NC State Extension Publications


Due to the recent flooding of areas of North Carolina that grow underground crops such as peanuts and sweet potatoes, questions arise as to whether the crops are salvageable. Many crops will spoil in the fields because wet soils interfere with harvest. Any salvaged produce has the potential for contamination with human pathogens and chemical contamination. Generally, public health regulations prevent the human use of any produce salvaged from grocery stores and other facilities that have been contacted by flood waters.

Assessing the safety

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Several questions need to be answered to assess the safety of flood-covered underground crops. The most obvious is "What was in the flood waters?" "Flood waters" are different from standing waters. Standing waters are not an unusual occurrence after a heavy rain. The present concern is flood waters, which may be grossly contaminated with agricultural runoff such as biosolids from farms, septic systems, lagoons, and treatment facilities, and possibly chemical contaminants from damaged and destroyed equipment and tanks. Indeed, any rising, standing, or receding water is suspect if its origin is other than local rainfall.

All these contaminants would have to be identified to assess the danger of waterborne pollutants, and then the uptake of contaminants in the crop would need to be measured. However, this isn't easy to determine in the field. Due to their considerable dilution with fresh rainwater, some scientists have noted that flood waters may not be concentrated sources of pesticides and other environmental contaminants. Indeed, in areas with localized ecological disasters, such as sewage overflow, chemical spills, or other catastrophes, exposure of crops is more critical.

Why can’t we recondition the crops?

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The second question is, “Is there a way to recondition these crops?” Recent increases in diseases from fruits and vegetables have come from applying wastewater and improperly composted manures to soils. Flood conditions in some areas may mimic these hazards. Root crops harvested in these soils may be contaminated. The Food and Agriculture Organization of the United Nations recommends that heavily contaminated fruits and vegetables receive a thorough potable water wash before washing in a disinfectant. However, this may not apply to the current situation in North Carolina.

Washing the produce

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When washing, produce should always be cleaned with water containing a free chlorine residual. The primary purpose of chlorinating wash water is to prevent microbial buildup in the processing waters from becoming another source of contamination. Without the chlorine residual in wash water, we can expect microbial growth, increasing microbial contamination on the produce surfaces. This wash does not disinfect the produce.


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How about attempting to disinfect the produce itself? Using 100-200 ppm chlorine in wash waters is a common practice. However, the literature shows that such disinfectant levels are not effective in destroying human pathogens on produce. The organic matter on the produce's surface decreases chlorine's effectiveness. At best, studies show that microbial populations can be reduced by only 1-2 log cycles. Produce that is mishandled and recontaminated will soon return to prewash or higher levels of microorganisms. Sometimes, destroying the existing mixed flora on produce surfaces may result in re-establishing a more concentrated flora of human pathogens.

Further processing

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The fourth question is, “What if we process further?” Further processing is an essential contributor to the safety of processed food. Products such as sweet potatoes are peeled, and some, like peanuts, are removed from the pod. Cooking destroys most pathogens. Processing certainly reduces the microbial load and may reduce some of the surface chemical contamination. This further processing does not necessarily assure safety because of the uncertainty as to the type and extent of the contaminants.

Applicable laws

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Federal food laws are more applicable to products after harvesting than before. The Food, Drug, and Cosmetic Act section 402(g)(4) prohibits preparing, packing, or holding human food under insanitary conditions where it may have become contaminated with filth or where it may have been rendered injurious to health. Under regulations in 21 CFR 117.110, evidence indicates that insanitary conditions deem the food adulterated. This is the case even if the amounts of natural or unavoidable defects are less than the established levels. Just the condition deems it adulterated. Root crops under contaminated flood waters can be assumed to be insanitary.

Market considerations

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Aside from the safety aspects, marketing considerations are also an issue. Extended submersion will reduce the quality of the produce, and early spoilage will probably be a factor in marketability. North Carolina works hard to sustain and enhance its markets. Irreparable damage could occur to these markets, not only by shipping a potentially contaminated product but also by shipping a product perceived by consumers to be suspect.

Priority: Food safety

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Because contaminated flood waters present microbial and chemical hazards that cannot be effectively controlled, foods that have contact with them should not be used for human food. Safety cannot be tested or adequately assured. This approach is conservative but sound, consistent with the principles found in current good agricultural practices. The safety of the food supply must take priority over other competing issues in this situation.


Food, Bioprocessing & Nutrition Sciences

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Publication date: July 31, 2022
Revised: April 8, 2024

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