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Joint FAO/IAEA Programme
Q & A - Nuclear Emergency Response

Joint Division Questions & Answers - Nuclear Emergency Response for Food and Agriculture

These questions and answers are intended to provide basic background information and not to give a complete overview, e.g. on actions taken at national level. This Q&A will be updated as appropriate.

Q: How can radioactive materials (radionuclides) enter agricultural products?
Radionuclides can enter the food chain by external and internal contact. External exposure may come from the atmosphere or from the contaminated ground and internal exposure is possible through inhalation or ingestion (e.g. of food).

There are three main pathways where radioactive contamination may enter the food chain in the route from the source of radioactivity- airborne, waterborne and through the soil. (See Fig. 1).
1. - For animals, external contact (air contamination) is the direct contact of the radioactive materials with the skin or mucose membranes of the body. It is far less dangerous than internal contamination. Usually skin contamination can be largely eliminated by thorough washing. Physical protection (keeping animals in a covered barn) is usually sufficient for protection from direct contamination.
2. - Internal contamination can occur due to inhalation or ingestion. Inhalation occurs when radionuclides are present in the external air (as aerosol). The risk from inhalation depends on their concentration in the air, their molecular mass (small molecules will be easily present in the droplets of the aerosol) and their chemical composition (solubility). Upon inhalation, the radionuclides are absorbed via the alveolar capillary system of the lungs.
3. - Ingestion occurs when the radionuclides are ingested during a normal feeding of contaminated plant materials (animal feed) or through the consumption of contaminated water. Contamination of the animal feed occurs by direct deposition of radionuclides from the air or from the rain onto feed materials (for examples grazing land and hay bales). Thus covered feed has a lower risk of contamination, compared to uncovered feed! Once ingested, the risk of contamination depends on the re-sorption rate of individual radionuclides.
4. - Contaminated soil is a very important factor for the contamination of agricultural products. Once radioactive materials from the air are deposited on the soil through dust deposition or rainfall events, they will enter the plants, which will later be ingested by animals.
5. - Radioactive contamination of agricultural land is varied, depending on the distance from a nuclear reactor and the prevailing meteorological conditions. In semi-natural ecosystems the vegetation biomass, including the presence of coniferous or deciduous forests is an important factor in determining how radionuclide pollutants, particularly caesium-137, may be deposited onto the soil. In areas with low vegetation biomass, <5% of radionuclides are intercepted, whereas in dense forest areas 60-100% can be retained by the forest canopy. Some of this radioactivity is stored in the canopy (grass, tree leaves etc.) for long periods. Radionuclides falling on lichen are almost completely retained, and can be present for years, contributing to long-term problems with animals that forage for these plants.
6. - The uptake of radioactive caesium (Cs-134 and Cs-137) from soils into plants via plant roots depends on the plant variety and the binding strength of different soils on deposited radioactive caesium. This binding strength is greatly dependent on soil pH and content of clay, potassium (K) and organic matter in soils. In mosses and lichens, radioactive caesium is present in high amounts due to interception and retention, but fungi have the highest levels, due to the presence of their hyphae that can take up radioactive caesium from contaminated soils.
7. - Animal feeding habits determine the amount of radionuclides ingested; small ruminants like sheep, goats, deer, pigs and wild boar that forage in semi-natural ecosystems where radioactive caesium persists, acquire often high levels.
Q: What immediate action should be taken in case of nuclear emergency?
Try to seek detailed information and instructions from the relevant government authority. If there is time before the contamination reaches your area, and if it is safe to do so, it is possible to take immediate actions to prevent or minimize the radioactive contamination of agricultural products.
1. - Protect growing crops, vegetables and animal fodder by covering them with plastic sheets or impermeable tarpaulins;
2. - Close the ventilation of greenhouses to protect growing vegetables and fruits;
3. - Bring livestock in from pastures and move animals into a closed shed or barn; and
4. - Harvest any ripe crops and place them under cover before any radioactive fallout has been recorded.
Until further instructions after contamination has been recorded, in the contaminated areas:
1. - DO NOT harvest any crops;
2. - DO NOT consume locally produced milk or vegetables;
3. - DO NOT slaughter animals;
4. - DO NOT consume or harvest aquatic animals and plants (including fish, shellfish, and algae); and
5. - DO NOT hunt animals or gather mushrooms or other wild food products.
Q: What is the most likely way by which radioactive material can enter animal products after a nuclear accident?
Radioactive materials, particularly Caesium-137 and Iodine-131, may enter animal products (i.e. meat and milk) when the animal is grazing on contaminated pasture, or feeding on contaminated feed. This refers to mostly cattle, sheep and goats, but pigs and poultry should also be kept in mind. Other products to consider are fish, wildfowl and animals that might be hunted for human consumption.
Q: What can be done to prevent (or mitigate) the effects of radioactive contamination on livestock?
The sources of contamination (e.g. contaminated feed, water or pastures) should be removed, or the animals under concern should be moved. The actions to be taken include:
1. - Remove the animals from pasture and keep them in pens or in shed and barns where they will be protected from further direct fallout. Fresh fodder and uncontaminated water should be provided that is sourced from areas where there is no contamination. This is most important at an early phase of the nuclear incident before contamination reaches the production areas.
2. - In low level contaminated areas, a long term policy would be to switch from milk to beef production. This will ensure that a regular supply of milk contaminated with iodine-131 would not enter the food chain, while beef animals with low level Caesium-137 contamination could be moved to non-contaminated areas a few weeks prior to slaughter.
3. - Increase the feeding of roughage like hay and silage as increased fibre content in the livestock diet can reduce uptake of radiocaesium (Caesium-137)¹.
4. - Do not slaughter animals indiscriminately; enable appropriate monitoring before taking action.
(¹ Radiocesium (Caesium 137) is not naturally occurring, but results from fallout from a nuclear incident.)
Q: What other measures can be taken to reduce the levels of radiocaesium in contaminated livestock?
Dose animals with a bolus, or salt licks of ammonium iron hexacyano ferrate (AFCF), an effective radiocaesium binder, or bentonite² , to reduce the uptake of radiocaesium in the gut of the animals.

(² Bentonite is a type of clay used for absorption or binding of radioactive elements in livestock.)
Q: What should be done if milk is found contaminated with Iodine-131?
Fresh milk should not be used for human consumption. Other dairy products such as cheese and butter can be produced and stored until Iodine-131 radiation levels in the product have declined sufficiently to allow human consumption. On a larger, industrial scale, milk can be decontaminated by techniques such as magnetic separation, ion exchange, and electrodialysis or ultrafiltration to reduce the level of contaminants.

To decrease the levels of strontium, cesium and iodine, milk can be processed into other milk products, such as sour cream (this could lead to a removal of about 85% of the present radioactive levels), butter (leading to about 95% reduction), and coagulation of the milk could lead to a reduction of about 90%.
Q: How long after the accident can an animal still be exposed to radioactive contamination?
Depending on the half-life of the major radioactive isotope profile, the soil and the environment can be contaminated for longer or shorter periods of time. Moreover, some isotopes form stable salts in the soil, which cannot be absorbed by the plants. If such salts have a long half-life, they will reappear during each raining/floods season, and may re-contaminate the animals grazing on such fields.
Q: With animal production systems in mind - how and which samples should be collected for detecting the contamination?
Samples should be taken in glass or plastic bottles (liquids) or in plastic bags (solid samples).

For soil collection - samples should be taken from many different locations within the contaminated area, as the distribution of the radioactivity is not equal across the fields (depends on humidity, rains, etc.). The results should be averaged after measurement.

For crop sampling - a systematic, random grid design should be applied. An amount of 25-50g of plant material - (such as leaves, stems, flowers and roots) should be collected in separate plastic bags. Edible parts of the crop have priority for sampling (e.g. cauliflower heads, pea pods, rice grains, radish roots). Samples are to be taken from parts of the plant with maximal expected levels of radiation (e.g. leaves or productive organs like grains, tubers).

For milk samples - milk is often the most important animal product to be monitored for several reasons: large quantities may be consumed by the population and in particular by infants; radionuclides deposited on grass are consumed by animals grazing on pasture and certain radionuclides are transferred effectively to milk.

Milk samples should be collected from bulk milk depots (i.e. the places where milk is gathered before distribution) and sanitary or health inspectorates, which are normally responsible for other aspects of food control. In case of a localized contamination, about 4 litres of raw milk should be sampled at individual dairy farms (if necessary, samples can be preserved with formaldehyde); the sample, should be taken from cows or/and goats which have been grazing in the contaminated area (i.e. they were not fed from stored feed).

For meat, fish, meat products and cheese - 1cm of the upper/exposed layer should be taken. Samples should be packed in bags or containers. More samples from one animal can be pooled. If more animals are sampled, samples should be taken from individual animals (no pooling between animals). If available, when sampling these products, it is strongly recommended to send a whole rib for example or 100g of the liver, heart and a kidney. It is important to note that live animals can be monitored using a NaI³ monitor that has been calibrated for use with cattle; the large muscle mass in the rear legs should be used and reading taken for one minute.

(³ Sodium iodide (NaI) is used in radiation detection.)
Q: How can contaminated milk be disposed of?
Large quantities of contaminated milk, which are not useful for human consumption, could require disposal (Fig. 2, 3). For milk, contaminated with Iodine-131 (with its short half-life), land spreading, as shown below, could be a useful option.

Take measures to ensure that environmental impact is minimized by appropriate selection of sites for disposal.
Q: How are crops and soil radioactively contaminated?
When a nuclear accident happens, it generally causes radioactive materials (radionuclides) such as Iodine-131, Caesium-134 and Caesium-137 to enter into the atmosphere. The fallout will lead to radioactive contamination on the surfaces of uncovered soil and crops via direct deposition or rainfall events. Once deposited on soil and plant leaves (Fig. 4), radioactive materials can enter into plants through absorption and uptake from soils through plant roots. The rate of radioactive contamination and accumulation within the plants depends on the amount of fallout, the crop variety and the soil properties. In general, it is important to note that:
1. - The deposition of radioactive materials on crops is higher for grass or leafy vegetables (e.g. spinach, cabbage etc.) than sparsely-leaved crops (e.g. onion or tomatoes), because of their broader leaf surface.
2. - Forest or tree crops are also associated with high deposition on their leaves, but relatively small proportions would be likely to be deposited on fruit and nuts etc.
3. - Root crops (e.g. carrots, potatoes, etc.) have little risk of immediate contamination by the fallout itself.
Q: Do weather conditions play a role in the radioactive contamination of soils and crops?
Yes, especially wind (direction and speed) and rainfall (amount and intensity) can affect the level of radioactive contamination. They influence the distribution and subsequently deposition of radioactive materials (radionuclides) on soils and crops. In addition, subsequent rainfall will also have the effect of washing off radionuclides deposited on the leaves into the soil.
Q: Can we protect vegetable crops and soil from radioactive contamination through rain or dust?
Radioactive contamination in areas, where high-value vegetable crops are grown, can be minimized by sheltering plants from contaminated rainfall using greenhouses and using only protected wells for irrigation.

For staple crops or grassland, avoiding radioactive contamination will not be logistically possible for large areas. It is recommended to leave these crops on the field, as a soil protective cover to avoid the contamination of the soils. Radionuclides may be retained on the surface of growing crops immediately after fallout. The transfer of this contamination to the soil may be minimized by removing such crops as soon as possible after fallout has stopped. The removed crop materials can then be buried by deep ploughing beyond the normal rooting depth of vegetable crops.
Q: How can we reduce contamination of arable land and its products in the post-accident phase, when deposition (fallout) of radioactive material has ceased?
Once radioactive contamination is spread through the environment, there is a wide range of agricultural countermeasures that may be implemented to reduce contamination of arable land. These measures take into account of the fact that radioactive material moves relatively slowly down through the soil profile and may be therefore available for crop uptake for several seasons after the initial deposit. The viability and period during which these countermeasures need to be applied will depend on the radioactive contamination levels.
1. - Application of potassium fertilizers and lime can potentially reduce the level of uptake of radioactive material by plants.
2. - Growing alternative crops that accumulate less radioactive materials than those normally grown in the region. For example, cereals in place of leafy vegetables and pasture.
3. - Growing crops where the edible product is processed for non-edible purpose and contamination of humans or livestock is thereby reduced, such as flax and cotton for fibre, oilseed for lubricants or biofuel.
4. - Burying the contaminated surface of the land by deep ploughing can be an effective procedure for large areas.
There is a need to quantify the efficiency of countermeasures involving ploughing and chemical amendments over and above those of normal agricultural practice, all as a function of the initial level of radioactive contamination.
Q: Can we reduce the spread of radioactivity from contaminated soil?
Yes, any factor that minimizes soil, water and wind erosion will reduce the spread of radioactive contamination. In addition activities that generate soil dust such as soil disturbance and vehicle movement should be minimized to reduce the spreading of radioactivity from contaminated soil. It is important to note that transportation of vegetable and fruit crops may result in their contamination with radioactive material (for example: Caesium-134 and Caesium-137) if they are exposed to road dust.
Q: Can crops accumulate radioactive materials from contaminated soils even when they are planted after the deposition (fallout) of radionuclides has ceased?
Yes, crops can accumulate radioactive materials (radionuclides) from the contaminated soils through root uptake. This uptake again depends on crop variety and the soil properties. Some crops have an ability to take up significant amount of radioactive materials from soils can be grown specifically to remove radioactive contamination in soils and subsequently provide soil rehabilitation, i.e. phytoremediation (uptake of radioactive material by plants).
Q: Can we use surface water to irrigate crops?
Yes, the best way is to use groundwater from deep wells for irrigation of high value vegetable crops in greenhouses. As the radionuclides move slowly in the soil, it is unlikely to have a significant radioactive contamination in deep groundwater. During the release of radioactive materials (radionuclides), the surface water will probably be contaminated. Thus the use of water from reservoirs or ponds for irrigation purposes is not recommended in the contaminated area.
Q: How do we measure radioactive contamination (radionuclides) in soil and crops?
The presence of radionuclides is measured either in the laboratory or in the field by high accuracy equipment (gamma detectors). Portable dosimeters that measure radiation in soil and agricultural products are helpful for initial screening of radioactive levels in collected soil and crop samples.
Q: Is an area-wide and continuous monitoring of radioactive contamination (radionuclides) in soil and crops needed?
Yes, an area-wide survey of radioactive contamination in soil and crops allows a classification of affected areas which takes into account the interactions of land use (from dense crop cover to sparsely crop cover) and landscape characteristics with regards to the contamination.

During the episode of release and fallout of radionuclides, this information gives a first assessment of the potential efficacy of early agricultural countermeasures to avoid radioactive contamination of soils and vegetable crops.

Such survey must be carried out in a detailed way and repeated over many years to assess the change in radioactive contamination levels in time. It is also essential that such survey is carried out in a stratified manner such that hot spots, which are small areas with contamination levels much higher than the surrounding area, are not missed. The use of Geographic Information Systems is very useful to visualize the area-wide distribution of contamination and in particular to show the presence of any such hot spots.
Q: What is the impact on crop production after the nuclear accident?
It will be crucial to seek detailed advice and instructions from the relevant government authority. To re-establish agricultural production in previously designated exclusion zones, it is important to know the area-wide distribution of radioactivity levels in the soil and plants of the specific area. Based on this and other data, the national authorities will judge if radiation levels permit agricultural workers to stay in these zones for extended periods.
Q: How should we handle agricultural crops in the vicinity of a nuclear emergency?
The national government will provide appropriate advice. Within the exclusion zone crops should generally be left on the field as a soil-protective cover to minimize contamination of the soil until fallout has ceased and then disposed of at a later date (see below for more details). Outside the exclusion zone with lower radioactive contamination, advice will be provided on a case-by-case basis and depending on the crop type and contamination levels, which should be continuously monitored on an area-wide basis.
Q: How should contaminated agricultural produce be disposed of?
Contaminated agricultural produce may be designated as low level radioactive waste. Methods of disposal will be advised by the national authorities. Such produce may be packaged in appropriate containers or buried by deep-ploughing into the soil (below the root zone). Burning should not be considered unless performed in specially designated facilities equipped with adequate filters and according to nuclear safety regulations. The ash may be disposed of in special landfills.
Q: How do we protect production in greenhouses outside of the exclusion zone⁴?
Contamination levels in existing greenhouses will be lower, depending on the degree of closure or ventilation. The following measures may be useful to avoid further contamination:
1. 1- Verify contamination of air, irrigation water and soil in the greenhouse
2. 2- Use only uncontaminated irrigation water, such as supplied by tank lorry or protected wells
3. 3- If the top soil is contaminated, bury it below the root zone
4. 4- Keep windows closed, regulate temperature with mobile cooling/heating devices
5. 5- Build in air filters according to nuclear safety regulations
6. 6- Use separate clothing for activities undertaken in the greenhouse.
(⁴ Zone designated by Government to have a level of contamination above a critical threshold and from which a majority of human activities, including agriculture, are excluded.)