The determination of Fukushima-derived cesium-134 and cesium-137 in Japanese green tea samples and their distribution subsequent to simulated beverage preparation

Do You Know What You Drink? Comparative Research on the Contents of Radioisotopes and Heavy Metals in Different Types of Tea from Various Parts of the World

The aim of this study was to assess the potential health risks of radioactive elements and heavy metals ingested through the consumption of various types of tea imported to the Polish market (black, green, red, oolong and white). The concentrations [Bq/kg] of radionuclides (40K, 137Cs, 226Ra, 210Pb and 228Th) in tea leaves before and after brewing were measured using γ-ray spectrometry with high-purity germanium (HPGe). The concentrations [mg/kg] of the studied elements (Fe, Cr, Cu, Mo, Al, Mn, Ni, P, V, Cd and Pb) were determined using a microwave-induced plasma optical emission spectrometer (MIP-OES). The results presented here will help to expand the database of heavy metals and radioactivity in teas. With regard to the potential health risk, the percentage of leaching of individual elements in different types of tea infusions was determined, and the assessment of the consumption risk was estimated. Since the calculated exposure factors, namely the HQ (Hazard Quotient) and THQ (Target Hazard Quotient), do not exceed critical levels, teas can still be considered health-beneficial products (most of the radionuclides as well as elements remain in the leaves (65-80%) after brewing).

Radioactivity concentration measurements in fish and shellfish samples from the west coast of Canada after the Fukushima nuclear accident (2011-2018)

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concern about seafood safety, particularly in coastal Indigenous communities. To address this, Health Canada and partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. While the vast majority of the ¹³⁷Cs and ¹³⁴Cs levels were below the Minimum Detectable Concentration (MDC, typically 0.7-1.0 Bq kg^-1 fw for a 6 h counting), further examination of 19 fish samples revealed ¹³⁷Cs concentrations of 0.17-0.53 Bq kg^-1 fw with an average value and uncertainty (k = 1) of 0.29 ± 0.02 Bq kg^-1 fw. Of these, only two samples were found to have trace levels of ¹³⁴Cs likely derived from the Fukushima accident. The global fallout contribution from atmospheric nuclear weapons testing to the observed ¹³⁷Cs in these two samples was determined to be 0.26 ± 0.08 Bq kg^-1 fw (49 ± 14%) and 0.12 ± 0.02 Bq kg^-1 fw (24 ± 4%) for collection years 2015 and 2016, respectively. The annual average level of ¹³⁷Cs in fish and shellfish was also determined by spectral summation for collection years 2014-2018. In fish, ¹³⁷Cs levels determined through spectral summation were relatively constant (0.18-0.25 Bq kg^-1 fw) with an average value and uncertainty of 0.21 ± 0.02 Bq kg^-1 fw. By contrast, 38 shellfish samples (bivalves) were measured and revealed no radiocesium or other anomalies in either tissue or shell. In all, measurements over eight years showed that the radioactivity in fish and shellfish was dominated by natural radionuclides and that the level of anthropogenic radionuclides, as indicated by the radioactive cesium content, remained small. An upper bound for ingested dose from ¹³⁷Cs was determined to be approximately 0.26 μSv per year, far below the worldwide average annual effective dose of 2400 μSv from exposure to natural background radiation. We can therefore conclude that fish, such as salmon, ground fish, and shellfish from the Canadian west coast are of no radiological health concern despite the Fukushima Dai-ichi nuclear accident of 2011.

Radiological evaluation of Ra-226, Ra-228 and K-40 in tea samples: A comparative study of effective dose and cancer risk

Activity concentrations of tea samples were determined using high resolution gamma spectrometry.The values ranged from (421.00 ± 17.00) to (732.00 ± 30.00) Bq.kg ^-1 for K-40 and from (3.00 ± 0.80) to (27.00 ± 3.00) Bq.kg^-1 for Ra-228. The values for Ra-226 were below 27.00 Bq.kg^-1. The committed effective dose was estimated at 4.74-78.89 μSv.y^-1 for adults and 13.55-445.84 μSv.y^-1 for children. The cancer risk was higher for females. However, results showed that the tea consumption do not represent a radiological health risk to the population.

Comparisons of effective half-lives of radiocesium in Japanese tea plants after two nuclear accidents, Chernobyl and Fukushima

The time-dependence of ¹³⁷Cs in new shoots of tea (Camellia sinensis (L.) Kuntze) following a¹³⁷Cs-deposition was analyzed and quantified in terms of effective half-lives. The underlying monitoring studies were performed after the accidents in the Chernobyl and the Fukushima Daiichi nuclear power plants for tea plants growing in Japan. The major transfer route for atmospherically deposited radiocaesium to the first new shoots sampled after the accidents were different: for the Fukushima accident, it was mainly translocation of radiocaesium deposited onto old leaves and twigs to the new growth, while direct deposition on the new leaves was the major source after the Chernobyl accident. The effective half-lives in new tea leaves representing the fast and slow components of the decline did not significantly differ between these accidents. Geometric means (ranges) of fast and slow effective half-lives of ¹³⁷Cs after the Chernobyl accident were 66 d (25-125 d) and 902 d (342-15900 d), respectively, and those after the Fukushima accident were 50 d (26-105 d) and 416 d (222-1540 d), respectively. From these results, ¹³⁷Cs declines in new tea leaves were similar although contamination conditions were different for these two accidents.

Radionuclides in tea and their behaviour in the brewing process

Tea plantations may be strongly affected by radioactive fallout. Tea plantations on the Turkish coast of the Black Sea were heavily contaminated by the fallout from the reactor fire at the Chernobyl nuclear power plant in 1986. Two years later, the contamination level was reduced by about 90%. When tea is brewed, the original contamination in the tea leaves is more or less leached into the tea water. While most of the radiocaesium (60-80%) is washed out by brewing, most of the radiostrontium remains in the leaves (70-80%). In food laws, a dilution factor of 40-50 is considered for tea brewing. Most laws only define limit values for radiocaesium. Radiostrontium is not specially regulated, even though its dose coefficients for ingestion are higher than the corresponding coefficients for radiocaesium. Radiostrontium in tea occurs primarily from global fallout (bomb tests from 1945-1965).

Japanese Food Data Challenge the Claimed Link between Fukushima's Releases and Recently Observed Thyroid Cancer Increase in Japan

Internal, high-dose exposure with radioiodine is known to increase the risk for thyroid cancer in children and adolescents. Ingestion of contaminated food is generally regarded a dominant route of internal exposure. We analyzed the huge data set of the post-Fukushima food monitoring campaign and deployed a conservative model for the estimation of the doses to the general public in a worst-case scenario. Our data suggest that the committed equivalent ingestion doses to the thyroids of the affected Japanese public, even in the utmost conservative approach, remained below the limit on ingestion of radioiodine in foodstuffs and beverages of 50 mSv (as thyroid equivalent dose). This level of 50 mSv is also the intervention level for the administration of stable iodine, mainly after inhalation. Our study hence suggests that, based on the food data, the internal exposure of Japanese residents was too low to cause a statistically discernible increase in thyroid cancer, even if the contribution from inhalation is taken into account. The data also indicate that the governmental efforts in the food monitoring campaign were successful and cut the thyroid doses to the public by a factor of approximately 3 compared to a scenario without any monitoring.