Mixed-methods characterization of the tasks and factors influencing occupational exposure during biosolids land application

Background: 
Pathogenic and chemical contaminants in biosolids may pose risks to workers during land application. Characterizing biosolids applicators’ exposures and risks requires information about the tasks and processes involved in the transportation, application, and use of biosolids, which is critically lacking.

Objective:
This mixed-methods study aims to characterize the tasks and processes that influence occupational exposure to biosolids during land application and generate preliminary task-specific exposure factors to refine exposure assessments for contaminants in biosolids.

Methods:
We conducted semi-structured, in-depth interviews with biosolids workers who apply, transport, and/or use biosolids in the United States and Canada. Following a framework approach to analysis, we identified the six tasks that constitute biosolids application and developed and administered a biosolids exposure questionnaire to collect preliminary data to derive exposure factors for use in occupational risk assessments.

Results:
Workers described frequent and direct contact with biosolids across six land application tasks: hauling, loading, spreading, post-application field work, cleaning, and maintenance. They mentioned instances of ingestion of biosolids, soil, dust, and aerosolized biosolids (spray), inhalation of dust, gases, odors, and aerosolized biosolids (spray), and dermal exposure to biosolids, soil, and dust. Cleaning and maintaining equipment and spreading biosolids were the most commonly reported tasks. Though workers reported spending the least amount of time cleaning and maintaining equipment, these tasks generally resulted in the greatest direct contact with biosolids.