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close this bookFood, Nutrition and Agriculture Review 02/03 : Nutrient Requirements (FAO, 1991, 72 p.)
close this folderRadionuclide contamination of foods: FAO recommended limits
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View the documentLimites recommandées par la FAO en cas de contamination d’aliments par des radionucléides
View the documentLímites recomendados por la FAO para la contaminación de los alimentos por radionucleidos

(introduction...)

A.W. Randell

Dr Alan Randell is Senior Officer (Food Standards), Food Quality and Standards Service, FAO, Rome.1

1 Most of the work reported in this paper comes from the reports of FAO invited experts in the fields of food control and radiological protection. Their names are listed in the FAO report of December 1986. Other experts have contributed either directly or indirectly through the comments of their national delegations to the Codex Alimentarius Commission or to FAO. Parts of this report have been previously presented by Mr J. Lupien, Director, Food Policy and Nutrition Division of FAO; by Mr R.J. Dawson, Chief, Food Quality and Standards Service, FAO; and by the present author. The cooperation of Mr B. Sigurbjornsson, Director, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture and Chairman of the FAO Standing Committee on the Effects of Radioactivity in Food and Agriculture, is warmly acknowledged.

The Food and Agriculture Organization (FAO) is responsible for advising its Member Governments on a wide range of topics affecting agriculture and food production, processing, storage and trade, including compliance with legislation that controls food quality and safety. This paper discusses appropriate approaches recommended by FAO for assuring orderly trade in foodstuffs in the event that foods are accidentally contaminated with radionuclides or other contaminants.

Releases of radioactive materials into the environment can have a significant effect on trade in agricultural and food commodities. This was apparent in 1986 when the fallout of radionuclides from Chernobyl over a wide geographic area of Europe and Asia caused serious disruptions to food production and trade in food products. These disruptions were exacerbated by the lack of uniformity of actions taken by national authorities and the lack of preparedness to respond to such an emergency.

PRINCIPLES FOR PROTECTION OF THE POPULATION

The principles for protection of the population in the case of releases of radioactive materials across borders should be the same as those principles for releases of materials confined to one country. Radiation protection principles should apply for protecting the population from radiation doses (from all sources) when they exceed agreed levels. In addition, food control legislation and food protection principles must apply to foods moving in trade across national boundaries, and within countries in many cases. International agreement on the application of these principles would assist national governments in determining their response to transboundary contamination of the environment and the food supply. Also important is an awareness of the perceptions of the national population and the political response to these perceptions, especially in countries which have not committed themselves to extensive nuclear energy programmes. Existing national food legislation must also be considered when proposing levels of maximum contamination by radionuclides in foods, since such legislation is normally paramount where food safety is concerned. One of the main decisions to be taken by national governments is to define those circumstances in which government response to transboundary contamination should be governed by radiological protection principles, bearing in mind that contamination of the food supply requires the application of national food control legislation and food protection principles which seek to reduce contamination to the lowest levels attainable, thereby controlling the contamination before it reaches the consumer.

FOOD CONTROL LEGISLATION AND RADIATION PROTECTION

International trade in foods, including food aid programmes, falls within the scope of national food control legislation. Food protection legislation and principles are applied to all food trade in order to reassure the consumer of the safety and quality of foods by providing wide margins of safety to the basic levels derived from public health considerations. Sound and effective national food control laws and regulations provide authorities with simple and uniform action levels which can be applied to all foods moving in trade, whatever their origin and whatever their destination in the distribution chain after clearance. Food control officials are therefore able to use these action levels in a way that is easily understood by the consumers and by food producers, exporters and importers. Such a system not only gives reassurance to consumers, but also provides quantified action levels which the food industry can use to assess whether or not its products will meet with approval.

There are differences between the radiation protection principles, which seek to limit the total exposure of individuals to radiation from all sources including air, food and water, and food protection principles, which are applied to prevent contaminated foods from freely entering the food chain if the contamination is above a conservatively set limit. Using radiation protection principles, derived intervention levels (DILs) have been estimated based on the current International Commission for Radiological Protection (ICRP) recommendation of a dose of 5 millisieverts (mSv) per year; this is the dose limit below which intervention is not warranted from a public health point of view according to radiation protection specialists. Two main radiation protection approaches have been used to estimate DILs for foods; the first is based on assumed intake rates of foodstuffs for critical groups (IAEA, 1986), while the second applies the “optimization of assumed health detriment costs against the cost of withdrawing the food from use”. Neither approach is applicable to the control of food moving in international trade.

In the case of the first approach, few countries have adequate information on national, regional and local dietary habits and patterns, especially for the most vulnerable groups such as infants, children and pregnant or nursing mothers. This approach assumes that a consignment of food arriving at the point of import in a country will be sold or distributed exclusively to the target group for which the DIL has been established. It also has the effect of establishing a multiplicity of DILs, even for the same foodstuff, depending on different levels of intake and the proportion of contaminated food in the diet. In addition, this method leads to DILs that are significantly higher in countries where imported foods are the main or only source of radionuclide contamination than in the countries where the foods were produced, which may have more widespread contamination. Finally, because of the multiplicity of DILs that would be generated on a worldwide basis, consumers in countries where high DILs were recommended would rightly distrust the competence of their national authorities and cease to have confidence in the safety and quality of the food supply. Even if they were willing to accept the resulting negative effect on international trade in foods, most governments would be unwilling to accept such a reaction by consumers.

The second approach that has been explored within the context of radiological protection is the development of guideline values. These are DILs based on the optimization of assumed health detriment balanced against the withdrawal of the food from use. This is an extension of the optimization procedure established for limiting controlled releases of radionuclides info the environment in accordance with the Basic Safety Standards of the International Atomic Energy Agency (IAEA), using an arbitrary monetary value assigned to the health detriment of unit collective dose (a) to be compared to the theoretical cost of production of various foodstuffs (IAEA, 1985). By making a number of broad assumptions, many of the difficulties associated with the “food intake” approach can be overcome so that DILs are applied only to two categories of food, namely high-cost and low-cost. However, within the Basic Safety Standards of IAEA this quantitative method for optimization was to be used mainly in facility design and establishing broad radiation protection programmes. The Basic Safety Standards admit that optimization becomes more qualitative as the concept is applied to operations in existing facilities (IAEA, 1982), and although IAEA has recommended that risk/benefit considerations in setting intervention levels should be taken into account, no attempt at applying quantitative optimization has been made, nor is one recommended in accident situations.

Within the context of international trade, this “optimization” approach is inapplicable to the control of radionuclide contamination of foods because of its failure to address adequately the costs of adverse effects on trade of radionuclide contamination of foods. The approach is also insensitive to the legitimate concerns of consumers in its use of cost-benefit analysis for assessing food safety and marketability. The apparent objectivity of cost-benefit analysis tends to confuse and/or impede the qualitative debate which is essential in an area inherently concerned with ethical and political issues. Decisions about the supply of safe consumer products and the recall of unsafe products, often involving matters of life and death, involve essential ethical and political judgements (NCAAC, 1987). National food laws provide for such judgements because they are formulated with the consent of consumers.

It is clear that consumers and governments demand conservative food contamination control policies in regard to food safety and that these policies be implemented with least cost, i.e. efficiently, by national authorities. In most countries, national food law describes contaminated food as “adulterated” and therefore unfit for sale. However, it is recognized that certain contaminants are unavoidably present in food, and maximum levels for their occurrence have to be set. In order to set contaminant levels certain safety information must be provided, such as acceptable daily intake recommendations for a pesticide or metallic contaminant based on toxicological considerations. In arriving at a contaminant level or “tolerance”, toxicological data on test animals are reviewed; if a no-effect level has been demonstrated in controlled animal feeding tests, that level is the departure point to which a series of conservative assumptions and safety factors are applied to arrive at a much lower contamination level for foods for human consumption. For contaminants such as radionuclides or mycotoxins where a no-effect level cannot be established, additional considerations are applied in setting contaminant levels which acknowledge the impossibility of avoiding all contamination of foods with these substances. This conservative approach is taken in order to reassure consumers and to allow compliance with food laws.

FAO RECOMMENDED LIMITS FOR RADIONUCLIDE CONTAMINATION IN FOODS

A conservative approach as described above was followed by the FAO Expert Consultation on Recommended Limits for Radionuclide Contamination of Foods. They proposed the use of “interim international radionuclide action levels for foods (IRALFs)”, levels below which neither intervention nor constraint would be justified in terms of international movement and trade in food and drink (FAO, 1987). In deriving the IRALFs from the post-accident radiation dose limits established by radiation protection authorities, the Consultation agreed that the levels should provide broad margins of safety and be applied as widely as possible to minimize unnecessary interruptions to international trade to help protect the welfare of otherwise affected agricultural and/or fisheries communities. Furthermore, their derivation and application should be simple and easily understood by all food and health authorities.

AFLATOXINS: AN ANALOGOUS SITUATION

There are clear parallels to be drawn between radionuclide contamination in food and feeds and contamination by other contaminants such as aflatoxins which, like radionuclides, are’ inadvertent and cannot always be avoided. Aflatoxin a carcinogenic by-product of mould growth, is formed in varying amounts when the mould Aspergillus flavus grows on different crops. Aflatoxins are most commonly found in maize, groundnuts and certain tree nuts but have been found in many other feeds that are susceptible to moulds. Under certain adverse climatic conditions aflatoxins can be found in crops throughout a very wide geographic area. This has required the establishment of a system of surveillance, sampling, analysis and compliance decisions based on the practices in different countries. Consignments of maize or other crops that exceed control levels are detoxified, fed to non-susceptible: animals, converted to industrial uses, used as fertilizer or destroyed, since no flexibility exists in the food, laws for higher levels to reach consumers. Although these remedial actions reduce returns to growers and others involved in the distribution and processing chain, some countries have established a payment system to farmers to cover some of the losses. Yet no country has allowed attempts to market known contaminated products because the food laws prohibit this and consumers expect the protection afforded by such laws. Small developing countries that depend heavily on export earnings: from groundnuts often suffer serious losses when importing developed countries, particularly in Europe, refuse to accept products with aflatoxin contamination above their detection levels. Under these circumstances, it is difficult or Impossible to accept that one type of accidental food contaminant with serious potential for carcinogenesis or mutagenesis can be treated differently under existing food laws than any other contaminant with a similar potential.

The figure of 5 mSv per year, as recommended by ICRP, was used as the basis for the calculation of the IRALFs. However, a number of conservative assumptions were applied as “safety factors” in accordance with normal procedures used for contaminants such as radionuclides or mycotoxins which have a linear, non-threshold dose-response. The conservative assumptions included the use of the most sensitive population group, the use of the most restrictive dose conversion factor and the supposition that the contaminated food supply would be 100 percent of the diet. Because of its conservative nature including the assumption that the entire food supply would be contaminated, the protection afforded by the FAO IRALF approach is not affected by differences in dietary habits and takes into account extreme cases, for instance infants fed entirely or primarily on one food, such as infant formula, for several months.

While all of these conditions would not be met normally, the IRALFs resulting from such an approach are entirely consistent with the principles of food protection referred to earlier. They should provide a margin of safety that meets the concerns of consumers while not impeding international trade unnecessarily. The IRALFs may also be applied for domestic trade if considered appropriate by national authorities. They can be applied immediately after an accident or at any time afterwards.

DERIVATION OF PROPOSED ACTION LEVELS

The IRALF for a particular radionuclide A is defined as follows:


The limiting annual radionuclide intake is calculated from the limiting dose using the appropriate dose conversion factor for ingestion as follows:

FAO interim international radionuclide action levels for foods
Niveaux d’intervention internationaux provisoires concernant les radionucles (FAO)
Niveles provisionales de la FAO en relacion una accinternacional en materia de radionucleidos

Radionuclide

Target organ

Dose level
(mSv)

Dose conversion factor
(Sv/Bq)

Radionuclide intake
(Bq)

Food intake
(kg)

IRALF
(Bq/kg)

Sr-90

Bone surface
(infant)






First year


50

1.9 x 10-6

26000

375

70

Following years


10

1.9 x 10-6

5200

375

20

I-131

Thyroid
(infant)






First year


50

2.9 x 10-6

17000

40

400

Cs-134

Whole body
(adult)






First year


5

2.0 x 10-8

250 000

750

350

Following years


1

2.0 x 10-8

50000

750

50

Cs-137

Whole body
(adult)






First year


5

1.4 x 10-8

360 000

750

500

Following years


1

1.4 x 10-8

71 000

750

100

Pu-239

Bone surface
(infant)






First year


50

1.7 x 10-5

3000

375

10

Following years


10

1.7 x 10-5

590

375

2

1 Bequerels corresponding to the annual dose.
Source: FAO, 1987.


The Consultation derived numerical IRALFs for two groups only, infants and adults, and agreed that the general IRALF to be adopted should be the lower of the two. For infants it was assumed that food intake would be 1 kg daily and the dose conversion factors would be based on Johnson and Dunsford (1983), and for adults it was assumed that food intake would be 2 kg daily and the ICRP dose conversion factors for workers should be used (ICRP, 1979). It was further assumed for the purpose of calculating IRALF values that:

· The contaminated food commodity would represent 100 percent of the total intake by the consuming individuals. Thus, the “reference annual intake” was assumed to be 375 kg for infants and 750 kg for adults.

· For radionuclides with half-lives of less than 70 days an “effective food intake” should be used, which corresponds to the food intake over a period equal to five radioactive half-lives. For radionuclides with half-lives greater than 70 days the total annual food intake value should be used, i.e. 375 kg per year for infants and 750 kg for adults.

In the Report of the Expert Consultation on Recommended Limits for Radionuclide Contamination of Food (FAO, 1987). Annex I illustrates IRALFs calculated for five radionuclides: strontium-90, iodine-131, caesium-134, caesium-137 and plutonium-239. It includes cases of the shorter or longer half-life radionuclides. Clearly IRALF values can and will be calculated for the range of significant radionuclides.

As calculated, the IRALF value for iodine-131 intake by infants is more restrictive than that for adults. Therefore, the IRALF value for infants is the one included in Annex I for general adoption. This approach obviates the need for segregating imported milk supplies destined for infants from those for adults. It also provides for the larger margin of safety. All the IRALF values are rounded off conservatively to two significant figures.

Finally, where two or more radionuclides are found to be present or are so declared at the time of export or import, it is assured that the overall IRALF will be satisfied provided the sum S (see below) is equal to or less than 1. The sum 5 is calculated as follows:


FAO/WHO CODEX ALIMENTARIUS LEVELS FOR RADIONUCLIDE CONTAMINATION

Controlling radionuclide contamination of foods moving in international trade requires simple, uniform and easily applied values. This approach can be uniformly applied by government authorities and achieves a level of public health protection of individuals that is considered more than adequate in the event of a nuclear accident. The joint FAO/WHO recommendations (Codex Alimentarius Commission, 1992) were made based on the following assumptions:

· The reference dose level is 5 mSv.
· In one year, 550 kg of food is consumed, all of which is contaminated.
· Dose per unit intake factors for the radionuclides of concern (iodine-131, caesium-134, caesium-137, strontium-90 and plutonium-239) can be conveniently divided into two classes: plutonium-239 with a dose per unit intake of 10-6 Sv/Bq and all others with 10-8 Sv/Bq. These classes of dose per unit intake can be applied to the general population.

Applying these assumptions to the above formula, the level for the radionuclides of concern other than plutonium-239 will be:


which can then be rounded to 1 000 Bq/kg. For 239Pu this value would be 10 Bq/kg, as the dose per unit intake factor is 100 times larger.

These levels are designed to be applied only to radionuclides contaminating food moving in international trade following an accident and not to naturally occurring radionuclides which have always been present in the diet. The guideline levels remain applicable for one year following a nuclear accident. An accident is defined as a situation where the uncontrolled release of radionuclides to the environment results in the contamination of food offered in international trade.

As these levels have extensive conservative assumptions built in, there is no need to add contributions between dose per unit intake groups, and each of the three groups should be treated independently. However, the activities of the accidentally contaminating radionuclides within a dose per unit intake group should be added together if more than one radionuclide is present. Thus the 1 000 Bq/kg level for the 10-8 Sv/Bq dose per unit intake group is the total of all contaminants assigned to that group. For example, following a power reactor accident, 134Cs and 137Cs could be contaminants of food, and the 1 000 Bq/kg refers to the summed activities of both these radionuclides.

These levels are to be applied to food prepared for consumption. They would be unnecessarily restrictive if applied to dried or concentrated foods prior to dilution or reconstitution.

The expert meeting reports of both FAO and WHO have called attention to the special consideration that might apply to certain classes of foods that are consumed in small quantities, such as spices. Some of the foods grown in the areas affected by the Chernobyl accident fallout contained very high levels of radionuclides following the accident, but because they represent a very small percentage of total diets they would contribute very small additions to the total dose. Application of the guideline levels to products of this type may be unnecessarily restrictive. FAO and WHO are aware that policies regarding such classes of food vary at present in different countries.

EFFECT OF CONSERVATIVELY ESTIMATED ACTION LEVELS ON FOOD MOVING IN INTERNATIONAL TRADE

At this time, nearly five years after the Chernobyl accident, the effect of applying IRALFs or similar limits to radionuclide contamination of foods moving in trade can be assessed qualitatively and in some cases quantitatively. Most countries, including those of the European Economic Community (EEC), the United States, Canada and others, established limits for foods moving in trade which were based on food protection principles in preference to establishing DILs for individual foods. The World Food Programme also applied IRALFs to food from non-EEC European donors in its food aid programmes (EEC levels were slightly more restrictive). Because the principles were the same, the levels applied were very similar, although some difference occurred when some of the nuclides were grouped together.

Few problems have been encountered; most of these concern trade in tea and spices. For example, in the year after 26 April 1986 the United States Food and Drug Administration analysed 1 035 samples of imported food for radionuclides using action levels quite similar to the FAO IRALFs. This sampling included all shipments of products offered for entry known to have originated within 400 km of the accident site. A total of 12 shipments, with a value of about US$200 000, was detained, including two cheese samples containing excess iodine-131. Samples containing excessive caesium-134 or caesium-137 were pasta (five samples), spices (four) and cheese (one). Calendar year 1986 imports of foods into the United States from Eastern and Western Europe, Turkey and the Soviet Union were valued at about US$5 000 million, so the regulatory control levels applied were obviously not too restrictive. Therefore, use of limits for radionuclide contamination developed along food protection principles and applied under existing food legislation did not create unwarranted barriers to trade, nor did it require national authorities to present to consumers new, unfamiliar and unacceptable principles for the control of food contamination.

CONCLUSIONS

In considering overall emergency responses to the impact of a transboundary release of radioactive materials, the basic principles of radiological protection and of food protection should be applied. As to the control of radionuclide contamination of foods moving in international trade, only established food protection procedures will have any validity. As shown, neither of the approaches for establishing derived intervention levels meet the criteria of assuring the consumer of the quality and safety of food as well as facilitating international trade.

Action levels established under existing principles for food contamination control, such as the FAO International Radionuclide Action Levels for Food (IRALFs) have provided the necessary consumer assurance and have facilitated trade in foods. Plans for emergency response to an accidental release of radioactive materials should specifically include the use of the FAO International Radionuclide Action Levels for Foods moving in international trade and, in appropriate situations, in domestic trade, or the guideline levels determined by the Codex Alimentarius Commission.

REFERENCES

Codex Alimentarius Commission. 1992. Section 6.1: Guideline levels for radionuclides in foods following accidental nuclear contamination for use in international trade, Codex Alimentarius, 1. General requirements, Rome, FAO/WHO, (2nd ed.)

FAO. 1987. Report of the Expert Consultation on Recommended Limits for Radionuclide Contamination of Food, Rome, 1-5 December 1986. ESN/MISC/87/1, Rome, FAO.

IAEA. 1982. Basic safety standards for radiation protection. Safety Ser. No, 9, Vienna, IAEA.

IAEA. 1985. Assigning a value to transboundary radiation exposure. Safety Ser, No. 67, Vienna, IAEA.

IAEA. 1986, Derived intervention levels for application in controlling radiation doses to the public in the event of a nuclear accident or radiological emergency. Safety Ser. No. 81. Vienna, IAEA.

ICRP. 1979, Limits for intakes of radionuclides by workers. Ann, ICRP, 2 (3/4), ICRP Publ. No. 30, Paris, International Commission for Radiological Protection.

Johnson, J.R. & Dunsford, D.W. 1983, Dose conversion factors for intakes of selected radionuclides by infants and children. Chalk River, Canada, Atomic Energy of Canada Ltd.

NCAAC. 1987, Consumer product safety, Canberra, Australia, National Consumer Affairs Advisory Council.