Development of a quantitative job exposure matrix for endotoxin exposure in agriculture

Abstract

Objective To develop a quantitative job exposure matrix (JEM) for the assessment of endotoxin exposure among farmers and other agricultural industry workers. Methods An exposure database containing 3,384 personal endotoxin measurements from Western European and Canadian workers employed in animal and crop production and related-industries with endotoxin exposure between 1992 and 2008 was established. Data were log-transformed and modelled with linear mixed effect models where job-titles, company (within job-titles) and worker (within company) identities were treated as random effects. Fixed effects were year and season of measurement, sampling duration and an exposure prior (none, low, high) for every job code (ISCO-68) from an existing JEM for general population studies. Results The model results suggested overall levels of endotoxin exposure to decline annually by almost 2%. Season was a strong determinant of endotoxin exposure with measured concentrations being higher during the winter (b = 0.64; p <.0001) compared to the summer. Effects of sampling duration on the exposure were rather small. Predicted exposure levels were highest among wheat, vegetable, crop and poultry farmers and lowest among nursery garden workers, gardeners and horticulture farmers. Derived exposure estimates showed good agreement with endotoxin levels reported in the literature and not included in the database. Perspectives The model predictions will be used to develop a quantitative JEM with a time axis for endotoxin exposure to be used in epidemiological studies among farmers and agricultural industry workers.