Humic Acid Complexes Research Articles

Complex-forming properties of peat humic acids from a raised bog profiles

Humic substances (HS) belong to the most powerful complex-forming agents, significantly affecting major and trace element speciation in natural environment. Several authors have focused on humic–metal interactions, using differing methods and comparing humic substances on different sources. However, the intrinsic differences among the HS of different origin and the impact of humification degree on the complex formation between humic substances and metals have not received the necessary attention until now.The aim of this study is to determine the Cu(II) complexing capacity and stability constants of Cu(II) complexes of humic acids (HA) isolated from two well-characterized raised bog peat profiles in respect to the basic properties and humification characteristics of the studied peats and their humic acids. Elemental and functional analysis of the isolated HA were determined by elemental composition (C, H, N, O), UV spectrophotometry, and the total acidity method, as well as the copper (Cu2+) ion selective electrode was used in complexing analysis of humic acids and metal ions.The complex stability constants are within the range of stability constants of the humic substances isolated from other sources (soil, coal, water, and peat). The complex stability constants significantly changed within the bog profiles and are well correlated with the age and the degree of peat decomposition.A comparison of the complex stability constant and the actual copper concentration in peat humic acids shows significant correlation, indicating the importance of tight metal binding for the actual presence of metal in peat and peat humic acids. None of the basic characteristics of humic acids (concentration of carboxylic groups and total acidity, hydrophobicity, etc.) alone can fully explain the complex-forming capacity of humic acids, which suggests a contribution of other factors that are yet to be determined.

DEPOSITION OF ORGANIC TRACE METAL COMPLEXES AS FEED ADDITIVES IN FARM ANIMALS

Trace elements are essentials for maintenance and production of farm animals, but most of the feedingstuffs do not contain adequate amount of most of them, therefore supplementation of complete feeds with trace elements is necessary. However, the rate of absorption and tissue deposition of trace elements from different complexes is also different which may have food safety aspects because of the maximum level of some trace minerals. The present review, based on scientifically proved data, discuss about the rate of absorption and deposition of different metal (Cu, Zn, Fe and Mn) proteinates, amino acid chelates (e.g lysine, methionine, methyl-hydroxy-methionine) and humic acid complexes of trace elements. The results showed that metal proteinates have higher rate of tissue accumulation as compared to inorganic salts, and additionally some metal-proteinates (e.g. copper-proteinate) also improves the tissue deposition of manganese. Metal propionates, as possible new trace element supplements have positive effects on the rate of absorption which was proved by the higher blood serum levels. In the case of humic acid chelates there are some data about their positive effect on bioavailability of trace minerals but those were not scientifically proven. In conclusion it can be stated that organic metal complexes have better bioavailability than their inorganic counterparts, in particular modern farm animal genotypes with higher requirement level and also in stress conditions.

Humic acid characteristics and effects on the reactivity of nano-scale zero-valent iron particles during nitrate reduction

ABSTRACT Humic acid (HA) comprises a significant fraction of natural organic matter (NOM), greatly influencing the performance of water and wastewater treatment processes. HA is expected to significantly affect the reactivity of nano-scale zero-valent iron (NZVI), which is receiving increasing attention due to its high reactivity. The effects of HA on nitrate reduction by NZVI were investigated to evaluate the potential of NZVI in practical applications. HA was characterized to identify the mechanism whereby HA affects. Nitrate reduction was enhanced at low HA concentration, but inhibited as HA concentration increased. HA decreased to reach a plateau and considerable amount of Fe3+ was detected when HA was present in dissolved phase. The increase in the degree of condensation of HA was verified by UV–vis spectroscopy, fluorescence spectroscopy, and size exclusion chromatography. Fourier transform infrared spectra confirmed that the Fe3+–HA complexes were formed in both the dissolved and solid fractions, without coexisting metal ions. The HA aggregation on NZVI and discrete HA macroaggregates were observed by transmission electron microscopy. The results suggest that HA induces complex effects on NZVI reactivity by improving iron dissolution, inhibiting readsorption of released iron, enhancing electron transfer, and inhibiting nitrate mass transfer via forming HA accumulation. It indicates that the clogging by aggregated NOM should be considered when NZVI is used for groundwater treatment or in combination with porous materials.

Changes in the Humic Acid–Metal Complexation Characteristics Depending on Humification Degree / Humīnskābju – Metālu Kompleksveidošanās Rakstura Izmaiņas Atkarībā No Humifikācijas Pakāpes

The aim of this study is to determine the Cu(II) complexing capacity and stability constants of Cu(II) complexes of humic acids isolated from two well-characterized raised bog peat profiles in respect to the basic properties and humification characteristics of the studied peats and their humic acids. The complex stability constants significantly change within the studied bog profiles and are well correlated with the age and decomposition degree of the peat layer from which the humic acids have been isolated. Among factors that influence this complexation process, molecular mass and ability to form micellar structures (supramolecules) of humic substances are of key importance.

Competitive ligand exchange between Cu–humic acid complexes and methanobactin

Copper has been found to play a key role in the physiology of methanotrophic micro-organisms, and methane oxidation may critically depend on the availability of Cu. In natural environments, such as soils, sediments, peat bogs, and surface waters, the presence of natural organic matter (NOM) can control the bioavailability of Cu by forming strong metal complexes. To promote Cu acquisition, methanotrophs exude methanobactin, a ligand known to have a high affinity for Cu. In this study, the capability of methanobactin for Cu acquisition from NOM was investigated using humic acid (HA) as a model substance. The kinetics of ligand exchange between Cu-HA and methanobactin was observed by UV-vis spectroscopy, and the speciation of Cu bound to methanobactin was determined by size-exclusion chromatography coupled to an ICP-MS. The results showed that Cu was mobilized from HA by a fast ligand exchange reaction following a second-order rate law with first-order kinetics for both methanobactin and Cu-HA complexes. The reaction rates decreased with decreasing temperature. Equilibrium experiments indicated that methanobactin was not sorbed to HA and proved that methanobactin is competitive with HA for Cu binding by forming strong 1:1 Cu-methanobactin complexes. Consequently, our results demonstrate that methanobactin can efficiently acquire Cu in organic-rich environments.

Coupled transport of humic acids and copper through saturated porous media

The mechanism of mediated transport of copper (Cu) by humic acids (HA) in pore water was studied taking account of colloid filtration theory and by means of breakthrough experiments of HA in water‐saturated columns filled with quartz sand. The influence of pH and Cu2+ concentration on Cu–HA binding and retention of Cu–HA complexes in the matrix were analysed with colloid‐surface attachment models. Experiments were performed for differing Cu concentrations (0–20 mg l−1) and pH (5–7). Copper binding to HA increased with pH and Cu2+ addition, according to ion–humic complexation theory. The zeta potential of the HA became less negative with increasing amounts of Cu, which led to less electrostatic repulsion and an increase in the retention of the HA in the column. A kinetic colloid transport model with a random sequential adsorption (RSA) blocking function was well fitted to the experimental breakthrough curves (BTCs). The model accounted for heterogeneity in the adsorption sites in the quartz sand for all of the electrochemical conditions. For pH = 7, the transport of Cu was coupled with the HA, while at pH = 5, the transport occurred mostly as free Cu2+. Models of the influence of dissolved soil organic matter and electrochemical conditions on the fate of trace elements in the soil may contribute to a quantitative exploration of strategies for soil remediation and disposal of contaminated soil containing excessive amounts of trace elements.

Effect of organic-complexed superphosphates on microbial biomass and microbial activity of soil

Organic complexed super-phosphates (CSPs) are formed by the complexation of humic acid (HA) with calcium monophosphate. The aim of this study was to determine whether two CSPs, characterized by different HA concentrations, added to a calcareous soil at an agronomic dose, were able to maintain the phosphorus (P) in a soluble form longer than the superphosphate fertilizer. Another important goal was to verify if CSP could positively influence soil microbial biomass and soil microbiological activities. Organic complexed super-phosphates were capable of keeping a large portion of P in a soluble form under different soil water conditions. In particular, the CSP with the highest organic C content was the most effective product, capable of maintaining, in an available form, the 73 % of the initially added P at the end of the experiment. In addition, it was the most effective in increasing C–CO2 soil emission, microbial biomass carbon (C) and nitrogen (N), fluoresceine diacetate hydrolysis and activities of alkaline phosphomonoesterase, β-glucosidase and urease. The addition of CSPs to soil probably produced a priming effect, increasing several times C–CO2 release by the treated soil. The significant correlation (p < 0.05) between C–CO2 emission and the amount of C added to soil by CSP suggests that the added HA acted as trigger molecules.

Studying arsenite–humic acid complexation using size exclusion chromatography–inductively coupled plasma mass spectrometry

Arsenic (As) can form complexes with dissolved organic matter (DOM), which affects the fate of arsenic in waste sites and natural environments. It remains a challenge to analyze DOM-bound As, in particular by using a direct chromatographic separation method. Size exclusion chromatography (SEC) hyphenated with UV spectrophotometer and inductively coupled plasma mass spectrometry (ICP-MS) was developed to characterize the complexation of arsenite (AsIII) with DOM. This SEC–UV-ICP-MS method is able to differentiate AsIII–DOM complexes from free As species and has the advantage of direct determination of both free and DOM-bound AsIII through mild separation. The suitability of this method for studying AsIII–DOM complexation was demonstrated by its application, in combination with the Scatchard plot and nonlinear regression of ligand binding model, for characterizing AsIII complexation with humic acid (HA) in the absence or presence of natural sand. The results suggest that, consistent with polyelectrolytic nature of HA, the AsIII–HA complexation should be accounted for by multiple classes of binding sites. By loosely classifying the binding sites into strong (S1) and weak (S2) sites, the apparent stability constants (Ks) of the resulting As–DOM complexes were calculated as logKs1=6.5–7.1 while logKs2=4.7–5.0.

Aluminium competitive effect on rare earth elements binding to humic acid

Competitive mechanisms between rare earth elements (REE) and aluminium for humic acid (HA) binding were investigated by combining laboratory experiments and modeling to evaluate the effect of Al on REE–HA complexation. Results indicates that Al3+ competes more efficiently with heavy REE (HREE) than with light REE (LREE) in acidic (pH=3) and low REE/HA concentration ratio conditions providing evidence for the Al high affinity for the few HA multidentate sites. Under higher pH – 5 to 6 – and high REE/HA conditions, Al is more competitive for LREE suggesting that Al is bound to HA carboxylic rather than phenolic sites. PHREEQC/Model VI Al–HA binding parameters were optimized to simulate precisely both Al binding to HA and Al competitive effect on REE binding to HA. REE–HA binding pattern is satisfactorily simulated for the whole experimental conditions by the ΔLK1A optimization (i.e. ΔLK1A controls the distribution width of logK around logKMA). The present study provides fundamental knowledge on Al binding mechanisms to HA. Aluminium competitive effect on other cations binding to HA depends clearly on its affinity for carboxylic, phenolic or chelate ligands, which is pH dependent. Under circumneutral pH such as in natural waters, Al should lead to LREE-depleted patterns since Al is expected to be bound to weak HA carboxylic groups. As deduced from the behavior of Al species, other potential competitor cations are expected to have their own competitive effect on REE–HA binding. Therefore, in order to reliably understand and model REE–HA patterns in natural waters, a precise knowledge of the exact behavior of the different REE competitor cations is required. Finally, this study highlights the ability of the REE to be used as a “speciation probe” to precisely describe cation interactions with HA as here evidenced for Al.

Thermodynamics of Equilibrium Adsorption of Antibiotics by Clay Minerals and Humic Acid–Clay Complexes

The sorption interaction of three widely used tetracycline antibiotics, tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC), has been determined at three different temperatures from dilute solutions of montmorillonite, humic acid and humic acid-montmorillonite complex saturated with Na+, Ca2+ and Al3+ cations using batch equilibrium technique. The presence of humic acid enhanced the adsorption of antibiotics while rise in temperature decreases the adsorption. Adsorption isotherms were of ‘L’ type. The adsorption of antibiotics was in the order OTC > CTC > TC. The adsorption was maximum for Al-saturated complexes and followed the order Al- > Na- > Ca. The standard free energy changes (ΔG0) for the adsorption reactions were negative, signifying a spontaneous reaction. The enthalpy changes (ΔH0) calculated from the temperature coefficient of the equilibrium constant showed that process is exothermic. The adsorption of tetracyclines on adsorbents give rise to an entropy loss as antibiotics molecules adsorbed on surface had fewer translational and rotational degrees of freedom than antibiotics molecules in solution. Various studies e.g. IR and X-ray, as well as thermodynamic parameters and Freundlich adsorption isotherms revealed the existence of protonation or coordination (or both) between exchangeable cation and oxygen of >C=O group of antibiotics. The values of thermodynamic parameters indicated towards a partial physical adsorption. Antibiotics present in soil/water in small amount encouraging the development of antibiotics resistant bacteria pose a threat to human health. The results of present study showed that antibiotics are more retained in soils which contain higher amount of humic acid. The sorption on motmorillonites was spontaneous, exothermic and depends on nature of tetracycline and cation. The values of thermodynamic parameters indicated a partial physical adsorption and partial chemisorption.

Structural Features and Fe(II)-Binding Capacities of Humic Acids from Reservoir Sediments

Reservoirs frequently require dredging to remove accumulated sediment. This sediment is currently unused, but represents a possible source of humic acids (HAs) that have potential as iron-binding supplements in fertilizers. In order to evaluate the utility of these materials, we investigated the structural features and Fe(II)-binding constants or capacities of some HAs obtained from reservoir sediments. The histidine content in the HAs was correlated to the Freundlich binding constant for an Fe(II)-HA complex, indicating that indole moieties in histidine function as strong binding sites for Fe(II). The binding capacities (2.2–3.2 mmol g−1) indicated that the HAs have the capacity to be loaded with 12–18% Fe(II), comparable to the iron content of previously reported Fe fertilizers that employ HAs from other sources (2–17%). The Fe(II)-binding capacities were positively correlated with the content of phenolic hydroxyl groups. In addition, the positive correlation between Fe(II)-binding capacity and vanillyl moieties in the HAs indicates that 3,4-dihydroxybenzene and/or benzoic acid derivatives also serve as Fe(II) binding sites.

Gel–water partitioning of soil humics in diffusive gradient in thin film (DGT) analysis of their metal complexes

Environmental contextMetal species can have significant toxic effects in aquatic systems, and therefore their occurrence should be reliably monitored. Although many methods to measure metal species are available, they all have limitations and are sensitive to physicochemical complications. It is shown that, in techniques based on diffusive gradients in thin films, sorption of humic acids affects metal speciation inside the diffusive gel layer and the nature of the ensuing flux response. AbstractMetal complexes of humic and fulvic acids are ubiquitous in aqueous environmental media. In metal speciation analysis by DGT (diffusive gradient in thin film) with polyacrylamide hydrogels, soil humic acid species have been shown to significantly accumulate in the diffusive gel layer. As a result, the speciation of their metal complexes inside the gel is changed with respect to that in the sample medium. In low ionic strength samples, the effects of sorption of the charged humic species are compounded by Donnan partitioning. Here we lay out the basic features that govern the partition of humic species between gel and water, and discuss their effect on the properties of the DGT metal flux.

Desorption of arsenic from clay and humic acid-coated clay by dissolved phosphate and silicate

Arsenic (As) contaminated aquifers contain iron minerals and clays that strongly bind As at their surfaces. It was suggested that As mobilization is driven by natural organic matter (including fulvic acids (FA) and humic acids (HA)) present in the aquifers either via providing reducing equivalents for reductive dissolution of Fe(III) (hydr)oxides or via competitive desorption of As from the mineral surfaces. In the present study we quantified sorption of As(III) and As(V) to Ca 2+-homoionized illite (IL) and to kaolinite (Kao) as well as to HA-coated clays, i.e., illite–HA (IL–HA) and kaolinite–HA (Kao–HA) at neutral pH. Clay–HA complexes sorbed 28–50% more As than clay-only systems upon addition of 100 μM As(III)/As(V) to 0.5 g of clay or HA–clay with Ca 2+ probably playing an important role for HA binding to the clay surface and As binding to the HA. When comparing sorption of As(V) and As(III) to clay and HA–clay complexes, As(V) sorption was generally higher by 15–32% than sorption of As(III) to the same complexes. IL and IL–HA sorbed 11–28% and 6–11% more As compared to Kao and Kao–HA, respectively. In a second step, we then followed desorption of As from Kao, Kao–HA, IL and IL–HA by 100 and 500 μM phosphate or silicate both at high (0.41–0.77 μmol As/g clay), and low (0.04 to 0.05 μmol As/g clay) As loadings. Phosphate desorbed As to a larger extent than silicate regardless of the amount of As loaded to clay minerals, both in the presence and absence of HA, and both for illite and kaolinite. At high loadings of As, the desorption of both redox species of As from clay–HA complexes by phosphate/silicate ranged from 32 to 72% compared to 2–54% in clay only systems meaning that As was desorbed to a larger extent from HA-coated clays compared to clay only systems. When comparing As(III) desorption by phosphate/silicate to As(V) desorption in high As-loading systems, there was no clear trend for which As species is desorbed to a higher extent in the four clay systems meaning that both As species behave similarly regarding desorption from clay surfaces by phosphate/silicate. Similarly, no significant differences were found in high As-loading systems in the amount of As desorbed by phosphate/silicate when comparing Kao vs. IL and Kao–HA vs IL–HA systems meaning that both clay types behave similarly regarding desorption of As by phosphate/silicate. At low As loadings, up to 80% of As was desorbed by phosphate and silicate with no noticeable differences being observed between different As species, different types of clay, clay vs clay–HA or the type of desorbant (phosphate and silicate). The results of this study showed that HA sorption to Ca 2+-homoionized clay minerals can increase As binding to the clay although the As sorbed to the clay–HA is also released to a greater extent by competing ions such as phosphate and silicate. Desorption of As depended on the initial loadings of As onto the clay/clay–HA. Based on our results, the effect of humic substances on sorption of As and on desorption of As by phosphate and silicate has to be considered in order to fully understand and evaluate the environmental behavior of As in natural environments.

Structural analysis and binding domain of albumin complexes with natural dietary supplement humic acid

Humic acid, a natural ionic molecule, is rapidly being recognized as one of the crucial elements in our modern diets of the new century. A biophysical protocol utilizing circular dichroism (CD), steady state and time-resolved fluorescence for the investigation of the complexation of the humic acid to the staple in vivo transporter, human serum albumin (HSA), as a model for protein-humic substances, is proclaimed. The alterations of CD and three-dimensional fluorescence suggest that the polypeptide chain of HSA partially folded after complexation with humic acid. The data of fluorescence emission displayed that the binding of humic acid to HSA is the formation of HSA–humic acid complex with an association constant of 10 4 M −1; this corroborates the fluorescence lifetime measurements that the static mechanism was operated. The precise binding domain of humic acid in HSA has been verified from the denaturation of albumin, hydrophobic ANS displacement, and site-specific ligands; subdomain IIA (Sudlow's site I) was earmarked to possess high-affinity for humic acid. The observations are relevant for other albumin–humic substance systems when the ligands have analogous configuration with humic acid.

Influences of redox transformation, metal complexation and aggregation of fulvic acid and humic acid on Cr(VI) and As(V) removal by zero-valent iron

This study investigated the removal kinetics and mechanisms of Cr(VI) and As(V) by Fe(0) in the presence of fulvic acid (FA) and humic acid (HA) by means of batch experiments. The focus was on the involvements of FA and HA in redox reactions, metal complexation, and iron corrosion product aggregation in the removal of Cr(VI) and As(V) removal by Fe(0). Synthetic groundwater was used as the background electrolyte to simulate typical groundwater. The results showed faster Cr(VI) removal in the presence of HA compared to FA. Fluorescence spectroscopy revealed that no redox reaction occurred in the FA and HA. The results of the speciation modeling indicate that the free Fe(II) concentration was higher in the presence of HA, resulting in a higher removal rate of Cr(VI). However, the removal of As(V) was inhibited in the HA solution. Speciation modeling showed that the concentration of dissolved metal-natural organic matter (metal-NOM) complexes significantly affected the aggregation of the iron corrosion products which in turn affected the removal of As(V). The aggregation was found to be induced by gel-bridging of metal-NOM with the iron corrosion products. The effects of metal-NOM on the aggregation of the iron corrosion products were further confirmed by TEM studies. Larger sizes of iron corrosion products were formed in the FA solution compared to HA solution. This study can shed light on understanding the relationships between the properties of NOM (especially the content of metal-binding sites) and the removal of Cr(VI) and As(V) by Fe(0).

Combining electrophoresis with detection under ultraviolet light and multiple ultrafiltration for isolation of humic fluorescence fractions

Polyacrylamide gel electrophoresis of chernozem soil humic acids (HAs) followed by observation under UV (312 nm) excitation light reveals new low molecular weight (MW) fluorescent fractions. Ultrafiltration of HAs sample in 7 M urea on a membrane of low nominal MW retention (NMWR, 5 kDa) was repetitively used for separation of fluorescent and non-fluorescent species. Thirty ultrafiltrates and the final retentate R were obtained. Fluorescence maxima of separate ultrafiltrates were different and non-monotonously changed in the range of 475–505 nm. Fluorescence maxima of less than 490 nm were detected only in the four first utrafiltrates. For further physical–chemical analyses all utrafiltrates were combined into a fraction called UF < 5 (NMW < 5 kDa). Retentate R demonstrated very weak fluorescence under 270 nm excitation, while fluorescence intensity of UF < 5 was about six times higher than of the bulk HAs. Fraction UF < 5 was further ultrafiltrated on membranes of MNWR 3 kDa and 1 kDa, yielding three subfractions UF3-5, UF1-3 and UF < 1 with NMW 3–5 kDa, 1–3 kDa and <1 kDa, respectively. The validation of the UF procedure was performed by size exclusion chromatography on Sephadex G-25 column. The fluorescence maxima were found to be at 505, 488 and 465 nm for UF3-5, UF1-3 and UF < 1, respectively, with increasing of fluorescence intensity from UF3-5 to UF1-3 to UF < 1 fraction. EPR analysis showed that the amount of free radicals was the largest in retentate R and drastically decreased in fluorescent ultrafiltrates. The results demonstrate that more than one fluorophore is present in chernozem soil HAs complex.

Europium(III) complexed by HPSEC size-fractions of a vertisol humic acid: Small differences evidenced by time-resolved luminescence spectroscopy

The size fractionation of a humic acid (HA) by high performance size exclusion chromatography (HPSEC) was used as a proxy for the filtration effect during HA transport through a porous medium with minimum specific chemical interactions. The modification of the Eu(III)–HA complexes’ formation with the different size-fractions, as compared to the bulk HA, was studied in time-resolved luminescence spectroscopy (TRLS). Clear modifications in Eu(III)–HA complexes’ structures were shown and related to the molecular characteristics of the separated size-fractions. The properties of most of size-fractions did not induce a major alteration of the affinity towards Eu(III). Only the most hydrophilic fractions eluted in the tail of the chromatographic peak, representing about 11% of total fractions-weight, gave some significantly different parameters. Using a simplistic complexation model, it was found that the available complexation sites decreased with the size reduction of humic fractions.

Fluorescence spectroscopic investigation of the interaction between triphenyltin and humic acids

The interaction between triphenyltin (TPT) and humic acid (HA) was investigated using UV–vis and fluorescence spectra techniques. The experimental results showed that the fluorescence quenching of HA by TPT was a result of the interaction of TPT with HA. The binding constant K b and corresponding thermodynamic parameters were measured at different temperatures. The binding of TPT molecule to HA is a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased. Hydrophobic interaction force plays a major role in stabilizing the TPT–HA complex. The three-dimensional fluorescence contour spectra revealed that TPT could enter into the hydrophobic cavities in some domain of HA.

Binding of cadmium to soil humic acid as a function of carboxyl group content

The binding of Cd(II) to soil humic acid (HA) at pH 6.5 and in 0.1 mol/L KNO3 ionic medium, was studied by potentiometric titration with a cadmium ion selective electrode. The influence of carboxyl groups in cation-humic interactions was investigated by selective blocking of humic acid carboxyl groups with thionyl chloride and methanol. Infrared spectroscopic analysis confirmed that esterification took place. Differences between underivatized and derivatized HA complexation properties are ascribed to carboxyl groups. The Scatchard plots and incremental formation constants were used to obtain values for Cd-binding constants, for both HAs. The derivatization decreased the number of HA complexing sites by approximately 60 %, which correlates with acid-base properties of both HAs, studied by barium hydroxide and calcium acetate exchange methods. The stability constants for binding at the strongest sites (logKINT) was larger for underivatized HA (5.40) than for derivatized HA (4.92), indicating greater stability in the case when carboxyl groups are involved in complexation reaction.

Influence of humified organic matter on copper behavior in acid polluted soils

The main purpose of this work was to identify the role of soil humic acids (HAs) in controlling the behavior of Cu(II) in vineyard soils by exploring the relationship between the chemical and binding properties of HA fractions and those of soil as a whole. The study was conducted on soils with a sandy loam texture, pH 4.3–5.0, a carbon content of 12.4–41.0 g kg −1 and Cu concentrations from 11 to 666 mg kg −1. The metal complexing capacity of HA extracts obtained from the soils ranged from 0.69 to 1.02 mol kg −1, and the stability constants for the metal ion–HA complexes formed, log K, from 5.07 to 5.36. Organic matter-quality related characteristics had little influence on Cu adsorption in acid soils, especially if compared with pH, the degree of Cu saturation and the amount of soil organic matter.