Search

A strain of Klebsiella oxytoca DSM 29614 is grown on sodium citrate in the presence of 50 mg l−1 of Hg as Hg(NO3)2. During growth, the strain produces an extracellular polymeric substance (EPS), constituted by a mixture of proteins and a specific exopolysaccharide. The protein components, derived from the outer membrane of cells, are co-extracted with the extracellular exopolysaccharide using ethanol. The extracted EPS contains 7.5% of Hg (total amount). This indicates that EPS is an excellent material for the biosorption of Hg2+, through chemical complexation with the EPS components. The binding capacity of these species towards Hg2+ is studied by cyclic voltammetry, and Hg L3-edge XANES and EXAFS spectroscopy. The results found indicate that Hg2+ is mainly bound to the nitrogen of the imidazole ring or other N-heterocycle compounds. The hydroxyl moities of sugars and/or the carboxyl groups of two glucuronic acids in the polysaccharide can also play an important role in sequestring Hg2+ ions. However, N-heterocyclic groups of proteins bind Hg2+ faster than hydroxyl and carboxyl groups of the polysaccharide.

The PCBs are known recalcitrant and toxic pollutants and significant values of contamination could be found in water. PCBs can be hydrodechlorinated using Pd-based catalysts and hydrogen, but the research to identify more efficient heterogeneous catalysts, able to work in an aqueous phase, less sensible to deactivation and easily removable at the end of the treatment, remains a considerable interesting goal. A strain of Klebsiella oxytoca, DSM 29614, known to produce a specific exopolysaccaride (EPS), was grown in different media with sodium citrate or with sodium citrate plus ferric citrate, as sole energy and carbon sources under anaerobic conditions. The cultures were amended with 50 mg of palladium as Pd(NO3)2 to generate Pd-EPS (Pd content 13%) or FePd-EPS (Pd content 8.4%; Fe 7.4%) species which were secreted from the cells, isolated by treatment with a cold ethanol solution (70%) and dried under vacuum as powders. The catalytic ability of these mono- and bi-metallic species was tested in the hydrodechlorination reaction of the Aroclor 1260 PCBs mixture under aqueous biphasic conditions. Here we demonstrate that the degree of PCBs hydrodechlorination is dependent by the nature of catalyst and of base used to neutralize HCl produced, the bimetallic species being more active and an organic base resulting more effective. Working with a substrate/catalyst 8/1 molar ratio, at 3 MPa H2 and 60°C in 20 h a significant removal of highly chl orinated PCBs was obtained under the best conditions. The result seems promising for remediation of groundwater contaminated with PCBs.

A closed chlor-alkali plant (CAP) discharged Hg for decades into the Aussa River, which flows into Marano Lagoon, resulting in the large-scale pollution of the lagoon. In order to get information on the role of bacteria as detoxifying agents, analyses of anions togetherwith the determination of total Hg (Hg-T) and methylmercury (MeHg) in the superficial part (0-1 cm) of sediments were conducted at four stations in the Aussa River. In addition,measurements of biopolymeric carbon (BPC) as a sum of the carbon equivalent of proteins (PRT), lipids (LIP), and carbohydrates (CHO) were performed to correlate with bacterial biomass such as the number of aerobic heterotrophic cultivable bacteria and their percentage of Hg-resistant bacteria. All these parameters were used to assess the bioavailable Hg fraction in sediments and the potential detoxification activity of bacteria. In addition, fifteen isolates were characterized by a combination of molecular techniques, which permitted their assignment into six different genera. Four out of fifteen were Gram negative with two strains of Stenotrophomonas maltophilia, one Enterobacter sp., and one strain of Brevibacterium frigoritolerans. The remaining strains (11) were Gram positive belonging to the genera Bacillus and Staphylococcus. We found merA genes in only a few isolates. Mercury volatilization from added HgCl2 and the presence of plasmids with the merA gene were also used to confirm Hg reductase activity. We found the highest number of aerobic heterotrophic Hg-resistant bacteria (one order magnitude higher) and the highest number of Hg-resistant species (11 species out of 15) at the confluence of the River Aussa and Banduzzi’s channel, which transport Hg from the CAP, suggesting that Hg is strongly detoxified [reduced to Hg(0)] at this location.

During primary colonization of rock substrates by plants, mineral weathering is strongly accelerated under plant roots, but little is known on how it affects soil ecosystem development before plant establishment. Here we show that rock mineral weathering mediated by chemolithoautotrophic bacteria is associated to plant community formation in sites recently released by permanent glacier ice cover in the Midtre Lovénbreen glacier moraine (78 degrees 53'N), Svalbard. Increased soil fertility fosters growth of prokaryotes and plants at the boundary between sites of intense bacterial mediated chemolithotrophic iron-sulfur oxidation and pH decrease, and the common moraine substrate where carbon and nitrogen are fixed by cyanobacteria. Microbial iron oxidizing activity determines acidity and corresponding fertility gradients, where water retention, cation exchange capacity and nutrient availability are increased. This fertilization is enabled by abundant mineral nutrients and reduced forms of iron and sulfur in pyrite minerals within a conglomerate type of moraine rock. Such an interaction between microorganisms and moraine minerals determines a peculiar, not yet described model for soil genesis and plant ecosystem formation with potential past and present analogues in other harsh environments with similar geochemical settings.

The role of sulfur species in the formation and stability of mucus aggregates in the Adriatic Sea was studied. Natural aggregates were compared with a mixed diatom culture. A sample from the sea bottom collected from the northern Adriatic Sea was cultivated and transferred to f/2 medium to isolate benthic diatoms. Diatom cultures were incubated at room temperature and irradiated with dim light (30 to 40 mmol m-2 s-1). Subcultured samples were incubated at room temperature under anaerobic conditions for up to 1 mo, with different concentrations of sulfide (10-4 and 10-3 mol l-1). In diatom cultures, interactions between sulfide and organic matter were investigated and followed for 10 d through: (1) formation of organosulfur species ; (2) changes in surfactant activity and (3) degradation of pennate diatoms followed by cell lysis and release of large amount of polysaccharides. A large increase in dissolved organic carbon (DOC) concentration was recorded in the ambient water of the sulfide-treated samples. A DOC concentration of 7.17 mg l-1 was determined in the ambient water of untreated diatom cultures increasing to 40 mg l-1 in sulfide-treated samples. Simultaneously, in the same sulfide-treated samples (both ambient water and aggregates of enriched diatom cultures), surfactant activity was observed to increase by 2 orders of magnitude. The concentration of surface-active substances (SAS, expressed as Triton-X-100 conc.) increased from 0.35 mg l-1 in the aggregate and 0.59 mg l-1 in the ambient water of the untreated diatom cultures to 20 mg l-1 in sulfide-incubated samples. Epifluorescence microscopy observations showed that diatoms decomposed under sulfide treatment and released a large amount of polysaccharides, as revealed by a specific molecular probe for glucose and mannose, i.e. Con-A lectin conjugated by fluorescein. These comparative experiments indicated that one of the factors triggering mucilage formation in the Adriatic Sea could be massive diatom lysis in bottom or anoxic microzones where, due to microbial activity, reduced sulfur species are prominent and have an important role in the formation and stability of mucilage development.

An iron-poor stream of nearly neutral pH polluted by mine tailings has been investigated for a natural phenomenon responsible for the polishing of heavy metals in mine wastewaters. A white mineralized mat, which was determined to be hydrozincite [Zn5(CO3)2(OH)6] by X-ray diffraction analysis, was observed in the stream sediments mainly in spring. The precipitate shows a total organic matter residue of 10% dry weight and contains high concentrations of Pb, Cd, Ni, Cu, and other metals. Scanning electron microscopy analysis suggests that hydrozincite is mainly of biological origin. Dormant photosynthetic microorganisms have been retrieved from 1-year-old dry hydrozincite. The autofluorescent microorganisms were imaged by a scanning confocal laser microscope. A photosynthetic filamentous bacterium, classified as Scytonema sp. strain ING-1, was found associated with microalga Chlorella sp. strain SA1. This microbial community is responsible for the natural polishing of heavy metals in the water stream by coprecipitation with hydrozincite. Abandoned mines present a high environmental hazard in all countries today. In several parts of the world where mining activities have shut down, the problem of the control and reclamation of polluted areas for new activities arises. The polishing of metals from a mining area is a difficult task. The transformation of metals into harmless species or their removal in a suitable recycled mineral form such as carbonates (1, 15) is a possible solution for the remediation of a mining area. Therefore, research in this field continues, with the isolation of new strains with more-successful mechanisms for the reduction of metal toxicity. At Ingurtosu (southwestern Sardinia, Italy) lead and zinc sulfide ore deposits were mined until 1968 and tailings were deposited along the Rio Naracauli creek. The MontevecchioIngurtosu deposit consists of galena-sphalerite veins in a quartz gangue containing iron, calcium, and magnesium carbonate minerals. Pyrite, chalcopyrite, barite, cerussite, and anglesite are the most commonly associated minerals (22). Previous studies in this area have shown that waters are highly polluted by heavy metals, in spite of their near-neutral pH (4‐6, 30).

One hundred six strains of aerobic bacteria were isolated from the Fiora River which drains an area of cinnabar deposits in southern Tuscany, Italy. Thirty-seven of the strains grew on an agar medium containing 10μg/ml Hg (as HgCl2) with all of these strains producing elemental mercury. Seven of the 37 strains also degraded methylmercury. None of 106 sensitive and resistant strains produced detectable monomethylmercury although 15 strains produced a benzene-soluble mercury species. Two strains of alkylmercury (methyl-, ethyl- and phenylmercury) degrading bacteria were tested for the ability to degrade several other analogous organometals and organic compounds, but no activity was detected toward these compounds. Mercury methylation is not a mechanism of Hg resistance in aerobic bacteria from this environment. Growth of bacteria on the agar medium containing 10μg/ml HgCl2 was diagnostic for Hg detoxification based on reduction.

The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.

The terrestrial biogeochemical cycle of mercury between humus and fungi was investigated in a mercury-contaminated former mining area of Germany. We used a variable volume extraction procedure and aqueous sodium boron tetraethyl derivatization to determine accurately and precisely methylmercury bioconcentration factors for fungi. The methylmercury and total mercury content for fungi carpophores ranged from 0.08 to 7.94 μg/g of Hg as methylmercury and from 6.2 to 144.0 μg/g of inorganic Hg, respectively. The levels in humus material were between 0.01 and 0.09 μg/g of Hg as methylmercury and 15.8 and 140.2 μg/g of inorganic Hg, respectively. The bioconcentration factors obtained are generally lower than 1 for total mercury and between 3.0 and 199.0 for methylmercury. By an in vitro methylation experiment with two axenic cultures of Coprinus comatus and Coprinus radians, we could show for the first time that these saprophytic macromycetes are able to methyl ate mercury.

The bioindex percentage of element-resistant microorganisms is suggested to study airborne pollution near geothermal plants. A new method of determining the percentage of element-resistant bacteria is described. The index was calculated as the percentage ratio of the metal-resistant colony-forming units grown on agar plates to the whole cultivable eterotrophic colony forming units. Element resistance was regarded as the ability of bacteria to grow on media amended with high concentrations of toxic compounds: HgCl2 (10 μg/ml), NaAsO2 (750 μg/ml) and H3BO3 (1000 μg/ml). Available elements induced activity of the element-resistance in epiphytic bacteria. The mosses from which the bacteria were isolated were collected in winter from two different areas near Siena: ten sites in the geothermal area around Radicondoli and five sites in an unpolluted part of the Chianti region. Percentages of element-resistant bacteria were found to be directly correlated with concentrations of acid-leachable mercury, arsenic and boron. The percentages of mercury- and arsenic-resistant bacteria were significantly higher in the geothermal area, especially in the GEO-6 station. High concentrations of leachable boron were found in the geothermal area and in a wooded patch surrounded by vinyards in the Chianti region. Boron-resistant bacteria responded only to boron from geothermal emissions.

In this work, gold microelectrodes are employed as traps for the detection of volatilized metallic mercury produced by mercuric reductase (MerA) extracted from an Hg-resistant Pseudomonas putida strain FB1. The enzymatic reduction of Hg (II) to Hg (0) was induced by NADPH cofactor added to the samples. The amount of Hg(0) accumulated on the gold microelectrode surface was determined by anodic stripping voltammetry (ASV) after transferring the gold microelectrode in an aqueous solution containing 0.1 M HNO(3) + 1 M KNO(3). Electrochemical measurements were combined with spectrofluorometric assays of NADPH consumption to derive an analytical expression for the detection of a relative MerA activity of different samples with respect to that of P. putida. The method developed here was employed for the rapid determination of MerA produced by bacteria harbored in soft tissues of clams (Ruditapes philippinarum), collected in high Hg polluted sediments of Northern Adriatic Sea in Italy.

A sensitive and specific technique, gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR), has been used to detect traces of methane from the biodegradation of methylmercury due to the detoxification process of Pseudomonas putida strain FB1, which was isolated from cinnabar mines in southern Tuscany (Italy). The cured strain FB4 was used together with uninoculated samples as controls for the experiment. The calibration curve of methane was linear up to 1.3 ..mu..g/mL when 0.3 mL of headspace was injected into the GC/FTIR. The detection limit of methane determination in the closed system was 10 ng/mL. The biodegradation of methylmercury was measured during the 130-min experiment by means of elemental mercury analysis, which was determined specifically in the headspace by atomic absorption spectroscopy (AAS), by methylmercury analysis, and by consideration also of the growth rate of the bacterial strains.

The kinetics of pyrite oxidation by Metallosphaera sedula were investigated with mineral pyrite and two coals with moderate (Pittsburgh no. 8) and high (New Brunswick, Canada) pyritic sulfur content. M. sedula oxidized mineral pyrite at a greater rate than did another thermophile, Acidianus brierleyi , or a mesophile, Thiobacillus ferrooxidans . Maximum rates of coal depyritization were also greater with M. sedula , although the magnitude of biological stimulation above abiotic rates was notably less than with mineral pyrite. Coal depyritization appears to be limited by the oxidation of pyrite with ferric ions and not by the rate of biotic oxidation of ferrous iron, as evidenced by the maintenance of a high ratio of ferric to ferrous iron in solution by M. sedula . Significant precipitation of hydronium jarosite at elevated temperature occurred only with New Brunswick coal.

The hydroxylation of phenol with aqueous H2O2 to afford catechol and hydroquinone was studied in a biphasic reaction medium, as well as in pure water, in the presence of a bio-generated iron(III) catalyst. This catalyst was purified from a culture of Klebsiella oxytoca BAS-10 growing under anaerobic conditions, with Fe(III)-citrate as the energy and carbon source. The overproduction of an exopolymer (EPS) encrusted bacterial cells. The EPS, binding Fe3+, (Fe-EPS), was extracted and studied before and after a reaction with phenol. Some of the reaction’s parameters, such as temperature, pH, and molar ratio between reagents and catalyst, were investigated to identify the best compromise between conversion and selectivity. The results could be useful either from a synthetic point of view or to support the biodegradation of aromatic substrates.

We report a novel aqueous derivatization of methylmercury chloride by NaBH 4 to mehtymercury hydride (CH 3 HgH), a volatile and unexpectedly stable species which we determined has a half-life of approximately 2 h. The analytical apparatus consisted of a purge and trap (PT) unit linked to a gas chromatograph (GC), in line with a Fourier transform infrared spectrometer (FTIR). The sample was purged with nitrogen, and volatile compounds were concentrated in a cold trap

Bacteria are resistant to Hg compounds by virtue of two specific enzymes: mercuric reductase and organomercurial lyase. We investigate these specific enzyme systems 1) to determine McHg in biological samples by its enzymatic transformation to the respective hydrocarbon and 2) as an environmental index of Hg pollution in geothermal areas, by studying the distribution of the percentage of Hg-resistant bacteria. The first application is based on the enzymatic conversion of McHg to CH4. by whole cells of the Pseudomonas putida strain FBI. A 1 ml aliquot of 0.01N aqueous solution of thiosulphate containing MeHg, extracted from a biological sample by a conventional procedure was mixed with a dense (1 mg cells/mL dw) culture of FBI strain in a microreaction vessel. After a suitable period of incubation (from 4 to 18 hours), methane was assayed in the headspace by gas chromatograph equipped with flame ionization detector. In the second application, Hg-resistant bacteria (MRB) isolated from mosses collected in a geothermal area (Travale) in Tuscany showed almost the same distribution pattern as total Hg in briophytes. Mosses and MRB are both suitable bioindicators for mapping contaminated areas. The finding of Hg-resistant strains depends on the availability of the metal for cell accumulation and interaction at molecular level in the cytoplasm to produce mercuric reductase. MRB/g dw is therefore an indirect measure of the enzyme in this terrestrial geothermal environment.

A new method is suggested for determining methylmercury in biological samples. The determination is based on the use of whole cells of a broad-spectrum mercury-resistant bacterium, Pseudomonas putida, strain FB1, which is induced to produce the enzymes organomercurial lyase and mercuric reductase. These biocatalysts convert organomercurials to elemental mercury and their derivative hydrocarbons. The extraction procedure for methylmercury in biological samples follows the conventional toluene extraction method, which is retained until methylmercury is concentrated in an aqueous phase containing 0.01 M Na{sub 2}S{sub 2}O{sub 3}. This solution is mixed with bacterial cells in exponential growth phase and then incubated in microreaction vessels. A complete biological degradation of methylmercury to methane occurs. The efficiency of derivatization depends on the organomercurial concentration, the incubation time, and the cell density. The detection limit is 15 ng of methylmercury in 1 g of biological tissue and the coefficient of variation is 1.9% in 10 replicate samples with 100 ng/mL.

This study reports the assessment of a novel process combining sequential treatments of a historically contaminated soil from the ACNA site (Cengio, Savona, Italy), a decommissioned industrial area. The soil was leached with 0.5 M citric acid leading to a removal of metals in the following order: Pb (74.2%) > Cu (72.6%) > Zn (40.2%) > Ni (55.7%) > Cd (41.5%) > Cr > (21.7%) Co > (19%) Fe (8.2%) with a concomitant low removal of organic contaminants (12%). The leachate was then incubated with the metal-resistant Klebsiella oxytoca strain BAS-10, capable of using residual citrate to produce an iron gel that co-precipitated metals. Concomitantly, the leached solid waste was bioaugmented with the autochthonous isolate of Allescheriella sp. DABAC 1 leading to a complete degradation of several organic contaminants, including trichlorobenzene, naphtalene, dichloroaniline and pentachloroaniline. The overall removals of organic contaminants by the fungus were 44.3% and 63.8% in non-leached and leached soil.

Contaminated soil from a historical industrial site and containing sulfide ore ashes and aromatic hydrocarbons underwent sequential leaching by 0.5 M citrate and microbial treatments. Heavy metals leaching was with the following efficiency scale: Cu (58.7%) > Pb (55.1%) > Zn (44.5%) > Cd (42.9%) > Cr (26.4%) > Ni (17.7%) > Co (14.0%) > As (12.4%) > Fe (5.3%) > Hg (1.1%) and was accompanied by concomitant removal of organic contaminants (about 13%). Leached metals were concentrated into an iron gel, produced during ferric citrate fermentation by the metal-resistant strain BAS-10 of Klebsiella oxytoca. Concomitantly, the acidic leached soil was bioaugmented with Allescheriella sp. DABAC 1, Stachybotrys sp. DABAC 3, Phlebia sp. DABAC 9, Pleurotus pulmonarius CBS 664.97, and Botryosphaeria rhodina DABAC P82. B. rhodina was most effective, leading to a significant depletion of the most abundant contaminants, including 7-H-benz[DE]anthracene-7-one, 9,10-anthracene dione and dichloroaniline isomers, and to a marked detoxification as assessed by the mortality test with the Collembola Folsomia candida Willem. The overall degradation activities of B. rhodina and P. pulmonarius appeared to be significantly enhanced by the preliminary metal removal.

A sediment sample from Venice Lagoon was found to be contaminated with 475 mg Kg(-1) polycyclic aromatic hydrocarbons (PAHs). Naphthalene was the principal pollutant at 26% of total PAHs. Two strains of Pseudomonas SN1 and SB1 were isolated from sediment amended with 2% naphthalene. 16S rRNA gene sequence analysis indicated that the two strains have about 99% nucleotide identity with strains of the genus Pseudomonas, and are very Close to Pseudomonas stutzeri. Their metabolic profiles showed significant nutritional differences, the most significant of which was that SN1 grows in marine mineral medium spiked with naphthalene and SB1 grows with biphenyl as sole carbon and energy sources. Pseudomonas sp. SN1 had a doubling time of 3.1 h with 2% naphthalene and SB1 had a doubling time of 19.5 h with 2% biphenyl. Strain SN1 oxidised naphthalene at 564 32 mg O-2 l(-1) d(-1) and SB1 oxidised biphenyl at 426 25 mg O-2 l(-1) d(-1) in respirometry reaction vessels under controlled conditions. Screening of the two strains for dioxygenase genes involved in the first step of the two hydrocarbon degradation pathways, by polymerase chain reaction, showed naphthalene dioxygenase in SN1 and biphenyl dioxygenase in SB1. The strains each have a different catechol 2,3-dioxygenase responsible for cleavage of the aromatic ring. (c) 2006 Elsevier Ltd. All rights reserved.

A sensor responsive to Hg2+ (pDL20) was constructed by fusing part of a narrow spectrum mer operon, including its regulatory elements, to promoterless lux genes. This was compared with another mer::lux fusion (pRB28) in order to estimate the available Hg in moss, a conventional bioindicator used for surveying Hg pollution in terrestrial environments. Hg(II) was measured as the relative luminescence unit (RLU) emitted by E. coli cells carrying either pRB28 or pDL20. The linearity ranges of standard curves were measured by spiking HgCl2 at different nanomole levels in a phosphate buffered solution (PBS). The level of correlation between RLU and spiked HgCl2 depended on the incubation time of E. coli cells: the correlation factors (R2) of the regression lines were highly significant only after 150 min of incubation. pDL20 detected Hg(II) concentrations in the linear range between 0.05 nM and 0.5 nM and was approximately 27 times more sensitive than pRB28. The latter was less sensitive and showed a different range of linearity, from 20 nM to 200 nM. Measurements of bioavailable Hg were performed in buffered solutions leached from moss. Concentrations of Hg(II) were determined by external standard addition of HgCl2. pDL20 was found to be more reliable than pRB28 in the estimation of very low concentrations of bioavailable Hg (II). Both sensors were unable to determine Hg(0) emitted by geothermal activities.

Massive mucilage events occur in the Northern Adriatic Sea presumably by cytoplasmic excretions from deteriorated diatoms. During three such events in the summer of 1991, 1997 and 1998 the presence of reduced sulfur species (RSS) was determined in samples of macroaggregate using electrochemical methods (in-phase alternating current (AC) and linear sweep voltammetry). The detected levels of sulfur, expressed as equivalent to sulfide concentrations, were about 200 nM. In the same mucilage samples, concentrations of organic matter were determined in the range from 60 to 600 mg/l of total organic carbon (TOC). The physico-chemical properties of organic matter in the macroaggregates correspond to those of polysaccharides of very high molecular mass. Scanning confocal laser microscopy (SCLM) and fluorescent molecular probes for sugars (the lectins concanvaline A (Con-A)) showed the transformation of polysaccharide polymer structure resulting in the formation of very stable filaments and layers after the treatment of mucilage samples with sodium sulfide. Commercial polysaccharides of bacterial and algal origin (xanthan, carrageenans types I and II, dextran-T-500) have been used to simulate macroaggregate formation under laboratory conditions after treatment with sodium sulfide. Raman spectroscopy indicated that for all model polysaccharides used, sulfide interaction occurred, as evidenced by visible change of the O–H stretching region in the vibration spectra of the water molecules. Our data suggest that the aggregated polysaccharides from the Adriatic Sea are: (1) structurally affected by addition of sulfide as was the case for most of the model polysaccharides, and (2) the stabilizing effect of sulfide on the aggregated polysaccharides is due to the formation of sulfur-organic compounds.

Beneficial and detoxifying mechanisms in microorganisms are described in relation to their potential exploitation for metal and radionuclide bioremediation. Metal toxicity and essentiality are amphibolous aspects of metals in regards to their homeostatic and non homeostatic metabolism. Metals are energy sources, electron acceptors, and are essential for secondary metabolism Metals are effluxed by specific systems to reduce cytoplasmic content to subtoxic levels. Metals may be converted to harmless species by specific enzymes and by the intermediates or final products of microbiological metabolism. In certain circumstances metals are precipitated as colloids, or crystals may be formed; conversely they may be removed by bioleaching, or volatilized by methylation and hydriditization. Most of these microbiological processes can be exploited to reduce metal and radionuclide contamination. Various technologies ranging from different bioreactor configurations to in situ operations have been developed An attempt of radionuclide bioremediation in situ of soil at Chernobyl, Ukraine, is described.

The transformation of MeHg under anaerobic conditions in axenic cultures of Desulfovibrio desulfuricans strain LS is compared to that in anoxic marine sediments contaminated by Hg of industrial origin. MeHg was added to cultures of D. desulfuricans strain LS and incubated at 28°C for two weeks. Significant amounts of dimethylmercury and metacinnabar were produced. These two Hg compounds were formed from the slow decomposition of the intermediate dimethylmercury-sulfide. Other collateral compounds, such as methane and ionic Hg, were also detected during the MeHg degradation process. On the other hand a sample of fresh sediment (1.5 g d.w.) was spiked with 10 μg of MeHg and 2 mmoles.ml−1 of pyruvate, as carbon source for sulfate-reducing bacteria. After 9 days of incubation at 28°C, significant amounts of dimethylmercury were produced. A lower content of this volatile species was found in a sub-sample of sediment supplemented with sodium molybdate, which is a strong inhibitor of sulfate-reducing activity. A kinetic study showed the disappearance of monomethylmercury from the sediment and the formation of dimethylmercury over the incubation period. The environmental significance of dimethylmercury and dimethylmercury-sulfide in the natural biogeochemical cycle of Hg is discussed.

Several mercury‐resistant bacteria were isolated from sites in Italy that surrounded natural mercury deposits. Bacterial strains resistant to 5 mg mercuric chloride per liter reduced Hg2+ to elemental mercury by an inducible process. One bacterial strain was resistant to methylmercuric chloride and produced elemental mercury when incubated with several organomercurial compounds. No methylmercury was detected in bacterial cultures growing in the presence of 2 mg mercuric chloride per liter. Mercury reduction is the major mercury transformation in mercury‐resistant bacteria isolated from these environments.

One-hundred-ninety-five specimens of higher fungi and their substrata collected in the Hg mining area of M. Amiata and around Siena (Central Italy), were analyzed for their total Hg content. Whereas wood decomposers and many species of mycorrhizal fungi accumulated the metal at a very low rate, some mycorrhizal species and all the humus decomposers may accumulate up to 100 ..mu..g.g/sup -1/ d.w. of Hg and in the least contaminated sites, up to 63 times as much Hg as the substratum. Instead in mineralized areas the concentration factor rarely exceeded 1. The methyl mercury content of 35 species (almost all edible), ranged between 0.01 and 3.7 ..mu..g.g/sup -1/ d.w. The possible significance of these findings and the toxicologic implications for local consumers are considered.

Three sediment cores were sampled from the continental shelf of the Tyrrhenian Sea close to two areas contaminated by mercury from two different sources: the cinnabar deposits of southern Tuscany, and the outlet of a chlor-alkali plant at Rosignano Solvay (Livorno). The accumulation of mercury in marine sediment cores is influenced mainly by the high carbonate content of both natural and industrial origin. The grain-size of sediment particles plays an important role in the distribution of mercury in one core (CB 7), in which the highest concentration is associated with the coarse fraction, indicating that the abundance of organic matter in sediment, except at the top of of the lack of variability in the abundance of organic matter in the sediment, except at the top of the core, its influence on mercury distribution could not be determined. We have tentatively calculated the sedimentation rate (0.82 cm year −1 ) in one core (RO 14) by means of the peaks of the carbonates and mercury concentrations combined with data supplied by the chemical company. The results show that in both areas over the last decade mercury concentrations have decreased significantly.

Samples of soils and mosses were collected near a geothermal power plant, which is located in one of the most active geothermal fields of the world (Southern Tuscany). High concentrations of Hg (up to 1.8 μg g−1 d.w.) occur in mosses as far as 0.6 km from the geothermal plant, and the Hg uptake of mosses is unrelated to the species except for Bryum torquescens. The Hg in the soil was lower than in mosses, and the greatest concentrations in soil were near the Travale-22 well, which feeds the most powerful geothermal plant (30 MW) in the area. In addition, the concentrations of Hg detected in soil cores and in old bottom leaves of several specimens of Hypnum cupressiforme show that this element has been emitted into the air also in the past probably since the discovery of T-22 well in 1972.

This paper investigates mercury contamination in recent marine sediment of the Tyrrhenian continental shelf near the mouths of three rivers draining an area with cinnabar deposits (M. Amiata, Italy). By means of chemical leaching, two fractions of the total mercury were distinguished: a ‘non-leachable’ fraction, consisting of mercury held in relatively stable forms and a ‘leachable’ fraction, composed of forms that are more weakly bound to the sediments. The two Hg fractions are correlated to the organic matter content, the distribution of which is strictly dependent on the sediment surface area. In order to eliminate the effects of grain size variations among the samples, the Hg concentrations were normalized to the unit of surface area (ng/m2). Following this procedure, the ‘non-leachable’ Hg was found to be concentrated mostly in a belt along the coast, while the ‘leachable’ Hg fraction was shown to accumulate largely in the zones with high depositional dynamics near the mouths of the rivers. Hypotheses to account for the discrepancy between the low concentrations of ‘leachable’ Hg in the sediment of the outer continental shelf and the high concentrations in the fauna of the same area, reported in previous papers, are presented.

Marine surficial sediments, intertidal molluscs and reed leaves collected in the Bay of Follonica are slightly contaminated by Pb, Ni, Zn and Fe. The main pollution sources are the waste water and the atmospheric emission of industrial plants. Probably, the weathering of the pyrite deposits along the eastern coast of Elba Island and adsorption and coprecipitation with hydrous Fe-Mn oxides increase the trace metal concentrations in sediments from the Piombino Channel. Mussels and limpets are contaminated by Hg because of the higher background level of the northern Tyrrhenian Sea.