Environ. Sci. Technol. 1904, 18, 404-409
Sedimentological Reconstruction of the Recent Pattern of Mercury Pollution in the Niagara River Ronald J. Breteier”
Battelle New England Marine Research Laboratory, Duxbury, Massachusetts 02332 Vaughan T. Bowen+and David L. Schneider
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Richard Henderson$
Health Sciences and Toxicologic Research, Olin Corporation, New Haven, Connecticut 06511 Since 1952 there have been a number of sharp changes in the rates of delivery, or in the ratios delivered, of several long-lived artificial radionuclides distributed worldwide from atmospheric nuclear tests. Analyses of these nuclides in suitably selected, and collected, aquatic sediment cores indicate several dated horizons that can yield more refined estimates of recent pollution history than are otherwise available. This approach has been applied to several cores in eastern Lake Erie, the Niagara River, and its delta in Lake Ontario, and a selection of the sediments so dated have been analyzed for total mercury. On the basis of the assigned, and verified, dated horizons of several sediment cores, the history of mercury pollution in the Niagara River has been reconstructed.
Introduction It is generally recognized ( I ) that present day industrial activities are responsible for a substantial fraction of the flux of mercury through the environment. This manproduced fraction of the mercury flux has certainty increased more or less steadily, in the northern hemisphere, since the early nineteenth century; the record of this increase has been discerned in freshwater (2,3)and in marine ( 4 , 5 ) sediments from a variety of locations. Superimposed on this general hemispheric increase in the mercury flux, there have been much more abrupt local phenomena caused by industrial waste disposal practices, among other variables. Most of these local pulses have not been immediate sources of environmental or public health concern and so have not, especially in their early phases, been well monitored. In this report we discuss the use of mercury analyses of well-dated, carefully selected, freshwater sediment cores to reconstruct the complicated his‘tory of industrial mercury releases to the Niagara River, NY. Niagara Falls has long been a major locus of the electrochemical industry. Beginning in 1893, a rocking-cell mercury electrode electrolytic chloralkali process was first put into operation by the then Mathieson Alkali Corp. (later, the Olin Corp.) with substantially all the mercury loss going into the Niagara River. The gradual replacement of the rocking-cell process with new flatbed mercury cells may have resulted in some increase in mercury loss as chloralkali production about doubled. In the early 1960s a second company (Hooker Electrochemical) built a chloralkali plant in Niagara Falls, providing a second source releasing mercury into the Niagara River. During all this period little or no data were collected concerning +Presentaddress: Box 504, Wayne, PA 19087. *Present address: 51 Hilltop Road, Bethany, CT 06520. 404
Environ. Sci. Technol., Vol. 18, No. 6, 1984
either the rates or patterns of mercury release to the river, or the fates of the releases. In 1970, however, after the discovery of the formation of methylmercury by certain microorganisms, both the Niagara Falls chloralkali plants made major efforts to reduce their loss of mercury to wastewater streams. Routinely since then, the wastewater discharges from these plants have been analyzed for mercury content. However, because of the paucity of data describing the environmental results of the long history of mercury discharges into the Niagara River, it appeared desirable to make an independent reconstruction of the mercury deposition from the Niagara River into the sediments of Lake Ontario. As part of a relatively long-term project to examine the biogeochemistry of fallout radionuclides, especially the artificial actinide elements, in Lake Ontario, we had available several cores of sediment, both below and above the points of mercury introduction by the chloralkali plants. Some of these cores showed evidence of continuous deposition of sediment at quite rapid rates of accumulation. Furthermore, as we describe below, the presence of abrupt changes in the fallout mixture ratios between various nuclides or radioelements provides several event markers that can be used to date specific levels in such cores. This means that, unlike the situation when zloPb or fallout I3’Cs alone was used to date recent sedimentary material, we were not tied to average sedimentation rates but could extract variations in these values that apply to relatively brief periods in the last 30 years, the time of major interest in regard to mercury pollution.
Materials and Methods The Niagara River is a short channel connecting Lake Erie and Lake Ontario, the flow being toward the latter. At Niagara Falls the river passes over a high limestone escarpment, providing the setting for extensive hydroelectric development. In the 1958-1961 period, two substantial storage reservoirs were created, one Canadian and one U.S., as a means of increasing the availability of hydroelectric power at peak demand times of day. Water not needed during off-peak periods is pumped into these reservoirs to be run back through the generators at periods of peak demand for power. While resting in the reservoirs the river water deposits a significant fraction of its sediment load which, in the US.reservoir, has been continuously accumulating since 1961. In Figure 1are shown, schematically, the Niagara River, together with the east end of Lake Erie, the west end of Lake Ontario, the U S . pumped storage reservoir, power plant, and diversion canal, and the locations of the two Niagara Falls chloralkali plants. The water discharged from one chloralkali plant enters the river above the intake
0013-936X/84/0918-0404$01.50/0
0 1984 American Chemical Society
LAKE
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NIAGA~~RIVER
EASTERN L A K E ERIE
WESTERN L A K E ONTARIO
Flgure 1. Schematic sketch of eastern Lake Erie, the Niagara River, and western Lake Ontario showing the location of the sediment cores discussed in text. The detailed insert shows the two chloralkali plants (their waste discharges indicated by arrows) in relation to the U S . hydroelectrlc power system, its diversion canal, and the pumped storage reservoir.
of the diversion canal, the other plant enters below. The locations of the six sediment cores are also shown in Figure 1. All of these cores were collected with 21-cm diameter sphincter corers (6). In 1979, an improved model of this corer began to be used (7), and a portable research catamaran (8) was put into service; both these resulted in substantially better quality or reliability of coring operations. The procedures for extrusion and sampling of these large diameter sediment cores are described by Burke et al. (7). Except for core 0-73-6, the samples used for mercury analyses were stored wet in sealed polystyrene jars since being sampled for radionuclide analysis. The sections of core 0-73-6 had been dried, at about 90 OC, to constant weight before storage; mercury concentrations measured in sections of this core were converted from dry to wet basis by using the wet to dry ratios originally measured. Analytical Methods. (1) Radiochemistry. For dating the various cores considered here we have measured concentrations of 137Cs,238Pu,239p240Pu, 241Am,and 2uCm and their various ratios. Our methods for these analyses and the performance we have achieved in various intercalibration excercises are reported in the literature (S12). The measurement uncertainty for radionuclide concentrations is l a of the nuclear counting statistics. (2) Mercury. Only total mercury was measured on well-homogenized core sections by using the cold-vapor atomic absorption technique and sample preparation procedures fully described elsewhere by Breteler et al. (13). As noted above, most of these core samples had been preserved wet. We take the agreement of mercury concentrations at comparably dated levels in cores 0-73-6 (dried) and 0-79-1 (wet) to show that even at the highest mercury concentrations only very small fractions of this element could have been present in forms easily volatile at 90 OC. Standards were prepared from blanks, treated as the samples, and spiked with aliquots of a freshly prepared 1mg/L mercury solution. A linear regression of the standard curve (r = 0.999) was used to calculate mercury in the samples. The precision and accuracy of the method were checked by analyzing National Bureau of Standards Standard Reference Material No. 1645 (river sediment) in quintuplicate. The measured value of 0.9 f 0.2 mg of Hg/kg (2 standard deviations) compared well with the certified value of 1.1 f 0.5 mg of Hg/kg. The detection
Figure 2. Relationship of sediment concentrations of 23a~240Pu and ratios 238Pu:2383240Pu to time of sediment deposition in the two cores taken at the same site in the eastern part of the Niagara River delta in Lake Ontario.
limit (2 SD above the mean blank response) of the procedure was 7 ng of mercury. Sediment Core Dating. Introduction of artificial radionuclides to the atmosphere commenced with the first atomic explosions in 1945, continued through the next decade, and culminated in the early 1960s just prior to the Partial Test Ban Treaty of 1963; since then there have been relatively few atmospheric weapons tests. The northern hemisphere depositional record of global fallout from nuclear weapons is well-known and shows two primary input periods: a main peak in 1963-1964 and a lesser pulse in the late 1950s. In a high-sedimentation rate regime like the Niagara River delta in Lake Ontario, a record of fallout deposition is preserved in the sediments. Figure 2 shows the 2393240Pu activity profiles of two delta cores taken in different years at the same location. The sediment surface of each corresponds to the collection date of the core, the peak represents the 1963-1964 period of maximum fallout. On both curves a distinct shoulder marks the 1957-1958 period of high fallout from the 1950s test series, and the first appearance of measurable plutonium (or 137Cs)we assign to 1952. By use of these time markers, time scales can be constructed for different sediment intervals. In these intervals, sections representing particular time spans were selected for analysis of mercury. The other four cores were not analyzed for radionuclides in the same detail as 0-73-6 and 0-79-1. Consequently, core sections were dated from 2391240Pu concentration distributions by defining the sedimentation rates of two intervals, one between the surface (date of collection) and peak fallout (1963-1964) and the other from peak to first significant activity (1952). The exception is core NR-79-2; the bottom of this core was dated as 1961, the start of water diversion to the reservoir.
Results Most of the radionuclide data on which we have based our assignment of ages to sections of cores 0-73-6 and 0-79-1 are shown in Figures 2 and 3. Because of the brevity of the time intervals involved, no corrections have been made for radioactive decay. In Figure 2 on the left side are plotted the concentrations of 2399240Pu that were measured at the various levels of both cores and on the right side the corresponding ratios of 238Puto 239,240Pu. In Figure 3 on the left side are shown the 241AmconcentraEnviron. Sci. Technol., Vol. 18, No. 6, 1984
405
Table I. Depth in Core (cm) vs. Time Assigned to Section Analyzed for Mercury
time span represented by core segment analyzed
0-73-6
1978-1979 1974-1975 1972-1973 1971-1972 1969-1970 1967-1968 1963-1964 1960-1962 1956 1953-1954 1952 1949-1950 1946-1947 1943-1944 1941 1937 1934-1935
western Lake Ontario 0-79-1 0-77-3
ABS" ABS
0-1 7-8 NA 11-12 13-14 NA 19-20 NA NA 30-32 NA 38-40 42-46 NA 50-54 58-62 62-66
0-1
2-3 4-5 NA 10-12 NA 20-22 NA 30-32 36-38 44-46 50-54 ABS ABS ABS
ABS NA~ NA NA NA NA 2-3 2-3 NA NA NA NA 8-9 NA NA NA NA
Niagara River pumped storage reservoir NR-79-2 0-1 5-6 8-9 NA 14-16 NA 20-22 NA ABS ABS ABS ABS ABS ABS ABS ABS ABS
eastern Lake Erie E-79-2 oc-1-2 ABS NA NA 2-3 NA 5-6 8-9 NA NA NA 24-26 NA NA NA 56-58 NA NA
0-1 NA NA NA NA NA 12-14 NA NA NA NA NA NA NA NA NA NA
" Levels not represented in core. Not analyzed. Table 11. Mercury Concentrations (ppm in Wet Weight) in Selected Core Segments vs. Time Assigned to Sections Analyzed time span represented by core segment analyzed
0-73-6
western Lake Ontario 0-79-1
1978-1979 1974-1975 1972-1973 1971-1972 1969-1970 1967-1968 1963-1964 1960-1962 1956 1953-1954 1952 1949-1950 1946-1947 1943-1944 1941 1937 1934-1935
ABS" ABS 0.45 & 0.04 1.1 0.1 1.3 f 0.8 NA 3.6 f 2.6' NA 3.2 0.4 NA 8.4 f 2.3 6.0 f 0.1 2.2 0.4 0.32 f 0.01 ABS ABS ABS
0.21 0.06 0.46 0.03 NA 0.75 f 0.16 1.7 f 0.2 NA 3.2 f 0.1 NA NA 6.0 f 1.5 NA 5.7 f 0.28 0.86 f 0.16 NA 0.18 f 0.04 0.036 f 0.001 0.013 f 0.007c
* *
*
Levels not remesented in core. _ _ _ _ _ _ ~ _____ ~ ~
* *
0-77-3
Niagara River pumped storage reservoir NR-79-2
ABS NAb NA NA NA NA 1.9 0.4 1.9 f 0.4 NA NA NA NA 0.13 f 0.02 NA NA NA NA
0.17 f 0.01 0.46 & 0.08 0.42 0.21 NA 1.6 f 0.4 NA 1.5 f 0.1 NA ABS ABS ABS ABS ABS ABS ABS ABS ABS
0.072 f 0.004 NA NA NA NA NA 0.054 & 0.023' NA NA NA NA NA NA NA NA NA NA
ABS NA NA 0.29 0.16 NA 0.17 f 0.01 0.087 0.019 NA NA NA 0.076 f 0.007 NA NA NA 0.034 f 0.001 NA NA
*
*
Not analvzed. 'Quintuplicate analvses; all others done in duplicate.
tions and on the right side the 137Cs concentrations. In Table I are shown the depths in the cores of each of the slices that were analyzed for total mercury and the age interval that we have assigned to each. In Table 11, correspondingly, are shown the mercury concentrations, in parts per million of wet sediment, measured on these core samples. Table I11 shows the calculated sediment accumulation rates for Lake Ontario cores determined for the intervals between the time markers and used in the construction of the time scale. In Figure 4 as in Figures 2 and 3, only the time scales were used to set vs. the mercury concentrations measured in cores 0-73-6 and 0-79-1. On the basis of the earliest sedimentation rate observed from the radiochronology, 406
*
*
eastern Lake Erie E-79-2 oc-1-2
Environ. Sci. Technol., Vol. 18, No. 6, 1984
Table 111. Calculated Sediment Accumulation Rates (cm/year) of Corresponding Lake Ontario Cores
time intervals between dated horizons 1978-1979t0 1972-1973 1972-1973 to 1963-1964 1963-1964 to 1957-1958 1957-1958 to 1952 1952to1934-1935
calculated sediment accumulation rates 0-73-6 0-79-1 NA" 1.1 1.3 2.4 2.4
Not amlicable: core was taken in 1973.
1.5 1.1 0.8 1.6 1.6
dpm kg
Am-241 0
2:
40
60
80
Cs- 137
100
0
5000
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15,000
e o
0-79-1
0
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-1975-
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.
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Figure 3. Concentrations of 241Amand 13’Cs vs. time of deposition in cores 0-73-6 and 0-79-1. TOTAL MERCURY, ppm w e t w t
+-
I19571
1956 1955 ~
1954 I953
1952
+--e
-+ + Figure 4. Mercury concentrations vs. time of deposition in cores 0-73-6 and 0-79-1. Horizontal bars show the standard deviations calculated from replicate analyses, and vertical bars show the time spans represented by the samples analyzed.
both time scales have been extrapolated backward to depths in the cores that could not be directly dated with artificial radionuclides. We take the evident correspondence of the early mercury concentration curves so generated as evidence that this extrapolation introduced no serious discrepancies. The period covered by the extrapolated time scale is the period of relatively uncomplicated mercury release history. In total, 34 horizontal sections from six cores were analyzed for total mercury concentrations (Tables I and 11)with the majority selected from the well-characterized Niagara River delta cores. By use of the sediment dating technique already described, the sections have been grouped into time spans for comparison. Attempts to identify the chemical form of mercury in the sediments were inconclusive. However, Lindberg and Turner (14) found that solid waste products from the production of chlorine and caustic soda using the mercury-cell process contained mercury which appeared to be to a large extent in the elemental form. The speculation
that at least some of the mercury contained in our sediments was present in the elemental form seems therefore justified. Following findings by Smith and Loring (15) and Breteler et al. (16),we believe that most of the mercury in the sediments was associated with organic matter. In dealing with curves of wet concentrations vs. depth in sediment cores, one is always concerned lest an inflection may represent a sharp change in water content of the matrix. We have carefully examined our data in this respect and can confidently affirm that all the phenomena we report are exhibited just as well when we plot concentrations on a dry weight basis. Because the wet weight data are more easily used to calculate nuclide inventories in the sediment columns, we have used that basis for our reporting here.
Discussion Discussion of Sediment Dating. There are several additional dated events whose effects should be observed in sediment profiles like those shown in Figures 2 and 3; these can be used to verify, or even further refine, the time scales we have assigned. In order of their appearance in the cores, these events are as follows: First, the earliest pulse of plutonium in our Niagara delta cores is characterized by a relatively high ratio of 238Puto 2393240Pu.Worldwide fallout should at the time assigned to this level have been dominated (17) by debris from the Ivy-Mike Test (Oct 1952),but this signal was not high in 23aPu(18-20). It is likely, rather, that the high 238239,240 ratio should be attributed to one or more local events from tropospheric clouds of debris from the Nevada test site, like that reported by Clark (21). The signal from this source evidently was soon diluted out as the pace of atmospheric testing increased, with highest yield devices, from 1952 on, but we believe its observation at the lowest level of both cores, 0-73-6 and 0-79-1, provides valuable confirmation that our time assignment is correct and that the plutonium signal has been little blurred by downmixing of sediment after deposition. Second, the beginning of operation of the pumped storage lagoons, about 1961, we believe is correlated with the reduction in the rate of sediment accumulation (see Table 111)soon after 1958. That the nuclide signals do not quite coincide with the time of the onset of sediment diversion prevents an exact correlation, but the approximation is enough to lend further confidence to the time scale. Third, in early 1964, at high altitude over the southern hemisphere, the 238Pu-poweredSNAP-SA navigational satellite failed and vaporized. The amount of 238Puinvolved represented a large addition to that released by atmospheric weapons testing (22,23);the northern hemisphere began to see the effect of SNAP-SA, as a rapid increase in the 238Puto 23g3240Pu ratio in surface air, only about mid-1966 (19). By the end of 1966 this ratio had risen above 0.2 from the 0.02-0.03 characteristic of worldwide fallout (24);by 1971 it began to fall again, the SNAP-SA effect being no longer measurable in surface fallout by the end of that year. The curve at the right of Figure 2 showing the ratios 238Puto 2391240Pu in cores 0-73-6 and 0-79-1 clearly confirms the onset of this signal in the sharply increased ratio in the 1966 slice of 0-73-6. The corresponding increase in core 0-79-1, however, appears in the slice we had dated to 1965, close enough to provide general confirmation of the assigned time line but strongly suggesting that the lower rate of sediment accumulation estimated for this core in the 1957-1958 to 1963-1964 period (Table 111),prevailed also through 1966. The 1971 return to nnormal” of the 238239,240 ratio was not obEnviron. Sci. Technoi., Vol. 18, No. 6, 1984
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servable in either of these cores. This fact corresponds exactly to the expectation following from the next event. Lastly, from 1966 to 1971, a commercial nuclear fuel reprocessing plant was operated near West Valley, NY, by Nuclear Fuel Services, Inc. (NFS). During this period, measurable amounts of low-level wastes were released in liquid form to a nearby creek from which they finally reached Lake Erie. The liquid wastes from this operation, like those from the British plant at Windscale (25), were characterized by plutonium with a ratio 238:239,240 much higher than that of fallout and by small, but measurable, amounts of curium, another transuranium element (26) and one that was present in fallout only at very low concentrations (27). ' W m was not measurable in core 0-73-6 before 1968 but was just measurable in that year and easily measurable in each subsequent year. The Nuclear Fuels Services, Inc., plant effluent, we are confident, was the source of this curium and of the continued excess of 238Pu that compensated for the exhaustion of the signal from SNAP-SA. At about this same level in both cores, also, the ratio 137Csto 239*240Pu began to increase above the characteristic of fallout. The appearance, in core 0-73-6, of the NFS tracer signal in the 1968-dated section fits quite well with reasonable estimates of the travel time from the plant and with the 1966 start of its operation. Like the other independently datable signals in this system, the timing is so close to that expected as to lend confidence to the time scales we have established. In core 0-79-1 the NFS 244Cmsignal appeared, as we noted above did the SNAP-SA 238Pusignal, a year or two earlier than expected or than was observed in core 0-73-6. In addition to these more or less independently dated variables that confirm the details of the sediment column time scales adopted, it is important to note the comparison between Figures 2 and 3. The peak positions of 239,240Pu (Figure 2), 241Am,and 13'Cs (Figure 3) occur in the same relative sections in both cores, indicating the stability of the sediments in this region. Discussion of Mercury Concentrations. The cores that were selected for the mercury analyses shown in Table I1 support discussion of the time course of the sources and sinks of mercury pollution of the Niagara River. As noted earlier, there has been a northern-hemisphere-wide increase in mercury, atmospherically delivered, coincident with the increase in industrialization since the mid-1800s. This we expected to be reflected in the sediments of Lake Erie (cores E-79-2 and Oc-1-2), possibly complicated by a supply from the contaminated sediments of Lake St. Clair, or other local releases; Lake Erie sediments should, as described, represent the only significant distant source of mercury to the Niagara River. There is some confusion about what may have been the preindustrial mercury level of either Lake Erie or Lake Ontario and what may have been added to this source by the distributed, industrial mercury fallout. Thomas (2) concluded from his studies of a large series of Lake Ontario sediment grabs and cores that the preindustrial mercury level ranged closely about 350 ppb of dry sediment; this would correspond to about 170 ppb of wet sediment at the mean wet-to-dry ratios that we have seen in sediments of this lake. Thomas' value compares well with the 286 ppb dry (1400-1800 A.D.) or 122 ppb dry (500-1300 A.D.) found in a Lake Windermere sediment core by Aston et al. (3) and the 200-300 ppb dry reported as background level in Puget Sound (28, 29). Neither of these ranges corresponds, however, to the report of Young et al. (5) of Santa Barbara Basin sediments ranging about 50 ppb dry before 1870, nor do they fit with our oldest sediment samples (Table 11)showing 34 ppb wet 408
Environ. Sci. Technol., Vol. 18, No. 6, 1984
in Lake Erie in 1941 or 13-36 ppb wet in Lake Ontario Niagara Delta Sediments in the 1930s. Probably no strong correspondence should be expected, reservoir-to-reservoir, in the mercury concentrations attributable to the distributed natural or anthropogenic fluxes, since the concentrations must be determined by local sediment properties and rates of accumulation. Our data in Table I1 convince us that before the late 1930s the local mercury flux, due to the chloralkali plants of Niagara Falls, had scarcely increased the mercury content of sediments deposited on the Niagara River delta over that in the materials supplied from Lake Erie. There seems to be general agreement that the major current flow eastward carrying sediment toward the Niagara River is that along the northern shore of the lake. There is some sediment transport also along the southern shore, and as discussed above in the context of curium and 238Pusupply, we had observed materials in delta sediments that certainly were supplied to Lake Erie by a point source draining from this shore. For that reason, we examined core E-79-2 for its mercury content; these analyses confirm there was no special mercury supply along the south shore. Between about 1940 and 1950 (Table 11)mercury in the Lake Erie sediments increased by no more than a factor of 2, whereas in those of the Niagara River delta the increase was 10-20-fold, largely attributable to the local sources. The peak delta mercury concentrations occurred in the 1950-1954 period, corresponding to the time when the older style rocking mercury electrodes were being replaced, evidently with attendant extra losses of mercury. By 1956-1964, this process was completed, and the delta mercury concentrations leveled off at somewhat less than half their peak. As we discussed earlier in the context of the dating of the delta cores, about 1961 the pumped storage reservoir began operation, with the effect of retaining a significant fraction of the river's sediment load, as shown by diminution of the sedimentation rates of both cores; Figure 1shows that this sediment diversion into the reservoir should have been accompanied by a proportionally larger diversion of any mercury wastes released from the upper (Hooker Electrochemical) chloralkali plant but no diversion of releases of mercury from the lower (Olin Corp.) chloralkali plant. Qualitatively, this is clearly reflected in the mercury values from the reservoir core (NR-79-2) compared to those of the delta cores. The earliest reservoir sediment analyzed (1963-1964) contained about half the mercury concentration that characterized the delta cores in that year. Surprisingly to us, however, the reservoir sediment concentration held at the same level through 1969-1970, while the concentrations in the delta cores had, by that time, been reduced by about half; the conclusion seems inescapable that there was in this period an improvement in the mercury housekeeping at the Olin plant but that this improvement was not matched at Hooker. This assumes other factors such as rates of production at the two plants remained constant. Immediately following upon the 1970 discovery of unacceptable mercury levels in fish from Lake St. Clair, actions taken at both Niagara Falls chloralkali plants began to be effective in reducing mercury concentrations in the delta sediments. These were already diminished, by perhaps as much as one-third, by 1971-1972 and at a time when the Lake Erie source term was shown by core 02-1-2 to be still increasing. By 1973-1975, the delta and reservoir sediments showed indentical mercury levels, at about one-fourth the 1969-1970 range, and by 1978-1979 these were down again to about half the 1973-1975 values; this brought them back to about the 1941 concentration. A
reasonable extrapolation of the data from the two most recent sections of the eastern Lake Erie cores suggests to us, in fact, that by 1979 the Niagara Falls chloralkali plant releases were no more than doubling the mercury levels already obtaining in the sediments being transported down the Niagara from Lake Erie. S u m m a r y and Conclusions
This work demonstrates that, on the basis of sedimentary records, the pattern of mercury releases from a point source (the Niagara River) into the delta area of Lake Ontario can be reconstructed very precisely. In this case history, substantially all the sediment and water transport of the river came from Lake Erie; contributions from several creeks draining into the river and runoff from bordering farmland were trivial. Consequently, each of the observed changes in the mercury concentrations of the Niagara River delta sediments could be related directly to known perturbations in the pattern of mercury releases by the Niagara Falls chloralkali plants. The timing of these changes, estimated from the independent variables described, elegantly corresponded with that of the perturbations, up or down as appropriate, providing further confidence in the dating assignments made from the radionuclide data. The pollution reconstruction scheme we described in this work may be applied to any situation which meets the following criteria: (1)The pollutant should originate from an identifiable point source, resulting in elevated concentrations of the material in the settleable suspended sediment load of a body of water. This material should, at least locally, be deposited at a high rate. (2) The pollutant should be characterized by an absence of biodegradation or chemical transformation. (3) The sediments of the water body at the deposit site should be relatively free of bioturbation. The latter criterion usually excludes marine or estuarine systems in which bioturbation is generally substantial. However, when these prerequisite conditions are met, it should be possible to accurately trace the sedimentological history of pollutant discharges. Acknowledgments
The samples described could not have been obtained nor could the radiochemical data have been developed without the assistance of many colleagues;John C. Burke especially deserves mention. We are grateful also to P. M. Krey and H. D. Livingstone for critical review of the report; none of the remaining errors or confusions can be put on their shoulders. Registry No. Hg, 7439-97-6; 239Pu,15117-48-3;240Pu,1411933-6; 238Pu,13981-16-3; 241Am,14596-10-2; 137Cs,10045-97-3. L i t e r a t u r e Cited (1) Goldberg, E. D. “Yearbook of Science and Technology”; McGraw-Hill: New York, 1970. (2) Thomas, R. L. Can. J.Earth Sei. 1972, 9, 636-651. (3) Atson, S. R.; Bruty, D.; Chester R.; Padgham, R. C. Nature (London) 1973,241,450-451. (4) Klein, D. H.; Goldberg, E. D. Environ. Sci. Technol. 1670,4, 765-768. (5) Young, D. R.; Johnson, J. N.; Soutar, A,; Isaacs, J. D. Nature (London) 1973,244, 273-275.
(6) Burke, J. C. Limnol. Oceanogr. 1968,13, 714-718. (7) Burke, J. C.; Hamblin, R. E.; Casso, S. A. Woods Hole Oceanographic Institution, 1983, Technical Report WHOI-83-36, pp 1-13. (8) Burke, J. C.; Clarke, W. R.; Heit, M.; Volchok, H. L. U.S. Department of Energy, Environmental Measurements Laboratory, Environmental Quarterly, 1980, Report EML-381, pp 1-17-1-41. (9) Wong, K. M.; Noshkin, V. E.; Bowen, V. T. Tech. Rep. Ser.-IAEA 1970, No. 118, 119-127. (10) Livingston, H. D.; Mann, D. R.; Bowen, V. T. Adu. Chem. Ser. 1975, No. 147, 124-138. (11) Volchok, H. L.; Feiner, M. A. Radioanalytical Laboratory Intercomparison Exercise, U.S. Department of Energy, Environmental Measurements Laboratory, 1979, Report EML-366, pp 1-43. (12) Bowen, V. T.; Noshkin, V. E.; Livingston, H. D.; Volchok, H. L. Earth Planet. Sci. Lett. 1980, 49, 411-434. (13) Breteler, R. J.; Teal, J. M.; Valiela, I. Mar. Environ. Res. 1981,5, 211-225. (14) Lindberg, S. E.; Turner, R. R. Nature (London) 1977,268, 133-136. (15) Smith, J. N.; Loring, D. H. Environ. Sei. Technol. 1981, 15, 944-951. (16) Breteler, R. J.; Valiela, I.; Teal, J. M. Estuarine, Coastal Shelf Sei. 1981, 12, 155-166. (17) Zander, I.; Araskog, R. Nuclear Explosions 1945-1972 Basic Data, Research Institute of National Defense, Sweden, 1973, Report FAO-4-A4505-A1, pp 1-56. (18) Diamond, H.; Fields, P. R.; Stevens, C. S.; Studier, M. H.; Fried, S. M.; Ingram, M. G.; Hess, D. C.; Pyle, G. L.; Mech, J. F.; Manning, W. M.; Ghioroso, A.; Thompson, S. G.; Higgins, G. H.; Seaborg, G. T. Phys. Rev. 1960, 119, 2000-2004. (19) Thomas, C. W.; Perkins, R. W. U.S. Environmental Research and Development Administration, Health and Safety Laboratory, Environmental Quarterly, 1975, Report HASL-291, pp 1-80-1-103. (20) deBortoli, M. C.; Gaglione, P. Health Phys. 1969, 16, 197-204. (21) Clark, H. M. Science (Washington, D.C.) 1954, 119, 619-622. (22) Hardy, E. P.; Krey, P. W.; Volchok, H. L. Global Inventory and Distribution of Pu-238 from SNAP-SA, U.S. Atomic Energy Commission, 1972, Heath and Safety Report HASL-250, pp 1-31. (23) Hardy, E. P.; Krey, P. W.; Volchok, H. L. Nature (London) 1973,241, 444-445. (24) Harley, J. H. U.S. Environmental Research and Development Administration, Health and Safety Laboratory, Environmental Quarterly, 1975, Report HASL-291, pp 1104-1- 109. (25) Pentreath, R. J.; Lovett, M. B. Mar.Bio1. 1978,48,19-26. (26) Kelleher, W. J. Radiat. Health Data Rep. 1969, 10, 329. (27) Holm, E.; Persson, B. R. R. Nature (London) 1978, 273, 289-290. (28) Crecelius, E. A.; Bothner, M. H.; Carpenter, R. Enuiron. Sci. Technol. 1975, 9, 325-333. (29) Bothner, M. H.; Jahnke, R. A.; Peterson, M. L. Geochim. Cosmochim. Acta 1980,44, 273-285. Received for review September 10, 1982. Accepted December 22,1983. This work was variously supported at the Woods Hole Oceanographic Institution by the U.S. Department of Energy (and its predecessors) under contracts E Y - 76-S-02-3568-AO01, DE-ACO2- 76EV03563.AO05, and DE-AC02-81EV10694; the mercury analyses at Battelle New England Marine Research Laboratory were supported by the Olin Corp. This is Contribution No. 5219 from the Woods Hole Oceanographic Institution.
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