Showing papers on "Mercury (element) published in 2000"

Molecular Interactions with Mercury in the Kidney

Abstract: Mercury is unique among the heavy metals in that it can exist in several physical and chemical forms, including elemental mercury, which is a liquid at room temperature. All forms of mercury have toxic effects in a number of organs, especially in the kidneys. Within the kidney, the pars recta of the proximal tubule is the most vulnerable segment of the nephron to the toxic effects of mercury. The biological and toxicological activity of mercurous and mercuric ions in the kidney can be defined largely by the molecular interactions that occur at critical nucleophilic sites in and around target cells. Because of the high bonding affinity between mercury and sulfur, there is particular interest in the interactions that occur between mercuric ions and the thiol group(s) of proteins, peptides and amino acids. Molecular interactions with sulfhydryl groups in molecules of albumin, metallothionein, glutathione, and cysteine have been implicated in mechanisms involved in the proximal tubular uptake, accumulation, transport, and toxicity of mercuric ions. In addition, the susceptibility of target cells in the kidneys to the injurious effects of mercury is modified by a number of intracellular and extracellular factors relating to several thiol-containing molecules. These very factors are the theoretical basis for most of the currently employed therapeutic strategies. This review provides an update on the current body of knowledge regarding the molecular interactions that occur between mercury and various thiol-containing molecules with respect to the mechanisms involved in the renal cellular uptake, accumulation, elimination, and toxicity of mercury.

Novel Sorbents For Mercury Removal From Flue Gas

Abstract: A laboratory-scale packed-bed reactor system is used to screen sorbents for their capability to remove elemental mercury from various carrier gases When the carrier gas is argon, an on-line atomic fluorescence spectrophotometer (AFS), used in a continuous mode, monitors the elemental mercury concentration in the inlet and outlet streams of the packed-bed reactor The mercury concentration in the reactor inlet gas and the reactor temperature are held constant during a test For more complex carrier gases, the capacity is determined off-line by analyzing the spent sorbent with either a cold vapor atomic absorption spectrophotometer (CVAAS) or an inductively coupled argon plasma atomic emission spectrophotometer (ICP-AES) The capacities and breakthrough times of several commercially available activated carbons as well as novel sorbents were determined as a function of various parameters The mechanisms of mercury removal by the sorbents are suggested by combining the results of the packed-bed testing with

Mercury toxicity in plants

Abstract: 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.

Phytodetoxification of hazardous organomercurials by genetically engineered plants.

Abstract: Methylmercury is a highly toxic, organic derivative found in mercury-polluted wetlands and coastal sediments worldwide. Though commonly present at low concentrations in the substrate, methylmercury can biomagnify to concentrations that poison predatory animals and humans. In the interest of developing an in situ detoxification strategy, a model plant system was transformed with bacterial genes (merA for mercuric reductase and merB for organomercurial lyase) for an organic mercury detoxification pathway. Arabidopsis thaliana plants expressing both genes grow on 50-fold higher methylmercury concentrations than wild-type plants and up to 10-fold higher concentrations than plants that express merB alone. An in vivo assay demonstrated that both transgenes are required for plants to detoxify organic mercury by converting it to volatile and much less toxic elemental mercury.

Engineering Deinococcus radiodurans for metal remediation in radioactive mixed waste environments.

Abstract: We have developed a radiation resistant bacterium for the treatment of mixed radioactive wastes containing ionic mercury. The high cost of remediating radioactive waste sites from nuclear weapons production has stimulated the development of bioremediation strategies using Deinococcus radiodurans, the most radiation resistant organism known. As a frequent constituent of these sites is the highly toxic ionic mercury (Hg) (II), we have generated several D. radiodurans strains expressing the cloned Hg (II) resistance gene (merA) from Escherichia coli strain BL308. We designed four different expression vectors for this purpose, and compared the relative advantages of each. The strains were shown to grow in the presence of both radiation and ionic mercury at concentrations well above those found in radioactive waste sites, and to effectively reduce Hg (II) to the less toxic volatile elemental mercury. We also demonstrated that different gene clusters could be used to engineer D. radiodurans for treatment of mixed radioactive wastes by developing a strain to detoxify both mercury and toluene. These expression systems could provide models to guide future D. radiodurans engineering efforts aimed at integrating several remediation functions into a single host.

Review : evaporation of mercury from soils. An integration and synthesis of current knowledge

Abstract: Understanding the mechanisms of mercury evaporation from soil to the atmosphere is necessary for tracing the fate of mercury in the biological environment and for assessing potential health effects and the impact of anthropogenic mercury emissions on the environment. In this article an integrating overview of the current knowledge of the mechanisms of mercury evaporation is presented. Abiological and biological formation of Hg(0) and/or (CH3)2Hg in the uppermost soil layers are the rate limiting processes of mercury evaporation from soils in background areas; the evaporation rate in background areas is probably strongly influenced by deposited airborne mercury. The evaporation rate limiting factors in mercury enriched mineralized areas with large fractions of total mercury being volatile mercury species (relative to background soil in the non-mineralized vicinity) meteorological variations and the transport characteristics of soils for volatile mercury species. Mercury evaporation rates from background soils are usually <0.2 μg·m–2·h–1 and significantly smaller than from mercury-enriched mineralized areas.

Methyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted Ecosystems

Abstract: We examined microbial methylmercury (MeHg) degradation in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), three freshwater environments that differ in the extent and type of mercury contamination and sediment biogeochemistry. Degradation rate constant (kdeg) values increased with total mercury (Hgt) contamination both among and within ecosystems. The highest kdeg's (2.8−5.8 d-1) were observed in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of the former New Idria mercury mine, where Hgt ranged from 4.5 to 21.3 ppm (dry wt). A reductive degradation pathway (presumably mer-detoxification) dominated degradation at these sites, as indicated by the nearly exclusive production of 14CH4 from 14C-MeHg, under both aerobic and anaerobic conditions. At the upstream control site, and in the less contaminated ecosystems (e.g. the Everglades), kdeg's were low (≤0.2 d-1) and oxidative demethylation (OD) dominated degradation, as evident from 14CO2 produc...

Constants of mercury methylation and demethylation rates in sediments and comparison of tracer and ambient mercury availability

Abstract: A method was developed to measure mercury methylation and demethylation rate constants simultaneously in aquatic samples. Solutions containing stable isotope tracers of 199 Hg 2+ and CH 3 202 Hg + were spiked into lake sediments at subambient concentrations. The formation of CH 3 199 Hg + and the decrease in CH 3 202 Hg were measured simultaneously in time series experiments using gas chromatographic separation and isotope-specific detection by inductively coupled plasma mass spectrometry. Specific rate constants for the two processes were calculated and compared to rate constants obtained by monitoring changes in concentration of the ambient methylmercury in the same sample. The inorganic mercury tracer 199 Hg 2+ was methylated at a faster rate compared with the ambient inorganic Hg 2+ , which indicates that the added tracer Hg 2+ is more available for transformation reaction than the ambient Hg 2+ . The degradation of tracer and ambient methylmercury proceeded at a similar rate, showing no significant differences between added tracer and ambient methylmercury. The calculated half-life for methylmercury in sediments was 1.7 d, suggesting a rapid turnover and low persistence of methylmercury in lake sediments. Different Hg species were investigated regarding their availability for methylation reactions. Compared to Hg(NO 3 ) 2 , Hg-fulvate showed reduced availability and freshly precipitated HgS was hardly available.

Methylmercury exposure affects motor performance of a riverine population of the Tapajós river, Brazilian Amazon

Abstract: Gold mining and deforestation in the Brazilian Amazon are increasing mercury pollution of the extensive water system, exposing riverine populations to organic mercury through fish-eating. The aim of the present study was to evaluate the effect of such exposure on motor performance. This cross-sectional study was carried out in May 1996, in a village located on the banks of the Tapajos river in the Amazonian Basin, Brazil. Information concerning sociodemographics, health, smoking habits, alcohol drinking, dietary habits and work history were collected using an interview-administered questionnaire. Mercury concentrations were measured by cold vapor atomic absorption in blood and hair of each participant, of whom those aged between 15 and 79 years were assessed for motor performance (n=84). Psychomotor performance was evaluated using the Santa Ana manual dexterity test, the Grooved Pegboard Fine motor test and the fingertapping motor speed test. Motor strength was measured by dynamometry for grip and pinch strength. Following the exclusion of 16 persons for previous head injury, working with mercury in the gold-mining sites, or for diabetes, the relationship between performance and bioindicators of mercury was examined using multivariate statistical analyses, taking into account covariables. All participants in the study reported eating fish, which comprised 61.8% of the total meals eaten during the preceding week. The median hair total mercury concentration was 9 μg/g. Organic mercury accounted for 94.4 ± 1.9% of the total mercury levels. Multivariate analysis of variance indicated that hair mercury was inversely associated with overall performance on the psychomotor tests, while a tendency was observed with blood mercury. Semipartial regression analyses showed that hair total mercury accounted for 8% to 16% of the variance of psychomotor performance. Neither hair nor blood total mercury was associated with the results of the strength tests in women and men. Although dose-effect relationships were observed in this cross-sectional study, they may reflect higher exposure levels in the past. The findings of this study demonstrated neurobehavioral manifestations of subtle neurotoxic effects on motor functions, associated with low-level methylmercury exposure.

Estimation of Mercury Emission from Coal Combustion in China

Abstract: The mercury emissions of coal combustion and the mercury concentration of coals in China were studied. The average mercury concentration of coals is 0.22 mg/kg. By founding a monitor program, we measured the mercury emission factors of coal-fired boilers, which are from 64.0% to 78.2%. On the basis of other data, we estimated that the total amount of mercury emission from coal combustion was 302.87 t in 1995, including 213.8 t into atmosphere and 89.07 t into ash and cinder. The results show that 2493.8 t of mercury was emitted into the atmosphere during the coal combustion process from 1978 to 1995, and the mercury emission intensity is higher in Beijing, Shanghai, and Tianjin.

Mercury speciation in sediments affected by dumped mining residues in the drainage area of the Idrija mercury mine, Slovenia.

Abstract: Mercury (Hg) concentrations and Hg phases were investigated in contaminated sediments and flooded soils in the drainage area of the Idrija Hg mine, Slovenia. The main aim of this study was the analytical separation and quantification of cinnabar (HgS) and noncinnabar Hg compounds in sediments contaminated by mining residues. Separation of Hg phases was performed by means of a solid-phase-Hg-thermo-desorption technique complemented by selective extraction of organically bound Hg. Speciation measurements indicate the occurrence of two major Hg forms: cinnabar the primary ore and an unspecified group of matrix-bound, noncinnabar Hg compounds. The results show that Hg concentrations and dispersion of the two Hg phases within the river system depend on the distribution of different sediment grain size fractions. Accumulation of cinnabar predominately occurs in coarse grained river sediments, where it constitutes on average more than 80% of total Hg (up to 1000 mg/kg) in present- and past day sediments. In con...

Mercury Contamination from Historical Gold Mining in California

Abstract: Printed on recycled paper Mercury contamination from historical gold mines represents a potential risk to human health and the environment. This fact sheet provides background information on the use of mercury in historical gold mining and processing operations in California, with emphasis on historical hydraulic mining areas. It also describes results of recent USGS projects that address the potential risks associated with mercury contamination. Miners used mercury (quicksilver) to recover gold throughout the western United States. Gold deposits were either hardrock (lode, gold-quartz veins) or placer (alluvial, unconsolidated gravels). Underground methods (adits and shafts) were used to mine hardrock gold deposits. Hydraulic, drift, or dredging methods were used to mine the placer gold deposits. Mercury was used to enhance gold recovery in all the various types of mining operations; historical records indicate that more mercury was used and lost at hydraulic mines than at other types of mines. On the basis of USGS studies and other recent work, a better understanding is emerging of mercury distribution, ongoing transport, transformation processes, and the extent of biological uptake in areas affected by historical gold mining. This information has been used extensively by federal, state, and local agencies responsible for resource management and public health in California.

Mercury speciation in the presence of polysulfides

Abstract: Environmental mercury methylation appears modulated by sulfide concentrations, possibly via changes in mercury availability to sulfate reducing bacteria, the major agents of this process in aquatic systems. Consequently, there has been much recent interest in quantifying the chemical speciation and lipid solubility of mercury in the presence of sulfide and of polysulfides, which form by reaction of sulfide with elemental sulfur or as intermediates in sulfur cycling. We quantify a large increase in the solubility of cinnabar (HgS(s)) in the presence of elemental sulfur, particularly at high pH. Based on our data and those of Paquette and Helz, we propose that the complex, Hg(Sx)22-, dominates the speciation of Hg(II) in such waters. At lower sulfide concentrations and at high pH, the data are best fitted by considering also the formation of the species HgSxOH-. Octanol−water distribution (Dow) experiments confirm the charged nature of the dominant mercury−polysulfide complexes and imply the presence of a m...

Compressibility effect in evaluating the pore-size distribution of kaolin clay using mercury intrusion porosimetry

Abstract: The objective of the present research is to quantitatively evaluate the compression that can occur during the evaluation of pore-size distribution of cohesive soil using mercury intrusion porosimet...

Mercury in the soil-plant-deer-predator food chain of a temperate forest in Slovenia.

Abstract: Total mercury and methylmercury concentrations from long-term monitoring of the terrestrial soil-vegetation-herbivore-carnivore food chain with regard to accumulation and transformation processes were studied in areas of Slovenia contaminated with mercury to differing degrees, as well as uncontaminated areas. Assessment of the inhaled and ingested contribution of mercury from the environment in roe deer (Capreolus capreolus L.), the selected wild mammal species living in these areas, showed that while the ratio between these two routes of uptake is relatively constant, food intake of mercury in roe deer is much more important than inhaled mercury, which represents only up to 0.2% of ingested Hg. Although the plant species comprising roe deer foodstuffs were not active accumulators of mercury from soil or air, vegetation mediates significant transfer of Me-Hg to herbivores, and this becomes subject to further accumulation in the higher trophic levels of this food chain. Besides roe deer other bioindicators...

Discovery of calcium in Mercury's atmosphere

Abstract: The composition and evolutionary history of Mercury's crust are not well determined. The planet as a whole has been predicted to have a refractory, anhydrous composition: rich in Ca, Al, Mg and Fe, but poor in Na, K, OH, and S. Its atmosphere is believed to be derived in large part from the surface materials. A combination of effects that include impact vaporization (from infalling material), volatile evaporation, photon-stimulated desorption and sputtering releases material from the surface to form the atmosphere. Sodium and potassium have already been observed in Mercury's atmosphere, with abundances that require a volatile-rich crust. The sodium probably results from photon-stimulated desorption, and has a temperature of 1,500 K (ref. 10). Here we report the discovery of calcium in the atmosphere near Mercury's poles. The column density is very low and the temperature is apparently very high (12,000 K). The localized distribution and high temperature, if confirmed, suggest that the atmospheric calcium may arise from surface sputtering by ions, which enter Mercury's auroral zone. The low abundance of atmospheric Ca may indicate that the regolith is rarefied in calcium.

Application of a mer-lux biosensor for estimating bioavailable mercury in soil

Abstract: A previously described bioassay using a mer-lux gene fusion for detection of bioavailable mercury was applied for the estimation of the bioavailable fraction of mercury in soil. The bioavailable fraction is defined here as being part of the water leachable fraction. Due to masking of light emission of soil particles leachates had to be cleaned prior to assays. Filtration of leachates through nitro-cellulose filters using pressure resulted in an underestimation of bioavailable mercury. Gravity filtration and centrifugation showed elevated (as compared with untreated leachate) and very similar responses. The utility of the mer-lux biosensor assay was tested by relating measurements of bioavailable and total mercury to the response of the soil microbial community to mercury exposure. Two different soil types (an agricultural and a beech forest soil) were spiked with 2.5 μg Hg(II) g−1 in microcosms and the frequency of mercury resistant heterotrophs and changes in community diversity, defined as the number of different 16S rDNA bands observed in DGGE gels, were monitored. In the agricultural soil the initial concentration of bioavailable mercury was estimated to be 40 ng g−1. This concentration did not change during the first 3 d and coincided with increased degrees of resistance and a decrease in diversity. The concentration of bioavailable mercury decreased subsequently rapidly and remained just above the detection level (0.2 ng g−1) for the remainder of the experiment. As a possible consequence of the decreased selection pressure of mercury, the resistance and diversity gradually returned to pre-exposure amounts. In the beech forest soil the concentration of bioavailable mercury was found to be about 20 ng g−1 throughout the experiment. This concentration did not at any time result in changes in resistance or diversity. This study showed that the bioassay using the mer-lux biosensor is a useful and sensitive tool for estimation of bioavailable mercury in soil.