31-17 Organic Metal and Metalloid Complexes (OMMC): Analytical Method Development and Applications

Session: Environmental Geochemistry and Health (Posters)

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Abstract:

Organic metal and metalloid complexes (OMMC), formed when aqueous metal(oid)s bind to organic ligands ranging from natural organic matter (NOM) and biological metabolites to industrial synthetic compounds, are likely an important control on the mobility and bioavailability of trace elements in the hydrologic environment. OMMCs may be especially prevalent in mining-impacted environments where elevated trace element concentrations co-occur with strong chelating agents such as ethylenediaminetetraacetic acid (EDTA) and/or other synthetic acids often used in hydrometallurgical extraction processes.  Yet these compounds are seldom measured in field samples and their consequences for metal(oid) fate and transport remain largely unknown.  Analytical challenges have prevented routine quantification of OMMCs, leaving a critical gap in the ability to characterize trace element speciation, address research questions related to source tracking, and inform bioavailability and risk assessment models used by land and water resource managers.

Here we present progress toward a suite of analytical methods designed to measure inorganic and organic speciation of critical metals and metalloids in natural waters. Using high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS), we assessed analytical protocols for redox speciation and OMMC of arsenic, selenium, antimony, and vanadium, and for separation of metal-EDTA complexes for cobalt, copper, and lead. Geochemical modeling (PHREEQC) was used to optimize method conditions and provide independent validation. Our results demonstrate that separation of organometallic complexes from free metal ions is analytically feasible for several elements, that quantitation of redox oxyanion speciation is especially promising, and that weakly bound metal-natural organic matter complexes are not sufficiently stable for the methods tested.

Once optimized, these capabilities could have broad application across use cases including critical mineral recovery from mine waste, wildfire-driven metal mobilization, municipal wastewater treatment, and harmful algal bloom biogeochemistry. By enabling source characterization through co-occurring anthropogenic chelating agents and improved speciation measurements, this work supports watershed management, contaminant source apportionment, and remediation strategies relevant to Tribal communities, regulatory agencies, utilities, and the broader research community.

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