Methylmercury in mosquitoes related to atmospheric mercury deposition and contamination

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 microg 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 (Ochlerotatus atlanticus < Culex nigripalpus < Anopheles crucians); this may be related to differences in biogeochemical characteristics of the aquatic habitat that affect dietary accumulation of MeHg during the larval stage. Mosquito MeHg was related positively to wet atmospheric Hg deposition among locations where atmospheric deposition is the principal source of Hg, and it was greatly enhanced in Hg-polluted environs near the Sulphur Bank Mine in Lake County, California. These results suggest that MeHg in mosquitoes may be a useful and sensitive indicator of Hg loadings to aquatic systems, including that derived from atmospheric deposition.     

Methylmercury in freshwater fish linked to atmospheric mercury deposition

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 thatthese 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.     

Residues of total mercury and methyl mercury in eel products

Fifty-two samples of broiled eels and broiled eel liver were analyzed for total mercury (total Hg) and methyl mercury. The mean concentrations of total Hg in broiled eels and broiled eel liver were 0.21 ppm and 0.10 ppm, respectively. Meanwhile, the mean concentrations of methyl mercury in broiled eels and broiled eel liver were 0.085 ppm and 0.039 ppm, respectively. The rate of methyl mercury to total Hg mainly ranged from 60 to 80% in broiled eels and from 35 to 65% in broiled eel liver. The total Hg concentrations of 2 samples of broiled eels and one sample of broiled eel liver exceeded the provisional regulation limit (0.4 ppm) of total Hg in fish in Japan. In these samples, the rates of methyl mercury to total Hg were lower than 20%. The muscles and the skin of broiled eels were measured separately. The ratios of skin to muscle concentration of total Hg and methyl mercury were mainly in the range from 1/10 to 1/4. The mean intakes of total Hg from broiled eels and broiled eel liver per individual were 24.6 microg and 3.1 microg, respectively. The mean intakes of methyl mercury from broiled eels and broiled eel liver per individual were 10.4 microg and 1.2 microg, respectively.     

Modeling mercury in power plant plumes

Measurements of speciated mercury (Hg) downwind of coal-fired power plants suggest that the Hg(II)/(Hg0 + HgII) ratio (where HgII is divalent gaseous Hg and Hg0 is elemental Hg) decreases significantly between the point of emission and the downwind ground-level measurement site, but that the SO2/(Hg0 + HgII) ratio is conserved. We simulated nine power plant plume events with the Reactive & Optics Model of Emissions (ROME), a reactive plume model that includes a comprehensive treatment of plume dispersion, transformation, and deposition. The model simulations fail to reproduce such a depletion in HgII. A sensitivity study of the impact of the HgII dry deposition velocity shows that a difference in dry deposition alone cannot explain the disparity. Similarly, a sensitivity study of the impact of cloud chemistry on results shows that the effect of clouds on Hg chemistry has only minimal impact. Possible explanations include HgII reduction to Hg0 in the plume, rapid reduction of HgII to Hg0 on ground surfaces, and/or an overestimation of the HgII fraction in the power plant emissions. We propose that a chemical reaction not included in current models of atmospheric mercury reduces HgII to Hg0 in coal-fired power plant plumes. The incorporation of two possible reduction pathways for HgII (pseudo-first-order decay and reaction with SO2) shows better agreement between the model simulations and the ambient measurements. These potential HgII to Hg0 reactions need to be studied in the laboratory to investigate this hypothesis. Because the speciation of Hg has a significant effect on Hg deposition, models of the fate and transport of atmospheric Hg may need to be modified to account for the reduction of HgII in coal-fired power plant plumes if such a reaction is confirmed in further experimental investigations.     

Correlation of fat content and dioxins, total mercury and methyl mercury levels in tuna

In this study, we analyzed the concentrations of mercury and dioxins in tuna with various fat contents (akami; the leaner meat, Chutoro; the belly area of the tuna along the side of the fish between the akami and the otoro. Otoro; the fattiest portion of the tuna) in wild and farmed bluefin tuna and farmed southern bluefin tuna. In the three kinds of tuna, average dioxins concentrations in Akami, chutoro and otoro were 1.7, 4.7 and 9.6 pg TEQ/g, respectively. The dioxins concentration in all three regions of tuna was in direct proportion to the fat content. In the farmed bluefin tuna, the dioxins concentration was almost the same as that of the wild tuna, but differed from that of the farmed southern bluefin tuna. Average total mercury concentration based on wet weight in akami was 0.42 μg/g, being higher than the values of 0.36 μg/g of chutoro and 0.31 μg/g of otoro, and in inverse proportion to the fat content. In all three regions, the total mercury concentration of the wild bluefin tuna was equal to that of the farmed tuna. The total mercury concentration in the latter was two to three times higher than that of the farmed southern bluefin tuna. If the Japanese intake is one fin of tuna (80 g) a day, the daily intake levels of dioxins and methyl mercury can be estimated as 0.48-37 pg TEQ/kg bw and 0.21-0.90 μg/kg bw, respectively.     

Determination of total mercury in foods of plant origin in Poland by cold vapour atomic absorption spectrometry.

Total mercury concentrations were determined in 573 samples of agricultural crops and foods of plant origin which included cereals, fruit and vegetables and their products commercially available on the Polish market. The method of cold vapour atomic absorption spectrometry (CVAAS) after a wet-acid digestion in a closed-vessels and microwave oven was used and the reliability of the procedure demonstrated. Mercury concentrations in the agricultural crops and plant foods were generally below the maximum permissible limits in Poland and rarely exceeded 5 microg x kg(-1). Values ranged from <0.1 to 14 microg x kg(-1), mean 2.4 +/- 2.3 microg x kg(-1) in wheat and rye grains; from <0.1 to 2.4 microg x kg(-1), mean 0.5 +/- 0.4 microg x kg(-1) in nine varieties of vegetables; from <0.1 to 5.1 microg x kg(-1), mean 1.1 +/- 0.9 microg x kg(-1) in seven varieties of fruit; from <0.1 to 5.6 microg x kg(-1) in cereal products and jams; and from <0.1 to 3.0 microg x l(-1) in fruit and vegetable juices, nectars and beverages. The contribution of the mercury in the analysed agricultural crops and foods of plant origin to the weekly dietary intake of total mercury was 8 microg/person, which represents only 3% of the provisional tolerable weekly intake (PTWI) for this metal.     

Voltammetric determination of ultra-trace total mercury and toxic metals in meals

This paper reports the sequential voltammetric determination of Hg(II) and Cu(II) at the gold electrode (GE), and of Cu(II), Pb(II), Cd(II), Zn(II) at the hanging mercury drop electrode (HMDE) by square wave anodic stripping voltammetry (SWASV).     

Importance of the forest canopy to fluxes of methyl mercury and total mercury to boreal ecosystems

The forest canopy was an important contributor to fluxes of methyl mercury (MeHg) and total mercury (THg) to the forest floor of boreal uplands and wetlands and potentially to downstream lakes, at the Experimental Lakes Area (ELA), northwestern Ontario. The estimated fluxes of MeHg and THg in throughfall plus litterfall below the forest canopy were 2 and 3 times greater than annual fluxes by direct wet deposition of MeHg (0.9 mg of MeHg ha(-1)) and THg (71 mg of THg ha(-1)). Almost all of the increased flux of MeHg and THg under the forest canopy occurred as litterfall (0.14-1.3 mg of MeHg ha(-1) yr(-1) and 110-220 mg of THg ha(-1) yr(-1)). Throughfall added no MeHg and approximately 9 mg of THg ha(-1) yr(-1) to wet deposition at ELA, unlike in other regions of the world where atmospheric deposition was more heavily contaminated. These data suggest that dry deposition of Hg on foliage as an aerosol or reactive gaseous Hg (RGM) species is low at ELA, a finding supported by preliminary measurements of RGM there. Annual total deposition from throughfall and litterfall under a fire-regenerated 19-yr-old jack pine/birch forest was 1.7 mg of MeHg ha(-1) and 200 mg of THg ha(-1). We found that average annual accumulation of MeHg and THg in the surficial litter/fungal layer of soils since the last forest fire varied between 0.6 and 1.6 mg of MeHg ha(-1) and between 130 and 590 mg of THg ha(-1) among sites differing in drainage and soil moisture. When soil Hg accumulation sites were matched with similar sites where litterfall and throughfall were collected, measured fluxes of THg to the forest floor (sources) were similar to our estimates of longterm soil accumulation rates (sinks), suggesting that the Hg in litterfall and throughfall is a new and not a recycled input of Hg to forested ecosystems. However, further research is required to determine the proportion of Hg in litterfall that is being biogeochemically recycled within forest and wetland ecosystems and, thus, does not represent new inputs to the forest ecosystem.     

Survey of total mercury in infant formulae and oral electrolytes sold in Canada

Total mercury (Hg) was measured in 150 infant formula products (as sold) and oral electrolyte solutions purchased in Canada in 2003. Results less than the limit of detection (LOD) were reported as the numeric value of the LOD. Electrolytes contained the lowest concentrations, averaging 0.026?ng/g. Average levels in milk-based ready-to-use, concentrated liquid and powdered concentrate were 0.028, 0.069 and 0.212?ng/g, respectively. In soy-based formulae, the respective mean concentrations were 0.049, 0.101 and 0.237?ng/g. These concentrations cannot be considered on an absolute basis because 76% of sample concentrations fell below the limit of detection. Despite the inability to measure many of the actual background concentrations, the method was sufficiently sensitive to identify clear cases of low-level Hg contamination (up to 1.5?ng/g) of individual lots of powdered formula. Also, all the different lots of one brand of concentrated liquid infant formulae had significantly higher concentrations of Hg than those of all other concentrated liquid products. After dilution with preparation water, the Hg concentrations in all products would be lower than the Canadian Drinking Water Guideline for Hg of 1?ng/mL and too low to impact on health.     

Levels of total mercury in predatory fish sold in Canada in 2005

Total mercury was analysed in 188 samples of predatory fish purchased at the retail level in Canada in 2005. The average concentrations (ng g(-1), range) were: sea bass 329 (38-1367), red snapper 148 (36-431), orange roughy 543 (279-974), fresh water trout 55 (20-430), grouper 360 (8-1060), black cod 284 (71-651), Arctic char 37 (28-54), king fish 440 (42-923), tilefish 601 (79-1164) and marlin 854 (125-2346). The Canadian standard for maximum total mercury allowed in the edible portions of fish sold at the retail level is 1000 ng g(-1) for shark, swordfish, marlin, orange roughy, escolar and both fresh and frozen tuna. The standard is 500 ng g(-1) for all other types of fish. In this study, despite the small number of samples of each species, the 1000 ng g(-1) maximum was exceeded in five samples of marlin (28%). The 500 ng g(-1) maximum was exceeded by six samples of sea bass (20%), four of tilefish (50%), five of grouper (24%), six of king fish (40%) and one of black cod (13%).     

Survey of total mercury in total diet food composites and an estimation of the dietary intake of mercury by adults and children from two Canadian cities, 1998-2000

Total mercury was measured in 259 total diet food composites from two Canadian cities. Levels were generally low, with 46% of the composites having concentrations below the limit of detection, which ranged from 0.026 to 0.506 ng g^-1. The fish category contained the highest mercury concentrations, which averaged 67 ng g^-1 and ranged from 24 to 148 ng g^-1. All composites were below the Canadian guideline for total mercury in fish of 0.5 ppm. Dietary intakes of mercury averaged 0.022 μg kg^-1 body weight/day (μg kg^-1 day^-1), and ranged from 0.012 μg kg^-1 day^-1 for females over 65 years old to 0.062 μg kg^-1 day^-1 for 0-1-month-old infants. For fish consumers, fish contributed to more than half of the ingested mercury. All intakes were well below Joint FAO/WHO Expert Committee on Food Additives Provisional Tolerable Weekly Intakes, expressed on a daily basis, of 0.71 μg kg^-1 day^-1 total mercury and 0.47 μg kg^-1 day^-1 methyl mercury, and also below a recent Health Canada recommended maximum methyl mercury intake of 0.2 μg kg^-1 day^-1 for children and women of child-bearing age.     

Survey of total mercury and methylmercury levels in edible fish from the Adriatic Sea

Total mercury and methylmercury concentrations were measured in the muscle tissue of different fish species from the Adriatic Sea to ascertain whether the concentrations exceeded the maximum level fixed by the European Commission. Large species-dependent variability was observed. The highest total mercury mean concentrations were in benthic (0.20-0.76 μg g^-1 wet wt) and demersal fish (0.22-0.73 μg g^-1 wet wt), while pelagic species showed the lowest levels (0.09-0.23 μg g^-1 wet wt). In 15% of frost fish, in 42% of skate and in 30% of angler fish samples total mercury concentrations exceeded the maximum level fixed by the European Commission (Hg = 1 μg g^-1 wet wt); for the species for which the maximum level was set to 0.5 μg g^-1 wet wt, concentrations exceeding the prescribed legal limit were observed in 6.4% of bokkem, in 6.6% of pandora, in 20% of megrin, in 12.5% of four-spotted megrim, in 16% of striped mullet, in 5.0% of forkbeard and in 5.3% of picarel samples. In all the different species, mercury was present almost completely in the methylated form, with mean percentages between 70 and 100%. Weekly intake was estimated and compared with the provisional tolerable weekly intake recommended by the FAO/WHO Expert Committee on Food Additives. A high exposure was associated with the consumption of only skates, frost fish and angler fish, thought the consumption of the other species, such as, megrim, four spotted megrim, red fish striped mullet and forkbeard, resulted in a weekly intake slightly below the established provisional tolerable weekly intake.     

Spectrofluorometric method for determination of the total mercury content in natural waters

A simple and highly selective spectrofluorometric method for the determination of the total mercury (Hg) in natural waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, has been made the basis of this sensitive method. Organic and inorganic Hg compounds in water samples were decomposed with sulphuric acid and potassium permanganate. Precipitated manganese dioxide and excess oxidants (permanganate) were destroyed with hydroxylammonium chloride. Hg(II) was reduced by tin(II) chloride and Hg vapour driven by an air stream into an absorption solution containing potassium permanganate and sulphuric acid, using a closed, recirculating air stream. In this solution fluorescence quenching of rhodamine B at an excitation wavelength of 485 nm and emission wavelength of 586 nm was measured. This method is suitable for the determination of total Hg in drinking and surface waters. The method gives reliable results down to a concentration of 0.5 g Hg per litre of water. The water samples analysed by this method gave a mean recovery and standard error of 97.3±2.39 for added Hg.

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Spektrofluorometrische Methode zur Bestimmung des Gehalts an Gesamtquecksilber im Wasser

Zusammenfassung Es wurde eine einfache, schnelle und hochselektive spektrofluorometrische Methode zur quantitativen Bestimmung des Gehalts an Gesamtquecksilber in Wasser beschrieben. Diese empfindliche Methode begründet sich auf der Fluorescenzlöschung in Rodamin-B-Lösung mittels Hg(II) bei Anwesenheit von Jodid und nach einem Verfahren, das den Zweck einer Quecksilberanreicherung hat. In Wasserproben wurden die organischen als auch anorganischen Quecksilberverbindungen mit H₂SO₄ aufgeschlossen und mit KMnO₄ oxydiert. Nach der Beseitigung des entstandenen MnO₂-Niederschlags bzw. des überschüssigen Permanganats mit HONH₃Cl wurde das Quecksilber mit SnCl₂ reduziert. Dann wurde das flüchtige Quecksilber durch einen Luftstrom in wässerige Absorptionslösung mit H₂SO₄ und KMnO₄ eingeleitet und damit angereichert. In dieser Meßlösung wurde die Fluorescenzlöschung des Rodamin-B bei der Anregungswellenlänge von 485 nm und Emissionswellenlänge von 586 nm ermittelt. Das entwickelte Untersuchungsverfahren ist für die Bestimmung des Gehalts an Gesamtquecksilber in Trinkwasser und Oberflächengewässern anwendbar. Die Nachweisgrenze liegt bei etwa 0,5 g Quecksilber/L Wasser. Zusätze von Quecksilber zu untersuchten Wasserproben ergaben eine Wiederfindungsrate und Standardfehler von im Durchschnitt 97,3±2,39.

     

Ingestion and retention of mercury by sheep grazing near a chlor-alkali plant

An experiment is described in which a flock of sheep was kept for 23 months on a field contaminated with mercury as a result of atmospheric emissions from a chloralkali site. The mercury concentration found in the flesh of the sheep during the trial was within the range present in other commercially available meat. Levels of mercury found in the kidney and liver were elevated, although < 10% of the mercury in the organs or the flesh was in the methylated form. About 0.1% of the total mercury taken in by inhalation and ingestion was retained by the sheep. The breeding performance of the flock was normal. It is concluded that contamination of grass as a result of atmospheric discharges of inorganic mercury from UK chlor-alkali sites causes no hazard either directly to grazing animals or indirectly to humans who might ultimately consume their flesh.     

Survey of total mercury in some edible fish and shellfish species collected in Canada in 2002

Total mercury was measured in the edible portions of 244 selected fish and shellfish purchased in Canada at the retail level. By species, average mercury concentrations ranged from 0.011 μg g^-1 for oysters to 1.82 μg g^-1 for swordfish. The predatory fish contained the highest concentrations of mercury: swordfish (mean 1.82 μg g^-1, range 0.40-3.85 μg g^-1), marlin (1.43, 0.34-3.19 μg g^-1), shark (1.26, 0.087-2.73 μg g^-1), and canned, fresh and frozen tuna (0.35, 0.020-2.12 μg g^-1). Levels of mercury in the fresh and frozen tuna contained a mean of 0.93 μg g^-1 (range 0.077-2.12 μg g^-1) and were substantially higher than in the canned tuna (0.15, 0.02-0.59 μg g^-1). In the canned tuna, mercury concentrations varied with subspecies, with the highest average concentrations being found in Albacore tuna (mean 0.26 μg g^-1, range 0.19-0.38 μg g^-1) and the lowest (0.047, 0.025-0.069 μg g^-1) in five samples for which the subspecies of tuna were not identified. Mean concentrations of mercury in swordfish and fresh and frozen tuna were up to three times higher than reported for the USA. Dietary intake estimations found that provided fresh and frozen tuna, marlin, swordfish or shark are consumed once a month or less, the dietary intakes of total mercury by women of child-bearing age, averaged over 1 month, would fall below the Joint FAO/WHO Expert Committee on Food Additives provisional tolerable weekly intake for total mercury. The current Canadian advisory to children and women of child-bearing age is to limit their consumption of fresh and frozen tuna, swordfish and shark to no more than one meal per month.     

Cadmium and total mercury in some cephalopods from the South Adriatic Sea (Italy)

In the framework of a wide monitoring programme on the presence of heavy metals in marine organisms caught in the South Adriatic Sea, cadmium and total mercury concentrations were determined in flesh and hepatopancreas of 512 specimens of two species of cephalopods. The aim of the study was to establish the quality of the marine food with respect to the health of consumers and to investigate cadmium and mercury distribution in organisms representing different habitats. For both elements, higher levels were found in spider octopus (Octopus salutii) than in broadtail squid (Illex coindeti). Between the two different tissues analysed, higher concentrations were observed in hepatopancreas than flesh. According to the rules in force, no flesh sample showed cadmium and total mercury concentrations exceeding the peak permitted values of 2mg/kgwetwt and 0.5mg/kgwetwt respectively.     

Spatial and habitat-based variations in total and methyl mercury concentrations in surficial sediments in the San Francisco Bay-Delta

Recent studies indicate significant amounts of mercury (Hg) are annually transported into the San Francisco Bay-Delta (Bay-Delta) as a result of historic gold and Hg mining activities. We examined temporal and spatial variation in concentrations of total Hg (Hg(T)) and monomethylmercury (MMHg) in surficial sediments of various ecosystem types in the Bay-Delta. We sampled surficial sediments across the Bay-Delta system and found Hg(T) sediment concentrations in the central Delta were generally 100-200 ng g(-1) and increased westward through Suisun Bay to 250-350 ng g(-1). MMHg concentrations in the central Delta were between 1 and 3 ng g(-1), while those in sediments in the perimeter waterways and adjacent bays were less than 1 ng g(-1). Six sites were monitored monthly for over a year to identify seasonal changes in Hg sediment concentrations. Hgtau sediment concentrations ranged from 48 to 382 ng g(-1) and varied as a function of location not season. However, MMHg concentrations varied seasonally, increasing from 1 ng g(-1) during winter months to 6 ng g(-1) during spring and summer. Transects conducted at three marshes in the central Delta revealed MMHg sediment concentrations of 4-8 ng g(-1) at the interior and 2 ng g(-1) at the exterior of the marshes. Habitat type was a major factor controlling MMHg concentration and the MMHg to Hg(T) ratio in sediments of the Bay-Delta. MMHg was significantly correlated to Hgt (r2 = 0.49) in marsh sediments.