Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances

Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P _OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible.     

Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances

Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P _OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible. Received: 8 December 1997 / Revised: 2 March 1998 / Accepted: 4 March 1998     

Mechanisms and kinetics of humic acid adsorption onto chitosan-coated granules

Chitosan, a naturally abundant biopolymer, has widely been studied for metal adsorption from various aqueous solutions, but the extension of chitosan as an adsorbent to remove humic substances from water has seldom been explored. In this study, chitosan was coated on the surface of polyethyleneterephthalate (PET) granules through a dip and phase inversion process and was examined for humic acid removal in a series of batch adsorption experiments. Scanning electron microscopic (SEM) images showed that the PET granules were uniformly covered with a layer of chitosan and the chitosan layer possessed numerous open pores on the surface. Zeta potential study indicated that the chitosan-coated granules had positive zeta potentials at pH < 6.6 and negative zeta potentials at pH > 6.6. Adsorption of humic acid onto the chitosan-coated granules was found to be strongly pH-dependent. Significant amounts of humic acid were adsorbed under acidic and neutral pH conditions, but the adsorption capacity was reduced remarkably with increasing solution pH values. The adsorption isothermal data under various initial humic acid concentrations (at the same solution pH value) can be adequately modeled by the Langmuir and Freundlich models. X-ray photoelectron spectroscopy (XPS) revealed that the amino groups of the chitosan layer were protonated due to humic acid adsorption, suggesting the formation of organic complex between the protonated amino groups and humic acid. Kinetic study indicated that the adsorption process was transport-limited at low solution pH values, but became both transport- and attachment-limited at high solution pH values.     

Solid-phase extraction of polycyclic aromatic hydrocarbons in surface water. Negative effect of humic acid

The effect of humic acid on solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from surface water was studied. The hydrophobic PAHs show significant association with humic acid, and this was confirmed to be the cause of negative effect when conventional reversed-phase solid-phase extraction (RP-SPE) was employed to extract the analytes from aqueous samples. As an alternative, dynamic ion-exchange (DIE) SPE could simultaneously extract both the fraction of the analytes which was associated with humic acid, and that which was freely dissolved. Using the 16 US Environmental Protection Agency priority PAHs as model compounds, the recoveries of the highly hydrophobic components by DIE-SPE were 10-30% higher than those by RP-SPE for a 1000-ml water sample dissolved with Aldrich humic acid (of 4.1 mg/l dissolved organic carbon content). A similar result was also obtained for 500 ml of natural surface water although the difference in recoveries between the two methods for this sample was smaller than that for the simulated sample. For validation of the method, the artifacts in connection with DIE-SPE in extracting the fraction of analytes which was freely dissolved and that which was associated with humic acid were investigated.     

Concentrations of aluminium, iron, and copper in water of some Shatskiye Lakes and specificity of their distribution among different forms of occurrence

The results of studies on the occurrence of aluminum, iron, and copper in water of Lyutsimir and Chernoe Bol’shoe Lakes belonging to the large group of Shatsk Lake system are discussed. Iron was shown to migrate mostly as suspended particles, and copper, as soluble species. The average annual fraction of suspended aluminum is about 40%. The ratio of suspended and dissolved aluminum depends not only on the concentration of suspended particles in water, but also on their nature. Anionic complexes predominate among soluble forms of the examined metals; their fractions in water of Lyutsimir and Chernoe Bol’shoe Lakes are on the average 86 and 70% (Al), 73 and 59% (Cu), and 60 and 47% (Fe). This is determined by the major contribution of humic substances to the total content of organic matter in water of both lakes and their participation in the complexation with metals. The metals compete for active centers in humic macroligands. Carbohydrates constitute the second important group of organic substances that participate in the complexation. Neutral complexes were found to consist mainly of iron compounds. Compounds with a molecular weight not exceeding 2.0 kDa predominate among anionic metal complexes.     

Adsorption of vapor mixtures of water and organic substance on activated carbons

The isotherms of water adsorption in the presence of an organic substance vapor with a specified concentration are calculated from experimental data on the joint frontal dynamics of adsorption of water vapor and several organic substances (benzene, hexane, cyclohexane, tetrachloromethane, and perfluorotripropylamine) on two samples of activated carbons. The influence of the organic substances on the equilibrium water adsorption decreases with an increase in the molecule size.     

Determination of Organic Compounds,Fulvic Acid,Humic Acid,and Humin in Peat and Sapropel Alkaline Extracts

Black, brown, and light peat and sapropel were analyzed as natural sources of organic and humic substances. These specific substances are applicable in industry, agriculture, the environment, and biomedicine with well-known and novel approaches. Analysis of the organic compounds fulvic acid, humic acid, and humin in different peat and sapropel extracts from Lithuania was performed in this study. The dominant organic compound was bis(tert-butyldimethylsilyl) carbonate, which varied from 6.90% to 25.68% in peat extracts. The highest mass fraction of malonic acid amide was in the sapropel extract; it varied from 12.44% to 26.84%. Significant amounts of acetohydroxamic, lactic, and glycolic acid derivatives were identified in peat and sapropel extracts. Comparing the two extraction methods, it was concluded that active maceration was more efficient than ultrasound extraction in yielding higher amounts of organic compounds. The highest amounts of fulvic acid (1%) and humic acid and humin (15.3%) were determined in pure brown peat samples. This research on humic substances is useful to characterize the peat of different origins, to develop possible aspects of standardization, and to describe potential of the chemical constituents.     

Kinetic Aspects of the Adsorption on Aluminum Oxide Drying Agents Doped with Alkali Metal Ions

Fundamental dynamic (kinetic) aspects of the process in which water vapor interacts with the surface of drying agents that are synthesized on the basis of low-temperature modification of aluminum oxide produced from a pseudoboehmite-containing hydroxide and are modified (doped) with alkali atoms (K, Na). It is shown that the kinetics of adsorption on the samples under study, formed from the fine fraction (0.5–1.0 mm) of aluminum oxide adsorbents, can be described with the Glueckauf equation, which rather well describes the dynamics of water vapor absorption in the course of time. The equation parameters were determined: adsorption rate constants and the equilibrium adsorption capacities (a*). It was found that the alkaline modification of the surface of aluminum oxide adsorbents results in that a* increases (by ~40%) as compared with the unmodified drying agent. A correlation is observed between the equilibrium adsorption capacity of the samples under study and the acid-base properties of the surface.     

Quantification of refractory organic substances in freshwaters: further insight into the response of the voltammetric method

A recently published method for quantifying refractory organic matter (often referred to as humic substances) in freshwaters was applied to a wide range of International Humic Substance Society (IHSS) humic compounds in order to (i) gain a better understanding of the mechanism of the voltammetric response which is the basis of the analytical method and (ii) provide guidance on choosing the optimal standard to be used. At the same time, the sensitivity of the technique has been increased by switching from the pulse mode initially proposed to the square-wave mode. The results obtained show that (i) differences in adsorption onto the electrode rather than differences in complexation strength are responsible for the differences in the intensity of the signal obtained for the different humic compounds, (ii) carboxylate, N- and S-containing groups do not play a role in the voltammetric signal.     

Ultra-trace-level determination of polar pesticides and their transformation products in surface and estuarine water samples using column liquid chromatography-electrospray tandem mass spectrometry.

A method is developed for the determination of polar pesticides and their transformation products [atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachlor] in surface, estuarine and sea water samples at the low ng/l level. Solid-phase extraction is combined off-line with column liquid chromatography-electrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridges and graphitized carbon black extraction disks, is evaluated. The influence of the organic solvent used in gradient LC, as well as the amount of co-extracted humic material on the ESI process is studied. The eluotropic strength of the organic solvent was found to have a distinct effect on the sensitivity of ESI-MS if coupled with LC gradient separations. Methanol gave much better results than acetonitrile and phenylurea compounds are more susceptible to solvent changes than triazines. Co-extracted humic material causes signal suppression in ESI-MS-MS detection. The degree of suppression depends upon the sample pH and the nature of the samples, i.e., surface or estuarine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, with the exception of DPU (8 ng/l). The applicability of the procedure was demonstrated by analyzing surface and estuarine water.     

Hydrophilic interaction liquid chromatography method for measuring the composition of aquatic humic substances

A hydrophilic interaction liquid chromatography (HILIC) method was developed to measure the composition of humic substances from river, reservoir, and treated wastewater based on their physicochemical properties. The current method fractionates the humic substances into four well-defined groups based on parallel analyses with a neutral and a cationic HILIC column, using mobile phases of varied compositions and pH. The results indicate that: (i) the proportion of carboxylic acids in the humic substances from terrestrial origins is less than half of that from treated wastewater (Jeddah, KSA), (ii) a higher content of basic compounds was observed in the humic substances from treated wastewater and Ribou Reservoir (Cholet, France) than in the sample from Loire River (France), (iii) a higher percentage of hydrophobic macromolecules were found in the humic substances from Loire River than in the other samples, and (iv) humic substances of treated wastewater contained less ionic neutral compounds (i.e., pK_a 5–9) than the waters from terrestrial origins. The physicochemical property disparity amongst the compounds in each humic substances sample was also evaluated. The humic substances from the lightly humic Loire river displayed the highest disparity, whereas the highly humic Suwannee river (Georgia, USA) showed the most homogeneous humic substances.     

Metals in surface water of Ukraine: the migration forms,features of distribution between the abiotic components of aquatic ecosystems,and potential bioavailability

We have generalized the results of long-term studies of coexisting forms of a series of metals (Al, Fe, Mn, Zn, Cu, Cr, Pb, Mo, Cd, and V) in surface water bodies of Ukraine, differing in the hydrological regime and the water chemical composition (rivers, reservoirs, lakes, and ponds). The studied metals content has ranged widely, the concentrations of aluminum, iron, and manganese being typically the highest, and the concentration of molybdenum, vanadium, and cadmium being typically the lowest. The ratio between the suspended and the dissolved forms of the metals has been established. Iron and aluminum migrate mostly as part of the suspended matter, whereas the other metals mainly migrate in the dissolved state. The dissolved manganese form predominates in the water bodies under anaerobic conditions. Copper and molybdenum are present almost always in the dissolved state, regardless of the water body type. The data on the relative content of the labile metal fraction (potentially toxic to aquatic organisms) are reported. The relatively low content of this fraction has been found to be majorly owing to the metal ions complexing with natural organic ligands. The humic compounds, the most widespread group of natural organic compounds, play the primary role in the complexation. Even metals with variable oxidation state (Cr, Mo, and V) are found mainly in the form of anionic complexes with the humic substances. Carbohydrates are also involved in the metals binding in the highly bioproductive water bodies, thus increasing the mass fraction of the neutral complexes during the summer and autumn periods. The molecular weight distribution of anionic metal complexes has been discussed; the substantial part of the metals constitutes the compounds with the molecular weight of below 5.0 kDa.     

Use of disposable clean-up columns for selective removal of humic substances prior to measurements with a nitrate ion-selective electrode

Measurements of nitrate in natural waters with a nitrate ion-selective electrode are seriously affected by the presence of humic substances. These can be removed quantitatively by a clean-up procedure with cheap disposable adsorption columns packed with chemically-bonded alkylamino silica. The method is applied to natural water samples with high contents of humic substances. The nitrate concentrations found were in good agreement with determination by ion chromatography.     

Competitive adsorption of organic matter with phosphate on aluminum hydroxide

The effects of orthophosphate on the adsorption of natural organic matter (NOM) on aluminum hydroxide were investigated using three organic compounds as surrogates, including humic acid (HA), phthalic acid, and 2,3-dihydroxybenzoic acid (2,3-DHBA). The adsorption of phthalic acid and 2,3-DHBA was very limited compared to that of HA, whereas their adsorption was reduced much more significantly than that of HA by phosphate. The efficiency of phosphate in reducing HA adsorption increased with increasing phosphate concentration. Phosphate adsorption was slightly reduced by phthalic acid and 2,3-DHBA but moderately suppressed by HA. The adjacent carboxylic groups mainly contributed to the adsorption of humic acid at low pH, while the adjacent phenol groups were responsible for the adsorption of humic acid at high pH. HPLC-SEC and SUVA analysis revealed that HA molecules with high molecular weight were adsorbed preferentially but were easily displaced by the specifically adsorbed phosphate. TM-AFM images revealed that the aggregation of HA molecules and the protonation of carboxylic groups at low pH facilitated the adsorption under acidic conditions. The presence of phosphate increases the coagulant dosage for NOM removal as some sites on the coagulant precipitates become utilized by phosphate.     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Interaction of ester functional groups with aluminum oxide surfaces studied using infrared reflection absorption spectroscopy

The bonding of two types of ester group-containing molecules with a set of different oxide layers on aluminum has been investigated using infrared reflection absorption spectroscopy. The different oxide layers were made by giving typical surface treatments to the aluminum substrate. The purpose of the investigation was to find out what type of ester-oxide bond is formed and whether this is influenced by changes in the composition and chemistry of the oxide. The extent by which these bonded ester molecules resisted disbondment in water or substitution by molecules capable of chemisorption was also investigated. The ester groups were found to show hydrogen bonding with hydroxyls on the oxide surfaces through their carbonyl oxygens. For all oxides, the ester groups showed the same nu(C = O) carbonyl stretching vibration after adsorption, indicating very similar bonding occurs. However, the oxides showed differences in the amount of molecules bonded to the oxide surface, and a clear relation was observed with the hydroxyl concentration present on the oxide surface, which was determined from XPS measurements. The two compounds showed differences in the free to bonded nu(C = O) infrared peak shift, indicating differences in bonding strength with the oxide surface between the two types of molecules. The bonding of the ester groups with the oxide surfaces was found to be not stable in the presence of water and also not in the presence of a compound capable of chemisorption with the aluminum oxide surface.     

Trace enrichment of polar pollutants from water and the influence of humic substances

Summary A practical liquid chromatographic early-warning system for polar pollutants in water ought to have detection limits at a level below a microgram per litre. Using ultraviolet absorbance detection this normally necessitates trace enrichment of the samples. In this study ten different sorbents have been tested with respect to their enrichment capacity. The hydrophobic polymeric PLRP-S material, in combination with a C-18 modified analytical column, proved to be the best choice. The influence of humic substances, present in surface water, was also studied. Lowering of the sample pH, resulted in a significant increase in the interferences due to the humic substances.     

Detection of glucosamine in the acid hydrolysis solution of humic substances

Several humic substances isolated from water and soil have been characterized applying acid hydrolysis to release defined components bound in these high molecular organic compounds. The hydrolysis solution have been analyzed by HPLC after precolumn derivatization with o-phthalaldehyde and 9-fluorenylmethylchloroformate. Under these conditions the nitrogen containing carbohydrate glucosamine could be detected and separated besides seventeen amino acids. The results show that 8.0 to 40.1% of the total nitrogen content of the investigated samples contributes to amino acids and up to 7.9% to the carbohydrate glucosamine. It could be deduced that defined amino acid carbohydrate building blocks were bound in humic substances, because the glucosamine nitrogen content correlates with the calculated amino acid nitrogen. Furthermore the total amino acid nitrogen amount of natural organic matter can be estimated from the results of the determination of glucosamine.     

Humic acid adsorption on fly ash and its derived unburned carbon

Fly ash is solid waste from combustion process, containing oxide minerals and unburned carbon. In this investigation, fly ash has been separated into metal oxide mineral section and unburned carbon. The fly ash with different contents of unburned carbon was employed for humic acid adsorption to investigate the influence of unburned carbon on adsorption. It is found that metal oxides and unburned carbon in fly ash exhibit significant difference in humic acid adsorption. The unburned carbon plays the major role in adsorption. Higher content of unburned carbon in fly ash results in higher surface area and thus higher humic acid adsorption. Fly ash and unburned carbon exhibit adsorption capacity of humic acid of 11 and 72 mg/g, respectively, at 30 degrees C, pH 7. Humic acid adsorption is also affected by ion strength, pH, and temperature. The thermodynamic calculations indicate that the adsorption is endothermic nature with DeltaH(0) and DeltaS(0) as 5.79 kJ/mol and 16.0 J/K mol, respectively.     

Detection of glucosamine in the acid hydrolysis solution of humic substances

Several humic substances isolated from water and soil have been characterized applying acid hydrolysis to release defined components bound in these high molecular organic compounds. The hydrolysis solution have been analyzed by HPLC after precolumn derivatization with o-phthalaldehyde and 9-fluorenylmethylchloroformate. Under these conditions the nitrogen containing carbohydrate glucosamine could be detected and separated besides seventeen amino acids. The results show that 8.0 to 40.1% of the total nitrogen content of the investigated samples contributes to amino acids and up to 7.9% to the carbohydrate glucosamine. It could be deduced that defined amino acid carbohydrate building blocks were bound in humic substances, because the glucosamine nitrogen content correlates with the calculated amino acid nitrogen. Furthermore the total amino acid nitrogen amount of natural organic matter can be estimated from the results of the determination of glucosamine.