Rates of As and Trace-Element Mobilization Caused by Fe Reduction in Mixed BTEX–Ethanol Experimental Plumes

Abstract

Biodegradation of organic matter, including petroleum-based fuels and biofuels, can create undesired secondary water-quality effects. Trace elements, especially arsenic (As), have strong adsorption affinities for Fe(III) (oxyhydr)-oxides and can be released to groundwater during Fe-reducing biodegradation. We investigated the mobilization of naturally occurring As, cobalt (Co), chromium (Cr), and nickel (Ni) from wetland sediments caused by the introduction of benzene, toluene, ethylbenzene, and xylenes (BTEX) and ethanol mixtures under iron- and nitrate-reducing conditions, using in situ push-pull tests. When BTEX alone was added, results showed simultaneous onset and similar rates of Fe reduction and As mobilization. In the presence of ethanol, the maximum rates of As release and Fe reduction were higher, the time to onset of reaction was decreased, and the rates occurred in multiple stages that reflected additional processes. The concentration of As increased from <1 μg/L to a maximum of 99 μg/L, exceeding the 10 μg/L limit for drinking water. Mobilization of Co, Cr, and Ni was observed in association with ethanol biodegradation but not with BTEX. These results demonstrate the potential for trace-element contamination of drinking water during biodegradation and highlight the importance of monitoring trace elements at natural and enhanced attenuation sites.

Redox controls on arsenic enrichment and release from aquifer sediments in central Yangtze River Basin

“…Arsenic-enriched sediment at ~20 m depth provides a source of As to the aquifer. Batch sediment incubations showed that the arsenic in this zone undergoes reductive dissolution, especially when stimulated by glucose addition (Figure 7 From the Jianghan plain, we surmise that As concentrations are altered by human activities changing subsurface hydrology and chemistry; land use changes that may alter arsenic include pond excavation (Neumann et al, 2010), groundwater extraction, and infiltration of organic compounds (Ziegler et al, 2015). Likewise, continued monitoring of As concentrations used for drinking and irrigation is necessary across Asia as we continue to understand the complex mechanisms leading to As contamination in Asian groundwater.…”

Trace metals in Northern New England streams: Evaluating the role of road salt across broad spatial scales with synoptic snapshots

“…First, Mn and Fe oxides in soils and sediments strongly sorb many cations [31]. In particular, As has strong adsorption affinities for reduced Fe species, Fe (III) oxyhydroxides, and can be released to groundwater during Fe-reducing biodegradation [32]. When these oxides are reduced, any sorbed cations are mobilized [33,34].…”

Potential Impacts of Shale Gas Development on Inorganic Groundwater Chemistry: Implications for Environmental Baseline Assessment in Shallow Aquifers

“…Moreover, a number of transformation products resulting from the degradation of organic substances are present in flowback/produced waters such as organic acids, acetate, and halogenated compounds. , The biodegradation of these organic compounds can produce secondary water quality impacts, similar to those produced by CH 4 oxidation (section ) (Figure ). For example, an experimental injection study showed that the biodegradation of BTEX and ethanol coupled with Fe reduction released naturally occurring As, Co, Cr, and Ni to groundwater . Moreover, groundwater depletion may occur in shale gas areas where large volumes of groundwater are withdrawn for hydraulic fracturing. , The associated water table decline increases the exposure of aquifer minerals to O 2 , which diffuses through the water-unsaturated zone.…”