Correlates of mercury in fish from lakes near Clyde Forks, Ontario, Canada.

Subsurface soils near Clyde Forks, Ontario, Canada, can have naturally high concentrations of mercury (Hg) from local geological sources. To investigate Hg in local aquatic food webs, Hg was measured in fish dorsal muscle (mainly yellow perch [YP] and pumpkinseed sunfish [PS]) and surface sediments from 10 regional lakes. Water chemistry, along with fork length, weight, and stable isotopes (delta15N, delta13C, delta34S) in fish were also measured. No lake sediments had elevated (>0.3microg/g dw) Hg, and average Hg concentrations in fish were not sufficiently high (<1microg/g dw) to be of concern for fish-eating wildlife. Variance in fish Hg was best explained by dietary carbon source (delta13C), and certain lake variables (e.g., pH for YP). PS with more pelagic feeding habits had higher delta34S and Hg than those with more littoral feeding habits. Potential biological linkages between fish Hg and delta34S, a parameter that may be related to the lake sulphate-reducing bacteria activity, requires further investigation.

Comparison of lead residues among avian bones.

To determine if significant differences exist in lead (Pb) accumulation in different bones, especially those most often used for bone-Pb studies in wildlife, we compared Pb concentrations in radius, ulna, humerus, femur, and tibia of Common Eider (Somateria mollissima); and radius/ulna (combined), femur, and tibia of American Woodcock (Scolopax minor). There were no significant differences in bone-Pb concentrations among woodcock bones over a wide range of Pb concentrations (3-311 microg/g). In eider, where bone-Pb concentrations were low (<10 microg/g), leg bones had significantly higher Pb concentrations (approximately 30-40%) than wing bones from the same individuals. The variation among individual birds was greater than the variation among different bones within a bird. Based on our findings, we conclude that one type of bone may be substituted for another in bone-Pb studies although the same bone type should be analyzed for all birds within a study, whenever possible.

Cholinesterase and monoamine oxidase activity in relation to mercury levels in the cerebral cortex of wild river otters.

Mercury (Hg) is a global pollutant that is neurotoxic to many mammalian species. The present study was conducted to determine if the bioaccumulation of Hg by wild river otters (Lontra canadensis) could be related to variations in the activities of key neurochemical enzymes. River otters were collected from Ontario and Nova Scotia (Canada) during the trapping seasons, spanning 2002-2004, and their brains were dissected into the cerebral cortex and cerebellum. The activities of cholinesterase (ChE) and monoamine oxidase (MAO) were measured from each sample and correlated with concentrations of brain Hg from the same animal. Significant negative correlations were found between concentrations of brain Hg and ChE (total Hg: r= -0.42; MeHg: r= -0.33) and MAO (total Hg: r= -0.31; MeHg: r= -0.42) activity in the cerebral cortex. The scatterplots relating concentrations of brain Hg and enzyme activity in the cerebral cortex were wedge-shaped, and could be fitted with quantile regression modeling, suggesting that Hg may act as a limiting factor for ChE and MAO activity. No relationships were found in the cerebellum. These data suggest that environmentally relevant concentrations of Hg may influence the activities of ChE and MAO in the cerebral cortex of river otters, and by extension, other fish-eating mammals.

Major correlates of mercury in small fish and common loons (Gavia immer) across four large study areas in Canada.

We investigated mercury (Hg) concentrations in small fish (mainly yellow perch, Perca flavescens; ∼60% of fish collected) and in blood of common loons (Gavia immer) that prey upon them during the breeding season on lakes in 4 large, widely separated study areas in Canada (>13 lakes per study area; total number of lakes = 93). Although surface sediments from lakes near a base metal smelter in Flin Flon, Manitoba had the highest Hg concentrations, perch and other small fish and blood of common loon chicks sampled from these same lakes had low Hg concentrations similar to those from uncontaminated reference lakes. Multiple regression modeling with AIC analysis indicated that lake pH was by far the most important single factor influencing perch Hg concentrations in lakes across the four study areas (R(2) = 0.29). The best model was a three-variable model (pH + alkalinity + sediment Se; Wi = 0.61, R(2) = 0.85). A single-variable model (fish Hg) best explained among-lake variability in loon chick blood Hg (Wi = 0.17; R(2) = 0.53). From a toxicological risk perspective, all lakes posing a potential Hg health risk for perch and possibly other small pelagic fish species (where mean fish muscle Hg concentrations exceeded 2.4 µg/g dry wt.), and for breeding common loons (where mean fish muscle Hg concentrations exceeded 0.8 µg/g dry wt., and loon chick blood Hg exceeded 1.4 µg/g dry wt.) had pH < 6.7 and were located in eastern Canada.

Binding of manganese in human and rat plasma.

Albumin, transferrin and 'transmanganin' have all been proposed as the major Mn-binding ligand in plasma. The present investigations were initiated in order to resolve these discrepancies. Compared to other metals tested (109 Cd2+, 65Zn2+, 59Fe3+), 54Mn2+ bound poorly to purified albumin. The addition of exogenous albumin to plasma did not result in an increased 54Mn radioactivity associated with this protein. Also, incubation of 65Zn-albumin in the presence of excess Mn2+ (1 mM) did not result in the displacement of Zn from albumin or Mn binding. In contrast to these results, 54Mn was bound to purified transferrin, not as readily as Fe3+, but better than Zn2+ or Cd2+. Saturation of transferrin with Fe3+ (1.6 micrograms Fe/mg) prevented the binding of 54Mn indicating that Mn probably binds to Fe-binding sites on the protein. Polyacrylamide gel electrophoresis further demonstrated the association of 54Mn with transferrin rather than with albumin in both human and rat plasma. The amount of 54Mn radioactivity recovered with transferrin increased as incubation time was increased, probably due to oxidation of Mn2+ to Mn3+. Mn binding to transferrin reached a maximum within 5 and 12 h of incubation. About 50% of 54Mn migrated with transferrin, whereas only 5% was associated with albumin. A significant portion (20-55%) of the 54Mn radioactivity migrated with electrophoretically slow plasma components whose identity was not determined. Possibilities include alpha 2-macroglobulin, heavy gamma-globulins and/or heavy lipoproteins.

Effects of heavy metal cations, sulfhydryl reagents and other chemical agents on striatal D2 dopamine receptors.

To investigate aspects of the biochemical nature of the membrane-bound D2 dopamine receptor, rat striatal homogenates were pretreated with heavy metal cations and a variety of other chemical agents, and their effects on D2 receptor density were subsequently determined using a standard [3H]spiperone binding assay. Preincubation of striatal membranes in the presence of 3 mM Mn2+, Fe2+, Co2+, EDTA, or ascorbate enhanced subsequently measured stereospecific binding of [3H]spiperone compared to control (e.g. control: Bmax = 140 fmoles/mg protein, KD = 0.21 nM; Mn2+-treated: Bmax = 253 fmoles/mg protein, KD = 0.20 nM). Another group of metal cations, that is Zn2+, Cd2+, Cu2+, Hg2+ and CH3Hg+, all of which have significant -SH reactivity, as well as the -SH alkylating agent N-ethylmaleimide (NEM), caused a decrease in specific binding sites. Pretreatment with 3 mM Cd2+ or Cu2+ resulted in a 40-60% reduction in the subsequently measured stereospecific binding of [3H]spiperone, whereas 1 mM Hg2+ or 3 mM NEM completely abolished specific [3H]spiperone binding. The effect of Hg2+ could not be reversed by washing the membranes, nor by further incubation of the membranes in the presence of excess EDTA or 2,3-dimercapto-1-propanesulfonic acid (DMPS). Further incubation in the presence of 3 mM dithioerythritol (DTE) resulted in the regeneration of about 40% of lost sites. Agents which enhanced receptor density, such as Mn2+ or EDTA, could not antagonize the effect of Hg2+, nor could the mercury-chelating agent DMPS, when added to crude homogenates prior to Hg2+. Ascorbate protected 25-35% of specific binding sites by virtue of its ability to reduce Hg2+ to insoluble Hg+. Only 3 mM DTE afforded complete protection against 1 mM Hg2+. Prior formation of the spiperone/receptor complex also demonstrated considerable ability to protect receptors from destruction by Hg2+. Preincubation of striatal membranes in the presence of 0.5 mM spiperone protected about 80% of sites from the subsequent addition of 1 mM Hg2+. A major conclusion of these studies is that one or more free -SH groups on or adjacent to the active site may be a requirement for specific antagonist binding to the membrane-bound D2 receptor. Occlusion of these -SH groups by sulfhydryl reagents results in partial to complete abolition of subsequently measured specific 3H-antagonist binding. Only agents which can regenerate free -SH groups, such as DTE, are able to induce any recovery in specific binding sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Erythrocyte delta-aminolevulinic acid dehydratase in birds. I. The effects of lead and other metals in vitro.

The effects of buffering ions, pH, temperature, and various metal cations on the activity of avian red blood cell aminolevulinic acid dehydratase (RBC-ALA-d) in blood hemolysates was studied. The pH optimum of the enzyme was approximately 6.6 in both citrate and morpholinethanesulfonic acid (MES) buffers, and maximal activity was comparable in both buffer systems. Enzyme activity was increased by about 20% at 42 degrees C (avian body temp.) relative to that at 37 degrees C. Pb2+ was 10-100-fold more potent than Cu2+, Cd2+, Hg2+ or CH3Hg+ as an inhibitor of RBC-ALA-d activity. The IC50 for Pb2+ was 0.03-0.04 mumol/ml blood. Zn2+ added to Pb-pretreated hemolysates was able to induce up to 65% recovery of enzyme activity. Pb2+ was a more effective inhibitor of delta-aminolevulinic acid dehydratase (ALA-d) activity in MES buffer than in citrate buffer, possibly because of chelation of Pb2+ by citrate.

Erythrocyte delta-aminolevulinic acid dehydratase in birds. II. The effects of lead exposure in vivo.

The effects of in vivo exposure to Pb2+ on avian aminolevulinic acid dehydratase (ALA-d) activity were studied, and the activity ratio (activated/non-activated enzyme activity) was assessed as a potential indicator of Pb exposure in birds. A significant negative correlation was observed between blood-Pb concentration and log ALA-d activity (r = -0.827) in Pb-dosed birds. An even better correlation was obtained when data were expressed as an activity ratio (r = 0.961), demonstrating that sample variability is decreased by expressing the results as an activity ratio rather than as enzyme activity. Red blood cell (RBC) ALA-d activity ratio was a sensitive, dose-responsive measure of Pb exposure regardless of the mode of administration of Pb. Dietary Pb concentrations as low as 5 ppm (dry wt) could be estimated through the use of the activity ratio method, and a highly significant positive correlation was observed between dietary Pb concentration over the 5-100 ppm range and the ALA-d activity ratio (r = 0.87). The RBC-ALA-d activity ratio may thus be a useful method for estimating average dietary concentrations of Pb over an environmentally relevant range in situations where the diet is the major source of exposure to Pb, and where it is also impossible or impractical to accurately measure dietary Pb content directly.

Metallothionein production: similar responsiveness of avian liver and kidney to chronic cadmium administration.

The accumulation of hepatic and renal Cd, Zn, Cu, and metallothionein (MT) was investigated in ringed turtle doves (Streptopelia risoria) chronically exposed to 3 different concentrations of dietary Cd. When only tissue-Cd was considered as an inducer of MT, kidney was found to be 35% as responsive as liver in producing MT. However, when all potentially relevant inducing metals (Cd + Zn + Cu) were taken into account, kidney was found to be 85% as responsive as liver. The greater production of MT/mol Cd in liver was accounted for mainly by a greater co-accumulation of Zn/mol Cd in liver than in kidney. We conclude that the apparent tissue specificity in expression of MT may be overestimated by failure to consider fluctuations in multiple inducers. Variability in tissue-MT concentrations after chronic dietary Cd administration is best accounted for by a consideration of tissue-Cd, -Zn, and -Cu, rather than tissue-Cd alone.

The interaction of zinc and cadmium in the synthesis of hepatic metallothionein in rats.

The interaction of injected zinc salts (Zn) and cadmium salts (Cd) with regard to the synthesis of metallothionein (MT) in adult rat liver was investigated. Male rats received an i.p. injection of Zn (20 mg/kg) or Cd (0.6 mg/kg) with or without pretreatment with Zn (20 mg/kg 16 h prior to the second injection). It was found that both metals, when administered singly, induced the synthesis of significant levels of hepatic MT, but that, when the Cd injection followed the Zn injection, synthesis of MT was not additive. When Zn pretreatment was followed by a second Zn injection, MT accumulation was additive (approx. 2-fold of that observed after a single Zn injection). Also, a highly significant positive correlation, (r = 0.97, P less than 0.01) was noted between hepatic Zn concentration and hepatic MT concentration, a relationship which was independent of the mode of MT induction. The results of the investigation indicate that: (1) in the presence of pre-existing hepatic Zn--MT, the ability of Cd to induce new MT synthesis is greatly reduced; rather, Cd is sequestered by the pre-existing MT; and (2) Zn may play a major role in the induction of MT synthesis both after Zn administration and after Cd administration.

The regional distribution of lead in normal rat brain.

A modified method of rat brain dissection resulting in the isolation of 13 discrete brain regions, namely: olfactory bulbs, frontal cortex, rest of cortex, corpus callosum, hippocampi, amygdalae, corpus striatum, colliculi, tegmentum, thalami, hypothalamus, pons-medulla and cerebellum was developed and is presented in detail. The method was then used to determine the region distribution of Pb in the normal rat brain. Considerable regional variation in Pb content was noted. The hippocampi revealed the highest concentration of the metal (487 +/- 64 ng/g) and the thalami the lowest (102 +/- 35 ng/g).

Bioaccumulation and toxicology of chromium: implications for wildlife.

The major source of exposure to Cr for wild birds and mammals is through ingestion with food. Chromium(VI) compounds are absorbed significantly more efficiently (2-10% of dose) from the GI tract than inorganic Cr(III) compounds (0.5-3%), due to the increased membrane permeability of the former. Transfer of Cr(VI) into mammalian fetuses has been documented at oral doses of 500 mg Cr/L in drinking water, and injected single doses of 5 mg Cr(VI)/kg BW in dams were teratogenic. Cr concentration data for mammalian and avian wildlife species and their potential food organisms are scarce. Worldwide, fewer than 50 species of free-living mammals and birds have been surveyed with regard to tissue Cr concentrations. Tissue concentrations in animals living in habitats remote from sources of Cr contamination range from approximately 0.1-15 micrograms/g DW depending on the species and tissue analyzed. In habitats experiencing Cr pollution, levels can be up to two orders of magnitude higher. Eisler (1986) suggested that tissue concentrations in wildlife > 4 micrograms/g DW be considered to indicate likely contamination by Cr. Bone tissue often accumulates higher concentrations than other tissues in animals chronically exposed to Cr. Measuring concentrations only in the liver and/or kidneys has been a common practice, yet these organs failed to show evidence of extant Cr contamination in some cases. It is recommended that analysis of the bone, liver, and kidneys be a minimum requirement for future Cr biomonitoring studies. Concentrations in fur or feathers can be extremely variable even among individuals within the same habitat. At best, concentrations in fur and feathers might be used to indicate relative levels of airborne Cr contamination. The toxicological significance of "elevated" Cr concentrations is largely unknown because toxicological data on free-living wildlife species are virtually nonexistent. Based on controlled dosing studies in which Cr compounds were administered orally to experimental animals, dietary Cr concentrations > or = 10 micrograms/g DW in food should be considered potentially harmful to the health and reproductive success of wildlife consumers. Certain species of fish and aquatic invertebrates are sensitive to Cr, showing reduced survival or growth at Cr(VI) concentrations > 10 micrograms/L. The elimination of these organisms from environments contaminated with Cr may have detrimental effects on wild birds and mammals that depend on such organisms for food.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cadmium on Pekin duck total body water, water flux, renal filtration, and salt gland function.

The following hypotheses were examined using Pekin ducks (Anas platyrhynchos) as a model for marine ducks: cadmium (Cd) intake affects (1) salt gland and/or kidney function of ducks and (2) osmoregulation differently in male and female ducks. Birds were fed 0, 50, or 300 microg Cd/g food. They were gradually acclimated to 450 mM NaCl and then drank 300 mM NaCl for 3 mo while salt gland secretion (SGS), glomerular filtration rate (GFR), total body water (TBW), and water flux (WF) were measured in ducks eating control and high-Cd diets. Cadmium ingestion did not markedly affect body mass, but significantly enlarged the salt glands and kidneys. Enhancement of kidney mass was greater in males. Cadmium ingestion did not affect TBW or WF, but tended to increase interstitial fluid space at the expense of intracellular fluid. Sex did not affect TBW, but males had greater WF. Birds that ate Cd diets, especially the higher Cd diet, exhibited renal tubular damage and lower GFR. Ducks that ate Cd had lower plasma sodium concentration and osmolality and, to activate SGS, required longer infusion of NaCl and larger increments

Effects of acidification on the availability of toxic metals and calcium to wild birds and mammals.

The effects of acidification on wildlife inhabiting aquatic or semi-aquatic environments are reviewed, with particular reference to the possibility for increased dietary exposure to Hg, Cd, Pb and/or Al, and decreased availability of essential dietary minerals such as Ca. It is concluded that: (1) piscivores risk increased exposure to dietary methyl-Hg in acidified habitats, and Hg concentrations in prey may reach levels known to cause reproductive impairment in birds and mammals; (2) piscivores do not risk increased exposure to dietary Cd, Pb or Al because these metals are either not increased in fish due to acidification, or increase are trivial from a toxicological perspective; (3) insectivores and omnivores may, under certain conditions, experience increased exposure to toxic metals in some acidified environments. Exposure levels are likely to be sufficiently low, however, that significant risks to health or reproduction are unlikely. More importantly, these wildlife species may experience a drastic decrease in the availability of dietary Ca due to the pH-related extinction of high-Ca aquatic invertebrate taxa (molluscs, crustaceans). Decreased availability of dietary Ca is known to adversely affect egg laying and eggshell integrity in birds, and the growth of hatchling birds and neonatal mammals. Acidification-related changes in the dietary availability of other essential elements, such as Mg, Se and P, have not been established and require further investigation; (4) herbivores may risk increased exposure to Al and Pb, and perhaps Cd, in acidified environments because certain macrophytes can accumulate high concentrations of these metals under acidic conditions. The relative importance of pH in determining the metal concentrations of major browse species, and the toxicological consequences for herbivores wildlife, is not well established and requires further study. A decreased availability of dietary Ca is also likely for herbivores inhabiting acidified environments.

Influence of reduced dietary calcium on the accumulation and effects of lead, cadmium, and aluminum in birds.

The influence of low dietary calcium on the accumulation and effects of dietary lead, cadmium and aluminum was examined in zebra finches and ring doves. In zebra finches fed a diet containing 0.3% Ca, the hepatic and renal accumulation of lead was enhanced approximately 400% and of cadmium about 150-200%, compared to birds fed a 3.0% Ca diet. Low dietary Ca also caused bones of female finches to lose an average of about 60% of their normal Ca content. Loss of bone-Ca was also observed in male finches, but was less than in females. In reproductively active ring doves, low (0.4%) dietary Ca enhanced the accumulation of lead and cadmium, but not of aluminum, compared with accumulation in doves consuming a 2.0% Ca diet. Enhanced accumulation of lead and cadmium was accompanied by increased synthesis of the metal-binding protein metallothionein and by greater inhibition of delta-aminolevulinic acid dehydratase activity. These results indicate that, under conditions of reduced dietary Ca availability, such as can occur in acid-impacted environments, wild birds risk increased uptake of certain toxic metals and may accumulate toxic concentrations of these metals more rapidly. Researchers should take account of dietary Ca levels when interpreting results of dosing studies in which metals such as lead and cadmium are administered to birds.

The chronic toxicity of aluminium, cadmium, mercury, and lead in birds: a review.

The toxicity of chronic dietary metal exposure in birds is reviewed. It is concluded that significant physiological and biochemical responses to such exposure conditions occur at dietary metal concentrations insufficient to cause signs of overt toxicity. Particularly important are reproductive effects which include decreased egg production, decreased hatchability, and increased hatchling mortality. Young, growing birds are typically more sensitive to the toxic effects of chronic metal exposure than adults, and altricial species are often more sensitive than precocial species. Factors which modify the absorption and toxicity of heavy metals, such as Se for the case of Hg, and Ca for the case of Pb and Cd, are discussed. Monitoring strategies for assessing environmental metal exposure in birds are evaluated.

Cadmium in caribou and muskoxen from the Canadian Yukon and Northwest Territories.

Cadmium, zinc, copper and metallothionein concentrations were measured in liver and kidney tissue of caribou and muskoxen collected from various sites in the Canadian Yukon and Northwest Territories. Cadmium concentrations in caribou tissues were substantially higher than in muskoxen for all age classes and were comparable to concentrations reported for caribou from northern Québec and Norway. No geographical site differences in cadmium concentration were observed. Cadmium concentrations were positively correlated with age for both caribou and muskoxen. The highest cadmium concentration observed (166 micrograms/g dry wt.) was in renal tissue of a 15-year-old caribou. Metal concentrations tended to be higher in spring than in fall for animals of comparable age. Renal cadmium concentrations were highly correlated with metallothionein concentrations, especially for cadmium concentrations exceeding 20 micrograms/g (dry wt.). It is estimated that the regular weekly consumption of kidney tissue from Arctic caribou of any age, and from muskoxen older than 1 year, will probably cause the WHO provisional weekly tolerable intake of cadmium to be exceeded.

Relationships between lake chemistry and calcium and trace metal concentrations of aquatic invertebrates eaten by breeding insectivorous waterfowl.

Ca, P, Al, and trace metal (Cu, Ni, Zn, Cd, and Pb) concentrations were measured in several aquatic invertebrate taxa used as food by breeding insectivorous waterfowl, sampled from three sites in eastern Canada with widely varying water chemistry. Ca concentrations were highest in molluscs (snails and clams), averaging 200-300 mg g(-1) (shells included). Aquatic insects of varying sizes, life stages and habits (caddisfly larvae, dragonfly larvae, adult backswimmers, waterstriders, and whirligig beetles) had much lower mean Ca concentrations, ranging from about 0.6 mg g(-1) (beetles) to 1.8 mg g(-1) (caddisflies). Invertebrate-Ca concentrations decreased with increasing body mass for several taxa, with smaller and larger individuals providing similar absolute amounts of Ca. Ca concentrations in most aquatic insects (but not molluscs) were reduced under acidic, low Ca, high Al, low dissolved organic carbon (DOC) and/or low total phosphorus (TP) conditions. In stepwise multiple regressions, pH was consistently the main factor explaining variability in invertebrate-Ca, after controlling for the negative relationship between invertebrate-Ca and body mass for some taxa. Molluscs were absent from lakes below pH 5.3. In general, concentrations of P and metals in invertebrate taxa were not significantly correlated with lake pH. Levels of Al, Cd, or Pb were not sufficiently high to be considered toxic to potential consumers of these organisms. For waterfowl and other birds breeding in acid-stressed habitats and relying on aquatic invertebrates as a source of food, a reduced availability of dietary Ca is more likely than an increased exposure to toxic metals to negatively affect reproductive success, especially when other adverse effects of acidification (lower diversity of prey) are considered.

Leeches as indicators of dietary mercury exposure in non-piscivorous waterfowl in central Ontario, Canada.

We collected and analysed 113 leeches (Hirudinea) from 17 small lakes in the acid-stressed Muskoka region of central Ontario, Canada to examine the relationship between lake chemistry and mercury (Hg) concentrations in leeches, and thus determine whether leeches and other benthic invertebrates posed a dietary risk of Hg exposure for non-piscivorous waterfowl. Hg concentrations in leeches were generally low and only a few-fold above the detection limit (0.78 ng g(-1) wet weight (ww)). Mean Hg concentration in the bloodsucker Macrobdella decora was 6.94 +/- 0.78 SE ng g(-1) ww (n=49) and was 5.98 +/- 0.46 ng g(-1) ww (n=64) in the scavenger Percymoorensis marmoratis. Leech Hg concentrations were correlated with calcium and dissolved organic carbon concentrations in the water, respectively. These data suggest that leeches are not suitable monitors of Hg (usually as methylmercury) biomagnification in central Ontario lakes, and do not pose a dietary risk to non-piscivorous waterfowl.

Mercury in fish from the Pinchi Lake Region, British Columbia, Canada.

Water, surface sediments, and <40 cm rainbow trout (Oncorhynchus mykiss) and northern pikeminnow (Ptychocheilus oregonensis) were collected from Pinchi Lake, British Columbia, and from several nearby reference lakes. Hg concentrations in sediment samples from Pinchi L. were highly elevated compared to sediments from reference lakes, especially in sites adjacent to and downstream of a former Hg mine. In both fish species examined, Hg concentration was positively related to age and/or fork length. In northern pikeminnow, Hg concentrations were also positively related to trophic level (deltaN). Hg concentrations in both fish species were highest in Pinchi L., and were higher in pikeminnow than in rainbow trout of similar size. Average Hg concentrations in small rainbow trout from all lakes, including Pinchi L., were lower than dietary levels reported to cause reproductive impairment in common loons (Gavia immer); however, Hg levels in small pikeminnow from Pinchi L. were sufficiently high to be of concern. The risk for Hg toxicity in the study area is greatest for animals that consume larger piscivorous fish such as larger northern pikeminnow or lake trout, which are known from previous studies to contain higher Hg concentrations.