Thermoluminescence detection of irradiated shellfish: international interlaboratory trial

An international interlaboratory trial was conducted using thermoluminescence for the detection of irradiated shellfish, aimed at validating the method for routine use. Nephrops norvegicus, mussels, brown shrimps, black tiger prawns, and king scallops were presented as nonirradiated and irradiated to 0.5 and 2.5 kGy. The protocol called for the use of 3 preparation methods: extraction of silicates from whole shellfish by acid hydrolysis and physical separation, and of carbonates from powdered shells. Homogeneity was tested on each product and each treatment. Results verified that all methods were able to distinguish between nonirradiated and irradiated samples regardless of dose. Silicate methods produced better discrimination than powdered shell, and acid hydrolysis showed some evidence of better separation between the 2 doses than the physical method. Participants received each product in each treatment category for blind analysis. Six participants returned results for acid hydrolysis, 7 for physical separation, and 5 for the powdered shell method. Their results confirmed the homogeneity testing. Qualitative results gave 100% correct classification for both silicate methods and 85.3% for powdered shell. Silicate methods are therefore preferable unless only shell is available. Overall, the results confirmed the case for validation.