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Japanese green tea


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Invited lecture by Sergio Manera at the NRC-8 EuCheMS conference in Como (16-21 september 2012)

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Japanese green tea

  1. 1. NRC8 - International Conference on Nuclear and Radiochemistry Session 13: radioactive elements in the environmental Japanese Green Tea - radioactivity measurments, radiochemical extraction yield determination and some radioprotection considerations 21st september, 2012 Authors: S.Manera1, M.Oddone2, A.Salvini1, L.Strada2 1LENA University of Pavia, 2Chemical Dept. University of PaviaDr. Sergio Manera - Radioprotection Adviser LENA (UniPv) - 1
  2. 2. Why Japanese Green Tea ?Of course because of the Fukushima Dai-ichi nuclear crisis.Everyone knows about Tea and how to prepare it, our context is wellknown.The consumption of tea is widespread in Japan (4th world top consumer,2nd largest producer) with about 1kg of leaves per person per year.Shizuoka Prefecture accounts for about 45% of Japan Green Teaproduction. Our green tea sample is from Shizuoka.MHLW selected Tea as a matrix of interest for monitoring radioactivity inthe environmental in Japan after the FD nuclear crisis for both domesticconsumption and export.Turkish tea analysis in the aftermath of Chernobyl accident are wellknown and we wanted to replicate those investigations for some “fresh”data. 2
  3. 3. Why Japanese Green Tea ?On June 17th, 2011, the French press reported that Shizuoka tea withdouble the accepted level of cesium was intercepted in Paris. EU ruleson acceptable levels of radiation are the same as Japan’s for 137Cs. Theofficial government statement indicated: “tea would be destroyed”.The radioactive releases and relative fallout over Japan started onmarch 12th 2011. Tea usually grows in soil from early April to mid-may (first harversting). There was the chance this matrix avoidedtotally the fallout and was exposed only the root uptake of Cesium inthe plant.Measurements of tea leaves started appearing early in 2011 but therehave been some misunderstandings about the measures. 3
  4. 4. A few informations about Green TeaThe classification of tea takes place on the basis of the processing of theleaves which is a key factor for the finished product.Tea may be fermented (Black Tea) where the oxidation of the leaves causesthe characteristic brown color or unfermented (Green Tea) in which thereare treatments with heat to prevent the oxidation of the leaves. There arealso semi-fermented tea. 4
  5. 5. A few informations about Green TeaGreen tea: tea is stabilized after harvest without being subjected to oxidationby means of dry heat, moist heat or roasting (Japanese common procedure).In Japan Tea means Green Tea, it’s the most common tea in the countryand green Tea is the most natural, undisturbed and interesting matrix toinvestigate the behavior of radioactivity such as Cesium and Potassium. …Black tea: tea made completely oxidize after harvest, tea fully fermented, typicalbrown color.Oolong tea: tea stabilized after partial oxidation.White tea: tea that undergoes whitering in dry air after harvest, silvery-white color.Yellow tea: tea stabilized and allowed to stand with the heat and moisture. It is morelike a green tea slightly post-fermented.Postfermeted Tea: tea stabilized and subsequently subjected to fermentation. 5
  6. 6. Material and methods: codex 2011 radionuclidesFor all the measurements we made a large use of high resolutionand low background gamma spectroscopy.FAO: “Codex Alimentarius Guideline Levels for radionuclides infood contaminated following a nuclear or radiologicalemergency” (may 2nd, 2011).The new Codex list of 20 (6) radionuclides: • 3H, 14C, 99Tc, 35S, 89Sr, 90Sr; • 60Co, 134Cs, 137Cs, 192Ir; • 129I, 131I, 103Ru, 106Ru, 144Ce; • 235U 238Pu, 239Pu, 240Pu, 241Am; • (in capitol our gamma investigation). • We added 40K (Potassium has the same behaviour as Cesium) and 238U, 232Th natural series to the list of the nuclides to be investigated. 6
  7. 7. Results: raw Green Tea gamma analysis 7
  8. 8. Results: ratio 134Cs/137Cs The activity ratio (134Cs/137Cs) is about 0.75, which is in good agreement, within the uncertainty of measure, with the initial ratio (scaled backwards to march 2011) of about 1:1 for the two isotopes which has already been world-wide assessed.Whole of LENAmeasures on the FD crisis 8
  9. 9. Results: raw material homogeneity testTo investigate homogeneity we mixed the sample and randomlydivided it in 3 sub-samples of about 60-70 g each, then wecounted them separately using the 100 ml bottle geometry.The sample dishomogeneity index is calculated as the simpledispersion from the mean value reported in column 4;The results show the raw material is actually well homogeneus. 9
  10. 10. Tea preparation and extraction YieldTo investigate the extraction Yield of Cesium and Potassium wepreparated Tea beverage in 4 different ways: 8-10g/100ml, 5min extraction time 8-10g/100ml, 10min extraction time 8-10g/100ml, 15min extraction time 8-10g/100ml, 5+5min extraction time (2 extractions)The extraction yield is the ratio (or the percentage) ofCesium/Potassium in the prepared beverage in respect to theammount of Cesium/Potassium in the dryed tea leaves.We used boiling deionizated water instead of tap water toachieve more reproducibility.All the prepared beverage have been stabilized in 100ml bottlegeometry adding 1ml of diluted technical grade hydrochloricacid. 10
  11. 11. Tea preparation and extraction YieldUsed tea leaves are usually disposed to urban waste on commonuse of the product.Tea leaves after preparation of the beverage have been packed up(still partially wet) and pressed in multifilter geometry to bemeasured again to investigate the eventual loss ofCesium/Potassium.The last step was required because of the very low specificradioactivity of the sample and we wanted to account for all theradioactivity processed step by step. 11
  12. 12. Results: the extraction Yield measurements (1) 12
  13. 13. Results: the extraction Yield measurements (2) 13
  14. 14. Results: the extraction Yield determination (3)The extraction Yield doesn’t seem to be affected by the extractiontime. The 3 radionuclides show a very similar behavior in theprocess.The 2 in-sequence extractions do seem to add-up lineary. 14
  15. 15. Results: residual radioactivity in used Tea leavesThe percentage of residual activity in the used Tea leaves seemstable for all the 3 measured radionculides.The 2 in-sequence extractions do seem to add-up lineary again onall the 3 measured radionuclides.The total lost of Cesium/Potassium was less than 10%, consideringthe uncertainty. 15
  16. 16. Food limits and food safety in JapanIn Japan food safety is checked by means of a direct comparisonbetween measured values and “limits”. Limits are shown above.Based on the results of the comparison Japanese authorities issue foodrestrictions. Ordinances usually concern Prefectures or municipalitiesof origin and prohibit the sale and consumption of the product. 16
  17. 17. Saitama and Shizuoka - Tea Contamination Saitama Prefecture Shizuoka Prefecture 1826 measures before 31.03.2012 200 measures before 31.03.2012 6,9% 3,5% > limits > limits < limits < limits 93,1% 96,5%before 31.03.2012 N°measures < limits > limits Saitama 1826 1708 127 (118) Shizuoka 200 193 7 (7)Note: (118) is the number of dryed Tea samples positive to checks. 17
  18. 18. Some radioprotection considerationsIn many cases in Japan and during the first year of monitoring the nuclearcrisis of FD lacked the indication “fresh or dried food”. Mushrooms and Teaare particularly affected (ratio dryed/fresh of 5-7 ).In many cases Tea leaves measures were compared with the limit of 500Bq/kg (category general food) for food restrictions. This is wrong becauseFAO Codex Alimentarius - 2011 edition reccomends to evaluate the risk forfood “ready for consumption” and so Tea must be prepared. The limits ofthe category “Drinking water” should be applied to Tea beverages.For Tea it’s easy to standardize the laboratory preparation using the ISOGuide 3103:1980 issued for “flavor test of Tea”. It’s requirements are easy:2g-100ml-6min extraction time.Extraction yields are very easy to be determined and so why not usingthem? It’s a cut of 60% of the raw-material radioactivity content. Not usingEY can be considered a bad conservative approach. 18
  19. 19. Results: our tea?Our Tea contamination level: Raw measure of Cs-tot: 420 Bq/kg. Tea beverage: 8.4 Bq/kg. (using ISO standard). Adding the extraction yield to the tea beverage: 3.4 Bq/kg.Comparison with Provisional limits (till 31.03.2012): < 500 Bq/kg OK (wrong use of limits for vegetables) < 200 Bq/kg OK (correct use of limits for drinking water)Comparison with New limits (from 1.04.2012): < 100 Bq/kg NO (wrong use of limits for general foods) < 10 Bq/kg OK (correct use of limits for drinking water)Our Tea is fit for human consumption and may be lawfully sold. 19
  20. 20. Committed Effective DoseBased on tea consumption of about 1 kg/y of tea leaves perperson in Japan, the correspondent intake of radioactivity is easycalculated using the extraction rate measured above: ACs-tot = 1 kg/y * 420 Bq/kg * 0.4 = 168 Bq/ytherefore using the ingestion dose coefficients for 134Cs and 137Csin the weight ratio, the committed effective dose is:DAdults = (96 Bq * 1.3*10-08 Sv/Bq) + (72 Bq * 1.9*10-08 Sv/Bq) = 0.0026 mSv/yDInfants = (96 Bq * 2.1*10-08 Sv/Bq) + (72 Bq * 2.6*10-08 Sv/Bq) = 0.0039 mSv/y 20
  21. 21. Future tasksIt’s our aim to further and more widely investigate both theconcentration of radioactive Cesium and the extraction yields ingreen tea samples produced in Japan, including other prefecturesof origin.The goal is to confirm the extraction yields calculated with thiswork and to promote it’s application in dose assessment.It’s also important to assess the extraction yields starting fromthe first year after the nuclear accident and keep monitoring it forstability purposes. 21
  22. 22. Japanese Green Tea - radioactivity measurments, radiochemical extraction yield determination and some radioprotection considerations 21st september, 2012 THANK YOU FOR YOUR ATTENTION !! 22Dr. Sergio Manera - Radioprotection Adviser LENA (UniPv) -