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The number of studies concerning Submarine Groundwater Discharge (SGD) grew quickly as we entered the 21st century. Many hydrological and oceanographic processes that drive and influence SGD were identified and characterized during this period. These processes included tidal effects on SGD, water and solute fluxes, biogeochemical transformations through the subterranean estuary, and material transport via SGD from land to sea. Here we compile and summarize the significant progress in SGD assessment methodologies, considering both the terrestrial and marine driving forces, and local as well as global evaluations of groundwater discharge with an emphasis on investigations published over the past decade. Our treatment presents the state-of-the-art progress of SGD studies from geophysical, geochemical, bio-ecological, economic, and cultural perspectives. We identify and summarize remaining research questions, make recommendations for future research directions, and discuss potential future challenges, including impacts of climate change on SGD and improved estimates of the global magnitude of SGD.

This study reports analyses of Ra isotopes in a Mediterranean stream, the Vidourle river, whose upper course drains the granitic and metamorphic basement of the SE part of the French Massif Central (Cévennes) and then flows through the karstified carbonates of Jurassic and Cretaceous ages. In these low-Ra waters (226Ra activities range from 1.5 to 4.9 mBq/L), all four Ra isotopes were successfully analyzed through gamma spectrometry during a single analysis. 226Ra activities and (228Ra/226Ra) ratios are distinctly higher in waters draining the Variscan basement than in waters affected by dissolution of Mesozoic carbonates, in agreement with U contents and Th/U ratios of both rock types. This results in a general N-S decrease, which parallels the evolution of the 87Sr/86Sr ratios. (228Ra/226Ra) ratios reported vs 1/(226Ra) display linear relationships suggesting mixing of several water components related to the lithology. Ra might thus have a more conservative behavior than usually assumed, possibly because of the high water/rock ratio and flow rate in karst environment. Short-lived Ra isotopes (224Ra and 223Ra) are often in excess compared to their equilibrium values, due to their supply through alpha-recoil processes. 223Ra activities in a Vidourle tributary can be explained by mixing of two water components, with a negligible radioactive decay of 223Ra during underground water flow. The calculated minimum flow rates (40–60 m/h) are in agreement with those deduced from artificial tracer experiments.

In order to characterize the features of radium isotopes in estuaries of Tianjin, a continuous survey and sampling of typical estuaries were conducted from 2013 to 2017 in this study. The activities of natural radioactive radium isotopes ( 223 Ra, 224 Ra, and 228 Ra) in groundwater and surface water were measured by the radium-delayed coincidence counting (RaDeCC) system. The non-conservative behavior of the radium isotopes was investigated under hydrogeochemical conditions and urbanization. The results indicated that in terms of horizontal distribution, the activities of radium in groundwater (Hangu, Tanggu, and Dagang) showed an upward trend from north to south and demonstrated a higher figure than surface water (Haihe River and Duliujian River). Concerning the vertical distribution, the activitives of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements. The activities of radium isotopes in the study area increased with the increase of total dissolved solids, and their desorption behavior on Fe-Mn oxides was constrained by the redox intensity. Different hydrogeological conditions resulted in variations in the vertical profile of radium activities. The activity of radium was regulated by seasonal variation and precipitation in groundwater and surface water. In addition, the rapid urbanization has caused a significant impact on the features of radium isotopes in typical estuaries of Tianjin. Meanwhile, radium isotopes can be applied to reflect the impact of urbanization on surface water-groundwater systems. Clarifying and cleverly utilizing the relationship between behavior of radium isotopes and urbanization will promote the development of the Tianjin Binhai New Area in a healthy way.

This is the first attempt in the world to depict the vertical distribution of radionuclides in the soil samples along several heights (900 feet, 1550 feet, and 1650 feet) of Marayon Tong hill in the Chittagong Hill Tracts, Bandarban by HPGe gamma-ray spectrometry. The average activity concentrations of 232 Th, 226 Ra, and 40 K were found to be 37.15 ± 3.76 Bqkg −1 , 19.69 ± 2.15 Bqkg −1 , and 347.82 ± 24.50 Bqkg −1 , respectively, where in most cases, 232 Th exceeded the world average value of 30 Bqkg −1 . According to soil characterization, soils ranged from slightly acidic to moderately acidic, with low soluble salts. The radium equivalent activity, outdoor and indoor absorbed dose rate, external and internal hazard indices, external and internal effective dose rates, gamma level index, and excess lifetime cancer risk were evaluated and found to be below the recommended or world average values; but a measurable activity of 137 Cs was found at soils collected from ground level and at an altitude of 1550 feet, which possibly arises from the nuclear fallout. The evaluation of cumulative radiation doses to the inhabitants via periodic measurement is recommended due to the elevated levels of 232 Th.This pioneering work in mapping the vertical distribution of naturally occurring radioactive materials (NORMs) can be an essential factual baseline data for the scientific community that may be used to evaluate the variation in NORMs in the future, especially after the commissioning of the Rooppur Nuclear Power Plant in Bangladesh in 2024.

The concentrations of primordial radionuclides (226Ra, 232Th and 40K) in commonly used building materials (brick, cement and sand), the raw materials of cement and the by-products of coal-fired power plants (fly ash) collected from various manufacturers and suppliers in Bangladesh were determined via gamma-ray spectrometry using an HPGe detector. The results showed that the mean concentrations of 226Ra, 232Th and 40K in all studied samples slightly exceeded the typical world average values of 50 Bq kg(-1), 50 Bq kg(-1) and 500 Bq kg(-1), respectively. The activity concentrations (especially 226Ra) of fly-ash-containing cement in this study were found to be higher than those of fly-ash-free cement. To evaluate the potential radiological risk to individuals associated with these building materials, various radiological hazard indicators were calculated. The radium equivalent activity values for all samples were found to be lower than the recommended limit for building materials of 370 Bq kg(-1), with the exception of the fly ash. For most samples, the values of the alpha index and the radiological hazard (external and internal) indices were found to be within the safe limit of 1. The mean indoor absorbed dose rate was observed to be higher than the population-weighted world average of 84 nGy h(-1), and the corresponding annual effective dose for most samples fell below the recommended upper dose limit of 1 mSv y(-1). For all investigated materials, the values of the gamma index were found to be greater than 0.5 but less than 1, indicating that the gamma dose contribution from the studied building materials exceeds the exemption dose criterion of 0.3 mSv y(-1) but complies with the upper dose principle of 1 mSv y(-1).

The sediment mixed layer (SML) in the deep ocean is an important interface with a rich diversity of benthic organisms. With increasing ocean mineral exploration, and eventual mining, the effect of sediment mixing on deep ocean ecosystems has raised considerable concern. We evaluate the distribution patterns and driving factors of SML depth in deep ocean nodule fields using naturally occurring 210Pb–226Ra isotopes. Results show that average SML depth has increased in Mn‐nodule fields since the end of the last century. SML processes are associated with significant desorption of 226Ra from sediments, resulting in a departure from radioactive equilibrium. By estimating possible driving factors, we conclude that anthropogenic exploration activities, rather than natural physical and/or biological drivers, are the most likely mechanism for intensified sediment mixing. 210Pb–226Ra disequilibria may be a potential tracer for quantifying the impact of human exploration on deep‐ocean sediment mixing and associated biological and geochemical effects. Plain Language Summary The surface sediment mixed layer (SML) in the deep ocean is essential to benthic community structure and the biogeochemical cycling of many elements. The typical depth of mixed layers in the global deep ocean is <15 cm, which is mainly driven by natural biological and/or physical forces. By mapping sediment excess 210Pb profiles throughout the ocean, we found the depth of the SML in manganese nodule fields has increased significantly since the end of the twentieth century (reaching to >40 cm). The determine that the deepened mixed sediment layer is related to human exploration activities rather than other previously recognized natural drivers like bioturbation, internal solitary waves, and submarine storms. Keen attentions should be paid to the deepening and associated effects of sediment mixing in the deep ocean as human demand for critical materials continues to increase in the Anthropocene. Exploration approaches that involve low or negligible disturbance to deep‐ocean sediment should be encouraged. Key Points Human exploration is the main reason for deepening of the sediment mixed layer in the manganese nodule area Sediment mixed processes are associated with significant desorption of 226Ra from sediments 210Pb–226Ra disequilibria is a potential tracer for quantifying the impact of human drivers on deep‐ocean sediment mixing

Soil can pose significant radiation hazard in areas with elevated radioactivity levels from geological or anthropogenic sources, potentially contributing to human exposure through the food chain and atmosphere. However, industrial activities can alter radionuclides distribution by releasing residues or effluents, leading to their accumulation in the environment. In general, soil provides clear insights into geological characteristics and heavy metal exploration, in addition to assessing the risks of radiation exposure. This study investigates the distribution of NORMs and assesses radiological hazards in twenty soil samples collected from two major industrial zones in the Chattogram City of Bangladesh: the Bayazid Industrial Area and the Kalurghat Heavy Industry Area. The activity concentrations of 226 Ra, 232 Th, and 40 K in the analyzed soil samples range from 8 ± 1–18 ± 1, 15 ± 1–35 ± 3, and 192 ± 17–420 ± 35 Bq/kg, respectively, remaining below the global average for soil. The radiological hazard indices indicate negligible health risks to the public or environment, suggesting that the industrial activities are not releasing any radiotoxic elements in the surrounding environment. Statistical analysis identified 40 K and 232 Th as the primary contributors to radiological hazards, supported by strong correlations and significant principal component loadings. Additionally, this study provides baseline data for monitoring environmental radioactivity levels, particularly in light of the upcoming commissioning of the Rooppur Nuclear Power Plant in 2025.

This study focuses on the measurement of the concentrations of radon (222Rn) indoors and in the soil as well as their ambient dose equivalent rate in the cobalt–nickel bearing area of Lomié in the Eastern region of Cameroon. A total of 98 radon track detectors (commercially RADTRAK2®, Radonova Laboratories AB, Uppsala, Sweden) were used for indoor 222Rn measurement. A soil radon detector (MARKUS 10) and a pocket survey meter (RadEye PRD-ER, Thermo Scientific) were used for radon in soil and ambient dose equivalent rate measurements, respectively. Activity concentrations of 226Ra were measured using a high purity germanium detector (HPGe). Annual inhalation and external exposure doses, building materials characteristics, and correlations between indoor 222Rn, 222Rn, and 226Ra in soil were evaluated. Indoor radon concentrations varied from 30 to 300 Bq m−3 with the arithmetic mean of 58 Bq m−3. All values of indoor radon concentrations were above the world average value of 30 Bq m−3 given by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Radon concentrations in soil varied from 3.6 to 63.2 kBq m−3 with the arithmetic mean of 25.8 kBq m−3. Annual external effective dose varied from 0.23 to 0.72 mSv with the arithmetic mean of 0.41 mSv. These annual external effective dose values were all below the world average value of 0.9 mSv. 222Rn and 226Ra in soil were moderately correlated with R2 value of 0.69. The excess lifetime cancer risk (ELCR) varied from 1.5 to 16.7% with a mean value of 3.6%. This mean is about three times the action level of 1.3% recommended by the United States Environmental Protection Agency (USEPA).

Impact assessment of building materials is a focused topic in the field of radioecology. A radiological survey has conducted to monitor radioactivity of most common building materials in Semnan Province, Iran, and assess the radiation risk. Activity concentrations of 226 Ra, 232 Th, and 40 K were measured in 29 samples including nine commonly used building materials that were collected from local suppliers and manufacturers, using a high purity germanium gamma-ray detector. The activity concentrations of 226 Ra, 232 Th, and 40 K varied from 6.7±1 to 43.6±9, 5.9±1 to 60±11, and 28.5±3 to 1085±113 Bq kg −1 with averages of 26.8±5, 22.7±4, and 322.4±4 Bq kg −1 , respectively. By applying multivariate statistical approach (Pearson correlation, cluster, and principal component analyses (PCA)), the radiological health hazard parameters were analyzed to obtain similarities and correlations between the various samples. The Pearson correlation showed that the 226 Ra distribution in the samples is controlled by changing the 232 Th concentration. The variance of 95.58% obtained from PCA resulted that the main radiological health hazard parameters exist due to the concentration of 226 Ra and 232 Th. The resulting dendrogram of cluster analysis also shows a well coincidence with the correlation analysis.

The size of deep-seated magma chambers is an important parameter for understanding pre-eruptive signals such as surface deformation. The constantly inflating Hekla volcano in Iceland has had relatively simple eruptive behaviour during the historical period. The eruptions start explosively with production of differentially evolved andesite magma to dacite, related to the length of the foregoing quiescence period, and ends with an emission of a basaltic andesite lava of uniform composition. The basaltic andesite is formed by fractional crystallisation from a deeper-seated basalt source in a steady-state manner. How fast such a differentiation mechanism operates is unknown. Measured Ra–Th radioactive disequilibrium in both the basalt and the basaltic andesite reveal a decrease from a 14% excess of 226 Ra over 230 Th to only 5% with magma differentiation. The decrease in 226 Ra excess to 5% in the basaltic andesite of Hekla is shown to be controlled by plagioclase fractionation alone. Therefore, the magma differentiation time from basalt to intermediate magma beneath Mt. Hekla is significantly shorter than three centuries, the time needed to detect significant 226 Ra-decay. Given the steady-state production of basaltic andesite magma and the estimated magma production rate, the volume of the basaltic andesite magma reservoir can be estimated as less than 2 km 3 .