Respiratory toxicity and inflammatory response in human bronchial epithelial cells exposed to biosolids, animal manure, and agricultural soil particulate matter

This study investigated cytotoxicity and inflammation caused by human bronchial epithelial cells exposed to respirable aerosols produced during the land application of stabilized sewage sludges (biosolids). BEAS-2B cells were exposed to respirable aerosols (PM₁₀) derived from soils, biosolids stabilized by mesophilic anaerobic digestion (MAD), temperature-phased anaerobic digestion (TPAD), and composting (COM) as well as animal manures stabilized by mesophilic anaerobic digestion (AMAD) and composting (ACOM). Anaerobically digested particles (MAD, TPAD, AMAD) induced the highest cytotoxicity with LD₅₀ levels of 70 μg/cm², 310 μg/cm² for, and 375 μg/cm² for MAD, AMAD, and TPAD, respectively. Conversely, there was no observed cytotoxicity for soils, composted biosolids, or composted manures at the in vitro doses tested. Inflammatory responses, measured by interleukin (IL)-6 and IL-8 release, were 2- to 15-fold greater in biosolids and manures than for equivalent doses in soils. Biosolids treatment rankings for human bronchial epithelial cell toxicity and inflammation were similar to the rankings found in recent biosolids pathogen content studies - from lowest pathogen content or toxicity to highest, rankings were as follows: COM < TPAD < MAD. Coupling in vitro responses with modeled tracheobronchial lung surface doses that may occur during a biosolids land application event suggests that an inflammatory aerosol exposure in the TB region could only occur under worst case scenarios (exercising human with reduced lung capacity at <65 m set backs), but examination of lower in vitro doses as well as consideration of the head and lower lung respiratory tract regions are needed to more definitively describe the links between biosolids aerosols and the potential for respiratory inflammation.