Dog Poop in the Sky: Are Urban Dogs Affecting Air Quality?

The AQMD (Air Quality Management District), the air-pollution-control agency for Los Angeles, Orange County, Riverside and San Bernardino--the smoggiest region of the U.S.--may have to develop new tests for air quality now that a team of researchers found the stuff in the air hovering above Detroit in winter wasn’t smog, as they expected, but bacteria from dog poop.

According to a study reported in Applied and Environmental Microbiology on July 29, 2011, Cleveland also had high counts of dog feces bacteria, while Chicago had less and tiny Mayville, Wis., surrounded by cornfields, had little. 

Does that imply that the concrete jungles of our nation deflect doggie emissions into the sky, rather than absorb or diffuse them?

Detroit was among the first group of cities to be studied for aerial bacteria because the air-sampling data had already been collected there, as it had for the three other cities included.

"It may be that this is just as common in other cities like New York or San Francisco.  We just don't know," stated Noah Fierer, an ecology professor at the University of Colorado and one of the authors of the study.

Nationwide, the average dog population is 37 percent of the human population, or about one dog for every three people. In Detroit, that would mean about 265,000 dogs. The study noted that Detroit has an estimated stray dog population of more than 10,000 dogs, which may not significantly differ from other large metropolitan cities.

Researchers studied 100 air samples from Detroit and three other Midwestern cities, looking for bacteria in winter air.  They found that the most dominant type is the same as that found in canine feces.  "This suggests that dog poop may be a potential source of bacteria to the atmosphere at these locations," said lead author Robert Bowers, of CU-Boulder's ecology and evolutionary biology department.

The team of researchers stated they hope to study more cities and map the airborne bacteria across the entire continent.

What does this mean from a public-health perspective?

Rob Knight, also a professor at University of Colorado, stated that the researchers don't know the health effects of this fecal bacteria on humans.

“Researchers have known for centuries that bacteria are everywhere, including in the air. But airborne bacteria have rarely been studied. Yet it's well known that they can cause allergenic asthma and seasonal allergies, which are increasingly prevalent in developed countries,” the researchers said.

In the study, the scientists looked at fine particulates, tiny airborne particles people inhale when they're outside. The samples were collected about 12 feet off the ground in summer and winter 2007.

Although the thoughts of inhaling particles of bacteria-ladened dog poop definitely takes a lot of the fun out of breathing, the researchers said that it is possible that metropolitan areas across America all have it. 

Whether or not there are negative health effects isn’t yet known because the original study wasn't designed to look at health issues. The scientists state that the canine fecal findings were unexpected.

"What it really says is how little we know about the bacteria we breathe in every day. In summer, there are more bacteria and the largest number came from soil, dust and leaves. But in winter, when the ground was frozen or covered with snow and the leaves gone, there were fewer bacteria and those from animal feces dominated. The animal feces bacteria are there year-round, but are more pronounced in winter because there are fewer other sources,” Fierer stated.

Impact on future animal sheltering and control and public health

Could this and subsequent studies have a significant impact on the future of urban animal population control/regulation, especially in areas such as Southern California, which do not traditionally experience snow or frozen ground in the winter?

It could be enlightening if future studies include statistics on local pet limits and the number of “no-kill” animal shelters and rescue facilities in their study areas.  These are facilities where hundreds of dogs and cats are warehoused in small, confined areas often for months or years.

Sources:  Bacteria from Dog Feces Present in Outdoor Air in Urban Areas, Science Daily (Aug. 18, 2011)http://www.sciencedaily.com/releases/2011/08/110818190602.htm

The Seattle Times (8/19/11) Study finds bacteria from dog feces floating in the air (Lam, Tina) Detroit Free Press,


Journal Ref:  R. M. Bowers, A. P. Sullivan, E. K. Costello, J. L. Collett, R. Knight, N. Fierer. Sources of bacteria in outdoor air across cities in the midwestern United States. Applied and Environmental Microbiology, 2011; DOI: 10.1128/AEM.05498-11


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