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G8 Mercury bioaccumulation and trophic transfer

Thursday, 28 July, 2011

RG8-P1 — 11:00-12:00 and 17:30-18:30
AVOIDANCE TESTS WITH EARTHWORMS FOR EVALUATING MERCURY BIOAVAILABILITY IN THREE TROPICAL SOIL CLASSES
Authors: CESAR, Ricardo1, PEREZ, Daniel2, COLONESE, Juan3, SILVA, Marianna3, BERTOLINO, Luiz Carlos4, EGLER, Silvia4, CASTILHOS, Zuleica4, POLIVANOV, Helena5, BIDONE, Edison6
(1) Federal Fluminense University (UFF), Niterói, RJ, Brazil., geo_ricardocesar@yahoo.com.br; (2) Brazilian Company for Agropecuary Research (EMBRAPA), Rio de Janeiro, RJ, Brazil; (3) Centre for Mineral Technology (CETEM), Rio de Janeiro, RJ, Brazil; (4) Centre for Mineral Technology (CETEM), RJ, Brazil; (5) Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil; (6) Federal Fluminense University (UFF), Niterói (RJ).

Mercury is a highly toxic metal, and well-known by its capacity of causing neurotoxic, teratogenic effects, as well as damages on respiratory and excretory systems. This work proposes the ecotoxicological assessment of three tropical soil classes (red ferralsol, yellow ferralsol and chernosol) artificially contaminated by divalent mercury, using avoidance tests with Eisenia andrei earthworms. Mercury concentrations to be used in the avoidance tests were established according to the surveillance results obtained with an acute bioassay, using a contact paper containing a solution with different mercury concentrations (OECD, 1984). To perform the avoidance tests, plastic boxes were divided in two equal sections containing contaminated and non-contaminated soil. The earthworms were put in the interface between the soils. After 48 hours of exposure, under a photoperiod of 12:6 (dark: light) and controlled temperature, the number of worms in the contaminated and non-contaminated soil was counted (ISO, 2002). When less than 20% of the organisms were not in the soil-test, it was considered that it could provoke significant avoidance responses. The concentrations of 10 and 15mg/kg revealed significant behavioral effects for the three soil classes (avoidance assay), indicating that those materials could be considered “habitats with limited functions” (ISO, 2002). Although the concentration of 5.0 mg/kg had not caused significant lethal effects under acute exposure, this dose was able to provoke significant avoidance responses on the organisms, for all tested soils. The concentration of 1.0 ppm did not cause significant avoidance responses in the red ferralsol, while in the chernosol and yellow ferralsol all the organisms avoided such concentration. In the ferrasol, the only concentration which did not cause avoidance responses was 0.5mg/kg. Those observations suggests that high levels of organic matter, in the red ferralsol, may have stimulated the reduction of mercury content in the soil solution, thus decreasing its bioavailability in comparison with the other soil classes. However, this hypothesis must be better investigated by using sequential or selective extraction methods. In conclusion, it is expected that those results can support the establishment of ecotoxicological reference values for tropical pedofauna, as well as future ecological risk assessments in areas contaminated by mercury.

RG8-P2 — 11:00-12:00 and 17:30-18:30
SENSIBLE SENTINELS: PRELIMINARY MERCURY DATA FOR DRAGONFLY NYMPHS (ODONATA: ANISOPTERA) ACROSS NORTHERN NEW ENGLAND CORROBORATE EXPECTED SPATIAL PATTERN
Authors: NELSON, Sarah J.1, CHEN, Celia Y.2, ROEBUCK, Hannah J. 2, ZOELLICK, Bill3
(1) University of Maine, sarah.nelson@umit.maine.edu; (2) Dartmouth College; (3) SERC Institute.

Mercury (Hg) is a potent neurotoxin that is delivered to ecosystems via deposition from a global atmospheric pool, and ultimately bioaccumulates in aquatic and terrestrial foodwebs. Around the Gulf of Maine, research sites in ‘pristine’ areas have fish and other biota that exceed thresholds considered safe for human consumption or wildlife protection. All Maine, Vermont, and New Hampshire surface waters are under fish consumption advisory and are considered impaired with respect to Hg because of these patterns and the difficulty in predicting which systems are most affected. Together with a team of citizen scientists, we are evaluating the utility of dragonfly nymphs (Odonata: Anisoptera) as indicators of Hg status in the Gulf of Maine region. We propose that dragonfly nymphs will be good sentinels because they are: (1) widespread and found in most surface waters in the region, (2) long-lived in aquatic systems (1-5 yr as nymphs), (3) exhibit site philopatry, (4) important prey species for fish that are consumed by humans, and (5) simple to capture, process, and analyze at meaningful Hg concentrations. Specifically, because dragonfly nymphs are themselves predators, Hg concentrations are high enough for laboratory and statistical analyses to be meaningful. The average Hg concentration in dragonfly nymphs sampled across Maine was 0.097 ppm (wet weight basis), greater than the proposed wildlife safety criterion (0.077 ppm). At sites across the region (ME, NH, VT, and MA), we used our data to address hypotheses regarding whether Hg varied with body size or by family; these characteristics were less important than a field site’s landscape setting. Data from a survey of a variety of surface water sites in or near four National Park areas in ME (Acadia), MA (Boston Harbor Island and Saugus Ironworks), and VT (Marsh Billings Rockefeller) confirmed that Hg in dragonfly nymphs was more variable among sites than within a site, suggesting that they are useful indicators for Hg. Further, three years of research by citizen scientists has confirmed correlation between Hg in dragonfly nymphs and DOC in five streams within Sunkhaze National Wildlife Refuge. Hg in dragonfly nymphs were related to concentrations in other media at three long term monitoring sites within Acadia National Park where Hg in mature forests has been shown to be greater than early successional forests. More research on dragonfly larval life history will help to develop a mechanistic understanding of this spatial variability in Hg bioaccumulation.

RG8-P3 — 11:00-12:00 and 17:30-18:30
SPATIAL PATTERNS OF MERCURY IN MACROINVERTEBRATES AND FISHES FROM STREAMS OF CONTRASTING FORESTED LANDSCAPES IN THE EASTERN UNITED STATES
Authors: MURRAY, Karen Riva1, CHASAR, Lia C.1, BRADLEY, Paul M.1, BURNS, Douglas A.1, SMITH, Martyn J.1
(1) U.S. Geological Survey, krmurray@usgs.gov

Ecological controls on mercury bioaccumulation in streams are complex and spatially variable. Because studies conducted in different environmental settings have produced seemingly conflicting results with respect to these controls, spatially and temporally intensive studies in diverse aquatic ecosystems are essential. We evaluated mercury bioaccumulation in two medium-sized (< 80 km2) forested basins in regions that differ in climate and topography – Fishing Brook, in the Adirondacks of New York and McTier Creek, in the Coastal Plain of South Carolina. Multiple stream locations were sampled seasonally in each basin during 2007-2009. Game fish were less piscivorous in Fishing Brook than in McTier Creek, so although mean Hg concentrations in most macroinvertebrate feeding groups were not significantly different between the two regions, mean Hg concentrations in game fish were lower in Fishing Brook (1300 ng/g, dry wt.) than SC (2400 ng/g, dry wt.). Topography and water chemistry were more spatially-variable in Fishing Brook, contributing to greater spatial variability in Hg in biota, positive correlations with dissolved methylmercury and organic carbon in streamwater, and negative correlations with overland flow distance (OFD, an indicator of hydrologic transport distance to the stream channel). OFD emerged as a robust predictor of Hg in aquatic macroinvertebrates within the Fishing Brook basin. This study demonstrates the importance of local-scale environmental factors to mercury bioaccumulation in topographically-heterogeneous landscapes, and provides support for the use of macroinvertebrates as effective sentinels of mercury contamination in streams.

RG8-P4 — 11:00-12:00 and 17:30-18:30
DOES THE VERTICAL MIGRATION OF THE PHANTOM MIDGE CHAOBORUS AFFECT MERCURY BIOMAGNIFICATION IN LAKES?
Authors: LEJEUNE, Anne-Hélène1, BOURDIOL, Floriane1, ALDAMMAN, Lama1, PERRON, Tania1, PINEL-ALLOUL, Bernadette1, AMYOT, Marc1
(1) Université de Montréal, lejeune.ahelene@yahoo.fr

The phantom midge Chaoborus (Insecta, Diptera), a well known invertebrate predator of plankton, has been described as a poor conveyor of methylmercury (MeHg) to upper trophic levels. We investigated the bioaccumulation and biomagnification capacity of three different Chaoborus species through their ontogenic development in an ecological context. We hypothesized that bioaccumulation and biomagnification of those larvae are related to the concentration of ingested prey. However, Chaoborus responds to fish predator by vertically migrating in the water column which affects their feeding activities. We thus expected that spatial segregation between habitat refuge and habitat resource would alter their capacity to biomagnify MeHg. All Chaoborus species bioaccumulated MeHg through their ontogenic development, and MeHg concentrations were related to aqueous concentrations. However, in the lake inhabited by fish, all instars of C. punctipennis characterized by a marked migrating behavior in food-depleted deep waters or sediment were not able to biomagnify MeHg whereas in the fishless lake C. americanus and C. trivittatus showing weaker vertical migration patterns biomagnified MeHg. Dietary and growth dilution effect could not explain such pattern of biomagnification, nor the trophic position according to d15N stable isotope analysis which were equivalent among species. Moreover, reduced biomagnification capacity of C. trivittatus, the coexisting species living with C. americanus was also ascribed to a progressive spatial segregation during larval development among the two coexisting species. Our findings demonstrate that vertical migration affects the biomagnification capacity of the most common invertebrate predator of planktonic food webs.

RG8-P5 — 11:00-12:00 and 17:30-18:30
BIOCONCENTRATION OF METHYLMERCURY IN MARINE PHYTOPLANKTON: EVIDENCES OF PASSIVE DIFFUSION
Authors: KIM, Hyunji1, KIM, Eunhee2, DUONG VAN, Hieu1, LEE, Byeonggweon3, HAN, Seunghee1
(1) Gwangju Institute of Science and Technology, hyunji@gist.ac.kr; (2) Korea Ocean Research & Development Institute; (3) Chonnam National University;

Methylmercury (MeHg) is a highly toxic form of mercury that readily accumulates in aquatic food webs. Human uptake of MeHg occurs primarily through dietary consumption of marine fish which obtain MeHg mainly from lower trophic organisms through bioaccumulation and biomagnification processes. The characteristics of MeHg bioconcentration in marine phytoplankton are largely unknown and it is unclear whether MeHg uptake by phytoplankton occurs through a passive or active transport in natural seawater. We observed, therefore, MeHg uptake in six marine phytoplankton cultured in unenriched seawater to understand the MeHg bioconcentration characteristics in natural conditions. We determined the volume concentration factors (VCFs) of MeHg for four species of diatom, one blue-green algae species and one green algae species, and the surface area to volume (S/V) ratio of each cell. The VCFs of MeHg, which ranged from 6.2 x 104 to 1.8 x 106, increased as the S/V ratio increased. This result suggests that the S/V ratio is one of important factors for MeHg partitioning between water and cells. Relatively low VCFs were obtained from blue-green algae and green algae, compared to their large S/V ratios, suggesting that physiological features may affect the MeHg partitioning between water and cells. A linear relationship was evident between the MeHg uptake rate and the MeHg concentrations in seawater, when the MeHg uptake rates were observed over a range of MeHg concentrations (from 20 to 2,500 pmol L-1). Measurement of the MeHg uptake rate under various Cl concentrations (pCl = 0.33 – 3.33) revealed that the MeHg uptake rate increased with decreasing pCl, which suggests that the MeHg diffusion rate increases with an increasing percentage of CH3HgCl. In conclusion, these results support that passive diffusion is the main MeHg uptake mechanism of marine phytoplankton.

RG8-P6 — 11:00-12:00 and 17:30-18:30
ALGAL MERCURY AND TRACE METAL ACCUMULATION DURING BIOFUEL PRODUCTION
Authors: PETERSON, Christianna1, GUSTIN, Mae1
(1) University of Nevada, Reno, cpeterson@cabnr.unr.edu

Evolving demands for biofuel production and limited water resources have lead researchers to explore the possibility of growing algae colonies in diluted wastewater centrate. The growth medium offers a dual benefit, by reducing total processing load for wastewater treatment plants and providing nutrients for algal growth. This technique would reduce total nitrogen and phosphorous contributions to natural ecosystems, produce viable oil for biofuels and a dried algal byproduct for use in animal feed and fertilizers. However, little is known about the bioaccumulation of mercury (Hg) and other trace metals in the algal colonies and subsequent solid byproducts. We have set out to identify the potential for accumulation of total and methyl Hg in three algal strains (freshwater, saltwater and a local freshwater strain), in addition to 6 trace metals identified as phytotoxic and of byproduct concern (As, B, Cd, Fe, Pb and Zn). The three strains will each grow in multiple centrate dilutions (10 to 40% centrate) for 6 weeks. We will then quantify Hg and trace metals in the initial and exhausted growth medium and dried algal biomass. Initial results indicate that total and methyl Hg concentrations in the centrate (30 ng L-1 and 6 ng L-1; respectively) are higher than reported for natural waters, and only As, B and Fe are above analytical detection limits (80 µg L-1, 0.3 mg L-1, 1.9 mg L-1; respectively). Total Hg in dried algal biomass grown in an identical manner to our study is 47 µg kg-1, which is higher than that reported for marine-based algae species (20 µg kg-1; Almela et al., J. Ag. and Food Chem. 2002). Over the next 4 months we will determine the accumulation of Hg, methylation rates between algal strains and growth media, and trace metals in our three algal strains and varying centrate dilutions. We plan to report on total and methyl Hg and trace metal concentrations and accumulation for two algal strains.

RG8-P7 — 11:00-12:00 and 17:30-18:30
STUDY ON INPUT APPROACH OF RANA CHENSINENSIS WITH METHOD OF STABLE ISOTOPE?
Authors: WEI, Wang1, NING, Wang1
(1) Northeast Normal University, wangw014@nenu.edu.cn

In the researched area of gold mine in Weisha River basin of the upper reaches of Songhua River in the northeast of China, water and sediments samples from the river, plants, insects and Rana chensinensis samples along the river have been collected respectively in spring and autumn in 2009. The process of pretreatment of samples are: plants samples were dried and ground; insect samples were freeze-dried, ground and defatted; Rana chensinensis samples were dissected, freeze-dried, ground and defatted. After pretreatment of samples, carbon and nitrogen isotope ratio of the samples have been tested using Finnigan MAT Delta V Advantage and Germany elemental analyzer Flash EA1112HT instrument, then issues such as food composition of Rana chensinensis and nutrients transfer in the food chain have been researched, and nutritional structure of food chain of plant - insect – Rana chensinensis has been discussed, and methylmercury levels in these samples have been determined, and then correlation between methylmercury level and isotope ratio has been analyzed in the end. The results show: d13C and d15N appeared enrichment with increasing of trophic level, and d15N increased 3.7 ‰ on average from the producers (plants) to primary consumers (insects), and d13C increased 1.02 ‰ on average from primary consumers (insects) to secondary consumers (Rana chensinensis), which showed that the food chain structure of Rana chensinensis terrestrial environment was plants - locust – Rana chensinensis, besides, methylmercury in visceral of Rana chensinensis was positively correlated with d13C, and the correlation coefficient R2 is 0.7507. It shows that methylmercury has bioaccumulated along the food chain, and mercury released from local gold mine has transformed into methylmercury and entered into the food chain structure of plant - locust - frog. The conclusions are: it can obtained that the food chain structure of Rana chensinensis terrestrial environment was plants - locust – Rana chensinensis based on the determination of stable isotope. Mercury and methylmercury in visceral of Rana chensinensis was positively correlated with d13C, which showed that mercury and other pollutants have bioaccumulated and the input approach was along trophic levels of the food chain.

RG8-P8 — 11:00-12:00 and 17:30-18:30
MERCURY EVALUATE IN PLANKTON OF DIFFERENTS MADEIRA RIVER AFFLUENTS, WESTERN AMAZON, BRAZIL.
Authors: NASCIMENTO, Elisabete1, HOLANDA, Igor2, CARVALHO, Dario2, MIRANDA, Marcio2, BASTOS, Wanderley2
(1) Environmental Biology Laboratoy, betalabmerc@yahoo.com.br; (2) Biogeochemistry Environmental Laboratory;

The energy transfer in aquatic alimentary chain is an important way of mercury entrance for the other trofics levels. The objective of this work was to evaluate the mercury concentrations in plankton in different affluents of the Madeira river (localized in Rondônia state, Occidental Amazon), there are Branco river, Contra river, Caripunas river, Jaci-Paraná river and river Jatuarana. The collections had been to each three months, April 2009 to November 2010 period. Plankton samples were collected in the water surface with boat in moviment (4,5Km/h) and three nets of nylon, with 160 µm, 70µm and the other with 20µm of mesh opening. After freeze-drying, the total mercury determination was done by atomic absorption spectrophotometry by cold vapor generation (FIMS-400). The mercury concentration in plankton, varied between 0,0060mgHg.Kg-1 in Branco river during rainy period and 0,1850mgHg.Kg-1 in Jatuarana river also rainy period. Generality the found values plankton mercury varied sufficiently throughout the period studied. Can be verified that the low values had been registered in plankton collected in rivers of clear waters (Branco and Contra rivers) that dark water rivers (Jaci-Paraná for example). Water dark rivers showed favorable conditions for mercury methylation, this factor can have contributed for the register of greater mercury values in plankton these environments. However, the found plankton mercury during the present study, meet below of the average values found by other plankton works of the Amazon region.

RG8-P9 — 11:00-12:00 and 17:30-18:30
SEASONAL DYNAMICS OF MERCURY IN PLANKTON IN AN ULTRAOLIGOTROPHIC LAKE: A ?13C APPROACH
Authors: ARCAGNI, Marina1, CAMPBELL, Linda2, RIZZO, Andrea1, ARRIBÉRE, María1, KYSER, Kurt 3, KLASSEN, Kerry3, RIBEIRO GUEVARA, Sergio 1
(1) Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, Argentina, marcagni@gmail.com; (2) School of Environmental Studies, Queen’s University Kingston, Canada; (3) Department of Geology & Geological Engineering, Queen’s University Kingston, Canada;

Total mercury concentration (THg) and stable carbon isotope ratios (d13C) were seasonally measured in three different plankton fractions (F1: 10-53 µm, F2: 53-200 µm, F3: >200 µm) to assess seasonal association between THg content and C sources to plankton in Lake Moreno, an ultraoligotrophic lake in Northeastern Patagonia (Argentina), which is divided in two basins, East (ME) and West (MW) that present differing hydrogeomorphic and catchment features.

THg contents were significantly higher in F1 (up to 209.4 µg g-1 dry weight (DW) and 257.9 µg g-1 DW in ME and MW, respectively) than in the other two fractions. A seasonal trend was observed in the THg contents in F1, with the highest concentrations in fall, and the lowest in summer. However, a different trend was observed in the other two fractions which presented lower THg in fall and winter (except F2 in ME) and higher concentrations in spring and summer.

d13C values were in general higher in ME than in MW and a seasonal trend was also observed in both basins. The highest and lowest values were observed in fall and spring respectively, in both basins for all fractions. A positive correlation was observed between THg and d13C in both basins, indicating that the high THg concentrations in plankton were probably associated with allochthonous C sources. This findings are also supported by another allochthony indicator evaluated in a previous work, the color:chlorophyla ratio which showed a seasonal pattern with a higher ratio in fall and lower in spring. Precipitations in the area are more abundant during fall and winter, being fall the season where it rains the most, with the consequent input of allochthonous material to the lake due to runoff and stream discharges.

The higher THg contents recorded in spring could be related to the deposition of mercury, via atmospheric transport, in the snowpack that accumulates in the high altitudes during winter, and flushing afterwards to the aquatic systems during the spring snowmelt. This water flowing to Lake Moreno in spring carries out much less organic materials when compared with the fall runoff, because it flows mostly through rocky surfaces.

RG8-P10 — 11:00-12:00 and 17:30-18:30
MERCURY IN CALIFORNIA LAKES AND RESERVOIRS: FACTORS INFLUENCING BIOACCUMULATION
Authors: NEGREY, John1, MELWANI, Aroon2, STEPHENSON, Mark 1, DAVIS, Jay2
(1) Moss Landing Marine Laboratories, negrey@mlml.calstate.edu; (2) San Francisco Estuary Institute;

To fully characterize mercury (Hg) concentrations in the aquatic food web, information on the factors driving methylmercury (MeHg) bioaccumulation is needed. This study investigated Hg and MeHg in 17 lakes and reservoirs in California. Largemouth bass MeHg was measured in individual muscle fillets collected from each lake. Surface water and sediment samples were analyzed for total Hg, MeHg, chlorophyll a, organic carbon, dissolved oxygen, pH, temperature, and sulfate. These data, combined with many lake morphometric (e.g., lake volume, surface area, and storage capacity) and land-use variables (e.g., catchment area, forested area, # mines, and total Hg in soil) were used to develop a statistical model to predict fish MeHg concentrations. MeHg in largemouth bass standardized to 350 mm varied from 60 – 1314 ng/g, wet weight. Several of the predictor variables were found to be correlated to size-standardized largemouth bass MeHg concentrations, and were a significant component of a multivariate regression model. The factors found to be statistically associated with MeHg bioaccumulation were total Hg in sediment and catchment soils, percent of forested area, and MeHg in surface water. Total Hg in lake sediment alone explained 50% of the variation in largemouth bass MeHg concentrations. These results were consistent with several studies that have suggested that broad land use characteristics can potentially influence MeHg bioaccumulation in lakes and reservoirs. Further study at these lakes is needed to evaluate whether MeHg is being incorporated through the pelagic or benthic pathway.

RG8-P11 — 11:00-12:00 and 17:30-18:30
MERCURY BIOMAGNIFICATION IN FOOD WEBS OF TROPICAL COASTAL ECOSYSTEMS OF BRAZIL
Authors: BISI, Tatiana1, LEPOINT, Gilles2, AZEVEDO, Alexandre F3, DORNELES, Paulo R1, FLACH, Leonardo4, DAS, Krishna2, MALM, Olaf1, LAILSON-BRITO, José3
(1) Federal University of Rio de Janeiro, tbisi@yahoo.com.br; (2) University of Liege; (3) University of Rio de Janeiro State ; (4) Boto-cinza Institute;

Some micropollutants, like mercury, undergo increase in concentrations upward trophic levels, reaching high concentrations in top-chain organisms. The present study investigated mercury flow through food webs of three tropical coastal ecosystems: Guanabara, Sepetiba and Ilha Grande Bays (Rio de Janeiro State, Brazilian Coast). The investigation was carried out by examining the relationship between ratios of stable isotopes nitrogen (d15N), as an indicator of trophic level, and total mercury (THg) concentrations in muscle samples from 34 species, including crustacean, cephalopod, fish and dolphin species (n = 346). Stable isotope measurements were performed on a V.G. Optima (Micromass) IR-MS coupled to an N-C-S elemental analyzer (Carlo Erba) and THg concentration was determined by Cold Vapor/Atomic Absorption Spectrometry. Trophic Magnification factor (TMF) was use for quantifying food web biomagnification. Average muscular THg concentration was lowest in Litopenaeus schmitti (Penaeidae) (3.65 ng/g in Guanabara Bay and 4.24 ng/g in Sepetiba Bay) and in Sardinella brasiliensis (Clupeidae) (4.63 ng/g in Ilha Grande Bay) and highest in Guiana dolphin, Sotalia guianensis (920.30 ng/g in Guanabara Bay, 269.23 ng/g in Sepetiba Bay and 688.45 ng/g in Ilha Grande Bay). THg concentrations in biota from Ilha Grande Bay were not only higher than in organisms from Sepetiba Bay (post-hoc test, p<0.05) but also comparable to the THg levels in animals from Guanabara Bay that is one of the most contaminated systems of the Brazilian coast. This finding is likely to be a consequence of a higher percentage of Hg bioavailable in Ilha Grande Bay as well it strengthens the hypothesis that South Atlantic Central Water (SACW) constitutes an additional source of Hg to the Ilha Grande Bay food web. A positive linear relationship was found between logarithmic concentrations of THg (log-transformed) and d15N values for Guanabara and Ilha Grande Bays (linear regression, p<0.005), but not for Sepetiba Bay (linear regression, p>0.09). Our findings showed TMF (antilog of the regression slope with base 10) above 1 for Guanabara (1.55) and Ilha Grande Bays (1.63), demonstrating that THg is being biomagnified up the food chains in Rio de Janeiro Bays.

RG8-P12 — 11:00-12:00 and 17:30-18:30
SEASONAL MERCURY CYCLING IN A NEW ENGLAND VERNAL POOL
Authors: BENOIT, J.M.1, DENISON, Katherine1, SACHA, Nicole1
(1)Wheaton College, jbenoit@wheatonma.edu;

Vernal Pools are small, shallow water bodies that commonly occur in wooded areas, possess no permanent inlet or outlet, and lack established fish populations. These seasonally-flooded pools support a rich invertebrate fauna, and they are critical habitat for amphibians. Although the ecology of vernal pools has been extensively studied, little is known about the cycling of mercury in these ecosystems. In our year-long investigation in Wheaton’s vernal pool in Norton, Massachusetts, we collected fresh leaf litter (litterfall) depositing on the pool between October 6 and December 1, 2010. Preliminary estimates indicate that the litterfall fluxes of total mercury (HgT) and methyl mercury (MeHg) were 11 ug m-2 and 80 ng m-2, respectively, over that time period. About 0.7% of the HgT in litterfall was present as MeHg. In order to determine the extent of MeHg production after deposition, we also collected detrital leaf litter year-round from the floor of both the vernal pool and the surrounding forest. The pool began to fill with water in mid-November and was completely filled by early January 2011. HgT concentrations in the litter layer increased slightly throughout the year, reaching 60±20 ng/gdw inside and 59±7 ng/gdw outside the pool. MeHg concentration remained at a relatively constant 1% in leaf litter on the forest floor. In contrast, MeHg concentrations increased in the vernal pool shortly after inundation, reaching 8% of HgT by early spring. Preliminary studies on pool invertebrates show that two detritivore groups, scuds (Amphipoda) and sow bugs (Isopoda), bioaccumulated MeHg about 8-fold relative to the leaf litter substrate. Overall, our results indicate significant production and bioaccumulation of MeHg in Wheaton’s vernal pool. This MeHg could be exported to the surrounding forest through the food web. We plan to quantify export of MeHg via emergent insects in the second spring of the study.

RG8-P13 — 11:00-12:00 and 17:30-18:30
MARINE SNOW AS A POTENTIAL TRANSPORT VECTOR AND SOURCE OF BIOACCUMULATION OF MERCURY IN THE BIVALVE MYTILUS EDULIS.
Authors: ORTIZ, Veronica L.1, MASON, Robert P.1, WARD, J. Evan1
(1) University of Connecticut, veronica.ortiz@uconn.edu

Bioaccumulation of mercury in the aquatic food web is a continuous concern to public health. Extensive research has been conducted regarding the uptake of mercury by various aquatic animals via three main vectors: sediment, food (i.e. phytoplankton) and water, but virtually no research exists with respect to uptake of mercury from aggregated particulate organic matter. Marine snow (a.k.a. flocs or aggregates), composed of transparent exopolymers (TEP), phytoplankton cells, detritus and dissolved organic matter has been studied as an effective vertical transporter of nutrients and metals scavenged from the euphotic zone to the benthos. Various aquatic species utilize this organic matter as a food source, particularly suspension feeding bivalve molluscs. Therefore, if mercury is incorporated into the aggregates these organisms could potentially assimilate and accumulate the heavy metal into their tissues. For this study, marine snow was produced from sieved seawater (210 µm) in 1L glass bottles at 18oC using the roller-table method. Prior to rolling, water was spiked with inorganic mercury and methylmercury standards. Marine snow was then fed to blue mussels, Mytilus edulis, for a maximum of two hours. Following the assay, feces were collected to analyze for mercury assimilation whereas the animals were dissected for tissue analysis. Feces were analyzed by cold vapor atomic fluorescence spectrometry (CVAFS). Mercury accumulation in the mussel tissues was analyzed using a Direct Mercury Analyzer (DMA-80). Tissues were analyzed in groups: the mantle and the gill, the foot and adductor muscles, and the visceral mass, thereby defining a total mercury body burden in each animal. Results indicate formation of marine snow increased incorporation of Hg into particulates compared to unrolled control water. Tissue and feces analyses are being conducted and results will be presented at the conference. This research will help to elucidate another important mechanism of mercury transport into the food chain.

RG8-P14 — 11:00-12:00 and 17:30-18:30
INFLUENCE OF FLOODPLAIN LAKES HYDROMORPHOLOGY ON MERCURY ACCUMULATION PATTERNS IN MACROINVERTEBRATES OF THE BOLIVAN AMAZON
Authors: MOLINA, Carlos I.1, GIBON, F.M.2, OBERDORFF, Thierry2, DUPREY, J.L.3, POINT, David4, ROULET, Marc†3
(1) Unidad de Limnología, Instituto de Ecología, UMSA, CP 10077, La Paz, Bolivia., camoar6088@gmail.com; (2) UMR BOREA, UMR IRD 207, Muséum National d’Histoire Naturelle (MNHN), Paris, France; (3) Institut de Recherche pour le Développement - IRD, CP 9214, La Paz, Bolivia; (4) UMR GET, UMR IRD 234, IRD, 31400, Toulouse, France.;

Using stable isotopes of d13C and d15N, we evaluated mercury accumulation in macroinvertebrates groups of five floodplain lakes of the Rio Beni, Bolivian Amazon. These lakes ware characterized by different degrees of connectivity to the main River. Nutrient sources and macroinvertebrates were collected in both the vegetation belt and the open waters area of each lake. The dominant group was insects followed by molluscs and gastropods. d13C signatures allowed the identification of six carbon sources: seston, bottom sediment (open water area), periphyton, terrestrial vegetation, macrophytes C3 and C4 (vegetation belt area). Most macroinvertebrates species showed significant variability among lakes and seasons, the main driving variables being carbon sources, trophic positions (d15N), and mercury accumulation. The degree of connectivity of the different lakes to the main river was found to influence significantly Hg accumulation and speciation in macroinvertebrates. A relatively higher fraction of methylmercury was found in invertebrates from older lakes (connected to the river only during exceptional flood events) compared to younger lakes (connected to the river during all wet seasons). These results showed that lakes hydromorphology was an important factor driving Hg accumulation and speciation in Amazonian food webs.

RG8-P15 — 11:00-12:00 and 17:30-18:30
DISTRIBUTION OF TOTAL MERCURY IN MULTI-ENVIRONMENTAL MEDIA OF LAKE AN-DONG, SOUTH KOREA
Author: HAN, Jin-Seok1
(1)NIER, nierhan@korea.kr

In this study, total mercury and methylmercury in water, plankton, freshwater fish and sediments from Lake An-dong were examined and the results were compared with previous national studies. Lake An-dong, an artificial freshwater lake is located on the upstream of River Nak-dong. Recently, the possibilities of its mercury contamination became an issue since there are the possibilities of historical mercury pollutions due to the locations of abandoned mines and a zinc smelter in the upper stream. The total and dissolved mercury levels in lake water were 2.06 and 0.95 ng/L and 46% of mercury existed in dissolved forms. The mercury level of predatory fish from Lake An-dong were quite higher than the national average and some species did not showed any correlation between the fish length and mercury content. The analytical results of carbon and nitrogen stable isotopes for bluegill caught in Lake An-dong and other lakes showed the bluegills from Lake An-dong were higher trophic level than other lakes. Mercury levels in core sediments were also higher than average national data and the configuration of sediments were compared with those of abandoned mining tails. The %methylation of the sediments were found to be 0.76~2.09%. To access the interrelationships between mercury and other chemical parameters in sediment, organic contents, sulfur contents and other metals (Cu, Ni, Pb, Zn, Fe and Mn) were examined and the concentrations of total mercury and manganese and irons also showed statistically significant correlation (RT-Hg-Mn=0.41, p<0.05) as well as other elements.

RG8-P16 — 11:00-12:00 and 17:30-18:30
TOTAL MERCURY CONCENTRATION IN DIFFERENT PLANKTON FRACTIONS IN LAKE MORENO (PATAGONIA, ARGENTINA) IN RELATION WITH ?15N
Authors: ARCAGNI, Marina1, RIZZO, Andrea1, CAMPBELL, Linda2, ARRIBÉRE, María1, KYSER, Kurt3, KLASSEN, Kerry3, RIBEIRO GUEVARA, Sergio1
(1) Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, Argentina, marcagni@gmail.com; (2) School of Environmental Studies, Queen’s University Kingston, Canada; (3) Department of Geology & Geological Engineering, Queen’s University Kingston, Canada;

The aim of this work was to assess association between total mercury (THg) and d15N (stable nitrogen isotope ratios) values in the plankton community in Lake Moreno (Northwest Patagonia, Argentina), an ultraoligotrophic double-basined lake. The Moreno East (ME) and West (MW) basins each have differing hydrogeomorphic and catchment features, allowing us to compare plankton dynamics. THg and d15N were measured in three plankton fractions (F1: 10-53 µm, F2: 53-200 µm, F3: >200 µm). F1 is composed of phytoplankton and mixotrophic ciliates, while both F2 and F3 contain mostly consumers such as ciliates, rotifers, copepods and cladocerans.

THg concentrations were not significantly different between ME and MW. Within each basin, the smallest fraction had significantly higher THg concentrations relative to F2 and F3. In both basins, fraction size was positively correlated with d15N values, with F1 having lowest values. The largest fraction F3 had higher d15N values in ME than MW. However, there were no other significant between-basin differences for F1 or F2. THg concentrations and d15N values were negatively correlated in MW, but there were no significant correlations for ME plankton.

The difference observed in the d15N values between ME and MW in the F3 fraction may be due to the relative species contribution; e.g. it is suspected that ME may have a higher proportion of species in F3 which presents higher d15N values than the dominant species in MW F3 samples. A different proportion of N-fixing algae or higher waste inputs in one basin than in the other could be also the cause for the different d15N observed between ME and MW. However, there is no significant difference in the d15N values of F1 and F2 between the basins, and an absence of heterocyst indicative of N-fixation in potential N-fixing algae from this lake.

Despite the smallest plankton fraction can be partially consumed by the larger fractions, it seems that only a small proportion of the THg is transferred to the consumers in F2 and F3 fractions.

RG8-P17 — 11:00-12:00 and 17:30-18:30
MERCURY BIOACCUMULATION ALONG FOOD WEBS IN AQUATIC ECOSYSTEMS COLONIZING BY AQUATIC MACROPHYTES IN THE LANDES AREA (SOUTH WESTERN FRANCE).
Authors: GENTÈS, Sophie1, LEGEAY, Alexia2, GUYONEAUD, Rémy3, MONPERRUS, Mathilde4, ANDRÉ, Jean-Marc3, DAVAIL, Stéphane3, MAURY-BRACHET, Régine5
(1) Environnement et Microbiologie (IPREM UMR 5254),Université de Pau et des Pays de l’Adour, France, sophie.gentes@univ-pau.fr; (2) Ecotoxicologie Aquatique (EPOC UMR 5805),Université Bordeaux 1, France; (3) Environnement et Microbiologie (IPREM UMR 5254); (4) Chimie Analytique Bio Inorganique et Environnement (IPREM UMR 5254), Université de Pau et des Pays de l’Adour, France; (5) Ecotoxicologie Aquatique (EPOC UMR 5805).

Mercury is considered as an important pollutant for aquatic ecosystems since its organic form, i.e., methylmercury, is a strong neurotoxic compound, easily bioaccumulated and bioamplified along the food web. Methylmercury may originate from anaerobic biological activities through sulfate and iron reducing prokaryotes. These organisms colonize anoxic niches (sediments, hypolimnions of stratified lakes) that are thus considered as methylmercury sources for the ecosystems. Nevertheless, some studies demonstrate the presence of sulfate reducers in biofilms developing at the surface of aquatic plant roots in water bodies. The activity of these microorganisms in such matrices, considered as a potential food resource for fishes and invertebrates, could induce a direct contamination of food webs, through suspension feeders (bivalves) or grazing organisms (gasteropodes, fishes).

In south western France, invasive aquatic macrophytes (Ludwigia peploides, Lagarosiphon major, Myriophyllum aquaticum) colonize most of the lakes and rivers, cause damage to aquatic ecosystems and disrupt leisure or tourism activities. In this context, we describe the mercury contamination along food webs in five contrasting environments colonized by different aquatic plants. This work establishes original data concerning mercury and methylmercury bioaccumulation in organisms (fishes, crustaceans and molluscs) from these ecosystems, taking into account trophic levels of the individuals and physico-chemical parameters. The results show a significant level of total mercury in fishes, suggesting a production and bioaccumulation of methylmercury. Some carnivorous or omnivorous fishes exhibit mercury concentrations close (2.18 mg.kg-1 dw ± 0.77 in pike muscle, Esox lucius) or exceeding (4.23 mg.kg-1 dw ± 1.26 in eel muscle, Anguilla anguilla) the European toxicity norm (2.5 mg.kg-1 dw). The trophic dynamic (feeding relationships) can be clearly evidenced in some lakes whereas one sampling site is characterized by higher mercury concentrations in roach (Rutilus rutilus) in relation to their size and weight. Based on this study, the risk areas for mercury contamination are identified. The hypothesis considering aquatic plants and their root-associated microorganisms as a main cause for mercury bioaccumulation will be tested in microcosms in order to determine their actual implication. Besides these results will also allow a better understanding on the mercury biogeochemical cycle in aquatic ecosystems.

RG8-P18 — 11:00-12:00 and 17:30-18:30
MERCURY CONTAMINATION OF MACROINVERTEBRATES FROM GRASSLAND PONDS WITH AND WITHOUT FISH
Authors: HENDERSON, Byron L.1, CHUMCHAL, Matthew M.1, DRENNER, Ray W.1, DIAZ, Peter2, NOWLIN, Weston H. 2
(1)Texas Christian University, byronleehenderson@gmail.com; (2) Texas State University;

The purpose of this study was to examine mercury (Hg) in macroinvertebrate communities from grassland ponds with and without fish communities. We sampled macroinvertebrates from five ponds with fish and five ponds without fish, at the LBJ National Grassland in north Texas, USA. Ponds without fish contained a higher biomass of macroinvertebrates and taxa with higher concentrations of Hg, which led to a greater pool of Hg in the macroinvertebrate community of fishless ponds. Seventy-three percent of the macroinvertebrate biomass from ponds without fish was composed of taxa capable of emerging and these taxa have the potential to transport Hg out of ponds into terrestrial food webs.

RG8-P19 — 11:00-12:00 and 17:30-18:30
METHYLMERCURY CONCENTRATIONS IN DRAGONFLY LARVAE VARY BY GUILD: YOU ARE WHAT YOU EAT AND WHERE YOU EAT IT
Authors: NORTHWICK, Reid M.1, HARO, Roger J.1, ROLFHUS, Kristofer R.1, BAILEY, Sean W.1, SANDHEINRICH, Mark B.1, WIENER, James G.1
(1) River Studies Center, University of Wisconsin - La Crosse, northwic.reid@uwlax.edu

The bioaccumulation of methylmercury through the lower portions of aquatic food webs is poorly understood. This lack of understanding is, in part, due to the diversity of strategies used for energy acquisition among invertebrates that are secondary and tertiary consumers. For aquatic insects alone, dietary changes regularly occur through ontogeny. Among the “true” aquatic insect orders (Ephemeroptera, Odonata, Plecoptera, Megaloptera and Trichoptera), the dragonflies (Anisoptera: Odonata) standout as being diverse taxonomically, but very restricted in diet; all are generalist predators as larvae and adults. As such, they tend to bioaccumulate contaminants. However, bioaccumulation among dragonfly species can vary across genera and families within a single water body. For dragonfly larvae, these taxonomic levels fall into distinct habit guilds. These habit guilds aggregate species by modes of locomotion, attachment, and concealment. Consequently, dragonflies from different habit guilds are likely to encounter and consume different prey species at distinct rates. These behavioral differences may help explain the variability in methylmercury (MeHg) bioaccumulation among species within and across water bodies. Habit guilds include: burrowers (most species within the Family Gomphidae and all Cordulegastridae), sprawlers (most Libeludidae and some Corduliidae), and climbers (most Aeshnidae). We explored MeHg associations among guilds by combining data from two mercury surveys conducted in northern temperate freshwaters: (1) 15 water bodies in Voyageurs National Park (2003-2005) and (2) 25 water bodies across 6 park units in the Great Lakes Inventory and Monitoring Network (2008-2009). The majority of dragonfly species collected in this region spend 2 years as larvae underwater before emerging as terrestrial adults. Therefore differences in MeHg concentrations among guilds are not the result of somatic growth dilution, but likely reflect differences in foraging habit. Our initial findings suggest that mean MeHg concentrations among the guilds displayed similar slopes but different intercepts across the gradient of methylmercury contamination for the water bodies examined. Across this gradient, MeHg concentrations were greatest in the climbers followed by the clingers, sprawlers, and burrowers, respectively. Climbers, clingers, and sprawlers are active hunters feeding on prey located at or above the benthic zone, while burrowers are sit-and-wait predators feeding primarily on benthic prey. The frequency of piscivory and/or intraguild predation among the climbers and sprawlers (e.g., Hagenius brevistylus and Didymops transversa) may also explain differences in MeHg bioaccumulation among the guilds. Recognizing the differences in larval foraging behavior among the dragonflies will improve their utility as sentinel organisms.

RG8-P20 — 11:00-12:00 and 17:30-18:30
BIOACCUMULATION OF MERCURY IN BENTHIC AND PELAGIC ORGANISM – A MESOCOSM STUDY
Authors: JONSSON, Sofi1, SKYLLBERG, Ulf2, LUNDBERG, Erik1, ANDERSSON, Agneta1, NILSSON, Mats B2, BJÖRN, Erik1
(1)Umeå University, sofi.jonsson@chem.umu.se; (2) Swedish University of Agricultural Sciences;

Accumulation of mercury in the pelagic zone by plankton and in sediment by benthic organisms is of great importance for further bioaccumulation and magnification in the aquatic food web. Recent discussions have brought attention to the importance of newly deposited, contra aged, mercury for the production and bioaccumulation of methylmercury (CH3Hg). In this study bioaccumulation of isotopically enriched Hg tracers, simulating newly deposited and aged Hg, in plankton and benthic organism was studied in a mesocosm study utilizing 12 isolated tubes of 70 cm id and 5 m height with intact sediment cores (65 cm id) and brackish water sampled from an estuary located in the Bothnian bay. Isotopically enriched tracers was injected 0.5 cm below the sediment surface (black cinnabar (ß-HgS) as well as inorganic mercury (HgII) and CH3Hg bound to organic matter) and added to the water column (aqueous HgII and CH3Hg). Three different treatment regimens was applied; two levels of pelagic productivity (phytoplankton dominated food web) and one with increased inflow of humic material to the pelagic zone (bacteria dominated pelagic food web). After an incubation period of 8 weeks, accumulation of added tracers was determined in plankton (<50, 50-200 and >200 µm) and benthic organisms (mussels, worms, larva and isopod crustacean).

RG8-P21 — 11:00-12:00 and 17:30-18:30
MONITORING OF TOTAL MERCURY IN THE PLANKTON COMMUNITY OF PARA RIVER BASIN, AMAZON, BRAZIL
Author: PINHEIRO, Samara Cristina Campelo1
(1) Evandro Chagas Institute, samarapinheiro@iec.pa.gov.br

In the Amazon region the presence of mercury (Hg) in soils, rivers and atmosphere is attributed to natural processes and human activities as the process of amalgamation in gold mining. The use of plankton community as bioindicators of mercury environmental exposure is due to its importance in energy transfer to other aquatic trophic levels, including some species of fish consumed by local coastal communities. The aim of this work was to contribute to studies on mercury concentrations in organisms belonging to the plankton community in the Amazon region. Plankton samples were collected in the basin of the Pará River, the stretch between the towns of Barcarena and Abaetetuba, State of Pará, in two sampling points RPA03 (1°41’25.03”S) and RPA07 (1°34’59.07”S) during the months of January/09, April/09, July/09,October/09 and April/10. To collect plankton were performed in the sub-surface water with the use of plankton nets with mesh size of 20, 64 and 120µm. After collection, the plankton concentrated material was packed in amber glass bottles (1.0 L) and transported to the laboratory where were lyophilized. The total mercury determination, the samples were acidified, according to methodology described by Akagi (2004). The levels of total Hg were determined using Cold Vapor Atomic Absorption Spectrometry (CV-AAS). For quality control were used Certified Reference Material (BCR 060) with a good analytical recovery. The average concentrations recorded ranged from 0,038 ± 0,004 µg/g during the month July/09 (RPA03) to 0,584±0,546 µg/g in the month of January/09 (RPA07). The highest concentrations in both points were recorded during the month of January/09, this month considered of greatest rainfall for this region. These higher concentrations may relate to the entry of particles embedded in the Hg from soil to the aquatic environment through the leaching processes in the natural environment. The levels found in the plankton were indications that these organisms accumulate mercury and should be better investigated regarding their origins, occurrence, transport and importance in the steps of biomagnification through the aquatic food chain.

RG8-P22 — 11:00-12:00 and 17:30-18:30
THE ROLE OF INVASIVE BLOODY RED SHRIMP IN LAKE ONTARIO IN BIOMAGNIFICATION OF MERCURY
Authors: CAMPBELL, Linda M1, ZHANG, Liang1, ARNOTT, Shelley 1, JOHNSON, Timothy2
(1) Queen’s University, linda.campbell@queensu.ca; (2) Ontario Ministry of Natural Resources.

Hemimysis anomola (bloody red shrimp), an invasive invertebrate of Great Lakes, was first reported in Lake Ontario in 2006. Literature from their native range (Ponto-Caspian region of eastern Europe) suggests Hemimysis prefer nearshore, warmer waters and have rapid propagation and opportunistic omnivore feeding habits (zooplankton, phytoplankton, insect larvae, etc). To examine their influence on the food web dynamics of today’s Lake Ontario, We sampled multiple trophic levels, from algae to piscivorous fish, across a gradient of Hemimysis density in the Canadian waters of Lake Ontario in the spring, summer and fall of 2009 for mercury, stable nitrogen and carbon isotopes. Results showed that Hemimysis is now widely distributed in Lake Ontario, reaching densities of 200 individuals/ m3. The mercury concentrations of Hemimysis from Waupoos and Cobourg ranged from 11.9 ng/g ww to 21.1 ng/g ww, Those values are very close to those for the round goby Neogobius melanostomus and alewife Alosa pseudoharengus, which are reported to prey on Hemimysis in southeastern Lake Ontario. The food web results also indicate that small alewife prey on Hemimysis. However, the top trophic piscivores, brown trout, lake trout, and other top consumers are not directly impacted by Hemimysis in Lake Ontario to date. However, comparative food web analyses indicate that Hemimysis do elevate the mercury biomagnification in top trophic predators by lengthening the food chain.

RG8-P23 — 11:00-12:00 and 17:30-18:30
A TROPICAL PARADOX – MERCURY IS HIGH IN DEPOSITION, LOW IN THE FOOD WEB IN PUERTO RICO
Authors: SHANLEY, James B.1, LANE, Oksana2, ARENDT, Wayne3, MARVIN-DIPASQUALE, Mark C.1
(1) U.S. Geological Survey, jshanley@usgs.gov; (2) Biodiversity Research Institute; (3) U.S. Forest Service;

Wet deposition of mercury (Hg) at an unpolluted site in the Luquillo Mountains of northeastern Puerto Rico averaged 28 µg m-2 yr-1, higher than any site in the USA Mercury Deposition Network. The high input is reflected in extremely high total Hg (THg) flux in nearby Rio Icacos of 54 µg m-2 yr-1. This high stream THg flux may include contributions of legacy Hg from gold ore processing more than a century ago. Most of the stream THg flux is associated with particulates, and only about 0.5% is methylmercury (MeHg). Despite these high THg input and export values, assimilation in the food web appears to be quite low. In and around Río Icacos we collected 30 fauna samples including fly larvae, freshwater shrimp, spiders, tadpoles, coqui frogs, anole lizards, a scorpion, and a boa constrictor. These samples had a median THg concentration of 32 µg g-1 (dry weight basis) with the three highest values (near 140 µg g-1) from spiders. We also sampled bird blood from 31 individuals representing 8 species in various feeding guilds. Bird blood THg concentrations were quite low, ranging widely from 0.0002 to 0.032 µg g-1 wet weight, with a median of 0.0043 µg g-1. There are few mammalian predators on the island and many of the species we sampled represent some of the highest trophic levels (or insectivorous feeding guilds for birds) in the island food web, yet THg concentrations in these biota were still low. This result was surprising given the high Hg inputs and watershed features that would seem to favor Hg(II)-methylation – high soil moisture with anoxic zones, ample organic matter and sulfur, and year-round warm temperatures. However, in a synoptic study at the five USGS Water, Energy, and Biogeochemical Budgets (WEBB) sites across the USA, Río Icacos had the second lowest average stream bed sediment potential MeHg production rate (0.10 pg g-1 d-1) and the lowest average MeHg concentration (0.01 ng g-1) (both dry weight basis). The low MeHg concentrations and rates of production were at least partially attributed to the comparatively high redox status (+500 mv Eh) and low organic content (ca. 1% dry weight) of this sandy streambed, suggesting very rapid and complete organic matter decomposition in this tropical landscape. It is unclear if these results are representative for the Río Icacos landscape, but they are consistent with the low THg in the food web.

RG8-P24 — 11:00-12:00 and 17:30-18:30
DYNAMICS OF DIETARY METHYLMERCURY UPTAKE IN TWO ESTUARINE FISH: THE SHEEPSHEAD MINNOW (CYPRINODON VARIEGATUS) AND INLAND SILVERSIDE (MENIDIA BERYLLINA)
Authors: HEYES, Andrew1, ROWE, Christopher1, STEFANSSON, Emily1
(1) University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, heyes@umces.edu

The relationship between dietary exposure and methylmercury (MeHg) accumulation in fish remains poorly understood, particularly in lower trophic levels. It is also unclear how this relationship varies among species. We have observed that young of the year (YOY) perch accumulate Hg rapidly with concentrations of 10 ng g-1 achieved in less than 3 months, while YOY bass can achieve concentrations of 250 ng g-1 in the same time period. This accumulation can be an order of magnitude higher upon reaching reproductive age. While many standard uptake studies are short, often only 16 days, it is necessary to track accumulation over longer time periods and through reproductive development. The present research focuses on two estuarine forage fish species, which are predicted to differ in sensitivity: the sheepshead minnow (Cyprindon variegatus) and inland silverside (Menidia beryllina). In the first phase of our study, MeHg uptake will be investigated in fish fed one of five dietary MeHg concentrations (0.02 ug g-1, 1 ug g-1, 5 ug g-1, 10 ug g-1, and 20 ug g-1) over a 70-day dosing period. The primary goal of the study is to assess how these two species accumulate MeHg across the same range of dietary MeHg loads. Secondary goals include identifying any stress responses prior to sexual maturity, such as growth.

RG8-P25 — 11:00-12:00 and 17:30-18:30
TROPHIC TRANSFERENCE OF MERCURY AND SELENIUM IN THE SOUTHERN COAST OF RIO DE JANEIRO
Authors: SEIXAS, Tercia1, KEHRIG, Helena A2, MOREIRA, Isabel1, MALM, Olaf2
(1) PUC-Rio, terciaguedes@gmail.com; (2) IBCCF - UFRJ;

The present study evaluated mercury (Hg) and selenium (Se) concentrations in muscle tissues of three fish species with different feeding habits (Mugil liza, Micropogonias furnieri, and Trichiurus lepturus) from a oligotrophic Brazilian coastal area, Ilha Grande Bay (IB). The aims were to compare the possible differences in the trophic transfer of Hg and Se among the vertical trophic guilds (VTG). VTG were grouped according to fish diet, that is, in fish species that feed on similar food sources and use those sources in the same manner: voracious predator (VP - T. lepturus), intermediary voracious predatory (IVP - M. furnieri) and non-predatory (NP- M. liza). VP presents carnivorous habits, preferably piscivorous, actively pursuing their prey. In contrast, IVP feeds mainly on invertebrates and small fish. NP is a planktivorous species that live associated with the surface of the water mass. A significant difference (p < 0.05) was found in the concentrations of Hg and Se among the fish species. The mean concentration of Hg, in a dry weight basis, in PV, IPV and NP were 0.35 ± 0.16 mg/Kg, 0.66 ± 0.44 mg/Kg and 0.22 ± 0.01 mg/Kg, respectively. Se concentrations, in a dry weight basis, in PV, IPV and NP were 0.96 ± 0.78 mg/Kg, 3.26 ± 0.90 mg/Kg and 1.36 ± 0.71 mg/Kg, respectively. T. lepturus that represents the highest trophic guild and feeds on M. furnieri and M. liza, presented lower concentrations of Hg and Se than M. furnieri (intermediate trophic guild), representing an anomalous behavior of these elements in a tropical food webs. However, Hg concentrations in the muscle tissue of T. lepturus were 17.5 times higher than those found in the same tissue of their prey, M. liza (lower trophic guild), indicating a positive transference of Hg from the prey to predator. However, T. lepturus and M. liza presented similar Se concentrations, indicating no transference of Se from the prey to predator. According to the results, these elements did not suffer the biomagnification process in this web. However, more aquatic species must be studied to understand the behavior of these elements in this environment. Probably, the differences in Hg and Se among fish species can be related to the predominant food items for each species as well as the bioavailability of Hg and Se in the marine environment.

Thursday, 28 July, 2011