Temporal variations of 7Be, 40K, 134Cs and 137Cs in epiphytic lichens (genus Usnea) at the Sakhalin and Kunashir islands after the Fukushima accident

Abstract

Temporal variations of radionuclide levels in the epiphytic Usnea sp. lichens from the two islands Sakhalin and Kunashir, the Sakhalin region, Russia have been evaluated using the already published (2011)(2012)(2013) and new experimental data (2015). A total of 62 lichen samples were measured using high purity germanium γ-ray detectors and multichannel analyzers. In the period 2011-2015, activity concentrations of the anthropogenic radionuclides 134 Cs and 137 Cs and the natural radionuclides 7 Be and 40 K were found to be in the range of (<0.53)-41. 3, 0.55-50.6, 99-603 and 35-95 Bq kg -1 on dry weight, respectively. The activity concentrations of 134 Cs and 137 Cs in lichens were statistically significantly higher at Kunashir than at Sakhalin. The present-day levels of radiocesium activity concentrations in lichens are low: < 6 Bq kg -1 for 137 Cs and <1 Bq kg -1 for 134 Cs. A decline in the annual median 137 Cs activity concentrations in lichens from 2011 to 2015 corresponds to a biological half-life of 1.2 y for Kunashir and 1.1 y for Sakhalin. The activity concentrations of 137 Cs and 134 Cs in lichens were strongly correlated (r=0.978, P<0.01) and the 134 Cs biological half-life value of 1.2 y in the period 2011-2013 was similar to the corresponding 137 Cs biological half-life value. The soil-tolichens aggregated transfer factor, T ag , for 134 Cs at time t=0 after the Fukushima accident is calculated as 0.56 m 2 kg -1 at Sakhalin and 0.31 m 2 kg -1 at Kunashir. In contrast to radiocesium, the natural radionuclides 7 Be and 40 K did not show clear time-dependent variations in the Usnea lichens. No correlation was found between 7 Be and 40 K as well as between 40 K and cesium radioisotopes. However, positive and statistically significant (P<0.05) correlations were obtained between 7 Be and cesium radioisotopes. High abundance of the Usnea sp. lichens in the study area and large values of T ag for radiocesium in the lichens make these organisms suitable candidates for detection of low levels of airborne radioactive contamination of the environment.

Fukushima Fallout in Sakhalin Region, Russia, Part 3: 137cs and 134cs in Cow’s Milk

“…The precipitate of caesium antimony iodide was placed on an aluminium plate (diameter = 1.5 cm) and dried. Gammaspectrometry analyses were performed using high-purity germanium detectors and multichannel analysers (ORTEC) to determine the 134 Cs and 137 Cs activities [14,16]. The plates were placed at a distance of about 3 mm from the cup of the detector.…”

“…Одна из причин заключалась в том, что на момент подготовки и выхода книги [8] в 2012 г. оценки, касающиеся соотношения активностей 134 Cs/ 137 Cs в выпадениях, запаса радиоцезия в почве и радиоактивного загрязнения растений на лугах, были неполными. В настоящее время после публикации дополнительных экспериментальных данных и обобщенных оценок по вышеуказанным вопросам [14][15][16][17][18] параметры перехода радиоцезия в цепочке «почва -трава -корова -молоко» могут быть оценены количественно. Кроме того, у авторов была возможность отобрать и проанализировать еще одну серию проб коровьего молока в Сахалинской области в 2012 г. Это позволило оценить динамику уровня радиоактивного загрязнения в первый и второй год после аварии.…”

“…The activity concentration of pre-Fukushima 137 Cs was calculated as a difference between the total activity concentration of 137 Cs and the activity concentration of Fukushima-derived 137 Cs. To calculate the activity concentration of Fukushimaderived 137 Cs, we applied the 134 Cs/ 137 Cs activities ratio of 1.0 in Fukushima fallout as of 15 March 2011 [14,16]. The half-life of 137 Cs and 134 Cs is 30.0 y and 2.06 y, respectively [24].…”

“…One of the reasons was the fact that at the moment of publishing the book [8] in 2012, the assessments of the 134 Cs/ 137 Cs activities ratio in Fukushima fallout, the radiocaesium inventories in soils and the radioactive contamination of plants in grasslands were incomplete. Currently, after publication of additional experimental data and generic estimations focused on the above mentioned issues [14][15][16][17][18], the transfer parameters in the "soil-grass-cow-milk" pathway can be evaluated quantitatively. Additionally, the authors had an opportunity to collect and analyze a new series of cow's milk samples in Sakhalin Region in 2012.…”

FUKUSHIMA FALLOUT IN SAKHALIN REGION, RUSSIA, PART 2: 137Cs AND 134Cs IN GRASSLAND VEGETATION

“…Разница между значениями T ag , полученными для проб, отобранных в 2011 г., и проб, отобранных в 2012 г., была статистически значимой (тест Манна -Уитни, P<0,05; n1 = 19, n2 = 8). Следовательно, экологический период полуочищения -T eco [5,28] Cs. Чтобы оце-нить коэффициент переноса из почвы в растение для on soil minerals or/and humus, and 2) migration of some proportion of the "aged" radiocaesium deeply down the soil profile, below the rooting zone [2,20].…”