The methylation of inorganic tin by humic materials in an aquatic environment

This paper presents a study of methylation of inorganic tin (SnCl₄·5H₂O) by humic materials (humic and fulvic acids) isolated from the sediment of Tianjin Harbor, Tianjin, China, and the effects of pH, salinity, and the concentration of inorganic tin on the production of methyltin were investigated. These humic materials could methylate inorganic tin, and the methyltin product was mainly monomethyltin. Low molecular weight compounds of the humus fraction (i.e. fulvic acid) were more active in the methylation, which could be facilitated by salinity and affected by pH.     

土壤腐殖质各组分红外光谱研究

土壤腐殖质是土壤中所特有的一类特殊的高分子化合物,具有重要的肥力和环境调节功能。其中胡敏素的提取和纯化很困难,从而限制了对其性质和结构的研究。为揭示胡敏素的结构性质,本研究按Pallo分组,将胡敏酸(HA)分为焦磷酸钠提取的胡敏酸(HAP)、氢氧化钠提取的胡敏酸(HAS);富里酸(FA)分为焦磷酸钠提取的富里酸(FAP)和氢氧化钠提取的富里酸(FAS);胡敏素(HM)分为铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)和不溶性胡敏素(HMr)三个组分,采用红外光谱法对黑土、草甸土以及黑土底土加入大量玉米秸秆培养后腐殖质各组分的结构特征进行研究。腐殖质各组分按Pallo法分组。结果表明:铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)与胡敏酸(HA)、富里酸(FA)具有相似的光谱特征,但存在明显差异。黑土、草甸土中HMi和HMc的脂族性强于HA和FA;HMi与HMc相比,HMi具有较高的脂族性。黑土中氢氧化钠提取的胡敏酸(HAS)的脂族性强于焦磷酸钠提取的胡敏酸(HAP);NaOH提取的富里酸(FAS)的脂族性强于Na4P2O7提取的富里酸(FAP)。草甸土中HAP的脂族结构较多,而HAS脂族结构相对较少。在培养土中,新形成的FA脂族性强于HA、HMi和HMc组分。新形成的HMc脂族性强于HMi和HMc的脂族性强于HAP,而弱于HAS。     

Characterization of humic and fulvic acids from Gorleben groundwater

Summary The humic material extracted from one of the Gorleben groundwaters is separated into humic and fulvic acids, and characterized, together with a commercial humic acid from Aldrich Co., for their chemical composition, size distribution, proton exchange capacity and spectroscopic characteristics. The results are compared with one another and with the literature data of other humic acids. The humic acid is fractionated by gel permeation chromatography into different size groups and the fractions are subjected to IR and ¹H-NMR spectroscopy. The high molecular weight fractions (>70000 Dalton) are poor in carboxylic groups, whereas the major fractions (approx. 10000 Dalton) contain organic acids of large molecular entities.     

Ultrasound-Assisted Extraction of Humic Substances from Peat: Assessment of Process Efficiency and Products’ Quality

Results of efficiency of obtaining humic substances (HSs) from peat in traditional alkaline extraction (TAE) and ultrasound-assisted alkaline extraction (UAAE) are presented. The influence of the duration of the process and ultrasound intensity on the efficiency of extraction of humic acids (HAs) and fulvic acids (FAs) extraction was determined. The composition of the fulvic acid fraction was examined depending on the type of eluent used. Fulvic acids were divided into fractions using columns packed with DAX-8 resin. For this process, 0.1 M NaOH and 0.5 M NH₃∙H₂O were used as eluents. For the quality assessment of specific fulvic acids fractions, spectroscopic methods (UV-Vis and FTIR) were used. Ultrasound had a positive effect on HS extraction efficiency, especially in increasing the amount of a desired hydrophobic fraction of fulvic acids (HPO). However, a negative effect of the excessive prolongation and ultrasound intensity (approximately 400 mW∙cm⁻²) on the extraction efficiency of HPO eluted with 0.1 M NaOH solution was observed. Using peat as a raw carbon material for the HS extraction process can be used as an alternative industrial application of peat. UAAE may be considered as an alternative method to TAE, which provides a higher efficiency in HS isolation from peat.     

Conductometric characterization of dissolved humic materials

Conductometric replacement titrations of humic and fulvic acids dissolved in a slight excess of hydroxide were carried out with standard acid. The slope of the titration curve corresponding to the protonation of humate/fulvate was related to the electrophoretic mobility of the polyanions or aggregates, and hence to their dimensions. Promising qualitative agreement was found between sizes of a number of these species and their conductance slopes. Both the separation of humic fractions and size reduction by photolysis and sonication led to the anticipated decrease in slope. The slight reduction in slope observed during the course of the titration was tentatively ascribed to contraction of the expanded (drained) humic aggregates.     

Preparation and characterization of humic and fulvic acid working standards—practical experience

Two fractions of both fulvic acids (FA) and humic acid (HA) were prepared by fractionation method of Pierce and Felbeck⁵ involving acid hydrolysis of soil rests. This step increases recovery of both FA and HA considerably what suggest us need for slight modification of IHSS method in some cases. The weight loss, change in organic carbon content and visible spectra are figures of merit discussed. After detailed characterization these humic substances (HS) will serve as the working standards for study of interactions between organomercurials and organic part of soil.     

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.     

Fractionation analysis of trace metals in humic substances of soils irrigated with wastewater in Central Mexico by particle induced X-ray emission

The Mezquital Valley in Central Mexico has received wastewater from Mexico City for nearly 100 years. Wastewater brings in organic matter and nutrients but also trace metals. Humic substances, the main components of organic soil matter, are responsible for retaining and regulating the mobility of trace metals in soils. In this study, humic substances were extracted from the soil and separated into distinct fractions (humic acids, fulvic acids and humins). The particle induced X-ray emission (PIXE) technique was applied to determine the metal content in bulk soil as well as in humic acids and fulvic acids not soluble in H₃PO₄. In order to assess whether the long-term input of organic matter and metals modifies the metal association with these humic substances, parcels irrigated for three time periods (5, 47 and 89 years) were selected for this study. It was observed that metals such as Zn and Cu are mainly associated with the humic acids. Fulvic acids retain mainly Cr while Pb is distributed among humic and fulvic acids. It was also observed that in general, metal retention by humic substances increases with irrigation time. Depth also affects metal association with the humic substances.     

NMR characterization of humic acid fractions from different Philippine soils and sediments

Humic acids from a peat soil, an agricultural soil and a lake sediment from the Philippines were fractioned by sorption chromatography on cross-linked dextran gels (Sephadex¹). The NMR spectra of these fractions have sharp, well resolved bands which can be attributed to lignin-like structures, carbohydrates and aliphatic groups. Similar bands have been observed in the NMR spectra of humic acid fractions from other environments; however, the chemical shifts of some of the lines vary from one humic acid to another. These lines appear to arise from well defined, partially decomposed plant components and probably are diagnostic of the types of plants that decomposed into these humic acids. The lines in the carbohydrate region are the best resolved and may prove to be the most useful in identifying the plant precursors of any particular humic acid fraction.     

Investigation of distribution of soil antimony using sequential extraction and antimony complexed to soil-derived humic acids molar mass fractions extracted from various depths in a shooting range soil

Trace metal contamination from bullet fragments in shooting ranges is a major environmental concern. In particular, trace metals such as lead, antimony, and copper are toxic and have the potential to enter groundwater supplies and to be absorbed by plants. Soil humic acids can play a critical role in mobilizing some of these released metals through complexation. The purpose of this study is to investigate the antimony complexed to soil-derived humic molar mass fractions extracted from various depths in a shooting range soil and to examine the distribution of antimony in various fractions of shooting range soils using sequential chemical extraction approach. The surface soil and soil core samples from a local shooting range were collected. Soil-derived humic acids were extracted from different depths of the top soil layer and characterized by various spectroscopic methods. Results of sequential chemical extraction demonstrated that Sb was found in shooting range in the upper 30 cm depth of the soil core. Highly elevated Sb is present in the exchangeable and ammonium acetate extracted fractions. Antimony is also present in the residual fraction in both surface and core soil samples, but is most likely present in a lithic phase which may not be readily bio-available. Leached antimony complexed to soil humic acid molar mass fractions was determined by size exclusion chromatography coupled to inductively coupled plasma-mass spectrometry (SEC-ICP-MS). The results demonstrate that Sb is ‘tightly’ bound to humic acid mass molar mass fractions and confined in the top 10 cm of soil-derived humic acids.     

The uniqueness of humic substances in each of soil,stream and marine environments

Definitive compositional differences are shown to exist for both fulvic acids and humic acids from soil, stream and marine environments by five different methods (¹H and ¹³C NMR spectroscopy, ¹⁴C age and δ¹³C isotopic analyses, amino acid analyses and pyrolysis-mass spectrometry). Definitive differences are also found between fulvic acids and humic acids within each environment. These differences among humic substances from various sources are more readily discerned because the method employed for the isolation of humic substances from all environments excludes most of the non-humic components and results in more purified humic isolates from water and soils. The major compositional aspects of fulvic acids and humic acids which determine the observed characteristic differences in each environment are the amounts and composition of saccharide, phenolic, methoxyl, aromatic, hydrocarbon, amino acids and nitrogen moieties.     

Radio-tracer methods for studying speciation in natural waters

Radio-tracer experiments have shown that antimony, mercury and zinc interact to form complexes with humic and/or fulvic acids, whose molar masses can be estimated by gel chromatography. Sb(III) and (V) humates are stable in the pH range 7–11, but are largely dissociated below pH 4; humic acid does not reduce Sb(V) to Sb(III) in solution. Mercury forms a strong complex with humic+fulvic acids. Zinc forms complexes with both humic acids and glycine, and the humic acid complex has similar elution behaviour on dextran gel to a fraction from river water equilibrated with⁶⁵Zn. At least one other form of zinc, in addition to Zn²⁺, occurs in this river.     

Size exclusion (radio) chromatography of aqueous humic acid solutions with cesium and strontium

The high-performance size-exclusion chromatography (HPSEC) and radiochromatography (HPSERC) was used for the identification of radiocesium and radiostrontium interaction with humic acid. It was found that the behavior of humic acid on size-exclusion chromatography is sensitive to the salt concentration and pH of the mobile phase. At lower ionic strength and in acidic region of pH, the Aldrich humic acid exhibited three main fraction within the ranges >760 kDa, 25–100 kDa and <5 kDa. Radiocesium was found in the low-molecular fractions (<1 kDa) of humic acids but radiostrontium interacts preferably with the fractions of humic acid of molecular weight within the range 2–5 kDa.     

Use of the cation exchange equilibrium method for the determination of stability constants of Co(II) with soil humic and fulvic acids

The stability constants for tracer concentrations of Co(II) complexes with both the red earth humic and fulvic acids were determined at pH 5.9 and ionic strength 0.010 mol/l by using theArdakani-Stevenson cation exchange equilibrium method and the radiotracer⁶⁰Co. It was found that the 1:1 complexes of Co(II) with the red earth humic and fulvic acids were formed and that the average values of logβ (stability constant) of humic and fulvic acid complexes were 5.76±0.19 and 4.42±0.03, respectively.     

Characterization of humic substances: Implications for trihalomethane formation

Humic substances are precursors of carcinogenic trihalomethanes (THMs) formed during disinfection by chlorination in water treatment processes. In an effort to understand the relationship between trihalomethane formation potential (THMFP) and physicochemical properties of humic substances, UV-visible absorbance, fluorescence in emission and synchronous scan modes, and NMR spectra were measured for several aquatic fulvic and humic acids. For comparison, a soil fulvic acid was also examined using these methods. The feasibility of the gradient modified spin-echo (GOSE) NMR experiment to selectively measure singlet resonances arising from isolated protons was examined. In addition, diffusion coefficients were measured for DMSO solutions of the fulvic acids using BPPLED and GOSE-edited pulse sequences. Although none of the methods tested produced results that correlated with THMFP, the GOSE intensities determined for different regions of the NMR spectra did reflect the relative abundance of different types of functional groups produced by lignin oxidation. In addition, the GOSE-edited diffusion results suggest that the isolated protons, those most reactive to chlorination, are more likely contained in the larger molecular weight fractions of fulvic acids.     

Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water = 80:19.3:0.7 at [K⁺] = 0.02 M enabled to measure the potential change in a wide range of pOH (=−log [OH⁻]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.     

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.     

Assessing the trihalomethane formation potential of aquatic fulvic and humic acids fractionated using thin-layer chromatography

The significance of this research is the application of thin-layer chromatography (TLC) to fractionate well-characterized aquatic humic materials coupled with the novel evaluation of the trihalomethane formation potential (THMFP) of the fractionated materials. Disinfection by-products such as trihalomethanes (THMs) form when natural water is treated by chlorination. Nordic Aquatic and Suwannee River fulvic and humic acids, obtained from the International Humic Substances Society, were prepared at pH 6 and 9 and fractionated on silica gel plates using a mobile phase consisting of methanol and ethyl acetate (2:1, v:v). Based on retention factor (R(f)) values, three common fractions were identified in all substances examined. Additionally, other fractions were noted that were characteristic of specific humic substances. Each of the three primary fractions derived from Nordic Aquatic fulvic acid at pH 6 demonstrated the potential to contribute to formation of THMs. This research provides data to support the hypothesis that differences in the chemical structure and composition of natural organic matter (NOM) significantly affect the potential to react with chlorine to form THMs.     

A new analytical approach for humin determination in sediments and soils

In this work a new analytical approach is proposed for the recovery of humin present in soil and sediments. The procedure is based on microwave oven treatment for humin deashing. In this way both the treatment time and the concentration of the HCl/HF mixture are significantly reduced (minutes rather than hours, 10% rather than concentrated). By means of the proposed scheme organic matter present in sediment and soil samples can be subdivided into the different fractions (hydrophobic and hydrophilic compounds, fulvic and humic acids, humin) making up the balance of organic carbon. Results obtained for samples characterised by different organic carbon content showed a loss of carbon ranging between 20% and 30%, consistent with previous reports about humin deashing.