Protection action levels for radionuclides in foodstuffs in the context of an emergency, based on Health Canada guidance.

Transcription

1 DEEP GEOLOGIC REPOSITORY PROJECT JOINT REVIEW PANEL File: 2.05 e-doc: UNDERTAKING RESPONSE No. 30 by the Canadian Nuclear (CNSC) staff UNDERTAKING: Protection action levels for radionuclides in foodstuffs in the context of an emergency, based on Health Canada guidance. Introduction The fundamental goal behind emergency planning and response is protecting the public from the potential harmful effects of radiation exposure resulting from an unplanned release of radiation to the environment. In the event of a nuclear emergency, response organizations will be called upon to provide advice and guidance on measures that should be taken by the public in order to reduce or avoid unnecessary dose. These measures, referred to as countermeasures or protective actions include the consideration of sheltering, evacuation, administration of stable iodine and the restriction of food and water that is contaminated. The subject of this undertaking are the Canadian guidelines [Ref. 1] that are in place to restrict the ingestion of contaminated foodstuffs, and the basis of those guidelines. However, it is important to note that guidelines that relate to other countermeasures are in place in Canada and are fully described elsewhere [Ref. 2]. Scope The guidelines discussed herein, published by Health Canada, have been developed with two principal objectives: - to minimize the health risk associated with the consumption of contaminated foodstuffs - to preserve public confidence in the safety of the commercial food supply The guidelines apply solely to the control of commercial foodstuffs and public drinking water supplies resulting from a nuclear emergency. That is, they do not apply to non-commercial food supplies or private water supplies. Note that the Health Canada Guidelines discussed in this undertaking are currently under review. 1 of 7

2 Intervention and Action Levels Intervention levels are expressed in terms of a dose that is expected to be avoided overtime by a specific protective action or countermeasure. In the case of restriction on commercial foodstuffs and water, Health Canada has chosen an intervention level of approximately 3 msv divided equally between the following three food groups: fresh liquid milk, drinking water and other commercial foods and beverages. That is, each food group has an intervention level of 1 msv. This means that if the contamination of a food group would result in a dose of approximately 1 msv or greater, intervention - the withdrawal of food and water from sale or distribution - should be taken. Action levels are directly measurable quantities that are derived based on the intervention level. In this case, the action level corresponds to an activity concentration (for example in units of Bq per kg) of a radionuclide that would lead to a dose of approximately 1 msv. Since the dose received depends on a variety of factors and assumptions, action levels are needed so that those responsible for food screening and safety can effectively screen the food to determine whether or not it can be made commercially available or withdrawn from distribution. Development and Basis of the Action Levels As was previously mentioned, action levels have been developed for three separate food groups: - Fresh Liquid Milk - Other Commercial Foods and Beverages - Public Drinking Water In the derivation of the action levels, the following key assumptions and/or input parameters were used: - for Public Drinking Water and Fresh Liquid Milk, it is assumed that the intake consists entirely of contaminated sources. This assumption was based on the fact that milk and drinking water are usually obtained from local supplies. - for the Other Commercial Foods and Beverages Group, it is assumed that 20% of the food is contaminated and the rest is contamination free (i.e., has not been contaminated as a result of the emergency). This is in line with the fact that individuals receive their food (in this food group) from a variety of widespread sources; few of which are likely to be impacted by contamination as a result of an accident. - 6 age groups were assessed (discussed below). - annual intakes for the food groups are based on Canadian consumption data [Ref. 3]. - Food is assumed to be consumed for the entire duration of the assessment period: o The assessment period is 1 year for radionuclides with long half lives. o The assessment period is 2 months for radionuclides with short half lives (less than 300 hours). 2 of 7

3 The action levels were calculated according to equation 1: IL ALi, j, k = (equation 1) M DC f j, k i, k j where AL i,j,k = action level for radionuclide i in food group j and age group k (Bq kg -1 ) IL = intervention level (Sv) M j,k = mass of food group j consumed by age group k over the assessment period (kg) DC i,k = ingestion dose coefficient for radionuclide i and age group k (Sv Bq -1 ) f 1 = contamination factor, equivalent to the fraction of an individual s dietary intake of food group j assumed to be uniformly contaminated to the full value of AL i,j,k Action levels have been developed for the radionuclides that are expected to be the most significant contributors to dose through the ingestion pathway. Data available from previous nuclear reactor accidents indicate that these radionuclides are: Sr-89, Sr-90, Ru-103, Ru-106, I-131, Cs-134, Cs-137, Pu-238, Pu-239, Pu-240, Pu-242 and Am-241. However, depending on the type of facility that has undergone an emergency and the specifics of the event, other radionuclides may be released into the environment. For example, at CANDU reactors tritium will also be released. Therefore, other radionuclides which contribute less to the ingestion dose have also been identified and action levels developed. Thus, the radionuclides have been divided into two groups: those having the most contribution to dose, in table 1, and those of lesser radiological concern, referred to by Health Canada as supplemental action levels, in table 2. The methodology used in the calculation is the same for both types. Table 1: Recommended action levels for radionuclides of potential significance to dose from the ingestion of contaminated food. Radionuclide Action levels (Bq/kg) * Fresh Liquid Milk Other Commercial Foods and Beverages Public Drinking Water Sr Sr Ru Ru I Cs-134, Cs Pu-238, Pu-239, Pu- 240, Pu-242, Am * Bq/L for drinking water 3 of 7

4 Table 2: Recommended action levels for radionuclides of lesser significance to dose from the ingestion of contaminated food. Radionuclide Action Levels (Bq/kg) * Fresh Liquid Milk Other Commercial Foods and Beverages Public Drinking Water H-3 30, , ,000 C-14 3,000 10,000 3,000 Cr-51 30, ,000 10,000 Fe-55 1,000 3,000 1,000 Fe-59, Co , Zn-65, Y , Zr-95 1,000 3,000 1,000 Nb-95 1,000 10,000 1,000 Mo-99 10,000 30,000 10,000 Ag-110m 300 1, Te-132 1,000 3,000 1,000 Ba-140 1,000 10,000 1,000 La-140 3,000 10,000 1,000 Ce-141 1,000 3,000 1,000 Ce Np Np-239 3,000 30,000 3,000 Pu , Pu * Bq/L for drinking water Guidelines implemented to protect the general population must protect the most sensitive in the population. Therefore, action levels for each radionuclide of concern (shown in tables 1 and 2) were calculated for six age groups, using age specific consumption rates and ingestion dose coefficients 1. However, to achieve practical and straightforward guidelines, a single action level was chosen for each radionuclide based on the most restrictive of all six age groups. Further, in order to reflect uncertainties and simplify implementation, the calculated action levels were grouped into similar categories and assigned representative single values of either 1, 3, 10, 30, 100, 300, 1000, 10, 000, 30,000 or 100,000 Bq/kg. For these reasons, along with the different consumption rates, the values between the action levels for milk and water in tables 1 and 2 sometimes differ. In the case of tritium (H-3), action levels are based on organically bound tritium for fresh liquid milk and tritiated water for public drinking water, leading to larger differences between the 2 action levels. 1 The 6 age groups are: 3 months, 1 year, 5 year, 10 year, 15 year, and adult. These are based on age categorizations recommended by the ICRP [Ref. 4]. 4 of 7

5 Screening In order to screen potentially contaminated foods, levels of radioactivity in the foods are compared to the appropriate action levels. When applying the action levels, each sample of food is assumed to be representative of the total amount of the food type consumed by a person. - In the case of fresh liquid milk and water, it is assumed that a person s entire milk intake is contaminated at the same level as the milk sample in question. - In the case of a food in the Other Commercial and Beverages Group, such as meat, it is assumed that 20% of a person s beef intake is contaminated at the same level as the meat sample in question. This 20% is referred to as the contamination factor, shown as f in equation 1. For fresh liquid milk and water, the contamination factor is 1. Food samples containing only one radionuclide are screened for acceptance by comparing the sampling result with the appropriate action Level. If several radionuclides are present in a sample, the action level for each of the radionuclides present is taken into account. This is done by ensuring the following criteria is met: i (A i /AL i ) 1 (equation 2) Where A i is the measured activity concentration of radionuclide I, for example in Bq/kg, and AL i is its corresponding action level. Compliance with the guidelines is a straight forward pass or fail criteria as described previously. Foods failing the conditions would be withdrawn from sale and replaced with alternative sources, if possible. An example is shown below. A sample of beef contains 500 Bq/kg of Cs-134 and 800 Bq/kg of Cs-137. The corresponding action levels for these radionuclides are 1,000 Bq/kg for each of Cs-134 and Cs-137. Since there are 2 radionuclides, the summation criteria must be used: 500Bq / kg 800Bq / kg + 1,000Bq / kg 1,000Bq / kg = 1.3 Because the summation exceeds 1, the criteria are not met in this case and the supply from which the sample was taken must be withdrawn from the market. Note that in the case of the Other Commercial Food and Beverages group, each food is treated independently. That is, the action levels are based on total dietary consumption of the group and not of individual food or food types. 5 of 7

6 Action levels are applied to food as prepared for consumption and are assessed on the basis of fresh weight. Despite the fact that washing and peeling fruits and vegetables are an effective means of reducing contamination, this is not accounted for and is therefore a conservative assumption. Relationship to the FAO/WHO Codex Alimentarius Various international organizations play a role in the protection of people in a radiological emergency. These organizations include the International Commission on Radiological Protection, the International Atomic Energy Agency, the World Health Organization and the Food and Agriculture Organization (FAO). The FAO/WHO codex Alimentarius Commission is a body that was set up jointly by the FAO and WHO that adopted guidelines that apply to the international trade of food that has been contaminated with radionuclides in the first year following an accident. These guidelines will be referred to as the Codex [Ref. 5], herein. Since consistency among national jurisdictions allows for less disruption to international trade, Health Canada looked for opportunities to harmonize with the Codex. While differences in values are expected due to the methodology and contributing factors such as age group considerations and dietary consumption rates, for most radionuclides in the Other Commercial Food and Beverages groups, the calculated action levels were very similar to the Codex recommendations for Foods Destined for General Consumption. As a result, most of the values in this group were harmonized with the Codex. In the case of Fresh Liquid Milk, most of Health Canada s calculated action levels were less than the Codex values for Milk and Infant Foods and for this reason most were not harmonized with the Codex values. However, as fresh milk is not usually a traded commodity, harmonization is not necessary. The Codex does not have values for public drinking water. The radionuclides provided in table 2 of this document are not listed in the Codex and therefore, harmonization was not possible. Authority Health Canada, under the Food and Drugs Act has the primary responsibility for the safety of all domestic and imported food for sale in Canada. This authority applies in the event of contamination of commercial food supply. Thus, the guidelines for food described in this document would be implemented in the case of an emergency. However, in the case of drinking water, the authority lies within provincial, territorial or municipal jurisdiction. Therefore, provinces may choose to adopt the guidelines in whole or in part, or develop their own criteria. However, harmonization of any applicable guidelines is encouraged due to the benefits of doing so with regards to public confidence. The Canadian Food Inspection Agency (CFIA) is responsible for monitoring and enforcing the food and safety standards and guidelines established by Health Canada. 6 of 7

7 References: 1. Canadian Guidelines for the Restriction of Radioactively Contaminated Food and Water Following a Nuclear Emergency, Health Canada, Canadian Guidelines for Intervention During an Emergency, Health Canada, Reference Values for Canadian Populations. Environmental Health Directorate Working Group on Reference Values, Health Canada, Age-Dependent Doses to Members of the Public from Intake of Radionuclides. Part 5 Compilation of Ingestion and Inhalation Dose Coefficients. ICRP Publication 72. Ann. ICRP Codex Alimentarius, General Requirements, Section 6.2, Guideline Levels for Radionuclides in Foods Following Accidental Nuclear Contamination for use International Trade, Joint FAO/WHO Food Standard Program, of 7