Evaluation of spiking methods for the preparation of a proficiency testing material in cereal matrices : measurements of 131I, 134Cs and 137Cs in cereal matrices

Among many radionuclides released to the environment during a radiological emergency 131I, 134Cs and 137Cs are usually the most abundant ones. They are transferred to air, water and soil and from those media readily relocated to plants, including those intended for human consumption and for animal feed. Ensuring safe feed is an important component of the efforts to reduce and prevent food safety hazards, especially now, as consumers are increasingly aware of food safety issues and their linkage to animal production, including feeding practices. Therefore it is of utmost importance to ensure that the results of measurements of those three radionuclides delivered by the monitoring laboratories across the EU are reliable in order to guarantee a high degree of feed and food safety. It would be also beneficial to establish a standardised method of analysis for those radionuclides, which requires intra- and interlaboratory tests. In order to conduct such tests a reliable reference material is needed. Since one of the radionuclides (131I) is very short-lived (T1/2 = 8.0233 ± 0.0019 days) a spiking method for preparing test samples is necessary. Therefore procedures for spiking of powder were tested. Two methods of material preparation were tested - spiking a bulk sample of powder and individual spiking, where radioactive solution was introduced directly into containers in which samples were being measured. Both methods provided satisfying results. The bulk spiking method was proven to give homogenous samples, which was confirmed by one way analysis of variance (ANOVA) test. In the second method the relative deviation between the amount of the activity added and the calculated activity values was low and lower than the values of uncertainty calculated for the measured activity values. Therefore it can be stated that the closeness of agreement between the activity added to the sample and activity measured was satisfactory. This proves that these samples may be used as a reference material for the method validation and for the next proficiency test planned by the JRC Geel.