An Assessment of Groundwater Contamination Risk with Radon Based on Clustering and Structural Models

Exposure to radon gas in groundwater in southwest Angola (Lubango-Huíla): Implications of geology and climate change

In southern African countries most of the population uses groundwater collected in dug wells for domestic consumption instead of water from public distribution systems. To investigate the impact of natural and human factors on urban groundwater quality, 276 samples were collected in the Lubango region (Angola) in water distribution systems and dug wells ranging from a few meters to almost one hundred meters in depth. Radon concentrations (RC) were determined by liquid scintillation counting according to ISO 13164-4:2015. Geology is the main source of the variability of RC, with median values higher than 100 Bq/L in granitoid units and lower values in mafic and sedimentary units (ranging from 5 to 38 Bq/L). On average, RC was higher in dug wells compared to public water distribution systems. The annual effective dose due to ingestion of radon in water is, on average, ten times lower in the later compared to dug wells. Therefore, from a public exposure perspective, water distribution systems are preferred as means for water distribution. A severe multi-year meteorological drought over the past decade affecting 76-94 % of the population in southern Angola has been linked with climate change. Consequently, a regional lowering of the water table was observed, as well as a reduction in the productivity of shallower wells, leading to a search for water at greater depths. This work demonstrates an increase in median RC from 66 Bq/L in wells shallower than 30 m to values over 100 Bq/L with increasing depth of water extraction and for the same geological unit. The highest RC observed were also observed at the deepest wells. The dose ingested is proportional to RC, being also higher at deeper water extraction depths. The increase in public radiation exposure from radon ingestion due to water extraction at greater depths is attributed to the underlying issue of climate change. Monitoring water quality in terms of radionuclide concentration is advised to ensure the exposure to ionizing radiation remains at acceptable levels in the future.

Radon level in groundwater in Kwara State, Nigeria, and the potential radiation dose due to intake

Radon in groundwater for domestic purposes contributes to indoor radon and at high concentration levels could be hazardous to inhabitants. Rn-222 concentrations in 101 groundwater samples from some Local Government Areas (LGAs) of Kwara State, Nigeria, were determined by AlphaGUARD portable radon monitor. The mean activity concentrations for the LGAs varied from 4.28 ± 2.29 to 14.59 ± 8.92 Bq.l-1. Radon concentrations were <100 Bq.l-1 guidance level recommended by CEC and WHO. Eighteen percent exceeded the recommended 11.1 Bq.l-1 by the United States Environmental Protection Agency. All the samples exceeded the 0.1 Bq.l-1 Maximum Permitted Level of the Standard Organization of Nigeria for radionuclide contaminant. Mean effective dose from ingestion was estimated for adults, children and infants. Inhalation dose was also estimated. The mean annual effective doses in five LGAs were higher than the 0.1 mSv reference dose level of committed effective dose from the intake of drinking water for 1 y as recommended by the ICRP.

HIGHLIGHTS

Modeling the effects of temperature on the migration and transformation of nitrate during riverbank filtration using HYDRUS-2D

Riverbank filtration is a natural aquifer-based process. The nitrogen dynamics in a riverbank filtration system are affected by many factors, including temperature, water quality, and travel time, which cannot be quantified easily. In this study, a field experiment was conducted to investigate nitrogen transport during riverbank filtration. The HYDRUS-2D software package was used to investigate and quantify the factors that affect the fate of nitrogen. The effects of temperature, water quality, and travel time on nitrate transport were considered. The model was calibrated and validated using field experimental data from the river water and groundwater during riverbank filtration at different periods. The results showed that HYDRUS-2D adequately simulated nitrate transport during riverbank filtration. The denitrification rate constant exhibited a positive exponential relationship with temperature. An empirical formula describing this relationship in riverbank filtration was developed and validated. In addition, the denitrification rate can be quantified within a specified temperature data range under field conditions. Compared with indoor experimental conditions, for the same temperature, there was a 10-fold increase in the denitrification rate constant under field conditions. The results showed that most of the nitrate removal occurred in the riparian zone at high temperatures during riverbank filtration. We concluded that the fate of nitrate in the riparian zone is strongly controlled by groundwater temperature. Travel time also plays an important role in nitrate removal during riverbank filtration.

Distribution and correlation of radon and uranium and associated hydrogeochemical processes in alluvial aquifers of northwest India

The spatial and vertical distributions of radon and uranium are evaluated in relation to the hydrogeology, geomorphology, and hydrochemistry of southwest Punjab. Radon activity of the groundwater ranges from 580 to 3633 Bq/m³ (shallow groundwater 580 to 2438 Bq/m³ and deep groundwater 964 to 3633 Bq/m³), and uranium concentration varies from 24.4 to 253 μg/L (shallow groundwater 24.4 to 253 μg/L and deep groundwater 27.6 to 76.3 μg/L). Shallow groundwater shows higher U concentration compared with deeper ones, which can be attributed to the presence of dissolved oxygen (DO) and NO₃^- as oxidants and HCO₃^- as stabilizing agent in shallow zone. Unlike uranium, the radon activities were found to be similar in both shallow and deep groundwater. Rn_excess over secular equilibrium was used to confirm the possibility of additional sources of radon, such as secondary minerals present in the subsurface. Surface manifestations show significant influence on radon and uranium distributions in the shallow zone but not in deep zone due to limited hydraulic connectivity. Depth profiles and correlations of radon and uranium with trace elements and hydrochemical parameters indicate that groundwater exhibits different redox characteristics in shallow (younger and oxidizing) and deep zones (older and reducing). The present study provides critical information that can be helpful for planning sustainable groundwater development in this region and other similar regions without contaminating the relatively safer deep aquifers.

A new radon prediction approach for an assessment of radiological potential in drinking water

Inhaled radon from groundwater used for domestic purposes is one of the sources of natural radioactivity into indoor air. Due to uranium-bearing minerals occurrences, hydrogeochemical conditions, tectonic structures, and hydraulic circuits, the radon pathway from rocks to groundwater is quite unpredictable. High radon potential from bedrocks is not always associated with high radon levels in groundwater. Besides, inhaled radon from domestic use may also increase the exposure toindoor radon levels. This innovative methodology using hydrogeochemical conditions and groundwater flow transport was used for radon predictions in the underground to ensure safe drinking water ingestion and inhalation. This innovative radon prediction methodology is based on classic hydrogeochemical analyses (Eh-pH, Piper, Schöeller and Gibb's diagrams) and multivariate statistical analyses (Principal Component Analysis and Pearson's correlation). High dissolution of major ions does not imply high radon mobilization from rocks to groundwater. The travel time was estimated to developed a flow transport of contaminated groundwater. Radiological results show that of the 25 sampled springs, five of them contained radon concentrations above the Portuguese imposed limit (²²²Rn = 500 Bq·L^-1), and 16 of them with values above the WHO recommended limit (²²²Rn = 100 Bq·L^-1). Overall, this new approach of radon prediction showed that uranium enrichment in rocks at ideal hydrochemical conditions and emanation coefficient, and shallow circuits, are responsible for radon increasing in drinking water. The proposed approach allow to predict the areas with high radon potential groundwaters, being a tool to be used by water planners and policy makers for corrective and preventive measures in shallow groundwater flows. To safeguard clean water within the predefined deadline of Sustainable Development Goals (2030) and to ensure human health in compliance with WHO guidelines for safe drinking water, should be established priority water protection policies to reduced radon in this contaminated springs (n = 16).

The Role of Landscape Configuration, Season, and Distance from Contaminant Sources on the Degradation of Stream Water Quality in Urban Catchments

Water resources are threatened by many pollution sources. The harmful effects of pollution can be evaluated through biological indicators capable of tracing problems in life forms caused by the contaminants discharged into the streams. In the present study, the effects on stream water quality of landscape configuration, season, and distance from contaminant emissions of diffuse and point sources were accessed through the evaluation of a Portuguese macroinvertebrate index (IPtIN) in 12 observation points distributed within the studied area (Ave River Basin, Portugal). Partial least-squares path models (PLS-PMs) were used to set up cause–effect relationships between this index, various metrics adapted to forest, agriculture, and artificial areas, and the aforementioned emissions, considering 13 distances from the contaminant sources ranging from 100 m to 56 km. The PLS-PM models were applied to summer and winter data to explore seasonality effects. The results of PLS-PM exposed significant scale and seasonal effects. The harmful effects of artificial areas were visible for distances larger than 10 km. The impact of agriculture was also distance related, but in summer this influence was more evident. The forested areas could hold onto contamination mainly in the winter periods. The impact of diffuse contaminant emissions was stronger during summer, when accessed on a short distance. The impact of effluent discharges was small, compared to the influence of landscape metrics, and had a limited statistical significance. Overall, the PLS-PM results evidenced significant cause–effect relationships between land use metrics and stream water quality at 10 km or larger scales, regardless of the season. This result is valid for the studied catchment, but transposition to other similar catchments needs to be carefully verified given the limited, though available, number of observation points.