Crude Oil Metabolites in Groundwater at Two Spill Sites

Bekins, Barbara A.; Cozzarelli, Isabelle M.; Erickson, Melinda L.; Steenson, Ross A.; Thorn, Kevin A.

doi:10.1111/gwat.12419

Cited by 51 publications

(47 citation statements)

References 44 publications

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“…Chronic aquatic toxicity tests on 3 freshwater species (green algae, daphnids, and fathead minnow) conducted with whole groundwater samples from 14 terminals did not result in adverse effects or responses that could be attributed to metabolites present in the samples at a maximum tested metabolites mixture concentration of 1800 mg/L (A Tiwary, Exponent, Houston, TX, USA, personal communication, March 2015). These toxicity test results suggest that for aquatic receptors, adverse responses to dissolved organics in the "water-accommodated-fraction" of biodegraded or weathered crude oil, products, or oil sands produced waters described in the literature (Neff et al 2000;Rogers et al 2002;Mao et al 2009;Melbye et al 2009) and often cited by others (Bekins et al 2016) may not be applicable to metabolites from biodegrading fuel sources in natural groundwater.…”

Section: Implications For Risk Management Of Metabolites In Groundwatmentioning

confidence: 84%

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

Zemo

O’Reilly

Mohler

et al. 2016

Integr Envir Assess & Manag

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This paper summarizes the results of a 5-y research study of the nature and toxicity of petroleum biodegradation metabolites in groundwater at fuel release sites that are quantified as diesel-range "Total Petroleum Hydrocarbons" (TPH; also known as TPHd, diesel-range organics (DRO), etc.), unless a silica gel cleanup (SGC) step is used on the sample extract prior to the TPH analysis. This issue is important for site risk management in regulatory jurisdictions that use TPH as a metric; the presence of these metabolites may preclude site closure even if all other factors can be considered "low-risk." Previous work has shown that up to 100% of the extractable organics in groundwater at petroleum release sites can be biodegradation metabolites. The metabolites can be separated from the hydrocarbons by incorporating an SGC step; however, regulatory agency acceptance of SGC has been inconsistent because of questions about the nature and toxicity of the metabolites. The present study was conducted to answer these specific questions. Groundwater samples collected from source and downgradient wells at fuel release sites were extracted and subjected to targeted gas chromatography-mass spectrometry (GC-MS) and nontargeted two-dimensional gas chromatography with time-of-flight mass spectrometry (GCÂGC-MS) analyses, and the metabolites identified in each sample were classified according to molecular structural classes and assigned an oral reference dose (RfD)-based toxicity ranking. Our work demonstrates that the metabolites identified in groundwater at biodegrading fuel release sites are in classes ranked as low toxicity to humans and are not expected to pose significant risk to human health. The identified metabolites naturally attenuate in a predictable manner, with an overall trend to an increasingly higher proportion of organic acids and esters, and a lower human toxicity profile, and a life cycle that is consistent with the low-risk natural attenuation paradigm adopted by many regulatory agencies for petroleum release sites. Integr Environ Assess Manag 2017;13:714-727. C

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Section: Implications For Risk Management Of Metabolites In Groundwatmentioning

confidence: 84%

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

Zemo

O’Reilly

Mohler

et al. 2016

Integr Envir Assess & Manag

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“…The remaining fraction not already included in the five buckets was described as branched alkanes that were assumed to be recalcitrant. The toxicity and behavior of NVDOC, also referred to as polar metabolites, is an area of focused research at this time (Bekins et al ; Zemo et al ). Most existing hydrocarbon source attenuation models are dissolution based where biodegradation occurs only in the dissolved phase (e.g., Huntley and Beckett ; Molson ). However, the Ng et al () model accounts for direct outgassing of short‐ and long‐chained alkanes without the need for an intermediate aqueous phase step. Dissolved gas phases for CO 2 , CH 4 , O 2 , and inert N 2 were modeled to simulate outgassing.…”

Section: Modeling Lnapl Composition Change During Nszdmentioning

confidence: 99%

“…Ng et al ( 2015 ) stated, " Our proposed conceptual model includes direct outgassing of CO 2 and CH 4 from the oil body source zone in order to match surface efflux measurements from Sihota [ 2014 ]. Biodegradation of petroleum constituents can be modeled as firstorder decay process Suarez and Rifai 1999 Biodegradation of oil constituents can occur without solubilization into bulk groundwater Hua and Wang 2014 ;Meckenstock et al 2014 Some hydrocarbon constituents inhibit the biodegradation of other hydrocarbons Sherry et al 2014 Petroleum hydrocarbons can generate polar metabolites Zemo et al 2013 ;Bekins et al 2016 Zero vs. first-order reaction rate order for bulk petroleum biodegradation Siddique et al 2008 In the model, we attribute this mechanism to poorly soluble short and long-chain n-alkanes that degrade in pore spaces within the oil body. "…”

Section: Modeling Lnapl Composition Changementioning

confidence: 99%

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Garg¹,

Newell²,

Kulkarni³

et al. 2017

Groundwater Monitoring Rem

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Natural source zone depletion (NSZD) has emerged as a practical alternative for restoration of light non‐aqueous phase liquid (LNAPL) sites that are in the later stages of their remediation lifecycle. Due to significant research, the NSZD conceptual model has evolved dramatically in recent years, and methanogenesis is now accepted as a dominant attenuation process (e.g., Lundegard and Johnson ; Ng et al. ). Most of the methane is generated within the pore space adjacent to LNAPL (Ng et al. ) from where it migrates through the unsaturated zone (e.g., Amos and Mayer ), where it is oxidized. While great progress has been made, there are still some important gaps in our understanding of NSZD. NSZD measurements provide little insight on which constituents are actually degrading; it is unclear which rate‐limiting factors that can be manipulated to increase NSZD rates; and how longevity of the bulk LNAPL and its key constituents can be predicted. Various threads of literature were pursued to shed light on some of the questions listed above. Several processes that may influence NSZD or its measurement were identified: temperature, inhibition from acetate buildup, protozoa predation, presence of electron acceptors, inhibition from volatile hydrocarbons, alkalinity/pH, and the availability of nutrients can all affect methanogenesis rates, while factors such as moisture content and soil type can influence its measurement. The methanogenic process appears to have a sequenced utilization of the constituents or chemical classes present in the LNAPL due to varying thermodynamic feasibility, biodegradability, and effects of inhibition, but the bulk NSZD rate appears to remain quasi‐zero order. A simplified version of the reactive transport model presented by Ng et al. has the potential to be a useful tool for predicting the longevity of key LNAPL constituents or chemical fractions, and of bulk LNAPL, but more work is needed to obtain key input parameters such as chemical classes and their biodegradation rates and any potential inhibitions.

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“…In most cases, volatile PHCs and CH 4 would be degraded in situ and not reach the atmosphere, or comprise a very small fraction of the total efflux. Polar compounds created as intermediates of PHC degradation (e.g., oxygenated hydrocarbons quantified as nonvolatile dissolved organic carbon [NVDOC]) are likely to be retained in pore water in the vadose zone and/or be degraded to carbon dioxide or methane (Zemo et al , ; Bekins et al ). With regard to flux by GW‐NSZD, Figure shows that the local downgradient fluxes include carbon from PHCs and mineralized degradation products (DIC and CH 4 ), but also include NVDOC, as discussed in prior publications (Bekins et al ; Mackay et al ).…”

Section: Introductionmentioning

confidence: 99%

Comparing Natural Source Zone Depletion Pathways at a Fuel Release Site

Mackay

Hathaway

Sieyes

et al. 2018

Groundwater Monitoring Rem

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Natural source zone depletion (NSZD) refers to processes within chemically impacted vadose and saturated zones that reduce the mass of contaminants remaining in a defined source control volume. Studies of large petroleum hydrocarbon release sites have shown that the depletion rate by vapor phase migration of degradation products from the source control volume through the vadose zone (V‐NSZD) is often considerably higher than the rate of depletion from the source control volume by groundwater flow carrying dissolved petroleum hydrocarbons arising from dissolution, desorption, or back diffusion, and degradation products arising from biodegradation (GW‐NSZD). In this study, we quantified vadose zone and GW‐NSZD at a small unpaved fuel release site in California typical of those in settings with predominantly low permeability media. We estimated vadose zone using a dense network of efflux monitoring locations at four sampling events over 2 years, and GW‐NSZD using groundwater monitoring data downgradient of the source control volume in three depth intervals spanning up to 9 years. On average, vadose zone was 17 times greater than GW‐NSZD during the time interval of comparison, and vadose zone was in the range of rates quantified at other sites with petroleum hydrocarbon releases. Estimating vadose zone and GW‐NSZD rates is challenging but the vadose zone rate is the best indicator of overall source mass depletion, whereas GW‐NSZD rates may be useful as baselines to quantify progress of natural or engineered remediation in portions of the saturated zone in which there are impediments to loss of methane and other gases to the vadose zone.

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Crude Oil Metabolites in Groundwater at Two Spill Sites

Cited by 51 publications

References 44 publications

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

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

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Comparing Natural Source Zone Depletion Pathways at a Fuel Release Site

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