The accumulation of organic mercury from sea water by the plaice, Pleuronectes platessa L

The accumulation of organic mercury from sea water by plaice eggs, larvae and adult fish has been studied using CH₃²⁰³HgCl as a tracer. The isotope was rapidly accumulated, the largest fraction being taken up by muscle tissue. High concentration factors were attained by many internal organs, particularly blood, spleen, and kidney. Longer biological half-times than previous estimates with ²⁰³HgCl₂ were obtained: the possible consequences of inorganic mercury accumulated from sea water being excreted at the rate for methylmercury have been calculated.     

The accumulation of mercury by the thornback ray, Raja clavata L.

The accumulation of inorganic and organic mercury by the thornback ray has been studied using ²⁰³HgCl₂ and CH₃²⁰³HgCl. Observations have been made on the rates of intake and loss of ²⁰³Hg, from both labelled food and sea water, and the internal distributions of the isotope compared with that of total mercury. Both forms were readily absorbed from sea water. Retention of the two forms from food was, however, dissimilar in that, in contrast to inorganic mercury, methylmercury was readily absorbed and only slowly eliminated. The results are compared with data on the accumulation of mercury by the plaice.     

Methods for Measuring Specific Rates of Mercury Methylation and Degradation and Their Use in Determining Factors Controlling Net Rates of Mercury Methylation

A method was developed to estimate specific rates of demethylation of methyl mercury in aquatic samples by measuring the volatile ¹⁴C end products of ¹⁴CH₃HgI demethylation. This method was used in conjunction with a ²⁰³Hg²⁺ radiochemical method which determines specific rates of mercury methylation. Together, these methods enabled us to examine some factors controlling the net rate of mercury methylation. The methodologies were field tested, using lake sediment samples from a recently flooded reservoir in the Southern Indian Lake system which had developed a mercury contamination problem in fish. Ratios of the specific rates of methylation/demethylation were calculated. The highest ratios of methylation/demethylation were calculated. The highest ratios of methylation/demethylation occurred in the flooded shorelines of Southern Indian Lake. These results provide an explanation for the observed increases in the methyl mercury concentrations in fish after flooding.     

Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with 203Hg‐radiolabeled compounds

Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with ²⁰³Hg‐labeled HgCl₂ and CH₃HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl ²⁰³Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of ²⁰³Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.     

Some further studies on the accumulation and retention of 65Zn and 54Mn by the plaice, pleuronectes platessa L.

Some further studies on the accumulation and retention of ⁶⁴Zn and ⁵⁴Mn by plaice, Pleuronectes platessa L., have been made. Direct accumulation from water, by eggs and larvae, is insufficient to account for the concentrations of these metals in young fish. It appears, therefore, that, from the earliest stages, food constitutes the major pathway for accumulation. Stable element analyses of liver, muscle, and bone samples from fish of differing weights and ages show that their concentrations, in adult fish, remain fairly constant. On this basis it has previously been estimated that biological half-times of these metals via food should be shorter than those observed after accumulation from labelled water. Experiments following the loss of the isotopes from fish which had been fed labelled polychaete worms support this view.     

Mode of in vitro interaction of mercuric mercury with selenite to form high-molecular weight substance in rabbit blood

Mode of interaction of mercuric mercury and selenite in rabbit blood was investigated in vitro. After the incubation of rabbit blood with 10^?5 M each of ²⁰³HgCl₂ and Na₂⁷⁵SeO₃, the amounts of both ²⁰³Hg and ⁷⁵Se incorporated into erythrocytes were markedly larger than the case where the blood was treated separately with one of these compounds. Most of ²⁰³Hg and ⁷⁵Se distributed into plasma and erythrocytes were found in high-molecular weight substance(s) (HMWS) fractionated by gel filtration at a molar ratio of 1:1. The ²⁰³Hg and ⁷⁵Se in HMWS found in plasma and erythrocytes were hardly diffusable through the erythrocytes membrane. The formation of the HMWS containing mercury and selenium was observed in stroma-free hemolysate incubated with mercuric chloride and selenite, but not in plasma. Addition of reduced glutathione (GSH) to the plasma, however, gave the HMWS as reaction products containing equimolar amounts of mercury and selenium. Further the binding properties of selenium to proteins were studied in the plasma incubated with selenodiglutathione (GSSeSG) or with selenite in the presence of GSH. The results indicated that GSH, a cellular component, is essential for the formation of an active selenium compound from selenite and that the interaction of mercuric mercury and selenite in plasma in the presence of GSH may occur through the other mechanism than the formation of GSSeSG.     

An in situ study of rock bass (Ambloplites rupestris) physiology: effect of season and mercury contamination

Selected physiological and biochemical variables were examined in rock bass, Ambloplites rupestris, which were collected on five different sampling dates from an area of chronic mercury contamination and a reference site on the South River, Virginia.The onset of spawning represented the most significant seasonal influence in the physiological profile of the fish, with elevations in hematocrit, hemoglobin, plasma protein, and plasma glucose. Sex-related differences in plasma calcium, liver glycogen and liver ascorbic acid were also unique to the period. Female rock bass had significantly higher levels of liver glutathione than did males on all but one of the sampling dates, although the cause of this difference is not clear.Rock bass from the mercury contaminated site had an average muscle mercury concentration of 1.37 mg Hg g^–1, and an average liver mercury concentration of 2.86 mg Hg g^–1. These levels were approximately an order of magnitude greater than those found in the tissues of the reference fish which averaged 0.165 and 0.101 mg Hg g^–1 in muscle and liver respectively. In July 1987, mercury concentrations in the liver of both reference and contaminated fish increased significantly, possibly the result of greater uptake of the metal through increased feeding or changes in the mercury level of selected prey items. Rock bass collected from the two sites in July also had significantly different levels of liver glutathione: reference fish exhibited an elevation and contaminated fish a depression. When fish from the two sampling stations received a 96-hr exposure to 150 µg HgCl₂ in the laboratory, both groups exhibited elevated liver mercury and decreased liver glutathione. Mercury levels in the gall bladders of the exposed fish were also elevated, suggesting that glutathione may have been lost through excretion with the metal in the bile.On the whole, physiological differences between the two groups of rock bass were limited, indicating that exposure to the mercury is not having a significant impact on the rock bass from the contaminated area. This is further supported by field examination of the fish and comparison of condition indices from rock bass previously taken from the same two stations.Those factors which significantly altered the physiology of the rock bass were unique to certain times of the year, indicating that the most appropriate sampling approach in future studies is one which examines a number of variables over a range of environmental conditions.     

Comparative Study of Uptake and Cellular Distribution of Hg203-Labeled Phenyl-Mercuric Acetate and Mercuric Acetate by Pea Roots

Uptake and cellular distribution of mercury²⁰³ from dilute mercuric acetate or phenylmercuric acetate solutions by excised pea roots (Pisum sativum) have been investigated. The time course of uptake showed that the amount of mercury uptake was increased with the time of incubation, and was similar for inorganic mercury or phenylmercuric acetate. The trend of mercury²⁰³ incorporation into cellular components from mercuric acetate and phenylmercuric acetate differed greatly as the time of incubation increased. The concentrations of mercuric acetate and phenylmercuric acetate solutions or the temperature of incubation also affected the mercury²⁰³ uptake as well as its cellular distribution. Longer time of exposure or higher concentration resulted in a greater mercury incorporation into mitochondrial fraction from phenylmercuric acetate than from inorganic mercury. This difference in intracellular distribution may be responsible for the degree of toxicity between inorganic mercury and phenylmercuric acetate in biological systems.     

Mercury in the marine food chain in the Southern Ocean at Macquarie Island: an analysis of a top predator,Patagonian toothfish (<Emphasis Type="Italic">Dissostichus eleginoides</Emphasis>) and a mid-trophic species,the warty squid (<Emphasis Type="Italic">Moroteuthis ingens</Emphasis>)

The characteristics and habitat of the Patagonian toothfish (Dissostichus eleginoides) are typical of fish that accumulate high concentrations of mercury. In this study, mercury determinations were made on samples of muscle tissue from Macquarie Island toothfish and the Southern Ocean deepwater warty squid (Moroteuthis ingens). The analysis of mercury in the biological tissues was made by cold vapour-atomic absorption spectrometry following acid digestion. Performance of the analytical procedure was assessed by analysis of certified reference material (DORM-2, dogfish muscle). Mercury concentrations of 16 Macquarie Island toothfish ranged from 0.12 mg kg^–1 (550 g, 381 mm TL) to 0.59 mg kg^–1 (6,100 g, 823 mm TL), with a mean concentration of 0.33±0.12 mg kg^–1. A significant correlation was found between mercury and either toothfish weight or total length. The fish analysed were juveniles, which suggests that larger individuals would have higher mercury concentrations well exceeding food standard code limits for mercury in fish (typically 0.5 mg kg^–1). Warty squid, also from around Macquarie Island, had a low mean mercury concentration of 0.086 mg kg^–1 in mantle tissue; no significant correlation existed between mercury concentration and either squid mantle length or total weight. It is postulated that the squid have a mechanism, possibly involving the digestive gland, that prevents bioaccumulation of mercury in the mantle, and presumably other body tissues.     

Bioaccumulation of Trace Mercury in Trophic Levels of Benthic, Benthopelagic, Pelagic Fish Species, and Sea Birds from Arvand River, Iran

In this study, concentration of mercury was determined in the trophic levels of benthic, benthopelagic, pelagic fish species, and river birds from Arvand River, located in the Khuzestan province in the lowlands of southwestern Iran at the head of the Persian Gulf. The order of mercury concentrations in tissues of the fish species was as follows: liver>gill>muscle and in tissues of the kingfisher species was as follows: feather>liver>kidney>muscle. Therefore, liver in fish and feather in kingfisher exhibited higher mercury concentration than the other tissues. There was a positive correlation between mercury concentrations in fish and kingfisher species with size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. The results of this study show that the highest mean mercury level were found in the kingfisher (Anas crecca), followed by benthic (Epinephelus diacanthus), benthopelagic (Chanos chanos), and pelagic fish (Strongylura strongylura). Mean value of mercury in fish species, S. strongylura were (0.61 μg g^?1 dry weight), C. chanos (0.45 μg g^?1 dry weight), E. diacanthus (0.87 μg g^?1 dry weight), and in kingfisher species A. crecca was (2.64 μg g^?1 dry weight). Significant correlation between mercury concentration in fish and kingfisher may be related to high variability of mercury in the fish.     

Laboratory Study of Chemical Speciation of Mercury in Lake Sediment and Water under Aerobic and Anaerobic Conditions

Chemical speciation and partitioning of radiolabeled HgCl₂ were studied in model aquatic systems consisting of undisturbed eutrophic lake sediment and water in plastic cylinders. The cylinders were either gradually made anaerobic by a gentle flow of N₂-CO₂ or kept aerobic by air flow. The proportion of methylated ²⁰³Hg was significantly higher, in both water and sediment, in the anaerobic systems than in the aerobic systems. The composition and total concentration of fatty acids originating from bacterial phospholipids, as well as the concentration of vitamin B₁₂, including related cobalamins, were similar in sediments from the anaerobic and aerobic systems. Bacterial cell numbers were, on average, 3.6 times higher in the anaerobic water columns than in the aerobic ones. Volatilization of ²⁰³Hg occurred in all systems except in an autoclaved control and was of similar magnitudes in the anaerobic and aerobic systems. Incorporation of ²⁰³Hg into the sediment was significantly faster in the aerobic systems than in the anaerobic systems. These results suggest that episodes of anoxia in bottom waters and sediment cause an increase in net mercury methylation and, hence, an increase in bioavailable mercury.     

The reaction of mercuric acetate with histidine and tyrosine

The reaction of mercuric acetate with polypeptides in an appropriate buffer system has been found to result in the selective binding of two atoms of mercury to each tyrosine and histidine residue. These heavy atom labels are stable to the high chloride concentrations used to displace the excess mercury (II) from other binding sites on the polypeptide. The kinetics and stoichiometry of these reactions have been studied by the binding of radioactive (²⁰³Hg) mercuric acetate to synthetic polymers of these amino acids and by ultraviolet-visible spectroscopy. For a polymer containing tyrosine the mercuration kinetics closely match those for the following mechanism:

At 60°C, and in a buffer containing 0.05M TRIS-acetate, k₁ was determined to be 9.47 ± 0.27 M^?1 min^?1. The best match to the data was for k₁/k₁ = 5.5 It was discovered that there is an inverse relationship between k₁ and the TRIS buffer concentration. The activation energy of k₁ was determined to be 18.9 ± 0.1 kcal/mole.Chemical analyses of the products obtained from the reaction of mercuric acetate with tyrosine amide, L(-)-histidine and the methyl ester of L(-)-histidine have established that mercuration results in the formation of a Hg-C bond at the C₃ and C₅ sites on the phenolic ring in tyrosine and at the C₄ site in the imidazole ring in histidine. The site of the second mercury retained by histidine in the presence of high chloride concentrations is uncertain but does involve the amine functions of the imidazole ring.The reaction conditions employed also cause the oxidation of methionine and cysteine to methionine sulfoxide and cysteic acid, respectively. Cystine, however, resists oxidation.     

Mercury removal by immobilized algae in batch culture systems

The accumulation and volatilization of mercury by non-immobilized and immobilizedChlorella emersonii have been studied in batch culture systems. Reduction in the mercury concentration in the growth medium by non-immobilized cells was highly dependent on inoculum density, whilst reduction in mercury concentration by immobilized cells was rapid at all inoculum densities. Mercury accumulation by immobilized cell biomass was significantly greater than by non-immobilized cells with 10⁶ and 10⁵ cells bead^–1 or ml^–1. Volatilization of mercury by non-immobilized cell systems was greatest at higher inoculum densities, whereas more mercury was volatilized from immobilized cell systems at lower inoculum densities, and was greatest with unstocked alginate beads. Thus, in immobilized systems, mercury removal from solution is complex and involves mercury accumulation by the cells and volatilization by the matrix and cells. Further studies of mercury accumulation and volatilization by unstocked immobilization matrices revealed that agarose volatilized much less mercury than alginate or agar. The precise mechanism of mercury volatilization by alginate remains unclear, though it is thought to be a chemical effect.     

The accumulation from sea water of 65Zn, 54Mn, 58Co and 59Fe by the thornback ray, Raja clavata L.

The accumulation of ⁶⁵Zn and ⁵⁴Mn from water by the thornback ray, Raja clavata L., has been studied at tissue level and their levels of accumulation have been related to stable element concentrations. The accumulation of ⁵⁸Co and ⁵⁹Fe has also been studied on a whole body basis and comparisons have been made of the ⁵⁹Fe levels in the tissues after 84 days with those of the stable element. It was found that lower values of accumulation of the radionuclides were obtained than in the case of the teleost Pleuronectes platessa L.. Such differences are discussed in relation to the relative permeabilities of the two species to sea water and the relative ratios of the radionuclides from sea water to blood plasma, and of blood plasma to organ. It is concluded that for both species direct input from water plays only a minor rôle in the accumulation of the four radionuclides studied.     

Mercury in Scalp Hair Near the Mid-Atlantic Ridge (MAR) in Relation to High Fish Consumption

The aim of this study was to evaluate the potential risk of mercury contamination near the Mid-Atlantic Ridge relating total mercury (THg) concentrations in the human scalp hair (n?=?110) and high fish consumption levels. THg was quantified in human scalp hair, and volunteers were questioned about age, gender, and smoking habits being subsequently grouped in categories based on the individual average intake of fish meals per week. THg concentrations ([THg]) in hair samples ranged from 0.05 to 2.24 μg g^?1, and significant differences were found according to age (p?<?0.05) and also among volunteers presenting different fish consumption rates (p?<?0.001) being the highest [THg] observed on the adult population and also on volunteers that indicated consuming five or more meals of fish per week. Results indicate a pattern of increased mercury accumulation with increasing fish consumption. Despite mercury availability and a potential mercury intake of up to seven times, the WHO provisional tolerable weekly intake of mercury value, in consequence of high fish consumption, mercury concentrations in scalp hair are comparatively low regarding recommended levels by WHO.     

The accumulation and retention of 59Fe and 58Co by the plaice, Pleuronectes platessa L.

The accumulation of ⁵⁹Fe and ⁵⁸Co from water by plaice (Pleuronectes platessa L.) has been studied in tissues, and their levels of accumulation related to stable element concentrations. The retention of both radionuclides from labelled Nereis and labelled pellets has also been examined, and the loss of activity from intraperitoneal injections followed over a three-month-period. Biological half-times of the exchange with water have been calculated for many organs, although the rate of accumulation for some tissues could only be expressed as a linear function; however, for both radionuclides the direct accumulation from water resulted in concentration factors of less than 1 % of the values inferred from the stable element data. The relevance of such observations to heavy metal pollution at the higher trophic levels is discussed.     

Muscle FBPase is targeted to nucleus by its 203KKKGK207 sequence

It has been recently found that muscle fructose 1,6‐bisphosphatase (FBPase) is actively transported into cells' nuclei. Results of an analysis in silico of muscle FBPase structure gave rise to a hypothesis that sequence ₂₀₃KKKGK₂₀₇ is responsible for nuclear targeting of the enzyme. To test this, HL‐1 cardiomyocytes were transfected with FITC‐labeled muscle FBPase constructs, bearing mutations within the putative nuclear localization signal (NLS). Results revealed that integrity of the ₂₀₃KKKGK₂₀₇ motif is critical to nuclear targeting of muscle FBPase and even a single amino‐acid change within this sequence results in significant decrease of nuclear accumulation of the enzyme. Although it has long been recognized as a canonical NLS in theoretical and computational research, to the best of our knowledge this is the first experimental evidence confirming that the KKKGK motif can act as a functional NLS in a protein. Proteins 2009. © 2009 Wiley‐Liss, Inc.     

The cycling of cadmium and mercury between substrate and fruiting bodies of Agrocybe aegerita (a fungal model system)

Summary The cycling of cadmium and mercury between substrate and fruiting bodies in a model system with wood colonizing basidiomycete Agrocybe aegerita was studied. When radiolabeled ¹⁰⁹CdCl₂ and ²⁰³HgCl₂ were applied to the fruiting bodies of the first flush, they were translocated via substrate into successive harvests. Cadmium and mercury displayed different patterns of distribution in the system. On a percent basis, more cadmium went from the fruiting bodies into the substrate and was retained there. Only minor portions of the metal were translocated into consecutive crops. In contrast, more mercury was retained in the treated fruiting bodies. The fraction which had penetrated into the substrate, however, was more easily translocated into fruiting bodies of successive crops. When calculated on a dry weight basis, the amount of both metals decreased in consecutive harvests.At the end of the experiment, in following distribution patterns for cadmium and mercury were observed: Cd²⁺: first crop (treated), 9.5%; substrate, 77%; combined successive crops (untreated), 9.5%; Hg²⁺: first crop (treated), 36.5%; substrate 21.5%; combined successive crops (untreated), 37%. The patterns reveal that mercury is more mobile in the substrate and therefore more easily translocated to successive fruiting body generations. Hence, from a nutritional point of view, mercury would seem to be more hazardous than cadmium.     

The stable carbon isotope ratios of fish and their invertebrate prey in four New Zealand rivers

SUMMARY.

• 1 Sources of carbon utilized by invertebrates and fish in four New Zealand streams were investigated using stable carbon isotope analysis. Complementary analyses were made to determine σ¹³C alteration (fractionation) by fish reared on a known food and to examine the distribution of ¹³C/¹²C ratios in different tissues.
• 2 σ¹³C values of hatchery-reared rainbow trout (white muscle tissue) were ¹³C-enriched compared with their food (trout pellets) by an average of 1.7%₀. σ¹³C values of different organs and tissues never differed by more than 1.8%_o in any fish species; white muscle always had an intermediate value.
• 3 σ¹³C values of invertebrates ranged from-28.4 to –20.4%_o– At the more open sites invertebrates were ¹³C-depleted, reflecting some use of algal carbon. However, invertebrates from the most heavily shaded stream site were unusually enriched in ¹³C. An undetected carbon source of terrestrial origin, perhaps ¹³C-enriched dissolved organic carbon in groundwater, may have been contributing indirectly to invertebrate biomass carbon.
• 4 σ¹³C values for fish were not closely linked to aquatic invertebrate ratios; instead, at all sites their carbon was isotopically similar to terrestrial organic carbon. The reasons for this apparent anomaly are unclear.

     

Otolith chemistry of prey fish consumed by a fish predator: does digestion hinder Russian doll techniques?

The effect of digestion by a predatory fish (largemouth bass Micropterus salmoides) on stable isotopic (δ¹³C and δ¹⁸O) and trace elemental (Sr:Ca and Ba:Ca) compositions of prey fish (bluegill Lepomis macrochirus) otoliths was investigated in a laboratory experiment. Trace element and stable‐isotopic signatures of L. macrochirus otoliths were not significantly altered for up to 16 h after L. macrochirus were consumed by M. salmoides. Prey fish otoliths recovered from predator digesta can retain environmental stable isotopic and trace elemental signatures, suggesting that determination of environmental history for prey fishes by stable‐isotope and trace‐element analysis of otoliths recovered from stomachs of piscivorous fishes will be feasible.