Journal of environmental radioactivity最新文献

Natural radioactive environments serve as valuable resources for discovering microorganisms adapted to extreme conditions, and these organisms hold significant potential for environmental biotechnological applications. Radiation-resistant bacteria are particularly remarkable for their adaptation to high-energy stress factors such as gamma radiation, and their unique properties can be utilised in biomedical and industrial contexts. In this study, radiotolerant bacteria were isolated and characterised from radon-active groundwater collected from the Agora Archaeological Site in İzmir, Türkiye. A total of 65 environmental isolates and two reference strains were exposed to chronic ¹³⁷Cs gamma irradiation (0-1.2 kGy; 50 Gy h^-1); almost all isolates survived up to 300 Gy, while only three (Rhodococcus sp. AGO54K, Acinetobacter sp. AGO52, Microbacterium sp. AGO38) remained viable at 1.2 kGy. These three isolates were subsequently subjected to chronic beta irradiation using a ⁹⁰Sr/⁹⁰Y source (1.06 kGy total dose; ∼11 Gy h^-1), and all maintained culturability after exposure. Thermal, pH, and salinity tolerances were also assessed: Rhodococcus sp. displayed a broad pH range and moderate salinity tolerance; Acinetobacter sp. tolerated moderately acidic conditions and temperatures up to 50 °C; and Microbacterium sp. showed high salinity tolerance (7.5% NaCl) and the highest thermal tolerance 55 °C. The isolates additionally demonstrated stable ⁹⁹ᵐTc radiotracer binding, retaining >98% labelling efficiency after three washing cycles. 16S rRNA gene sequencing confirmed genus-level identification with GenBank accession numbers PX445739, PX445737, and PX445738. Overall, this study highlights the combined ionizing-radiation tolerance and physicochemical stress resilience of bacteria isolated from naturally radioactive groundwater.

Radon-222 ingestion from drinking water is commonly treated as a minor exposure pathway relative to inhalation of radon released into indoor air. This interpretation derives largely from the modelling framework consolidated by the U.S. National Academy of Sciences (NAS), which estimated that ingestion contributes approximately 10% of the total radon-in-water dose. However, the NAS explicitly recognised that the ingestion risk partition is governed by a poorly constrained biological parameter - the fraction of radon absorbed across the gastric wall prior to exhalation - and noted that plausible values could span up to two orders of magnitude. Because this parameter directly determines the ingestion dose coefficient, the widely cited 10% contribution represents a central estimate within a broad admissible range rather than a quantitatively constrained value. Despite this, the 90/10 partition has been embedded in subsequent international guidance without empirical narrowing of the governing biokinetic parameter. In parallel, radon-222 is excluded from total indicative dose screening frameworks for drinking water, reinforcing its marginalisation within ingestion-based assessments. The ingestion coefficient is therefore operationally stabilised in regulatory practice, while its quantitative basis remains sensitive to unresolved biological assumptions. This technical note argues that radon ingestion should not be regarded as a quantitatively resolved exposure pathway from an environmental radioactivity perspective. We show that (i) earlier assessments assigning a larger ingestion contribution remain compatible with the uncertainty bounds acknowledged by the NAS; (ii) standard ingestion models treat in-vivo decay and downstream progeny production as negligible under the same biokinetic assumptions that govern radon absorption and clearance; and (iii) radon dissolved in water functions within the uranium-238 decay chain as a transfer mechanism linking short-lived and longer-lived contributors to ingestion dose. Together, these considerations indicate that the apparent stability of the inhalation-ingestion partition reflects modelling continuity and regulatory convention more than empirical constraint.

Radon exhalation rate (ERR) represents a key link between subsurface radon sources, soil processes, and atmospheric transport, with relevance for environmental tracing, radiation protection, and greenhouse gas flux estimation. Its temporal variability is mainly controlled by soil moisture and temperature through the effective diffusion coefficient (D_ef,Rn). In this study, six commonly used D_ef,Rn parameterisations (D1 - D6) and three theoretical ERR formulas (E1, E2, E4) were combined into 18 EiDj models and evaluated against continuous four-year field measurements (October 2020 - June 2024) obtained with an automated accumulation chamber in sandy-silt soil in Bratislava, Slovakia. All D_ef,Rn parameterisations showed almost identical temporal behaviour and differed mainly by a constant magnitude shift, with D1 and D5 providing the most realistic values under local soil conditions. Using a combination of statistical performance measures and agreement analyses, three EiDj formulas: E1D1, E4D1 and E4D5 were consistently identified as the most reliable in reproducing both the magnitude and temporal evolution of measured ERR. All three combinations successfully captured the characteristic annual ERR cycle as well. These findings demonstrate the importance of moisture-dependent D_ef,Rn parameterisations and highlight the strong predictive capability of combined theoretical and semi-empirical approaches for estimating radon exhalation under real environmental conditions, validated against comprehensive multi-year field observations.

This study evaluates potential differences in ⁷Be activity concentrations measured using two aerosol sampling systems equipped with PM₁₀ and total suspended particles (TSP) inlets under real atmospheric conditions. During the study period, mean ⁷Be activity concentrations were 4.4 ± 1.4 mBq m^-3 for PM₁₀ and 3.7 ± 1.2 mBq m^-3 for TSP samples. A strong temporal correlation was observed between both datasets (ρ = 0.882, p < 0.001), indicating consistent response to atmospheric variability. Although individual weekly differences are not always statistically significant when measurement uncertainties are considered, the overall distribution revealed a systematic tendency toward higher ⁷Be concentrations in the PM₁₀ fraction, with relative differences ranging from 4% to 44%, consistent with the preferential association of ⁷Be with fine aerosol particles. Six sampling weeks showed higher ⁷Be values in TSP than in PM₁₀, but only three met the criterion for statistically significant difference. Back-trajectory analysis showed that only one sampling week corresponded to a well-defined Saharan dust intrusion, whereas the two other cases were more linked to regional resuspension processes and accumulation of locally or regionally derived coarse particles that may enhance the relative contribution of the TSP fraction. These findings indicate that episodic increases of ⁷Be in the TSP fraction may arise from both mineral dust advection and locally driven coarse-particle accumulation. Multivariate analysis identified two dominant atmospheric regimes controlling radionuclide variability. The first component linked ⁷Be concentrations with temperature and wind direction, reflecting the influence of large-scale atmospheric transport and vertical mixing processes. The second component grouped dust concentrations and wind speed, indicating the importance of mechanically driven aerosol resuspension and transport. Overall, the results demonstrate that while PM₁₀ and TSP sampling systems provide highly comparable measurements of atmospheric ⁷Be activity, differences in particle size distribution during dust transport episodes can lead to systematic variations between both fractions. These findings highlight the importance of considering inlet-dependent size selectivity when comparing long-term radionuclide records obtained using different aerosol sampling configurations.

The inadvertent melting of "orphan" radioactive sources containing Cesium-137 (¹³⁷Cs) during steel recycling processes results in the concentration of this radionuclide found in steel ash, posing a significant radiological and waste management challenge. Although pyrometallurgical methods are commonly employed for steel ash treatment, their applicability to ¹³⁷Cs decontamination is limited by high energy demands, inadequate selectivity for radionuclides, and substantial capital investment. This review examines aqueous hydrometallurgical approaches as a more viable alternative for the selective removal of ¹³⁷Cs. Several leaching strategies were systematically evaluated, encompassing conventional water and acid/base treatments as well as advanced techniques, including ion exchange and precipitation. Evidence suggests that a two-stage hydrometallurgical approach beginning with selective leaching using cations such as NH₄⁺ or K⁺ to displace Cs⁺ and followed by recovery from the leachate via ion exchange or precipitation offers a technically robust, economically feasible, and environmentally sustainable solution. This method enhances ¹³⁷Cs removal efficiency while enabling the retention and recovery of valuable elements such as zinc, significantly minimizing the volume of final radioactive waste. However, challenges such as high reagent consumption, secondary waste generation, and economic bottlenecks for scale-up must be addressed to achieve industrial viability. The review concludes by identifying directions for future research, including process intensification, integration of physical enhancement methods, and development of hybrid systems, for advancing this decontamination strategy toward commercial application.

An atmospheric dispersion model was used to assess the global transport and deposition of ¹³¹I and ¹³⁷Cs released into the air during the Fukushima accident in 2011. Simulations results showed that the radionuclides traveled eastward across the Pacific by the westerlies. The radioactive plume estimated to reach the U.S. West Coast approximately 5 days after the accident, Europe after about 12 days, and Mongolia and China after around 16 days. It subsequently dispersed across the entire Northern Hemisphere approximately within 17 days. The calculated concentrations of radionuclides were generally consistent with observations, including monitoring data from CTBTO and Korea. A substantial portion of the released radionuclides was deposited into the Pacific Ocean, with about 54% of ¹³¹I and 76% of ¹³⁷Cs settling on the sea surface. Further analysis confirmed that the ¹³⁷Cs detected in seawater samples from the central Pacific and U.S. West Coast in April and May 2011, originated from atmospheric deposition onto the ocean rather than direct release into the sea from the Fukushima accident.

This study clarifies when Bayesian analysis provides a practical advantage, particularly in large-area searches, hazardous or inaccessible environments, and low signal-to-noise ratio (SNR) scenarios where direct source approach is not feasible. We present a PyMC-based Bayesian framework for localizing a single unshielded gamma-emitting source and estimating its activity, with the ability to switch between generic priors and measurement-derived informed priors. Model performance was evaluated using 1240 synthetic datasets spanning varying source activities, detector-to-source distances, and background levels, and further tested using controlled field experiments. Two workflows were assessed: a rapid single-step analysis using generic priors and a two-step approach in which preliminary estimates of source distance and activity define an informed prior and constrain the effective search area. Informed priors improved parameter stability near detection limits and reduced computation compared with generic priors. Savitzky-Golay smoothing enhanced SNR and improved robustness in marginal cases but could not compensate for insufficient signal strength. These results define practical conditions under which Bayesian localization is operationally beneficial.