17:15 〜 18:30
[AHW22-P20] Quantitative evaluation of groundwater pollution at Ryukyu limestone area in southern Okinawa Island: Trial application of boron isotope
キーワード：boron isotope, contamination, column separation, MC-ICP-MS
Boron concentration and its isotopic composition can be potential tracers for the evaluation of groundwater contamination. We developed a simple method to separate boron (B) from groundwater by utilizing a mini-column of 0.1 mL cation-exchange resin (AG® 50W-X12), which is modified from Nakamura et al. (1992) and Tanimizu et al. (2018). B isotopic composition is analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). To validate our analytical method, determination of δ11B values was performed for seawater reference standards (NASS-5 and NASS-7); our results were in the range of recommenced values.
This study focused on two realms of Komesu and Giza Subsurface Dams in southern Okinawa Island. We collected 21 groundwater samples, a spring sample and a river sample from Aug. 19th to 23rd, 2020, and a groundwater sample on Sep. 4th, 2020. After the first investigation, we selected 7 observation well sites in southern Okinawa Island for monthly monitoring of water quality. Besides, two rainwater samples were collected on Aug. 24th, 2020, and Jan. 22nd, 2021. We measured boron concentrations of samples by Q-ICP-MS and analyzed δ11B by MC-ICP-MS.
Using these data for the southern Okinawa Island, we characterize and evaluate relative contributions of pollutant sources. The water samples have wide variability in B concentrations (from 18.11 ppb to 168.40 ppb) and B isotopic compositions (from 19.49 ‰ to 38.10 ‰). NO3-N contents are positively correlated with B concentrations and B isotopic compositions. When we assume analyzed rainwaters (having the lowest B and NO3-N contents) as one endmember, these trends can be explained by mixing with possible contaminants (e.g., chemical fertilizer and manure). Although quantitative examination still awaits, our results demonstrate that boron isotopic composition can be utilized as a tracer for groundwater contamination processes.
This study focused on two realms of Komesu and Giza Subsurface Dams in southern Okinawa Island. We collected 21 groundwater samples, a spring sample and a river sample from Aug. 19th to 23rd, 2020, and a groundwater sample on Sep. 4th, 2020. After the first investigation, we selected 7 observation well sites in southern Okinawa Island for monthly monitoring of water quality. Besides, two rainwater samples were collected on Aug. 24th, 2020, and Jan. 22nd, 2021. We measured boron concentrations of samples by Q-ICP-MS and analyzed δ11B by MC-ICP-MS.
Using these data for the southern Okinawa Island, we characterize and evaluate relative contributions of pollutant sources. The water samples have wide variability in B concentrations (from 18.11 ppb to 168.40 ppb) and B isotopic compositions (from 19.49 ‰ to 38.10 ‰). NO3-N contents are positively correlated with B concentrations and B isotopic compositions. When we assume analyzed rainwaters (having the lowest B and NO3-N contents) as one endmember, these trends can be explained by mixing with possible contaminants (e.g., chemical fertilizer and manure). Although quantitative examination still awaits, our results demonstrate that boron isotopic composition can be utilized as a tracer for groundwater contamination processes.