Reply on RC2

We observed 3H activity concentrations and the 137Cs activity concentrations during the SoSo 5 rivers cruise in 2014 and at the Tomioka port in 2014–2018. The 3H activity concentrations at coastal stations located close to the Fukushima coast ranged from 90 Bq m−3 to 175 Bq m−3, and decreased between 67 Bq m−3 to 83 Bq m−3 at the stations located 12–16 km from the coast. The 3H activity concentration at the estuaries and ports, except at 56 north canal of the FNPP1 site, are around 200–500 Bq m−3 and slightly lower than the 3H activity concentration of 500–600 Bq m−3 observed in the rivers. These gradients of the 3H activity concentrations in the coastal region might indicate the large effect of 3H flux through the rivers. On the other hand, the 3H activity concentration at 56N of the FNPP1 site was significantly high compared to the 3H activity concentration in surrounding waters both north and south of the FNPP1 site and in river waters. It should also be noted that the 3H activity concentrations were similar at the stations located both north and south of the FNPP1 site, while the 137Cs activity concentrations were lower at the stations north of the FNPP1 site and higher at the stations south of the FNPP1 site. This indicated that the major sources of 137Cs could be the FNPP1 site as the point source while the source of 3H should be more diffuse and linked to riverine inputs located north and south of the FNPP1 site. The 3H / 137Cs activity ratios in coastal waters were 1.2–2.2 as obtained via the slopes by standardised major axis regressions between the 3H activity concentration and the 137Cs activity concentration of SoSo samples and Tomioka Port observed in 2014–2018, which is significantly high compared to that of the released radionuclides derived from the FNPP1 site, which was 0.01 in 2011 just after the accident. The open-water 3H activity concentration contribution to coastal waters was estimated to be 67 ± 20 Bq m−3 and 66 ± 17 Bq m−3 as the intercepts also by standardised major axis regressions. These estimates are consistent with 50 Bq m−3 obtained at the Kuroshio region as the background levels of 3H activity concentration in open water. The 3H and 137Cs fluxes to the coastal region of Fukushima based on the open-water movement, freshwater flux from the rivers based on their respective catchment, and mean monthly precipitation were estimated. The largest 3H flux is the open-water inflow from the north of the FNPP1 site and it reaches 52 GBq day−1, while the rivers north of the FNPP1 site showed 3–5 GBq day−1 fluxes. We obtained a 3H flux as 1.9–4.5 GBq day−1 of 3H using the 3H activity concentration in the port, which is comparable with the fluxes obtained from the rivers located north of the FNPP1 site. While using 3H activity concentration at the 56 north canal of FNPP1, we obtained 28–86 GBq day−1 fluxes, which is one order of magnitude larger than those estimated using 3H activity concentration in the FNPP1 port. One of the reasons could be the very high variability of the 3H levels at 56 north canal and in the port of FNPP1, explaining variable 3H/137Cs activity ratio observed at 56 north canal and in the port of FNPP1. The 3H activity concentration of TFWT in the fish filets collected close to the FNPP1 site ranged from 97 ± 11 Bq m−3 to 144 ± 11 Bq m−3, which were similar to the 3H activity concentrations in the surrounding seawater, in agreement with the knowledge that the bioconcentration factor of 3H is approximately 1. In contrast, higher values were found in TOBT, which can be linked to life-history traits.

Cruise SoSo 5 Rivers took place during October 2014 off the coast of Fukushima Prefecture shortly after the passage of two typhoons. Detection of dissolved 134Cs and 137Cs in all samples reflected contamination caused by accidental releases of radiocaesium from the Fukushima Dai-ichi Nuclear power plant (FNPP1) accident. The dissolved activities were generally higher at coastal sites and decreased with distance from shore, and they were higher in the surface than in the bottom water. The tendency of 137Cs activities to decrease with distance from the coast reflected mixing of coastal water and open-ocean water of which 137Cs activity concentration was ~1.5 Bq m−3. At stations very close to the coast, we observed high particulate 137Cs activity concentration that exceeded dissolved 137Cs activity concentration. 137Cs activities were generally 1–2 orders of magnitudes lower in organic particles than in dissolved form, and the ratios of 137Cs activity concentration in organic particles to 137Cs activity concentration in dissolved form ranged from 0.01 ± 0.00 to 0.12 ± 0.01. The ratio of 137Cs to 134Cs activity concentrations in organic particles did not change with distance from shore or with 137Cs activity concentration and generally remained around 1, even in samples collected far from the coast. This pattern indicated that the organic particles had come from rivers or a source very close to the coast. The 137Cs / 134Cs activity ratio in dissolved form north of FNPP1 region was estimated to be 1.074 ± 0.015, a ratio that is in good agreement with the 137Cs / 134Cs activity ratio in the core of Unit 1 of the FNPP1 while the 137Cs / 134Cs activity ratio at Tomioka port which located south of FNPP1 was 0.998 ± 0.017. Therefore we can conclude the source of radiocaesium in seawater in the coastal region north of FNPP1 was deposited radiocaesium released from the core of Unit 1 of FNPP1, while the source of radiocaesium observed in the coastal region south of FNPP1 was a mixture of deposited radiocaesium released from the core of Unit 2 and the core of Unit 1 of FNPP1. During September–October of each year, the typhoon season in Japan, the 137Cs activity concentration generally increased at Ukedo port, Tomioka port, FNPP1, and Iwasawa beach, and showed a good relationship with the 7-day modified antecedent precipitation index (API) while there is less correlation between the modified API and 137Cs activity concentration near the outlet of canal from unit 5 and 6 of FNPP1 to the sea.

Results of systematic, long-term measurements of (137)Cs activities in wheat for the period 1965-2003 are summarized. Radiocaesum fallout activities affect wheat activity concentrations, the coefficient of correlation being 0.91. In the observed period, the highest activity of (137)Cs deposited by fallout, 6321 Bq m(-2), was recorded in 1986, i.e., in the year of Chernobyl accident, causing peak (137)Cs activity concentration in wheat of 38.0 +/- 13.0 Bq kg(-1). After the Chernobyl nuclear accident the (134)Cs:(137)Cs activity ratio in wheat was approximately 0.5, and did not differ from the value found in other environmental samples. The transfer coefficient from (137)Cs fallout deposition to wheat was calculated to be 8.6 x 10(-3) Bq y kg(-1) per Bq m(-2), indicating the low transfer of radiocaesium from fallout to wheat. The upper limit for the collective effective dose for the Croatian population due to (137)Cs and (134)Cs ingestion by wheat and wheat products consumption for period 1965-2003 was estimated to be 665 person-Sv, the upper limit for the annual collective effective dose in 2003 being only about 0.061 person-Sv.

Persistence of 137Cs in the litter layers of forest soil horizons of Mount IDA/Kazdagi, Turkey

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 (2011–2013) 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 134Cs and 137Cs and the natural radionuclides 7Be and 40K 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 134Cs and 137Cs 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 137Cs and <1 Bq kg–1 for 134Cs. A decline in the annual median 137Cs 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 137Cs and 134Cs in lichens were strongly correlated (r=0.978, P<0.01) and the 134Cs biological half-life value of 1.2 y in the period 2011–2013 was similar to the corresponding 137Cs biological half-life value. The soil-tolichens aggregated transfer factor, Tag, for 134Cs at time t=0 after the Fukushima accident is calculated as 0.56 m2 kg–1 at Sakhalin and 0.31 m2 kg–1 at Kunashir. In contrast to radiocesium, the natural radionuclides 7Be and 40K did not show clear time-dependent variations in the Usnea lichens. No correlation was found between 7Be and 40K as well as between 40K and cesium radioisotopes. However, positive and statistically significant (P<0.05) correlations were obtained between 7Be and cesium radioisotopes. High abundance of the Usnea sp. lichens in the study area and large values of Tag for radiocesium in the lichens make these organisms suitable candidates for detection of low levels of airborne radioactive contamination of the environment.

Fish pollution with anthropogenic 137Cs in the southern Baltic Sea

Activity concentration measurements of selected radionuclides in seals from Canadian Arctic

The Norwegian mountain lake, Ovre Heimdalsvatn, received major fallout from the Chernobyl accident in the spring of 1986. Activity concentrations of 137Cs have been monitored annually in the brown trout (Salmo trutta) population of the lake over a 22-year period since 1986. The activity concentrations of 137Cs in brown trout have declined over the period, although in recent years there has been little or no reduction in activity concentrations. Throughout the period, there has been considerable individual variation in 137Cs activity concentrations. Within a single year, fish weight was the most significant factor affecting activity concentrations of 137Cs in individual fish, although sex and age·weight were significant explanatory variables. The “size effect” was not significant during the initial period after fallout and in some recent years. During the first years after fallout, the ecological half-life of 137Cs in brown trout was 3–4 years, but during the last decade this has increased significantly and has approached the physical half-life of 30 years for 137Cs, suggesting a dynamic equilibrium between catchments inputs, possible remobilisation from lake sediments and lake outputs of 137Cs.

<p>The <sup>137</sup>Cs (t<sub>1/2</sub> =30 years) is a principal radioisotope that was artificially introduced into the environment through the atmospheric bomb tests took place from the middle of the 1940s to the 1980s and from the major nuclear accidents (i.e., Chernobyl, 1986 and Fukushima, 2011). From the atmosphere, <sup>137</sup>Cs easily adsorbs to particles and it returns to lithosphere (pedosphere) by wet and dry deposition as a radioactive fallout component. Due to the Chernobyl nuclear accident, the released contaminated air mass, containing Cs-137, largely propagated, deposited, and distributed across several European countries in the ambient environment (Balonov et al., 1996). These particles also reached houses (e.g. through open windows, cracks, and vents) in an urban environment and deposited inside resulting in the exposition of the habitants to <sup>137</sup>Cs, especially in areas that are not accessible for a regular cleaning like attics. Following the nuclear accidents, primary attention was drawn to agricultural areas and less attention was paid to urban environments. Accordingly, the goal of this study is to compare the <sup>137</sup>Cs activity in attic dust as undisturbed samples, and urban soils as disturbed environmental materials to determine the <sup>137</sup>Cs distribution in urban environment. </p><p>Attic dust (AD) samples were collected from 14 houses, which were built between 1900 and 1990 14 urban soil (US) samples were collected nearby the houses at a depth of 0-15 cm in Salgótarján, a former industrial city. To obtain a representative local undisturbed soil sample, a forest soil sample was collected from the upwind direction (NW) of the city. To check the <sup>137</sup>Cs content of the local industrial waste material, we also collected fly-ash slag sample from a waste dump.   AD and US samples were analyzed by a well-type HPGe and with an n-type coaxial HPGe detector in a low background iron chamber, respectively.</p><p>Cs-137 activity in the studied AD ranges from 5.51±0.9 to 165.9±3.6 Bq kg<sup>-1, </sup>with a mean value of 75.4±2.5 Bq kg<sup>-1 </sup>(decay corrected in 2016). In contrast, US samples show <sup>137</sup>Cs activity ranging between 2.3±0.4 and 13.6±0.6 Bq kg<sup>-1</sup>.  The brown forest soil sample has elevated <sup>137</sup>Cs activity concentration (18.5<strong>±</strong>0.6 Bq kg<sup>-1</sup>), compared to the urban soils. The fly-ash slags activity is below the detection limit (0.7±0.5 Bq kg<sup>-1</sup>).</p><p>The average <sup>137</sup>Cs activity in AD is ~15 times higher than that of US. This result clearly indicates that attic area provides a protected (hardly or unchanged) environment, therefore physical condition of the dust remains constant in time, and there is a small chance for chemical reaction. Forest soil proves that US were highly disturbed by anthropogenic activity. This is supported by fly-ash slag activity results.  Whereas, <sup>137</sup>Cs activity concentration of the AD samples shows significantly higher than that of the studied soils in Hungary. This confirms again US cannot show the historical atmospheric <sup>137</sup>Cs pollution such as attic dust. A statistically significant relationship (p=0.003, r<sup>2</sup>=0.05) were found between the AD and US samples. Therefore, it can be considered that attic dust remained undisturbed for decades and preserve past record of components of atmospheric pollution.</p><p> </p><p> </p>

The radioactive fission product 90Sr has a long biological half-life (˜18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Assessing 90Sr is therefore extremely important in case of a nuclear disaster. In this work 16 soil samples were collected from the exclusion zone (<30 km) of the earthquake-damaged Fukushima Daiichi nuclear power plant, to measure 90Sr activity concentration using liquid scintillation counting. 137Cs activity concentration was also measured with gamma-spectroscopy in order to investigate correlation with 90Sr. The 90Sr activity concentrations ranged from 3.0 ± 0.3 to 23.3 ± 1.5 Bq kg−1 while the 137Cs from 0.7 ± 0.1 to 110.8 ± 0.3 kBq kg−1. The fact that radioactive contamination originated from the Fukushima nuclear accident was obvious due to the presence of 134Cs. However, 90Sr contamination was not confirmed in all samples although detectable amounts of 90Sr can be expected in Japanese soils, as a background, stemming from global fallout due to the atmospheric nuclear weapon tests. Correlation analysis between 90Sr and 137Cs activity concentrations provides a potentially powerful tool to discriminate background 90Sr level from its Fukushima contribution.

The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released large amounts of radioactive materials into the environment. River systems play an important role in the terrestrial redistribution of FDNPP‐derived 137Cs in association with water and sediment movement. We examined the seasonal fluctuations in dissolved and particulate 137Cs activity concentrations and clarified the biological and physicochemical factors controlling 137Cs seasonality in the Abukuma River's middle course in the region affected by the FDNPP accident. The results showed seasonal fluctuations in the dissolved 137Cs activity concentration, with an increase in summer and a decrease in winter, although there was no clear seasonal change in the particulate 137Cs activity concentration. Water temperature and K+ concentration dominated the seasonality of the dissolved 137Cs activity concentration. The volumetric activity concentration of the organically bound 137Cs was found to be several orders of magnitude lower than that of the dissolved 137Cs. Therefore, we concluded that the 137Cs in organic matter is not a source of dissolved 137Cs in river water. The study also revealed the temperature dependence of Kd in riverine environments from a Van't Hoff equation. The standard reaction enthalpy of 137Cs in the Abukuma River was calculated to be approximately −19.3 kJ/mol. This was the first study to clearly reveal the mechanisms by which the dissolved 137Cs activity concentration and Kd are influenced by chemical and thermodynamic processes in the middle course of a large river, and it is expected to lead to an improved model of 137Cs dynamics in rivers.

Recent spatial and vertical distributions of 137Cs activity concentration in the Aegean Sea are presented almost 30 years after the Chernobyl accident. The study aims to provide the current radioactivity levels of 137Cs in the Aegean Sea and to combine the 137Cs activity concentration with typical oceanographic parameters (T, S) in order to utilize them as tracers to identify/validate the different water masses that are present in the Aegean Sea. This work was performed in the frame of the “KRIPIS” project in 2017 for continuous investigations of the deep basins from all over the Aegean Sea and includes samplings from the water column layers of seven stations. The 137Cs activity concentrations were determined via lab-based gamma ray spectroscopy after appropriate chemical pre-concentration of 137Cs, while the salinity and temperature of the water column were obtained by in-situ measurements. The activity concentration values of 137Cs varied from 1.6 to 5.5 Bq m−3. Clear distinction of the Black Sea and Levantine Waters was obtained based on the combination of temperature and salinity values with 137Cs activity concentration. Furthermore, including 137Cs as a supplementary tracer, the Transitional Subsurface Aegean Waters were identified at the Myrtoan and Antikythera Straits, combining the salinity, temperature and 137Cs activity concentration.

Results of the Cs activity concentration measurements in the ground-level air in the Ignalina Nuclear Power Plant (Ignalina NPP) region in 1978–2006 are presented and discussed. The peculiarities of the trend of mean annual radiocaesium activity concentrations in the air during the studied period are explained and described empirically. The analysis of the radiocaesium concentration course after the Chernobyl accident shows that mean annual Cs activity concentrations in the air are decreasing slower than it is expected due to its radioactive decay and aerosol, as the Cs carrier, removal processes in the atmosphere. The Hybrid Single-Particle Lagrangian Integrated Trajectory model of the global dispersion and deposition of the admixture in the air is used to study episodic increases in the Cs activity concentration in the ground-level air of more than 8 μBq m. Modelling results show the transport of resuspended radiocaesium with air mass from the Chernobyl NPP accident polluted regions to be an important source of the radionuclide to the environment of the Ignalina NPP. It is shown that Cs emissions from its generation sources (nuclear industry objects) and, probably, the depositional flux of the radiocaesium from the stratospheric reservoir, can contribute up to 10% to the mean annual Cs activity concentration value. Mean arithmetic and mean geometric Cs activity concentrations in the air during a year are calculated and compared.

About 21 years after the Chernobyl accident, 137Cs and 40K activity concentration measurements using gamma-ray spectroscopy and elemental analysis using energy dispersive X-ray spectroscopy were performed in five different lichen species collected from the Giresun province of northeastern Turkey. Being a symbiosis of algae and fungi, lichens are mostly used for environmental measurements since the fungal partner is responsible for the uptake of necessary nutrients or harmful substances, such as heavy metals of radionuclides. The gamma activity results showed that 137Cs, an artificial radionuclide released from the Chernobyl power plant accident, is still eminent in the environment of the province. The mean activity concentrations of 137Cs and 40K ranged from 24 to 254 with the mean value of 102 Bq kg−1 and from 345 to 2103 with the mean value of 1143 Bq kg−1 in dry weight. The results of the elemental analyses showed potassium, calcium, titanium, iron, tin, and barium in different concentrations.

Fern accumulates radionuclides in abundance, including 137Cs. Tranfer of 137Cs and 40K in plants which have different root systems (fern or grass), or have no roots at all (moss) was compared. Samplings were performed in regions contaminated with 137Cs after Chernobyl Nuclear Power Plant (ChNPP) accident in 1994 and 1997–2000. The male fern (Dryopteris filix‐mas) most prevailing in Lithuania was studied. Fern accumulates 137Cs more effectively than grass or moss. The average 137Cs activity concentration in fern is 180±60 Bq kg−1 and the transfer factor is 0,074 m2kg−1. The fern stipe accumulates 137Cs most of all (200±90 Bqkg‐1), the transfer factor is 0,087 m2 kg−1. Accumulation of 137Cs is influenced by the content of K in the soil. 137Cs and 40K activity concentrations in fern are higher than those in the soil what shows that fern accumulates 137Cs better than 40K. Fern can clean the soil because this plant accumulates radionuclides in its stipe rather than roots.