Mercury concentrations in fish in a remote Canadian Arctic lake

Lac Ste. Thérèse, a remote Canadian Arctic lake in the Northwest Territories, Canada, has high natural (non-point source) mercury concentrations in fish. The high mercury levels have persisted for over 18 years. Lac Ste. Thérèse has had consistently higher mercury concentration in fish than the other three lakes sampled within the basin, regardless of species tested.     

Bioinformatic Analyses of Bacterial Mercury Ion (Hg2+) Transporters

Currently, there are five known types of mercury transporters in bacteria: MerC, MerE, MerF, MerH, and MerT. Their general function is to mediate mercuric ion uptake into the cell in preparation for reduction to Hg°. They are present in several bacterial phyla and comprise five distinct families. We have utilized standard statistical bioinformatic tools and the superfamily principle to show that they are related by common descent. After using programs such as Global Alignment Program and SSearch to establish homology, we aligned and analyzed their amino acid sequences to find a single well conserved motif. Although these proteins exhibit 2, 3, or 4 transmembrane helical segments (TMSs), TMSs 1 and 2 are common to all superfamily members. An ancestral sequence was determined, and reliable phylogenetic trees were constructed. The results support the conclusion of homology, establishing that these proteins belong to a single superfamily. This important discovery allows extrapolation of information about structure, function, and mechanism from one protein to all superfamily members to degrees inversely proportional to their phylogenetic distances.     

Freshwater Fish Mercury Concentrations in a Regionally High Mercury Deposition Area

We sampled and analyzed individually, edible dorsal muscle from largemouth bass (LMB), Micropterus salmoides (n?=?138) and yellow perch (YP), Perca flavescens (n?=?97) from 15 lakes to investigate potential local impacts of mercury emission point sources in northeastern Massachusetts (MA), USA. This area was identified in three separate modeling exercises as a mercury deposition hotspot. In 1995, 55% of mercury emissions to the environment from all MA sources came from three municipal solid waste combustors (trash incinerators) and one large regional medical waste incinerator in the study area. We determined the mercury accumulation history in sediments of a lake centrally located in the study area. Recent maximum mercury accumulation rates in the sediment of the lake of ~ 88 μg/m²/year were highly elevated on a watershed area adjusted basis compared to other lakes in the Northeast and Minnesota. Fish from the study area lakes had significantly (p?=?0.05) greater total mercury concentrations than fish from 24 more rural, non-source-impacted lakes in other regions of the state (LMB n?=?238, YP n?=?381) (LMB: 1.5–2.5 x; YP: 1.5 x). The integration of this extensive fish tissue data set, depositional modeling projections, historical record of mercury accumulation in sediments of a lake in the area, and knowledge of substantial mercury emissions to the atmosphere in the area support designation of this area as a mercury depositional and biological concentration hotspot in the late 1990s, and provides further evidence that major mercury point sources may be associated with significant local impacts on fisheries resources.     

Development of a Mercury Vapour Air Analyser for Measurement of Hg in Solution

The Tekran 2537A mercury vapour analyser, designed to measure Hg in air by cold vapour atomic fluorescence spectrometry, has been modified to determine Hg in solution. The new ‘front-end’, required to generate Hg° vapour from acidified waters or acid leachates, is described. Using 1% NaBH4 as reducing agent, a 12 mL water sample can be analysed, at a rate of 1 every 6 min, for Hg to a detection limit of 0.8 ppt (ng L-1). Instrumental precision is typically 1% relative standard deviation (RSD) at levels of Hg from 10 to 200 ppt. Results for 10 analyses of the international water standard, NIST 1642b, are 1530±20 ppt Hg, agreeing well with the certified value of 1480±130 ppt. Nineteen geological standard reference materials (soils, sediments and tills) were used to assess accuracy. Results for these samples, digested in aqua regia in triplicate, showed good agreement with recommended values for all but two, SO-3 and TILL-1. However, results by this method for these two standards were confirmed by an independent method, direct atomic absorption spectrometry. Average method precision was shown to be 5% RSD over the range 10 ng g- 1 to 35 μg g-1 Hg.     

Mercury Transport in a High-Elevation Watershed in Rocky Mountain National Park, Colorado

Mercury (Hg) was measured in stream water and precipitation in the Loch Vale watershed in Rocky Mountain National Park, Colorado, during 2001–2002 to investigate processes controlling Hg transport in high-elevation ecosystems. Total Hg concentrations in precipitation ranged from 2.6 to 36.2 ng/L and showed a strong seasonal pattern with concentrations that were 3 to 4 times higher during summer months. Annual bulk deposition of Hg was 8.3 to 12.4 μ g/m² and was similar to deposition rates in the Midwestern and Northeastern U.S. Total Hg concentrations in streams ranged from 0.8 to 13.5 ng/L and were highest in mid-May on the rising limb of the snowmelt hydrograph. Stream-water Hg was positively correlated with dissolved organic carbon suggesting organically complexed Hg was flushed into streams from near-surface soil horizons during the early stages of snowmelt. Methylmercury (MeHg) in stream water peaked at 0.048 ng/L just prior to peak snowmelt but was at or below detection (< 0.040 ng/L) for the remainder of the snowmelt season. Annual export of total Hg in Loch Vale streams ranged from 1.2 to 2.3 μ g/m², which was less than 20% of wet deposition, indicating the terrestrial environment is a net sink of atmospheric Hg. Concentrations of MeHg in stream water and corresponding watershed fluxes were low, indicating low methylation rates or high demethylation rates or both.     

Factors Controlling Mercury Transport in an Upland Forested Catchment

Total mercury (Hg) deposition and input/output relationships were investigated in an 11-ha deciduous forested catchment in northern Vermont as part of ongoing evaluations of Hg cycling and transport in the Lake Champlain basin. Atmospheric Hg deposition (precipitation + modeled vapor phase downward flux) was 425 mg ha-1 during the one-year period March 1994 through February 1995 and 463 mg ha-1 from March 1995 through February 1996. In the same periods, stream export of total Hg was 32 mg ha-1, respectively. Thus, there was a net retention of Hg by the catchment of 92% the first year and 95% the second year. In the first year, 16.9 mg ha-1 or about half of the annual stream export, occurred on the single day of peak spring snowmelt in April. In contrast, the maximum daily export in the second year, when peak stream flow was somewhat lower, was 3.5 mg ha-1 during a January thaw. The fate of the Hg retained by this forested catchment is not known. Dissolved (< 0.22 µm) Hg concentrations in stream water ranged from 0.5-2.6 ng L-1, even when total (unfiltered) concentrations were greater than 10 ng L-1 during high flow events. Total Hg concentrations in stream water were correlated with the total organic fraction of suspended sediment, suggesting the importance of organic material in Hg transport within the catchment. High flow events and transport with organic material may be especially important mechanisms for the movement of Hg through forested ecosystems.     

Grain Size Partitioning of Mercury in Sediments of the Middle Odra River (Germany/Poland)

The Odra River is the second largest river in Poland, running from Czech Republic through a large part of Poland before entering the Baltic Sea. For the last century its catchment area has been heavily polluted by anthropogenic emissions. The aim of this study is to determine the distribution of mercury in different grain size fractions of surface sediments from the middle course of the Odra River. Mercury concentrations were determined in bulk sediments of different grain size fractions using the cold vapor atomic fluorescence spectrometry method. The total mercury concentration in bulk sediments varied from 0.051 to 1.31 mg/kg dry weight. The concentration of total mercury was determined in the grain size fractions <0.2, 0.2–0.5, 0.5–1.0, 1.0–2.0 and >2.0 mm to be (in mg/kg d.w.): 0.118–2.99, 0.033–0.99, 0.034–1.17, 0.035–1.97 and 0.017–3.65, respectively. Gradual decrease in the mercury concentration with increasing grain size from fine to coarse fraction has been observed only for sediments taken from the river bed. Although, no similar gradual decrease in the mercury concentrations has been observed for sediments from the river banks, finer sediments (<0.2 mm) still tend to show higher concentrations of mercury.     

Determination of Mercury Content in a Shallow Firn Core from Greenland by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

The total mercury content was determined in 6 cm sections of a shallow 7 m firn core and in surrounding surface snow from Summit, Greenland (elevation: 3238 m, 72.58^°N, 38.53^°W) collected in May 2001 by isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS). The focus of this research was to evaluate the capability of the ID-CV-ICP-MS technique for measuring trace levels of Hg typical of polar snow and firn. Highly enriched ²⁰¹Hg isotopic spike is added to approximately 10 mL melted core and thoroughly mixed. The Hg²⁺ in the sample is reduced on line with tin(II) chloride (SnCl₂) and the elemental Hg (Hg^°) vapor pre-concentrated onto gold gauze using a commercial amalgam system. The Hg is then thermally desorbed and introduced into a quadrupole ICP-MS. The blank-corrected Hg concentrations determined for all samples ranged from 0.25 to 1.74 ng/L (ppt) (average 0.59 ± 0.28 ng/L (1σ)) and fall within the range of those previously determined by Boutron et al. [Geophys. Res. Lett. 25, 1998, 3315–3318] (≤ 0.05–2.0 ng/L) for the Summit site. The average blank value was 0.19 ± 0.045 ng/L (n = 6, 1σ) and the method detection limit was 0.14 ng/L. The Hg values specifically for the firn core range from 0.25 to 0.87 ng/L (average 0.51 ± 0.13 ng/L (1σ)) and show both values declining with time and larger variability in concentration in the top 1.8 m.     

Mercury Concentrations in Stream and River Water: An Analytical Framework Applied to Minnesota and Wisconsin (USA)

The total concentration of all mercuryspecies in water, [THg]_w, is a key water qualitymeasure. This paper proposes an analytical framework forthe analysis, interpretation and eventual projection ofstream (and river) [THg]_w. Mercury (Hg) isconceptualized as being distributed among four carriergroups in water: suspended mineral particles, particulateorganic carbon, dissolved organic carbon, and inorganiccomplexes and ions. The conceptual understanding is used asa statistical analytical framework and turned into aquantitative model for Minnesota and Wisconsin based on some1000 data cases from 18 streams (watershed area: 9 ha–115500km²). The resultant model yields a coefficient ofdetermination of 92% for [THg]_w of the fitting datasubset, or 94% for the evaluation subset. Its coefficientshave well defined physical meanings, and are generallyconsistent with independent field measurements from the sameregion or elsewhere. The model provides a comprehensive andquantitative view of the Hg contents of the carriers: thecontents increase with the proportion of watershed area aswetlands or as forests, rise drastically and then fallprecipitously during spring snowmelt, and otherwise peak inthe growing season and reach a minimum in the presence ofsnowpack. The model further reveals that dissolved Hg tendsto increase with emission-related wet sulfate depositionacross the data region.     

Characterisation of cold-tolerant fungi from a decomposing High Arctic moss

Given that changes in the patterns of vegetation and size of carbon (C) pools in the Arctic are likely to be profound by the end of this century, it is necessary to characterise the identity and ecological groupings, in terms of temperature response and C substrate utilisation, of saprotrophic (decomposer) fungi in organic matter in Arctic soils. Thus, the aims of this study were: (1) to identify the fungi isolated from standing-dead material of Schistidium apocarpum, as an example of a High Arctic moss, (2) to determine mycelial extension rates of these fungi at a range of temperatures (4, 10 and 25 °C), and (3) to characterise the functional potential, defined by C substrate utilisation at 6 °C, of fungal taxa.Fungi were isolated at 4 °C from standing-dead material of S. apocarpum from an area of polar semi-desert (79 degrees N), close to Ny-Ålesund, Svalbard, in the High Arctic. From a collection of 662 isolates, 43 pure cultures were identified by DNA extraction, amplification, and sequencing. Phoma sclerotioides, previously known as a temperate snow mould, was isolated most frequently. The ecology of fifteen fungal isolates was characterised in detail. In terms of temperature response, two groups were apparent, one of truly psychrophilic/psychrotrophic fungi and one of more mesophilic fungi which were generally less frequently isolated. In terms of carbon substrate utilisation in semi-defined solid media, most fungi could utilise a variety of carbon substrates (degradation of casein, cellulose and starch was widespread), except for tannic acid (degraded by only two of the five P. sclerotioides isolates and Scytalidium lignicola) and lignin and chitin (not decomposed by any isolate). The majority of isolates had been recorded previously from polar environments and/or as being able to survive at low temperatures.Fungi in tundra ecosystems, therefore, have significant potential to mineralise C at temperatures below 10 °C. A better understanding of the ecology of these fungi will allow us to improve predictions of C dynamics in arctic biomes in the future.     

Half a Century of Mercury Contamination in Lake Vänern (Sweden)

Lake Vänern is Sweden's largest freshwater reservoir. It has been significantly affected by mercury contamination during the latter half of the 20th century. The aim of this study was to analyse the spatial and vertical mercury distribution, whereas 46 sediment cores were sampled in 2001 and analysed for total mercury. Several of these cores were dated presenting sediment accumulation rates varying from 6–8 mm yr^?1 outside major rivers to ～2 mm yr^?1 in the deeper areas. This was made using ¹³⁷ Cs, which was verified by ²¹⁰ Pb dating. Cluster analysis was used to identify five areas with similar accumulation and mercury concentration regimes. In areas far from shore, surface concentrations ranged from 0.1 to 0.5 ppm Hg, while the deeper layers in contaminated areas held concentrations up to 11 ppm Hg. In total, ～50 tonnes of mercury accumulated in the lake's sediment between ～1940–2001; almost 80% (or 37 tonnes) originate from before the mid 70's when the recovery period began, and at least 30 tonnes can be attributed to the former point source – a chlor-alkali industry.     

Mercury and selenium content in Bouri (Mugil cephalus)

This study was carried out to estimate the levels of total, organic, inorganic-Hg, total Se and the interaction between both elements in the muscle and other body organs of bouri (Mugil cephalus). The results showed that strong closeness of correlation between length of fish and each of. (a) total, inorganic, organic Hg, and total Se in muscle, (b) total and organic Hg in backbone, (c) total and inorganic Hg in viscera.     

Mercury accumulation in Ipomoea aquatica (forsk) near a caustic soda factory in Thailand

Ipomoea aquatica is commonly used as a vegetable and pig food in Thailand. The present study shows that the leaves and floating stems of this plant collected near a caustic soda factory in Thailand had accumulated between 0.75 to 1.26 ppm (average 0.95 ppm) Hg in the leaves and 0.28 to 0.68 ppm (average 0.43 ppm) Hg in the floating stems. Leaves and floating stems from unpolluted areas had Hg contents between 0.01 to 0.17 ppm and 0.01 to 0.06 ppm, respectively. The contaminated I. aquatica in the study area represents an additional source of Hg, since fish from the same area are also polluted with Hg. This constitutes a serious risk to public health.     

有机肥对土壤-小麦系统汞污染影响的研究

以冬小麦为试验对象,采用盆栽试验,研究了不同有机肥、不同外源汞施用量对土壤和小麦的汞污染、迁移和累积的影响。结果表明,随着汞施入量的增加,土壤全汞和有效汞含量逐渐增加,使小麦吸收汞增加。在小麦整个生育期,土壤有效汞与小麦根、茎叶、籽粒吸收的汞之间呈极显著正相关性。随着有机肥施用量的增加,土壤有效态汞含量逐渐减少,继而降低小麦对汞的吸收。相关分析表明,有机肥施用量与土壤有效汞呈显著负相关。有机肥对土壤有效汞的抑制效果以低汞高有机肥处理效果最为显著,苗期达到58.94%,收获期达到62.29%。有机肥施用量与苗期低汞处理下小麦茎叶和根部汞含量呈显著负相关,与收获期的所有汞处理下小麦茎叶、根部和籽粒汞含量呈极显著或显著负相关,在低汞处理,施用有机肥完全抑制了土壤中汞向籽粒中转移。所有处理小麦各器官汞含量的分布规律为根〉茎叶〉籽粒。     

Hydrology of a small Canadian High Arctic basin during the snowmelt period

Investigations were carried out in a small Canadian High Arctic basin to determine the influence of snowmelt on the hydrologic behaviour of the active layer and on basin discharge. The snowpack was characteristically thin but rapid melting in late June released a substantial amount of water to a thinly-thawed active layer, resulting in overland flow or standing water conditions. Owing to an uneven distribution of basin snow cover, the meltwater source area was highly variable both in time and in space, thus giving rise to different active layer hydrologic regimes in different parts of the basin. Slopes with a snowbank often had a high water table while the water table in the slopes bared of snow showed a gradual decline. Since streamflow represents a basinwide integration of these two active layer hydrologic regimes, there was a progressive reduction in daily peak flow accompanied by a prolonged lag time between daily discharge and snowmelt as the basin snow storage decreased. Spatially, inhomogeneity of snow cover also affected the downstream changes in discharge so that the ratio of discharge between two gauging stations depends on the relative magnitudes of snowmelt, evaporation and storage requirements of the two sub-basins. Rapid melting of an unevenly distributed Arctic snowpack therefore strongly influences the hydrologic behaviour of the active layer which in turn affects the streamflow regime.     

Long-Term Changes in the Bioaccumulation of As, Cd, Pb, and Hg in Macroinvertebrates from the Elbe River (Czech Republic)

The Elbe River was extremely loaded by heavy metals and arsenic during the second half of the 20th century as a consequence of intensive chemical industry activities. To assess long-term contamination trends in the Elbe after socio-economical changes in 1989, selected macroinvertebrate species were used to identify biotic accumulation levels in the period from 1993 to 2005. Concentrations of As, Cd, Pb, and Hg were determined in Asellus aquaticus (Crustacea), Bythinia tentaculata (Mollusca), Erpobdella spp. (Hirudinea), and larvae of the family Chironomidae (Diptera) over a 3-year period along the longitudinal profile of the Czech part of the Elbe River and the lower Vltava (the main Elbe tributary). In this study, new evaluative approaches were used to assess these multiparameter data sets. The results showed that the most contaminated Czech sites were located in the industry-heavy middle Elbe region between Valy and Ob?íství. Surprisingly high concentrations of As, Cd, and Pb were observed in the upper stretch near the headwaters. Probably as a consequence of former mining activities and the metallurgic and glass industries, the lower Vltava was loaded with Cd and Pb. Despite substantial improvements in the water quality of the Elbe River within the studied time period, we found no general decreasing trend of As, Cd, and Pb in macrozoobenthos. A significant decrease of Hg was revealed, however, occurring already between 1993 and 1996. The results of interspecies comparisons showed that the investigated elements were most accumulated by chironomid larvae and Erpobdella spp.