Charles H. Jagoe

Mercury in alligators (Alligator mississippiensis) in the southeastern United States

Mercury methylation may be enhanced in wetlands and humic-rich, blackwater systems that crocodiles and alligators typically inhabit. Given their high trophic level and long life-spans, crocodilians could accumulate significant burdens of Hg. Our objectives were to survey Hg concentrations in alligators from several areas in the southeastern United States to test their utility as sentinels of Hg contamination, to examine relationships among Hg concentrations in various tissues and to look for any differences in tissue Hg concentrations among locations. We measured total Hg concentrations in alligators collected in the Florida Everglades (n = 18), the Okefenokee National Wildlife Refuge, Georgia (n = 9), the Savannah River Site (SRS), South Carolina (n = 49) and various locations in central Florida (n = 21), sampling tissues including blood, brain, liver, kidney, muscle, bone, fat, spleen, claws and dermal scutes. Alligators from the Everglades were mostly juvenile, but Hg concentrations in tissues were high (means: liver 41.0, kidney 36.4, muscle 5.6 mg Hg/kg dry wt.). Concentrations in alligators from other locations in Florida were lower (means: liver 14.6, kidney 12.6, muscle 1.8 mg Hg/kg dry wt.), although they tended to be larger adults. Alligators from the Okefenokee were smallest and had the lowest Hg concentrations (means: liver 4.3, kidney 4.8, muscle 0.8 mg Hg/kg dry wt.). SRS alligators had the greatest size range and intermediate Hg levels (means: liver 14.9, muscle 4.8 mg Hg/kg dry wt.). At some locations, alligator length was correlated with Hg concentrations in some internal organs. However, at three of the four locations, muscle Hg was not related to length. Tissue Hg concentrations were correlated at most locations however, claw or dermal scute Hg explained less than 74% of the variation of Hg in muscle or organs, suggesting readily-obtained tissues, such as scutes or claws, have limited value for non-destructive screening of Hg in alligator populations.

Morphological and morphometric changes in the gills of mosquitofish (Gambusia holbrooki) after exposure to mercury (II)

Abstract Physiological measurements suggest that mercury (Hg) affects ion regulation in aquatic organisms. This implies that Hg should cause morphological changes in gills, the major ionoregulatory organ of fish. Previous studies have shown severe Hg-induced gill damage at acutely lethal Hg concentrations, but in soft fresh waters, where ionoregulatory disturbances should be most pronounced, there have been no quantitative studies to date of the effects of dissolved Hg at sublethal concentrations. We exposed mosquitofish ( Gambusia holbrooki ) to nominal concentrations of 75, 150 and 300 nM Hg (II) in natural stream water of low ionic strength (Ca = 4.8 μ M) in a static-renewal experiment. Mercury concentrations dropped rapidly after Hg additions, and most dissolved Hg was probably complexed with humic substances. Gills were sampled after 7 and 14 days exposure. Examination with scanning electron microscopy (SEM), indicated that Hg caused progressive loss of secondary lamellae and loss of cell surface microridges. Effects became more severe at higher Hg concentrations. Using light microscopy and morphometric techniques, the percent of gill filament occupied by chloride cells (volume density) was significantly greater in all Hg treatments than in controls, and thickness of the primary lamellar epithelium increased with Hg exposure. Thickening of the primary lamellar epithelium filled some interlamellar spaces, obliterating secondary lamellae. However, width of the exposed portions of secondary lamellae was not affected by Hg, suggesting that blood-to-water diffusion distances did not increase in response to Hg exposure. Autometallographic staining for Hg showed that the metal was distributed throughout the gill epithelium, and not concentrated inside chloride cells.

Adverse effects of ecologically relevant dietary mercury exposure in southern leopard frog (Rana sphenocephala) larvae

Southern leopard frog (Rana sphenocephala) larvae were exposed to experimental diets supplemented with aufwuchs from control and mercury-enriched mesocosms combined in proportions intended to mimic mercury concentrations and speciation in aufwuchs observed from aquatic systems contaminated by atmospheric deposition. Observations on rates of mortality, malformation, and larval growth and development were made for 254 d. Increased incidence of mortality, malformation, and changes in growth and development were observed at concentrations that reflect the highest concentrations expected in the amphibian diet from atmospheric deposition (1,500-3,300 ng Hg/g dry wt). The results of this study are probably more ecologically realistic than results obtained from previous studies of aqueous mercury toxicity and suggest that dietary mercury exposure in habitats contaminated primarily by atmospheric deposition has the potential to cause adverse effects in amphibian larvae.

Lake acidity and mercury content of fish in Darwin National Reserve, Russia

Darwin National Reserve is a protected natural area on the north-west shore of the Rybinsk Reservoir, 350 km north of Moscow. In June 1989, six lakes in the Reserve and the reservoir were surveyed to assess lake acidity and the mercury content of perch, Perca fluviatilis. Five were seepage lakes with no permanent inlets or outlets and one was a drainage lake with both an inlet and an outlet. The seepage lakes were acidic (mean pH 4.6-4.8) and varied in colour from 20 to 200 Hazen units. The drainage lake and reservoir were alkaline (mean pH 8.0-8.1) and colour spanned a similar range. The mean mercury content of perch dorsal epaxial muscle ranged from 0.5 to 1.1 microg g(-1) wet weight in the five acidic lakes and from 0.1 to 0.2 microg g(-1) in the alkaline lakes. Fish mercury content was negatively correlated with lake pH (r=-0.93, P=0.002) if all waters were considered together, and positively correlated with apparent colour (r=0.91, P=0.03) in the seepage lakes.

Perch mercury content is related to acidity and color of 26 Russian Lakes

We determined mercury in fish (perch Perca fluviatilis) from 26 Russian lakes in three regions over four years. The lakes ranged in size from 2 to 395,000 ha, in pH from 4.5 to 10.0, and in color from 3 to 190 hazen. Sixteen lakes were drainage lakes, with permanent outlets, and 10 were seepage lakes, with no permanent inlets or outlets. The lakes were generally located in forested regions with little or no human habitation in the watershed. The three regions were geologically distinct: Precambrian Shield granitic bedrock covered with thin soil; Triassic bedrock covered with thick glacial tills; and Triassic bedrock covered with thin sediments. At each lake water samples were collected and analyzed for pH, add neutralizing capacity (ANC), major cations, and anions. Dissolved mercury species were estimated with a thermodynamic equilibrium model (MINTEQA2). Mercury content of dorsal muscle varied from 0.04 to 1.0 μg/g wet weight, and was linearly related to calculated HgCH3Cl (r20.68, p<0.001). Lake HgCH3Cl, in turn, was related to lake pH (r2=0.86, p<0.001). Stepwise multiple regression selected lake HgCH3Cl and color as the factors most highly related to fish mercury content, with the model accounting for 75% of the variation.

Gill Na+,K+-ATPase activity in largemouth bass (Micropterus salmoides) from three reservoirs with different levels of mercury contamination

Abstract Exposure to high concentrations of dissolved mercury (Hg) causes gill pathologies and interferes with ion and osmoregulation in fish. Although the gill ion-exchange enzyme Na+,K+-ATPase is inhibited by Hg in laboratory experiments, the concentrations that produce such effects are much higher than normally found in natural waters. However, Stagg et al. (1992, Mar. Environ. Res., 33: 255–266) found a significant correlation between gill Na+,K+-ATPase activity and muscle Hg concentrations in flounder (Platicthyes flesus) collected at polluted and clean sites in estuaries, suggesting that exposure to environmentally realistic Hg levels may affect ion regulation in estuarine fish. We tested for a similar relationship in a freshwater species, largemouth bass (Micropterus salmoides). Liver, muscle, and gill Hg concentrations differed significantly among bass from three reservoirs with similar water chemistry but different levels of Hg contamination. However, mean gill Na+,K+-ATPase activity did not vary among the reservoirs. For individual fish, gill Na+,K+-ATPase activity was not related to liver, muscle, or gill Hg concentration. Liver and muscle Hg concentrations were related to fish size, but gill Na+,K+-ATPase activity did not vary with fish size or sex. Gill Hg levels were not related to fish size. Exposure of gill homogenates to 0–10 μmol Hg 1−1 demonstrated that Na+,K+-ATPase can be inhibited by Hg in vitro, and 50% inhibition (IC50) occurred at 0.5 μmol Hg 1−1 Although our results support the idea that Hg can interfere with Na+,K+-ATPase activity, we were unable to detect an association between environmental exposure and gill Na+,K+-ATPase activity in wild freshwater fish.

Dietary mercury exposure and bioaccumulation in southern leopard frog (Rana sphenocephala) larvae

Aufwuchs was collected from three reservoirs, a constructed wetland used for groundwater treatment, and mercury (Hg)-enriched mesocosms to examine the relationship between inorganic Hg and methylmercury concentrations in the diet of tadpoles. Four diets were then formulated with Hg-enriched aufwuchs to concentrations that bracketed those of Hg observed in aufwuchs from the field and reported in the literature from sites contaminated by atmospheric deposition. The diets were fed to southern leopard frog tadpoles in the laboratory for the entire larval period (60-254 d). Metamorphs and tadpoles were analyzed for inorganic Hg and methylmercury contents by gas chromatography-cold-vapor atomic fluorescence spectrophotometry. Methylmercury concentration increased with total Hg concentration in aufwuchs, but the proportion of methylmercury to inorganic Hg decreased with increasing total Hg concentration. In the feeding experiment, there was an inverse relationship between Hg exposure concentration and the bioaccumulation factor for each Hg species. We concluded that neither methylmercury nor inorganic Hg in aufwuchs is highly bioavailable to tadpoles and that bioaccumulation is not well explained by a simple partitioning model. This suggests that bioaccumulation factors as currently used are not the best predictors of dietary Hg bioaccumulation.

A transgenic strain of the nematode Caenorhabditis elegans as a biomonitor for heavy metal contamination

Metallothionein (MT), a protein involved in metal regulation and detoxification, has been used widely as a biomarker of metal exposure. In the present study, a transgenic strain of the free-living soil nematode Caenorhabditis elegans was developed using the C. elegans MT-2 (mtl-2) promoter to control the transcription of green fluorescence protein (GFP) reporter. Response of this transgenic system to Cd, Hg, Cu, Zn, Ni, Pb, and As exposure in aquatic media was tested by quantifying GFP expression after 24 h of exposure. Response in Cd-spiked soil was tested in a similar manner. The mtl-2 transcription also was measured using real-time reverse transcription-polymerase chain reaction to gain a mechanistic understanding of the transgene expression. Green fluorescence protein is induced by Cd, Hg, Cu, and Zn in a time- and concentration-dependent manner; mtl-2 transcription is consistent with the GFP response. The minimum concentrations of Cd, Hg, Cu, and Zn that induce GFP response are 2- to 1000-fold lower than concentrations affecting traditional endpoints, such as lethality or behavioral change. The system responds to Cd in soil in a similar manner. Neither Ni nor Pb induces GFP, and neither induces mtl-2 transcription. Arsenic does not induce GFP, yet an increase in mtl-2 transcription was found, suggesting that As may interfere with GFP signaling. This mtl-2::GFP transgenic bioassay represents an alternative approach to quantify, both easily and quickly, a surrogate of MT in response to metal exposure (e.g., Cd, Hg, Cu, and Zn) in a variety of environments and potentially may be used for quantitative or semiquantitativebiomonitoring of metal contamination in soils and aquatic systems.

MERCURY IN BALD EAGLE NESTLINGS FROM SOUTH CAROLINA, USA

Bald eagles (Haliaeetus leucocephalus) may be at risk from contaminants in their diet and young birds may be particularly sensitive to contaminant exposure. To evaluate potential risks from dietary mercury exposure to eagle nestlings in South Carolina (USA), we surveyed mercury concentrations in 34 nestlings over two breeding seasons (1998 and 1999). Samples were also obtained from several post-fledging eagles in the region. Nestling feather mercury ranged from 0.61–6.67 μg Hg/g dry weight, nestling down mercury from 0.50–5.05 μg Hg/g dry weight, and nestling blood mercury from 0.02–0.25 μg Hg/g wet weight. We did not detect significant differences in tissue mercury between nestlings from coastal and inland regions in contrast to some other studies of piscivorous birds. Mercury concentrations were much higher in the post fledging birds we sampled. Our data show that nestling eagles in South Carolina are accumulating mercury, and that concentrations in older birds may exceed regulatory guidelines.

Effect of beryllium on fish in acid water is analogous to aluminum toxicity

Trace metals such as aluminum, when mobilized by acid deposition, may be important toxic agents in acidified waters. Beryllium is chemically similar to aluminum, and its solubility and aqueous speciation properties suggest that it may also be a problem in some acidic waters. Elevated beryllium levels have been found in some waters, but little is known of the potential toxic effects of beryllium in soft water at low pH. We exposed juvenile perch Perca fluviatilis and roach Rutilus rutilus to beryllium at two levels of pH. Beryllium concentrations of 10 μg/l or more caused increased mortality at pH 4.5 in perch, but only higher concentrations (>50 μg/l) were lethal at pH 5.5. In roach, beryllium concentrations ≥100 μg/l killed most fish within 96 h, regardless of pH. Beryllium also produced gill abnormalities similar to those caused by aluminum at concentrations as low as 10 μg/l. The abnormalities became more severe at higher beryllium levels, and included development of chloride cell apical crypts, increased mucus production, microridge loss, epithelial hyperplasia, and fusions of primary lamellae. The effects of beryllium and aluminum are similar, but beryllium causes gill damage at lower concentrations, suggesting that it may be an important, unrecognized contaminant in some acidic waters.