Theoretical aspects and experimental evidence of the capacity of humic substances to bind herbicides by charge-transfer mechanisms (electron donor-acceptor processes)

Theoretical aspects of the possible occurrence of electron donor-acceptor processes involving free radical intermediates and leading to stable charge-transfer complexes between electron donor herbicides and acceptor quinone-like units of humic acids have been discussed on the basis of similar mechanisms occurring on biological scale in the chloroplasts. Experimental evidence of the former hypotheses was given by the analyses of infrared and electron spin resonance data obtained from interaction complexes of a number of s-triazines and substituted ureas (photosynthesis inhibitor herbicides) with soil humic acids. In the case of s-triazines it was shown that with decrease of the capacity of humic molecules to form ionic and hydrogen bonds, the tendency to act as electron acceptor increased, as shown by the higher free radical generation observed after the interaction process. The existence of correlations between the bioactivity of substituted ureas - expressed as inhibitory potency in the Hill reaction (pI₅₀ indexes) - and free radical concentrations in the humic acid - herbicide complexes was also demonstrated.     

Removal of humic substances from water by means of calcium-ion-enriched natural zeolites.

The ability of the natural zeolited Neapolitan Yellow Tuff (NYT) enriched with calcium ions to remove humic acids from water was evaluated by batch adsorption equilibrium tests and dynamic experiments carried out by percolating humic acid solutions through a small NYT column (breakthrough curves). Under the experimental condition explored, the sorption capacity increases with the ionic strength and has the highest value at pH 7.4. The partition coefficient for a low concentration of humic acid ([humic acid] --> 0), at pH 7.4 in 0.01 M sodium chloride, was approximately 1000 L/kg, versus the value of approximately 100 L/kg in the absence of the alkaline metal salt. Therefore, after humic acids have been adsorbed in a column filled with the calcium-ion-enriched tuff, a reduction of the salt concentration in the ongoing solution enhances the release of the adsorbed material. These findings show that NYT can be used for the removal of humic acids from water.     

The formation and control of disinfection by-products using chlorine dioxide

In this study, chlorine dioxide (ClO2) was used as an alternative disinfectant with vanillic acid, p-hydroxybenzoic acid, and humic acid as the organic precursors in a natural aquatic environment. The primary disinfection by-products (DBPs) formed were trihalomethanes (THMs) and haloacetic acids (HAAs). Under neutral conditions (pH = 7) for vanillic acid, more total haloacetic acids (THAAs) than total trihalomethanes (TTHMs) were found, with a substantial increase during the later stages of the reaction. In the case of p-hydroxybenzoic acid, the amount of THAAs produced was minimal. Raising the concentration of ClO2 was not favorable for the control of THAAs in low concentrations of vanillic acid. ClO2 could reduce the total amount of TTHMs and THAAs for higher concentration of vanillic acid. It was found that the humic acid treatment dosage was not significant. Under alkaline conditions (pH = 9), the control of TTHMs and THAAs for the treatment of vanillic acid was better and more economical, however, an appreciable amount of inorganic by-products were observed. Under the same alkaline condition, the control of THAA for the treatment of p-hydroxybenzoic acid was not beneficial and for the treatment of humic acid was not significant.     

Migration of uranium(IV)/(VI) in the presence of humic acids in quartz sand: a laboratory column study

The migration behavior of U(IV) and U(VI) in the presence of humic acid was studied in a quartz sand system. Laboratory column experiments were performed using humic acid, U(VI) in humic acid absence, U(IV) and U(VI) in humic acid presence, and for comparison a conservative tracer. In experiments using humic acid, both redox species of U migrate nearly as fast as the conservative tracer. Humic acid accelerates the U(VI) breakthrough compared to the humic acid-free system. There are strong indications for a similar effect on the U(IV) transport. At the same time, a part of U(IV) and U(VI) associated with the humic acid is immobilized in the quartz sand due to humic colloid filtration thus producing a delaying effect. Tailing at a low concentration level was observed upon tracer elution. The experimental breakthrough curves were described by reactive transport modeling using equations for equilibrium and kinetic reactions. The present study demonstrates that humic acids can play an important role in the migration of actinides. As natural organic matter is ubiquitous in aquifer systems, the humic colloid-borne transport of actinides is of high relevance in performance assessment.     

凹凸棒土对腐殖酸的低温吸附性能研究

首次研究凹凸棒土对饮用水中腐殖酸的低温吸附性能,考察5℃条件下,吸附时间与腐殖酸初始浓度、吸附剂投加量、pH对凹凸棒土吸附腐殖酸的影响,确定吸附剂的吸附等温线、吸附动力学和热力学等相关理论参数,研究凹凸棒土对腐殖酸的吸附性能与机理。结果表明,江苏盱眙凹凸棒土在温度5℃、pH=4、水中腐殖酸初始浓度为5 mg/L,投加量为15 g/L的条件下,吸附180 min后对腐殖酸的去除率可达97.26%。凹凸棒土对腐殖酸的吸附符合二级吸附动力学方程与Freundlich吸附等温式,吸附过程由孔隙内扩散过程控制,吸附为自发的吸热过程,包括物理吸附与化学吸附。根据Fre-undlich吸附等温式拟合计算,5℃、pH=7时理论最大吸附量为9 mg/g,说明凹凸棒土对于低温饮用水中腐殖酸具有良好的吸附效果。     

Effect of humic acid on water chemistry, bioavailability and toxicity of aluminium in the freshwater snail, Lymnaea stagnalis, at neutral pH

The influence of humic acid on the water chemistry of environmentally relevant concentrations of Al at neutral pH was studied, together with its effect on the bioavailability and toxicity of Al in Lymnaea stagnalis. Humic acid significantly reduced the loss of Al from the water and increased the fraction of filterable Al, although this was a relatively small fraction of total Al. Filterable Al concentration in the presence or absence of humic acid was independent of initial Al concentration. Humic acid only partly reduced toxicity, as observed by a reduction in behavioural suppression, and had no effect on the level of Al accumulated in tissues. These results suggest that humic acid maintains Al in a colloidal form that is bioavailable to L. stagnalis. However, these colloidal Al-humic acid species were less toxic since behavioural toxicity was reduced. Humic acid may play an important role in limiting the toxicity of Al to freshwater organisms.     

Bacterial abundance and community structure in response to nutrients and photodegraded terrestrial humic acids in a eutrophic lake

The exposure of humic substances to solar radiation can alter their concentration and composition and subsequently influences their bioavailability in aquatic food webs. With eutrophication increasingly prominent in lakes, nutrients, such as inorganic N and P, are a prerequisite for heterotrophic bacteria that use organic matter. Here photodegradation of terrestrial humic acids and nutrient addition were performed to investigate the response of bacterial abundance and community structure to photodegraded humic acids and increased nutrient concentrations in a eutrophic lake. Results showed that the decreasing level of absorption coefficient at 460 nm in the treatment irradiated with 40 W UV lamps was more remarkable than that of the treatment irradiated with 20 W UV lamps and the control. This reduced coefficient corresponds to the greatest decrease in humic acid concentration in the 40 W group. Bacteria showed high abundance after incubation with humic acids which underwent strong irradiation intensity. An increased nutrient concentration significantly affected bacterial abundance. The dominant bacteria were Aquabacterium for the irradiated group, Aquabacterium and Limnobacter for the 20 W group and Flavobacterium and Limnobacter for the 40 W group. Armatimonadetes-gp4 and Sediminibacterium showed evident response to high nutrient concentration. Our results showed that the exposure of terrestrial humic acids to UV light and the increasing concentration of nutrients have obviously changed bacterial community.

     

Formation of chloroacetic acids from soil,humic acid and phenolic moieties

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe(2+), Fe(3+) and H(2)O(2) leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.     

Removal of organic polyelectrolytes and their metal complexes by adsorption onto xonotlite

Natural organic polyelectrolytes (humic and fulvic acids) and their metal complexes were removed by adsorption onto xonotlite. The removal percentages of humic and fulvic acids by xonotlite were approximately 80% and 30%, respectively. Humic acid removal from solution by adsorption onto xonotlite took place more readily than fulvic acid removal. The molecular weight distributions of the humic substances remaining in solution after adsorption with the xonotlite were measured with size exclusion chromatography. A comparison of molecular weight distributions demonstrated conclusively that large molecular weight components were adsorbed preferentially, indicating that adsorption efficiency depends on the number of functional groups of humic substances. Furthermore, the surface topography of the adsorbent was observed before and after adsorption by scanning electron microscopy. The calculated heat of adsorption was of 330 kJ mol(-1) which was evaluated from the Clapeyron-Clausius equation. Therefore, the adsorption type can be considered chemical. Since xonotlite can be easily synthesized and obtained at low cost, the adsorption method of humic and fulvic acids is superior to their precipitation.     

Distribution and incorporation mode of the herbicide MCPA in soil derived organo-clay complexes

The incorporation of xenobiotics into soil, especially via covalent bonds or sequestration has a major influence on the environmental behavior including toxicity, mobility, and bioavailability. The incorporation mode of 4-chloro-2-methylphenoxyacetic acid (MCPA) into organo-clay complexes has been investigated under a low (8.5 mg MCPA/kg soil) and high (1000 mg MCPA/kg soil) applied concentration, during an incubation period of up to 120 days. Emphasis was laid on the elucidation of distinct covalent linkages between non-extractable MCPA residues and humic sub-fractions (humic acids, fulvic acids, and humin). The cleavage of compounds by a sequential chemical degradation procedure (OH^?, BBr₃, RuO₄, TMAH thermochemolysis) revealed for both concentration levels ester/amide bonds as the predominate incorporation modes followed by ether linkages. A possible influence of the soil microbial activity on the mode of incorporation could be observed in case of the high level samples. Structure elucidation identified MCPA as the only nonextractable substance, whereas the metabolite 4-chloro-2-methylphenol was additionally found as bioavailable and bioaccessible compound.     

Joint influence of surfactants and humic matter on PAH solubility. Are mixed micelles formed?

Mobilization of polycyclic aromatic hydrocarbons (PAH) by surfactants, present at contaminated sites or deliberately introduced for remediation purposes, is inevitably associated with the influence of humic substances, which are ubiquitous in natural systems. Therefore, the solubilizing effects of anthropogenic and natural amphiphiles must be considered in their combined action since synergistic or antagonistic effects may be expected, for instance, as a consequence of mixed micellization.

In this paper, solubilization of ¹⁴C-labeled pyrene in single-component and mixed solutions of surfactants and humic acid (coal-derived) was investigated up to the micellar concentration range. At low concentrations, antagonistic effects were observed for systems with cationic as well as anionic surfactants. Solubility enhancements in the presence of humic acid were canceled on addition of a cationic surfactant (DTAB) since charge compensation at humic colloids entailed precipitation. Solubility was also found to be decreased in the presence of an anionic surfactant (SDS), which was attributed to a competitive effect in respect of pyrene–humic interaction. This explanation is based on octanol–water partitioning experiments with radiolabeled humic acid, yielding evidence of different interaction modes between humic colloids and cationic/anionic surfactants. At higher concentrations, the effects of humic acid and SDS were found to be additive. Thus, a formation of mixed micelles is very unlikely, which was confirmed by size exclusion chromatography of mixed systems. It can be concluded that remediation measures on the basis of micellar solubilization are not significantly affected by the presence of natural amphiphilic compounds.     

Distribution of PAHs and PCBs to dissolved organic matter: high distribution coefficients with consequences for environmental fate modeling

Dissolved organic carbon/water distribution coefficients (K(DOC)) were measured for a selection of PCBs with octanol/water partition coefficients (K(OW)) ranging from 10(5.6) to 10(7.5). A solid phase dosing and sampling technique was applied to determine K(DOC) to Aldrich humic acid. This technique is in particular suitable for determining the distribution of very hydrophobic chemicals to complex matrices like humic acids. The K(DOC) values were calculated from the experimental data using a linear model. Determined K(DOC)'s were evaluated in relation to octanol/water partition coefficients of the test compounds, and compared to literature data. Measured K(DOC) values were somewhat higher than literature data, which can probably be attributed to the overestimation of freely dissolved aqueous concentration as a result of incomplete phase separation in other studies, and to the unique character of Aldrich humic acid as a "sorbent" or co-solute or to the fact that Aldrich humic acid is not a typical DOC, and other (adsorption) processes can occur. This study reports DOC distribution coefficients that belong to the highest ones ever measured. In addition, the DOC distribution was discussed in relation to current risk assessment modeling.     

Competition between alga (Pseudokirchneriella subcapitata), humic substances and EDTA for Cd and Zn control in the algal assay procedure (AAP) medium

The chemical speciation of trace metals in natural waters has important implications for their biogeochemical behavior. Trace metals are present in natural waters as dissolved species and associated with colloids and particles. The complexation of one trace metal (Cd and Zn at 200 and 390 microg/l respectively) with a green alga Pseudokirchneriella subcapitata in colloid-free algal culture medium and in presence of colloidal humic substances (HS) is presented. The influence of the nature of colloids was also addressed using three "standard" HS: fulvic acid (FA) and, soil (SHA) and peat humic acids (PHA). The chemical speciation model, MINTEQA2, was used to simulate the influence of pH and standardized culture medium on metal association with humic substances. The model was successfully modified to consider the differences in the metal complexation with fulvic (FA) and humic acids (HA). The deviations of concentrations of metals associated with HS between experimental results and model predictions were within a factor of approximately 2. The results of speciation model highlight the influence of the experimental conditions (pH, EDTA) used for alga bioassay on the behavior of Cd and Zn. The computed speciation suggests working with a pH buffered/EDTA-free mixture to avoid undesirable competition effects. The behavior of Cd and Zn in solution is more strongly influenced by HS than by alga. Metal-HS associations depend on metal and humic substance nature and concentration. Cd is complexed to a higher extent than Zn, in particular at larger HS concentration, and the complexation strength is in the order FA相似文献   

Biodeterioration of cardboard-based liquid containers collected for fibre reuse

Liquid packaging board (LPB) collected in Germany is processed in Finland as recycled fibre and as plastic reject for incineration. The chemical, biological and physical changes occurring in recycled LPB bales were monitored during storage of six and 18 months. The moisture content in the core of the bales ranged from 7% to 53%, and pH values varied from 6.0 to 8.5. The average amount of mesophilic bacteria per container was 1.5 x 10(7) - 5 x 10(8), which means that recycled LPB pulp cannot be recommended for sanitary use. The concentration of CO2 inside the bale is an indicator of the activity of aerobic microorganisms and might be suitable for identifying deteriorated bales and removing them from the production line. Insects were found in some bales and the more deteriorated the bale was the more species of insects were found. The results showed the conversion of cellulose into humic acids to be clearly underway in some recycled LPB bales. The bale samples were extracted into hot water and into fulvic acids and humic acid (HA) fractions. The concentration of the humic acid fraction varied in the range 0.3-0.6% of the organic matter in fresh bales and 2.2% in one old bale. During aging nitrogen was enriched in all fractions.     

Sorption of naphthalene and phenanthrene by soil humic acids

Humic acids are a major fraction of soil organic matter (SOM), and sorption of hydrophobic organic chemicals by humic acids influences their behavior and fate in soil. A clear understanding of the sorption of organic chemicals by humic acids will help to determine their sorptive mechanisms in SOM and soil. In this paper, we determined the sorption of two hydrophobic organic compounds, naphthalene and phenanthrene by six pedogenetically related humic acids. These humic acids were extracted from different depths of a single soil profile and characterized by solid-state CP/MAS 13C nuclear magnetic resonance (NMR). Aromaticity of the humic acids increased with soil depth. Similarly, atomic ratios of C/H and C/O also increased with depth (from organic to mineral horizons). All isotherms were nonlinear. Freundlich exponents (N) ranged from 0.87 to 0.95 for naphthalene and from 0.86 to 0.92 for phenanthrene. The N values of phenanthrene were consistently lower than naphthalene for a given humic acid. For both compounds, N values decreased with increasing aromaticity of the humic acids, such an inverse relationship was never reported before. These results support the dual-mode sorption model where partitioning occurs in both expanded (flexible) and condensed (rigid) domains while nonlinear sorption only in condensed domains of SOM. Sorption in the condensed domains may be a cause for slow desorption, and reduced availability and toxicity with aging.     

Fractionation of heavy metals and distribution of organic carbon in two contaminated soils amended with humic acids

The effects of humic acids (HAs) extracted from two different organic materials on the distribution of heavy metals and on organic-C mineralisation in two contaminated soils were studied in incubation experiments. Humic acids isolated from a mature compost (HAC) and a commercial Spaghnum peat (HAP) were added to an acid soil (pH 3.4; 966 mg kg(-1) Zn and 9,229 mg kg(-1) Pb as main contaminants) and to a calcareous soil (pH 7.7; 2,602 mg kg(-1) Zn and 1,572 mg kg(-1) Pb as main contaminants) at a rate of 1.1g organic-C added per 100g soil. The mineralisation of organic-C was determined by the CO(2) released during the experiment. After 2, 8 and 28 weeks of incubation the heavy metals of the soils were fractionated by a sequential extraction procedure. After 28 weeks of incubation, the mineralisation of the organic-C added was rather low in the soils studied (<8% of TOC in the acid soil; <10% of TOC in the calcareous soil). Both humic acids caused significant Zn and Pb immobilisation (increased proportion of the residual fraction, extractable only with aqua regia) in the acid soil, while Cu and Fe were slightly mobilised (increased concentrations extractable with 0.1M CaCl(2) and/or 0.5M NaOH). In the calcareous soil there were lesser effects, and at the end of the experiment only the fraction mainly related to carbonates (EDTA-extractable) was significantly increased for Zn and decreased for Fe in the humic acids treated samples. However, HA-metal interactions provoked the flocculation of these substances, as suggested by the association of the humic acids with the sand fraction of the soil. These results indicate that humic acid-rich materials can be useful amendments for soil remediation involving stabilisation, although a concomitant slight mobilisation of Zn, Pb and Cu can be provoked in acid soils.     

Photodegradation of humic acids in the presence of hydrogen peroxide

A batch photoreactor was used to evaluate the UV/H2O2 oxidation process for the removal of humic acids in water. A 450-W UV lamp with high-pressure mercury vapor was employed as the light source. The residues of humic acids and hydrogen peroxide were measured for assessment of process performance and understanding of process reaction behavior. The UV photolysis alone can play an important role in the degradation of humic acids. The presence of hydrogen peroxide was found to promote the degradation efficiency. However, excessive dosage of H2O2 does not further improve the degradation of humic acids. On the contrary, the lower the H2O2 dosage the higher the amount of humic acids which can be removed. Aeration with air does not favor the removal efficiency of humic acids as the oxidation lasts for a sufficiently long time. The presence of carbonate species deteriorates the humic acids' removal, whereas it results in a larger amount of H2O2 decomposition.     

Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid–liquid distribution that depends on geochemical parameters.In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. ¹⁶⁰Tb(III) and ¹³¹I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials.The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb.A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid–liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal–humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.     

Surface charge and adsorption from water onto quartz sand of humic acid

The surface charge of humic acid under different conditions of ionic strength, pH, and the presence of various cationic ions (Cu(2+), Zn(2+), Ba(2+), and Ca(2+)) was determined by a titration method using a cationic polyelectrolyte as titrant. Adsorption isotherms in batch experiments of the polymer from water onto quartz sand were determined at 20 degrees C, 40 degrees C, and 60 degrees C and under different conditions of ionic strength, pH, and the presence of various cationic ions (Cu(2+), Zn(2+), Ba(2+), and Ca(2+)). The data indicate significant decrease of humic acid surface charge by decreasing the pH value from 10.0 to 4.1. Similar decrease of humic acid surface charge was observed by increasing either the ionic strength or the affinity of the divalent cation toward the humic acid. At ambient temperature the adsorption of humic acid on the quartz sand seems to be controlled mainly by electrical interaction between the organic particle and the solid substrate. A correlation is found between the surface charge and the adsorbed amount of the polymer, the adsorbed amount increases when the surface charge of humic acid decreases. The increase of the adsorbed amount with the temperature suggests that adsorption process is endothermic.     

矿物复合PAC混凝去除给水中腐殖酸的研究

为了降低饮用水中有机微污染物的浓度,对矿物高岭土复配聚合氯化铝（PAC）吸附混凝共沉降去除腐殖酸进行了研究,结果表明：矿物高岭土与PAC复配的最佳量均为12 mg/L,此时水样浊度、腐殖酸去除率分别达到98.9%和97.9%,出水残余铝浓度0.16 mg/L。高岭土复配对于处理后水中铝形态也产生了影响,与单独使用PAC相比,总铝浓度降低了24%,特别是对人体毒害较强的溶解态铝浓度降低了71%。