Purpose: The objective was to evaluate the influence of a range of on-site conditions on bioaerosol concentrations, transport, and deposition, and then use dispersion models to determine set-back distances between fresh produce operations and farm manure sources of fecal bacteria.
Methods: Several field experiments were conducted during typical animal rearing/manure handling operations. Bioaerosols from poultry house ventilation exhaust and during poultry litter and dairy manure handling and composting operations were collected 3-182 m downwind using Anderson impactors, SpinCon cyclonic air samplers, and open-face filters. Deposition was determined using tomato, lettuce, spinach, and basil plants and sterile water basins. Total aerobic bacteria, fecal coliform and E. coli concentrations were determined by conventional plating and MPN procedures (n=300 samples). Emission rates were derived and used to model airborne concentrations and deposition at various distances downwind of the sources under a range of meteorological and landscape conditions.
Results: Source strength, manure handling and moisture content, along with meteorological conditions, downwind distance, and vegetative buffer belts impacted the concentrations of viable airborne target bacteria and their downwind deposition onto plants and water surfaces. The complexity of multiple interacting factors makes atmospheric dispersion and deposition modeling essential methods to predict the likelihood of produce contamination events and the most conducive conditions.
Significance: Determining reasonable setback distances from suspected sources of zoonotic pathogens in order to protect nearby fresh produce crops from contamination via bioaerosol deposition will benefit from consideration of site-specific factors and use of atmospheric dispersion models.