Experimental Evidence of a Linear Relationship between Inorganic Mercury Loading and Methylmercury Accumulation by Aquatic Biota

Orihel, Diane M.; Paterson, Michael; Blanchfield, Paul J.; Bodaly, R. A.; Hintelmann, Holger

doi:10.1021/es063061r

Cited by 109 publications

(77 citation statements)

References 35 publications

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“…3). Previous studies have shown that, on the short term, there is a proportional response of rates of production (24,25) and bioaccumulation (26) of new methylmercury to new additions of inorganic mercury. However, when new mercury is added to a system that already contains older inorganic mercury, both the new and older mercury contribute to methylation (although not necessarily equally), so on the short term the overall rate of mercury methylation (new ϩ old) does not respond in direct proportion to the amount of new mercury added.…”

Section: Resultsmentioning

confidence: 99%

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

Harris

Rudd²,

Amyot

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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409

333

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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.bioaccumulation ͉ mercury methylation ͉ stable isotopes ͉ whole-ecosystem experimentation ͉ methylmercury

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Section: Resultsmentioning

confidence: 99%

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

Harris

Rudd²,

Amyot

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

409

333

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“…An alternative interpretation could be that most of the standing oceanic inventory is not bioavailable; with a small and rapidly cycling pool of bioavailable Hg, inputs that are quickly converted to bioavailable forms could produce a rapid biotic response proportional to the input, as they do in lakes (see ref. [89]). However, this interpretation is not supported by MeHg inventory calculations for the Arctic Ocean, which lead to the striking finding that most of the MeHg already in the upper Ocean is not accumulated by marine biota, i.e.…”

Section: Lessons About the Fulcrums Controlling Biological Hg Trendsmentioning

confidence: 99%

A mass balance inventory of mercury in the Arctic Ocean

et al. 2008

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Environmental context. Mercury (Hg) occurs at high concentrations in Arctic marine wildlife, posing a possible health risk to northern peoples who use these animals for food. We find that although the dramatic Hg increases in Arctic Ocean animals since pre-industrial times can be explained by sustained small annual inputs, recent rapid increases probably cannot because of the existing large oceanic Hg reservoir (the 'flywheel' effect). Climate change is a possible alternative force underpinning recent trends.Abstract. The present mercury (Hg) mass balance was developed to gain insights into the sources, sinks and processes regulating biological Hg trends in the Arctic Ocean. Annual total Hg inputs (mainly wet deposition, coastal erosion, seawater import, and 'excess' deposition due to atmospheric Hg depletion events) are nearly in balance with outputs (mainly shelf sedimentation and seawater export), with a net 0.3% year −1 increase in total mass. Marine biota represent a small fraction of the ocean's existing total Hg and methyl-Hg (MeHg) inventories. The inertia associated with these large non-biological reservoirs means that 'bottom-up' processes (control of bioavailable Hg concentrations by mass inputs or Hg speciation) are probably incapable of explaining recent biotic Hg trends, contrary to prevailing opinion. Instead, varying rates of bioaccumulation and trophic transfer from the abiotic MeHg reservoir may be key, and are susceptible to ecological, climatic and biogeochemical influences. Deep and sustained cuts to global anthropogenic Hg emissions are required to return biotic Hg levels to their natural state. However, because of mass inertia and the less dominant role of atmospheric inputs, the decline of seawater and biotic Hg concentrations in the Arctic Ocean will be more gradual than the rate of emission reduction and slower than in other oceans and freshwaters. Climate warming has likely already influenced Arctic Hg dynamics, with shrinking sea-ice cover one of the defining variables. Future warming will probably force more Hg out of the ocean's euphotic zone through greater evasion to air and faster Hg sedimentation driven by higher primary productivity; these losses will be countered by enhanced inputs from coastal erosion and rivers.

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“…Sources of Hg in these basins include historical gold and cinnabar mines, releases from chemical manufacturing and coal-fired power plants, atmospheric deposition, and wetlands (Rudd 1995;Brumbaugh et al 2001;Eisler 2004;Paller et al 2004;Warner et al 2005). Orihel et al (2007) demonstrated that organic mercury deposited directly to aquatic ecosystem was readily converted to methylmercury, which is available to biota. This relationship may explain the high fish concentrations and associated risk of mercury in the southeastern United States and Yukon River Basin, where mercury methylation rates are known to be high (Brumbaugh et al 2001).…”

Section: Dieldrin -Mink Dieldrin -Bald Eaglementioning

confidence: 99%

Environmental contaminants in freshwater fish and their risk to piscivorous wildlife based on a national monitoring program

Hinck

Schmitt

Chojnacki

et al. 2008

Environ Monit Assess

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Organochlorine chemical residues and elemental concentrations were measured in piscivorous and benthivorous fish at 111 sites from large U.S. river basins. Potential contaminant sources such as urban and agricultural runoff, industrial discharges, mine drainage, and irrigation varied among the sampling sites. Our objectives were to provide summary statistics for chemical contaminants and to determine if contaminant concentrations in the fish were a risk to wildlife that forage at these sites. Concentrations of dieldrin, total DDT, total PCBs, toxaphene, TCDD-EQ, cadmium, chromium, mercury, lead, selenium, and zinc exceeded toxicity thresholds to protect fish and piscivorous wildlife in samples from at least one site; most exceedences were for total PCBs, mercury, and zinc. Chemical concentrations in fish from the Mississippi River Basin exceeded the greatest number of toxicity thresholds. Screening level wildlife risk analysis models were developed for bald eagle and mink using no adverse effect levels (NOAELs), which were derived from adult dietary exposure or tissue concentration studies and based primarily on reproductive endpoints. No effect hazard concentrations (NEHC) were calculated by comparing the NOAEL to the food ingestion rate (dietary-based NOAEL) or biomagnification factor (tissue-based NOAEL) of each receptor. Piscivorous wildlife may be at risk from a contaminant if the measured concentration in fish exceeds the NEHC. Concentrations of most organochlorine residues and elemental contaminants represented no to low risk to bald eagle and mink at most sites. The risk associated with pentachloroanisole, aldrin, Dacthal, methoxychlor, mirex, and toxaphene was unknown because NOAELs for these contaminants were not available for bald eagle or mink. Risk differed among modeled species and sites. Our screening level analysis indicates that the greatest risk to piscivorous wildlife was from total DDT, total PCBs, TCDD-EQ, mercury, and selenium. Bald eagles were at greater risk to total DDT and total PCBs than mink, whereas risks of TCDD-EQ, mercury, and selenium were greater to mink than bald eagle.

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Experimental Evidence of a Linear Relationship between Inorganic Mercury Loading and Methylmercury Accumulation by Aquatic Biota

Cited by 109 publications

References 35 publications

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

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

A mass balance inventory of mercury in the Arctic Ocean

Environmental contaminants in freshwater fish and their risk to piscivorous wildlife based on a national monitoring program

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