S14 Mercury fate in marine ecosystems: From sources to consumers

Tuesday, 26 July, 2011

TS14-P1 — 11:00-12:00 and 17:30-18:30
Author: ANDERSON, M. Robin1
(1) Northwest Atlantic Fisheries Centre, m.robin.anderson@dfo-mpo.gc.ca

Mercury burden in freshwater and marine fish is known to be a function of trophic position and directly related to body size. However, mercury burdens are rarely compared between fish from marine and freshwater systems. Data from large scale surveys of mercury in fish in Newfoundland and Labrador, Canada were examined to compare the effects of freshwater, estuarine and marine residence on mercury burden in various diadromous or euryhaline species. Comparisons were made on a size-weighted basis as mercury burden generally increases with size in most fish populations. Anadromous atlantic salmon, arctic char and sea trout have significantly lower mercury levels than do landlocked populations. Estuarine populations of other species such as northern pike, longnose and white suckers and round whitefish also have lower mercury levels than nearby freshwater populations. Duration of the at-sea phase, trophic level and prey mercury burden may all contribute to these patterns. Size-weighted comparisons of trout and salmon populations from the same river system (Kenamu River, Labrador) indicate that salmon with a truly marine life history phase, have lower mercury levels than do sea trout who tend to remain within the estuary for their marine phase. Although trophic levels of the two species are similar, sea trout are at sea for only a few months suggesting that some of the observed mercury burden accumulated during their freshwater phase.

TS14-P2 — 11:00-12:00 and 17:30-18:30
Authors: BOWMAN, Katlin L.1, NALLURI, Deepthi1, FITZGERALD, William F.2, HAMMERSCHMIDT, Chad R.1
(1) Wright State University, bowman.49@wright.edu; (2) University of Connecticut;

Benthic mobilization of methylmercury (MeHg) from sediments on the continental shelf and slope is posited to be a major source of the contaminant to marine biota. However, and unfortunately, there is a near absence of either measured or diffusional estimates of MeHg exchange across the sediment-water interface on the continental margin. With benthic shipboard flux chambers (SBFCs) and diffusional calculations based on measured pore water concentrations, we quantified the efflux of MeHg from sediment at multiple sites on the continental shelf and slope of the northwest Atlantic Ocean during three oceanographic cruises in 2008–2010. Intact sediment cores and overlying water for use in SBFCs were sampled successfully from ocean depths ranging between 60 and 3000 m. Preliminary results suggest that sediment fluxes are comparable to those estimated from vertical gradients of MeHg in the overlying water column and are in general agreement with a prior report of the oceanographic magnitude of this flux. Production and mobilization from sediment on the continental margin is an important source of MeHg to coastal fisheries and, potentially, the open ocean.

TS14-P3 — 11:00-12:00 and 17:30-18:30
Authors: WELLER, Robbie1, FINIGUERRA, Michael2, FITZGERALD, William F.2, HAMMERSCHMIDT, Chad R.1
(1) Wright State University, weller.20@wright.edu; (2) University of Connecticut;

Accumulation by plankton is a key process influencing the trophic transfer of monomethylmercury (MMHg) in aquatic food webs and its levels in fish. Although humans are exposed to toxic MMHg principally by the consumption of seafood, there is a near absence of information on MMHg distributions in marine phytoplankton and zooplankton. As part of a comprehensive study of mercury and MMHg cycling on the continental margin of the northwest Atlantic Ocean, we are investigating the spatial and temporal variability of MMHg in planktonic communities, bioconcentration factors of MMHg between water and phytoplankton, trophic transfer between phyto- and zooplankton, and differences in MMHg bioaccumulation among size fractions of zooplankton communities. Phytoplankton and zooplankton were sampled with trace-metal clean techniques from 31 locations ranging from near-shore waters (e.g., Cape Cod Bay) to remote stations near the offshore extent of the continental margin during three oceanographic cruises in 2008–2010. Preliminary results suggest that MMHg in primary producers (i.e., phytoplankton) is related to the amounts in filtered water, which is indicative of a relatively constant bioconcentration factor. Additionally, MMHg increases in concentration within the planktonic community from primary producers to grazers and differs among size fractions of the zooplankton community. Results of this study will improve our knowledge of environmental and biological factors influencing MMHg incorporation into marine food webs and help constrain oceanic budgets and cycling models of this contaminant.

TS14-P4 — 11:00-12:00 and 17:30-18:30
Authors: AUSTIN, Carrie1, RIDOLFI, Kat2, MELWANI, Aroon3, GRENIER , J. Letitia3
(1) CalEPA, SF Bay Water Board, caustin@waterboards.ca.gov; (2) Formerly SFEI, Now LimnoTech; (3) San Francisco Estuary Institute (SFEI);

Tomales Bay demonstrates downstream improvements from mercury mine remediation. Mercury mining in Tomales Bay occurred in the 1960’s), and the single mine was remediated in 2000. Hydrodynamics confine mine pollution to one area, Walker Creek (WC) delta, where it is buried by cleaner sediments. WC delta surface sediment TotHg (mean, ug/g, dry wt) was 1.6 in 2000, 0.9 in 2009; elsewhere in Tomales Bay, 2009 surface sediment TotHg was 0.1–0.2.

Mercury in sediment, particularly at deltas with high primary productivity, is key to bioaccumulation in Tomales Bay. Mercury is methylated and bioaccumulated through the food web and at times exceeds health thresholds for humans and wildlife.

Human health was the initial driver. In ~2000, both wild and farmed filter-feeding shellfish had mean MeHg concentrations well below thresholds; shellfish farms are the largest industrial operation in Tomales Bay. A favorite sport fish (halibut) consistently has TotHg (mean, skinless filet, ug/g, ww) at 0.2, and other sport fish (surfperch, jacksmelt, wild crabs) consistently have lower concentrations. However, the less frequently consumed sharks and rays have much higher concentrations (0.5–1.4).

It now appears that threats to wildlife are the primary concern, particularly in the tidal marshes. In 2009, prey fish TotHg (mean, ug/g, ww, composites) was equal to the threshold that protects piscivorous birds. Baywide, TotHg was 0.05 in small (40–110 mm), whole prey fish caught in subtidal areas. In 2010, we only sampled at WC delta; TotHg was 0.11 in prey fish caught from the intertidal channels, and 0.16 in prey fish caught in tidal marsh channels. MeHg (mean, ug/g, ww, composites) in small marsh crabs (carapace width 12–26 mm) was 0.06, which is six times greater than the threshold for piscivorous birds that also consume invertebrates.

We plan to monitor mercury trends in WC delta sediment and biota over the next decade to ensure that concentrations decline to safe levels. Additional information is available at www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/ and www.sfei.org/documents.

TS14-P5 — 11:00-12:00 and 17:30-18:30
Authors: HARRIS, Reed C.1, POLLMAN, Curtis D.2, LANDING, William M.3, AXELRAD, Donald M.4, MOREY, Steven3, EVANS, David W.5, HUTCHINSON, David H.1, DUKHOVSKOY, Dmitry3, ADAMS, Douglas H.6, RUMBOLD, Darren7, SUNDERLAND, Elsie M.8
(1)Reed Harris Environmental Ltd., reed@reed-harris.com; (2) Aqua Lux Lucis Inc.; (3) Florida State University; (4) Florida Department of Environmental Protection; (5) National Oceanic and Atmospheric Administration; (6) Florida Fish and Wildlife Conservation Commission; (7) Florida Gulf Coast University; (8) Harvard University.

The Gulf of Mexico (Gulf) is a vast waterbody with an area of 1.6 million km2, draining 41% of the area of the 48 contiguous states in the US. It accounts for more than 40% of the US marine recreational fish catch and ~14% of the country’s marine commercial fish landings. Elevated mercury (Hg) concentrations in Gulf fish have resulted in consumption advisories for dozens of coastal and offshore species. There is evidence that some species of fish in the Gulf have Hg concentrations higher than those in the adjacent Atlantic Ocean, suggesting enhanced rates of Hg loading, net methylation and/or trophic biomagnification. Differences in fish Hg concentrations among estuaries and among coastal regions suggest variability in Hg sources and/or cycling within the Gulf. There is a need to understand Hg sources and environmental factors controlling elevated MeHg levels in Gulf fish in order to develop options to reduce risks associated with fish consumption. A screening-level mechanistic model of Hg dynamics and bioaccumulation was developed to organize our understanding and information needs for Hg cycling in the Gulf. A course scale spatial grid was used with 15 coastal cells and 4 offshore cells. Estimates of atmospheric Hg deposition were derived with outputs from the US EPA’s CMAQ model. Water circulation was estimated by aggregating outputs of the Navy Coastal Ocean Model to fit the screening model’s grid structure. A simplified box model of estuarine Hg cycling was also constructed to provide a preliminary view of two-way interactions between Hg in estuarine waters and the open Gulf. Model results indicate that water mixing in the Gulf is sufficient that regions cannot be treated in isolation in terms of Hg sources, but not complete enough to consider the Gulf well-mixed. Atmospheric, terrestrial and Atlantic Ocean Hg inputs are all predicted to be important sources to the Gulf with respect to Hg that ultimately accumulates in fish, but the relative importance of these sources varied widely among Gulf regions in model simulations. Each of these three sources is predicted to be the largest input to at least one model region. A Gulf-wide approach to Hg is needed due to linkages between estuarine, coastal and pelagic zones. Total and methyl Hg measurements in the water column and lower food web are sparse in the Gulf (non-existent in offshore areas) and monitoring and research are needed in multiple regions.

TS14-P6 — 11:00-12:00 and 17:30-18:30
Authors: LANDING, William1, HOLMES, Christopher D.2
(1) Florida State University, Earth, Ocean and Atmospheric Science, wlanding@fsu.edu; (2) UC Irvine, Atmospheric Chemistry, Earth System Science.

Due to the lack of ground-based monitoring sites, the transport and deposition of atmospheric mercury in the Tropics has been inferred from global models. The situation is somewhat better in the Gulf of Mexico, with active MDN sites along the USA gulf coast and numerous monitoring projects covering various time periods over the past 20 years. The current state of the various global models with respect to their predictions regarding deposition and re-evasion of Hg from the tropical marine environment and the Gulf of Mexico will be summarized, and compared to monitoring data (where available).

TS14-P7 — 11:00-12:00 and 17:30-18:30
Authors: EVANS, David1, ROCHELLE, Colleen2, CERINO, David3
(1)NOAA, david.w.evans@noaa.gov; (2) East Carolina University; (3) Pitt Community College.

Mobile Bay is the estuary of the sixth largest watershed by area in the United States, with the fourth greatest freshwater flow. An extensive deltaic wetland lies at its head. The 1068 km2 bay downstream from the delta debouches into the Gulf of Mexico. During late summer, part of the shallow bay (mean depth 3 m) can become hypoxic. Freshwater residence times are typically about one week.

We sampled total mercury and methylmercury in the waters of Mobile Bay quarterly between February 2008 and August 2009 to define freshwater inputs, exports to the Gulf of Mexico, and evidence of losses or gains within the estuary. In Mobile Bay, methylmercury is a small fraction of the total mercury in the water column (median value 3.9%). The majority (mean 74%) of the methylmercury in the water column was associated with suspended sediments. Total mercury was even more-particle associated than methylmercury.

Methylmercury concentrations in filtered water samples ranged from 0.174 ng/L down to the detection limit (<.020 ng/L in 2008 and <.010 ng/L in 2009) with one significant exception. In February 2008, we measured 0.652 ng/L methylmercury in filtered water within an algal bloom (Prorocentrum minimum) in the northeast bay. Total mercury in filtered water was also high in the bloom.

Highest dissolved methylmercury concentrations were observed in more freshwater habitats: the Mobile and Tensaw rivers and Delta, Most measurements of dissolved methylmercury in the southern half of the bay (salinity > 16 PSU) were below detection limits. Plots of dissolved methylmercury concentrations versus salinity indicated rapid removal of methylmercury to suspended or bottom sediments in the upper bay.

Mobile Bay results can be compared with results from Florida Bay, a known mercury hotspot in the Gulf of Mexico. In the latter locale, highest methylmercury concentrations were also found in the brackish water area of the estuary. Here, however, methylmercury as a percentage of total mercury in the water column was higher (median value 8.2%). Methylmercury concentrations were also higher, reaching 1.512 ng/L. Total Hg was not any higher in Florida Bay than in Mobile Bay. The differences are likely due to modestly higher inputs of methylmercury from the Florida Bay watershed, enhanced mercury methylation within Florida Bay sediments, and the very much greater river flow and tidal exchange in Mobile Bay, which effectively dilutes and flushes introduced methylmercury out of the Bay and into the Gulf of Mexico.

TS14-P8 — 11:00-12:00 and 17:30-18:30
Author: SEIXAS, Tercia G1
(1) PUC-Rio, terciaguedes@gmail.com

Guanabara Bay (GB) and Ilha Grande Bay (IB) are two important estuaries regarding the productivity in the southeastern Brazilian coast. GB is heavily impacted by industrial sewage and untreated domestic waste and presents hyper-eutrophic environmental conditions. IB presents typical oligotrophic environmental conditions and is considered a non-contaminated area. This estuary is one of the important recreational areas of Rio de Janeiro state. The objective of the present work is to compare the total mercury (Hg) levels in a carnivorous fish species (Micropogonias furnieri), measured at the beginning and the end of a 19-year interval (1990 – 2009). In order to compare total mercury levels along the time, Hg length normalized concentrations in fish were evaluated in different periods in both areas. No differences were found between the length normalized Hg concentrations in fish from the two bays at the beginning and the end of a 19-year interval. The Hg length normalized concentrations in fish from GB has probably remained constant for the last 19 years (0.12 ± 0.07 µg/g wet wt.), with possible isolated fluctuations attributed to occasional changes in water quality. In GB the large inputs of suspended matter, is probably reducing the residence time of Hg in water column decreasing its bioavailability and making the Hg levels lower than expected. A highly significant difference (p < 0.0001) was found in Hg length normalized concentrations between the sampling years (1990 and 2009) at IB, indicating an increase of Hg along the 19-year interval. Hg length normalized concentrations in fish collected at IB were 0.12 ± 0.07 µg/g wet wt. and 0.18 ± 0.11 µg/g wet wt. in 1990 and 2009, respectively. Probably, an increase on Hg inputs has been occurring in the last 19 years in IB ecosystem. This bay did not present any known anthropogenic source of mercury and its watershed presents low levels of organic matter and low biological productivity. In this situation, mercury inputs become more available to the aquatic organisms.

TS14-P9 — 11:00-12:00 and 17:30-18:30
Author: KEHRIG, Helena A.1
(1) IBCCF-UFRJ, kehrig@biof.ufrj.br

The present study evaluated the methylmercury concentrations (MeHg), carbon (d13C) and nitrogen (d15N) stable isotopes in two top-predators Pontoporia blainvillei (cetacean) and Trichiurus lepturus (fish), with feeding overlap from the Brazilian coast, northern Rio de Janeiro State, and their representative prey species, which are distributed in different habitats along the water column, five fish species with different feeding habits (Isopisthus parvipinnis, Cynoscion jamaicensis, Stellifer rastrifer, Chirocentrodon bleekerianus and Pellona harroweri), two cephalopod species (Loligo sanpaulensis and Lolliguncula brevis) and one crustacean species (Xiphopenaeus kroyeri). T. lepturus and P. blainvillei exploit coastal waters to obtain their food sources, preying upon neritic species, both pelagic and demersal. The stable isotopes were used as a tool to assess the modes of MeHg bioaccumulation and biomagnification along the coastal food web. The muscle tissue of the top-predators, voracious predator fish and cetacean presented similar MeHg concentrations (mean: 1.03 ± 0.90 µg/g dry wt.). T. lepturus muscle displayed higher d15N than in cetacean (mean: 14.1‰ and 11.8‰, respectively), which reflected its higher trophic level nutrition. The voracious predator fish presents preferably piscivorous habits, actively pursuing their preys feeding on larger prey species than those ingested by P. blainvillei. Higher d13C were found in cetacean than in voracious predator fish (mean: -15.2‰ and -17.4‰, respectively). The values of d13C are reflecting the coastal habits of both top-predators. The crustacean species consumed mostly by T. lepturus, displayed the lowest values found for MeHg concentrations and d15N in the muscle tissue (mean: 0.07 ± 0.03 µg/g dry wt. and 10.3 ± 0.3‰, respectively). However, similar d13C was found between crustacean (-15.2‰) and cetacean muscle. MeHg and d15N increased successively with increasing trophic levels along the food web. The relationship between these variables can be expressed by the following equation: log [MeHg] = 0.58*(d15N) – 8.13, (r = 0.81; p < 0.05), indicating that biomagnification may be occurring among the trophic levels, as well as along the food web. The regression slope of the equation (0.58) indicated that the studied food web presented an elevated biomagnification rate that can be related to the environmental water quality of the studied area. This area belongs to a faunistic transition zone that is a very dynamic area with great estuarine and marine biodiversity and presents many endemic species.

TS14-P10 — 11:00-12:00 and 17:30-18:30
Author: KEHRIG, Helena A1
(1) IBCCF - UFRJ, kehrig@biof.ufrj.br

The feeding preference of the two costal dolphins Pontoporia blainvillei and Sotalia guianensis in south-eastern Brazil was assessed through the prey’s index of relative importance (IRI), mercury concentrations (Hg) and isotopic signatures, in order to compare their efficiency in the discrimination of prey contribution to the predators’ diet. Dolphin stomach contents were analyzed in order to identify prey species and calculate their original size. The IRI of each prey represented around 95% of the total IRI were selected. In general, P. blainvillei feeds on juveniles or small-sized fish and cephalopod species, up to 10.0 cm length. S. guianensis has a higher plasticity in relation to prey size, reaching more than 100.0 cm length. IRI was the best tool to describe the dolphins’ preference, while Hg seems to be efficient as a trophic marker when the diet is specific or made up of prey of varying sizes. Hg in muscle tissue was threefold higher for S. guianensis than for P. blainvillei. Hg in predators was significantly higher than in their preys. Among S. guianensis preys, there was a positive (but non-significant) correlation between Hg and IRI, whereas for P. blainvillei this correlation was weaker. There was no significant correlation between Hg and isotopic signatures, or between the preys’ IRI and isotopic signatures. Both dolphins presented lighter d15N than their prey species, indicating that trophic position cannot be related to this isotope. Moreover, no correlation was observed between Hg and d15N in muscle tissue. The d13C values characterized a typical coastal food chain, and, although this isotope is not usually applied to distinguish trophic levels, it was more consistent with species trophic position than d15N.

TS14-P11 — 11:00-12:00 and 17:30-18:30
Authors: EVERS, David1, BUCK, David 1, CHEN, Celia2, DRISCOLL, Charley 3, FRANKLIN, Julie1, GILMOUR, Cindy4, HAMMERSCHMIDT, Chad5, SUNDERLAND, Elsie6
(1) BioDiversity Research Institute, david.evers@briloon.org; (2) Dartmouth College; (3) Syracuse University; (4) Smithsonian Environmental Research Center; (5) Wright State University; (6) Harvard University.

Climate change is a global issue caused by greenhouse gases and aerosols of predominantly anthropogenic, but also natural origin; of primary concern are CO2, CH4, carbon particles and N2O. Various models have predicted the influence of climate change on the hydrology and biogeochemistry of coastal wetlands, from sea level rise, increased precipitation, and warmer waters, to increased primary productivity - among other projected influences. Warmer temperatures are currently and projected to lead to melting glaciers, permafrost degradation, ice and snowmelt and increased forest fires; all processes which have the potential to convert mercury sinks into mercury sources. In this study, we consider a broad range of factors related to climate change that may influence methylmercury production and bioavailability in three coastal biomes: tundra-dominated shorelines of the Arctic, spartina-dominated shorelines of temperate regions, and mangrove-dominated shorelines of the tropics. In addition to considering factors that may lead to increased Hg input to aquatic ecosystems, we also evaluate factors influencing methylmercury production and bioavailability in wetlands, such as enhanced wetting and drying cycles.

TS14-P12 — 11:00-12:00 and 17:30-18:30
Authors: COSTA, Monica F1, BARROCAS, Paulo R2, BARLETTA, Mario1, KEHRIG, Helena A3, MALM, Olaf4, HACON, Sandra5, MOREIRA, Josino C6, VASCONCELLOS, Ana C2, LANDING, William7, EVERS, David8, BUCKS, David8
(1) Departamento de Oceanografia. Universidade Federal de Pernambuco, mfc@ufpe.br; (2) Departamento de saneamento e Saude ambiental. Escola Nacional de Saúde Pública. Fundação Oswaldo Cruz; (3) Laboratório de Radioisótopos Eduardo Penna Franca. IBFCCF, CCS, Universidade Federal do Rio de Janeiro; (4) Laboratório de Radioisótopos Eduardo Penna Franca. IBFCCF, CCS. Universidade Federal do Rio de Janeiro; (5) Departamento de Endemias. Escola Nacional de Saúde Pública. Fundação Oswaldo Cruz; (6) CESTEH. Escola Nacional de Saúde Pública. Fundação Oswaldo Cruz; (7) Oceanography Department, Florida State University; (8) BioDiversity Institute;

In tropical and sub-tropical coastal environments mercury cycling is driven by many forces, among them the strongest ones are rainfall (river flow) and human interferences. The number of studies in these areas is low, and works remain sparse in space and time, with rare exceptions to some systems that are relatively better known than others. The tropical and sub-tropical belt encircles different countries of every existing development level including, partially or totally, some of the ten largest global economies. However, most are developing countries struggling to conciliate population well being with environmental conservation. Health and environment policies also vary tremendously among these countries, and some might not even be covered by policies elaborated by international institutions. Therefore, coastal populations are at different levels of risk in terms of exposure to mercury from different sources (food and urban and industrialized environments). One of the most prominent policy threats, recurrent around countries of the tropical and sub-tropical belt is the disconnection between river basins and coastal environments management plans and actions. Although a clearly necessary approach from environmental scientist’s points of view, this is hardly ever acknowledged by public administrators, who tend to “box” natural environments according to budget and political issues. Consequently, the poor basin and estuarine management practices concerning water quality as a whole, and mercury loads in particular, are transferred and sometimes amplified in coastal waters. Tropical coasts harbor a large variety of natural biomes, ecosystems, and habitats that are home to a still uncertainly known number of microbial, vegetal, and animal species. Some might be already disappearing before being described and known due to physical habitat loss and biological community changes. Therefore important links and processes of the mercury cycle that involve these diverse habitats and biological species might be lost. The consequences for the remaining elements of the coastal mercury cycle are unpredictable. Some groups of very abundant and resilient coastal and estuarine fish and shellfish might become the only available food option for humans and other large aquatic vertebrates (marine mammals and reptiles). Simplification of coastal tropical food webs and consequent lower diet diversity can bring up new patterns of mercury cycling in the biological compartment and its contamination. Easily enough it might mean we will face unknown and challenging human health issues in the near future.

TS14-P13 — 11:00-12:00 and 17:30-18:30
Authors: BOTARO, Daniele1, MALM, Olaf1, TORRES, Joao Paulo1
(1) UFRJ, danibot13@gmail.com

Trace metals are not obvious pollutants present in shrimp farm effluents. However, some trace metals are present as natural components in aquafeeds, as impurities in fertilizers or as active principles of pesticides, which can be accumulated in shrimp tissue. Were analyzed 90 muscle samples of fresh and frozen farmed shrimp and pond water collected in three farms in Brazil, between September 2007 and May 2010. It were determined total mercury concentrations by a flow injection mercury system and, lead, arsenic and cadmium concentrations by graphite furnace atomic absorption spectrophotometry. Mercury levels in the farmed shrimp ranged from 0.01 – 0.18 mg.kg-1 in fresh shrimp, and from 0.002 – 0.008 mg.kg-1 in frozen shrimp (wet weight). A similar behavior was observed to lead concentrations, since frozen shrimp presented markedly lower lead concentrations (0.30 – 0.89 mg.kg-1) than fresh shrimp (0.92 – 2.89 mg.kg-1). In the case of arsenic, were observed concentrations of 0.01 – 0.77 mg.kg-1 in fresh shrimp muscle, and were no detected concentrations of this trace metal in muscle of frozen shrimp (Limit of detection of 0.002 mg.kg-1). The shrimp freezing process consists of a preliminary washing thoroughly in chlorinated water (5 ppm) to remove any remaining mud or sand, and to reduce bacterial contamination. The shrimp are drained as much as possible and are then ready for freezing through quick-freezing tunnel (individually quick frozen). The is no evidence indicating that this process contributed to reduce trace metals levels in frozen shrimp, but is clear that lead, arsenic and mercury levels are markedly lower in frozen than fresh shrimp. It was observed low concentrations of trace metals in pond water and consenquentley in shrimp muscle. In relation to years monitored, in 2008 it was possible to observe a slightly higher concentration of all trace metals in fresh shrimps compared to other years. Episodes of intensive precipitation caused recurrent devastating floods in the region in 2008, and caused harm to farms evaluated. Thus, increased concentrations of these trace metals in the rainy season may be related to resuspension of particles deposited in the sediment of the bottom in the ponds and therefore available for incorporation into these trace metals by aquatic biota. It can be concluded that farmed shrimp in Brazil is safe for human consumption. Thanks go to CNPq/MAPA/SDA 577906/2008-9 for finantial support and scholarships conceded.

TS14-P14 — 11:00-12:00 and 17:30-18:30
Authors: DIMENTO, Brian P.1, MASON, Robert P.1
(1) University of Connecticut, brian.dimento@uconn.edu

Photochemical degradation is a known sink for methylmercury (MeHg) in freshwater lakes, but less is known about its importance in marine waters. The fate and stability of MeHg in oceanic waters has been studied relatively little, although decomposition rates have been observed to be slower in seawater than in freshwater. The reason for the differing relative stability to photodegradation in fresh and sea water is not completely clear. Many have proposed that an indirect photochemical mechanism involving reactive oxygen species (ROS), namely singlet oxygen (1O2) and hydroxyl radicals (•OH), is responsible for the degradation of MeHg. In this work, degradation pathways and rates were investigated by varying reaction conditions including salinity, dissolved organic carbon (DOC) levels (50-500 µM), and the presence of different ROS scavengers. Experiments were conducted at or near natural MeHg levels to avoid potential artifacts from elevated concentrations. In addition, the use of MeHg isotopes allowed for further analysis of the end products of the degradation reactions. The ultimate goal of this research was to increase the mechanistic knowledge of the photodegradation process, including the effects of parameters such as radiation wavelength (ultraviolet vs. visible light) and complexation.

TS14-P15 — 11:00-12:00 and 17:30-18:30
Authors: TRAORE SCHARTUP, Amina1, BALCOM, Prentiss H.1, MASON, Robert P.2
(1) University of Connecticut, amina.traore@uconn.edu; (2) NSF.

Mercury (Hg) in its methylated form, methylmercury (MeHg), is a dangerous neurotoxin that affects marine apex predators and humans through fish consumption. Biogeochemical factors affecting mercury speciation in sediments, porewater and the water column of Long Island Sound (LIS) were examined during summer and fall 2009 and spring 2010. The relative importance of factors such as organic matter quality and quantity (using loss on ignition-LOI and carbon content), and sulfide and sulfur content on sediment and porewater MeHg and Hg was assessed at two biogeochemically contrasting stations: western (WLIS) and central Long Island Sound (CLIS). WLIS is clay-like and relatively high in organic content (on average 2.5 mmol C.g-1 and 11% LOI) and in bulk Hg content (total Hg of about 2 nmol.g-1 and MeHg of 5 pmol.g-1), while CLIS is sandy with low organic content (0.5 mmol C.g-1 and 3% LOI) and lower bulk Hg content (average total Hg of about 0.2 nmol.g-1 and MeHg of 0.7 pmol.g-1). Higher partition coefficients (Kd) of inorganic mercury (HgII) are found in WLIS (log Kd of 4.7) as compared to CLIS (log Kd of 3.7) and imply a greater bioavailability of HgII for methylation at CLIS. This is confirmed by a higher % MeHg (percentage of Hg as MeHg; often used as a proxy for methylation rate) in both bulk sediment and porewater in CLIS. Results suggest that mercury speciation is strongly controlled by organic matter in CLIS, but sulfur appears to play a more important role in WLIS, with associated mechanistic differences between the two stations. Bottom water hypoxia can indirectly affect sediment mercury methylation by increasing the acid volatile sulfides (AVS) content of the sediment. AVS has previously been shown to reduce mercury methylation and bioavailability by limiting mercury partitioning into porewater. Additionally, the Kd for MeHg is lower in CLIS suggesting that the MeHg formed in this environment may be more mobile and bioavailable to the aquatic food chain. The differences in the factors associated with the production, mobility and bioavailability will be discussed and contrasted in this presentation.

TS14-P16 — 11:00-12:00 and 17:30-18:30
Author: KEHRIG, Helena A.1
(1) IBCCF-UFRJ, kehrig@biof.ufrj.br

Methylmercury (MeHg) and inorganic mercury (Hginorg) were evaluated in the water of a polluted Brazilian estuary, Guanabara Bay, with one size classes of plankton, microplankton (≥70 µm). Chlorophyll a and the total of organic carbon (TOC) were evaluated in suspended particulate matter (SPM). Samples were collected at five sampling stations within the lower estuary. Chlorophyll a and TOC in SPM ranged from 6.6 to 27.7 µg L-1 and 0.9 to 2.3 mg.L-1, respectively. MeHg concentrations in SPM ranged from 8.3 to 47.2µg.g-1 and were approximately 13% of the total mercury (Hg). Dissolved MeHg in water was low and ranged from 0.16 to 0.42 ng L-1. The predominant chemical species of mercury in estuarine water is inorganic, since only 11.2% of Hg in water was presented as MeHg. The highest concentrations of MeHg in water were found in sampling stations close to the bay mouth, near the confluence of Atlantic Ocean and estuarine waters. However, SPM samples from these stations presented the lowest MeHg concentrations. Water partition coefficients (PCs) in microplankton were approximately fourfold higher for MeHg than for Hginorg when averaged across the five sampling stations within estuary. Only 60.0 % of Hg in microplankton samples was presented as MeHg. MeHg in microplankton ranged from 9.3 to 23.0 µg.kg-1 dry wt. The microplankton samples collected at these stations were composed of cyanobacteria (approximately 2% of the total sampled microplankton). MeHg found in microplankton and the number of cyanobacteria presented in it showed a positive and significant correlation (R2=0.72; p<0.01). The activity of sulfate-reducing bacteria, or cyanobacteria, is associated to the methylation process of Hginorg; i.e. with the formation of methylmercury. MeHg in microplankton and TOC in SPM showed an inverse and significant correlation (R2=0.85; p<0.001). The samples from the point close a Marina (point 2) presented the lowest MeHg in microplankton (9.3µg.kg-1) and also, the highest concentrations of TOC (2.3mg.L-1) in SPM. In point 2, the samples of microplankton were composed of diatoms (approximately 60%) and did not present any cyanobacteria in its composition. A significant and positive correlation was observed between the concentration of chlorophyll a and the number of cyanobacteria presented in plankton (R2=0.75; p<0.05). According to the results found for chlorophyll a, this environment presents a high primary productivity that is accomplished by the autotrophic organisms presented in microplankton, as cyanobacteria and diatoms.

TS14-P17 — 11:00-12:00 and 17:30-18:30
Authors: MASON, Robert P1, CHOI, Anna2, FITZGERALD, William F1, HAMMERSCHMIDT, Chad 3, LAMBORG, Carl4, SUNDERLAND, Elsie M2
(1) University of Connecticut, robert.mason@uconn.edu; (2) Harvard School of Public Health; (3) Wright State University; (4) Woods Hole Oceanographic Institute;

This presentation will provide through a mass balance and synthesis exercise an update on the biogeochemical cycling of mercury (Hg) and the formation and transport of methylated Hg (CH3Hg and (CH3)2Hg) in the ocean. Information on the atmospheric input of Hg species and details of the air-sea exchange of mercury through gas evasion and wet and dry and deposition will be presented. The importance of inorganic Hg and CH3Hg input from the margins (rivers + estuaries) will be examined, as well as other sources and sinks, such as production and export from the shelf and slope, water column methylation and input from deep ocean sediments, including hydrothermal inputs. The presentation will further examine recent studies looking at sediment and water column methylation, and how these relate to the remineralization of organic matter in the ocean. The vertical distributions of various Hg species and modeling will be presented to further examine water column processes, and how these relate to environmental variables and production and recycling of biotic material, and the potential relationship to microbial processes. Differences in concentration and distribution across ocean basins will be presented and the importance of ocean circulation examined. Finally, the presentation will highlight what is known and unknown concerning the movement of CH3Hg through the pelagic food chain. Through model evaluation and data mining, the presentation will evaluate our best available understanding of spatial and temporal trends in ocean CH3Hg and the potential changes in fish concentration over time. Overall, this paper will provide a necessary synthesis of the available information that can inform and provide a basis for future open ocean studies.

TS14-P18 — 11:00-12:00 and 17:30-18:30
Authors: BUGGE, Deenie 1, WARD, Darren2, WILLIAMS, Jason3, MASON, Robert 4, CHEN, Celia1
(1) Dartmouth College, Deenie.bugge@dartmouth.edu; (2) Humboldt State University; (3) TerraGraphics Environmental Engineering; (4) University of Connecticut;

Estuaries are major repositories of pollutants derived from adjacent watersheds. They are also important nursery grounds for many coastal and open ocean species. Estuarine food webs provide important links between sediment contaminants such as Hg and coastal fish and shellfish species consumed by humans and wildlife. Mercury concentrations in estuarine biota depend in part on bioaccumulation and trophic transfer patterns within estuarine food webs. We analyzed food web structure and organism total Hg and methylmercury burden in estuarine food webs at ten sites on the East Coast (from the Hackensack River, NJ to the Gulf of Maine) along a Hg sediment contamination gradient. Across sites, MeHg concentrations in sediments varied by approximately 100 fold, whereas Hg concentrations in biota varied by only 3-8 fold. MeHg concentrations in sediments were not predictive of biotic concentrations (fish, crabs, mussels) except for polychaete worms. However, there was a significant positive relationship between MeHg in sediments and organic carbon (%LOI) across sampling sites. Biota-sediment concentration factors, a measure of bioaccumulation, showed a negative relationship with organic carbon (% LOI) in sediments, suggesting organic carbon regulates the bioavailability of total Hg. MeHg in the water column (dissolved and particulate) was predictive of MeHg concentrations in fish (killifish and Atlantic silversides) and MeHg concentrations were higher in pelagic fauna than in benthic-feeding fauna suggesting that chemical flux into the water column may be more important than bioaccumulation from the sediment for these food webs. Our results indicate that both biogeochemical and ecological characteristics of estuarine food webs influence the bioaccumulation and trophic transfer of MeHg in estuarine food webs.

TS14-P19 — 11:00-12:00 and 17:30-18:30
Authors: LEHNHERR, Igor1, KIRK, Jane L.2, ANDERSSON, Maria3, BRAUNE, Birgit M.2, CHAN, Laurie4, LOSETO, Lisa L.5, STEFFEN, Alexandra6, ST. LOUIS, Vincent L.1
(1) University of Alberta, lehnherr@ualberta.ca; (2) Environment Canada; (3) Gothenburg University; (4) University of Northern British Columbia; (5) Fisheries and Oceans Canada; (6) Enivronment Canada;

The main exposure pathway of methylmercury (MeHg) to humans is through the consumption of marine-based foods. The ability to link atmospheric Hg deposition, MeHg sources and bioaccumulation in marine ecosystems to human exposure is therefore crucial to mitigate environmental and health impacts of Hg contamination. The Arctic region poses many unique challenges to researchers trying to address these issues, both from a physical science and human/social science perspective. For example, Arctic marine ecosystems are free from Hg point sources but not from long-range transport of Hg originating from emissions in Europe, Asia and North America; atmospheric inputs are enhanced due to atmospheric Hg depletion events; sea-ice is an important, but as of yet unquantified, controlling factor for a number of processes such as air-water gas exchange and photochemical transformations; and climate change will continue to impact Hg cycling in the Arctic in drastic ways. From a social perspective, human exposure is a particularly salient issue for Inuit populations across the Arctic relying on a traditional diet comprised primarily of marine country foods such as fish, seal and beluga. For example, Hg concentrations in beluga (1-39 µg g-1 in livers) and seal (5-35 µg g-1 in livers) tissues can be extremely high and well above consumption guidelines for Hg in fish (generally between 0.3-0.5 µg g-1). However the cultural and health (e.g., source of omega-3 fatty acids) benefits of country foods are also very important considerations. We will present here an overview of the state-of-knowledge of Hg science in Arctic marine ecosystems, starting from external inputs (e.g., atmosphere, rivers) to in-ocean processes (e.g., methylation/demethylation), bioaccumulation and spatial/temporal trends in marine organisms, and human exposure and health considerations, identifying gaps that need to be addressed in the future. Finally, relevant policy questions with respect to fate, transport, cycling, human health and risk communication will be addressed where possible.

TS14-P20 — 11:00-12:00 and 17:30-18:30
Authors: BUCK, David G1, GRAHAM, Rachel T2, DIVOLL, Tim1, EVERS, David C1
(1) BioDiversity Research Institute, david.buck@briloon.org; (2) Wildlife Conservation Society;

Research on mercury (Hg) bioaccumulation and pathways for contaminant transfer within food webs have historically been conducted in freshwater aquatic ecosystems and there is a gap in our understanding of these dynamics in coastal and marine environments. Recent research in the Gulf of Honduras suggests that certain apex predators (e.g., goliath grouper) bioaccumulate potentially toxic levels of Hg. Here we present data on mercury bioaccumulation and trophic transfer in fishes from the Gulf of Honduras, with a focus on common food fish. Mercury data are presented on fishes that occupy multiple trophic levels including snook, snapper, barracuda, and mackerel. Data suggest that Hg in fishes of the Gulf of Honduras represents a human and ecological health risk requiring attention. The Gulf of Honduras is a highly productive fishery that provides an important livelihood for numerous coastal communities of Belize and marine fish is a significant component of the diet of many Belizeans. Future research in the region should focus on identifying potential atmospheric and terrestrial-derived sources for Hg in the region.

Tuesday, 26 July, 2011