Location: Northwest Irrigation and Soils Research
Title: A quantitative microbial risk assessment for center pivot irrigation of dairy wastewaters Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 21, 2014
Publication Date: N/A
Technical Abstract: In the western United States where livestock wastewaters are commonly land applied, there are concerns over individuals being exposed to airborne pathogens. In response, a quantitative microbial risk assessment (QMRA) was performed to estimate infectious risks from inhaling pathogens aerosolized during center pivot irrigation of dairy wastewaters. Four irrigation scenarios and associated pathogen emission rates from a 396 m long center pivot were developed based upon available information. The dispersion of bacterial pathogens (C. jejuni, E. coli O157:H7, non-O157, L. monocytogenes, and Salmonella spp.) was modeled using the steady-state Gaussian plume model, AERMOD. Pathogen concentrations at downwind receptors were used to calculate infectious risks during one-time (1, 8, and 24 h) and multi-day (7 d at 1 h/d) exposure events using a Beta-Poisson dose-response model. This assessment considered risk of infection in adult non-immunocompromised residential populations that were 1 to 10 km from a center pivot that was spraying 5 to 20% dairy wastewater during day or night conditions. Overall infectious risks were estimated to be the greatest in individuals closest to the center pivot as a result of a higher pathogen dose. During daytime applications of dairy wastewater, the simulations indicate that residential populations have a very low risk of infection (< 1 in 1 million) from the bacterial pathogens if they are located = 1 km downwind from a center pivot. In contrast, infectious risks during nighttime were estimated to be higher. If infectious risks > 1 in 1 million are not considered acceptable, then downwind populations could be exposed to unsafe levels of airborne pathogens during nighttime applications of dairy wastewaters. Based on the results from this QMRA, it is recommended that wastewaters only be applied during daylight hours when inactivation and dilution of airborne pathogens is highest.