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(45) Seifert, W. K., see ref 14, p 21. (46) Pym,J. G.; Ray, J. E.; Smith, G. W.; Whitehead, E. V. Anal. Chem. 1975,47, 1617. (47) Datillung, M.; Albrecht, P. Mar. Pollut. Bull. 1976, 7,13. (48) Ensminger, A,; Joly, G.; Albrecht, P. Tetrahedron Lett. 1978,18, 1575. (49) Simoneit, B. R. T.; Kaplan, I. R. Mar. Enuiron. Res. 1980, 3, 113. (50) Seifert, W. K.; Moldowan, J. M.; Smith, G. W.; Whitehead, E. V. Nature (London) 1978,271, 436. (51) Eganhouse,R. P.; Simoneit,B. R. T.;Kaplan, I. R. Enuiron. Sci. Technol. 1981, 15, 315. (52) Simoneit, B. R. T.; Mazurek, M. A.; Cahill, T. A. J. Air Pollut. Control Assoc. 1980, 30, 387. (53) Crisp, P. T.; Brenner, S.; Venkatesan, M. I.; Ruth, E.; Kaplan, I. R. Geochim. Cosmochim. Acta 1979,43,1791.
(54) Swisher, R. D. J. Am. Oil Chem. SOC.1963,40, 648. (55) Lake, J. L.; Nonvood, C.; Dimock, C.; Bowen, R. Geochim. Cosmochim. Acta 1979,43, 1847. (56) Youngblood, W. W.; Blumer, M. Geochim. Cosmochim. Acta 1975, 39, 1303. (57) Bates, T. S.; Carpenter, R. Geochim. Cosmochim.Acta 1979, 43, 1209. (58) Wenzel, B.; Aiken, R. L. J. Chromatogr. Sci. 1979,17,503. (59) Ho, T. Y.; Rogers, M. A.; Drushel, H. V.; Koons, C. B. Am. Assoc. Petrol. Geol. Bull. 1974, 50, 2338.
Received for review August 31, 1981. Accepted April 6, 1982. Financial assistance from the Department of Energy and Bureau of Land Management (Contract No. EY-76-3-03-0034) is acknowledged.
Deposition and Chemistry of Pollutant Metals in Lakes around the Smelters at Sudbury, Ontario Jerome 0. Nriagu,” Henry K. T. Wong, and Robert D. Coker
National Water Research Institute, Burlington, Ontario L7R 4A6, Canada Analyses of the suspended particulates in lakes within a 30-km radius of the smelting complex at Sudbury show average Ni, Cu, Zn, and P b concentrations of 1500,420, 540, and 360 pg g-l, respectively. Organic matter constitutes 35-60% of the suspended material in the lakes but plays a minor role in the transport of metals to the sediments. The rates of metal accumulation in the sediments have been estimated typically to be 100-600, 50-300, 10-60, and 5-30 mg m-2 year-’ for Ni, Cu, Zn, and Pb, respectively. The enrichment factors for metals in surficial sediments typically are 12-115 for Ni, 10-77 for Cu, 2-10 for Pb, and 2-8 for Zn. These enrichment factors and deposition rates for Ni and Cu are among the highest recorded anywhere in the world. Some of the lakes with pH values of 4.5 or less show no enrichment or accumulation of pollutant metals in their surface sediments, indicating that pollutant metals previously stored in the sediments have since been leached away. This documentation that the contaminated sediments can release substantial quantities of toxic metals to the overlying water must have interesting ramifications with regard to the limnological impacts of acid rains. Introduction Emissions from the mining and smelting activities in Sudbury, Ontario have engendered extensive biogeochemical changes in the surrounding lakes. Numerous studies have focused on the impacts of smelter exhausts on the acidification, metal contamination, and community structure of lakes in the area (e.g., ref 1-11). None of these previous studies has addressed the flux rates for the pollutant metals into the lakes or the transfer of the metals from the surface waters into the sediments. This report deals with the particulate and dissolved trace metals in lakes around Sudbury. The chemical analysis of the suspended material has been linked with studies of the underlying sediments in order to examine the cycling and removal of the pollutant metals in the lake water. Extensive studies have now documented the fact that lake sediments preserve a good historical record of the natural vs. anthropogenic fluxes of heavy metals into the lake basin (see ref 12-23, for instance). So that the historical record of metal pollution could be deciphered, the 0013-936X/82/0916-0551$01.25/0
ages and hence the accumulation rates of the recent sediments have been determined by the lead-210 technique. In this report, the changes in the metal profiles of dated sediment cores have then been used to reconstruct the history of anthropogenic metal influx into lakes around Sudbury. The nickel deposit at Sudbury was discovered in 1883. The roast yard and smelter were first set up in 1888 at Copper Hill, which could handle 80-100 tons of ore per day, yielding a matte containing 50% of copper and nickel (24). The uncontrolled open-air roasting process released significant quantities of pollutant metals to the air which would have impacted the local lakes; the fumigation of the surrounding areas with the SO2 has destroyed the surrounding vegetation. Metal production in Sudbury grew gradually and reached about 45 000 tons of Ni and 20 000 tons of Cu at the end of the First World War. Sharply increased metal output commenced during the early 1930s and early 1950s (25), and in 1977, the mines at Sudbury produced about 180000 tons of Ni and 175000 tons of Cu. The use of roasting beds was discontinued around 1923 when the 510-ft (170 m) stack and sulfur-recovery plant was completed at Copper Cliff. The 1250-ft (381 m) superstack was installed in 1972. In 1977, the smelters in Sudbury daily emitted about 2.6 tons of Ni, 2.6 tons of Cu, 0.7 tons of Pb, and 6.3 tons of Fe (26);the daily outpouring of 2500 tons of SO2from the 381-m superstack makes it the single largest point source of this pollutant in the world (26). It has been estimated (27) that about 40% of the Cu and 70% of the Ni emitted are deposited in the immediate vicinity of Sudbury. The area around Sudbury thus represents a unique “laboratory” for studying the long-term impacts of airborne pollutants on aquatic ecosystems. Methodology The lakes studied are located within a radius of 30 km from the metallurgical works in Sudbury, Ontario (Figure 1). These Precambrian shield lakes encompags a wide diversity of physical and chemical characteristics and show varying degrees of stress from the acid rains. The geological settings and the general limnology of lakes in the region have been outlined in reports by Conroy et al. (4,
0 1982 American Chemical Society
Environ. Sci. Technol., Vol. 16, No. 9, 1982 551
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Figure 1. Locations of Sudbury and area lake sampling sites, August-October 1979.
5), Allan and Timperley (12), and Semkin (28). Samples were collected in May (Ramsey Lake only) and August, 1978. Water samples were collected by means of pumps with all-plastic tubing. In stratified lakes, the samples were taken about 2 m below the air-water interface and in the middle of the hypolimnetic column; otherwise the sampling was from 2 m and the midwater column. Typically, the sampling stations were located in the middle of the deepest basins of each lake. The suspended particulates in about 1200 L of the water samples were recovered by centrifugation through a Westfalia four-bowl continuous flow centrifuge (Model KDD 605). At the flow rate of 6 L min-l used in the study, the centrifuge had an extraction efficiency of 90-95% for particles with diameters above 0.26 pm (29). The particulate samples were stored frozen until freeze-dried. Five-gallon (about 19 L) aliquots of the unfiltered water samples were also collected in carefully washed, acid-rinsed, polyethylene plastic containers. Each of the later samples was quickly acidified with Ultrex HC1 to a pH value of about 2.0 and used subsequently in the determination of the total metal concentrations by the modified cobalt pyrrolidine dithiocarbamate method (30). The error range in the analytical methodology is estimated to be *lo% of the reported concentrations. Sediment cores (8 cm in diameter) were taken by means of a lightweight coring device (31);only cores that came up with their sediment-water interfaces intact and undeformed were processed. Within 1h after retrieval, each core was subsectioned at 1.0-cm (top 10 cm layer) or 2.0-cm (layers deeper than 10 cm) intervals, and the subsections quickly frozen. Subsequently, the sediments were freeze-dried, and the percentage dried weight was recorded. The carbon and nitrogen contents of the suspended particulates were determined by means of Perkin-Elmer CHN analyzer. Organic carbon (weight loss) in the sediments was determined by dry combustion in a Leco furnace after removal of the carbonate carbon with sulfurous 552
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acid (32). The determination of the metal contents of the sediment and suspended particulate samples and the analysis of the total lead-210 activity in the sediments followed the procedures described previously (16, 30). Briefly, the samples were digested in Teflon-lined Parr digestion bombs (33) and the metal concentrations determined by atomic absorption spectrometry. The precision of the technique is f15% of the reported trace-metal concentration. The lead-210 in the digestate was plated onto a polished silver disc and its activity (actually, the a activity of its daughter, polonium-210) measured in an NMC 271. proportional counter (from Nuclear Measurements Corp., IN). The Lead-210Geochronology. The profile of lead-210 activity in a core can be used to estimate the ages of the different sediment intervals assuming that (a) the 210Pb, 210Bi,and 210Poare in secular equilibrium and there is no postdepositional mobility of any of these radionuclides and (b) the 210Pbbackground is constant throughout the sediment column. The age calculations have been made by using two models: (a) The constant initial concentration (cic) model, which assumes that the concentration of the unsupported 210Pbin the depositing material (i.e., at the sediment-water interface) is constant in time at any given location in the lake (see ref 34-39). The cic model has been used more widely in geochronologicalwork reported in the literature (e.g., ref 35-39). (b) The constant rate of supply (crs) model, which assumes a constant net rate of supply of unsupported lead-210 to the sediment despite any variations in dry mass sedimentation rates in a given core (see ref 40-44). In the latter calculations, the reference time horizon was set at 150 years or about 5 half-lives of the 210Pb. Results and Discussion
The conductivity and trace metal data from a synoptic survey of 20 lakes around the mining and smelting complex at Sudbury are summarized in Table I. The anomalously
Table I. Total Metal Concentrations and approx dist from lake Sudbury, mi Kelley 2.0 Robinson 2.0 Hannah 2.5 Nepahwin 3.0 Middle 3.0 St. Charles 3.0 Silver 4.0 Ramsey 4.5 McFarlane 6.0 Lohi 6.5Whitewater 6.5 Richard 7.0 8.0 Raft Tilton 9.0 Wavy 12 Lac St. Jean 16 Vermillion 16 Joe 18 Nelson 18 Windv 20
Conductivities of Lake pH 9.2 6.5 6.5 6.7 6.6 6.1 4.1 6.8 7.6 4.8 7.3 6.8 6.3 5.1 5.4 6.2 7.1 5.6 6.3 6.3
conductivity, pmho cm-' 1150 3 04 245 290 170 140 250 200 134 85 2 80 60 73 58 58 56 56 69
high levels of nickel and, to a lesser extent, of copper are evident. The Ni concentrations are among the highest recorded anywhere in the world and at times exceed by far the generally accepted standard of 25-50 pg L-' for domestic and potable waters (45). The conductivities of the lake waters range from 50 to 300 pmho cm-' (Table I), Kelley Lake being a notable exception. There is no obvious enrichment of cadmium in these waters, the data in Table I being comparable to the levels often reported in many unpolluted natural waters (46). Notice also that the Cd concentrations do not show a definite generic affiliation with the smelting operations; natural sources tend to override the small contributions from the smelters. Few reliable data have so far been reported on the cadmium concentrations of soft-water lakes in Ontario. In many instances, the elevations in Zn concentration may be associated with increased dissolution from lithological sources induced by a drop in the pH value. The nickel contents of the lake waters decrease sharply with distance from the local smelters at Sudbury (Figure 2). Lakes more than 55 km from Sudbury typically show Ni concentrations of
