Environ. Sci. Technol. 1989, 23, 1116-1 126
Siak, J.; Chan, T. L.; Gibson, T. L.; Wolff, G. T. Atmos. Environ. 1985, 19, 369-376. Tokiwa, H.; Kitamori, S.; Nakagawa, R.; Horikawa, K.; Matamala, L. Mutat. Res. 1983, 121, 107-116. Miller, M.; Alfheim, I.; Larssen, S.; Mikalsen, A. Environ. Sci. Technol. 1982, 16, 221-225. Lewtas, J.; Goto, S.; Williams, K.; Chuang, J. C.; Petersen, B. A.; Wilson, N. K. Atmos. Environ. 1987,21,443-449. Chuang, J. C.; Mack, G. A.; Petersen, B. A.; Wilson, N. K. Polynuclear Aromatic Hydrocarbons: Chemistry, Characterization, and Carcinogenesis; Cooke, M., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1986;pp 155-171. Lewis, R. G.; Jackson, M. D. Anal. Chem. 1982,54,592-594. Mumford, J. L.; Harris, D. B.; Williams, K.; Chuang, J. C.; Cooke, M. Environ. Sci. Technol. 1987,21, 308-311. Chuang, J. C.; Mack, G. A.; Mondron, P. J.; Petersen, B. A. EPA/600/4-85/065; Environmental Systems Monitoring Laboratory, U.S. EPA, Research Triangle Park, NC, 1987. Ortiz, C. A.; McFarland, A. R. J . Air Pollut. Control Assoc. 1985,35, 1057-1060. Harris, C. M. Handbook of Noise Control, 2nd ed.; McGraw-Hill: New York, 1979, pp 28-8, 28-9. Chuang, J. C.; Hannan, S. W.; Wilson, N. K. Enuiron. Sci. Technol. 1987,21, 798-804.
(16) Chuang, J. C.; Naber, S. J.; Kuhlman, M. R.; Hannan, S.
W.; Mack, G. A. EPA/600/X-87/372; Environmental Systems Monitoring Laboratory, U S . EPA, Research
Triangle Park, NC, 1987. (17) Wilson, N. K.; Chuang, J. C. Polynuclear Aromatic Hydrocarbons, Proceedings, 1I t h International Symposium, Cooke, M. J., May, W. E., Eds.; Lewis Publishers: Chelsea, MI, in press. (18) Mack, G. A.; Stockrahm, J. W.; Chuang, J. C. EPA/6OO/
4-88/000, Atmospheric Research and Exposure Assessment Laboratory, U.S. EPA, Research Triangle Park, NC, in press.
Received for review May 6, 1988. Revised manuscript received April 6, 1989. Accepted May 3, 1989. Although the research described in this article was funded wholly or in part by the United States Environmental Protection Agency through Contract 68-02-4127 to Battelle Columbus Division, it has not been subjected to Agency review. Therefore, it does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
Accumulation and Diagenesis of Chlorinated Hydrocarbons in Lacustrine Sediments Steven J. Elsenrelch,**tPaul D. Capel,$ John A. Robbin$,§ and Rlchard BourbonniereII
Environmental Engineering Sciences, Department of Civil and Mineral Engineering, University of Minnesota, Minneapolis, Minnesota 55455, Water Resources Division, U S . Geological Survey, St. Paul, Minnesota 55101, Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration, 2205 Commonwealth Blvd., Ann Arbor, Michigan 48 104, and National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario L7R 4A6, Canada Two sediment cores were taken from the Rochester Basin of eastern Lake Ontario and analyzed for the radionuclides 210Pband 137Csand several high molecular weight chlorinated hydrocarbons (CHs). The two sites are geographically proximate but differ in sedimentation rate, permitting sedimentation-dependent processes to be factored out. The 210Pbchronology showed a mixed depth of 3-5 cm and an intrinsic time resolution of 11-14 years. Vertically integrated numbers of deposit-feeding oligochaete worms and burrowing organisms are insufficient to homogenize the sediment on the time scale of CH inputs, which are non steady state. US. production and sales of polychlorinated biphenyls (PCBs), DDT, Mirex, and hexachlorobenzene (HCB), as determinants of the shape of the input function, adequately predict the overall shape and, in many cases, details in the sedimentary profile. Sediment focusing factors (FF) inferred from 13"Cs and 21"Pbinventories averaged 1.17 and 1.74 for cores E-30and G-32, respectively. This permitted CH accumulation rates to be corrected for focusing. Apparent molecular diffusion coefficients modeled for many of the CHs were about (1-3) x cmz/s.
Introduction Hydrophobic organic compounds (HOCs) of anthropogenic origin are delivered to lacustrine and marine systems t University
of Minnesota.
* U.S. Geological Survey. 0 NOAA. 'I Canada
1118
Centre for Inland Waters.
Environ. Sci. Technol., Vol. 23, No. 9, 1989
by atmospheric transport and deposition, direct and indirect discharges, and riverine inputs. Examples of these organic compounds are polychlorinated biphenyls (PCBs) and other chlorinated hydrocarbons (CHs) used as pesticides (e.g., DDT; Lindane) or generated as byproducts of industrial production [e.g., hexachlorobenzene (HCB)], PCBs, for example, are characterized by their low aqueous solubilities ( 10-9-10-6 mol/L), low vapor pressures (10-8-104 Torr), and resistance to extensive chemical and biological transformation (1,2). Low aqueous solubilities and general hydrophobic nature of these CHs result in high partition coefficients applied to abiotic and biotic particles of 104-106 L/ kg. The primary removal process for these organic compounds in large lakes is adsorption to or partitioning into particles and subsequent sedimentation. The sorptive properties of HOCs are largely controlled by the organic carbon (OC) content of particles, which is itself concentrated in the clay- or fine-size particles (3-5). Thus HOCs will follow the path of the average clay-size particles and be focused into the more quiescent, depositional basins of the lake, estuary, or bight. In the Laurentian Great Lakes, organic contaminant residence times are about 2-3 times the fine-particle residence times of 1year determined from mass balance and radioactive tracer studies (6-1 1). Once delivered to the bottom sediments, contaminant and particle burial is slowed by the effects of resuspension (9,12,13)and mixing of surface sediments by aquatic organisms (7, 14-17). The net effect of these processes is to increase the residence time of the contaminant in the ecosystem, inhibit burial in deep sediments, and alter the depositional history of the contaminant in-
0013-936X/89/0923-1116$01.50/0
-
0 1989 American Chemical Society
ferred from sediment profiles (7). Other processes such as molecular diffusion and biotransformation of CHs, although little studied in lacustrine or marine sediments, will also alter the input history of the contaminant recorded in the sediment profile. Dated sediment cores have the potential for providing detailed chronologies of organic contaminant input as long as diagenetic processes of bioturbation, molecular diffusion, and biotransformation are (or considered to be) negligible. Concentrations and accumulations of organic contaminants in dated cores have been published for polycyclic aromatic hydrocarbons (PAHs) (18-20), phthalate esters (21,22), Kepone (23),chlorinated benzenes (24,W), and chlorinated dioxins and furans (26,27). The depositional history of PCBs in sediments has been reported for relatively few cores in the Great Lakes (2,25,28-30),the Hudson River and estuary (31),the Santa Barbara Basin (32),and New Bedford Harbor (33). DDT and its metabolites have been analyzed in dated cores from the Hudson River (31),the Southern California Bight (32,341,and the Great Lakes (35). With the exception of a few studies on the in situ alteration of PAHs by microorganisms, no study has dealt sufficiently with the sedimentary diagenesis of HOCs, although bulk sediment mixing by benthic organisms continues to be studied (7,15,36-39). In this paper, we examine the processes responsible for the accumulation, transformations, and mobility of selected CHs in sediments from the eastern depositional basin of Lake Ontario. Our strategy was to obtain box cores from depositional areas of the Great lakes that are geographically proximate but differ in mass sedimentation rates, are remote from local sources, and possess high sedimentation rates with correspondingly high degrees of time resolution. Comparison of chemical profiles in cores from neighboring sites permits the sedimentation-dependent processes to be identified and quantified and diagenetic processes elucidated. Tracers of sedimentation and mixing employed in this study are 210Pband 13'Cs. Understanding the physicalchemical-biological behavior of CHs in sediments is essential in the calibration and use of quantitative models describing particle-selective and depth-dependent processes. Methods Two box cores were obtained in the Rochester Basin of eastern Lake Ontario in May 1981 by use of the Canadian research vessel CSS LIMNOS. The box corer had dimensions of 50 cm X 50 cm X 60 cm and was a modification (New Bedford Institute) of the Soutar corer used previously in studies on the Great Lakes (e.g., ref 2, 28, and 40). Care was taken not to disturb the sediment surface by maintaining about 10-20 cm of clear bottom water above the core. Numerous fecal pellet mounds were present on the surface. Each box core was subdivided into as many as 12 subcores (34.4-cm2area) for later study of radionuclide tracers, metals, geolipids, organic carbon, nonpolar HOCs, benthic infauna, particle size distribution, and descriptive characteristics by photography. The subcore was extruded hydraulically on board ship within 2 h of sample collection. The cores were segmented into 1 cm depth increments in the upper 20 cm, and 2-cm increments to the bottom (about 40-50 cm). Sediment samples were placed in cleaned glass jars with foil-lined lids and stored frozen in the dark. Prior to extraction, the frozen samples were thawed a t room temperature for 24 h and the water was decanted and extracted separately. After sample homogenization and determination of water content and bulk density, 20-40 g of wet sediment was mixed with 115 g of anhydrous
Na8O4 to remove residual water. The sample matrix was ground and extracted for 12-18 h in a Soxhlet apparatus with 100-175 mL of dichloromethane (DCM), depending on sample size. The DCM extract combined with the hexane extract of the free water was reduced in volume to 10 mL in a Kudurna-Danish apparatus concomitant with a solvent change to hexane. The hexane extract was fractionated on a 1.25% water deactivated Florisil column (13 g, 2-cm i.d.) into a hexane fraction (60 mL) containing PCBs, DDE, Mirex, and HCB and a 9:l hexane-diethyl ether fraction (50 mL) containing the remaining CHs of interest. In sample workup, the 4-5-cm sample from core G-32 and the hexane fraction of the 9-10-cm sample from core E-30 were lost. Elemental sulfur was removed with activated Cu filings. Each fraction was reduced in volume to 1 mL with a gentle stream of clean N2 and stored in autosampler vials with gas-tight seals at -10 OC until analyzed. Sample extracts were analyzed for CHs with a HP 5840A gas chromatograph equipped with a 63Nielectron capture detector using splitless injection onto a 25-m glass capillary column (SE-54; 0.32 mm i.d.) and a H P 7672A autosampler. Operating conditions were as follows: temperature program of 150 OC for 4 min, ramping to 230 OC a t 1.2 "C/min with run times of 70 min; injector temperature of 335 "C; Nz column flow of -1 mL/min with makeup flow to 30 mL/min. Individual PCB congeners and other CHs were quantified by comparing their peak areas to the corresponding peak area of standards chromatographed y d e r identical conditions at similar concentrations. A 1:l mixture of Aroclor 1242 and Aroclor 1254 and a multiple linear regression program, PCBQ (41),was used to calculate total PCBs and the fraction of total PCBs best represented statistically by combinations of Aroclor 1242 and 1254. PCB congeners, total PCBs, and Aroclor compositions have been determined accurately by using glass capillary gas chromatography (GC) and PCBQ on a variety of air, water, and sediment samples, simulated environmental samples, and certified EPA standards (41). Confirmation of identity and concentration of some CHs was achieved by GC-MS (HP 5985B) operated under identical conditions when sufficient analyte was present. Recoveries of CHs spiked into four sediment samples and carried through the analytical procedure were as follows: hexachlorocyclohexanes(HCHs), 83% ;p,p'-DDE, 138%; p,p'-DDD, 109%; p,p'-DDT, 95%; Mirex, 100%. Twenty PCB congeners spiked into four sediment samples at the concentration range observed in the field and carried through the same procedure yielded a mean congener recovery of 100.6% and an overall mean total PCB recovery of 100.3%. Analytical and field blanks evaluated by analysis of deep-sediment samples from each core were less than measured concentrations above depth corresponding to the year 1900. Analysis of duplicate sediment samples gave precision of 10-20%.
-
Sediment Dating and Mixing Model The radionuclides 210Pb(tl/2 = 22.3 yr) and 13'Cs (tlI2 = 30.2 yr) were measured in the two Lake Ontario cores to determine sedimentation rates and mixed depth according to protocols used previously (7, 42). The determination of 210pbcontent is based upon the measurement of the daughter 210Poactivity in secular equilibrium with its parent. Up to 5-g aliquots of freeze-dried, ground sediments were digested a t 80 O C in 10% HCl (v/v) with periodic additions of 30% H202. A t the beginning of the digestion (24-h period) a well-determined amount of -Po (tl,z = 3 yr) or 209Po(tllz= 100 yr) was added to establish Environ. Sci. Technol., Vol. 23, No. 9, 1989
1117
the absolute activity of 210Po.Following digestion the Po isotopes were self-plated from the filtered extract on to silver or copper disks and their activities determined by conventional (Y spectroscopy. Typical counting errors ranged from 1 to 5%. 13Tsy activity was determined on 5-20 g of freeze-dried sediment by counting up to 800 min with a lithium-drifted germanium detector coupled to a multichannel analyzer. Robbins and Edgington (42) and Robbins (7) have shown that a rapid steady-state mixing model similar to that proposed by Berger and Heath (43) is adequate to describe the 210pband 13%s profiles of many Great Lakes' sediments where surface sediments are intensely mixed by bioturbation. This model requires that new material (A,) added to the sediment surface is mixed homogeneously throughout a mixed zone (S,cm) and S moves upward at the rate of sedimentation ( W ,cm/yr). As the mixed zone moves upward, material is transferred to underlying deposits, which presumably conserves the historical profile as no additional mixing occurs. For a constant 210Pbflux (cf. ref 7)
where
A, = A g / ( l+ 7S/W
(210Pbin S)
(2)
A , is the activity in new settling material (dpm/g) and 7 is the decay constant (0.693122.3 yr = 0.0311 yr-l). The distribution of excess 210Pbin the sediment is then given by A(z) = A, for z I S (3)
A(z) = A,e-T(Z-S)/Wfor z > S
(4)
where z is the depth in centimeters. For the case of a time-dependent flux of 13Ts (i.e., dA,/dt # 0), the corresponding W s distribution is given by A ( z ) = A,(T) for z I S (5) A(%)= A,(T
+ ( S - z))/We-r(z-S)/wfor z L S
(6)
where t = 0 corresponds to a very deep sediment layer, t = T corresponds to the sediment-water interface, and 7 is the decay constant (0.693/30 yr = 0.023 yr-l).
(7) v =
s/w
(8)
For the case of 210Pb,the activity profile below the mixed zone, S, is exponential and permits the determination of a mean sedimentation rate. Application of a least-squares analysis to eq 2 and 3 yields W and S. The influence of compacting sediments is removed if W is expressed in g/cm2.yr and S in g/cm2. In many areas of the Great Lakes, W is small while S is the order of 2-10 cm. Thus, reliable values of W are not often obtained from leastsquares analysis of the 137Csactivity, although the mixed depth can be determined. These relationships are expected to apply to regimes of the lake where mixing is sufficiently intense to completely homogenize sediments within the zone of bioturbation. In areas of high sedimentation, densities of organisms have been shown (44) to be insufficient to achieve complete mixing. As shown below, these cores collected in the high sedimentation area of Lake Ontario are subject to the effects of incomplete biotur1118
Environ. Sci. Technol., Vol. 23, No. 9, 1989
.
m i
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Table I. Sedimentation, Mixing, and Foeusing Data for Lake Ontario Cores core E-30
location
0.0443 i 0.0027
210PbWIim, c m / p '"CS w,g/cm'.yr mixed depth ( S ) ?'OPb S, g/cm' IlaPb Sum, em '91CsS, a/cm2 intrinsic re3
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Figure 2. Distributbn of excess "OPb and '%s in Lake Ontarb sediment cores E 3 0 and G32. SolM lines are test fils obtained wim the steady-state mixing model. The shaded histogram indicates the distribution of '*'Cs expected from direct fallout wiM no Sediment mixing
shorter time periods, in agreement with recent modeling studies of laboratory microcosms (7,16,44,47,49). The intrinsic resolution (t*)(15) is defined as the time span over which an alteration in the input rate of a chemical species will not be observed in the sediment record. It may be estimated as t* = S(cm)/ W(cm/yr) or more definitively as t* = S(g/cm2)/W(g/cm2.yr). The validity of this concept is dependent on mixing being an enduring steadystate process. The intrinsic time resolution for these two cores (Table I) is -11 and 14 years based on the ''OPh chronology, and somewhat less based on I3'Cs. If true, chemicals for which the atmospheric flux has decreased over the last decade, such as Ph (50) and PCBs (Z),should not be noted in the sedimentary record except for slowly decreasing concentrations in the mixed zone. The recent sediments of the Great Lakes are in contact with oxygenated water and often undergo surface mixing by the amphipod Pontoporeia hoyi and various species of oligochaete worms including Tubijex tubijex, Limnoddus hojfmeisteri, and heringianus (44,51,52). Pontoporeia abundance generally exceeds 1000 individuals/mz throughout the Great Lakes. The amphipod species burrow in the upper 1-2 cm of sediment in a manner that has been modeled as a diffusive process (16).The oligochaete worms are "conveyor-belt" feeders in that they feed at depths of 3-6 cm and deposit sand-size fecal pellets at the sediment surface. They can mix sediments perhaps up to 10 cm, hut the intensity of feeding is not constant with depth; maximum rates are observed in the subsurface (15,47,49,53). These organisms feed selectively on sediment fines or clay-size material and preferentially transport the small and organic-rich particles to the surface encapsulated in fecal pellets. The curious byproduct of Environ. SCI.Technol.. Voi. 23. No. 9. 1989 1119
ACCUMULATION ( no/cm2,vr)
10
PCBs
'"I
G-32
0
1940
I
I
20
40
0
60
G - 9 1
1
50
100
1
150
I
1
I
I
10
20
30
40
PCB SALES IN U.S.(t)
1
f
l
20
l
l
40
M,
l
80
DDT PRODUCTION IN U.S.(+)
200
CONCENTRATION (ng/g)
ACCUMULATION (ng /cm2.yr)
F w e 3. Distribution of PCBs, CDDT, Mirex, and HCB in Lake Ontario sediment cores E-30 and G32. Mixed depth estimated from *loPb geochronology is 3 cm in core E-30 and 5 cm in core G32.
this process is the enrichment of rejected coarse, inorganic particles a t the base of the mixed zone. Oligochaete densities often exceed 50 000 individuals/m2 in contaminated sediments of the Great Lakes and their abundance is related to organic carbon flux (7). The worm densities in E 3 0 and G-32 cores were 1450 and 3200 individuals/m2, respectively. The depth above which 90% of the organisms occur (Zw) is 8.5 and 11cm, considerably deeper than the 3-5 cm depths of the mixed zone, but consistent with the porosity profiles. This result contrasts with the earlier observation that the depth of the mixed zone closely correlated with the 2, values (7).The 2, depths in these cores are better correlated with changes in sediment porosity a t depth (Figure l). Whether sufficient numbers of oligochaete worms are present to homogenize new sediment flux in the mixed zone may be determined by comparing the total dry sediment displacement rate to the sedimentation rate. A reasonable estimate of the bulk sediment displacement rate is 1g of dry sediment/wormyr for bottom temperatures of 4-6 "C (44, 54). Robbins (15) has provided a means for determining whether conveyor-belt deposit feeders occur in sufficient densities to homogenize sediments within the zone of bioturbation. He defines the reworking efficiency, t, as the ratio of the rate of feeding by organisms present (g of dry sediment/cm2.yr) to the mass sedimentation rate, W(g/ cm2.yr). If N is the number of organisms (cm") and 'I is their individual feeding rate (g/yr), then t = hT/W. When t 2 10, the 210Pbactivity will be homogeneous within the zone occupied by the organisms (15). In the present case, oligochaetes have comparable feeding rates of 1g/ yr (44, 47). At worm densities of 0.1450 and 0.3200 individual/cm2 a t E-30 and G-32, respectively, the associated reworking efficiencies are 3.3 and 4.2. Thus it is expected that 210Pb would not be completely homogeneous and transient tracers such as many of the CHs could retain much chronological structure. We may conclude that mixing intensity by worms in these cores is adequate to homogenize particle-bound tracers delivered a t constant flux with half-lives longer than t* (210Pb)but not tracers for which the input function has changed in the last 11-14 years, that have short radioactive half-lives (e.g., 'Be, 53.4 days), or both. The mixing by P. hoyi, although intense, is restricted to the upper 1-2 cm. Chlorinated Hydrocarbon Profiles. The discussion of CH profiles will emphasize four organic chemicals or classes of chemicals prominent in the Lake Ontario ecosystem: PCBs, CDDT (DDT + DDE DDD), Mirex, and HCB. The CH profiles for cores E-30 and G-32 presented
-
-
+
1120 Environ. Sci. Technol., Voi. 23, No. 9, 1989
P---:+,b
1 9 6 0 ~ - - - - - - -
A E-30 0
"
9
1 1940
G-32
loo zoo 300 400 MIREX SALES g x106
(+I
d +
loo
200
3x3
CHLOROBENZENE PROD. ( + ) gxlo9
Figure 4. Relationship of chlorinated hydrocarbon accumulations (ng/cm2.yr)with U.S. production and sales data in Lake Ontario sediment cores E-30 and G32. (A, top) E FCBs and ZDDT. (B,bottom) Mirex and HCB.
in Figure 3 are generally characterized by a subsurface peak, decreasing concentrations to the surface, and an exponential decrease in concentrations below. The concentration peaks for PCBs, Mirex, and HCB all occur a t the base of the 21Pbmixed zone in core E-30 (3-4 cm) and G-32 (5-6 cm). The CDDT peak occurs a t 5-6 and 7-8 cm in the two cores. The data also clearly show that the four organic chemicals do not exhibit well-mixed concentration profiles in the 210Pbmixed zone. Note that the CDDT peak concentration has penetrated well below the mixed zone and is preserved in the buried sediment. Source Characteristics and Time-Dependent Fluxes. The time-dependent fluxes of selected CH and corresponding U.S. sales and production figures are plotted in Figure 4 as a possible determinant of the historical input function. Several investigators (2, 24, 55-57) suggested that the PCB sales curve accurately describes the PCB input function with the exception that new fluxes, although reduced in quantity, continue. DDT was first produced in the latter stages of World War 11, reaching peak production and use in North America in 1958-1960. Use of DDT was banned in the United States and Canada in 1972. A DDT input function closely matching the production curve in Figure 4 has recently been verified through the analysis of peak profiles across the midlatitudes of eastern North America a t sites receiving only atmospheric inputs (57, 58). The story for PCBs (57) and toxaphene (59) appears to be similar. Mirex input to Lake Ontario has been attributed to discharges to the Niagara River (western basin) and to the Oswego River (eastern basin) from chemical manufacturing companies, both in the mid-1960s. The majority of the Mirex reaching the eastern depositional areas is thought to result from the latter source, although this is not unequivocal (60-62). Total US. chlorobenzene production as a determinant of historical HCB input is in general agreement with the
dated sediment profiles of di- through hexachlorobenzenes in western Lake Ontario (25) and tetra- through octachlorodibenzodioxins and furans in Lake Huron (26). Thus, total chlorobenzene production should a t least provide the general shape of the HCB input function. Hexachlorobenzene is mostly derived as a byproduct of general chlorobenzene production. Sediment profiles may accurately mimic lakewide input rates if a major mechanism controlling the loss of CH from the lake is attachment to particles and subsequent accumulation in sediment. The average residence time of a contaminant in large lakes (T,) with respect to particle settling is (11) T,= T,(1 + [TSM]K,-J)/[TSM]K~) (9) where T, is the mean lifetime of a particle settling through the water column, TSM is the total suspended material (kg/L), and Kd is the chemical distribution coefficient between particle and water (L/kg). For chemicals having Kd values of 106-106 L/kg and [TSM] lo4 kg/L, T, is -0.24 year, and T, is on the order of 2 years or less. The compounds of special interest here have Kd values on the order of 106-106 L/ kg or greater based on measured field values (2,63)or estimated from aqueous solubilities and octanol-water partition coefficients ( 4 , 5 ,64). For Lake Ontario, T8 are short relative to the water residence time of 8 years (i.e., T,
