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The precision and bias of monomethylmercury (MMHg) determinations in environmental samples can be improved by directly coupling and automating the numerous steps involved with analysis of this toxic Hg species. We developed a simple and robust mercury speciation analyzer (MSA) for measurement of MMHg in environmental matrixes. This on-line hyphenated system couples the main analytical steps, including sample introduction, aqueous-phase ethylation, Tenax preconcentration, and gas chromatographic separation, to cold vapor atomic fluorescence detection and data acquisition. Here we describe the MMHg-MSA, present results of laboratory optimization and performance tests, and compare the reproducibility between dual analytical channels. With alternating sample concentration and analysis, a dual-channel system permits six high-accuracy MMHg determinations per hour. Additional advantages compared to the traditional manual method include ease of operation and high precision (

We examined monomethylmercury (MMHg) in sediment reference material IAEA-405 and sediments from Long Island Sound. MMHg was extracted by both aqueous distillation and leaching with dilute solutions of nitric acid. MMHg was formed from both ambient and added inorganic mercury in extracts of IAEA-405 by either technique. Artifact MMHg in IAEA-405 was related linearly with ambient reactive mercury ([Hg.sub.R]) in leachates having > 1.2 M acid, but little or no artifact was measured in less acidic extracts. Addition of potassium chloride enhanced extraction of [Hg.sub.R] from IAEA-405 but had no effect on artifact MMHg for each leachate molarity tested. Mercury methylation occurred in solution and was a function of both the availability of [Hg.sub.R] and a methylation potential, being limited by [Hg.sub.R] in less acidic solutions (0.5-1.2 M) and by the methylation potential in more acidic ones (> 1.2 M). Formation of artifact MMHg in Long Island Sound sediments was inconclusive, but additions of inorganic mercury demonstrated that a potential exists. A potential for abiotic mercury methylation seems always present in sediment, and the availability of [Hg.sub.R] appears to control MMHg production under environmental conditions. Abiotic methylation of mercury may occur in environs where the reactivity of inorganic mercury is enhanced, such as river-seawater mixing zones.

The research work related to biogeochemistry, speciation, distribution, behavior, and status of mercury in the ocean and global is reviewed. The findings will help to address international problems associated with to monomethylmercury (MMHg) which is highly toxic form of Hg that accumulates in aquatic and terrestrial organisms.

Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and cause toxicity at high concentrations. We studied how the oxidation of surface sediment that occurs during aging alters the partitioning and toxicity of Ni. Two sediments (Burntwood and Raisin) were amended with Ni, equilibrated, incubated in a flow-through flume, and examined for sediment physicochemistry and toxicity to Hyalella azteca (7 day growth). Through time, the sediment surface (5 mm) was oxidized, acid-volatile sulfide concentrations declined in Raisin sediment, and amorphous Fe oxides increased. Porewater Ni concentrations declined through time but total Ni concentrations in sediment were unchanged, suggesting changes in Ni partitioning through time. Both sediments elicited a toxic dose-response by H. azteca early in the aging process; but only Burntwood, for which Ni was primarily partitioned to Fe oxide minerals, exhibited a consistent dose-response during aging. Low total Ni concentrations (20 mg kg-1) in Raisin sediment reduced H. azteca growth at initiation, but all Ni treatments (up to 3000 mg kg-1) exhibited similar growth after 12 days of aging. The dynamic toxicity observed in Raisin sediment was likely due to the instability of NiS in surface sediments early in the aging process. These data suggest that short-term toxicity assays with homogenized Ni-amended sediment (i.e., standard sediment toxicity tests) may be accurate for sediments where Ni speciation is dominated by oxidized ligands; however, under high-AVS and high-Fe conditions, calculated toxicity thresholds may be overly conservative (here by >100-fold) with respect to natural sediment conditions. [ABSTRACT FROM AUTHOR]

To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (~5200 mol y-1) and MeHg (~120 mol y-1) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of total Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than from atmospheric deposition. However, fluxes from rivers are significant sources of MeHg to estuaries and coastal regions of the northern GOM. [ABSTRACT FROM AUTHOR]

The bioavailability of transition metals in sediments often depends on redox conditions in the sediment. We explored how the physicochemistry and toxicity of anoxic Cu-amended sediments changed as they aged (i.e., naturally oxidized) in a flow-through flume. We amended two sediments (Dow and Ocoee) with Cu, incubated the sediments in a flow-through flume, and measured sediment physicochemistry and toxicity over 213 days. As sediments aged, oxygen penetrated sediment to a greater depth, the relative abundance of Fe oxides increased in surface and deep sediments, and the concentration of acid volatile sulfide declined in Ocoee surface sediments. The total pool of Cu in sediments did not change during aging, but porewater Cu, and Cu bound to amorphous Fe oxides decreased while Cu associated with crystalline Fe oxides increased. The dose-response of the epibenthic amphipod Hyalella azteca to sediment total Cu changed over time, with older sediments being less toxic than freshly spiked sediments. We observed a strong dose-response relationship between porewater Cu and H. azteca growth across all sampling periods, and measurable declines in relative growth rates were observed at concentrations below interstitial water criteria established by the U.S. EPA. Further, solid-phase bioavailability models based on AVS and organic carbon were overprotective and poorly predicted toxicity in aged sediments. We suggest that sediment quality criteria for Cu is best established from measurement of Cu in pore water rather than estimating bioavailable Cu from the various solid-phase ligands, which vary temporally and spatially. [ABSTRACT FROM AUTHOR]

Accumulation of monomethylmercury (MMHg) by plankton is a key process influencing concentrations of this toxic mercury species in marine food webs and seafood. We examined bioaccumulation and biomagnification of MMHg in microseston and four size fractions of zooplankton on the continental shelf, slope, and rise of the northwest Atlantic Ocean. The bioaccumulation factor (BAF, L/kg) for MMHg in microseston averaged 104.3±0.3 among 21 locations, and concentrations were unrelated to those in colocated, filtered surface water. Instead, concentrations and the BAF of MMHg in microseston were related inversely with total suspended solids in surface water, a proxy for planktonic biomass at these remote locations. MMHg was biomagnified by a factor of 4 from microseston to zooplankton, and both concentrations of MMHg and the fraction of total mercury as MMHg increased with larger size fractions of zooplankton. These results suggest that the initial magnitude of MMHg uptake into pelagic marine food webs is influenced by the degree of primary production in surface waters and propagated up through large zooplankton. Accordingly, biological productivity, in addition to inputs of MMHg to surface waters, must be considered when predicting how MMHg bioaccumulation will vary spatially and temporally in the ocean. [ABSTRACT FROM AUTHOR]

Sunlight-induced decomposition is the principal sink for methylmercury (CH3Hg+) in arctic Alaskan lakes and reduces its availability for accumulation in aquatic food webs. However, the mechanistic chemistry of this process in natural waters is unknown. We examined experimentally the mechanism of photochemical CH3Hg+ decomposition in filter-sterilized epilimnetic waters of Toolik Lake in arctic Alaska (68° 38'N, 149° 36'W), a region illuminated by sunlight almost continuously during the summer. Results from in situ incubation tests indicate that CH3Hg+ is not decomposed principally by either direct photolysis (i.e., no degradation in reagent-grade water) or primary photochemical reactions with dissolved organic material. The preeminent role of labile Fe and associated photochemically produced reactive oxygen species is implicated by tests that show 1) additions of Fe(III) to reagent-grade water enhance CH3Hg+ photodecomposition, 2) strong complexation of ambient Fe(III) with desferrioxamine B inhibits the reaction in lake water, and 3) experimental additions of organic molecules that scavenge hydroxyl radicals specifically among reactive oxygen species (dimethylsulfoxide and formic acid) inhibit CH3Hg+ degradation. Lake-water dilution and Fe(III) addition experiments indicate that Fe is not the limiting reactant for CH3Hg+ photodecomposition in Toolik Lake, which is consistent with prior results indicating that photon flux is a major control. These results demonstrate that CH3Hg+ is decomposed in natural surface water by oxidants, apparently hydroxyl radical, generated from the photo-Fenton reaction. [ABSTRACT FROM AUTHOR]

A connection between accumulation of methylmercury (MeHg) in wild fish populations and atmospheric mercury deposition has not been made. Large databases for both MeHg in fish and atmospheric mercury deposition have been assimilated from monitoring efforts spanning the contiguous United States. Here, we compare results of these data sets and show that state-wide average concentrations of MeHg in a cosmopolitan freshwater fish, the largemouth bass Micropterus salmoides, are related positively to wet atmospheric Hg fluxes among most of the 25 states that are analyzed, which span a 5-fold range in Hg deposition. Differences in largemouth bass MeHg concentrations among states are unrelated to average precipitation depth, wet atmospheric acid deposition, or interstate variations in the type of water body (river, lake, reservoir) from which the fish were sampled. There are modest correlations between MeHg in bass and surface water pH, temperature, and wet atmospheric deposition of sulfate. However, when fish and atmospheric mercury results are combined at the state level, wet atmospheric Hg deposition accounts for about two-thirds of the variation in bass MeHg among most states, and stepwise multiple regression analysis reveals that these variables do not improve the linear model significantly. This suggests the accumulation of MeHg in wild fish populations is linked to atmospheric Hg loadings, two-thirds of which are estimated to be from anthropogenic sources. [ABSTRACT FROM AUTHOR]

Sunlight-induced decomposition of monomethylmercury (MMHg) reduces its availability for accumulation in aquatic food webs. We examined MMHg degradation in epilimnetic waters of Toolik Lake (68° 38′ N, 149° 36′ W) in arctic Alaska, a region illuminated by sunlight almost continuously during the summer. MMHg decomposition in surface water of Toolik Lake is exclusively abiotic and mediated by sunlight; comparable rates of MMHg decomposition were observed in filter-sterilized and unfiltered surface waters incubated under in situ sunlight and temperature conditions, and no MMHg was degraded in unfiltered aliquots incubated in the dark. Rates of photodecomposition are first order with respect to both MMHg concentration and the intensity of photosynthetically active radiation (PAR), except at the lake surface where rates of photochemical degradation are enhanced relative to PAR intensity and may be attributed to an additional influence of ultraviolet light. The estimated annual loss of MMHg to photodecomposition in Toolik Lake, though limited to a 100-d ice-free season, accounts for about 80% of the MMHg mobilized annually from in situ sedimentary production, the primary source in Toolik Lake. These results suggest that greater light attenuation in lacustrine surface waters, a potential result of increased loadings of dissolved organic matter due to continued warming in the Arctic, may result in less photodecomposition and subsequently greater availability of MMHg for bioaccumulation. [ABSTRACT FROM AUTHOR]

The fate of atmospherically deposited and environmentally active Hg is uncertain in the Arctic, and of greatest toxicological concern is the transformation to monomethylmercury (MMHg). Lake/watershed mass balances were developed to examine MMHg cycling in four northern Alaska lakes near the ecological research station at Toolik Lake (68° 38′ N, 149° 36′ W). Primary features of the cycle are watershed runoff, sedimentary production and mobilization, burial, and photodecomposition in the water column. The principal source of MMHg is in situ benthic production with 80–91% of total inputs provided by diffusion from sediments. The production and contribution of MMHg from tundra watersheds is modest. Photodecomposition, though confined to a short ice-free season, provides the primary control for MMHg (66–88% of total inputs) and greatly attenuates bioaccumulation. Solid-phase MMHg and gross potential rates of Hg methylation, assayed with an isotopic tracer, vary positively with the level of inorganic Hg in filtered pore water, indicating that MMHg production is Hg-limited in these lakes. Moreover, sediment-water fluxes of MMHg (i.e., net production at steady state) are related to sediment Hg loadings from the atmosphere. These results suggest that loadings of Hg derived from atmospheric deposition are a major factor affecting MMHg cycling in arctic ecosystems. However, environmental changes associated with warming of the Arctic (e.g., increased weathering, temperature, productivity, and organic loadings) may enhance MMHg bioaccumulation by stimulating Hg methylation and inhibiting photodecomposition. [ABSTRACT FROM AUTHOR]

Development of the early life stages of fishes can be affected adversely by methylmercury (MeHg) transferred from the maternal parent to the developing egg. We examined maternal transfer of MeHg to eggs of fathead minnows Pimephales promelas and evaluated the role of maternal MeHg burden versus that in the maternal diet during oogenesis on egg concentrations. Juvenile fish were fed one of four diets until sexual maturity (phase 1): A control diet (0.06 μg of Hg g-1 dry weight) and three that were contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 μg of Hg g-1 (high). At sexual maturity, female fish were paired with a male, again fed one of the four diets, and allowed to reproduce (phase 2). To assess the significance of female dietary exposure during oogenesis on MeHg in eggs, some fish were fed diets during phase 2 that differed from those during phase 1. Mean concentrations and burdens of MeHg in eggs from fish fed the same diet throughout the experiment varied with MeHg content of the maternal diet and were related positively to levels in the carcass of the maternal fish. However, MeHg in eggs was not proportional to that in carcasses among dietary treatments; MeHg in eggs from adults fed the control, low, medium, and high MeHg diets averaged 14%, 25%, 32%, and 35% of that in adults. For fish fed the control diet as juveniles and MeHg-contaminated diets after reaching sexual maturity, MeHg in eggs increased rapidly with duration of maternal dietary exposure prior to spawning. Moreover, concentrations of MeHg in eggs from fish fed the same contaminated diet as both juveniles and sexually mature adults were not related to the duration of adult exposure, and they were not appreciably greater than those from fish fed contaminated diets only just prior to spawning. These results indicate that the diet of the maternal adult during oogenesis, and not adult body burden, is the principal source of MeHg in fish eggs. Accordingly, the exposure of embryonic wild fishes to MeHg depends on levels of the contaminant in prey of the adult during oogenesis,which can vary intra- and interannually. [ABSTRACT FROM AUTHOR]

A connection between loadings of inorganic Hg, especially from the atmosphere, and accumulation of methylmercury (MeHg) in aquatic biota has not been firmly established. Mosquitoes (Diptera: Culicidae)may be a useful indictor of Hg contamination or MeHg accumulation in aquatic ecosystems because they have aquatic life stages, and their ubiquitous distribution permits sampling across wide ranges of climate, biological productivity, and atmospheric Hg deposition. We examined MeHg in adult mosquitoes from subtropical (Florida), maritime (California), continental (Michigan), and arctic (Alaska) regions of North America that span a range in wet atmospheric Hg deposition (1.5- 15 μg m-2 y-1). More than 90% of the Hg in mosquitoes was MeHg, and concentrations varied among locations. Levels of MeHg differed among mosquito species at six sites in northwest Florida (Ochierotatus atlanticus < Culex nipripalpus

We examined temporal differences in sedimentary production of monomethylmercury (MMHg) at three sites in Long Island Sound (LIS). Sediment-phase concentrations of Hg species decreased from west to east in LIS surface sediments, following the trend of organic matter, However, Hg methylation potentials, measured by incubation with an isotopic tracer (200Hg), increased from west to east. 200Hg methylation potentials were enhanced in August relative to March and June, attributable to differences in activity of sulfide-reducing bacteria. Organic matter and acid-volatile sulfide influenced the distribution Coefficient (KD) of inorganic Hg (Hg(II) = total Hg - MMHg) and inhibited 200Hg methylation in surface sediments. 200Hg methylation varied inversely with the KD of Hg(II) and positively with the concentration of Hg(II), mostly as HgS0, in LIS pore waters. Accordingly, we posit that a principal control on MMHg production in low-sulfide, coastal marine sediments is partitioning of Hg(II) between particle and dissolved phases, which regulates availability of Hg substrate to methylating bacteria. Most of the partitioning in LIS sediments is due to Hg- organic associations. This suggests that reductions in the organic content of coastal sediments, a potential result of nutrient abatement programs intended to inhibit eutrophication of near-shore waters, could enhance MMHg production by increasing the bioavailability of the large reservoir of "legacy Hg" buried within the sediment. [ABSTRACT FROM AUTHOR]

Investigates the effects of dietary methylmercury (MeHg) on the reproduction of fathead minnows in North America. Experimentation of juvenile fish for the study on dietary effects; Assessment on the outcome of MeHg during gametogenesis; Concentration of total mercury in the carcasses of tested fish.

Analyzes the methylmercyry content of eggs in yellow perch from Wisconsin. Influence of maternal mercury on the content; Determination of mercury in samples; Concentration of mercury in eggs; Effect of bioaccumulation to the development of perch embryo.

A new method for the determination of the concentration and conditional stability constant of dissolved organic matter that binds mercury (Hg) has been developed using an in vitro assay of reducible Hg. The technique is a wet chemical analogue to electrochemical approaches now in use for ligand studies of many other trace transition metals in natural waters. Ligand characteristics are obtained from additions of ionic Hg to buffered lake, river water, and seawater and determination of the wet chemically reducible fraction following equilibration of the spike. This approach is robust, as demonstrated by (i) analysis using three reducing agents of varying strengths, (ii) replicate analyses, (iii) comparison to well-characterized complexing species (chloride and EDTA) using a competitive ion-exchange resin, and (iv) kinetic studies. Results indicate that Hg-complexing equivalents are present in the dissolved phase (<0.2 microm) ranging from <1 to >60 nN concentrations and with log conditional stability constants (log K') in the range of 21-24. Only one ligand class was found in the natural waters analyzed. There was indirect evidence for a class of organic ligands that formed reducible complexes with Hg in freshwater. Such ligand characteristics indicate that the vast majority of ionic inorganic Hg dissolved in freshwater and coastal saltwaters is associated with organic complexes. Concentrations, affinities, and kinetics implicate multidentate chelation sites as the principal complexing moieties for Hg and discourage the use of humic carboxylic acids as a proxy for the ligands/functional groups.