Investigations into the Vertical Distribution of PCDDs and Mineralogy

Sep 2, 2004 - In this study, we report the PCDD and mineralogical results from the analyses of 27 different samples from three ball clay cores from di...
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Environ. Sci. Technol. 2004, 38, 4956-4963

Investigations into the Vertical Distribution of PCDDs and Mineralogy in Three Ball Clay Cores from the United States Exhibiting the Natural Formation Pattern D A M I E N G A D O M S K I , * ,†,‡ MATS TYSKLIND,† ROBERT L. IRVINE,‡ PETER C. BURNS,‡ AND ROLF ANDERSSON† Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana, 46556, and Environmental Chemistry, Department of Chemistry, Umea˚ University, SE-901 87 Umea˚, Sweden

In this study, we report the PCDD and mineralogical results from the analyses of 27 different samples from three ball clay cores from different locations in Kentucky and Tennessee. One goal of this study was to determine if there is a correlation between the mineralogy of the ball clay samples and the PCDD concentrations and/or homologue profiles in each sample. Samples from each of the three cores exhibited the natural formation profile with extremely high PCDD concentrations with low and mostly undetectable levels of polychlorinated dibenzofurans (PCDFs). The maximum toxic equivalents (TEQs) for Cores C-E were 2500, 440, and 15 000 pg WHO-TEQ/g, respectively. Although there does not seem to be a direct correlation between mineralogy and PCDD concentrations or homologue profiles, the mineralogy of Core C is substantially different than that of Cores D and E, which may in part explain the differences in congener patterns we observed among the three cores.

Introduction In recent years, there have been many reports of an unusual PCDD/F profile in certain environmental matrixes, which cannot be traced back to any known anthropogenic source(s). These include wetland and marine sediment samples (1-5) as well as ball clay and kaolin samples from different parts of the United States, Germany, and Spain (6-11). All these samples contained elevated levels of PCDDs, dominated in most cases by OCDD and decreasing concentration with decreasing chlorination. PCDFs were found at low or even undetectable levels in all samples. Moreover, the 1,2,3,7,8,9HxCDD peak (which is coeluted with 1,2,3,4,6,7-HxCDD on a DB-5 column but will be referred to as 1,2,3,7,8,9-HxCDD throughout this paper) dominates the 2,3,7,8-substituted HxCDD isomers, which are not found in known sources, such as combustion related samples. One general difference between the profiles reported for the sediment and clay samples exhibiting the natural formation profile is that the * Corresponding author phone: +46 90 7869241; fax: +46 90 128133; e-mail: [email protected]. † Umeå University. ‡ University of Notre Dame. 4956

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lower chlorinated 2,3,7,8-substituted PCDD congeners are found in much higher concentrations in the clay samples. Although it has been suggested by many researchers that the dioxins found in these particular environmental samples are of natural origin, no definitive evidence has been brought forward to explain the mechanisms and precursors involved in the formation and transformation of these compounds. In 2000, Ferrario et al. reported results from the analysis of eight raw and four processed ball clay samples from Sledge, MS (6). Each of the raw ball clay samples was dominated by OCDD followed by 1,2,3,4,6,7,8-HpCDD, or in two cases, 1,2,3,7,8,9-HxCDD among the 2,3,7,8-substituted PCDDs. 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD were found at extremely high concentrations in the raw ball clay samples with averages of 711 and 508 pg/g dry weight (dw), respectively. Average PCDF values were lower than what was reported for an urban background sample, indicating the clear dominance of PCDDs. There was a distinct change in homologue profiles from the raw to processed samples analyzed by Ferrario et al. (6). Although OCDD was also found in the highest concentration in the processed clay samples, its absolute and relative concentration was much higher than in the raw ball clay samples, with an average OCDD concentration exceeding 200 000 pg/g. Additionally, there was a dramatic decrease in the concentration of TCDD in the processed samples. The average 2,3,7,8-TCDD concentration of the raw ball clay samples was 711 pg/g, whereas the processed samples had an average of 50 pg/g. The authors could not confirm if the extreme differences in the homologue profile of the raw clay samples to that of the processed ones were due to the processing or if the changes reflected the loss and/or formation of specific isomers. Later, Rappe et al. reported PCDD/F results from the analysis of U.S. and German kaolin samples and U.S. ball clay samples (8). The data from the study indicated that the German kaolin and U.S. ball clay both contained elevated concentrations of PCDDs and low or undetectable levels of PCDFs. In addition, the tetra-, penta-, and hexaCDD patterns were similar in both the U.S. ball clay and the German kaolin. Although the patterns were similar, the absolute concentrations were much higher in the U.S. ball clay. The mean WHOTEQ (WHO-TEQ values established by Van den Berg et al. (12)) of the German kaolin was 128 pg/g, whereas the mean of the U.S. ball clay samples was 1035 pg WHO-TEQ/g dm. This study clearly demonstrated that the distinct nonanthropogenic pattern in ball clays and kaolin is not limited to the southern U.S. In 2002, Ferrario et al. reported additional results from the analysis of processed ball clay mined in the U.S. (10). The 2,3,7,8-substituted PCDD concentrations of the processed ball clay samples were extraordinarily high with an average WHO-TEQ value of 3200 pg/g. Congener distribution and the homologue profile of the samples were remarkably similar to previously analyzed samples with the elevated levels of the tetra- to octa-PCDDs. Results demonstrated the stable and reproducible nature of the isomer patterns in the ball clay (10). Recently, Abad et al. reported the results from a comprehensive study of PCDD contents in binder and anticaking agent feed additives from Spain (11). The samples analyzed included minerals such as sepiolite, bentonite, zeolite, vermiculite, and kaolin. All 16 samples reported except kaolin had TEQ levels lower than the European Union (EU) limit of 0.5 pg WHO-TEQ/g. The results from the two kaolin 10.1021/es049579h CCC: $27.50

 2004 American Chemical Society Published on Web 09/02/2004

samples were up to 10 000 times higher than the other minerals, 461 and 232 pg WHO-TEQ/g, respectively. The kaolin profiles were dominated by OCDD, with levels as high as 132 000 pg/g. The profile expressed in pg WHO-TEQ/g was dominated by 1,2,3,7,8-PeCDD, 2,3,7,8-TCDD, and 1,2,3,7,8,9-HxCDD. In addition, 1,2,3,7,8,9-HxCDD was the dominate isomer among the three toxic hexa isomers. The ratio among the 2,3,7,8-substituted hexa isomers (1,2,3,4,7,8HxCDD, 1,2,3,6,7,8-HxCDD, and 1,2,3,7,8,9-HxCDD) was 1:2: 7, which is in accordance to what others have reported for kaolin and ball clay samples. It is apparent from that study that the PCDD results from the kaolin samples are another case of this unique and unexplained natural formation pattern. These results and the aforementioned are a further indication that these high levels of PCDDs with this unique PCDD profile are limited to a certain type of mineral, in particular, kaolin and ball clay, as well as certain sediment samples (e.g., Mississippi (2) and Queensland, Australia (3, 4)). Although it has been clearly demonstrated that the unique PCDD/F profile found in reported ball clay and kaolin samples is not restricted to one geographical location, nearly all PCDD/F results from these analyses thus far have been from grab samples. It has been suggested that a systematic evaluation of the dioxins in these clay deposits may provide information needed to develop a testable hypothesis as to the possible natural origin of these compounds (6). In this study, we present the vertical distribution of PCDD/Fs and mineralogy throughout three ball clay cores from three different mines in the U.S.. One goal of this study was to determine if there is a correlation between the mineralogy and the PCDD concentrations and/or homologue profiles.

Materials and Methods Sampling. The three cores were obtained in August 2002 from three different mines in the U.S.. Each core was drilled without using any oils or lubricants. They were stored at the University of Notre Dame until October of 2002, at which time multiple samples from each core were identified and prepared for PCDD/F and mineralogical analysis. Sampling of Core C (from southwest Kentucky) began at what corresponds to 10.1 m below ground surface (BGS) and continued throughout the length of the core. The samples were taken at 10.1, 11.3, 12.5, 14.3, 15.8, 16.2, 17.7, and 18.9 m BGS and labeled C1-C8, respectively. Seven samples were taken from Core D, which was obtained approximately 20 km southeast of Core C in Kentucky. Sampling began at 7.0 m BGS and continued throughout the length of the core at 8.2, 9.4, 11.3, 12.8, 13.4, and 14.6 m BGS and labeled D1-D7, respectively. The first sample from Core E (obtained approximately 70 km southeast of Core D in Tennessee) was at 10.7 m BGS and continued at 11.0, 11.3, 11.6, 12.5, 14.3, 17.1, 18.6, 21.0, 23.5, 24.7, and 26.5 m BGS and labeled E1-E12, respectively. Each of the 27 ball clay samples was split into two representative samples. One-half of the sample was kept at the University of Notre Dame for mineralogical analysis and organic carbon content determination. The other half of each clay sample was packaged and sent to Umeå University, Sweden for the PCDD/F analysis. PCDD/F Analysis. The analytical protocol has previously been reported by Rappe et al (2). Briefly, each sample was homogenized before extraction. Sixteen 13C-labeled internal standards were added to each sample, and each sample was then Soxhlet-extracted for 16 h in 150 mL of toluene. The 2,3,7,8-substituted PCDD/F internal standards used were 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 1,2,3,4,7,8-HxCDD, 1,2,3,6,7,8HxCDD, 1,2,3,7,8,9-HxCDD, 1,2,3,4,7,8,9-HpCDD OCDD, 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8HxCDF, 1,2,3,6,7,8-HxCDF, 2,3,4,6,7,8-HxCDF, 1,2,3,7,8,9HxCDF, 1,2,3,4,6,7,8-HpCDF, and OCDF. The extracts were

first purified in a multistep silica column followed by a basic alumina column. The final step of cleanup was made on a Carbon AX/21 Celite column. The final extracts were evaporated in 30 µL of tetradecane. Sample analysis was performed using HRGC/HRMS with a 60 m JW DB-5 column directly attached to a VG instrument (70/70S). Prior to GC/ MS analysis, two 13C recovery standards were added, viz., 1,2,3,4-TCDD and 1,2,3,4,7,8,9-HpCDF. All peaks were identified, and the 2,3,7,8-substituted PCDD/Fs were quantified and corrected for internal standards. Non-2,3,7,8-substituted congeners were identified based on known retention order on the DB-5 GC column and quantified against the response of the 2,3,7,8-substituted congeners in the standard for each homologue group, respectively. For peak detection, a signalto-noise ratio of 3:1 was set. Mineralogical Analysis. X-ray diffraction (XRD) was performed on each corresponding duplicate sample from the University of Notre Dame. A Rigaku Miniflex Diffractometer was utilized for the analysis with CuKR 1.540562 wavelength radiation and a nickel filter. The samples were run from 3 to 80° 2θ with a step size of 0.02 and a count time of 0.6 s. Each sample was run four times; bulk, air-dried, ethylene glycolated, and heat treated to 300 °C. On completion of the X-ray diffraction, Jade version 3.1 software was used to identify the mineral assemblages. This program facilitates for background corrections, instrument error, and KR2 peaks.

Results Core C. Results from the 2,3,7,8-substituted PCDD analyses of the eight core samples from Core C are shown in Figure 1a. OCDD dominated each sample, followed by 1,2,3,4,6,7,8HpCDD and 1,2,3,7,8,9-HxCDD. OCDD concentrations range from 6200 (C8) to 68 000 pg/g dw (C2). Interestingly, the 1,2,3,4,6,7,8-HpCDD isomer is found in higher concentrations, ranging between 1.2 and 2.6 times greater than 1,2,3,4,6,7,9-HpCDD. 1,2,3,7,8,9-HxCDD had the highest concentrations among the toxic HxCDD isomers. 1,2,3,7,8,9HxCDD was on average 1.53 times greater than 1,2,3,6,7,8HxCDD. 2,3,7,8-TCDD concentrations ranged from 8 to 53 pg/g dw, and 1,2,3,7,8-PeCDD concentrations ranged from 63 to 960 pg/g dw. The only PCDFs detected were 1,2,3,4,6,7,8HpCDF (1.3 and 4.5 pg/g dw) and OCDF (6.6 and 3.9 pg/g dw) in samples C1 and C4, respectively. The nondetects are not reported in this paper. The average limits of detection (LOD) for the 2,3,7,8-substituted PCDFs in Core C are 1.2, 1.8, 2.7, 4.0, and 9.5 pg/g dw for 2,3,7,8-TCDF, PeCDFs, HxCDFs, HpCDFs, and OCDF, respectively. Percent contribution of each PCDD homologue group to the ∑PCDDs along the depth of Core C is illustrated in Figure 1b. It is clear that the contribution from each PCDD homologue group is similar throughout the length of Core C. Contribution of the TCDDs range from 2.2 to 4.1, PeCDDs from 4.6 to 7.9, HxCDDs from 14 to 22, HpCDDs from 27 to 32, and OCDD from 38 to 51%. The toxic equivalents (TEQs) for the eight core samples range from 180 (C8) to 2500 pg WHO-TEQ/g dw (C2). The contribution of individual 2,3,7,8-substituted PCDDs to the WHO-TEQ is shown in Figure 1c, generally in order of increasing congener contribution. 1,2,3,7,8-PeCDD contributed the greatest percentage to the total WHO-TEQ of each sample, followed by 1,2,3,7,8,9-HxCDD with an average of 40.7 and 24.4%, respectively. Although OCDD was found in the highest concentrations throughout the core, it only contributed, on average 0.28%, to the overall WHO-TEQ for Core C. Core D. Figure 2a illustrates the results of the 2,3,7,8substituted PCDDs analyses of the seven samples from Core D. Furans were not included in Figure 2a since the only VOL. 38, NO. 19, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. (a) 2,3,7,8-Substituted PCDD concentrations throughout the length of Core C. (b) Percent contribution of each homologue group to the ∑PCDDs throughout the length of Core C. (c) Contribution of 2,3,7,8-substituted PCDDs to the WHO-TEQ throughout the length of Core C (generally shown in order of increasing isomer contribution for ease of viewing). 2,3,7,8-substituted PCDF above the LOD was OCDF in samples D1 and D2, at 6.4 and 17 pg/g dw, respectively. Average LOD for 2,3,7,8-substituted PCDFs in Core D are 1.4, 1.9, 3.03, 3.8, and 6.1 pg/g dw for 2,3,7,8-TCDF, PeCDFs, HxCDFs, HpCDFs, and OCDF, respectively. It is apparent that OCDD dominates the first three samples, ranging between 310 000 pg/g dw (D1) and 110 000 pg/g dw (D2). Percent contribution of OCDD to the ΣPCDDs 4958

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in the first three samples (D1-D3) ranged between 82 and 97% indicating the clear dominance of OCDD in the top 2.4 m of the core (7-9.4 m BGS), as shown in Figure 2b. Concentration and percent contribution of OCDD to the ΣPCDDs dramatically drops between samples D3 and D4. OCDD concentration in sample D4 is only 1200 pg/g dw, as compared to 200 000 pg/g dw in D3. Percent contribution of OCDD to the ΣPCDDs in D4 is only 23.1% as compared

FIGURE 2. (a) 2,3,7,8-Substituted PCDD concentrations throughout the length of Core D. (b) Percent contribution of each homologue group to the ∑PCDDs throughout the length of Core D. (c) Contribution of 2,3,7,8-substituted PCDDs to the WHO-TEQ throughout the length of Core D (generally shown in order of increasing isomer contribution for ease of viewing). to 87.4% in D3. Surprisingly, PeCDDs contribute the greatest percentage (28.9%) to the ΣPCDDs in sample D4. WHO-TEQs ranged between 6.8 (D7) and 440 pg WHOTEQ/g dw (D3), with average and median values of 204 and 170 pg WHO-TEQ/g dw, respectively. The contribution of the 2,3,7,8-substituted PCDDs to the WHO-TEQs is illustrated in Figure 2c, generally in order of increasing concentration. As with Core C, 1,2,3,7,8-PeCDD contributes most to the

WHO-TEQ of each sample, again followed by 1,2,3,7,8,9HxCDD (except for D4, where the contribution of 2,3,7,8TCDD is greater than 1,2,3,7,8,9-HxCDD to the WHO-TEQ). Core E. Figure 3a illustrates the results of the 2,3,7,8substituted PCDDs for the 12 samples analyzed from Core E. Furan concentrations were below the LOD in all samples except E1; therefore, they are not included in Figure 3a. OCDF and 1,2,3,4,6,7,8-HpCDF were detected at concentrations of VOL. 38, NO. 19, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. (a) 2,3,7,8-Substituted PCDD concentrations throughout the length of Core E. (b) Percent contribution of each homologue group to the ∑PCDDs throughout the length of Core E. (c) Contribution of 2,3,7,8-substituted PCDDs to the WHO-TEQ throughout the length of Core E (generally shown in order of increasing isomer contribution for ease of viewing). 3.1 and 2.3 pg/g dw, respectively, for sample E1. Average 2,3,7,8-substituted PCDF LODs for Core E are 1.2, 1.9, 2.4, 3.7, and 3.8 pg/g dw for 2,3,7,8-TCDF, PeCDFs, HxCDFs, HpCDFs, and OCDF, respectively. Generally, PCDD concentrations in this core are extraordinarily high, again being dominated by OCDD. OCDD ranges from 240 pg/g dw in a sandy overburden sample (E1) to 430 000 pg/g dw in sample E8. 2,3,7,8-TCDD was found in concentrations as high as 1200 pg/g dw (E10) with average and median values of 285 and 109 pg/g dw, respectively. 1,2,3,7,8-PeCDD ranged between 0.6 (E1) and 7900 pg/g dw 4960

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(E3). Not surprisingly, 1,2,3,7,8,9-HxCDD was at the highest concentrations among the toxic hexa-isomers ranging between 2.4 (E1) and 42 000 pg/g dw (E3), with average and median concentrations of 10 160 and 3200 pg/g dw, respectively. The ratio between 1,2,3,7,8,9-HxCDD and 1,2,3,6,7,8HxCDD ranged between 2.2 and 6.4 with an average of 4.3. Percent contribution of each PCDD homologue group to the ∑PCDDs along the depth of Core E is illustrated in Figure 3b. Surprisingly, OCDD was not the greatest contributor to the ΣPCDDs in two samples, E3 and E10. In these two samples,

TABLE 1. Average and Median Mineralogical Values for Cores C-Ea Core Cb

Core Dc

Core Ed

E1

mineralogy

average

median

average

median

average

median

overburden

percent kaolinte percent illite percent smectite percent quartz percent chlorite

23 17 33 8 20

23 15 35 8 23

81 4 nd 9 nd

85 0 0 10 0

86 1 nd 8 nd

90 0 0 5 0

20 0 0 70 10

a Sample E1 (sandy overburden) was included to demonstrate the contrasting difference between it and the average and median values for Core E. b n ) 8. c n ) 7. d n ) 11.

FIGURE 4. The score plot (a) and the corresponding loading plot (b) based on the PCDD, LOI, organic carbon, and mineralogical data for Cores C-E, respectively. HpCDDs and HxCDDs contribute more to the ΣPCDDs than does OCDD. In the middle section of the core (E4-E9), OCDD clearly is the dominate contributor to the ΣPCDDs with an average contribution of 75%. TEQ values for the 2,3,7,8-substituted PCDDs for each sample in Core E are shown in Figure 3c. WHO-TEQs range from 1.6 (E1) to 15 000 pg WHO-TEQ/g dw in samples E3 and E10. Average and median WHO-TEQs are 4040 and 1160 pg WHO-TEQ/g dw, respectively. The extremely high values for E3 and E10 are primarily due to the concentrations of 1,2,3,7,8-PeCDD and 1,2,3,7,8,9-HxCDD. TEQs in the middle section of the core (E4-E9) are substantially lower since these samples are dominated by OCDD. Mineralogy. One goal of this study was to determine if there is a correlation between the mineralogy of the ball clay samples and the PCDD concentrations and/or homologue profiles observed. The average and median mineralogical values for the three ball clay cores are listed in Table 1. Included separately in Table 1 is sample E1 since it is sandy overburden. It is apparent from Table 1 that the mineralogy of Core C differs considerably from that of Cores D and E. Furthermore, this is illustrated in Figure 4. Figure 4 shows the principal component analysis (PCA) score (a) and loading plots (b) of the PCDD data along with mineralogical, loss on ignition (LOI), and organic carbon (OC) data for each of the 27 samples. The two-component model presented explained 83.4% of the variance in the data set. Principal component (PC) one (t1) explained 62.2% of the variance, which is mainly dominated by the concentration differences of PCDDs in the different clay samples. The second PC (t2) explained 21.2% of the variance and clearly separates Core C from D and E. Thus, it is clear from both PCDD and mineralogical data that all samples from Core C are quite similar. Core C contains considerable amounts of smectite, chlorite, and illite, whereas Cores D and E do not (see Table 2 in Supporting Information). Samples from the bottom half of Core D (D4-D6), as well the bottom of Core E (E12), are clustered together due to their relatively lower PCDD concentrations, LOI and OC

values. Sample E1 (sandy overburden) is dominated by quartz and contains low dioxin concentrations is to the far left of Figure 4a.

Discussion Similarities and Differences among the Cores. There are some distinct similarities and differences among the three cores and even differences within the same core. One similarity is that all the samples analyzed from the cores contain elevated levels of dioxins exhibiting homologue profiles different from any known anthropogenic source. The absence of furans at comparable detections limits is another feature that is in accordance with samples exhibiting the natural formation pattern (1-10). Furthermore, it is clear that among the toxic hexa-isomers, 1,2,3,7,8,9-HxCDD is the dominant congener. The average ratios among the three toxic hexa-isomers (1,2,3,4,7,8-HxCDD/1,2,3,6,7,8-HxCDD/1,2,3,7,8,9-HxCDD) is 1:5.2:8.4, 1.3:1:3.0, and 1:1.3:6 for Cores C-E, respectively. No known anthropogenic source(s) have been reported where 1,2,3,7,8,9-HxCDD is the dominate isomer among the 2,3,7,8-substituted hexa-isomers. Ferrario et al. did a thorough job describing the homologue patterns of known anthropogenic sources and concluded in that study that the concentrations and homologue profiles from the analysis of raw and processed ball clay samples did not match any from known sources (6). The cores from this study were all obtained in the same geological region as the samples from Ferrario et al. study, and as stated before, all samples throughout the cores exhibit the natural formation pattern. Evaluating each core independently, there did not seem to be any trend of dioxin concentration with respect to depth. There were also poor correlations between total organic carbon and PCDD concentrations among all three cores, which was not expected since PCDDs are among some of the most hydrophobic organic compounds. It is interesting to note that even toward the bottom of Cores C and E, for example, E11, which corresponds to 24.7 m BGS, the TEQ is VOL. 38, NO. 19, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 5. Average tetra through heptaCDD isomer specific contribution from the top and bottom strata of Cores C and D. Core E was separated into three sections (top, middle, and bottom) due to the core length. still extremely high (6000 pg WHO-TEQ/g dw). It is highly unlikely that any contemporary PCDD source could migrate the depth of these highly impermeable clay lenses. Variation in PCDD Homologue Contribution. One distinct difference between the results thus far reported for the natural formation pattern observed in sediments in Mississippi and Australia (1, 3, 4) and that of ball clay and kaolin samples is that OCDD usually contributes more than 90% to the ΣPCDDs in the sediment samples. In general, the ball clay and kaolin samples have much higher levels of the lower chlorinated PCDD congeners, especially 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD. The analysis of processed ball clay samples that Ferrario et al. reported exhibited a PCDD homologue profile similar to what has been reported for sediments exhibiting the natural formation pattern. The authors did not speculate whether the changes observed in the profiles between the raw ball clay samples reported in that same study and that of the processed clay samples were due to the processing or whether the changes reflected the loss and/or formation of specific congeners (6). The results from our study indicate that this change may not have been from the processing of the ball clay but from the location where the samples were obtained, both within the same core and among the varying geographical locations. For example, the percent contribution from OCDD to the ΣPCDDs in Core E ranges from 22.2% (E3) to 93.9% (E8). Samples from Core E exhibit profiles similar to what has been reported for sediments as well as other raw and processed ball clay and kaolin samples (6-8). Furthermore, results from Core D clearly show that the first three samples are dominated by OCDD contributing from 81.6 to 96.5% to the ΣPCDDs. In 2002, Ferrario reported additional results from the analysis of processed ball clay samples obtained from mines from Kentucky, Tennessee, or Mississippi (10). The samples contained extraordinarily high levels of 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD with concentrations of 1479 and 1215 pg/g dw, respectively. It is interesting to note that the concentrations of 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD in the 2002 Ferrario et al. study are more than twice the concentration 4962

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than what was reported for the average of the raw ball clay samples in the 2000 study (6, 10). Ferrario’s results from those two studies as well as the ones reported herein suggest the change observed in homologue profiles from the raw and processed ball clay samples (as reported in Ferrario et al. in 2000) are not due to the processing itself but more likely from where the samples were obtained. Dechlorination Patterns. The HeptaCDD ratio in the samples analyzed from Core C are very different from Cores D and E and also what others have observed (13). 1,2,3,4,6,7,8HpCDD was on average 2.1 times greater than 1,2,3,4,6,7,9HpCDD in Core C. The mean 1,2,3,4,6,7,8-HpCDD/1,2,3,4,6,7,9-HpCDD ratio reported by Ferrario et al. was 0.67 (6). Prange et al. found that the ratio ranged from 0.36 to 0.83 in kaolin samples from Queensland, Australia (14). Using congener specific PCDD data from sediment cores, Gaus et al. observed a unique dechlorination pattern throughout the depth of two cores from Queensland, Australia (4). The authors proposed that transformation processes produced a PCDD profile that resulted in a distinct dominance of congeners chlorinated in the 1,4,6,9-positions. The 1,2,3,4,6,7,9-HpCDD/1,2,3,4,6,7,8-HpCDD ratio was found to increase with depth and hence had a direct correlation to an increase in lower chlorinated 1,4,6,9-congeners. Given that the initial results from Core C in this study show a contrasting HeptaCDD ratio from what others have reported, as well as what was observed for Cores D and E, congener specific evaluation of the data, based on the separation obtained on the DB-5 GC column, was performed. Figure 5 (see also Table 3 in Supporting Information) represents the average isomer specific contribution from the tetra, penta, hexa, and hepta PCDD homologue groups, respectively, from the top and bottom strata of Cores C and D (C1-C2, C7-C8, D1-D2, and D6-D7) as well as the top, middle, and bottom strata for Core E (E2-E3, E6-E7, and E10-11). Overall, it is apparent from Figure 5 that the observed dechlorination patterns found in Cores D and E are similar to that of Core C, even though Core C has a contrasting HeptaCDD ratio. In general, there is a higher

contribution from the 1,4,6,9-peak from the top to the bottom strata of each core except for the tetraCDD isomers in Core D (percent contribution of coeluted 1,2,4,7/1,2,4,8/1,3,7,8/ 1,4,6,9-TCDD in D1-D2 is 40% whereas only 18% in D6D7). The results from this congener specific data appear to support what Gaus et al. reported with respect to the HeptaCDD ratio having an affect to the contribution of lower chlorinated congeners (4). However, the congener specific results from this study also demonstrate that the 1,4,6,9peak is not as distinct as the one observed in sediment samples exhibiting the natural formation pattern. Other isomer pairs from each of the other homologue groups contribute nearly as much or more to the overall contribution (e.g., 1,2,3,6,7,9/1,2,3,6,8,9-HxCDD and 1,2,4,6,8/1,2,4,7,9PeCDD for all three cores). Gaus et al., by comparison, reported average 1,4,6,9-substituted congener contributions for two sediment cores of 80 and 84% among the HpCDDs, 77 and 87% among the HxCDDs, 34 and 53% among the PeCDDs, and 25 and 57% among the TCDDs (4). Continuing Research. Although this is the first study reporting the results of the vertical distribution of PCDD/Fs throughout the length of ball clay cores from different areas, more research is needed to formulate a plausible hypothesis as to the possible formation mechanism as well as specific transformation processe(s), which may be occurring. In 2001, Rappe et al. reported the chemical composition of four U.S. ball clay, three U.S. kaolin, and four German kaolin samples (8). The dioxin homologue profiles of the U.S. ball clay and German kaolin were similar, although the overall PCDD concentrations were higher in the U.S. ball clay. From the preliminary evaluation of the chemical composition data, the data indicated similar elemental composition in the U.S. ball clay and German kaolin. Interestingly, the U.S. kaolin samples, with the low PCDD content, deviated from the U.S. ball clay and German kaolin with respect to elemental composition. With the knowledge from that previous study, we will be determining the elemental composition of each sample from this current study to determine if the concentrations of specific elements and/or oxides can be correlated with the possible dechlorination patterns we have observed throughout the three cores. The information from these data may also provide a more definite answer as the role of the ball clay (i.e., is the clay only a sink for the PCDDs?). If it is determined that the clay is acting as a sink for the dioxins and certain elements and/or oxides are aiding in the dechlorination patterns we have reported, then a better understanding of the formation of the ball clay is needed. Another aspect of our ongoing research involves the characterization of the carbonaceous material found in ball clay, which is incorporated into it when it is laid down in lenses (15). These studies could provide insight as to the possible

origin of the extraordinarily high levels of PCDDs in this environmental matrix.

Acknowledgments The authors thank Georgia-Pacific Corporation, Atlanta, Georgia for funding this project. We also thank Tami Talalas and Lauran Sturm for their contribution with the analyses of the mineralogy.

Supporting Information Available Mineralogical data for each of the 27 analyzed samples in this study (Table 2); isomer specific contribution data of the seven averaged core strata; C1-C2 and C7-C8 for Core C; D1-D2 and D6-D7 for Core D; and E2-E3, E6-E7, and E10-E11 for Core E (Table 3). This material is available free of charge via the Internet at http://pubs.acs.org.

Literature Cited (1) Rappe, C.; Andersson, R. Chemosphere (in press). (2) Rappe, C.; Andersson, R.; Bonner, M.; Cooper, K.; Fiedler, H.; Howell, F.; Kulp, S.; Lau, C. Chemosphere 1997, 34, 1297-1314. (3) Gaus, C.; Pa¨pke, O.; Dennison, N.; Haynes, D.; Shaw, G.; Connell, D.; Mu ¨ ller, J. Chemosphere 2001, 43, 549-558. (4) Gaus, C.; Brunskill, G. J.; Connell, D. W.; Prange, J.; Mu ¨ ller, J. F.; Pa¨pke, O.; Weber, R. Environ. Sci. Technol. 2002, 26, 35423549. (5) Tysklind, M.; Andersson, R.; Rappe, C.; Stout, D. Organohalogen Compd. 2002, 57, 341-344. (6) Ferrario, J. B.; Byrne, C. J.; Cleverly, D. H. Environ. Sci. Technol. 2000, 34, 4524-4532. (7) Ferrario, J.; McDaniel, D.; Byrne, C. Organohalogen Compd. 1999, 40, 95-99. (8) Rappe, C.; Tysklind, M.; Andersson, R.; Burns, P. C.; Irvine, R. L. Organohalogen Compd. 2001, 51, 259-262. (9) Jobst, H.; Aldag, R. Umweltchem. Okotox. 2000, 1, 2-4. (10) Ferrario, J.; Byrne, C. Chemosphere 2002, 46, 1297-1301. (11) Abad, E.; Llerena, J.; Saulo´, J.; Caixach, J.; Rivera, J. Chemosphere 2002, 46, 1417-1421. (12) Van den Berg, M.; Birnbaum, L.; Bosveld, B. T. C.; Brunstro¨m, B.; Cook, P.; Feeley, M.; Giesy, G. P.; Hanberg, A.; Hasegawa, R.; Kennedy, S. W.; Kubiak, T.; Larsen, J. C.; van Leeuwen, F. X. R.; Liem, A. K. D.; Nolt, C.; Peterson, R. E.; Poellinger, L.; Safe, S.; Schrenk, D.; Tillitt, D.; Tysklind, M.; Younes, M.; Waern, F.; and Zacharewski, T. Environ. Health Perspect. 1998, 106(12), 775792. (13) Gadomski, D.; Tysklind M.; Irvine, R. L.; Burns, P. C.; Andersson, R.; Talalas, T. Organohalogen Compd. 2003, 61, 373-376. (14) Prange, J. A.; Gaus, C.; Pa¨pke, O.; Connell, D. W.; and Mu ¨ ller, J. F. Organohalogen Compd. 2000, 50, 534-537. (15) Mineral Industry Surveys. Clay & Shale. 1998 Annual Review; U.S. Department of the Interior, U.S. Geological Survey: Denver, CO, October 1999.

Received for review March 18, 2004. Revised manuscript received July 24, 2004. Accepted July 26, 2004. ES049579H

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