Manure: How far away is far enough?

Over the past several years, high profile recalls of fruits and veggies have become the new norm in the American food landscape. These recalls follow outbreaks of foodborne illnesses caused by microbes like E. coli and can send unsuspecting consumers rushing to the nearest restroom or, worse yet, the hospital. In addition, outbreaks have major consequences for supermarkets and growers who must regain public trust or face possible financial ruin after being linked to an outbreak.

Of concern lately is how farming practices can taint produce with bacteria. This can happen when farmers apply animal manure to fields near fresh produce. Tiny particles, including bacteria, may go airborne and drift to nearby fields — infecting produce on its way. Scientists weren't completely sure just how likely it is for microbes to travel from manure application sites to produce downwind until now, thanks to new field research from Clarkson University in upstate New York.

According to a recent article, Shane Rogers, an associate professor of civil and environmental engineering, led a team of researchers who measured how far common bacteria, including Salmonella and E. coli, are likely to travel downwind from manure application sites.

"Our goal was to provide a logical framework to study this pathway," Rogers said in the article. This helped them make science-based recommendations for setback distances that protect human health.

The team used field data to understand how these bacteria travel from manure application sites to produce. They took samples at several distances over the course of three years from manure application sites and measured the presence of illness-causing bacteria.

The researchers also used computer models to expand their understanding. "It is not possible to obtain measurements for every possible set of circumstances that may exist," Rogers said. "The models allow us to predict produce contamination over a larger range of probable conditions than our raw measurements would provide." These include the type of manure, the terrain of the farm, and weather conditions at the time the manure is applied, he continued.

The team also evaluated the risk of illness and gave a better understanding of how likely someone is to get sick from produce when a certain amount of bacteria is present.

Combining all the data, the team found that produce fields should be set back from areas of manure application by at least 160 meters (about 175 yards). That distance should help lower the risk of foodborne illness to very low levels (1 in 10,000).

Rogers emphasized that the advice is for a minimum setback. "(160 meters is) the minimum distance that produce growers should maintain between manure application activities and produce growing areas.” Additional distance and delay between manure application and harvest would provide further protection, he added.

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