Microg Hg Research Articles

How Might Selenium Moderate the Toxic Effects of Mercury in Stream Fish of the Western U.S.?

The ability of selenium (Se) to moderate mercury (Hg) toxicity is well established in the literature. Mercury exposures that might otherwise produce toxic effects are counteracted by Se, particularly when Se:Hg molar ratios approach or exceed 1. We analyzed whole body Se and Hg concentrations in 468 fish representing 40 species from 137 sites across 12 western U.S. states. The fish samples were evaluated relative to a published wildlife protective Hg threshold (0.1 sg Hg x g(-1) wet wt.), the currenttissue based methylmercury (MeHg) water quality criterion (WQC) for the protection of humans (0.3 microg Hg x g(-1) wet wt) and to presumed protections against Hg toxicity when Se:Hg molar ratios are >1. A large proportion (56%) of our total fish sample exceeded the wildlife Hg threshold, whereas a smaller, but significant proportion (12%), exceeded the MeHg WQC. However, 97.5% of the total fish sample contained more Se than Hg (molar ratio >1) leaving only 2.5% with Se: Hg ratios <1. All but one of the fish with Se:Hg <1, were of the genus Ptychochelius (pikeminnow). Scientific literature on Se counteracting Hg toxicity and our finding that 97.5% of the freshwater fish in our survey have sufficient Se to potentially protect them and their consumers against Hg toxicity suggests that Se in fish tissue (Se:Hg molar ratio) must be considered when assessing the potential toxic effects of Hg.

Multisyringe flow injection analysis hyphenated with liquid core waveguides for the development of cleaner spectroscopic analytical methods: improved determination of chloride in waters

In this work, the hyphenation of the multisyringe flow injection analysis technique with a 100-cm-long pathlength liquid core waveguide has been accomplished. The Cl-/Hg(SCN)2/Fe3+ reaction system for the spectrophotometric determination of chloride (Cl(-)) in waters was used as chemical model. As a result, this classic analytical methodology has been improved, minimizing dramatically the consumption of reagents, in particular, that of the highly biotoxic chemical Hg(SCN)2. The proposed method features a linear dynamic range composed of two steps between (1) 0.2-2 and (2) 2-8 mg Cl- L(-1), thus extended applicability due to on-line sample dilution (up to 400 mg Cl- L(-1)). It also presents improved limits of detection and quantification of 0.06 and 0.20 mg Cl- L(-1), respectively. The coefficient of variation and the injection throughput were 1.3% (n = 10, 2 mg Cl- L(-1)) and 21 h(-1). Furthermore, a very low consumption of reagents per Cl- determination of 0.2 microg Hg(II) and 28 microg Fe3+ has been achieved. The method was successfully applied to the determination of Cl- in different types of water samples. Finally, the proposed system is critically compared from a green analytical chemistry point of view against other flow systems for the same purpose.

Evaluation of Metallothionein Expression as a Biomarker of Mercury Exposure in Scatophagus argus

The effect of mercury exposure to total Metallothionein (MT) response and bioaccumulation under control and acute mercury exposure were investigated in scats (Scatophagus argus). Scats were exposed to different mercury concentrations (10, 20 and 30 microg Hg L(-1)) for 24, 48 and 72 h. Total MT levels were determined by Enzyme-Linked Immunosorbent Assay (ELISA) method. Mercury contents were determined through cold Vapour atomic Absorption spectrometry. Induction of MT during exposure was tissue specific, displaying different response pattern in gill and liver. Mercury accumulated much stronger in liver than gill and the latter also showed lower MT level. MT biosynthesis in liver showed a significant increase after exposure to different mercury concentration during different times. This increase was significantly correlated with mercury bioaccumulation. In contrast, presence of different mercury concentration during different times did not significantly modify total MT except for 72 h exposure at 30 microg L(-1) in gills. The results suggest that this form of MT existing in S. argus was Hg-inducible and could be extended the as a biomarker of mercury pollution in ecosystems.

Modeling the Past Atmospheric Deposition of Mercury Using Natural Archives

Historical records of mercury (Hg) accumulation in lake sediments and peat bogs are often used to estimate human impacts on the biogeochemical cycling of mercury. On the basis of studies of lake sediments, modern atmospheric mercury deposition rates are estimated to have increased by a factor of 3-5 compared to background values: i.e., from about 3-3.5 microg Hg m(-2) yr(-1) to 10-20 microg Hg m(-2) yr(-1). However, recent studies of the historical mercury record in peat bogs suggest significantly higher increases (9-400 fold, median 40x), i.e., from about 0.6-1.7 microg Hg m(-2) yr(-1) to 8-184 microg Hg m(-2) yr(-1). We compared published data of background and modern mercury accumulation rates derived from globally distributed lake sediments and peat bogs and discuss reasons for the differences observed in absolute values and in the relative increase in the industrial age. Direct measurements of modern wet mercury deposition rates in remote areas are presently about 1-4 microg m(-2) yr(-1), but were possibly as high as 20 microg Hg m(-2) yr(-1) during the 1980s. These values are closer to the estimates of past deposition determined from lake sediments, which suggests that modern mercury accumulation rates derived from peat bogs tend to overestimate deposition. We suggest that smearing of 210Pb in the uppermost peat sections contributes to an underestimation of peat ages, which is the most important reason for the overestimation of mercury accumulation rates in many bogs. The lower background mercury accumulation rates in peat as compared to lake sediments we believe is the result of nonquantitative retention and loss of mercury during peat diagenesis. As many processes controlling time-resolved mercury accumulation in mires are still poorly understood, lake sediments appear to be the more reliable archive for estimating historical mercury accumulation rates.

Distribution and accumulation of mercury in tissues of captive‐reared common loon (Gavia immer) chicks

We determined the distribution and accumulation of Hg in tissues of common loon (Gavia immer) chicks maintained for up to 15 weeks on either a control diet with no added methylmercury chloride (MeHgCl) or one containing either 0.4 or 1.2 microg Hg (as MeHgCl)/g wet-weight food. Total Hg and MeHg tissue concentrations were strongly positively correlated (r2 > 0.95) with the amount of Hg delivered to individual chicks throughout the course of the experiment. The pattern of differential Hg concentration in internal tissues was consistent within each treatment: Liver > kidney > muscle > carcass > brain. Feather Hg concentrations were consistently higher than those of internal tissues and represented an important route of Hg elimination. Feather mass accounted for 4.3% +/- 0.1% (average +/- standard error) of body mass, yet 27.3% +/- 2.6% of total Hg intake was excreted into feathers. Our calculations indicate that 26.7% +/- 4.9% of ingested Hg was not accounted for and, thus, either was never absorbed or was absorbed and subsequently eliminated in feces. With the additional excretion into feathers, 54% of ingested Hg was excreted. Demethylation was evident in the liver at all treatment levels and in the kidneys of chicks dosed at 1.2 microg Hg/g. Mercury concentrations were strongly positively correlated (r2 > or = 0.95) among internal tissues and with blood Hg concentration. Mercury concentrations of secondary feathers were moderately correlated (r2 = 0.82-0.93) with internal tissues. We supply regression models that may be used to provide perspective and a useful means of interpreting the variety of measures of Hg exposure reported in the literature.

Mercury Concentration in Fish from Streams and Rivers Throughout the Western United States

We collected and analyzed 2,707 large fish from 626 stream/river sites in 12 western U.S. states using a probability design to assess the regional distribution of whole fish mercury (Hg) concentrations. Large (>120 mm total length) fish Hg levels were strongly related to both fish length and trophic guild. All large fish that we sampled exceeded the wet weight detection limit of 0.0024 microgxg(-1), and the mean Hg concentration in piscivores (0.260 /microgxg(-1)) was nearly three times that of nonpiscivores (0.090 microgxg(-1)). Fish tissue Hg levels were not related to local site disturbance class. After partialing out the effects of fish length, correlations between Hg and environmental variables were low (r < 0.3) for the most common genera (trout and suckers). Stronger partial correlations with Hg (r > 0.5) were observed in other genera for pH, stream size, and human population density but patterns were not consistent across genera. Salmonids, the most common family, were observed in an estimated 125,000 km of stream length, exceeded 0.1 microg Hg x g(-1) (deemed protective for fish-eating mammals) in 11% of the assessed stream length, and exceeded the filet equivalent of 0.3 microg Hgxg (-1) (USEPA tissue-based water quality criterion) in 2.3% of that length. Piscivores were less widespread (31,400 km), but they exceeded the 0.1 and 0.3 microg Hgxg(-1) criteria in 93% and 57% of their assessed stream length, respectively. Our findings suggest that atmospheric transport is a key factor relative to Hg in fish across the western United States.

Effect of Loading Rate on the Fate of Mercury in Littoral Mesocosms

The effects of changes in atmospheric mercury (Hg) deposition on aquatic ecosystems are poorly understood. In this study, we examined the biogeochemical cycling of Hg in littoral mesocosms receiving different loading rates (7-107 microg Hg m(-2) year(-1)). We added a 202Hg-enriched preparation to differentiate the experimentally added Hg from the ambient Hg in the environment. This approach allowed us to follow the distribution and methylation of the isotopically enriched ("spike") Hg in the mesocosms. Within 3 weeks, spike Hg was distributed throughout the main environmental compartments (water, particles, periphyton, and sediments) and began to be converted to methylmercury (MeHg). Concentrations of spike total Hg and MeHg in these compartments, measured after 8 weeks, were directly proportional to loading rates. Thus, Hg(II) availability was the limiting factor for the major processes of the biogeochemical Hg cycle, including methylation. This is the first study to demonstrate a proportional response of in situ MeHg production to atmospherically relevant loading levels. On the basis of mass balances, we conclude that loading rate had no effect on the relative distribution of spike Hg among the main compartments or on the fraction of spike Hg converted to MeHg. Therefore, loading rate did not change the relative magnitude of biogeochemical pathways competing for Hg within the mesocosms. These data suggest that reductions of Hg deposition to lake surfaces would be equally effective across a broad range of deposition rates.

Foliar Mercury Accumulation and Exchange for Three Tree Species

The goals of this study were to (1) investigate plant mercury (Hg) uptake using different air and soil Hg concentrations near natural background values for three tree species, and (2) test if measured foliar Hg fluxes could explain observed foliar Hg concentrations. Plants were exposed to three soil treatments (<0.01, 0.09 +/- 0.02, and 0.92 +/- 0.27 microg Hg g(-1)), and to three atmospheric exposure concentrations (5.9 +/- 2.3, 14.3 +/- 2.7, and 30.1 +/- 3.5 ng Hg m(-3)). Foliar Hg concentrations were found to be influenced primarily by atmospheric Hg concentrations and to a lesser extent by soil Hg exposures. Data indicated that deciduous species might play a more active role in ecosystem Hg cycling than evergreen trees. Foliar mercury fluxes quantified using a dynamic single-plant gas-exchange chamber for two species were variable and accumulation rates were lower than those predicted based on foliar Hg concentrations. A hypothesis to explain this discrepancy is that the plant gas-exchange chamber measures net flux which includes emission, deposition, adsorption, and reemission of Hg at the leaf surface, while total foliar accumulation represents only deposition and assimilation.

Valve movement response of the mussel Mytilus galloprovincialis to metals (Cu, Hg, Cd and Zn) and phosphate industry effluents from Moroccan Atlantic coast

Valve activity was measured in the Mediterranean mussel Mytilus galloprovincialis in response to sublethal concentrations of four metals (Hg, Cu, Zn and Cd) and two phosphate industry effluents from the Atlantic coast of Morocco. Valve movements were monitored using a proximity inductive sensor which could display all activity figures from full closure to wide opening of the shell valves. In a 1 h exposure experiments, all metals induced a decrease in the time of normal opening and the appearance of sequences of stress behaviour, including enhanced valve adductions and complete closure at high concentrations. Mercury (tested from 5 to 75 microg Hg l(-1)) was the most toxic to the valve activity, with a threshold effective concentration at 10 microg Hg l(-1) and full valve closure occurring at 50 microg Hg l(-1). Copper (15-150 microg Cu l(-1)) showed a toxic effect starting at threshold concentration of 20 microg Cu l(-1) and induced full valve closure at 150 microg Cu l(-1). Zinc (100-500 microg Zn l(-1)) was effective in reducing the time of normal opening (threshold concentration at 100 microg Zn I(-1)) but no complete closure was recorded in any of the tested concentrations. For cadmium (1000-5000 microg Cd l(-1)), the valve activity was insensitive for exposures under 2000 microg Cd l(-1). Results for the testing of several samplings of the phosphate industry effluents (Safi and Jorf Lasfar) showed that their toxicity varied over the time. The effluent of the Jorf Lasfar plant (2-9.4%) was, however, more toxic than that of Safi (1-25%). In the light of these results, the sensitivity of the valve activity of Mytilus galloprovincialis to pollutants and its usefulness for in situ monitoring of coastal pollution in Morocco are discussed.

Total mercury determination in sand boxes from Montreal

Direct mercury analysis was successfully applied to determine trace levels of total mercury in samples from sand boxes in Montréal (Québec, Canada). Twenty sand boxes were sampled from across the city and divided into two size fractions, a fine fraction (<100 microm) and a whole fraction. The concentrations of mercury ranged from 1.6 to 35 microg Hg kg(-1) dry soil for the fine fraction and from 0.7 to 6 microg Hg kg(-1) dry soil for the whole fraction. The mercury concentrations correlated with the soil organic carbon content (R2= 0.67) in the sand. The ratio of the concentration of mercury in the fine over the whole fraction varied from 2.2 to 18. Using published soil ingestion rates for children, the calculated daily intake values varied from 0 to 0.5 ng Hg kg(-1) bw d(-1) with an estimated oral ingestion of 200 mg of sand and from 0.2 to 4.7 ng Hg kg(-1) bw d(-1) with an ingestion of 1750 mg of sand. None of the sand boxes contain sufficient amounts of mercury so as to exceed the currently accepted daily intake threshold of 0.105 microg Hg kg(-1) bw d(-1) established by Health Canada.

Mercury in chemical fractions of recent pelagic sediments of the sea of Japan.

The distribution of mercury (Hg) in chemical fractions (H2O, 0.05 M Na2-EDTA pH 3, 1 M HCl, humic and fulvic acids, and non-hydrolysing residue) of recent pelagic sediment cores of the Sea of Japan (East Sea) was studied. Total Hg content in the sediments was rather low: 83 +/- 30 (21-173) etag g(-1), indicating the absence of substantial specific sources of the element in the deep part of the sea. Hg content within the sediment core varied by a factor of 1.3-1.8, showing peaks that coincide with the near-surface and buried sediment slices of light brown and brown "oxidized" colours and evidencing Hg redox-sensitive diagenetic redistribution. Hg exerted its maximum mobility in the near-surface sediment strata as a component of water-soluble organic matter. Despite the predominance of fulvic acids in extracted humus fractions, humic acids were a much more efficient concentrator for Hg (0-79 vs. 188-233 microg Hg g(-1) C(org), respectively). Nevertheless, the most refractory non-hydrolyzing residue (humin) fraction contained the principal Hg pool in the sediments. Hg content in all the extracted fractions decreased with core depth, thus indicating Hg immobilization as a principal tendency in Hg fate during post-depositional diagenesis.

Effects of dietary methylmercury on reproduction of fathead minnows.

We examined effects of dietary methylmercury (MeHg) on reproduction of fathead minnows (Pimephales promelas). Juvenile fish were fed one of four diets until sexual maturity (phase 1): a control diet (0.06 microg Hg g(-1) dry weight) and three diets contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 microg Hg g(-1) dry weight (high). At sexual maturity, male and female fish were paired, again fed one of the four diets, and allowed to reproduce (phase 2). To assess effects of MeHg during gametogenesis, some fish were fed diets during phase 2 that differed from those during phase 1. Spawning success of pairs fed the same diet during phases 1 and 2 was 75% for controls and 46%, 50%, and 36% for the low-, medium-, and high-MeHg treatments, respectively. Spawning success of pairs fed a contaminated diet during phase 1 and a control diet during phase 2 was 63%, 40%, and 14% for the low-, medium-, and high-MeHg treatments, respectively, whereas exposure to dietary MeHg only during phase 2 did not reduce spawning success. Dietary MeHg delayed spawning, and days to spawning was positively correlated with concentration of total mercury in the carcasses of test fish. MeHg reduced the instantaneous rate of reproduction of fish fed the same diets during phases 1 and 2. Both the gonadosomatic index and reproductive effort of female fish were inversely correlated with mercury in carcasses, whereas developmental and hatching success of embryos, 7-d survival, and 7-d growth of larvae were unrelated to mercury concentrations in parental fish or their diets. MeHg decreased reproduction of adult fathead minnows at dietary concentrations encountered by predatory fishes in aquatic systems with MeHg-contaminated food webs, implying that exposed fish populations could be adversely affected by this widespread contaminant.

Effects of mercury on antioxidant mechanisms in the marine phanerogam Posidonia oceanica.

Biochemical markers of oxidative stress such as catalase activity, glutathione S-transferase (GST) activity and levels of lipid peroxidation evaluated in terms of thiobarbituric acid reactive substances (TBARS) were measured in the sheaths of the marine phanerogam Posidonia oceanica (L.) Delile experimentally exposed to 0.01, 0.1 and 1 microgHg l(-1) for 48 h. Up to a threshold concentration of 0.1 microg Hg l(-1), an increase in catalase and GST activities and TBARS levels was observed, indicating that the antioxidant mechanisms were overtaxed and could not prevent membrane lipid peroxidation. Paradoxically, at 1 microg Hg l(-1), the damage seemed to decrease, as the lipid peroxidation levels of exposed sheaths were lower than those of controls and as catalase and GST activities were not different from those of controls. A possible rapid induction of phytochelatins detoxifying mercury could occur at this high level of mercury.

Mercury Contamination in Freshwater, Estuarine, and Marine Fishes in Relation to Small-Scale Gold Mining in Suriname, South America

The extent of mercury contamination in Surinamese food fishes due to small-scale gold mining was investigated by determination of the total mercury concentration in 318 freshwater fishes, 109 estuarine fishes, and 110 fishes from the Atlantic Ocean. High background levels were found in the piranha Serrasalmus rhombeus (0.35 microg Hg x g(-1) muscle tissue, wet mass basis) and the peacock cichlid Cichla ocellaris (0.39 microg x g(-1)) from the Central Suriname Nature Reserve. Average mercury levels in freshwater fishes were higher in piscivorous species than in nonpiscivorous species, both in potentially contaminated water bodies (0.71 and 0.19 microg x g(-1), respectively) and in the control site (0.25 and 0.04 microg x g(-1), respectively). Mercury concentrations in piscivorous freshwater fishes were significantly higher in rivers potentially affected by gold mining than in the control site. In 57% of 269 piscivorous freshwater fishes from potentially contaminated sites, mercury levels exceeded the maximum permissible concentration of 0.5 microg Hg x g(-1). The highest mercury concentrations (3.13 and 4.26 microg x g(-1)) were found in two piranhas S. rhombeus from the hydroelectric reservoir Lake Brokopondo. The high mercury levels in fishes from Lake Brokopondo were to some extent related to gold mining because fishes collected at eastern sites (i.e., close to the gold fields) showed significantly higher mercury concentrations than fishes from western localities. In the estuaries, mercury levels in ariid catfish (0.22 microg x g(-1)) and croakers (0.04-0.33 microg x g(-1)) were distinctly lower than those in piscivorous fishes from contaminated freshwater sites. In the isolated Bigi Pan Lagoon, the piscivores snook Centropomus undecimalis (0.04 microg x g(-1)) and tarpon Megalops atlanticus (0.03 microg x g(-1)) showed low mercury levels. Mercury levels were significantly higher in marine fishes than in estuarine fishes, even with the Bigi Pan fishes excluded. High mercury concentrations were found in the shark Mustelus higmani (0.71 microg x g(-1)), the crevalle jack Caranx hippos (1.17 microg x g(-1)), and the barracuda Sphyraena guachancho (0.39 microg x g(-1)), but also in nonpiscivorous species such as Calamus bajonado (0.54 microg x g(-1)), Haemulon plumieri (0.47 microg x g(-1)), and Isopisthus parvipinnis (0.48 microg x g(-1)). Mercury levels were positively correlated with the length of the fish in populations of the freshwater piscivores S. rhombeus, Hoplias malabaricus, and Plagioscion squamosissimus, in estuarine species (Arius couma, Cynoscion virescens, and Macrodon ancylodon), and in S. guachancho from the Atlantic Ocean.

Determination of mercury in biological fluids by potentiometric stripping analysis.

A method is described for the determination of mercury by potentiometric stripping analysis. The analyte, Hg(2+), is employed for oxidizing a fixed amount of cadmium, previously reduced and amalgamated at a thin mercury film preplated on a glassy carbon electrode. The cadmium stripping signal correlates well with the amount of Hg(2+) added. Correlation coefficients of 0.9971 and 0.9960 were obtained for the two working ranges: (25 ng-2.5 microg) and (5.0-50) microg Hg(2+), respectively, in spiked water samples. The method was investigated with respect to precision and accuracy by spiking a natural water sample with 25 microg Hg(2+).Nine replicate determinations gave a mean value of 24.8 microg with a standard deviation +/-0.31 microg. The 95% confidence limit of the mean suggested the absence of systematic errors. Using the highest possible sensitivity, detection limits of 2.0 ng (167 ng/l) and 0.5 ng (4.2 ng/100 ml of whole blood) were obtained in water and blood samples, respectively. The applicability of the method was successfully extended to include the more complex matrices after recording a zero blank from authentic samples spiked with Cd(2+) (25 microg).The described PSA procedure is a simple and rapid method compared with the cold-vapor technique, with a 5.2% and 4.9% RSD, respectively.

Effects of mercury exposure on ionic regulation in the crayfish Orconectes propinquus.

Hemolymph sodium, potassium and calcium concentrations were determined in crayfish (Orconectes propinquus) exposed to (203)HgCl(2) mixed with food to a concentration of 1 microg Hg g(-1). Dummy-fed animals were exposed to Hg-dosed food wrapped in dialysis tubing to control for mercury reaching the animals via leaching from food to water. Hemolymph analyses were made following 14-day Hg exposures and again after a further 21-day 'depuration' period during which all animals were fed Hg-free food. After 14 days, the mercury reached a concentration of 0.175 microg g(-1) in the hepatopancreas and approximately half this level in the gills of Hg-fed animals. No depuration occurred from the hepatopancreas although the gills lost approximately two-thirds of their labelled mercury during the depuration period. Hemolymph sodium concentrations in Hg-exposed crayfish, both fed and dummy-fed, after 14 days were significantly lower than in Hg-free controls and remained low following the 21-day depuration period. Hemolymph calcium concentrations were lower in Hg-fed animals than in dummy-fed and control animals after 14 days although calcium levels rose in all treatments after 35 days. This may have been due to the incidence of pre-molt animals in all experimental groups, although the relationship between this and mercury exposure was not established unequivocally. Hemolymph potassium levels showed no differences between treatments.