Interlaboratory study of toxaphene analysis in ambient air

ARTICLE IN PRESS

Atmospheric Environment 38 (2004) 3713–3722

Interlaboratory study of toxaphene analysis in ambient air Terry F. Bidlemana,*, Sylvia Cussionb, Liisa M. Jantunena a

Centre for Atmospheric Research Experiments, Meteorological Service of Canada, 6248 Eighth Line, Egbert, Ont., Canada L0L 1N0 b Laboratory Services Branch, Quality Management Unit, Ontario Ministry of the Environment, 125 Resources Road, Etobicoke, Ont., Canada M9P 3V6 Received 30 December 2003; accepted 20 January 2004

Abstract An interlaboratory study was conducted for total toxaphene and selected congeners in an extract of ambient air from the southern United States. All participating labs were experienced in toxaphene analysis and used GC-MS techniques. Ten labs reported the concentration of total toxaphene in a technical toxaphene solution, with a 113% average recovery of the target value and 40% relative standard deviation (RSD). Only six of the 10 labs fell within 730% of the target value, a criterion recommended by good laboratory practice standards. The interlaboratory RSD was 65% for total toxaphene in the air sample extract (lowered to 43% when one outlying lab was omitted). Nine labs reported the concentrations of five toxaphene components (B8-1413, B8-1414+B8-1945, B8-806+B8-809, B8-2229 and B9-1679) with 33–47% RSD for the technical toxaphene unknown and 34–62% for the air sample. The precision was poorer for a sixth component, congener B9-1025, which has a very low response by electron capture negative ion mass spectrometry (ECNI): 59% RSD for the technical toxaphene unknown and 196% for the air sample. Factors contributing to the interlaboratory variability for total toxaphene and single components are discussed, and follow-up studies are required to identify and minimize the causes of variability. Based on the average analysis, B8-1413 was enriched and B8-806+B8-809 was depleted in the air sample relative to the technical toxaphene standard. Crown Copyright r 2004 Published by Elsevier Ltd. All rights reserved. Keywords: Interlaboratory study; Toxaphene; Organochlorine pesticides; Air

1. Introduction Toxaphene and similar products have been produced and used throughout the world as agricultural insecticides. Toxaphene is manufactured by chlorination of camphene, which results in a Wagner–Meerwein rearrangement to yield mainly chlorinated bornanes and some chlorinated camphenes. The resulting mixture is highly complex. In theory, over 22,000 polychlorinated bornanes containing 5–10 chlorines are possible (Vetter, 1993). However when considering that certain substitu*Corresponding author. Meteorological Service of Canada, ARQP, 4905 Dufferin Street, Downsview, Ontario, Canada M3H 5T4. Fax: +1-416-739-5708. E-mail address: [email protected] (T.F. Bidleman).

tion patterns are unfavorable, the number of relevent chlorinated bornane and camphene isomers likely to occur in the environment is only 197 (Hainzl et al., 1994). Still, analysis of toxaphene residues in environmental samples is a daunting challenge. Components of technical toxaphene and mixtures of single congeners are only partially resolved by capillary gas chromatography (GC) on columns containing a variety of stationary phases (Nikiforov et al., 2000; Oehme and BaycanKeller, 2000; Vetter et al., 1997), and some workers have resorted to multidimensional GC for separations (deBoer et al., 1997; Shoeib et al., 2000). Much of the toxaphene residue data in the literature is for ‘‘total toxaphene’’, which is usually calculated from the total area of all peaks matching those of a technical toxaphene standard. There are a host of problems with

1352-2310/$ - see front matter Crown Copyright r 2004 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.01.047

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this approach. Interferences may occur from coeluting compounds. The relative proportion of toxaphene components in environmental samples is often quite altered compared to the standard due to differential volatility and metabolism. Variable GC profiles are obtained for technical toxaphene standards from different sources (Carlin and Hoffman, 1997). The commercial availability of some individual chlorobornane and chlorocamphene standards within the last decade has resulted in a growing trend toward reporting residues on a single congener basis. However, far fewer congeners are available as standards than the number likely to occur as environmental residues, and incomplete separation of coeluting peaks makes reporting on a single congener basis problematic (Nikiforov et al., 2000; Oehme and Baycan-Keller, 2000; Vetter et al., 1997). Thermal degradation of some congeners occurs when using split/splitless injection, especially chlorobornanes having gem dichloro substitution (Buser et al., 2000; Oehme and Baycan-Keller, 2000). Fragmentation in the mass spectrometer is extensive in the electron impact (EI) mode (Swackhamer et al., 1987), and for that reason most workers use electron capture negative ion (ECNI) mass spectrometry. This generally yields (M–Cl)
ions, although fragments from multiple chlorine loss are also produced, and their abundance varies with the congener (Braekevelt et al., 2001; Swackhamer et al., 1987; Witte et al., 2000). ECNI response factors vary greatly among the different toxaphene congeners (Shoeib et al., 2000; Witte et al., 2000). Atmospheric transport is recognized as a major route of toxaphene dispersal. Several surveys of airborne toxaphene have been done near the North American Great Lakes (Glassmeyer et al., 1999; James et al., 2001; Jantunen and Bidleman, 2003; McConnell and Bidleman, 1998; Shoeib et al., 1999, 2000) and in the southern United States, a source region (Bidleman and Leone, 2004a, b; Bidleman et al., 1998; James and Hites, 2002; Jantunen et al., 2000). Toxaphene has also been reported in arctic air (Barrie et al., 1993; Bidleman et al., 1995; Braekevelt et al., 2001; Jantunen, 1997). Only a few interlaboratory studies (ILS) have been done for toxaphene using fish oils (Alder et al., 1997; Andrews, 1996; Andrews et al., 1995), cleaned up extracts of fish liver and blubber samples (deBoer et al., 2000; Stokker, 2003), and soil and sewage sludge (Carlin et al., 2000). Compared to biota, toxaphene residues in air are lower in concentration and have profiles enriched in the lighter, more volatile congeners. In 1978, an ILS of polychlorinated biphenyls (PCBs) and organochlorine pesticides in ambient air was carried out using extracts of ambient air from Columbia, SC and Boston, MA (Bidleman, 1981). Nine labs participated and six reported total toxaphene in the Columbia sample. At that time, all labs used packed-column GC with electron capture detection (ECD).

Toxaphene is a chemical of interest in the Integrated Atmospheric Deposition Network (IADN), a binational Canada—US program which monitors atmospheric concentrations and loadings of persistent organic pollutants and metals to the North American Great Lakes. A suite of organochlorine pesticides is routinely monitored in IADN, but toxaphene is presently not included except as a research topic. At an internal IADN workshop, a recommendation was made that an ILS be conducted to assess performance in the analysis of total toxaphene and some single chlorobornane congeners in an extract of ambient air and a technical toxaphene standard, using modern methods of analysis. This ILS is the outcome of that recommendation.

2. Experimental methods 2.1. Study design Eleven labs with experience in toxaphene analysis took part in the ILS, six from Canada, four from the USA and one from Europe. Participants were given two unknowns: a solution of technical toxaphene and an extract of ambient air from the southern USA Participants were asked to quantify the concentration of total toxaphene and seven chlorobornane congeners in the technical toxaphene solution and air sample extract. They were provided with standard solutions of the seven congeners, but asked to use their own technical toxaphene standards for total toxaphene. All solutions provided to the labs were in heat-sealed amber glass vials. The samples and standards were accompanied by an instruction sheet and methodology questionnaire. 2.2. Analytical methods A summary of methods employed by the eleven labs is given in Table 1, however these are not associated with individual labs to ensure confidentiality. The most popular instrumentation, favored by nine labs, was low-resolution mass spectrometry in the electron capture negative ion mode (ECNI-LRMS). One of the labs which employed ECNI-LRMS also used high-resolution mass spectrometry in the electron impact mode (EI-HRMS) and one lab used ECNI-HRMS exclusively. Nine labs used GC columns with polydimethylsiloxane—5% phenyl stationary phases (DB-5, DB-5MS, HP-5, HP-5MS, MDN-5), one lab used DB-XLB and one lab used both HP-Ultra 2 and HP-1. These columns were generally 30–60 m length, although the HP-Ultra 2 was 25 m and the HP-1 was 15 m. All labs used helium as the carrier gas. Sample cleanup involved florisil, silica or silica-alumina columns. Nine labs added a labeled (three labs) or unlabeled (six labs) internal standard for volume correction. Five labs added a labeled (four labs) or

ARTICLE IN PRESS T.F. Bidleman et al. / Atmospheric Environment 38 (2004) 3713–3722 Table 1 Summary of methodologies used in the interlaboratory study

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Table 1 (continued) Number of laboratories

Number of laboratories Sample storage

Refrigerator Freezer

4 7

Recovery surrogates

None

6

Labeled pesticides or PCB congeners Unlabeled PCB congeners

4

None

2

Labeled pesticides or PCB congeners Unlabeled PCB congeners Chloronaphthalenes and/or bromobenzenes

3

Florisil Silica Silica+alumina No information given

2 4 1 4

Final solvent

Hexane isooctane

6 5

GC columns

DB-5, 30 m DB-5, 60 m DB5-MS, 30 m DB5-MS, 60 m DB-XLB, 30 m HP5-MS (no length given) HP Ultra 2, 25 m and HP-1, 15 m MDN-5, 30 m

1 2 1 3 1 1

1

unlabeled (one lab) surrogate to monitor recovery. Calibration was based on a single point (five labs), two points (one lab) or multiple points (five labs). Homologs included in the determination of total toxaphene varied from Cl6 to Cl10 (six labs), Cl6 to Cl9 (two labs), Cl7 to Cl9 (one lab) and Cl8 to Cl9 (one lab). Five labs monitored ions to correct for chlordane and endosulfan interferences.

Start 80–90 C, end 280–315 C Start 80–90 C, end 265–270 C Start 40 C, end 300 C Start 120 C, end 280 C

7

2.3. Technical toxaphene unknown

2

A stock solution of technical toxaphene was obtained from Restek Corp. (Lot # AO45221, State College, PA, USA), diluted to 141 ng ml
1 with isooctane, and distributed in 2-ml aliquots as an unknown.

Internal standard

Cleanup

Oven program

Carrier gas

Helium

Instrumentation

ECNI-LRMS ECNI-LRMS, EI-HRMS ECNI-HRMS

Calibration

Single point 2 points Multiple points

5 1 5

Correct for recovery

Yes

7

No

4

Total toxaphene Homologs

Cl6–Cl10 Cl6–Cl9 Cl7–Cl9 Cl8–Cl9 Total toxaphene not reported

6 2 1 1 1

Source of technical Toxaphene standard Used for calibration

Hercules

4

US EPA

1

Radian

1

Supelco Other or not reported

1 4

Yes

5

No

6

1

4 2

1

1 1

Correct for chlordane and Endosulfan interferences

2.4. Toxaphene congener solutions 11 9 1 1

A mixture of six toxaphene congeners was obtained from Promochem (Lot #80416CY, Wesen, Germany). The congeners, designated by the Andrews–Vetter and (Parlar, P) numbering schemes (Vetter and Sherer, 1998), were: B8-1413 (P26), B8-1414 (P40), B8-1945

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shown for reference in Fig. 1. A summary of the quantitative results from all 11 labs is given in Table 2.

(P41), B8-2229 (P44), B9-1679 (P50) and B9-1025 (P62). This solution was diluted with isooctane to 30 ng ml
1 and 2-ml aliquots were distributed. Separate vials were also supplied which contained 2-ml aliquots of congeners B8-806+B8-809 (P42a+P42b) at a total concentration of 34 ng ml
1, prepared from a stock solution obtained from Axact Standards (Lot #41202, Commack, NJ, USA).

3.1. Technical toxaphene unknown Ten labs reported total toxaphene in the technical toxaphene unknown, with results ranging from 65 to 256 ng ml
1. Although the ILS mean (159 ng ml
1) was close to the target value of 141 ng ml
1, the relative standard deviation (RSD) was 40% and individual results ranged from 46% to 181% of the target. The labs based their determinations on different homolog groups (Table 1), but surprisingly, there was no relationship of the total toxaphene result to the number of homologs quantified (r2 ¼ 0:0028). According to good laboratory practices (GLP), results should be within 30% of target values, or between 99 and 183 ng ml
1. This was achieved by only 6 of the 10 labs that reported total toxaphene. Eleven peaks in technical toxaphene that correspond to the retention times of individual congeners are shown in Fig. 1 (Bidleman and Leone, 2003; Braekevelt et al., 2001; Buser et al., 2000; James and Hites, 2002; Shoeib et al., 1999). Seven of these congeners were included in the ILS and were reported by nine labs. Octachlorobornanes B8-1414 and B8-1945 elute closely to one another (peaks 5 and 6, Fig. 1). These two congeners were reported separately by four labs, their sum by four labs, and only B8-1414 by one lab. The latter result was assumed to include B8-1945 in the statistical analysis. ECNI response factors differ for the two congeners, and the difference is likely to be dependent on instrumental

2.5. Ambient air extract Large-volume air samples were collected in June, 1999 at the Tennessee Valley Authority reservation, a federal government research facility near Muscle Shoals, AL, USA Daily samples were collected for a week using glass fiber filters backed up with polyurethane foam (PUF) plugs (Jantunen et al., 2000). The filters and PUF plugs were extracted separately with petroleum ether and dichloromethane, respectively, filtered through glass wool and exchanged into isooctane by rotary evaporation. No further cleanup was provided. Extracts of all filters and PUF plugs were pooled into one extract which represented 8300 m3 air and diluted with isooctane to 100 ml in a volumetric flask. Aliquots of 5 ml, representing 415 m3 air, were distributed as an unknown.

3. Results ECNI-LRMS chromatograms obtained in the lead author’s lab for the Cl7–Cl9 homologs in the technical toxaphene solution and in the air sample extract are 1

Cl-7, ion 343 20000 10000 0 6

7

Abundance

5 3

30000

4

Cl-8, ion 379

8

2

20000 10000 0

Cl-9, ion 413 9

30000

10 11

20000 10000 0

30.00

35.00

40.00

45.00

50.00

55.00

Minutes Fig. 1. ECNI chromatograms of Cl7–Cl9 homologs in the technical toxaphene unknown, 60-m DB-5 column. Numbered congeners: 1=B7-1001, 2=B8-1413, 3=B8-1412, 4=B8-531, 5=B8-1414, 6=B8-1945, 7=B8-806/809, 8=B8-2229, 9=B9-1679, 10=B9-1025, 11=B9-2206. Compounds 2,5 and 6–10 were included in this study.

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Table 2 Results for total toxaphene and individual congeners, ng ml
1 Laboratorya 1

2

3

Technica toxaphene solution Total toxaphene B8-1413 B8-1414 B8-1945 B8-1414+B8-1945 B8-806/809 B8-2229 B9-1679 B9-1025

134 0.50 1.27 0.34 1.61 3.98 6.04 1.52 11.0

117 0.36

133

Air sample extract Total toxaphene B8-1413 B8-1414 B8-1945 B8-1414+B8-1945 B8-806/809 B8-2229 B9-1679 B9-1025

19.1 0.21 0.13 0.089 0.22 0.42 2.06 0.28 1.18

2.20 3.98 3.42 1.44 9.79

44.2 0.20

0.30 0.074 0.99 0.12 11.5

4

5

6

7

8

9

10

11

mean

s.d.

%rsd

177 0.46 1.76 0.49 2.25 3.70 0.50 1.75 3.13

215

0.54 1.21 0.25 1.46 3.89 4.79 1.38 3.59

250 1.07

65 0.87

256 1.56

131 0.75 0.91

0.92 4.73 3.68 1.83 18.0

1.94 5.64 4.25 1.65 8.52

112 0.44 1.55 0.54 2.09 3.99 1.84 1.34 4.23

3.93 10.7 6.09 3.29 14.0

0.91 5.17 o1.5 1.52 5.31

159 0.73 1.34 0.41 1.92 5.09 3.83b 1.75 8.62

63 0.39 0.33 0.13 0.91 2.21 1.94b 0.60 5.12

40 53 24 33 47 43 51 34 59

37.2 0.53 0.46 0.011 0.47 0.63 0.32 0.48 0.24

89.2

0.11 0.37 0.12 0.49 0.36 2.01 0.44 0.07

21.9 0.51

9.5 0.31

27.5 0.24

44.3 0.48 0.41

0.25 0.48 1.64 0.54 NDc

0.56 0.71 1.97 0.47 NDc

0.60 0.67 1.98 0.11 0.61

0.41 0.62 o0.7 0.57 o0.8

34.2 0.32 0.36 0.09 0.43 0.49 1.49b 0.38 2.30d

22.3 0.15 0.14 0.05 0.14 0.20 0.66b 0.17 4.52d

65 47 37 62 34 40 44 45 196

26.3

22.3 0.31 0.45 0.13 0.58 0.46 0.91 0.39 0.20

a

No entry: not reported. Omits Lab 11. c ND=not detectable, no limit given. d Omit labs 7, 8 and 11. b

conditions. In the lead author’s lab, the response factor for B8-1414 is about 40% of that for B8-1945. Unequal response factors leads to uncertainty when quantifying peaks in technical toxaphene and the air sample in which the ratio of the two congeners differs from 1:1, however the level of this uncertainty could not be evaluated here. Interlaboratory variability was similar for total toxaphene and single congener results. RSDs for the single congeners ranged from 33% to 59%, compared to 40% for total toxaphene. The largest RSD was for B9-1025, which has a very low ECNI response factor using the (M-Cl)
ion (Braekevelt et al., 2001; Lau et al., 1996; Shoeib et al., 1999; Witte et al., 2000), and (in our analysis) appears as a small shoulder on the front of a larger peak in the chromatogram (peak 10, Fig. 1). 3.2. Air sample extract Results for total toxaphene in the air sample extract from the 10 reporting labs ranged from 9.5 to with an ILS mean7SD of 89.2 ng ml
1, 34.2722.3 ng ml
1 (RSD=65%) (Table 2). Removing lab 6 result of 89.2 lowered the ILS mean7SD to 28.2711.8 and the RSD to 42%. Based on these statistics from the remaining nine results, lab 6 was an outlier at po0:01: As for the technical toxaphene

unknown, there was no correlation between the reported total toxaphene concentration and the number of homologs quantified, either including or leaving out lab 6 result (r2 ¼ 0:029 and 0.0041, respectively). Nine labs reported single congeners in the air sample extract with RSDs for most congeners ranging from 34% to 62% (Table 2). As for the technical toxaphene unknown, the interlaboratory variability for most single congener determinations was about the same or somewhat greater than for total toxaphene. The exception was B9-1025, for which the RSD was 196%. Values for B9-1025 in the air sample were given by only six labs and listed as below detection by three labs. Because the number of reporting labs was so small, no results were excluded in calculating this RSD. Difficulties with B9-1025 determination in the technical toxaphene unknown were mentioned above, and these were even more of a problem with the air sample because the peak was very small (peak 10, Fig. 2). An examination was done of total toxaphene results to determine whether labs which were high or low for the technical toxaphene unknown were also high or low for the air sample. The total toxaphene results for the air sample reported by each lab in Table 1 were expressed as percentages of the interlaboratory mean, and these percentages were regressed against similar data for the

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25000 20000 15000 10000 5000 0

1

Cl-7, ion 343

Abundance

Cl-8, ion 379

8

6

20000 15000 10000 5000 0

5

3

7

2 4

Cl-9, ion 413

9

10000 5000 0

10 11

30.00

35.00

40.00

45.00

50.00

55.00

Minutes

Fig. 2. ECNI chromatograms of Cl7–Cl9 homologs in the air sample extract, column and congener numberings as in Fig. 1.

technical toxaphene results. The regressions were not significant for all 10 laboratories (p > 0:36) nor when one lab (with the high air sample result) was omitted (p > 0:76). 3.3. Replicate analyses Although not requested to do so, three labs provided their precisions for replicate determinations. Lab 1 reported RSDs for triplicates: 6% for total toxaphene in both the technical toxaphene unknown and air sample extract, 7–18% for congeners B8-1413, B8-1414+B81945, B8-806+B8-809, B8-2229, B9-1679 and B9-1025 in technical toxaphene and 3–24% for these congeners in the air sample. Lab 4 reported duplicates for the congeners as % difference=100 (result 1
result 2)/ mean. The % difference was 0–37% for congeners in technical toxaphene, and 0–29% for congeners in the air sample. Lab 8 reported duplicates for the air sample extract: 2% difference for total toxaphene and 0.6–15% difference for congeners except B9-1025, which was below detection. In general, precision within the same lab was better than among the labs. In a previous ILS using two technical toxaphene solution unknowns, a Youden Pairs plot showed that intralaboratory precision was very good even though the RSD among labs was 43% and 48% for the two solutions (Stokker, 2003).

4. Discussion 4.1. Factors contributing to interlaboratory variability Due to the small number of participants in the ILS, it is difficult to deduce reasons for the interlaboratory variability. The use of ECNI-LRMS was a common

factor among most labs, which otherwise employed a variety of cleanup techniques, GC columns and temperature programs, and addition (or not) of surrogates and internal standards. An obvious factor that might affect the total toxaphene result is the number of homologs included in the quantitation, but as mentioned above, no relationship was found for either the technical toxaphene unknown nor the air sample extract. Another variable is the source of technical toxaphene used as a quantitation standard. Standards from at least four sources were used by the various participating labs (Table 1). Differences among commercial standards have been found with respect to the relative proportions of toxaphene homologs measured by GC-ECNI-LRMS (Howdeshell and Hites, 1996) and peak profiles obtained GC-electron capture detection (Carlin and Hoffman, 1997). The baseline construction for integration of the total toxaphene envelope is another factor which likely differed among the labs. Referring to the chromatograms in Figs. 1 and 2, one could choose to draw a flat baseline or use a valley-to-valley construction. However, information on the constructions used by the different labs was not available. Among the eight labs which used LRMS and reported total toxaphene, five monitored ions to correct for interferences due to endosulfans and/or chlordanes and another three did not. These pesticides were likely to be present in the air sample extract, but not in the technical toxaphene unknown. Total toxaphene in the air sample extract averaged 41.8727.8 ng ml
1 by the correcting group and 23.0713.9 ng ml
1 by the group which did not apply corrections. The standard deviations in each case are large and the means are not significantly different (p > 0:2). Chlordanes and endosulfans may

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have interfered with specific toxaphene peaks, but this did not appear to have affected the result in the calculation of total toxaphene. Perhaps the summation of many peaks in the calculation diluted the effect of interference with a few of them. Also, the number of labs in each group was small. The interlaboratory variability for single congener determinations was similar or somewhat greater than for total toxaphene. This occurred, despite the fact that the labs were supplied with standard solutions of the congeners, thereby removing one source of variability. Although these standards were single compounds, the peaks in technical toxaphene and the air sample were not. Difficulties in resolving B8-1414 and B8-1945 were mentioned above, and some labs reported only their sum. Multidimensional GC analysis has revealed the multicomponent nature of many toxaphene peaks (deBoer et al., 1997; Shoeib et al., 2000), and moreover the proportion of the components differed between technical toxaphene and air samples from southern Ontario (Shoeib et al., 2000). For example, in the latter study the peak assigned as B8-2229 was characterized by ECNILRMS as being octachlorinated. Multidimensional GC-ECD analysis showed that this peak contained at least seven components in technical toxaphene and four in air. Two labs noted a slight discrepancy between the retention time of B8-2229 in the two unknowns (peak 8, Figs. 1 and 2) and the authentic B8-2229 standard. The ECNI response differs greatly for octachlorobornane isomers (Shoeib et al., 2000; Witte et al., 2000) and they show different degrees of thermal degradation during split/splitless analysis (Buser et al., 2000), which might be expected to be laboratory-dependent. Such factors may have contributed to the interlaboratory variability seen for the toxaphene congener analyses. 4.2. Comparison to other interlaboratory studies Nine labs participated in an ILS of PCBs and organochlorine pesticides in extracts of ambient air from Columbia, SC and Boston, MA, collected in 1978 (Bidleman, 1981). Six labs reported air concentrations of total toxaphene by packed-column GC-ECD; with a RSD of 116%. By comparison, RSDs for some other substances in Columbia and Boston were: total PCBs as Aroclors=26–39% (eight labs), p; p0 -DDE=50% (six labs, Columbia only), p; p0 -DDT=47% (four labs, Columbia only), hexachlorobenzene=35–43% (four labs). Two round robin comparisons were run for toxaphene in a National Institute of Standards and Technology cod liver oil standard reference material (NIST #1588) were carried out by Health Canada (Andrews, 1996; Andrews et al., 1995). In the first round (Andrews et al., 1995), eight labs using ECNI-LRMS

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reported total toxaphene (quantified versus a supplied standard of Hercules toxaphene) with a mean concentration of 3.96 mg kg
1 and a RSD of 40%. One lab reported 2.35 mg kg
1 using EI-HRMS. Four labs also reported total toxaphene as the sum of eleven congeners with 47% RSD. In the second round (Andrews, 1996), RSDs ranging from 68% to 133% were reported for individual congeners B7-515, B8-1413, B9-1679 and B9-1025. Results of the first toxaphene ILS carried out by the Quality Assurance of Information for Marine Environmental Monitoring in Europe (QUASIMEME) program were reported by deBoer et al. (2000). In the first phase, fifteen labs determined B7-515, B8-1413, B9-1679 and B9-1025 in a standard mixture of the four congeners. In the second phase, 13 labs determined B8-1413, B9-1679 and B9-1025 in a standard solution of the three congeners and in cleaned up extracts of pilot whale blubber and hake liver. RSDs ranged from 6% to 21% for the standard mixtures and 16–39% for the biota extracts. For the labs which reported detection methods, five used ECD, five ECNI-LRMS, one EI-LRMS and one EI-HRMS. No specific influence of the detection technique was found. Eleven labs participated in an ILS of total toxaphene and selected congeners in pure standard solutions and a lipid-free extract of burbot liver (Stokker, 2003). The study was sponsored by the Northern Contaminants Program (NCP) of Indian and Northern Affairs, Canada. Eight labs used GC-ECNI, two used an ion trap in the GC-MS-MS mode and one combined results from GC-MSD and GC-ECD analyses. RSDs were 43% and 48% for total toxaphene in two standard solutions, and 56% for total toxaphene in the burbot liver extract. Results for total toxaphene in the two standard solutions were bimodal, with one group of four labs reporting 90–120% of the target value and another group of six labs reporting 45–60% of the target. One lab found only about 25% of the target. Ten labs reported individual congeners, with RSDs ranging from 7% to 25% for pure standard solutions and 18–49% for the burbot liver extract. Performance was also assessed in the NCP for polychlorinated biphenyls (PCBs), with 14 labs participating. The RSDs for PCB congeners in mixed standard solutions was 20–30%. The RSDs for biological samples depended on the congener concentrations, up to 30% for concentrations >10 ng g
1 and up to 50% for concentrations 1–10 ng g
1 (Stokker, 2003). Three labs compared GC-ECD for total toxaphene in sludge and soil (Carlin et al., 2000). All labs used the US EPA SW-846 Method 8081A (US Environmental Protection Agency, 1996). RSDs ranged from 6.9% to 19% when toxaphene residues were calculated as the sum of peak heights measured from the baseline, and from 11% to 20% when using heights measured from the base of each peak.

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In summary, the RSDs for total toxaphene in this study (40–65%) were similar to those found in the Health Canada (Andrews et al., 1995) and NCP (Stokker, 2003) ILS of technical toxaphene standards and extracts of biological matrices (40–57%). RSDs for single congeners in this study ranged from 33% to 62% (excluding B9-1025 in the air sample). Comparable or somewhat better precision (16–49% RSD) was found for single congeners in the QUASIMEME (deBoer et al., 2000) and NCP (Stokker, 2003) ILS with biological matrices. An earlier Health Canada ILS found 68–133% RSD in a cod liver oil standard (Andrews, 1996).

Table 3 Proportions of toxaphene congeners in technical toxaphene and ambient air extract % of total toxaphenea Technical toxapheneb

Air sample

Congener

Mean

SD

Mean

SD

B8-1413 B8-1414+B8-1945 B8-806+B-809 B8-2229 B8-1679 B9-1025

0.46 1.21 3.20 2.41 1.10 5.42

0.30 0.75 1.88 1.56 0.58 3.88

0.94c 1.26 1.44d 4.36 1.11 6.73

0.76 0.93 1.10 3.44 0.88 13.91

a

4.3. Characteristics of toxaphene residues in air Some agricultural soils in the southern US contain high toxaphene residues (Bidleman and Leone, 2004a, b; Kannan et al., 2003; Harner et al., 1999), which are thought to be responsible for regional toxaphene emissions into the atmosphere (Bidleman and Leone, 2004a, b; Harner et al., 2001; Li et al., 2001). Soils in the southern USA show depletions of certain toxaphene components which may be related to their ease of degradability (Bidleman and Leone, 2004b). The toxaphene profiles in air are influenced by those in the soil, modified by the differential volatility of the congeners (Bidleman and Leone, 2004b). Compared to the Restek technical toxaphene, air sample profiles are generally enriched in the lower molecular weight, more volatile congeners, as can be seen from the relative abundances of the Cl7–Cl9 homologs in Figs. 1 and 2. Considering the air profile in more detail, the labile compounds B8806/809 and B8-531 are depleted within the Cl8 homolog, and the Cl9 homolog is greatly simplified with two identified peaks (B9-1679 and B9-2206) and one unidentified peak (at 46.25 min) prominent. These features have been noted for other air samples from the southern US and Great Lakes region (Bidleman and Leone, 2004b; Jantunen and Bidleman, 2003; Jantunen et al., 2000; James and Hites, 2002; Shoeib et al., 1999). Table 3 compares the relative proportions of six toxaphene congeners or congener pairs in the Restek technical toxaphene and air sample extract, based on the mean compositional information in Table 2. The percentages of B8-1413 (0.46%) and B9-1679 (1.10%) from the consensus results agreed well with reported values (0.40–0.52% B8-1413 and 1.0–1.5% B9-1679) (Jantunen and Bidleman, 2003; Nikiforov et al., 1999; Shoeib et al., 1999). B8-1413 was significantly enriched (one-tailed t-test, po0:05) and B8-806+B8-809 was significantly depleted (po0:01) in the air sample compared to technical toxaphene. No significant differences were found for the other congeners. Jantunen et al. (2000) collected air samples at the same location during 1996–1997. As percentages of total toxaphene, B81413=1.972.0% and B9-1679=3.373.4% over the

Based on the mean percent composition in Table 2 SD propagated. b Restek product. c Significantly enriched compared to technical toxaphene (po0:05). d Significantly depleted compared to technical toxaphene (po0:01).

year, both significantly enriched compared to the technical product.

5. Conclusions This was the first ILS of toxaphene in air in which all participants were experienced in toxaphene analysis and used GC-MS techniques. Precisions among 10 labs for the determination of total toxaphene and single congeners in a technical toxaphene unknown and an air sample extract ranged from 33% to 65% RSD, similar to the interlaboratory variability reported for biological matrices (Andrews et al., 1995; Stokker, 2003). Only six of the 10 labs fell within 730% of the target value for the technical toxaphene unknown, as recommended by GLP standards. Because of this high variability, it is difficult to compare toxaphene results from different labs. It is recommended that follow-up ILS be done to identify and minimize factors responsible for this variability. A tiered approach is recommended in which participating labs begin by analyzing pure standards of technical toxaphene and single congener solutions, progressing to a more complex level involving some sample handling (e.g., column cleanup) and finally to real environmental matrices. Common sets of technical toxaphene and congener solutions to be used as standards should be provided to all labs. At least two concentration levels for technical toxaphene and congener solution unknowns should be provided and replicate analyses should be requested. Finally, it should be recognized that due to the complexity of toxaphene, the tendency for compound coelutions, and variable NIMS response factors, determination of this chemical

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may never be as precise as for other organochlorine pesticides.

Acknowledgements The authors wish to gratefully acknowledge the assistance of Sathi S. Selliah and Ray Leger of the Laboratory Services Branch, Ontario Ministry of the Environment in the preparation of the study materials, and 11 labs who took part in the ILS.

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