2:30 PM - 2:45 PM
[AHW27-16] Development of a Solid-Phase Extraction Method for Simultaneous Trace Metal and Rare Earth Element Analysis: Application to Groundwater and Submarine Groundwater Discharge
Keywords:trace metals, rare earth elements, solid-phase extraction, biogeochemical cycling
Trace elements, including rare earth elements (REEs) and trace metals, play a crucial role in understanding biogeochemical processes in aquatic environments. Trace metals such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb function as essential micronutrients that regulate primary productivity and influence marine ecosystems. Their biogeochemical behavior varies significantly, with some metals exhibiting scavenging-type distributions, while others follow nutrient-like profiles, reflecting biological uptake and remineralization. REEs, particularly heavy REEs (HREEs), serve as valuable tracers for oceanic and coastal processes due to their conservative nature and characteristic fractionation patterns.
However, precise quantification of these elements in environmental waters remains challenging due to their ultra-trace concentrations and the complexity of the surrounding matrix. To overcome these challenges, this study employed a solid-phase extraction system using InertSep ME-2 resin, enabling the simultaneous, automatic, and rapid separation of multiple trace metals and REEs. The ability to simultaneously determine REEs and trace metals allows for direct analysis, improving time, sample volume, and energy efficiency. This study focuses on the application of the developed method across diverse environmental water samples, including groundwater, river water, submarine groundwater discharge (SGD), and seawater, to evaluate the transport and transformation of trace metals and REEs.
This method is designed for the preconcentration and analysis of trace metals and REEs in groundwater, river water, SGD, and seawater using the InertSep ME-2 resin column. To account for the varying compositions of these water types, each 40 mL sample undergoes a standardized preparation process. To ensure the reproducibility of trace metal and REE measurements, all samples were analyzed in triplicate using an ICP-MS, Agilent 7700x.
The results showed recovery rates for trace metals in the range of 90–105%, HREEs is 92%, and light REEs 93–100%, demonstrating high accuracy in extraction and quantification. The precision of REE measurements was notably high, with variability remaining below 3%, indicating strong reproducibility. While trace metals such as Cr, Mn, and Zn exhibited slightly higher variability, they still remained within an acceptable range, below 5%. To further validate the method, CRMs (NASS-7, NMIJ 7204A, and NMIJ 7202-c) were analyzed, showing variability below 5% for both REEs and trace metals. This confirms the reliability and robustness of the analytical approach.
Interestingly, river water also plays a significant role in transporting trace metals to the coastal environment. Among all the trace metals, Fe exhibited the highest concentration. The transport of HREEs further supports the influence of riverine input, with Yb concentrations in river water measured at the highest concentration. Strongly elevated HREEs concentrations were observed in the surface layer of Toyama Bay, while deeper layers (300 m) showed a significant decrease in Yb concentration. This trend suggests active surface-layer enrichment and subsequent depletion at depth. Trace metals in the bay exhibit diverse behaviors, reflecting different geochemical and biogeochemical processes. Co follows a scavenging-type profile, with higher concentrations in the surface layer and lower concentrations in deeper waters. Cu concentrations are highest in the surface layer, decline in the subsurface, and then gradually increase toward the bottom. Cd and Ni display a classic nutrient-like profile, with low surface concentrations that increase with depth.
Further analysis of SGD samples, fractionation patterns, and isotopic composition could provide deeper insights into the mechanisms driving trace metal and REEs transport in Toyama Bay and other coastal environments. The SGD part will be further discussed during the presentation.
However, precise quantification of these elements in environmental waters remains challenging due to their ultra-trace concentrations and the complexity of the surrounding matrix. To overcome these challenges, this study employed a solid-phase extraction system using InertSep ME-2 resin, enabling the simultaneous, automatic, and rapid separation of multiple trace metals and REEs. The ability to simultaneously determine REEs and trace metals allows for direct analysis, improving time, sample volume, and energy efficiency. This study focuses on the application of the developed method across diverse environmental water samples, including groundwater, river water, submarine groundwater discharge (SGD), and seawater, to evaluate the transport and transformation of trace metals and REEs.
This method is designed for the preconcentration and analysis of trace metals and REEs in groundwater, river water, SGD, and seawater using the InertSep ME-2 resin column. To account for the varying compositions of these water types, each 40 mL sample undergoes a standardized preparation process. To ensure the reproducibility of trace metal and REE measurements, all samples were analyzed in triplicate using an ICP-MS, Agilent 7700x.
The results showed recovery rates for trace metals in the range of 90–105%, HREEs is 92%, and light REEs 93–100%, demonstrating high accuracy in extraction and quantification. The precision of REE measurements was notably high, with variability remaining below 3%, indicating strong reproducibility. While trace metals such as Cr, Mn, and Zn exhibited slightly higher variability, they still remained within an acceptable range, below 5%. To further validate the method, CRMs (NASS-7, NMIJ 7204A, and NMIJ 7202-c) were analyzed, showing variability below 5% for both REEs and trace metals. This confirms the reliability and robustness of the analytical approach.
Interestingly, river water also plays a significant role in transporting trace metals to the coastal environment. Among all the trace metals, Fe exhibited the highest concentration. The transport of HREEs further supports the influence of riverine input, with Yb concentrations in river water measured at the highest concentration. Strongly elevated HREEs concentrations were observed in the surface layer of Toyama Bay, while deeper layers (300 m) showed a significant decrease in Yb concentration. This trend suggests active surface-layer enrichment and subsequent depletion at depth. Trace metals in the bay exhibit diverse behaviors, reflecting different geochemical and biogeochemical processes. Co follows a scavenging-type profile, with higher concentrations in the surface layer and lower concentrations in deeper waters. Cu concentrations are highest in the surface layer, decline in the subsurface, and then gradually increase toward the bottom. Cd and Ni display a classic nutrient-like profile, with low surface concentrations that increase with depth.
Further analysis of SGD samples, fractionation patterns, and isotopic composition could provide deeper insights into the mechanisms driving trace metal and REEs transport in Toyama Bay and other coastal environments. The SGD part will be further discussed during the presentation.