Physico-chemical processes of humic acid-trace element interactions

Experiments were carried out under various pH conditions since this factor may strongly influence the equilibrium of various physico-chemical forms in which a certain trace element may occur in the aquatic environment. Pick-up processes were investigated for iron, cobalt, zinc, ruthenium and mercury under various experimental conditions. The rate and type of bonding or association of trace metals in humic acids was investigated by means of their replacement with other ions. For this reason the pick-up of a radionuclide of a certain trace metal by humic acid was performed, and when equilibrium was reached, the humic acids were transferred to another system where a known concentration of another ion was present. Replacement reactions took place and their yields were followed by radioactivity measurements in the liquid phase. The shape of each curve indicates the specific kinetics of the interaction of a particular trace element with humic acids under experimental conditions. Speed, total yield and time needed to reach equilibrium are specific for each particular case. The purpose of our work is to investigate the nature of trace-element interactions with humic acids. Having in mind the large variations that may occur in the constitution of humic acids, our attention focussed primarily on the search for the role these chemical variations and the different processes of their formation play on the ability of humic acids to bind trace elements. Our results demonstrated that charge-dependent processes, such as ion exchange and sorption-desorption, present a major interaction mechanism in humic acidtrace element interaction. Another important mechanism by which some trace elements are associated with humic acids seems to be chelation.     

Strong adsorption of DNA molecules on humic acids

Analysing soil microbial communities is often hampered by DNA adsorption on soil organic compounds such as humic acids. However the role of humic acids in DNA adsorption and stability in soils remains controversial. To characterize DNA–humic acid interactions, we studied DNA adsorption on two commercially available humic acids and a soil humic acid extracted from an Andosol. Desorption of the adsorbed DNA using 4 different solutions—distilled water, 0.1 M NaCl, 0.1 M sodium phosphate buffer (pH 6.0), and 1% sodium dodecyl sulfate solution—was also studied to understand the mechanism of DNA adsorption on humic acids. Here, we show that humic acids play an important role in DNA adsorption to soils. DNA molecules were adsorbed on the humic acids, with adsorption increasing proportionally with the DNA concentrations in the solution. The adsorption on all humic acid samples was fitted with Freundlich equation, and the parameters obtained from the equation indicated a high affinity between the humic acids and DNA molecules. The total amount of DNA desorbed by the 4 solutions was less than 2% of the total DNA adsorbed on all the humic acids. The results demonstrate that DNA molecules are able to bind strongly to humic acids by ligand binding, hydrophobic interaction, aggregation, or precipitation.     

Chloroacetic acids in environmental processes

The fate of chloroacetic acids (CAA) in forest soils was studied using radio-indicator methods. We showed that chloroacetic acids are both microbially degraded and simultaneously formed by chloroperoxidase-mediated chlorination of acetic and humic acids. The degree of biodegradation of chloroacetic acids in soil depends on their concentration. Dichloroacetic acid (DCA) is degraded faster than trichloroacetic acid (TCA). Chlorination of acetic acid led to a fast formation of dichloroacetic acid, whereas chlorination of humic acids gave rise to trichloroacetic acid. Both processes lead to a steady state in soil, participate in the chlorine cycle and possibly also in decomposition of organic matter in forest ecosystems.     

Rapid incorporation and short-term distribution of a nonylphenol isomer and the herbicide MCPA in soil-derived organo-clay complexes

Organo-clay complexes in soil are a major sink for xenobiotics and, thus, often enhance their persistence dramatically. However, the knowledge on environmental processes of non-extractable residue formation on a short time scale is very restricted. Therefore, this study examined the distribution of 4-(3,5-dimethylhept-3-yl)phenol (NP) and 4-chloro-2-methylphenoxyacetic acid (MCPA) in soil over a short time period of 48 h and in different soil sub-fractions. The overall proportion of organo-clay-associated bound residues was not only abundant but also in the same range for both substances (MCPA: 8%; NP: 11% of applied ¹⁴C-radioactivity). However, a more detailed view revealed two different distribution patterns: a higher proportion of clay-associated NP was accompanied by a lower content of bound residues, whereas a smaller fraction of clay-associated MCPA was characterized by a higher proportion of non-extractable residues. Further on, a selective accumulation of bound residues among clay-associated humic fractions was observed. NP residues were linked predominantly to humic acids, whereas MCPA residues tended to be incorporated more into fulvic acids. It was evident that the overall distribution was influenced primarily by the physico-chemical properties of the contaminants. This study demonstrates in detail a rapid initial incorporation accompanied by a specific distribution into soil sub-fractions for selected xenobiotics in soil and points to a complex interaction of clay-associated organic matter with low molecular weight compounds.     

Variation in humic and fulvic acids during thermal sludge treatment assessed by size fractionation,elementary analysis,and spectroscopic methods

Thermal pretreatment can be applied to sludge anaerobic digestion or dewatering. To analyze the variation in humic substances during thermal sludge treatment, sludge humic and fulvic acids were extracted before and after 30-min thermal treatment at 180℃, and then their contents, molecular weight distributions, elementary compositions, and spectral characteristics were compared. The results showed that the total contents of humic and fulvic acids in the sludge almost remained constant during thermal treatment, but 35% ofhumic and fulvic acids were dissolved from the sludge solids. Moreover, both humic and fulvic acids were partly decomposed and 32% of humic acids were converted to fulvic acids. The median value of the molecular weights of humic acids decreased from 81 to 41 kDa and that of fulvic acids decreased from 15 to 2 kDa. Besides the reduction in molecular size, the chemical structures of humic and fulvic acids also exhibited a slight change, i.e. some oxygen functional groups disappeared and aromatic structures increased after thermal sludge treatment.     

涕灭威及其复合物对茎线虫DNA的影响

选择了一种毒性很高的氨基甲酸酯农药涕灭威、一种最常见的阴离子表面活性剂十二烷基苯磺酸钠(SDBS)及一种土壤中普遍存在的天然物质腐殖酸,组成两种复合污染体系;研究了它们对茎线虫的生态毒理效应和对DNA的影响.结果发现,涕灭威-SDBS复合体系在4 d内对茎线虫的DNA造成了明显的损伤,而涕灭威-SDBS-腐殖酸复合体系在8 d内对茎线虫DNA造成的损伤却远远低于未加入腐殖酸的复合体系.关于涕灭威及其复合污染物对茎线虫的生态毒理效应和对DNA损伤的研究尚未见文献报道.     

Formation of Soluble Complexes of Metals with Humic Acid and Its Environmental Significance

In order to investigate the role of functional groups present in humic acid(s) (HA) during complex formation, water soluble complexes between HA isolated from soil and metals (Pb, Ca, As, Ni, Cr, Co, Cu, Cd, Fe, Mn, Mg and Zn) were prepared and subjected to infrared (IR) spectroscopy. the IR data revealed the involvement of the - OH group of humic acid in complex formation with all metals except copper and arsenic, whereas the - COOH group of HA was found to be the preferred site of binding for all the metals. the significance of findings in relation to detoxification of environmental pollutants is discussed in this paper.     

Antioxidant effect of lignite humic acids and its salts on the thermo-oxidative stability/degradation of polyvinyl alcohol blends

We demonstrate the antioxidant potential of humic acids in (green) polymer chemistry. Lignite humic acids and its sodium and ammonium salts were mixed at different concentrations with polyvinyl alcohol and thermogravimetry was used to assess the influence on the thermo-oxidative stability of resulted blends. Both protonized form and ammonium salt of humic acids caused increased stability of investigated polymers in the studied concentration range (0.5–10% of humic acids in polymer). In contrast to protonized form, the ammonium salt also showed moderating effect on polymer degradation kinetics. Sodium salts caused substantially lower stabilizing effect and presence of 10% of humic matter caused even destabilization. In all cases, however, when the degradation has already started, the presence of humic acids and its salts caused more intensive polymer decomposition, which resulted in lower weight of char.     

Enhanced degradation of trichloroethylene using bentonite-supported nanoscale Fe/Ni and humic acids

Nanoscale zero-valent iron, named nano-Fe⁰, is a reagent used to degrade trichloroethylene in groundwater. However, the efficiency of nano-Fe⁰ is moderate due to issues of dispersion and reactivity. As an alternative we synthesized bentonite-supported nanoscale Fe/Ni bimetals, named bentonite-Fe/Ni, to test the degradation of trichloroethylene in the presence of Suwannee River humic acids, as a representative of natural organic matter. 0.1 mmol/L trichloroethylene was reacted with 0.5 g/L of nano-Fe⁰, bentonite-Fe, Fe/Ni, and bentonite-Fe/Ni nanoparticles. Results show first that without humic acids the reaction rate constants k _obs were 0.0036/h for nano-Fe⁰, 0.0101/h for bentonite-Fe, 0.0984/h for Fe/Ni, and 0.181/h for bentonite-Fe/Ni. These findings show that bentonite-Fe/Ni is the most efficient reagent. Second, the addition of humic acids increased the rate constant from 0.178/h for 10 mg/L humic acids to 0.652/h for 40 mg/L humic acids, using the bentonite-Fe/Ni catalyst. This finding is explained by accelerated dechlorination by faster electron transfer induced by humic quinone moieties. Indeed, the use of 9, 10-anthraquinone-2, 6-disulfonate as a humic analogue gave similar results.     

Investigations of some trace elements in the Bay of Lim

Sea water was collected at several stations in the Bay of Lim at a depth of one meter below the surface, and before analysis, was filtered with 0.45-μm Millipore filters. Shallow water sediments were collected at the same locations. Humic acids used in this work were separated from near-shore sediments taken from various saline waters of the Bay of Lim. The prepared humic acids were then analysed for their elementary composition and also for positions of their hydrolytic products to obtain more data on how and to which characteristic part, the trace elements were related. The hydrolysis of humic acids was done by chemical methods in order to obtain four main components: amino acids, sugars, phenols and condensed benzene core. Neutron activation analysis was used for trace element analysis in evaporated portions of filtered sea water, sediments, soil, living organisms, humic acids and their hydrolytic products. This work was undertaken to obtain more data on the organic matter present in sediments and in seagrass flats, and also to collect more data on trace elements that are associated with typical and representative samples for the Bay of Lim. Analyses of trace elements associated with either humic acids or their hydrolytic products were performed with the purpose of gaining evidence as to which part of humic acids metals are bound. Humic acids or their decomposition products play an important role in the distribution and availability of a number of essential or nonessential trace elements. Results of this work indicate that humic acids influence the process of redistribution of trace elements in the investigated local coastal area.     

Plant Bioavailability of “natural” and “model” Humic acid‐bound [14c] Atrazine residues

The release of bound [14C] atrazine residues and their uptake by maize plants was investigated.

“Natural”; humic acids, extracted from a brown soil, and “model”; humic acids, prepared from catechol, both containing bound [14C] atrazine residues were incubated with plants in soil. After 21 days, the maize plants contained 0.7% (plants grown in soil mixed with “natural”; humic acids) to 1.7% (plants grown in soil mixed with “model”; humic acids) of the radioactivity originally introduced.

The roots contained 55 to 70% of the [14C] residues whereas the remainder was present in the shoots. A significant amount of the total [14C] residues (29 to 53%) became again bound in plant tissues, whereas the, majority of extractable [14C] residues was present in the form of conjugates.

The behaviour of “model”; humic acid‐bound residues was comparable to that of “natural”; humic acid‐bound residues or soil‐bound residues.     

A new photoproduct of the drug furosemide in aqueous media

The solar phototransformation of furosemide has been investigated in aqueous media. Irradiation of the drug in distilled water, in water and humic acids or nitrate ions, and in sewage sludge water affords a new dehalogenated dimer. The formation of the dimer has been explained by the formation of a cation radical intermediate. The low-measured environmental concentration of furosemide with respect to predicted environmental concentration in the Po and Lambro Rivers could be justified by its phototransformation.     

Two-step hydrothermal conversion of biomass waste to humic acid using hydrochar as intermediate

Converting biomass materials to humic acid is a sustainable method for humic acid production and achieve biomass valorization. A two-step hydrothermal treatment method was adopted in this study to produce humic acid from corn stalks. In the first step of the process, hydrochar was prepared at different hydrothermal temperatures and pH values. Their chemical properties were then analyzed, and the hydrochar-derived humic acids were produced under alkaline hydrothermal conditions (denoted as HHA_alk). The hydrochar, prepared under high temperature (200 °C) and strong acidic (pH 0) conditions, achieved high HHA_alk yields (i.e., 67.9 wt% and 68.8 wt% calculated based on weight of hydrochar). The sources of HHA_alk formation were as follows: 1) production in the hydrochar preparation stage, and 2) increment under the alkaline hydrothermal treatment of hydrochar. The degree of hydrochar unsaturation was suggested as an indicator for evaluating the hydrochar humification potential under alkaline hydrothermal conditions. This study provides an important reference for the preparation of suitable hydrochar with high hydrothermal humification potential.     

UV light induces Ag nanoparticle formation: roles of natural organic matter,iron, and oxygen

Nanoparticles occurring in the environment originate either from engineered, synthetically produced nanoparticles, or from naturally produced nanoparticles. The latter can be formed in natural media by light-induced reduction of metal ions in presence of natural organic matter, such as humic substances occurring widely in waters, soils and sediments. There is actually few knowledge on the effect of sunlight and of the nature of organic matter on nanoparticle formation. Therefore, we studied here the photoreduction of silver(I) ion to silver nanoparticles with and without ferrous ion under oxic and anoxic conditions, using humic and fulvic acids as proxies of natural organic matter. UV light-induced formation of silver nanoparticles was monitored up to 60 min by measuring surface plasmon resonance in air-saturated mixture and nitrogen-saturated mixture of silver(I) ion–organic matter. Results show that the surface plasmon resonance intensity was about 2.5 times higher in the nitrogen-purged solution mixture than the air-saturated solution. This finding suggests the oxygen-containing species had no major role in forming silver nanoparticles. Therefore, photo-driven formation of silver nanoparticles most likely involved photoactivation of silver(I) ion and natural organic matter complexes. We observed also that both iron(II) and iron(III) ions highly modified the surface plasmon resonance spectra of the particles with broader features. Results also reveal that in the presence of humic acid, the intensity of the surface plasmon resonance peak decreased by at least 50 %, while almost no change in the intensity was seen when fulvic acid was used. Overall, our findings demonstrate that the ligand–metal charge transfer process, affected by the nature of organic matter, i.e., humic acid versus fulvic acid, was influenced by redox iron species.     

微生物降解褐煤产生的腐植酸化学特性研究

本文对微生物降解褐煤产生的腐植酸的化学特性进行了分析.结果表明,褐煤经微生物降解后其腐植酸与降解前相比,氢和氧百分含量增加,碳百分含量减少,分子量减小 ,而絮凝极限明显增大,红外吸收光谱也发生明显变化.     

Scanning Electron Microscopy of Humic Substances Produced During Cellulose Decomposition

Humic substances (HS) produced during the aerobic decomposition of polysaccharides still need to be recognized as such and characterized. Humic (HA) and fulvic (FA) acids extracted at different time intervals during composting of cotton residues from carding, where no decomposition of lignin occurred, were investigated by scanning electron microscopy (SEM) size exclusion chromatography and infrared spectroscopy. Throughout the experiment, fulvic acids possessed a larger number of carboxyl groups but a lower number of weak acidic groups (negatively charged acid groups at pH 11) than humic acids. the number of carboxyl groups increased with time in both fulvic and humic acids, while that of phenolic groups decreased. Infrared spectra showed that the ratio between carboxyl and methyl groups decreased from 8.5 to 4 in FA after 18 days. This change corresponded with the disappearance of flat sheet structures observed by SEM at pH 6. Our results suggest that the shape of humic molecules as observed by SEM reflects the strength of hydrophilic/hydrophobic interactions with the solvent molecules. About 80% of FA molecules had a molecular weight lower than 3500 as deduced from column calibration with HS standards obtained by ultrafiltration. About 40% of humic acids were composed of small molecules; only 20% HA had a molecular weight larger than 45000. Polysaccharide-derived HS may not be limited to the high molecular weight poorly transformed fraction containing bonded polysaccharide structures, but may also consist of low molecular weight components with no structural similarity to the original material.     

The reduction of selenate by fulvic acids in soils of a high gastric cancer risk area in Sri Lanka∗

In order to elucidate the probable etiological factors for the incidence of gastric cancer, the interaction between selenate and fulvic acids was investigated under chemically controlled conditions. The reduction ability of selenate by fulvic acids was enhanced in acidic conditions. The fulvic acids may play an important role in the nitrosation process. Thus the investigations of the mechanism by which selenate interact with fulvic acids will provide a new insight into the chemical activation process by which selenium supplementation is supposed to act as an anticarcinogen.     

褐煤风化过程中化学特性的变化

本文测定了６种不同风化程度褐煤的化学性状。结果表明，随着在自然界堆积风化时间的延长，褐煤的总碳，总氮含量及碳氮比都下降，灰分含量则增大，可提取的腐植酸及黄腐酸量明显增大，且紫外吸光值呈系统变化，尤其是黄腐酸中聚乙烯吡咯烷酮树脂可吸附部分（黄腐酸中腐植部分）随风化加深而降低，各种不同风化程度褐煤中腐植酸的红外吸收光谱变化不是很明显，且与土壤腐植吸收光谱相似。     

First determination of Cu adsorption on soil humin

Humic substances are heterogeneous mixtures of organic compounds occurring in huge amounts mainly in waters, soils, sediments and organic wastes. They are formed during the decay of living organisms. They play a very important role in many environmental processes including carbon sequestration, water cleaning and retention, soil erosion, fertility and pollutant retention. However, due to their complex nature, humic substances are still poorly characterized and much less known than living matter. Humin is the most insoluble and, in turn, the least understood fraction of humic substances. To our knowledge, no information is currently available on the adsorption and desorption behaviors of metal ions on soil humin. Here, we report the adsorption and desorption properties of Cu(II) on humin and humic acids isolated from a forest soil in northeast China using the batch equilibration method. Solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR) spectroscopy was used to characterize and compare the chemical structures of humin and humic acid. The batch experiments’ results show that humin has a lower adsorption capacity and higher adsorption reversibility for Cu(II) than humic acid. The adsorption isotherms well fitted both the Langmuir and Freundlich equations. Humin, therefore, plays an important role in controlling the fate, transport and bioavailability of Cu(II) in the environment. The ¹³C CPMAS NMR spectra showed that compared with humic acid, humin was higher in alkyl C, carbohydrate C and phenolic C and was lower in methoxyl C, aryl C and carbonyl C. These findings mean that humin was less alkylated, more aliphatic and more hydrophobic.