Ultra-trace determination of Persistent Organic Pollutants in Arctic ice using stir
bar sorptive extraction and gas chromatography coupled to mass spectrometry
S. Lacorte1*, J. Quintana2, R. Tauler1, F. Ventura2, A.Tovar-Sánchez3 and C. M. Duarte3
1
Department of Environmental Chemistry, IDAEA-CSIC, Jordi Girona 18-26, 08034
Barcelona, Catalonia, Spain.
2
Aigües de Barcelona, Av. General Batet 4, 08028 Barcelona, Catalonia, Spain.
3
Department of Global Change Research, IMEDEA-CSIC-UIB, Miquel Marqués 21, 07190
Esporles, Mallorca, Spain.
* corresponding author: slbqam@cid.csic.es
Abstract
The present study presents the optimization and application of an analytical method based on
the use of stir bar sorptive extraction (SBSE) gas chromatography coupled to mass spectrometry
(GC-MS) for the ultratrace analysis of POPs (Persistent Organic Pollutants) in Arctic ice. In a
first step, the mass-spectrometry conditions were optimized to quantify 48 compounds
(polycyclic aromatic hydrocarbons, brominated diphenyl ethers, chlorinated biphenyls, and
organochlorinated pesticides) at the low pg/L level. In a second step, the performance of this
analytical method was evaluated to determine POPs in Arctic cores collected during an
oceanographic campaign. Using a calibration range from 1 to 1800 pg/L and by adjusting
acquisition parameters, limits of detection at the 0.1-99 and 102-891 pg/L for
organohalogenated compounds and polycyclic aromatic hydrocarbons, respectively, were
obtained by extracting 200 mL of unfiltered ice-water. α-hexachlorocyclohexane, DDTs,
chlorinated biphenyl congeners 28, 101 and 118 and brominated diphenyl ethers congeners 47
and 99 were detected in ice cores at levels between 0.5 to 258 pg/L. We emphasise the
advantages and disadvantages of in situ SBSE in comparison with traditional extraction
techniques used to analyze POPs in ice.
1. Introduction
Because of long range transport and dispersion throughout the environment, Persistent
Organic Pollutants (POPs) have been detected in remote areas such as the Arctic [1] and
Antarctic [2] ecosystems. The main sources of these compounds in polar environments are
atmospheric transport and continental run-off. Although the concentrations encountered in ice-
1
water are at the low pg/L level [3, 4], there is evidence that these compounds are released upon
snow and ice melt [5] and are accumulated in apical predators in polar food webs, such as seals,
whales, polar bears [6] and humans [7]. There are reasons for concern on the potential risks they
may pose for fauna and, ultimately, for human health.
Yet, data on contaminant loads in Arctic ice is very scarce. To date, resolving POP
levels in Arctic ice is particularly important due to accelerated rates of ice melting [8], which
releases the POPs trapped in ice into the surrounding waters [9].
Considering the low concentration of POPs in ice samples, analytical methods should be
sufficiently sensitive and selective to meet quantification limits at the pg/L level. The
measurement of such low levels is analytically complex, especially when performed in the field
(e.g. on board of an oceanographic vessel) where sampling, processing and storage require a
rigorous analytical control to reach the required sensitivity and at the same time avoid any
external source of contamination [4]. Traditionally, large ice volumes are extracted to detect
pg/L concentration. In a very early study performed in 1983, Tanabe et al. extracted 200-1200 L
of ice melt water using an Amberlite XAD-2 resin column which were reconstituted in 100 µL
of hexane and analyzed by gas chromatography coupled to mass spectrometry (GC-MS) using a
packed column, measuring concentrations of 1500-4900 pg/L in Antarctic ice and snow [10].
Donald et al. melted 20 L of water equivalents of snow and ice and liquid-liquid extracted
(LLE) target compounds, yielding limits of detection (LODs) of 2 pg/L for organochlorinated
(OC) compounds [6]. Villa et al. (2003) LLE-extracted 1-5 L of ice water to obtain limits of
detection of 0.25-1 ng/L for several OC pesticides [11]. Gustafsson et al. (2005) collected 200 L
of ice which were melted on an ice-melter and using LLE, levels of 0.005 to 0.44 pg/L of
polychlorinated biphenyls (PCBs) were detected in Arctic ice and snow [4]. To avoid the use of
large solvent volumes in LLE, Solid Phase Extraction (SPE) base techniques have been
deployed. Using C18 cartridges, 1-6 L of snow were preconcentrated and yielded LODs between
0.63 and 27 pg/L for polybromo diphenyl ethers (PBDEs) [12]. Speedisks were also evaluated
to process high sample volumes (up to 50 L) without the need for sample filtration and provided
mean recoveries of 68% and LODs between 0.2 and 124.8 pg/L for 75 organic compounds in
snow samples [13].
Progress in sample-prep techniques and technological improvements, especially in the
analytical instrumentation has led to minimize extracted sample volumes and solvents or either
use solventless analytical procedures. Semi-permeable membrane devices (SPMDs) have been
identified as an alternative to extract POPs in snow [14] and provide an integrated measure of
freely dissolved contaminants, reaching LOD of 0.2-0.4 ng after exposure of SPMD for 12-20
days. Solid Phase Microextraction (SPME) has been used to determine OC pesticides in
Himalayan ice using only 35 mL of water [15]. This technique is solvent-free and is
characterized by the fact that analytes are extracted on a fiber which is then injected in a GC-
2
MS, minimizing sample manipulation and increasing in sensitivity since all extracted analytes
are detected. The outcome of Stir Bar Sorptive Extraction (SBSE) followed by thermal
desorption and GC-MS further improves the method sensitivity since it has higher capacity than
SPME. By using 100 mL of water, all preconcentrated compounds are detected, lowering the
LODs to ng/L for PAHs, PCBs and pesticides [16]. This technique has additional advantages
such as minimal sample manipulation, implying minimal external contamination risk and is also
solventless. This recent development was timely, as its application could be instrumental in
achieving an increase of knowledge on pollutant loads in the polar ice sought as one of the aims
of the International Polar Year (IPY 2007-08).
The aim of the present study was to develop an ultra sensitive methodology based in
SBSE-GC-MS to identify a large number of POPs in Arctic ice cores collected during the 2007
ATOS oceanographic campaign. First, in situ extraction conditions (considering boat movement
and limited laboratory facilities) were optimized in an attempt to: (i) reduce the amount of ice
extracted in comparison to state of the art methods; (ii) avoid the burden to store and transport
large water volumes and (iii) increase the sample throughput. Second, the analytical conditions
were carefully optimized to reach the 0.1 pg/L sensitivity for 4 chemical families of POPs. We
report here the new approach and its performance, as well as its utility to determine the levels of
contaminants in Arctic cores, which are then compared with values reported in the literature
using other analytical methods.
2. Experimental
2.1. Chemicals and Reagents
Compounds analyzed are indicated in Table 1. Sixteen Environmental Protection
Agency (EPA) PAHs were purchased from AccuStandard (New Haven, CT, USA) as a mix
solution at 200 mg/L in methanol. The internal standard solution used to quantify these
compounds contained naphthalene-d8, acenaphthylene-d8, acenaphthene-d10, phenanthrene-d10,
chrysene-d12 and perylene-d12 at 2 mg/L in methanol (Supelco, Bellefonte, USA). PCBs were
purchased as a mix solution at 10 mg/L in iso-octane and OC pesticides at 100 mg/L in
methanol (Dr. Ehrenstorfer, Augsburg, Germany). The main PBDE congeners studied were
bromodiphenyl ether (BDE) 28, BDE 47, BDE 100, BDE 99, BDE 154, BDE 153 and BDE
183, purchased at 1 µg/mL in nonane (Cambridge Isotope Laboratories, Inc., Andover, MA,
USA). BDE 209 was not analyzed since it implied a separate GC method. PCB 65 and 200 (Dr.
Ehrenstorfer) were used as internal standards for all halogenated compounds. Methanol and
HPLC grade water were from Merck (Darmstadt, Germany).
3
2.2. Sampling area
The cruise was conducted on board of the Spanish Research Vessel (R/V) “Hespérides”
from June 28th to July 28th, 2007, sailing from Iceland to the Fram Strait. Seven ice stations were
sampled along the cruise track (Figure 1), corresponding to multi-year ice ranging in thickness
from 2 to 3 m. At each station, 1 m deep x 7.25 cm diameter ice cores were collected using a
motorized Mark III coring device (Kovacs Enterprise Inc.), removing the unconsolidated
surface snow and ice before sampling. The blades of the coring device were stainless steel and
were rinsed with MilliQ water prior to each sampling event. The individual ice cores were
inserted inside a precleaned PVC core holder and transported to the research vessel, where they
were kept at – 12 º C until sectioned, typically within two hours after sampling. From each 1 m
long ice core, the 20 cm extremes were cut using an acetone precleaned knife and placed in a
PFTE bag, sealed totally and left in a cooler at the side of the ship (0-5 ºC) until melted.
2.3 Extraction procedure
SBSE extraction was performed in situ in the vessel laboratories. 100 mL ice melt water
was transferred in a water-methanol-acetone pre-washed Erlenmeyer flasks where 10 mL of
MeOH were added together with 100-500 pg of the internal standards. At this step, new
precleaned stir bars (or Twisters) were added in the Erlenmeyer flask which were immediately
capped and placed on the 15 position magnetic stirrer (Gerstel, GmbH, Mülheuim a/d Ruhr,
Germany) at room temperature, in the dark. Extractions were carried out with new 20 mm
length × 1.0 mm film thickness polydimethylsiloxane (PDMS) coated stir bars which
corresponded to 126 µL of phase. Each sample was extracted in duplicate. Samples were
agitated at 900 rpm during 24 h to reach an equilibrium partitioning between the dissolved
chemical and the PDMS phase of the stir-bar. The extraction of solutes from aqueous phase into
PDMS phase is controlled by the PDMS/water partition coefficient (approximated by the
octanol water coefficient, log Kow) to the mass of analyte present in the aqueous sample of a
known volume, according to:
Kow » K PDMS/W =
Where K
C
PDMS
PDMS/w
CPDMS
CW
=
mPDMS VW
mW
VPDMS
=
mPDMS
mW
β
is the distribution coefficient between polydimethylsiloxane and water;
and Cw is the concentration of a solute in the polydimethylsiloxane phase and in the
water; m
PDMS
y m
w
is the mass of the solute in the polydimethylsiloxane phase and in the
aqueous phase and ß is the phase ratio (ß = VS /VPDMS, which represents the volume of the
4
PDMS coated Twister and the volume of water, respectively [17, 18]). All target analytes
studied exhibit Kow that reflect high hydrophobicity and thus have a high tendency to diffuse
onto the PDMS phase. A theoretical percent recovery for a given analyte i initially dissolved in
water is given by:
%R SBSE =
K iPDMD/w / β
1+K
i
PDMS/w
X
100
/β
If the KSBSE for any specific compound is substituted by its Kow, the theoretical
percentage recovery can be calculated. In our specific case, and using BDE 47 as an example,
considering the Kow = 5.9 x 106, the sample volume of 100 mL and the volume of the PDMS
fiber of 126 µL, substituting these values to the above equation, we obtain:
%R SBSE =
5.9 x 106 / (126/105)
X
100 ≈ 100
1 + 5.9 x 106 / (126/105)
This calculation predicts that the recovery for this specific analyte would be of 100%.
As demonstrated by other authors, Kow higher than 3.5 ensures an efficient partitioning of
solutes to the PDMS phase within 2 h, and partitioning increases with longer extraction times,
leading to higher sensitivities [19, 20]. After 24 h extraction, time chosen for the above
mentioned conditions, stir bars were removed with tweezers, rinsed with HPLC grade water,
dried with a lint-free tissue and placed into the insert of a 2 mL vial and capped. The preconcentrated SBSE bars were kept at 4º C in the refrigerator of the boat during 4 months, time
that took the ship to reach Spain. Once samples were gathered from the ship, they were
immediately processed in the land-based laboratory.
To prevent any external source of contamination and to ensure full recovery of target
analytes, some precautions were taken in the extraction and storage steps in the boat conditions:
(i) ice cores pieces were placed from the holders into the Teflon bags inside a cool room
avoiding any contact with hands; (ii) teflon bags were sealed until melted; (iii) 100 mL of melt
water (in duplicate) were place directly inside the precleaned Erlenmeyer flask and capped
immediately after so that there was no contact with ship atmosphere; (iv) storage conditions
were controlled by measuring the recoveries of internal standards in each sample.
2.4. Instrumental analysis
An Agilent 6890GC/5975B MS system (Agilent Technologies, Palo Alto, CA, USA)
equipped with a programmed-temperature vaporization (PTV) injector was used. Two stir bars
5
(corresponding each to 100 mL of extracted melt water) were placed inside a precleaned Twister
Desorption Liners (Gerstel), capped with a sealed Transportation Adapter and placed on a
Autosample Tray. Stir bars were thermally desorbed in a thermal desorption unit (TDU from
Gerstel) connected to the PTV injector CIS-4 (Gerstel) by a heated transfer line. TD was
performed from 15 ºC (holding time 0.8 min) and then increased at 60 ºC/min to 280 ºC held
during 7 min (desorption parameters). Helium flow was set at 50 mL/min. The PTV injector
temperature was held at 8 °C during 0.1 min and then increased to 325 ºC at 10 ºC/s and finally
held during 7 min. An Agilent HP-5MS (30 m × 0.25 mm i.d. × 0.25 μm film thickness)
capillary column was used. The oven temperature was programmed from 70 ºC (holding time 2
min) to 150 ºC at 25 ºC/min, to 200 ºC at 3 ºC/min and finally to 280 ºC at 8 ºC/min, keeping
the final temperature for 10 min. Transfer line and ion source temperatures were 280 ºC and 230
ºC, respectively.
Data acquisition was performed simultaneously using full scan conditions over a mass
range of 44 to 750 amu and time scheduled Selected Ion Monitoring (SIM) using three or four
ions per compound (Table 2). To enhance sensitivity, the SIM program was optimized using the
autoSIM option and resulted in 27 chromatographic windows where 1 to 7 compounds were
included, thus diminishing the number of ions displayed in each window and therefore,
increasing in sensitivity. The sum of the two most abundant ions per compound was used for
quantification. Peak detection and integration was carried out using MSD ChemStation
(Agilent) software using external standard quantification. The concentration of target analytes
was corrected by the recovery of each surrogate standard in cases where recoveries were lower
than 70% (Table 3).
2.5. Quality Control/Quality Assurance
To prevent contamination and to obtain reliable POPs data, special care was given to
blank analysis and to sensitivity and identification criteria.
As for blank analysis, HPLC grade water was extracted in boat conditions to evaluate
possible external contributions of any of the target compounds. We also performed laboratory
blanks using HPLC grade water and we evaluated the memory effect of empty Twister
Desorption Liners used in the TDU of the GC to evaluate carry over effects among samples.
Method optimization was performed with HPLC grade water. A calibration curve at 1,
5, 10, 20, 50, 90, 180, 460, 900, 1360 and 1800 pg/L (the last 2 concentrations were measured
only for PAHs) with internal standards at 500 pg for deuterated PAHs and 100 pg for PCBs was
used. Recoveries were tested in HPLC water spiked at 10 pg/L level. LODs for
organohalogenated compounds were calculated by dividing the sum of the intercept value plus 3
6
times its standard deviation by the slope, both obtained from the calibration curve. This
technique relies on the overall performance of the calibration, not just the response at one
concentration. For PAHs, since boat blanks contained traces between 98-300 pg/L, LODs were
calculated using 3 times the standard deviation of 3 blanks.
All target compounds should undergo the following identification and confirmation
criteria: (i) each compound was identified using at least 3 specific ions; (ii) the retention time of
target compounds should be within 3 s to that of a standard; (iii) the isotope ratio of the two ions
monitored per congener should be within 20% of the theoretical isotopic ratio, and (iv) the
signal to noise ratio for the sum of 2 ions of a specific compound should be S/N=3 or higher.
3. Results and discussion
3.1. GC-EI-MS performance
GC-quadrupole mass spectrometer (Q-MS) with electron impact (EI) ionization has
been identified as the technique most often applied to the analysis of a large number of POPs
given their easy calibration and operational features [21, 22]. The multiresidual SBSE method
herein developed included the main OC pesticides, PCB and PBDE congeners according to their
use in technical formulations. The chromatographic conditions were optimized to resolve 48
compounds in 40 min (Figure. 2). Due to the nature of compounds, 3 coelutions were observed:
(i) PCB 101 and α-endosulfan, which could be resolved at their specific m/z and fully identified
using 3 or 4 acquisition ions; (ii) benzo(a)anthracene and chrysene and (iii) 4,4’-DDD and 2,4’DDT which had the same ions and their concentration is given as the sum of both compounds.
Calibration range was performed at an ultra-low level, from 1 to 1800 pg/L (900 pg/L
for organohalogenated compounds since they are expected at the low pg/L concentration in
Arctic waters). Table 2 provides the calibration parameters obtained using external standard
quantification. In this specific case, the surrogate standards were used to determine recovery
efficiency and the stability of the compounds stored in the SBSE bars, but were not used for
quantification purposes since their concentration exceeded the concentration levels of target
compounds in the samples. In general, good linear calibration curves were obtained (typically,
R2 > 0.990) (Table 2). Overall, these results imply that a linear range was maintained over at
least 2 orders of magnitude, which ensures a good reliability to quantify compounds present at
the pg/L level.
3.2. Sensitivity and detection limits
7
The method was developed and finely refined to increase its sensitivity as much as
possible, while maintaining the identification capabilities of the EI ion source. By optimizing
the time scheduled SIM conditions, 27 retention time windows were obtained with 4 to 14 ions
per window. By decreasing the number of ions per window, it is possible to enhance up to 10
times the sensitivity of the method by increasing the dwell time of each ion. Another feature of
the method is that the base peak and the second most abundant ion were summed to increase the
ion sensitivity. By doing so, it is possible to almost double the signal of any particular ion,
depending on the intensity of each. Table 2 provides the LODs obtained after pre-concentrating
200 mL of water spiked over 1 to 1800 pg/L (900 pg/L for organohalogenated compounds).
These LODs range from 0.1 to 99 pg/L for PCBs, PBDEs and chlorinated pesticides. For PAHs,
given that a small contribution was observed from blanks performed on board of the vessel, the
LODs were calculated using 3 times the standard deviation of three boat blanks. Levels ranged
from 102 to 891 pg/L, which are also adequate to determine PAHs in ice since they are present
at higher levels than organohalogenated compounds. Comparing to other studies where SBSE
was optimized [16, 19, 20], herein we provide LODs 10-100 times lower due to the calibration
optimization at ultra-trace levels.
3.3. Recoveries and stability
At a10 pg/L level, the optimized method provided recoveries from 71 to 139 % with an
acceptable standard deviation (1-25%) (Table 2). These extraction recoveries correspond to the
dissolved and particulate phase of the melt water, since samples were not filtered. The SBSE
method is suitable for dissolved chemicals, yet particulate matter was present in the melt water
samples. In principle, the fraction of compounds associated with the particulate matter
(presumably quite low) is not efficiently extracted by the SBSE method. However, the purpose
of adding 10% methanol was to detach contaminants from glass adsorption and also to desorb
compounds bound to particulate matter. By doing so, most compounds were efficiently
extracted. Exceptions were β-HCH (27% recovery), aldrin (51%), heptachlor and heptachlor
epoxide (50 and 53% respectively). Naphthalene, acenaphthene, acenaphthylene, fluorene and
PCB 52 were not detected at this low concentration level. Volatile PAHs, along with
naphthalene-d8 and acenaphthylene-d8 were not recovered after spiking water samples (Table 2
and 3) since we did not use a criofocussing system to entrap the more volatile compounds
during the desorption step. For that reason, volatile compounds could not be quantified from the
samples. PCB 52 was not recovered at a level of 10 pg/L (Table 2) due to its lower sensitivity in
a GC-MS in electron ionization compared to negative chemical ionization or ion electron
capture detection. The multiresidue method developed has the advantage to detect low pg/L
8
concentrations of different chemical families of POPs in ice cores in detriment of good
sensitivity for all of them [21], so compounds not detected at 10 pg/L level were not quantified
in ice cores. However, PCB 52 is an important, persistent legacy analyte throughout the world
and therefore, a higher amount of water should be extracted if this compound has to be detected
in Arctic waters [3, 4].
Surrogate standards provide evidence for good method performance and were recovered
between 95 and 112% just after spiking (CV 9%) except naphthalene-d8 and acenaphthylene-d8
which were not recovered at 500 pg level. The extent of analytes loss during SBSE preservation
(4 months) was tested using these same surrogate standards (Table 3). Again since naphthalened8 and acenaphthylene-d8 were not recovered, their corresponding native compounds could not
be surveyed in the ices cores. The other deuterated PAH surrogates were detected from 42%
(acenaphthtene-d10) to 121 % (perylene-d12). PCB 65 and 200 were recovered in 97 and 47%,
respectively. The recovery of the surrogate standards indicate that preservation conditions
during 4 months produced looses of some of the surrogates. Also, the lower recoveries in ice
compared to HPLC grade water might be due to the presence of particulate matter in ice cores.
However, any losses of target compounds could be corrected by calculating the recovery rate of
surrogate standards in each sample. In addition to that, the reproducibility of the method ranged
from 7 to 24%, which is reasonable for the low level concentrations resolved in this work.
3.4. Blank analysis
Ultra-trace analysis of POPs in Arctic ice requires that sample manipulation is
minimised, which in turns avoids sample contamination and improves the precision of the
analysis. In our particular case, ice cores were directly transferred to pre-cleaned Teflon bags
just after collection and cutting. Once they were melted, 100 mL were transferred in precleaned
capped Erlenmeyer flasks, and extracted on board (in duplicate). Figure 2 shows that blank
chromatograms obtained from HPLC grade water extracted in the ship and those obtained in the
land-based laboratory were very similar, except for a big contribution of nonylphenol in boat
blanks (Figure 2 C). PAHs were detected in boat blanks and at lower level, in laboratory blanks.
Organohalogenated compounds were not present in any blank sample, indicating that possible
external sample contamination from the ship’s atmosphere, which may contain e.g. PCBs [23],
was not detected. To control carry over effects, empty Twister Desorption Liners were also
analyzed (Figure 2 A) and they showed no memory effects.
In the context of the ice sampling procedure, since the ice coring device system was
running with gasoline, high levels of PAHs were detected in the analyzed ice samples, with no
9
clear apparent patterns. Due to this external source of contamination, PAHs were not quantified
in ice core samples.
3.5. Utility of the method to detect POPs in Arctic ice cores
POPs were detected in the ice cores collected in the Arctic ATOS expedition in summer
2007 (Table 4), thus proving the utility of the method to reach the pg/L concentration. Levels
varied between 0.5 and 258 pg/L with concentrations in surface ice cores (0-20 cm) not
differing statistically from concentrations in deep ice cores (80-100 cm) (t-test one side, p =
0.05). Also, there was no significant difference among POP concentrations in the 7 sampling
locations, given their proximity. Figure 3 shows a SIM chromatogram corresponding to an ice
sample, with specific traces for PBDE 47 and 99 as an example, where the different ions with
their specific abundance show the identification capabilities of the developed method.
Among OC pesticides, α-HCH was present in all samples and its mean concentration
was of 141±83 pg/L. α-HCH has been used in large amounts worldwide and although a global
decrease in its use has been observed since 1962 [15], it has been detected in the Arctic
atmosphere at concentrations of 0.25-747 pg/m3 [1]. DDTs were detected in a fewer number of
samples at a mean concentration of 44±32 pg/L. Only the main 4,4’-DDT isomers from
technical DDT were identified in Arctic ice at levels from 4.7 to 117 pg/L. In most sites, 4,4’DDT concentrations were higher than their main metabolites, indicating no degradation of this
still in-use pesticide. Drins, HCB and heptachlor were not detected in ice cores in agreement
with their reduced usage worldwide. Concentrations and patterns of OC pesticides detected in
Arctic waters using 200 mL of melt water are consistent with the levels of OC pesticide found
in other parts of the world using other methods (Table 5).
In the ATOS campaign, the presence of PCB 118, 101 and 28 in a lesser extent
dominated among all the PCB7 analyzed (Table 4). The presence of these more volatile PCBs is
in agreement with the global distillation effect, which suggests the worldwide transport of
lighter compounds to remote areas where atmosphere-surface water exchange takes place [24,
25]. The mean PCB3 concentration in ice melt water was of 20 ± 22 pg/L. These levels range
within those reported earlier. In a pioneering study performed in 1983, Tanabe et al. detected
PCB between 310 and 610 pg/L in Antarctic ice by extracting 200-1200 L of water [10]. By
extracting 180-200 kg of ice, concentrations of 2-15 pg/L and 3-40 pg/L of PCB15 in the ice
dissolved and particulate fraction, respectively, were detected in the Arctic Marginal Ice Zone,
with predominance of PCB 52 [4]. Other studies detected PCB9 concentrations between 200
and 700 pg/L in Ob-Yenisey River (Arctic) watershed by extracting 1 L of water [26]. A study
from an Italian Alps glacier reports PCB15 between 10 and 195 pg/L by extracting 0.6 L of
10
melt water [27] and very recently, SBSE-GC/MS has been proven to detect PCBs in snow from
the Aconcagua mountains (South America), at levels up to 330 pg/L with predominance of 4 to
6 chlorinated congeners [28].
In this study, we provide first evidence for the presence of PBDEs in Arctic ice. Only
PBDE 47 and 99 were detected, coinciding with the main congeners present in technical penta
PBDE formulations used in a wide array of products such as building materials, electronic
devices, furnishings, motor vehicles, plastics, polyurethane foams, and textiles [29]. PBDE
concentrations ranged between 0.5 and 2.3 pg/L, and they were in general 1 or 2 orders of
magnitude lower than for PCBs, according to their more recent and moderate usage [29]. Only a
very recent study on PBDEs in snow from the Alps, reported PBDEs 47, 99, 100, 153 and 183
at levels between 5.2 and 56 pg/L [12], more than 10-fold higher concentrations than the ones
detected in our ice samples.
Comparison of the POP levels detected in this study (Table 4) with those values
previously reported from ice elsewhere (Table 5), indicate that the procedure developed here
yield results analogous to those obtained using other analytical methods which in general extract
higher melt water volumes. The additional ability of the proposed method to monitor several
chemical families in Arctic ice may provide a comprehensive survey on the loads of POPs
stored in ice. Since the method can process many samples, it is envisaged that it can be used to
generate large data sets which can then contribute to evaluate the release of contaminants into
the Arctic ecosystem and to study their bioavailability and associated risks for the receiving
ecosystems [30].
3.6. Advantages of in situ SBSE extraction on board of oceanographic vessels
The use of SBSE for in situ extraction of POPs in ice cores improve the following
issues:
1. Sampling: the method used here only needs 200 mL of ice samples to detect POPs,
compared to much higher sample volumes needed in more conventional sample extraction
systems (up to 1200 L, see table 5). Given the higher sensitivity of the new generation of GCMS equipment, extracted water volumes may be decreased while preserving the LODs. This in
turn facilitates sampling procedures in such harsh environment as in the Arctic.
2. Storage space: by extracting the samples on board of the research vessel (30 samples
each 24 h), sample throughput is enormously enhanced and sample transport drastically
reduced. This leads also to optimization of cool room space since ice is “stored” in little SBSE
rods in a refrigerator.
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3. External sample contamination: sample manipulation is minimized and this leads to
improved performance in quality analysis since the risk of sample contamination is reduced.
Finally, our initial intention was to install and evaluate the performance of a SBSE-GCMS on board of the R/V Hespérides. Although unfortunately this ideal situation could not be
achieved, the results presented here demonstrate that by doing the SBSE extraction step on
board, the number of samples extracted during a sampling campaign can be enormously
increased (we extracted 200 samples within 1 month cruise, including ice and water). Thus the
efficiency as regards to number of samples analyzed and space requirements on board during
the cruise campaign can be considerably improved.
4. Conclusions
This paper describes the potential use of the SBSE method to extract POPs from Arctic
ice. We have demonstrated that the on board in situ SBSE extraction of 200 mL of ice samples
together with the careful optimization of MS acquisitions parameters can lead to detection limits
down to the low pg/L levels. This very high sensitivity allowed the detection of the main POPs
in Arctic ice, with concentrations detected within the range of those values previously reported
in ice from other parts of the world (Table 5). The method described here is easily applicable on
board of research oceanographic vessels, and can considerably simplify the technical challenges
associated with the resolution and quantification of POP loads in Arctic ice. Provided the
present and future conditions toward extensive melting of Arctic ice, and the toxicological risks
associated with the release of POPs towards that rich and vulnerable ecosystem, we believe that
the analytical procedure described here can trigger an additional stimulus and an alternative
methodology for the determination of POPs in Arctic ice. The results obtained in this study
confirm that in spite of the established legislations for POPs, they are detected in Arctic ice in
quantifiable amounts and thus, studies to evaluate their presence and potential risk are justified
and should be prompted.
Acknowledgements
This research is a contribution to the ATOS project, funded by the Ministry of
Education (ref. POL2006-00550/CTM). J. Dachs, N. Berrojalbiz and M. J. Ojeda are thanked
for technical support before the campaign and T. Davila for assisting in the MS processing. The
crew of R/V Hespérides and our colleagues are sincerely acknowledged for their assistance and
for ensuring a successful and pleasant cruise.
12
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13
Table 1. GC-EI-MS SIM mass spectral data with compounds listed in elution order, with
retention time window (SIM window, min), retention time (Rt), and the ions (m/z) used for
identification. Quantification ions are m/z 1 plus m/z 2. Surrogates are indicated in italics.
Compound
Naphthalene-d8
Naphthalene
Acenaphthylene-d8
Acenaphthylene
Acenaphthtene-d10
Acenaphthene
Fluorene
HCB
α-HCH
β -HCH
Lindane
Phenanthrene-d10
Phenanthrene
Anthracene
-HCH
PCB 28
Heptachlor
PBC 52
PCB 65
Aldrin
Heptachlor epoxide
Fluoranthene
Pyrene
PCB 101
α -endosulfan
2,4'-DDE
4,4’-DDE
Dieldrin
2,4'-DDD
Endrin
β -endosulfan
BDE 28
PCB 118
4,4’-DDD
2,4'-DDT
PCB 138
4,4-DDT
PCB 153
Benzo(a)anthracene
Chrysene
Chrysene-d12
PCB 200
PCB 180
BDE 47
BDE 100
Benzo(b)fluoranthene
Benzo(k)fluoranthene
BDE 99
Benzo(a)pyrene
Perylene-d12
BDE 154
BDE 153
BDE 183
Indeno(123cd)pyrene
Dibenzo(ah)anthracene
Benzo(ghi)perylene
SIM window
4.5-6.95
6.95-8.21
8.21-9.31
9.31-11.5
11.18-13.57
13.57-14.40
14.40-15.16
15.16-16.38
16.38-17.40
17.40-18.18
18.18-19.79
19.79-21.65
21.65-23.34
23.34-24.57
24.57-24.96
24.96-26.64
26.64-27.82
27.82-29.05
29.05-30.72
30.72-31.92
31.92-32.84
32.84-34.05
34.05-35.17
35.17-36.05
36.05-37.22
37.22-38.77
38.77-end
Rt (min)
5.39
5.42
8.10
8.12
8.39
8.47
9.95
12.37
12.02
12.91
13.44
13.70
13.85
14.07
14.67
16.14
16.76
17.94
18.47
18.50
20.82
20.90
22.26
22.66
22.66
22.58
23.81
24.08
24.54
24.78
25.18
25.30
25.39
25.72
25.72
26.23
27.12
27.17
28.41
28.41
28.46
28.93
29.25
29.33
31.48
32.21
32.28
32.33
33.23
33.46
34.45
35.75
36.46
38.01
38.26
39.29
m/z 1
m/z 2
m/z 3
m/z 4
128.1
127.1
129.1
102.1
152.1
151.1
153.1
76
153.9
166.1
283.7
180.9
182.9
180.9
188
178.1
178.1
180.9
255.8
271.8
291.8
291.7
262.9
352.8
202.1
202.1
325.7
194.9
245.8
245.8
79.1
234.9
262.9
194.9
245.8
325.5
235
234.8
359.7
235
359.7
228.1
228.1
240
429.6
393.7
485.7
403.7
252.1
252.1
403.7
252.1
264.2
483.6
483.6
483.6
276.1
278.1
276.1
152.9
167.1
285.7
218.9
218.9
182.9
187
176.1
176.1
218.9
257.8
100.0
289.8
289.7
66.1
81.0
200.1
200.1
327.7
206.9
247.8
317.9
262.9
236.8
81.0
206.9
247.8
327.5
237
236.8
361.7
237
361.7
226.1
226.1
151.9
82.4
248.7
182.9
180.9
218.9
250.7
111.0
152.1
152.1
182.9
185.9
273.8
219.8
219.8
260.9
354.8
203.1
203.1
253.8
240.9
317.8
175.9
276.9
164.9
244.9
236.9
405.6
253.8
165
164.9
289.7
165
289.8
229.1
229.1
89
89
109
427.6
395.7
487.7
563.6
250.1
250.1
563.6
250.1
260.1
643.5
643.5
643.5
274.1
276.1
274.1
357.7
323.7
325.8
405.7
253.1
253.1
405.7
253.1
287.7
325.7
327.8
565.6
485.6
485.6
485.6
277.1
279.1
277.1
645.5
645.5
645.4
138
139
138
236.8
221.8
221.7
292.9
262.8
101
255.8
264.9
175.9
247.8
236.8
316.9
264.9
407.7
255.8
199
291.8
199
291.7
565.6
126
14
Table 2. Quality parameters obtained for the linear calibration of the SBSE-GC-EI-MS method,
with their slopes (aX), offsets (b), and correlation coefficients (R2) over a concentration range of
1-900 pg/L (1-1800 pg/L for PAHs); percentages of recovery and standard deviation (% R±SD)
with seawater spiked at 10 pg/L (n=4); reproducibility as % coefficient of variation (% CV); and
LODs (pg/L).
Compound
Acenaphthylene
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzo(a)pyrene
Indeno(123cd)pyrene
Dibenzo(ah)anthracene
Benzo(ghi)perylene
4,4-DDE
4,4-DDD
4,4-DDT
2,4'-DDE
2,4'-DDD
2,4'-DDT
HCB
α-HCH
Lindane
β-HCH
Aldrin
Dieldrin
Endrin
Heptachlor
Heptachlor epoxide
PCB 28
PCB 101
PCB 118
PCB 138
PCB 153
PCB 180
BDE 28
BDE 47
BDE 100
BDE 99
BDE 154
BDE 153
BDE 183
Calibration
aX
b
12.28 11267
19.27 1898
9.112 368
41.86 16094
41.28 3051
59.08 9878
62.09 16004
62.96 11241
39.77 13518
71.30 9183
76.80 10835
62.50 7736
53.11 10045
41.70 8339
34.57 8871
649
325
2215
1577
14.4
5261
734
37.5
938
127
1991
-912
515.4 242.9
64.81 -43.7
55.21 530
1.202 260
237.9 632
41.50 23.37
5.63
10.5
190.7 85.3
152.5 620
32.15 15571
18.92 251
25.70 1389
22.16 329
19.91 290
20.54 275
3.061 354
2.613 254
390.4 -289
71.51 467
18.51 -1.04
17.33 12.41
28.12 27.41
R2
%R±SD
% CV
0.9524
0.9748
0.9608
0.9905
0.9996
0.9953
0.9915
0.9909
0.9959
0.9980
0.9933
0.9941
0.9980
0.9856
0.9904
0.9985
0.9911
0.9928
0.9998
0.9998
0.9997
0.9984
0.9670
0.9988
0.9944
0.9844
0.9952
0.9949
0.9994
0.9996
0.9956
0.9996
0.9889
0.9995
0.9997
0.9991
0.9967
0.9920
0.9995
0.9997
0.9997
0.9996
0.9967
n.r.
n.r.
n.r.
139±9
89±7
127±10
112±13
82±6
93±7
87±4
71±2
79±1
91±12
95±10
114±25
111±15
94±11
105±17
106±12
102±16
106±7
109±16
102±15
107±7
27±8
51±15
110±10
108±14
50±10
53±9
101±16
103±12
79±28
108±12
108±15
100±16
90±14
107±12
107±10
106±12
107±9
108±10
105±14
7
20
2
9
6
10
6
7
10
2
3
5
6
6
11
3
5
3
3
4
6
8
4
5
28
6
5
4
5
19
10
9
9
8
8
12
4
1
2
2
3
3
11
LOD
pg/L
432*
102*
390*
891*
318*
572*
545*
612*
555*
342*
343*
382*
507*
515*
154*
1.2
2.5
3.5
0.1
4.5
1.5
0.4
1.8
0.5
15
1.2
0.6
0.8
0.6
0.3
0.5
0.3
0.3
8.5
7.0
11
48
0.1
99
0.2
0.2
0.2
0.5
* LOD for PAHs were calculated as 3*SD of boat blank levels (n=3). Naphthalene and PCB 52
were not linear over the concentration range studied in this work and not included in the table.
15
Table 3. Recoveries (% R) and reproducibility (% CV) obtained in the analysis of the surrogate
standards immediately after spiking HPLC grade water at 500 pg/L for PAHs and 100 ng/L for
PCBs (n=3), and in ice cores 1 to 4 (both extremes, n=8) after extraction with SBSE and storage
at 4ºC for 4 months.
Surrogate standard
Naphthalene-d8
Acenaphthylene-d8
Acenaphthene-d10
Phenanthrene-d10
Chrysene-d12
Perylene-d12
PCB 65
PCB 200
Immediately after
spiking
(HPLC water)
%R
% CV
n.r.
n.r
n.r.
n.r.
112
9
100
4
99
2
98
2
102
3
95
7
After 4 month storage
(ice cores)
%R
n.r.
n.r.
42
89
71
121
97
47
% CV
n.r.
n.r.
22
15
7
24
7
23
n.r. = not recovered.
Footnote: in ice cores, surrogate standard recovery correspond to both dissolved and
particulate phase of melt water.
16
Table 4. Concentration levels of target organochlorinated pesticides, PCBs and PBDEs (pg/L) in
superficial (S) and deep (D) ice cores from the Arctic Ocean collected in July 2007. Compounds
not included in the table were not detected. Sample codes as in Figure 1.
Compounds
α-HCH
4, 4’-DDT
4, 4’-DDE
4, 4’-DDD+2,4’-DDT
PCB 28
PCB 101
PCB 118
PBDE 47
PBDE 99
Core 1
S
D
72
51
Int. Int.
Int. n.d.
n.d. 34
n.d. n.d.
22 n.d.
2.2 n.d.
0.8 0.9
0.5 0.5
Core 2
S
D
129 230
81
116
15
15
73
18
n.d. n.d.
1.5
7.3
n.d. n.d.
2.2
2.3
1.5
1.6
Core 3
S
D
94
55
70
80
n.d. n.d.
n.d. n.d.
30
14
22
21
13
14
0.5 n.d.
n.d. n.d.
Core 4
S
D
253 172
43 117
n.d. n.d.
n.d. n.d.
n.d. n.d.
1.9 n.d.
n.d. n.d.
0.9
0
0.6 0.5
Core 5
S
D
88
0.8
35 n.d.
19
4.7
n.d. n.d.
n.d. n.d.
2.5 n.d.
16 n.d.
0.7 0.4
0.7 n.d.
Core 6
S
D
155 221
37
20
26
19
n.d. n.d.
n.d. n.d.
11 n.d.
98 n.d.
0.5 n.d.
0.5 n.d.
Core 7
S
D
200 258
21 n.d.
33
29
n.d. 62
n.d. n.d.
28
16
42
25
n.d. n.d.
n.d. n.d.
Int. = interference in this specific sample
n.d.= not detected
17
Table 5. Selected studies indicating POP concentrations (pg/L) in ice with indication of the
amount of extracted (in L) and of the used preconcentration technique.
L extracted
HCHs
DDTs
PCBs
HCB
PBDEs
This study
(Arctic)
0.2 L, SBSE
0.8-258 αHCH
4.7-117
1.5-98
n.d.
0.5-2.2
Tanabe et al.,
1983 (Antarctic)
200-1200 L,
XAD2 SPE
2000-2200
ΣHCH
9.8-11
ΣDDTs
310-610
ΣPCBs
n.a.
n.a.
Gustafsson et
al., 2005
(Barents Sea)
180-200 kg
n.a.
n.a.
0.04-6.44
n.a.
n.a.
Chiuchiolo et
al., 2004
(Antarctic)
100-130 L,
particulate
matter
10-40 (α
and 
HCH)
5-78
n.a.
n.a.
n.a.
Usenko et al.,
2005 (Oregon
Cascades)
50 L,
Speedisk
77.8
n.a.
n.a.
n.a.
n.a.
Donald et al.,
1999 (Alberta
glacier)
20 L water-eq,
LLE
30-1000
10-50 ΣDDTs
n.a.
25
n.a.
Melnikov et al.,
2003 (Ob
Yenisey River)
1 L, LLE
500-1100
ΣHCH
200-1400
ΣDDTs
100-700
ΣPCBs
n.a.
n.a.
Villa et al., 2003
(Alpine glacier)
0.6-1 L, LLE
1000
1000-3000
4,4’-DDT
n.a.
500
n.a.
Villa et al., 2006
(Alpine glacier)
0.6 L, LLE
120-2435
(-HCH)
59-547
ΣDDTs
585-1994
ΣPCBs
21-168
n.a.
0.035 L,
SPME
500-6500
α-HCH
100-1800
ΣDDTs
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
5.2-38*
n.a.
n.a.
n.d.-330
n.a.
n.a.
Wang et al.,
2008 (Central
Himalaya)
Quiroz et al.,
2008
(Alps/Tatra
Mountains)*
Quiroz et al.,
2009
(Aconcagua)*
1-6 L,
SPE
40 mL
n.d. = not detected; n.a. = not analyzed; * = snow
18
Figure Legends
Figure 1. Map showing the locations where ice cores were sampled during the Arctic ATOS
campaign carried out in July 2007.
Figure 2. GC-EI-MS chromatograms of different blank samples: (A) empty Twister Desorption
lines, (B) laboratory SBSE, and (C) boat SBSE. Surrogate standards are indicated in italics.
Figure 3. GC-EI-MS chromatogram of an ice core sample (Surface Ice 6) with the specific ion
traces for PBDE 47 and 99 and their mass spectrum, to provide unequivocal identification.
19