                                                                                2
              Nature of exposures in agriculture 
                  •   Seasonal  
                  •   Often outdoors
                  •   Highly variable
                       – Type of agent and exposure
                       – Biological, chemical and physical
                       – Individual agents (active ingredients)
                       – Intensity, duration and frequency
                                                                                3
            Given nature of exposures in 
             agriculture and potential for 
                    misclassification
                It is a miracle we find any 
              exposure-response relation at all
                                                    4
                       How bad is it?
            Based on inhalation exposure database 
            (Kromhout et al. Annals Occup Hyg 1993):
              – Individuals working outdoors in intermittent process 
                have on average:
                 Day-to-day concentrations vary up to a factor 150
                 Between-worker averages vary up to a factor 10
              – Individual working indoors in intermittent process 
                have on average: 
                 Day-to-day concentrations vary up to a factor 90
                 Between-worker averages vary up to a factor 10
                                                      5
                                 How bad is it?
                •   Based on dermal exposure database     
                    (Kromhout & Vermeulen, Annals Occup Hyg 2001):
                     – For re-entry workers exposed to pesticides on average:
                         Day-to-day concentrations vary up to a factor 10-40
                         No between-worker differences in average exposure
                     – For sheep dippers:
                         Day-to-day concentrations vary up to a factor 300
                         Between-worker averages vary up to a factor 30
                     – Huge differences between body parts!!! 
                                                                                6