Radon (Rn 222) is a significant contributor to natural radiation exposure in residential environments such as single-family houses and multistory buildings. This study monitored radon activity concentration (RAC) in 455 apartments in 30 multistory buildings in Buzău, Romania. Integrated measurements of the RAC using CR-39 nuclear track detectors were conducted for a period of 3 to 4 months. The results revealed that the RAC varies between buildings, with an annual average between 33 and 77 Bq/m³. This variation may be attributed to poor ventilation and the chimney effect in common ventilation ducts, which may facilitate radon displacement vertically. Also, apartments with low occupancy or inadequate ventilation showed higher radon levels of up to 285 Bq/m³. The study highlights the potential risk of increased radon exposure in energy-efficient buildings due to poor ventilation, emphasizing the need for special attention to radon mitigation measures in building design. The results emphasize that the RAC is influenced by building characteristics, room use, and ventilation, with significant implications for health risks in urban residential environments.

The geogenic radon potential is primarily controlled by the geological characteristics of the site, such as the rock type and structural elements, as well as the permeability of the soil. Depending on the scope of the survey, the geogenic radon potential can be mapped based on measurements conducted in the field at various resolutions. Detailed surveys are generally labour-intensive and time-consuming. Therefore, a balance should be reached between the desired level of precision and the required amount of effort, delivering the best results with the least number of resources. The international literature describes a variety of surveying techniques. This study was undertaken in a region of the central zone of the Poiana Rusca Mountains (Southern Carpathians, Romania) that contains several metamorphic, volcanic, and sedimentary rock types. The primary objective of the study is to compare alternative sampling point configurations, which vary in number and arrangement. The objective was to achieve the most accurate representation of the calculated geogenic radon potential while limiting the number of measurements and the time and effort associated with them. Radon activity concentration and soil permeability data were collected from 34 locations using seven alternative layouts of the sampling points. The proposed layouts were based on various configurations of fifteen, nine, five, and three sampling points. Locally, in some of the metamorphic units and in the regions containing sedimentary deposits with volcanic intercalations, the geogenic radon potential was found to be elevated. The results indicate that the three-measuring-point configuration is acceptable for general geogenic radon potential surveys.

Due to the higher susceptibility of children to ionizing radiation, it is imperative to evaluate the radon activity concentration (RAC) in educational buildings, conduct additional investigations to identify radon entry routes, and implement remedial measures to minimize exposure to this radioactive gas. In Romania, educational buildings are a category of public buildings where it is mandatory to perform RAC measurements. The present study examines data obtained from 41 Romanian educational buildings, where initial and additional radon investigations were performed. The first objective was to identify the factors influencing the variability of the RAC inside the buildings. The second objective was to emphasize the importance of short-term (a few days), continuous measurements in identifying buildings with RAC exceeding the reference level. High RAC values were associated with the classrooms located on the ground floor of the building compared to the administrative ones. The multiple linear regression led to a coefficient of determination of 0.11, the relative humidity and the amount of precipitation being the main variables with a significant impact, kept in the model, the lack of a significant association between the indoor RAC and the radon potential in the soil being obtained. Comparison of the radon long-term integrated measurements with continuous, short-term, led to the suggestion of three different scenarios for the measurement work protocol. By following the suggested modifications, it is possible to accelerate the procedure in situations where the time needed to plan renovations and radon remedial measures is shorter than the time needed to conduct integrated measurements.

Radon is a naturally occurring radioactive gas that has high carcinogenic potential and may constitute a significant public health problem. The long-term effectiveness of radon mitigation systems is often assumed, yet rarely questioned beyond initial implementation. This study investigates the long-term performance of mitigation systems after installation, based on continuous monitoring conducted over several years. Ten Romanian dwellings served as case studies illustrating the interaction between technical remediation measures and various patterns of occupant behaviour. The remediation methods included sub-slab depressurization (SSD), heat recovery ventilation, both centralized (CHRV) and decentralized (DHRV), and the use of radon barriers. The results showed a variable efficiency of the remediation methods, with average radon concentration reduction values ranging from -8 % to 91 %, and an overall median of 59 %. The SSD-based remediation methods demonstrated superior performance and better stability over time, recording an average efficiency of 86 %, while the CHRV and DHRV systems showed much higher variability and a decline in efficiency over time. One of the most critical factors contributing to the success of the remediation was user behaviour, with intermittent use, disconnecting of systems, or lack of maintenance leading to increases in post-remediation radon concentration, in some cases even above pre-remediation levels. In contrast, the active involvement of the occupants, including constant monitoring and prompt reaction to malfunctions, ensured that low radon levels (below 50 Bq/m³) were maintained. The findings suggest that maintaining low radon levels over time requires more than just technical interventions, highlighting the importance of a balanced interaction between automated systems and occupant engagement. These results highlight the need for public policies that combine engineering solutions with behavioural, educational, and ongoing support strategies to maintain the effectiveness of residential radon safeguards.

Historically, the Transylvanian basin is one of the most important natural gas-producing areas in Europe. The existence of commercial gas reserves was incidentally discovered in the early 1900's while drilling for potassium salts in the Miocene deposits that fill the basin. Well #2 Sarmasel, that was positioned close to an area with natural gas emissions, has intercepted very shallow strata containing gas. Drilling had to be stopped on 22 April 1909, after 5 months of work, at a depth of 300 m, due to overwhelming technical difficulties related to the high pressure of gas. Thus, this date marks the beginning of the gas extraction in Transylvania. The well has been left open until 23 June 1910, when a first attempt at closure was made. Twenty hours after closure, gas was observed escaping in a neighbouring field, which required the reopening of the well. A second closure attempt occurred on 31 July 1911, subsequent to the external encasement of the well for the initial 120 meters of depth. No gas leak was detected, and the closure seemed to be effective at this stage. On 29 October 1911, a powerful gas eruption occurred in the fields east of the well, accompanied by considerable gas emissions in the surrounding area, local seismic activity, saline water leakage, and the appearance of several craters located between 100 and 400 meters from the well. The well was reopened once again, until the end of 1913, when it was connected to the pipeline conveying gas to consumers. More than 1.3×109 m3 of gas has been released to the atmosphere during a span of four years. An additional 556×106 m3 of gas was supplied to consumers from 1913 to 1935, when the well was capped. The total volume is around 2 billion cubic meters of gas from a single, 300-meter-deep well! The main crater generated by the 1911 outburst, despite being filled with soil post-explosion, persists in emitting gas that sustains a perpetual fire. Our research demonstrated that Sarmasel is a case of ongoing, prolonged gas leakage caused by manmade activities (drilling and gas extraction) conducted over a century ago, functioning in conjunction with, and likely intensified by, a natural seepage process. Sarmasel can thus be regarded as a hybrid leakage-seepage system. This study exemplifies the risk of generating fugitive emissions when drilling occurs within a natural seepage system. Acknowledgments: This work was supported by the Project DTIE21-EN3485 funded by UNEP and by the Project 14/11.11.2023—ENGAGE, PNRR-III-C9-2022—I8, supported by the EU through the Romanian Govt.

Natural gas seeps and mud volcanoes are widely distributed across terrestrial and shallow submarine sedimentary basins and contribute considerable amounts of fossil methane to the atmosphere. Methane emissions from these systems are commonly interpreted as dominantly thermogenic in origin; however, microbial activity may significantly contribute to, or overprint, these emissions through secondary methanogenesis or methane oxidation during gas migration and storage.Conventional bulk isotope composition (δ¹³C and δD) and hydrocarbon concentration ratios are often insufficient to distinguish secondary microbial contributions from an initial thermogenic source. Independent of bulk isotopic signatures, methane clumped isotopes (Δ¹³CH₃D and Δ¹²CH₂D₂) provide direct constraints on methane formation pathways and post-generation alteration processes. Recent studies have revealed low-temperature near-equilibrium clumped-isotope signatures in mud-volcano systems in Azerbaijan1, indicative of strong microbial overprinting, whereas methane from Japanese mud volcanoes exhibits clumped isotope signatures spanning from far from equilibrium to near equilibrium values2. For the latter, clumped isotope signatures of methane correlate with 13C-position-specific isotope composition of propane, suggesting the biodegradation of higher hydrocarbons is associated with progressive modification of methane clumped isotopes.Here, we investigate methane emissions from mud volcanoes and gas seeps in central and southern Italy (n = 14) and Romania (n = 15). Methane bulk and clumped isotope composition (δ¹³C, δD, Δ¹³CH₃D and Δ¹²CH₂D₂) are analyzed using a quantum cascade laser absorption spectrometer (QCLAS) equipped with a customized gas-inlet system at Empa3. Propane concentrations span from below detection to 0.8%, indicating a wide range of potential microbial influence. Selected samples are further characterized by propane position-specific isotope analyses at Science Tokyo following established protocols by Gilbert et al. 4, providing constraints on the extent of secondary microbial processes affecting higher hydrocarbons.Preliminary clumped-isotope results from Italian mud volcanoes indicate near-equilibrium signatures consistent with strong microbial influence, comparable to patterns reported from Azerbaijan mud-volcano systems. In contrast, Romanian samples exhibit pronounced variability in propane concentrations, providing a critical test case to explore whether methane clumped-isotope systematics transition toward more thermogenic-dominated patterns with secondary microbial influence, similar to those observed in Japanese systems. By integrating new datasets from Italy and Romania with published clumped-isotope and propane intramolecular isotope data, this study explores whether microbial influences on methane emissions follow consistent or system-specific patterns across mud-volcano and gas-seep systems globally. [1] Liu et al., 2023 Geology[2] Gilbert et al., 2025 EGU2025 Abstract[3] Zhang et al., 2025 Anal. Chem.[4] Gilbert et al. 2019 Proc. Natl. Acad. Sci.