Introduction Endotoxin has been hypothesized to partly account for the observed deficit of lung cancer in farmers; however, most epidemiologic studies have relied on surrogate metrics, such as number of animals.

Objective To obtain task-specific estimates of endotoxin exposure for agricultural tasks using meta-regression models of published data.

Methods We extracted the geometric means (GM, in EU/m3) and geometric standard deviations (GSD) of endotoxin measures for various farming activities from 43 published studies (1989–2018). We linked each measure to an activity within the questionnaire used in the Biomarkers of Exposure and Effect in Agriculture Study. When necessary, we calculated the GM and GSD from other available measures. We used mixed-effects meta-regression models with the weighted log-transformed GM as the dependent measure, task as the independent measure, and summary statistic identifier as a random effect to account for between-study heterogeneity. We grouped the tasks into three categories (crop, animal, stored seed/grain), and analyzed each category separately. We conducted sensitivity analyses by restricting data to only North America, only task-based, and only inhalable fraction.

Results We extracted 30 crop, 90 livestock, and 10 seed/grain-related summary statistics. Among animal tasks, most had predicted GMs above 1000 EU/m3, including work in poultry confinement (GM=1470 EU/m3), cleaning poultry confinements (1470), grinding feed (1410), work in swine confinement (1310), cleaning swine confinement (1270), feeding swine (1070), and veterinarian services (1030). Among crop tasks, predicted GMs were below 100 EU/m3, including harvesting corn/grains (30), hauling grain (60), and mowing (80). For stored seed/grain tasks, the predicted GM of cleaning grain bins was 1130 EU/m3 and other work with stored grains/seeds was 230 EU/m3.

Conclusion Our characterization of task-specific endotoxin concentrations can be used in conjunction with questionnaire responses on agricultural activities, including task duration, to improve future endotoxin assessments in epidemiologic studies.