Sinikka Pinnioja

Identification of irradiated foods by the thermoluminescence of mineral contamination

ZusammenfassungGegenstand dieser Untersuchung ist die strahleninduzierte Thermolumineszenz (TL) der in Lebensmitteln enthaltenen Mineralien als Mittel zur Identifizierung strahlenbehandelter Lebensmittel. Untersucht wird nicht der Eigengehalt der Lebensmittel an Mineralien, sondern die Mineralienkontamination. Die positive Identifizierung von Lebensmitteln, die mit einer Dosis von 1–10 kGy bestrahlt worden waren, ist abhängig vom Gehalt und der Zusammensetzung der Mineralienkontamination sowie von der Zeitspanne zwischen Bestrahlung und TL-Analyse. Noch nach Ablauf von maximal einem halben Jahr konnten sämtliche Gewürzund Kräuterproben (insgesamt 20 Stück) ohne irgendwelche Vergleiche mit unbestrahltem Material identifiziert werden. Von insgesamt 60 bisher überprüften Losen waren drei so sauber, daß ihr Mineraliengehalt für eine TL-Analyse nicht ausreichte. Wenn der Boden eines Kartoffelfelds Feldspate enthält, kann auch die Keimhemmungsbehandlung der Kartoffeln mit Dosen von 100 bis 200 Gy noch bis nach Ablauf von einem Jahr erkannt werden; für die Bewertung wird dabei der Niedrigtemperaturanteil des TL-Spektrums im Bereich von 90 bis 250 °C herangezogen.SummaryThis investigation assessed the radiation-induced thermoluminescence (TL) of food minerals for identifying irradiated foods. Mineral contamination, rather than the inherent mineral content, of foods was studied. Positive identification of foods given 1–10-kGy doses depends on the contents and composition of the mineral contamination and the time span between irradiation and TL analysis. All 20 irradiated spice and herb samples could be identified without comparing them with unirradiated material. Three out of 60 lots of spices and herbs examined so far were so pure that the mineral contents were too low to allow TL analysis. If the soil where potatoes are grown contains feldspars, sprout inhibition treatment with 100–200-Gy doses can also be detected for up to one year, using the 90–250° C low-temperature part of the TL spectrum for evaluation.

Import control of irradiated foods by the thermoluminescence method

ZusammenfassungEine Thermoluminescenz-Methode (TL) wurde für die Einfuhrkontrolle bestrahlter Lebensmittel verwendet. Diese Methode basiert auf der Messung der Thermoluminescenz von in den Lebensmitteln vorhandenen mineralischen Verunreinigungen. Diese Methode, eine Bestrahlung festzustellen, wurde im Frühjahr 1990 in das offizielle finnische Kontrollverfahren aufgenommen. Lebensmittel mit reduziertem Mikrobengehalt, ohne feststellbare Begasungsrückstände werden mit der TL-Methode auf eventuelle Bestrahlung überprüft. Die mineralischen Stoffe werden mit verschiedenen Verfahren aus den Lebensmitteln abgetrennt. Dabei werden bei Gewürzen die mineralischen Partikel manuell entnommen, bei Kräutern, Gewürzen, Beeren und Pilzen werden diese mit Wasser abgespült, bei Meeresfrüchten wird mit hochkonzentrierter Lösung behandelt und das organische Material wird von der anorganischen Fraktion bei Lebensmitteln, die mit Wasser gelieren, mit Kohlenstofftetrachlorid abgetrennt. Bis jetzt sind zu Kontrollzwecken etwa 140 Lebensmittelproben analysiert worden: 50 Kräuter- und Gewürzproben, 25 Beeren- und Champignonproben und 65 Proben von Meeresfrüchten. Dabei konnte bei 14 Kräuter- und Gewürzproben sowie bei 5 Proben von Meeresfrüchten eine Bestrahlung nachgewiesen werden. Zwischen den bestrahlten und den unbestrahlten Proben zeigten sich in der TL-Intensität Unterschiede von mindestens einer, meist jedoch von drei bis zu vier Größenordnungen.SummaryA thermoluminescence (TL) method was applied for the import control of irradiated foods. The method is based on the determination of the TL of mineral contaminants in foods. Detection of irradiation was incorporated in official Finnish control procedures in spring 1990. For foodstuffs with a reduced microbe content and in which no fumigant residues are found, possible irradiation is investigated by the TL method. The minerals are separated from the foods in different ways: picking is used for spices; water rinsing for herbs, spices, berries and mushrooms; high-density liquid to separate the organic material from the mineral fraction in seafood; and carbon tetrachloride for foods forming gels with water. To date about 140 food samples have been analysed for control purposes: 50 samples of herbs and spices, 25 samples of berries and mushrooms and 65 samples of seafood. Of these, 14 samples of herbs and spices and 5 samples of seafood were shown to have been irradiated. Differences in TL intensity between irradiated and unirradiated samples were at least 1 and usually 3–4 orders of magnitude.

Suitability of the thermoluminescence method for detection of irradiated foods

Abstract Irradiated foods can be detected by thermoluminescence (TL) of contaminating minerals. Altogether about 300 lots of herbs, spices, berries, mushrooms and seafood were studied by the TL method. Irradiated herbs and spices were easily differentiated from unirradiated ones two years after irradiation of a 10 kGy dose. The mineral composition of seafood was variable; and while calcite was suitable for the TL analysis, aragonite and smectite gave unreliable results. Control analyses during two years confirmed the reliability of TL method.

Thermoluminescence of minerals useful for identification of irradiated seafood

Abstract Irradiated seafood can be identified by determining thermoluminescence of minerals isolated from the intestines. In this study the suitability of different minerals was investigated. The main mineral fractions isolated from the intestines of seafood were single silicate grains, shell pieces and clays. Silicate minerals are best suited for the detection of irradiation because of their stable and strong TL signal. However, shell pieces, mostly carbonates, and clays, also allowed a reliable detection.

Detection of irradiated foods by luminescence of contaminating minerals—effect of mineral composition on luminescence intensity

Laboratory irradiated rock and mineral samples were studied for their luminescence properties. The effect of alteration of feldspars on luminescence intensity was determined by the autoradiographic method for porphyritic granodiorite planar rock samples and with the TL reader for crushed minerals. Feldspars and quartz exhibited more intensive luminescence than mafic minerals, and luminescence of fresh K feldspar was the most intense. Potassium concentration did not have any effect on luminescence intensity for K feldspars but the intensity was highly dependent on the alteration degree of the mineral. Decrease in luminescence was found without a change in the element composition of the mineral and alteration was due to sericitization of K feldspar.

Effect of feldspar composition on thermoluminescence in minerals separated from food

Abstract Study was made of factors influencing the thermoluminescence (TL) intensity of feldspars separated from irradiated foods. Autoradiography and optical densitometry with application of digital image processing was found to be a suitable method for determining the mineral specific differences in irradiated feldspars. Alteration of K feldspar was observed to reduce the luminescence intensity. A structural change from unaltered mineral to fully seriticized form without marked change in element composition was accompanied by a decrease in TL from very intensive to nonobservable. Likewise increase in FeO concentration during alteration was accompanied by decrease in the TL intensity. Thermoluminescence of plagioclase increased with the CaO/Na 2 O ratio.

Effect of mineral composition on thermoluminescence detection of irradiated seafood

Abstract Data from import control of irradiated seafood were collected from 300 batches of seafood. Thermoluminescence (TL) analysis of the seafood, based on measurement of thermoluminescent minerals separated from intestinal tract, was carried out with a Riso TL-DA-10 instrument. As identified by X-ray diffraction and SEM/EDS analysis, four main categories of minerals were extracted: tectosilicates, phyllosilicates, carbonates and sulphates. Detection of irradiation was reliable when based on the TL of tectosilicate minerals, i.e. quartz and feldspar. Suitable minerals were found in most seafood: only about five percent of all samples could not be successfully analysed because no minerals or only non-thermoluminescent clays or carbonates were found. False positive results were never obtained. A false negative decision results if analyses are based on hydrous clays or carbonates in the form of aragonite.

Comparison of batch and autoradiographic methods in sorption studies of radionuclides in rock and mineral samples

Sorption of /sup 89/Sr, /sup 58/Co, /sup 134/Cs and /sup 241/Am in rock and mineral samples was determined by the batch method using crushed samples and by autoradiographic method using rock thin sections. The rock samples were tonalite and rapakivi granite, representing the Olkiluoto and Loviisa nuclear power plant sites, respectively. The autoradiographic method was found to be applicable sorption of radionuclides in rock and mineral samples. The sorption order of nuclides in rock and mineral samples was K/sub a//sup Am/ > K/sub a//sup Cs/ > K/sub a//sup Co/ > K/sub a//sup Sr/ the sorption order of the different minerals was biotite > hornblende > plagioclase > potassium feldspar > quartz. Distribution coefficients (K/sub a/) obtained by the batch and autoradiographic methods were of the same order of magnitude. K/sub a/-values of Sr, Co, Cs/sub 2/, and Am for tonalite were 5, 20, 190 and 40 x 10/sup -4/ m/sub 2//m/sup 2/ by the batch method and 1, 9, 130 and 170 x 10/sup -4/ m/sup 3//m/sup 2/ by the autoradiographic method. 5 references, 1 figure, 5 tables.