Ultra-trace determination of Persistent Organic Pollutants in Arctic ice using stir bar sorptive extraction and gas chromatography coupled to mass spectrometry

Journal of Chromatography A, 1216 (2009) 8581–8589

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Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma

Ultra-trace determination of Persistent Organic Pollutants in Arctic ice using stir bar sorptive extraction and gas chromatography coupled to mass spectrometry S. Lacorte a,∗ , J. Quintana b , R. Tauler a , F. Ventura b , A. Tovar-Sánchez c , C.M. Duarte c a b c

Department of Environmental Chemistry, IDAEA-CSIC, Jordi Girona 18-26, 08034 Barcelona, Catalonia, Spain AGBAR Aigües de Barcelona, Av. General Batet 4, 08028 Barcelona, Catalonia, Spain Department of Global Change Research, IMEDEA-CSIC-UIB, Miquel Marqués 21, 07190 Esporles, Mallorca, Spain

a r t i c l e

i n f o

Article history: Received 11 August 2009 Received in revised form 7 October 2009 Accepted 9 October 2009 Available online 14 October 2009 Keywords: Artic ice Persistent Organic Pollutants Stir bar sorptive extraction Gas chromatography Mass spectrometry

a b s t r a c t This 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. ␣-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. © 2009 Elsevier B.V. All rights reserved.

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 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

∗ Corresponding author. Tel.: +34 934006133; fax: +34 932045904. E-mail address: [email protected] (S. Lacorte). 0021-9673/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2009.10.029

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 was reconstituted in 100 ␮L 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. 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. collected 200 L of ice which was melted on an ice-melter and using LLE, levels of 0.005–0.44 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 was preconcentrated and yielded LODs between 0.63 and 27 pg/L for polybromodiphenyl 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%

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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

SIM window

m/z 1

m/z 2

m/z 3

m/z 4

Naphthalene-d8 Naphthalene

4.5–6.95

Rt (min) 5.39 5.42

128.1

127.1

129.1

102.1

Acenaphthylene-d8 Acenaphthylene

6.95–8.21

8.10 8.12

152.1

151.1

153.1

76

Acenaphthtene-d10 Acenaphthene

8.21–9.31

8.39 8.47

153.9

152.9

151.9

Fluorene

9.31–11.5

9.95

166.1

167.1

82.4

HCB ␣-HCH ␤-HCH Lindane

11.18–13.57

12.37 12.02 12.91 13.44

283.7 180.9 182.9 180.9

285.7 218.9 218.9 182.9

248.7 182.9 180.9 218.9

250.7 111.0

Phenanthrene-d10 Phenanthrene Anthracene

13.57–14.40

13.70 13.85 14.07

188 178.1 178.1

187 176.1 176.1

152.1 152.1

89 89

␦-HCH PCB 28 Heptachlor PCB 52 PCB 65 Aldrin

14.40–15.16 15.16–16.38 16.38–17.40 17.40–18.18 18.18–19.79

14.67 16.14 16.76 17.94 18.47 18.50

180.9 255.8 271.8 291.8 291.7 262.9

218.9 257.8 100.0 289.8 289.7 66.1

182.9 185.9 273.8 219.8 219.8 260.9

109 236.8 221.8 221.7 292.9

Heptachlor epoxide Fluoranthene

19.79–21.65

20.82 20.90

352.8 202.1

81.0 200.1

354.8 203.1

262.8 101

Pyrene PCB 101 ␣-Endosulfan 2,4 -DDE 4,4 -DDE

21.65–23.34

22.26 22.66 22.66 22.58 23.81

202.1 325.7 194.9 245.8 245.8

200.1 327.7 206.9 247.8 317.9

203.1 253.8 240.9 317.8 175.9

255.8 264.9 175.9 247.8

Dieldrin 2,4 -DDD

23.34–24.57

24.08 24.54

79.1 234.9

262.9 236.8

276.9 164.9

236.8

Endrin

24.57–24.96

24.78

262.9

81.0

244.9

316.9

␤-Endosulfan BDE 28 PCB 118 4,4 -DDD 2,4 -DDT PCB 138

24.96–26.64

25.18 25.30 25.39 25.72 25.72 26.23

194.9 245.8 325.5 235 234.8 359.7

206.9 247.8 327.5 237 236.8 361.7

236.9 405.6 253.8 165 164.9 289.7

264.9 407.7 255.8 199

4,4-DDT PCB 153

26.64–27.82

27.12 27.17

235 359.7

237 361.7

165 289.8

199 291.7

Benzo(a)anthracene Chrysene Chrysene-d12 PCB 200

27.82–29.05

28.41 28.41 28.46 28.93

228.1 228.1 240 429.6

226.1 226.1

229.1 229.1

427.6

357.7

287.7

PCB 180 BDE 47

29.05–30.72

29.25 29.33

393.7 485.7

395.7 487.7

323.7 325.8

325.7 327.8

291.8

BDE 100

30.72–31.92

31.48

403.7

563.6

405.7

565.6

Benzo(b)fluoranthene Benzo(k)fluoranthene BDE 99

31.92–32.84

32.21 32.28 32.33

252.1 252.1 403.7

250.1 250.1 563.6

253.1 253.1 405.7

565.6

Benzo(a)pyrene Perylene-d12

32.84–34.05

33.23 33.46

252.1 264.2

250.1 260.1

253.1

126

BDE 154 BDE 153 BDE 183

34.05–35.17 35.17–36.05 36.05–37.22

34.45 35.75 36.46

483.6 483.6 483.6

643.5 643.5 643.5

485.6 485.6 485.6

645.5 645.5 645.4

Indeno(123cd)pyrene Dibenzo(ah)anthracene

37.22–38.77

38.01 38.26

276.1 278.1

274.1 276.1

277.1 279.1

138 139

Benzo(ghi)perylene

38.77–end

39.29

276.1

274.1

277.1

138

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 use solvent-

less 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

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Fig. 1. Map showing the locations where ice cores were sampled during the Arctic ATOS campaign carried out in July 2007.

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–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 2007–2008). 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 four 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.

these compounds contained naphthalene-d8 , acenaphthylene-d8 , acenaphthene-d10 , phenanthrene-d10 , chrysene-d12 and perylened12 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 ␮g/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). 2.2. Sampling area

2. Experimental

The cruise was conducted on board of the Spanish Research Vessel (R/V) “Hespérides” from June 28 to July 28, 2007, sailing from Iceland to the Fram Strait. Seven ice stations were sampled along the cruise track (Fig. 1), corresponding to multi-year ice ranging in thickness from 2 to 3 m. At each station, 1 m deep × 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 ◦ C until sectioned, typically within 2 h 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 ◦ C) until melted.

2.1. Chemicals and reagents

2.3. Extraction procedure

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

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

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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 ␮L 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 »KPDMS/W =

CPDMS mPDMS VW mPDMS = = ˇ CW mW VPDMS mW

where KPDMS/W is the distribution coefficient between polydimethylsiloxane and water; CPDMS and CW are the concentration of a solute in the polydimethylsiloxane phase and in the water, respectively; mPDMS and mW are the mass of the solute in the polydimethylsiloxane phase and in the aqueous phase, respectively and ˇ is the phase ratio (ˇ = Vw /VPDMS , which represents the volume of the 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 =

i KPDMD/W /ˇ i 1 + KPDMD/W /ˇ

× 100

If the KSBSE for any specific compound is substituted by its KOW , the theoretical percent recovery can be calculated. In our specific case, and using BDE 47 as an example, considering the KOW = 5.9 × 106 , the sample volume of 100 mL and the volume of the PDMS fiber of 126 ␮L, substituting these values to the above equation, we obtain: % R SBSE =

5.9 × 106 /(126/105 ) 1 + 5.9 × 106 /(126/105 )

× 100 ≈ 100

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 4 ◦ 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) was 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 (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 ◦ C (holding time 0.8 min) and then increased at 60 ◦ C/min to 280 ◦ C 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 ◦ C at 10 ◦ C/s and finally held during 7 min. An Agilent HP-5MS (30 m × 0.25 mm i.d. × 0.25 ␮m film thickness) capillary column was used. The oven temperature was programmed from 70 ◦ C (holding time 2 min) to 150 ◦ C at 25 ◦ C/min, to 200 ◦ C at 3 ◦ C/min and finally to 280 ◦ C at 8 ◦ C/min, keeping the final temperature for 10 min. Transfer line and ion source temperatures were 280 and 230 ◦ C, respectively. Data acquisition was performed simultaneously using full scan conditions over a mass range of 44–750 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 one to seven 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 two concentrations were measured only for PAHs) with internal standards at 500 pg for deuterated PAHs and 100 pg for PCBs. 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 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 and 300 pg/L, LODs were calculated using 3 times the standard deviation of three blanks. All target compounds should undergo the following identification and confirmation criteria: (i) each compound was identified using at least three 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

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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 ␣-HCH Lindane ␤-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

R2

Calibration aX

b

12.28 19.27 9.112 41.86 41.28 59.08 62.09 62.96 39.77 71.30 76.80 62.50 53.11 41.70 34.57 649 2215 14.4 734 938 1991 515.4 64.81 55.21 1.202 237.9 41.50 5.63 190.7 152.5 32.15 18.92 25.70 22.16 19.91 20.54 3.061 2.613 390.4 71.51 18.51 17.33 28.12

11,267 1,898 368 16,094 3,051 9,878 16,004 11,241 13,518 9,183 10,835 7,736 10,045 8,339 8,871 325 1,577 5,261 37.5 127 −912 242.9 −43.7 530 260 632 23.37 10.5 85.3 620 15,571 251 1,389 329 290 275 354 254 −289 467 −1.04 12.41 27.41

% R ± SD

% CV

LOD pg/L

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

432a 102a 390a 891a 318a 572a 545a 612a 555a 342a 343a 382a 507a 515a 154a 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

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

a LOD for PAHs was 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.

for the sum of two 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 (Fig. 2). Due to the nature of compounds, three coelutions were observed: (i) PCB 101 and ␣-endosulfan, which could be resolved at their specific m/z and fully identified using three or four 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 are given as the sum of both compounds.

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 1–4 (both extremes, n = 8) after extraction with SBSE and storage at 4 ◦ C 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)

After 4 month storage (ice cores)

%R

% CV

%R

% CV

n.r. n.r. 112 100

n.r. n.r. 9 4 99 2 3 7

n.r. n.r. 42 89 2 121 97 47

n.r. n.r. 22 15 71 24 7 23

98 102 95

n.r. = not recovered. Footnote: in ice cores, surrogate standard recovery corresponds to both dissolved and particulate phase of melt water.

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ular ion, depending on the intensity of each. Table 2 provides the LODs obtained after pre-concentrating 200 mL of water spiked over 1–1800 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

Fig. 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.

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 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 4–14 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 partic-

At a 10 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 ␤-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 (Tables 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 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 naphthalene-d8 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.

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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 Fig. 1. Compounds

␣-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

Core 2

Core 3

Core 4

Core 5

Core 6

Core 7

S

D

S

D

S

D

S

D

S

D

S

D

S

D

72 Int. Int. n.d. n.d. 22 2.2 0.8 0.5

51 Int. n.d. 34 n.d. n.d. n.d. 0.9 0.5

129 81 15 73 n.d. 1.5 n.d. 2.2 1.5

230 116 15 18 n.d. 7.3 n.d. 2.3 1.6

94 70 n.d. n.d. 30 22 13 0.5 n.d.

55 80 n.d. n.d. 14 21 14 n.d. n.d.

253 43 n.d. n.d. n.d. 1.9 n.d. 0.9 0.6

172 117 n.d. n.d. n.d. n.d. n.d. 0 0.5

88 35 19 n.d. n.d. 2.5 16 0.7 0.7

0.8 n.d. 4.7 n.d. n.d. n.d. n.d. 0.4 n.d.

155 37 26 n.d. n.d. 11 98 0.5 0.5

221 20 19 n.d. n.d. n.d. n.d. n.d. n.d.

200 21 33 n.d. n.d. 28 42 n.d. n.d.

258 n.d. 29 62 n.d. 16 25 n.d. n.d.

Int. = interference in this specific sample; n.d. = not detected.

3.4. Blank analysis Ultra-trace analysis of POPs in Arctic ice requires that sample manipulation is minimized, which in turns avoids sample contamination and improves the precision of the analysis. In our particular case, ice cores were directly transferred to precleaned 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). Fig. 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 (Fig. 2C). 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 (Fig. 2A) 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 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 seven sampling locations, given their proximity. Fig. 3 shows a SIM chromatogram corresponding to an ice sample, with specific traces for PBDEs 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, ␣-HCH was present in all samples and its mean concentration was of 141 ± 83 pg/L. ␣-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 inuse 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 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 four to six chlorinated congeners [28]. In this study, we provide first evidence for the presence of PBDEs in Arctic ice. Only PBDEs 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 yields 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].

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Fig. 3. GC–EI-MS chromatogram of an ice core sample (Surface Ice 6) with the specific ion traces for PBDEs 47 and 99 and their mass spectrum, to provide unequivocal identification.

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.

This study (Arctic) Tanabe et al. [10] (Antarctic) Gustafsson et al. [4] (Barents Sea) Chiuchiolo et al. [2] (Antarctic) Usenko et al. [13] (Oregon Cascades) Donald et al. [6] (Alberta glacier) Melnikov et al. [26] (Ob-Yenisey River) Villa et al. [11] (Alpine glacier) Villa et al. [27] (Alpine glacier) Wang et al. [15] (Central Himalaya) Quiroz et al. [12] (Alps/Tatra Mountains)a Quiroz et al. [28] (Aconcagua)a n.d. = not detected; n.a. = not analyzed. a Snow.

L extracted

HCHs

DDTs

PCBs

HCB

PBDEs

0.2 L, SBSE 200–1200 L, XAD2 SPE 180–200 kg 100–130 L, particulate matter 50 L, speedisk 20 L water-eq., LLE 1 L, LLE 0.6–1 L, LLE 0.6 L, LLE 0.035 L, SPME 1–6 L, SPE 40 mL

0.8–258 ␣-HCH 2000–2200 HCH n.a. 10–40 (␣-and ␥-HCH)

4.7–117 9.8–11 DDTs n.a. 5–78

1.5–98 310–610 PCBs 0.04–6.44 n.a.

n.d. n.a. n.a. n.a.

0.5–2.2 n.a. n.a. n.a.

77.8 30–1000 500–1100 HCH 1000 120–2435 (␥-HCH) 500–6500 ␣-HCH n.a. n.a.

n.a. 10–50 DDTs 200–1400 DDTs 1000–3000 4,4 -DDT 59–547 DDTs 100–1800 DDTs n.a. n.a.

n.a. n.a. 100–700 PCBs n.a. 585–1994 PCBs n.a. n.a. n.d.–330

n.a. 25 n.a. 500 21–168 n.a. n.a. n.a.

n.a. n.a. n.a. n.a. n.a. n.a. 5.2–38a n.a.

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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 GC–MS 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. 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 an SBSE-GC–MS 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

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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). 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 help and for ensuring a successful and pleasant cruise. References [1] C.J. Halsall, R. Bailey, G.A. Stern, L.A. Barrie, P. Fellin, D.C.G. Muir, B. Rosenberg, F.Ya. Rovinski, E.Ya. Kononov, B. Pastukhov, Environ. Pollut. 102 (1998) 51. [2] A. Chiuchiolo, R.M. Dickhut, M.A. Cochran, H.W. Ducklow, Environ. Sci. Technol. 38 (2004) 3551. [3] A. Sobek, Ö. Gustafsson, Environ. Sci. Technol. 38 (2004) 2746. [4] Ö. Gustafsson, P. Andersson, J. Axwlman, T.D. Bucheli, P. Kömp, M.S. McLachlan, A. Sobek, J.O. Thörngren, Sci. Total Environ. 342 (2005) 261. [5] T. Meyer, Y. Duan Lei, I. Muradi, F. Wania, Environ. Sci. Technol. 43 (2009) 663. [6] D.B. Donald, J. Syrgiannis, R.W. Crosley, G. Holdworth, D.C.G. Muir, B. Rosenberg, A. Sole, D.W. Schindler, Environ. Sci. Technol. 33 (1999) 1794. [7] J. Van Oostdam, S.G. Donaldson, M. Feeley, D. Arnold, P. Ayotte, G. Bondy, L. Chan, É. Dewaily, C.M. Furgal, H. Kuhnlein, E. Loring, G. Muckle, E. Myles, O. Receveur, B. Tracy, U. Gill, S. Kalhok, Sci. Total Environ. 351–352 (2005) 165. [8] S.V. Nghiem, I.G. Rigor, D.K. Perovich, P. Clemente-Colón, J.W. Weatherly, G. Neumann, Geophys. Res. Lett. 34 (2007) L19504. [9] F. Wania, Environ. Sci. Technol. 40 (2006) 569. [10] S. Tanabe, H. Hidaka, R. Tatsukawa, Chemosphere 12 (1983) 277. [11] S. Villa, M. Vighi, V. Maggi, A. Finizio, E. Bolzacchini, J. Atmos. Chem. 46 (2003) 295. [12] R. Quiroz, L. Orellano, J.O. Grimalt, P. Fernandez, J. Chromatogr. A 1192 (2008) 147. [13] S. Usenko, K.J. Hageman, D.W. Schmedding, G.R. Wilson, S. Simonich, Environ. Sci. Technol. 39 (2005) 6006. [14] K. Booij, B. van Drooge, Chemosphere 44 (2001) 91. [15] X.P. Wang, B.Q. Xu, S.C. Kang, Z.Y. Cong, T.D. Yao, Atmos. Environ. 42 (2008) 6699. [16] E. Pérez-Carrera, V.M. León León, A. Gómez Parra, E. González-Mazo, J. Chromatogr. A 1170 (2007) 82. [17] P. Sandra, B. Tienpont, J. Vercammen, A. Tredoux, T. Sandra, F. David, J. Chromatogr. A 928 (1) (2001) 117. [18] E. Baltussen, P. Sandra, F. David, H.G. Janssen, C. Cramers, Anal. Chem. 71 (1999) 5213. [19] A. Prieto, O. Telleria, N. Etxebarria, L.A. Fernández, A. Usobiaga, O. Zuloaga, J. Chromatogr. A 1214 (2008) 1. [20] J. Sánchez, J. Quintana, R. Tauler, F. Ventura, C. M. Duarte, S. Lacorte, Mar. Pollut. Bull. (in press), doi:10.1016/j.marpolbul.2009.08.028. [21] S. Lacorte, I. Guiffard, D. Fraisse, D. Barceló, Anal. Chem. 72 (2000) 1430. [22] F.J. Santos, M.T. Galceran, Trends Anal. Chem. 21 (2002) 672. [23] R. Lohmann, K. Breivik, J. Dachs, D. Muir, Environ. Pollut. 150 (2007) 150. [24] T.N. Brown, F. Wania, Environ. Sci. Technol. 42 (2008) 5202. [25] P.A. Helm, T.F. Bidleman, H.H. Li, P. Fellin, Environ. Sci. Technol. 38 (2004) 5514. [26] S. Melnikov, J. Carroll, A. Gorshkov, S. Vlasov, S. Dahle, Sci. Total Environ. 306 (2003) 27. [27] S. Villa, C. Negrelli, V. Maggi, A. Finizio, M. Vighi, Ecotoxicol. Environ. Saf. 63 (2006) 17. [28] R. Quiroz, P. Popp, R. Barra, Environ. Chem. Lett. 7 (2009) 283. [29] C.A. De Wit, Chemosphere 46 (2002) 583. [30] T. Meyer, F. Wania, Water Res. 42 (2008) 1847.