G9 (II) Mercury exposure in wildlife

Little is known about mercury bioaccumulation in strictly terrestrial ecosystems that are remote from point-sources of contamination. Here we show that mercury concentrations in the leaf litter and organic soil layer increased with elevation in a densely forested watershed of New York’s Catskill Mountains. Closely-related forest thrushes (genus Catharus) arrayed along this elevational gradient also showed a significant positive relationship between blood mercury concentration and elevation. This spatial pattern may have important health and conservation implications for Bicknell’s Thrush (C. bicknelli), which is restricted exclusively to forests above 1000 m in the northeastern United States. Bicknell’s Thrush showed significantly greater blood mercury concentrations than lower elevation congeners, Hermit Thrush (C. guttatus) and Veery (C. fuscescens). Additionally, blood mercury levels declined with time during the breeding season for all species, indicating that early season thrushes either carry mercury burdens from their winter grounds or consume a diet higher in mercury during the early part of the breeding season (1 May – 14 June). We analyzed samples from wintering Bicknell’s Thrush at multiple sites on their Hispaniolan wintering grounds to further explore the possibility of winter grounds carry-over, and found the highest blood mercury levels of any birds in this study. We also documented wide, site-specific variance, potentially reflecting local deposition patterns. We will be modeling Hispaniolan weather patterns and sources of local mercury outputs to determine site-specific mercury deposition patterns for the island; this will be the first such mercury-monitoring data for a Caribbean island. We additionally analyzed mercury concentrations in thrush dietary items from both the New York and Hispaniolan sites, including spiders, carabid beetles and a species of strictly terrestrial salamander, to elucidate food web patterns of biomagnification.

The objective of this study was to quantify mercury availability for each subspecies of Nelson’s Sparrows (Ammodramus nelsoni) at sites throughout its annual cycle. We sampled blood, breast feathers and the first primary feather from sparrows during two non-breeding seasons in salt marshes near Wrightsville Beach, NC, USA and during two breeding seasons in wetlands near Grand Forks, ND, USA (A. n. nelsoni) and James Bay, ON, Canada (A. n. alterus). Sparrows were sampled at Grand Manan Island, NB, Canada (A. n. subvirgatus) and J. Clark Salyer National Wildlife Refuge (near Upham, ND, USA; A. n. nelsoni) during one breeding season. We pooled data within sites sampled in two seasons because there was no significant variation due to season in mercury levels for any tissue. Primary feather mercury was consistently highest of the three tissues regardless of site and was significantly higher in sparrows from Grand Forks and Grand Manan than those sampled during the non-breeding period. Breast feather mercury was higher in non-breeding sparrows than in breeding sparrows at both James Bay and Grand Forks. Blood mercury was significantly higher at Grand Forks than any other site and on average was 2.6 times as high as that for the second A. n. nelsoni site approximately 260 km away. Inversely, blood mercury from non-breeding sparrows was significantly lower than at any other site, and average mercury levels were only 13% of those at Grand Forks. Significantly lower blood mercury and higher breast feather mercury in sparrows near Wrightsville Beach indicate that mercury exposure is lower at this non-breeding site than at any of the sampled breeding locations. High levels of mercury availability near Grand Forks appear to be anomalous and are especially intriguing since selenium levels are also high in this area. Selenium has been suggested to decrease the magnitude of bioaccumulation of methylmercury and is also thought to alleviate mercury toxicity at intermediate levels of selenium exposure. Further research is necessary to understand why both mercury and selenium levels are elevated at this site and why high selenium levels do not appear to be dampening methylmercury bioaccumulation in this area. Our data provide a better understanding of how and where Hg exposure may be a threat to Nelson’s Sparrows and other birds with obligate ties to aquatic systems throughout their annual cycles.

Recent estimates of the mercury cycle feature that ~60 % of all mercury is found in terrestrial environments, making it an important factor of transfer and bioaccumulation through terrestrial food chains.[1] However, most research has been devoted to aquatic environments, and little information is available for terrestrial environments, with information about Hg species distribution among animal tissues very scarce, and even less known about the interaction of Hg with biomolecules.

In the present study, our case of study is the terrestrial biota is the area of the recently closed Almadén mercury mine (Ciudad Real province, Southern Spain). This is the largest (285,000 t of Hg) and the oldest (more than 2,000 years) mercury mine/refining operation site in the world. Exposure of animals to mercury can occur through food, water or direct ingestion/licking of soil. Here, we studied liver and kidney tissue of red deer and wild boar from the area of the Almadén mercury mine in Spain obtained through regular shooting allocations.

Mercury speciation analysis was done using GC coupled to AFS or ICP-MS. 90% of Hg in liver and kidney was inorganic mercury. Concentration factors between carnivorous and herbivorous were calculated and they were higher for MeHg than for inorganic mercury, but mercury accumulation in terrestrial food chains was less expressed than in aquatic ecosystems. Hg containing biomolecules have been studied very rarely to date. Here we present the first data on Hg biomolecules in terrestrial animal tissues. As an initial step towards their characterization, the fractionation of Hg binding biomolecules was investigated by size exclusion chromatography-ICP-MS. Similar profiles are observed in red deer and wild boar tissues. In kidney, there is a single peak at high molecular weight (MW) protein retention time. However, in liver, Hg is distributed in two peaks, Hg is bound both to high and low MW proteins, and co-elution of Hg with Fe, Ni, Zn and Cu was observed.

[1] Fitzgerald, W.F.; Mason, R. P. In Global and Regional Cycles: Sources, Fluxes and Mass balances; Baeyens, W., Ebinghaus, R., Vasiliev, O. Eds.; Kluwer Academic Publishers: Dordrecht, Boston, London, 1996; pp 85-108.

Concentrations of mercury (Hg) have risen substantially in the past decades in apical predators (e.g., polar bears, beluga whales) in the Arctic region. The concentrations of total methylmercury (MeHg), the most bioavailable form of Hg for biomagnification and neurotoxicity; in beluga typically range from 0.35 to 3.16 µg g^-1 (wet wt.) in muscle and 0.11 to 6.13 µg g^-1 (wet wt.) in liver, frequently well exceeding the Canadian guideline of 0.5 µg g^-1 (wet wt.) for MeHg in fish for human consumption. This raises concerns over the health of marine mammals as well as the health of Northerners who consume these animals as part of their traditional diet. With the recent development of a new high performance liquid chromatography – inductively coupled plasma mass spectrometry (HPLC-ICP-MS) technique for MeHg speciation, here we report, for the first time, the distribution of various MeHg species, as well as selenium (Se), in different tissues (e.g., muscle, liver, kidneys and brain) of beluga from the Beaufort Sea region. Our results show that the dominant species of MeHg in all the tissues analyzed is MeHg-cysteine complex, a specific form of MeHg that is believed to be able to transport across the blood-brain barrier. Another MeHg-thiol complex, MeHg-glutathione complex, was also detected in the muscle and liver tissues, supporting the involvement of glutathione in the in vivo detoxification of MeHg. Furthermore, a profound inorganic Hg peak was detected in the liver at the same retention time as a Se peak, suggesting the presence of a Hg-Se compound, most likely an inorganic Hg complex with a seleno-amino acid. Our results provide the first analytical support that the binding of MeHg with glutathione and Se may have protected beluga from the toxic effect of high concentrations of MeHg in their body. Further studies are undergoing to probe the identity of this Hg-Se compound, and to study the uptake and detoxification mechanisms of MeHg at various trophic levels in the Arctic marine ecosystems. Such molecular level understanding will shed new light on how Arctic animals are coping with Hg contamination and on the development of remediation strategies.