Here is some information that has been gleaned from various sources, mainly the FDA and Extension Services...
Priority: Food safety
Because contaminated floodwaters present both microbial and chemical hazards which cannot be effectively controlled, foods which have contacted them should not be used for human food. Safety cannot be tested or adequately assured. This approach is a conservative one, but it is a sound one 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. The present concern is for floodwaters 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. Certainly, any rising, standing or receding water is suspect if its origin is other than local rainfall.
FOODS THAT SHOULD BE DESTROYED
If the edible portion of a crop is exposed to flood waters, it is considered adulterated and should not enter human food channels. There is no practical method of reconditioning the edible portion of a crop that will provide a reasonable assurance of human food safety. Therefore, the FDA recommends that these crops be disposed of in a manner that ensures they are kept separate from crops that have not been flood damaged to avoid adulterating "clean" crops.
Disposition of crops in proximity to, or exposed to a lesser degree of flooding, where the edible portion of the crop has NOT come in contact with flood waters, may need to be evaluated on a case-by-case basis. Factors to consider in the evaluation include:
• What is the source of flood waters and are there potential upstream contributors of human pathogens and/or chemical contaminants?
• Type of crop and stage of growth, e.g., is the edible portion of the crop developing? How far above the ground does the lowest edible portion grow?
• Were conditions such that the crop may have been exposed to prolonged periods of moisture and stress which could foster fungal growth, and possibly, development of mycotoxins?
• Grains and similar products stored in bulk can also be damaged by flood waters. These flood damaged products should not be used for human and animal food.
Fresh Fruits and Vegetables
Fresh fruits and vegetables that have been inundated by flood waters cannot be adequately cleaned and should be destroyed. Fresh fruits and vegetables that have begun to spoil due to the lack of refrigeration should also be destroyed. These food items may be considered for diversion to animal feed under certain circumstances.
As painful as it may be to do, all crops with edible portions that have come in contact with flood waters should be destroyed or discarded.
Safety Precautions from FDA for crops and workers
Discard all crops that have edible portions that have come in contact with flood water. Before cleaning up or destroying crops in flooded fields, check with your crop insurance and/or their local Farm Services Agency (FSA) representatives regarding exact documentation to certify losses, procedures for initiating claims, possible financial assistance.
Although root crops are usually cooked and often peeled before consumption, if under flood waters, they are considered to be grown in unsanitary conditions.
Why can’t we recondition the crops?
“Is there a way to recondition these crops?” Recent increases in diseases from fruits and vegetables have come from the application of 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 should receive a thorough potable water wash prior to washing in a disinfectant. However, this may not be applicable to the current situation in North Carolina.
Washing the produce
When washing, produce should be washed with water that contains a free chlorine residual at all times. 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 which will increase microbial contamination on the surfaces of produce. This wash does not disinfect the produce.
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 levels of disinfectants are not found to be effective in destroying human pathogens on produce. The organic matter present on the surface of the produce decreases the effectiveness of chlorine. At best, studies show that microbial populations can be reduced only 1-2 log cycles. Produce that is mishandled and recontaminated will soon return to prewash levels or higher levels of microorganisms. Sometimes destruction of the existing mixed flora present on produce surfaces may actually result in reestablishment of a more concentrated flora of human pathogens.
The fourth question is, “What if we process further?” Further processing is an important contributor to the safety of food processed. Products such as sweet potatoes are peeled. 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. Because of the uncertainty as to the type and extent of the contaminants, this further processing does not necessarily provide an assurance of safety.