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Abstract As a part of establishing a regional database on natural radioactivity, the atmospheric concentrations of 210Pb and 7Be were measured over a three and half year period (2014–2017) in Mangalore and Kaiga in the South West Coast of India. A total of 99 air samples, collected in the different months of the year, were analysed in this study. The mean activity concentrations of 7Be and 210Pb were found to be 5.5 ± 3.1 mBq m−3 and 1.1 ± 0.73 mBq m−3, respectively. Both the radionuclides exhibited strong seasonal variations, with maximum concentration of 7Be occurring in the summer and that of 210Pb in the winter season. The concentration of both the radionuclides was minimum in the rainy season. Higher 210Pb concentration during winter was attributed to the ingression of continental air masses due to the wind regime from the North East. The sunspot number index of the solar activity also plays an important role in the increase and decrease of 7Be concentration in the air. A clear trend of increased and lowered concentration of 7Be with lower and higher solar activity (low and high sunspot number), respectively, in accordance with the 11-year solar cycle, was observed in this study. The temporal variation of PM 10 concentration was also studied and it showed maximum value in the winter and minimum in the rainy season with an average of 56.9 μg m−3. Statistically significant positive correlation was observed between the PM 10 and 210Pb activity concentration, whereas a weak correlation was observed between PM 10 and 7Be. This is due to the fact that 7Be is largely associated with sub-micrometer size particles, whereas PM 10 is contributed by larger sizes. The dependence of the activity concentrations of 7Be and 210Pb with meteorological parameters such as rainfall, temperature, and humidity was studied through linear regression analysis. A significant correlation was observed between 7Be and 210Pb concentrations with rainfall intensity (with identical correlation coefficients), which suggested that the removal mechanisms of these two radionuclides were similar. 7Be showed a strong correlation with temperature, whereas 210Pb with humidity. A comparison of the data obtained in the present study for the South West Coast of India with the global literature values of 7Be and 210Pb in aerosols showed that the values did not reflect the well-known latitudinal dependence of the 7Be tropospheric fluxes. Overall, the study provides an improved understanding of the correlation and variability of 210Pb and 7Be concentrations in the atmosphere in the South West Coast of India. Highlights • Regional database on activity of atmospheric 7Be and 210Pb in Southwest Coast of India was established. • Rainfall is the major removal pathway for the 7Be and 210Pb from the atmosphere. • Dependence of solar activity with cosmogenic 7Be was studied. • A clear dependence of 7Be activity on solar activities was observed. • Causal factors for the temporal variability of 7Be and 210Pb concentrations were identified. [ABSTRACT FROM AUTHOR]

The results of the first detailed study, involving a large number of samples, on water equivalent factor (WEQ p), non-exchangeable organically bound tritium (NE-OBT) and tissue free water tritium (TFWT) activity concentrations in predominant plant species of the tropical monsoonal climatic region, are presented. A total of 369 samples from the vicinity of the PHWR nuclear power plant (NPP) at Kaiga, West Coast of India, and 47 samples of the control region (region not affected by local anthropogenic sources) were analysed. The WEQ p varied in the range of 0.347–0.666 L kg−1 with an overall mean value of 0.540 ± 0.045 L kg−1. The NE-OBT activity concentration varied in the range of <9.8–60.9 Bq L−1 of combustion water (mean = 24.6 ± 11.5 Bq L−1) and that of TFWT in the range of 9.2–60.5 Bq L−1 (mean = 30.7 ± 10.9 Bq L−1) in the vicinity of the NPP. Rigorous statistical analysis of the data confirmed that (i) the activity concentrations of both forms of tritium decreased with the increase in the distance between the sampling location and NPP, and beyond 10 km, it was similar to that of the control region, (ii) the incorporation of tritium released from the NPP into wild plant leaves is not species-dependent, (iii) the NE-OBT activity concentration in the 5–10 km zone exhibited a dependence on the prevailing wind regime with respect to the NPP, but not in the 2.3–5 km zone which suggests that the transport of tritium, released into the atmosphere as the gaseous effluent, through diffusion is a dominating factor governing its activity concentration in the 2.3–5 km zone. The NE-OBT to TFWT specific activity concentration ratio (R-value) had a mean value of 0.82 ± 0.27 (range: 0.38–1.64) for samples collected from the vicinity of the NPP and 1.93 ± 0.50 (range: 1.35–3.19) for the control region. Recording higher NE-OBT activity concentration and R-value at the control region highlights the necessity of detailed studies to understand the mechanism of NE-OBT partitioning in the terrestrial environment. • First study on NE-OBT and TFWT in wild plants of tropical monsoon climate region. • Robust database on important forms of tritium in terrestrial plants is established. • Incorporation of tritium as NE-OBT into wild plant is not species-dependent. • No significant variation was recorded in the NE-OBT activity in different seasons. • NE-OBT to TFWT ratio for NPP region was 0.82 and that for clean air region was 1.89 [ABSTRACT FROM AUTHOR]

Accelerator mass spectrometry and benzene synthesis coupled with liquid scintillation spectrometry are often used for accurate measurements of 14C activity in the environmental matrices. Thermal oxidation is one of the methods employed for 14C determination in environmental matrices. In this method, the sample is oxidised at high temperature (600–900 °C) to convert carbon species to CO 2 and trapped in an amine-based absorber for determining the activity in a liquid scintillation counting (LSC) system. In this study, the performance of a commercially available tube furnace system (pyrolyser), for batch combustion of samples, was evaluated for the determination of 14C specific activity in terrestrial biota samples. Significant improvements over the manufacturer specified method, which is primarily designed for analysis of samples with activity well above the environmental background level, was implemented to achieve accurate determination of 14C specific activity at ambient background level. In the improved method, the CO 2 produced from the combustion of the sample was isolated from the combustion products through cryogenic trapping and then absorbed in the absorber (Carbo-Sorb E) through a simple off-line transfer process. This allowed (i) optimisation of CO 2 absorption by the absorber (2.2477 g of CO 2 /10 mL), (ii) achieving good accuracy and precision in the measurements, and a minimum detectable activity value of 13 Bq kg−1C for a counting time of 300 min (7 Bq kg−1C for 1000 min), (iii) avoiding uncertainty associated with the determination of recovery of 14C in the combustion and trapping process, and (iv) elimination of the need for an independent determination of carbon content (%) for expressing the results in terms of 14C specific activity. The method is capable of yielding accurate results with a deviation of <2.4% from the target value for IAEA C3 quality assurance reference material (with a relative standard deviation of 1.40%, and relative error of 0.34%). The combined uncertainty (1σ) associated with the measurements was computed to be 3.4%. Upon optimisation, the suitability of the method for the determination of 14C specific activity in typical terrestrial biota samples of clean air region (region not affected by local anthropogenic sources) and for the quantification of a small increase in the 14C activity above ambient levels in the vicinity of a nuclear power plant is demonstrated. • Method based on batch combustion using a tube furnace was optimised for 14C measurement in environmental biota. • CO 2 produced from the combustion of the sample was cryogenically isolated from the combustion products. • MDA value of 13 Bq kg−1C for a counting time of 300 min was achieved. • Accurate results with a deviation of <2.4% from the target value was achieved. • Small excess 14C in the vicinity of the nuclear power plant was quantified. [ABSTRACT FROM AUTHOR]

This is a detailed study on oxide (CO 2) and reduced (hydrocarbons, C n H m) forms of 14C releases through gaseous effluents from the Kaiga nuclear power plant (NPP), on the West Coast of India, where 4 × 220 MW(e) pressurized heavy water reactors (PHWRs) are operating. The gaseous effluent from the common stack of reactor units 3 and 4 (each of 220 MW(e)) was sampled from 2017 to 2020 for 14C activity monitoring and analysed for 14C activity by liquid scintillation counting. The normalized release rate corresponding to the four-year monitoring period had a geometric mean value of 0.12 TBq GW(e)−1 a−1 (geometric standard deviation = 7.4), and the arithmetic mean with associated standard deviation was 0.75 ± 1.47 TBq GW(e)−1 a−1. The relative percentage contribution of reduced form (CH 4) of 14C species was less than 1.27% of the total release. The normalized release rate from Kaiga NPP was similar to those reported for the other PHWR NPPs of the world. The 14C specific activity in the ambient air in the vicinity of the NPP was monitored at four locations. The maximum excess 14C activity values in the ambient air in the vicinity of the NPP, evaluated by comparing the specific activity recorded for the clean air region at ∼300 km from the NPP, were 65.1 Bq kg−1C (28.76 pMC) and 222.4 Bq kg−1C (98.23 pMC) for the years 2019 and 2020 respectively. In addition, the release rates were calculated from the Gaussian plume model using site-specific atmospheric dilution factors and the excess 14C specific activity measured at four off-site monitoring stations. The calculated values of release rates were in agreement (within a factor of ∼3) with the measured values. • 14C release in oxide and reduced forms from Kaiga PHWR NPP, India were quantified. • Mean value of the normalized release rate was 1.08 ± 1.80 TBq GW(e)−1 a−1. • 14C release in reduced form was <1.27% of the total release. • Maximum excess 14C activity in ambient air in the vicinity of the NPP was 222 Bq kg−1C 97 pMC (980.7‰). [ABSTRACT FROM AUTHOR]