GEOCHEMICAL CONTROLS ON DOM-ARSENIC COMPLEXES

In environmental systems, dissolved organic matter (DOM) provide strong binding sites for metal ions and impact the mobility of metal ions in these systems. However, changes in environmental conditions can impact complexation of DOM and metal ions. For example, pH can impact complexation through ionization of functional groups^1, whereas increases in salinity creates competition between cations in solutions and impacts the activity coefficients of species^1. This work focuses on the mobility of DOM-arsenic (DOM-As) complexes over a range of pH and salinity.

Here, we describe preliminary results from experiments using DOM from two different coals, one from Hot Springs County, Arkansas and one from Dolet Hills, Louisiana. The coals have DOM fractions with different structural functional groups that could influence As complexation. Various concentrations of sodium arsenite ( 0 – 500 µg/L) are added to each of these water-soluble extracts. Solutions are prepared with a range of pH values (3-10) and salinity (0-20 psu), representing a variety of geochemical conditions. Each solution is fractionated using size-exclusion filters, then the total arsenic concentration in each solution is determined through inductively coupled plasma mass spectrometry (ICP-MS). Our results will determine the geochemical conditions that promote complexation furthermore contributing to current understanding of arsenic bioavailability in aqueous systems.

(1) Stevenson, F. J. Humus Chemistry: Genesis, Composition, Reactions, Second Edi.; John Wiley & Sons: New York, NY, 1994.