Arsenic Cycling in Hydrocarbon Plumes: Secondary Effects of Natural Attenuation

Abstract

Monitored natural attenuation is widely applied as a remediation strategy at hydrocarbon spill sites. Natural attenuation relies on biodegradation of hydrocarbons coupled with reduction of electron acceptors, including solid phase ferric iron (Fe(III)). Because arsenic (As) adsorbs to Fe-hydroxides, a potential secondary effect of natural attenuation of hydrocarbons coupled with Fe(III) reduction is a release of naturally occurring As to groundwater. At a crude-oil-contaminated aquifer near Bemidji, Minnesota, anaerobic biodegradation of hydrocarbons coupled to Fe(III) reduction has been well documented. We collected groundwater samples at the site annually from 2009 to 2013 to examine if As is released to groundwater and, if so, to document relationships between As and Fe inside and outside of the dissolved hydrocarbon plume. Arsenic concentrations in groundwater in the plume reached 230 µg/L, whereas groundwater outside the plume contained less than 5 µg/L As. Combined with previous data from the Bemidji site, our results suggest that (1) naturally occurring As is associated with Fe-hydroxides present in the glacially derived aquifer sediments; (2) introduction of hydrocarbons results in reduction of Fe-hydroxides, releasing As and Fe to groundwater; (3) at the leading edge of the plume, As and Fe are removed from groundwater and retained on sediments; and (4) downgradient from the plume, patterns of As and Fe in groundwater are similar to background. We develop a conceptual model of secondary As release due to natural attenuation of hydrocarbons that can be applied to other sites where an influx of biodegradable organic carbon promotes Fe(III) reduction.

Life cycle of petroleum biodegradation metabolite plumes, and implications for risk management at fuel release sites

“…Our results are generally similar to the well‐studied groundwater plume emanating from a very large biodegrading crude oil release near Bemidji, Minnesota, USA, where the “non‐volatile dissolved organic carbon” in the low‐oxygen shadow downgradient of the dissolved hydrocarbon plume 1) extends farther than the dissolved hydrocarbons and 2) is primarily composed of organic acids (Eganhouse et al ; Essaid et al ; Cozzarelli et al ). The overall scale and associated anaerobic geochemical footprint of the Bemidji release is larger than the sites we studied, and the Bemidji source is crude oil whereas our study focused on refined fuels.…”

Arsenic Release and Attenuation Processes in a Groundwater Aquifer During Anaerobic Remediation of TCE with Biostimulation

“…Others (Amirbahman et al ; He et al ; Hering et al ) have observed natural attenuation of As with the formation of Fe and Mn oxides as the groundwater moves into oxic sediments away from the biostimulated treatment zone. Likewise, Ziegler et al () and Ziegler et al () noted redistribution of As along the flow path in a crude‐oil contaminated sandy aquifer in Bemidji, Minnesota, with As being retained with distance from the plume by sorption of Fe oxides (Cozzarelli et al ). Amirbahman et al () described the role of Mn oxides in the oxidation of As(III) and natural attenuation of the produced As(V) through sorption.…”

“…Choosing the source of organic carbon and how much to add are critical decisions when attempting efficient dechlorination, but may be counter to controlling As mobilization. These considerations would also be relevant to many other plumes, where the biodegradation of organic materials coupled with reduction of Fe(III) oxides releases As to the groundwater within the biologically active zone, but attenuation would occur with distance from the plume, as observed at the leading edge of a crude‐oil plume in Bemidji, Minnesota (Cozzarelli et al ).…”

Anaerobic BTEX degradation in oil sands tailings ponds: Impact of labile organic carbon and sulfate-reducing bacteria

“…Except for sulfate, potential electron acceptors for anaerobic BTEX degradation like nitrate and reactive Fe(III) were low . However, ponds contain iron oxides in clay minerals (Kaminsky et al, 2008) presumably available for BTEX metabolisation (Cozzarelli et al, 2015). In addition, BTEX can be biodegraded during respiration with humic acids (Cervantes et al, 2001) and under methanogenic conditions (Grbic-Galic and Vogel, 1987).…”