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

Neurotoxic and cardiotoxic effects of pyrogallol on catfish (Clarias gariepinus)

Pyrogallol, a botanical hydrolysable tannin, has diverse medical and industrial applications. Its impact on aquatic ecosystems and fish health has been previously studied, revealing histopathological, immunological, biochemical, and haematological alterations in African catfish (Clarias gariepinus). In this study, the neurotoxic potential of pyrogallol was assessed through a 15-day exposure of catfish to concentrations of 1, 5, or 10 mg/L. Enzyme activities such as acetylcholinesterase (AchE), monoamine oxidase (MAO), aldehyde oxidase (AO), and nitric oxide (NO) were measured in serum and brain, along with histopathological examinations in the brain and heart. Pyrogallol exposure led to decreased AchE activity in the brain and serum, increased serum MAO activity, elevated AO in both brain and serum, and suppressed NO levels. Morphological abnormalities and dose-dependent pathological alterations were observed in the brain and heart, including neuropile deformities, shrunken Purkinje cells, cardiomyocyte degeneration, and increased collagen fibers. This suggests that pyrogallol induces adverse effects in fish.

Neurotoxic effects of different sizes of plastics (nano, micro, and macro) on juvenile common carp (Cyprinus carpio)

Using common carp as a model, we assessed the effects of polyethylene (PE) plastics on the brain. We measured activity of acetylcholinesterase (AChE), monoamine oxidase (MAO), and the content of nitric oxide (NO) in carp brain following exposure to 100 mg/L of either macroplastics (MaP), microplastics (MPs), or nanoplastic (NPs) for 15 days compared to an unexposed group. Following exposure, each biochemical biomarker was reduced 30–40%, with a higher magnitude of change corresponding to the smaller size of the particles (NPs > MPs > MaPs). In the carp tectum, exposure for 15 days to plastic particles caused varying degrees of necrosis, fibrosis, changes in blood capillaries, tissue detachment, edema, degenerated connective tissues, and necrosis in large cerebellar neurons and ganglion cells. In the carp retina, there was evidence for necrosis, degeneration, vacuolation, and curvature in the inner layer. Here we provide evidence that exposure to plastic particles can be associated with neurotoxicity in common carp.

Mercury levels in hair are associated with reduced neurobehavioral performance and altered brain structures in young adults

The detrimental effects of high-level mercury exposure on the central nervous system as well as effects of low-level exposure during early development have been established. However, no previous studies have investigated the effects of mercury level on brain morphometry using advance imaging techniques in young adults. Here, utilizing hair analysis which has been advocated as a method for biological monitoring, data of regional gray matter volume (rGMV), regional white matter volume (rWMV), fractional anisotropy (FA) and mean diffusivity (MD), cognitive functions, and depression among 920 healthy young adults in Japan, we showed that greater hair mercury levels were weakly but significantly associated with diminished cognitive performance, particularly on tasks requiring rapid processing (speed measures), lower depressive tendency, lower rGMV in areas of the thalamus and hippocampus, lower rWMV in widespread areas, greater FA in bilaterally distributed white matter areas overlapping with areas of significant rWMV reductions and lower MD of the widely distributed gray and white matter areas particularly in the bilateral frontal lobe and the right basal ganglia. These results suggest that even normal mercury exposure levels in Japan are weakly associated with differences of brain structures and lower neurobehavioral performance and altered mood among young adults.

Mercury and neurochemical biomarkers in multiple brain regions of five Arctic marine mammals

Mercury is a neurotoxic chemical that represents one of the greatest pollution threats to Arctic ecosystem health. Evaluating the direct neurotoxic effects of mercury in free ranging wildlife is challenging, necessitating the use of neurochemical biomarkers to assess potential sub-clinical neurological changes. The objective of this study was to characterize the distribution and speciation of mercury, as well as exposure-associated changes in neurochemistry, across multiple brain regions (n = 10) and marine mammal species (n = 5) that each occupy a trophic niche in the Arctic ecosystem. We found consistent species differences in mean brain and brain region-specific concentrations of total mercury (THg) and methyl mercury (MeHg), with higher concentrations in toothed whales (narwhal, pilot whales and harbour porpoise) compared to fur-bearing mammals (polar bear and ringed seal). Mean THg (μg/g dw) in decreasing rank order was: pilot whale (11.9) > narwhal (7.7) > harbour porpoise (3.6) > polar bear (0.6) > ringed seal (0.2). The higher THg concentrations in toothed whales was associated with a marked reduction in the percentage of MeHg (<40 %) compared to polar bears (>70 %) that had lower brain THg concentrations. This pattern in mercury concentration and speciation corresponded broadly to an overall higher number of mercury-associated neurochemical biomarker correlations in toothed whales. Of the 226 correlations between mercury and neurochemical biomarkers across brain regions, we found 60 (27 %) meaningful relationships (r>0.60 or p < 0.10). We add to the growing weight of evidence that wildlife accumulate mercury in their brains and demonstrate that there is variance in accumulation across species as well as across distinct brain regions, and that some of these exposures may be associated with sub-clinical changes in neurochemistry.

Metal brain bioaccumulation and neurobehavioral effects on the wild rodent Liomys irroratus inhabiting mine tailing areas

Ecotoxicological studies are necessary in order to evaluate the effects of environmental exposure of chemicals on wild animals and their ecological consequences. Particularly, neurobehavioral effects of heavy metal elements on wild rodents have been scarcely investigated. In the present study, we analyzed the effect of metal bioaccumulation (Pb, As, Mg, Ni, and Zn) in the brain and in the liver on exploratory activity, learning, memory, and on some dopaminergic markers in the wild rodent Liomys irroratus living inside mine tailings, at Huautla, Morelos, Mexico. We found higher Pb concentration but lower Zn in striatum, nucleus accumbens, midbrain, and hippocampus in exposed animals in comparison to rodents from the reference site. Exposed rodents exhibited anxious behavior evaluated in the open field, while no alterations in learning were found. However, they displayed slight changes in the memory test in comparison to reference group. The neurochemical evaluation showed higher levels of dopamine and 5-hydroxyindolacetic acid in midbrain, while lower levels of metabolites dihydroxyphenyl acetic acid and homovanillic acid in striatum of exposed rodents. In addition, mRNA expression levels of dopaminergic D2 receptors in nucleus accumbens were lower in animals from the mining zone than in animals from the reference zone. This is the first study that shows that chronic environmental exposure to metals results in behavioral and neurochemical alterations in the wild rodent L. irroratus, a fact that may comprise the survival of the individuals resulting in long-term effects at the population level. Finally, we suggest the use of L. irroratus as a sentinel species for environmental biomonitoring of mining sites.

In vivo and In vitro neurochemical-based assessments of wastewater effluents from the Maumee River area of concern

Wastewater treatment plant (WWTP) effluents contain potentially neuroactive chemicals though few methods are available to screen for the presence of such agents. Here, two parallel approaches (in vivo and in vitro) were used to assess WWTP exposure-related changes to neurochemistry. First, fathead minnows (FHM, Pimephales promelas) were caged for four days along a WWTP discharge zone into the Maumee River (Ohio, USA). Grab water samples were collected and extracts obtained for the detection of alkylphenols, bisphenol A (BPA) and steroid hormones. Second, the extracts were then used as a source of in vitro exposure to brain tissues from FHM and four additional species relevant to the Great Lakes ecosystem (rainbow trout (RT), river otter (RO), bald eagle (BE) and human (HU)). The ability of the wastewater (in vivo) or extracts (in vitro) to interact with enzymes (monoamine oxidase (MAO) and glutamine synthetase (GS)) and receptors (dopamine (D2) and N-methyl-D-aspartate receptor (NMDA)) involved in dopamine and glutamate-dependent neurotransmission were examined on brain homogenates. In vivo exposure of FHM led to significant decreases of NMDA receptor binding in females (24-42%), and increases of MAO activity in males (2.8- to 3.2-fold). In vitro, alkylphenol-targeted extracts significantly inhibited D2 (66% in FHM) and NMDA (24-54% in HU and RT) receptor binding, and induced MAO activity in RT, RO, and BE brains. Steroid hormone-targeted extracts inhibited GS activity in all species except FHM. BPA-targeted extracts caused a MAO inhibition in FHM, RT and BE brains. Using both in vivo and in vitro approaches, this study shows that WWTP effluents contain agents that can interact with neurochemicals important in reproduction and other neurological functions. Additional work is needed to better resolve in vitro to in vivo extrapolations (IVIVE) as well as cross-species differences.

Brain region-specific perfluoroalkylated sulfonate (PFSA) and carboxylic acid (PFCA) accumulation and neurochemical biomarker responses in east Greenland polar bears (Ursus maritimus)

Perfluoroalkyl substances (PFASs) is a growing class of contaminants in the Arctic environment, and include the established perfluorinated sulfonates (PFSAs; especially perfluorooctane sulfonate (PFOS)) and carboxylic acids (PFCAs). PFSAs and PFCAs of varying chain length have been reported to bioaccumulate in lipid rich tissues of the brain among other tissues such as liver, and can reach high concentrations in top predators including the polar bear. PFCA and PFSA bioaccummulation in the brain has the potential to pose neurotoxic effects and therefore we conducted a study to investigate if variations in neurochemical transmitter systems i.e. the cholinergic, glutaminergic, dopaminergic and GABAergic, could be related to brain-specific bioaccumulation of PFASs in East Greenland polar bears. Nine brain regions from nine polar bears were analyzed for enzyme activity (monoamine oxidase (MAO), acetylcholinesterase (AChE) and glutamine synthetase (GS)) and receptor density (dopamine-2 (D2), muscarinic cholinergic (mAChR) and gamma-butyric acid type A (GABA-A)) along with PFSA and PFCA concentrations. Average brain ∑PFSA concentration was 25ng/g ww where PFOS accounted for 91%. Average ∑PFCA concentration was 88ng/g ww where PFUnDA, PFDoDA and PFTrDA combined accounted for 79%. The highest concentrations of PFASs were measured in brain stem, cerebellum and hippocampus. Correlative analyses were performed both across and within brain regions. Significant positive correlations were found between PFASs and MAO activity in occipital lobe (e.g. ∑PFCA; rp=0.83, p=0.041, n=6) and across brain regions (e.g. ∑PFCA; rp=0.47, p=0.001, ∑PFSA; rp=0.44, p>0.001; n=50). GABA-A receptor density was positively correlated with two PFASs across brain regions (PFOS; rp=0.33, p=0.02 and PFDoDA; rp=0.34, p=0.014; n=52). Significant negative correlations were found between mAChR density and PFASs in cerebellum (e.g. ∑PFCA; rp=-0.95, p=0.013, n=5) and across brain regions (e.g. ∑PFCA; rp=-0.40, p=0.003, ∑PFSA; rp=-0.37, p=0.007; n=52). AChE activity and D2 density were negatively correlated with single PFCAs in several brain regions, whereas GS activity was positively correlated with PFASs primarily in occipital lobe. Results from the present study support the hypothesis that PFAS concentrations in polar bears from East Greenland have exceeded the threshold limits for neurochemical alterations. It is not known whether the observed alterations in neurochemical signaling are currently having negative effects on neurochemistry in East Greenland polar bears. However given the importance of these systems in cognitive processes and motor function, the present results indicate an urgent need for a better understanding of neurochemical effects of PFAS exposure to wildlife.

Recent progress on our understanding of the biological effects of mercury in fish and wildlife in the Canadian Arctic

This review summarizes our current state of knowledge regarding the potential biological effects of mercury (Hg) exposure on fish and wildlife in the Canadian Arctic. Although Hg in most freshwater fish from northern Canada was not sufficiently elevated to be of concern, a few lakes in the Northwest Territories and Nunavut contained fish of certain species (e.g. northern pike, Arctic char) whose muscle Hg concentrations exceeded an estimated threshold range (0.5-1.0 μg g(-1) wet weight) within which adverse biological effects begin to occur. Marine fish species generally had substantially lower Hg concentrations than freshwater fish; but the Greenland shark, a long-lived predatory species, had mean muscle Hg concentrations exceeding the threshold range for possible effects on health or reproduction. An examination of recent egg Hg concentrations for marine birds from the Canadian Arctic indicated that mean Hg concentration in ivory gulls from Seymour Island fell within the threshold range associated with adverse effects on reproduction in birds. Mercury concentrations in brain tissue of beluga whales and polar bears were generally lower than levels associated with neurotoxicity in mammals, but were sometimes high enough to cause subtle neurochemical changes that can precede overt neurotoxicity. Harbour seals from western Hudson Bay had elevated mean liver Hg concentrations along with comparatively high muscle Hg concentrations indicating potential health effects from methylmercury (MeHg) exposure on this subpopulation. Because current information is generally insufficient to determine with confidence whether Hg exposure is impacting the health of specific fish or wildlife populations in the Canadian Arctic, biological effects studies should comprise a major focus of future Hg research in the Canadian Arctic. Additionally, studies on cellular interactions between Hg and selenium (Se) are required to better account for potential protective effects of Se on Hg toxicity, especially in large predatory Arctic fish, birds, and mammals.

Applications and implications of neurochemical biomarkers in environmental toxicology

Thousands of environmental contaminants have neurotoxic properties, but their ecological risk is poorly characterized. Contaminant-associated disruptions to animal behavior and reproduction, both of which are regulated by the nervous system, provide decision makers with compelling evidence of harm, but such apical endpoints are of limited predictive or harm-preventative value. Neurochemical biomarkers, which may be used to indicate subtle changes at the subcellular level, may help overcome these limitations. Neurochemical biomarkers have been used for decades in the human health sciences and are now gaining increased attention in the environmental realm. In the present review, the applications and implications of neurochemical biomarkers to the field of ecotoxicology are discussed. The review provides a brief introduction to neurochemistry, covers neurochemical-based adverse outcome pathways, discusses pertinent strengths and limitations of neurochemical biomarkers, and provides selected examples across invertebrate and vertebrate taxa (worms, bivalves, fish, terrestrial and marine mammals, and birds) to document contaminant-associated neurochemical disruption. With continued research and development, neurochemical biomarkers may increase understanding of the mechanisms that underlie injury to ecological organisms, complement other measures of neurological health, and be integrated into risk assessment practices.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Methylmercury egg injections: part 2--pathology, neurochemistry, and behavior in the avian embryo and hatchling

Methylmercury (MeHg) is a toxic metal that has been frequently linked to neurochemical alterations, brain lesions, neurobehavioral changes, and reproductive impairments in wild and captive birds. Much less is known about the effects of MeHg on the developing avian brain and resulting effects on hatchling behavior. The objective of this work was to use air cell injection studies to investigate the effect of in ovo MeHg exposure on brain pathology and four neurochemical biomarkers (N-methyl-d-aspartate (NMDA) receptor, γ-aminobutyric acid (GABA) receptor, glutamine synthetase (GS) and glutamic acid decarboxylase (GAD)) that have previously been studied in wild birds, and on hatchling righting response, balance, and startle response. In a series of six studies, we exposed white leghorn chicken and Japanese quail embryos to methylmercury chloride (MeHgCl) (range: 0-6.4μg/g egg) via egg injection on embryonic day (ED) 0 and measured receptor levels and enzyme activity at different stages of embryonic (days 11, 14, and 19 in chicken; day 15 in quail) and hatchling (day 1 and day 7) development, and in whole brain or discrete brain regions (cerebrum, cerebellum, optic lobe). We assessed neurobehaviors on post hatch (PH) days 1 and 7. Despite accumulating relatively high levels of Hg in the brain, embryos and hatchlings did not consistently display neurochemical changes consistent with those seen in wild birds and laboratory mammals. Hatchlings also did not demonstrate behavioral alterations. Pathology did not indicate a difference in occurrence and types of lesions between control and dosed birds. These findings suggest that in ovo MeHg exposure alone may not be responsible for neurological impacts in bird. This work draws attention to factors, such as age and species, that may influence responses to MeHg in birds.

Mercury exposure and neurochemical biomarkers in multiple brain regions of Wisconsin river otters (Lontra canadensis)

River otters are fish-eating wildlife that bioaccumulate high levels of mercury (Hg). Mercury is a proven neurotoxicant to mammalian wildlife, but little is known about the underlying, sub-clinical effects. Here, the overall goal was to increase understanding of Hg's neurological risk to otters. First, Hg values across several brain regions and tissues were characterized. Second, in three brain regions with known sensitivity to Hg (brainstem, cerebellum, and occipital cortex), potential associations among Hg levels and neurochemical biomarkers [N-methyl-D-aspartic acid (NMDA) and gamma-aminobutyric acid (GABAA) receptor] were explored. There were no significant differences in Hg levels across eight brain regions (rank order, highest to lowest: frontal cortex, cerebellum, temporal cortex, occipital cortex, parietal cortex, basal ganglia, brainstem, and thalamus), with mean values ranging from 0.7 to 1.3 ug/g dry weight. These brain levels were significantly lower than mean values in the muscle (2.1 ± 1.4 ug/g), liver (4.7 ± 4.3 ug/g), and fur (8.8 ± 4.8 ug/g). While a significant association was found between Hg and NMDA receptor levels in the brain stem (P = 0.028, rp = -0.293), no relationships were found in the cerebellum and occipital cortex. For the GABA receptor, no relationships were found. The lack of consistent Hg-associated neurochemical changes is likely due to low brain Hg levels in these river otters, which are amongst the lowest reported.

Elevated mercury exposure and neurochemical alterations in little brown bats (Myotis lucifugus) from a site with historical mercury contamination

Despite evidence of persistent methylmercury (MeHg) contamination in the South River (Virginia, USA) ecosystem, there is little information concerning MeHg-associated neurological impacts in resident wildlife. Here we determined mercury (Hg) concentrations in tissues of insectivorous little brown bats (Myotis lucifugus) collected from a reference site and a MeHg-contaminated site in the South River ecosystem. We also explored whether neurochemical biomarkers (monoamine oxidase, MAO; acetylcholinesterase, ChE; muscarinic acetylcholine receptor, mAChR; N-methyl-D-aspartate receptor, NMDAR) previously shown to be altered by MeHg in other wildlife were associated with brain Hg levels in these bats. Concentrations of Hg (total and MeHg) in tissues were significantly higher (10-40 fold difference) in South River bats when compared to reference sites. Mean tissue mercury levels (71.9 ppm dw in liver, 7.14 ppm dw in brain, 132 ppm fw in fur) in the South River bats exceed (sub)-clinical thresholds in mammals. When compared to the South River bats, animals from the reference site showed a greater ability to demethylate MeHg in brain (33.1% of total Hg was MeHg vs. 65.5%) and liver (8.9% of total Hg was MeHg vs. 50.8%) thus suggesting differences in their ability to detoxify and eliminate Hg. In terms of Hg-associated neurochemical biomarker responses, interesting biphasic responses were observed with an inflection point between 1 and 5 ppm dw in the brain. In the reference bats Hg-associated decreases in MAO (r = -0.61; p < 0.05) and ChE (r = -0.79; p < 0.01) were found in a manner expected but these were not found in the bats from the contaminated site. Owing to high Hg exposures, differences in Hg metabolism, and the importance of the aforementioned neurochemicals in multiple facets of animal health, altered or perhaps even a lack of expected neurochemical responses in Hg-contaminated bats raise questions about the ecological and physiological impacts of Hg on the bat population as well as the broader ecosystem in the South River.

Multiple metals exposure and neurotoxic risk in bald eagles (Haliaeetus leucocephalus) from two Great Lakes states

In the present study, the authors determined concentrations of several elements (As, Cd, Co, Cu, Cr, Mn, Pb, Sb, Zn) in the brains and livers of 46 bald eagles (Haliaeetus leucocephalus) from two Great Lakes states, Michigan and Minnesota. To explore whether exposures are of neurological concern, the authors assessed their associations with neurochemical receptors (N-methyl-D-aspartate [NMDA] and γ-aminobutyric acid A [GABA(A)]) and enzymes (glutamine synthetase [GS] and glutamic acid decarboxylase [GAD]) that play critical roles in vertebrate neurobehavior and reproduction. For most elements, levels in the livers and brains did not differ between region and gender. Hepatic Pb levels averaged 33.1 ppm (dry wt), 30.4% of all carcasses exceeded proposed avian Pb thresholds (>26.4 ppm), and in 30.8% of the birds examined evidence of Pb pellets or fragments was found. Significant changes in the activities of GS and GAD were related to brain concentrations of several metals (Pb, Cd, Co, Cu, Zn). No relationships were found among any of the nine elements and NMDA or GABA(A) receptor levels. When combined with the authors' previous study on these same eagles that showed Hg-associated alterations in GS, GAD, and NMDA receptor levels, the present research suggests that bald eagles are exposed to various elements, especially Pb and Hg, that are capable of causing changes in GABAergic and glutamatergic neurotransmission. The functional significance of these neurochemical changes warrants attention.

Evaluating the potential of effluents and wood feedstocks from pulp and paper mills in Brazil, Canada, and New Zealand to affect fish reproduction: chemical profiling and in vitro assessments

This study investigates factors affecting reproduction in fish exposed to pulp and paper mill effluents by comparing effluents from countries with varying levels of documented effects. To explore the hypothesis of wood as a common source of endocrine disrupting compounds, feedstocks from each country were analyzed. Analyses included in vitro assays for androgenic activity (binding to goldfish testis androgen receptors), estrogenic activity (yeast estrogen screen), and neurotransmitter enzyme inhibition (monoamine oxidase and glutamic acid decarboxylase). Chemical analyses included conventional extractives, known androgens, and gas chromatograph index (GCI) profiles. All effluents and wood contained androgenic activity, particularly in nonpolar fractions, although known androgens were undetected. Effluents with low suspended solids, having undergone conventional biotreatment had lower androgenic activities. Estrogenic activity was only associated with Brazilian effluents and undetected in wood. All effluents and wood inhibited neurotransmitter enzymes, predominantly in polar fractions. Kraft elemental chlorine free mills were associated with the greatest neurotransmitter inhibition. Effluent and wood GCI profiles were correlated with androgenic activity and neurotransmitter enzyme inhibition. Differences in feedstock bioactivities were not reflected in effluents, implying mill factors mitigate bioactive wood components. No differences in bioactivities could be discerned on the basis of country of origin, thus we predict effluents in regions lacking monitoring would affect fish reproduction and therefore recommend implementing such programs.

Extracts from hardwood trees used in commercial paper mills contain biologically active neurochemical disruptors

Following on our discovery that pulp and paper mill effluents can interact with, and disrupt, various neurotransmitter receptors and enzymes important to fish reproduction, we tested wood and bark extracts of 14 Eastern North American hardwood trees used in pulp and paper production. Radioligand binding to neurotransmitter receptors, including the dopamine-2 receptor (D2), the gamma aminobutyric acid receptor A (GABA(A)), N-methyl-D-aspartic acid (NMDA) receptor, and muscarinic cholinergic receptor (mACh-R), were significantly changed following in vitro incubations with many but not all extracts. Activities of neurotransmitter-related enzymes monoamine oxidase (MAO), GABA-transaminase (GABA-T), acetylcholinesterase (AChE) and glutamic acid decarboxylase (GAD) were also significantly altered. Butternut wood extracts and the isolated compound juglone significantly inhibited the enzymatic activities of MAO and GAD which we suggest may be part of a mechanism that may negatively affect fish reproduction. Besides giving credence to the hypothesis that neuroactive compounds in pulp and paper effluent may originate in the trees used by mills, the results reported here also indicate important neuropharmacological activities in hardwoods which may help identify new sources of biologically active natural products.

Mercury exposure and neurochemical impacts in bald eagles across several Great Lakes states

In this study, we assessed mercury (Hg) exposure in several tissues (brain, liver, and breast and primary feathers) in bald eagles (Haliaeetus leucocephalus) collected from across five Great Lakes states (Iowa, Michigan, Minnesota, Ohio, and Wisconsin) between 2002-2010, and assessed relationships between brain Hg and neurochemical receptors (NMDA and GABA(A)) and enzymes (glutamine synthetase (GS) and glutamic acid decarboxylase (GAD)). Brain total Hg (THg) levels (dry weight basis) averaged 2.80 μg/g (range: 0.2-34.01), and levels were highest in Michigan birds. THg levels in liver (r(p) = 0.805) and breast feathers (r(p) = 0.611) significantly correlated with those in brain. Brain Hg was not associated with binding to the GABA(A) receptor. Brain THg and inorganic Hg (IHg) were significantly positively correlated with GS activity (THg r(p) = 0.190; IHg r(p) = 0.188) and negatively correlated with NMDA receptor levels (THg r(p) = -0245; IHg r(p) = -0.282), and IHg was negatively correlated with GAD activity (r(s) = -0.196). We also report upon Hg demethylation and relationships between Hg and Se in brain and liver. These results suggest that bald eagles in the Great Lakes region are exposed to Hg at levels capable of causing subclinical neurological damage, and that when tissue burdens are related to proposed avian thresholds approximately 14-27% of eagles studied here may be at risk.

Investigation of spatial trends and neurochemical impacts of mercury in herring gulls across the Laurentian Great Lakes

Herring gulls (Larus argentatus) bioaccumulate mercury (Hg) but it is unknown whether they are exposed at levels of neurological concern. Here we studied brain tissues from gulls at five Great Lakes colonies and one non-Great Lakes colony during spring of 2001 and 2003. Total brain Hg concentrations ranged from 0.14 to 2.0 microg/g (dry weight) with a mean of 0.54 microg/g. Gulls from Scotch Bonnet Island, on the easternmost edge of the Great Lakes, had significantly higher brain Hg than other colonies. No association was found between brain Hg concentration and [3H]-ligand binding to neurochemical receptors (N-methyl-D-aspartate, muscarinic cholinergic, nicotinic cholinergic) or nicotinic receptor alpha-7 relative mRNA expression as previously documented in other wildlife. In conclusion, spatial trends in Hg contamination exist in herring gulls across the Great Lakes basin, and herring gulls accumulate brain Hg but not at levels associated with sub-clinical neurochemical alterations.

Accumulation of mercury and selenium in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) from Nova Scotia, Canada

Total Hg, methyl-Hg (MeHg) and Se levels were measured in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) carcasses collected from Nova Scotia, Canada. Total Hg concentrations in the otters' brain were highly variable, ranging from 0.3 to 18.0 microg/g dw and were significantly higher in animals caught from inland areas of the province versus coastal animals. Similarly, inland otters contained significantly more MeHg in the brain than did coastal otters. MeHg was highly correlated with total Hg in both inland and coastal otters and represented on average approximately 82% of the total Hg. Selenium concentrations in the otter brain ranged from 1.0 to 7.8 microg/g dw but unlike Hg, there was no significant difference in Se levels between inland and coastal otters. There was a significant positive relationship between Se and total Hg concentrations in the otters with the molar ratio of Se:Hg approximately 1:1 for animals having an Hg concentration>18 nmol/g dw. The non-random sampling protocol for the mink precluded extensive statistical analysis of the data. However, unlike otters, virtually all (i.e. 98%) of the total Hg in mink brain was present as MeHg in both inland and coastal mink. Also unlike the otter results, Se concentrations showed no relationship with either total or MeHg in both inland and coastal mink. The data suggest that mink and otters may have different mechanisms for managing high levels of Hg in the brain.

Pulp and paper mill effluents contain neuroactive substances that potentially disrupt neuroendocrine control of fish reproduction

Here we show for the first time that components of pulp and paper mill effluents contain neuroactive substances that may impair fish reproduction. Grab samples of primary and secondary effluent were obtained from a representative pulp and paper mill in Eastern Canada. Effluents were fractionated using classic polarity and polyphenolic extraction methods into solvents of selected polarities (water, ethanol, ethyl acetate, and hexane). By means of in vitro, competitive assays on goldfish (Carassius auratus) brain tissues, the extracts were screened for their ability to interact with enzymes and receptors involved in gamma-aminobutyric acid (GABA), dopamine, glutamate, and acetylcholine-dependent neurotransmission. These neurotransmission pathways have essential regulatory roles in fish reproduction. Radioligand binding to the following neurotransmitter receptors were significantly impacted following in vitro incubations with extracts (percentage change from controls indicated in brackets): dopamine-2 (D2; 21-48% increase), GABA(A) receptor binding (65-67% decrease and 189% increase), N-methyl-o-aspartic acid (NMDA; 26-75% decrease), and muscarinic cholinergic (mACh; 42% increase). Activities of the following neurotransmitter-related enzymeswere significantly impacted: monoamine oxidase (MAO; 14-48% decrease), GABA-transaminase activity (33% decrease and 21-69% increase), and acetylcholinesterase (AChE; 21-50% decrease). No changes in glutamic acid decarboxylase (GAD) activity were detected. These findings provide a novel and plausible mechanism by which pulp and paper mills effluents impair fish reproduction by interacting with neurotransmitter systems. Furtherwork is required to identify the active compounds and explore whether these changes occur in vivo.

Mercury concentrations in wild mink (Mustela vison) and river otters (Lontra canadensis) collected from eastern and Atlantic Canada: relationship to age and parasitism

Total mercury (Hg) concentrations were measured in the fur, brain and liver of wild mink (Mustela vison) and river otters (Lontra canadensis) collected from eastern and Atlantic Canada. Total Hg concentrations in fur were strongly correlated with levels in the brain and liver. There was no difference in tissue concentrations between male and female mink; however, female otters had significantly higher fur, brain and liver Hg levels than males. Similarly, there was not a significant relationship between Hg concentration and age of mink, whereas in otters, Hg concentrations in all three tissues decreased significantly with age. In both species, only a very small percentage of the variability in Hg concentration was explained by age. After adjusting the data for site-to-site differences in Hg levels, Hg concentrations in the fur of mink infected by the parasite, Dioctophyma renale, were found to be significantly higher than Hg levels in uninfected mink.

Distribution of mercury in several environmental compartments in an aquatic ecosystem impacted by gold mining in northern Colombia

Mercury (Hg) used in gold amalgamation is a major source of contamination in developing countries. Water, sediments, plankton, fish, and human samples from Grande Marsh, a Hg-polluted marsh located in the south of Bolívar, municipality of Montecristo, Colombia, were collected during both the rainy and the dry seasons (2003-2006), at three different sampling sites, and analyzed for total Hg (T-Hg) content. Water, sediment, seston, phytoplankton, and zooplankton T-Hg concentrations were 0.33 +/- 0.03 microg/L, 0.71 +/- 0.03, 1.20 +/- 0.06, 0.52 +/- 0.03, and 0.94 +/- 0.05 microg/g dry weight (wt), respectively. T-Hg levels in these compartments were highly pair-correlated (p < 0.05), and for all of them, except sediments, greater values were found during the dry season. Significant differences were observed for T-Hg concentrations in fish according to their trophic position. Average highest T-Hg values were found in carnivorous species such as Caquetaia kraussi (1.09 +/- 0.17 microg/g fresh wt), Hoplias malabaricus (0.58 +/- 0.05 microg/g fresh wt), and Plagioscion surinamensis (0.53 +/- 0.07 microg/g fresh wt), whereas the lowest were detected in noncarnivorous species such as Prochilodus magdalenae (0.157 +/- 0.01 microg/g fresh wt). In those fish species where seasonal comparisons were possible, specimens captured during the dry season had greater T-Hg levels in muscle. Although the T-Hg mean level for all fish samples (0.407 +/- 0.360 microg/g fresh wt) did not exceed the recommended limit ingestion level, risk assessment based on the hazard index suggested that a fish intake of 0.12 kg per day (a small carnivorous specimen) could increase the potential health effects related to Hg exposure in the local human population, whose hair T-Hg median value was 4.7 microg/g, and presented a low but significant correlation with fish consumption (r = 0.250, p = 0.016). In short, Hg pollution from gold mining around Grande Marsh has permeated the food web, and currently levels in fish represent a serious concern for human health.

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.

Polychlorinated biphenyls, organochlorinated pesticides, and polybrominated diphenyl ethers in the cerebral cortex of wild river otters (Lontra canadensis)

We measured the levels of ortho-substituted polychlorinated biphenyls (PCB), organochlorinated pesticides (OCP), and polybrominated diphenyl ethers (PBDE) in the cerebral cortex of river otters (Lontra canadensis) trapped from Ontario and Nova Scotia between 2002 and 2004. The mean concentration of total PCBs was 70.9+/-12.1 ng/g l.w., and congeners 153, 180 and 138 accounted for nearly 60% of the sum. The mean concentration of total OCPs was 21.2+/-3.7 ng/g l.w., and hexachlorobenzene (32.6% of total) and DDE (28.1%) accounted for the majority. The mean concentration of total PBDEs was 3.2+/-0.6 ng/g l.w., and congeners 99 (44.9%), 153 (30.5%), and 100 (24.7%) were measured at the indicated percentages. There was no relationship between these residue data and concentrations of brain mercury or neurochemical receptors and enzymes as determined in earlier studies on these same animals.

Mink as a sentinel species in environmental health

The concept of "sentinel species" is important in the environmental health sciences because sentinel species can provide integrated and relevant information on the types, amounts, availability, and effects of environmental contaminants. Here we discuss the use of mink (Mustela vison) as a sentinel organism by reviewing the pertinent literature from exposure- and effects-based studies. The review focuses on mercury (Hg) and polychlorinated biphenyls (PCBs), as they are persistent, ubiquitous, and bioaccumulative contaminants of concern to both humans and wildlife. Mink are widely distributed, abundant, and regularly trapped in temperate, aquatic ecosystems, and this makes them an excellent model to address issues in environmental pollution on both temporal and spatial scales. As a high-trophic-level, piscivorous mammal, mink can bioaccumulate appreciable concentrations of certain pollutants and have been shown to be sensitive to their toxic effects. The husbandry and life history of mink are well understood, and this has permitted controlled dosing experiments to be conducted using animals reared in captivity. These manipulative studies have yielded important quantitative information on exposure-response relationships and benchmarks of adverse health effects, and have also allowed the cellular mechanisms underlying toxic effects to be explored. Furthermore, the data accrued from the laboratory continue to validate observations made in the field. Research derived from mink can bridge and integrate multiple disciplines, and the information collected from this species has allowed environmental health scientists to better understand and characterize pollution effects on ecosystems.