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Clinical Chemistry Division “Center for Environmental Health, Safety and Operations Manual for the Chemical Toxicant Laboratory”;Centers for Disease Control, Atlanta, GA, 1984. Hileman, F. D.; Mazer, T.; Kirk, D. E. A Program for Monitoring Potential Contamination in the Laboratory Following the Handling and Analyses of Chlorinated Dibenzo-p-dioxins and Dibenzofurans. Environmental Science Research: H u m a n and Environmental Risks of Chlorinated Dioxins and Related Compounds; Tudor, R. E.; Young, A. L.; Gray, A. P., Eds.; Plenum: New York, 1983;Vol. 26,p 697. Lapeza, C. R.; Patterson, D. G.; Liddle, J. A. “An Automated Apparatus for the Extraction and Enrichment of 2,3,7,8TCDD in Human Adipose Tissue”;Presented at the Sci-
entific Computing and Automation Conference and Exposition, Atlantic City, NJ, May 1-3, 1985. (6) McConnell, E.E.; Moore, J. A. Ann. N.Y. Acad. Sci. 1979, 320, 138. (7) “Polychlorinated Dibenzo-p-dioxins”;Report NRCC 18576; National Research Council of Canada, 1981. (8) Patterson, D. G.; Holler, J. S.; Groce, D. F.; Alexander, L. R.; Lapeza, C. R.; O’Connor, R. C.; Liddle, J. A. Enuiron. Toxicol. Chem. 1986,5(4), 355-360.
Received for review September 18,1985. Accepted February 18, 1986. Use of trade names is for identification only and does not constitute endorsement by the U S . Public Health Service or by the U.S. Department of Health and H u m a n Services.
Methylthio Metabolites of Polychlorobiphenyls Identified in Sediment Samples from Two Lakes in Switzerland Hans-Rudolf Buser” and Markus D. Mulier Swiss Federal Research Station, CH-8820 Wadenswil, Switzerland
Methylthio metabolites of polychlorobiphenyls (MeSPCBs) were identified in dated sediment samples from two lakes in Switzerland by using high-resolution gas chromatography (HRGC) and negative ion chemical ionization mass spectrometry (NICI-MS). MeS-PCBs and concomitant PCBs were found in all samples since the 1940s. This onset is earlier than that of other chlorinated pollutants including polychlorinated dioxins and furans and consistent with the first use of PCBs in the 1930s. The results indicate early environmental contamination from these important industrial chemicals. Complex mixtures of MeS-PCBs with various tri- to heptachlorinated congeners were observed. Total concentrations of MeS-PCBs were estimated to be as high as 1-5 ppb (dry weight basis) or up to 2% relative to the concentration of PCBs. MeSPCBs interfere in PCDD analyses and mimic the presence of certain PCDDs in environmental samples. W
Introduction Polychlororobiphenyls (PCBs) are important technical products. They were technically produced first in 1929 and used in a variety of applications. Cumulative production and use up to 1975 were estimated at 635 000 tons for the U.S.and at more than 1OOOOOO tons worldwide (1). The technical products are complex mixtures of various chloro homologues and isomers. Theoretically, 209 PCB isomers (mono- to decachlorinated) exist, and around 150 have been detected in various technical formulations. Aroclor 1254 and 1260, two common technical products, consist of tri- to heptachlorinated and penta- to nonachlorinated congeners, respectively. Polychloroterphenyls (PCTs) are another related group of compounds produced since the 1930s with a more limited use for similar applications. PCBs are now environmental contaminants on a global scale; they are found nowadays in specimens from such remote areas as the Arctica and Antarctica (2, 3). PCB pollution can be either direct (spills,dumps, accidents, and waste streams) or indirect via atmospheric transport. PCBs can also be combustion-generated ( 4 ) ; however, major pollution of the environment is by the technical products. The later conclusion is based on the fact that 730
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similar PCB isomer compositions are observed in environmental samples as in the technical products, and that environmental levels of PCBs are orders of magnitude higher than that of other combustion-generated compounds (like the polychlorinated dibenzo-p-dioxins, PCDDs, and dibenzofurans, PCDFs) present in emissions from combustion sources at similar concentrations. PCBs are chemically and biologically stable compounds that accumulate in food chains (5). Their environmental fate therefore is important. PCB metabolites have been detected in various substrates and biosystems; metabolites detected were mainly phenolic products (chlorinated hydroxy- and polyhydroxybiphenylsand their methyl ether compounds) and ring-degraded microbial oxidation products (benzoic acids) (5,6). Sulfur-containing metabolites (methylsulfonyls, methyl sulfones, and methylthio compounds) have been identified in mammals (mice, rats, guinea pigs, and seal) (7-9) and humans (IO),but not in fish (11). Photolytic dehalogenation of PCBs has been reported and may be of importance for the environmental degradation of PCBs (12). Comparatively less is known about environmental metabolites of PCBs in soil and sediments. Aquatic sediments are the ultimate sink for many anthropogenic compounds. Such sediments can preserve a historical record of their deposition. Analysis of suitably dated sediment cores may thus reveal the historical record of such contaminants, as has been shown for PCDDs and PCDFs in sediments from various lakes (13, 14). In this study, we report the identification of methylthio-substituted PCBs (MeS-PCBs) in dated sediment samples from two lakes in Switzerland. High-resolution gas chromatography (HRGC) and negative ion chemical ionization mass spectrometry (NICI-MS) revealed the presence of these metabolites and concomitant PCBs since the 1940s. To our knowledge, this is the first finding of environmental metabolites from these important industrial chemicals. Additional anthropogenic compounds, including PCDDs and PCDFs, were detected in more recent samples from the same locations. The results confirm qualitatively earlier data for PCDDs and PCDFs in sediments from the same lakes (14). The interference of MeS-PCBs in ultratrace (parts per trillion, ppt) environ-
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0 1986 American Chemical Society
mental analyses of PCDDs and PCDFs is pointed out. Experimental Section Sediment Cores and Dating. Sediments from Lake Zurich and Lake Baldegg were investigated. These lakes are in the Swiss middleland region and influenced from the more densely populated and industrialized areas of northern Switzerland. Short gravity (1m) cores were taken by the Geology Institute, Swiss Federal Institute of Technology (ETH), Zurich (courtesy of K. Kelts, F. Niessen, and C. Siegenthaler) from the deepest parts of these lakes (Lake Zurich, 1000 m off Thalwil, at a depth of 120 m; Lake Baldegg, 500 m off Retschwil, at a depth of 66 m) and close to locations where cores were taken for a previous study (14). The laminated sediment sequences in these lakes are comprised of varves (annual couplets) derived from an annual cycle of biologically induced calcite (light-colored) precipitation in spring to summer and deposition of organic matter and diatom frustules in autumn to spring (15). Preservation of these laminae is the result of eutrophication that leads to anoxic conditions (H2S,COz)for benthic organisms in the sediment. The dating under these circumstances is straightforward by counting annual varves; it was verified by comparison to known event markers and photographs (15,16). The cores were sliced in the ETH laboratory into 5-year intervals (segments), placed in glass jars and refrigerated until analyzed. A total of five segments covering the years 1913-1918,1929-1934,1945-1950, 1960-1965, and 1975-1980 from Lake Zurich, and two segments covering the years 1915-1920 and 1975-1980 from Lake Baldegg were analyzed. Extraction and Cleanup of Sediment Samples. Sediment samples (wet weight about 25 g) were dried at room temperature and the dry weights determined (12-15%). The samples were then treated with dilute HC1 (5%) until evolution of HzS and COz ceased. Extraction was done by shaking with four portions of acetonelnhexane on a mechanical shaker. Acetone was removed by reverse partitioning into water, and the concentrated nhexane phase was chromatographed on silica (Merck, 0.5 g, eluant 10 mL of n-hexane) and on alumina (Woelm, basic, activated at 130 O C, 1g, eluants 10 mL of 2% and 50% methylene chloride in n-hexane). Chromatography was carried out in disposable Pasteur pipettes (150 X 6 mm). The first alumina fraction contained PCBs, some MeS-PCBs, and other less polar pollutants; the second alumina fraction contained the bulk of the MeS-PCBs, PCDDs, PCDFs, and more polar pollutants. Extracts containing visible amounts of contaminants (sulfur and organics) were further treated by shaking with mercury (1min) and an additional chromatography on sulfuric acid (40%) treated silica. This treatment did not affect the methylthio and other compounds investigated. A few samples were fortified with small amounts (20 pg) of 13Clabeled PCDDs and PCDFs (2,3,7,8-tetra-CDD/CDF and octa-CDD) prior to extraction and cleanup. The final fractions were concentrated (10-50 pL) and aliquots (2 pL) injected in isooctane for NICI-MS analysis. NICI-MS Analysis. NICI-MS is a very sensitive (1-10 pg for full spectra, detection limit
