|BURCH, TUCKER - Us Geological Survey (USGS)|
Submitted to: Extension Publications
Publication Type: Government Publication
Publication Acceptance Date: 12/10/2015
Publication Date: 4/1/2016
Citation: Borchardt, M.A., Burch, T.R. 2016. Airborne pathogens from dairy manure aerial irrigation and the human health risk. Extension Publications. ERC 001-16.
Technical Abstract: Application of liquid dairy manure by traveling gun or center pivot irrigation systems is becoming more common in Wisconsin because it offers several potential benefits: reduced road impacts from hauling, optimal timing for crop nutrient uptake, and reduced risks of manure runoff and groundwater contamination. However, irrigation could also increase the risk of airborne pathogen transmission from manure to humans and livestock compared to other application methods. We measured air concentrations of four pathogens and three pathogen surrogates during 23 manure irrigation events on three Wisconsin dairy farms (center pivot, n = 8; traveling gun, n = 15) at multiple distances, typically up to 700 feet, downwind from the irrigated wetted perimeter. We also measured background air concentrations before irrigation and upwind concentrations during irrigation. Air was sampled by two methods at each distance: button samplers for qPCR analysis of microbial targets and Andersen impactors for culturable bacteria. Meteorological conditions during irrigation were measured with a portable weather station. Results show that microbial concentrations decline exponentially with distance, but can still be measurable at 700 feet downwind from irrigation depending on wind velocity and the microbe initial concentration in manure. Using quantitative microbial risk assessment, we estimate the risk for acute gastrointestinal illness for exposure to airborne pathogens 500 feet downwind from dairy manure irrigation is in the range of 0.0001 to 0.01 per irrigation event. The risk estimate depends primarily on pathogen type, pathogen prevalence on dairy farms, downwind distance from the irrigation equipment, and the number of irrigation events during a growing season. This comprehensive risk assessment is the first to use measured concentrations of airborne pathogens during manure irrigation. The findings will be useful to policymakers and public health officials for establishing safe setback distances from irrigated dairy manure.