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Keywords:

  • Polycyclic aromatic hydrocarbons;
  • Steranes;
  • Triterpanes;
  • Pristane;
  • Crude oil

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

An objective of a multiyear monitoring program, sponsored by the US Department of the Interior, Bureau of Ocean Energy Management was to examine temporal and spatial changes in chemical and biological characteristics of the Arctic marine environment resulting from offshore oil exploration and development activities in the development area of the Alaskan Beaufort Sea. To determine if petroleum hydrocarbons from offshore oil operations are entering the Beaufort Sea food web, we measured concentrations of hydrocarbons in tissues of amphipods, Anonyx nugax, sediments, Northstar crude oil, and coastal peat, collected between 1999 and 2006 throughout the development area. Mean concentrations of polycyclic aromatic hydrocarbons (PAH), saturated hydrocarbons (SHC), and sterane and triterpane petroleum biomarkers (StTr) were not significantly different in amphipods near the Northstar oil production facility, before and after it came on line in 2001, and in amphipods from elsewhere in the study area. Forensic analysis of the profiles (relative composition and concentrations) of the 3 hydrocarbon classes revealed that hydrocarbon compositions were different in amphipods, surface sediments where the amphipods were collected, Northstar crude oil, and peat from the deltas of 4 North Slope rivers. Amphipods and sediments contained a mixture of petrogenic, pyrogenic, and biogenic PAH. The SHC in amphipods were dominated by pristane derived from zooplankton, indicating that the SHC were primarily from the amphipod diet of zooplankton detritus. The petroleum biomarker StTr profiles did not resemble those in Northstar crude oil. The forensic analysis revealed that hydrocarbons in amphipod tissues were not from oil production at Northstar. Hydrocarbons in amphipod tissues were primarily from their diet and from river runoff and coastal erosion of natural diagenic and fossil terrestrial materials, including seep oils, kerogens, and peat. Offshore oil and gas exploration and development do not appear to be causing an increase in petroleum hydrocarbon contamination of the Beaufort Sea food web. Integr Environ Assess Manag 2012; 8: 301–319. © 2011 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

There is concern that offshore oil and gas exploration, development, and production activities in the Arctic, including waters off Alaska, Canada, Greenland, Norway, and Russia, are harming the local marine environment and, in particular, the biological resources that depend on it. Coastal indigenous people are concerned about long-term effects of these offshore development activities on their subsistence biological resources, particularly marine mammals and nearshore fish populations.

The main environmental concern associated with offshore oil and gas exploration and development in the Alaskan Beaufort and Chukchi Seas is that physical disturbance and permitted and accidental discharges of wastes associated with island construction, drilling, and production will harm the local marine ecosystem and introduce toxic chemicals into the local marine food web that supports commercial and subsistence species, such as fish, marine birds, and marine mammals. The wastes of greatest concern, because of the large volumes generated, are drilling muds and drill cuttings during exploratory and development drilling, and produced water during oil and gas production (NRC 2003). The current National Pollutant Discharge Elimination System (NPDES) permit for exploratory drilling in the Beaufort and Chukchi Seas allows ocean discharge of water-based drilling muds (WBM) and associated cuttings (USEPA 2006). Water-based drilling muds and associated cuttings were discharged during drilling of most of the 30 offshore exploratory wells in the Alaskan Beaufort Sea. However, no drilling muds and cuttings were discharged to the sea during development drilling at Northstar Island, the only facility producing oil from US Federal waters in 2006. Liquid and solid wastes were injected into a disposal well on the production island or transported to shore for recycling or disposal (Krieger et al. 2002). Produced water has never been discharged to coastal or offshore waters of the Alaskan Beaufort Sea. All produced water generated from offshore oil facilities is transported by pipeline to shore and reinjected as water-flood for enhanced oil production or disposal in a nonproductive geologic stratum. Some offshore facilities also have their own reinjection wells.

The complex nearshore and outer continental shelf (OCS) environment of the Alaskan Beaufort Sea has been studied for more than 3 decades by the scientific community, mostly under contract to the Bureau of Ocean Energy Management (BOEM: formerly the Minerals Management Service: MMS) or the Alaskan oil industry. The oil industry sponsored several studies in the 1980s of the fates and effects of drilling discharges from exploratory drilling operations in shallow Beaufort Sea waters (summarized by Neff 2010a). These studies found little harm to the local marine environment from drilling waste discharges; most effects were attributed to physical disturbance from island construction and deposition of drilling waste solids on the sea floor. However, it is essential to continue environmental monitoring to gain a better understanding of the long-term environmental impacts of development and oil production activities at the Northstar facility, planned development of the Liberty Prospect, and proposed future exploratory and development drilling activities in the Beaufort and Chukchi Seas.

Baseline conditions in the Beaufort Sea development area were characterized in the 1980s in the MMS Beaufort Sea Monitoring Project (BSMP) (Boehm et al. 1990). In 1999, MMS initiated the Arctic Nearshore Impact Monitoring in the Development Area (ANIMIDA) Project to monitor the environmental impacts of development of the Northstar and Liberty Prospects. The first field sampling was during the summer of 1999, before construction of Northstar. The continuation of the ANIMIDA (cANIMIDA) Project was initiated in 2004 and fieldwork was performed during the summers of 2004, 2005, and 2006. The results of the ANIMIDA and cANIMIDA Projects are summarized by Neff (2010b). As part of both ANIMIDA and cANIMIDA, bivalve mollusks, crustaceans, fish, and sediments were collected each year from sampling stations near Northstar Island, in the Liberty Prospect area, and at several historic BSMP monitoring stations throughout the development area of the Beaufort Sea. The biological and sediment samples were analyzed for petroleum hydrocarbons and several metals to determine if chemical contaminants from development and production activities were accumulating in Beaufort Sea sediments and the local food web. Amphipods were collected at more stations for more years than the other taxa.

The objective of this paper is to determine if petroleum hydrocarbons derived from oil development activities at the Northstar production facility or from regional exploration and development that occurred between 1981 and 2002 in the Beaufort Sea are accumulating in amphipods that are an important component of the Arctic marine food web. Three classes of hydrocarbons were analyzed in amphipod tissues: Polycyclic aromatic hydrocarbons (PAH), saturated hydrocarbons (SHC), and sterane and triterpane petroleum biomarkers (StTr). The composition of these 3 hydrocarbon assemblages in environmental samples can be used to identify sources of the hydrocarbons in amphipod tissues.

BACKGROUND

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

As new conventional crude oil and natural gas discoveries have declined and the existing proven reserves are being depleted, there is a growing urgency to find and develop new oil and gas resources. The extensive geologic prospecting and exploratory drilling in the Arctic over the last 80 y has revealed a strong potential for vast reserves of oil and gas on land and in marine waters throughout the Arctic (Gautier et al. 2009). Rising fossil fuel prices combined with improvements in technologies for safely developing offshore oil and gas resources in the Arctic have stimulated interest in developing these vast untapped resources in Arctic regions of the United States (Alaska), Canada, Norway, Greenland, and Russia.

MMS (2009) estimated that the Alaskan Beaufort and Chukchi Seas contain about 50 billion barrels of oil and natural gas equivalent of undiscovered, technically recoverable reserves. These vast untapped fossil fuel resources could play an important role in the US goal of energy independence, in conjunction with development of alternative energy sources, and energy conservation.

More than 30 exploratory wells were drilled in State and/or Federal lease tracts administered by BOEMRE in the Beaufort Sea between Barrow and Kaktovik between 1981 and 2002. Additional exploratory wells have been drilled in State lease blocks in nearshore Beaufort Sea waters. Eleven of the exploratory wells in the Beaufort Sea were discoveries (NRC 2003). Three producing fields include offshore production from deviated directional wells or from barrier islands. Five production facilities are on offshore, artificial gravel islands. Northstar is the only facility that gathers oil from Federal waters. Northstar Island lies outside the barrier islands about 9.7 km from shore in about 12 m of water (Figure 1).

thumbnail image

Figure 1. Map of the oil and gas development area in the Alaskan Beaufort Sea, showing locations of stations where amphipods were collected. The locations of the Northstar development, the Liberty Prospect, and the Arctic rivers sampled in this study also are identified.

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The Northstar facility is on a 0.02-km2 man-made gravel island constructed from gravel from the 1984 Seal Island Prospect. Island construction began in the winter of 1999–2000 and oil production began in 2001. Northstar is connected to onshore processing facilities by a double pipeline that was buried 2 to 3 m below the seafloor to avoid damage from ice scour. The facility uses ice roads constructed each winter for resupply of materials.

The Liberty Prospect is inside the barrier islands approximately 50 km southeast of the Northstar production facility and about 10 km east of the Endicott production facility, at a water depth of about 7 m (Figure 1). The original plan was to develop Liberty from an artificial Island similar to that at Northstar. However, BP Exploration, Alaska (BPXA 2007) now plans to develop the Liberty Prospect by ultraextended-reach drilling from an expansion of the existing Endicott satellite drilling island.

MONITORING OFFSHORE OIL AND GAS OPERATIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

Monitoring of environmental impacts of offshore oil and gas activities usually includes measurement of the distribution and concentrations of PAH in the affected ecosystems, because PAH are considered the most toxic components of crude and refined oils and sometimes are in the wastes discharged during exploration and development (Neff et al. 2005; Neff 2010a). The PAH in the marine environment are from 3 sources. They are present in fossil fuels, including petroleum and coal (petrogenic); they are products of the incomplete combustion of organic matter (pyrogenic); and a few are formed by biodegradation of recent organic, mainly plant, materials (biogenic) (Neff et al. 2005). The peat that covers most of the tundra lands bordering the Beaufort Sea (Jones and Yu 2010) often contains a mixture of petrogenic, pyrogenic, and biogenic PAH (Malawska et al. 2006). The compositions of the PAH assemblages from these 3 sources are different, and these differences can be used to identify the sources of PAH in tissues of marine animals.

Normal, branched, and cyclic alkanes (SHC) are abundant in Arctic marine sediments and are derived primarily from decay of marine and terrestrial plant material (Venkatesan and Kaplan 1982; Yunker et al. 1991, 2002). Most crude oils also contain high concentrations of SHC (Wang et al. 2003). The composition of the SHC assemblage is different in oil and recent biological materials. These differences can provide hints about sources of alkanes in amphipod tissues.

The biomarker StTr are derived from steroids and terpenoids synthesized by terrestrial and marine organisms, primarily bacteria, fungi, and algae (Peters et al. 2008). They are extremely stable in soils and sediments but biodegrade slowly at different rates, depending on diagenic conditions in the hydrocarbon-bearing strata (Prince and Walters 2007). They persist in sediment organic matter, crude oils, soft coals, and peat. The StTr assemblage in these organic deposits differs, depending on the age, sources of organic precursors, and diagenic history of the materials. Thus, the composition of the StTr assemblage can be used as a biomarker of petroleum, peat, and recent organic deposits from different sources in sediments and tissues of marine animals (Bartolomé et al. 2007; Wang et al. 2007).

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

The Beaufort Sea study area

The study area for the BSMP, ANIMIDA, and cANIMIDA Programs is defined as the nearshore Alaskan Beaufort Sea between Harrison Bay to the East and the Camden Bay to the West (Figure 1). This area encompasses both the Liberty and Northstar Prospect areas and is adjacent to the giant Prudhoe Bay and Kuparuk River production fields on the Arctic tundra. Open-water field surveys were performed in July to August of 1999, 2000, 2002, 2004, 2005, and 2006. Amphipods were collected each year from 4 (1999) to 21 (2006) sampling stations in the Northstar and Liberty Prospect areas (highlighted in the squares in Figure 1) and the BSMP area (stations outside the 2 squares) (Boehm et al. 2001; Brown et al. 2005, 2010; Neff et al. 2009). Two amphipod samples also were collected in 2006 at West Dock, an industrial dock area for the tundra oil fields, to serve as positive reference samples for comparison with the samples from the development areas. Hydrocarbon concentrations in amphipods were compared by year and by study area (Northstar, Liberty, Boulder Patch, BSMP, and West Dock). The Boulder Patch (Station BP01), a highly productive rocky reef area in the northern Liberty Prospect area, was sampled in 2005 and 2006. Hydrocarbon data for BP01 amphipods were included in both the Liberty and Boulder Patch groups. Surface sediments were collected from the stations where amphipods were collected and from several other stations in the Northstar, Liberty, and BSMP sampling areas.

Field sampling

A total of 61 samples of benthic amphipods, tentatively identified as Anonyx nugax (Fisk et al. 2001), was collected during 1 or more of the 6 annual surveys at 31 sampling stations. Amphipods were collected with Nitex® mesh-lined, Kynar®-coated minnow traps baited with sardines. The traps usually were deployed for 2 to 6 h (depending on other sampling activities at adjacent stations) with an anchor and float equipped with a radar reflector to facilitate retrieval of the traps. The sardine bait was place in an enclosed Nitex® mesh pouch to reduce the possibility of sardine particles becoming entrained with the amphipods. Large numbers of amphipods from each station were composited to obtain sufficient biomass for chemical analysis. Target sample weight for each sample was approximately 100 g wet wt. Sample sizes as small as 10 to 12 g were collected at some stations where amphipods were rare. The abundance of amphipods in the study area varied widely among sampling stations and from year to year, probably due to variations in the location and movements of offshore ice and the presence of dead animals and organic detritus suitable as prey for these benthic scavengers and carnivores. Sampling equipment blanks (a water-wash of the traps) were collected with the amphipod samples to characterize any contaminants that may have been introduced during sampling.

All amphipod samples were frozen immediately at −20 °C in precleaned 250-ml glass jars and shipped by air freight, under strict chain of custody, in coolers packed with frozen blue ice to the analytical laboratory.

Sample analysis

A 20–50 g wet weight subsample of each amphipod tissue sample was homogenized and the homogenate was divided into 3 aliquots for dry weight determination, hydrocarbon analysis, and metals analysis. The homogenate for hydrocarbon analysis was processed further and analyzed at Arthur D. Little, Inc., Cambridge, MA (ANIMIDA: 1999–2002) or Battelle, Duxbury, MA (cANIMIDA: 2004–2006).

Amphipods were analyzed for 3 classes of petroleum hydrocarbons. All tissue samples were analyzed for 41 target parent PAH and alkyl-PAH isomer groups (Table 1). Most tissue samples were analyzed for SHC. Target SHC included n-alkanes from nonane (nC9) through nC40, and 4 isoprenoid alkanes, including pristane and phytane. Most tissue samples also were analyzed for 16 target petroleum biomarker steranes and triterpanes (StTr) (Table 2). Samples of surface sediment collected in the development area in 2004 through 2006, peat from the mouths of 4 North Slope rivers in 2006, and Northstar crude oil also were analyzed for PAH, SHC, and StTr (Brown et al. 2010), and used as source samples to compare with hydrocarbon residues in amphipod tissues.

Table 1. Target PAH and alkyl-PAH isomer groups analyzed in tissues of amphipodsa
CompoundReporting codeCompoundReporting code
  • a

    Method detection limits for individual PAH are 1.2 to 4.7 ng/g dry wt, depending on mass spectrometer response factors for different PAH.

NaphthaleneNC2-Fluoranthenes/PyrenesC2FLU/PYR
C1-NaphthalenesC1NC3-Fluoranthenes/PyrenesC3FLU/PYR
C2-NaphthalenesC2NBenz[a]anthraceneBaA
C3-NaphthalenesC3NChryseneC
C4-NaphthalenesC4NC1-ChrysenesC1C
BiphenylBIPC2-ChrysenesC2C
AcenaphthyleneACYC3-ChrysenesC3C
AcenaphtheneACEC4-ChrysenesC4C
FluoreneFBenzo[b]fluorantheneBbFLU
C1-FluorenesC1FBenzo[k]fluorantheneBkFLU
C2-FluorenesC2FBenzo[e]pyreneBeP
C3-FluorenesC3FBenzo[a]pyreneBaP
AnthraceneAPerylenePER
PhenanthrenePIndeno[1,2,3-c,d]pyreneIcdPYR
C1-Phenanthrenes/AnthracenesC1PDibenzo[a,h]anthraceneDBahA
C2-Phenanthrenes/AnthracenesC2PBenzo[g,h,i]peryleneBghiPER
C3-Phenanthrenes/AnthracenesC3PTotal PAHTPAH
C4-Phenanthrenes/AnthracenesC4PSurrogate compounds 
DibenzothiopheneDBTNaphthalene-d8 
C1-DibenzothiophenesC1DBTAcenaphthene-d10 
C2-DibenzothiophenesC2DBTPhenanthrene-d10 
C3-DibenzothiophenesC3DBTBenzo(a)pyrene-d12 
FluorantheneFLUInternal standard 
PyrenePYRFluorene-d10 
C1-Fluoranthenes/PyrenesC1FLU/PYRChrysene-d12 
Table 2. Target sterane and triterpane (StTr) petroleum biomarkers analyzed in tissues of amphipods
CompoundReporting codeCompoundReporting code
C23-DiterpaneT413β,17α-Diacholestane-20SS4
C29-TricyclictriterpaneT913β,17α-Diacholestane-20RS5
C29-TricyclictriterpaneT105α,14α,17α,24-Methylcholestane-20RS24
18α(H)-22,29,30-Trisnorhopane-TST115α,14α,17α,24-Ethylcholestane-20SS25
17α(H)-22,29,30-Trisnorhopane-TMT125α,14α,17α,24-Ethylcholestane-20RS28
17α(H),21β(H)-30-NorhopaneT15Unidentified EthylcholestaneS28A
18α(H)-OleananeT18Surogate compound
17α(H),21β(H)-HopaneT19  
22S-17α(H),21β(H)-30-HomohopaneT215b(H)-Cholane
22R-17α(H),21β(H)-30-HomohopaneT22  

Tissue, sediment, and peat extraction methods used in the ANIMIDA and cANIMIDA Projects are described in detail by Brown et al. (2005, 2010) and Neff et al. (2009). Amphipod tissue homogenates were spiked with representative surrogate chemicals. The ANIMIDA samples were extracted by saponification and ether extraction. The cANIMIDA samples were processed by serial dichloromethane extraction. Analytical comparability was verified with an intercomparison exercise. The extracts were then treated with sodium sulfate to remove water and concentrated in a water bath.

Amphipod tissue extracts were analyzed for PAH, SHC, and StTr and, therefore, required extract fractionation to remove potential interference and improve the quality of the trace-level analysis. The sample extracts were loaded on an alumina cleanup column and eluted with dichloromethane. The eluate was concentrated and an aliquot was removed for lipid weight determination. The remaining extract was fractionated on a silica gel column to isolate the PAH, SHC, and StTr fractions. Each sample was eluted first with hexane (F1 fraction), followed by a mixture of hexane and methylene chloride (F2 fraction). The F1 fraction was spiked with recovery internal standards for SHC and StTr analysis, divided into 2 aliquots, and analyzed for SHC by gas chromatography with flame ionization detection (GC/FID) and for StTr by gas chromatography-mass spectroscopy (GC/MS). The F2 fraction was spiked with PAH recovery internal standards and analyzed by GC/MS.

The GC/MS analysis of the F1 and F2 fractions for StTr and PAH was performed by a modification of US Environmental Protection Agency (USEPA) Method 8270 that included additional target compounds (e.g., alkyl PAH and hydrocarbon biomarkers) and obtained lower detection limits and better specificity by operating the mass detector in the selected ion monitoring mode. Analytical instruments were calibrated before sample analysis with a 5-point calibration (minimum) and varying level check standards were analyzed every 10 samples bracketing field and quality control sample analyses. A North Slope crude reference oil, Northstar crude oil, and a series of other quality control (QC) samples were analyzed with the samples.

The concentrations of the individual PAH target compounds were calculated versus the internal standards that were spiked into the sample prior to analysis. The target compound concentrations were corrected for surrogate recoveries to best represent the original sample concentration. The PAH concentrations were quantified using average relative response factors (RRF) generated from the 5-point calibration. The RRF of the alkyl homologues were based on the RRF of the parent compound for each alkyl homologue series.

The concentrations of all target StTr were calculated versus the internal standard chrysene-d12. All target triterpane concentrations were quantified using the average relative response factor of 17b(H),21b(H)-hopane generated from the initial calibration. All target sterane concentrations were quantified using the average relative response factor of cholestane in the initial calibration. The target compound concentrations were corrected for surrogate recovery. Surrogate recovery of 5β(H)-cholane was calculated relative to the internal standard.

F1 fractions were analyzed by GC/FID for SHC. Instrumental methods, maintenance, and QC procedures for the GC/FID analysis of samples were performed by a modification of USEPA Method 8015. Analytical instruments were calibrated before sample analysis with a 5-point calibration (minimum) and check standards bracketed the analytical run of field and quality control samples.

The nC9 through nC40 n-alkanes, pristane, phytane, and other selected isoprenoids were determined in the F1 fractions. A reference sample of North Slope crude oil was analyzed with the samples. Quantification of the alkanes was based on the internal standard compound (d62-triacontane) that was spiked into the sample just prior to analysis. The target compound concentrations were corrected for surrogate recovery.

Analytical quality control

Analytical quality control procedures for tissue samples are described in detail by Brown et al. (2005, 2010) and Neff et al. (2009). The data quality objectives (DQOs) for hydrocarbon analyses were the same for ANIMIDA and cANIMIDA and were included in the laboratory quality assurance project plans to ensure that the data were of the quality necessary to attain the project goals, including comparability between the 2 projects.

Data interpretation

Several diagnostic hydrocarbon ratios were used to aid in identifying sources of the 3 hydrocarbon classes in amphipod tissues (Table 3). Diagnostic ratios for PAH, SHC, and StTr were chosen based on the hydrocarbons detected most frequently in amphipod tissues and in the source materials.

Table 3. Diagnostic indices used to help identify possible sources of hydrocarbons in the tissues of amphipods
IndexDefinitionInterpretationReference
Polycyclic aromatic hydrocarbons
 Pyrogenic Index(FLU + PYR)/(FLU + PYR) + (sum C2-C4P)Differentiate between pyrogenic and petrogenic PAHBence et al. (2007)
 Pyro/Petro RatioSum 4- through 6-ring parent PAH/sum 2- through 4-ring parent + alkyl PAHDifferentiate between pyrogenic and petrogenic PAHBrown et al. (2010)
 Perylene IndexPER/sum (BaA, BbFlu, BkFlu, BeP, BaP)Differentiate between pyrogenic and biogenic sources of PAHWang et al. (2009)
Saturated hydrocarbons
 % Pristane(Pristane/TSHC) x 100Identify source of hydrocarbons in amphipodsClark and Blumer (1967)
 Carbon Perference Index (CPI)C23+25+27+29+31+33/C24+26+28+30+32+34Differentiate between petrogenic and biogenic SHCWang et al. (2009)
Sterane and triterpane biomarkers
 T15/S2817α(H),21β(H)-30-Norhopane/5α,14α,17α,24-Ethylcholestane-20RIdentify source of hydrocarbons in amphipodsThis paper
 T15/S417α(H),21β(H)-30-Norhopane/13β,17α-Diacholestane-20SIdentify source of hydrocarbons in amphipodsThis paper
 T21/T2222S-17α(H),21β(H)-30-Homohopane/22R-17α(H),21β(H)-30-HomohopaneIdentify source of hydrocarbons in amphipodsBrown et al. (2010)

Because of the variability in the numbers of amphipod samples collected from year to year and in the 3 main sampling areas in each year, preliminary statistical analysis of the hydrocarbon data was limited to means, standard deviations, and ranges of hydrocarbon concentrations and diagnostic ratios in amphipod tissues, co located sediment samples, Northstar crude oil, and coastal peat samples. Temporal (6 y) and spatial (4 survey areas) trends in concentrations of total PAH, total SHC, and total StTr (TPAH, TSHC, and TStTr) in amphipods were evaluated statistically by the ANOVA procedure in Stata®. Because of the nonnormal distribution and variance of the data, both parametric and nonparametric tests were performed. The nonparametric analyses were performed with the Kolmogorov-Smirnov exact test, using the smirnov procedure in StatXact®. Tukey pairwise multiple comparison tests were used to characterize the nature of the year or area effect. Data for amphipod samples collected at West Dock (WD01) in 2006 were not included in the statistical comparisons, because WD01 was included as a positive reference industrial site. The Boulder Patch is located in the Liberty area, so tissue residue data for Boulder Patch were compared only with data from elsewhere in the Liberty area.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

Temporal trends in hydrocarbon concentrations

Concentrations of TPAH, TSHC, and TStTr in tissues of amphipods were highly variable within and among the years 1999 through 2006 throughout the Beaufort Sea development area (Table 4). Concentrations of Total PAH ranged from 6.06 to 348 ng/g dry wt, with the highest mean concentration in 1999 and lowest mean concentration in 2005. The mean total PAH concentration in amphipods collected in 2005 was significantly lower than that in amphipods collected in all other years. Concentrations of TSHC were high in amphipod tissues, ranging from 4600 to 141 000 ng/g dry wt (Table 4). The TSHC concentrations were significantly lower in amphipods collected in 2002 than in those collected in 1999, 2004, 2005, and 2006. Concentrations of target TStTr were consistently low in amphipods, ranging from undetectable to 52.6 ng/g dry wt. Mean StTr concentrations were significantly lower in amphipods collected in 2005 than in those collected in 2000, 2002, and 2004. Mean concentrations of TPAH, TSHC, and TStTr were highest in 1999, 2006, and 2004, respectively, indicating that concentrations of these 3 hydrocarbon classes did not covary in amphipods collected throughout the development area. Mean concentrations of TPAH and TStTr, but not TSHC, were significantly lower in amphipods collected throughout the development area in 2005 than in those collected in most other years (Table 4). Alkyl PAH concentrations, in particular, were lower in 2005 than in other years. Review of laboratory quality control data, including reanalysis of selected amphipod samples from 2004 and 2005, revealed that the interannual differences were not caused by analytical error, but could have been related to small differences in GC/MS response factors or internal standards used for quantification of PAH and StTr in these complex hydrocarbon mixtures (Neff et al. 2009).

Table 4. Mean, SD, and range of concentrations of total target PAH, total target SHC, and total target StTr in tissues of amphipods
Hydrocarbon classNumber of samplesYearMean ± SD (ng/g dry wt)Range (ng/g dry wt)
  • *

    PAH for 2005 are lower than for all other years.

  • **

    SHC for 2002 are lower than for 1999, 2004, 2005, and 2006.

  • ***

    StTr for 2005 are lower than for 2000, 2002, and 2004.

Total PAH41999138 ± 12161.7–348
6200074.3 ± 16.152.1–100
8200282.2 ± 36.547.1–153
9200467.3 ± 29.939.6–143
11200524.0 ± 13.0*8.25–50.0
21200655.5 ± 26.419.7–114
Total SHC4199928 600 ± 23 3007900–66 400
6200065 700 ± 29 40021 000–104 000
82002125 000 ± 95 100**20 000–325 000
9200430 000 ± 445024 200–37 700
11200527 400 ± 16 6006640–60 100
21200643 400 ± 35 5009800–141 000
Total StTr119995.525.52
6200016.4 ± 8.868.77–35.1
820029.32 ± 2.166.34–13.8
920048.79 ± 5.721.30–21.0
1120051.67 ± 2.21***0–7.41
1920067.28 ± 11.70–52.6

Spatial trends in hydrocarbon concentrations

Mean concentrations of TPAH were similar in amphipods collected during the monitoring program in 4 sampling areas (Northstar, Liberty, Boulder Patch, and BSMP), but were higher in amphipods collected at West Dock in 2006, an industrial dock area in Prudhoe Bay (Table 5). The mean TPAH concentration ranged from 52 to 76 ng/g dry wt in amphipods from the 4 sampling areas. There were no significant differences in mean TPAH concentrations in amphipods from the 4 study areas. Mean TPAH concentrations in amphipods from the Boulder Patch were not statistically different than those in the remainder of the Liberty area.

Table 5. Mean ± SD concentrations of total target PAH and values for source diagnostic ratios (defined in Table 3) in amphipods and sediment from 5 Beaufort Sea survey areas, peat from mouths of 4 North Slope rivers, and Northstar crude oila
Area/sampleNumberMean ± SD (ng/g dry wt)Pyrogenic indexPyro/petro ratioPerylene index
  • a

    Method detection limit for TPAH in tissues, sediment, and peat is about 10 ng/g dry wt. There were no significant differences in mean PAH concentrations in amphipods from the 4 study areas. Comparisons were not made with West Dock data.

  • b

    The Boulder Patch station is in the Liberty Prospect area and was sampled in 2005 and 2006. These data also are included in the Liberty means.

Amphipod tissues
 Northstar2952.4 ± 36.00.45 ± 0.320.14 ± 0.151.27 ± 1.24
 Liberty2175.9 ± 67.40.50 ± 0.340.12 ± 0.072.84 ± 5.97
 Boulder Patchb457.6 ± 18.10.82 ± 0.320.09 ± 0.040
 BSMP959.1 ± 16.30.27 ± 0.280.13 ± 0.041.21 ± 1.18
 West Dock2103 ± 19.60.51 ± 0.010.36 ± 0.090.31 ± 0.09
Source samples
 Sediment193693 ± 5070.28 ± 0.120.38 ± 0.372.84 ± 0.71
 Northstar Crude Oil715 260 000 ± 1 532 0000.014 ± 0.0020.005 ± 0.00050.007 ± 0.02
 Kogru River Peat11210.100.170.35
 Kuparuk River Peat11060.080.103.51
 Sag River Peat12910.090.103.03
 Colville River Peat17370.100.111.56

Mean concentrations of TSHC ranged from 34 900 to 86 200 ng/g dry wt in amphipods from the 4 study areas, and were higher than those in amphipods from West Dock (Table 6). Pristane (2,6,10,14-tetramethylpentadecane: C19H40), represented 86% to 96% of TSHC in amphipods from all areas. The mean TSHC concentration in amphipods from Northstar was significantly lower that for amphipods from Liberty.

Table 6. Mean ± SD concentrations of total target SHC and values for source diagnostic ratios (defined in Table 3) in amphipods and sediment from 5 Beaufort Sea survey areas, peat from mouths of 4 North Slope rivers, and Northstar crude oil
Area/sampleNumberMean ± SD (ng/g dry wt)% PristaneCPI
  • a

    The mean TSHC concentration in amphipods from Northstar was significantly lower than that for amphipods from Liberty. Comparisons were not made with West Dock data.

Amphipod tissues
 Northstar2934 900 ± 27 300a87.2 ± 17.91.85 ± 0.55
 Liberty2175 000 ± 75 30090.0 ± 114.01.80 ± 0.60
 Boulder Patch486 200 ± 36 00095.7 ± 0.91.60 ± 0.17
 BSMP945 000 ± 28 50085.7 ± 24.22.23 ± 0.46
 West Dock218 000 ± 127086.7 ± 0.42.07 ± 0.08
Source samples
 Sediment1935051 ± 43281.71 ± 0.654.78 ± 1.25
 Northstar Crude Oil7153 400 000 ± 11 500 0002.9 ± 0.091.54 ± 0.30
 Kogru River Peat1101 1620.052.68
 Kuparuk River Peat137 8060.0615.6
 Sag River Peat113 6000.266.94
 Colville River Peat127 9000.304.66

Traces of TStTr (usually < 20 ng/g dry wt) were detected in tissues of amphipods collected in all sampling areas, except West Dock, between 1999 and 2006 (Table 7). Mean TStTr concentrations in amphipods from the 4 study areas ranged from 6.09 to 11.7 ng/g dry wt and there were no significant differences in concentrations among the study areas.

Table 7. Mean ± SD concentrations of total target StTr and values for source diagnostic indices (defined in Table 3) in amphipods and sediment from 5 Beaufort Sea survey areas, peat from mouths of 4 North Slope rivers, and Northstar crude oila
Area/sampleNumberMean ± SD (ng/g dry wt)T15/S28T15/S4T21/T22
  • a

    There were no significant differences mean StTr concentrations in amphipods from the 4 study areas. Comparisons were not made with West Dock data. ND, Not detected (method detection limit, 0.01–4.7 ng/g dry wt depending on sample size).

Amphipod tissues
 Northstar297.65 ± 8.311.17 ± 0.852.23 ± 1.340.86 ± 0.17
 Liberty216.09 ± 4.091.34 ± 1.191.65 ± 1.290.76 ± 0.14
 Boulder Patch47.63 ± 5.521.45 ± 1.161.07 ± 0.770
 BSMP811.7 ± 16.01.94 ± 0.972.26 ± 1.111.25
 West Dock2ND   
Source samples
 Sediment19360.3 ± 59.60.97 ± 0.344.30 ± 1.870.57 ± 0.22
 Northstar Crude Oil7324 000 ± 15 1001.01 ± 0.170.40 ± 0.062.29 ± 0.38
 Kogru River Peat187.3031.30
 Kuparuk River Peat135.22.767.320.33
 Sag River Peat140.91.428.310.14
 Colville River Peat183.10.5910.60.46

Sources and characteristics of hydrocarbons in amphipod tissues

Information about the sources of the 3 classes of hydrocarbons in tissues of amphipods can be gained by an examination of the relative composition and concentrations of hydrocarbons in amphipod tissues, in representative petrogenic, pyrogenic, and biogenic hydrocarbon assemblages, and in different environmental matrices potentially accessible to the amphipods. Several diagnostic hydrocarbon ratios were used to aid in identifying sources of the 3 hydrocarbon classes in amphipod tissues (Table 3).

The values for all these diagnostic ratios in amphipod tissues may be altered by the wide range of relative bioavailability of different hydrocarbons in different environmental matrices (water, sediment, petroleum, peat, tissues of prey) (Neff et al. 2005), and differences in the ability of different species of amphipods to actively metabolize and excrete some types of bioaccumulated hydrocarbons (Fisk et al. 2001; Rust et al. 2004a).

Polycyclic Aromatic Hydrocarbons (PAH)

The PAH assemblage in crude oils and most refined oil products is dominated by 2- and 3-ring PAH (naphthalene, fluorene, phenanthrene) containing 1 to 3 (C1- to C3-) alkyl carbons (CH3 or -CH2-). Pyrogenic PAH assemblages, such as those in combustion soot and coal tar, usually are dominated by 4- through 6-ring PAH with smaller amounts of 2- and 3-ring PAH, all with no or 1 alkyl carbon (Neff et al. 2005). Biogenic PAH assemblages are simple; the biogenic PAH most frequently encountered in marine environmental samples are perylene (a 5-ring PAH) and retene (a C4-phenanthrene), both produced primarily by early diagenesis of di- and tri-terpenoid plant precursors in anoxic sediments (Venkatesan 1988; Yunker and Macdonald 1995; Peters et al. 2008; Grice et al. 2009). These biogenic PAH occur in both recent and fossil deposits. The pyrogenic index (Bence et al. 2007) and the pyrogenic/petrogenic ratio (Brown et al. 2010) were used to differentiate between petrogenic and pyrogenic PAH sources in tissues (Table 3). The perylene index was used to assess the relative contribution of biogenic PAH to the PAH assemblage in amphipod tissues (Wang et al. 2009).

The PAH assemblage in tissues of amphipods collected in the 4 study areas between 1999 and 2006 was dominated by alkyl-naphthalenes, followed by alkyl-phenanthrenes (Figure 2A). The mean sum of total alkyl-naphthalenes and total alkyl-phenanthrenes concentrations in amphipods from all stations ranged from 39% to 57% total PAH. The most abundant high molecular weight PAH in most amphipods was perylene. The high abundance of alkylated 2- and 3-ring PAH, with the highest abundance for the C2-congener groups, is a strong indication of a petrogenic source of some PAH in amphipod tissues. The high relative abundance of perylene in amphipod tissues suggests that some of the PAH were derived from peat or other early diagenic deposits.

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Figure 2. The PAH profiles (fraction TPAH of each analyte) in amphipods collected near the Northstar facility in 2006 (A) and in surface sediments collected in the Northstar area in 2006 (B). Individual PAH (x-axis) are identified in Table 1.

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The PAH profiles of Northstar area sediments, Northstar crude oil, and peat from 4 North Slope rivers also contained a high relative abundance of alkylated 2-ring (Northstar sediments and Northstar crude oil) and 3-ring (NorthStar sediments and river peat) PAH (Figures 2B and 3A,B). Perylene was abundant in Northstar sediment and river peat but not in Northstar crude oil.

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Figure 3. The PAH profiles (fraction TPAH of each analyte) in Northstar crude oil (A) and in peat collected in 2006 from river banks of 4 North Slope river deltas (B). Individual PAH (x-axis) are identified in Table 1.

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The 3 PAH diagnostic ratios (Table 3) were different in amphipod tissues, Northstar area sediments, Northstar crude oil, and river peat (Table 5). The pyrogenic index and the pyro-petro ratio increase with increases in the contribution of pyrogenic PAH to PAH assemblages. Both indices were higher in amphipod tissues than in Northstar crude oil and most peat samples. The pyrogenic index for Northstar sediments was in the lower part of the range for amphipods from the 4 study areas and the pyro-petro index was higher in Northstar sediments than in amphipod tissues and Northstar crude oil and peat. The pyro-petro ratio was similar in amphipods and sediments from West Dock and higher than that in amphipods from the 4 study areas and peat. These results indicate that amphipods and the sediments where they reside are enriched in pyrogenic PAH.

The perylene index, an indicator of the relative contribution of biogenic and pyrogenic PAH to the PAH assemblage in environmental samples, was higher than 1 in amphipods from Northstar, Liberty, and BSMP, in Northstar sediments, and in peat from 3 of the 4 rivers. The index was much lower in Northstar crude oil and amphipods collected in the Boulder Patch and at West Dock. The PAH assemblage in amphipods from the Boulder Patch was dominated by parent, unalkylated 2- and 3-ring PAH and fluoranthene and pyrene, all primarily pyrogenic PAH, explaining the unusual diagnostic ratios. These results indicate that the PAH in amphipod tissues were from mixed petrogenic, pyrogenic, and biogenic sources.

Saturated hydrocarbons (SHC)

The relative concentrations of n-alkanes and isoprenoid hydrocarbons usually are different in petroleum, peat, marine algae, and decaying terrestrial plant material. The most abundant SHC in most crude oils are low molecular weight, C8- to C16-alkanes and abundance decreases with increasing molecular weight (Wang et al. 2003). The most abundant n-alkane in distillate fuel oils usually is between C11 and C18, depending on the boiling point range of the petroleum product. The most abundant n-alkane in marine green, red, and brown macroalgae usually is C15 or C17, whereas the dominant n-alkane in planktonic diatoms is C20 (Clark and Blumer 1967; Mironov et al. 1981). The SHC assemblages in decaying terrestrial plant materials are dominated by higher molecular weight, C22- to C31-alkanes (Clark and Blumer 1967; Yunker et al. 2005; Wang et al. 2009). High molecular weight odd-numbered alkanes usually are more abundant than even-numbered alkanes in terrestrial plant detritus and in marine macroalgae, but not in marine diatoms.

Pristane, a C19-isoprenoid alkane, is derived primarily from biosynthesis by certain marine herbivorous crustaceans, particularly calanoid copepods (Blumer et al. 1964). Pristane also is abundant in crude and refined oils, with concentrations often ranging between 500 000 to 5 000 000 ng/g oil (Wang et al. 2003); Northstar crude oil contains about 4 500 000 ng/g oil of pristane, 2.9% of TSHC. Concentrations of pristane in adult sub-Arctic and Arctic calanoid copepods may exceed 1 000 000 ng/g dry wt and represent up to about 1% of the total mass of the copepod (Blumer et al. 1964; Short and Harris 2005). Concentrations are much lower in other marine plants and animals.

Two diagnostic ratios, percent pristane and the carbon preference index (CPI) (Table 3), were used to help identify sources of SHC in amphipod tissues. Percent pristane is a good indicator of potential sources of saturated hydrocarbons in amphipod tissues. The carbon preference index (CPI) is the ratio of the sum of odd-numbered C23–C33 n-alkanes to even-numbered C24–C34 n-alkanes and is useful for differentiating SHC assemblages from various modern plant and fossil petroleum sources.

The SHC profile in amphipods collected in all 5 study areas was different than those in Northstar area sediments, Northstar crude oil, and river peat (Figures 4 and 5). Mean percent pristane ranged from 85.7% to 95.7% of TSHC in tissues of amphipods from different areas, compared to means of 1.71% and 2.9% in Northstar sediments and Northstar crude oil and 0.05% to 0.30% in river peat (Table 6). The most abundant n-alkanes in amphipod tissues were C15 and C17, compared to C9 and C10 in Northstar crude oil, and C25 or C27 in Northstar sediments and river peat (Figures 4 and 5). The mean CPI was higher in amphipod tissues than in Northstar crude oil and lower than in Northstar sediments and river peat (Table 6). The CPI was lowest in amphipods from the Boulder Patch, where the abundance of pristane in amphipod tissues was highest, and highest in amphipods from the nearshore BSMP and West Dock areas, where percent pristane in amphipod tissues was lowest. These results suggest that much of the SHC in the amphipod tissues is from their diet of zooplankton and algal detritus.

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Figure 4. The SHC profiles (fraction TSHC of each analyte) in amphipods collected near the Northstar facility in 2006 (A) and in surface sediments collected in the Northstar area in 2006 (B).

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Figure 5. The SHC profiles (fraction TSHC of each analyte) in Northstar crude oil (A) and in peat collected in 2006 from river banks of 4 North Slope river deltas (B).

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Steranes and triterpanes (StTr)

Petroleum biomarker steranes and triterpanes are branched cycloalkanes consisting of multiple condensed 5- or 6-carbon rings (Stout and Wang 2007). The most common cyclic terpenoids in crude oil and coal are C19 through C30 tricyclic terpanes, C27 through C35 hopanes, and C20 through C30 steranes. The major precursors of the hopanes in oil-rich source rocks and crude oils are bacterial hopanoids; plant terpenes are precursors of triterpanes, and the steroids in fungi and plants are precursors of the steranes (Wang et al. 2009). The precursors are converted to petroleum biomarkers by chemical transformation at high temperatures and pressures or to anaerobic bacterial degradation at lower temperatures (<100 °C) over millions of years in subsurface, organic-rich geologic strata. Some steranes and triterpanes, such as diploptene (17 β(H),21, β(H)-hop-22(29)-ene), T19 (17α(H),21β(H)-hopane), and T22 (a 22R-homohopane), also are present in early diagenic plant organic matter in soils and peat (Yunker et al. 1995; Peters et al. 2008). The triterpane, 18α(H)-oleanane, derived from terrestrial angiosperms, is a biomarker of post-upper Cretaceous oils and coals (Moldowan et al. 1994). The target StTr monitored in this study are those most frequently found at high relative concentrations in crude oils and coals.

The presence and relative concentrations of different StTr provided information on possible contributions of petroleum and recent hydrocarbons to the hydrocarbon assemblage in amphipod tissues. The composition and relative concentrations of StTr, as well as different StTr diagnostic ratios, were used primarily to evaluate sources of petroleum hydrocarbons in sediments and soils (Stout and Wang 2007; Wang et al. 2009). Three biomarker ratios were used to help evaluate possible sources of hydrocarbons in amphipod tissues (Table 3).

No amphipod samples contained all 16 target StTr; some did not contain detectable concentrations of any target StTr. This may have been due to the low bioavailability of these nearly insoluble, highly nonpolar organic chemicals (Lewellen and Shea 2003). The most abundant StTr in amphipods collected in all areas between 1999 and 2006 were the triterpanes, T19 and T15, and the sterane S28 (5α,14α,17α,24-Ethylcholestane-20R) (Figure 6A). Only T19 was also abundant in Northstar sediments and crude oil, and river peat (Figures 6B, 7A,B). T19 frequently is abundant in recent diagenic and ancient fossil organic deposits. The sterane, 13β,17α-Diacholestane-20S (S4), was the most abundant target biomarker in Northstar crude oil (Figure 7A) but was not abundant in amphipod tissues, sediments, or peat.

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Figure 6. The biomarker StTr profiles (fraction TStTr of each analyte) in amphipods collected near the Northstar facility in 2000–2006 (A) and in surface sediments collected in the Northstar area in 2006 (B). Individual StTr (x-axis) are identified in Table 2.

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Figure 7. The biomarker StTr profiles (fraction TStTr of each analyte) in Northstar crude oil (A) and in peat collected in 2006 from river banks of 4 North Slope river deltas (B). Individual StTr (x-axis) are identified in Table 2.

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The biomarker 18α(H)-Oleanane (T18) was not detectable in Northstar crude oil but represented 21% of TStTr in Kogru River peat. T18 was present at low concentrations (0.20 to 1.0 ng/g dry wt) in 18 sediment samples, 11 of them from the Northstar area (collected in 2004), and in 2 amphipod samples from Liberty and 4 amphipod samples from Northstar, all collected in 2000. Kogru River peat contains about 18.4 ng/g dry wt T18.

Isomeric 18α- and 18β-(H)-oleananes are derived from terrestrial angiosperm precursors and so occur only in post-Cretaceous (<65 million years ago) petroleum and some recent terrestrial diagenic deposits (Wang et al. 2007). Most North Slope crude oils, including Northstar oil, are early Cretaceous or older; 3 crude oils from fields on the Kuparuk and Sagavanirktok Rivers are Tertiary (Hughes and Holba 1987; Banet 1994). The 18α(H)-oleanane in some amphipods may be from oil seeps at Angun and Kavik or peat deposits that contain traces of oleananes (Banet and Mowatt 1998).

The biomarkers T15, T21, T22, S4, and S28 were detected in the largest number of amphipod, Northstar crude oil, and peat samples, so selected ratios of these biomarkers were used to determine possible sources of petroleum biomarkers in the amphipods (Table 3). Mean biomarker ratios, T15/S28 and T15/S4, in amphipod tissues from the 4 study areas ranged from 1.17 to 1.94 and 1.07 to 2.26, respectively (Table 7). Mean T15/S28 ratios were lower in sediment, Northstar crude oil, and 2 peat samples than in amphipod tissues. Mean T15/S4 ratios were higher in sediments and peat and lower in crude oil than in amphipod tissues. Because T22 usually is more abundant than T21 in recent diagenic organic matter, the mean T21/T22 ratio is a good indicator of the presence of modern, early diagenic organic matter. The T21/T22 ratio was higher in Northstar crude oil and lower in Northstar sediments and river peat than in tissues of amphipods from the 4 study areas. The differences in the StTr profiles and biomarker ratios in amphipod tissues, Northstar crude oil, Northstar sediments, and river peat samples suggest that the hydrocarbon assemblage in Beaufort Sea amphipods included fossil fuel and recent diagenic hydrocarbons.

Amphipods collected at BSMP station 7E in 2006 contained a relatively high concentration of TStTr (52.6 ng/g dry wt). All target StTr, except tricyclic triterpanes-22S and -22R (T9 and T10) and T18 were present in amphipods from this site. These amphipods also contained a relatively high TPAH concentration (73.1 ng/g dry wt) and a relatively low pristane concentration as a percent of TSHC (17.7%). Sediments collected at station 7E in 2006 were 94% silt + clay and contained 2.2% total organic matter, including 1800 ng/g dry wt TPAH, 26 000 ng/g dry wt TSHC, and 170 ng/g dry wt TStTr (Brown et al. 2010). The diagnostic ratios for PAH, SHC, and StTr in amphipod tissues indicated that most of the hydrocarbons in amphipod tissues from this station probably were from early diagenic organic matter, probably peat and kerogens from the nearby Kogru and Colville Rivers (Figure 1).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

Lysianassid amphipods, such as Anonyx nugax, are key members of Arctic marine nearshore food webs (Svendsen et al. 2007). Adult A. nugax are both necrophagous scavengers and carnivorous, whereas juveniles consume small pelagic and benthic animals and plant detritus (Legenżyńska 2008). Anonyx in Conception Bay, Newfoundland, respond to the spring phytoplankton bloom and subsequent settling of dead phyto- and zoo-plankton by rapid accumulation of tissue lipid reserves, indicating the importance of settling particulate organic carbon in their diets (Parrish et al. 2009). Because of their carnivorous feeding behavior, they occupy a trophic level above those of benthic bivalves and many pelagic crustaceans, including calanoid copepods (Fisk et al. 2003). They are useful for monitoring the bioaccumulation and food chain transfer of natural and contaminant organic chemicals, because they are one of the most abundant epibenthic animals in shallow-water Arctic marine ecosystems, occupy an intermediate trophic level, and are easy to collect (Fisk et al. 2003; Svendsen et al. 2007).

Concentrations of TPAH, and TStTr, but not TSHC and pristane, were higher in Beaufort Sea sediments, river sediments, and peat, than in tissues of amphipods (Tables 5 to 7). Pristane was the most abundant alkane in amphipods. The concentration of TSHC minus pristane in amphipods was similar to the TSHC concentration in sediment but lower than the TSHC concentration in peat and Northstar crude oil. Pristane is rapidly biodegraded in surface sediments and, so, rarely persists there (Prahl et al. 1976). The presence of high concentrations of SHC and pristane and low concentrations of PAH and StTr in amphipod tissues is a strong indication that the hydrocarbons in Arctic sediments have a low bioavailability to marine animals. There was not a significant relationship between concentrations of TPAH in amphipod tissues and the sediments where they were collected, as indicated by an R2 of 0.003.

There were large differences in SHC profiles, diagnostic ratios, and relative concentrations of pristane and pentadecane in amphipods, Northstar area sediments, Northstar crude oil, and river peat (Table 6; Figures 4, 5). The main source of pristane in cold-water marine environments is from zooplankton, particularly calanoid copepods of several genera, including Calanus, Neocalanus, and Pseudocalanus, the dominant zooplankton in Beaufort Sea waters in most seasons (Horner and Murphy 1985; Griffiths and Thompson 2002). Calanoid copepods bioaccumulate phytol, a monounsaturated diterpenyl alcohol that is esterified with chlorophyll, from their phytoplankton and microzooplankton food (Sargent et al. 1981; Campbell et al. 2009) and convert it to pristane; the pristane accumulates to high concentrations in lipid droplets in the copepods (Avigan and Blumer 1968). Several species of adult calanoid copepods from the Gulf of Maine and the Gulf of Alaska contain 2 000 000 to 11 300 000 ng/g dry wt pristane (Blumer et al. 1964; Short and Harris 2005). Some micro- and macro-algae including cold-water planktonic diatoms and brown macroalgae, such as Laminaria, may contain high concentrations of isoprenoid alkanes, including pristane (Clark and Blumer 1967; Mironov et al. 1981). Pristane is readily bioaccumulated and passed through marine food webs by the many species of marine invertebrates, fish, birds, and mammals that rely on copepods or their predators for food.

The most abundant n-alkane in many species of brown macroalgae is pentadecane (n-C15), the most abundant n-alkane in amphipod tissues. The brown macroalga Laminaria solidungula is abundant in the Boulder Patch (Dunton et al. 2009) and kelp detritus may be a source of the high concentrations of TSHC, pristane, and pentadecane in amphipods residing there (Table 6). Heptadecane (n-C17) is the second most abundant n-alkane in amphipod tissues (Figure 4A) and is the dominant n-alkane in many species of phytoplankton (Blumer et al. 1971). This indicates that the SHC in amphipod tissues were derived primarily from consumption of marine carrion, probably primarily calanoid copepods, micro- and macro-algal detritus, and zooplanktivorous marine animals, such as arctic cod.

PAH profiles and diagnostic ratios were markedly different in amphipod tissues, Northstar area sediment, Northstar crude oil, and river peat (Table 5; Figures 2, 3). The PAH profile in amphipod tissues was dominated by alkyl-naphthalenes and alkyl-phenanthrenes; concentrations of high molecular weight 4- through 6-ring PAH, except perylene, were low, indicating that significant fractions of the PAH in amphipods were petrogenic and biogenic. PAH diagnostic ratios indicated that pyrogenic PAH also were present in amphipod tissues.

Although TPAH concentrations in Beaufort Sea amphipod tissues were lower than those in surface sediments at the locations where they were collected (Table 5), the PAH in sediments and amphipods probably were, at least in part, from common sources. PAH, SHC, and StTr profiles in river sediments and peat were similar to those in surficial sediments (Brown et al. 2010), indicating a common source of hydrocarbons in river sediments and the nearshore surficial sediments (Neff 2010b). Perylene, a biogenic PAH, produced by the microbial biodegradation of plant material (Venkatesan 1988; Grice et al. 2009), dominated the overall PAH distribution as the most abundant individual high molecular weight PAH in many offshore Beaufort Sea and North Slope river sediment samples (Brown et al. 2010). Perylene and 2 other biogenic PAH, simonellite and retene, usually are abundant in Arctic and sub Arctic marine sediments in Alaska (Venkatesan and Kaplan, 1982). Perylene often is abundant in biodegraded peat (Malawska et al. 2006), explaining the abundance of perylene in sediments from the mouths of several North Slope rivers that drain the vast peat deposits on the Alaskan North Slope (Steinhauer and Boehm 1992; Yunker et al. 1993, 2002; Yunker and Macdonald, 1995). Thus, river runoff probably is a major source of PAH in the nearshore marine sediments. Northstar crude oil contains about 100 ng/g oil of perylene, less than 0.001% of TPAH, and has a very low perylene index (Table 5). Thus, there was no indication that Northstar crude oil contributed PAH and SHC to Beaufort Sea sediments and amphipods, even those near the Northstar production facility.

Steinhauer and Boehm (1992), Yunker and MacDonald (1995), Yunker et al. (1991, 1993, 1996, 2002), Naidu et al. (2003, 2006), and Elmquist et al. (2008) have concluded, based on the abundance of perylene and petroleum biomarkers in Arctic sediments from sites with and without a past history of exploratory drilling, that most of the PAH in Beaufort Sea, Barents Sea, and other Arctic sediments, including those from former drill sites, comes from erosion of peat, coal, and black carbon deposits along the coast or from rivers emptying into the Arctic Ocean. Much of the black carbon (soot) enters coastal waters and sediments of the Beaufort Sea from dry and wet deposition from the atmosphere. The Arctic aerosol over northern Canada and Alaska contains relatively high concentrations of PAH and SHC (Macdonald et al. 2005). PAH in sediments from the Norwegian and Russian regions of the Barents Sea also have been derived in part from eroding natural deposits of kerogens, peat, oil shales, and coals (Dahle et al. 2003; Elmquist et al. 2008; Boitsov et al. 2009). The PAH are tightly bound to these aerosol particles and organic-rich natural deposits (Kraaij et al. 2002; Beckles et al. 2007) and, so, have a low bioavailability to marine plants and animals (Neff, 2002). This explains the lower abundance of PAH, StTr, and most SHC in amphipod tissues than in the sediments upon which they reside. Sediment-bound hydrocarbons, because of their low bioavailability, are not readily bioaccumulated and, so, have a low toxicity to marine organisms (Rust et al. 2004b; Neff et al. 2005).

The StTr profiles and diagnostic ratios indicate that the hydrocarbons in amphipod tissues from the Beaufort Sea development area, including the region adjacent to the Northstar facility, are not from Northstar crude oil. However, there are large numbers of different types of crude and seep oils, hydrocarbon-rich shales, and peats along the Beaufort Sea coast and in Arctic river drainages, including the Mackenzie River. These hydrocarbons have widely different StTr compositions (Anders and Magoon 1986; Becker and Manen 1988; Banet 1994; Yunker et al. 1995, 2002). The StTr profile in amphipods in the development area of the Beaufort Sea is consistent with a mixed petrogenic, pyrogenic and early diagenic source for the complex hydrocarbon mixture in amphipod tissues.

Concentrations of TPAH, TSHC, and TStTr in Anonyx from the Beaufort Sea development area are similar to those in the same and closely related species of epibenthic lysianassid amphipods in the northeast Chukchi Sea (Neff et al. 2010) and in the Canadian Beaufort Sea (KAVIK-AXYS, 2007). However, much higher TPAH concentrations have been reported in Arctic lysianassid amphipods from the Barents Sea (Svendsen et al. 2007) and in ampeliscid amphipods from Mississippi Canyon in the US Gulf of Mexico (Soliman and Wade 2008). The critical body residue (molar concentration in tissues causing toxicity) of PAH in tissues of amphipods is in the range of 6 to 12 µMol/g wet wt (Landrum et al. 2003). The mean concentration of total PAH in amphipods collected in 2006 is 3.4 µMol/g wet wt, about half the lowest critical body residue, indicating that the total PAH concentration in amphipod tissues is below toxic levels.

In summary, there is no evidence that environmentally significant amounts of hydrocarbons from offshore oil and gas operations are entering the food chain of the development area of the Alaskan Beaufort Sea. Hydrocarbons in amphipod tissues are primarily from river runoff and coastal erosion of natural diagenic and fossil terrestrial materials, including seep oils, kerogens, and peat.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES

We thank the 3 anonymous referees for their valuable comments. This paper is based on the results of the ANIMIDA and cANIMIDA Projects, sponsored by the US Department of the Interior, Bureau of Ocean Energy Management (BOEM). Study design, scientific oversight, and funding were provided by BOEM Environmental Studies Program, Alaska OCS Region, under Contract M04PC00020 to Battelle Memorial Institute. However, the conclusions are those of the authors and do not necessarily represent those of BOEM.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. BACKGROUND
  5. MONITORING OFFSHORE OIL AND GAS OPERATIONS
  6. MATERIALS AND METHODS
  7. RESULTS
  8. DISCUSSION
  9. Acknowledgements
  10. REFERENCES
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