Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad Radionuclides in tea and their behaviour in the brewing process Markus Zehringer * , Franziska Kammerer, Michael Wagmann State-Laboratory Basel-City, Kannenfeldstrasse 2, CH-4056 Basel, Switzerland ARTICLE INFO Keywords: Tea Radiocaesium Radiostrontium Brewing process Dose estimation ABSTRACT 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 con- tamination 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). 1. Introduction Tea is one of the most popular beverages; after drinking water, it is the most consumed drink worldwide. The tea plant, Camelia sinensis, is cultivated in many countries, including the People's Republic of China, India, Kenya, Sri Lanka, Turkey, Indonesia, Vietnam, Japan, Argentina and Iran. Black and green tea are the most consumed and most common teas marketed by commercial brands. Worldwide, it is estimated that over three million tons of tea is produced each year. Tea plantations need large areas for production. The tea plant reaches a height of 1–5m and carries many leaves, exposing a large surface to fallout (Abd El-Aty et al., 2014; Hirono and Nonaka, 2016). Therefore, tea is an ideal plant for the monitoring and investigation of radioactive fallout. Fallout reaches plantations via air and rain and radionuclides are deposited on the surface of leaves and on the soil. The tea plant takes up the radio- cesium from soil and translocates it quickly to the leaves (Takashi et al., 2018; Hinton et al., 1996). The part of 137 Cs deposited on the leave surface will be quickly removed by dissolution with water (Yasuhisa et al., 2015; Keiko et al., 2012). 137 Cs is reported to be present mainly in cationic form. However, there is also evidence of 137 Cs bound to polyphenols in tea (Emine, 2002). During the growing season, tea is harvested weekly. The main harvests are in March/April (first flush), in May/June (second flush) and in autumn (autumnal flush). This results in a continuous renewing of the tea leaves. After harvest, the process of tea manufacturing consists of several steps (withering, rolling, fer- mentation, drying) (Hirono and Nonaka, 2016; Pintauro, 1977). From 1945 to 1965, there were over 600 nuclear bomb tests in the atmosphere. In 1963 to 1965, global fallout, consisting mainly of long- lived radionuclides of caesium ( 134 Cs, 137 Cs), strontium ( 90 Sr) and plutonium ( 239 Pu, 240 Pu), reached a maximum in the northern hemi- sphere. Most important was the 90 Sr fallout. Until 1976, scientists es- timate a cumulated deposition of 90 Sr of 4,5 10 17 Bq in the Northern hemisphere and 9.3 10 16 Bq in the Southern hemisphere (Feely et al., 1978). In 1963, a partial test ban treaty was enacted (ban on all atmo- spheric bomb tests). Therefore, fallout was reduced remarkably after 1963. In 1964, the contamination level of tea cultivated in India was about 37 ± 36 Bq/kg dry weight (d.w.) of 137 Cs and 26 ± 11 Bq/kg d.w. of 90 Sr (Lalit et al., 1983). The contamination level started to de- cline, and from 1961 to 1985, activity levels in Indian tea did not ex- ceed 20 Bq/kg (Lalit et al., 1983). Table 1 summarises the con- tamination levels of tea from 1961 to 2011 found in literature and results from own investigations. A further global input of radionuclides came from the fallout re- leased in 1986, when the nuclear catastrophe at the Chernobyl NPP happened. The reactor fire caused a rise of the radio-contamination level in whole Europe and Turkey. Turkish tea, harvested in 1986, showed activities up to 30,000 Bq/kg d. w. of radiocaesium ( 134+137 Cs) and up to 430 Bq/kg d.w. of radiostrontium ( 90 Sr) (Zehringer, 2016; Gökmen et al., 1995). Turkish tea plantations on the south coast of the Black Sea were most affected, and 57% of analysed Turkish teas ex- ceeded the limit for radiocaesium (500 Bq/kg in tea water) (Gökmen et al., 1995). After 1987, the activity level in Turkish tea was reduced again to a level of 1–70 Bq/kg d.w. of 137 Cs (Zehringer, 2016; Gökmen https://doi.org/10.1016/j.jenvrad.2018.06.002 Received 14 March 2018; Received in revised form 31 May 2018; Accepted 2 June 2018 * Corresponding author. E-mail address: markus.zehringer@bs.ch (M. Zehringer). Journal of Environmental Radioactivity 192 (2018) 75–80 0265-931X/ © 2018 Elsevier Ltd. All rights reserved. T