Marc Amyot

Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition

Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.

Sunlight-induced formation of dissolved gaseous mercury in lake waters

Formation of dissolved gaseous mercury (DGM) was measured in lake water incubated at midday in Teflon bottles. DGM production was photoinduced as transparent bottles yielded DGM concentrations that were 2.4-9 times higher than dark controls. These results provide the first experimental evidence obtained in the field of a direct link between solar radiation and DGM production. A positive relationship was found between photoinduced DGM production at different times of the year and incident radiation. Removal of UV B light or addition of hydrogen peroxide during incubation did not result in significant changes in DGM levels. A diel pattern in DGM production was observed, and a depth profile of DGM revealed that most of the production was occuring in the epilimnion

The Arctic: a sink for mercury

Mercury is a persistent, toxic and bio-accumulative pollutant of global interest. Its main mass in the troposphere is in the form of elemental gas-phase mercury. Rapid, near-complete depletion of mercury has been observed during spring in the atmospheric boundary layer of frozen marine areas in Arctic, sub-Arctic and Antarctic locations. It is strongly correlated with ozone depletion. To date, evidence has indicated strongly that chemistry involving halogen gases from surface sea-salt is the mechanism of this destruction. Precisely which halogen gases are the main players has remained unresolved. Our novel kinetic data and multiscale modelling show that Br atoms and BrO radicals are the most effective halogens driving mercury oxidation. The reduction of oxidized mercury deposited in the snow pack back to Hg0 and subsequent diffusion to the atmosphere is observed. However, it cannot compensate for the total deposition, and a net accumulation occurs. We use a unique global atmospheric mercury model to estimate that halogen-driven mercury depletion events result in a 44% increase in the net deposition of mercury to the Arctic. Over a 1-yr cycle, we estimate an accumulation of 325 tons of mercury in the Arctic.

Mercury Physicochemical and Biogeochemical Transformation in the Atmosphere and at Atmospheric Interfaces: A Review and Future Directions

Atmosphere and at Atmospheric Interfaces: A Review and Future Directions Parisa A. Ariya,*,†,‡ Marc Amyot, Ashu Dastoor, Daniel Deeds,‡ Aryeh Feinberg,† Gregor Kos,‡ Alexandre Poulain, Andrei Ryjkov, Kirill Semeniuk, M. Subir, and Kenjiro Toyota †Department of Chemistry and ‡Department of Atmospheric and Oceanic Sciences, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada, H3A 2K6 Department of Biological Sciences, Universite ́ de Montreál, 90 avenue Vincent-d’Indy, Montreal, Quebec, Canada, H3C 3J7 Air Quality Research Division, Environment Canada, 2121 TransCanada Highway, Dorval, Quebec, Canada, H9P 1J3 Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada, K1N 6N5 Department of Chemistry, Ball State University, 2000 West University Avenue, Muncie, Indiana 47306, United States Air Quality Research Division, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada, M3H 5T4

New Evidence on Variations of Human Body Burden of Methylmercury from Fish Consumption

Epidemiologic studies commonly use mercury (Hg) level in hair as a valid proxy to estimate human exposure to methylmercury (MeHg) through fish consumption. This study presents the results yielded by a complete data set on fish consumption habits, Hg levels in edible fish resources, and corresponding Hg accumulation in hair, gathered in three distinct communities of eastern Canada. For one of these communities, the average hair Hg concentration was 14 times less than the expected value based on calculated daily oral exposure and current knowledge of MeHg metabolism. This finding could be explained by differences in specific genetic characteristics and/or interactive effects of other dietary components.

Potential for Mercury Reduction by Microbes in the High Arctic

ABSTRACT The contamination of polar regions due to the global distribution of anthropogenic pollutants is of great concern because it leads to the bioaccumulation of toxic substances, methylmercury among them, in Arctic food chains. Here we present the first evidence that microbes in the high Arctic possess and express diverse merA genes, which specify the reduction of ionic mercury [Hg(II)] to the volatile elemental form [Hg(0)]. The sampled microbial biomass, collected from microbial mats in a coastal lagoon and from the surface of marine macroalgae, was comprised of bacteria that were most closely related to psychrophiles that had previously been described in polar environments. We used a kinetic redox model, taking into consideration photoredox reactions as well as mer-mediated reduction, to assess if the potential for Hg(II) reduction by Arctic microbes can affect the toxicity and environmental mobility of mercury in the high Arctic. Results suggested that mer-mediated Hg(II) reduction could account for most of the Hg(0) that is produced in high Arctic waters. At the surface, with only 5% metabolically active cells, up to 68% of the mercury pool was resolved by the model as biogenic Hg(0). At a greater depth, because of incident light attenuation, the significance of photoredox transformations declined and merA-mediated activity could account for up to 90% of Hg(0) production. These findings highlight the importance of microbial redox transformations in the biogeochemical cycling, and thus the toxicity and mobility, of mercury in polar regions.

Effects of various cooking methods and food components on bioaccessibility of mercury from fish.

Fish consumption is the main source of human exposure to mercury. Studies from specific human populations have reported Hg levels lower than those modeled from consumption data. These discrepancies between expected and measured Hg levels may be explained by differences in dietary habits such as cooking methods and food components on fish Hg bioavailability. We assessed the effects of three cooking methods (no cooking, frying and boiling) and of the co-ingestion of selected food items (tea, coffee and corn starch) on Hg bioaccessibility in three fish species (tuna, shark and mackerel) containing between 1 and 4 μg/g dry weight of Hg. We used in vitro techniques simulating human digestion and each experiment was repeated three times with at least three different individuals for each fish species. For all fish species, Hg concentrations (dry weight) in boiled fish were slightly but not significantly higher than those in fried or raw fish. Boiling and frying reduced Hg bioaccessibility by 40% and 60%, respectively, compared to raw fish Hg bioaccessibility. Black coffee as well as green and black tea significantly reduced raw fish Hg bioaccessibility by 50-60%, whereas, corn starch did not. The combined effect of cooking and addition of tea or coffee led to very low levels of Hg bioaccessibility. This study suggests that Hg bioaccessibilty from fish can be modified by cooking and by the co-ingestion of tea and coffee. These results should be further validated in vitro with different fish species before proceeding with in vivo approaches using animal models.

Mercury in the marine environment of the Canadian Arctic: Review of recent findings

This review summarizes data and information which have been generated on mercury (Hg) in the marine environment of the Canadian Arctic since the previous Canadian Arctic Contaminants Assessment Report (CACAR) was released in 2003. Much new information has been collected on Hg concentrations in marine water, snow and ice in the Canadian Arctic. The first measurements of methylation rates in Arctic seawater indicate that the water column is an important site for Hg methylation. Arctic marine waters were also found to be a substantial source of gaseous Hg to the atmosphere during the ice-free season. High Hg concentrations have been found in marine snow as a result of deposition following atmospheric mercury depletion events, although much of this Hg is photoreduced and re-emitted back to the atmosphere. The most extensive sampling of marine sediments in the Canadian Arctic was carried out in Hudson Bay where sediment total Hg (THg) concentrations were low compared with other marine regions in the circumpolar Arctic. Mass balance models have been developed to provide quantitative estimates of THg fluxes into and out of the Arctic Ocean and Hudson Bay. Several recent studies on Hg biomagnification have improved our understanding of trophic transfer of Hg through marine food webs. Over the past several decades, Hg concentrations have increased in some marine biota, while other populations showed no temporal change. Marine biota also exhibited considerable geographic variation in Hg concentrations with ringed seals, beluga and polar bears from the Beaufort Sea region having higher Hg concentrations compared with other parts of the Canadian Arctic. The drivers of these variable patterns of Hg bioaccumulation, both regionally and temporally, within the Canadian Arctic remain unclear. Further research is needed to identify the underlying processes including the interplay between biogeochemical and food web processes and climate change.

Habitat-specific bioaccumulation of methylmercury in invertebrates of small mid-latitude lakes in North America

We examined habitat-specific bioaccumulation of methylmercury (MeHg) in aquatic food webs by comparing concentrations in pelagic zooplankton to those in littoral macroinvertebrates from 52 mid-latitude lakes in North America. Invertebrate MeHg concentrations were primarily correlated with water pH, and after controlling for this influence, pelagic zooplankton had significantly higher MeHg concentrations than littoral primary consumers but lower MeHg than littoral secondary consumers. Littoral primary consumers and pelagic zooplankton are two dominant prey for fish, and greater MeHg in zooplankton is likely sufficient to increase bioaccumulation in pelagic feeders. Intensive sampling of 8 lakes indicated that habitat-specific bioaccumulation in invertebrates (of similar trophic level) may result from spatial variation in aqueous MeHg concentration or from more efficient uptake of aqueous MeHg into the pelagic food web. Our findings demonstrate that littoral-pelagic differences in MeHg bioaccumulation are widespread in small mid-latitude lakes.

Mercury, arsenic and selenium concentrations in water and fish from sub-Saharan semi-arid freshwater reservoirs (Burkina Faso).

Despite intensive mining activities in Burkina Faso, little is known on the environmental impacts of metals and metalloids potentially released from these activities. Water samples and 334 fish from 10 reservoirs were taken in order to evaluate the extent of mercury (Hg), selenium (Se) and arsenic (As) contamination in aquatic systems and their potential health risk for humans and wildlife, taking into account their antagonistic interactions. Water and fish levels of these elements were relatively low and did not reveal an important impact of gold mining activities. Water temperature and conductivity were the key factors associated with higher levels of MeHg. Higher sulfate content was reported in sites with more particulate Hg, As and Se, suggesting anthropogenic origin of metal(loid) inputs in water reservoirs. Metal(loid) concentrations in fish were low and ranged from 0.002 to 0.607 μg/g wet weight (w.w.) for Hg, 0.023 to 0.672 for Se and 0.039 to 0.42 for As. These levels are similar or slightly higher than those reported in many other studies from Africa. Nevertheless, more than 70% of piscivore fish exceeded the threshold for wildlife protection for MeHg. Further, a traditional risk analysis performed ignoring Se antagonism indicated that these piscivores should be consumed by humans with caution. However, when taking into account the antagonistic effect of Se on Hg toxicity, up to 99% of all fish could be protected from Hg toxicity by their Se content. When considering both As/Se and Se/Hg antagonism, 83% instead the 99% of fish should be considered safe for consumption. Fish Se and As concentrations did not pose potential risk for both animals and humans. Overall, these reservoirs were relatively unaffected by As, Se and Hg contamination despite the rising gold mining activities. Further, considering antagonistic effects of As, Se and Hg may help refine consumption advisories.