Risk assessment for agricultural flooding events

After the November 2021 flooding events in British Columbia, many agricultural production areas were negatively impacted. Flooding may potentially expose food crops to food safety hazards. Growers are responsible to ensure that food products are produced as safely as possible for human consumption. Food safety starts at the farm with good agricultural practices and applicable food safety legislation.

Risk assessments

All flood-impacted producers are encouraged to carry out and keep records of a detailed risk assessment (PDF, 774KB), regardless of whether their operation is formally certified to a food safety standard.

A risk assessment will help determine the impact of the flooding on the entire operation, including the farmyard, fields, buildings and equipment, water sources, and existing and future crops. Producers will need to consider their own operations and neighbouring activities, as these provide clues as to what may have brought contamination or hazard sources onto their property.

Hazards

Potential sources of contamination can be categorized into biological, chemical, or physical hazards.

Biological hazards are microorganisms, some of which are disease-causing such as bacteria, viruses, parasites, fungi, and moulds. Common sources of biological hazards are manure, human sewage, and animal mortalities. Most biological hazards are broken down through exposure to microorganisms or UV light, over time. Healthy soil will accelerate the decomposition process.

Chemical hazards are poisonous or toxic substances. Common sources of chemical hazards are pesticides, fuels, paints, and industrial chemicals. Some chemical hazards are broken down by microorganisms or exposure to UV light such as some fuel-based chemicals and most pesticides.

Other chemical hazards such as heavy metals can not be broken down and levels will only decrease after a prolonged period of time (many years). An example is chromated copper arsenic (CCA) used for preservation of timber. The extent that those substances are available for uptake by crops varies widely depending on various soil properties. Healthy soils may help to immobilize some chemical hazards.

Physical hazards are foreign objects or unwanted materials such as glass, wood, metal, plastics, rocks.

Documentation, including photos and written records, are an important part of food safety. The most important data to collect and document following a natural disaster flooding event describes:

• Time/length of potential contamination period
• Sources of potential contamination
• What was affected by flood waters
• Any testing carried out to monitor the hazard(s)
• Corrective actions implemented

Guidelines for producers in flooded areas

Producers in flooded areas should be aware that:

• All unharvested food product in contact with flood waters should be identified and destroyed
• All stored food product in contact with flood waters should be identified and destroyed

Soil testing can be useful but will likely not be necessary for many sites. Before proceeding to soil sampling, consider whether testing will provide meaningful information:

• Soil testing for foodborne pathogens prior to planting will not be indicative of pathogen loads at harvest, as organisms break down over time
• Soil testing for chemical contaminants is recommended where a specific source of contamination (a spill on your property or a neighbouring property) is known or is reasonably suspected. Specialized collection methods may be required when soil testing for chemical contaminants. You may need to hire a qualified professional to do the testing and/or interpret the results

In general, the flood-related food safety hazards to above-ground perennial plants that were submerged in floodwaters and that will not be harvested until next summer, e.g. blueberries, will be reduced due to the length of time between the flood event and harvest and the exposure of above ground branches to environmental conditions. Extra care should be taken to prevent cross contamination through handling of plant material, gloves, and tools. 

For future plantings, ready-to-eat vegetable crops (consumed raw) and root crops can present a higher risk in areas where contamination occurred.

If chemical contamination is observed or reasonably suspected based on a spill nearby, consider the following options: 

• Delay planting of root crops or crops that can be eaten raw (e.g. salad greens, radishes, green onions) to give the soil a longer rest period. Plant a cover crop instead as a best management practice
• Test the soil. If test results show elevated levels that exceed environmental guidelines for agricultural soils, do not plant root crops or crops that can be eaten raw, but conduct further soil testing again at a later date. However, even relatively elevated concentrations of a substance in a soil may not necessarily pose a risk to safe food production due to the properties of the substance and its behavior in the soil/plant/water environment. Therefore, it is recommended to consult a qualified professional
• Water used for irrigation can be contaminated and can be a risk to food safety, particularly when applied directly to the harvestable portion of the crop
• Growers with organic certification should consult their certifier as there may be additional requirements required by their organic certification