High-resolution identification of mercury in particles in mouse kidney after acute lethal exposure – A study by Scanning Electron Microscopy coupled with X-ray Elemental Microanalysis

Contamination of the food chain by mercury is a major concern of Public Health of our day. Kidney and nervous system are the major targets of mercury toxicity in mammals. We show here that the detailed subcellular in vivo topography of microparticles of mercury in tissues can be achieved by scanning electron microscopy (SEM) coupled with X-ray elemental microanalysis (XRM). SEM-XRM offered the fine topography of mercury in the kidney of BALB/c mice that were submitted to an intraperitoneal lethal injection of mercuric chloride (HgCl₂). All of the renal mercury was seen inside blood vessels located in both cortex and medulla of the mouse kidney. This blood-born mercury was organised in spheroid particles of less than 50 nm in diameter (31.4±14.1 nm). They were seen attached either to aggregates of plasma proteins or to the surface of blood cells. No evidence of internalisation of mercury by blood, endothelial or kidney cells was found. The average kidney density of mercury microspheres was 1920±1320 particles per mmsup b2b sup. We propose SEM-XRM as an elective approach to further investigations, at the subcellular level, on the quantitative dynamics of mercury particles in the tissues.     

Chemical and physical effects on the shape and growth of the diatomBiddulphia sinensis Greville in batch cultures: A contribution to bioindication in plankton ecology

Summary Different influences, like changes in salinity and temperature, the effects of heavy metals like copper and mercury, and the influences of nitrate and silicate deficiencies on the shape, generation time, and yield of the marine plankton diatomBiddulphia sinensis were tested in batch cultures. Those cells which show multiple or missing setae are classified as seta-aberrant, teratological forms. Sudden changes in salinity and temperature (30–15%. S; 12–20°C) lead to no more than 5% of aberrant cells (control cultures below 1%). Heavy metals (copper and mercury) cause a significant increase of the generation time, a distinct decrease of the cell yield, and (in the case of copper) up to 50% of seta-aberrant cells. The cells die at concentrations of copper above 10^–5M.l^–1, though EDTA was added as chelant. At concentrations below 10^–5M.l^–1 of copper, addition of EDTA as well as an increase of temperature from 12 to 20°C cause a reduction of toxicity. During batch growth the cells adapt to mercury but not to copper. At mercury concentrations above 10^–8M.l^–1 the cells die, even if EDTA is added. Unlike in copper-treated medium, EDTA does not reduce the toxicity of mercury. However, a detoxicating effect (20 instead of 12°C) can be observed due to higher temperature. Silicate deficiency, like the influence of copper and mercury leads to an elongation of the pervalvar axes. Particularly at a temperature of 20°C bended pervalvar axes and sometimes lateral evaginations of the frustule will be formed; this does not happen under the influence of copper and mercury. Multiple setae never appear under silicate deficiency. Under nitrate deficiency more than 10% of the cells are seta-aberrant. The suitability ofBiddulphia sinensis for test experiments in shipboard cultures is shown. Water samples were tested on the lack of nitrate, silicate, and phosphate. The percentage of seta-aberrant cells, the generation times, and the yields were determined. Simultaneous lack of phosphate and nitrate causes up to 30% of teratological cells. The seta-aberrant cells always appear during the exponential growth phase.     

Engineering expression of bacterial polyphosphate kinase in tobacco for mercury remediation

To develop the potential of plants to sequester and accumulate mercurials from the contaminated sites, we engineered a tobacco (Nicotiana tabacum) plant to express a bacterial ppk gene, encoding polyphosphate kinase (PPK), under control of a plant promoter. The designated plant expression plasmid pPKT116 that contains the entire coding region of ppk was used for Agrobacterium-mediated gene transfer into tobacco plants. A large number of independent transgenic tobacco plants were obtained, in some of which the ppk gene was stably integrated in the plant genome and substantially translated to the expected PPK protein in the transgenic tobacco. The presence of Hg²⁺ did not cause considerable morphological abnormalities in the transgenic tobacco, which grew, flowered, and set seed similarly to the wild-type tobacco on the medium containing normally toxic levels of Hg²⁺. The ppk-transgenic tobacco showed more resistance to Hg²⁺ and accumulated more mercury than its wild-type progenitors. These results suggest that ppk-specified polyphosphate has abilities to reduce mercury toxicity, probably via chelation mechanism, and also to accumulate mercury in the transgenic tobacco. Based on the results obtained in the present study, the expression of ppk gene in transgenic tobacco plants might provide a means for phytoremediation of mercury pollution.     

Biosorption of inorganic and methyl mercury by a biosorbent from Aspergillus niger

A biosorbent prepared by alkaline extraction of Aspergillus niger biomass was evaluated for its potential to remove mercury species – inorganic (Hg²⁺) and methyl mercury (CH₃Hg⁺) – from aqueous solutions. Batch experiments were carried out to determine the pH and time profile of sorption for both species in the pH range 2–7. The Hg²⁺ exhibited more rapid sorption and higher capacity than the CH₃Hg⁺. Further, removal of both mercury species from spiked ground water samples was efficient and not influenced by other ions. Sorption studies with esterified biosorbent indicated loss of binding of both mercury species (>80%), which was regained when the ester groups were removed by alkaline hydrolysis, suggesting the involvement of carboxyl groups in binding. Further, no interconversion of sorbed species occurred on the biomass. The biosorbent was reusable up to six cycles without serious loss of binding capacity. Our results suggest that the biosorbent from Aspergillus niger can be used for removal of mercury and methyl mercury ions from polluted aqueous effluents.     

Phytoextraction and Accumulation of Mercury in Three Plant Species: Indian Mustard (Brassica Juncea), Beard Grass (Polypogon monospeliensis), and Chinese Brake Fern (Pteris vittata)

The objective of this research was to screen and search for suitable plant species to phytoextract mercury-contaminated soil. Our effort focused on using some of the known metal-accumulating wild-type plants since no natural plant species with mercury-hyperaccumulat ing properties has yet been identified. Three plant species were evaluated for their uptake efficiency for mercury: Indian mustard (Brassica juncea), beard grass (Polypogon monospeliensis), and Chinese brake fern (Pteris vittata). Four sets of experiments were conducted to evaluate the phytoremediation potential of these three plant species: a pot study with potting mix where mercury was provided daily as HgCl₂ solution; experiments with freshly mercury-spiked soil; and a study with aged soils contaminated with different mercury sources (HgCl₂, Hg(NO₃)₂, and HgS). Homemade sunlit chambers were also used to study foliar uptake of Hg from ambient air. Among the three plant species, Chinese brake fern showed the least stress symptoms resulting from mercury exposure and had the highest mercury accumulation. Our results indicate that Chinese brake fern may be a potential candidate for mercury phytoextraction. We found that mercury contamination is biologically available for plant uptake and accumulation, even if the original and predominating mercury form is HgS, and also after multiple phytoremediation cycles.     

Mercury toxicity in plants

Mercury poisoning has become a problem of current interest as a result of environmental pollution on a global scale. Natural emissions of mercury form two-thirds of the input; manmade releases form about one-third. Considerable amounts of mercury may be added to agricultural land with sludge, fertilizers, lime, and manures. The most important sources of contaminating agricultural soil have been the use of organic mercurials as a seed-coat dressing to prevent fungal diseases in seeds. In general, the effect of treatment on germination is favorable when recommended dosages are used. Injury to the seed increases in direct proportion to increasing rates of application. The availability of soil mercury to plants is low, and there is a tendency for mercury to accumulate in roots, indicating that the roots serve as a barrier to mercury uptake. Mercury concentration in aboveground parts of plants appears to depend largely on foliar uptake of Hg⁰ volatilized from the soil. Uptake of mercury has been found to be plant specific in bryophytes, lichens, wetland plants, woody plants, and crop plants. Factors affecting plant uptake include soil or sediment organic content, carbon exchange capacity, oxide and carbonate content, redox potential, formulation used, and total metal content. In general, mercury uptake in plants could be related to pollution level. With lower levels of mercury pollution, the amounts in crops are below the permissible levels. Aquatic plants have shown to be bioaccumulators of mercury. Mercury concentrations in the plants (stems and leaves) are always greater when the metal is introduced in organic form. In freshwater aquatic vascular plants, differences in uptake rate depend on the species of plant, seasonal growthrate changes, and the metal ion being absorbed. Some of the mercury emitted from the source into the atmosphere is absorbed by plant leaves and migrates to humus through fallen leaves. Mercury-vapor uptake by leaves of the C₃ speciesoats, barley, and wheat is five times greater than that by leaves of the C₄ species corn, sorghum, and crabgrass. Such differential uptake by C₃ and C₄ species is largely attributable to internal resistance to mercury-vapor binding. Airborne mercury thus seems to contribute significantly to the mercury content of crops and thereby to its intake by humans as food. Accumulation, toxicity response, and mercury distribution differ between plants exposed through shoots or through roots, even when internal mercury concentrations in the treated plants are similar. Throughfall and litterfall play a significant role in the cycling and deposition of mercury. The possible causal mechanisms of mercury toxicity are changes in the permeability of the cell membrane, reactions of sulphydryl (-SH) groups with cations, affinity for reacting with phosphate groups and active groups of ADP or ATP, and replacement of essential ions, mainly major cations. In general, inorganic forms are thought to be more available to plants than are organic ones. Plants can be exposed to mercurials either by direct administration as antifungal agents, mainly to crop plants through seed treatment or foliar spray, or by accident. The end points screened are seed germination, seedling growth, relative growth of roots and shoots, and, in some case, studies of leaf-area index, internode development, and other anatomical characters. Accidental exposures occur through soil, water, and air pollution. The level of toxicity is usually tested under laboratory conditions using a wide range of concentrations and different periods of exposure. Additional parameters include biochemical assays and genetical studies. The absorption of organic and inorganic mercury from soil by plants is low, and there is a barrier to mercury translocation from plant roots to tops. Thus, large increases in mercury levels in soil produce only modest increases in mercury levels in plants by direct uptake from soil. Injuries to cereal seeds caused by organic mercurials has been characterized by abnormal germination and hypertrophy of the roots and coleoptile. Mercury affects both light and dark reactions of photosynthesis. Substitution of the central atom of chlorophyll, magnesium, by mercury in vivo prevents photosynthetic light harvesting in the affected chlorophyll molecules, resulting in a breakdown of photosynthesis. The reaction varies with light intensity. A concentration and time-dependent protective effect of GSH seems to be mediated by the restricted uptake of the metal involving cytoplasmic protein synthesis. Plant cells contain aquaporins, proteins that facilitate the transport of water, in the vacuolar membrane (tonoplast) and the plasma membrane. Many aquaporins are mercury sensitive, and in AQP1 a mercury-sensitive cysteine residue (Cys-189) is present adjacent to a conserved Asn-Pro-Ala motif. At low concentrations mercury has a toxic effect on the degrading capabilities of microorganisms. Sensitivity to the metal can be enhanced by a reduction in pH, and tolerance of mercury by microorganisms has been found to be in the order: total population > nitrogen fixers > nitrifiers. Numerous experiments have been carried out to study the genetic effects of mercury compounds in experimental test systems using a variety of genetic endpoints. The most noticeable and consistent effect is the induction of c-mitosis through disturbance of the spindle activity, resulting in the formation of polyploid and aneuploid cells and c-tumors. Organomercurials have been reported to be 200 times more potent than inorganic mercury. Exposure to inorganic mercury reduces mitotic index in the root-tip cells and increases the frequency of chromosomal aberrations in degrees directly proportional to the concentrations used and to the duration of exposure. The period of recovery after removal of mercury is inversely related to the concentration and duration of exposure. Bacterial plasmids encode resistance systems for toxic metal ions, including Hg²⁺, functioning by energy-dependent efflux of toxic ions through ATPases and chemiosmotic cationproton antiporters. The inducible mercury resistance (mer) operon encodes both a mercuric ion uptake and detoxification enzymes. In gram-negative bacteria a periplasmic protein,MerP, an inner-membrane transport protein,MerT, and a cytoplasmic enzyme, mercuric reductase, theMerA protein, are responsible for the transport of mercuric ions into cells and their reduction to elemental mercury, Hg(II). InThiobacillus ferrooxidans, an acidophilic chemoautotrophic bacterium sensitive to mercury ions, a group of mercury-resistant strains, which volatilize mercury, has been isolated. The entire coding sequence of the mercury-ion resistance gene has been located in a 2.3 kb fragment of chromosomal DNA (encoding 56,000 and 16,000 molecular-weight proteins) from strain E-l 5 ofEscherichia coli. Higher plants andSchizosaccharomyces pombe respond to heavy-metal stress of mercury by synthesizing phytochelatins (PCs) that act as chelators. The strength of Hg(II) binding to glutathione and phytochelatins follows the order: γGlu-Cys-Gly(γGlu-Cys)₂Gly(γGlu-Cys)₃Gly(γGlu-Cys)₄Gly. Suspension cultures of haploid tobacco,Nicotiana tabacum, cells were subjected to ethyl methane sulfonate to raise mercury-tolerant plantlets. HgCl₂-tolerant variants were selected from nitrosoguanidine (NTG)-treated suspension cell cultures of cow pea,Vigna unguiculata, initiated from hypocotyl callus and incubated with 18 ⧎g/ml HgCl₂. Experiments have been carried out to develop mercury-tolerant plants ofHordeum vulgare through previous exposure to low doses of mercury and subsequent planting of the next generation in mercury-contaminated soil. Phytoremediation involves the use of plants to extract, detoxify, and/or sequester environmental pollutants from soil and water. Transgenic plants cleave mercury ions from methylmercury complexes, reduce mercury ions to the metallic form, take up metallic mercury through their roots, and evolve less toxic elemental mercury. Genetically engineered plants contain modified forms of bacterial genes that break down methyl mercury and reduce mercury ions. The first gene successfully inserted into plants wasmerA, which codes for a mercuric ion reductase enzyme, reducing ionic mercury to the less toxic elemental form.MerB codes for an organomercurial lyase protein that cleaves mercury ions from highly toxic methyl mercury compounds. Plants with themerB gene have been shown to detoxify methyl mercury in soil and water. Both genes have been successfully expressed inArabidopsis thaliana, Brassica (mustard),Nicotiana tabacum (tobacco), andLiriodendron tulipifera (tulip poplar). Plants currently being transformed include cattails, wild rice, andSpartina, another wetland plant. The problem of mercury contamination can be reduced appreciably by combining the standard methods of phytoremediation—removal of mercury from polluted areas through scavenger plants—with raising such plants both by routine mutagenesis and by genetic engineering. The different transgenics raised utilizing the two genesmerA andmerB are very hopeful prospects.     

Alteration in growth and peroxidase activity by heavy metals in Phaseolus seedlings

The aim of the present work was to see the effect of mercury and chromium on elongation growth of phaseolus seedlings and changes in chlorophyll content. Phaseolus seedlings were treated with two different concentrations of two heavy metals viz. mercury (0.05 mM and 0.4 mM HgCl₂, and chromium (0.5 mM and 1.0 mM K₂Cr₂O₇). Both mercury and chromium inhibited root and hypocotyl elongation growth. Changes in cytoplasmic and wall bound peroxidase activities were studied using guaiacol as a hydrogen donor. Peroxidase activity was higher in both mercury and chromium treated seedlings as compared to distilled water control; they showed a clear concentration effect. Peroxidase activity showed inverse relation with growth i.e. distilled water treated seedlings had maximum growth and minimum activity while higher concentration of heavy metal treated seedlings had minimum growth and maximum activity. Chlorophyll content was also decreased by mercury. The role of peroxidase activity in defense mechanism in response to heavy metal toxicity is discussed.     

Using Earthworms to Assess Hg Distribution and Bioavailability in Gold Mining Soils

Between 1980 and 2000, the municipality of Cachoeira do Piriá, located in Pará State, Brazil, experienced an intense gold rush with approximately 5,000 artisanal miners discharging more than four tonnes of mercury into soils, air and aquatic systems. Mercury is dispersed across an area of approximately 2,100 ha and concentrations in soils and sediments frequently exceed 1,000 μg.kg^?1. The metallic mercury discharged by miners into the environment has the potential to be transformed into a highly toxic form of mercury, methylmercury. A 28-day bioassay with the earthworm Eisenia fetida was used to assess mercury bioavailability in mine tailings, soils, and sediments. Experiments indicated that the highest Hg concentration in earthworms was associated with low-Hg-organic-rich soils collected from densely vegetated areas despite higher mercury concentrations in organic-poor tailings. This indicates that reaction with organic acids is an important pathway for mercury incorporation into food chains. The quick, inexpensive, and simple bioassay also provided a means to evaluate remedial measures (i.e. by capping “hotspots” with local soils). Earthworm experiments indicate that covering “environmental hotspots” (sites with high Hg bioavailability) with local clay-rich sediments is very effective in terms of preventing uptake of mercury from tailings, while organic-rich sediments are relatively ineffective.     

Progress report on a programme of insecticide analysis and toxicity-testing in relation to the marine environment

Summary 1. Toxicity experiments with 4 metals and phenol onPandalus montagui, Crangon crangon, Carcinus maenas andCardium edule are described and the results presented.2. Increase in temperature was found to cause a marked increase in the toxicity of some chemicals.3. The larger-size animals were shown to be less susceptible to mercury.4. Starvation of animals prior to experiments was demonstrated to reduce their tolerance to mercury.5. The toxicity of a number of detergents to the 4 test species is described.6. Results of pesticide analyses are given in terms of ranges and mean concentrations found in muscle tissue from 2 species of fish, the liver of one fish, and for whole shrimps and oysters.

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Fortschrittsbericht über ein Arbeitsprogramm der Insektizidanalyse und der Toxizitätsprüfung in bezug auf die marine Umwelt

Kurzfassung Seit 1965 läuft im Fischereilaboratorium von Burnham-on-Crouch ein Arbeitsprogramm zur Prüfung der Toxizität verschiedener chemischer Stoffe gegenüber Meerestieren. Die Konzentration chlorhaltiger Insektizide in Meeresfischen und Schalentieren wurde untersucht und die Toxizität von Metallen und von Phenol gegenüber drei Crustaceenarten und einer Molluskenart ermittelt. Ferner wurde der Einfluß der Temperatur, der Tiergröße und des Nahrungsangebotes auf die Toxizität geprüft. Eine Reihe von Detergentien wurde ebenfalls hinsichtlich toxischer Wirkungen untersucht. Die Konzentrationen von drei verschiedenen Insektiziden wurden in der Muskulatur und in der Leber des Kabeljaus(Gadus morhua) bestimmt.

     

Accumulation,regulation and toxicity of copper,zinc, lead and mercury in Hyalella azteca

Zinc, lead and mercury accumulation in the amphipod Hyalella azteca increases with increasing exposure to metals. During 10 week chronic toxicity tests, metal accumulated at the highest non-toxic/lowest toxic concentration was 126/136 µg Zn g^–1, 7.1/16 µg Pb g^–1 and 56/90 µg Hg g^–1 dry weight. Concentrations of lead and mercyry in control animals were substantially lower (1.3 µg Pb g^–1 and 0.4 µg Hg g^–1), but concentrations of zinc in controls (74 µg g^–1) were about one half those of the lowest toxic concentration. Copper was completely regulated. Accumulated copper concentrations after 10 weeks exposure to all waterborne copper concentrations resulting in less than 100% mortality were not significantly different from controls (79 µg g^–1). Lead and mercury concentrations in wild H. azteca should be useful indicators of potential toxicity. Zinc accumulation may also be a useful indicator of zinc toxicity, but careful comparison with control or reference animals is necessary because of the small differences between toxic and control concentrations. Copper is not accumulated by H. azteca under chronic exposure conditions and body burdens of field animals cannot be used as an indicator of exposure or potential toxic effects. Short term exposures to copper, however, result in elevated copper concentrations in H. azteca, even at concentrations below those causing chronic toxicity. Short term bioaccumulation studies might, therefore, provide a useful indication of potential chronic copper toxicity.     

Ecological strategy for soil contaminated with mercury

Aims

The paper presents results from plot experiments aimed at the development of an ecological strategy for soil contaminated with mercury. Meadow grass (Poa pratensis) was tested on mercury contaminated soil in a former chlor-alkali plant (CAP) in southern Poland for its phytoremediation potential.

Methods

The stabilisation potential of the plants was investigated on plots without additives and after the addition of granular sulphur. Biomass production, uptake and distribution of mercury by plants, as well as leachates and rhizosphere microorganisms were investigated, along with the growth and vitality of plants during one growing season.

Results

The analysed plants grew easily on mercury contaminated soil, accumulating lower amounts of mercury, especially in the roots, from soil with additive of granular sulphur (0.5 % w/w) and sustained a rich microbial population in the rhizosphere. After amendment application the reduction of Hg evaporation was observed.

Conclusions

The obtained results demonstrate the potential of using Poa pratensis and sulphur for remediation of mercury contaminated soil and reduction of the Hg evaporation from soil. In the presented study, methods of Hg reduction on “hot spots” were proposed, with a special focus on environmental protection. This approach provides a simple remediation tool for large areas heavily contaminated with mercury.

     

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.     

Tn1 generated mutants in the mercuric ion reductase of the Inc P plasmid, R702

Summary Physiological, biochemical and genetic aspects of resistance to inorganic mercury compounds were examined in a group of mercury sensitive derivatives generated in the Inc P plasmid, R702, by Tn1 insertion. Strains carrying each of these insertion mutations had no detectable mercuric ion reductase, were more sensitive to mercuric ion than a plasmidless strain, and exhibited inducible uptake of Hg²⁺. These characteristics indicate that the mutants are altered in the Hg(II) reductase. This hypothesis was supported by complementation and recombination analysis with known point and deletion mutations in the mer operon of the Inc FII plasmid, R100. Such experiments showed that the eight insertions studied had occurred in four distinct regions of the Hg(II) reductase structural gene (merA). Complementation data also demonstrated that the regulatory protein determined by the R702 plasmid has no effect on the expression of the micro-constitutive Hg(II) reductase activity expressed by merR mutants of R100.     

Volatilization of mercury byThiobacillus ferrooxidans

Thiobacillus ferrooxidans became significantly more tolerant to mercury stress after culturing in media of increasing mercury(II) concentrations. When mercuric chloride was added to the growth medium, the resistant organisms were found to volatilize elemental mercury (Hg⁰).T. ferrooxidans may be an important factor in the natural mercury cycle, since the environments whereT. ferrooxidans is found typically contain elevated levels of heavy metals, including mercury.     

Development of a transgenic tobacco plant for phytoremediation of methylmercury pollution

To develop the potential of plant for phytoremediation of methylmercury pollution, a genetically engineered tobacco plant that coexpresses organomercurial lyase (MerB) with the ppk-specified polyphosphate (polyP) and merT-encoding mercury transporter was constructed by integrating a bacterial merB gene into ppk/merT-transgenic tobacco. A large number of independent transgenic tobaccos was obtained, in some of which the merB gene was stably integrated in the plant genome and substantially translated to the expected MerB enzyme in the transgenic tobacco. The ppk/merT/merB-transgenic tobacco callus showed more resistance to methylmercury (CH₃Hg⁺) and accumulated more mercury from CH₃Hg⁺-containing medium than the ppk/merT-transgenic and wild-type progenitors. These results suggest that the MerB enzyme encoded by merB degraded the incorporated CH₃Hg⁺ to Hg²⁺, which then accumulated as a less toxic Hg-polyP complex in the tobacco cells. Phytoremediation of CH₃Hg⁺ and Hg²⁺ in the environment with this engineered ppk/merT/merB-transgenic plant, which prevents the release mercury vapor (Hg⁰) into the atmosphere in addition to generating potentially recyclable mercury-rich plant residues, is believed to be more acceptable to the public than other competing technologies, including phytovolatilization.     

Mercury resistance and volatilization by oil utilizing haloarchaea under hypersaline conditions

The hydrocarbon utilizing haloarchaea, Haloferax (two strains), Halobacterium and Halococcus from a hypersaline coastal area of the Arabian Gulf, had the potential for resistance and volatilization of Hg²⁺. Individual haloarchaea resisted up to between 100 and 200 ppm HgCl₂ in hydrocarbon free media with salinities between 1 and 4 M NaCl, but only up to between 20 and 30 ppm in a mineral medium containing 3 M NaCl, with 0.5% (w/v) crude oil, as a sole source of carbon and energy. Halococcus and Halobacterium volatilized more mercury than Haloferax. The individual haloarchaea consumed more crude oil in the presence of 3 M NaCl than in the presence of 2 M NaCl. At both salinities, increasing the HgCl₂ concentration in the medium from 0 to 20 ppm resulted in decreasing the oil consumption values by the individual haloarchaea. However, satisfactory oil consumption still occurred in the presence of 10 ppm HgCl₂. It was concluded that haloarchaea with the combined potential for mercury resistance and volatilization and hydrocarbon consumption could be useful in removing toxic mercury forms effectively from oil free, mercury contaminated, hypersaline environments, and mercury and oil, albeit less effectively, from oily hypersaline environments.     

Toxicological response of the green alga<Emphasis Type="Italic">Scenedesmus bijuga</Emphasis> to mercury and lead

Effect of mercury or lead on the growth, bioaccumulation and some enzyme activities of one of the most common algae in River Nile,Scenedesmus bijuga, was determined. The cell count and chlorophylla content decreased with an increase in mercury or lead concentrations in a culture medium, particularly at higher doses. Higher mercury and lead uptake was observed with increasing concentration of the elements. The alga accumulated appreciably more mercury than lead. At higher doses, the two elements strongly suppressed some enzyme activities of primaryS. bijuga metabolism.     

Temperature and species differences in susceptibility of kidney cell cultures to mercury toxicity

The effect of temperature on inorganic mercury toxicity was investigated using kidney tissue culture systems. The relative susceptibility of rabbit (homeothermic) kidney to mercury intoxication was compared to that of Coho salmon (poikilothermic) kidney to mercury intoxication was compared to that of Coho salmon (poikilothermic) kidney over temperature ranges consistent with the habitat of each of the two species. It was demonstrated that susceptibility to mercury toxicity is species dependent; that is, the rabbit kidney cells tolerated higher mercury concentrations in the medium than did the fish-derived cells. Within a given species, susceptibility to mercury toxicity was temperature dependent. Decreasing the temperature increased the toxicity of mercury to cultures of rabbit kidney cells, whereas decreasing temperatures decreased the effect of mercury toxicity on the salmon kidney cells. As a consequence, fish taken from arctic waters are liable to be more toxic when introduced into mammalian food chains. Albumin was shown to act as a protective agent in vitro against inorganic mercury toxicity.     

Expression of organomercurial lyase in eastern cottonwood enhances organomercury resistance

Summary Release of inorganic mercury pollutants into shallow aquatic environments has resulted in the bacterial production of a more toxic organic mercury species, methylmercury. The bacterial organomercurial lyase (MerB) catalyses the protonolysis of the carbon-mercury bond and releases Hg(II), a less toxic, non-biomagnified form of mercury. Our objective was to engineer eastern cottonwood (Populus deltoides), a fast-growing tree adapted to growth in riparian environments, with the merB gene to explore its potential for phytoremediation of mercury. We produced multiple eastern cottonwood clones expressing a modified bacterial merB gene, confirmed that the gene was expressed in the transclones and tested the regenerated plants for their ability to tolerate exposure to an organic mercury source, phenylmercuric acetate (PMA), in vitro and in hydroponic culture, compared to wild-type control trees. Transgenic merB plants expressed high levels of MerB protein and showed some evidence of higher resistance to the organic mercury than wild-type plants, producing longer roots under exposure to PMA in vitro, although hydroponic culture results were inconclusive. Our results indicate that in order for merB to be useful in eastern cottonwood trees designed to degrade methylmercury at mercury-contaminated aquatic sites, it will probably need to be combined with other genes such as merA.     

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.