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.     

Luminescent bacteria toxicity assay in the study of mercury speciation

The toxicities of solutions of 10 mercury compounds to luminescent bacteria were measured using the Microtox Toxicity Bioassay. The aim of this study was to assess the influence that the counter-ions have on the aquatic toxicity of mercury salts. The toxicities of these mercury compounds were very similar, except for mercurous tannate and mercuric salicylate. This can be attributed to differences in the ionization and speciation patterns of these compounds relative to the other compounds tested. In general, the toxicity of the solutions at pH 5 was not significantly different from the toxicity of these solutions at pH 6, but a clear reduction in toxicity was observed when the pH of the solution was adjusted to pH 9. Significant differences were found between the toxicity of Hg(I) and Hg(II) salts of the same anion at pH 9. When cysteine was added to a mercuric nitrate solution (at pH 6), a reduction in the toxicity was observed. This can be explained in terms of the strong binding of mercury to cysteine, thus reducing the concentration of mercury species available to cause an observable toxic effect to the bioluminescent bacteria.     

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.     

Animal experiments to determine the toxicity of mercury(II)-chloride in hemostasis

In the course of an experimental poisoning of rats with mercury(II)-chloride no disturbances of haemostasis occurred, from which the development of a consumption coagulopathy might be concluded. Only a diminution of the plasminogen level could be found which is due to a moderate damage of liver parenchyme. The increased activity of the free form of the plasminogen activator found in the kidney homogenate is considered as an enzymatic activation because of kidney cell necrosis.     

Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenediaminetetraacetic acid (EDTA)]. Three fractions (nominal added, dissolved and free) of cobalt were determined in the liquid media and were correlated with data from batch toxicity experiments. The average concentration of cobalt that was required for 50% inhibition of methanogenic activity (IC₅₀) for free Co²⁺ in the three sets of measurements was 13 μmol/L with a standard deviation of 22% and a similarity of 72% between the data obtained in the three different media for the range of cobalt concentrations investigated. The standard deviation of the IC₅₀ for the other two fractions was much higher, i.e. 85 and 144% for the added cobalt and dissolved cobalt, respectively, and the similarity was almost 0% for both fractions. Complexation (and precipitation) with EDTA, phosphates and carbonates was shown to decrease the toxicity of cobalt on methylotrophic methanogenesis. The free cobalt concentration is proposed to be the key parameter to correlate with cobalt toxicity. Thus, the toxicity of cobalt to granular sludge can be estimated based on the equilibrium-free cobalt concentration.     

Reactions of thioether carboxylic acids with mercury(II). Formation and X-ray crystal structure of mercury(II) mercaptoacetate

Reactions of Hg(II) salts with thioether carboxylic acids o-C₆H₄[CH(SCH₂COOH)₂]₂ (1a) and PhCH(SCH₂COOH)₂ (3) in water were found to lead to the decomposition of these ligands with the formation of mercury(II) mercaptoacetate Hg(SCH₂COOH)₂ (2) and aldehydes o-C₆H₄(CHO)₂ and PhCHO, respectively. A similar reaction was observed between Hg(NO₃)₂ and CH₃(CH₂)₂CH(SCH₂COOH)₂ (4). The X-ray structure of Hg(SCH₂COOH)₂ (2) shows a linear -S-Hg-S- moiety. The mechanism of the formation of 2 in the reactions between Hg²⁺ and thioether carboxylic acids in water is discussed.     

Highly sensitive oligonucleotide-based fluorometric detection of mercury(II) in aqueous media

This paper describes a highly sensitive and selective Hg(2+) sensor using a label free Hg(2+) specific probe (5'-18T-3') and an intercalation dye SYBR Green I (SG). The Hg(2+) specific probe is composed of thymines (T) and readily forms T-Hg(2+)-T complexes in the presence of Hg(2+). This specific T-Hg(2+)-T formation affects the hybridization of the Hg(2+) specific probe and the intercalation of SG. Upon treatment of 1 nM 5'-18T-3' with different amount of Hg(2+) (0.1-10nM), which is followed by hybridization with 1 nM 5'-18T-3' and incubation with 1 microL of SG, the solution fluorescence gave a linear response (R=0.996) to the concentration of Hg(2+). The detection limit for Hg(2+) was 0.5 nM (0.1 ppb). The overall test only takes few minutes and very little interference is observed from non-specific metal ions. This approach may find potential applications in monitoring the Hg(2+) concentration in drinking water.     

Aluminum toxicity studies in Vaucheria longicaulis var. macounii (Xanthophyta, Tribophyceae). II. Effects on the F-actin array

In this study, we test the hypothesis that exposure to environmentally significant concentrations of aluminum (Al, 80 μM) causes the microfilament array of Vaucheria longicaulis var. macounii vegetative filaments to become fragmented and disorganized. Changes in F-actin organization following treatment of vegetative filaments by Al are examined using vital staining with fluorescein phalloidin. In the cortical cytoplasm of the apical zone of pH 7.5 and pH 4.5 control cells, axially aligned bundles of F-actin lead to a region of diffuse, brightly stained material. Dimly stained focal masses are noted deeper in the cytoplasm of the apical zone whereas they are absent from the zone of vacuolation. The F-actin array is visualized in the cortical cytoplasm of the region of the cell, distal to the apical tip, which exhibits vigorous cytoplasmic streaming (zone of vacuolation) as long, axially aligned bundles with which chloroplasts and mitochondria associate. Thirty minutes following treatment with aluminum, and for the next 8-16 h, the F-actin array is progressively disorganized. The longitudinally aligned F-actin array becomes fragmented. Aggregates of F-actin, such as short rods, amorphous and stellate F-actin focal masses, curved F-actin bundles and F-actin rings replace the control array. Each of these structures may occur in association with chloroplasts or independently with no apparent association with organelles. Images are recorded which indicate that F-actin rings not associated with organelles may self-assemble by successive bundling of F-actin fragments. The fragmentation and bundling of F-actin in cells of V. longicaulis upon treatment with aluminum resembles those reported after diverse forms of cell disturbance and supports the hypothesis that aluminum-induced changes in the F-actin array may be a calcium-mediated response to stress.     

The role of chemical speciation,chemical fractionation and calcium disruption in manganese-induced developmental toxicity in zebrafish (Danio rerio) embryos

Manganese (Mn) is an essential nutrient that can be toxic in excess concentrations, especially during early development stages. The mechanisms of Mn toxicity is still unclear, and little information is available regarding the role of Mn speciation and fractionation in toxicology. We aimed to investigate the toxic effects of several chemical forms of Mn in embryos of Danio rerio exposed during different development stages, between 2 and 122 h post fertilization. We found a stage-specific increase of lethality associated with hatching and removal of the chorion. Mn(II), ([Mn(H₂O)₆]²⁺) appeared to be the most toxic species to embryos exposed for 48 h, and Mn(II) citrate was most toxic to embryos exposed for 72 and/or 120 h. Manganese toxicity was associated with calcium disruption, manganese speciation and metal fractionation, including bioaccumulation in tissue, granule fractions, organelles and denaturated proteins.     

Toxic effects of mercury(II), cadmium(II) and lead(II) porphyrins on Trypanosoma brucei brucei growth

The effects of free mercury(II), cadmium(II) and lead(II) ions and their metalloporphyrin-derivatives on Trypanosoma brucei brucei growth in culture were studied. All experiments were conducted in the dark. IC(50) values on growth obtained in 24-h time-course experiments were 1.5 x 10(-7), 2.4 x 10(-6), 4.4 x 10(-6) and 2.6 x 10(-5) M for mercury(II) porphyrin, cadmium(II) porphyrin, lead(II) porphyrin and free base porphyrin, respectively. While the IC50 values for Hg2+, Cd2+ and Pb2+ were 3.6 x 10(-6), 1.5 x 10(-5) and 1.6 x 10(-5) M, respectively. These results clearly indicate that the toxicity of the metalloporphyrin complexes of mercury(II), cadmium(II) and lead(II) to T. b. brucei parasites was much higher compared to their free metal ions and free base porphyrin at low concentrations. It was also observed after 8 h incubation that the metalloporphyrins were effective in inhibiting the division of the parasites at concentrations >1.25 x 10(-7) M for mercury(II) porphyrin, concentrations >1.2 x 10(-6) M for cadmium(II) and lead(II) porphyrins and at concentrations >3.6 x 10(-6) M for Hg2+ ion. These observations were not detected in samples treated with the free metal ions and the free base porphyrin at the same concentrations. Interestingly, trypanosomes treated with metalloporphyrin complexes displayed different morphological features from those cells treated with free base porphyrin or metal ions. The chemotherapeutic potential of the metalloporphyrins of H2TMPyP for treatment of African trypanosomiasis is discussed.     

The aggregative stability of human oxyhemoglobin in aqueous media in the presence of mercury(II) compounds]

It was shown that the mechanism regulating the oxyhemoglobin coagulation in presence of a mercury reagent in large amount differs from that in presence of the reagent in relatively small concentrations. The significance of a large class of ligands at mercury atom during the oxyhemoglobin coagulation was demonstrated. Several theoretical generalizations are drawn.     

The aggregative stability of human oxyhemoglobin in aqueous media in the presence of mercury(II) compounds]

The results are discussed of studies on oxyhemoglobin coagulation in neutral phosphate buffer and acidic acetate buffer at pH ranging from 5.85 to 4.90. Peculiarities are shown of the effect of strong complexon on the oxyhemoglobin-coagulum-mercuric acetate system in neutral tris-buffer. Coagulation characteristics are cited for polymeric oxyhemoglobin in presence of mercury ions.     

The aggregative stability of human oxyhemoglobin in aqueous media in the presence of mercury(II) compounds]

An analytical review of studies on human oxyhemoglobin coagulation has been performed by the author jointly with V. S. Koniaeva and L. D. Bogdanova within a period from 1985 to 1990. It was shown that the oxyhemoglobin coagulation modified by mercurials proceeded without any essential alteration of native protein conformation. A hypothesis is discussed that the oxyhemoglobin coagulation results from the primary polyaggregation of dimer fragments and that hydrophobic sites which provide for dimer-to-dimer contacts in native tetrameric oxyhemoglobin, participate in this process.     

Chemical speciation of ternary complexes of L-dopa and 1,10-phenanthroline with Co(II), Ni(II) and Cu(II) in low dielectric media

Abstract

A computer assisted pH-metric investigation has been carried out on the speciation of complexes of Co(II), Ni(II) and Cu(II) with L-dopa and 1,10-phenanthroline. The titrations were performed in the presence of different relative concentrations (M:L:X = 1.0:2.5:2.5; 1.0:2.5:5.0; 1.0:5.0:2.5) of metal (M) to L-dopa (L) and 1,10-phenanthroline (X) with sodium hydroxide in varying concentrations (0-60% v/v) of 1,2-propanediol-water mixtures at an ionic strength of 0.16 mol L^-1 and at a temperature of 303.0 K. Stability constants of the ternary complexes were refined using MINIQUAD75. The species MLXH, MLX, ML₂X and MLX₂H for Co(II) and Cu(II) and MLXH, MLX and MLX₂H for Ni(II) were detected. The extra stability of ternary complexes compared to their binary complexes was believed to be due to electrostatic interactions of the side chains of ligands, charge neutralisation, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositions of 1, 2-propanediol-water mixtures and plausible equilibria for the formation of species were also presented. The bioavailability of the metal ions is explained based on the speciation.     

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.     

Synthesis, chemical speciation and SOD mimic assays of tricarballylic acid-copper(II) and imidazole-tricarballylic acid-copper(II) complexes

The coordination behavior of copper(II) with tricarballylic acid (H₃TCA) and imidazole (Imz) is described. Speciation in aqueous solution has been determined at 25 °C and 0.15 M NaCl ionic strength by potentiometric measurements and EPR characterization of the species. Two new compounds CuTCAH · 3H₂O and CuTCAHImz · 2H₂O were obtained and characterized by elemental analysis diffuse reflectance, FTIR (Fourier transform infrared spectroscopy), EPR and thermal behavior. Their in vitro superoxide dismutase-mimetic activities have been tested.     

Effect of sediment elutriate on the chemical composition of Gymnodinium sp. (Dinophyceae). II.

Abstract

The chemical composition of Gymnodinium sp. was studied in cells grown in batch cultures with sediment elutriate, enriched or unenriched with F/2 as the culture medium. The cellular protein, chlorophyll a, nitrogen, carbon and phosphorus content were determined in conjunction with cell density. For the enriched media, a high density of biomass was always measured; differences in cellular composition between control and elutriate cells were not observed and the atomic C:N:P ratios were typical of unstarved phytoplankton. Unenriched media produced different effects on the algal growth, which also affected the biochemical composition of the cells. Relative to the control, some elutriates reduced the algal growth, affected the chemical composition of the cells which showed very high levels of carbon, nitrogen and protein, and resulted in an aberrant morphology. The stimulating growth elutriate affected the chemical composition of the cell in another manner: the greatest effect was a decrease of carbon content, whereas the other compounds remained similar to the control; aberrant forms were not observed.     

Computer simulation of Zn(II) speciation and effect of Gd(III) on Zn(II) speciation in human blood plasma

The speciation and distribution of Zn(II) and the effect of Gd(III) on Zn(II) speciation in human blood plasma were studied by computer simulation. The results show that, in normal blood plasma, the most predominant species of Zn(II) are [Zn(HSA)] (58.2%), [Zn(IgG)](20.1%), [Zn(Tf)] (10.4%), ternary complexes of [Zn(Cit)(Cys)] (6.6%) and of [Zn(Cys)(His)H] (1.6%), and the binary complex of [Zn(Cys)₂H] (1.2%). When zinc is deficient, the distribution of Zn(II) species is similar to that in normal blood plasma. Then, the distribution changes with increasing zinc(II) total concentration. Overloading Zn(II) is initially mainly bound to human serum albumin (HSA). As the available amount of HSA is exceeded, phosphate metal and carbonate metal species are established. Gd(III) entering human blood plasma predominantly competes for phosphate and carbonate to form precipitate species. However, Zn(II) complexes with phosphate and carbonate are negligible in normal blood plasma, so Gd(III) only have a little effect on zinc(II) species in human blood plasma at a concentration above 1.0×10⁻⁴ M.