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.

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.

The presence of contaminated aquitards has been recognized as one of the main obstacles that hamper the successful aquifer restoration and the forward and back diffusion processes were known as the primary mechanism of solute exchange between the aquifer-aquitard system. In this study, a series of 2-D flow chamber experiments were conducted using 1 g/L of bromide solution as a non-reactive tracer to evaluate back diffusion phenomenon and plume tailing behavior based on different clay types (kaolinite, montmorillonite, and bentonite). In order to determine appropriate values for clay tortuosity, simulated effluent concentrations using 1-D analytical solutions were compared to the measured effluent concentrations. The best fits were found with for bentonite, for kaolinite, and The bentonite tortuosity value close to 1 indicates that the solute flowpath is similar to the aquitard straight-line distance under the saturated condition. Simulation results using the calculated tortuosity showed that bromide effluent concentration due to back diffusion from the montmorillonite layer decreased to 3 orders of magnitude below the initial concentration after 60 days of back diffusion. For bentonite, calculated effluent concentrations decreased to 3 orders of magnitude below the initial concentration after 230 days of back diffusion. These results suggest that the aquitard with higher tortuosity has more capability to sustain long-term plume persistence for non-reactive contaminants and more potential risks as secondary contaminant sources.

Optimizing 10 ¹³ Ω amplifier configurations enables precise, low-level Li isotope analysis under conventional wet plasma conditions across defined operating ranges.