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What’s the risk of airborne manure particles?

Progressive Dairyman Intern Jennifer Janak Published on 11 September 2014

It would seem fair to say that dairy farms are beneficial to their local communities. Not only do they provide a nutritious food source, but have contributed nearly 900,000 jobs nationwide.

On the contrary, could dairy farms have negative effects on our livelihood?



Researchers have delved into the potential human health implications of livestock operations, specifically focusing on bioaerosols from manure. The results may surprise you.

Bioaerosols are airborne droplets composed of organic particles including bacteria, fungal spores and endotoxins. Consequently, the biological globules are found near all livestock farms and are of grave concern to residents living nearby, considering how far they can travel. Foot-and-mouth disease, an airborne microorganism, once traveled more than 1,000 miles from northern France across the English Channel.

The reason bioaerosols raise fear in people is because they can be easily transported into the human body through gaseous exchange. As Dr. Robert Dungan explains, there are three size-deposition sites in the respiratory tract – inhalable, thoracic and respirable, which in turn pose health concerns to those who breathe in air containing high concentrations of the organic molecules.

“In agricultural settings, the microbial component of dusts contribute to pulmonary diseases,” Dungan says, a research microbiologist for the USDA-ARS (Agriculture Research Service). “Animal movement, lot harrowing, compost turning and manure spreading are related to the formation of aerosols.”

Dungan conducted research on two 10,000-cow dairies in Idaho, one an open freestall and one an open lot, to determine the concentration of airborne organic particles relative to the distance from the farm, specifically collecting data on endotoxins. It is important to note that the U.S. does not have any regulations in place for the exposure to bioaerosols; however, Dungan referred to a proposed Dutch regulatory level of 50 endotoxin units per cubic meter (1.4 EU ft3) over an eight-hour exposure period as a benchmark for his findings.


Samples were collected one week per month for 12 months, during the morning, afternoon and evening using a button sampler. The button sampler measures inhalable airborne endotoxins.

“We tested for endotoxins because those are the bioaerosols people are most likely to encounter through inhalation,” Dungan says.

It was noted that chronic exposure to endotoxins could cause lung disease, such as Byssinosis in cotton workers. Interestingly enough, earlier studies suggest that dairy producers are at a lower risk for asthma and lung cancer due to their constant exposure to endotoxins in the air.

Dungan’s studies confirmed that there are endotoxins in the air we breathe, but the concentration of this type of bioaerosol depends on the distance downwind from the dairy facility.

For both test sites, the concentration of inhalable endotoxins upwind was well below the Netherland’s proposed regulatory threshold. Moving 50 meters downwind increased the concentration of endotoxins by a hundredfold, and levels reached the threshold at a distance of 200 meters downwind from the operations.

“There are three meteorological factors that affect the viability of bioaerosols. Those include solar radiation, temperature and humidity,” Dungan says. “Stable atmosphere conditions in the night allow endotoxins to hug the ground, resulting in higher concentrations.”


Air temperature and wind speed are directly related to the viability of endotoxins near the facilities. Likewise, humidity and solar radiation have a negative effect on these bioaerosols.

Bioaerosol levels were most pronounced during the evening samples at 50 meters downwind, as Dungan hypothesized would happen.

Putting everything into perspective, endotoxin levels will vary at different operations, with different management practices. It’s important to note that Dungan’s findings concluded that on average, the two dairies had levels of bioaerosols at 6.4 EU ft3, relatively low compared to other agricultural practices. It has been found that grain harvesting can generate endotoxin levels at roughly 142 EU ft3, and swine farms have been known to reach a shocking 195 EU ft3.

While natural bioaerosol drift is of concern, people in Wisconsin are more worried about drift from irrigated manure systems.

A work group of 18 stakeholders, including producers, public health and environment representatives and manure applicators, joined Dr. Becky Larson to assess the benefits and concerns of irrigated manure in comparison to other practices.

The research consisted of a process of collecting field data to determine pathogen drift, then predict when drift may occur and producing a risk assessment related to the drift. The study focused on the travelling gun and center pivot irrigation systems, both popular choices for dairy farmers in the Midwest.

“Similar to Dr. Dungan’s research, we don’t have a lot of data to express concerns for human health,” Larson says, an extension specialist at the University of Wisconsin – Madison.

These two methods of manure irrigation proved to be of little concern for human health. Manure droplet size directly affects how easily the contaminant is able to drift; the larger the droplet size, the shorter distance it will travel through the air.

Over the course of four trials in the fall of 2012, Larson, and those who assisted, discovered that the greater the distance from the irrigation system, the decreased number of pathogens present in the air – for both the travelling gun and center pivot. In instances when large amounts of bioaerosols were detected, wind speed played a significant role.

“There is still a lot of data that has to be collected,” Larson says. “But we can make a safe assumption that the risk of health issues in humans near the irrigated fields is low.”

Findings may differ across the country as arid climates create high amounts of dust, creating a greater concentration of endotoxins in the air, while rainfall helps mitigate the prevalence of bioaerosols.

So, are dairies worsening our health and livelihood? In short, the answer is no, Dungan says.

“Just because we can measure the endotoxins does not necessarily mean it’s an issue we need to worry about,” Dungan says.

In the meantime, as more data is being collected, Larson suggests that it wouldn’t hurt to create a risk assessment plan for potential bioaerosols that you are surrounded by on a daily basis, especially for those occupational workers on the dairy farms.

“Implementing easy, harmless mitigation strategies, such as buffer zones and dust control, can decrease bioaerosol transport and keep those working on the dairy protected,” Dungan says. PD

Dr. Dungan and Dr. Larson presented their research findings about bioaerosals during the webinar,“Bioaerosols from Feedlots and Dairy Farm Operations,” that was held on May 23. The Livestock and Poultry Environmental Learning Center hosted the webinar.