Selective desorption and analysis of humic substances on suspended particles in river water

The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes.     

AFM study on the adsorption and aggregation behavior of dissolved humic substances on mica

Humic substances (HS) are a category of naturally occurring, biogenic, heterogeneous organic materials found in or extracted from soils, sediments, and natu- ral waters that can generally be characterized as being yellow-to-black in color, of highly variable relative molecular masses, and refractory[1,2]. Derived from a variety of organic precursors (plant biopolymers such as lignin etc.), plant residues and animal debris via both transformation and synthesis processes[3] under the profound ge…     

Distribution of humic substances dissolved and particulated in water column in Ross Sea, Antarctica

Dissolved (DFA) and particulate (PFA) fulvic acids were studied in some areas of the Ross Sea (Antarctica) characterised by different water masses. Our interest was focused on their distribution in the water column. Moreover, their correlation with fluorescence data and structural characterisation in relation to the water masses was also studied. We found that PFA concentration was mainly influenced by the primary production in surface layers and by stratification of water masses along the water column. Conversely, the DFA are less influenced by primary production and by the stratification of the water masses. An early stage of the humification process can be hypothesised for PFA related to DFA as shown by elemental analyses and spectroscopic data. PFA collected in the bottom depths of the water column showed a relationship with age of water mass (the highest concentration was found for the oldest circulating water mass (CDW)). This relationship was not observed for DFA. Moreover, any significant difference in structure was found in the DFA and PFA extracted from samples collected at bottom depths.     

Tefluthrin Sorption to Mineral Particles: Role of Particle Organic Coatings

Abstract

The sorption of tefluthrin was studied on “pure” clay minerals and those that had been coated with aquatic humic substances over a mass percent carbon range of 0.02 to 2.15. Tefluthrin sorption onto humic-coated minerals was significantly greater than on to the clean minerals and increased with increasing quantities of sorbed humic substances. Humic acid, the most aromatic coating, was the strongest sorbent, followed by fulvic acid, hydrophilic macromolecular acid and natural coatings on estuarine suspended particles. This shows the significant impact of humic coatings on the sorptive capacity of mineral particles. The sorption was linear, also consistent with the operation of a partition process. The partition coefficient normalised to organic carbon (K_oc) after deduction of the contribution from the clean mineral, ranged from 120000 to 770000 and was highest for the most aromatic humic acid fraction.     

Capillary electrophoretic separation of humic substances using hydroxyethyl cellulose as a buffer additive and its application to characterization of humic substances in a river water sample

We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated. Figure Addition of Fe(III) ions or EDTA to a solution containing fulvic acid (FA) results in a distinct change in the electropherogram pattern, which reflects the conformational change of FA: this forms the basis for the characterization of humic substances in river water samples     

A rapid quantitative method for humic substances determination in natural waters

A simple and rapid method was proposed for humic substances (HS) determination at microgram levels in natural waters. This assay method is based on the binding of a dye, Toluidine Blue (TB), to HS molecules to produce a dye-HS complex, which causes a decrease in absorbance at 630 nm. This method was calibrated with HS samples with up to a concentration of 40 mg L⁻¹, which covered the range of dissolved HS concentrations present in natural waters. The detection limit was 0.8 mg L⁻¹ of HS, and the relative standard deviation of 10 replicate measurements for a 20-mg L⁻¹ standard sample was 3.5%. From the Langmuir adsorption isotherm theory, the binding equilibrium constant and total number of binding sites at neutral pH were calculated to be (8.17 ± 0.42) × 10⁵ L mol⁻¹ and N of 1.45 ± 0.04 mmol g⁻¹ HS, respectively. The determination results with five water samples from lake, river and pond were consistent with those measured with the reference methods, demonstrating that this quantification method for HS determination was rapid, sensitive and feasible.     

Chemical removal of humic substances interfering with the on-line solid-phase extraction—Liquid chromatographic determination of polar water pollutants

Summary Different methods for removing interference by humic substances in the analysis of polar pollutants have been compared in the analysis of environmental water by solid-phase extraction (SPE) with a chemically modified polymeric resin coupled on-line to liquid chromatography with UV detection. The methods were based on the use of chemical reagents. The best method was found to be addition of sodium sulphite to humic-containing water before SPE. The appropriate amount of sulphite depends on the amount of humic substances dissolved in the sample—for analysis of 50 mL tap and Ebro river water, respectively, 250 μL and 500 μL 10 % Na₂SO₃ solution had to be added. In both cases, the recovery values after chemical treatment were similar to those when a Milli-Q-quality water standard was analysed.     

The association between selenium and humic substances in forested ecosystems—laboratory evidence

In the soils and aquatic systems of coniferous forests, selenium is usually associated with humic substances. To clarify further some of the mechanisms involved, labelled and unlabelled selenite were added to two forest floors and to a brownwater lake. Sequential extraction procedures and chromatographic methods were used to evaluate the resulting association between selenium and humic substances. It was observed that the forest floors fixed most of the added selenite by means of microbial reductive incorporation and that selenium was preferentially incorporated into lowmolecular-weight fractions of the humic substances. By contrast, selenium reduction was much slower in the brown-water lake and instead, inorganic complexation of selenite to metal–humic complexes was important during the experiment, provided that the concentrations of competing ligands were low.     

Liquid chromatographic determination of per- and polyfluoroalkyl substances in environmental river water samples

Contaminants of emerging concern (CECs) such as per- and polyfluoroalkyl substances (PFAS) have attracted significant interest from researchers, policymakers, and water treatment facilities. This is because PFAS are highly persistent in the environment and tend to be bio-accumulative thus causing adverse effects on terrestrial and aquatic life. Therefore, there is a need for simpler and fast methods for the determination of PFAS in water sources. This work aims at the application of dispersive magnetic solid-phase extraction (DMSPE) for the enrichment of PFAS in various surface water samples. Magnetic Fe₃O₄@MIL-101 (Cr) was used as an adsorbent in MSPE. Fe₃O₄@MIL-101(Cr) was used for the first time for the preconcentration and extraction of PFAS in various river water samples. The concentrations of target analytes in water samples were determined using high performance liquid chromatography-diode array detector and ultra-high performance liquid chromatography-tandem mass spectrometry analysis. The combination of optimized DMSPE with HPLC-DAD and UHPLC-MS/MS provided wide linear range (1–5000 ng/L and 0.05–2000 ng/L, low limits of detection (0.3–0.66 ng/L and 0.011–0.04 ng/L) and limits of quantification (1.0–2.2 ng/L and 0.04–0.12 ng/L). Moreover, acceptable intraday and interday precision based on the relative standard deviation (RSD) lower than 5% were obtained. The developed method showed remarkable practicability for the analysis of ultra-trace PFAS in water samples.     

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.     

High-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) for qualitative detection of humic substances and dissolved organic matter in mineral soils and peats in Lithuania

High-performance liquid chromatography (HPLC) with size exclusion (SEC) separation function was used to isolate and examine the molecular mass (MM) distributions and polydispersity of humic substances (HSs) and dissolved organic matter (DOM) from mineral soils and peats. The aim was to improve their detailed characterisation and to inform of their soil carbon (C) sequestration and environmental quality. This is the first study conducted in Lithuania in which HSs and DOM, separated from two soil types, have been used to characterise soil at the molecular level. The HPLC-SEC, as a separation method, was coupled with diode-array detection (DAD), thus enabling the separation of molecular fractions. Results showed that HPLC-SEC can be used to determine the MM of HSs in soil, provided that the relation between retention time and MM is known and a suitable method for fitting the HS peak is available. The UV-spectra analysis showed that DOM has a larger MM (M_w = 2439–3436 Da), which contains more aliphatic C. The HS fraction has a smaller MM (M_w = 2776 Da), with aromatic structures that reflect a higher aromaticity. Separated fractions had characteristic MMs of humic acid (HA) and fulvic acid (FA) and DOM. The HSs separated from peat samples were characterised by higher aromaticity, humification and stability. The HSs extracted from mineral soil samples showed a higher degradability level. The results also show the MM distribution and polydispersity of HS and DOM fractions (M_w/M_n = 1.009–1.252) are relatively homogenous in both soil types. Findings confirm that chromatographic and spectrometric parameters can be used for characterisation of both HSs and DOM, and for detecting changes in organic matter quality. Moreover, they can also be used for a further understanding the C-cycle and could be applied for enhancing soil C-sequestration and informing environmental quality management.     

Influence of humic substances on sorption and methylation processes of inorganic- and organo-tin species

The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents.     

Differential pulse polarographic determination of europium in the presence of humic substances

Humic substances (HS) and other substance of similar nature (“building blocks” of HS, such as salicylates or phthalates) influence strongly a polarographic behaviour of europium at a mercury drop electrode. An addition of these substances into the supporting electrolyte causes an enhancement of the differential pulse polarographic (DPP) peak of Eu and an anodic shift of the maximum peak potential. It was deduced from the dependence of the peak height on the pulse time and from other experimental dependencies that an adsorption of the Eu-HS (salicylate, phthalate) complexes on the working electrode is the main mechanism responsible for the peak enhancement. Because no peak distortion or splitting were observed, the DPP determination of Eu can be realised readily in the presence of HS, e.g. in environmental samples. The sensitivity of the measurements increased in the presence of HS, whereas the limit of detection (LOD) decreased (LODs were 255 and 140 nmol/l in the absence and in the presence of HS, respectively). However, the calibration dependencies were non-linear in the presence of HS. It was found that the non-linear calibration dependencies may be approximated by the Langmuir-type equation. Special procedures, such as a method of (at least) two standard additions and numerical iterative calculations, are necessary for an evaluation of measurements.     

Influence of dissolved humic material and ionic strength on C8 extraction of pesticides from water

Summary A mixture of twelve intermediate polarity pesticides, mostly carbamate-type, have been chromatographied on an octadecyl-silica bonded-phase column using acetonitrile-water gradient mobile phase and UV detection. Pesticides were extracted from aqueous matrix by solid-phase extraction. The extraction system consisted of a glass microcolumn containing octyl-silica solidphase conditioned with methanol and water. The elution was by acetonitrile-dichloromethane (50:50). Studies of extraction factors like volume of sample, addition of 10% sodium chloride and presence of dissolved humic material are investigated. After extraction optimization, it was applied to waters from Lake La Albufera (Valencia, Spain). Some pesticides used in rice crops were found at concentrations above those allowed by the EEC for natural waters (1–3 μg L⁻¹).     

Laboratory and field evaluation of diffusive gradient in thin films (DGT) for monitoring levels of dissolved mercury in natural river water

The diffusive gradient in the thin films (DGT) technique was tested to measure dissolved mercury (Hg) both in laboratory aqueous solutions and in situ in river water. For this purpose, a commercial ready-to-use and specific-for-Hg DGT device was used. Each sampler consisted of a filter membrane-agarose gel as the diffusive layer and a Spheron-Thiol resin in polyacrylamide gel as the binding agent. Basic performance assays at the laboratory with this type of DGT unit confirmed the applicability of Fick's first law for DGT measurements. The diffusion coefficient of MeHg in the agarose diffusive gel was 8.50?×?10^?6?cm² s^?1 at 25°C. Several field studies were also carried out in two different rivers of the Ebro River basin (NE Spain) affected by Hg wastes released by the chlor-alkali industry. Hg concentrations determined by DGT were generally much lower than the results obtained through direct measurements of the river water. In addition, the results of a time series experiment also performed in the field show that the amount of Hg accumulated in the resin does not increase at all with the exposure time. This may be explained by the underestimation of the truly dissolved Hg fraction due to the formation of a biofilm layer on the surface of the samplers, thus clogging the filter and preventing Hg species from diffusing through it. Consequently, it was demonstrated that the DGT technique presents important limitations for measuring Hg in polluted rivers characterised by a high biomass load (eutrophic), whereas its performance was demonstrated to be correct in oligotrophic waters.     

Reduction of mercury(II) by tropical river humic substances (Rio Negro)-Part II. Influence of structural features (molecular size, aromaticity, phenolic groups, organically bound sulfur)

The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F₁>100 kDa and F₂: 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F₅: 5-10 kDa, F₆: <5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t_1/2 of I: 160 min, t_1/2 of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F₅>F₂>>F₁>F₃>F₄>>F₆). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex ‘competition’ between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested.     

固相萃取-气相色谱-质谱联用同时测定河水和海水中87种农药

采用固相萃取-气相色谱-质谱联用技术,建立了河水和海水中87种农药(24种有机磷、15种有机氯、12种唑类、9种拟除虫菊酯类、5种氨基甲酸酯类、7种酰胺类及15种其他新型农药)的多残留同时分析方法。优化了影响分离效果和灵敏度的仪器参数,考察了固相萃取柱柱型及水样体积、pH、盐度的影响,采用NH2柱优化了净化效果,内标法和替代物法用于数据的质量控制。结果表明: 在最佳条件下,各目标农药的方法检出限为0.1～6.6 ng/L;以实际河水和海水为基底,在5 ng/L和20 ng/L的加标水平下,绝大多数目标农药的回收率为60%～120%,相对标准偏差(n=4)为0.01%～9.7%。该法灵敏、准确,已成功地应用于福建九龙江河口区表层水样中多种类农药的复合污染监测,检出包括5种有机磷类、3种酰胺类、4种唑类、3种氨基甲酸酯类、2种拟除虫菊酯类等农药20种。     

Separation and determination of traces of heavy metals complexed with humic substances in river waters by sorption on indium-treated amberlite xad-2 resin

A nonionic macroreticular styrene/divnylbenzene copolymer, Amberlite XAD-2 resin is pulverized to 1–10 μm and treated with indium ions to saturate traced of cation exchange sites for the quantitative separation of humic complexes from cations. A 100-ml filtered sample is passed through an indium-treated XAD-2 column (16 diameter, 5 mm tall) at pH 5 at a flow rate of 2 ml min^? to sorb heavy metals complexed with humic and fulvic acids. Inorganic cations and anions, EDTA complexes and colloidal hydrated iron(III) oxide are not retained on the column at all. The heavy metals sorbed on the column are then ultrasonically desorbed with 0.5 M nitric acid and determined by graphite-furnace atomic absorption spectrometry. The results fo two river water samples obtained are in good agreement with those obtained when the macroreticular weak-base anion-exchanger DEAE-Sephadex A-25 is used.     

Extractability of dioxins from suspended substances in distributed water

The extractability of dioxins from suspended substances (SS) in distributed water was evaluated. Dioxins adsorbed on the collected SS were extracted by pressurized liquid extraction with various solvents. High-polarity solvents (acetone, alcohols) extracted considerably higher amounts of some lower-chlorinated dibenzo-p-dioxins (LoCDDs) than did low-polarity solvents (dichloromethane, toluene), whereas the extracted amounts of higher-chlorinated dibenzo-p-dioxins (HiCDDs) were roughly the same, regardless of the solvent. The extractability of the LoCDDs depended on the isomer. Daily variations in quantities for PCDDs, organic matter (OM), and iron in the SS were examined, and the results suggested that in the SS, LoCDDs and HiCDDs were associated, respectively, with raw water-derived organic matter and microparticles sequestered in iron oxy(hydr)oxide floc. It was also suggested that the low extractability of certain congeners was not attributable to the enormously coexisting ferric compounds but was probably attributable to OM with which they strongly associate.