Objectives: The aim of this study was to assess acute health effects on planters caused by planting conifer seedlings treated with two insecticides, with active ingredients imidacloprid and cypermethrin, in comparison with untreated seedlings. Methods: The investigation was a double-blind crossover study, which included a follow-up of 19 planters over a 3-week period. During Week 1, the 19 planters handled untreated conifer seedlings while they planted imidacloprid-and cypermethrin-treated

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... ings during study Week 2 and 3, respectively. Signs and symptoms of acute health effects were documented by a questionnaire, administered by the field staff, during these 3 weeks. Inflammation markers in the nasal mucous membrane were also measured as an objective test. Exposure to cypermethrin was further assessed by measuring 3-phenoxybenzoic acid (3-PBA) in urine. No validated biomarker was available to assess internal exposure to imidacloprid. Results: No clear, acute adverse health effects could be found in planters during the week of exposure to conifer seedlings treated with imidacloprid (Merit Forest) or cypermethrin (Forester), as compared to during the week of planting untreated seedlings. During the week of cypermethrin exposure, the individuals had 3-PBA values that were 12-54% higher (P < 0.05), depending on the worker, than those observed during the untreated week. There were no statistically significant correlations between the raised levels of 3-PBA and self-reported health problems. These results have been obtained during planting in late summer/early autumn and with good use of protective clothing. Conclusions: No clear, acute adverse health effects could be found in planters after exposure to conifer seedlings treated with imidacloprid (Merit Forest) or cypermethrin (Forester), as compared with planting untreated seedlings. The metabolite, 3-PBA, was found in low levels in urine and was increased after exposure to cypermethrin. However, no clear relationships could be found between exposure and reported symptoms or between elevated 3-PBA levels and reported symptoms.