Environ. Sci. Technol. 1992, 26, 1815-1821
Report, Scarborough, Ontario,1986; IJCW Scarborough, 1989. (35) Kelly, T. J.; Czuczwa, J. M.; Sticksel, P. R.; Sverdrup,G. M.; Koval, P. J.; Hodanbosi, R. F. J. Great Lakes Res. 1991, 17 (4), 504-516.
(36) Garland, J. A.;Nicholson, K. W. J . Aerosol Sci. 1991,22 (4), 479-499.
Receiued for review March 2,1992. Reuised manuscript received May 21, 1992. Accepted May 28, 1992.
Historical Inputs of Polychlorinated Biphenyls and Other Organochlorines to a Dated Lacustrine Sediment Core in Rural England Gordon Sanders, * Kevin C. Jones, and John Hamllton-Taylor
Institute of Environmental and Biological Sciences, Lancaster University, Lancaster LA1 4YQ, United Kingdom Helmut Dorr
Instltute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feid 366, D-6900 Heidelberg, Germany Lacustrine sediment cores were obtained from Esthwaite Water, a seasonally anoxic rural English lake. Samples were sectioned, radioisotopically dated, and analyzed for 22 individual polychlorinated biphenyl (PCB) congeners and 1,1,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites. The most abundant congeners in the sediments were 28,44,66,110,138,149,153, and 180. PCB fluxes to the sediment increased slowly from the late 1920s/early 1930s until the late 1940s, escalating sharply thereafter. Maximum PCB fluxes (3.26 ng cm-2 year-l) occurred to sediments dated from the late 1950s/early 1960s. During the following decade inputs of PCBs decreased rapidly, concurrent with restrictions on production and use. Present input levels are ca. 2.17 ng cm-2 year-', with lower chlorinated congeners making the major contribution. Inputs of DDT and its analogues peaked in the mid-1950s (19.2 ng CDDT cm-2 year-'), with DDD the major metabolite. The possible influence of postdepositional factors and coring artifacts on the concentration depth profiles and the apparent presence of PCBs in pre-1930 sediments are discussed.
Introduction Persistent organochlorine compounds (OCs), including the polychlorinated biphenyls (PCBs) and organochlorine pesticides, are among the most important environmental pollutants. PCBs were first produced commercially in 1929 and used in electrical transformers and capacitors (closed systems) as heat-transfer fluids, their chemical inertness and ability to withstand high temperatures making them ideal for this purpose. They were also incorporated into plasticising agents, cements, paints, and carbonless paper (open systems) (1). Over the years PCBs have entered the environment following direct release from 'open systems' and from industrial effluents, landfills, and the failure of electrical equipment. The pesticide l,l,l-trichloro-2,2bis(p-chloropheny1)ethane (DDT) has been widely used as a pest control agent in tropical regions since the end of World War 11. Indeed, its use in Third World countries may have increased recently, at a time when the development of newer pesticides and government legislation have restricted its use in many industrialized countries in the Northern Hemisphere (2). The PCBs and DDT (including its breakdown products DDD and DDE) enter the atmosphere by volatilization or in association with aerosols and can be transported over long distances before deposition onto land or water surfaces (3). Consequently OCs are now ubiquitous across the globe (2-51, even in remote polar regions (6, 7). They become 0013-936X/92/0926-1815$03.00/0
biomagnified through the food chain and may have adverse effects in aquatic and terrestrial organisms (6). These often subtle ecotoxicological effects have sustained and stimulated research on the environmental importance of PCBs and DDT into the 1990s. Although much effort is being directed toward determining current environmental levels of OCs, it is important to obtain data on long-term changes in their environmental burden. Prior to 1966 there was no information on PCBs in environmental samples, although production and use data have been used to infer that the bulk of PCBs were emitted into the environment prior to that date (8, 9). Historical data on the atmospheric loadings of pollutants can be reconstructed by analysis of dated undisturbed deposits of sediments, peat, and ice cores. Lacustrine sediments are particularly useful for this purpose, provided they are undisturbed and some distance from the lake shore, thereby receiving minimal catchment runoff inputs (8-12). Following aerial deposition to the lake surface, hydrophobic OCs become adsorbed onto organic-rich suspended material in the water column and are ultimately deposited to the underlying sediment. Due to their inert character, the bulk of OCs are likely to remain unchanged following deposition, although diagenesis within the water column is of greater importance for some groups. The sediment record can therefore be used to reconstruct a historical chronology of inputs. Eisenreich et al. (8)have previously demonstrated the validity of studying dated lake sediment cores for historical monitoring of OCs. However, the majority of such studies have been undertaken on lake sediments in North America, while European data are limited (13). In this paper the temporal trends of PCBs and CDDT in the dated sediments of Esthwaite Water, a rural lake in northern England are reported. Esthwaite Water is a small, eutrophic, and seasonally anoxic lake, situated 60 km north of Lancaster (see Figure 1). It receives a small amount of treated domestic sewage into the north basin, but is remote from major residential or industrial conurbations. Materials and Methods Sampling. Five Mackereth minicores (id. 6.5 cm) (14) supplemented by five Jenkin cores (i.d. 6.9 cm) (15)were taken at sample station X (grid reference 54'21' N, 3'00' W-see Figure 1)in the north basin of Esthwaite Water in February 1990. The sampling site was chosen to reflect an average sedimentation rate for the entire water body since it is situated at an intermediate water depth (10-11 m), away from any shoreline and stream influences (16).
0 1992 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 9, 1992
1815
Table I. Sediment Accumulation Rates and Radioisotope Inventories for Esthwaite Water 210Pbsediment accumulation rate, g cm-2 year-' bomb-13'Cs sediment accumulation rate, g cm-2 year-' 210Pbexc inventory, dpm c n P zloPb deposition dpm cm-2 b ~ m b - ' ~ ~inventory, Cs Bq cm'2 Chern~byl-l~~Cs inventory, Bq m-2
0.0699 f 0.0077 0.0708 f 0.0081 94.2 f 22.3 2.9 f 0.7 4327 f 405 1362 f 136
calculated from the total 137Csactivity and a Chernobyl137Cs/134Cs ratio of 2.1 f 0.1 (n = 2), as measured in (b~mb-l~= ~Cs Esthwaite Water on May 13,1986 (19,20), total 137Cs- 2.1 X 134Cs). The activities of 210Pband b ~ m b - ~ are ~ ~related C s to the date of measurement (Table I), which due to their longer half-lives is not significantly different from the date of sampling. The atmospheric zloPb (210Pbex,)component was obtained from the measured 210Pbby correction for in situ produced zloPb (from radioactive decay of 226Ra),assuming radioactive equilibrium between 226Raand zloPb (i.e., ignoring loss of in situ produced 210Pbby loss of 222Rn)over the sediment surface. PCB/CDDT Extraction and Analysis. PAH and heavy metals analysis were previously performed on the complete range of core sections (EWl.1-EW1.26) whereas OC analysis was restricted to the upper most 16 sections, the oldest of which dates back to the end of the last century, well beyond the time when PCBs were first commercially manufactured. Between 5 and 10 g of airdried sediment was Soxhlet extracted with pesticide-grade hexane for 24 h on a Buchi 810 fat extraction system. Copper turnings were incorporated during extraction to remove elemental S. After extraction, the sample was concentrated down to ca. 1 mL and loaded onto a 6-g Florisil column (i.d. 15 mm). PCBs and CDDT were then eluted with 40 mL of hexane. The eluent was spiked with congeners 30 and 209 which act as retention time correction references. Samples were finally reduced to 0.5 or 1 mL prior to analysis. The sample extracts were analyzed on a Hewlett-Packard HP5890 gas chromatograph equipped with a "Ni electron capture detector. Splitless injections of 1pL were automatically admitted onto a 25-m DB-5 column via an HP7673 autoinjector. The following temperature program was employed during separation: 100 "C for 2 min, 5 "C min-I to 200 "C, 200 "C for 6 min, ramping again at 4 "C mi& to 280 "C, and remaining at 280 "C for 17 min. Identification and quantification of PCBs, DDT, DDD, and DDE were achieved by overlaying the chromatogram of a standard mix containing 44 congeners and a separate OC standard onto the sample chromatogram, by matching, and by naming peaks by their retention times. This step was carried out automatically using a VG Minichrom data processing package. Individual chromatograms were checked and any baseline or identification alterations carried out manually. The standard mix contained 44 congeners, namely, the following IUPAC congeners (given in elution order): 3, 10,6, 8, 14, 30, 18, 15, 54, 28, 52, 104, 44, 37, 66, 155, 101, 77/110, 82/151,149,118,188,153,105,138,126,183,128,185,202, 156,204, 180, 169,170, 198,189, 208,194/205, 206,209. However, of the 44 screened, only 22 were quantified in all the samples and are reported here. Congeners with large variability in peak area between replicates or peak heights constituting no more than 4 times baseline noise were rejected. The limits of detection (LOD) for selected congeners were of the order of 20-40 pg mL-l for all the congeners, except IUPAC congener 3, which gave a very low response and a LOD of only 3000 pg mL-l. Spiking of samples to determine recoveries was carried out to
(In,
% Lon
- Sampling position Lon=London Flgure 1. Location and bathymetry of Esthwaite Water. X
On returning to Lancaster, samples were immediately placed in cold storage until required for subsampling (no longer than 3 days). Before sectioning, the length of the cores and any lithologicalvariations were noted. The cores were then hydraulically extruded and 2-cm sections sampled to a depth of 20 cm (samples coded EW1.1-EW1.10). Thereafter, 3-cm intervals were sectioned to a maximum depth of 68 cm (EW1.11-EW1.26). Sediment sections from corresponding depths in the various cores were bulked together and left to air dry at ambient temperature and pressure before milling and homogenization to a uniform fine powder. Bulking samples in this way was necessary to gather sufficient material for radiometric dating, and analysis of polynuclear aromatic hydrocarbons, heavy metals (17), and the OCs described here. Local core-to-core variability of metals at the same sediment depths has previously been determined at ca. 15% (18). Dating. The radioisotopes 210Pb,134Cs,and 13'Cs were measured by y spectroscopy using a planar, high-purity germanium detector. Correction for self-absorption was made by measuring the attenuation of the y lines of a natural U-standard by the individual sample. The average counting time was 2-3 days. The 134Csactivity was decay corrected with respect to May 1, 1986, the time of deposition of the Chernobyl fallout. B ~ m b - l ~activity ~ C was 1816 Environ. Scl. Technol., Vol. 26, No. 9, 1992
(In 210Pb-exc. I d p m / g l ) 0
0
-1
1
3
2
4
4
15
I
1
I (134
cslw gl,
0
0.05
0.1
0.2
0.15
2(bI
I
1 N -
E,
-
m
7
(Bomb- 137Cs18qigl)
0
0.1
0.2
0.3
2(c)
methods of dating are in good agreement. The flux of 210Pbto the sediment and the bomb-Cs inventories are higher than loadings in central Europe (21). This is probably due to the high rainfall over the catchment (a1700 mm/year). The fallout 137Csfigure is similar to that reported in soils within 100 m of the lake (4030 Bq inventory is within the mV2)(19),and the Chern~byl-l~~Cs range (1000-2000 Bq m-2) estimated from local measurements of rainfall at the time of Chernobyl deposition (20). The supply of 13Tsto the lake from the catchment, via river runoff, is unimportant for Esthwaite Water (22). Hilton et al. (16) have shown that sediment focusing in Esthwaite Water typically produces a factor of -3 increase in sedimentation rate at the deepest point, relative to the lake margins. However, the sedimentation rate at 10-11 m, the depth at which the cores were taken, is close to the mean rate for the lake as a whole, confirming the choice of sampling site for a study of this nature. The C h e r n ~ b y l - l ~ ~data C s (Figure 2) indicate a comparatively strong mixing in the topmost sediment layers, probably from bioturbation. At the sediment accumulation rate of -0.07 g cm-2 year-l (Table I), the Chernobyl-'Ws would be expected to occur at a depth corresponding to an accumulated weight of 0.28 g cm.-2. In fact Chernob ~ l - ' ~ ~isCpresent s down to a depth corresponding to an accumulated weight of ca. 1.6 g cm-2 (Le., to a depth corresponding to 1967 based on the 210Pband 137Csbomb fallout data). A mixing coefficient can be estimated from this broadening of the 'Ws peak. Following a peak input at the sediment surface, a Gaussian-like depth distribution would be expected after time t, where the mean path length f2 of the Gaussian peak is given by eq 1, and D is the mixing coefficient (in units of cm2/s),
cm s-l. The same From the 134Csprofile D = 7 X calculation applied to the b ~ m b - ' ~ ~peak C s gives, as expected, a lower value for D of (9-17) X lo4 cm s-l, implying that mixing is only significant in the topmost layers of the sediment. The latter value of D is in any case an overestimate since the simplified calculation ignores the effect of bomb fallout 137Csdeposition prior to the 1963/1964 7 7 maximum. The unresolved question is to what depth these Flgwe 2. *'%'b, "Cs, and I3'Cs actlvkies versus accumulated weights values of D apply. for the Esthwalte Water sediments. The higher mixing coefficient can be used to estimate the time resolution of the atmospheric input of any submonitor the efficiency of the extraction and preparation stance, which is reconstructed from the concentration procedure. Average external recoveries for the complete profile in the sediment. Within 1 year the information range of 22 congeners were 84%. All congeners gave re(concentration) at the surface is mixed to a mean depth coveries in excess of 80%, except congener 170 (67%). of 6.6 cm (cf. eq 1). The minimum interval of sediment Precision was good with a maximum standard deviation sectioned for this study was 2 cm, which relates to a 5-year between spiked samples of f11.2% ( n = 4). Recoveries period in the surface sample. The presence of Chernoobtained for DDE and DDD were typically >95%, and b~l-l~~ from C s 1986 was noted in sediment originally dethey were 65% and above for DDT. posited ca. 18-19 years previously. Only 34% of the total Results and Discussion 134Csinventory remains in the top 2 cm to which it would Sediment Dating. Figure 2 shows the 210Pbexc data have been deposited. This suggests that the core is mixed to at least 7-8 cm. This figure is in good agreement with plotted logarithmically against the accumulated weight of that calculated from the diffusion model above. sediment. The fact that a straight-line plot gives a reaIt is important to remember that the depth distribution sonable fit to the observed data indicates that the mass of the radioisotopes and OCs will probably be "blurred" deposition rate has remained more or less constant by bulking several cores for analysis. This is discussed throughout the time period represented by the core. below in relation to the OC record, but is also likely to have Hence, an average sediment accumulation rate can be calculated. The sediment accumulation rate can also be affected the resolution of the sediment dating. General Comments on PCB Time Trends. The obtained from the depth position of the bomb 13'Cs maximum (Figure 2), which occurred in 1963/1964. The avCPCB concentrations (defined as the sum of the 22 conerage sediment accumulation rates obtained from 210Pbexc geners 8,18) 28, 52,104,44,66, 101, 110,82/151,149, 118, 188, 153, 105, 138, 185, 180, 170, and 194/206), their esand b ~ m b - l ~ and ~ C sthe radioisotope inventories are listed in Table I. The accumulation rates derived from both timated annual flux, and the concentrations of the eight Environ. Sci. Technol., Vol. 26, No. 9, 1992
1817
Table 11. Concentrations of Selected Congeners, Total PCB Concentrations, and Fluxes for 22 Congeners section
depth, cm
yearn
28
44
66
110
138
149
153
180
EWI.1 EW1.2 EW1.3 EW1.4 EW1.5 EW1.6 EW1.7 EW1.8 EW1.9 EW1.10 EW1.11 EW1.12 EWl.13 EW1.14 EW1.15 EW1.16
0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 16-18 18-20 20-23 23-26 26-29 29-32 32-35 35-38
1988 1983 1978 1973 1968 1963 1958 1953 1948 1943 1936 1929 1922 1914 1907 1899
4.6 3.8 2.6 1.8 1.3 3.8 1.9 1.8 2.1 1.5 0.1 0.3 0.3 ND 0.1 0.3
1.9 1.6 1.5 1.3 1.3
3.0 4.0 4.5 4.8 6.0 7.5 9.0 8.5 3.3 1.6 0.9 0.5 0.2 0.2 0.2 0.2
1.6 2.0 2.4 3.1 3.2 4.5 5.8 5.6 3.5
1.1 1.3 1.3 1.3 1.6 2.3 1.5 1.5
1.5 1.6 1.4 1.3 1.8 2.1 2.5 1.6 0.6 0.7 0.3 0.2 ND ND ND ND
0.8 0.9 0.9 0.8 1.1
1.5 2.0 1.8 2.1 2.7
1.6
4.0
1.0
2.7 26 13
2.2
2.4 2.4 1.4 1.4 0.9 0.6 0.1 0.2 0.2 0.1
The year shown is the midpoint of the core section.
0.7
2.7
1.9 1.0 0.4 ND ND 0.1
0.6 0.4 0.1 NDb ND ND ND
0.9 0.4 0.4 0.2
1.0
0.1
ND ND ND ND
0.6 0.1 ND ND ND ND
ZPCB, fig kg-'
total flux, ng year''
30.8 31.0 29.5 28.8 31.5 46.3 42.3
2.17 2.19 2.08 2.03 2.22 3.26 2.98 2.92 1.93 1.33 0.74 0.35 0.64 0.10 0.12 0.52
41.1
27.4 18.9 10.5 5.0 9.0 1.4 1.7 7.3
ND, congener not detected or concentration below detection limit.
Table 111. E P C B Concentration and Flux Data from Various Other Regions sample site Dark Lake, WI"
Emrick Lake, WI"
Lake Boshkung, Ontariob Lake Opeongo, Ontariob Lagoon of Venice, Italy'
Milwaukee Harbor, WId
sediment depth, cm
CPCB concn, (dry wt)
a kg-'
0-2 2-4 4-6 6-8 0-2 2-4 4-6 6-8 8-10 0-3 0-3 0-4 4-6 6-9 9-12 12-15.5 15.5-19 19-22 22-25.5 25.5-29 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80
19.2 20.4 8.8 2.2 89.0 12.8 12.7 26.3 13.3 27.2 53.9 15 23 27 10 15 5 5
