SCOPE 53 - Methods to Assess the Effects of Chemicals On Ecosystems

12.1 INTRODUCTION

The concept of "cold" climate is a relative one, and it will be examined mainly by reference to methods being used to study contamination of aquatic ecosystems in arctic drainage of Canada. The most pervasive chemical contamination problems in this area are posed by a few stable contaminants (e.g., PCBs, heavy metals) found consistently in animal and human tissues. The presence of these materials has prompted questions about their sources, the pathways that supplied them, their geographic distribution, their future trends, and the biological implications associated with them. Few, if any, new chemical products are developed for exclusive use in the Arctic, and so the requirement is for a retrospective evaluation of contaminants already present. The source of these contaminants to the people is largely animal tissues consumed as a normal part of the diet (Kinloch et al., 1992) hence value judgments must be made in which the risks of consuming such foods are weighed against their nutritional benefits.

Evaluating the biological meaning of known exposures requires knowledge of associations between exposures and responses. These typically rely on experimental laboratory toxicology, but few laboratories have worked experimentally with arctic species. Furthermore, the more highly valued arctic species like whales and walrus seem unlikely to ever be studied toxicologically in laboratory settings. Most experimental work has been done instead with temperate species convenient to maintain in laboratories; extension of results and conclusions to arctic species is by inference. An emerging effort is the examination of animals and plants for "bioindicators," biochemical or other changes that may be associated with exposure to contaminants, and this approach allows the direct examination of arctic species.

A significant difference between arctic and temperate settings is in the exposure to those contaminants that are subject to decomposition by processes dependent on heat or light. Rates of decomposition are slow under arctic winter conditions, so exposure to these materials can be more prolonged than might be expected from an experience in temperate climates. The presence of ice cover for much of the year impedes the exchange of oxygen and other materials between water and atmosphere. This situation means that phenomena like the "weathering" (Payne and McNabb, 1984) of petroleum oils do not occur readily in arctic waters for much of the year.

The aquatic organisms of greatest concern in the Arctic are those that have economic and cultural values and those that are consumed by people, namely fish, marine mammals, and birds. These animals typically live a long time and reach large sizes. Ecosystem studies by Rapport et al. (1985) and toxicity studies by Neuhold (1987) indicate that these biological characteristics are associated with high sensitivity to stress. Most of these animals are long-lived predators, and so they integrate processes over long periods of time and several trophic levels, and often over wide geographic ranges. Given the economic, nutritional, cultural, and ecological importance of these animals, both residue and biological studies have been focused on them. This choice is partly a matter of sampling opportunities in the Arctic; these are the animals being taken in traditional subsistence hunting, hence tissue samples can be obtained without killing additional animals.

12.2 ORGANOCHLORINE COMPOUNDS IN ARCTIC FISHES, MARINE MAMMALS, AND SEA BIRDS

Interest in stable organochlorine compounds has been derived not only from their potential for exerting biological effects, but also for their power to illustrate hemispheric or global dispersal processes. These materials (polychlorinated camphenes (PCCs, toxaphene), DDT- and chlordane-related compounds, and PCBs, chlorinated dioxins and furans, hexachlorocyclohexanes, chlorobenzenes, dieldrin, and mirex) are reported consistently in tissues of arctic fishes and marine mammals (Muir et al., 1992). Persistent chlorinated hydrocarbons and heavy metals have been detected in seabirds from different Arctic regions in Canada (Vermeer and Reynolds, 1970; Vermeer and Peakall, 1977; Nettleship and Peakall, 1987; Elliot et al., 1992; Hart et al., 1991) and in Norway (Fimreite and Bjerk, 1979; Holt et al., 1979; Norheim and Kjos-Hansen, 1984; Ingebrigtsen et al., 1984; Barrett et al., 1985; Norheim, 1987; Norheim and Borch-Iohnsen, 1990; Daelemans et al., 1992). Contamination levels in birds from Russian Arctic (Savinova, 1991, 1992), Greenland (Braestrup et al., 1974), and Alaska regions (Ohlendort et al., 1982) are less well known.

12.2.1 SPATIAL AND TEMPORAL TRENDS

Ringed seals (Phoca hispida) have been used for temporal and spatial trend studies, because they are a widely distributed and relatively sedentary species. Care must be taken to evaluate seals of similar sex, age, and blubber thickness, because these factors are known to influence levels of organochlorines in blubber (Addison and Smith, 1974; Muir et al., 1988).

Figure 12.1. Relative åPCB levels in blubber of male (lightly hatched), female (black), and combined sexes (unshaded) of ringed seals from Canadian and Alaskan locations

Ringed seals from seven locations in the Canadian Arctic (Muir et al., 1993) and the Chukchi Sea (Becker et al., 1989) had very similar åPCB levels in blubber (Figure 12.1), with mean concentrations ranging from 0.51 to 1.2 µg per g. Levels of åPCB in ringed seals from Spitzbergen were about twice as high as concentrations in the Canadian Arctic, consistent with the relative proximity of Spitzbergen to agricultural and industrial areas of Europe (Oehme et al., 1988). PCB levels in Canadian arctic ringed seals are 10 times lower than reported for land-locked ringed seals in Finland (Helle et al., 1983), and up to 50 times lower than reported for the same species in the Baltic Sea during the mid-1970s (Bergman et al., 1981). The elevated levels of PCBs, especially coplanar congeners (Olsson et al., 1990), in Baltic ringed seals have been associated with the reproductive failure of this population (Helle et al., 1976). In a 2-year laboratory study, common seals (Phoca vitutina) fed fish from the Wadden Sea, with high levels of PCBs, had significantly reduced retinol and thyroid hormones relative to controls and reduced reproductive success (Reijnders, 1986; Brouwer et al., 1989).

An additional complication in evaluating possible effects of organochlorine compounds in marine mammals is the decline in concentrations due to bans on open uses of PCB oils and the application of many chlorinated pesticides that were implemented in the 1970s and 1980s. Addison et al. (1986) concluded that PCBs declined about threefold in ringed seals from Holman Island, in the western Canadian Arctic, between 1972 and 1981. For åDDT, however, much of the decline (30-40 percent) between 1972 and 1981 could be explained by thicker blubber of the animals collected in 1981. Little is known, however, about temporal trends of chlordane or PCCs in marine mammals, because measurement of these groups in arctic animals began only in the mid-1980s.

Levels of chlorinated hydrocarbons in Arctic seabirds vary widely depending for the most part on the species of bird and its ecology-feeding mode, migration route, sex, age, physiological, and biochemical parameters (rate of normal metabolic processes, quantity and composition on lipids, and hepatic microsomal mono-oxygenases activities). Levels of organochlorine substances have been monitored in sea birds eggs in different Arctic regions from the 1960s. In 1968-1969, concentrations of DDT in kittiwake (Ryssa tridactyta) eggs from the Atlantic Canadian coast were 2-13 ppm (Vermeer and Reynolds, 1970). In 1968-1973, the level of DDT in kittiwake eggs from Norway was, on average, 1.2 ppm (Holt et al. , 1979). Eggs from the same species collected in the mid-1970s at Prince Leopold Island in the Canadian Arctic archipelago had higher PCB levels (5.2 ppm) than eggs of the northern fulmar (Fulmarus glacialis) (1.93 ppm) or the thick-billed murre (Uria lomvia) (0.01 ppm). DDE/PCB ratios in eggs and livers of fulmars and murres were much lower than in kittiwakes, probably reflecting the lower levels of DDE in the latter. Compared with other seabirds, kittiwakes appear to have a greater capacity to metabolize and excrete organochlorine substances (Nettleship and Peakall, 1987). This capacity is probably related to the metabolic rates of kittiwakes, being higher that those of other species (Gabrielsen et al., 1987). Values in the range 0.05-1.0 ppm DDT and 1.1-2.4 ppm PCB have been reported in the livers of kittiwakes from different Arctic regions (Bourne and Bogan, 1976; Nettleship and Peakall, 1987; Savinova, 1991). The concentrations of DDT and PCB found in kittiwakes from the east coast of the Kola peninsula (Savinova, 1991) were 3-5 times lower than in those from David Strait and Bear Island (Bourne, 1976).

A decrease of 55-60 percent in åDDT and 69-86 percent in PCBs was observed in thick-billed murre eggs collected at Prince Leopold Island, Lancaster Sound, between 1976 and 1987. Similar declines in DDT and PCB residues occurred in livers of kittiwakes and northern fulmars, but not in those of thick-billed murres from the same region (Nettleship and Peakall, 1987). In livers and muscles of herring gulls (Larus argentatus) from the Barents Sea åDDT content declined three- to sixfold during the last decade, but the decline was not observed for PCBs (Savinova, 1992).

In 1982-1983, puffin (Fratercula arctica) eggs from two colonies in Northern Norway contained, on average, about 20 percent higher residues of PCBs and p,p'- DDE than corresponding meal\ levels in Alaskan puffin eggs (Ingebrigtsen et al. , 1984; Ohlendort et al., 1982). By contrast, lower PCB residues were found in eggs and adult brain tissues collected from puffins in eastern Canadian coastal waters (Pearce et al., 1989).

From a toxicological viewpoint, some congeners are more significant than others, and may account for most of the toxic effects. Daelemans et al. (1992) report on PCB congeners in glaucous gulls (Larus hyperboreus) and black guillemots (Cepphus grylle) from the Svalbard area. Particularly high levels of organochlorine compounds have been recorded in glaucous gulls (Bourne, 1976). This species acts partly as a predator; during the breeding season gulls prey on other seabird's eggs and chicks. The average PCB concentration in the liver of the glaucous gull from Svalbard was 20.9 ppm, i.e., about 160 times higher than that found in the liver of the black guillemot (Daelemans et al., 1992). The total concentration of three selected non-ortho-congeners represented only 0.18 percent of total PCB concentration. Congener 126 showed the highest average concentration (0.11 percent of total PCB) followed by 169 (0.04 percent) and 77 (0.03 percent).

The concentration levels in arctic seabirds, in the main, have been considerably below those expected to produce lethal effects. On the other hand, much evidence demonstrated that levels high enough to produce sublethal effects are frequently attained. As a group, birds are more resistant to acutely toxic effects of PCBs than mammals. LD₅₀s for various species of birds varied from 604 to more than 6000 mg Aroclor per kg diet (Eisler, 1986).

Predacious fish such as burbot and lake trout can also be used to assess spatial and temporal trends in organochlorine compounds in freshwater ecosystems. Temporal trend studies of PCBs in lake trout in the Great Lakes have demonstrated the need to compare fish of the same age class (Devault et al., 1986). PCB levels in lake trout among inland lakes in Ontario, receiving similar inputs of contaminants from the atmosphere, appear to vary with the length of the pelagic food chain and the lipid content of the trout. Thus, lake trout from lakes with Mysis or smelt have higher PCB levels than those from lakes lacking Mysis or pelagic forage fish (Rasmussen et al., 1990). A 16-year temporal trend study in Lake Storvindeln in northern Sweden showed that DDT and PCB levels in pike (Esox lucius) declined about three- to fourfold during the period from 1968 to 1984, coinciding with the ban on DDT and PCB use in Western Europe during that time. Concentrations of organochlorine substances were reported in burbot liver from seven locations on a northwesterly transect from northwestern Ontario to Fort McPherson in Northwest Territories (Muir et al., 1990). Lipid normalized concentrations of åPCB and åDDT showed significant declines with increasing north latitude (åPCB in Figure 12.2). The decreasing concentrations were most apparent for hexa-, hepta- and octachlorobiphenyls, which were close to detection limits in the northern fish but readily detected in fish of similar size and sex in northwestern Ontario lakes. However, more volatile organochlorine compounds such as a-HCH, toxaphene, and tri- and tetrachlorobiphenyls showed no decline. The results were consistent with the hypothesis that inputs of semi-volatile organochlorines decrease with increasing north latitude and distance from North American sources.

Figure 12.2. Lipid normalized relative total PCB concentrations in burbot liver from locations in western and northern Canada; maximum bar height is 1.9 µg/g (Muir et al., 1990)

12.3 METALS

Metals are always detected in biological samples, and the major difficulty is in delineating "normal" from "abnormal." Several approaches have been used:

1. Comparing tissue levels in animals of the same species from many different geographic areas, taking into account their age and other biological variables.
2. Comparing tissue levels in animals from a given study area with those in animals from a "pristine" area. Unfortunately, no such areas may remain.
3. Comparing tissue levels in animals from the study area with previously established no-observed-effect levels in controlled studies with other animals.
4. Comparing tissue levels (hard tissues) in the study area with those in prehistoric specimens of the same or similar species and assuming that the prehistoric levels, not having been subject to anthropogenic sources of contaminants, are "normal."

Comparing levels found in animals from different habitats is one of the most common designs in point-source pollution studies. Subtle variations in the concentrations of mercury, lead and cadmium, particularly the latter, in tissues of some arctic marine mammals have been reported, depending on the species and the location of capture. In the Canadian Arctic, some ringed seals (Phoca hispida) were reported to have high levels of mercury and lead (Smith and Armstrong, 1975; Wagemann, 1989). High cadmium levels were found in northern fur seals (Callorhinus ursinus) and narwhal (Monodon monoceros) (Goldblatt and Anthony, 1983; Wagemann et al., 1983). Wagemann et al. (1990) found relatively higher levels of cadmium in liver and kidneys of beluga (Delphinapterus leucas) from some arctic locations compared to others (Figure 12.3).

Figure 12.3. Relative Cd concentration (µg/g) in kidney of beluga whales from various locations in the Canadian Arctic and the St Lawrence estuary; the highest bar represents 106 µg/g.

To date, only belugas and polar bears (Ursus maritimus) have been systematically surveyed for heavy metals in tissues over a large geographic area of the Canadian Arctic (Norstrom et al., 1986; Wagemann et al., 1990). These surveys indicated some dependence of the cadmium, lead, and mercury concentrations in organs on geographic area. Cadmium in the kidney of belugas (both cortex and medulla homogenized) was higher in animals from the eastern Arctic than the western Arctic (Figure 12.3); lead in liver increased from northwest to southeast, as did mercury , with the exception of the group from the Mackenzie Delta, which had higher mercury levels than other arctic groups. Anomalously high mercury levels in animals from the Beaufort Sea have also been reported for other marine mammals (Smith and Armstrong, 1975). The trend of increasing cadmium from west to east in belugas was also reported for liver cadmium in polar bears (Norstrom et al., 1986).

Figure 12.4. Mean Hg vs. mean Cd in beluga liver of groups from different locations in the Canadian Arctic

A compounding factor when comparing metal levels is the influence of other metals and the interrelationships among them. For example, a highly significant inverse relationship between mercury and cadmium was found for belugas from the various arctic locations; the higher the cadmium concentration, the lower the mercury and vice versa (Figure 12.4). The biochemical basis of this relationship remains unexplained. Additional correlations among metals in marine mammal tissues have been reported repeatedly, and can be accepted as having general validity, such as that between mercury and selenium in liver and between zinc and cadmium in liver and kidney. The former correlation apparently arises largely because of the formation of mercuric selenide particles in the liver, and the latter because both metals are constituents of metallothionein, and can replace each other in that metalloprotein (Webb, 1979).

The heavy metals content of arctic seabirds has not been as well investigated as chlorinated hydrocarbon levels. Heavy metals have been determined in different bird species collected in the 1980s off the west coast of Spitsbergen (Norheim and Kjos-Hansen, 1984; Norheim, 1987; Norheim and Borch-Iohnsen, 1990); in gulls, fulmar, long-tailed duck (Clangula hyemalis) from the eastern coast of Kola peninsula in 1989 (Savinova, 1992); in black guillemot, kittiwake, eider (Somaterla mollissima), glaucous gull, fulmar, and Brunnich's guillemot (Uria aalge) from Greenland (Nielsen and Dietz, 1989).

The concentrations of trace elements in Arctic seabirds examined in these studies are in a good agreement with values reported in the literature for Atlantic Canadian seabirds (Elliott et al. 1992), and generally represent normal physiological levels. By contrast, the content of Cu in liver of eider duck from Spitsbergen was about 40 times higher than in other species (Norheim and Kjos-Hansen, 1984; Norheim, 1987). The high level of Cu in either may reflect the fact that this species feeds mainly on mussels, snails, and crustaceans, which have haemocyanin as their blood pigment.

12.4 BIOCONCENTRATION AND BIOACCUMULATION

Given the emphasis on arctic animals as vectors of contaminants to people consuming them, the processes that brought the contaminants to the animals themselves are of interest. The accumulation of organic contaminants has been described using several types of models (Landrum et al., 1992; Thomann et al., 1992), and these work well for fish and other aquatic organisms if the required model input data are available. For arctic animals generally, and especially for the marine mammals, some parameters to model are not known, and so they have to be extrapolated from temperate species.

12.5 CONTAMINANT HISTORIES REPRESENTED IN LAKE SEDIMENTS

Sediments have been recognized increasingly as long-term sinks for several contaminants, especially in harbours and areas receiving industrial wastes (Smith and Levy, 1990; MacDonald et al., 1992). Campbell et al. (1985) examined field samples of the yellow water lily Nuphar variegatum, and used correlations with sediment and water levels of metals to show that much of the copper in the plants was derived from the sediment, while the zinc was derived from the water column. Sediments accumulate over time, and analysis of sediment layers allows calculation of rates of change and hence predictions of future concentrations. Dated layers of lake sediments have been analyzed for trace metals (Johnson, 1987), polycyclic aromatic hydrocarbons (Gschwend and Hites, 1981), and organochlorine compounds (Eisenreich et al., 1989). These studies have allowed reconstruction of the histories of contaminant inputs to several areas. With some precautions, past and current fluxes can be extrapolated to predict future trends. This approach is particularly relevant to arctic cases where inputs are derived largely from atmospheric deposition. 

Some sediment cores are mixed by natural or coring processes, and are not suitable for chronological contaminant analyses; processes of mixing and diffusion in sediments are not understood fully. Virtually all sediments are mixed to some extent, even annually laminated sediments, either by resuspension, in situ particle mixing, or diffusion. A general indication of the in situ integrity of the sediment column sample (core) is the appearance of simple profiles of percent water, loss on ignition (organic matter), and some conservative parameters of inorganic, non-biological, non-contaminant elements, such as Fe, Al, Si, or Ti. The depth integral of Pb²¹⁰ and CS¹³⁷ can be used as an indication of the degree of success at recovering the sediment-water interface, if annual fluxes or depositional history of these nuclides is generally known (Crusius and Anderson, 1991; Anderson et al., 1987). Interpretation of the chronology of the sediment core from Pb²¹⁰ and other radiochemical tracers of sediment accumulation, sediment mixing, and diffusion can be done using models (Robbins, 1986). This approach requires some knowledge of the annual fluxes of Pb²¹⁰ and other sedimentation tracers for the sampled region that can be obtained from soil or glacier unit area samples.

Cores are usually taken from the maximum depth of the lake, where fine, organic sediments are deposited after cycles of deposition and resuspension in shallower, more turbulent water. Lakes focus these sediments into smaller, deeper locations, and bathymetric information is required to find these locations and to judge the importance of the focusing. The annual flux and cumulative burden of contaminants in such deep water sediments need to be corrected for focusing. As an estimate of the focusing factor, the ratio of excess Pb²¹⁰ integral has been used by calculating excess Pb²¹⁰ flux from the profundal lake sediment cores, and comparing it to the excess Pb²¹⁰ integral from several soil profiles (hopefully not focused) in the lake drainage basin.

An example of the application of these techniques is given in Figure 12.5 (in units of concentration) for a core taken in 1988 from Far Lake, Northwest Territories, a site with no local pollution sources within the drainage (63°38'N, 90º40'W). Mean ages for these slices have been assigned from simple models of Pb²¹⁰ accumulation, and are considered reliable down to slice 11; values below those dates were estimated by extrapolation from the upper slices. The profile of mercury concentrations in the slices indicates an accelerating increase in mercury supply rate to the sediments over the time covered. During the current century , the concentration has approximately doubled, in keeping with changes indicated in air concentrations of mercury in the northern hemisphere (Slemr and Langer, 1992). Taking the sedimentation rate as indicated by the mass of sediment accumulated per unit area and time (77 g per m² per yr), the background and contaminant flux of mercury (Hg) to the site can be calculated (background flux = 77 g per m² per yr x 40 ng Hg per g= 3080 ng per m² per yr; contaminant Hg flux = 77 g per m² per yr x [100 -40] ng Hg per g = 4620 ng Hg per m² per yr). Over the 80 years of excess Hg inputs to the lake, approximately 360 micrograms of Hg have been deposited per m² (the integral contaminant burden), and are potentially available to lake biota from the top 20 cm of the lake sediments. Johnson (1987) made flux calculations for several lakes in Ontario, and found that the flux often correlated with Hg levels in fish from the same lakes.    

Figure 12.5. Hg concentrations in dated slices of sediment from Far Lake, Northwest Territories, Canada; dates are calculated using Pb²¹⁰ for the top eleven slices, and extrapolated for deeper slices

12.6 BIOLOGICAL RESPONSES

Relatively little pollution response work has been done in the Arctic or with arctic species. The question for biologists is whether the increasingly well-documented inputs of contaminants are significant biologically. The response to chemicals by animals has sometimes been determined by measurements on populations rather than on individuals. Case histories like the disappearance of several species of fish from acidified lakes (Beamish et al., 1975) or the loss of fish from an area receiving pulp mill effluent (Kelso, 1977) provide convincing examples of effects observed directly on the abundance and distribution of animals. Two problems exist with the use of population characteristics to indicate effects of chemicals. One is that the population must already have been affected before changes in its structure can be established. The second is that to establish causal relationships using population surveys by themselves is extraordinarily difficult. Nonetheless, the population, not the individual, must be maintained, and population responses must be used as the standard against which the usefulness of other approaches must ultimately be judged. Individual responses can help to test the hypothesis that the effect is, or is not, due to the suspected cause.

A useful tool to test for some causal relationships is the tissue level of the hypothesized causative agent. If dose-response relationships have been established linking biological responses with tissue levels, then the tissue levels themselves can be used as surrogates for biological responses that may be more difficult to measure. This analysis requires some knowledge of how these may change with other biological variables like species, age, gender, reproductive history, and the type of tissue. For all avian species tested, PCB residues of 310 mg per kg fresh weight or higher in brain were associated with an increased likelihood of death from PCB poisoning (Stickel et al., 1984). Applying this line of argument to exposed populations, PCBs were judged the probable cause of death of glaucous gull from Bear Island in 1972 (Bourne, 1976), and puffin mortality of Lofoten Islands in the 1970s (Walker, 1990). At this time, relatively high levels of PCBs and other organochlorine residues were being reported in sea birds, and toxic effects may have occurred following the rapid mobilization of such compounds from the storage fat of the birds (Walker, 1990).

Several studies have been concerned with the effects of chlorinated hydrocarbons on reproduction in seabirds, and two major types of effects have been considered: eggshell thinning and direct toxicity to the embryos. Cases of eggshell thinning associated with DDE and PCB residues have been reported for gannets (Sula bassana) in Canada (Parslow et al., 1973) and Norway (Nygard, 1983). Eggshell thickness of the peregrine falcon (Falco peregrinus) from Norway declined 85 percent between 1854 and 1976; addled eggs containing dead embryos collected in 1976 had 724 ppm of PCBs in lipids and up to 110 ppm on a fresh weight basis (Nygard, 1983). In the Canadian study on the gannet, DDE-induced eggshell thinning was suspected of being responsible for reduced reproductive success and consequent population decline in the 1960s. These effects were associated with DDE levels of 20-30 ppm in the eggs (Parslow et al., 1973). For most avian species, a reduction in eggshell thickness of 15-20 percent is suggested as a critical value beyond which population numbers are expected to decline (Nygard, 1983).

Embryotoxicity of organochlorines in different species of birds is discussed by Cooke (1973) and Peakall and Fox (1987). Elliott et al. (1988) reported higher levels of several organochlorines in gannet eggs that failed to hatch compared to levels in fresh eggs.

Several field and laboratory  studies have shown that organochlorine compounds are associated with biological effects on marine mammals, freshwater and marine fish, as well as in fish-eating birds in temperate climates (Gilbertson, 1989). These effects, which are mainly associated with coplanar PCBs and chlorinated dioxins and furans, include elevated hepatic cytochrome P₄₅₀-associated enzyme activities, histopathological abnormalities, altered steroid hormone levels in individual animals, and reproductive failure in populations. Therefore, concern may be understandable that the presence of PCBs and other organochlorine contaminants in arctic biota could adversely affect the populations, particularly marine mammals and birds which accumulate the highest concentrations. The effects of toxaphene and chlordane-related compounds, that are generally present at similar levels to total PCBs in arctic animals (unlike fish and birds in the Great Lakes or marine mammals in the Baltic Sea), are unknown. Toxaphene has been shown to affect the mechanical strength and biochemistry of bone in fish, (Mayer and Mehrle, 1977) and to produce cancer in rats and mice (National Institutes of Health, 1979).

As consumers of arctic biota, humans are also a focus of concern for possible toxicity from exposure to organochlorine substances. Levels of PCBs, coplanar PCBs, chlordane, and toxaphene components have been found to be elevated in human milk from northern Quebec, as compared with levels in southern Quebec residents (Dewailly et al., 1989). Dewailly et al. (1992) reported a negative and statistically significant correlation between size of newborn male children and organochlorine exposure (estimated using mother's milk) in northern Quebec. These results are parallel to findings that infants of Michigan women, whose calculated PCB consumption from fish exceeded 1 µg per kg per day, had reduced birth weight, smaller head circumference, and compromised neuromuscular development (Hwang et al., 1984; Gladen et al., 1985).

12.7 LABORATORY TOXICOLOGY

Laboratory studies can provide some of the clearest answers on whether contaminants at levels found in arctic biota are biologically significant. Unfortunately the larger animals important to arctic people are not well suited to laboratory studies, because of the logistics of maintaining them in captivity. Seals and small cetaceans have been studied occasionally (Engelhardt et al., 1977; Geraci et al., 1983; Reijnders, 1986); however, only very few such experiments are likely ever to be conducted in view of the high value placed on individual marine mammals. Arctic fish can be studied more frequently and at reasonable cost. Craddock ( 1977) and Lockhart et al. ( 1992b ) have reviewed some of the laboratory toxicity tests with arctic fish and invertebrates. Where comparisons are possible, arctic species appear quite similar to temperate species. Given the growing body of data describing concentrations of various contaminants in arctic animals, these data cannot be interpreted clearly in terms of toxic responses (McCarty, 1991).

12.7.1 ACUTE TOXICITY TESTING

Many acute toxicity bioassay systems have been developed for different purposes. However, with the exception of petroleum hydrocarbons (Craddock, 1977), little acute toxicology has been reported for arctic species. The acute toxicity of two petroleum oils to several Alaskan species was comparable to that of temperate species (Rice et al., 1979). For relevance to arctic winter conditions, the testing of petroleum oils under normal bioassay conditions offers a useful illustration. Volatile components of several oils were lost rapidly under normal bioassay conditions employing a continuous stream of air bubbles to maintain oxygen levels, giving the impression that the oils were non-toxic (Lockhart et al., 1987). However, such losses would not occur readily in the Arctic during winter; so the bioassays were repeated under conditions that minimized the loss of volatile components, at which time the oils were clearly toxic. Given the nature of the contamination problem in the Arctic, many acute toxicity data have limited application. Since the residues are present ubiquitously, the exposures must be essentially continuous. Indeed, examination of PCB residues as a function of age in beluga whales has shown that residues are present throughout the entire life cycle. Kenaga (1982) has shown that chronic effects are mostly within a factor of twenty-five of acute effects, but with some unpredictable exceptions. In examples of chronic studies with cutthroat trout (Salmo clarki), Woodward et al. (1981, 1983) have shown that petroleum oils have chronic, sublethal effects not evident in short-term (96-hour) conventional bioassays.

Aquatic sediments serve as sinks for many contaminants, prompting the need for methods to assess the importance of sediment-associated materials. Several bioassay systems have also been developed to examine the toxicity of contaminants associated with sediments (Long et al., 1990); Krantzberg and Boyd, 1992; Tay et al., 1992). Similarly, Payne et al. (1988) and Truscott et al. (1992) have reported subtle effects in flounders (Pseudopleuronectes americanus) maintained for long periods in contact with sediments contaminated with petroleum.

12.7.2 BEHAVIOUR

Chemicals in the water have often been hypothesized to alter some aspect of the behaviour of fish (Sprague et al. , 1964 ), and a variety of laboratory tests have been developed to measure these effects. Scherer (1992) has reviewed these tests, and grouped them into three general types: unconditioned reflexes, locomotor behaviour, and intra- and interspecific responses. McNicol and Scherer (1991) used a preference-avoidance design to test the locomotor responses of lake whitefish (Coregonus clupeaformis) to cadmium dissolved in the water. Curiously, the fish responded to levels lower than 1 µg per litre and to levels greater than 8 µg per litre, but showed little response to levels in between. Furthermore, at a given concentration, some individuals avoided the cadmium solution and others preferred it. No explanation is apparent for this dichotomous response.

Figure 12.6. Mean taste panel scores for arctic char treated with varying amounts of Norman Wells crude oil following uptake (upper panel) and clearance (lower panel) (Lockhart and Danell, 1992)

Some behaviour testing has also been done with arctic invertebrates. Percy and Mullin ( 1977) reported the effects of 24-hour exposures to several crude oils on the locomotor activity of the amphipod Onisimus affinis and the coelenterate Halitholus cirrattus. The activity of O. affinis was reduced by as much as 98 percent by the highest dosages, and was quite consistent among the three crude oils tested.

Norman Wells and Pembina crude oils inhibited the activity of H. cirrattus, but the other two oils had little effect. Cross and Thomson (1987) noted the rapid emergence of several benthic infaunal species following exposure to chemically dispersed oil, and their apparent recovery and return to the sediment shortly  thereafter.

12.7.3 SENSORY EVALUATION

With fishery products destined for human consumption, the products must be acceptable in the market-place. For example, Krishnaswami and Kupchanko (1969) reported tainting of fish by effluent from an oil refinery. Recently tainting by several types of wastewater from a plant producing synthetic crude oil from oil sands has been detected. Exposure to petroleum products has often been associated with the production of oily tastes and odours in fish (Motohiro, 1983). Similarly, fish undergoing exposure to effluent from bleached kraft pulp mills have developed undesirable tastes and odours (Whittle and Flood, 1977). These effects are detected best by sensory evaluation panels trained to detect the presence and severity of off- flavours (York and Sereda, in press). Several different protocols for such tests have been used (Poels et al., 1988); they all provide valid evaluations.

Petroleum tainting tests with arctic charr (Salvelinus alpinus) exposed experimentally to extracts of Norman Wells crude oil were described by Lockhart and Danell (1992). Oil and water were mixed in a mixing tank from which an outflow at the bottom drew off the water phase to be used (after appropriate dilution exposure). Charr were taken for sensory testing at intervals during the 72- hour oil uptake phase of the experiments, and the remaining fish were transferred to clean flowing water for a clearance phase lasting several weeks. Initial results of taste panel evaluations are shown in Figure 12.6, and dose-dependent tainting was produced; the low exposure threshold to produce tainting was below the lowest mixing ratio of 3 ppm. Furthermore, the tainting effect was not entirely lost by the end of the clearance phase at 600 hours. This observation clearly has practical implications for the time a fishery might remain unusable after an oil spill.

12.8 FIELD STUDIES

Some populations of fish and marine mammals are monitored by resource management agencies, but population effects become evident only after the fact. Nonetheless, adverse changes at the population level are the primary concern. Field experiments in which a known contaminant is introduced into an experimental site can give the best description of effects at ecological levels, but relatively few such experiments have been done, especially where the species of interest are large in size.

12.8.1 ECOSYSTEM EXPERIMENTS

At the Experimental Lakes Area in northwestern Ontario, several whole lake experiments have been done to evaluate ecosystem scale effects (Schindler, 1988). Lake trout responded to acidification with decreased growth rates and decreased condition factors, and, finally, with failure of recruitment of young into the population. Similarly, experimental treatments of northern streams with petroleum oils have been carried out in order to observe effects on downstream flora and fauna (Miller et al., 1986). Perhaps the most complex field experiment within the tundra biome has been the Baffin Island oil spill (Sergy and Blackall, 1987), in which crude oil was intentionally introduced into a small bay near Pond Inlet, Northwest Territories, in an experiment to describe its chemical fate and biological effects, and to explore possible countermeasure options. While whole ecosystem experiments such as those mentioned above are definitive, they are increasingly difficult to do for two reasons: (1) increasingly stringent environmental protection legislation and (2) the long time over which support funding is required.

12.8.2 ENCLOSURE/MESOCOSM EXPERIMENTS

Partial ecosystems have been built to enclose small portions of freshwater or marine ecosystems, and then experimental manipulations have been performed within the enclosed portions (Schindler, 1988). These enclosures ranged in size from a few litres to partitioned embayments of lakes. They have most frequently been used for experiments with planktonic or benthic species; however, they have sometimes been used with fish. Snow and Scott (1975) described the weathering of petroleum oil spilled experimentally into enclosed areas of two lakes in the Mackenzie River Delta. They noted that adult insects were killed and that periphyton growth increased, probably as a result of oil stimulation of nitrogen-fixing organisms. Shindler et al. (1975) also reported increases in nitrogen-fixing bacteria following treatments of ponds with crude oil. Fish have been used less frequently in enclosure experiments, but Ramsey (1990) used a limnocorral system to show that mercury was taken up more rapidly by fish when a rich source of organic carbon was present than in control enclosures lacking supplemental carbon. These experiments are attractive for experiments designed to describe movements of some contaminants and responses of small organisms; however, they are impractical for most large, powerful animals of interest in the Arctic.

12.8.3 POPULATION EXPERIMENTS

Another approach is to manipulate the population of interest without manipulating the habitat. Lockhart et al. (1972) used this approach to estimate the natural rate of loss of mercury from a population of northern pike Esox lucius. Fish from a highly contaminated lake were tagged and transplanted to a relatively clean lake, and then recaptured at intervals to determine the rate of decline of mercury in tissues. A serious limitation of this design was the possibility of introducing parasites or diseases along with the transplanted fish, as in fact happened in this experiment; consequently, such experiments are unlikely to be done often. An extension of population manipulation approach is a partial ecosystem experiment underway at the Experimental Lakes Area. It represents an attempt to evaluate the importance of three organic contaminants, toxaphene, chlordane and 2,3,4,7,8- pentachlorodibenzofuran to fish populations without contaminating the entire lake. Lake trout and white suckers from a lake at the Experimental Lakes Area were marked and injected intraperitoneally with one of these compounds and released back to the lake. Subsequently, these fish have been recaptured on several occasions and at spawning time for use in experimental breeding crosses. In this way, information is being obtained on survival, growth, and reproduction of the treated fish as compared with untreated and sham-treated fish from the same lake. Although these experiments do not mimic "natural" exposure, they can provide information about the effect of known body burdens of these specific contaminants on the ecological performance of the fish without the experimental contamination of the whole lake.

12.8.4 EXAMINATION OF ANIMALS FROM NATURAL POPULATIONS

Perhaps the most widely applied approach has been the examination of individual animals subject to some known exposure in their natural habitat to search for indicators of exposure and pathologies (Uthe et al., 1980; Dixon et al., 1985). This approach, often called the "bioindicators" or "biomarkers" approach, has the advantage of describing real exposures and responses, and so avoids the uncertainties inherent in extrapolating results from a laboratory setting to real populations. It has the disadvantage of limited specificity in that multiple variables influence the animals, and so the result observed cannot be proven rigorously to be the result of the hypothesized "cause." In spite of this limitation, the biomarker approach is probably the closest an investigator can come to testing causal hypotheses in natural populations; the approach has been applied to a wide range of contamination issues including acidification (Lockhart and Lutz, 1977; Brown et al., 1990), metal pollution (Munkittrick and Dixon, 1988; Klaverkamp et al., 1991), organochlorine pollution (Helle et al., 1976; Stegeman et al., 1986; Subramanian et al., 1987), hydrocarbon pollution (Dunn, 1980; Johnson et al., 1988; Lockhart et al., 1989), and radionuclide pollution (Swanson, 1982; Waite et al., 1988, 1989).

The bioindicator approach has been applied many times in the Sub-Arctic, and studies are starting with field populations in the Arctic and in laboratory experiments with arctic species. Several correlations have been described linking biomarker responses with other toxic responses (Safe, 1990), but whether the two are linked by necessity or by coincidence is seldom clear. Nonetheless, these sub-lethal responses are sensitive and relatively inexpensive to measure; they can help to identify the need for more expensive ecological and chemical studies. The most obvious bioindicator is one that is visible. Physical deformities in fish have been associated with polluted habitats (Beamish et al., 1975; Munkittrick et al., 1992), in marine mammals (Zakharov and Yablokov, 1990), and in invertebrates (Warwick, 1985). Several populations of fish have been reported to have unusually high incidences of tumours, presumably as a result of exposure to chemicals in their habitat (Sonstegard and Leatherland, 1976; Baumann, 1984). However, the presence of tumours does not necessarily imply a chemical etiology; Yamamoto et al. (1985) have described skin tumours of walleye (Stizostedion vitreum) with a viral etiology. The most convincing approach has been the experimental demonstration that tumours are induced by treatment with the suspected causative agents. For example, polluted sediments extracted from bullheads were shown to induce cancer. Metcalfe et al. (1988) extracted sediment from Hamilton harbour (Lake Ontario, Canada), and injected it into rainbow trout sac fry; a year later, the fish were sacrificed and examined visually and microscopically for liver cancers. The extracts from Hamilton harbour induced cancer in 3-9 percent of the fish, while extracts from a clean site induced none. These active extracts were prepared from sediments containing high levels of polycyclic aromatic hydrocarbons (P AH), and so these probably contributed to the biological activity of the extracts; however, they may not have been the exclusive source of carcinogenic activity.

A most widely applied bioindicator has been the cytochrome P₄₅₀ system; it has been used to indicate exposure to several ubiquitous contaminants (Stegeman and Kloepper-Sams, 1987). Laboratory experiments have shown that the system responds to PAH (James and Bend, 1980), and to some chlorinated compounds including some PCBs (Forlin and Lidman, 1981; Gooch et al., 1989) and chlorinated dioxins and furans (Hahn et al., 1989; van der Weiden et al., 1990). All of these contaminants have been detected in northern fish. Cytochrome P₄₅₀ activities have been used to detect subtle responses to oil spills (Payne, 1976), and petroleum hydrocarbons are found widely in parts of the Arctic, most notably the Mackenzie River drainage (Carey et al., 1990). Several recent studies have shown that the system responds to effluent of bleached kraft pulp mills in Scandinavia (Andersson et al., 1988) and Canada (Rogers et al., 1989; McMaster et al., 1991; Hodson et al., 1992), although the identities of all the inducers present are still unclear. Chlorinated dioxins and furans are present in these effluents, but it seems unlikely that they are the only inducers. The induction of enzymes has also been reported in several species of birds (Ronis and Walker, 1989).

Other sublethal effects (including behavioural disturbances and immunotoxicity) on seabirds may be caused by chlorinated hydrocarbons, but sound evidence for them is still lacking (Walker, 1990). Mutagenic, carcinogenic, and teratogenic effects of PCBs are not documented for arctic seabirds.

Similar in concept to the cytochrome P₄₅₀ system is the metallothionein response to metals (Klaverkamp et al., 1984). Fish exposed to several metals increase the production of this protein, and the increased levels can serve as a bioindicator of previous exposure. However, metals are not the only vectors that can cause increased synthesis of this protein. Fish from a series of lakes with differing levels of metal contamination were analyzed and found to have a very high correlation between the metallothionein content and zinc in the water. For biomarkers generally in field settings, the preferred design has been the comparison of samples from populations exposed to higher exposures of the contaminants of interest with samples from otherwise comparable populations exposed to lower quantities. Often species, sexual, and seasonal differences in biomarkers are seen, but these are relatively simple to eliminate as sources of treatment effects through well-designed sampling programmes.

A promising approach is the examination of the same individual animals both for chemical residues and for evidence of biological responses. For example, Giesy et al. (1986) examined statistical associations between organochlorine residues and rearing mortality in chinook salmon from Lake Michigan. Galgani et al. (1991) reported a correlation between ethoxyresorufin-O-deethylase (EROD) activities and total PCBs (r=0.620) in postmitochondrial supernatants of plaice (Pleuronectes platessa) from the Bay of Seine, France. Within the Arctic, two microsomal mono-oxygenase activities, EROD and aryl hydrocarbon hydroxylase (AHH), were measured in burbot liver microsomes, and the results failed to show a geographic trend similar to that shown by PCB residues (Lockhart and Metner, 1992). However, further residue analysis for mono-ortho substituted congeners indicated that enzymatic activities were actually correlated with some of these residues, notably with congener 156 (Lockhart et al., in press). The apparent relationship between mono-ortho PCBs and EROD seems likely to reflect the presence of non-ortho PCBs, especially PCB 126 (3,3',4,4',5-pentachlorobiphenyl), a potent inducer in fish (Janz and Metcalfe 1991) that was not determined in burbot liver. Much more striking correlations were found between cytochrome P₄₅₀ catalytic activities and several non-ortho and mono-ortho PCB congeners in a group of beluga whales that became trapped in freshwater lakes in the Mackenzie Delta (Lockhart et al., 1972, 1992b ). These whales were, on average, about 200 kg lighter in weight than other arctic belugas of the same age. The working hypothesis is that these animals had mobilized blubber during the starvation, thereby releasing contaminants stored in the blubber.

A surprising result with biomarkers in beluga whales has been the observation that aromatic DNA adducts were no different in arctic whales than in whales from the Gulf of St. Lawrence where pollution levels are generally several times higher (Ray et al., 1991).

Many other biomarkers have been used to detect biological changes due to chemical inputs. For example, brain cholinesterase activities in young walleye (Stizostedion vitreum) were sensitive to aerial spraying with the organophosphorous pesticide, malathion (Lockhart et al., 1985). Circulating levels of several steroid hormones are influenced by exposure to effluent from some pulp mills (McMaster et al., 1991; Munkittrick et al., 1991; Hodson et al., 1992). Energy stores have been depleted in white suckers from lakes where food supplies have been reduced by metal pollution (Munkittrick and Dixon, 1988). Lockhart et al. (1989) reported reduced lipid stores in burbot from the Mackenzie River where they were rejected for human consumption due to the appearance of their livers. Neff et al. (1987) determined energy stores (glycogen, other carbohydrates, lipids) in clams (Mya truncata) subjected to experimental oil spills on Baffin Island, but found that the oil had little apparent effect. The authors noted that the biochemical values were highly variable, possibly the result of sampling techniques, and so large differences were required in order to isolate them from normal variation.

In summary , chemical contaminants are ubiquitous throughout the Arctic, mainly as a result of aerial transport from lower latitudes and deposition in the Arctic. Chemical analyses have revealed the circumpolar dispersal of organochlorines and several toxic metals in animals at the top of aquatic food chains. These tissue analyses provide the best measures of intakes by people who hunt and consume the animals, and they also provide the best measures of dosages experienced by the animals. Cores of lake sediments have shown that inputs of several pollutants (mercury, polycyclic aromatic hydrocarbons) have been continuous for decades, but that levels are often relatively low compared with those at sites at lower latitudes.

The existing data on contamination levels in arctic biota generally serve as a good base for future toxicological investigations in this region. The sensitivity of arctic animals to these loadings is largely unknown. With the exception of petroleum, very little experimental toxicology has been done with arctic species, but the limited data suggest that individual sensitivities are comparable to species from further south. The application of "bioindicators" is just starting, but already some correlations with levels of some PCB congeners have been detected in fish and whales. Many unknown aspects remain concerning the effects of contaminants on Arctic seabirds; clearly studies of biological effects are needed.

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