Environ. Sci. Technol. 2010, 44, 1551–1558
Determining Exposure History of Northern Pike and Walleye to Tailings Effluence Using Trace Metal Uptake in Otoliths LISA A. FRIEDRICH* AND NORMAN M. HALDEN Department of Geological Sciences, University of Manitoba, Winnipeg MB, Canada R3T 2N2
where the bioavailability of specific metals can be linked to spatial or temporal variations. To interpret environmental changes from this record, it is necessary to establish what constitutes normal or expected variations in otolith microchemistry for a given environment or species. This preliminary study is an examination of northern pike (Esox lucius) and walleye (Sander vitreus) otoliths from the vicinity of mine tailings using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A suite of trace elements (Sr, Ba, Mn, Zn, Cu, Pb, and Cd) was analyzed across annuli to determine a typical chemical signature in the area for these two species and to identify any periods where the chemistry might be considered anomalous.
Received July 2, 2009. Revised manuscript received January 13, 2010. Accepted January 18, 2010.
Study Area and Geologic Setting
Determining the effects of mining activity on fish populations is complicated by the uncertainty of fish residency in an affected area. Otoliths are considered to be metabolically inert and can contain complete chemical records of environments in which individuals have lived. When coupled with the annular structure, otoliths provide temporal information to the history of exposure to pollutants. In this preliminary study, northern pike and walleye otoliths collected from two lakes adjacent to base metal mine tailings at Lynn Lake, Manitoba, Canada, were analyzed using laser ablation inductively coupled plasma mass spectrometry to determine background levels of trace metals. The presence of overlapping Zn, Cu, and Pb peaks above background levels in some otoliths is interpreted as a record of elevated levels in the environment. These otoliths provided a record of the history of fish movement into and out of the affected area.
The town of Lynn Lake, Manitoba, is approximately 1100 km northwest of Winnipeg (Figure 1), in an area underlain by Precambrian volcanic and sedimentary rocks (14). Sulphide mineralization occurs as massive and disseminated deposits of pyrrhotite [Fe(1-x)S], pentlandite [(Fe, Ni)9S8], and chalcopyrite [CuFeS2] (ibid), with small amounts of pyrite [FeS2] and trace amounts of sphalerite [ZnS] (15). The Lynn Lake nickel mine was operated by Sherritt-Gordon from 1953 to 1976, during which time over 20 million tonnes of Ni-Cu ore was produced and approximately 21.8 million tonnes of tailings were generated (16). The tailings pile in the East Tailings Management Area (ETMA) consists of pyrrhotite, chalchopyrite, pentlandite, and pyrite and has been oxidizing for over 30 years (17). A number of rehabilitation activities are ongoing and several have been completed, including the installation of a trial permeable reactive barrier to treat contaminated groundwater and construction of a diversion to divert clean rain and meltwater around ETMA (18). Eldon Lake is situated southeast of Lynn Lake and drains northeast into Lynn River. The river flows past ETMA and into Cockeram Lake, which is approximately 5 km east of Eldon Lake.
Introduction Otoliths are calcified structures in the inner ear of teleost fish, composed of aragonite layers in a protein matrix deposited continuously throughout the fish’s lifetime (1). Both the inorganic portion (2) and protein matrix (3) have the capacity to incorporate a broad range of trace elements, many of which can now be detected at the parts per million (ppm) to parts per billion (ppb) level. Periodic changes in trace metal concentrations in the environment may influence amounts available for incorporation into otoliths through food or ambient water (4). Unlike many biominerals, otoliths are acellular and metabolically inert, offering a permanent record of the bioavailability of certain metals (5). Although the interpretation of otolith chemistry is complex, numerous studies have successfully used chemical analysis of otoliths as a proxy for water temperature variations, to distinguish migratory behavior, and for stock discrimination (6-8). Contaminated river and estuarine systems in industrial areas have received considerable attention [e.g., refs 9 and 10], whereas less attention has been placed on pollution connected to mine tailings. Several recent studies have examined the link between the chemistry of the environment, particularly watershed geochemistry, and the microchemistry of otoliths in lakes near mining operations (11-13). Coupling annular structure to the chemistry of otoliths may provide a chronology of environmental history of fish, particularly * Corresponding author e-mail:
[email protected]. 10.1021/es903261q
2010 American Chemical Society
Published on Web 02/05/2010
Materials and Methods Fish were collected from Eldon and Cockeram Lakes in August, 2008, as part of a Lynn River health survey by TetrES Consultants, Inc. (Winnipeg, MB). Otoliths were obtained for microchemical analysis from three northern pike and three walleye from Eldon Lake and from three northern pike from Cockeram Lake. This preliminary sample set contained mature male and female specimens that ranged from 7 to 16 years old. To prepare for microbeam analysis, sagittal otoliths were embedded in epoxy resin and cut to create a dorsoventral cross section through the core of the otolith, exposing all annuli. The posterior half of each sectioned otolith was re-embedded with epoxy resin in a 25 mm Lucite microprobe mount and then ground and polished. Prior to analysis, samples were rinsed with double distilled water and allowed to air-dry. LA-ICP-MS analyses were done using a Thermo Finnigan Element 2 ICP-MS coupled to a Merchantek LUV 213 Nd:YAG laser. Running conditions were set to optimize sensitivity and resolve annular growth features and included a 30 µm diameter beam traveling 2 µm s-1, similar to those used by Friedrich and Halden (11). Calcium at 56 wt % CaO was used as an internal standard, and external calibration was done using NIST glass 610 (19). Line scans were run from otolith core to edge, perpendicular to annuli in scanning mode. Standard analyses were collected prior to each analytical run. Measured trace element concentrations, VOL. 44, NO. 5, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of Eldon and Cockeram Lakes also showing the position of Lynn River and the East Tailings Management Area (ETMA) at Lynn Lake.
TABLE 1. Range of Trace Element Concentrations (in ppm) in Otoliths of Northern Pike and Walleye from the Study Areaa Mn Northern Pike Walleye typical 1σ analytical error typical detection limit a
Ni
Cu
Zn
Cd
Ba
Pb
0.18-186.50 0.00-1.76 0.00-2.91 0.32-165.10 123.90-1581.90 0.00-0.48 1.09-33.38 0.00-0.14 0.05-6.23 0.07-1.63 0.07-2.59 0.05-2.25 118.28-566.50 0.00-0.46 0.86-10.15 0.00-0.11 N/A 0.29 0.36 N/A N/A 0.08 N/A 0.011 0.05
0.13
0.15
0.06
0.03
0.05
0.01
0.01
Typical 1σ error values are given for elements that did not produce oscillatory signatures.
standard deviations, and detection limits were processed using GLITTER software (20). Trace elements Mn55, Ni60, Cu63, Zn66, Sr88, Cd144, Ba138, and Pb208 were analyzed to provide information on characteristic chemical signatures for the two species in the Lynn River area. Nickel, Cu, and Zn were analyzed to determine if the otoliths contain a chemical signature related to the geochemistry of the surrounding environment. However, Zn is a biologically important element and may also serve as a signature relating to diet, as may Ba and Mn (21). Lead was included as a potential indicator of the deposit, as it commonly occurs with Cu and Zn in sulphide minerals and oxidation of galena (PbS) is assumed to be the source of Pb in ETMA (17). Cadmium is toxic to aquatic animals at low concentrations and may indicate anthropogenic influence (22). However, the source of Cd in pore waters of the ETMA is considered to be Cd substituting for Zn in sphalerite (15, 17).
Results Northern pike otoliths typically contain 250-650 ppm Sr in relatively flat profiles with occasional peaks, and 50-140 ppm Zn, which is highest in the core and decreases with age (Table 1, Figure 2). Zinc signatures in northern pike contain periodic oscillations that correspond with the annuli (Figure 3). Manganese and Ba profiles are oscillatory, with maximum concentrations of approximately 185 and 30 ppm, respectively. Manganese and Ba concentrations are usually highest in the core and decrease with age. Typical concentrations of the metals are 0.1-0.4 ppm Cu, 0.5 ppm Ni, 0.05 ppm Cd, and 0.01 ppm Pb, all of which produce relatively flat profiles. Walleye otoliths typically contain 120-550 ppm Sr and 0.4 ppm Zn, both in relatively flat signatures (Table 1, Figure 4). Manganese and Ba are oscillatory, but concentrations are an order of magnitude less than those in northern pike otoliths; typical Mn concentrations in walleye are less than 5 ppm, and Ba ranges from 1-10 ppm. Characteristic trace metal concentrations are 0.1 ppm Cu, 1552
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0.6 ppm Ni, 0.05 ppm Cd, and 0.01 ppm Pb. These typical values for walleye otoliths are consistent across all annuli, with the exception of two instances. A Zn peak of about 1.2 ppm occurs approximately 170 µm along the laser traverse from the core of a 5 year old Eldon Lake walleye (Figure 5). Overlaying Cu and Pb scans shows that elevated levels of Cu and Pb, 0.9 and 0.1 ppm, respectively, correspond to the Zn peak. Comparison with the optical image of the otolith indicates that the fish encountered slightly higher levels of these elements within the first year of life, possibly near the spawning location.
Discussion Otoliths have the capability to incorporate a wide range of trace elements that can provide information on a fish’s environment and behavior [e.g., refs 8, 11, 12, and 23]. Otoliths from Eldon and Cockeram Lakes give a general idea of what background signatures should be for metals in the area. Zinc is an important, biologically mediated element but becomes toxic at high concentrations (24). Increased levels of Zn in otoliths are not uncommon (12, 25, 26). Signals detected above background levels may be related to diet or metabolism. Therefore, the identification of a Zn peak may indicate ontogenetic change and is not necessarily indicative of contamination. However, the coincidence of elevated levels of Cu and Pb with the Zn peak strongly suggests a link to tailings effluence and could be regarded as an anomalous signature. The chemical profiles of two Eldon Lake walleye indicate that these individuals encountered elevated concentrations of Cu, Pb, and Zn in a relatively sudden or different way from how they typically encounter these and other elements. Similar, Cu-Pb-Zn peaks were also found in five northern pike otoliths collected from Lynn River in 2006, one of which contained two separate peaks (Figure 6). Lake trout otoliths from Athapapuskow Lake, Manitoba, contained Cu-Pb-Zn signatures above background levels that were
FIGURE 2. Representative trace element distribution profiles from LA-ICP-MS line scans of northern pike otoliths from the study area. Smoothed lines in Ni, Cu, Cd, and Pb plots represent a moving average trendline with a 25 point period. attributed to contact with tailings effluence from Cu-Pb-Zn mining activity in nearby Flin Flon, Manitoba (12). Melanc¸on (27) injected yellow perch with Sr and Ba isotopes and found that enriched levels of the isotopes began to rise in otoliths in as little as hours to days after injection. This suggests that wild fish coming in contact with elevated levels of trace elements in the environment might incorporate such signals into their otoliths within a relatively short period of time after exposure. These signals would appear as sudden increases in concentration compared to any natural periodicity to the signal or above background levels.
Geochemical coherence of Cu, Pb, and Zn is to be expected in nature because these elements occur together in sulphide minerals. Sulphides are commonly present as accessory phases in certain major rock types; therefore, it is reasonable to anticipate some level of these elements to be present at background levels. Coherent, elevated levels of these metals are above any background or natural signature in Eldon and Athapapuskow Lakes. Both locations are in close proximity to mine tailings containing these elements, which are identifiable as potential sources of the elevated concentrations. Anomalous peaks above background levels in otoliths provide a retrospective view VOL. 44, NO. 5, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Overlay of LA-ICP-MS Zn distribution profile on an image of a northern pike otolith from Cockeram Lake showing correlation between Zn peaks and position of annuli, represented by vertical bars. of exposure to these elements. The annular time scale allows the determination if fish contacted elevated levels of metals, when contact happened, and how frequently [e.g., ref 13]. Defining variations in life history within a population using otolith microchemistry requires establishing a relationship to environmental parameters, without which interpretations are limited and movements between different environments cannot be identified (28). Concentrations of metals in Cockeram Lake are at background for the area (0.002 ppm Cu,
