CHAMPAIGN, Ill., 8/30/22: Potential exposure to legionella bacteria in municipal wastewater used to irrigate crop fields will likely not pose a health threat to residents living downwind, according to a postdoctoral researcher at the Illinois Natural History Survey.
Using reclaimed wastewater from water treatment plants to irrigate crops can be a viable solution to ease the effects of drought and reduce stress on local surface and groundwater resources. Yet, legionella pneumophila, which is widespread in man-made water systems, can survive the aeration and air transport from irrigation systems with potential harmful effects. People who inhale the tiny water droplets can contract Legionnaires’ disease, a serious form of pneumonia.
“Legionella in wastewater hasn’t really been looked at in academia, especially for irrigation,” said Jameson Mori, principal investigator of the U.S. Department of Agriculture-funded study. “I can count on one hand the number of studies that looked directly at legionella in irrigation water of any kind, even though research is starting to suggest that respiratory pathogens in irrigation water can pose a risk to exposed individuals.”
To assess an adult’s risk of infection from a single exposure to irrigated wastewater, Mori developed a microbial risk assessment scenario of irrigation spray in central Illinois during the growing seasons in 2017–2019. Mori collected data from various sources from multiple disciplines and used computer models to determine factors such as the average amount of time that people spend outdoors—less than two hours—and what volume of water an individual standing downwind might inhale. Weather and environmental conditions as well as the possible contaminant level of legionella that a person might be exposed to were also factors.
Mori found that the setback distance from irrigators, or safe distance from harmful exposure when spending time outdoors and downwind, is 1 kilometer (just over one-half mile) when low-pressure irrigation is used and 2 kilometers (slightly over 1 mile) for high-pressure irrigation. At these distances, the airborne bacteria do not exceed the contaminant threshold.
The exception is in the cases of high winds, a high bacterial level in irrigation water, and a long exposure time.
“This study adds credibility and support for the careful and conservative use of treated wastewater for irrigation while providing practical guidelines that we can’t spread wastewater willy-nilly,” Mori said. “It’s important to be conscious of weather conditions and people living nearby.”
Mori recommends that farmers avoid irrigating plants on windy days, irrigate when the sun is out, and notify nearby residents prior to irrigation. Using low-pressure instead of high-pressure irrigation will reduce the risk and the distance that legionella can spread.
For farmers using irrigators, Mori suggested avoiding standing downwind of active irrigators or using face masks to avoid inhaling water droplets. Another suggestion is to dilute the wastewater with fresh water to help keep bacteria from growing when water is stored on the farm.
Findings from the study can contribute to public health guidelines and policies for using wastewater to irrigate crops.
The study was published in the journal Risk Analysis. The co-author is Rebecca Smith, who is affiliated with the U of I Department of Pathobiology, Carle-Illinois College of Medicine, and Carl R. Woese Institute for Genetic Biology.
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Media contact: Jameson Mori, 217-850-2990, brennac2@illinois.edu
news@prairie.illinois.edu
