Fulvic acids: structure and metal binding

Equilibrium calculations have been carried out at 25°C and an ionic strength of 0.04 to determine the predominant metal binding sites on a well-characterized fulvic acid for magnesium(ll), calcium(ll), manganese(ll), iron(lll), copper(ll) and zinc(II). Statistical estimates of the concentration of 14 sites are obtained from a random molecular model of fulvic acid. Protonation and metal formation constants are estimated from those of simple model ligands and corrected to the above conditions. Results indicate the importance of phthalate sites for all metals except iron(III), salicylate sites for iron(lll) and acetylacetonate sites for copper(ll). Iron (III) ions are found to form ML₂ type complexes extensively. The affinity of the metal ions for fulvic acid as a whole is found to decrease in the order iron(III) > copper(II) > zinc(II) > manganese(Il) > calcium(II) > magnesium (II).     

Chemical Behavior of U(VI) in the Presence of Soil Components

Soil components from different environments (forest (OF), semiarid (SZ), and sand (AS)) were separated from fulvic and humic substances, characterized by DRX, EDS(SEM), and zero-charge points were determined. The sorption of U(VI) by these materials was determined considering contact time, concentration of U(VI), pH, ionic strength, and presence of sodium chloride and humic acids. The time to reach the kinetic sorption equilibrium was ca. 1 min for the components of the SZ and AS soils, whereas those from OF required longer times. The zero-charge points of the materials indicate that in the experimental conditions, the surfaces of the materials are positively charged, as are uranyl ions. The sorption kinetic data were well fitted to the pseudo-second-order model, which indicates chemical sorption. The maximum sorption capacities for U(VI) obtained from data fitted to the Langmuir model of OF and SZ were 49 and 19.8 mg g^?1 respectively. Sorption isotherm data for AS were best fitted to the Freundlich model (q_e?=?5.4 mg g^?1). The maximum values of distribution coefficients (K_d) were 23?±?7 L kg^?1, 545?±?64 L kg^?1, and 1178?±?229 L kg^?1 for AS, SZ, and OF, respectively; these values may depend on pH, contact time, initial concentration of U(VI), and the composition of the materials. Sodium chloride in the aqueous solutions affects U(VI) sorption by the materials SZ and AS. The effect of humic acids depends on pH, only in acid media soluble humate complexes may be formed.     

THE OCCURRENCE OF COPPER-PORPHYRIN COMPLEXES IN SOIL HUMIC ACIDS

Electron paramagnetic resonance (e.p.r.) spectroscopy has been used to show that humic acids, which were isolated from a range of soils and from which most of the iron was removed by boiling with hydrochloric acid, contain copper in the form of porphyrin complexes. The amounts of porphyrin-bound copper in the acid-boiled humic acids were estimated to be ≤ 20 mg/kg (equivalent to 0.05-0.9 mg/kg in the soils). The acid-boiled humic acids from cultivated mineral soils showed no great capacity for further uptake of copper as copper porphyrin when treated with CuSO₄, most of this additional copper being held by groups not involving N-donor groups. In contrast, copper treatment of the acid-boiled humic acid from a raised bog peat produced a large increase in copper-porphyrin signal strength, indicating that in the peat there are considerable amounts of porphyrin by which added copper could be complexed. It is suggested that porphyrin groups may be involved in the fixation of copper by organic matter in soils.     

Etude des diphenol oxydases extraites d'une litiere de foret

Study of diphenol oxidases extracted from beech litter. Lyophilized neutral sterile extract from the fermentation (F) layer of beech litter (NALF Extract) exhibited the chemical characteristics of humic acids. It possessed diphenol oxidase activities. The specific activities (sp. act.), given in parentheses, are expressed in nmoles O₂ absorbed mg C^?1 min^?1: p-crcsol (19.5); catechol (0.6); dl-3(3,4-dihydroxyphenyl)alanine (5.7); d(+) catechine (4.8) and p-phenylenediamine (7.1). The NALF Extract was polydispersed by G100 Sephadex column chromatography. The firsi peak kd ~ 0.05 (fraction I), the intermediate band (fractions II + III) and the second peak k_d ~ 1.02 and 1.38 (fractions IV + V). Diphenol oxidases were localized in fractions I, II and III. Electrophoretic studies have shown that the fractions I, II and III are heterogeneous. Chromatography on DEAE cellulose of fraction I permitted the separation of 30 per cent of the laccase activity in a form which is free from humic material.     

THE HUMIC ACIDS EXTRACTED BY VARIOUS REAGENTS FROM A SOIL

The infra-red, visible, and ultra-violet absorption spectra of humic acids extracted from a red-brown earth by various reagents, are described. The variations in the intensity of various absorption bands in the infra-red spectra are related to the method of extraction, yield, and titration data. For example, the humic acids extracted by milder reagents give rise to spectra which show relatively weak aliphatic C-H absorption whilst the intensity of the bands arising from oxygen-containing groups (carboxyl and ketone carbonyl) is relatively strong. The opposite behaviour is shown by the corresponding bands in the spectra of humic acids extracted by stronger reagents. The intensities of other infra-red bands are also considered. The optical density of the C═O band at 1720 cm^?1 in the humic-acid spectra and of the carboxylate ion band at 1380 cm^?1 in the spectra of the K salt is linearly related to the exchange capacity. The presence of carboxyl groups ionizing above pH 7 and extending to as high as pH 11, is demonstrated.     

Paramagnetic Properties of Humic Substances in Taiga and Tundra Soils of the European Northeast of Russia

The study of paramagnetic activity of humic substances in taiga and tundra soils of the Komi Republic and the assessment of the influence of soil hydromorphism on concentrations of free radicals in the structure of humic acids (HAs) and fulvic acids (FAs) have been performed. The concentration of free radicals in HA specimens was up to 11 times higher than that in FA specimens due to a higher content of aromatic and other condensed structures in HA molecules. This fact attests to the high capacity of HAs to polymerization and complexation reactions with participation of radicals. The average value of g-factor is higher for FA specimens than for HA specimens, which attests to a greater electron density shift of unpaired electron to oxygen atom in the structure of FAs because of its spin-orbital interaction with oxygen-containing functional groups, the concentrations of which are significantly higher in FAs than in HAs. An increase in the concentration of free radicals in the molecular structure of HAs is observed in taiga soils with an increase in the degree of their hydromorphism (from automorphic to semihydromorphic soils), which is related to the biohydrothermal conditions of humus formation in bog-podzolic soils with retarded biochemical processes and low degree of plant litter humification. As a result, HAs with the high content of free radicals in their structure are formed. An opposite situation is observed for HAs in tundra soils with a decrease in the content of unpaired electrons under conditions of the increased hydromorphism. The difference in the character of changes in the paramagnetic activity of HAs in taiga and tundra soils with different degrees of hydromorphism may be related to different natures of plant residues participating in humification processes. A tendency for a decrease in the paramagnetic activity in both HAs and FAs from the south to the north is observed, which may be related to a general decrease in the content of poly-conjugated systems in the structure of humic substances in tundra soils.     

Metal-Metal Interactions in Biological Systems. Part V. Steinernema Carpocapsae (Steinernematidae) and Heterorhabditis Bacteriophora (Heterorhabditidae) Entomopathogenic Nematodes

In spite of a lack of acute toxicity of single metal ions, in 96 hour laboratory tests there was a long term toxicity againstS. carpocapsae andH. bacteriophora nematodes. The 96 hour laboratory tests were carried out in order to prove possible synergistic and antagonistic interactions between pairs of metal ions. Thus, the pairs of ions were arranged from each of Al, Cd, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Li, Mo(VI), Ni(II), Sc(IV), V(V) and Zn on one side and Mn(II) and Mg on the other. Mn(II) and Mg ions considerably reduced the nematode mortality and increased their infectivity againstGalleria mellonella caterpillars.     

Copper(II) binding by free and kaolinite-sorbed humic substances

Humic preparations isolated from different sources—soils (a soddy-podzolic soil and a typical chernozem), high-moor peat, and brown coal—have been used. To analyze the binding of copper ions by humic substances (HSs), the preparations were obtained in two forms: solutions and humic-clay complexes (HSs irreversibly sorbed on kaolinite). With this approach, the binding of copper(II) ions by HSs has been studied in different systems: (1) Cu(II)-HSs irreversibly sorbed on kaolinite, (2) Cu(II)-dissolved HSs, and (3) Cu(II)-dissolved HSs-HSs irreversibly sorbed on kaolinite. In the systems containing both dissolved HSs and humic-clay complexes, HSs of similar structure isolated from the same source were used. The quantitative estimation of the copper binding was based on the constant of sorption (K) for HSs in humic-kaolinite complexes and the stability constant (β) of complexes for free (dissolved) substances. Both parameters were expressed in similar units: L/kg. The values of logK = 3.31—3.33 are independent of the quantity and quality of the HSs in the sorption complexes but reliably exceed the K value for pure kaolinite (2.92). The value of β is not affected by the presence of insoluble HSs together with their soluble forms, but it depends on the source of HSs. The value of logβ varies in the range from 5.62 to 6.93, which significantly exceeds K and indicates a significantly higher affinity of dissolved HSs for copper ions than that of irreversibly sorbed HSs. The revealed regularities have shown that the content of HSs in the soil solution can significantly affect the mobility of a heavy metal bound to the soil organic matter.     

复合氨基酸微量元素螯合肥制备工艺研究

以废弃鸡毛水解液为复合氨基酸来源,研究其与微量元素铁、锌、锰、铜螯合的最佳工艺条件,并利用有机溶剂沉淀分离法制备固体复合氨基酸亚铁、锌、锰、铜螯合物,以螯合率为指标考察影响制备工艺的主要因素。结果表明,最佳工艺参数为:复合氨基酸与亚铁、锌、锰和铜螯合反应的最佳配位体摩尔比均为2∶1;最佳pH值范围分别为5.0、8.0、4.0～5.0和6.0～7.0;反应温度为室温(222～6℃);反应时间为30.min。在上述条件下,复合氨基酸与各微量元素的螯合率均超过95%;所得复合氨基酸螯合物可与0.2.mol/L磷酸二氢钾复配,克服了传统微肥完全不能与磷酸盐复配的缺陷。     

Effect of Metal Ions on the Entomopathogenic Nematode Heterorhabditis Bacteriophora Poinar (Nematoda: Heterohabditidae) Under Laboratory Conditions

The effect of sixteen metal ions: Al, Cd, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Li, Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Se(IV), V(V), and Zn on the mortality and infectivity ofHeterorhabditis bacteriophora were observed over a 96 hr period. All ions except Pb(II) even at naturally unrealistic concentrations did not cause the mortality of the nematodes. A weak vitalizing effect could eventually be observed with Mn(II), Mg, Fe(III) and Ni(II) (Table 1). However, such treatment generally lowered infectivity of the nematodes with respect to wax moth caterpillars.Galleria mellonella. This effect was particularly significant with Ni(II) and Pb(II).     

Metal-metal interactions in biological systems. Part IV. Freshwater snail Bulinus globosus

The toxicity against title snails of all Al, Cd, Co(II), Cr(III), Cu(II), Fe (III), Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Se(VI), V(V) and Zn ions was checked in 96 h tests in the water of Kariba Lake. Based on the mortality — concentration relationship the toxicity order of the above ions against Bulinus globosus is Cu(II) > Ni(II) > Cd > Pb(II) > Zn > Al > V(V)> Cr(III)> Se(VI) > Fe(III) =Co(II)> Mn(II) > Mg > Mo(VI). Only Mg, Pb(II), Cu(II), Cd, Zn and Ni(II) ions are harmful to these snails as their mortality is observed at the naturally occuring concentrations. Other metal ions cause lethality at naturally unrealistic concentrations. The following pairs of metal ions were also checked for mutual interactions: Cd-Al, Cd-Co, Cd-Cr, Cd-Cu, Cd-Fe, Cd-Mg, Cd-Mn, Cd-Mo, Cd-Ni, Cd-Pb, Cd-Se, Cd-V, Cd-Zn, Cu-Al, Cu-Co, Cu-Cr, Cu-Fe, Cu-Mg, Cu-Mn, Cu-Mo, Cu-Ni, Cu-Pb, Cu-Se, Cu-V, Cu-Zn, Ni-Al, Ni-Co, Ni-Cr, Ni-Fe, Ni-Mg, Ni-Mn, Ni-Mo, Ni-Pb, Ni-Se, Ni-V, Ni-Zn, Pb-Al, Pb-Co, Pb-Cr, Pb-Fe, Pb-Mg, Pb-Mn, Pb-Mo, Pb-Se, Pb-V, Pb-Zn, Zn-Al, Zn-Co, Zn-Cr, Zn-Fe, Zn-Mg, Zn-Mn, Zn-Mo, Zn-Se, Zn-V. Synergism and antagonism were several times observed in various combinations of ions. The effect of metal-metal interactions on an accumulation of those metals in the flesh and shells of snails was also observed and measured.     

Effect of metal ions under laboratory conditions on the entomopathogenic Steinernema carpocapsae (Rhabditida: Steinernematidae)

The effects of sixteen metal ions: Al, Cd, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Li, Mg, Mn(H), Mo(VI), Ni(II), Pb(II), Se(IV), V(V), and Zn on the mortality and infectivity of Steinernema carpocapsae were observed in 96 hour laboratory tests. All ions except Cu(II), Pb(II), and Zn even at naturally unrealistic concentrations did not cause the mortality of S. carpocapsae. However, such treatment lowered infectivity of nematodes with respect to wax moth caterpillars, Galleria mellonella.     

The metal — Metal interactions in biological systems Part III. Daphnia magna

The toxicity of single metal ions: Al, Co(II), Cr(III), Cu(II), Fe(III), Mg, Mn(II), Mo(VI), Ni(II), Se(VI), V(V) and Zn and the following pairs of them: Al-Co, Al-Mg, Al-Mo, Al-Se, Al-Zn, Cr-Co, Cr-Mg, Cr-Mo, Cr-Se, Cr-Zn, Cu-Co, Cu-Mg, Cu-Mo, Cu-Se, Cu-Zn, Fe-Co, Fe-Mg, Fe-Mo, Fe-Se, Fe-Zn, Mn-Co, Mn-Mg, Mn-Mo, Mn-Se, Mn-Zn, Ni-Co, Ni-Mg, Ni-Mo, Ni-Se, Ni-Zn, V-Co, V-Mg, V-Mo, V-Se, V-Zn, Zn-Co, Zn-Mg, Zn-Mo, and Zn-Se on Daphnia magna was examined. The most prominent antagonism in the toxicity was observed in the following ion pairs: Al-Mo(VI), Cr(III)-Co(II), Cr(III)-Mg, Cr(III)-Mo(VI), Cr(III)-Se(VI), Cr(III)-Zn, Fe(III)-Se(VI), Mn(II)-Mg, Mn(II-Se(VI), Zn-Mg and Zn-Mo(VI). The strong synergism was found for the following ion systems: Cr(III)-Se(VI), Cr(III)-Zn, Fe(III)-Se(VI), Mn(II)-Zn, Mn(II)-Se(VI), Ni(II)-Co(II), Ni(II)-Mo(VI), Ni(II)-Se(VI), Ni(II)-Zn, V(V)-Co(II), V(V)-Mo(VI), V(V)- Se(VI), and V(V)-Zn. Synergism and antagonism in toxicity were dependent on water hardness as well as on the ion concentration. Adaptive procesess of the animals to the toxic environment could also be observed. Thus, the toxicity of the single ions and their pairs was not linear with respect to time.     

Comparison of thermal and chemical stability of Cu–humic complexes

Purpose

The purpose of this study was to investigate relationships between chemical and thermal stabilities of Cu–humic complexes. The study of the chemical stability was based on pedological methods used for the determination of the bond strength of metal ions in soils by chemical leaching agents. The samples with various contents of the Cu(II) ions and their bond strength were put to the thermal analysis in order to correlate their thermo-oxidative behavior with their stability determined by leaching.

Materials and methods

The humic acid was extracted from the South-Moravian lignite by standard alkaline extraction. The humic sample was used in two different forms: as the solid powder and as the hydrogel prepared by the acidic precipitation of humate. Six various concentrations of copper(II) solutions were used for the complexation of the humic powder and the hydrogel, in order to study the influence of their initial concentration on both the determined stabilities of the prepared complexes. Their chemical stability was assessed in terms of the Cu(II) ions release from the humic acid structure into two different extraction agents (MgCl₂ and HCl solutions). Their thermo-oxidative behavior was investigated employing the thermogravimetry.

Results and discussion

The complexation capacity of the humic hydrogel was higher in comparison with the humic powder. The amounts extractable from the Cu–humic complexes by the used leaching agents are higher for the humic powder, which shows on the lower chemical stability. The thermal degradation of the prepared complexes proceeds in several steps and this character remains also after the removal of the mobile and the ion-exchangeable fractions by the MgCl₂. The elimination of these fractions as well as the extraction of the strongly bound Cu(II) ions shift the thermal degradation to higher temperatures. The incombustible residue increases with the Cu(II) content in the complexes except for the samples extracted by the HCl.

Conclusions

The form of humic sample used for the preparation of the Cu–humic complexes influences both the chemical stability and the thermal one. The main reason is probably a better accessibility of the functional groups in the humic gel, which enables forming stronger binding copper(II) ions. The results showed that the thermal and chemical stabilities are closely related, which corresponds with the shift of the thermal degradation to higher temperatures after removing the less stable fractions from the humic complexes.     

The metal-metal interactions in biological systems Part II. Saccharomyces cerevisiae

The effect of eleven metal ions: Co(II), Cr(VI), Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Se(IV), Ti(III), V(IV) and Zn and several combinations of them were tested for their effect on the growth of Saccharomyces cerevisiae (Mautner). The effects depended on the metal and its concentration as well as in some cases on the duration of the experiment.     

豫中植烟土壤有效态微量元素与pH和有机质的关系

为探明豫中植烟土壤p H和有机质对微量元素有效态含量的影响，在豫中许昌市的建安、禹州、襄城和漯河市的城区、临颍和舞阳6个植烟县(区)采集了191个典型烟田耕层(0～20 cm)土样，测定了微量元素(有效铜、铁、锰、锌、钼)含量、p H和有机质含量，采用Pearson相关分析法与曲线回归方法分析了有效态微量元素含量与pH、有机质之间的关系。结果表明，有效铜、铁、锰、锌和钼的平均含量分别为1.20、49.24、84.80、1.71和0.02mg/kg，有效锰总体上充足，有效钼整体极为缺乏，个别样点有效铜、铁和锌缺乏；p H平均为7.90，总体上偏高；有机质平均为17.78g/kg，总体上适宜；微量元素有效态与pH、有机质之间均存在二次函数关系，随p H升高，有效铜呈增加趋势，有效铁和锌呈先升后降趋势，有效锰和钼呈先降后升趋势；随有机质升高，有效铜、锰、锌和钼呈增加趋势，有效铁呈先升后降的趋势。     

石灰岩土中微量元素的含量与分布

我国南方广西、贵州和云南省境内分布着大面积的石灰岩山地丘陵,在四川、湖北、湖南、江西、广东等省也有一定面积的石灰岩山丘地区.各地的石灰岩均为泥盆纪—三迭纪的沉积灰岩.     

An Experimental and Modelling Study of Cu2+ Binding on Humic Acids at Various Solution Conditions. Application of the NICA-Donnan Model

Humic substances are characterized by a strong binding capacity for both metals and organic pollutants, affecting their mobility and bioavailability. The understanding of the mechanisms of proton and metal binding to humic substances is of fundamental importance in geochemical modelling and prediction of cation speciation in the environment. This work reports results on copper binding on humic acids obtained through a thorough experimental and modelling approach. Two humic acids, a reference purified peat humic acid isolated by the International Humic Substances Society (IHSS) and a humic acid from a Greek soil, were experimentally studied at various pH values (4, 6 and 8), humic acid concentrations (ranging from 20 to 200 mg?L^?1) and ionic strength (0.1 and 0.01 M NaNO₃). The binding of copper to humic acids was determined over wide ranges of copper ion concentrations using a copper ion selective electrode. The copper binding isotherms obtained at different conditions have shown that copper binding is dependent on the pH and ionic strength of the solution and on the concentration of both humic acids. Copper binding experimental data were fitted to non-ideal competitive adsorption NICA-Donnan model and the model parameter values were calculated. Both Cu²⁺ and CuOH⁺ species binding to humic acid with different binding affinities were considered. Two sets of the NICA-Donnan parameters have been calculated: one for humic acid concentrations of ??100 mg?L^?1and one for humic acid concentration of 20 mg?L^?1. The meaning of the parameters values for each concentration level is also discussed.     

氧化/磺化腐殖酸对潮土中Cu、Zn、Fe、Mn有效性的影响

【目的】研究比较改性腐殖酸对潮土微量元素有效性的影响及其作用机理,以期为开发提高微量元素有效性的专用腐殖酸功能材料提供科学依据。【方法】采用土壤培养法,将腐殖酸 (HA)、氧化腐殖酸 (YHA) 和磺化腐殖酸 (SHA) 分别按30、100、300 mg/kg用量与干土混匀装入培养瓶中,调节含水量至田间持水量的60%,置于25℃人工气候箱中进行恒温培养,并保持土壤湿度恒定。分别在培养第3、7、15、30、60天取样,测定土壤有效铜、锌、铁、锰含量。【结果】三种腐殖酸对土壤Cu、Zn、Fe、Mn有效性的影响大小依次为HA>YHA>SHA。施用30～300 mg/kg 腐殖酸 (HA) 可显著提高土壤有效铜含量,特别是在15～30天内,土壤有效铜含量提升幅度可达51.3%,明显优于氧化腐殖酸和磺化腐殖酸;施用三种腐殖酸30～300 mg/kg可在15天内增加土壤有效锌含量,其中以腐殖酸 (HA) 效果最好,土壤有效锌含量增幅可达11.8%～20.3%,优于氧化腐殖酸、磺化腐殖酸;30～100 mg/kg用量下,施用腐殖酸 (HA) 可在15天内使土壤有效锰含量提升5.6%,效果优于氧化腐殖酸和磺化腐殖酸,300 mg/kg用量下,磺化腐殖酸可使土壤有效锰含量提升13.6%;施用30～300 mg/kg的腐殖酸 (HA) 一周后,土壤有效铁含量提高4.3%～7.2%,磺化腐殖酸或氧化腐殖酸用量分别在30 mg/kg和300 mg/kg时可提高土壤铁有效性。【结论】施用腐殖酸可显著提升潮土铜的有效性,但对潮土锌、锰、铁有效性的影响呈现出阶段性变化,不同结构腐殖酸对潮土微量元素有效性的影响差异较大,以HA对元素有效性的影响最大。因此,腐殖酸应用于提升微量元素有效性时,需考虑腐殖酸本身性质及施用时期等因素。