No abstract

The Clinch River is located in northeastern Tennessee (TN) and southwestern Virginia (VA) of the United States, and contains a diverse mussel assemblage of 46 extant species, including 20 species listed as federally endangered. To facilitate quantitative monitoring of the fauna, quadrat data were collected from 2004 to 2009 at 18 sites in the river, including 12 sites in TN and 6 sites in VA. Thirty‐eight mussel species were collected alive in total from quadrat samples taken annually at sites in the TN section of the river. Over the five‐year study period, mussel density averaged 25.5 m−2 at all sites sampled in TN. In contrast, mussel density averaged only 3.1 m−2 at sites sampled in VA. The best historical site in VA was Pendleton Island in Scott County, where mussel density was estimated as high as 25 m−2 in 1979, comparable to current densities recorded in TN. Mussel densities are now <1 m−2, indicating a collapse of the fauna. A severe reduction in mussel abundance has occurred in a 68‐km section of the river from St. Paul, VA, downstream to approximately Clinchport, VA (river kilometers 411.5‐343.3). While the environmental factors responsible for the faunal decline are largely unknown, they must have been severe and sustained to reduce such large populations to their current low levels. Long‐term water and habitat quality monitoring is needed to determine whether environmental degradation is still occurring in the river.

This study examines mercury exposure in bats across the northeast U.S. from 2005 to 2009. We collected 1,481 fur and 681 blood samples from 8 states and analyzed them for total Hg. A subset (n = 20) are also analyzed for methylmercury (MeHg). Ten species of bats from the northeast U.S. are represented in this study of which two are protected by the Endangered Species Act (ESA 1973) and two other species are pending review. There are four objectives in this paper: (1) to examine correlates to differences in fur–Hg levels among all of the sampling sites, including age, sex, species, and presence of a Hg point source; (2) define the relationship between blood and fur–Hg levels and the factors that influence that relationship including age, sex, species, reproductive status, and energetic condition; (3) determine the relationships between total Hg and MeHg in five common eastern bat species; and (4) assess the distribution of Hg across bat populations in the northeast. We found total blood and fur mercury was eight times higher in bats captured near point sources compared to nonpoint sources. Blood–Hg and fur–Hg were well correlated with females on average accumulating two times more Hg in fur than males. On average fur MeHg accounted for 86 % (range 71–95 %) of the total Hg in bat fur. Considering that females had high Hg concentrations, beyond that of established levels of concern, suggests there could be negative implications for bat populations from high Hg exposure since Hg is readily transferred to pups via breast milk. Bats provide an integral part of the ecosystem and their protection is considered to be of high priority. More research is needed to determine if Hg is a stressor that is negatively impacting bat populations.

Historical discharges of Hg into the South River near the town of Waynesboro, VA, USA, have resulted in persistently elevated Hg concentrations in sediment, surface water, ground water, soil, and wildlife downstream of the discharge site. In the present study, we examined mercury (Hg) levels in in little brown bats (Myotis lucifugus) from this location and assessed the utility of a non-destructively collected tissue sample (wing punch) for determining mitochondrial DNA (mtDNA) damage in Hg exposed bats. Bats captured 1 and 3 km from the South River, exhibited significantly higher levels of total Hg (THg) in blood and fur than those from the reference location. We compared levels of mtDNA damage using real-time quantitative PCR (qPCR) analysis of two distinct regions of mtDNA. Genotoxicity is among the many known toxic effects of Hg, resulting from direct interactions with DNA or from oxidative damage. Because it lacks many of the protective protein structures and repair mechanisms associated with nuclear DNA, mtDNA is more sensitive to the effects of genotoxic chemicals and therefore may be a useful biomarker in chronically exposed organisms. Significantly higher levels of damage were observed in both regions of mtDNA in bats captured 3 km from the river than in controls. However, levels of mtDNA damage exhibited weak correlations with fur and blood THg levels, suggesting that other factors may play a role in the site-specific differences.

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.