Knowledge Transfer Task Force

Article 11 - Distance from CAFOs - What are the risks and how to mitigate.

April 23, 2020

Related Resources:
Berry - E.Coli O157:H7 in bioaerosols from cattle production areas: evaluation of proximity and airborne transport on leafy green crop contamination
Hoar - Developing buffer zone distances between sheep grazing operations and vegetable crops to maximize food safety
Jay-Russell - Reducing the risk of transfer of zoonotic foodborne pathogens from domestic and wild animal to vegetable crops in the Southwest desert
Rock - Agriculture Water Treatment - Southwest Region
Thakur - Establishment of vegetative buffer zones to reduce the risk of STEC and Salmonella transmission from animal operations to fresh produce on co-managed farms
Thakur - Food safety risks at the fresh produce animal interface: identifying pathogen sources and their movement on diversified farms

This article originally appeared in The Packer, and is reprinted here with permission. © 2020 The Packer

Even as COVID-19 rampages around the world, we must not lessen our efforts to minimize produce-specific foodborne illness.  Let’s explore a challenging, complex and sensitive food safety question: How can our industry operate more safely in proximity to concentrated animal feeding operations (CAFOs)?

The animal and produce industries are both important. Both are governed by federal, state and local regulations – for CAFOs that includes protecting ground and surface water like us, as well as managing animal waste, and air quality emissions including dust.  Over the years, our industry has worked to find common ground with the livestock feeding sector. I hope these efforts continue, to allow both sectors to succeed while also supplying safe food. In the meantime, what do we know – and need to know – to enhance the safety of fresh produce grown near CAFOs? As with all produce safety topics, we must start with identifying the risks we face, and then study current and develop next generation science to determine how to manage them.

Evaluating risk

Research to date about potential CAFO risks has focused on zoonotic pathogens – pathogens that can move from animals to cause illness in humans, such as E. coli O157:H7 – and the vectors that can transfer them. Studies have shown that many potential vectors could carry pathogens from CAFOs to fresh produce fields, including birds and other wildlife, flies, airborne dust, high wind events, and rainstorms causing unanticipated run-offs.

In recent years, CAFOs have become an object of interest because high concentrations of animals are confined to a relatively small area creating the potential for high pathogen loads that could be dispersed by vectors.  While livestock feeders can control some transmission vectors, even the best managed CAFOs churn up dust, especially at twilight when animals are most active.  Studies demonstrate that it can be difficult to evaluate potential risk of dust (pathogenic aerosol dispersal) to fresh produce fields.

Trevor Suslow, Ph.D., University of California-Davis, and now at Produce Marketing Association, was one of the early researchers to study the subject. Starting in 2007, Suslow took airborne samples at several produce fields located near dairy operations, including a commercial field of baby spinach donated by a grower. Suslow reports that experimentation can be difficult to execute as weather conditions do not always cooperate and the levels of contamination can be variable and hard to measure with current technology.  Further, it was impossible to sample on “the other side of the fence”, so one could not determine if the pathogens were present in the first place. Other Western studies similarly found aerosol dispersal difficult to predict.

The science around set-back distances from animal areas and produce fields is insufficient.   The size and makeup of CAFO’s, potential vectors, environmental conditions, seasonality and testing complexity all play confounding roles.   There is no definitive answer on what a safe set-back distance is, but we do know that under the right conditions, contaminated particulates can travel long distances. Meanwhile, in 2018 the Leafy Greens Marketing Agreement recommended setting fields back at least 1,200 feet.  

More recent predictive modeling gives us some indication of how pathogenic aerosols might move under certain conditions, but not to the level of giving growers the surety they need to make planting or harvesting decisions – that will take more work. 

Researching solutions

Recognizing this topic’s importance to much of our industry, Center for Produce Safety is funding both on-farm and modeling research to better identify when aerosolized pathogens might transfer to fresh produce fields. This research requires rigorous on-farm sampling as well as analysis of metadata – CAFO specifics, wind direction and speed, presence or absence of wind breaks or vectors that might transport pathogens, to list a few.

While our industry commonly samples and tests irrigation water and soil amendments before applying them to fields, it is not practical to sample our fields or their crops for pathogens routinely and as extensively as is needed to reliably evaluate whether pathogens are present.

In fact, testing for pathogens on plants in the field is like trying to find a needle in a haystack. You simply cannot sample enough product to obtain statistical significance when looking for such a sporadic, low-level contamination given the time between harvest and shipping. Alternatively, our industry needs a rapid, portable, easy-to-use test that can give us immediate feedback on the likely presence of pathogens or their biomarkers.

Last year, CPS awarded three “GRABIT” challenge grants toward this end. These grants seek to develop on-farm tools to help our industry identify animal-related food safety risks so that we can intervene before crops are even planted or harvested; they also seek to gather high-granularity data about the livestock-specialty crop interface. We are not necessarily looking for tools to detect pathogens directly – but look for the evidence of chronic or acute indicators or biological evidence (biomarkers) that pathogens could have been transferred from a domesticated animal point source.  

Such tools will allow our industry to better manage the relationship between plant and animal agriculture.

While work funded by these CPS grants is still in process, one grant recipient reports they are making significant progress. Nano Reagents LLC is developing a rapid analysis that will use aptamers – like synthetic antibodies – to bind to protein biomarkers including animal-borne pathogens.

“Our goal is to provide farmers with a portable, easy-to-use device that can provide results within 30 minutes,” says Nano Reagents’ Jim Byron. “We are close to moving our solution out of the lab and into field tests.”

The company plans to work with universities on validation testing, and then move to commercialization. Nano Reagents is also collaborating with tech companies to assess farms from the air by drones for concentrations of pathogenic particulates, to help prioritize areas to sample.

We often hear concerns about open water sources near confined animal operations and the potential for them to become contaminated. Periodic water testing for indicators or pathogens is inadequate to control the risk; therefore the industry needs to close knowledge and practical gaps around water treatment.

Concurrently, CPS is fast-tracking research of ag water treatments – where and when treatment is appropriate, and what options work in the real world. For example, over the course of one growing season and four growing regions, University of Arizona’s Channah Rock, Ph.D., and colleagues will evaluate three antimicrobial treatments: peroxyacetic acid (PAA), calcium hypochlorite, and ultraviolet light. This project should yield data that will allow Southwestern produce growers to better manage their use of antimicrobial agriculture water treatments.

Intuitively, the farther away our fields are from CAFOs, the better for produce safety. However, putting too much distance between our plants and their animals can remove massive tracts of farmland from production, land that is needed to feed a hungry planet.  For higher-risk situations, it may be better to plant vegetative buffer zones (such as animal feed) rather than planting for fresh produce production.  The science, fortified by common sense, hazard analysis and risk assessment must prevail, as every situation is unique. 

With CPS’s help, I can see a day in the not too distant future when research and technology solutions converge to help us make more informed choices about co-existing with animal agriculture.