An Investigation of Total Mercury in Sediments and Interstitial Water in the North Fork Holston River below Saltville,Virginia, USA

The North Fork Holston River (NFHR) is historically renowned for having one of the most diversity rich unionid populations (Unionidae) worldwide; however, in recent decades, drastic reductions in mussel diversity, abundance, and recruitment have been documented. Unionid declines have been blamed on anthropogenic influences, specifically mercury-contaminated wastewater from a now closed chlorine-alkali plant in Saltville, VA. The objective of this research was to evaluate total mercury (Hg) contamination of sediments and interstitial waters in the NFHR beginning below Saltville and downstream for approximately 50 river miles. Mercury contaminated sediments and interstitial water were found downstream of the closed plant with the highest sediment concentration of 2.82 mg/kg dry weight total Hg found at river mile (rm) 80 and the highest interstitial water value at rm 30.4 with 2.1 μg/l. After 60-d in situ testing, total Hg concentrations in Asian clam (Corbicula fluminea) tissues were found to range from 0.016 to 0.13 mg/kg, while resident clams had Hg concentrations of 0.094 and 0.11 mg/kg wet weight. Although chronic toxicity was not observed, based on Corbicula growth and survival tests, nor in testing with cladocerans, mercury contamination is still a persistent problem at sites in the NFHR below the closed plant with negative correlations between mean clam growth and sediment Hg concentrations.     

Experiments with large enclosed ecosystems.

Three of the major advantages of enclosure experiments are that they ensure (1) that the same populations are sampled over a long period; (2) that populations of at least three trophic levels are initially enclosed in naturally occurring proportions and that they are self sustaining over a long experimental period; and (3) that replicate enclosed populations can be experimentally manipulated. There are two disadvantages which must be mentioned. These are (1) that vertical mixing, which may be reduced by as much as an order of magnitude compared to the open sea, will undoubtedly affect the sinking rates of phytoplankton and may influence the structure of the population; and (2) that as a general rule the larger and therefore more expensive the enclosures become, the more difficult it is to run sufficient replicates. An experiment is described in which 1 microgram Hg/l was added to two 95 m3 bags (3 mdiameter by 17 m deep) and the response of the pelagic population monitored over the following 20 days. A further 10 micrograms Hg/l was then added to each enclosure and the response measured for a further 20 days. The results indicated that: (i) inorganic mercury added to the water column is very rapidly transformed into 'bound' or 'non-reactive' mercury and that about 25% of the mercury added was recovered associated with the organic material settling to the bottom of the bags; (ii) the response of the biological population to 1 microgram Hg/l was very limited and in fact a transient reduction in photosynthetic carbon uptake per unit chlorophyll was the only noticeable effect and there were no changes in population size or structure that could be attributed to mercury; (iii) at 10 micrograms Hg/l the zooplankton population was reduced markedly and this did produce changes in the structure of both the zooplankton and phytoplankton populations. These results are similar to the results of a comparable experiment carried out in Vancouver Island (Cepex) and point to the conclusion that the levels of mercury found in surface waters around the coast of the U.K. (0.001--0.022 microgram Hg/l) are one or two orders of magnitude below the levels at which a response of the biological population can be demonstrated. The usefulness of large scale enclosed ecosystems for further pollution research is discussed and it is concluded that those facilities that provided a link between the water column and the sediments would be most useful since they would (1) enable estimates to be made of the flux rates of pollutants from the water column to the sediments; and (2) allow experiments to be carried out with the pollutant in contact with sediment in its natural form.     

Effects of methylmercury and inorganic mercury on periphytic diatom communities in freshwater indoor microcosms

The effects of inorganic mercury (HgII) and methylmercury (MeHg) on the colonization of artificial substrates by periphytic diatoms were studied using indoor freshwater microcosms. These consisted of a mixed biotope– water column + natural sediment – with rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea).The periphyton was collected on glass slides in the water column after 34and 71 days. The two Hg sources were introduced either by daily additions to the water column, or once at the beginning into the sediment, using two nominal concentrations: water column, 0.5 μgL^-1 and 2 μg L^-1 for both compounds: sediment, 0.5 mg kg^-1 (fw) and 2 mgkg^-1 (fw) for MeHg and 1 mg kg^-1 (fw) and 10 mgkg^-1 (fw) for HgII. Several complementary criteria were used to analyse the structural and functional perturbations induced: cell density, species richness, diatom size, relative abundance. Exposure to MeHg added to the water column resulted in reduced cell density and changes in species composition with enhancement of e.g. Fallacia pygmaea or Nitzschia palea; inorganic Hg had less effect on the population structure. After contamination via the sediment, the effects of the two compounds were less pronounced than for the water source. This revised version was published online in August 2006 with corrections to the Cover Date.     

Disturbed microtubule function and induction of micronuclei by chelate complexes of mercury(II)

Interactions of mercury(II) with the microtubule network of cells may lead to genotoxicity. Complexation of mercury(II) with EDTA is currently being discussed for its employment in detoxification processes of polluted sites. This prompted us to re-evaluate the effects of such complexing agents on certain aspects of mercury toxicity, by examining the influences of mercury(II) complexes on tubulin assembly and kinesin-driven motility of microtubules. The genotoxic effects were studied using the micronucleus assay in V79 Chinese hamster fibroblasts. Mercury(II) complexes with EDTA and related chelators interfered dose-dependently with tubulin assembly and microtubule motility in vitro. The no-effect-concentration for assembly inhibition was 1 microM of complexed Hg(II), and for inhibition of motility it was 0.05 microM, respectively. These findings are supported on the genotoxicity level by the results of the micronucleus assay, with micronuclei being induced dose-dependently starting at concentrations of about 0.05 microM of complexed Hg(II). Generally, the no-effect-concentrations for complexed mercury(II) found in the cell-free systems and in cellular assays (including the micronucleus test) were identical with or similar to results for mercury tested in the absence of chelators. This indicates that mercury(II) has a much higher affinity to sulfhydryls of cytoskeletal proteins than to this type of complexing agents. Therefore, the suitability of EDTA and related compounds for remediation of environmental mercury contamination or for other detoxification purposes involving mercury has to be questioned.     

Methods and recent advances in speciation analysis of mercury chemical species in environmental samples: a review

Mercury (Hg) and its compounds are much concerned for their high toxicity and wide presence in the environment. Since the toxicity of Hg is species dependent, various methods have been developed for the speciation analysis of Hg. This review focus on the determination and speciation analysis of Hg chemical species in water, sediment, and soil samples. Recent developments on sample pre-treatment and extraction/pre-concentration, separation, and quantification of Hg chemical species, and associated analytical challenges have been reviewed and briefly discussed based on recent reports.     

Methylation and demethylation of mercury under controlled redox, pH and salinity conditions.

In estuarine sediments, the microbially mediated processes of methylation, demethylation, and volatilization determine the state and overall toxicity of mercury pollutants. The effects of redox potential (Eh) and salinity on the above microbial processes were investigated in reactors constructed to allow for continuous monitoring and adjustment of the pH (6.8) and Eh of freshly collected estuarine sediments. For measurements of methylation and demethylation activity, sediment slurries adjusted to appropriate salinity were spiked with HgCl2 or CH3HgCl, respectively, and were incubated in the reactors. Methylmercury was measured by gas chromatography. Volatilized elemental mercury (Hg0) was trapped and determined by cold vapor atomic absorption spectrometry. Volatilization of Hg0 and CH3HgCH3 were found to be minimal. Methylation of Hg2+ was favored at Eh-220 mV as compared to +110 mV. At -220 mV, high salinity (2.5%) inhibited methylation, and low salinity (0.4%) favored it. At +110 mV, the salinity effect was less pronounced. Demethylation of CH3HgCl was favored at +110 mV regardless of the salinity level. Low redox potential under low salinity conditions inhibited demethylation, but high salinity reversed this inhibition. These findings are helpful for interpreting and predicting the behavior of mercury pollutants in estuarine sediments.     

Potential causes of enhanced transfer of mercury to St. Lawrence River Biota: implications for sediment management strategies at Cornwall, Ontario, Canada

We examined factors and pathways involved in the transfer of mercury (Hg) to the food web in St. Lawrence River embayments near Cornwall, Ontario, where natural remediation of contaminated sediments (eventual burial by settling of cleaner sediments) has been adopted as a management strategy. Yellow perch (Perca flavescens) from one of the study zones (Zone 1) along the river by Cornwall contained significantly higher total mercury (THg) concentrations than perch from other equally contaminated zones. While THg concentrations in benthic invertebrates did not vary among contaminated zones, THg concentrations in yellow perch and invertebrate prey recovered from the perch stomachs were 1.5–2.5 times higher in Zone 1 than those from other zones, suggesting that prey selection affects THg accumulation more than habitat location. No significant differences were found in THg concentrations among different prey species within Zone 1, although there were significant differences in THg concentrations in the same prey species within Zone 1. In contrast, THg concentrations among different prey species increased significantly with trophic level in other contaminated and reference zones. The lack of correspondence between trophic position and THg accumulation in Zone 1 suggests two possibilities: (1) yellow perch in Zone 1 are highly mobile and are assimilating THg from a wide range of prey across Zone 1 with variable THg concentrations and (2) there may be an important non-dietary source of THg to the Zone 1 food web. Potential waterborne Hg sources to Zone 1 were investigated. Whereas THg and MeHg values in discharges from a disused canal were similar to Zone 1 surface water values (0.97 and 0.04 ng l^?1, respectively), concentrations in storm sewer and combined sewer overflows discharging in the vicinity of Zone 1 were 19–45-fold (THg) and 2–4-fold (MeHg) higher than upstream river water. Contributions of Hg to the water column from sediment–water diffusion, estimated using a simple, well-mixed reactor model, ranged 0.05–0.1% of the surface water THg concentration and 1–2% of the MeHg concentration measured in summer months in Zone 1. Although not investigated in the other zones, a strong correlation (r ² = 0.82) was found between MeHg in porewater and amphipod concentrations in Zone 1, indicating that the sediment porewater is bioavailable and likely an important pathway for transfer of sediment Hg to the foodweb. Large areas of Zone 1 contain bark deposits and produce high rates of gas ebullition, and may not provide favourable conditions for progressive burial with clean sediments and attenuation of Hg transfer to biota through natural remediation. Careful monitoring of surface sediment concentrations and biota is required in these areas. Failure to reduce concentrations of Hg in these media would indicate alternative or additional management measures are required.     

MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay,France)

Hg cycling in biologically productive coastal areas is of special importance given the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. Field experiments were performed during three different seasons in Arcachon Bay, a mesotidal lagoon (SW France), to assess the variability of the water column concentrations, sediment–water exchanges and potential formation and degradation of MMHg. The objectives were to evaluate the contribution of intertidal mudflats to MMHg production and the various pathways of Hg species export. Dissolved and bulk concentrations of Hg species in the water column downstream of tidal flats were measured throughout several tidal cycles. The Hg benthic fluxes at the sediment–water interface were determined by means of benthic chambers for three different stations. Hg methylation and demethylation potentials were determined in surficial sediments and the water column using isotopic tracers. The tidal surveys demonstrated that benthic remobilization of Hg occurs primarily in association with sediment erosion and advection during ebb tide. However, elevated dissolved Hg concentrations observed at low tide were found to be caused by a combination of pore-waters seeping, benthic fluxes and methylation in the water column. Benthic fluxes were more intense during late winter conditions (median MMHg and inorganic Hg (IHg) fluxes: 64 and 179 pmol m^?2 h^?1, respectively) and subsequently decreased in spring (median 0.7 and ?5 pmol m^?2 h^?1, respectively) and fall (median ?0.4 and ?1.3 pmol m^?2 h^?1, respectively). The trends in methylation and demethylation potentials were at the opposite of the fluxes, two times lower during winter than for spring or fall conditions. In this tidal environment, MMHg production in surface sediments and its subsequent release is estimated to be the major source of MMHg to the water column during winter and spring time. However, during the more productive summer period, the Hg methylation extent in the water column may be very significant and equivalent to the sediment contribution.     

Bioassay responses to sediment elutriates and multivariate data analysis for hazard assessment of sediment-bound chemicals

A sediment study, involving both chemical and biological analyses, was carried out in the Hamburg harbour area. A total of 71 stations were sampled during 1988 and the sediments extracted using a 1:4 sediment:water ratio either with or without an addition of a water-soluble detergent to solubilize organic compounds. The resulting extracts were applied in algal and bacterial assays to measure toxicity. A principal components analysis showed that no single bioassay explained all the variation in toxicity among the locations studied. Hierarchical cluster analysis was used to rank sediments into four groups based on their toxicity. The relationship of toxic responses to the chemistry of the sediments was determined using varimax factor analysis. One factor was loaded with algal responses and mercury contents of sediments, another with bacterial responses and Lindane contents of sediments.     

Limited sinking of Phaeocystis during a 12 days sediment trap study

There is a controversy discussion about the contribution of the genus Phaeocystis to the vertical carbon export with evidence for and against sedimentation of Phaeocystis. So far, the presence of Phaeocystis in sinking matter was investigated with methods depending on morphological features (microscopy) and fast degradable substances (biochemical analyses). In this study, we determine the occurrence and abundance of Phaeocystis antarctica in short‐term sediment traps and the overlying water column during a 12‐day time period in the Atlantic sector of the Southern Ocean with 454‐pyrosequencing and microscopy counting. In the sediment trap samples, we only found few sequences belonging to Phaeocystis, which was not reflecting the situation in the water column above. The cell counts showed the same results. We conclude that Phaeocystis cells are not generally transported downwards by active sinking or other sinking processes.     

Sulfate-reducing Bacteria and Mercury Methylation in the Water Column of the Lake 658 of the Experimental Lake Area

Sulfate-reducing bacteria (SRB) appear to be the main mediators of mercury methylation in sediments, which are deemed to be major sites of methylmercury (MMHg) production. However, recent studies have also found significant MMHg formation in the water column of lakes across North America. To investigate the potential involvement of SRB in mercury methylation in the water column of a stratified oligotrophic lake, two of the main families of SRB (Desulfobacteraceae and Desulfovibrionaceae) were quantified by Real-Time Polymerase Chain Reaction of the 16S rRNA gene. MMHg production was measured applying a stable isotope technique using ¹⁹⁸HgCl. Methylation assays were conducted at different water depths and under stimulation with lactate, acetate or propionate and inhibition with molybdate. Desulfobacteraceae and Desulfovibrionaceae16S rRNA gene copies in control samples accounted for 0.05% to 33% and <0.01% to 1.12% of the total bacterial 16S rRNA, respectively. MMHg formation was as high as 0.3 ng L^?1 day^?1 and largest in lactate amended samples. Strain isolation was only achieved in lactate amended media with all isolated strains being SRB belonging to the Desulfovibrio genus according to their 16S rRNA gene sequence. Isolated strains methylated between 0.06 and 0.2% of ¹⁹⁸HgCl per day. Acetate and propionate did not stimulate mercury methylation as much as lactate. Two strains were identified as Desulfovibrio sp. 12ML1 (FJ865472) and Desulfovibrio sp. 12ML3 (FJ865473), based on partial sequences of their 16S rRNA and DSR gene. Methylation assays and bacteria characterization suggest that Desulfovibrionaceae is an important mercury methylators in Lake 658. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.     

Biotoxicity of mercury as influenced by mercury(II) speciation

Integration of physicochemical procedures for studying mercury(II) speciation with microbiological procedures for studying the effects of mercury on bacterial growth allows evaluation of ionic factors (e.g., pH and ligand species and concentration) which affect biotoxicity. A Pseudomonas fluorescens strain capable of methylating inorganic Hg(II) was isolated from sediment samples collected at Buffalo Pound Lake in Saskatchewan, Canada. The effect of pH and ligand species on the toxic response (i.e., 50% inhibitory concentration [IC50]) of the P. fluorescens isolated to mercury were determined and related to the aqueous speciation of Hg(II). It was determined that the toxicities of different mercury salts were influenced by the nature of the co-ion. At a given pH level, mercuric acetate and mercuric nitrate yielded essentially the same IC50s; mercuric chloride, on the other hand, always produced lower IC50s. For each Hg salt, toxicity was greatest at pH 6.0 and decreased significantly (P = 0.05) at pH 7.0. Increasing the pH to 8.0 had no effect on the toxicity of mercuric acetate or mercuric nitrate but significantly (P = 0.05) reduced the toxicity of mercuric chloride. The aqueous speciation of Hg(II) in the synthetic growth medium M-IIY (a minimal salts medium amended to contain 0.1% yeast extract and 0.1% glycerol) was calculated by using the computer program GEOCHEM-PC with a modified data base. Results of the speciation calculations indicated that complexes of Hg(II) with histidine [Hg(H-HIS)HIS+ and Hg(H-HIS)2(2+)], chloride (HgCl+, HgCl2(0), HgClOH0, and HgCl3-), phosphate (HgHPO4(0), ammonia (HgNH3(2+), glycine [Hg(GLY)+], alanine [Hg(ALA)+], and hydroxyl ion (HgOH+) were the Hg species primarily responsible for toxicity in the M-IIY medium. The toxicity of mercuric nitrate at pH 8.0 was unaffected by the addition of citrate, enhanced by the addition of chloride, and reduced by the addition of cysteine. In the chloride-amended system, HgCl+, HgCl2(0), and HgClOH0 were the species primarily responsible for observed increases in toxicity. In the cysteine-amended system, formation of Hg(CYS)2(2-) was responsible for detoxification effects that were observed. The formation of Hg-citrate complexes was insignificant and had no effect on Hg toxicity.     

Biotoxicity of mercury as influenced by mercury(II) speciation.

Integration of physicochemical procedures for studying mercury(II) speciation with microbiological procedures for studying the effects of mercury on bacterial growth allows evaluation of ionic factors (e.g., pH and ligand species and concentration) which affect biotoxicity. A Pseudomonas fluorescens strain capable of methylating inorganic Hg(II) was isolated from sediment samples collected at Buffalo Pound Lake in Saskatchewan, Canada. The effect of pH and ligand species on the toxic response (i.e., 50% inhibitory concentration [IC50]) of the P. fluorescens isolated to mercury were determined and related to the aqueous speciation of Hg(II). It was determined that the toxicities of different mercury salts were influenced by the nature of the co-ion. At a given pH level, mercuric acetate and mercuric nitrate yielded essentially the same IC50s; mercuric chloride, on the other hand, always produced lower IC50s. For each Hg salt, toxicity was greatest at pH 6.0 and decreased significantly (P = 0.05) at pH 7.0. Increasing the pH to 8.0 had no effect on the toxicity of mercuric acetate or mercuric nitrate but significantly (P = 0.05) reduced the toxicity of mercuric chloride. The aqueous speciation of Hg(II) in the synthetic growth medium M-IIY (a minimal salts medium amended to contain 0.1% yeast extract and 0.1% glycerol) was calculated by using the computer program GEOCHEM-PC with a modified data base. Results of the speciation calculations indicated that complexes of Hg(II) with histidine [Hg(H-HIS)HIS+ and Hg(H-HIS)2(2+)], chloride (HgCl+, HgCl2(0), HgClOH0, and HgCl3-), phosphate (HgHPO4(0), ammonia (HgNH3(2+), glycine [Hg(GLY)+], alanine [Hg(ALA)+], and hydroxyl ion (HgOH+) were the Hg species primarily responsible for toxicity in the M-IIY medium. The toxicity of mercuric nitrate at pH 8.0 was unaffected by the addition of citrate, enhanced by the addition of chloride, and reduced by the addition of cysteine. In the chloride-amended system, HgCl+, HgCl2(0), and HgClOH0 were the species primarily responsible for observed increases in toxicity. In the cysteine-amended system, formation of Hg(CYS)2(2-) was responsible for detoxification effects that were observed. The formation of Hg-citrate complexes was insignificant and had no effect on Hg toxicity.     

Distribution and partitioning of mercury in a river catchment impacted by former mercury mining activity

Mercury distribution and partitioning was studied in the River Idrijca system, draining the area of the former Idrija mercury mine, Slovenia. Mercury dynamics were assessed by speciation analysis of mercury in water and river bed sediment samples during a 2-year study at locations on the River Idrijca and its major tributaries. Simultaneously, the influence of some major physico-chemical parameters that influence the fate of mercury in the aquatic environment was investigated. The distribution of mercury species in the River Idrijca catchment indicated contamination from mine tailings distributed in the town of Idrija and erosion of contaminated soils. The partitioning between dissolved and particulate mercury phases in river water was found to be mostly controlled by the variable content of suspended solids resulting from changing hydrological conditions and complexation with various ligands present in river water, among which dissolved organic carbon (DOC) seems to be the most important. Overall results indicate that mercury is transported downstream from the mining area mainly as finely suspended material including colloids rather than in the dissolved phase. This riverine transport occurs mostly during short, but extreme hydro-meteorological conditions when remobilization of mercury from the river bed sediments occurs. A significant part of the mercury particulate phase in water corresponds to cinnabar particles. During its transport, important Hg transformation mechanisms that increase the risk of mercury uptake by biota take place, evidenced by the increase in the relative contribution of reactive mercury (Hg_R), dissolved gaseous mercury (DGM) and monomethylmercury (MeHg) downstream from the Idrija mine. However, our data revealed relatively low methylation efficiency in this contaminated river system. We attribute this to the site specific physico-chemical conditions responsible for making inorganic mercury unavailable and limiting the capacity of methylating bacteria.     

Accelerating recovery of the mercury-contaminated Wabigoon/English River system

Mercury levels (essentially methyl mercury — MeHg) in sportfish in a 250 km section of the Wabigoon-English River system remain seriously elevated as a result if the discharge of approximately 10 tonnes of inorganic Hg from a chlor-alkali plant at Dryden, Ontario, Canada which occurred primarily between 1962 and 1970. The discharges resulted in elevated mercury concentrations in water, sediments and biota. For example, Hg in adult Northern Pike in Clay Lake routinely exceeded 3 µg/g (ppm). Field studies in 1978–1981 suggest that partitioning of inorganic and MeHg between surface sediment, water and suspended particles occurs within days. MeHg levels in water were partitioned with total (essentially inorganic) Hg. Temperature affects both Hg and MeHg levels in water; concentrations fluctuated seasonally by an order of magnitude at some sites. Hg in contaminated surface sediments is almost certainly the primary source of the mercury now entering the water and biota in this contaminated watercourse. Mercury levels in biota decline less dramatically with distance downstream of Dryden than mercury concentrations in sediments. Natural erosion, resuspension and sedimentation processes have helped to reduce the amount of mercury in the active layer at the sediment/water interface and the most effective means of accelerating the recovery of the system will probably involve measures to accelerate these natural processes. Enclosure experiments, regional surveys and geochemical studies all provide evidence that the biological uptake of upstream anthropogenic Hg loadings at any given site would likely be reduced dramatically by the continuous addition of very modest quantities of pristine clay sediment. The quantities contemplated, when resuspended, would result in suspended solids concentrations on the order of 15–25 ppm, a value higher than for most shield waters but well within the range of many other productive watercourses in North America. The ability to mitigate local sources and ameliorate the adverse biological effects of anthropogenic loadings from upstream sources by resuspension of clean clay sediments permits targeting of sites for restoration and opens a wide array of ameliorative options. The authors believe that some of these options would be more effective and less costly than other restoration procedures commonly considered such as dredging and on land disposal of contaminated sediment.The views expressed are those of the authors and do not necessarily reflect the views of the Ontario Ministry of the Environment or the International Joint Commission. No endorsement should be inferred.     

Biosorption of mercury by the inactivated cells of pseudomonas aeruginosa PU21 (Rip64)

Biomass of a mercury-resistant strain Pseudomonas aeruginosa PU21 (Rip64) and hydrogen-form cation exchange resin (AG 50W-X8) were investigated for their ability to adsorb mercury. The maximum adsorption capacity was approximately 180 mg Hg/g dry cell in deionized water and 400 mg Hg/g dry cell in sodium phosphate solution at pH 7.4, higher than the maximum mercury uptake capacity in the cation exchange resin (100 mg Hg/g dry resin in deionized water). The mercury selectivity of the biomass over sodium ions was evaluated when 50 mM and 150 mM of Na(+) were present. Biosorption of mercury was also examined in sodium phosphate solution andphosphate-buffered saline solution (pH 7.0), containing 50mM and 150 mM of Na(+), respectively. It was found that the presence of Na(+) did not severely affect the biosorption of Hg(2+), indicating a high mercury selectivity ofthe biomass over sodium ions. In contrast, the mercury uptake by the ion exchange resin was strongly inhibited by high sodium concentrations. The mercury biosorption was most favorable in sodium phosphate solution (pH 7.4), with a more than twofold increase in the maximum mercury uptake capacity. The pH was found to affect the adsorption of Hg(2+)bythe biomass and the optimal pH value was approximately 7.4. The adsorption of mercury on the biomass and the ion exchange resin appeared to follow theLangmuir or Freundlich adsorption isotherms. (c) 1994 John Wiley & Sons, Inc.     

Synthesis of a highly metal-selective rhodamine-based probe and its use for the in vivo monitoring of mercury

This protocol describes detailed procedures for the preparation of a rhodamine-based mercury probe and for its applications to the detection of mercury in cells and vertebrate organisms. The mercury probe 1, which is prepared in two steps from rhodamine 6G, responds rapidly to Hg2+ in aqueous solutions with a 1:1 stoichiometry. Owing to the fact that the probe reacts with Hg2+ in an irreversible manner, it has advantages over other reversible mercury probes in in vivo assays with respect to both sensitivity and selectivity. In addition, fluorescent imaging assays of Hg2+ in live cells and zebrafish by using this mercury probe are detailed in this protocol. The approximate time frame for the preparation of the probe is 24 h and for its use in imaging assays is 1.5 h.     

东湖茶港排污口底泥对稀有鮈鲫的毒性

以东湖茶港排污口底泥复溶水为试验相,采用96h急性毒性试验和胚胎—卵黄囊吸收阶段毒性试验方法,研究了东湖茶港排污口底泥对稀有的鮈鲫毒性。结果显示,高浓度的复溶水对稀有鮈鲫胚胎、仔鱼和幼鱼具有明显的毒性效应,而胚胎—卵黄囊吸收阶段更为敏感。随着复溶水浓度的增加,稀有鮈鲫受精卵孵化率降低,仔鱼畸形率增高、成活率降低、生长减慢;对胚胎—卵黄囊吸收阶段的NOEC、LOEC和MATC分别为12.5%、25%和17.68%;对幼鱼96h LC50为69.1%。本文的研究还表明,底泥经晾晒后毒性大幅降低,暗示恢复东湖通江状态并让水位自然涨落,可能有助于缓解污染、恢复生态环境。     

Formation of Methyl Mercury by Bacteria

Twenty-three Hg2+-resistant cultures were isolated from sediment of the Savannah River in Georgia; of these, 14 were gram-negative short rods belonging to the genera Escherichia and Enterobacter, six were gram-positive cocci (three Staphylococcus sp. and three Streptococcus sp.) and three were Bacillus sp. All the Escherichia, Enterobacter, and the Bacillus strain were more resistant to Hg2+ than the strains of staphylococci and streptococci. Adaptation using serial dilutions and concentration gradient agar plate techniques showed that it was possible to select a Hg2+-resistant strain from a parent culture identified as Enterobacter aerogenes. This culture resisted 1,200 mug of Hg2+ per ml of medium and produced methyl mercury from HgCl2, but was unable to convert Hg2+ to volatile elemental mercury (Hg0). Under constant aeration (i.e., submerged culture), slightly more methyl mercury was formed than in the absence of aeration. Production of methyl mercury was cyclic in nature and slightly decreased if DL-homocysteine was present in media, but increased with methylcobalamine. It is concluded that the bacterial production of methyl mercury may be a means of resistance and detoxification against mercurials in which inorganic Hg2+ is converted to organic form and secreted into the environment.