Transformation of vanadinite [Pb5(VO4)3Cl] by fungi

Saprotrophic fungi were investigated for their bioweathering effects on the vanadium‐ and lead‐containing insoluble apatite group mineral, vanadinite [Pb₅(VO₄)₃Cl]. Despite the insolubility of vanadinite, fungi exerted both biochemical and biophysical effects on the mineral including etching, penetration and formation of new biominerals. Lead oxalate was precipitated by Aspergillus niger during bioleaching of natural and synthetic vanadinite. Some calcium oxalate monohydrate (whewellite) was formed with natural vanadinite because of the presence of associated ankerite [Ca(Fe²⁺,Mg)(CO₃)₂]. Aspergillus niger also precipitated lead oxalate during growth in the presence of lead carbonate, vanadium(V) oxide and ammonium metavanadate, while abiotic tests confirmed the efficacy of oxalic acid in solubilizing vanadinite and precipitating lead as oxalate. Geochemical modelling confirmed the complexity of vanadium speciation, and the significant effect of oxalate. Oxalate–vanadium complexes markedly reduced the vanadinite stability field, with cationic lead(II) and lead oxalate also occurring. In all treatments and geochemical simulations, no other lead vanadate, or vanadium minerals were detected. This research highlights the importance of oxalate in vanadinite bioweathering and suggests a general fungal transformation of lead‐containing apatite group minerals (e.g. vanadinite, pyromorphite, mimetite) by this mechanism. The findings are also relevant to remedial treatments for lead/vanadium contamination, and novel approaches for vanadium recovery.     

Biosorption of lead phosphates by lead-tolerant bacteria as a mechanism for lead immobilization

The study of metal-tolerant bacteria is important for bioremediation of contaminated environments and development of green technologies for material synthesis due to their potential to transform toxic metal ions into less toxic compounds by mechanisms such as reduction, oxidation and/or sequestration. In this study, we report the isolation of seven lead-tolerant bacteria from a metal-contaminated site at Zacatecas, México. The bacteria were identified as members of the Staphylococcus and Bacillus genera by microscopic, biochemical and 16S rDNA analyses. Minimal inhibitory concentration of these isolates was established between 4.5 and 7.0 mM of Pb(NO₃)₂ in solid and 1.0–4.0 mM of Pb(NO₃)₂ in liquid media. A quantitative analysis of the lead associated to bacterial biomass in growing cultures, revealed that the percentage of lead associated to biomass was between 1 and 37% in the PbT isolates. A mechanism of complexation/biosorption of lead ions as inorganic phosphates (lead hydroxyapatite and pyromorphite) in bacterial biomass, was determined by Fourier transform infrared spectroscopy and X-ray diffraction analyses. Thus, the ability of the lead-tolerant isolates to transform lead ions into stable and highly insoluble lead minerals make them potentially useful for immobilization of lead in mining waste.     

Transformation of galena to pyromorphite produces bioavailable sulfur for neutrophilic chemoautotrophy

The aqueous concentration of lead [Pb(II)] in geochemical environments is controlled by the solubility of Pb‐bearing minerals and their weathering products. In contaminated soils, a common method for in situ stabilization of Pb(II) is the addition of phosphate to convert more redox sensitive sulfide minerals into sparingly soluble pyromorphite [Pb₅(PO₄)₃X]. In this study, we conducted experimental studies to investigate the fate of reduced sulfur during the conversion of galena [PbS] to chloropyromorphite [Pb₅(PO₄)₃Cl]. Powder X‐ray diffraction analysis indicated that the reaction of phosphate with galena under oxic conditions resulted in the oxidation of sulfide and formation of elemental sulfur [S₈]. Under oxic abiotic conditions, the S₈ was retained in the solid phase, and negligible concentrations of sulfur as sulfide and thiosulfate were detected in the aqueous phase and only a small amount of sulfate. When PbS reacted in the presence of the chemoautotrophic organism Bosea sp. WAO, the S₈ in the secondary mineral was oxidized to sulfate. Strain WAO produced significantly more sulfate from the secondary S₈ than from the primary galena. Microscopic analysis of mineral–microbe aggregates on mineral‐embedded slide cultures showed that the organism was colocalized and increased in biomass over time on the secondary mineral surface supporting a microbial role. The results of this study indicate that stimulation of sulfur‐oxidizing activity may be a direct consequence of phosphate amendments to Pb(II)‐contaminated soils.     

Zinc Phosphate and Pyromorphite Solubilization by Soil Plant-Symbiotic Fungi

Acidolysis, complexolysis and metal accumulation were involved in solubilization of zinc phosphate and pyromorphite by a selection of soil fungi representing ericoid and ectomycorrhizal plant symbionts and an endophytic/entomopathogenic fungus, Beauveria caledonica. Zinc phosphate was much more readily solubilized than pyromorphite. According to the relationship between metal mobilization and pH, acidolysis (protonation) was found to be the major mechanism of both zinc phosphate and pyromorphite dissolution for most of the fungi examined. In general, the more metal tolerant fungal strains yielded more biomass, acidified the medium more and dissolved more of the metal mineral than less tolerant strains. However, B. caledonica 4 excreted a substantial amount of oxalic acid (～ 0.8 mM) in the presence of pyromorphite that coincided with a dramatic increase in lead mobilization providing a clear example of complexolysis. Organic acid excretion by fungi was inter- and intraspecific and was strongly influenced by the presence of the toxic metal minerals. When grown on zinc phosphate or pyromorphite, Hymenoscyphus ericae DGC3(UZ) accumulated the lowest metal concentration, but Thelephora terrestris accumulated the highest metal concentration in the biomass. The ability to accumulate water-soluble lead species, representing mainly cytosolic and vacuolar pools, seemed to be connected with pyromorphite-solubilizing ability. B. caledonica 4, which demonstrated the highest ability to dissolve pyromorphite, accumulated the highest water-soluble fraction and total lead concentration in the mycelium. Generally, isolates with a higher zinc-tolerance accumulated significantly less total zinc from zinc phosphate (including the sum of water-soluble and NaCl-extractable zinc) than non-tolerant strains.     

Interaction of lead ions with bovine carbonic anhydrase: further studies

Lead-substituted bovine carbonic anhydrase is investigated and the return to the holoenzyme form with exchange of Pb²⁺ by Zn²⁺ is followed by uv difference spectroscopy and by esterase activity methods. Equimolar amounts of Pb²⁺ added to apocarbonic anhydrase release one hydronium ion per molecule below pH 6. Above this pH there is a net gain of hydronium ions by the enzyme, due to Pb(OH)⁺ → Pb(OH₂)^{2 +}, when the metal is bound within the active site of the enzyme molecule. The reduced hydrolysis by lead when it is bound to the enzyme is relevant to the theory of Zn²⁺ hydrolysis as a mechanism for carbon dioxide hydration by the holoenzyme and to the idea of an altered pK_hydrolysis when Zn²⁺ is bound in the enzyme active site cavity. Lead appears to be bound to a His residue in the active site and to interact with a Tyr residue nearby. The Tyr interaction is disrupted by a high concentration of chloride ions, (also by lower concentrations of cyanide ions), but such anions do not displace lead from the enzyme. At pH 8.0 the buffer-free exchange of Pb²⁺ by Zn²⁺ is found to be consistent with a second-order process with an effective β = (95 ± 7) M^?1 sec^?1. Thus lead is more rapidly replaced by zinc than is Mn²⁺ or VO²⁺ whose replacement kinetics have been reported by others. Comparison of esterase-activation and spectral curves with second-order models shows that the effective β is both large and buffer dependent, indicating that a proton transfer process or buffer anion effects may be rate limiting in the buffer-free case.     

Assessment of lead speciation by organic ligands using speciation models

Abstract

The biogeochemical behaviour of lead (Pb) in ecosystems greatly depends on its chemical species. Organic ligands strongly influence Pb species and mobility in soil solution. In the present study, two metal speciation models, Windermere Humic Aqueous Model (WHAM) and Visual Minteq are used to compute Pb speciation in nutrient solution in the presence and absence of organic ligands. The three organic ligands used include ethylenediamine tetraacetic acid (EDTA), citric acid (CA) and fulvic acid (FA). The results show that in the absence of organic ligands, Pb²⁺ is the dominant form under acidic conditions and Pb–OH under alkaline conditions. The presence of organic ligands strongly influences Pb speciation. EDTA is more effective than are CA and FA concerning its influence on Pb speciation due to high Pb binding capacity. The results also indicate that Pb binding capacity of organic ligands varies with solution pH.     

Metal-induced inhibition of anaerobic metabolism of volatile fatty acids and hydrogen

The effects of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb) and zinc (Zn) on the biotransformation of organic acids (acetate, propionate and butyrate) and H₂ were assessed in serum-bottle microcosms. Experiments were performed over a range of metal concentrations (20–200 mg/1) using biomass from an anaerobic bioreactor fed continuously with ethanol distillery waste as inoculum. In general, the added metals inhibited the biotransformation of organic acids with increasing metal concentration. However, the extent of inhibition varied for the different biotransformations and for the different metals tested. For example, the concentration of CuCl₂ effecting a 50% reduction in the rate constant for biotransformation of acetate, propionate and butyrate was 60, 75 and 30 mg/1, respectively. Cu and Cr (VI) were the most inhibitory metals in organic acid transformation, whereas Pb was the least toxic. The rate of biotransformation of acetate was reduced by half at Cu and Cr concentrations of 60 and 40 gm/1 respectively, whereas Cd, Pb, and Zn concentrations of 160 to 200 mg/l had little effect. The activities of hydrogenotrophic methanogens were much less affected by the same metals and metal concentrations.     

Removal of lead(II) by Saccharomyces cerevisiae AUMC 3875

The removal of lead(II) from artificial aqueous solution using live and dead biomass of Saccharomyces cerevisiae AUMC 3875 was investigated. The minimum inhibitory concentration (MIC) value of S. cerevisiae AUMC 3875 for lead(II) was 600 mg/l. For live and dead biomass, maximum lead(II) uptake capacities were achieved at pH?5.0, initial metal ion concentration 300 mg/l, and biomass dosage 3 g/l. Maximum biosorption capacities were reached after 3 h and 20 min for live and dead cells, respectively. Fourier Transform Infrared spectroscopy (FTIR) results revealed the important role of C?=?O,? OH,? NH, protein amide II band, $ \mathrm{PO}_2^{-} $ , mannans, sulphur and sulphur-oxygen compounds in lead(II) uptake. Scanning electron microscopy analysis (SEM) showed that the cell surface morphology and surface area/volume ratio changed greatly after lead(II) uptake. Transmission electron microscopy analysis (TEM) confirmed the involvement of both extracellular adsorption and intracellular penetration through the cell wall. X-ray powder diffraction (XRD) analysis revealed the presence of Pb(SO₄),Pb₂OSO₄ by dead biomass and Pb₃O₂(SO₄),Pb₂OSO₄ by live biomass. Energy dispersive X-ray microanalysis (EDAX) confirmed the occurrence of sulphur, oxygen and lead(II) on the cell wall. The removal of lead(II) from storage battery industry wastewater was performed by dead biomass efficiently.     

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb_total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56?mg Pb?ha^?1 for TML and 222?kg Pb?ha^?1 for Pb_total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb_total (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall?+?litterfall fluxes, amounted to 3.7?mg Pb?ha^?1 year^?1 for TML and 52?g Pb?ha^?1 year^?1 for Pb_total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb_total in wet precipitation were: fog?>?throughfall?>?bulk precipitation. The annual fluxes with runoff from the catchment was 0.5?mg Pb?ha^?1 year^?1 for TML and 2.8?g Pb?ha^?1 year^?1 for Pb_total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t) of 33.5 days. The degradation of TML in Fen (t?=?421 days) and in the mineral soil (Bw-C horizon, t?=?612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen?>?Oa?>?A?≥?Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb_total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pb_total. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.     

Biosorption of heavy metal ions by brown seaweeds from southern coast of Korea

Heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, Cu²⁺, and Cr₂O₇ ^2?) were biosorbed by brown seaweeds (Hizikia fusiformis, Laminaria japonica, and Undaria pinnatifida) collected from the southern coast of South Korea. The biosorption of heavy metal ions was pH-dependent showing a minimum absorption at pH 2 and a maximum biosorption at pH 4 (Pb²⁺, Cd²⁺, Mn²⁺, and Cr₂O₇ ^2?) or pH 6 (Cu²⁺). Biosorption increased most noticeably for pH changes from 2 to 3. In the latter pH range, biosorption increased, because a higher pH decreased the electrostatic repulsion between metal ions and functional groups on the seaweed. In the pH range of 2 ～ 4, biosorption of negatively-charged chromium species (Cr₂O₇ ^?2) followed the pattern of positively-charged metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺). This suggests that the most prevalent chromium species were positively-charged Cr³⁺, reduced from Cr⁶⁺ in Cr₂O₇ ^?2. Whereas positively-charged heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) reached a plateau after the maximum level, biosorption of chromium ions decreased noticeably between pH 5 and 8. Kinetic data showed that biosorption by brown seaweed occurred rapidly during the first 10 min, and most of the heavy metals were bound to the seaweed within 30 min. Equilibrium adsorption data for a lead ion could fit well in the Langmuir and Freundlich isotherm models with regression coefficients (R ²) between 0.93 and 0.98.     

The naturally trans-acting ribozyme RNase P RNA has leadzyme properties

Divalent metal ions promote hydrolysis of RNA backbones generating 5′OH and 2′;3′P as cleavage products. In these reactions, the neighboring 2′OH act as the nucleophile. RNA catalyzed reactions also require divalent metal ions and a number of different metal ions function in RNA mediated cleavage of RNA. In one case, the LZV leadzyme, it was shown that this catalytic RNA requires lead for catalysis. So far, none of the naturally isolated ribozymes have been demonstrated to use lead to activate the nucleophile. Here we provide evidence that RNase P RNA, a naturally trans-acting ribozyme, has leadzyme properties. But, in contrast to LZV RNA, RNase P RNA mediated cleavage promoted by Pb²⁺ results in 5′ phosphate and 3′OH as cleavage products. Based on our findings, we infer that Pb²⁺ activates H₂O to act as the nucleophile and we identified residues both in the substrate and RNase P RNA that most likely influenced the positioning of Pb²⁺ at the cleavage site. Our data suggest that Pb²⁺ can promote cleavage of RNA by activating either an inner sphere H₂O or a neighboring 2′OH to act as nucleophile.     

Lead toxicity and phosphate deficiency in chlamydomonas

The addition of lead salts to phosphate-containing Chlamydomonas reinhardtii media caused precipitation of Pb₃(PO₄)₂, effectively removing phosphate from solution. The effect of Pb²⁺ on growth of Chlamydomonas in liquid cultures depended strictly on the ratio of the equivalents of Pb²⁺ to phosphate present. When the amount of Pb²⁺ approached equivalency with phosphate, cell growth was initially slow as cells adhered to the surface of the precipitated Pb₃(PO₄)₂. Later, cells grew at a normal rate, spread throughout the solution, and reached the same densities obtained in the absence of Pb²⁺. Cells did not survive when the amount of Pb²⁺ in the culture exceeded the equivalents of phosphate.

Elemental analysis showed that in the presence of equivalent Pb²⁺ and phosphate, considerable Pb²⁺ remained in solution. The concentration of dissolved Pb²⁺ did not vary significantly when the amount of Pb²⁺ added to the culture was increased slightly, from an amount which permitted growth to an amount which completely prevented growth. The concentration of phosphate was decreased to an undetectable level when the amount of Pb²⁺ approached equivalency with phosphate.

In the presence of the chelating agent nitrilotriacetic acid, higher concentrations of Pb²⁺ remained in phosphate-containing media. The chelated Pb²⁺ did not retard the growth of Chlamydomonas.

It appears that Pb²⁺ is not toxic to Chlamydomonas, but kills cells by depriving them of phosphate.

     

The effect of pre-incubation of Allium cepa L. roots in the ATH-rich extract on Pb uptake and localization

The positive influence of anthocyanin (ATH) on toxic metal-treated plant material is well documented; however, it is still not explained if it is caused by changes in element absorption and distribution. Therefore, detailed analysis of the effect of the ATH-rich extract from red cabbage leaves on Pb uptake and localization at morphological, anatomical and ultrastructural level was the goal of this study. Two-day-old adventitious roots of Allium cepa L. (cv. Polanowska) were treated for 2 h with the aqueous solution of Pb(NO₃)₂ at the concentration of 100 μM with or without preliminary incubation in the anthocyanin-rich extract from Brassica oleracea L. var. capitata rubra leaves (250 μM, 3 h). The red cabbage extract did not change the total Pb uptake but it enhanced the translocation of accumulated metal from roots to shoots. Within the pretreated roots, more Pb was deposited in their basal part and definitely smaller amount of the metal was bound in the apoplast of the outer layers of cortex cells. The ultrastructural analysis (transmission electron microscopy and X-ray microanalysis) revealed that the ATH-rich extract lowered the number of Pb deposits in intracellular spaces, cell wall and cytoplasm of root meristematic cells as well as in such organelles important to cell metabolism as mitochondria, plastids and nucleus. The Pb deposits were preferably localised in those vacuoles where ATH also occurred. This sequestration of Pb in vacuoles is probably responsible for reduction of metal cytotoxicity and consequently could lead to better plant growth.     

Uptake and accumulation of lead by roots,hypocotyls and shoots of Indian mustard [Brassica juncea (L.)]

The effects of different concentrations of lead nitrate on root, hypocotyl and shoot growth of Indian mustard (Brassica juncea var. Megarrhiza), and the uptake and accumulation of Pb²⁺ by its roots, hypocotyls and shoots were investigated in the present study. The concentrations of lead nitrate (Pb(NO₃)₂) used were in the range of 10⁻⁵–10⁻³ M. Root growth decreased progressively with increasing concentration of Pb²⁺ in solutions. The seedlings exposed to 10⁻³ M Pb exhibited substantial growth reduction and produced chlorosis. Brassica juncea has considerable ability to remove Pb from solutions and accumulate it. The Pb content in roots of B. juncea increased with increasing solution concentration of Pb²⁺. The amount of Pb in roots of plants treated with 10⁻⁴, 10⁻³ and 10⁻⁵ M Pb²⁺ were 184-, 37- and 6-fold, respectively, greater than that of roots of the control plant. However, the plants transported and concentrated only a small amount of Pb in their hypocotyls and shoots, except for the group treated with 10⁻³ M Pb²⁺.     

2D Holodirected lead(II) bromide coordination polymers constructed of rigid and flexible ligands

Three new 2D Pb^II coordination polymers containing 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethane (bpa) and 1,2-bis(4-pyridyl)ethene (bpe) with bromide anions, [Pb(μ-4,4′-bipy)(μ-Br)₂]_n (1), [Pb(μ-bpa)(μ-Br)₂]_n (2) and [Pb(μ-bpe)(μ-Br)₂]_n (3) have been synthesized and characterized by elemental analysis, IR spectroscopy and their structures studied by X-ray crystallography. The thermal stability of compounds 1-3 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single-crystal X-ray data shows that the Pb²⁺-ions have coordination numbers of six and contain the rarely holodirected geometries.     

Metal-phenoxyalkanoic acid interactions. Part 15. The crystal structures of diaquabis(phenoxyacetato)cadmium(II) and catena-μ-[aquabis(phenoxyacetato-O)lead(II)-bis(phenoxyacetato)lead(II)]

The crystal structures of the cadmium(II) and lead(II) complexes of phenoxyacetic acid (PAH) have been determined by single crystal X-ray diffraction techniques. The cadmium complex, [Cd(PA)₂(H₂O)₂] (1), space group C2, with Z = 2 in a cell of dimensions, a = 11.801(2), b = 5.484(1), c = 13.431(3) Å, β = 100.87(2)°, possesses a distorted trapezoidal bipyramidal coordination around the metal atom, involving two water oxygens [2.210(5) Å] and four carboxyl oxygens from two symmetrical bidentate phenoxyacetate ligands [2.363(4), 2.365(4) Å] with Cd lying on the crystallographic two- fold axis. The lead complex, [Pb₂(PA)₄(H₂O)]_n(2) is triclinic, space group P$\text{1}$, Z = 2, with a cell of dimensions, a = 10.135(4), b = 10.675(3), c = 19.285(9) Å, α = 114.66(3), β = 91.94(3) and γ = 114.99(3)°. (2) is a two-dimensional polymer with a repeating dimer sub-unit. The first lead [Pb(1)] has an irregular MO₈ coordination [2.34?2.96(2) Å: mean, 2.63(2) Å] involving the water molecule, two oxygens from an asymmetric bidentate carboxylate group, two from a bidentate chelate [O(ether), O(carboxylate)] group and three from bridging oxygens, one of which also provides a polymer link to another symmetry generated lead. The second lead [Pb(2)] is irregular seven-coordinate [PbO, 2.48?2.73(2) Å: mean, 2.61(2) Å] with three bonds from the bridging groups, two from an unsymmetrical bidentate carboxylate (O, O′) group and one from a second carboxyl group which also bridges two Pb(2) centres in the polymer.     

Channel CO2 in feldspathoids: New data and new perspectives

The study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paper we present new data on the volatile (particularly CO₂) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO₂ in their structure in addition to other molecular and anionic species such as H₂O, OH, F, Cl, SO₄, SO₃ etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO₂ at different temperatures, due to the different connectivity of their pores. Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere.      

Lead mineral transformation by fungi.

Pyromorphite (Pb5(PO4)3Cl), the most stable lead mineral under a wide range of geochemical conditions [1], can form in urban and industrially contaminated soils [2] [3] [4] [5]. It has been suggested that the low solubility of this mineral could reduce the bioavailability of lead, and several studies have advocated pyromorphite formation as a remediation technique for lead-contaminated land [3] [5] [6], if necessary using addition of phosphate [6]. Many microorganisms can, however, make insoluble soil phosphate bioavailable [7] [8] [9] [10], and the solubilisation of insoluble metal phosphates by free-living and symbiotic fungi has been reported [11] [12] [13] [14] [15]. If pyromorphite can be solubilised by microbial phosphate-solubilising mechanisms, the question arises of what would happen to the released lead. We have now clearly demonstrated that pyromorphite can be solubilised by organic-acid-producing fungi, for example Aspergillus niger, and that plants grown with pyromorphite as sole phosphorus source take up both phosphorus and lead. We have also discovered the production of lead oxalate dihydrate by A. niger during pyromorphite transformation, which is the first recorded biogenic formation of this mineral. These mechanisms of lead solubilisation, or its immobilisation as a novel lead oxalate, have significant implications for metal mobility and transfer to other environmental compartments and organisms. The importance of considering microbial processes when developing remediation techniques for toxic metals in soils is therefore emphasised.     

The Effect of Copper and Lead Ions on Growth and Lipid Composition of the Fern Matteuccia sthruthiopteris

In the present study, the effect of copper (Cu²⁺) and lead (Pb²⁺) ions on the growth and lipid composition of various parts of the fern, Matteuccia sthruthiopteris, was examined. Plants were incubated in the presence or absence of 1, 10, 100 μM of Cu(NO₃)₂ or Pb(NO₃)₂. Cu²⁺ and Pb²⁺ ions at concentrations of 1 and 10 μM caused an increased growth of the roots and leaves. A higher concentration of Pb²⁺ did not show any effect on growth, whereas that of Cu²⁺ slowed down the growth of the whole plants. The roots accumulated more than 700 μg of Cu²⁺ and 400 μg of Pb²⁺ per 1 g dry weight when the plants were incubated with the higher concentrations of metals, whereas in the leaves the concentration of Cu²⁺ was much lower and did not exceed 12 μg/g dry weight. No accumulation of Pb²⁺ ions by leaves was detected. The lipid composition of photosynthetic leave tissues was shown to be affected by the presence of metal ions in the root medium at either concentration studied. Various changes in lipid classes were noted as responsive reactions of M. sthruthiopteris to the heavy metal ions in nutrient medium. Cu²⁺ ions decreased the content of total lipids, total phospholipids, and individual phosphatidylcholines and phosphatidylethanolamines, whereas Pb²⁺ ions caused a decrease in the content of total lipids and glycolipids. Changes in the lipid composition were more pronounced in the mature leaves than in the scrolls of the studied fern.     

重金属铅与两种淡水藻的相互作用

为了研究重金属铅与淡水藻类之间的相互作用,采用不同Pb2+浓度处理铜绿微囊藻(Microcysis aeruginosa Kutz.)和斜生栅藻[Scenedesmus obliquus(Turp.)Kutz.],分别对两种藻的生物量、藻液电导率、O-·2含量、过氧化物酶(POD)、过氧化氢酶(CAT)活性以及藻对Pb2+的吸收作用等进行了测定,并通过扫描电镜观察了不同Pb2+浓度处理下两种藻细胞的表面结构。结果显示:(1)Pb2+浓度低于3 mg/L促进铜绿微囊藻生长,高于9 mg/L抑制其生长;但在3—12 mg/L范围内,Pb2+均明显抑制了斜生栅藻的生长,说明斜生栅藻对Pb2+毒性的敏感程度要高于铜绿微囊藻。(2)受到铅离子的胁迫,两种藻细胞膜通透性均有一定改变,扫描电子显微镜的照片观察,两种藻细胞表面的絮状物随着Pb2+的升高而增多,尤其是斜生栅藻细胞结构改变明显,多数细胞变形破裂;同时,O-·2含量升高,POD、CAT活性早期均可随Pb2+的增加而上升,表明氧自由基的产生增多以及由其引起的细胞生理生化改变可能是铅离子作用于藻细胞的主要机制。(3)两种淡水藻对Pb2+均有吸收作用,单位量藻细胞内,斜生栅藻对Pb2+的吸收能力好于铜绿微囊藻。所有结果提示:斜生栅藻不仅可以作为对重金属敏感的指示生物来监测水体Pb2+污染程度;同时由于斜生栅藻比铜绿微囊藻具有更好的Pb2+吸收能力,因此还可以利用斜生栅藻作为处理水体Pb2+的生物材料。