Physicochemical soil parameters affecting sequestration and mycobacterial biodegradation of polycyclic aromatic hydrocarbons in soil

Six soils, obtained from grasslands and wooded areas in Northeastern Illinois, were physicochemically characterized. Measured parameters included total organic carbon (TOC) content, contents of humic acid, fulvic acid and humin, pore volume and pore size distribution, and chemical makeup of soil organic matter (determined using solid-state 13C-NMR). Moistened, gamma-sterilized soils were spiked with 200 ppm of either phenanthrene or pyrene (including 14C label); following 0, 40, or 120 days of aging, the contaminant-spiked soils were then inoculated with Mycobacterium austroafricanum strain GTI-23, and evolution of 14CO2 was assessed over a 28-day period. Results for both phenanthrene and pyrene indicated that increased contact time led to increased sequestration and reduced biodegradation, and that TOC content was the most important parameter governing these processes. One soil, although only tested with phenanthrene, showed significantly lower-than-expected sequestration (higher-than-expected mineralization) after 40 days of aging, despite a very high TOC value (>24%). Because the level of sequestration in this soil was proportional to the others after 120 days of aging, this implies some difference in the temporal progression of sequestration in this soil, although not in its final result. The primary distinguishing feature of this soil was its considerably elevated fulvic acid content. Further experiments showed that addition of exogenous fulvic acid to a soil with very low endogenous humic acids/fulvic acids content greatly enhanced pyrene mineralization by M. austroafricanum. Extractabilities of 13 three- to six-ring coal tar PAHs in n-butanol from the six soils after 120 days of sequestration were strongly TOC-dependent; however, there was no discernible correlation between n-butanol extractability and mycobacterial PAH mineralization.

Release of substituents from phenolic compounds during oxidative coupling reactions

Phenolic compounds originating from plant residue decomposition or microbial metabolism form humic-like polymers during oxidative coupling reactions mediated by various phenoloxidases or metal oxides. Xenobiotic phenols participating in these reactions undergo either polymerization or binding to soil organic matter. Another effect of oxidative coupling is dehalogenation, decarboxylation or demethoxylation of the substrates. To investigate these phenomena, several naturally occurring and xenobiotic phenols were incubated with various phenoloxidases (peroxidase, laccase, tyrosinase) or with birnessite (delta-MnO(2)), and monitored for chloride release, CO(2) evolution, and methanol or methane production. The release of chloride ions during polymerization and binding ranged between 0.2% and 41.4%. Using the test compounds labeled with 14C in three different locations (carboxyl group, aromatic ring, or aliphatic chain), it was demonstrated that 14CO(2) evolution was mainly associated with the release of carboxyl groups (17.8-54.8% of the initial radioactivity). Little mineralization of 14C-labeled aromatic rings or aliphatic carbons occurred in catechol, ferulic or p-coumaric acids (0.1-0.7%). Demethoxylation ranged from 0.5% to 13.9% for 2,6-dimethoxyphenol and syringic acid, respectively. Methylphenols showed no demethylation. In conclusion, dehalogenation, decarboxylation and demethoxylation of phenolic substrates appear to be controlled by a common mechanism, in which various substituents are released if they are attached to carbon atoms involved in coupling. Electron-withdrawing substituents, such as -COOH and -Cl, are more susceptible to release than electron-donating ones, such as -OCH(3) and -CH(3). The release of organic substituents during polymerization and binding of phenols may add to CO(2) production in soil.

The pinyon rhizosphere, plant stress, and herbivory affect the abundance of microbial decomposers in soils

In terrestrial ecosystems, changes in environmental conditions that affect plant performance cause a cascade of effects through many trophic levels. In a 2-year field study, seasonal abundance measurements were conducted for fast-growing bacterial heterotrophs, humate-degrading actinomycetes, fungal heterotrophs, and fluorescent pseudomonads that represent the decomposers in soil. Links between plant health and soil microbiota abundance in pinyon rhizospheres were documented across two soil types: a dry, nutrient-poor volcanic cinder field and a sandy-loam soil. On the stressful cinder fields, we identified relationships between soil decomposer abundance, pinyon age, and stress due to insect herbivory. Across seasonal variation, consistent differences in microbial decomposer abundance were identified between the cinders and sandy-loam soil. Abundance of bacterial heterotrophs and humate-degrading actinomycetes was affected by both soil nutritional status and the pinyon rhizosphere. In contrast, abundance of the fungal heterotrophs and fluorescent pseudomonads was affected primarily by the pinyon rhizosphere. On the cinder field, the three bacterial groups were more abundant on 150-year-old trees than on 60-year-old trees, whereas fungal heterotrophs were unaffected by tree age. Fungal heterotrophs and actinomycetes were more abundant on insect-resistant trees than on susceptible trees, but the opposite was true for the fluorescent pseudomonads. Although all four groups were present in all the environments, the four microbial groups were affected differently by the pinyon rhizosphere, by tree age, and by tree stress caused by the cinder soil and insect herbivory.

Biosorption of humic and fulvic acids to live activated sludge biomass

Biosorption of high molecular weight humic substances (HS) to activated sludge (AS) biomass may be considered as a preliminary step previous to enzymatic hydrolysis breakdown and biological uptake. Two standard HS, Suwannee River humic and fulvic acids, were biosorbed onto live AS biomass collected from full-scale wastewater treatment plants. Biosorption isotherms were corrected for interference from organic matter desorbed from AS biomass. The effect of pH, calcium and ionic strength on biosorption was tested. HS biosorption to live AS biomass obeyed the Freundlich isotherm equation. Biosorption increased with decreasing pH, increasing calcium and ionic strength concentration. Higher biosorption at low pH may be attributed to hydrophobic interactions between HS and AS biomass extracellular polymers (EPS). Hydrophobic and cationic bridging effects between HS and AS EPS were the mechanisms responsible for biosorption under the presence of divalent cations; however, the former was most significant at low pH, whereas the latter was predominant near neutral pH. The effect of ionic strength on HS biosorption followed the colloidal chemistry theory as the electric double layer became compressed when the ionic strength increased, resulting in closer approach of HS and AS biomass. The humic acid fraction of Suwannee River was removed more efficiently than its fulvic acid fraction because the humic acid was more hydrophobic. These results showed that pH, divalent cation concentration and ionic strength play an important role in the fate and removal of influent wastewater HS in full-scale treatment plants.

[Isolation and characterization of humin-like substances produced by wood-degrading fungi causing white rot]

Three samples of high-molecular-weight humin-like substances were obtained by solid-phase cultivation of Coriolus hirsutus and/or Cerrena maxima on oat straw. The yield of humin-like substances amounted to 1.38-2.26% of the weight of the plant substrate consumed. These substances, produced both by individual and mixed cultures of the basidiomycetes, were shown to be similar in their structure and physicochemical properties. According to the data of IR and 13C-NMR spectroscopy, the substances contained aromatic fragments and were close to soil humic acids. Studies of the dynamics of laccase production suggested that the humin-like substances were produced bia direct degradation of lignin macromolecules with direct involvement of extracellular laccase.

Mechanisms underlying the impact of humic acids on DNA quantification by SYBR Green I and consequences for the analysis of soils and aquatic sediments

DNA quantification of soils and sediments is useful for the investigation of microbial communities and for the acquisition of their genomes that are exploited for the production of natural products. However, in such samples DNA quantification is impaired by humic acids (HA). Due to its lack of specificity and sensitivity, UV spectrophotometry cannot be applied. Consequently, fluorimetric assays applying Hoechst (H) 33258 or PicoGreen (PG) are used. Here, we investigated the SYBR Green I (SG) assay, which was also affected by HA, but was found to be 25- and 1.7-fold more sensitive compared to the H 33258 and PG assays, respectively. Spectrophotometric, fluorimetric and quenching studies as well as gel mobility shift assays suggested that the effect of HA on the SG assay was based on an inner filter effect, collisional quenching and binding of SG to HA. As to the latter finding, the standard 6250-fold dilution of the SG reagent was optimised to a 2000-fold dilution. Although the sensitivity of the optimised SG assay was reduced by a factor of 1.3, the interfering effect of HA could be reduced up to 22-fold. A significant reduction of HA interferences by lowering the pH of the assay was not observed. Finally, the performance of the modified SG assay and the corresponding evaluation methods were verified by the determination of DNA recoveries and concentrations of standards and environmental samples in comparison to the PG assay.

Disinfection of water containing natural organic matter by using ozone-initiated radical reactions

Ozone is widely used to disinfect drinking water and wastewater due to its strong biocidal oxidizing properties. Recently, it was reported that hydroxyl radicals ((.)OH), resulting from ozone decomposition, play a significant role in microbial inactivation when Bacillus subtilis endospores were used as the test microorganisms in pH controlled distilled water. However, it is not yet known how natural organic matter (NOM), which is ubiquitous in sources of drinking water, affects this process of disinfection by ozone-initiated radical reactions. Two types of water matrix were considered for this study. One is water containing humic acid, which is commercially available. The other is water from the Han River. This study reported that hydroxyl radicals, initiated by the ozone chain reaction, were significantly effective at B. subtilis endospore inactivation in water containing NOM, as well as in pH-controlled distilled water. The type of NOM and the pH have a considerable effect on the percentage of disinfection by hydroxyl radicals, which ranged from 20 to 50%. In addition, the theoretical T value of hydroxyl radicals for 2-log B. subtilis removal was estimated to be about 2.4 x 10(4) times smaller than that of ozone, assuming that there is no synergistic activity between ozone and hydroxyl radicals.

Protection by natural blackwater against disturbances in ion fluxes caused by low pH exposure in freshwater stingrays endemic to the Rio Negro

Stenohaline freshwater stingrays (Potamotrygon spp.) are endemic to the very dilute (Na(+), Cl(-), Ca2(+) <or=30 micromol L(-1)), often acidic blackwaters of the Rio Negro despite gill Na(+) and Cl(-) transport characteristics that appear unfavorable (high K(m), low J(max)). We evaluated the possible protective role of blackwater itself, which is rich in dissolved organic carbon (DOC), as well as the importance of Ca(2+) in allowing this tolerance of dilute, acidic conditions. Responses of stingrays in natural blackwater (DOC=8.4 mg L(-1)) were compared with those in a natural reference water with similar ion levels but low DOC (0.6 mg L(-1)). Comparing these two water types, we found that differences in Na(+) and Cl(-) unidirectional fluxes (JXin, JXout; measured with radiotracers) and net fluxes (JXnet), influx and outflux kinetic relationships, and net ammonia excretion (J(Amm)) were generally small at pH 6.3, though the balance points where Jin=Jout shifted from >300 micromol L(-1) in reference water (low DOC) to about 100 micromol L(-1) in blackwater (high DOC). In reference water, both JNain and JClin were inhibited >90%, both JNaout and JClout more than doubled, and J(Amm) did not change at pH 4.0. In blackwater, the inhibition of influxes was attenuated, the increases in outflux did not occur, and J(Amm) increased by 60% at pH 4.0. Addition of 100 micromol L(-1) Ca(2+) to reference water prevented the increases in JNaout and JClout and allowed J(Amm) to increase at pH 4.0, which demonstrates that the gills are sensitive to Ca(2+). However, addition of Ca(2+) to blackwater had no effect on the responses to pH 4.0. Addition of commercial humic acid to reference water did not duplicate the effects of natural Rio Negro blackwater at the same DOC level; instead, it greatly exacerbated the increases in JNaout and JClout at low pH and prevented any protective influence of added Ca(2+). Thus, blackwater DOC appears to be very different from commercial humic acid. Biogeochemical modeling indicated that blackwater DOC prevents Ca(2+) binding, but not H(+) binding, to the gills and that the protective effects of blackwater cannot be attributed to its higher buffer capacity or its elevated Al or Fe levels. Natural DOC may act directly at the gills at low pH to exert a protective effect and, when doing so, may override any protective action of Ca(2+) that might otherwise occur.

Selective enrichment of Geobacter sulfurreducens from anaerobic granular sludge with quinones as terminal electron acceptors

A quinone-respiring, enrichment culture derived from methanogenic granular sludge was phylogenetically characterized by using a combined cloning-denaturing gradient gel electrophoresis (DGGE) method, which revealed that the consortium developed was dominated by a single microorganism: 97% related, in a sequence of 1520 base pairs, to Geobacter sulfurreducens. The enrichment culture could grow with acetate, formate or H2 when humic acids, the humic model compound, anthraquinone-2,6-disulfonate (AQDS), or chelated Fe(III) was provided as a terminal electron acceptor. The occurrence of a humic acid- or quinone-respiring microorganism in the microbial community of a wastewater treatment system suggests that this type of microorganisms may play a potential role in anaerobic bioreactors treating humus-containing wastewaters.

Retention and extractability of phenol, cresol, and dichlorophenol exposed to two surface soils in the presence of horseradish peroxidase enzyme

The retention of phenol, o-cresol, 2,4-dichlorophenol (DCP), and their peroxidase-catalyzed polymerization products was evaluated on two surface soils. The extractability of the parent solutes and their polymerization products was also investigated. (14)C-Labeled radioisotopes were used to quantify the contaminant retained on soil as water-extractable, methanol-extractable, humic/fulvic (HA/FA) acid-bound, and soil/humin bound. Between 2 and 20% of the solute retained on soil after a 7-day contact period remained bound to the HA/FA and soil/humin components in unamended soils; in the presence of peroxidase this amount was as high as 40-75%. The alkali-extractable HA/FA component contained the largest fraction of radioactivity in peroxidase-amended soils. Whereas the soil organic matter content was the predominant factor controlling the extent of sorption of the parent phenols, the clay content and particle surface area appeared to contribute to the retention of the polymerization products. High molecular weight oligomers produced during peroxidase-mediated polymerization of phenols associate strongly with soil components and are likely incorporated into the soil organic matter via oxidative coupling reactions.

Influence of dissolved humic acid on hydrophobic chemical uptake in juvenile rainbow trout

This study measured the chemical uptake of three hydrophobic chemicals (1,2,4-trichlorobenzene (1,2,4-TCB), 1,2,3,4,5-pentachlorobenzene (PeCB) and 2,2',4,4',6,6'-hexachlorobiphenyl (HCBP) with differing octanol-water partition coefficients (log K(ow) values of 3.95, 5.05 and 7.55, respectively) in juvenile rainbow trout (Oncorhynchus mykiss) after 2-day and 4-day aqueous exposures. Because of the affinity of hydrophobic compounds for dissolved organic carbon (DOC) and previous work demonstrating that fish gills take up these three hydrophobic chemicals, we predicted that chemical uptake into the fish would be lowered by the addition of humic acid to the water (1.54, 4.81 and 14.3 mg/l) compared with control fish (no humic acid added to the water). As predicted, humic acid concentrations of >or=4.81 mg/l significantly reduced the whole body concentrations of all three chemicals when compared with 1.54 mg/l humic acid. This effect of humic acid was greatest for HCBP, the chemical with the highest log K(ow), such that chemical uptake was reduced by 3.4-fold for 14.3 mg/l humic acid compared with the control exposure. However, an unexpected finding was that, compared with the control exposure, the lowest concentration of humic acid tested (1.54 mg/l humic acid) significantly increased chemical uptake by up to 112% for the two chemicals with the lower log K(ow), PeCB and 1,2,4-TCB, and did not affect uptake of the high log K(ow) chemical HCBP. We conclude that the ability of DOC to inhibit aqueous uptake of hydrophobic chemicals was dependent on both the concentration of DOC and the log K(ow) of the chemical, but that low humic acid concentrations of approximately 1.5 mg/l can significantly increase uptake of certain chemicals with a log K(ow) between 4 and 5.

Contaminant transport in dual-porosity media with dissolved organic matter and bacteria present as mobile colloids

In riverbank filtration, contaminant transport is affected by colloidal particles such as dissolved organic matter (DOM) and bacterial particles. In addition, the subsurface heterogeneity influences the behavior of contaminant transport in riverbank filtration. A mathematical model is developed to describe the contaminant transport in dual-porosity media in the presence of DOM and bacteria as mobile colloids. In the model development, a porous medium is divided into the mobile and immobile regions to consider the presence of ineffective micropores in physically heterogeneous riverbanks. We assume that the contaminant transport in the mobile region is controlled by the advection and dispersion while the contaminant transport in the immobile region occurs due to the molecular diffusion. The contaminant transfer between the mobile and immobile regions takes place by diffusive mass transfer. The mobile region is conceptualized as a four-phase system: two mobile colloidal phases, an aqueous phase, and a solid matrix. The complete set of governing equations is solved numerically with a fully implicit finite difference method. The model results show that in riverbank filtration, the contaminant can migrate further than expected due to the presence of DOM and bacteria. In addition, the contaminant mobility increases further in the presence of the immobile region in aquifers. A sensitivity analysis shows that in dual-porosity media, earlier breakthrough of the contaminant takes place as the volumetric fraction of the mobile region decreases. It is also demonstrated that as the contaminant mass transfer rate coefficient between the mobile and immobile regions increases, the contaminant concentration gradient between the two regions reverses at earlier pore volumes. The contaminant mass transfer coefficient between the mobile and immobile regions mainly controls the tailing effect of the contaminant breakthrough. The contaminant breakthrough curves are sensitive to changes in contaminant adsorption and desorption rate coefficients on DOM and bacteria. In situations where the contaminant is released in the presence of DOM and bacteria in dual-porosity media, the early breakthrough and tailing occur due to the colloidal facilitation and presence of immobile regions.

Desulfitobacterium metallireducens sp. nov., an anaerobic bacterium that couples growth to the reduction of metals and humic acids as well as chlorinated compounds

Strain 853-15A(T) was enriched and isolated from uranium-contaminated aquifer sediment by its ability to grow under anaerobic conditions via the oxidation of lactate coupled to the reduction of anthraquinone-2,6-disulfonate (AQDS) to anthrahydroquinone-2,6-disulfonate (AHQDS). Lactate was oxidized incompletely to acetate and carbon dioxide according to the reaction CH3CHOHCOO(-)+ 2AQDS+H2O --> CH3COO(-)+ 2AHQDS+CO2. Additional electron donors utilized included formate, ethanol, butanol, butyrate, malate and pyruvate. Lactate also supported growth with Fe(III) citrate, Mn(IV) oxide, humic substances, elemental sulfur, 3-chloro-4-hydroxyphenylacetate, trichloroethylene or tetrachloroethylene serving as the electron acceptor. Growth was not observed with sulfate, sulfite, nitrate or fumarate as the terminal electron acceptor. The temperature optimum for growth was 30 degrees C, but growth was also observed at 20 and 37 degrees C. The pH optimum was approximately 7.0. The 16S rDNA sequence of strain 853-15A(T) suggested that it was most closely related to Desulfitobacterium dehalogenans and closely related to Desulfitobacterium chlororespirans and Desulfitobacterium frappieri. The phylogenetic and physiological properties exhibited by strain 853-15A(T) (= ATCC BAA-636(T)) place it within the genus Desulfitobacterium as the type strain of a novel species, Desulfitobacterium metallireducens sp. nov.

Effect of shelterbelt on two kinds of soils on the transformation of organic matter

The changes of the total nitrogen, average yearly concentration of ammonia, nitrate ions, urease activity, total amount of amino acids in humic acids (HA) and the structure of humic acids were monitored in relation to the effect of shelterbelt as biogeochemical barrier located on a mineral and mineral-organic soil. The transformation of different forms of nitrogen in the soil under shelterbelt was strongly connected with the humification process and the molecular structure of humic acids.

Utilization and transformation of aquatic humic substances by autochthonous microorganisms

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

Biodegradation of acetanilide herbicides acetochlor and butachlor in soil

The biodegradation of two acetanilide herbicides, acetochlor and butachlor in soil after other environmental organic matter addition were measured during 35 days laboratory incubations. The herbicides were applied to soil alone, soil-SDBS (sodium dodecylbenzene sulfonate) mixtures and soil-HA (humic acid) mixtures. Herbicide biodegradation kinetics were compared in the different treatment. Biodegradation products of herbicides in soil alone samples were identified by GC/MS at the end of incubation. Addition of SDBS and HA to soil decreased acetochlor biodegradation, but increased butachlor biodegradation. The biodegradation half-life of acetochlor and butachlor in soil alone, soil-SDBS mixtures and soil-HA mixtures were 4.6 d, 6.1 d and 5.4 d and 5.3 d, 4.9 d and 5.3 d respectively. The biodegradation products were hydroxyacetochlor and 2-methyl-6-ethylaniline for acetochlor, and hydroxybutachlor and 2,6-diethylaniline for butachlor.

Photoinductive efficiency of soil extracted humic and fulvic acids

Humic and fulvic acids extracted from soils of different genesis were investigated for their ability to photoinduce the transformation of fenuron (2 x 10(-4) mol(-1)) at 365 nm. The ratio of the initial rate of fenuron consumption over the rate of light absorption by humic substances was found to be higher for fulvic acids (range 2.0 x 10(-3) to 9.0 x 10(-5)) than for humic acids (range 1.7 x 10(-4) to - 3.6 x 10(-5)). Within the FAs population, this ratio decreased as the specific absorption coefficient at 365 nm increased. It seems therefore that most of 365-nm absorbing components have no photoinductive activity and even reduce that of photoinductive chromophores.

Degradation of humic acids by the litter-decomposing basidiomycete Collybia dryophila

The basidiomycete Collybia dryophila K209, which colonizes forest soil, was found to decompose a natural humic acid isolated from pine-forest litter (LHA) and a synthetic (14)C-labeled humic acid ((14)C-HA) prepared from [U-(14)C]catechol in liquid culture. Degradation resulted in the formation of polar, lower-molecular-mass fulvic acid (FA) and carbon dioxide. HA decomposition was considerably enhanced in the presence of Mn(2+) (200 microM), leading to 75% conversion of LHA and 50% mineralization of (14)C-HA (compared to 60% and 20%, respectively, in the absence of Mn(2+)). There was a strong indication that manganese peroxidase (MnP), the production of which was noticeably increased in Mn(2+)-supplemented cultures, was responsible for this effect. The enzyme was produced as a single protein with a pI of 4.7 and a molecular mass of 44 kDa. During solid-state cultivation, C. dryophila released substantial amounts of water-soluble FA (predominantly of 0.9 kDa molecular mass) from insoluble litter material. The results indicate that basidiomycetes such as C. dryophila which colonize forest litter and soil are involved in humus turnover by their recycling of high-molecular-mass humic substances. Extracellular MnP seems to be a key enzyme in the conversion process.

Pesticide soil sorption parameters: theory, measurement, uses, limitations and reliability

The soil sorption coefficient Kd and the soil organic carbon sorption coefficient KOC of pesticides are basic parameters used by environmental scientists and regulatory agencies worldwide in describing the environmental fate and behavior of pesticides. They are a measure of the strength of sorption of pesticides to soils and other geosorbent surfaces at the water/solid interface, and are thus directly related to both environmental mobility and persistence. KOC is regarded as a 'universal' parameter related to the hydrophobicity of the pesticide molecule, which applies to a given pesticide in all soils. This assumption is known to be inexact, but it is used in this way in modeling and estimating risk for pesticide leaching and runoff. In this report we examine the theory, uses, measurement or estimation, limitations and reliability of these parameters and provide some 'rules of thumb' for the use of these parameters in describing the behavior and fate of pesticides in the environment, especially in analysis by modeling.

Diversity and ubiquity of bacteria capable of utilizing humic substances as electron donors for anaerobic respiration

Previous studies have demonstrated that reduced humic substances (HS) can be reoxidized by anaerobic bacteria such as Geobacter, Geothrix, and Wolinella species with a suitable electron acceptor; however, little is known of the importance of this metabolism in the environment. Recently we investigated this metabolism in a diversity of environments including marine and aquatic sediments, forest soils, and drainage ditch soils. Most-probable-number enumeration studies were performed using 2,6-anthrahydroquinone disulfonate (AHDS), an analog for reduced HS, as the electron donor with nitrate as the electron acceptor. Anaerobic organisms capable of utilizing reduced HS as an electron donor were found in all environments tested and ranged from a low of 2.31 x 10(1) in aquifer sediments to a high of 9.33 x 10(6) in lake sediments. As part of this study we isolated six novel organisms capable of anaerobic AHDS oxidation. All of the isolates coupled the oxidation of AHDS to the reduction of nitrate with acetate (0.1 mM) as the carbon source. In the absence of cells, no AHDS oxidation was apparent, and in the absence of AHDS, no cell density increase was observed. Generally, nitrate was reduced to N(2). Analysis of the AHDS and its oxidized form, 2,6-anthraquinone disulfonate (AQDS), in the medium during growth revealed that the anthraquinone was not being biodegraded as a carbon source and was simply being oxidized as an energy source. Determination of the AHDS oxidized and nitrate reduced accounted for 109% of the theoretical electron transfer. In addition to AHDS, all of these isolates could also couple the oxidation of reduced humic substances to the reduction of nitrate. No HS oxidation occurred in the absence of cells and in the absence of a suitable electron acceptor, demonstrating that these organisms were capable of utilizing natural HS as an energy source and that AHDS serves as a suitable analog for studying this metabolism. Alternative electron donors included simple volatile fatty acids such as propionate, butyrate, and valerate as well as simple organic acids such as lactate and pyruvate. Analysis of the complete sequences of the 16S rRNA genes revealed that the isolates were not closely related to each other and were phylogenetically diverse, with members in the alpha, beta, gamma, and delta subdivisions of the PROTEOBACTERIA: Most of the isolates were closely related to known genera not previously recognized for their ability to couple growth to HS oxidation, while one of the isolates represented a new genus in the delta subclass of the PROTEOBACTERIA: The results presented here demonstrate that microbial oxidation of HS is a ubiquitous metabolism in the environment. This study represents the first description of HS-oxidizing isolates and demonstrates that microorganisms capable of HS oxidation are phylogenetically diverse.

Photodegradation of diafenthiuron in water

Diafenthiuron, 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea, is an effective insecticide and acaricide. Sunlight degradation of diafenthiuron in various aqueous solutions and pure hexane yielded two major identified products: 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)-carbodiimide (CGA-140,408) and 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxy-phenyl)urea (CGA-177,960). CGA-140,408 was further photo-transformed into CGA-177,960 by sunlight. Direct photolysis appeared to be a major photolysis pathway of diafenthiuron in the environment. Photodegradation of CGA-140,408 and CGA-177,960 was enhanced in humic acid water, paddy water and aqueous acetone solutions, and followed first-order kinetics. Isopropanol (a radical quencher) and de-aeration strongly inhibited the photolysis of these chemicals, which suggested oxygen radical-mediated reactions.

Inhibition of endogenous thyroid hormone receptor-beta and peroxisome proliferator-activated receptor-alpha activities by humic acid in a human-derived liver cell line

Humic acid (HA), know to be ubiquitous in the natural environment, is present in almost all soil, surface water, and plants. Earlier studies indicate that HA can affect thyroid economy via binding with iodide, inhibiting both thyroid peroxidase and hepatic 5'-deiodinase in rodents. However, the effect of HA, a peroxisome proliferator in rodents, on thyroid hormone receptor (TR) and peroxisome proliferator-activated receptor (PPAR) in human cells has not yet been examined. In this study, we demonstrate that the malic enzyme activity and the transcriptional activities of endogenous TR and PPAR were inhibited after treatment with HA in human hepatocyte Chang liver cell line. Although the protein expression levels of TR-beta, PPAR-alpha and retinoid X receptor-alpha (RXRalpha) were not changed significantly by HA treatment, both the binding abilities of endogenous TR-beta on thyroid hormone response element (TRE) and PPAR-alpha on the PPAR response element (PPRE) were inhibited by HA treatment. The study of the subcellular distribution of HA, relying on the inherent HA fluorescence, showed that HA distributed in the intracellular compartments including cytoplasm and nucleus. The 50% binding inhibition values (CI(50)) of HA on ME-TRE (malic enzyme gene-TRE) and ACOX-PPRE (acylCoA oxidase gene-PPRE) were 19.31 and 19.94 microg/mL, respectively. These results suggest that HA-induced endemic goiter may link in part to the disruption of TRbeta and PPARalpha function in human Chang liver cells. This model may be useful in the investigation of environmental goitrogens.

Molecular structures and associations of humic substances in the terrestrial environment

Here we show, for the first time, evidence of the primary molecular structures in humic substances (HS), the most abundant naturally occurring organic molecules on Earth, and their associations as mixtures in terrestrial systems. Multi-dimensional nuclear magnetic resonance (NMR) experiments show us that the major molecular structural components in the mixtures operationally defined as HS are aliphatic acids, ethers, esters and alcohols; aromatic lignin derived fragments; polysaccharides and polypeptides. By means of diffusion ordered spectroscopy, distinct diffusion coefficients consistent with relatively low molecular weight molecules were observed for all the components in the mixtures, and saccharides were the largest single class of component present. Liquid chromatography NMR confirmed that HS components can be easily separated and nuclear Overhauser effect (NOE) enhancements support the finding that the components are of relatively low molecular weight <approximately 2,000 Da. The widely recognized properties of HS, i.e., characteristics indicative of crosslinked, macromolecular networks, can now be explained as aggregation of mixtures, most likely instigated by complexation with metal cations.

Formation of disinfection by-products in chlorinated swimming pool water

The formation of five volatile disinfection by-products (DBPs: chloroform, bromodichloromethane, chloral hydrate, dichloroacetonitrile, and 1,1,1-trichloropropanone) by the chlorination of the materials of human origin (MHOs: hair, lotion, saliva, skin, and urine) in a swimming pool model system was examined. Chlorination reactions took place with a sufficient supply of chlorine residuals (0.84 mg Cl2/l < total chlorine < 6.0 mg Cl2/l) in 300 ml glass bottles containing either ground water or surface water as a reaction medium at 30 degrees C and pH 7.0, for either 24 or 72 h. A longer reaction period of 72 h or a higher content of organic materials led to the increased formation of DBPs. Of the DBPs formed by the reaction, chloroform was a major compound found in both ground and surface waters. The formation of chloroform and bromodichloromethane per unit total organic carbon (TOC) concentration was suppressed when all types of MHOs were added to the surface water that already contained DBP precursors such as humic substances. However, the formation of dichloroacetonitrile was promoted, probably due to the increased degradation reactions of nitrogen-containing compounds such as urea and proteins of human origin. In conclusion, the materials of swimmers' origin including hair, lotion, saliva, skin, and urine add to the levels of DBPs in swimming pool water, and any mitigation measures such as periodic change of water are needed to protect swimmers from elevated exposures to these compounds.

Interaction of 2,4,6-trinitrotoluene (TNT) and 4-amino-2,6-dinitrotoluene with humic monomers in the presence of oxidative enzymes

Oxidative coupling of nitroaromatic compounds involving soil organic matter was examined as a means of soil remediation. Humic monomers, serving as model compounds for soil humic substances, were used as cosubstrates, applying phenoloxidases (laccase from Trametes villosa and peroxidase from horseradish) as oxidative biocatalysts. Without the addition of a cosubstrate, only 30% of 4-amino-2,6-dinitrotoluene (4ADNT) and no 2,4,6-trinitrotoluene (TNT) were transformed in the presence of the laccase. Adding various phenolic monomers produced differing effects on the enzyme-mediated transformation, which indicated that xenobiotics are preferentially bound to quinoid and phenolic moieties of soil humic substances. In the presence of the humic monomer catechol and the enzyme, up to 100% of 4ADNT and up to 80% of TNT were transformed. Enzymatic transformation of 4ADNT in the presence of catechol reached a maximum at pH 6.8. TNT transformation, however, further increased at pH values above 6.8, even in the absence of the enzyme, due to chemical polymerization of catechol. We postulate a two-step reaction mechanism. The humic monomer is initially oxidized to a semi-quinone radical by a phenoloxidase. Subsequent oxidative coupling involves reactions with additional humic monomers or anilinic products derived from TNT, forming an anilinoquinone via nucleophilic addition or a benzoquinone-imine through condensation.

Limits of anaerobic biodegradation

The main factors responsible for anaerobic recalcitrance are reviewed. Anaerobic recalcitrance is associated with hydrocarbons lacking functional groups, branched molecules (gasoline oxygenates), aromatic amines and aromatic sulfonates. The most recalcitrant compounds are high molecular weight nonhydrolyzable polymers such as plastic, lignin and humus, which cannot be taken up by cells. Recently new capabilities of anaerobic microorganisms have been discovered to degrade compounds previously considered to be recalcitrant. For example, anaerobic bacteria initiate the degradation of alkylbenzenes and alkanes with an unusual addition reaction with fumarate, forming a hydrocarbon-succinate adduct. Finally, new evidence indicates that the most recalcitrant compounds (humic substances) are not so inert and can play important roles in aiding the biodegradation of other compounds by serving as an electron acceptor or redox mediator.

Reduction of humic substances by halorespiring, sulphate-reducing and methanogenic microorganisms

Physiologically distinct anaerobic microorganisms were explored for their ability to oxidize different substrates with humic acids or the humic analogue, anthraquinone-2,6-disulphonate (AQDS), as a terminal electron acceptor. Most of the microorganisms evaluated including, for example, the halorespiring bacterium, Desulfitobacterium PCE1, the sulphate-reducing bacterium, Desulfovibrio G11 and the methanogenic archaeon, Methanospirillum hungatei JF1, could oxidize hydrogen linked to the reduction of humic acids or AQDS. Desulfitobacterium dehalogenans and Desulfitobacterium PCE1 could also convert lactate to acetate linked to the reduction of humic substances. Humus served as a terminal electron acceptor supporting growth of Desulfitobacterium species, which may explain the recovery of these microorganisms from organic rich environments in which the presence of chlorinated pollutants or sulphite is not expected. The results suggest that the ubiquity of humus reduction found in many different environments may be as a result of the increasing number of anaerobic microorganisms, which are known to be able to reduce humic substances.

Reducing the formation of disinfection by-products by pre-ozonation

The objective of this study is to apply the pre-ozonation process to reduce the formation of disinfection by-products (DBPs). The raw water sample, collected from the Te-Chi Reservoir in central Taiwan, has been polluted by fertilizer. Three types of resins were used to isolate the natural organic matter into seven types of organic fractions. The pre-ozonation was used to oxidize each organic fraction to study the reduction of DBPs of each fraction. Experimental results indicated that the pre-ozonation could reduce the concentration of dissolved organic carbon resulting in the reduction of DBP formation. With the pre-ozonation, 9-54% of DOC and more than 40% of DBPs were reduced. With the analysis of UV adsorption and Fourier transform infrared spectrometer (FTIR), the reduction of A254 and unsaturated functional groups such as aromatic ring and C=C bond containing in the water sample is the major reaction mechanism.

Analytical determination of the microbial utilization and transformation of humic acids extracted from municipal refuse

Humic substances are usually the refractory part of natural organic matter, and in a landfill they can retain inorganic and organic micropollutants. This study has investigated analytically whether humic acids (HA) extracted by use of alkali from either fresh municipal refuse or from refuse disposed of in a landfill for up to 12 months can resist microbial degradation under aerobic conditions. When added as a supplementary nutrient source, up to 63.6% of HA was utilized and this percentage was enhanced to a mean value of 88.5% when different HA preparations were used as the sole source of carbon. In cultures of a soil microbial community containing the same preparations as sole sources of nitrogen, HA was usually completely utilized. The remaining HA re-isolated from some microbial cultures were highly depleted in carbon and, simultaneously, the nitrogen content was enhanced. The FTIR spectra were indicative of strong participation of aliphatic structural units in the refuse-related HA preparations. Because of the microbial activity, different carbonaceous substances were primarily removed from the HA structure, and an increase in nitrogenous molecular groups became apparent. The structural transformations brought about by soil microorganisms "in vitro" corresponded to those occurring naturally in HA obtained from refuse aged for 12 months in a landfill.

Evaluation of the treatment performance of a multistage ozone/hydrogen peroxide process by decomposition by-products

The performance of a multistage ozone/hydrogen peroxide (O3/H2O2) process was evaluated with respect to total organic carbon (TOC) removal of waste waters. An aqueous humic acid solution (5.2 mgC l(-1) as TOC) and a sand filtered secondary sewerage effluent (5.6mgC l(-1) as TOC) were used as model waste waters. Appropriate range of hydrogen peroxide (H2O2) dose at each stage depended upon the components of the tested solutions that changed as the process proceeded. Higher hydrogen peroxide dose was required at later stages in which low reactivity compounds with hydroxyl radical (HO*), low molecular fatty acids, were predominant. And, oxalic acid concentration related to H2O2 demand at later stages. This was assumed that the slow decomposition of oxalic acid was rate-determining step for TOC removal after its accumulation. Also, it is important to maintain dissolved ozone at low concentration for efficient TOC removal because rapid ozone consumption is required for the rapid formation of hydroxyl radical (HO*).

Anaerobic mineralization of toluene by enriched sediments with quinones and humus as terminal electron acceptors

The anaerobic microbial oxidation of toluene to CO(2) coupled to humus respiration was demonstrated by use of enriched anaerobic sediments from the Amsterdam petroleum harbor (APH) and the Rhine River. Both highly purified soil humic acids (HPSHA) and the humic quinone moiety model compound anthraquinone-2,6-disulfonate (AQDS) were utilized as terminal electron acceptors. After 2 weeks of incubation, 50 and 85% of added uniformly labeled [(13)C]toluene were recovered as (13)CO(2) in HPSHA- and AQDS-supplemented APH sediment enrichment cultures, respectively; negligible recovery occurred in unsupplemented cultures. The conversion of [(13)C]toluene agreed with the high level of recovery of electrons as reduced humus or as anthrahydroquinone-2,6-disulfonate. APH sediment was also able to use nitrate and amorphous manganese dioxide as terminal electron acceptors to support the anaerobic biodegradation of toluene. The addition of substoichiometric amounts of humic acids to bioassay reaction mixtures containing amorphous ferric oxyhydroxide as a terminal electron acceptor led to more than 65% conversion of toluene (1 mM) after 11 weeks of incubation, a result which paralleled the partial recovery of electron equivalents as acid-extractable Fe(II). Negligible conversion of toluene and reduction of Fe(III) occurred in these bioassay reaction mixtures when humic acids were omitted. The present study provides clear quantitative evidence for the mineralization of an aromatic hydrocarbon by humus-respiring microorganisms. The results indicate that humic substances may significantly contribute to the intrinsic bioremediation of anaerobic sites contaminated with priority pollutants by serving as terminal electron acceptors.

[Effect of long-term single application of chemical fertilizer on soil properties and crop yield]

A long-term located experiment showed that single application of chemical fertilizer basically sustained the quantity level of soil organic matter, nitrogen and phosphorous, reduced the energy level of soil humus and enhanced its condensation degree, aromaticity and aging function. The corp yield was basically the same as that of combined application with organic manure.

Enhancing pyrene mineralization in contaminated soil by the addition of humic acids or composted contaminated soil

The addition of composted PAH-contaminated soil to PAH-contaminated soil spiked with 14C-labeled pyrene resulted in rapid mineralization of pyrene (more than 57% after 21 days compared with 3.4% in un-amended soil). The addition of the humic acid fraction of the composted soil also increased the mineralization potential of the soil significantly, but to a lesser extent (37.5% mineralization after 106 days compared with 20.6% in unamended soil). Increasing the humic acid concentration increased mineralization up to a maximum of more than three times the unamended rate, after which the rate of pyrene mineralization decreased, possibly due to inhibitory pH or concentrations of salts. The amendment of PAH-contaminated soil with materials containing humic acids or humic acid extracts is suggested as a method of bioremediation.

In situ bioremediation through mulching of soil polluted by a copper-nickel smelter

Bioremediation of a heavy metal-polluted soil was investigated in a 3-yr field experiment by adding mulch to a polluted forest floor. The mulch consisted of a mixture of compost and woodchips. The remediation treatment decreased the toxicity of the soil solution to bacteria as determined by the [3H]-thymidine incorporation technique, that is, by measuring the growth rate of soil bacteria extracted from unpolluted humus after exposing them to soil solution containing heavy metals from the experimental plots. Canonical correlation analysis was performed in order to identify the chemical and microbiological changes in the soil. The pH of the mulched organic layer increased by one unit. The concentration of complexed Cu increased and that of free Cu2+ decreased in the soil solution from the mulch treatment. According to basal respiration and litter decomposition, microbial activity increased during the 3 yr following the remediation treatment. The [3H]-thymidine incorporation technique was also used to study the growth rate and tolerance of bacteria to Cu. The bacterial growth rate increased and the Cu tolerance decreased on the treated plots. The structure of the microbial community, as determined by phospholipid fatty acid (PLFA) analysis, remained unchanged. The results indicate that remediation of the polluted soil had occurred, and that adding a mulch to the forest floor is a suitable method for remediating heavy metal-polluted soil.

Screening of four species of detritivorous (humus-former) earthworms for sustainable vermicomposting of paper waste

Four specices of detritivorous (humus-former) earthworms were tested for their ability to vermicompost paper waste blended with cowdung in 6:1 (w/w) ratio. The anecic Lampito mauritii, Kinberg and the epigeic Eudrilus eugeniae, Kinberg were the most effective of the four species employed; 20 animals of each of these species generated castings amounting to about 52% of the feed mass (75 g) per fortnight. The performance of these two species was followed by the anecic Drawida willsi, Michaelsen and the epigeic Perionyx excavatus, Perrier; they achieved approximately 46% vermiconversion in comparable settings. The vermireactors were sustainable as the animals have remained consistently healthy and reproductive over a period of six months, and are continuing to remain so, turning in a steadily rising vermicast output. During this period E. eugeniae have grown to 2.3 times their original weight while the other three species have more than trebled their weights. The studies establish the feasibility of vermicomposting as a viable process for the gainful utilization of paper waste in an environmentally clean manner. They also indicate that all the four species of the worms screened by us are suitable for the process, with L. mauritii and E. eugeniae a shade more efficient than the other two species.

Variations of landfill leachate's properties in conjunction with the treatment process

A study was done on the variations of water quality parameters, in conjunction with the processing steps, installed for the treatment of leachate from a sanitary landfill. The leachate was primarily subjected to biological treatment, composed of anaerobic digestion, aerobic treatment, and rotating biological contact in series. The effluent from the rotating biological contact process was further treated by combination of flocculation-sedimentation and adsorption processes. Finally, it was polished by the reverse osmosis process before discharge. The quality of raw leachate, of influents to and of effluents from the reverse osmosis process was assessed and compared. To determine size--dependent behavior of organic materials, analyses were also made for the fractionated samples through ultrafiltration. The overall treatment efficiency was about 98% for removal of organic materials. Most of the organic materials were in the low molecular weight range. In particular, about 95% of the biological oxygen demand was found to be exerted by the fraction of organic material of which cut -off molecular weight was less than 500. The analysis of molecular weight distribution confirmed that the organic materials resistant to the removal by the treatment process were humic substances, of which cut off molecular weight was greater than 500. The reverse osmosis process showed a high efficiency for removal of high molecular weight constituents. However, the final effluent showed an unexpectedly high oxygen demand.

Degradation pathways of pentachlorophenol by photo-Fenton systems in the presence of iron(III), humic acid, and hydrogen peroxide

The degradation characteristics and pathways of pentachlorophenol (PCP) by the photo-Fenton systems were studied in H2O2 aqueous solutions, which contained Fe(III) only [H2O2/Fe(III) system] and Fe(III) + humic acid (HA) [H2O2/Fe(III)/HA system] at pH 5.0. Although 40% of the PCP was degraded after 5 h of irradiation in the H2O2/Fe(III) system, more than 90% was degraded in the H2O2/Fe(III)/HA system. This shows that at pH 5.0 the degradation of PCP is clearly enhanced by the presence of HA in the photo-Fenton system. In the H2O2/Fe(III) system, the production of octachlorodibenzo-p-dioxin (OCDD) was detected, and 2-hydroxy nonachlorodiphenyl ether was also identified as a precursor of OCDD. However, no OCDD production was observed in the H2O2/Fe(III)/HA system. This indicates that the presence of HA represses the production of OCDD during the degradation of PCP by the photo-Fenton system. Such an effect by HA can be attributed to a reaction sequence wherein reaction intermediates derived from PCP, such as PCP., are incorporated into HA. This was verified by 13C NMR and pyrolysis-GC/MS studies.

Organic matter components, aggregate stability and biological activity in a horticultural soil fertilized with different rates of two sewage sludges during ten years

The effects of the application as fertilizer during ten years of two sewage sludges (aerobically and anaerobically digested, at rates of 400, 800, and 1200 kg of N/ha yr), on the aggregate stability and contents of related organic matter components, microbial biomass and levels of five enzymatic activities (alkaline phosphomonoesterase, phosphodiesterase, urease, arylsulphatase and dehydrogenase) were investigated. The application of both sludges at mid and high rates gave rise to significant increases of organic matter, humified substances and humic acids, but no effects on carbohydrates, microbial gums and aggregate stability were observed. As for biological activity in soils, the high variability of data led to a general absence of statistical significance despite the large differences between treatments observed. Significant increases of phosphodiesterase activity were nevertheless produced by the high rate of aerobic sludge and the mid and high rates of the anaerobic sludge.

Interaction of imidazolinone herbicides with soil humic acids. Experimental results and molecular modeling

Adsorption and desorption isotherms of the herbicides imazapyr, imazethapyr and imazaquin on a soil humic acid have been performed at pH 2.8 and 4.0 (below and above the pKa of the herbicides). At both pH, adsorption increased according to the lipophilic character of the molecules (imazapyr < imazethapyr << imazaquin). The extent of adsorption was higher at pH 2.8 than at pH 4.0 because of the partial ionization of the carboxylic groups of both herbicides and humic acids at increasing pH. Desorption of imazapyr and imazethapyr was nearly complete at pH 4 and higher than 60% at pH 2.8 while desorption of imazaquin was 45 and 8% at pH 4 and 2.8, respectively. No differences between adsorption isotherms at 10 degrees C and 25 degrees C were observed a pH 4.0 indicating that adsorption involved very weak bonds while at pH 2.8, adsorption was higher at 10 degrees C than at 25 degrees C indicating an exothermic process. The isosteric enthalpy of adsorption of each herbicide was low (about -1 kJoule mole(-1)) suggesting that low energetic bonds were involved. Adsorption on different humic acids has indicated that for each herbicide, the extent of adsorption expressed as Kd was correlated with the amount of carboxylic and aromatic groups of humic acids suggesting that hydrogen bonding and/or charge-transfer complexes formation could take place. Molecular modeling and geometry optimization of humic acid and soil organic matter (SOM) herbicide complexes were also performed. The results obtained with this theoretical approach gave a consistent chemical interpretation of the experimental results. To the best of our knowledge this is the first report to contribute to a better understanding of site-specific bonding of herbicides in SOM complexes by nanochemical modeling and distinct energy descriptors.

Evaluation of the transformation of organic matter to humic substances in compost by coupling sec-page

Humic acids (HAs) from soil and compost at the beginning (S0) and at the end of the stabilization process after 130 days (S130) have been fractionated by coupling size exclusion chromatography (SEC) and polyacrylamide gel electrophoresis (PAGE). Preparative quantities of HA fractions (HAFs) with different molecular sizes (MSs) and exactly defined electrophoretic mobility (EMs) have been obtained from all samples and the HAFs weight content has been studied. A high degree of similarity in HAFs weight content between soil HA and a stabilized compost HAs130 has been observed. Such data seem to be reliable for monitoring the evolution of the compost organic matter to humic substances for their agricultural uses.

Biotransformation of Ni-substituted hydrous ferric oxide by an Fe(III)-reducing bacterium

The reductive biotransformation of a Ni(2+)-substituted (5 mol %) hydrous ferric oxide (NiHFO) by Shewanella putrefaciens, strain CN32, was investigated under anoxic conditions at circumneutral pH. Our objectives were to define the influence of Ni2+ substitution on the bioreducibility of the HFO and the biomineralization products formed and to identify biogeochemical factors controlling the phase distribution of Ni2+ during bioreduction. Incubations with CN32 and NiHFO were sampled after 14 and 32 d, and both aqueous chemistry and solid phases were characterized. By comparison of these results with a previous study (Fredrickson, J. K.; Zachara, J. M.; Kennedy, D. W.; Dong, H.; Onstott, T. C.; Hinman, N. W.; Li, S. W. Geochim. Cosmochim. Acta 1998, 62, 3239-3257), it was concluded that coprecipitated/sorbed Ni2+ inhibited the bioreduction of HFO through an undefined chemical mechanism. Mössbauer spectroscopy allowed analysis of the residual HFO phase and the identity and approximate mass percent of biogenic mineral phases. The presence of AQDS, a soluble electron shuttle that obviates need for cell--oxide contact, was found to counteract the inhibiting effect of Ni2+. Nickel was generally mobilized during bioreduction in a trend that correlated with final pH, except in cases where PO4(3-) was present and vivianite precipitation occurred. CN32 promoted the formation of Ni(2+)-substituted magnetite (Fe2IIIFe(1-x)IINixIIO4) in media with AQDS but without PO4(3-). The formation of this biogenic coprecipitate, however, had little discernible impact on final aqueous Ni2+ concentrations. These results demonstrate that coprecipitated Ni can inhibit dissimilatory microbial reduction of amorphous iron oxide, but the presence of humic acids may facilitate the immobilization of Ni within the crystal structure of biogenic magnetite.

Evaluation of refractory organic removal in combined biological powdered activated carbon--microfiltration for advanced wastewater treatment

Biological powdered activated carbon (BPAC) was incorporated with a microfiltration (MF, 0.2 micron pore size) system to remove the refractory organic matter contained in secondary sewage effluent. A synthetic secondary sewage effluent was used as influent in this study, containing both non-biodegradable organic substances (such as humic acid, lignin sulfonate, tannic acid and arabic gum powder) and biodegradable ones. These refractory organic materials were possibly degraded in contact with microorganisms for 20-27 days. Although humic acid and arabic gum were weakly adsorbed on the activated carbon, they could be effectively removed in the BPAC reactor. The TOC removal at a powdered activated carbon (PAC) concentration of 20 g/L was higher than at 0.5-2 g PAC/L (83% and 66-68%, respectively). The higher removal efficiency was due to the increased rejection at the membrane module in which most of the PAC was accumulated. More than 90% of non-biodegradable compounds removal (detected as E280, UV absorption at 280 nm) occurred in the BPAC reactor. The biological growth parameter b/Y, used in system design, was estimated to be 0.017 d-1. Relatively high permeate flux of 1.88 m/d could be obtained even at higher PAC concentration of 20 g/L.

Artificial recharge of humic ground water

The purpose of this study was to investigate the efficiency of soil in removing natural organic matter from humic ground waters using artificial recharge. The study site, in western Denmark, was a 10,000 ml football field of which 2,000 m2 served as an infiltration field. The impact of the artificial recharge was studied by monitoring the water level and the quality of the underlying shallow aquifer. The humic ground water contained mainly humic adds with an organic carbon (OC) concentration of 100 to 200 mg C L(-1). A total of 5,000 mS of humic ground water were sprinkled onto the infiltration field at an average rate of 4.25 mm h(-1). This resulted in a rise in the water table of the shallow aquifer. The organic matter concentration of the water in the shallow aquifer, however, remained below 2.7 mg C L(-1). The organic matter concentration of the pore water in the unsaturated zone was measured at the end of the experiment. The organic matter concentration of the pore water decreased from 105 mg C L(-1) at 0.5 m to 20 mg C L(-1) at 2.5 m under the infiltration field indicating that the soil removed the organic matter from the humic ground water. From these results we conclude that artificial recharge is a possible method for humic ground water treatment.

Removal of color substances using photocatalytic oxidation for membrane filtration processes

This study aims to remove the color substances, which normally cause difficulties in membrane filtration processes due to fouling using heterogeneous UV/TiO2/H2O2 reactor. It is confirmed that the technique used in this study was effective to remove TOC at 38% and color400 at 89% within 150-min irradiation. The experiment results showed that low concentrations of hydrogen peroxide dosage (less than 0.016 M) to UV/TiO2 system accelerated the TOC and Color400 removal rate from 9% to 38% and 40% to 89% respectively, while over-dosage made this positive effect decline. The humic acid solution treated by photo catalytic oxidation in UV/TiO2/H2O2 reactor did not change the zeta potential on membrane surface and membrane rejection rate.

The formation and control of disinfection by-products using chlorine dioxide

In this study, chlorine dioxide (ClO2) was used as an alternative disinfectant with vanillic acid, p-hydroxybenzoic acid, and humic acid as the organic precursors in a natural aquatic environment. The primary disinfection by-products (DBPs) formed were trihalomethanes (THMs) and haloacetic acids (HAAs). Under neutral conditions (pH = 7) for vanillic acid, more total haloacetic acids (THAAs) than total trihalomethanes (TTHMs) were found, with a substantial increase during the later stages of the reaction. In the case of p-hydroxybenzoic acid, the amount of THAAs produced was minimal. Raising the concentration of ClO2 was not favorable for the control of THAAs in low concentrations of vanillic acid. ClO2 could reduce the total amount of TTHMs and THAAs for higher concentration of vanillic acid. It was found that the humic acid treatment dosage was not significant. Under alkaline conditions (pH = 9), the control of TTHMs and THAAs for the treatment of vanillic acid was better and more economical, however, an appreciable amount of inorganic by-products were observed. Under the same alkaline condition, the control of THAA for the treatment of p-hydroxybenzoic acid was not beneficial and for the treatment of humic acid was not significant.

Polymerization of humic substances by an enzyme-catalyzed oxidative coupling

A novel understanding of the structural features of humic substances supports the self-assembly supramolecular association of relatively small molecules rather than their polymeric nature. An increase in the conformational stability of humus may thus be achieved through promotion of intermolecular covalent bondings between heterogeneous humic molecules by an enzyme-catalyzed oxidative reaction. We present evidence from high performance size exclusion chromatography (HPSEC) and diffuse reflectance infrared spectrometry (DRIFT) that oxidation of a humic material catalyzed by horseradish peroxidase stabilizes the humic structure by the formation of aryl and alkyl ethers and permanently enhances its molecular size.

Electrochemical degradation of humic acid

The treatment of natural water for drinking water production goes through the degradation of humic substances. In this study, humic acid, extracted from a peat area located at the margins of the Mogi Guaçu River at São Paulo State, Brazil, was used to perform electro-oxidation essays in order to evaluate the possibilities of electrochemical methods in the degradation of humic substances. The working electrodes were dimensionally stable anodes (DSA) type with the following compositions: Ti/Ir0.3Ti0.7O2; Ti/Ru0.3Ti0.7O2; and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed by using a solution composed of an electrolyte support (0.1 mol l(-1) KCL) and 30 mg l-1 of the humic acid. Samples were taken during the electrolyses and analysed by the pH, transmittance, UV-vis spectra and chromatography. The results show that the Ti/Ru0.3Ti0.7O2 electrode presents the best performance considering the elimination of most of the electro-oxidation products after approximately 2 h of electrolysis at 40 mA cm(-2).

Degradation of humic acids by manganese peroxidase from the white-rot fungus Clitocybula dusenii

The depolymerization of humic acids (HAs) obtained from low-rank coal (lignite) to fulvic acids (FAs) was investigated in a cell-free system (in vitro) using manganese peroxidase (MnP) from the white-rot fungus Clitocybula dusenii b11. MnP was produced in surface cultures of C. dusenii which were induced with manganese (II) ions (Mn2+, 300 microM). The optimum conditions for the action of MnP were determined by varying following parameters of the enzyme assay: i) concentration of Mn2+, ii) concentration of hydrogen peroxide (H2O2), iii) pH value and iv) temperature. Optimum parameters determined were used in subsequent in vitro depolymerization studies of humic acids. For that purpose, following parameters of the reaction mixture were additionally varied: concentration of HAs, concentration of the thiol mediator glutathione (GSH), presence and concentration of organic solvents. As the result, following parameters were found to be optimal for the MnP-catalyzed in vitro depolymerization of HAs into low-molecular weight FAs (MnP activity 0.12 U/ml): 250 micrograms/ml HAs, 1 mM MnCl2, 46 microM/min H2O2 (continuously supplied by glucose oxidase), 600 microM GSH, 4% (v/v) N,N-dimethylformamide (DMF), pH 4.0, and 37 degrees C.

Sorption of phenols to dissolved organic matter investigated by solid phase microextraction

The sorption of phenol and different halogenated phenols to natural organic matter of a brown water lake (HO14), of a compost extract, of Aldrich humic acid (Aldrich-HA), and to the protein bovine serum albumin (BSA) was investigated using solid phase microextraction (SPME). The limit of determination for the SPME analysis was < 15 microg/l for all phenols investigated. The extraction coefficients K(F) were calculated according to a first-order extraction kinetics. In general, the extraction equilibrium was established faster due to the presence of dissolved organic matter (DOM). The highest sorption capacity of phenols was observed for BSA with log K(OC) values in the range between 2 and 6. For the compost extract and HO14 only a small sorption of the investigated phenols was determined. On the other hand, Aldrich humic acid showed a reasonable sorption of phenols with log K(OC) values between 2 and 3. The sorption to DOM decreased when the pH of the solution was increased.