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PubMed2005

Distribution of aged 14C-PCB and 14C-PAH residues in particle-size and humic fractions of an agricultural soil.

Organic matter is considered to be the single most importantfactor limiting availability and mobility of persistent organic pollutants (POPs) in soil. This study aimed to characterize the distribution of 14C-PCB (congeners 28 and 52) and 14C-PAH (fluoranthene and benzo[a]pyrene) residues in an Orthic Luvisol soil obtained from two lysimeter studies initiated in 1990 at the Agrosphere Institute (Forschungszentrum Jülich GmbH, Germany). The lysimeter soils contained a low-density OM fraction, isolated during soil washing, which contained a significant fraction (3-12%) of the total 14C-activity. Soils were also fractionated according to three particle sizes: >20, 20-2, and <2 microm. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) approximately (>20 microm) for the PCBs. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) > (>20 microm) for the PAHs. The distribution of 14C-PCB or 14C-PAH residues in the organic and inorganic matrixes of the particle-size fractions was determined using methyl isobutyl ketone (MIBK). 14C-PCB and 14C-PAH-associated activities were primarily located in the humin fraction of the 20-2 and <2 microm particle-size fractions of the soil. A small fraction was associated with the fulvic and humic acid fractions; these were quantitatively more important for the PAHs than the PCBs. There appeared to be a high degree of association of 14C-activity with the mineral fraction following MIBK separation of the humic fractions, ranging between 8 and 52% for 14C-PCBs and 57-80% for 14C-PAHs. The mineral (inorganic) component of the soils apparently played a significant (previously unreported) role in the sequestration of both PCBs 28 and 52 and the PAHs fluoranthene and benzo[a]pyrene.

Agriculture↗

PubMed2005

Immobilization of humic acid in nanostructured layer-by-layer films for sensing applications.

Humic acids (HAs), naturally occurring biomacromolecules, were incorporated into nanostructured polymeric films using the layer-by-layer (LbL) technique, in which HA layers were alternated with layers of poly(allylamine hydrochloride) (PAH). Atomic force microscopy (AFM) revealed very smooth films, with mean roughness varying from 0.89 to 1.19 nm for films containing 5 and 15 PAH/HA bilayers, respectively. The films displayed electroactivity, with the presence of only one reduction peak at ca. 0.675 V (vs Ag/AgCl). Such a well-defined electroactivity allowed the films to be used as highly sensitive pesticide sensors, with detection of pentachlorophenol (PCP) in solutions at concentrations as low as 10(-9) mol L(-1).

Biosensing Techniques↗

PubMed2006

Conditioning-annealing studies of natural organic matter solids linking irreversible sorption to irreversible structural expansion.

The assumption of reversibility underpins the sorption term in current models dealing with the fate and impact of organic compounds in the environment, yet experimentally sorption of organic compounds in soils and sediments often shows "irreversible" behaviors such as hysteresis and the conditioning effect (enhanced repeat sorption). The objective of this study was to test whether a glassy polymer irreversibility model applies to natural organic matter (NOM) solids. Irreversible sorption in polymers is believed to be caused by irreversible expansion and creation of internal micropores by penetrating molecules, leading to enhanced affinity during desorption or subsequent resorption. Using chlorobenzene as a conditioning agent and polychlorinated benzenes as test compounds in a second sorption step, we observed conditioning effects for a peat soil, a soil humic acid, and a model glassy polymer, poly- (vinyl chloride), but not for a model rubbery polymer, poly- (ethylene). The conditioning effect for the two natural solids, probed bythe enhancement in the sorption distribution coefficient of 1,2,4-trichlorobenzene, relaxed upon sample annealing between 45 and 91 degrees C in a manner similar to the relaxation of free volume and enthalpy of glassy polymers. Relaxation of the conditioning effect in the NOM solids depended on annealing temperature and, at a given temperature, followed a double additive exponential rate law with a nonzero constant term descriptive of the final state that depends inversely on temperature. At environmentally relevant temperatures, the conditioning effect may "never" completely relax. The results provide compelling evidence for the glassy, nonequilibrium nature of natural organic matter solids and for irreversible structural expansion as a cause of irreversible sorption.

Adsorption↗

PubMed2005

Effect of pH and aging time on the kinetic dissociation of 243Am(III) from humic acid-coated gamma-Al2O3: a chelating resin exchange study.

The chelating resin was studied to assess its influence on metal availability and mobility in the environment. The association of organic-inorganic colloid-borne trace elements was investigated in this work. The radionuclide 243Am(III) was chosen as the representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. The kinetic dissociation behavior of 243Am(III) from humic acid-coated gamma-Al2O3 was studied at pH values of 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2 with a contact time of 2 days after the addition of a chelating cation exchanger resin. The concentrations of the components were: 243Am(III) 3.0 x 10(-7) mol/L, gamma-Al2O3 0.5 g/L, HA 10 mg/L (pH 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2) and 50 mg/L (pH 6.0 +/- 0.2), respectively. The kinetics of dissociation of 243Am(III) after different equilibration time with humic acid-coated gamma-Al2O3 was also investigated at pH 5.0 +/- 0.2. The experiments were carried out in air and at ambient temperature. The results suggest that the fraction of irreversible bonding of radionuclides to HA-coated Al2O3 increases with increasing pH and is independent of aging time. The assumption of two different 243Am(III)-HA-Al2O3 species, with "fast" and "slow" dissociation kinetics, is required to explain the experimental results. 243Am(III) species present on HA-Al2O3 colloids moves from the "fast" to the "slow" dissociating sites with the increase of aging time.

Actinoid Series Elements↗

PubMed2005

Chemical extractions affect the structure and phenanthrene sorption of soil humin.

Humin is a major fraction of soil organic matter and strongly affects the sorption behavior and fate of organic contaminants in soils and sediments. This study evaluated four different extraction methods for soil humins in terms of their organic carbon structural changes and the consequent effects on phenanthrene sorption. Solid-state 13C NMR demonstrated that 0.1 M NaOH exhaustively extracted humin and humin extracted with 6 M HF/HCl at 60 degrees C had a relatively high amount of aliphatic components as compared with 1 M HF-extracted humin. The treatment of 6 M HF/HCl at 60 degrees C greatly reduced carbohydrate components (50-108 ppm) from humin samples, i.e., more than 50% reduction. In addition, the humin from this 6 M HF/HCl treatment contained relatively more amorphous poly(methylene) domains than the humins extracted by other methods. With the respect to phenanthrene sorption, the linearity of sorption isotherm (N) and sorption affinity (Koc) varied markedly among the humin samples extracted by different methods. The NaOH exhaustively extracted humin had the most nonlinear sorption isotherm and the HF-extracted humin had the lowest Koc. It is concluded that humin samples from different extraction procedures exhibited substantial differences in their organic carbon structure and sorption characteristics, even though they were from the same soil. Therefore, one needs to be cautious when comparing the structural and sorption features of soil humins, especially when they are extracted differently. The 6 M HCl/HF extraction at elevated temperature is not encouraged, due to the modifications of chemical structure and physical conformation of organic matter.

Humic Substances↗

PubMed2005

Comparative sorption and desorption of benzo[a]pyrene and 3,4,3',4'-tetrachlorobiphenyl in natural lake water containing dissolved organic matter.

The sorption and desorption of two model compounds, benzo[a]pyrene (BaP) and 3,4,3',4'-tetrachlorobiphenyl (TCBP), were studied in natural lake water with high dissolved organic matter (DOM) content using the equilibrium dialysis and Tenax extraction methods. The sorption of TCBP was lower and reached steady value more slowly than did BaP. Tenax extraction revealed at least two differently desorbing fractions for both model compounds, which also supported the conclusion that DOM-HOC associations may involve several mechanisms. The rapidly desorbing fraction may be attributed to freely dissolved and loosely sorbed compound, whereas the more strongly sorbed fraction may indicate the presence of specific binding sites. The data indicated that the association between hydrophobic organic contaminants (HOC) and DOM is not simply absorption that is solely driven by the lipophilicity of the sorbates. Although contact time had a rather negligible effect on the sorption of BaP, the proportion of desorption resistant fraction increased with time, whereas the desorption of TCBP was less affected by contact time. Steric factors may be the cause of the lower sorption and smaller desorption resistant fraction of TCBP. The results indicate potential differences in the behavior of PAHs and PCBs in the aquatic environment.

Adsorption↗

PubMed2005

Humic material induces behavioral and global transcriptional responses in the nematode Caenorhabditis elegans.

Humic materials are complex organic molecules constituting the most abundant source of natural organic matter (NOM) in freshwater and soil ecosystems. Recent advances have identified that they interfere with biological systems, via the induction of biotransformation enzymes, the inhibition of photosynthetic oxygen release (in freshwater plants), the production of internal oxidative stress, or through the feminization of fish and amphibians. The nematode model organism Caenorhabditis elegans was chosen to investigate whether a natural and a synthetic humic material induce (i) a behavioral attraction, (ii) the reproduction, and (iii) a response in whole genome transcriptional expression. The phenomenological attractant experiments provided evidence that both humic material sources attract the worm and exert distinct chemical cues. In the reproduction assay, only the highest concentration (32 mg/L DOC of Fuchskuhle NOM, 38 mg/L DOC of HS 1500) resulted in a decrease in brood size, highlighting an overall intrinsic tolerance toward humic material. Finally, oligonucleotide-based whole genome DNA microarray experiments were performed from control and humic material treated worms. Significant transcriptional changes (exceeding a 2-fold increase or decrease) were identified in chemosensors, olfactory receptors, as well as enzymes of the biotransformation system (cytochromes P450, UDP-glucuronosyltransferases, glutathione S-transferases), thereby confirming that humic material is recognized as an environmental signaling chemical.

Animals↗

PubMed2005

Design of quinonoid-enriched humic materials with enhanced redox properties.

The primary goal of this work was to develop quinonoid-enriched humic materials with enhanced redox properties that could be used as potentially effective redox mediators and reducing agents for in situ remediation of soil and aquatic environments. Two different strategies were formulated and tested to derive these materials. The first strategy called for the oxidation of phenolic fragments associated with the humic aromatic core. In a second strategy, polycondensation of these phenolic fragments was carried out with hydroquinone and catechol. The oxidized derivatives and copolymers obtained were characterized using elemental and functional group analyses, and capillary zone electrophoresis. The redox properties were evaluated using ESR spectrometry and reducing capacity determinations. The reducing capacities of copolymers ranged between 1 and 4 mmol/g, which were much higher than the parent material and the oxidized derivatives. Hence, preference should be given to the copolycondensation approach. The quinonoid-enriched humics are nontoxic, water soluble, and resistant to biodegradation; thus, they could be applied as soil amendments to reduce highly mobile oxoanions of heavy metals and radionuclides, or as redox mediators to enhance in situ bioremediation. Otherwise, cross-linked copolymers could be created to serve as inexpensive reductants in permeable reactive barriers designed to remove highly oxidized contaminants from polluted groundwaters.

Electron Spin Resonance Spectroscopy↗

PubMed2006

Binding constants of divalent mercury (Hg2+) in soil humic acids and soil organic matter.

Distribution coefficients (K(OC)) for Hg2+ binding by IHSS Pahokee peat humic acid (PHA) and humic acids separated from O-horizons and peats in a northern temperate forest were determined using a competitive ligand-exchange method. All measurements were made at low ratios of added Hg2+ to reduced S. The commonly used chelating agents, EGTA and DTPA, were found to be ineffective competitive ligands; thus, we used DL-penicillamine, a synthetic amino acid with a thiol group. Calculated free [Hg2+] at equilibrium is very low, ranging from 10(-26.4) at pH 1.9 to 10(-36.9) at pH 5.8. Corresponding log Koc values ranged from 22.6 to 32.8. The slope of the plot of pH versus log K(OC) was 2.68, suggesting that two or more protons are released when each Hg2+ is bound. This is consistent with binding of Hg2+ to bidentate thiol sites with some participation of a third weak-acid group, presumably a thiol. The 1:2 stoichiometry is consistent with X-ray spectroscopy data for Hg2+ bound to HA and with other pH-dependency results showing release of two protons with the binding of each Hg2+. Our K(OC) values are much greater than indicated by the data from most previous studies.

Chelating Agents↗

PubMed2005

Acceleration and quenching of the photolysis of PCB in the presence of surfactant and humic materials.

The photodecay of a polychlorobiphenyl (PCB) congener, 2,3,4,5-tetrachlorobiphenyl (TeCB), in a surfactant-aided soil-washing process was investigated. The surfactant was found to be a useful hydrogen source in improving the TeCB photodecay via photoreduction process, while the light attenuation effect resulted from the nontarget compounds in the solution, and the impact of humic materials that co-extracted from the soil played important roles in the process of photolytic destruction of TeCB. A well-defined sediment, EPA-11, was used as the source of humic materials in examining the acceleration and quenching effects in the photolysis process. Experimental results indicated that the low dose of humic materials mainly acted as a supplementary hydrogen source to improve the photodegradation rate, while at a higher dose its amphoteric property of being a photochemical quencher become perceptible gradually, thus retarding the reaction. These effects were inspected and the dominant rate constants were quantified through the examination of possible sub-reactions in the assistant of proposed linear models in this study. The models under three different conditions at zero, low, and high humic levels associated with a light attenuation model were successfully developed to solve the dominant rate constants of the process. The good correlations between the experimental data and the models verify that the proposed reaction mechanisms of rate acceleration (resulting from the hydrogen source characteristics of the surfactant and humic material) and rate retardation (high levels of humic materials) coexist in the process.

Humic Substances↗

PubMed2006

Model predictions of metal speciation in freshwaters compared to measurements by in situ techniques.

Measurements of trace metal species in situ in a softwater river, a hardwater lake, and a hardwater stream were compared to the equilibrium distribution of species calculated using two models, WHAM 6, incorporating humic ion binding model VI and visual MINTEQ incorporating NICA-Donnan. Diffusive gradients in thin films (DGT) and voltammetry at a gel integrated microelectrode (GIME) were used to estimate dynamic species that are both labile and mobile. The Donnan membrane technique (DMT) and hollow fiber permeation liquid membrane (HFPLM) were used to measure free ion activities. Predictions of dominant metal species using the two models agreed reasonably well, even when colloidal oxide components were considered. Concentrations derived using GIME were generally lower than those from DGT, consistent with calculations of the lability criteria that take into account the smaller time window available forthe fluxto GIME. Model predictions of free ion activities generally did not agree with measurements, highlighting the need for further work and difficulties in obtaining appropriate input data.

Benzopyrans↗

PubMed2006

Kinetics and mechanism of the degradation of methyl parathion in aqueous hydrogen sulfide solution: investigation of natural organic matter effects.

The kinetics of the transformation of methyl parathion have been investigated in aqueous solution containing reduced sulfur species and small concentrations of natural organic matter (NOM) from different sources such as soil, river, and peat. It was shown that NOM mediates the degradation of methyl parathion in aqueous solutions containing hydrogen sulfide. After evaluating and quantifying the effect of the NOM concentration on the degradation kinetics of methyl parathion in the presence of hydrogen sulfide, it was found that the observed pseudo-first-order reaction rate constants (k(obs)) were proportional to NOM concentrations. The influence of pH on the degradation of methyl parathion in the aqueous solutions containing hydrogen sulfide and NOM has been studied. The rate of degradation of methyl parathion was strongly pH dependent. The results indicate k(obs) with a commercially available humic acid has a maximum value at approximately pH 8.3. Two main reaction mechanisms are identified to dominate the degradation of methyl parathion in aqueous solution containing hydrogen sulfide and NOM based on the products aminomethyl parathion and desmethyl methyl parathion. The two mechanisms are nitro-group reduction and nucleophilic attack at the methoxy-carbon. The reduction of the nitro-group is only observed in the presence of NOM. The results of this study form an important base for the evaluation and interpretation of transformation processes of methyl parathion in the environment.

Humic Substances↗

PubMed2005

Photoirradiation of dissolved humic acid induces arsenic(III) oxidation.

The fate of arsenic in aquatic systems is influenced by dissolved natural organic matter (DOM). Using UV-A and visible light from a medium-pressure mercury lamp, the photosensitized oxidation of As(III) to As(V) in the presence of Suwannee River humic acid was investigated. Pseudo-first-order kinetics was observed. For 5 mg L(-1) of dissolved organic carbon (DOC) and 1.85 mEinstein m(-2) s(-1) UV-A fluence rate, the rate coefficient k degrees exp was 21.2 +/- 3.2 10(-5) s(-1), corresponding to a half-life <1 h. Rates increased linearly with DOC and they increased by a factor of 10 from pH 4 to 8. Based on experiments with radical scavengers, heavy water, and surrogates for DOM, excited triplet states and/or phenoxyl radicals seem to be important photooxidants in this system (rather than singlet oxygen, hydrogen peroxide, hydroxyl radicals, and superoxide). Photoirradiation of natural samples from freshwater lakes, rivers, and rice field water (Bangladesh) showed similar photoinduced oxidation rates based on DOC. Fe(III) (as polynuclear Fe(III)-(hydr)oxo complexes or Fe(III)-DOC complexes) accelerates the rate of photoinduced As(III) oxidation in the presence of DOC by a factor of 1.5-2.

Arsenic↗

PubMed2006

Chemicals from wastes: compost-derived humic acid-like matter as surfactant.

Compost humic acid-like (cHAL) polymeric matter (MW = 15610), isolated in 12% yield from food and green waste compost, exhibits very good surfactant properties in aqueous solution: i.e., critical micelle concentration (cmc) = 403 mg/L and surface tension at cmc = 36.1 mN/m. Values of cmc are confirmed also by conductivity and phenanthrene solubility measurements. These results, compared with those for other major commercial and research surfactants, propose cHAL as a competitive low-cost biosurfactant.

Humic Substances↗

PubMed2006

Molecular and quantitative analysis of metal ion binding to humic acids from sewage sludge and sludge-amended soils by fluorescence spectroscopy.

Humic acids (HAs) isolated from sewage sludge (SS) and control and SS-amended soils were characterized by fluorescence spectroscopy. The main feature of fluorescence spectra was a broad band with the maximum centered at excitation/emission wavelengths that were much shorter for SS-HA (340/438 nm) than for any soil HA (440/510 nm). Titration with Cu(II), Zn(II), Cd(II), and Pb(II) ions decreased fluorescence intensities of HAs. Titration data were fitted to a single-site fluorescence quenching model, and metal ion complexing capacities of each HA sample and stability constants of metal ion-HA complexes were calculated. The binding capacities of HAs and strengths of metal ion-HA complexes followed the order Pb(II) > Cu(II) > Cd(II) > Zn(II). With respect to the control soil HA, SS-HA, which showed the smallest contents of acidic functional groups and the lowest humification degree, was characterized by much smaller binding capacities and stability constants. The binding capacities and affinities of SS-amended soil HA were intermediate between those of native soil HA and SS-HA but closer to the former, thus suggesting a partial incorporation of HA fractions of SS into native soil HAs. These effects are expected to have a great impact on the behavior of metals in SS-amended soils.

Humic Substances↗

PubMed2006

Partitioning CO2 effluxes from an Atlantic pine forest soil between endogenous soil organic matter and recently incorporated 13C-enriched plant material.

Soil CO2 effluxes from recently added 13C-labeled phytomass versus endogenous soil organic matter (SOM) were studied in an acid soil from Atlantic pine forests (NW Spain). After several cultures to incorporate fresh 13C-enriched Lolium perenne to a Humic Cambisol with predominance of humus--Al over humus--Fe complexes, potential soil C mineralization was determined by laboratory aerobic incubation (84 days). Isotopic 13C analyses of SOM fractions were assessed to know in which organic compartments the 13C was preferentially incorporated. Although in the 13C-labeled soil the C mineralization coefficient totalized less than 3% of soil C, the 13C mineralization coefficient exceeded 14%, indicating a greater lability of the newly incorporated organic matter. Organic compounds coming from added phytomass showed a higher lability and contributed considerably to the total soil CO2 effluxes (52% of total soil CO2 evolved during the first decomposition stages and 27% at the end), even though added-C comprised less than 4% of total soil C. Good determination coefficients, when values of CO2--C released were fitted to a first-order double exponential kinetic model, support the existence of two C pools of different lability. Kinetic parameters obtained with this model indicated that phytomass addition augmented the biodegradability of the labile pool (instantaneous mineralization rate k increased from 0.07 d(-1) to 0.12 d(-1)) but diminished that of the recalcitrant pool (instantaneous mineralization rate h decreased from 2.7 x 10(-4) d(-1) to 1.6 x 10(-4) d(-1)). Consequently, the differentiation between both SOM pools increased, showing the importance of SOM quality on CO2 emissions from this kind of soil to the atmosphere.

Aluminum↗

PubMed2006

Sorption of Aldrich humic acid onto hematite: insights into fractionation phenomena by electrospray ionization with quadrupole time-of-flight mass spectrometry.

Sorption induced fractionation of purified Aldrich humic acid (PAHA) on hematite is studied through the modification of electrospray ionization (ESI) quadrupole time-of-flight (QToF) mass spectra of supernatants from retention experiments. The ESI mass spectra show an increase of the "mean molecular masses" of the molecules that constitutes humic aggregates. The low molecular weight fraction (LMWF; m/z < or = 600 Da) is preferentially sorbed compared to two other fractions. The resolution provided by ESI-QToF mass spectrometer in the low-mass range provided evidence of further fractionation induced by sorption within the LMWF. Among the two latter fractions, the high molecular weight fraction (HMWF; m/z approximately 1700 Da) seems to be more prone to sorption compared to the intermediate molecular weight fraction (IMWF; m/z approximately 900 Da). The IMWF seems to be more hydrophilic as it should be richer in O, N, and alkyl C from the proportion of even mass, and poorer in aromatic structures from mass defect analysis in ESI mass spectra.

Adsorption↗

PubMed2006

Investigating the role of mineral-bound humic acid in phenanthrene sorption.

Contaminant-soil interaction studies have indicated that physical conformation of organic matter atthe solid-aqueous interface is important in governing hydrophobic organic compound (HOC) sorption. To testthis, organo-clay complexes were constructed by coating montmorillonite and kaolinite with peat humic acid (PHA) in Na+ or Ca2+ dominated solutions with varying pH and ionic strength values. The solution conditions encouraged the dissolved PHA to adopt a "coiled" or "stretched" conformation prior to interacting with the clay mineral surface. Both kaolinite and montmorillonite organo-clay complexes exhibited higher phenanthrene sorption (Koc values) with decreasing pH, indicating that the coiled configuration provided more favorable sorption conditions. Evidence from 1H high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) indicated that polymethylene groups were prevalent at the surface of the organo-clay complexes and may enhance sorptive interactions. Preferential sorption of polymethylene groups on kaolinite and aromatic compounds on montmorillonite may also contribute to the difference in phenanthrene sorption by PHA associated with these two types of clay. This study demonstrates the importance of solution conditions in the sorption of nonionic, hydrophobic organic contaminants and also provides evidence for the indirect role of clay minerals in sorption of contaminants at the soil-water interface.

Adsorption↗