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Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/3/2014 Publication Date: 5/6/2014 Citation: Dungan, R.S. 2014. Estimation of infectious risks in residential populations exposed to airborne pathogens during center pivot irrigation of dairy wastewaters. Environmental Science and Technology. 48:5033-5044. Interpretive Summary: Dairy wastewaters, which are often land applied via spray irrigation, contain a variety of pathogens that can cause infection in both humans and animals. In the western United States where this practice in commonly implemented, there are concerns over downwind residential populations being exposed to airborne pathogens. In response, a quantitative microbial risk assessment (QMRA) was performed to estimate the risk of human infection from the inhalation exposure of pathogens aerosolized during center pivot irrigation of diluted dairy wastewaters. Four conservative irrigation scenarios and associated bioaerosol emission rates were developed based upon available scientific information. The airborne transport of bacterial pathogens was then modeled using the U.S. EPA atmospheric dispersion model, called AERMOD. Bacterial pathogens investigated in this QMRA were Campylobacter jejuni, Escherichia coli O157:H7, non-O157 E. coli, Listeria monocytogenes, and Salmonella spp. After the dispersion model inputs were optimized, downwind bioaerosol concentrations were used in a dose-response model to calculate infectious risks. This assessment only considered risk of infection in non-immunocompromised residential populations that were 1 to 10 km from a center pivot operation. In the simulations, infectious risks were estimated to be the greatest in individuals closest to the center pivot, but decreased with increasing distance from the pivot. This QMRA suggests that individuals downwind of center pivots that are spraying dairy wastewaters could potentially be exposed to unsafe levels of airborne pathogens during nighttime applications. Therefore, it is recommended that wastewaters only be applied during daylight hours when inactivation and dilution of airborne pathogens is highest. Technical Abstract: In the western United States where dairy 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 after inhalation exposure of pathogens aerosolized during center pivot irrigation of diluted dairy wastewaters. The dispersion of pathogens (Campylobacter jejuni, Escherichia coli O157:H7, non-O157 E. coli, Listeria monocytogenes, and Salmonella spp.) was modeled using the atmospheric dispersion 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 residential populations that were 1 to 10 km from a center pivot operation. In the simulations, infectious risks were estimated to be the greatest in individuals closest to the center pivot, as a result of a higher pathogen dose. 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. Further refinement of the dispersion and dose-response models should be considered to increase the utility of this QMRA. |
