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.

Mercury empirical relationships in sediments from three Ontario lakes.

Total mercury (THg), methyl mercury (MeHg), total organic carbon (TOC), sediment bulk density (SBD), redox potential (Eh) and percent fines measurements were made on sediment cores collected along transects from littoral to profundal depths in Harp, Dickie, and Blue Chalk lake located on the Canadian Shield near Dorset, Ontario, Canada to determine whether empirical relationships exist among these sediment properties. MeHg was positively correlated with THg in all sediments with a MeHg:THg ratio (0.004+/-0.004) comparable to other uncontaminated profundal lakes. MeHg, MeHg:THg and TOC decreased with sediment depth within the core for all lakes, whereas THg only showed a decrease in Harp Lake. MeHg:THg ratio in surficial sediments was positively correlated with Eh and negatively correlated with TOC [MeHg:THg=-0.009 TOC (%)+0.001 Eh (mV)-1.902, p=0.026]; whereas THg was positively correlated with TOC [log THg (ppb)=0.026 TOC (%)+1.400, p<0.0001].

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.

Relationships among mercury, selenium, and neurochemical parameters in common loons (Gavia immer) and bald eagles (Haliaeetus leucocephalus).

Fish-eating birds can be exposed to levels of dietary methylmercury (MeHg) known or suspected to adversely affect normal behavior and reproduction, but little is known regarding Hg's subtle effects on the avian brain. In the current study, we explored relationships among Hg, Se, and neurochemical receptors and enzymes in two fish-eating birds--common loons (Gavia immer) and bald eagles (Haliaeetus leucocephalus). In liver, both species demonstrated a wide range of total Hg (THg) concentrations, substantial demethylation of MeHg, and a co-accumulation of Hg and Se. In liver, there were molar excesses of Se over Hg up to about 50-60 microg/g THg, above which there was an approximate 1:1 molar ratio of Hg:Se in both species. However, in brain, bald eagles displayed a greater apparent ability to demethylate MeHg than common loons. There were molar excesses of Se over Hg in brains of bald eagles across the full range of THg concentrations, whereas common loons often had extreme molar excesses of Hg in their brains, with a higher proportion of THg remaining as MeHg compared with eagles. There were significant positive correlations between brain THg and muscarinic cholinergic receptor concentrations in both species studied; whereas significant negative correlations were observed between N-methyl-D-aspartic acid (NMDA) receptor levels and brain Hg concentration. There were no significant correlations between brain Se and neurochemical receptors or enzymes (cholinesterase and monoamine oxidase) in either species. Our findings suggest that there are significant differences between common loons and bald eagles with respect to cerebral metabolism and toxicodynamics of MeHg and Se. These interspecies differences may influence relative susceptibility to MeHg toxicity; however, neurochemical responses to Hg in both species were similar.

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.

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.

Lead contamination in American woodcock (Scolopax minor) from Wisconsin.

An initial survey of lead levels in American woodcock (Scolopax minor) from Wisconsin was conducted in 1998 using wing bones from hunter-donated woodcock. The results of this initial survey indicated that young-of-year woodcock were accumulating extremely high levels of lead in their bones. Similar collections were made (using steel shot) between 1999 and 2001. The combined results of this collection indicated that 43.4% of young-of-year woodcock (range 1.5-220.0 microg/g dry wt) and 70% of woodcock chicks (range 9.6-93.0 microg/g dry wt) had bone lead levels in the elevated range (>20 microg/g dry wt). Blood samples were collected from chicks at a site considered elevated based on bone lead results (Mead Wildlife Area) and a site considered background (Navarino Wildlife Area). These samples were analyzed for lead concentration and aminolevulinic acid dehydratase activity. The mean blood lead concentrations of woodcock chicks from both sites did not reach levels that are considered elevated in waterfowl (>0.200 microg/ml). However, blood lead concentrations of chicks from the Mead Wildlife Area were significantly higher than lead levels in chicks from Navarino Wildlife Area (p = 0.002). Although the ultimate sources of lead exposure for Wisconsin woodcock currently remain unidentified, anthropogenic sources cannot be ruled out. Our results indicate that elevated lead exposure in Wisconsin woodcock is common and begins shortly after hatch.

Effects of nontoxic shot regulations on lead accumulation in ducks and American woodcock in Canada.

Prior to the first nontoxic shot zones being established in Canada, a nationwide survey of lead (Pb) concentrations in wing bones of hatch year (HY) dabbling and diving ducks determined the incidence of elevated Pb exposure in waterfowl in different parts of the country (Scheuhammer and Dickson 1996). The main objectives of the present study were (1) to compare these previously collected data with the incidence of elevated Pb accumulation in the same species several years after the establishment of a national regulation in 1997 prohibiting the use of Pb shot for waterfowl hunting; and (2) to survey waterfowl hunters to determine reported levels of compliance with the nontoxic shot regulation. Average bone-Pb concentrations in dabbling ducks (mallards [Anas platyrhyncos] and American black ducks [Anas rubripes] combined) decreased significantly between 1989+1990 and 2000 (11 microg/g vs. 4.8 microg/g, respectively [p < 0.01]). Ring-necked ducks (Aythya collaris) showed a similar decrease in mean bone-Pb concentrations, from 28 microg/g to 10 microg/g (p < 0.01). These declines in bone-Pb concentration were consistent with the results of a large anonymous hunter survey, which indicated a high level of reported compliance (>80%) with the nontoxic shot regulation among waterfowl hunters residing in Ontario and British Columbia. Conversely, American woodcock (Scolopax minor), an important upland game species not affected by the nontoxic shot regulation, showed no decrease in mean bone-Pb concentration since the national regulation came into effect (19 microg/g in 1995 vs. 21 microg/g in 2000). A majority (70%) of waterfowl hunters in British Columbia and Ontario who also hunt upland game birds report continued (legal) use of Pb shot for upland game bird hunting.

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.

Monitoring of umbilical cord blood lead levels and sources assessment among the Inuit.

Analyses completed on samples collected between 1993 and 1996 showed that about 7% of 475 Inuit newborns from northern Quebec (Canada) had a cord blood lead concentration equal to or greater than 0.48 micromol/l, an intervention level adopted by many governmental agencies. A comparison between the cord blood lead isotope ratios of Inuit and southern Quebec newborns showed that lead sources for these populations were different. Our investigation suggests that lead shots used for game hunting were an important source of lead exposure in the Inuit population. A cohort study conducted in three Inuit communities shows a significant decrease of cord blood lead concentrations after a public health intervention to reduce the use of lead shot. Lead shot ammunition can be a major and preventable source of human exposure to lead.

Lead poisoning in upland-foraging birds of prey in Canada.

We examined the degree of lead exposure, based on tissue-lead concentrations, in 184 raptors of 16 species found dead across Canada. The most prevalent species available for examination were Red-tailed hawks, Great horned owls, and Golden eagles (n = 131). The majority of individuals examined had very low lead accumulation, however 3-4% of total mortality in these 3 most commonly encountered species was attributed to lead poisoning. In addition, 1 of 9 Bald Eagles found dead far from aquatic environments was lead poisoned; and a single Turkey Vulture had a highly elevated bone-lead concentration (58 microg/g dry weight). Evidence from our study, along with other published research, indicates that upland-foraging birds of prey and scavengers that typically include game birds and mammals in their diets, are at risk for lead poisoning from the ingestion of lead projectiles from ammunition used in upland hunting. The use of non-lead ammunition for hunting upland game would effectively remove the only serious source of high lead exposure and lead poisoning for upland-foraging raptors.

Common loon eggs as indicators of methylmercury availability in North America.

Increased anthropogenic mercury (Hg) deposition since pre-industrial times, and subsequent transformation of inorganic Hg to methylmercury (MeHg) in aquatic environments, has created areas in North America where Hg poses a relatively high risk to wildlife, especially long-lived, piscivorous species. From 1995 to 2001, we opportunistically collected 577 eggs abandoned by Common Loons from eight states. Egg-Hg concentrations ranged from 0.07 to 4.42 microg/g (ww) or 0.10 to 19.40 microg/g (dw). Mercury was higher in eastern than in western North America. Female blood-Hg concentrations strongly correlated with those of eggs from the same territory even though the mean intraclutch Hg difference was 25%. In New England, egg volume declined significantly as egg-Hg concentrations increased. Fertility was not related to egg-Hg concentrations. Based on existing literature and this study's findings, egg-Hg risk levels were established and applied to our US data set and an existing Canadian data set. Regionally, we found the greatest risk levels in northeastern North America. With few exceptions, loon eggs are suitable indicators of methylmercury availability on lakes with territorial pairs.

Assessment of white blood cell phagocytosis as an immunological indicator of methylmercury exposure in birds.

White blood cell (WBC) phagocytosis was investigated as a potential immunological indicator of methylmercury (MeHg) exposure in birds. The assay was first assessed using chicken WBCs dosed with MeHg in vitro either in whole blood or as isolated cells and later using blood of wild common loons exposed in vivo to a range of dietary MeHg and having a range of blood-Hg concentrations. Whole blood and isolated WBCs from captive chickens were exposed to a range of MeHg concentrations for 3 h. After MeHg exposure, cells were incubated with fluorescent latex microbeads (diameter = 1.75 microm), fixed, and analyzed for size, complexity, and fluorescent intensity by flow cytometry. MeHg significantly depressed phagocytic activity when added to isolated WBCs at concentrations > 0.01 microg/ml, but not when added to whole blood up to 50 microg/ml. Similarly, no significant relationship between the concentration of Hg in whole blood and phagocytic capacity of WBCs in free-living loons was observed. Our results suggest that the phagocytosis assay, although rapid and convenient for use in field studies with wildlife species, is not a responsive immunological indicator of MeHg exposure at environmentally realistic concentrations of blood-Hg in wild loons. Assays that measure other immunologic endpoints (e.g., bacterial killing assay, PHA skin test, and mitogen-induced lymphocyte proliferation) should be assessed with respect to their ability to detect MeHg immunotoxicity in wild birds.

Metal and metallothionein concentrations in Scoter (Melanitta spp.) from the Pacific northwest of Canada, 1989-1994.

Eighty-six surf ( Melanitta perspicillata) and nine white winged (M. fusca) scoters were collected from 1989-1994 at 11 locations in British Columbia and the Yukon. Their kidney and liver tissues were analyzed for cadmium (Cd), copper (Cu), zinc (Zn), and metallothionein (MT) concentrations. Individual kidney Cd values ranged from 2.4 microg/g dry weight (DW) in birds from northern Vancouver Island to 390.2 microg/g (DW) in birds from the Queen Charlotte Islands, which is in the range of values potentially associated with kidney damage. Birds from the Queen Charlotte Islands also had high kidney Zn concentrations, which were significantly higher than values in birds from Naniamo and Westham Island on the south coast of BC. Cd values were significantly (p < 0.001) correlated with both Zn and MT concentrations in kidney tissue (r = 0.66 and 0.62, respectively). Male surf scoters had significantly higher kidney Cd and Zn levels than females, with mean Cd values of 47.3 and 19.7 microg/g DW (p < 0.002) for males and females, respectively. Mean Zn values were 120.8 and 108.0 microg/g DW (p < 0.05) for males and females, respectively. However, no sex differences were observed for either Cu or MT concentrations in kidney tissue. Individual MT values ranged from 2.7 to 416.8 microg/g wet weight (WW). Individual kidney Cu values ranged from 15.1 to 48.4 microg/g DW for both sexes. Kidney and liver Cd concentrations were significantly correlated (r = 0.90, p < 0.05) with kidney levels almost always higher than liver values. Although Cd accumulation by the Skidegate scoters was high, comparable tissue Cd values have been documented in other seabirds collected from the same general area, indicating elevated Cd concentrations in marine food chains around the Queen Charlotte Islands (Haida Gwaii) region of the Pacific coast.

Mercury, methylmercury, and selenium concentrations in eggs of common loons (Gavia immer) from Canada.

Concentrations of Hg and Se were determined for a total of 125 Common Loon (Gavia immer) eggs collected from lakes in Alberta, Saskatchewan, Ontario, Quebec, New Brunswick and Nova Scotia, Canada between 1972 and 1997. Resulting data were compared to Hg and/or Se concentrations known or suspected to cause reproductive impairment in birds. Organic (methyl) Hg analyses were also performed on a subset of 24 loon eggs. Thirty-nine of 125 eggs had total Hg levels exceeding those (0.6 microg g(-1) ww, or approximately 2.5 microg g(-1) dw) previously reported to be associated with reproductive impairment in common loons (Barr, 1986), and 9 of 125 eggs had Hg concentrations higher than the level associated with reproductive impairment in birds generally 1 microg g(-1) ww; (Thompson, 1996). Selenium concentrations in loon egg samples were less than levels known to cause reproductive impairment in birds. A weak but significant positive correlation was observed between egg-Hg and -Se concentrations (r = 0.511, p < 0.05). On average, methylmercury accounted for about 87% of total Hg in 24 eggs analysed for both total and organic Hg. In this subset of eggs, the relationship between organic (methyl) Hg and Se was significant (r = 0.538, p = 0.007) while that found between inorganic Hg and Se in the same eggs was not significant (r = 0.353, p = 0.091). This relationship was unexpected and was contrary to relationships established for organic and inorganic Hg vs. Se in adult loon liver and kidney tissue (Scheuhammer et al., 1998b).

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

Contaminant exposure and biomarker responses in spectacled eiders (Somateria fischeri) from St. Lawrence Island, Alaska.

Effects of chemical contaminant exposure may be contributing to the decline of spectacled eiders (Somateria fischeri) nesting in coastal areas of western Alaska. We evaluated chemical exposure and potential effects in 20 male eiders collected near St. Lawrence Island, Alaska. Analytes included metals, trace elements, chlorinated organics, and (137)Cesium ((137)Cs). Effects of contaminant exposure were evaluated using histopathology and biochemical measures of porphyrin profiles, cytochrome P450 activities, and metallothionein (MT) concentrations. Copper, cadmium, and selenium concentrations were elevated in spectacled eiders when compared to literature values for other marine birds. Only a few samples had trace concentrations of chlorinated organic compounds. Muscle (137)Cs levels were all below the average minimum quantifiable concentration of 0.079 Bq/g. No histopathological lesions were associated with elevated contaminant concentrations in liver, kidney, or testes. Protoporphyrin was found in highest concentration in both the liver and kidneys, followed by coproporphyrin and uroporphyrin, respectively. Hepatic uroporphyrin concentrations correlated significantly to hepatic arsenic concentrations. Mean activities of hepatic EROD, MROD, BROD, and PROD were consistent with other avian species. Comparisons of cadmium/MT ratios from this study to published literature ratios in seven marine avian species suggest that, although adult male spectacled eiders have elevated liver concentrations of certain MT-inducing metals, their MT concentrations are not as strongly induced as would be predicted based on literature values. Despite elevated metal concentrations, the apparent good health of the St. Lawrence Island birds suggests that should these contaminants be a factor in population declines, they likely act by decreasing fecundity or survival of young rather than via direct health impacts on adult male spectacled eiders.

Elevated lead exposure in American woodcock (Scolopax minor) in Eastern Canada.

We investigated the degree and incidence of elevated lead (Pb) accumulation in the American woodcock (Scolopax minor) in eastern Canada by measuring the concentration of Pb in undamaged wing bones of 1,588 birds from Ontario, Quebec, Nova Scotia, and New Brunswick. Overall median bone-Pb concentrations were 21 microgram/g (DW) for adults and 11 microgram/g for young of the year. A high proportion of birds had elevated Pb concentrations, compared with other wild bird species. Fifty-two percent of adults and 29% of young of the year had bone concentrations exceeding 20 microgram/g. Pb concentration varied significantly with age, gender, and geographical region (p

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.