S11 (I) Ecotoxicology of mercury

Monday, 25 July, 2011

MS11-O1 — 8:30-8:45
Authors: CRISTOL, Daniel A.1, EVERS, David C.2
(1) College of William & Mary, dacris@wm.edu; (2) BioDiversity Research Institute.

There is a long history of mercury dosing studies going back a half-century, but many have been designed to determine lethal concentrations, whereas today’s ecotoxicologist is often interested in establishing whether sub-lethal injury has occurred. There have been some recent experimental attempts to determine sub-lethal effects of lower doses of mercury on behavioral and physiological indicators of fitness, including endocrine disruption, reproductive physiology, and immunocompetence. The goal of establishing robust lowest adverse effects levels for mercury in birds is still several studies away, but important progress has been made. The goal of determining mercury concentrations below which effects are unlikely is extremely important both for determining where to focus limited restoration funding and what levels of atmospheric pollution are acceptable. The main hurdles to defining the low effects level for mercury in birds has been interspecific and interindividual variability, inconsistent methods between studies, and most importantly, difficulty translating the results of captive dosing studies to effects in free-living birds. It is becoming clear that the effects of mercury on birds may only be detectable when other environmental stressors are present, such as adverse weather, predators or food-limitation, conditions often missing from experimental dosing studies. We will discuss recent progress towards unifying the results of studies of environmental versus experimental mercury exposure in an attempt to narrow down the range of estimates for effects of environmental mercury on free-living birds.

MS11-O2 — 8:45-9:00
Authors: EVERS, David1, CRISTOL, Daniel2
(1) BioDiversity Research Institute, david.evers@briloon.org; (2) College of William and Mary.

Understanding the effects of environmental mercury on wildlife is an ongoing scientific challenge that has policy and management ramifications for avian conservation. For decades, the guideline for the toxicity of methylmercury to wild birds was based on laboratory studies of one species, the mallard. While the relationship between experimental and environmental doses still remain relatively undefined, the single species approach also did not consider differences in species sensitivities – a distinction that is now quantitatively realized, especially among broad foraging guilds, such as granivores, invertivores and piscivores. Point estimate toxicity concentrations, as those defined by lowest observed adverse effect levels (LOAELs), are often used as an approach to determine changes measured in the target organism that are significantly distinguishable from the control. Fundamental reasons for improving on the use of LOAELs are that they do not fully reflect the magnitude of the biological effect. We will present (1) LOAEL data that illustrate taxonomic differences using reproductive endpoints from wild bird populations as well as (2) an approach using effects concentrations (ECx) that integrate demographic and natural history knowledge that more fully represent injury from environmental mercury loads. The shift to acknowledge the importance of studies on wild populations, differences in sensitivity within avian taxa, and the need for a higher resolution approach toward assessing the full adverse effects of methylmercury toxicity is timely.

MS11-O3 — 9:00-9:15
Authors: BURGESS, Neil1, BRAUNE, Birgit1
(1) Environment Canada, neil.burgess@ec.gc.ca

Gary Heinz and colleagues at the USGS recently developed a new method for comparing the sensitivity of developing embryos of different bird species to methylmercury (MeHg) toxicity (Heinz et al. 2009). We adopted this method to compare the toxicity of MeHg injected into the eggs of four seabirds: arctic tern, Atlantic puffin, herring gull and thick-billed murre. Freshly-laid seabird eggs were collected from colonies in Newfoundland and Nunavut, Canada. The eggs were incubated artificially until day 4 of development, and then injected with one of a range of doses of MeHg that produced an environmentally relevant range of egg concentrations. The eggs were then incubated until the embryos started to hatch by breaking the eggshell (pipping) or died. Dead eggs were opened and each embryo’s stage of development was determined. Many embryos died within a couple of days of pipping. We assumed this was an artifact of artificial incubation, so we considered all embryos that survived 90% of incubation to have survived, for the purpose of calculating an LC50. We will present the LC50 for each species and the distribution of the stages of development of the embryos that died for each dose level. We will also present the concentrations of mercury, MeHg and selenium measured in some of the embryos. We will compare our results to those obtained by Heinz and coworkers, and will classify the four species as having low, medium or high sensitivity to MeHg toxicity.

MS11-O4 — 9:15-9:30
Authors: LEMELIN, Sarah1, CRISTOL, Daniel1, BRADLEY, Eric 1, RAMOS, Claire1
(1) The College of William and Mary, sarah.lemelin@gmail.com

Mercury is a ubiquitous environmental contaminant associated with a host of adverse effects in wild birds. Although songbirds accumulate mercury at rates equivalent to well-studied species, the effects of mercury bioaccumulation in songbirds remain understudied. Songbirds are an important part of many ecosystems and a growing number of species are experiencing precipitous declines. Little is known about mercury’s effect on endocrine physiology, yet mounting evidence indicates that mercury may disrupt the function of the Hypothalamic-Pituitary-Adrenal (HPA) and Hypothalamic-Pituitary-Thyroid (HPT) axes. The HPA and HPT axes play fundamental physiological roles in stress responses, metabolic activity, development, and reproduction. Hence, proper functioning of these endocrine systems is imperative in maximizing individual fitness. Correlations from studies of environmental exposure suggest that mercury may alter levels of the primary avian stress hormone, corticosterone, as well as thyroid hormones T3 and T4. Thus, mercury exposure may compromise fitness through deregulation of the HPA and/or HPT axes. Adult zebra finches, a model system songbird, dosed with 0, 0.5, and 1.0 ppm dietary methylmercury (environmentally relevant levels) were sampled for corticosterone after 10 weeks. Birds were re-sampled approximately 25 weeks later while caring for late-stage fledglings. Corticosterone was not statistically significantly affected by mercury treatment. However, there were indications of a slight decrease in corticosterone with increasing mercury exposure. There was no effect of mercury exposure on total T3 (a thyroid hormone) levels, although a highly significant effect of sex was detected. A sex-based difference in T3 concentration in reproductively active songbirds has not been reported in the literature. There was no significant effect of mercury exposure on another thyroid hormone, T4, however, females in the high dose group had higher concentrations of the hormone than control or low-dose females. As T4 facilitates the onset of metabolically costly seasonal processes, increased concentrations in reproductively active birds may be maladaptive and additional research into possible mechanisms is needed. We are currently investigating the effects of mercury on T3 and T4 in juvenile and nestlings, which have shown responses to environmental mercury doses.

MS11-O5 — 9:30-9:45
Authors: ACKERMAN, Josh1, EAGLES-SMITH, Collin A1
(1)US Geological Survey, jackerman@usgs.gov

Methylmercury is a potent neurotoxin, and can have effects on birds throughout the breeding cycle. We examined both mercury bioaccumulation and bird reproduction in wetlands surrounding the San Francisco Bay Estuary and found impaired reproduction in several species and lifestages. Upon arrival within the Estuary, birds rapidly accumulated mercury prior to and during the breeding season. Forster’s Terns mercury concentrations increased by 3-fold within the 2 months prior to breeding, resulting in 48% of the population being considered at risk (>3 µg/g wet weight in blood). We found sublethal effects of mercury on adult birds, including demethylation of mercury in bird livers above 8.5 µg/g dry weight. Methylmercury concentrations in parents were strongly correlated with concentrations in eggs, indicating maternal transfer of mercury was proportional to adult concentrations. In Forster’s Terns, we found that: 1) failed-to-hatch eggs and abandoned eggs had higher mercury concentrations than randomly sampled eggs, 2) the likelihood of an embryo being malpositioned increased with egg mercury concentrations, 3) the probability of an egg successfully hatching decreased with egg mercury concentrations, and 4) the probability of nest survival decreased with egg mercury concentrations. For those eggs that hatched, resulting chicks were still vulnerable to the effects of residual in ovo mercury exposure, especially shortly after hatching when maternally deposited mercury levels were still relatively high. Thereafter, mercury concentrations in chicks rapidly declined as chicks aged and diluted their body burden of mercury through growth and depuration into growing feathers. In Black-necked Stilts, we found that dead chicks had higher mercury concentrations than live, randomly sampled chicks of similar young age (<7 days old). Altogether, these results suggest that mercury contamination is currently impairing bird reproduction with San Francisco Bay.

MS11-O6 — 9:45-10:00
Authors: EAGLES-SMITH, Collin1, ACKERMAN, Josh1
(1) US Geological Survey, ceagles-smith@usgs.gov

Waterbirds are at particularly high risk to mercury (Hg) toxicity because they forage in wetland habitats where methylmercury production can be elevated, they often occupy a high trophic position in their respective food chains, and they are especially sensitive to the neurological impairment caused by mercury. However, we still lack thorough insight regarding the relative importance of various factors regulating bioaccumulation in waterbird communities. Thus, understanding the processes contributing to elevated mercury exposure in waterbirds is important for identifying populations at risk, as well as for developing management strategies to reduce exposure. In a multi-year effort, we evaluated mercury bioaccumulation among different trophic guilds of breeding, estuarine waterbirds, and assessed the habitat, trophic, and temporal factors associated with mercury exposure during the breeding season. Although there was a general trend of increasing mercury concentrations with trophic position, we found that foraging habitat was a far more important driver of avian mercury bioaccumulation than trophic position. Through a combination of radio telemetry, stable isotopes, and diet analyses, we found that birds foraging in muted-tidal, pickleweed marshes, and seasonal salt ponds had higher mercury exposure than those foraging in other habitats, such as tidal mudflats, sloughs, and open bays. Mercury concentrations in prey fish varied similarly among habitats, with those from seasonally-flooded and high salinity evaporation ponds generally having the highest concentrations. Importantly, mercury concentrations in prey fish varied substantially over time in these habitats. Prey fish concentrations increased by 40% from March - June, then declined by 40% between June and August. As a result, Hg exposure in Forster’s terns (Sterna forsterii) was greatest when 74% of nesting birds were developing eggs and initiating their nests. This work suggests that the magnitude and timing of exposure to mercury may present substantial risk to waterbird reproduction, and highlights the need for additional research on Hg effects in the wild.

MS11-O7 — 10:00-10:15
Author: RUTKIEWICZ, Jennifer1
(1) University of Michigan, rutkiewj@umich.edu

Mercury (Hg) is an established neurotoxicant that can induce neurobehavioral changes that may impact survival and reproduction in wild fish-eating birds. Field and laboratory studies have identified Hg associated brain lesions, behavioral changes, and reproductive impairments in several avian species. Before inducing overt toxicity, even low levels of Hg bind to protein thiols and disrupt a variety of cellular components, including receptors, enzymes, and transporters involved in neurotransmission. Such biochemical changes relate directly to brain function and because they typically precede overt neurotoxicity, offer a sensitive indication of change before the brain is permanently damaged. Recent work has demonstrated the value of these changes as biomarkers of Hg’s earliest effects on the brain in a variety of fish-eating birds, and the goal of this presentation is to review these studies and provide recommendations for future work. Briefly, a study of bald eagles and common loons collected across Canada found associations between brain Hg and muscarinic cholinergic and N-methyl-D-aspartic acid (NMDA) receptor levels. A more recent study of bald eagles collected across the US Great Lakes found a similar association between brain Hg and the NMDA receptor, as well as new relationships with the enzymes glutamic acid decarboxylase and glutamine synthetase. However, studies of wild herring gulls and common loons that experience relatively low-level Hg exposure failed to find associations between brain Hg and various neurochemical receptors, thus suggesting that a threshold for neurological change may exist. Research currently focuses on relating tissue Hg burdens in wild birds to neurochemistry to determine toxic thresholds for risk assessment. Laboratory studies using chicken embryos are now underway to validate new biomarkers, identify Hg thresholds for neurochemical change, and to elucidate the relationship between changes in neurochemistry and changes in ecologically important behaviors. In addition to being applied to assess risk for Hg induced neurotoxicity and related behavioral changes, studies of neurochemical biomarkers in wildlife increase our knowledge of the subclinical changes involved in neurotoxicity and help explain species differences in Hg responses, therefore expanding our overall understanding of the mechanisms of Hg toxicity.

MS11-O8 — 10:15-10:30
Authors: SANDHEINRICH, Mark1, BHAVSAR, Satyendra2, BODALY, Drew3, DREVNICK, Paul4, PAUL, Eric5
(1) University of Wisconsin-La Crosse, sandhein.mark@uwlax.edu; (2) Ontario Ministry of Energy and Environment; (3) Penobscot River Mercury Study; (4) Université du Québec; (5) New York Department of Environmental Conservation.

Contamination of fish populations with methylmercury is common in the region of the Laurentian Great Lakes, primarily as a result of atmospheric deposition and methylation of inorganic mercury. Using mercury data from government monitoring agencies and information on tissue concentrations injurious to fish, we conducted a risk assessment of mercury to populations of walleye (Sander vitreus), northern pike (Esox lucius), smallmouth bass (Micropterus dolomieui), and largemouth bass (Micropterus salmoides) in the Great Lakes and in interior lakes, impoundments, and rivers of the Great Lakes region. The assessment included more than 43,000 measurements of mercury in fish from more than 2000 locations. The size of first reproduction of female fish of each species was selected as the standard-size fish for the risk assessment. Concentrations of methylmercury in standard-size fish were estimated from the relation between mercury concentration and total length of individual fish at each location and compared to toxicity reference values for mercury from the literature. The results suggest that from 8% (largemouth bass) to 44% (walleye) of the populations are at risk and exceeded calculated threshold tissue concentrations of 0.20 µg g-1 wet weight in the whole body. Populations of standard-size fish at 2-18% of sites are at high risk and exceeded 0.30 µg g-1 where significant injury is predicted to occur. Most populations at high risk were from interior lakes and impoundments. In the Great Lakes, only 3 of 67 sites had walleye and no sites had northern pike, smallmouth bass or largemouth bass that exceeded threshold concentrations. Large female fish make a greater contribution than small fish to total reproductive output and are also more likely to be at risk from mercury due to the positive relation between mercury concentrations and fish size. Many water bodies had fish slightly larger than the size of first reproduction with predicted mercury concentrations that exceeded threshold values, although concentrations in smaller, first-spawning fish did not. Our assessment is, therefore, conservative and a greater percentage of fish populations are potentially at risk of injury from methylmercury contamination. Conclusions about the percentage of sites with populations at risk should not be extrapolated to unsampled populations and to the region as a whole. However, results do indicate that fish populations at a substantive number of locations within the Great Lakes region are at risk from methylmercury contamination and would benefit from reduction in mercury concentrations.

Monday, 25 July, 2011