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

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

Wastewater Disposal from Unconventional Oil and Gas Development Degrades Stream Quality at a West Virginia Injection Facility

The development of unconventional oil and gas (UOG) resources has rapidly increased in recent years; however, the environmental impacts and risks are poorly understood. A single well can generate millions of liters of wastewater, representing a mixture of formation brine and injected hydraulic fracturing fluids. One of the most common methods for wastewater disposal is underground injection; we are assessing potential risks of this method through an intensive, interdisciplinary study at an injection disposal facility in West Virginia. In June 2014, waters collected downstream from the site had elevated specific conductance (416 μS/cm) and Na, Cl, Ba, Br, Sr, and Li concentrations, compared to upstream, background waters (conductivity, 74 μS/cm). Elevated TDS, a marker of UOG wastewater, provided an early indication of impacts in the stream. Wastewater inputs are also evident by changes in ⁸⁷Sr/⁸⁶Sr in streamwater adjacent to the disposal facility. Sediments downstream from the facility were enriched in Ra and had high bioavailable Fe­(III) concentrations relative to upstream sediments. Microbial communities in downstream sediments had lower diversity and shifts in composition. Although the hydrologic pathways were not able to be assessed, these data provide evidence demonstrating that activities at the disposal facility are impacting a nearby stream and altering the biogeochemistry of nearby ecosystems

Examining Natural Attenuation and Acute Toxicity of Petroleum-Derived Dissolved Organic Matter with Optical Spectroscopy

Groundwater samples containing petroleum-derived dissolved organic matter (DOM_HC) originating from the north oil body within the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, MN, USA were analyzed by optical spectroscopic techniques (i.e., absorbance and fluorescence) to assess relationships that can be used to examine natural attenuation and toxicity of DOM_HC in contaminated groundwater. A strong correlation between the concentration of dissolved organic carbon (DOC) and absorbance at 254 nm (<i>a</i>₂₅₄) along a transect of the DOM_HC plume indicates that <i>a</i>₂₅₄ can be used to quantitatively assess natural attenuation of DOM_HC. Fluorescence components, identified by parallel factor (PARAFAC) analysis, show that the composition of the DOM_HC beneath and adjacent to the oil body is dominated by aliphatic, low O/C compounds (“protein-like” fluorescence) and that the composition gradually evolves to aromatic, high O/C compounds (“humic-/fulvic-like” fluorescence) as a function of distance downgradient from the oil body. Finally, a direct, positive correlation between optical properties and Microtox acute toxicity assays demonstrates the utility of these combined techniques in assessing the spatial and temporal natural attenuation and toxicity of the DOM_HC in petroleum-impacted groundwater systems

Degradation of Crude 4‑MCHM (4-Methylcyclohexanemethanol) in Sediments from Elk River, West Virginia

In January 2014, approximately 37 800 L of crude 4-methylcyclohexanemethanol (crude MCHM) spilled into the Elk River, West Virginia. To understand the long-term fate of 4-MCHM, we conducted experiments under environmentally relevant conditions to assess the potential for the 2 primary compounds in crude MCHM (1) to undergo biodegradation and (2) for sediments to serve as a long-term source of 4-MCHM. We developed a solid phase microextraction (SPME) method to quantify the <i>cis</i>- and <i>trans</i>-isomers of 4-MCHM. Autoclaved Elk River sediment slurries sorbed 17.5% of <i>cis</i>-4-MCHM and 31% of <i>trans</i>-4-MCHM from water during the 2-week experiment. Sterilized, impacted, spill-site sediment released minor amounts of <i>cis</i>- and up to 35 μg/L of <i>trans</i>-4-MCHM into water, indicating 4-MCHM was present in sediment collected 10 months post spill. In anoxic microcosms, 300 μg/L <i>cis</i>- and 150 μg/L <i>trans</i>-4-MCHM degraded to nondetectable levels in 8–13 days in both impacted and background sediments. Under aerobic conditions, 4-MCHM isomers degraded to nondetectable levels within 4 days. Microbial communities at impacted sites differed in composition compared to background samples, but communities from both sites shifted in response to crude MCHM amendments. Our results indicate that 4-MCHM is readily biodegradable under environmentally relevant conditions

GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquifer

The functional gene diversity and structure of microbial communities in a shallow landfill leachate-contaminated aquifer were assessed using a comprehensive functional gene array (GeoChip 3.0). Water samples were obtained from eight wells at the same aquifer depth immediately below a municipal landfill or along the predominant downgradient groundwater flowpath. Functional gene richness and diversity immediately below the landfill and the closest well were considerably lower than those in downgradient wells. Mantel tests and canonical correspondence analysis (CCA) suggested that various geochemical parameters had a significant impact on the subsurface microbial community structure. That is, leachate from the unlined landfill impacted the diversity, composition, structure, and functional potential of groundwater microbial communities as a function of groundwater pH, and concentrations of sulfate, ammonia, and dissolved organic carbon (DOC). Historical geochemical records indicate that all sampled wells chronically received leachate, and the increase in microbial diversity as a function of distance from the landfill is consistent with mitigation of the impact of leachate on the groundwater system by natural attenuation mechanisms

Correction to GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquifer

Correction to GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquife