OCS Study MMS 2003-057

Final Report

Trace Metals and Hydrocarbons in Sediments

of Elson Lagoon (Barrow, Northwest Arctic Alaska)

as Related to the Prudhoe Bay Industrial Region

by

A. Sathy Naidu

John J. Kelley

Principal Investigators

John J. Goering

Institute of Marine Science

University of Alaska Fairbanks

Fairbanks, AK 99775-7220

and

M. Indira Venkatesan

Institute of Geophysics and Planetary Physics

University of California

Los Angeles, CA 90095-1567

E-mail: ffsan@uaf.edu

ffjjk@uaf.edu

goering@ims.uaf.edu

indira@ucla.edu

September 2003
ii

Contact information

e-mail: cmi@sfos.uaf.edu

phone: 907.474.7707

fax: 907.474.7204

postal: Coastal Marine Institute

School of Fisheries and Ocean Sciences

University of Alaska Fairbanks

Fairbanks, AK 99775-7220
iii

Table of Contents

List of Tables ............................................................................................................... iv

List of Figures .............................................................................................................. iv

Abstract ........................................................................................................................ 1

Background and Relevance to Framework Issues .......................................................... 2

Study Objectives/Hypotheses ........................................................................................ 7

Materials and Methods .................................................................................................. 7

Samples and analytical methods ............................................................................. 7

Results ........................................................................................................................ 11

Discussion .................................................................................................................. 21

Trace metal studies ............................................................................................... 21

Hydrocarbon studies ............................................................................................. 24

Conclusions ................................................................................................................ 26

Ackowledgements ....................................................................................................... 27

Acronyms and Abbreviations ...................................................................................... 28

Study Products ............................................................................................................ 29

References .................................................................................................................. 30
iv

List of Tables

Table 1. Locations of sediment samples, water depth of locations, and

contents (%) of solids, sand, silt and clay in the sediments

[after Braddock and Gannon 2000] .............................................................................. 6

Table 2. Results of QA/QC analysis ......................................................................................... 10

Table 3. Trace metals in freeze-dried sediments of Elson Lagoon grab

samples (EL-1 to EL-5) and core sample EL-3 ......................................................... 12

Table 4. Comparison of the mean concentrations of trace metals in the mud

 fraction (<63 μm size) of sediments from two nearshore/lagoon

regions of the North Slope of Alaska ......................................................................... 14

Table 5. Correlations between trace elements, and between elements and

clay % of muds from Elson Lagoon ........................................................................... 15

Table 6. Concentrations of n-alkanes in Elson Lagoon sediments and in

sample 6G from the Colville River Delta [Naidu et al. 2001] .................................. 16

Table 7. Polycyclic aromatic hydrocarbons (PAHs) in Elson Lagoon

sediments and sample 6G from the Colville River Delta

[Naidu et al. 2001] ...................................................................................................... 18

Table 8. Comparison of the mean concentrations of selected trace metals

in Elson Lagoon sediments with ERL and ERM guideline values,

and percent incidence of biological effects in concentration ranges

defined by the two values as reported by Long et al. [1995] .................................... 24

Table 9. Comparison of the mean concentrations of selected hydrocarbons

in Elson Lagoon sediments with ERL and ERM guideline values,

and percent incidence of biological effectsin concentration ranges

defined by the two values asreported by Long et al. [1995] ....................................... 26
v

List of Figures

Figure 1. Map showing the North Slope of Alaska, Elson Lagoon,

and the Colville River–Prudhoe Bay region ................................................................ 3

Figure 2. Sample sites in Elson Lagoon ...................................................................................... 6

Figure 3. Stratigraphic variations of trace metals in core EL-3 ................................................ 13

Figure 4. Typical mass chromatogram from GC/MS analysis of

triterpenoid distribution in sediments from Elson Lagoon

(EL-2 and EL-3) and Prudhoe Bay ............................................................................ 20
1

Abstract

A one-year study (2001–2002) in Elson Lagoon consisted of determining the concentrations of

total mercury (THg) and methylmercury (MeHg) in five van Veen grab gross sediment samples

from the lagoon, and a suite of heavy metals (arsenic, barium, cadmium, chromium, copper, lead,

manganese, nickel, tin, vanadium and zinc) in the mud fraction (<63 μm size) of the sediments,

as well as from stratigraphic sections of a gravity core sample. Additionally, hydrocarbons

(normal and isoprenoid alkanes, triterpanes, steranes and polycyclic aromatic hydrocarbons

[PAHs]) were analyzed in three of the five gross sediments. The geochronology of the core was

established by 210Pb- and 137Cs-based methods.

The concentration levels of all the trace metals in the lagoon are generally below or similar to

those in shales and unpolluted nearshore marine sediments. Encompassing the past ~70 years,

stratigraphic samples show a net significant increase (p <0.05) up the core in Ba, Cr and Mn

accompanied by a significant (p <0.05) down core increase in THg, and no significant change

in the other metals. The up core increase in the three metals may be explained in terms of three

possibilities: 1) the lagoon is getting contaminated with the metals, 2) a reflection of up core

stratigraphic changes in lithology and/or organic matter, or 3) diagenetic upward mobilization

of the metals in solution from anoxic sediments and subsequent oxidative precipitation at the

surface. The down core increase in THg may be due to increased concentration of Hg by

methylation in progressively anoxic sediment layers.

Long et al. [1995] defined the guideline values effects range–low (ERL) and effects

range–median (ERM), representing possible-effects ranges, pertaining to concentrations of trace

metals and organics in sediments, for the occurrence of adverse effects on biota at varying

frequencies. ERL and ERM were determined for nine trace metals and several categories of

organic compounds. The concentrations of eight metals in Elson Lagoon sediments were

compared with corresponding metals in Long et al.’s study (their ninth metal, silver, was not

included in this study). The comparison indicates that the concentrations of As, Cr, Cu and Ni in

Elson Lagoon sediments are at levels such that adverse effects on biota would occasionally occur,

whereas the concentrations of Cd, Pb, Zn and THg are below such levels. However, we suggest

that the conclusions, based on the extrapolation of Long et al.’s [1995] guidelines to Elson

Lagoon, must be verified by detailed site-specific investigations, including assessment of the

proportion of a total metal in sediment that may be available for bioaccumulation and studies

involving cause & effects relating to individual metals on resident organisms of the lagoon.

Trace metal data in mud from the urban-impacted Elson Lagoon were compared with those from

the oil-related industrialized region of Colville Delta–Prudhoe Bay. By comparison, the Elson

Lagoon muds have significantly higher concentrations (p <0.05) of Cr, Ni, V and THg, with no

significant regional difference in other metals. A possibility for the higher concentrations of

the four metals in Elson Lagoon is a greater input of natural or anthropogenic metals from local

sources. Alternate possibilities are a relatively lower rate of sedimentation in Elson Lagoon

resulting in lower dilution of metals in sediments, or local focusing in Elson Lagoon of

anthropogenic metal contaminants derived from Eurasia via long-distance atmospheric transport

and subsequent deposition in precipitating snow and rain. The latter explanation is consistent
2

with the report of Snyder-Conn et al. [1997] and Garbarino et al. [2002] of relatively higher

concentrations of several metals in Elson Lagoon snow samples than samples from the Colville

Delta–Prudhoe Bay region, under similar snow and rain accumulation rates in both regions. A

lack of significant (p <0.05) correlation between all of the trace metals and clay percent in mud

either suggests that the sediment granulometry is not an important factor partitioning the metals,

or it is an artifact of the limited samples analyzed.

The overall molecular compositions of alkanes and polycyclic aromatic hydrocarbons, which are

very similar to those reported in our previous study for sediments of the Colville Delta–Prudhoe

Bay region, are characteristic of biogenic origin and very little petroleum input is reflected in

their composition. Preliminary qualitative analyses indicate the presence of small amounts of

coprostanol, a sewage sterol, and coprostanone, but no linear alkylbenzenes, a sewage tracer from

household laundry. This suggests that sewage input in the sediments, if at all present, may not be

important. Among a selected group of the PAHs examined, in context of Long et al.’s [1995]

guidelines, the concentration of 2-methylnaphthalene in only one of the three samples (EL-3) of

Elson Lagoon sediments is between ERL and ERM threshold levels wherein adverse effects on

biota would occasionally occur. As suggested for the trace metals, these conclusions must be

clarified by site-specific studies on resident organisms.

In summary, our study indicates that Elson Lagoon (as well as the Colville Delta–Prudhoe Bay

nearshore of the North Slope of Alaska) has remained generally a relatively clean environment as

far as sediment trace metals and hydrocarbons are concerned, despite the minor increase in some

metals subsequent to accelerated anthropogenic activities in the lagoon during the past 30 years.

The database on Elson Lagoon should be considered a baseline for monitoring inorganic and

organic chemical contaminants in the lagoon region, an urban-impacted section of the North

Slope of Alaska. These data will be useful for efforts relating to ecological risk assessment of

the study area in the context of contaminant inputs.

Background and Relevance to Framework Issues

In recent years, there has been great concern about the Arctic marine environment, especially

relating to the presence of anthropogenic contaminants and their possible biological effects.

Until recently the Alaskan Arctic seas were considered generally free of contaminants. However,

during the past decade organic and inorganic contaminants have found their way into the above

so-called ‘pristine’ environment [Barrie et al 1992; Chernyak et al. 1996; Naidu et al. 1997,

2001]. Several possible sources could supply anthropogenic contaminants to the Beaufort Sea

nearshore:

1. Local petroleum-related developmental activities including drilling operations

[Snyder-Conn et al. 1997; Naidu et al. 2001].

2. Discharge of municipal litter from rural villages (e.g., Barrow) where adequate

sewage and waste disposal and treatment facilities do not exist.
3

3. Debris deposited on the beaches and tundra adjacent to Elson Lagoon, at the west

end of the Beaufort Sea coast (Figure 1), during the oil and gas exploration of the

1940s as well as the construction of the U.S. Air Force DEW (distant early

warning) Line in the 1950s. Some of this debris was dispersed during occasional

storms and washovers into Elson Lagoon, which could result in possible metal

contamination.

Canada Bering

Sea

Chukchi Sea

Beaufort Sea

North Slope

Prudhoe Bay

Elson

Lagoon

400 km

400 mi

Gulf of Alaska

Alaska

Colville

Delta

Figure 1. Map showing the North Slope of Alaska, Elson Lagoon, and the

Colville River–Prudhoe Bay region.

4. There is also the possibility of long-range atmospheric and marine transport of

anthropogenic contaminants to the Alaskan Arctic [Rahn and Lowenthal 1986;

Barrie et al. 1992; Chernyak et al. 1996; AMAP 1997; Fitzgerald et al. 1998;

Garbarino et al. 2002] especially from the highly polluted regions of Eurasia

[Molnia and Taylor 1994]. Results of modeling exercises imply that northwest

Alaska, including Elson Lagoon, is on the transport pathway of contaminants

originating from Eurasia [Levno-Chythlook et al. 1999].
4

5. Several environmental factors unique to the Arctic may lead to biomagnification

of toxic metals and organics. For example, the Arctic marine organisms which

are lipid-rich are prone especially to accumulate lipophilic (fat loving)

contaminants, and the relatively short/simple linear food chains in the Arctic

can transfer contaminants readily from lower to higher trophic levels and result

in their biomagnification in marine subsistence food sources [Ayotte et al. 1995;

Mulvad et al.1996; Naidu et al. 2001].

6. Marine sediments, which act as an initial sink for particle-reactive trace metals

and hydrocarbons [Förstner and Wittmann 1979; Chapman et al. 1998] could

be a major source of contaminants to the benthos [Geffard et al. 2002; Lee and

Wiberg 2002; Mountouris et al. 2002] and other organisms which have a close

link with sediments [Long et al. 1995, 1998; Thompson et al. 1999; ValetteSilver 1999; Krantzberg et al. 2000].

For contaminant monitoring it is, therefore, important to record the regional concentrations of and

understand the natural biogeochemical processes of trace metals and hydrocarbons in sediments.

Such information is crucial to ecological risk assessment and management of marine areas with

contaminant input. In this context, several investigations have reported the concentrations and

partitioning of trace metals and hydrocarbons in sediments of the Alaskan Arctic seas [Naidu and

Hood 1972; Shaw et al. 1979; Venkatesan and Kaplan 1982; Sweeney and Naidu 1989; Crecelius

et al. 1991; Steinhauer and Boehm 1992; Snyder-Conn and Lubinski 1993; Naidu et al. 1997,

2001, 2003; Valette-Silver et al. 1999]. More recently, under a contract from CMI/MMS,

historical changes in trace metals and hydrocarbons in sediments were reported for the Colville

Delta–Prudhoe Bay region of the North Slope (Figure 1), with an objective to assess the impact

on contaminant input resulting from oil-related developmental activities [Naidu et al. 2001].

By comparison, little environmental data are available for the Elson Lagoon region (Figure 2),

[Hume et al. 1972; Schell 1975; Nummedal 1979; Walker 1991; Braddock and Gannon 2000].

In September 2000 Kelley and Naidu (unpublished) conducted a side-scan sonar survey of

Elson Lagoon to identify the nature and extent of industrial and municipal debris. Brown et al.

[in press] have reported the long-term erosion rates of the Elson Lagoon coast. The results of

sea-ice–related research in Elson Lagoon and its environs, including preliminary data from our

ongoing CMI study [Naidu and Kelley 2002; Naidu et al. 2003], appear in the proceedings of a

recently concluded workshop [FRSGC/IARC 2002]. Lindberg et al. [2002] have monitored the

photochemically-driven oxidation of gaseous mercury in the troposphere at Barrow. We believe

that any extrapolation to Elson Lagoon of site-specific chemical data collected from the Colville

Delta–Prudhoe Bay region [Venkatesan and Kaplan 1982; Sweeney and Naidu 1989; Crecelius

et al. 1991; Steinhauer and Boehm 1992; Naidu et al. 2001]), as a benchmark for monitoring

contaminants in that lagoon, will be of limited practical use. This is because the environmental

settings and potential sources of contaminants in the above two regions are quite different. Elson

Lagoon is essentially a large, shallow embayment with relatively little fluvial input of water and

sediment, and sheltered from the open ocean by a continuous barrier spit (Figure 2). In contrast,

the Colville Delta–Prudhoe Bay region, located to the east, is dominated by a lagoon-barrier

chain, receives relatively large fluxes of particulates from rivers and high coastal erosion, and has
5

greater access to the open ocean. Consequently, rates of deposition of sediment and associated

contaminants in the latter region are likely to be higher and sediment reworking by ice gouging

more pervasive. Additionally, the major potential source of contaminants to Elson Lagoon is of

municipal origin (sewage and garbage litter disposal and community recreational activities),

relatively higher input via long-distance atmospheric transport, and past defense-related activities

(e.g., rocket firing experiments, road and airstrip building and maintenance, oil exploration, DEW

Line construction) as opposed to the more easterly slope region where the dominant potential

source of contaminants is presumably local ongoing petroleum-related activities.

One of the trends in petroleum exploration on the North Slope is progressively towards the west

of Prudhoe Bay. It is quite possible that eventually Elson Lagoon and vicinity will be potential

grounds for oil and gas exploration. It, therefore, seems timely to establish inorganic and organic

chemical baselines to monitor contaminants in this environmentally-sensitive region. In fall 1999,

with funding from the National Oceanic and Atmospheric Administration Office of Oceanic

Resources Conservation and Assessment (NOAA/ORCA) and logistic support from the Barrow

Arctic Science Consortium (BASC), Sathy Naidu, University of Alaska Fairbanks (UAF),

collected samples of surficial sediments and gravity cores from five representative locations in

Elson Lagoon (Figure 2, Table 1). Joan Braddock, also from UAF and under contract with CMI,

investigated the microbial degradation potential of petroleum hydrocarbons in splits of the

sediment samples. This present report is on the analyses of a suite of trace metals (As, Ba, Cd,

Cr, Cu, Pb, Mn, Ni, Sn, V, Zn, and total and methyl mercury [THg and MeHg]) in the five

surficial sediments and hydrocarbons (normal and isoprenoid alkanes, triterpenoids, steranes,

and polycyclic aromatic hydrocarbons [PAHs]) in three of the five surficial sediments collected

from Elson Lagoon in 1999. We also report stratigraphic variations in the metals in one core

sample collected from the lagoon, the geochronology of the core, and historical changes in the

metals consequent to increased urbanization, since 1970, of the community of Barrow lying

adjacent to the lagoon (Figure 2). The data collected in this study, which are the first of their kind

for Elson Lagoon, will provide a chemical baseline for an environmentally-sensitive region of the

North Slope. A premise in this study has been that comparison of the data of Elson Lagoon with

those we collected earlier from the Colville Delta–Prudhoe Bay region [Naidu et al. 2001] will

help to set a basis for differentiating sources of contaminants derived from urban-impacted and

petroleum-related activities for the North Slope nearshore region.
6

Pt. Barrow

Barrow

Elson Lagoon

Chukchi Sea

Research Beaufort Sea Site

71 15′

71 20′

156 50′ 156 40′ 156 30′ 156 20′

4

5

1

2

3

Figure 2. Sample sites in Elson Lagoon.

Table 1. Locations of sediment samples, water depth of locations, and contents (%) of solids,

sand, silt and clay in the sediments [after Braddock and Gannon 2000].

Station Latitude

N

Longitude

W

Water

Depth

(m)

Solids

(%)

Sand

(%)

Silt

(%)

Clay

(%)

EL-1 71° 20.00′ 156° 33.58′ 1.5 79 92.5 1.25 6.25

EL-2 71° 19.18′ 156° 32.47′ 1.8 64.6 55 20.75 16.25

EL-3 71° 17.53′ 156° 24.71′ 3.7 49.6 54 10 36

EL-4 71° 22.82′ 156° 26.78′ 2.8 97.8 3.75 43.75 52

EL-5 71° 21.18′ 156° 30.89′ 2.5 77.9 46.25 27.5 26.25
7

Study Objectives/Hypotheses

1. To determine the concentrations of a suite of trace metals (As, Ba, Cd, Cr, Cu,

Pb, Mn, Ni, Sn, V, Zn) in the mud fraction (<63 μm size) of contemporary

sediments, and THg, MeHg and hydrocarbons (normal and isoprenoid alkanes,

triterpenoids and steranes, and PAHs) in gross surficial sediments of Elson

Lagoon.

2. To analyze historical changes in concentrations of the trace metals, based on

stratigraphic changes in the metals in a dated sediment core.

3. To develop a geochronology for the sediment core, using 210Pb- and 137Cs-based

dating methods and AMS (accelerator mass spectrometry) 14C dating of

calcareous fossils.

4. To compare the sediment trace metals and hydrocarbons of Elson Lagoon with

those of the Colville Delta–Prudhoe Bay region of the North Slope, with a

motive to identify differences in the nature and concentrations of contaminants

derived from urban-impacted and petroleum-related industrial activities.

5. To examine concentrations of the metals and hydrocarbons in the context of

thresholds of varying rates of occurrence of adverse effects on marine organisms

that live in and close to sediments [Long et al. 1995].

One of our hypotheses is that there have been no significant historical changes in sediment trace

metal concentrations in Elson Lagoon during the past 30 years, despite increased anthropogenic

activities resulting from urban development in Barrow and its impact on the lagoon. The second

hypothesis is that there are no significant differences in the concentrations of sediment trace

metals and the distribution pattern of hydrocarbons of urban-impacted Elson Lagoon and the

Colville Delta–Prudhoe Bay region, which is impacted by petroleum-related activities.

Materials and Methods

Samples and analytical methods

In this study the sediments analyzed consist of five van Veen grab samples and one of the three

gravity cores collected in fall 1999 in Elson Lagoon at selected locations (Figure 2, Table 1).

Each of the grab samples was split into three subsamples and transferred into I-Chem glass jars.

The core sample was sectioned at 1-cm intervals from the core top, and each of the sections was

split into three subsamples and placed in pre-baked I-Chem jars. All the above sediment samples

were stored frozen until analysis. One split of the five grab samples and sections of one core

(core EL-3) were shipped frozen to Frontier Geosciences Inc., Seattle for analysis of trace metals,

and splits of three grab samples (EL-1, EL-2 and EL-3) were sent to M. Indira Venkatesan

(University of California, Los Angeles) for analysis of hydrocarbons. Because of limited funds

received from CMI it was not possible to analyze the metal content in the entire core and the

hydrocarbons in two (EL-4 and EL-5) of the three grab samples collected. The metal analyses

were restricted to 1-cm intervals of continuous sections from the core top to 9 cm below and one
8

section taken at the bottom of the core at the19-cm depth. Presumably, the trace metal data on the

basal sediment section (about 70 years of age based on 210Pb geochronology, see results section)

provide a baseline for metal concentrations prior to intense urbanization of Elson Lagoon.

The trace metals and hydrocarbons were analyzed according to the methods followed in the

previously funded CMI/MMS projects on sediments collected elsewhere along the North Slope

nearshore [Crecelius et al. 1991; Steinhauer and Boehm 1992; Naidu et al. 2001]. As in

previous studies, the mud fraction, consisting of the silt plus clay sizes (<63 μm) of each of the

sediment samples, was taken for the metal analyses. By using this fraction the effect of varying

granulometry on the trace metal contents between the samples was minimized [Daskalakis and

O’Connor 1995; Naidu et al. 2001]. Further, in this fraction, which is generally enriched in clay

minerals and organics, the particle-reactive metals are usually concentrated by ion exchange,

adsorption and clay–metal–organic complex formation. The analyses on Elson Lagoon muds will

have an additional use—that of comparing metal data with samples collected on the same size

sediments in previous studies from other parts of the North Slope and Chukchi Sea nearshore

[Naidu et al. 2001 and references therein]. Consequently, the mud fraction is a more desirable

sediment component for monitoring metal pollution.

For separation of the mud fraction, a 5-g split of a thawed grab or core subsample was taken and

suspended in deionized distilled water and homogenized. The suspension was sieved through a

230-mesh nylon screen, and the separated mud particles were then freeze-dried and powdered

using an agate mortar and pestle. It is possible that during the process of separating the mud

fraction by wet sieving the gross sediments may have hydrolyzed some metals, or desorbed them

from the sediment (or both). If this occurred then some metal portions were lost to the water that

was subsequently siphoned and discarded. It is assumed that the fraction of metals thus lost, and

excluded from the analysis, was negligible.

A 0.5-g aliquot of the dried powder was taken into a 140-ml Teflon bomb and digested in 15 ml

of a high-purity concentrated 7-ml-HF+15-ml-HNO3+3-ml-HCl acid mixture in a conventional

oven at 130 °C for 12 hours. After cooling to room temperature, the digest was diluted to 100 ml

with water processed by a Milli-Q Ultrapure Water Purification System, and the diluted sample

was returned to its original bomb. The resulting solution was dried and then again dissolved in

10% HNO3 and made up to 20 ml by adding deionized distilled water. From this final solution

Ba, Cd, Cr, Cu, Pb, Mn, Ni, Sn, V, and Zn were analyzed using either an inductively coupled

plasma mass spectrometer (PerkinElmer Elan 6100 quadrupole ICP-MS) or by graphite furnace

atomic absorption spectrometry (GF-AAS). Arsenic was analyzed in a separate split of the dry

mud with a PSA Excalibur automated hydride generation atomic fluorescence spectrometry

(AFS) system, using EPA method 1632.

Total mercury and the more toxic methyl mercury were analyzed on the whole sediment rather

than the mud fraction, to avoid any possible loss of the highly volatile Hg from the gross

sediment during the sieving process. Total Hg was analyzed on 0.01–1.0 ml aliquots from the

solution retained in the bomb, using SnCl2 reduction, dual gold amalgamation pre-concentration,

and cold-vapor atomic absorption spectrometry (CVAAS). Methyl mercury was analyzed on

leachates of an acidic bromide–methylene chloride extraction of sediment, using aqueous phase
9

ethylation, followed by purging onto Carbotrap adsorbent resin, isothermal GC (gas

chromatograph) separation, and cold-vapor atomic fluorescence spectrometry (CVAF). Further

details on the methods of the THg and MeHg analyses are described in Bloom [1989, 1992] and

Bloom and Fitzgerald [1988].

The QA/QC (quality assurance/quality control) protocol prescribed by the U.S. Environmental

Protection Agency (EPA) for metal analysis was followed. It consisted of determining analytical

precision through replicate runs, checking analytical accuracy via analyses of certified standard

reference materials (1632-b, coal; NIST-2710, soil; NRCC DORM-2, dogfish tissue [for MeHg

only]; and NIST-600, bauxite), analyzing spiked sample and reagent blanks, and using ultrapure

reagents. The estimated method detection limits, MDL, (with three standard deviations, SD, of

the blanks) for the trace metals, and the QA/QC results are shown in Table 2. There is close

agreement between the analytical results for the reference materials and their certified values.

It should be noted that the concentrations of MeHg in a few samples are below the MDL (i.e.,

0.036 ng g–1) and, therefore, the results for these samples should be considered close to the MDL,

at best. As in our previous CMI-funded study, the trace metal analyses were subcontracted to

Frontier Geosciences Inc., Seattle, which in 1997 participated successfully in the NOAA/NIST

(National Institute of Standards and Testing) round robin interlaboratory exercise NOAA/11 for

certification of QA/QC. This exercise was conducted by the National Research Council of

Canada (NRCC). The Frontier Geosciences rating was good to excellent.

The analyses of hydrocarbons were on gross sediments, according to well established methods

[Venkatesan et al. 1987; Venkatesan 1994] and as described in detail in our previous study on

Colville Delta–Prudhoe Bay region sediments [Naidu et al. 2001]. After solvent extraction and

GC separation into individual compounds, the alkanes were quantified using a flame ionization

detector. Tricyclic di- and pentacyclic triterpenoids and PAHs were measured by GC/mass

spectrometry. As in our last CMI-funded investigation [Naidu et al. 2001] 24 PAHs were

analyzed, as well as six additional PAHs, which are routinely analyzed by NOAA/NS&T

(National Status and Trends Program). To maintain continuity and high standards, the

hydrocarbon analysis was subcontracted to M. Indira Venkatesan (University of California,

Los Angeles), who first in 1992 and then in 1999 successfully participated in interlaboratory

round-robin exercises conducted by NIST/NOAA-NS&T, for the QA/QC program.

The geochronology (sediment accumulation rate) of a sediment core (EL-3) from Elson Lagoon

was established by the age–depth model using 210Pb and 137Cs dating [Weiss and Naidu 1986;

Baskaran and Naidu 1995; Naidu et al. 1999]. The activities of the two radionuclides in

stratigraphic sections of core EL-3 (Figure 2) were measured by high resolution gamma ray

mass spectrometry. The radionuclide analysis was subcontracted to Mark Baskaran, Wayne State

University, Detroit. The 1-cm stratigraphic sections from the core were microscopically examined

in search of calcareous fossil shell/test samples for the purpose of AMS 14C dating. However, no

such samples were to be found in any of the core sections.

Grain size distributions of the grab samples [Braddock and Gannon 2000] were used to explain

elemental and hydrocarbon distributions in the study area.
10

Table 2. Results of QA/QC analysis.

Trace Metals (μg g–1 dry weight basis [MeHg ng g–1])

Sample As Ba Cd Cr Cu Pb Mn Ni Sn V Zn 

blank–1 0.0 0.1 –0.01 0.2 –0.13 0.2 0.17 0.03 0.6 0.1 –0.16 blank–2 –0.3 0.3 0.02 0.1 –0.09 0.2 0.21 0.04 0.7 0.1 –0.09 blank–3 0.0 0.6 –0.02 0.2 –0.14 0.1 0.21 0.08 0.5 0.1 –0.1blank–4 0.2 0.1 –0.01 0.3 0.01 0.1 0.18 0.18 0.6 0.1 –0.19 blank–5 –0.4 0.1 –0.01 0.0 –0.14 0.1 0.14 0.03 0.4 –0.2 –0.13 blank–6 –0.2 0.1 0.01 0.0 –0.06 0.2 0.22 0.05 0.6 0.0 –0.1blank–7 –0.1 0.5 0.04 0.1 –0.14 0.3 0.18 0.06 0.4 –0.2 –0.14 blank–8 –0.3 0.1 0.04 –0.1 –0.10 0.3 0.12 0.06 0.7 –0.2 –0.10 

mean –0.1 0.2 0.01 0.1 –0.10 0.2 0.18 0.07 0.6 0.0 –0.14 

estimated MDL 0.6 0.5 0.07 0.4 0.16 0.3 0.10 0.15 0.4 0.4 0.1

EL-5 rep 1 (2.0–3.0 cm

for MeHg only) 16.8 500 0.213 83.3 26.1 14.7 283 39.7 2.1 129 102 

EL-5 rep 2 (2.0–3.0 cm

for MeHg only) 16.6 487 0.162 85.7 26.4 14.3 273 39.5 2.2 128 99 

mean 16.7 494 0.187 84.5 26.3 14.5 278 39.6 2.1 129 100 

RPD (%) 1.1 2.7 27.1 2.9 1.1 2.9 3.6 0.5 4.1 1.0 3.2 

matrix spike level 218 not spkd 218 218 218 218 218 218 218 218 218 

EL-5 + MS (2.0–3.0 cm

+ MS for MeHg only) 217 517 193 282 228 221 477 242 206 326 297 

% recovery 91.8 not spkd 88.3 90.7 92.4 94.5 91.2 92.5 93.5 90.3 90.3 

matrix spike dup level 216 not spkd 216 216 216 216 216 216 216 216 216 

EL-5 + MSD (2.0–3.0 cm

+ MS for MeHg only) 207 504 187 281 225 216 477 239 199 324 283 

% recovery 88.0 not spkd 86.4 91.1 91.9 93.2 92.2 92.2 91.0 90.3 84.7 

mean recovery 89.9 not spkd 87.4 90.9 92.2 93.8 91.7 92.5 92.3 90.3 87.5 

RPD (%) 4.1 not spkd 2.1 0.5 0.5 1.5 1.0 0.7 2.7 0.0 6.4 

1632-b (coal) (DORM-2

[dogfish] for MeHg only) 3.26 60.7 0.053 9.9 6.30 3.85 11.47 6.34 0.4 13.0 12.17 

true value 3.72 67.5 0.057 not cert 6.28 3.67 12.40 6.10 not cert 14.0 11.89 

% recovery 87.7 90.0 93.3 not cert 100.3 104.9 92.5 103.9 not cert 92.9 102.4 

NIST-2710 (soil) (mL

spike for MeHg only) 549 623 19.0 27.6 2710 5165 9561 13.3 6.0 67.9 5991 

true value 626.0 707 21.8 not cert 2950 5532 10100 14.3 not cert 76.6 6952 

% recovery 87.7 88.1 87.1 not cert 91.9 93.4 94.7 93.3 not cert 88.6 86.2 

NIST-600 (bauxite) 16.6 55.5 0.04 132 14.0 17.3 106 4.26 7.8 334 24.2 

true value not cert not cert not cert 164 not cert not cert 101 not cert not cert 336 24 

recovery not cert not cert not cert 80.3 not cert not cert 105.3 not cert not cert 99.5 100.7 

*anomalous dataMDL = method detection limit, RPD (%) = relative percent difference, MS = matrix spike, MSD = matrix spike duplicate, NP = not 

10
11

Statistical analysis consisted of determining correlation coefficients (r-values) between the metal

concentrations and clay percent in mud, which were calculated by prorating the proportion

of silt plus clay in the gross sample at 100%, (Table 1). The statistical analysis also included a

comparison of mean concentrations of the individual metals in sediments of Elson Lagoon and

of Colville Delta–Prudhoe Bay [Naidu et al. 2001]. The Student-t test and null hypothesis [Zar

1984] were considered in the latter analysis.

The significance of up core stratigraphic net variation in metal concentrations was verified using

regression analysis. In this analysis the data on the basal core section were also considered. The

correlation coefficient (r-value) and Student-t values were considered significant if p <0.05.

Results

The percents of solids, sand, silt and clay in the individual sediment samples are included in

Table 1. Table 3 shows the concentrations (on dry weight basis) of the trace metals in the mud

fraction (<63 μm size) of the five sediment samples of Elson Lagoon. With the exception of Cr

and Mn, the concentrations of each of the metals in four out of five samples (excepion EL-1) are

similar. This is reflected in the overall relatively low standard deviation (SD) for all metals except

Cr and Mn (Table 4). The stratigraphic variations of the metal concentrations are also shown in

Table 3 and illustrated in Figure 3. Regression analysis indicates that there are significant net

increases (p <0.05) up core in Cr, Mn and Ba, and an up core decrease in THg, accompanied

by no significant stratigraphic variations in the remaining metals. It should be noted that the

determination of the up core net trends is based on all metal data from the core, including those

from the disjointed core section, but with no data from core sections in between the upper

9 cm of the core and the core bottom section. The 210Pb- and 137Cs-based linear sediment

accumulation rates for Elson Lagoon are 0.27 cm yr–1 and 0.23 cm yr–1, respectively, and

the mass accumulation rate based on the 210Pb method is 0.34 g cm–2 

yr

–1 as estimated by

subcontractor Mark Baskaran at Wayne State University. Therefore, the stratigraphic data on the

19-cm long core, EL-3, encompasses time-series variations in metals during the past 70–83 years.
12

Table 3. Trace metals in freeze-dried sediments of Elson Lagoon grab samples (EL-1 to EL-5) and core sample EL-3. R-

indicated for regression analysis on down-the-core net metal stratigraphic changes for core EL-3.

Trace Metals (μg g–1 dry weight basis [MeHg ng g–1])

Sample As Ba Cd Cr Cu Pb Mn Ni Sn V Zn 

Grab EL-1 31.4 559 0.171 188 36.7 25.6 1,388 52.3 3.1 211 146 

EL-2 17.6 631 0.195 134 35.7 19.3 406 51.6 2.5 186 141 EL-3 14.8 520 0.176 91.3 31.2 15.5 320 45.3 2.1 147 114 EL-4 21.9 531 0.143 96.9 35.0 18.1 341 50.6 2.5 168 126 EL-5 18.4 525 0.160 94.1 33.1 16.8 331 47.9 2.3 157 120 

Core 0–1 cm 23.3 553 0.859 203 35.5 24.7 1,144 50.1 2.5 178 131 

EL-3 1–2 cm 19.1 562 0.515 358 30.1 16.8 921 75.3 3.8 156 108 

2–3 cm 22.8 777 0.234 486 30.9 19.7 914 47.2 6.5 184 126 3–4 cm 15.6 683 0.288 245 26.3 16.1 382 36.6 3.2 158 111 4–5 cm 11.2 542 0.101 190 27.0 13.9 259 43.0 2.1 147 107 5–6 cm 12.5 568 0.112 136 30.3 15.7 270 45.4 3.4 164 124 6–7 cm 14.3 532 0.178 130 29.6 16.7 263 45.4 3.0 174 122 7–8 cm 17.0 579 0.225 198 28.7 16.7 271 43.0 2.7 178 122 8–9 cm 23.2 561 0.269 171 34.3 22.5 258 50.8 7.8 212 137 

18–19 cm 22.1 432 0.224 99 26.9 20.0 197 39.3 2.2 166 115 

r-value 0.14 –0.61 –0.44 –0.58 –0.35 0.06 –0.67 –0.42 –0.12 0.13 0.00 

12
13 30 40 50 60 70 80

Ni

(μg g–1)

26 28 30 32 34 36

Cu

(μg g–1)

Zn

(μg g–1)

100 110 120 130 140

As

(μg g–1)

8 12 16 20 24 

0 200 400

Cr

(μg g–1)

140 160 180 200 220

V

(μg g–1)

Depth (cm)

2016

12

8

4

0

0.05 0.06 0.07

THg

(μg g–1)

0 

12 16 20 24 28

Pb

(μg g–1)

400 500 600 700 800

Ba

(μg g–1)

2468

Sn

(μg g–1)

0 0.2 0.4 0.6 0.8 1

Cd

(μg g–1)

Depth (cm)

2016

12

8

4

0

Figure 3. Stratigraphic variations of trace metals in core EL-3. Refer to Table 3 for raw data.
14

Table 4 compares the mean concentrations in muds of trace metals from the urban-impacted

Elson Lagoon with those we collected from the oil-related industrialized region of Colville

Delta–Prudhoe Bay [Naidu et al. 2001]. By comparison, the Elson Lagoon muds have relatively

higher mean concentrations (p <0.05) of Cr, Ni, V and THg accompanied by no significant

regional differences in the means of the remaining metals.

Table 4. Comparison of the mean concentrations of trace metals in the mud fraction (<63 μm

size) of sediments from two nearshore/lagoon regions of the North Slope of Alaska. The

concentration of THg is in ng g–1 whereas that of other elements is in μg g–1.

As Ba Cd Cu Cr Pb Mn Ni V Zn THg

Elson Lagoon

Mean 21 553 0.169 34 121 19 557 50 174 129 74

Std. Dev. 6.4 46 0.019 2.2 41.4 3.9 466 2.9 25 13.7 19

Colville Delta–

Prudhoe Bay

Mean 16 569 0.264 27 63 15 540 34 117 96 17

Std. Dev. 7 114 0.115 7 13 6 337 7 23 18 7

Table 5 shows correlation coefficient values between metals. For example, it is clear that V

covaries with Cu, Pb, Ni, Sn, and Zn; and Ba with Cr; whereas there is no correlation between

THg or MeHg with any of the other metals or clay percent. It is to be noted that no significant

correlation was found between any of the metals and the clay percent in mud.
15

Table 5. Correlations between trace elements, and between elements and clay % of muds from

Elson Lagoon. (bold type = significant correlation for n = 5 at p <0.05 = 0.878; other

correlations are in gray type)

As Ba Cd Cr Cu Pb Mn Ni Sn V Zn THg MeHg Clay %

As 1.00

Ba 0.05 1.00

Cd –0.22 0.74 1.00

Cr –0.29 0.92 0.66 1.00

Cu 0.77 0.60 0.06 0.35 1.00

Pb 0.93 0.37 0.14 0.00 0.85 1.00

Mn 0.92 0.14 0.10 –0.24 0.65 0.95 1.00

Ni 0.71 0.64 0.08 0.43 1.00 0.80 0.58 1.00

Sn 0.96 0.31 0.00 –0.03 0.89 0.99 0.92 0.84 1.00

V 0.84 0.58 0.27 0.24 0.93 0.97 0.86 0.90 0.96 1.00

Zn 0.71 0.74 0.39 0.45 0.94 0.89 0.73 0.93 0.87 0.98 1.00

THg –0.28 –0.42 –0.25 –0.30 –0.44 –0.39 –0.30 –0.44 –0.38 –0.45 –0.48 1.00

MeHg –0.78 –0.36 0.07 –0.12 –0.85 –0.79 –0.66 –0.83 –0.83 –0.81 –0.78 0.77 1.00

Clay % 0.58 –0.36 –0.03 –0.64 0.04 0.52 0.73 –0.05 0.46 0.33 0.15 0.31 –0.01 1.00

Table 6 lists the concentrations (ng g–1) of total and individual homologs of n-alkanes and ratios

of selected alkanes for Elson Lagoon and sample 6G from the previous Colville River–Prudhoe

Bay study [Naidu et al. 2001]. The Elson Lagoon gas chromatograms showed a trimodal

distribution with maxima at n-C17, n-C23 and n-C27, and with alkanes >n-C25 predominating in

the samples. The odd/even ratios in all the samples are greater than one. Among the triterpanes

27(17β), 29ββ and diploptene are the major components (Figure 4). The former two hopanes are

the most dominant in EL-1 and EL-2 and diploptene is in EL-3. 29αβ and 30αβ hopanes are

present in smaller amounts relative to biogenic hopanes. Extended hopanes with >n-C31 are

present only in trace quantities and only the R isomer is detected.
16

Table 6. Concentrations of n-alkanes in Elson Lagoon sediments and in sample 6G

from the Colville River Delta [Naidu et al. 2001].

Sample ID

Elson Lagoon Colville Delta

n-alkane (ng g–1 dry) EL-1 EL-2 EL-3 6G*

n-C10 41 21 164 66

n-C11 5 30 234 110

n-C12 25 122 604 115

n-C13 4 38 232 150

n-C14 3 29 203 99

n-C15 3 39 246 160

n-C16 3 33 177 123

n-C17 11** 67 336 204

Pr 3 27 135 99

n-C18 7 55 273 138

Ph 2 17 66 44

n-C19 15 115 612 242

n-C20 15 109 598 129

n-C21 43 366 2163 574

n-C22 35 260 1477 422

n-C23 101 826 5482 1179

n-C24 33 253 1443 395

n-C25 75 668 4312 1221

n-C26 20 158 932 300

n-C27 98 1020 6691 2053

n-C28 16 101 598 205

n-C29 74 809 5097 1529

n-C30 8 66 1086 175

n-C31 61 611 3692 1417

n-C32 3 27 126 203

n-C33 18 178 969 457

n-C34 7 33 149 34

n-C35 4 20 108 72

n-C36 1 nd 9 7

Total n-alkanes 725 6054 38017 11778

Σ C12–C19 70 499 2684 1230

Σ C20–C33 598 5450 34668 10259

pr/ph 1.07 1.59 2.05 2

odd/even*** 1.92 2.97 3.00 4

*n = 3

**three most dominant homologs >n-C-14 for Elson Lagoon are underscored for each sample

***summed from n-C15 to n-C36
17

Qualitatively, the thermally mature (αβ hopanes) biomarker content in the samples follows the

order: EL-3 >EL-2 >EL-1. Steranes are about 10× lower than triterpanes. The alkane and PAH

contents in the three samples decrease in the following order: EL-3>EL-2 >EL-1, with EL-3

containing the maximum concentrations of identifiable components.

Table 7 shows the concentrations of polycyclic aromatic hydrocarbons in Elson Lagoon

sediments and sample 6G from the Colville River Delta [Naidu et al. 2001]. For Elson Lagoon

the PAH composition is dominated by the homologous series of naphthalenes and phenanthrenes.

With the exception of naphthalene all other parent PAHs dominate over their methylated

homologs. Compared to the lower molecular weight PAHs, 4- and 5-ring PAHs are relatively

less, perylene is always the most dominant PAH, and chrysene/triphenylene is the next most

dominant PAH in the samples analyzed. Perylene is the most dominant PAH of all the parent

PAHs in two of the three samples and second most dominant in the third. Preliminary and

qualitative analysis indicates the presence of small amounts of coprostanol and coprostanone

in all the samples, but no linear alkylbenzenes (LABs) were found. However, the identification

of fecal sterols needs to be confirmed by GC/MS, especially in view of the large amounts of

biogenic sterols in the samples, which are present at levels of 10 to 60× fecal sterols.

Comparison of the composition of the n-alkanes and PAHs in the Elson Lagoon sediments

(Tables 6 and 7) with those from Colville Delta–Prudhoe Bay [Naidu et al. 2001] shows some

minor differences. Sample EL-3 has nearly three times greater total n-alkanes than sample 6G

from the Colville River Delta, which has a maximum level of all the samples analyzed by us in

the previous CMI study encompassing the Colville Delta–Prudhoe Bay region. Similarly, sample

EL-3 from Elson Lagoon has nearly twice the amount of total PAHs compared to sample 6G

from the Colville Delta, which again has the maximum PAH content of all the samples analyzed

from Colville Delta–Prudhoe Bay. Except for these differences, the remaining two Elson Lagoon

sediments (EL-1 and EL-2) have comparable levels of total n-alkanes and PAHs, and a similar

distribution pattern of triterpenoids (Figure 3) to the Colville Delta–Prudhoe Bay sediments.
18

Table 7. Polycyclic aromatic hydrocarbons (PAHs) in Elson Lagoon sediments and

sample 6G from the Colville River Delta [Naidu et al. 2001].

Sample ID

Elson Lagoon Colville

PAH (ng g–1 dry) EL-1 EL-2 EL-3 6G*

naphthalene nd 10.84 76.22 16.72

C1-naphthalenes nd 56.08 353.71 94.54

2-methylnaphthalene nd 28.97 186.30 51.04

1-methylnaphthalene nd 27.16 167.74 43.63

C2-naphthalenes nd 50.47 293.95 168.91

2,6-dimethylnaphthalene** nd 25.94 108.73 18.19

C3-naphthalenes nd 41.92 222.12 129.70

2,3,5-trimethylnaphthalene nd 10.86 44.45 22.17

C4-naphthalenes nd 11.33 58.46 52.71

biphenyl nd 9.68 56.40 14.47

acenaphthylene nd 2.82 16.01 nd

acenaphthene nd 0.96 5.10 1.39

fluorene nd 6.91 34.23 9.04

2-methylfluorene nd 15.69 56.89 8.13

C1-fluorenes nd 7.64 31.69 30.39

C2-fluorenes nd 11.91 42.43 39.30

C3-fluorenes nd 13.65 36.62 70.26

phenanthrene 2.84 39.07 205.58 50.46

1-methylphenanthrene nd 24.50 106.35 24.44

anthracene nd 1.21 5.25 22.96

C1-phenanthrenes/anthracenes 6.81 41.59 120.79 160.85

C2-phenanthrenes/anthracenes nd 42.57 117.03 132.00

3,6-dimethylphenanthrene nd 18.63 17.05 5.89

C3-phenanthrenes/anthracenes nd 22.16 72.97 103.10

C4-phenanthrenes/anthracenes nd nd nd 12.68

2,3-benzofluorene nd nd 62.64 8.38

1,1′-binaphthalene nd nd nd nd

dibenzothiophene# nd 3.52 38.38 nd

C1-dibenzothiophenes# nd nd 6.02 2.59

C2-dibenzothiophenes# nd nd nd 0.55

C3-dibenzothiophenes# nd nd nd nd

C4-dibenzothiophenes# nd nd nd nd

fluoranthene nd 6.82 29.36 12.10

pyrene nd 9.65 45.38 14.80

C1-fluoranthenes/pyrenes nd 13.94 65.56 34.43

C2-fluoranthenes/pyrenes nd 14.59 48.38 32.84

C3-fluoranthenes/pyrenes nd nd 24.19 13.82

C4-fluoranthenes/pyrenes nd nd nd 10.53

benz(a)anthracene nd 3.10 18.20 3.43
19

Table 7. continued

Sample ID

Elson Lagoon Colville

PAH (ng g–1 dry) EL-1 EL-2 EL-3 6G*

chrysene/triphenylene nd 28.27 117.18 27.19

C1-chrysenes/triphenylenes 1.02 17.46 69.37 57.81

C2-chrysenes/triphenylenes nd 8.15 40.41 64.98

C3-chrysenes/triphenylenes nd nd nd 50.02

C4-chrysenes/triphenylenes nd nd nd nd

benzo(k)fluoranthene 1.36 14.47 50.20 1.94

benzo(b)fluoranthene 0.93 nd 4.27 17.44

benzo(e)pyrene 1.88 21.00 99.52 21.78

benzo(a)pyrene nd 3.64 22.40 4.86

9,10-diphenylanthracene nd nd nd nd

perylene 2.08 50.86 258.41 166.74

indeno(1,2,3-cd)pyrene nd nd 19.94 8.20

dibenz(a,h)anthracene nd nd nd 5.47

picene nd nd nd 23.70

benzo(ghi)perylene nd 22.33 110.56 28.60

anthanthrene nd nd nd 1.18

coronene nd 21.81 89.89 14.45

1,2,4,5-dibenzopyrene nd 29.03 128.35 26.87

C1-C20H12 aromatics nd 14.37 92.86 70.27

C2-C20H12 aromatics nd nd 35.27 44.78

C3-C20H12 aromatics nd nd nd 33.46

C4-C20H12 aromatics nd nd nd nd

sum naphthalenes (N) nd 170.63 1004.46 480.77

sum fluorenes (F) nd 40.11 144.98 148.98

sum phenanthrenes/anthracenes (PA) 9.65 146.59 521.62 482.05

sum dibenzothiophenes (D) nd 3.52 44.40 3.14

sum fluoranthenes/pyrenes (FP) nd 45.00 212.86 118.54

sum chrysenes (C) 1.02 53.88 226.95 200.19

sum C20H12 aromatics (C20) 6.26 104.33 562.94 361.13

sum 4,5 P-PAH 6.26 137.80 644.93

sum 4,5 PAH (4,5 PAH) 7.28 191.94 892.83 534.59

sum PAH(t-PAH) 16.93 653.80 3225.30 1912.67

N/PA nd 1.16 1.93 1.00

N/perylene nd 3.35 3.89 2.88

F/perylene nd 0.79 0.56 0.89

PA/perylene 4.63 2.88 2.02 2.90

FP/perylene nd 0.88 0.82 0.70

t-PAH/perylene 8.12 12.85 12.48 11.42

nd: not detected, below MDL * n = 3 ** coelutes with another isomer

# very low recovery because of activated cu treatment for sulfur removal

% recovery of some methylated homologs assumed to be the same as that of methylated

phenanthrenes
20

100

75

50

25

0

Mass 191

EL-2

18α

17α

27 17β

29αβ 29βα

30αβ

29ββ

31ββ

30ββ

Dip

31αβ

R

hopene

100

75

50

25

0

Mass 191

EL-3

18α

17α

27 17β

29αβ 29βα

30αβ

29ββ

31ββ

30ββ

Dip

31αβ

R

hopene

100

75

50

25

0

Mass 191

Prudhoe

Bay

5(10)/3

18α

17α

27 17β

29αβ 29βα

30αβ

29ββ

31ββ

30ββ

Dip

31αβ

R

S

Figure 4. Typical mass chromatogram from GC/MS analysis of triterpenoid distribution in

sediments from Elson Lagoon (EL-2 and EL-3) and Prudhoe Bay.
21

Discussion

Trace metal studies

The mean concentrations of all metals in the Elson Lagoon muds (Table 3) are at or below those

from unpolluted argillaceous marine sediments of the world (including the Arctic Ocean), natural

baseline levels of regions now presumed polluted (based on data in core sections representing the

pre-industrial age), and mean concentrations in shale which represent argillaceous rocks with

natural metal values [Förstner and Wittman 1979 and references therein; Bruland et al. 1974;

Salomons and Förstner 1984; Naidu et al. 2001]. However, regression analysis of the stratigraphy

of the metals in core EL-3, in conjunction with the geochronology of the core, indicates

significant (p <0.05) net increases in concentrations of Ba, Cr and Mn in Elson Lagoon during the

past ~70 years (Table 3, Figure 3). In contrast, a significant up core net decrease in THg is found,

but no statistically significant (at p <0.05) stratigraphic changes in concentrations of other metals,

including MeHg, are detected. It should be noted that in the regression analysis, to assess net

stratigraphic trends in the metal variations, data from the disjointed basal section of core EL-3

were also taken into account. It could be argued that the regression analysis incorporating data

from the basal (18–19 cm) core section in the absence of data from the 10–18 cm core section

would give extra emphasis to the basal section and, therefore, the analysis may be invalid.

However, we contend that by including data from the basal section the net stratigraphic trends

provide a better means to assess long-term temporal changes in the context of the presumed

baseline provided by the basal core section. It would have been, of course, desirable to include

metal data from the entire core, but limited funds precluded this. Taking the above into account,

the up core increase in Ba, Cr and Mn may either suggest that the lagoon is getting contaminated

in the above metals, or the trend may be a manifestation of up core stratigraphic changes in

lithology and/or organic matter in the mud fraction, which generally control the abundance of

particle-reactive metals, such as the ones we have analyzed, by processes of adsorption and/or

organic chelation. Alternatively, the up core increase in Cr and Mn could be due to diagenetic

upward mobilization in solution from subsurface anoxic layers and subsequent co-precipitation

of the metals in oxic surficial sediments. Because of limited funds we were not able to verify

the possible control of lithology and diagenesis on the stratigraphic changes in the metal

concentrations. If the reason is recent contamination, we do not then have knowledge of the

possible sources for the metals. It is to be noted that Elson Lagoon and its vicinity are a popular

place for recreation (snow machining, fishing, hunting, boating, camping) for Barrow residents,

and in the past the lagoon has been a site for municipal garbage disposal (including machine

parts), and accumulation of debris from rocket firing by the U.S. Navy. The region has also been

impacted by oil and gas exploration. It is quite possible that any or all of these activities could

have contributed to contaminant input. We recommend that cautionary measures, such as

avoidance of litter disposal into the lagoon, must be enforced to prevent any further increase in

metal concentration in the environment.

The down core net increase in THg presumably reflects higher methylation of Hg in subsurface

anoxic sediment layers, as suggested by the presence of increasing levels of MeHg from the

upper 4 cm composite of the core (representing possibly oxic layers) to about 7 cm down the core

(Figure 2, Table 3). Results of regression analysis of the stratigraphic variations in MeHg values,

including data from the upper 7 cm core, indicate that the regression is significant at the 5% level
22

(P = 0.0069). It is interesting to note that a similar down core increase in MeHg was also reported

for the Colville Delta–Prudhoe Bay area [Naidu et al. 2001], and also suggested that the down

core increase in MeHg was likely due to greater methylation of Hg in subsurface anoxic

sediments. Further detailed investigations will be necessary to better understand the processes

of methylation in sediments from Elson Lagoon and Colville Delta–Prudhoe Bay.

One of our stated objectives in this study was to compare the mean concentrations of trace metals

and hydrocarbons in sediments of Elson Lagoon and those of the Colville Delta–Prudhoe Bay

region, with a motive to identify differences in the nature of and concentrations of contaminants

in sediments derived from urban-impacted and petroleum-related industrial activities. Elson

Lagoon sediments have been taken as a representative of the former activities, whereas the

Colville Delta–Prudhoe Bay sediments have been considered to represent deposits influenced

by petroleum-related industrial activities. As indicated (Table 4), there are significantly higher

(p <0.05) mean concentrations of Cr, Ni, V and THg in mud samples of the urban-impacted

Elson Lagoon than in muds of the nearshore of the petroleum-related industrial area of Colville

Delta–Prudhoe Bay region [Naidu et al. 2001]. The reason for these differences is unknown.

Some of the possible factors contributing to this disparity are relatively higher input of metals

into Elson Lagoon from confined natural terrestrial sources from the hinterland, anthropogenic

local contributions, and/or regional differences in mass sediment accumulation rates (MSAR).

The MSAR in the Colville Delta–Prudhoe Bay region is 0.77 g cm–2 

yr

–1 [Naidu et al. 2001]

as opposed to 0.34 g cm–2 

yr

–1 in Elson Lagoon. The higher rate would tend to dilute the

concentrations of metals in sediments and, thus, could account for differences in the metal

levels in the above two regions. Alternatively, a relatively higher atmospheric deposition of

anthropogenic metals (metals derived from human or human-related activities) into Elson Lagoon

than the Colville Delta–Prudhoe Bay, via long-distance transport from Eurasia [Barrie et al. 1992;

Rahn and Lowenthal 1986], may result in regional differences in sediment metal concentrations.

The Eurasian region of China and Russia (Siberia) is highly industrialized and populated, and the

environment there is widely contaminated with a variety of organic and inorganic chemicals

[AMAP 1997]. The above premise, relating to regional differences in metal input from long

distance transport, is supported by the presence generally of a west to east concentration gradient

of metals in snow along the North Slope coast of Alaska. It is shown that relatively higher

concentrations of Cr, Ni, V and THg and several other metals, as well as a few anthropogenic

organics, exist in freshly precipitated snow from Elson Lagoon in the west through the Colville

Delta–Prudhoe Bay region to Demarcation Bay in the east [Snyder-Conn et al. 1997; Garbarino et

al. 2002]. The above authors have shown that snow is a significant medium in the Alaskan Arctic

for sequestering and entraining atmospheric-borne metals, with subsequent co-precipitation in the

lagoon. As there is no marked difference in the annual depositional rate of precipitation between

Elson Lagoon (snow: 74.17 cm yr–1; rain: 11.40 cm yr–1) and Colville Delta–Prudhoe Bay (snow:

82.55 cm yr–1; rain: 9.12 cm yr–1) (Theodore Fathauer, National Weather Service, pers. comm.),

it is possible that over the years higher metal fluxes tied to the depositional snow result in greater

concentrations of metals in the muds of Elson Lagoon. Consistent with the above premise is

the contaminant transport model developed by Levno-Chythlook et al. [1999], which has

implications for the trans-boundary transport pathway of airborne contaminants from Eurasia to

northern Alaska. The model suggests that there will be a focusing of air-borne contaminants at

Elson Lagoon compared to other coastal regions in the east of the Alaskan North Slope.
23

In this study the use of the correlation coefficient analysis (Table 5), to get insight into

geochemical partitioning of the metals, appears tenuous, at best. It would seem that in Elson

Lagoon the amounts of the clay fraction in the muds have a relatively minor role in the

sequestering of metals, as suggested by a lack of positive correlation between all of the metals

and clay percent (prorated for mud based on gross sediment data in Table 1). This finding is

inconsistent with that for mud samples from the Colville Delta–Prudhoe Bay region, where strong

positive correlations between several metals and clay percent are noted [Naidu et al. 2001].

Almost invariably, clay is a major sequester of particle-reactive metals (such as the ones we have

investigated in this study), by adsorption and/or metal–clay–organic complex formation. Perhaps

the oddity in the case of Elson Lagoon can be explained as an artifact imposed by the limited

number of samples (n = 5) that were analyzed. In contrast, 62 samples were analyzed from the

Colville Delta–Prudhoe Bay area [Naidu et al. 2001].

We have evaluated the mean concentrations of selected heavy metals in Elson Lagoon sediments

to determine their potential for adverse effects on resident benthic and demersal organisms,

following the guidelines proposed by Long et al. [1995]. Long et al., using a broad database

consisting of equilibrium-partitioning modeling, laboratory bioassays and field studies, have

developed “two guideline values (an effects range–low, and an effects range–median)”. Further,

“the two values defined concentration ranges that were: (1) rarely, (2) occasionally, or (3)

frequently associated with adverse effects”. Comparison of the mean concentrations of heavy

metals from our study with the above ERL and ERM and the three ranges for the selected metals

listed in Long et al. 1995 (Table 8), indicates that the mean concentrations of As, Cr, Cu and Ni

in Elson Lagoon muds fall into the ERL–ERM category, whereas mean concentrations of Cd, Pb,

Hg, and Zn are below ERL. This implies that the concentrations of As, Cr, Cu and Ni in Elson

Lagoon sediments are at or above the threshold level where adverse effects on biota would

occasionally occur. However, whether the extrapolation of the guidelines suggested by Long et

al. is relevant or applicable to Elson Lagoon is a question that needs to be further explored with

detailed site-specific cause & effect investigations on resident organisms. Nevertheless, the above

assessments suggest that measures must be taken to minimize the anthropogenic input of the

above four metals of concern.
24

Table 8. Comparison of the mean concentrations of selected trace metals in Elson Lagoon

sediments with ERL and ERM guideline values, and percent incidence of biological

effects in concentration ranges defined by the two values asreported by Long et al. [1995].

THIS STUDY DATA FROM LONG ET AL. [1995]

Guidelines Percent (ratios) incidence of effects*

Elson Lagoon

ng g–1 dry wt

ERL ERM

ppb dry wt

<ERL ERL–ERM >ERM

As 21 8.2 70 5.0 (2/40) 11.1 (8/73) 63.0 (17/27)

Cd 0.17 1.2 9.6 6.6 (7/106) 36.6 (32/87) 65.7 (44/67)

Cr 121 81 370 2.9 (3/102) 21.1 (15/71) 95.0 (19/20)

Cu 34 34 270 9.4 (6/64) 29.1 (32/110) 83.7 (36/43)

Pb 19 46.7 218 8.0 (7/87) 35.8 (29/81) 90.2 (37/41)

Ni 50 20.9 51.6 1.9 (1/54) 16.7 (8/48) 16.9 (10/59)

Zn 129 150 410 6.1 (6/99) 47.0 (31/66) 69.8 (37/53)

THg 0.07 0.15 0.71 8.3 (4/48) 23.5 (16/68) 42.3 (22/52)

* Number of data entries within each concentration range in which biological effects were observed divided

by the total number of entries within each range.

Hydrocarbon studies

The alkane and PAH contents in the three gross sediment samples decrease in the order

EL-3 >EL-2 >EL-1 (Tables 6 and 7). This pattern of decrease is consistent with the sediment

granulometry, reflected in the content of mud (<63 μm size), which is EL-3 >EL-2 >EL-1

(Table 1). The mud fraction is the most reactive fraction of the total sediment for hydrocarbon

adsorption and/or organic–inorganic complex formation.

The composition of hydrocarbons documented in our study provides clues to their source,

biogenic or petrogenic, as enumerated below.

Alkanes: The gas chromatogram is trimodal with maxima at n-C17, n-C23 and n-C27, and

alkanes >n-C25 predominate in the samples. The n-C17 is characteristic of aquatic algae and the

n-C23 maximum in the unresolved complex mixture of alkanes (which is illustrated as a broad

hump in the GC chromatogram) reflect microbial degradation. Normal alkanes dominant in odd

carbon alkanes ≥n-C25 are derived from higher terrestrial plants. This is also documented by the

odd/even ratio, which is much greater than one. The n-C20 and n-C21 olefins identified are

derived from plankton and bacteria.

Triterpanes: These are mostly biogenic, and 27(17β), 29ββ, 30ββ and diploptene are the four

major components (Figure 4). The former two hopanes are the most dominant in EL-1 and EL-2

and diploptene in EL-3. Qualitatively, thermally mature (αβ hopanes) biomarker content in the
25

samples follows the order: EL-3 >EL-2 >EL-1 and these hopanes are most probably derived from

peat and/or coal.

Steranes: These are about 10× lower than triterpanes. Their profile is very different from that of

oil and most probably reflects diagenetic origin.

PAHs: As mentioned, PAH composition (Table 7) is dominated by the homologous series of

naphthalenes and phenanthrenes. With the exception of naphthalene, all other PAHs dominate

over their methylated homologs. This suggests the general absence of significant petroleum

input in the sediments. Compared to the lower molecular weight PAHs, 4- and 5-ring PAHs are

relatively less, perylene is always the most dominant PAH, and chrysene/triphenylene is the next

most dominant PAH in this suite. Perylene is the most dominant in the EL-3 sample, consistent

with its origin in Alaskan peats similar to that found in coastal sediments of Alaska.

The qualitative analysis on sewage organic tracers in PAH and sterol fractions has allowed

some tentative deductions. Linear alkylbenzenes (LABs), which are sewage tracers derived from

household laundry, were not detected upon examination of the qualitative analysis of the

GC/MS run of the PAH fractions in any of the three sediment samples. However, coprostanol,

a sewage sterol, and coprostanone were found in small amounts in all the three samples. Their

identification needs to be confirmed by GC/MS, especially in view of the large amounts of

biogenic sterols in the samples, which are present at levels of 10 to 60× fecal sterols. A detailed

investigation of these tracers was out of the scope of the CMI-funded project. Nonetheless, the

very low relative proportions of fecal sterols would indicate that sewage input in the sediments,

if at all present, may not be important.

Among a selected group of the PAHs considered, in the context of Long et al.’s [1995] guidelines

for identifying hydrocarbon pollution in terms of effect range–low and effect range–median (refer

to the related discussion above on trace metals), the mean concentration of 2-methylnaphthalene

and the EL-3 total PAH are between the ERL and ERM, indicating that they are at or above the

threshold level where adverse effects on biota would occasionally occur (Table 9). As suggested

for the trace metals, this conclusion must be clarified by site-specific studies on resident

organisms.

Therefore, the normal and cyclic alkane distribution is characteristic of biogenic origin in all of

the three samples and very little petroleum and sewage input is reflected in their composition.

Additionally, the overall profiles of alkanes and PAHs are similar to those of inner shelf

sediments from the Beaufort Sea [Naidu et al. 2001 and Figure 2 for comparison with Figure 4

in the present report].
26

Table 9. Comparison of the mean concentrations of selected hydrocarbons in Elson Lagoon

sediments with ERL and ERM guideline values◊, and percent incidence of biological

effects in concentration ranges defined by the two values asreported by Long et al. [1995].

THIS STUDY DATA FROM LONG ET AL. [1995]

Guidelines Percent (ratios) incidence of effects*

Elson Lagoon

ng g–1 dry wt

ERL ERM

ppb dry wt

<ERL ERL–ERM >ERM

naphthalene 29.0 160 2100 16.0 (4/25) 41.0 (16/39) 88.9 (24/27)

2-methylnaphthalene◊ 71.8 70 670 12.5 (2/16) 73.3 (11/15) 100.0 (15/15)

acenaphthylene 6.3 44 640 14.3 (1/7) 17.9 (5/28) 100.0 (9/9)

acenaphthene 2.0 16 500 20.0 (3/15) 32.4 (11/34) 84.2 (16/19)

fluorene 13.7 19 540 27.3 (3/11) 36.5 (19/52) 86.7 (26/30)

phenanthrene 82.5 240 1500 18.5 (5/27) 46.2 (18/39) 90.3 (28/31)

anthracene 2.2 85.3 1100 25.0 (4/16) 44.2 (19/43) 85.2 (23/27)

fluoranthene 12.1 600 5100 20.6 (7/34) 63.6 (28/44) 92.3 (36/39)

pyrene 18.3 665 2600 17.2 (5/29) 53.1 (17/32) 87.5 (28/32)

benz(a)anthracene 7.1 261 1600 21.1 (4/19) 43.8 (14/32) 92.6 (25/27)

chrysene/triphenylene# 48.5 384 2800 19.0 (4/21) 45.0 (18/40) 88.5 (23/26)

benzo(a)pyrene 8.7 430 1600 10.3 (3/29) 63.0 (17/27) 80.0 (24/30)

dibenz(a,h)anthracene nd 63.4 260 11.5 (3/26) 54.5 (12/22) 66.7 (16/24)

Sum PAH◊ 1298.7 4022 44792 14.3 (3/21) 36.1 (13/36) 85.0 (17/20)

◊ 2-methylnaphthalene has the only mean concentration between ERL and ERM. The EL-3 total PAH

and 2-methylnaphthalene (3225.3 and 76.2 ng g–1, respectively) are between ERL and ERM. Low and

high molecular weight PAHs are not defined in Long et al., and are, therefore, not computed here. Total

PAH may be different for the same reason.

* Number of data entries within each concentration range in which biological effects were observed divided

by the total number of entries within each range.

# Reported as chrysene in the Long et al. study.

nd = not detected

Conclusions

The analyses from Elson Lagoon of eleven trace metals in mud fractions of five grab sediment

samples and stratigraphic sections of a core, and total mercury and methylmercury in gross grab

sediment samples show mean concentrations that are generally similar or below levels that are

reported for unpolluted marine nearshore sediments and shales. By comparison, the mean

concentrations of Cr, Ni and V in mud and of THg in gross sediments of Elson Lagoon are

significantly higher than in similar deposits from the Colville Delta–Prudhoe Bay region. These

differences may be due either to relatively higher natural or anthropogenic metal input to the

lagoon, or to greater depositional flux of anthropogenic metals that are associated with snow and

derived from Eurasia via long-distance atmospheric transport. This is consistent with the general

west to east decrease in the concentrations and fluxes of Cr, Ni and V and several other metals in

coastal snow as reported in the literature for the North Slope of Alaska. Stratigraphic variations in
27

metals indicate significant increases up core in Ba, Cr and Mn during the past ~70 years, which

suggest minor contamination recently in the above metals. In contrast, a net increase down core

is noted in THg, which may be related to greater methylation of Hg in progressively intense

anoxic sediment layers down the core. The mean concentrations of eight metals in Elson Lagoon

muds were compared with those examined in Long et al.’s [1995] analysis of guideline values for

the incidence of adverse biological effects. The comparison indicates that the concentrations of

As, Cr, Cu and Ni in Elson Lagoon sediments are at levels where adverse effects on biota would

occasionally occur, whereas the concentrations of Cd, Pb, Hg and Zn are below such levels.

However, we suggest that the conclusions, based on the extrapolation of the Elson Lagoon data in

context of Long et al.’s [1995] guidelines, must be verified by detailed site-specific investigations

involving cause & effect studies on resident organisms.

The hydrocarbon concentrations in gross sediments are also relatively low and are comparable to

those found in our previous investigation on coastal sediments from the Colville Delta–Prudhoe

Bay region and by others from the Beaufort Sea nearshore. The origin of the hydrocarbons is

essentially biogenic, with no significant input from natural or anthropogenic petroleum products.

Among the PAHs examined, the concentration of 2-methylnaphthelene in one sample is between

Long et al.’s [1995] effective range–low and effective range–median guidelines, with an

expectation of occasional adverse effects on resident organisms.

In summary, Elson Lagoon, like the Colville Delta–Prudhoe Bay nearshore, has remained a

relatively clean environment despite the slight increase recently in some metal levels subsequent

to accelerated anthropogenic activities there during the past 30 years. The data from this

investigation should serve as a baseline for monitoring chemical contaminants in Elson Lagoon.

Acknowledgements

This study was funded by the Minerals Management Service, U.S. Department of the Interior

through Cooperative Agreement 1435-01-98-CA-30909 (Task Order 15181) between the MMS

Alaska OCS Region and the Coastal Marine Institute, University of Alaska Fairbanks. Matching

funds were provided by the Institute of Marine Science, University of Alaska Fairbanks; Frontier

Geosciences, Inc. (Seattle); Department of Wildlife Management, North Slope Borough

(Barrow); and the University of California, Los Angeles. We thank the NOAA Office of Oceanic

Resources Conservation and Assessment (Silver Spring, Maryland) for providing funds to collect

the sediment samples from Elson Lagoon. This help was arranged by Jawed Hameedi. We thank

John Sweetman and Kathleen Gannon for sample collection. Thanks are due to Mark Baskaran,

Wayne State University, Detroit, and Misty Kennard, Frontier Geosciences, Inc. for help, under

subcontracts, with the analyses of sediment geochronology and trace metals, respectively.

Debasmita Misra assisted in the statistical analysis at no cost to this project. The continued

encouragement by Vera Alexander, director, CMI, and the excellent cooperation of Ruth Post of

CMI and Kate Wedemeyer and Cleve Cowles of MMS (Anchorage) throughout this study is

appreciated. Grateful thanks are also due to Maggie Billington for providing assistance in the

final report preparation.
28

Acronyms and Abbreviations

AFS atomic fluorescence spectrometry

AMAP Arctic Monitoring and Assessment Programme

AMS accelerator mass spectrometry

BASC Barrow Arctic Science Consortium

CVAAS cold-vapor atomic absorption spectrometry

CVAF cold-vapor fluorescence spectrometry

ERL effect range–low

ERM effect range–median

EPA Environmental Protection Agency

FRSGC Frontier Research System for Global Change

GC gas chromatograph

GC/MS gas chromatograph/mass spectrometer

GF-AAS graphite furnace atomic absorption spectrometry

IARC International Arctic Research Center

ICP-MS inductively coupled plasma mass spectrometer

LAB linear alkylbenzene

MDL method detection limit

MeHg methyl mercury

MSAR mass sediment accumulation rate

NIST National Institute of Standards and Technology

NOAA National Oceanic and Atmospheric Administration

NRCC National Research Council of Canada

NRCC DORM-2 dogfish muscle tissue (a standard reference material)

NS&T National Status and Trends Program (NOAA)

ORCA Office of Ocean Resources Conservation and Assessment (NOAA)

PAH polycyclic aromatic hydrocarbon

QA/QC quality assurance/quality control

THg total mercury
29

Study Products

The concentrations and depositional fluxes of the trace metals and hydrocarbons are available in

readily accessible electronic format through the Minerals Management Service. Please refer to the

tables attached showing results of the statistical analysis, station-wise specific sediment trace

metal and hydrocarbon data, which are also available in computer-aided graphic or tabulated

form.

Naidu, A.S., and J.J. Kelley. 2002. Trace metals and hydrocarbons in sediments in Elson

Lagoon (Barrow, northwest Arctic Alaska) as related to the Prudhoe Bay industrial region,

p. 102. In University of Alaska Coastal Marine Institute Annual Report No. 8. OCS Study MMS

2002-001, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region.

Naidu, A.S., and J.J. Kelley. 2002. Trace metals and hydrocarbons in sediments in Elson

Lagoon (Barrow, northwest Arctic Alaska) as related to the Prudhoe Bay industrial region.

University of Alaska Coastal Marine Institute Annual Research Review, February 2002,

Fairbanks, Alaska.

Naidu, S., and J. Kelley. 2002. Monitoring contaminants in Elson Lagoon, Northwest Arctic

Alaska: Progress of investigations on heavy metals and hydrocarbon concentrations in sediments,

p. 11. In Proc. 1st Workshop on Collaborative Marine Physical and Biogeochemical Research in

Barrow. Fairbanks, 18 October 2002. Frontier Research System for Global Change/International

Arctic Research Center, Univ. Alaska Fairbanks.

Naidu, A.S., J.J. Kelley and J.J. Goering. 2003. Trace metals and hydrocarbons in sediments in

Elson Lagoon (Barrow, northwest Arctic Alaska) as related to the Prudhoe Bay industrial

region, p. 49–56. In University of Alaska Coastal Marine Institute Annual Report No. 9. OCS

Study MMS 2003-003, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region.

Naidu, A.S., J.J. Kelley and J.J. Goering. 2003. Three decades of investigations on heavy metals

in coastal sediments, North Arctic Alaska: A synthesis. Paper orally presented by A.S. Naidu at

the XII International Conference on “Heavy Metals on the Environment”, 26–30 May 2003,

Grenoble, France. The full paper is published in Journal de Physique IV, Vol. II, 107:913–916.

Naidu, A.S. and M.I. Venkateson. 2003. Highlights of the trace metal study and hydrocarbon

investigations on Elson Lagoon sediments. MMS Information Transfer Meeting on Elson

Lagoon, Anchorage and Barrow, March 2003.

Naidu, A.S., J.J. Kelley, J.J. Goering and M.I. Venkateson. 2003. Trace metals and

hydrocarbons in sediments in Elson Lagoon (Barrow, northwest Arctic Alaska) as related to the

Prudhoe Bay industrial region. Final Report. OCS Study MMS 2003-057, University of Alaska

Coastal Marine Institute, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS

Region, 33 p.
30

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