Research Polychlorinated Naphthalene Congener Profiles in Background Sediments Compared to a Degraded Halowax 1014 Technical Mixture U . G . J A¨ R N B E R G , * L . T . A S P L U N D , A . - L . E G E B A¨ C K , B . J A N S S O N , M. UNGER, AND U. WIDEQVIST Laboratory for Analytical Environmental Chemistry and Laboratory for Aquatic Ecotoxicology, Institute of Applied Environmental Research, Stockholm University, S-106 91 Stockholm, Sweden
Polychlorinated naphthalenes were quantified in 10 lake and sea sediment samples from sites with no known present local pollution source. Levels ranged from 0.14 to 7.6 ng/g (dry weight). The chlorinated naphthalene (CN) congener profiles showed an increased relative abundance of 1,3,5,7- and 1,4,6,7-substituted congener profiles as compared to the reported CN congener profiles of technical PCN and PCB. Further, a dominance of 1,2,3,4,5,6,7-heptaCN over 1,2,3,4,5,6,8-heptaCN was found in all samples in contrast to the ratio reported for technical PCN and PCB products. Some samples showed traces of 2,3,6,7-substituted CN congeners, indicative of thermal sources, such as municipal waste incineration. These profiles were compared with the profiles obtained from a Halowax 1014 technical mixture subject to aerobic microbial degradation and sunlight photolysis. The aerobic microbial culture gave no alteration of the CN congener profile of over a 28-day period, whereas sunlight exposure of Halowax 1014 in methanol yielded a more low chlorinated CN congener profile. Furthermore, CN congeners with chlorines in 1,8positions were more affected than those with 1,3,5,7- or 1,4,6,7-substitution. These results indicate that photolysis may explain the enhancement of the relative abundance of some of the 1,3,5,7- and 1,4,6,7-substituted CN congeners in the environment but not the heptaCN profile.
Introduction During the past three decades halogenated aromatic compounds such as polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) have attracted much attention from the scientific society and decision makers. This is due to their inherent properties such as persistence and lipophilicity causing them to bioaccumulate in food webs but also due to their serious biological effects. Much effort has been put into the study of the transportation and transformation processes affecting these substance classes. This knowledge proves to be of great value also for elucidating the behavior of other halogenated compounds with similar structure and properties. A far less investigated class of substances is polychlo* Corresponding author phone: +46-8-6747152; fax: +46-86747636; e-mail:
[email protected]. 10.1021/es980360a CCC: $18.00 Published on Web 11/13/1998
1998 American Chemical Society
rinated naphthalenes (PCNs). The PCNs consist of 75 congeners with one to eight chlorine atoms on the rings. Most of these congeners have been identified either in technical mixtures or municipal waste incineration (MWI) fly ash (1-4), although the presence of all of them in environmental samples has not been verified. Several investigations have been presented during the past years on the occurrence of PCNs in the environment (5-12). Also, some of the more important sources have been pointed out, such as co-contaminants in commercial PCB formulations (13, 14), municipal waste incineration (MWI) (15-18, 2, 3), metallurgical processes (19, 16), and chlorine production through the chloroalkali process (20, 9, 21). Although the industrial production of technical PCN formulations began to decline in the 1960s, products containing these formulations are still present in the technosphere and will continue to leach PCNs to the environment (22). PCNs were recognized early on as hazardous substances due to several cases of intoxication of workers during manufacture and use and of cattle by accidental contamination of food with technical PCN (23-25). The toxicological properties of PCNs have been investigated to some extent both for technical mixtures and individual congeners. The acute effects of PCNs, i.e., liver damage and dermal alterations such as chloracne, hyperkeratosis, and edema appear to be associated with the higher chlorinated naphthalenes (CNs), i.e., penta- and hexaCNs (23, 26). PCNs also exhibit AHH (aryl hydrocarbon hydroxylase) and EROD (7-ethoxy-resorufin-o-deethylase) enzyme induction similar to 2,3,7,8tetrachlorodibenzo-p-dioxin (TCDD). The reported enzyme induction potency of a mixture of 1,2,3,4,6,7/1,2,3,5,6,7hexaCN (CN66/67) was in the same range as for octachlorodibenzo-p-dioxin (OCDD) and 3,3′4,4′-tetrachlorobiphenyl (CB77) (27). Information regarding the behavior of PCNs in the environment was scarce in the literature. PCNs have been reported in samples from arctic areas, indicating that they are amenable to long-range transport (5, 9). Similar to PCBs and PCDDs/PCDFs they are lipophilic and persistent and tend to bioaccumulate and biomagnify (9, 28, 29). Limited information is presently available on the transportation processes specifically related to PCNs in the atmosphere, aquatic, marine, or terrestrial environment. A few reports exist on the levels and congener compositions of PCNs in air close to ground level (30-32), indicating that they are transported through the atmosphere. Regarding transformation of PCNs, Ruzo et al. (34-37) and Gulan et al. (33) previously reported on photolysis of some of the lower chlorinated congeners (mono-tetraCNs) in methanol and water, indicating that 1,8-substituted congeners are readily dechlorinated upon UV irradiation. Data on microbial aerobic degradation was limited to 1- and 2-chloronaphthalene (38), indicating a conversion to hydroxylated metabolites, whereas the only information available on higher chlorinated CNs stated that CNs with three to five chlorines were nonbiodegradable using a standard degradability test (39). A previous study performed at our laboratory focused on the comparison of congener profiles in several environmental samples and various source-related samples (40). The samples in that investigation included sediment samples from several locations in Sweden, both from contaminated sites and from sites with no known point source pollution (background) as well as different biological samples, air and VOL. 33, NO. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Sampling Sites and Location Data location
type
sampling site depth, m
year
core depth, m
ignition loss, %
L. Storvindeln L. Gro¨ velsjo¨ n L.Siljan L. Yngern L. Ska¨ resjo¨ n L. Sjunnen L. Aspo¨ dammen Bothnian Bay Baltic Proper Gulph of Gotland
alpine alpine forest/rural forest forest forest/rural rural/municipality brackish sea brackish sea brackish sea
(29)a 20 40 11 (13)a 1.5 (2-3) 71 190 112
1989 1988 1988 1997 1991 1996 1996 1989 1989 1989
0-2 0-2 0-2 0-2 0-1 0-2 0-2 0-2 0-2 0-2
11 21 8 29 39 32 29 8 15 13
a
No data available, maximum depth given in parentheses.
water samples, chloroalkali graphite sludge samples, MWI fly ash, and several commercial PCB and PCN formulations. The results from that study indicated that some congeners are more abundant than others in background sediment as well as biological samples as compared to potential source samples and the air samples. Most of these congeners all have chlorines substituted in the 1,3,5,7- or 1,4,6,7-positions, i.e., 1,3,5,7-tetraCN (CN42), 1,2,3,5,7- (CN52) and/or 1,2,4,6,7pentaCN (CN60), CN66 and/or CN67, and 1,2,3,4,5,6,7heptaCN (CN73). In particular it was observed that the CN73 congener was far more abundant than would be expected from the relative abundance of this congener in the investigated source samples. These results called for further studies on the congener composition of PCNs distributed into the environment. In the present investigation the variation in CN congener profiles and concentrations in background sediment samples from 10 locations around Sweden was studied. Since it was anticipated that aging of technical PCN through microbial and/or abiotic transformation could account for the differences in profiles between sediments and known sources, a technical PCN mixture was subject to aerobic microbial degradation and photolysis.
Materials and Methods Samples and Sampling Sites. The samples used in this investigation were taken both from samples stored from previous investigations and one freshly collected sample. Data on these samples and sampling sites are given in Table 1. The samples were chosen from sites in and around Sweden where no present point source pollution of PCNs could be expected, thus reflecting medium to long-range air and/or water transport. The sampling sites are indicated in Figure 1. Biodegradation Assay. The biodegradation assay developed for this study was partly adapted from a study of Fava et al. (41) and from experiences at our laboratory. To avoid bias from a solvent, spiked natural sediment was used in the assay to resemble environmental conditions. The 250mL Erlenemeyer flasks used for the experiment were silanized prior to use to avoid selective adsorption losses. An Amberlite XAD-2 trap (Fluka Chemie AG, Buchs, FRG; Soxhlet prewashed; methanol, acetonitrile, diethyl ether, methanol) was used to allow gas exchange with the vessel without evaporation losses of the lighter PCNs during the experiment. One milliliter of a solution of Halowax 1014 (Koppers Co., Inc. PA), 1.46 pg/µL in n-hexane was administered to 5 g of dried sediment (oven dried, 110 °C overnight) from the Lake Yngern. After equilibration with the sediment overnight, the solvent was gently evaporated on a waterbath at room temperature using a nitrogen stream for 30 min. A mineral medium and 100 µL of the inoculum from the supernatant phase of a freshly collected and settled municipal sewage sludge were added to the vessel. An abiotic control was prepared in a 2
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FIGURE 1. Map of Scandinavia showing sampling sites in Sweden and in the Baltic Sea. The bar graphs show the levels of total PCNs (4-7 Cl) expressed as nanograms per gram dry weight. similar way and immediately extracted. The degradation vessel was left for 28 days in complete darkness with continuous stirring, using a Teflon bar. The vessel was opened and allowed to exchange air every fifth day. During the experiment the temperature was constant at 25 °C. Photolysis Experiment. Approximately 1 µg of technical Halowax 1014 (solid flakes) was dissolved in 10 mL of methanol (Analytical grade, Merck, Darmstadt, Germany) in a quartz tube with stopper. After 60 min of ultrasonication, an aliquot of the solution (2 mL) was taken out as a control and kept in the dark at room temperature during photolysis. Sunlight irradiation was performed on the roof of the laboratory building against a near black surface for a total of 10 h at midday during 2 days of uninterrupted sunlight in the end of May 1997. The tube was declined in a 90° angle toward incident light. A second 2-mL aliquot was taken after 4 h. The control and irradiated samples were diluted with 2 mL of Milli-Q water and extracted with 2 mL of n-hexane. The hexane phase was then taken to GC-MS analysis.
Analytical Procedure. All sediment samples including the biodegradation samples were analyzed using the same procedure. This procedure was essentially the same as in a previous report (9). Wet centrifuged (1800 rpm, 10 min) sediment was batch extracted twice in a screw-cap vial with acetone (LiChrosolv Merck Darmstadt, Germany) and acetone/n-hexane (LiChrosolv Darmstadt, Germany), according to Jensen et al. (42). The combined extracts were then extracted in a separation funnel with a water solution of sodium chloride (0.2 mol/L)/phosphorous acid (2 mol/L). Reextraction of the water phase was done using two 10-mL portions of diethyl ether (10 vol %)/n-hexane (90 vol %). The XAD trap was eluted with three 10-mL portions of diethyl ether into the Erlenemeyer flask. Bulk matrix constituents were removed by shaking with sulfuric acid (98%, BDH Laboratory Supplies, Poole, England). Reextraction of the acid phase with n-hexane was performed to provide a quantitative transfer of analytes. Elemental sulfur was removed by complexation with a tetrabutylammonium sulfite reagent in a n-hexane/2-propanol (Analytical grade, Merck, Darmstadt, Germany) system saturated with sodium bisulfite, according to Jensen et al. (42). Recovery standard, 13C12-labeled 3,3′,4,4′5-pentachlorobiphenyl (CB 126, Cambridge Isotope Laboratories Inc., Andover, MA) was added to the samples prior to the extraction. Except for the degradation samples, further purification was performed with two HPLC gel permeation columns (PLgel, 5 µm, 50 Å, 300 mm × 7.5 mm Polymer Laboratories, U.K.) coupled in series. The eluent was dichloromethane:n-hexane, 2:3 at a flow rate of 0.7 mL/min. All samples were then fractionated on two 2-(1-pyrenyl)ethyldimethylsilylated silica HPLC columns (Cosmosil PYE 5 µm, 150 mm × 4.6 mm, Nacalai Tesque, Japan) coupled in series. The eluent was n-hexane saturated with water at a flow rate of 0.5 mL/min and the flow was reversed after 19 min. The columns were thermostated at 20 °C. A fraction containing the CN congeners with four to eight chlorines was collected between 22 and 29 min while backflushing the columns at a flow rate of 1.2 mL/min. Final determination was performed on a Hewlett-Packard GC-MSD (5890/5970b HP; Avondale, PA) equipped with a 60 m × 0.25 mm × 0.25 µm fused silica capillary column (DB5-MS, 5% phenyl methyl polysiloxane, J&W Scientific; Folsom, CA) and the same GC equipment in combination with a Finnigan MAT95 high-resolution magnetic sector mass spectrometer operating at a resolution of more than 4000. Analytes were quantified against a series of standard solutions of one authentic reference substance for each homologue group, i.e., 1,3,5,7-tetra- (CN42), 1,2,3,5,7-penta(CN52), 1,2,3,5,6,7- and 1,2,3,4,6,7-hexaCN (CN66/67), and 1,2,3,4,5,6,7-heptaCN (CN73) using 2,2′,3,3′,4,5,6′-heptachlorobiphenyl (CB174, Bureau Central de Reference, BCR, EEC) as volumetric standard. Individual CN standards were obtained as kind gifts from Professor Udo A. Th. Brinkmann, Free University, Amsterdam, or Dr. Eva Jakobsson, Department of Environmental Chemistry, Wallenberg Laboratory, Stockholm University. Identification of CN peaks according to their GC elution order was based on retention time compared to Halowax 1014 and a MWI fly ash sample, as well as a proper isotopic ratio. Where relevant, identification of individual CN congeners other than those used for quantification, was based on previously published retention data (1-3). A procedural blank was analyzed within each sample series and solvent blanks were run immediately after the highest concentration of standard solution to monitor possible carry-over effects. The photolysis samples were analyzed on a HewlettPackard GC-JEOL Automass MS (Japan) equipped with a 30 m × 0.25 mm × 0.25 µm fused silica capillary column (DB
17Ht, 50% phenyl methyl polysiloxane, J&W Scientific; Folsom, CA).
Results Sediment Samples. The analytical procedure was capable of distinguishing between 42 individually resolved peaks covering a total of 48 CN congeners with four to seven chlorine atoms. In most of the sediment samples however, only 32 peaks could be detected, i.e., 40 congeners. A few samples showed traces of 1,2,3,6,7-pentaCN (CN54) and 1,2,3,6,7,8-hexaCN (CN70) which may be indicative of thermal sources (2, 9, 40). The levels expressed as the sum of four to seven chlorinated CNs ranged between 0.14 and 7.6 ng/g on a dry weight basis. The lowest values were found in the lake samples from the northern half of Sweden (Figure 1), whereas the samples from the southern part showed somewhat elevated levels. The five lowest levels are lower than those reported by Koistinen et al. (7) for background sediments. There was also a marked difference in CN levels between the sample from the northern part of the Baltic sea, compared to the samples from the southern part. This finding agrees with the increase in the levels of PCB generally encountered when going from the northern part of the Baltic sea toward the southern part (43) and may indicate a similar behavior and/or source for these compound groups. The elevated levels of PCNs in the Gulph of Gotland sample as compared to the Baltic Proper sample may be due to a PCB pollution source at the Swedish coast (100 km distance). It should be stressed at this point that the number of samples analyzed excludes the use of a statistical significance test. Furthermore, the sedimentation rates and conditions at the sampling sites were not known. Therefore the differences in levels found should only be regarded as indicative. Although each sample displayed a unique congener profile, some properties were common between the profiles of the 32 major peaks as shown in Figure 2. All samples except two displayed a dominance of 1,2,4,6-/1,2,4,7-tetra- (CN33/ CN34), 1,2,3,5,7-/1,2,4,6,7-penta- (CN52/CN60), 1,2,3,5,6,7and 1,2,3,4,6,7-hexa- (CN66/CN67), and 1,2,3,4,5,6,7-heptaCN (CN73) within each homologue group. Some of the samples also showed a higher relative level of 1,2,4,5,6pentaCN (CN57). Both L. Gro¨velsjo¨n and L. Aspo¨dammen showed markedly higher relative levels of CN42 and the latter also contained a higher proportion of CN52/CN60 compared to the other samples. Biodegradation Assay. The 28-day degradation experiment did not show any measurable change in the congener composition of tetra- through hexaCNs as compared to the abiotic control. The variations found were not large enough to be distinguished from the response variation between subsequent standard runs. The variation in the ratio of the areas of two adjacent peaks between three runs was found to be less than 8%. The lower chlorinated congeners (monotriCNs) may have been affected, but these could not be determined using the present methodology. The analysis of the sediment sludge from the abiotic control also verified that no selective losses of the added congeners occurred in the experimental setup and throughout the analytical procedure. Sunlight Irradiation. The interpretation of the photolysis results is complicated by the possibility that some lower chlorinated congeners could be degradation products of higher chlorinated congeners. It is apparent from the chromatograms in Figure 3 that apart from a general shift toward lower chlorinated congeners due to a loss of higher chlorinated CNs, several of the 1,8-substituted congeners were selectively lost during sunlight irradiation. This was particularly pronounced for the 1,3,8-triCN (CN22), 1,2,4,8VOL. 33, NO. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Bar graphs of the major 32 congeners quantified in the sediment samples, identified with their CN numbers. Levels are expressed as nanograms per gram on a dry weight basis. (CN35) and 1,2,5,8-tetraCN (CN38), 1,2,4,7,8- (CN62) and 1,2,3,5,8-pentaCN (CN53), and 1,2,3,5,7,8-hexaCN (CN69). Among the more persistent and/or product congeners were found 1,4,6-triCN (CN24), 1,2,5,7- (CN37), 1,2,4,6-/1,2,4,7(CN33/CN34), and 1,4,6,7-tetraCN (CN47), and 1,2,3,5,7-/ 4
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1,2,4,6,7- (CN52/CN60) and 1,2,4,5,6,8-/1,2,4,5,7,8-hexaCN (CN71/CN72). The identity and relative contribution of the coeluting (/) congeners were not checked. These results confirms the previously reported results on photolysis of some of the individual lower chlorinated CNs (33-37).
FIGURE 3. GC-LRMS chromatograms of control and sunlight exposed technical Halowax 1014. Conditions: Column, DB 17Ht 30 m × 0.25 mm × 0.25 µm. Carrier gas, helium at a head pressure of 90 kPa. Temperature program: 90 °C (held 2 min)sramp 25 °C/mins180 °Csramp 3 °C/mins290 °C (held 15 min)sramp 12 °C/mins300 °C. Asterisks denote congeners showing a drastically reduced relative intensity. CN numbers are given in parentheses. The relation between the two heptaCNs was found to be similar in the irradiated samples and in the control, indicating that the relative photolysis rate or product ratio of these two congeners in methanol may be of the same order. The identities of the peaks in the chromatogram resulting from the GC-MS analysis on the polarizable DB17Ht column was checked by authentic reference substances for most of the tri- and tetraCNs as well as by comparing the elution order reported by Nakano et al. (1) and Imagawa et al. (2). For some of the triCNs, the identity could not be established due to contradictory results. It should also be noted that some of the tetraCNs (e.g., CN37) elute in a reversed order on this column as compared to a 5% phenyl methyl silylated silica column.
Conclusions The results from this investigation verified the increased relative abundance of some of the 1,3,5,7- and 1,4,6,7substituted congeners in the background sediments as compared to PCB contaminated sites as well as technical PCB and PCN products. The higher relative abundance of CN73 was confirmed in all 10 sediment samples. A similar ratio of CN73 to CN74 has been verified in both particulate and gas phase from a municipal air sample (32), indicating that this ratio may be related to some source process, i.e., thermal sources. The anomalous tetra- and pentaCN congener profiles of two samples may indicate an unknown local source or result from differences in the conditions at these sites. Previous investigations of air sampled at AmVOL. 33, NO. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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marna¨s, close to L. Storvindeln, and at the southern part of Gotland in the Baltic Sea gave no indications of geographical differences in the CN congener profiles, regardless of the wind direction at these sites (30). Photolysis may account for the increased abundance of CN33/34 and CN52/60 encountered in background sediment samples. Since the present study was performed in methanol, these results may not necessarily reflect the situation in the environment regarding photolysis rates. Considerable differences in photolysis rates can be expected in natural waters due to the presence of quenching and sensitizing substances. The results from this study, however, indicate that photolysis needs to be accounted for when comparing CN congener profiles in source and environmental samples. Aerobic microbial degradation appeared to be less important than photolysis in altering the congener profile of CNs with four to eight chlorines. Microbial anaerobic degradation may, however, be of importance for the dechlorination of PCNs and there is a need for further studies in that area.
Acknowledgments The authors wish to express their gratitude to Michael Strandell for invaluable assistance with the HR-MS runs.
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Received for review April 9, 1998. Revised manuscript received August 19, 1998. Accepted October 1, 1998. ES980360A
