EVALUATING THE IMPACT OF PH AND MOLECULAR CHARACTERISTICS ON THE FORMATION OF AS-DOM COMPLEXES
We used two types of DOM: Suwanee Reverse Osmosis Humic acid and DOM derived from two distinct coal samples representing diverse molecular characteristics. DOM molecular weights were characterized using high performance liquid chromatography coupled with a size exclusion column (HPLC-SEC) and a fluorescence and absorbance detector. We investigated aromaticity, carboxylic, and phenolic functional groups; these molecular structures are potentially responsible for As-DOM mechanisms. Carboxylic and phenolic functional group content were quantified through potentiometric acid base titrations, while aromaticity was assessed through specific ultraviolet absorbance (SUVA254), with an Agilent UV-VIS.
As-DOM complexation was determined through a series of dialysis experiments prepared with various concentrations of sodium metaarsenite (5 – 500 µg/L) and pH conditions (3-10). Once equilibrium was reached, As concentrations outside and inside the dialysis tube were analyzed through inductively coupled plasma mass spectrometry (ICP-MS). In parallel, As-DOM solution was analyzed with HPLC-SEC-ICP-MS which directly measures free and complexed As. By combining these methods, we received a novel data on mechanisms of As-DOM complexation, conditional distribution coefficients DOM by dialysis experiment, and molecular weight of As-DOM complexation sites. Results were used to build isotherms based on As concentration and pH. To investigate the impact of molecular characteristics and establish trends in As-DOM complexation, we compared DOM values to molecular characteristics of DOM from different origin. Our results evaluate trends in As-DOM complexation with direct evidence of complexation furthermore contributing to our current understanding of As cycling.