Assessing Risk of Raw Manure

The FDA is accepting scientific data, information, and comments until May 3, 2016, to help it assess the risk to human health posed by crops fertilized with raw manure. The aim is to evaluate and possibly quantify the risk of human illness associated with consumption of produce that could potentially be contaminated with enteric pathogens such as E. coli O157:H7, which can live in the intestines of some cattle, or Salmonella, found in the intestines of some poultry.

The risk assessment is part of the Produce Safety Rule mandated by the FDA Food Safety Modernization Act. Information submitted by stakeholders in the produce industry, academia, animal agriculture industry, and the public will help the FDA evaluate the impact of certain interventions on the predicted risk, including use of a time interval between application of the manure and harvest of the crop.

A nine-month interval between the application of raw manure and crop harvest was proposed in 2013, but many in the produce industry objected, saying that the data were limited to support such a decision. A final decision about the minimum application interval was delayed in the final version of the Produce Safety Rule issued in November 2015, pending evaluation of further research and completion of a risk assessment.

Until the risk assessment is completed, the FDA has indicated it will not stand in the way of farmers using the USDA’s National Organic Program standards, which call for a 120-day interval between application of raw manure for crops in contact with the soil and 90 days for crops not in contact with the soil.

Phillip Tocco, extension educator at Michigan State University Extension, says that much is known about the potential hazards of raw manure, but “there is also a lot we don’t know. We know that a lot of the pathogens that make people sick occur normally inside the guts of a lot of these cows. We also know somewhat how the pathogens spread through the environment and how they go from the animal, from the cow patty into the field.

“But we don’t know how long the pathogens in manure survive in the environment, given a lot of different environmental parameters,” Tocco continues. “They survive differentially based on soil moisture that is based on the temperature of the soil and the microbial content of the soil. All of those things are variable across the U.S.”

According to Tocco, Michigan State University Extension is preparing a comment to submit to the FDA during the comment period. “Manure is a valuable nutrient source. Manure is also a risk; there is no doubt about that. The question is what to do about it and how to mitigate that risk,” he says.

To submit scientific data, comments, or information about this issue, click here.