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What Is FDA Doing to Promote the Safe Use of Manure and Compost on Crops? Questions and Answers with Michael Mahovic

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The proposed Produce Safety rule, published in January 2013 to help implement the FDA Food Safety Modernization Act, addresses the safe agricultural use of raw and composted manure and other biological soil amendments of animal origin. The proposed rule also includes water quality and testing standards, among other provisions. The FDA expects to issue a final Produce Safety rule in 2015.

FDA’s Michael Mahovic, center, with Agricultural Research Service (ARS) scientists Patricia Millner, left, and Manan Sharma

FDA’s Michael Mahovic, center, with Agricultural Research Service (ARS) scientists Patricia Millner, left, and Manan Sharma. They are examining a manure-treated soil sample taken at ARS’ research facility in Beltsville, MD. Millner and Sharma, both microbiologists, are the principal investigators in an ARS team conducting FDA-funded research into the safe use of manure and compost. ARS is part of the U.S. Department of Agriculture (USDA). (Photo by Peggy Greb, ARS/USDA)


Strategic Approach

During the public comment period, concerns were raised about a proposed nine-month interval between the application of raw manure and the harvest of produce crops covered by the rule, and a proposed 45-day interval after the application of composted manure (also known as humus). Many commenters felt the provisions would be too burdensome for farmers and may be more restrictive than necessary to achieve the intended benefit to public health under certain conditions.

The FDA proposed changes, published in September 2014, to the originally proposed rule that include deferring a decision on an appropriate application interval for raw manure and removing the interval for composted manure when the produce rule becomes final.  In the case of raw manure, the FDA is planning to conduct more research and a risk assessment on the safe use of raw manure in agriculture. The compost interval was withdrawn, in part, to encourage use of compost as a safer and more environmentally beneficial alternative to raw manure.

Michael Mahovic, Ph.D., a member of FDA’s Produce Safety Staff, helped draft both the originally proposed produce rule and the proposed revisions. He talks about how the FDA is moving forward with its work to research and promote the safe use of biological soil amendments, which include raw manure and compost.

Q: Why is the FDA so concerned about the use of raw manure on crops?
It’s a food safety issue. Pathogens (disease-causing bacteria) that live in the intestines of animals can be transmitted to produce, and from there to people, through contact with raw manure. For example, E. coli O157:H7 (a particularly dangerous pathogen) lives in the intestines of some cattle.

Q: So why do some farmers continue using raw manure?
There are a number of reasons why growers, especially organic farmers, use raw manure. They see it as an effective way of providing nitrogen and other nutrients to the soil, and maintaining soil quality and health, especially when multiple crops are produced in the same field in one growing season. There’s a cost factor, too, since it’s generally free. A dairy farmer, for example, may dispose of manure by giving it to a neighboring farm.

Q: So what happens now? Is the raw manure interval gone forever?
No. In five years, or longer if needed, the FDA intends to revisit this issue and define the interval of time needed between application of raw manure and harvest to keep produce free of contamination. One of the criticisms some commenters made regarding the originally proposed nine-month interval was that the available science doesn’t back it up, and that was an argument we took to heart. We used the best science available, but we acknowledged that a nine-month interval may be more than what is necessary for public health protection in certain circumstances. There’s a lot more to learn, especially given the diversity of farming, the farming environment, conditions, and manure use.

The first step will be to work on a broad risk-assessment model to identify critical knowledge gaps. Then we’ll know what research must be conducted to fill in those gaps before the risks and parameters of safe use can be evaluated in greater detail.

Q: At this time, the FDA does not intend to object to farmers complying with USDA’s National Organic Program (NOP) standards, which call for a 120-day interval between the application of raw manure and harvest for crops in contact with the soil and 90 days for crops not in contact with the soil. Why not just stay with that standard?
The NOP standards are not public health standards, and some peer-reviewed literature suggests that the NOP intervals may not provide sufficient protection in all circumstances. Among the questions we intend to address in our research and risk assessment are: When is there more risk that produce will become contaminated? And when can we afford to be more flexible in the standard?

Q: Will FDA be working on the research and risk assessment alone or will it have partners?
The FDA plans to reach out to multiple partners for these efforts. Already, the FDA has funded research through one of our Center for Excellence Partnerships—the Western Center for Food Safety, established by FDA in a cooperative agreement with the University of California, Davis—to investigate some of these knowledge gaps. Further, researchers with the Agricultural Research Service (ARS) in the U.S. Department of Agriculture (USDA) are already in the third year of FDA-funded research on agricultural use of manure and compost. Their work has included applying non-pathogenic E. coli to fields in Maryland, Pennsylvania, and Vermont and testing soil samples to see to what extent the bacteria dies off and how long that takes under various conditions. Produce is grown on the fields to determine the likelihood of pathogen transfer to produce crops.

ARS has a compost facility on its Maryland farm as part of research into the safest and most effective composition and production methods for compost. Stability and maturity of the compost—which may include manure, animal bedding, hay and wood shavings—are measured throughout the process. Under the FDA-funded research, they will also expand the program to further investigate pathogen reduction during composting.

Q: Why does the FDA expect it to take five years or longer to complete this research and risk assessment?
This research involves collecting data over a period of years, in different seasons and in different parts of the country. Short-term research could be skewed by weather or other environmental factors. When you also factor in the time it will take to determine what research is needed and the time that will be needed to analyze the data, the FDA expects it to take at least five years to complete this process.

Q: Why is the FDA encouraging a transition to compost use?
We believe compost is safer than raw manure because the composting process that decomposes the manure also reduces any pathogens that may be present. Many other organizations, both in and out of the government—including some organic groups—agree that the use of compost reduces the risk of food becoming contaminated and is more environmentally sustainable than using raw manure. Compost also improves the nutrient content and water retention of soil, a benefit that is long-term.

Q: What standards would growers using compost have to follow under the revised proposed rule?
The compost would have to meet the microbial standard originally proposed in the Produce Safety rule for compost and would have to be applied in a manner that minimizes the potential for contact with produce both during and after application. The originally proposed waiting period of 45 days would no longer apply to properly composted soil amendments.

Q: Does this mean that the growers will have to regularly test the compost, as is the case with agricultural water?
No. The microbial standards in the original version of the proposed Produce Safety rule are not meant to be a testing regime for growers. Instead, they establish what soil amendment treatments must accomplish. The rule also establishes validated composting processes that, when properly implemented and monitored, would be expected to meet the microbial standard for compost. So anyone properly using one of those established composting processes would meet the relevant microbial standard. If growers choose to use an alternate composting process, one not outlined in the rule, they would have to obtain or produce scientifically valid information to support the conclusion that the alternate process meets the microbial standard.

Q: How do you plan to promote the use of compost?
As we proceed with developing the risk assessment model and identifying the knowledge gaps regarding the safe use of raw manure, we intend to follow two parallel tracks in promoting and facilitating the use of compost. One track will focus on educating growers and providing guidance on the benefits of using compost—such as improved safety (compared to raw manure), nutrient management, and erosion prevention—and best practices to follow. The second track will focus on determining resource needs, and exploring the potential for expanding grower capacity for on-farm composting or establishing regional composting facilities. We will be working with many partners, including USDA, to work toward these goals.

Q: How did your career become so focused on manure?
I’m a plant pathologist by training, specializing in post-harvest plant pathology. With this background in the study of plant diseases caused by pathogens or environmental conditions, focusing on human pathogens on plants was a logical extension. Biological soil amendments of animal origin have been identified as a major source of pre-harvest microbial contamination of produce.

Page Last Updated: 11/13/2015
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