A systematic review of methods used to assess exposure to pesticides in occupational epidemiology studies, 1993-2017

Objective: Numerous exposure assessment methods (EAM) exist for investigating health effects of occupational exposure to pesticides. Direct (e.g. biomonitoring) and indirect methods (e.g. self-reported exposures) are however associated with degrees of exposure misclassification. We systematically reviewed EAM in studies of occupational pesticide exposure. Methods: We searched for articles reporting observational epidemiological studies in Medline and Embase published 1993-2017. The relative frequency of EAM was analyzed according to EAM type (direct and indirect methods), health outcome, study design, study location (country), and specificity of assessment. Temporal trends in EAM were analyzed. Results: In 1,298 included articles 1,521 EAM occurrences were documented. Indirect EAM (78.3%), primarily self-reported exposures (39.3%) and job titles assessments (9.5%), were mainly applied in case-control studies (95.0%), in high-income countries (85.0%), and in studies of doctor-diagnosed health outcomes (>85%). Direct EAM (20.8%), primarily biomonitoring of blood (15.6%) or urine (4.7%), were predominantly applied in cross-sectional studies (29.8%), in lower middle-income countries (40.9%), and in studies of neurological (50.0%) outcomes. Between 1993-2017 no distinct time trends regarding the ratio indirect to direct methods was seen. Within the category of indirect methods use of self-reported exposures and job-exposure matrices increased while assessments by job titles and registers decreased. The use of algorithms showed no trend. The specificity of pesticide assessment increased since studies assessing exposure by using job title as a proxy declined. Assessments of type of pesticide increased. Conclusion: Over the last 25 years, the ratio (5:1) of indirect to direct EAM applied in articles on occupational pesticide epidemiology stayed relatively constant; changes were mainly attributable to increasing use of self-reported exposures and job-exposure matrices. This review, combined with studies assessing EAM validity, will inform on magnitudes of exposure misclassification and help improve the quality of studies on occupational pesticides exposure.