Rhizofiltration experiments were conducted using uranium-contaminated groundwater and lettuce (Lactuca sativa), Chinese cabbage (Brassica campestris L.), radish (Raphanus sativus L.), and buttercup (Oenanthe javanica), which are commonly grown and consumed in South Korea. The results of the rhizofiltration experiments with artificial solutions with different initial uranium concentrations (18, 32, 84, 116, 173, and 263 μg/L) show that the uranium accumulation and bioconcentration factor (BCF) of plant roots increase with increasing uranium concentration in the groundwater. Among the four plants, the uranium concentration in the roots of Raphanus sativus L. is 1215.8 μg/g dry weight, with a maximum BCF value of 2692.7. The BCF value of the artificial solutions with various pH values (pH 3, 5, 7, and 9) is the highest under acidic conditions (pH 3) for all four plants. The uranium BCF values based on different hydroponic conditions range from 170.5 to 11580.3 and the results are comparable with those of other studies using similar methods; the highest BCF value was determined for Brassica campestris L. at pH 3. The BCF values of Raphanus sativus L. after the rhizofiltration experiments with genuine groundwater contaminated with uranium are the highest among the four species; that is, 1684.7 and 1700.1 in Oesam-dong and Bugokdong groundwater samples with uranium concentrations of 83 and 173 μg/L, respectively. The results of the scanning electron microscope/electron dispersive X-ray spectroscope analyses show that uranium in contaminated groundwater is adsorbed as a solid phase on the root surface. These results demonstrate that Raphanus sativus L. has a high tolerance to high concentrations of uranium and low pH conditions and a remarkable potential for uranium accumulation.

Rock permeability, an important factor in subsurface fluid migration, can be influenced by microcracks and chemical weathering due to water–rock interactions. Understanding the relationship between permeability, chemical weathering, and microcracks is crucial for assessing fluid flow in rocks. This study focuses on the hydrogeological characteristics of granite and gneiss, potential host rocks for high-level radioactive waste disposal in South Korea. Samples were analyzed for permeability, porosity, P-wave velocity, and chemical weathering indices. Regression analysis revealed a weak correlation between permeability and both porosity and rock density, while an inverse correlation was observed between permeability and chemical weathering indices. Interestingly, some samples showed low permeability (10⁻²¹ to 10⁻²² m²) despite high weathering, while others showed high permeability (10⁻¹⁸ to 10⁻¹⁹ m²) despite low weathering. SEM-EDS analysis indicated the presence of microcracks within the rocks or the filling of these cracks with secondary minerals. The findings suggest that chemical weathering generally increases pore size and porosity, but actual permeability can vary depending on the presence and connectivity of microcracks and the extent to which they are filled with secondary minerals. Therefore, both chemical weathering and microcrack connectivity must be considered when evaluating the hydrogeological characteristics of crystalline rocks.

This study conducted a rhizofiltration experiment for uranium-removal with the edible plants (Lactuca sativa, Brassica campestris L., Raphanus sativus L., and Oenanthe javanica) which generally consumed in South Korea. Various batch experiments were performed with different initial uranium concentrations, pH conditions, and genuine groundwater. The results showed the uranium accumulation and bioconcentration factor (BCF) of plant roots increase with an increase in initial uranium concentrations in the solution. Of the four plants, the amount of uranium accumulated in Raphanus sativus L. roots was 1215.8 μg/g DW with the maximum BCF value of 2692.7. The BCF value based on various pH conditions (pHs 3, 5, 7 and 9) of artificial solutions was highest at pH 3 for all four plants, and the BCF value of Brassica campestris L. was the maximum of 11580.3 at pH 3. As a result of rhizofiltration experiments with genuine groundwater contaminated with uranium, the BCF values of Raphanus sativus L. were 1684.7 and 1700.1, the highest among the four species, in Oesam-dong and Bugokdong groundwater samples with uranium concentration of 83 and 173 μg/L. From SEM/EDS analysis, it was confirmed that uranium in contaminated groundwater was adsorbed as a solid phase on the root surface. These results demonstrate that Raphanus sativus L. not only has a high tolerance to high concentrations of uranium and low pH conditions but also has a remarkable potential for uranium accumulation capacity.

Nitrate (NO3–) is the final product of the microbial nitrification process in the subsurface environment and can play a significant factor in potential contamination, causing seasonal hypoxia or eutrophication in the aquatic ecosystem. Excessive nitrogen (N) input by anthropogenic activities is well known as one of the major nitrogen sources such as dissolution of organic or synthetic (NH4+, NO3–) fertilizer, leakage of the municipal and industrial landfill, and manure or septic wastewater. This study implemented dual nitrate isotopes approach to investigate the spatial distribution of nitrate contamination and its relative contribution of multiple nitrate sources in Daejeong region, Jeju island, South Korea. A total of 26 groundwater samples were collected from Sangmo, Hamo, and Dongil areas in Daejeong region and their nitrate concentrations were measured. The isotope ratios of N (δ15 NNO3) and O (δ18 ONO3) were analyzed using a denitrifier which converts the dissolved nitrate in the groundwater sample into gaseous nitrous oxide (N2O). The NO3-N concentration above the DWS (drinking water standard, 10 mg/L) was found in 11 out of 19 wells only in Sangmo, while the average NO3-N concentrations of Hamo and Dongil were 2.95 and 2.58 mg/L, respectively. More than 80% of land use in Daejeong region was reported as agricultural farming, and massive synthetic fertilizer usage was expected. However, the δ15 NNO3 ranged from 8.3‰ to 10.2‰, with an average of 9.22‰ and δ18 ONO3 ranged from 3.2 to 6.9‰ with an average of 5.58‰, which are similar values of manure and septic wastewater. Thus, further investigation on land use changes, historical fertilizer consumption and its isotopic shifting in Daejeong region need to be considered for the relative contribution of nitrate sources.