Trace level determination of perfluorinated compounds in water by direct injection

Chemosphere 73 (2008) S24–S30

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Trace level determination of perfluorinated compounds in water by direct injection Vasile I. Furdui a,b, Patrick W. Crozier b, Eric J. Reiner b, Scott A. Mabury a,* a b

University of Toronto, Department of Chemistry, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6 Ontario Ministry of the Environment, Laboratory Services Branch, 125 Resources Road, Etobicoke, Ontario, Canada M9P 3V6

a r t i c l e

i n f o

Article history: Accepted 20 July 2007 Available online 23 May 2008 Keywords: Perfluorinated compounds PFOS PFOA Quantification bias Great Lakes

a b s t r a c t A new, fast LC–MS/MS method for the determination of perfluorinated surfactants in water samples by direct injection without pre-concentration is reported. The current method requires only 4 min to analyze nine perfluoroalkyl compounds in a single analytical run. Standard addition and internal standard quantification were used to determine the level of some perfluorinated carboxylic and sulfonic acids, including perfluorooctanoic sulfonate (PFOS) and perfluorooctanoic acid (PFOA), in Great Lakes water samples. Statistically significant differences were observed between the results obtained using different quantification methods. A relatively small difference between the PFOS values obtained with the standard addition method, with and without peak area normalization, clearly indicates that standard addition is the best quantification method when mass-labeled standards are not available. Based on the paired ttest statistical analysis, the concentrations calculated using external standardization were the least accurate, with the highest mean difference from the standard addition calculated values. Both PFOS and PFOA were present at less than 10 ng l 1 in all Great Lake samples. Higher levels were detected in tributaries of Lake Ontario and effluents from sewage treatment plants. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Considerable effort has been made in the last few years to determine the level of perfluorinated chemicals (PFCs) in the environment, particularly perfluoro-carboxylic acids (PFCA) and perfluoro-sulfonic acids (PFSA) (Kannan et al., 2001; Moody et al., 2001). The unique physicochemical properties of perfluorinated compounds have contributed to their considerable industrial and household use over the last 50 years. These chemicals are part of a large number of surface treatment and surfactant formulations such as fire-fighting foams, stain repellants, special cleaners, mining surfactants and insecticides. Perfluoroalkylated surfactants bind to blood proteins, influencing hormone feedback systems and cause a multitude of toxicological effects including thyroid/liver tumors, reproduction problems, reduction in cholesterol/triglyceride levels and changes in cell membrane permeability (Renner, 2001; Hekster et al., 2003; Schultz et al., 2003). Animal studies have shown that PFOS concentrations in liver and serum increase dramatically with exposure. Bioconcentration factors in fish can exceed 105, with the magnitude directly related to the alkyl chain length (Martin et al., 2003a,b). Once present in biota or ecosystems, most PFCs are extremely persistent, with no known degradation pathway. PFCs, including PFOS and PFOA, have been detected in human serum, * Corresponding author. Tel./fax: +1 416 978 3596. E-mail address: [email protected] (S.A. Mabury). 0045-6535/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2007.07.085

biota, sediments, sewage treatment plant sludge, dust and various surface waters, in both industrialized and remote locations throughout the world (Moriwaki et al., 2003; Kannan et al., 2004; Higgins et al., 2005). More recently longer chain PFCA were found in biota samples (Martin et al., 2004b). The First Worldwide Interlaboratory Study on Perfluorinated Compounds in Human and Environmental Matrices also showed significant differences between the results obtained in different laboratories analyzing the same samples (Lindström et al., 2005). Therefore, it is imperative to identify sources of the differences between analytical results and minimize them in the future. This paper reports the direct determination of PFCs from aqueous samples at the part-per-trillion (ppt) level, without the need for extraction/ concentration steps used in previous studies (Boulanger et al., 2004; Yamashita et al., 2004). The goal of this investigation was to determine the level of selected PFCs in water samples using a simple, fast, reliable method, with reduced manipulation of the original sample to minimize potential laboratory background contamination. This method incorporates 100 ll injections, since larger volume injections (500 ll) were used previously to determine these compounds in sewage treatment plant (STP) samples (Schultz et al., 2006). Previous studies about PFCs from the Great Lakes considered locations from Lake Ontario – Lake Erie (Boulanger et al., 2004; Sinclair et al., 2006) and Lake Michigan (Simcik and Dorweiler, 2005). We report results for nine perfluorinated contaminants including sulfonates, carboxylates and one sulfonamide in water samples from the Great Lakes, except Lake Michigan, as

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well as Lake Ontario tributaries and STP effluents. Statistically significant differences were observed between the results obtained using different quantification methods, particularly standard addition, internal and external standardization. 2. Experimental

bottles attached). PET bottles were rinsed twice with sample water before final filling and stored in the dark at 4 °C until analysis. A 300 ll aliquot of each water sample was mixed with an equal volume of MeOH containing the internal standards 13C2-PFOA and 13 C2-PFDA giving final concentrations of 20 fg ll 1 and 50 fg ll 1, respectively. The sample/MeOH mixtures were filtered using Mini-UniPrep syringeless filter devices having 0.2 lm polypropylene (PP) filter media and PP housings (Whatman, Forham Park, NJ, USA). Preliminary tests were also performed using 0.45 lm PP and 0.2 lm Nylon Mini-UniPrep syringeless filter devices. TM

2.1. Standards and chemicals Potassium perfluorohexane sulfonate (PFHxS, 99.9%), potassium PFOS (86.4%) and heptadecafluorooctane sulfonamide (PFOSA, 99.9%) were provided by the 3M Company (St. Paul, MN, USA). Standards of perfluoroheptanoic acid (PFHpA, 99%), PFOA (96%), perfluorononanoic acid (PFNA, 97%), perfluorodecanoic acid (PFDA, 98%), perfluoroundecanoic acid (PFUnA, 95%) and perfluorododecanoic acid (PFDoA, 95%) were purchased from Sigma–Aldrich (Oakville, ON, Canada). Optima grade methanol (MeOH) and HPLC grade water were obtained from Fisher Scientific (Toronto, ON, Canada). Two labeled standards, 13C mass-labeled PFOA (13C2-PFOA, Perkin–Elmer Life Sciences, Boston, MA, USA) and 13C mass-labeled PFDA (13C2-PFDA, Wellington Laboratories, Guelph, ON, Canada), were used as internal standards. 2.2. Water samples Samples (0.5–1.5 l) were collected at a depth of 1.5 m from Lake Ontario (LO-02, September 2002; LO-04, September and November 2004; LO-05, September 2005), Lake Erie (LE-04, November 2004), Lake Huron (LH-04, November 2004; LH-05, May 2005) and Lake Superior (LS-05, September 2005) at off-shore and near shore locations (Fig. 1). Water samples were also collected (April 2005) from three tributaries of Lake Ontario (Mimico Creek, Etobicoke Creek and Humber River) as well as final effluent samples from STPs (November–December 2004) from five locations in Southern Ontario (Toronto Main, Pickering, Highland Creek, Humber and Grand River) and one site in Northern Ontario (Kenora). Lake water samples were collected using a Teflon-free peristaltic pump with platinum cured silicon tubing or a Teflon-free polypropylene/ polycarbonate plastic Vandoren bottle and transferred to polyethylene terephthalate (PET) bottles having solid polyethylene screw caps. Tributary and STP grab samples were collected directly in PET bottles by gloved (nitrile) hand or extended metal pole (PET

TM

2.3. Instrumental analysis by LC/MS/MS Analysis of target analytes (PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA, PFHxS, PFOS and PFOSA) was performed using a high performance liquid chromatograph-tandem mass spectrometer system (HPLC-MS/MS), consisting of an unmodified Agilent 1100 Series liquid chromatograph coupled with a 4000QTRAP triple quadrupole mass spectrometer (Applied Biosystems – MDS Sciex, Concord, ON, Canada). Water and MeOH solvents (0.01 M ammonium acetate) were passed through an Agilent degasser and delivered by the binary pump system at a total flow rate of 250 ll min 1. One hundred microliter aliquots of the sample/ MeOH mixtures were injected with the Agilent autosampler through a C18 guard column (2 mm i.d.  4 mm, Phenomenex, Torrance, CA, USA) with chromatographic separation performed on a Genesis C18 column (2.1 mm i.d.  50 mm, 4 lm; Chromatographic Specialties, Brockville, ON, Canada). Target analyte separation was obtained in 4 min under isocratic conditions with a mobile phase consisting of 80% MeOH and 20% water. The mass spectrometer was operated in negative electrospray ionization multiple reaction monitoring (MRM) mode. Mass spectrometer source/gas (N2) related parameters were ion spray voltage 4500 V, turbo ion spray 60 psi at 400 °C, nebulizer gas 45 psi, curtain gas 10 psi, interface heater 100 °C and collision gas 3  10 5 Torr. MRM transition related parameters were optimized for each analyte, monitoring SO3F (m/z = 99) for sulfonates, SO2N (m/z = 78) for PFOSA and a loss of CO2 for carboxylates (Supplementary material, Table S1). Prior to this study the instrument was used only to analyze samples having less than 5000 ng l 1 of each perfluorinated compound, to avoid instrumental contamination.

LS-05-3

Hamilton Harbor

LS-05-2

Lake Superior

LO-05-2 LS-05-1 LH-05-1 LH-05-2 LH-05-3

LO-05-1

Lake Ontario

Lake Huron

Lake Ontario

LH-04-1 LO-04-3 LO-04-4 LO-04-1 LO-04-2 LO-04-5 LO-05-3 LO-05-2 LO-05-1

Lake Ontario LE-04-1

LO-02-1

LE-04-3

LE-04-2

Lake Erie

Fig. 1. Sampling locations.

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Quantification was performed using internal standard correction and standard additions. Standard mixtures containing 0.5, 1, 2, 5, 10, 20, 50 and 100 ng l 1 (fg ll 1) were used to create calibration curves for each analyte. Based on chromatographic retention times, peak area counts for PFHxS, PFOS, PFHpA, PFOA and PFNA were corrected using the 13C2-PFOA internal standard response and PFOSA, PFDA, PFUnA and PFDoA were corrected based on the 13 C2-PFDA internal standard response. The correlation coefficients R2 of the multipoint calibration equations varied between 0.9960 (PFDoA) and 0.9998 (PFNA and PFDA). For the sole purpose of enhancing the statistical comparison of quantification method results, multiple injections of replicate samples were done. Three replicates were analyzed for each sample, with four injections per replicate. The results reported for the standard addition method are based on the peak area counts from three replicates of the sample plus three standard additions (2, 5 and 10 ng l 1) injected four times, resulting in a total of 24 injections per sample. The STP samples were analyzed similarly, but with three higher level standard additions (10, 20 and 50 ng l 1). The limit of quantification (LOQ) represents the lowest analyte concentration required to produce a signal-to-noise (S/N) ratio of 10:1 in the water matrixes analyzed. The LOQ values varied between 0.3 for PFOSA and 1.6 ng l 1 for PFHpA (Table 1). Values determined below LOQ, but higher than the limit of detection (S/N > 3) were reported in brackets. 3. Results and discussion 3.1. Direct injection method The advantage of this new method is the lack of pre-concentration steps, which limits possible contamination and target compound losses. The isocratic conditions used for the separation, allowing a quick analysis (4 min) with low LOQs (14–80 fg on column) makes this method ideal for multi-sample monitoring requirements. The analysis was performed on an unmodified LC system, although it was suggested to replace the LC parts contain-

Table 1 Concentrations of perfluorinated substances (ng l

ing fluorinated residuals, including Teflon tubing (Yamashita et al., 2004). In this study only the Teflon filters were replaced with stainless steel filters in the solvent reservoir bottles. By using isocratic instead of gradient conditions, major modifications of the system could be avoided, since the analytes, particularly PFOA and PFNA, leach at a constant rate from the fluorinated components and maintain a uniform background. The relatively high level of PFOA reported for blanks in the previous studies (Boulanger et al., 2004; Yamashita et al., 2004) was not observed, since this direct injection method uses an isocratic separation instead of the gradient approach typically used (Fig. 2). A relatively large volume (100 ll) was injected from 50% MeOH solutions to facilitate target analyte focusing on the head of the analytical column and narrow the chromatographic peaks. The peaks obtained for a 10 ng l 1 standard had half-width at half-height between 3.7 s (PFHpA, TR = 1.44 min) and 7.5 s (PFDoA, TR = 3.34 min). Since a large volume was injected from non-buffered solutions, a disturbance in the background level of the chromatograms was observed between 0.5 and 1.4 min. The disturbance is smaller for standard samples containing no salts than for samples containing varying amounts of natural salts. The effect can be explained considering the difference between electrospraying from a buffered solution and a non-buffered plug of sample. All standards had no salt content and created a smaller disturbance compared with the water samples which had salts present at unknown levels (Supplementary material). No peaks were observed in the blanks when the volume injected was 10 ll or less. With larger injection volumes (e.g. 100 ll) the difference in MeOH content between the mobile phase (80%) and injected solution (50%) becomes more significant and produces a baseline shift disruption at the void volume and a small PFOA peak from the analytical system. The size of the background PFOA peak observed in the blank is directly related to the injection volume and the difference in MeOH content between the sample injected and the mobile phase. Although a 100 ll injection of 80% MeOH solution created no background peak and minimal baseline disruption for all analytes, the samples were not introduced at this level

1

) determined with the standard addition method for Great Lakes water samples

Sample

Date

PFHxS

PFOS

PFOSA

PFHpA

PFOA

PFNA

PFDA

PFUnA

PFDoA

LO-02-1 LO-04-1 LO-04-2

09/2002 09/2004 09/2004 11/2004 09/2004 11/2004 09/2004 11/2004 09/2005 09/2005 09/2005 11/2004 11/2004 11/2004 11/2004 11/2004 11/2004 05/2005 05/2005 05/2005 09/2005 09/2005 09/2005

nd nd nd (0.5) (0.7) (0.6) nd 1.8 (0.5) nd nd nd 1.8 (0.4) (0.7) (0.1) (1.1) nd nd (0.4) nd nd nd 1.4

6.6 6.8 3.6 8.4 6.8 4.9 7.1 5.4 37.6 3.6 4.8 5.3 4.2 4.0 2.0 3.2 2.9 1.2 1.2 1.8 (0.3) (0.1) (0.3) 0.5

nd (0.2) (0.1) (0.1) (0.1) nd (0.1) (0.1) 0.6 0.5 (0.1) (0.2) 0.6 nd nd (0.2) nd 0.3 0.4 (0.1) nd (0.2) (0.1) 0.3

nd nd nd nd nd nd nd nd (0.8) (0.9) 2.1 nd nd nd nd nd nd (0.4) nd nd nd (0.2) nd 1.6

5.9 6.7 3.3 2.9 2.5 5.7 2.3 2.0 6.4 2.0 1.8 1.6 2.2 1.9 (0.9) (0.1) (0.4) (0.4) (1.1) (0.4) (0.2) (0.5) (1.2) 1.3

2.0 (0.9) (1.0) (0.3) (0.6) (0.7) (0.7) (0.4) 1.9 (1.0) (0.7) (0.5) (0.3) (0.5) nd nd (0.3) 1.7 1.3 1.4 nd nd nd 1.2

nd (0.1) nd nd nd nd nd nd 1.5 2.4 0.8 nd nd nd nd nd nd 0.9 1.0 (0.5) nd (0.2) (0.1) 0.8

(0.1) (0.1) nd nd (0.1) nd nd (0.2) (0.8) (0.3) nd nd nd nd nd nd nd 1.0 (0.5) 1.2 nd (0.1) nd 1.4

(0.6) (0.1) 1.2 nd nd (0.7) (0.1) nd 2.0 (0.2) nd nd (0.3) nd nd (0.4) nd 2.4 1.1 2.6 nd nd nd 0.9

LO-04-3 LO-04-4 LO-04-5 LO-05-1 LO-05-2 LO-05-3 LE-04-1 LE-04-2 LE-04-3 LH-04-1

LH-05-1 LH-05-2 LH-05-3 LS-05-1 LS-05-2 LS-05-3 LOQ

LOQ = limit of quantification (ng/l). () = analytes detected with S/N > 3, but at levels lower than LOQ. nd = not detected.

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1.42 min

PFHxS Max. 3679 cps.

1.75 min

PFOS Max. 1850 cps.

2.42 min

PFOSA Max. 8937 cps.

S27

losses on the filtering media, reduce PFCs adsorption on particles and maintain low LOQs for all analytes. Nine Lake Superior water samples spiked at 5 ng l 1 and 50 ng l 1 gave average PFOS/PFOA recoveries of 92%/106% and 97%/94%, respectively. Target analytes were completely retained on the filtering media when samples with low PFCs levels (1–10 fg ll 1) were injected from solutions with less than 10% MeOH content. Matrix effects were observed in all field samples tested based on monitoring the peak area counts of the two internal standards. The analytes with less retention were more affected, including the 13 C2-PFOA internal standard. The effect was less evident for the second internal standard 13C2-PFDA. The decrease in response for the mass-labeled analytes is a good indication of matrix effects, since they are not present in any real sample and are quantitatively added to all samples, and their response is only affected by the sample composition. 3.2. Comparison between different quantification methods

1.44 min

PFHpA Max. 9112 cps.

1.58 min

PFOA Max. 15000 cps.

1.78 min

PFNA Max. 7810 cps.

2.10 min

PFDA Max. 5260 cps.

2.59 min

PFUnA

The results obtained using different quantification methods were compared in order to explain significant differences between the results obtained by different laboratories analyzing the same samples in an intercalibration study (Lindström et al., 2005), and also between reported concentrations from another study (Boulanger et al., 2004) and our findings. We focused on determining and explaining quantification method based differences, using only one chromatographic separation method. Separation method based differences were not investigated in this study. Standard addition and internal standard methods were used to quantify the analytes. For both methods, 13C2-PFOA was used as an internal standard for PFOA and PFOS. The differences between the PFOS values obtained with the standard addition and internal standard quantification methods were smaller for Lake Ontario samples, than for more complex samples with higher levels of dissolved matter and organic content (tributaries and STP samples), although there is no stoichiometric relationship between the dissolved matter sample content and the difference between PFOS values. The values of PFOS determined with the internal standard were usually higher than the values determined with the standard addition method (Fig. 3), generally showing a statistically significant difference. The significant differences between the values determined for PFOS with the two methods can be explained based on the choice of the internal standard used. At the time of this study mass-labeled PFOS was not available; therefore

Max. 5952 cps.

PFDoA

3.34 min

Max 2634 cps.

1.0

0.5

1.5

2.0

2.5

3.0

3.5

Time, min Fig. 2. LC–MS–MS chromatograms (unsmoothed) for a 10 ppt standard (thick trace) and a 50% MeOH blank (thin trace).

of MeOH for chromatographic reasons and to minimize dilution of the sample. Mini-UniPrep syringeless polypropylene (PP) filter devices were used to protect the instrument from the particulates present in the samples. Samples were mixed 1:1 with MeOH to minimize TM

Fig. 3. Concentrations of PFOA and PFOS (ng l 1 ± standard error (SE) of the mean) determined for Lake Ontario (only 2004 samples) and some tributaries. Average values were determined using the standard addition (SA) and internal standard (IS) method with 13C2-PFOA as internal standard.

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V.I. Furdui et al. / Chemosphere 73 (2008) S24–S30

13

10

Concentration (ng l -1)

8

6

4

2

0 SA & IS SA & IS (C13-PFOA) (C13-PFDA)

SA

IS (C13PFOA)

IS (C13PFDA)

External Calibration

Fig. 4. Average concentration of PFOS (ng l 1 ± SE) determined for all 2004 Lake Ontario samples with different quantification methods: standard addition (SA), internal standard (IS) method, with and without compensation based on internal standards (13C2-PFOA or 13C2-PFDA), and external calibration. Standard addition represents the most accurate determination of concentration.

0.00002 < p < 0.001 0.01 < p < 0.04

1.0

0.2 < p < 1.0

0.8

p value

C2-PFOA was used as an internal standard. PFOS and PFOA are two different chemical compounds with different retention times and physical chemical properties. Differences between the levels of PFOS determined with internal standard and standard addition methods, with and without compensation based on two different mass-labeled standards can be observed in Fig. 4. PFOS elutes chromatographically between 13C2-PFOA (Dt = 0.17 min) and 13C2-PFDA (Dt = 0.34 min). Standard addition method using 13C2-PFOA for peak area normalization was identified as the best quantification method to compensate for possible matrix effects. The PFOS concentrations of seven samples collected from Lake Ontario were determined with the standard addition and internal standard methods, utilizing both, 13C2-PFOA and 13C2-PFDA peak area normalization. The two internal standards, 13C2-PFOA and 13 C2-PFDA, offered a unique possibility to compare results obtained with different levels of ion suppression (67% and 55%, respectively, reduction of signal observed for the Lake Ontario samples compared to the levels observed in standards). External standardization values were also calculated (Fig. 4). Analytical results produced with six different quantification methods were statistically analyzed for significant differences between calculated concentrations at the 95% confidence interval (Fig. 5). Significant differences were determined for all sets of values compared (p < 0.05), with only three exceptions mentioned in this paragraph, including the pair of values calculated using compensation based on 13C2-PFDA for both, standard addition and internal standardization (p = 0.270), and also between internal standard values (13C2PFDA) and standard addition without any peak area compensation (p = 0.189). A ‘‘moderate” level of significant difference (0.02 < p < 0.05) were determined for the standard addition values obtained after compensation with the two different internal standards available (p = 0.021), and for values obtained without compensation and compared with the values obtained after compensation with 13 C2-PFOA (p = 0.035). No significant difference was observed between the standard addition values determined without using an internal standard and the values compensated with 13C2-PFDA (p = 0.952). In the presence of a reduced level of ion suppression, standard addition quantification can provide accurate concentrations, without using any internal standard for compensation. As the level of ion suppression increases an internal standard might be considered for compensation as the differences between the results obtained can become statistically significant at 95% confi-

0.6 0.4

SA & IS1 SA & IS2 SA IS1 IS2

0.2 E

0.0 SA & IS1 SA & IS2

SA

IS1

IS2

E

Fig. 5. Statistical comparison between the quantification methods used: standard addition (SA) without and with compensation based on internal standards (13C2PFOA as IS1 and 13C2-PFDA as IS2), internal standardization (IS) and external standardization (E). p Values were determined using the paired samples t-test for the mean PFOS values. All p values smaller than 0.05 indicate a statistically significant difference between the concentrations obtained with different quantification methods.

dence. Detailed information about the statistical analysis performed is provided in the Supplementary material. The values determined with the standard addition method (with normalization using the two internal standards available and without normalization; first three columns in Fig. 4) do not differ as much as the values determined with the internal standard only. The higher level determined when 13C2-PFOA is used as an internal standard can be explained by the higher ion suppression observed for 13 C2-PFOA, than for 13C2-PFDA. When compensating with 13C2PFOA the values obtained would assume similar ion suppression for PFOS as for 13C2-PFOA and similarly for 13C2-PFDA. Since the three analytes are not ionized simultaneously and under identical ion source conditions, ion suppression is different for each analyte and values obtained with the internal standard method can result in large variability. The values determined with the external calibration are lower then any other set of values, since no ion suppression effects are considered. Clearly using a perfluorinated carboxylate to compensate for a perfluorinated sulfonate is not ideal since fragmentation kinetics and ionization are different. This is evidenced by the significant differences in compound dependent parameters between PFOA and PFOS, with declustering potential 44 V vs. 103 V and collision energy 14 V vs. 75 V, respectively (Supplementary material). In contrast to PFOS, the values of PFOA determined with the internal standard were usually lower than the values determined with the standard addition, but did not show a statistically significant difference. This fact can be explained since 13C2-PFOA has the same retention time as PFOA and experiences similar conditions in the electrospray ionization process. Isotope dilution (use of isotopically labeled internal standards) provides the most accurate and precise results. Standard addition does not significantly change the value obtained with an isotopically labeled internal standard, since ion suppression/enhancement is the same for both, analyte and internal standard. The lack of mass-labeled PFCs can be identified as a possible source of error for previous studies. As demonstrated here with PFOS and PFOA, for minimal quantification errors using the internal standard quantification method, a large number of mass-labeled standards would be required. Ideally, a full isotope dilution method for each analyte would provide the best results. The relatively small difference between the PFOS values obtained with and without compensation using the standard addition method,

V.I. Furdui et al. / Chemosphere 73 (2008) S24–S30

clearly showed that the standard addition is the best quantification method if mass-labeled standards are not available. Another possible source of error in quantification procedures used in previous studies could be the use of a single internal standard, usually less retained chromatographically than the analytes of interest, e.g. 7H-dodecafluoroheptanoic acid (Martin et al., 2004a). This particular internal standard could be associated with higher ion suppression effects, as the level of suppression is diminished for more retained analytes, based on our observations of higher levels of suppression for 13C2-PFOA than for 13C2-PFDA. If 7H-dodecafluoroheptanoic acid is used as an internal standard for the internal standard method, the area correction and the corresponding quantification error is different for each analyte and the resulting values may be significantly biased (typically biased high). Therefore, the standard addition method coupled with a fast LC–MS/MS method should be considered, particularly when a reduced number of mass-labeled internal standards are available. The current isocratic method requires only 16 min to analyze a sample with three standard additions, assuming one injection for each sample, which would be the case for routine sample analysis.

S29

PFDA, PFUnA, PFDoA). For the 2005 samples from Lake Ontario, the highest level of PFCs was observed for the near shore sample LO-05-1, collected in Hamilton harbor, and decreased with distance from the harbor (LO-05-2 and LO-05-3, Fig. 1). The values determined for the Hamilton harbor area were not considered when calculating the average levels for Lake Ontario, since this represents an enclosed water body with significant industrial inputs. All PFOS/PFOA average values determined for the 2002–2005 samples were lower than 6.5 ng l 1. Sinclair et al. (2006) reported similar levels of PFOS with our findings and slightly higher levels of PFOA for Lake Ontario and Lake Erie, using an LC–MS–MS method. A higher level of PFOS/PFOA was reported by Boulanger et al. (2004) for water samples collected off-shore in 2002 from Lake Erie and Lake Ontario (40–100 ng l 1). The study was performed using an LC–MS instrument with external calibration, while the values in this study were obtained using an LC–MS–MS instrument and standard addition quantification. Another major difference is the use of a relatively high concentration factor, which was not required in our study. 3.4. PFCs in Lake Ontario tributaries

3.3. PFCs in Great Lakes The analytes monitored in all samples included: PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA, PFHxS, PFOS and PFOSA. The values reported in Table 1 were calculated using the standard addition method with the area counts corrected using an internal standard. The two major analytes detected in the samples were PFOS and PFOA. The highest level of PFOS was detected in Hamilton harbor (38 ng l 1 for LO-05-1), an area recognized as being contaminated with other persistent organic pollutants (Zeman and Patterson, 2003). Both, PFOS and PFOA were detected in all samples at levels as high as 8 ng l 1. Several samples from Lake Huron and Lake Superior showed trace levels of PFOA and PFOS, at lower levels than our determined LOQ (1.3 ng l 1 and 0.5 ng l 1, respectively). A spatial trend was observed for the average values of PFOS/ PFOA for each lake (Fig. 6), with the lowest levels determined from the off-shore Lake Superior samples. The level of PFOS/PFOA increased from Lake Superior to Lake Huron, Lake Erie and Lake Ontario. This is an expected trend, considering the likelihood of continual input of PFCs from industrial and domestic point sources (tributaries, outfalls, run-off, etc.) as the water progresses through the Great Lakes basin. The other monitored perfluorinated analytes did not show a clear trend (PFHxS), were below the MLOQ (PFOSA, PFNA) or were detected in less than 50% of the samples (PFHpA,

PFOS PFOA PFOSA

-1

Concentration (ng l )

6

4

2

0 Superior

Huron

Erie

Ontario

Fig. 6. Average levels of PFOS, PFOA and PFOSA (ng l 1 ± SE) determined for samples from the Great Lakes (per lake). The values determined for Hamilton harbor area (LO-05-1) were not included.

Water samples were analyzed from three tributaries of Lake Ontario (Humber River, Etobicoke Creek and Mimico Creek), whose inputs may influence PFCs levels in the areas where near shore lake water samples were collected. Etobicoke Creek was targeted because of a major aqueous fire-fighting foam spill which occurred in 2001 (Moody et al., 2001, 2002). As expected the highest level of contamination was determined in Etobicoke Creek, at 15.4 ng l 1 PFHxS, 22.9 ng l 1 PFOS, 13.4 ng l 1 PFHpA and 38.1 ng l 1 PFOA. Although current values are much lower than immediately after the spill, the levels are still elevated for PFHpA and PFOA. Tributaries did not show significant differences for the level of longer chain acids (PFNA, PFDA, PFUnA and PFDoA; Table 2). The level of shortchain acids and sulfonates in Mimico Creek is 2–4 times higher than in Humber River. One possible explanation for this difference, in addition to industrial inputs, is the much lower flow in Mimico Creek vs. the Humber River. The level of PFCs were higher (Etobicoke Creek, Mimico Creek) or similar (Humber River) with the levels in Lake Ontario, suggesting that tributaries may be a source of contamination for the Great Lakes. 3.5. PFCs in STP samples STP effluents and sewage sludge may contain a significant amount of PFCs as demonstrated in previous studies (Boulanger et al., 2005; Higgins et al., 2005; Schultz et al., 2006; Sinclair and Kannan, 2006). Six STP final effluents were tested, with five coming from highly populated areas located at the north-western end of Lake Ontario. The two major perfluorinated contaminants were PFOS (10–210 ng l 1) and PFOA (6–55 ng l 1) (Table 2). Lower levels of PFHxS (3–10 ng l 1), PFHpA (2–7 ng l 1), PFNA (3–5.4 ng l 1) and PFDA (1.5–5 ng l 1) were detected in all samples, while PFOSA (0–4 ng l 1), PFUnA (0–6 ng l 1) and PFDoA (0–8 ng l 1) were detected only in a few samples. The perfluorinated contaminants in STP effluents were at higher levels than in the water samples tested, but had similar pattern distributions. The levels determined in Humber River and Humber STP effluent could not be directly related, since the sampling was not simultaneous. The levels determined for the north-western Ontario urban area (Kenora) are comparable with the average from the other effluents, but with a relatively higher level of PFOSA and lower level of PFOS. At the Grand River STP, both, the influent and the effluent waters were tested. The effluent showed lower levels of sulfonates and long-chain acids compared to the influent (60% PFHxS, 51%

S30

V.I. Furdui et al. / Chemosphere 73 (2008) S24–S30

Table 2 Concentrations of perfluorinated substances (ng l influent (I) Sample

PFHxS

Tributaries Etobicoke Creek Mimico Creek

15.4 nd

Humber River

nd

STPs Toronto Main Pickering Highland Creek Humber Kenora Grand River (I) Grand River

3.0 4.5 9.4 4.5 6.4 10.7 6.4

1

PFOS

) determined with the standard addition method for water samples from tributaries of Lake Ontario, STP effluents and one

PFOSA

PFHpA

PFOA

PFNA

PFDA

PFUnA

PFDoA

22.9 10.9

0.6 0.9

13.4 5.5

38.1 11.7

4.0 4.1

2.0 1.3

(0.5) 1.1

(0.7) (0.2)

2.6

0.3

nd

4.1

1.6

0.8

(0.5)

(0.8)

nd (0.2) 0.7 1.0 3.8 nd 2.8

6.5 1.9 3.1 7.1 3.8 1.9 3.6

24.6 54.7 15.3 34.9 26.7 6.5 9.4

4.0 3.0 4.6 5.4 4.0 4.2 3.9

1.5 1.9 1.2 4.9 2.7 1.6 2.8

nd (0.8) (0.5) 1.5 (0.7) 5.7 nd

2.1 nd 3.1 1.0 4.2 8.1 nd

42.5 67.0 208.5 9.7 8.6 20.0 10.2

PFOS, <2% PFUnA and PFDoA), while the level of short-chain acids increased (190% PFHpA, and 145% PFOA). As recently observed the STPs affect the level of PFCs in effluent, depending on the treatment processes involved and possible sorption to the sludge (Schultz et al., 2006). Acknowledgements Special thanks to Gilles Arsenault from Wellington Laboratories for providing the mass-labeled perfluorodecanoic acid. The authors would like to thank also Paul Helm (Ministry of the Environment), Alice Dove and Chris Marvin (Environment Canada) for providing samples collected from the Great Lakes. Appendix A. Supplementary material MRM acquisition parameters, comparison of PFOA/PFOS levels determined with standard addition and internal standard quantification methods, and perfluorinated surfactant profiles of Lake Ontario and its tributaries are available. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemosphere.2007.07.085. References Boulanger, B., Schnoor, J.L., Hornbuckle, K.C., Vargo, J.D., 2005. Evaluation of perfluorooctane surfactants in a wastewater treatment system and in a commercial surface protection product. Environ. Sci. Technol. 39, 5524–5530. Boulanger, B., Vargo, J., Schnoor, J.L., Hornbuckle, K.C., 2004. Detection of perfluorooctane surfactants in Great Lakes water. Environ. Sci. Technol. 38, 4064–4070. Hekster, F., Laane, R., de Voogt, P., 2003. Environmental and toxicity effects of perfluoroalkylated substances. Rev. Environ. Contam. Toxicol. 179, 99–121. Higgins, C.P., Criddle, C.S., Luthy, R.G., Field, J.A., 2005. Quantitative determination of perfluorochemicals in sediments and domestic sludge. Environ. Sci. Technol. 39, 3946–3956. Kannan, K., Aldous, K.M., Corsolini, S., Falandysz, J., Fillmann, G., Kumar, K.S., Loganathan, B.G., Mohd, M.A., Olivero, J., Van Wouwe, N., Yang, J.H., 2004. Perfluorooctanesulfonate and related fluorochemicals in human blood from several countries. Environ. Sci. Technol. 38, 4489–4495. Kannan, K., Koistinen, J., Beckmen, K., Evans, T., Gorzelany, J.F., Hansen, K.J., Jones, P.D., Helle, E., Nyman, M., Giesy, J.P., 2001. Accumulation of perfluorooctane sulfonate in marine mammals. Environ. Sci. Technol. 35, 1593–1598. Lindström, G., Kärrman, A., Zammitt, A., Van Bavel, B., Van Der Veen, I., Kwadijk, C., De Boer, J., Van Leeuwen, S., 2005. The 1st worldwide interlaboratory study on

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