(10)Eisenreich, S. J.; Elzerman, A. W.; Armstrong, D. E. Enuiron. Sci. Technol. 1978, 12, 413-7. (11) Garrett, W. D. Limnol. Oceanogr. 1965, 10, 602-5. (12) Paraluz, C. M. Appl. Spectrosc. 1978,22, 520-6. (13) Kundu, N. K. Fette, Seifen, Anstrichm. 1977, 79, 170-3. (14) Sinclair, A,; Hallam, T. R. Analyst 1971,96, 149-54. (15) Giam. C. S.: Chan. H. S.: Neff, G. S. Anal. Chem. 1975, 47, 2225-9. (16) Van Vleet, E. S.; Quinn, J . G. Enciron Sci. Technol 1977, 1 1 , 1086-92. (17) Horner, H. J.; Weiler, ,J. E.; Angelottl, N. C. Anal. Chem. 1960, 32, 858-61. (18) Smith, A. L., E:d. "Analysis of Silicones"; Wiley: New York, 1974; 407 pp. (19) Barger, W.R.; Daniel, W.H.; Garrett, W,D. Deep-sea Res 1974,
21, 83-9. (20) Pellenbarg, R. E. Estuarine Coastal Mar. Sci. 1978, 6, 18795. (21) Hatcher, P. G.; Keister, L. E.; McGillivary, P. A. Bull. Enuiron. Contam. Toxicol. 1977,17, 491-8. (22) Maggi. P.; Alzieu, C. Sei. Peche 1977,269, 1-3. (23) Nies, Dirk, Department of Chemistry, University of Maryland, personal communication, 1978. Received for review August 30, 1978. Accepted December 11,1978. Work supported in part by Postdoctora/ Research Associateship from the National Research Council. Ship time aboard RIV Ridgely Warfield provided b y National Science Foundation Grant No. NSF-OCE-77-2079 to Dr. Church, I'niuersity of Delaware.
Accumulation of Polychlorinated Biphenyls (PCBs) in Surficial Lake Superior Sediments. Atmospheric Deposition Steven J. Eisenreich" and Gregory J. Hollod Environmental Engineering Program, Department of Civil and Mineral Engineering, University of Minnesota, Minneapolis, Minn. 55455
Thomas C. Johnson Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minn. 55455
w Sediment cores were obtained from Lake Superior by means of an oceanographic box corer and analyzed for polychlorinated biphenyls (PCBs). Concentration of PCBs in the top 0.5 cm averaged 0.17 f 0.13 pglg of sediment on a lakewide basis. The maximum PCB concentrations were found in surficial sediments between the Keweenaw Peninsula and Thunder Bay in the prevailing downwind direction of Thunder Bay, Ontario. Depth-fractionated sediments yielded no detectable PCBs a t depths greater than 3 cm below the sediment-water interface, and they often were not detected below a burial depth of 1 cm. The depth of sediment turbation by biotic or physical processes appears to be less than 1cm. PCB input to Lake Superior from the atmosphere (dry, wet, gaseous) is estimated as 3-8 X lo6 gyear-I, and can account for sedimentary PCB concentrations. The PCB sedimentation rate in Lake Superior is estimated as -0.3-0.4 pg-m-*.year-'. T h e results of this study suggest that atmospheric transport and deposition may dominate PCB input to the Lake Superior ecosystem.
is likely to be the major source of PCBs to Lake Superior, since the lake has a large surface area compared to its drainage basin, has minimum tributary inflow, lacks industrial and urban activity in the basin, and greater than 50% of total water budget occurs in the form of rain. Although recent studies (1, 4, 11, 12) indicate the PCB concentrations in certain commercial fish species are approaching or are greater than the FDA action limit of 5 pg/g, the water concentrations remain a t or below detection levels (12). Since lake sediments act as sinks for PCBs entering the lake system (2) (and PCBs may be recycled by the biological community inhibiting permanent burial ( 1 3 ) ) ,a study was conducted of the PCB content of surficial bottom sediments in Lake Superior and compared to estimated PCB inputs to the lake from the atmosphere and tributary inflow.
The introduction of polychlorinated biphenyls (PCBs) and other chlorinated hydrocarbons (e.g., DDT group pesticides, aldrin, dieldrin, mirex) into the Great Lakes has resulted in their accumulation in every level of the food chain. Measured concentrations of PCBs in some fish species in Lake Michigan (1-3) and the other Great Lakes ( I , 4 ) have confirmed that levels exceed the U.S. Food and Drug Administration's current guidelines of 5 pglg. As a result of high PCB concentrations in Lake Michigan fish, the commercial fishing industry has been curtailed and warnings of the hazards of human consumption of fish obtained by recreational activities have been issued. The potential hazards of PCB intake to human health and the well being of the ecological system have been aptly described ( 5 ) . Atmospheric deposition has been implicated as the major source of PCB input to Lake Michigan (6) and other natural waters (7-11). The effect of such input has been the accumulation of PCRs in water, phytoplankton, zooplankton, abiotic particulates, fish, and lake sediments. The atmosphere 0013-936X/79/0913-0569$01.00/0
@ 1979 American Chemical Society
Experimental Sediment cores were collected at nine deepwater locations in Lake Superior from aboard the USCGC Woodrush in July 1977 (Figure 1).Collection sites were chosen to correspond to areas where sediment was accumulating a t different rates in the lake. Sediment does not accumulate in Lake Superior in most areas where the water depth is less than 110 m, apparently due to surface wave action a t depth ( 1 4 ) .Depositional environments were located in this study with a seismic-reflection-profiling system, and sediment cores were collected with an oceanographic box corer (0.25 m2 surface area). The box corer is ideal for collecting sediments for determination of PCBs in lakes with low sedimentation rates because surface sediment disturbance is minimized and sample volume in the top 0.5 cm of sediment is sufficient for extensive analysis. Sediment cores were fractionated carefully into 0-0.5,0.5-1, and 1-3 cm depth intervals below the sediment-water interface, and sediment at greater depths was obtained in some cores for evaluation of natural, precultural concentrations of PCBs, sampling and analytical blanks, and PCB recovery from spiked samples. The fractionated sediments were stored in all-glass, hexane-acetone washed containers and stored a t 4 "C aboard ship and frozen on return to the laboratory. Volume 13, Number 5, May 1979
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TOTAL PCBs IN SURFICIAL LAKE SUPERIOR SEDIMENTS
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Figure 1. Distribution of PCBs in surficial bottom sediments in Lake Superior. PCB concentrations in cores noted are in units of p g / g (ppm) dry weight, in the top 0.5 cm, and represent total values
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The sediment samples were extracted and concentrated by the exhaustive steam distillation procedure described by Veith and Kiwas ( 1 5 ) .Approximately 50-100 g of representative wet sediment was obtained from each sample by inserting an 8 mm i.d. glass tube to the bottom of the sediment container. The sediment was first homogenized in a Waring Blendor with distilled water, and the slurry was then transferred quantitatively to a 3-L round-bottomed flask and diluted to the 2.5-L mark with distilled water. The sediment-water slurry was boiled vigorously for 5 h in a modified Dean-Starke apparatus, with the distillate being extracted in 25 mL of toluene. The toluene was dried over anhydrous Na2S04, fractionated on silicic acid (161, concentrated in a Kuderna-Danish apparatus, and finally analyzed for PCBs by electron-capture gas chromatography (GC). Each sediment extract was chromatographed on at least two different columns using a Varian Aerograph 2700 GC equipped with a Sc3H electron capture detector and Varian A-25 strip chart recorder. The liquid phases used were 2.5% DL 200155 2.50/0QF-1 and 5% DL-2001500, both coated on Chromosorb W. The chromatographic conditions were as follows: column temperature 190 "C, injection temperature 225 "C, detector temperature 250 "C, and nitrogen flow 30 mL/min. The nitrogen was passed through a series of adsorbents to remove any residual water, oxygen, halogenated hydrocarbons, or organics prior to entering the GC. In addition to dual column identification, standard addition using known Aroclor 1242 and 1254 standards was used to further quantify the unknown peaks. Blanks carried through the experimental procedures and sediment samples collected at depths greater than 4 cm yielded PCB concentrations below the detection limit of 0.001 pglg. Sediment-spiked PCBs were subjected to steam distillation and GC analysis and gave recoveries of 80-90% for Aroclor 1221, 1232, 1242, and 1254 isomer mixtures.
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Results and Discussion P o l y c h l o r i n a t e d B i p h e n y l s in L a k e S u p e r i o r Sediments. The distribution of total PCBs in surficial Lake Su-
perior sediments is shown in Figure 1. The concentration of PCBs was determined by the method of Webb and McCall ( I 7) and the total PCB concentration is reported as the sum of Aroclor 1242 and 1254 isomers. The reported results of PCB concentrations in the top 0.5-cm layer of collected sediment represent -15-25 years of sediment accumulation (28-21 ). T h e concentration of total PCBs in the upper 0.5 cm of Lake Superior sediments ranged from 0.005 to 0.39 p g l g with an arithmetic mean of 0.17 f 0.13 p g l g ( n = 9). The hfghest concentrations were noted near Duluth-Superior (extreme western end) and in the central part of the lake between the Keweenaw Peninsula and Thunder Bay. Swain ( 4 ) has shown 570
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Environmental Science & Technology
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Figure 2. PCBs in depth-fractionated surficial sediments in Lake Superior. Core number refers to samples obtained at sites noted in Figure 1
that elevated concentrations of PCBs have been found in fish, water, and precipitation in Siskiwet Lake on Isle Royale. The lack of man's influence on the island and the predominance of industrial activity in the prevailing upwind direction suggest that Thunder Bay and vicinity may be a major source of airborne transport and deposition of PCBs to Isle Royale and surrounding Lake Superior. The minimum PCB value of 0.005 pg/g was obtained in box core no. 26 collected -18 km southeast of Silver Bay, Minn. Sediment a t this site is dominated by taconite tailings discharged by the Reserve Mining co. over the past 25 years, and which presently cover much of the lake bottom offshore (22). PCBs entering the sediment via the atmosphere in this area may be diluted by the rapidly accumulating tailings, and therefore PCB concentrations in the tailings do not reflect natural sedimentary conditions in the lake. Other minimum values occur in the eastern sector of the lake. The arithmetic mean concentration of 0.17 pg of PCB per g of sediment exceeds by 2 to 10 times the values of 0.06 and 0.007 pg of PCB/g observed for sediments in Lake Superior by Glooschenko et al. ( I I j and Veith et al. ( 2 2 ) ,respectively. This may be attributed in part to the superior sampling capabilities of the box corer used in this study. Sediment collection with a grab sampler or gravity or piston corer may result in the loss of the fluffy, low density, organic floc representing the recently deposited material. In southern Lake Michigan, which potentially receives considerably more atmospheric input from urban and industrial centers, PCB concentrations in the sediment vary from 0.012 to 10 pg/g ( 2 , 3 , II ) . In every study a gravity or grab sampler was used in sample collection, suggesting that actual concentrations may be 2-10 times higher than reported. If not, PCB concentrations in surficial sediments of Lakes Superior and Michigan are comparable. If this is the case, regional dispersion, transport, and deposition of airborne PCBs must be dominating PCB concentrations and cycling in the Great Lakes. The concentration of PCBs found in various sediment fractions is given in Table I, with site-specific profiles of
Table 1. PCBs in Lake Superior Sediments box core no.
2 3 3 5 5 5 7 7 8 8 11 11 11 14 14 17 17 17 20 20 20 23 23 23 26 26 26 a
sedlrnent depth, crn
water depth, rn
1242
PCB, P g l g 1254
total
0-0.5 0- 1 1-3 0-0.5 0.5-1 1-3 15 30 0-0.5 0.5-1 0-0.5 0.5-1 1-3 0-0.5 0.5-1 0-0.5 0.5-1 30 0-0.5 0.5-1 4 0-0.5 0.5-1 1-3 0-0.5 0.5-1 4
60 60 60 185 185 185 215 215 250 250 130 130 130 230 230 305 305 305 230 230 230 200 200 200 256 256 256
0.14 0.20 0.09 0.27 0.05 NDa ND ND 0.16 0.12 0.05 0.03 ND 0.12 ND 0.07 0.06 ND ND ND ND 0.34 0.02 0.004 ND ND ND
0.05 0.06 0.01 0.02 0.01 0.01 ND ND 0.03 0.02 0.08 0.03 0.004 0.02 ND 0.04 0.02 ND 0.007 0.005 ND 0.05 0.01 0.009 0.005 ND ND
0.19 0.26 0.10 0.29 0.06 0.01 ND ND 0.19 0.14 0.13 0.06 0.004 0.14 ND 0.1 1 0.08 ND 0.007 0.005 ND 0.39 0.03 0.01 0.005 ND ND
ND, not detectable
sediment PCBs shown in Figure 2. There is a rapid decrease in the PCB concentrations in sediment with depth, with no detectable values (
