Sorption of arsenic to biogenic iron (oxyhydr)oxides produced in circumneutral environments

Abstract

Arsenic (As) is a widespread and problematic pollutant that can be derived from natural or anthropogenic sources. Iron (oxyhydr)oxides readily sorb As and thus play critical roles in As cycling in terrestrial environments; however, little is known about the affinity and mechanism of As sorption by biogenic iron (oxyhydr)oxides formed in circumneutral environments. To investigate this, we conducted sorption isotherm and kinetics experiments to compare As(V) and As(III) sorption to synthetic 2-line ferrihydrite and iron biominerals harvested from the hyporheic zone of an uncontaminated creek. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify both As(V) and As(III), and X-ray absorption spectroscopy (XAS) was utilized to obtain As and Fe K-edge spectra for As(V) and As(III) sorbed to environmentally collected and laboratory produced Fe(III) minerals. All environmental Fe(III) biominerals were determined to be structurally similar to 2-line ferrihydrite. However, environmental Fe(III) biominerals have a surface area normalized affinity for As(V) and for As(III) that is greater than or equivalent to synthetic 2-line ferrihydrite. Whereas the extent of sorption was similar for As(III) on all minerals, As(V) sorption to environmental Fe(III) biominerals was approximately three times higher than what was observed for synthetic 2-line ferrihydrite. Structural modeling of EXAFS spectra revealed that the same surface complexation structure was formed by As(V) and by As(III) on environmental Fe(III) biominerals and ferrihydrite. These results suggest that, despite similarities in binding mechanisms, Fe(III) biominerals may be more reactive sorbents that synthetic surrogates often used to model environmental reactivity.

Assessing Biomineral Formation by Iron‐oxidizing Bacteria in a Circumneutral Creek

“…There was a high abundance of canopy vegetation that limited light penetration. The second location was Rocky Branch Creek (RBC: 35° 46' 48.6" N, 78° 40' 1.9" W) located on North Carolina State University Campus in Raleigh, North Carolina (Andrews and Duckworth 2016;Sowers et al 2017). There were two site locations along the south side of the creek bank (RBC1 and RBC2), as well as a seep located downstream on the north side of the creek (RBC3) and a midstream location (RBCM).…”

“…The importance of FeOB and iron oxides originates from their sorptive capacity and influence on delivered water quality in distribution systems through pipe oxidation (Cullimore and McCann 1978;Søgaard et al 2001;Fleming et al 2014;Sowers et al 2017), importance in microbial…”

“…Generally, less is known about the formation and chemistry of these minerals, as well as microbes that oxidize iron at circumneutral pH, than most other aspects of iron biogeochemistry. The importance of FeOB and iron oxides originates from their sorptive capacity and influence on delivered water quality in distribution systems through pipe oxidation (Cullimore and McCann 1978;Søgaard et al 2001;Fleming et al 2014;Sowers et al 2017), importance in microbial Journal of Contemporary Water Research & Education UCOWR ecology and evolution (Posth et al 2014), and potential for use in soil remediation (Emerson et al 2010). These applications, combined with their natural abundance, motivated our interest in understanding the physical, chemical, and biological characteristics of environments capable of supporting biogenic formation of iron oxides.…”

Organo-Modified Vermiculite: Preparation, Characterization, and Sorption of Arsenic Compounds

“…Contamination of water with arsenic compounds is one of the most significant scientific challenges. Natural activities that increase As concentration in aqueous systems are weathering, volcanic emissions, erosion of soils/rock, and biological metabolism [3,4], while mining wastes, ceramic manufacturing industries, agricultural chemicals, petroleum refining, coal fly ash, and military operations contribute to the anthropogenic sources of arsenic [5,6]. Hence, rapidly increasing urbanization and industrialization activities considerably enhance the degree of arsenic pollution.…”

Soil and Water Iron Microbes in North Carolina (SWIMNC) Outreach: Positive Impact of Combining Classroom and Field Experiences to Promote Learning and Shift Attitudes

“…The greenway is a wide, paved path immediately adjacent to the Rocky Branch Creek stream, providing both easy access to the site and a safe place to assemble. This site has been sampled frequently as part of an ongoing study investigating the formation of iron oxides by iron oxidizing bacteria in circumneutral streams in North Carolina (Andrews and Duckworth, 2016;Sowers, 2016;Almaraz et al, 2017;Sowers et al, 2017;.…”