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Canadian Guidelines for the Restriction of Radioactively Contaminated Food and Water Following a Nuclear Emergency
Appendix B: International Guidance on Food Intervention
Prior to the 1986 Chernobyl accident, general principles on the planning of intervention in the event of a nuclear emergency had been given by several national and international radiation protection agencies, including the ICRP (1984), WHO (1984) and IAEA (1985). Recommended intervention levels for various countermeasures were based on two levels of effective dose, the lower below which intervention would unlikely be warranted, and the higher above which it would almost certainly be necessary.
Since that time, the ICRP has published new recommendations for protection against ionizing radiation under both normal and emergency situations (ICRP 1991, 1993). Following an uncontrolled release to the environment, the ICRP recommends that the levels at which countermeasures are introduced and later withdrawn should be expressed in terms of the dose expected to be avoided by the action, and should be optimized to produce the maximum net benefit. This approach has also been recommended by the IAEA in its Basic Safety Series (IAEA 1996). However, these recommendations are not binding on individual countries.
The following section discusses the current approaches to intervention in the distribution of food by various national and international organizations. A comparison of methodologies (Table B.1) is provided first. This table, together with the comparison of action levels recommended by different organizations (Part 2: Table 2.6) demonstrates that although the methodologies may vary, there is a general consistency in the recommended action levels for food and water.
Table B.1 Comparison of methodologies adopted by various international organizations
International Commission on Radiological Protection
In 1993, the ICRP introduced revised guidance on intervention following a radiological emergency, superceding its previous recommendations (ICRP 1984). The ICRP recommends that intervention be justified and optimized in order to produce the maximum net benefit, recognising that any action that minimizes radiation risk may itself be associated with its own degree of cost and detriment. The ICRP advocates the use of these two principles to determine the appropriate level at which intervention should be considered, rather than the use of pre-determined limits as the basis for providing intervention. Justification and optimization studies should be based on the dose averted by a specific protective action. The sum of the remaining doses from all pathways after implementation of protective actions should be kept under review.
To aid in the implementation of its recommendations, generic intervention levels for which action is almost always justified have been established for various protective measures. For the control of radiologically-contaminated food and water, the ICRP recommends that for any single foodstuff, an intervention level that is almost always justified is an averted effective dose of 10 mSv in a year, providing that there are nutritionally adequate alternative supplies.
Using the cost of the food per unit mass, the consumption rate of the food per person, and the appropriate dose coefficients, a simplified generic optimization has been carried out, resulting in the optimized intervention levels shown in the following table. Higher values would be expected in the case of severe food shortages. It is assumed that, in general, contaminated food contributes only a fraction of the total diet of a consumer.
International Atomic Energy Agency
The latest IAEA recommendations provide a set of generic intervention levels for the major protective measures to be taken in the event of a nuclear emergency, based on justification and optimization (IAEA 1994, 1996). Generic levels have been based on radiological protection principles, and on the premise that the level of effort allocated to such protection should be at least as great as the level of effort and resources allocated to the protection of public health from other risks of a similar magnitude and nature. Psychological and political factors have been excluded in the development of generic levels, in order to form a common baseline for decisions on protective measures. Although excluded from the generic optimizations, these factors may contribute to, or even dominate, some decisions, in which case deviation from the generic levels becomes a matter of national policy, circumstances or site-specific factors (IAEA 1994).
Generic action levels for the withdrawal of food have been calculated by applying a simple cost-benefit analysis. The food supply has been classified into two broad groups defined by their value per kilogram, with associated annual consumption rates. Action levels are specified for three groups of radionuclides with similar dose coefficients, leading to a set of six generically optimized ranges of values for which withdrawal and substitution of foods should be considered. On the basis of these ranges, but with account taken of existing national and international legislation and of the issue of practicality, a single set of action levels has been selected that encompass the Codex Alimentarius Commission's guideline values for foods moving in international trade (FAO/WHO 1991).
These levels apply to food as consumed. Levels are applied independently of one another; however, within a single group, the radionuclide concentrations are additive. Classes of food consumed in small quantities (less than 10 kg y-1 ) may have action levels ten-fold higher.
World Health Organization
WHO issued guidelines in 1988 (WHO 1988), intended to assist national authorities in countries at some distance from the accident site in developing intervention levels for food.8 WHO recommends a simple and conservative methodology based on a limiting annual individual dose, and the assumption that all food is contaminated at the intervention level. WHO has chosen an intervention level of 5 mSv in a year, based on a comparison with global variations in the effective dose due to natural radiation, and because no remedial measures have been recommended for avoiding exposure from other natural sources at doses of 5 mSv or less. WHO has pointed out that cost-benefit analysis based on a population dose criterion results in an intervention level of several mSv per year. However, when the cost of intervention is low, it may well be justified to reduce the detriment to a lower level of dose. An intervention level of dose for the thyroid of 50 mSv has been set as a secondary limit.
WHO has divided the food supply into eight categories, including drinking water. The annual consumption rate of a particular food category is derived from a hypothetical diet based on above-average consumption rates of different food components in different parts of the world, normalized to a total consumption of 550 kg y-1 . The radionuclides most likely to be of significance in food pathways after a nuclear emergency have been grouped into 2 broad categories of high and low dose coefficients. Separate guidelines were developed for infants on a milk and water diet, as it was felt that the rounded dose coefficients and normalized hypothetical diet did not provide adequate protection.
If several food categories are contaminated by one or more radionuclides, a summation over all radionuclides and food groups is required to ensure that the 5 mSv level is not exceeded. Guideline values apply to food as it is consumed.
FAO/WHO Codex
Alimentarius Commission
The FAO/WHO Codex Alimentarius Commission, a body set up jointly by the Food and Agriculture Organization (FAO) of the United Nations, and the WHO, adopted guideline levels for radionuclides in food in 1989 (FAO/WHO 1989, 1991, 1995). These guidelines apply only to potentially contaminated food moving in international trade during the first year following an emergency. Although not binding on a country, Codex recommendations will be referred to in the event of trade disputes regarding differences in national guidelines.
Codex guidelines are largely based on WHO guidance, but with further simplification. An intervention level of 5 mSv is used, but there is minimal distinction between food types. The Codex Commission has recommended intervention levels for two food groups: Foods Destined for General Consumption, and Milk and Infant Food. Infant foods are those foods prepared and packaged specifically for infants in their first year of life. Levels in both groups are based on a single annual consumption rate 550 kg y-1, all of which is contaminated.
The Codex Commission has grouped the dose coefficients for the radionuclides of concern into three classes (10-5 or 10-6 depending on food group, 10-7 and 10-8 Sv Bq-1). Levels for representative radionuclides in each dose coefficient group are listed, although any radionuclide can be placed into its appropriate group. There is no provision in the Codex guidelines for summation across radionuclide groups; each level applies independently of one another. Within groups, radionuclide contributions are to be added for comparison with the level.
Nuclear Energy Agency of the Organization for Economic Co-operation and Development
The Nuclear Energy Agency (NEA) has issued guidance (OECD 1989, 1990) intended to assist national authorities in the development of policies and criteria for the management of the consequences of a nuclear emergency. As with the ICRP and IAEA, the basic principles for intervention are those of justification and optimization, while recognizing the value to emergency planning of predetermined criteria. In the planning and preparedness phase, a generic optimization is recommended in order to develop generic intervention levels for use immediately following an emergency. In the event of a real emergency, a more precise optimization is recommended, resulting in specific intervention levels for use in the medium and long-term (OECD 1990).
While no specific action levels for food have been given, the NEA suggests that these be derived on the basis of groupings of radionuclides rather than for individual nuclides. Radionuclides may be grouped on the basis of comparable radiotoxicity, and the most restrictive dose coefficient in each group, for the most restrictive age group, should be selected as the basis for the derived intervention level. Four radionuclide groups are suggested, namely, iodine isotopes (e.g., 131I), cesium isotopes (e.g., 137Cs), other long-lived radionuclides (e.g., 90Sr), and alpha-emitting radionuclides (e.g., 239Pu). Derived intervention levels should be developed only for the major components of the diet; additivity should be considered only if the contributions to the ingestion dose from different foods are of a similar degree of importance, and individually represent a significant fraction of the corresponding derived intervention level.
Council of the European Communities; National Radiological Protection Board of the United Kingdom
Following the 1986 Chernobyl accident, the Council of the European Communities (CEC) issued Regulations on maximum permitted levels of radionuclides in food that would be legally binding on its member countries following a radiological emergency (CEC 1989, 1989a, 1989b, 1990, 1992). There are further Regulations dealing with foods imported from, and exported to, countries outside of the European Communities (CEC 1987a, 1989b).
Council Food Intervention Levels (CFILs) have been established for four radionuclide groups, and five food categories, and apply to food as marketed, rather than to food as consumed. Within each radionuclide and food group, the sum of the concentrations of all the specified radionuclides detected in the food is compared with the intervention level. However, each intervention level is applied independently of one another. CFILs have also been derived for radioisotopes of Cs in animal feeds.
Although the liquid foods group does not explicitly cover drinking water, the Regulations state that CFILs for such foods should be applied to drinking water at the discretion of competent authorities in member states. In its guidelines, the National Radiological Protection Board (NRPB 1994) has recommended that levels for liquid food be adopted for all drinking water supplies in the United Kingdom.
The NRPB emphasizes that these intervention levels represent the approach of the CEC towards balancing the harm and benefit of food restrictions. Consumption of food contaminated at levels well in excess of the intervention levels for short periods (up to a few weeks) need not give rise to significant radiation risks. Therefore, for the purpose of avoiding significant doses from food consumption, the immediate withdrawal of contaminated food supplies is, in general, not essential.
United States Food and Drug Administration
The USFDA, Department of Health and Human Services, has issued recommendations for state and local agencies for intervention following accidental contamination of food and animal feeds (USFDA 1998). Derived intervention levels (DILs) for the distribution of food in the United States are based on a Protective Action Guide for committed effective dose from ingestion of 5 mSv, or 50 mSv committed equivalent dose to any organ or tissue, whichever is more limiting.9They are intended to apply to the distribution and use of food produced during the first year after an emergency. If contamination extends beyond the first year, an evaluation of local longer-term conditions should be conducted to determine if the DILs should be continued, or if other guidance may be more appropriate. Food with concentrations below the DILs is permitted unrestricted distribution. However, State and local officials have flexibility in whether or not to apply restrictions in special circumstances.
DILs recommended by the USFDA have been derived for those radionuclides, under various accident scenarios, that are expected to deliver the major portion of the radiation dose from ingestion during the first year following an emergency. For each class of radionuclide, DILs have been calculated for the six ICRP age groups based on the total annual dietary intake for each age group, and assuming that contamination would occur in 30% of the dietary intake. An exception was made for 131I in the diets of the 3-month and 1-year age groups, where the entire intake over a sixty-day period was assumed to be contaminated. Dose coefficients were taken from ICRP Publication 56 (ICRP 1989). A single DIL was selected for each radionuclide group based on the most limiting age group for the radionuclide group.
| Radionuclide Group | Derived Intervention Level (Bq kg-1) for Components of the Total Diet |
||||
|---|---|---|---|---|---|
| 90Sr | 160 | ||||
| 131I | 170 | ||||
| 134Cs + 137Cs | 1 200 | ||||
| 238Pu + 239Pu + 241Am | 2 | ||||
| 103Ru + 106Ru(1) |  |
||||
Notes:
(1) The USFDA states that, "Due to the large differences in DILs for 103Ru and 106Ru, the individual concentrations of 103Ru and 106 Ru are divided by their respective DILs and then summed. The sum must be less than one" (USFDA 1998). C(103Ru) and C(106Ru) are the concentrations at the time of measurement.
The DIL for each radionuclide or radionuclide group is applied to all components of the diet, and to foods as prepared for consumption. They are applied independently for each radionuclide group since they relate to different types of accidents, or in the case of nuclear reactor accidents, to different limiting age groups.
8. WHO has not issued new guidance following the latest recommendations of the ICRP
(1991), which include revisions in its methodology and terminology for expressing
radiation doses. WHO uses terminology previously defined in the former ICRP recommendations
(ICRP 1977).
9. The USFDA uses terminology defined in the former ICRP (1977) recommendations, as there is
not yet a consensus among federal agencies in the United States on the use of the 1990 ICRP
recommendations, which include revisions in its methodology and terminology for expressing
radiation doses.
