Role of Neutral Fraction of Dissolved Organic Matter in the Migration of Metals in Surface Waters: II. Neutral Metal Complexes in Water Bodies of Different Types

The results of long-term studies on the contents and seasonal dynamics of neutral carbohydrate metal complexes in the surface water bodies of different types (lakes, rivers, reservoirs) are summarized. It is established that the weight fraction of the mentioned complexes characteristically varies significantly depending on the type of the water body and the component composition of dissolved organic substances. In water bodies with a highly colored water, the relative contents of dissolved metals in neutral complexes are low due to their preferential binding to anionic complexes with humic substances. In small eutrophic water bodies with a relatively low content of humic substances, the carbohydrate concentrations are the highest and, accordingly, the weight fractions of metals in their neutral complexes is also very noticeable. The molecular weight distributions of neutral metal complexes are discussed. The neutral complexes with the molecular weight ≤5.0 kDa form a significant part of metals associated with carbohydrates. The seasonal dynamics of these metal complexes are discussed.     

A speciation methodology to study the contributions of humic-like and fulvic-like acids to the mobilization of metals from compost using size exclusion chromatography-ultraviolet absorption-inductively coupled plasma mass spectrometry and deconvolution analysis

High performance size-exclusion chromatography (HP-SEC) with UV absorption for organic matter detection and inductively coupled plasma mass spectrometry (ICP-MS) for elemental detection have been used to study the mobilization of metals from compost as a function of pH and the molecular mass of their complexes with dissolved organic matter (DOM). Due to its heterogeneous nature, organic matter mobilized from compost shows a continuous distribution of molecular masses in the range studied (up to 80 kDa). In order to differentiate between the contribution of humic and fulvic acids (FA) to the organic matter mobilized in the pH range 5-10, their UV absorption chromatographic profiles have been deconvoluted with respect to the adjusted gaussian profiles of the humic and fulvic acids isolated from compost. Results show a preponderant contribution of fulvic acids at low pH values and an increasing percentage of humic acids (HA) mobilized at basic pH (up to 49% of total DOM at pH 10). A similar deconvolution procedure has been applied to the ICP-MS chromatograms of selected metals (Co, Cu, Pb and Bi). In general, both fulvic and humic acids contribute to the mobilization of divalent transition metals, such as copper or cobalt, whereas bismuth or lead are preferably associated to humic acids. Non-humic substances (HS) also contribute to the mobilization of cations, especially at acidic pHs. These conclusions have been extended to different elements based on deconvolution analysis results at pH 7.     

Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples ("Grosses Gifhomer Moor", Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8-5), finally by the chelator EDTA and 0.1 mol L(-1) hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP-OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25-674, Cd: 0.05-0.2, Cu: 5-15.4, Fe: 77-1785, Mn: 21-505, Ni: 2-33, Pb: < 1, Zn: 9-715 (microg L(-1)); Na: 8-45, K: 1.3-14.9, Ca: 2-51, Mg: 1.1-7.9 (mg L(-1)); 26-73 mg L(-1) DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.     

Functional speciation of metal-dissolved organic matter complexes by size exclusion chromatography coupled to inductively coupled plasma mass spectrometry and deconvolution analysis

High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (HP-SEC–ICP-MS), in combination with deconvolution analysis, has been used to obtain multielemental qualitative and quantitative information about the distributions of metal complexes with different forms of natural dissolved organic matter (DOM). High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry chromatograms only provide continuous distributions of metals with respect to molecular masses, due to the high heterogeneity of dissolved organic matter, which consists of humic substances as well as biomolecules and other organic compounds. A functional speciation approach, based on the determination of the metals associated to different groups of homologous compounds, has been followed. Dissolved organic matter groups of homologous compounds are isolated from the aqueous samples under study and their high performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry elution profiles fitted to model Gaussian peaks, characterized by their respective retention times and peak widths. High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry chromatograms of the samples are deconvoluted with respect to these model Gaussian peaks. This methodology has been applied to the characterization of metal–dissolved organic matter complexes in compost leachates. The most significant groups of homologous compounds involved in the complexation of metals in the compost leachates studied have been hydrophobic acids (humic and fulvic acids) and low molecular mass hydrophilic compounds. The environmental significance of these compounds is related to the higher biodegradability of the low molecular mass hydrophilic compounds and the lower mobility of humic acids. In general, the hydrophilic compounds accounted for the complexation of around 50% of the leached metals, with variable contributions of humic and fulvic acids, depending on the nature of the samples and the metals.     

光化学降解溶解有机物及其对生物过程的影响

溶解有机物对控制海洋和淡水水生系统的化学、生物和物理特性有重要的影响.光化学降解溶解有机物改变了生态体系的溶解有机碳、有机物的分子量及光学特性,并且产生复杂的反应性氧化合物、二氧化碳、一氧化碳、小分子量的有机酸、氨基酸、二硫化碳等,对生物过程有重要的影响.本文简要综述了光化学降解溶解有机物的过程机理及其对生物过程的影响.     

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.     

Determination of organically-associated trace metals in estuarine sea-water by solvent extraction and atomic-absorption spectrometry

Chloroform extraction of trace metals (Ni, Cu, Mo, Mn, Cd and Pb) in estuarine sea-water was studied at pH 8 and pH 3, on the basis that the metals would be associated with dissolved organic matter (DOM), which has recently been characterized by reversed-phase liquid chromatography. Ni, Cu, Mo and Mn were extracted more at pH 8 than at pH 3. Cd and Pb were not associated with the DOM at either pH 8 or 3. The percentage of the total dissolved trace metals in sea-water associated with DOM varied from 0 to 14%. The metals extracted into chloroform at pH 8 were assumed to be associated with neutral or weakly basic DOM while at pH 3 they could be associated with either the neutral (or weakly basic) DOM or two types of acidic DOM.     

Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples (“Großes Gifhorner Moor”, Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8–5), finally by the chelator EDTA and 0.1 mol L^–1 hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP–OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25–674, Cd: 0.05–0.2, Cu: 5– 15.4, Fe: 77–1785, Mn: 21–505, Ni: 2–33, Pb: < 1, Zn: 9– 715 (μg L^–1); Na: 8–45, K: 1.3–14.9, Ca: 2–51, Mg: 1.1– 7.9 (mg L^–1); 26–73 mg L^–1 DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.     

HPLC approach for revealing age-related changes of aquatic dissolved organic matter in sediment core

Analytical method based on HPLC has been used to characterize aquatic dissolved organic matter (DOM) from sediment core of Lake Võrtsjärv, South- Estonia. High-performance size exclusion chromatography (HPSEC) as separation method was coupled with diode-array detection (DAD) and separated molecular fractions of DOM were subject to qualitative and semi-quantitative analysis. Qualitative analysis based on UV- spectra revealed the presence of proteins and humic constituents in separated high molecular weight fraction and aromatic constituents in low molecular weight fraction. Statistical data treatment methods enabled clustering sediment layers into 4 periods according to sediment depth and age. The upper 0-30 cm sediment DOM had statistically relevant differences in comparison to other periods as revealed by lower total peak and humic substances (HS) fraction areas, and molecular weights. Samples from 80-120 cm depth differed from others by decreased low molecular weight (LMW) fraction content. The observed down-core trends suggest polymerization of LMW organic constituents and increasing humification. The statistical analyses revealed that some chromatographic and spectrometric parameters can be used to differentiate between sediment layers and to evaluate environmental changes.     

Effect of Liquid Animal Manure Application on the Solubilization of Heavy Metals from Soil

Abstract

The effect of liquid animal manure on heavy metal solubilization in soil has been studied in the laboratory; three different types of experiments were carried out:

1) aerobic and anaerobic incubation of soil/manure mixtures

2) desorption of heavy metals from soil, as affected by manure liquid fraction

3) gel permeation chromatography of soil/manure aqueous extracts to identify components responsible for heavy metal solubilization.

Alf three different approaches showed that complexation involving high molecular weight dissolved organic matter from the soil/manure matrix is (together with pH) the most important driving force for heavy metal solubilization. As a consequence, chemical and microbial processes (e.g. nitrification) that influence dissolved organic matter concentrations in the soil solution, determine the degree of heavy metal solubilization in manured soil.     

Development of solid-phase microextraction to study dissolved organic matter—Polycyclic aromatic hydrocarbon interactions in aquatic environment

Solid-phase microextraction coupled with gas chromatography and mass spectrometry (SPME–GC–MS) was developed for the study of interactions between polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter (DOM). After the determination of the best conditions of extraction, the tool was applied to spiked water to calculate the dissolved organic carbon water distribution coefficient (K_DOC) in presence of different mixtures of PAHs and Aldrich humic acid. The use of deuterated naphthalene as internal standard for freely dissolved PAH quantification was shown to provide more accuracy than regular external calibration. For the first time, K_DOC values of 18 PAHs were calculated using data from SPME–GC–MS and fluorescence quenching; they were in agreement with the results of previous studies. Competition between PAHs, deuterated PAHs and DOM was demonstrated, pointing out the non-linearity of PAH–DOM interactions and the stronger interactions of light molecular weight PAHs (higher K_DOC values) in absence of high molecular weight PAHs.     

Hydrochemical Regime of the Kiliya Delta of the Danube River in Retrospective and Modern Conditions: II. Metal Content and Speciation

Past and present data on the concentration and speciation of metals (Al, Fe, Cu, Zn, Pb, Cr, Cd, Mo, Ni) in the Kiliya Danube delta have been generalized, and variations in their concentrations have been compared. It has been shown that the highest pollution of the Danube lower reach has occurred from the second half of 1980s to the first half of 1990s due to intensive anthropogenic impact on the river delta ecosystem. Subsequently, decrease of the metal concentration was observed as a result of industrial crisis in the late 1990s–early 2000s. The major part of metals is transferred by water flow in the form of suspended solids, which is related to their relatively high content in water of the Kiliya part of the Danube delta. The results of studying dissolved metal species, in particular the ratio of the labile fraction that is potentially toxic to hydrobionts and complexes with dissolved organic matter, have been discussed. Data on the distribution of metals among complexes with dissolved organic substances of different chemical natures and molecular weights are given. Humic substances have been shown to contribute most to the complexation. Compounds with molecular weights of 1 to 5 and less than 1 kDa constitute the major part of anionic metal complexes with humic substances.     

Labile rhizosphere soil solution fraction for prediction of bioavailability of heavy metals and rare earth elements to plants

A labile rhizosphere soil solution fraction has been recommended to predict the bioavailability of heavy metals and rare earth elements to plants. This method used moist rhizosphere soil in combination with a mixture of 0.01 mol L(-1) of low-molecular-weight organic acids (LMWOAs) as extractant. The extracted soil solutions were fractionated into two colloidal fractions of <0.45 microm (F(3)) and <0.2 microm (F(2)), and one truly dissolved fraction including free metal ions and inorganic and organic complexes (fractionr(0.2 microm, LMWOAs) approximately r(0.45 microm, LMWOAs). In the case of rare earth elements the good correlation was obtained for both the wheat roots and shoots. Generally, the correlation coefficients obtained by LMWAOs were better than that obtained by the first step of BCR method. Therefore, LMWAOs and F(lrss) were strongly recommended to predict the bioavailability of metals in soil pools to plants.     

Utilization of PARAFAC‐Modeled Excitation‐Emission Matrix (EEM) Fluorescence Spectroscopy to Identify Biogeochemical Processing of Dissolved Organic Matter in a Northern Peatland

In this study, we contrast the fluorescent properties of dissolved organic matter (DOM) in fens and bogs in a Northern Minnesota peatland using excitation emission matrix fluorescence spectroscopy with parallel factor analysis (EEM‐PARAFAC). EEM‐PARAFAC identified four humic‐like components and one protein‐like component and the dynamics of each were evaluated based on their distribution with depth as well as across sites differing in hydrology and major biological species. The PARAFAC‐EEM experiments were supported by dissolved organic carbon measurements (DOC), optical spectroscopy (UV‐Vis), and compositional characterization by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectroscopy (FT‐ICR MS). The FT‐ICR MS data indicate that metabolism in peatlands reduces the molecular weights of individual components of DOM, and oxygen‐rich less aromatic molecules are selectively biodegraded. Our data suggest that different hydrologic and biological conditions within the larger peat ecosystem drive molecular changes in DOM, resulting in distinctly different chemical compositions and unique fluorescent fingerprints. PARAFAC modeling of EEM data coupled with ultrahigh resolution FT‐ICR MS has the potential to provide significant molecular‐based information on DOM composition that will support efforts to better understand the composition, sources, and diagenetic status of DOM from different terrestrial and aquatic systems.     

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.     

HPSEC-UV-ICP-MS法测定天然水体中元素在不同分子量段DOM中的分布

溶解有机物(DOM)对痕量金属的形态、生物可利用性及其最终归属都有着很大的影响. 由于腐殖质(HS)是DOM的最大组成部分, 占溶解有机碳比重的40％-70％, 而HS是由芳香族、酚族、 醌族和杂环的结构单元无规则缩合连接成的大分子. 这种多官能团的结构使得HS与痕量金属有着很强的络合能力, 从而增加了天然水体中的金属浓度. 本文利用此技术首次获得了11种元素在海水水体中DOM上不同分子量的天然分布, 探讨了DOM对痕量金属在天然水体中的形态及迁移的影响.     

Sonochemical reactions of dissolved organic matter

Property changes of Aldrich and Pahokee peat dissolved organic matter (DOM) at different ultrasonic frequencies and energy densities were systematically investigated. Exposure of DOM to ultrasound resulted in decreases in TOC, Color₄₆₅, specific UV absorbance (SUVA), aromaticity and molecular weight, while DOM acidity increased. Compared to 20 kHz ultrasound, greater sonochemical transformation of DOM occurred at 354 kHz and at higher energy density, due to greater ^·OH radical production. The changes to DOM properties suggest that ultrasound may significantly affect DOM-pollutant interactions (e.g.facilitate desorption of hydrophobic organics from DOM or promote complexation between metallic cations and DOM).     

Effect of UVR on Lake Water and Macrophyte Leachates in Shallow Andean-Patagonian Lakes: Bacterial Response to Changes in Optical Features

The aim of this study was to identify bacterial responses in two shallow lakes from Patagonia to UV-irradiated dissolved organic matter (DOM) coming from different sources. We carried out laboratory experiments in which natural lake water and Potamogeton linguatus leachates were irradiated (UVA-340 fluorescent tubes Q-Panel) or kept in darkness. Natural bacterial assemblages were then incubated in four treatments: natural lake water, irradiated lake water, macrophyte leachate and irradiated macrophyte leachate. We estimated bacterial abundance, composition and activity, and changes in the optical features of DOM. Our results showed that the addition of leachates caused an increase in the DOM mean molecular size. After UV exposure, a high bacterial activity was observed in lake water treatments. On the contrary, carbon uptake by bacteria was reduced in the irradiated leachate treatment. The degree of aromatization in the leachate treatments increased and thus may contribute to a dissolved carbon less available for bacterial activity. Regarding the bacteria assemblage we observed that β -Proteobacteria outcompete the other groups in the leachate treatments, this group being more efficient at utilizing the high molecular weight DOM. These results highlight the importance of UVR interacting with different DOM sources in bacteria responses of shallow lakes.     

Strategies for the extraction of free and bound polycyclic aromatic hydrocarbons in run-off waters rich in organic matter

The objective of this study was to optimize and characterise extraction methods to examine the effects of wood ash application on polycyclic aromatic hydrocarbons (PAHs) concentrations in run-off waters for the evaluation of their distribution by storage in the different compartments (free and bound to dissolved organic matter, DOM), what influence their stability and persistence. The feasibility of solid phase extraction (SPE) and stir bar sorptive extraction (SBSE) for the determination of eight PAHs in run-off water samples has been evaluated. Both are appropriate to determine PAHs in run-off waters, but SPE is suitable for the determination of overall PAHs, while SBSE is used for the determination of free PAHs. The combination of both extraction techniques can then be used to estimate PAHs bound to DOM. Another approach based in the only use of SBSE is proposed for the estimation of all PAHs fractions (free, bound to DOM, and overall), once we are able to estimate the fraction percentage the free concentration represents. The percentage of free fraction was variable in the run-off waters with medium levels of DOM depending on the number of aromatic rings, molecular weight and water solubility of PAHs.     

Comparison of changes in metal toxicity following exposure of water with high dissolved organic carbon content to solar, UV-B and UV-A radiation

This study examines the effects of natural solar radiation on the metal-binding capacity of dissolved organic matter (DOM). Newington Bog water (35.5 mg L⁻¹ dissolved organic carbon [DOC]) was irradiated for 20 days under UV-B lamps in the laboratory and under natural solar radiation. In the presence of irradiated DOM, IC₅₀ (contaminant concentration required to reduce algal growth by 50%) was significantly decreased with UV-B treatment for four metals: Pb, 64%; Cu, 63%; Ni, 35% and Cd, 40%. Solar radiation also significantly decreased IC₅₀ of Pb (58%) and Cu (49%), DOC concentration (11%), DOM fluorescence (DOMFL, 33%) and DOC-specific UV absorbance. Further experiments on Raisin River water (20.7 mg DOC L⁻¹) exposed to 20 days of artificial UVA and UV-B radiation produced significant decreases in IC₅₀ for Cu (48%) with UV-A and for Pb (43%) with UV-B. DOC concentration was decreased 20% by UV-B and 24% by UV-A. DOMFL decreased 51.5% in the first 5 days of UV-A exposure, an effect that was not observed with the UV-B treatment. The UV-A treatment decreased UV absorbance more at longer wavelengths and over a broader wavelength band than did the UV-B treatment. Change in toxicity with UV irradiation was inconsistent among the metals tested in this study, indicating that some organic metal-binding ligands were more quickly removed or altered than others. The DOM remaining after irradiation appears to be qualitatively different from the unirradiated DOM. The much greater irradiance of UV-A makes its contribution to the removal and/or alteration of DOM at least as important as the influence of higher energy UV-B.