The production of phosphoric acid from natural phosphate rock by the wet process gives rise to an industrial by-product called phosphogypsum (PG). About 5 tons of PG are generated per ton of phosphoric acid production, and worldwide PG generation is estimated to be around 100-280 Mt per year. This by-product is mostly disposed of without any treatment, usually by dumping in large stockpiles. These are generally located in coastal areas close to phosphoric acid plants, where they occupy large land areas and cause serious environmental damage. PG is mainly composed of gypsum but also contains a high level of impurities such as phosphates, fluorides and sulphates, naturally occurring radionuclides, heavy metals, and other trace elements. All of this adds up to a negative environmental impact and many restrictions on PG applications. Up to 15% of world PG production is used to make building materials, as a soil amendment and as a set controller in the manufacture of Portland cement; uses that have been banned in most countries. The USEPA has classified PG as a "Technologically Enhanced Naturally Occurring Radioactive Material" (TENORM). This work reviews the different environmental impacts associated with PG storage and disposal. The methods described in the literature to minimise the negative effects of this waste are classified by treatment type, i.e. physical, chemical, thermal, etc., and different suggested applications for PG are detailed.
Radionuclides are hazardous materials which impose ionizing radiation on humans and are valuable proxies for tracking environmental processes. Radionuclides are widely reported in global marine sediments, which are recognized as the final destination of radionuclides. As one of the typical marine ecosystems, coral reefs are “hotspots” of high biodiversity providing rich biological resources and significant tourist sites for humans. Seafood consumption and SCUBA diving would induce internal and external radiation on humans, respectively. However, radioactivity is rarely studied in coral reef ecosystems. Here, we exhibited radionuclides in marine sediments collected from the fringing and atoll reefs with a latitudinal coverage of 14° (~1500 km) in the South China Sea (SCS). Naturally occurring radionuclides (40K, 226Ra, 228Ra, and, 238U) were quantified by Standard River Sediment (GBW08304a) and were validated by Irish Sea Sediment (IAEA-385) using High Purity Germanium (HPGe) γ spectrometry (Canberra BE6530). The energy resolution of HPGe γ-spectrometry (~2 keV) is much better than that of NaI γ-spectrometry (~50 keV). Overall, radioactivity in marine sediments was in the order of 238U (28.96 Bq/kg) >40K (24.36 Bq/kg) >228Ra (5.08 Bq/kg) >226Ra (3.34 Bq/kg). Radioactivity was higher in marine sediments collected from the fringing reefs than the atoll reefs due to the influence of terrigenous minerals in the fringing reefs. The occurrence of terrigenous minerals was confirmed by the mineral components (K-feldspar, illite, and quartz) using X-ray diffraction analysis. Additionally, the rare earth elements (REE) are generally used to trace terrigenous inputs. In the present study, the ranking pattern of the 40K activity was consistent with the concentration of REE in marine sediments (sediments outside the coral reef regions > sediments from fringing reefs > sediments from atoll reefs), giving supporting evidence of the influence of terrigenous minerals. A comparison of radionuclides in marine sediments from coral reefs and other sea regions indicated that the radioactive level (Radium equivalent activity, Ra eq) of marine sediment in coral reefs was only 1%−10% of that of other marine sediments and global soil. The value of Ra eq in marine sediments collected from coral reefs (3−42 Bq/kg) was also lower than that in marine sediments collected from the pristine environment of the Arctic Ocean (70.62 Bq/kg) and Southern Ocean (76.92 Bq/kg). Particularly, the mean value of Ra eq in marine sediments of the atoll reefs in the SCS (3.97 Bq/kg) was less than 5% of that in global average soil (108.70 Bq/kg). Therefore, radioactivity in marine sediment was extremely low in coral reefs relative to other sea regions. Marine sediments in coral reefs had three unique characteristics of low 40K activity, low 226Ra and 228Ra activity, and low 226Ra/238U ratio. It was worth noting that the abnormally low 226Ra/238U activity ratio (<0.1) of marine sediments was observed in the atoll reefs and was attributed to the biological process of active uptake of 226Ra and 238U from seawater by coral polyps rather than the ingrowth process of the 238U-230Th-226Ra decay chain. The mechanism of radioactive characteristics in marine sediments was attributed to the fragmentation and weathering of biominerals in coral reefs in contrast to the weathering and subsequent transport of soil and rocks in other marine sediments outside the coral reef region. These three characteristics have potential to be novel geochemical proxies for tracking particle dynamics in coral reefs in addition to other traditional approaches including the Al, Ti, REE, and mineral components.
This study aimed to evaluate the activity concentrations of naturally occurring radionuclides (NORs) in Nasser Lake water, assess the associated radiological risks, and investigate the potential health and environmental impacts. The presence of these NORs is attributed to both natural geological formations, such as uranium-rich granitic and metamorphic rocks, and anthropogenic activities, including agricultural runoff. Water samples were analyzed for radium-226 (Ra-226), thorium-232 (Th-232), and potassium-40 (K-40). The Ra-226 concentration ranged from 0.08 ± 0.003 to 1.28 ± 0.06 becquerel per liter (Bq/l), mostly between 0.2 and 1.0 Bq/l, reflecting geological and anthropogenic influences. The symbol (±) represents the measurement uncertainty associated with gamma spectrometric analysis. According to international radiation safety guidelines, Ra-226 levels below 1 Bq/l are considered safe for consumption. The Th-232 concentration varied from 0.04 ± 0.001 to 0.96 ± 0.06 Bq/l, showing significant spatial variation. Similarly, K-40 concentrations ranged from 1.35 ± 0.11 to 16.57 ± 1.43 Bq/l, with some notably high values. The annual effective dose (E<sub>ff</sub>) ranged from 15.8 to 266.15 micro sievert per year (µSv/y) for adults, reaching 362.92 µSv/y for children and 221.54 µSv/y for infants. The doses for children and infants exceeded the recommended thresholds. Cancer risk (CR) assessments showed that men's mortality risks ranged from 2.56 × 10<sup>-5</sup> to 4.10 × 10<sup>-4</sup>, while women's ranged from 2.68 × 10<sup>-5</sup> to 4.29 × 10<sup>-4</sup>. Morbidity risks varied between 3.72 × 10<sup>-5</sup> and 5.95 × 10<sup>-4</sup> for men and 3.89 × 10<sup>-5</sup> to 6.22 × 10<sup>-4</sup> for women. These risks correlate with specific lake locations, highlighting hot spots with elevated radioactive content. Water acidity levels (pH) ranged from 6.23 to 7.9, indicating predominantly neutral to slightly alkaline conditions. These variations correlated with electrical conductivity (EC), reflecting complex interaction between pH, EC, and NORs. The study assesses gamma radiation hazards from external exposure and internal risks from alpha-emitting radionuclides, such as Ra-226 and Th-232, through water ingestion. While most samples comply with standard radiation limits, elevated radionuclide levels in certain areas pose potential health risks, particularly for vulnerable populations like children. Continuous monitoring of radiological parameters in Naser Lake is essential to trace long-term trends and ensure safety compliance. Additionally, advanced water treatment methods could help mitigate radionuclide concentrations in affected areas.
The geological formations of Dessie town contain rocks that release radon gas, the second leading cause of lung cancer after smoking. To date, there have been no investigations of geology-based radon health risks in Dessie town. The main objective of this study was to evaluate and map the temporal and spatial distribution of radon gas concentrations within Dessie town. The evaluation and mapping were done using advanced geological and geospatial techniques, employing Quantum Geographic Information Systems (QGIS) software to integrate the research area's weather conditions and geological data using shape files for the study area and masking with its geological map. Geological analysis helps to know whether the geological formation of Dessie town is composed of basaltic rocks, as shown on the geological map of Dessie town, which was obtained from the Ethiopian Geological Institute. Based on these geological formations and geospatial analysis, radon gas activity concentrations were estimated in two different ranges: from 3[Formula: see text]for the emanation coefficient 0.3 and from [Formula: see text]for the emanation coefficient 0.1 for this study area. The radon gas distribution map indicates radon levels in Dessie town fall into two ranges, each with its own potential hotspots, as shown by circles of different colors on the map. These results indicate that there exist health-related problems at nine stations due to prolonged exposure to radon gas, and for further investigation of radon gas activity concentrations and their health impact, we recommend experimental measurements provide more accurate results.
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