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PubMed2005

Removal of humic substances from soil DNA using aluminium sulfate.

Direct extraction of soil DNA has become essential for the study of soil microorganisms. Humic substances co-extracted during DNA retrieval is a big problem because it greatly inhibits the enzymes involved in manipulating DNA. Popular commercial kits available for soil DNA extraction are unable to overcome this problem. Here we report an effective protocol for the removal of humic substance from soil DNA. The protocol involves flocculation of the humic substance by excessive Al(3+), then removal of superfluous Al(3+) via pH adjustment and finally release of soil microbial DNA by SDS lysis. This technique is superior to that employed by the UltraClean Soil DNA Kit and can be applied to a wide variety of soils.

Alum Compounds↗

PubMed2003

Diffusion coefficients of humic substances in agarose gel and in water.

Measurements of the diffusion coefficients of five different humic substances (HS) have been performed in water and in agarose hydrogels at several pH values (in the range of 3-10) and gel concentrations (in the range of 0.7-3% w/w). Fluorescence correlation spectroscopy (FCS) and classical diffusion cells were used in parallel to probe diffusion over both microscopic and mesoscopic distance scales. In general, agreement between the techniques was reasonable, which indicated that local nonhomogenities in the gel did not play an important role. Diffusion coefficients (D) in the gel were generally in the range of 0.9-2.5 x 10(-10) m2 s(-1) but were generally only 10-20% lower than in solution. At low pH values, one of the studied humic substances (a peat humic acid, PPHA) formed large aggregates that could not penetrate into the gel and therefore could not be defined by a single D value. The observed decreases of D in the gel for other HS were too large to be explained by the tortuousity and obstructive effects of the gel alone. D decreased slightly with increasing gel concentration and increased slightly with pH. Because modifications of D due to pH were similar in both the gel and the free solution, it is unlikely that complexation with the gel was greatly influenced by the pH. Rather, the main effect that appeared to decrease the diffusive flux in gels was likely small increases in the hydrodynamic radii of the humic macromolecules. An anomalous diffusion model was used to describe the FCS data in the gel. The characteristic exponent determined by fitting the autocorrelation functions with this model decreased only slightly (from 0.96 to 0.90) with increasing gel concentration providing support that HS complexation with the gel fibers was not very important. The results have important implications for our understanding of the fate and behavior of the HS and their associated pollutants and for interpreting metal speciation data obtained using gel-covered analytical sensors.

Diffusion↗

PubMed2001

Effect of functional groups of humic substances on uf performance.

The role of different functional groups present in humic substances on the membrane flux is unclear. This study is undertaken to (1) separate the carboxyl and phenolic groups from a humic solution, and (2) evaluate the effect of each fractionated humic substances on the ultrafiltration (UF) performance. A weak-base amine resin was used for the adsorption (pH 7) and the subsequent desorption (pH 13) of the phenolic groups from a commercial humic solution. These fractions were evaluated qualitatively (via Fourier transform infrared spectroscopy) and quantitatively (titration); they were further subjected to the analyses of the trihalomethane formation potential (THMFP) and ultrafiltration performance. Although, a complete separation of the phenolic and carboxyl groups is not possible, the results nevertheless provide useful information about their effects on UF performance. The fraction with a higher content of the phenolic OH group exhibits the highest THMFP (190 microg/mg C), whereas the fraction with a higher content of the carboxyl groups exhibits more flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in high THMs in permeate. The use of powdered activated carbon for the pretreatment of these fractions fails to improve membrane fouling. The pore size of UF membrane does not appear to affect the membrane flux, and the switch from the hydrophobic to hydrophilic membrane only slight improves the permeate flux.

Adsorption↗

PubMed2001

The molecular properties of humic substances isolated from a UK upland peat system: a temporal investigation.

The study concerns the possible changes in the molecular characteristics of humic materials isolated from the same source as a function of time. A great deal of data has been reported concerning the contrast in molecular characteristics of humic substances isolated from different environments. This has primarily been an attempt to identify source-specific molecular characteristics. However, data presented in this paper suggests that humic substances isolated from a single catchment have significant changes in molecular characteristics over time. Two naturally occurring peat pools (X and Y) situated upon a small organic catchment on Great Dun Fell, Cumbria, UK were sampled monthly between November 1994 and November 1996. Dissolved organic matter (DOM) from the pool water samples was fractionated using macroporous nonionic resins (XAD8 and 4), and the humic, fulvic and hydrophilic acids were collected. These fractions were analysed for elemental composition (C, H and N), weight average molecular weight, functional group content and adsorption (340 nm) of a 1 g l(-1) solution measured in a 1-cm spectrophotometer cell. The molecular characteristics were compared to those of natural DOM described by Scott et al. (1998). Scott et al. reported that drought conditions and seasonal climatic changes could have appreciable effects upon molecular characteristics of natural DOM. Results showed that the atomic H/C ratio of the humic substances increased immediately after strong drought conditions experienced in the summer of 1995. This change was temporary with atomic H/C ratio decreasing gradually over the following months. A similar decrease was observed in the carboxyl group content of the isolated compounds. The data set suggested that atomic H/C ratio in the fulvic and hydrophilic fractions exhibited seasonal characteristics of higher ratios during the late summer/early autumn months. This was not observed in the humic fraction. Humic acids exhibited a seasonal pattern of higher weight average molecular weight during the summer months. These trends were explained in terms of summer production of DOM in the catchment soils, their sequestering in the soil due to limited soil water movement during the summer months and their relative ease of dissolution when rainfall and soil water movement increased during the late summer/early autumn period. The results were found to support seasonal and long-term patterns observed in natural DOM as reported by Scott et al. (1998).

Benzopyrans↗

PubMed2004

Effect of phosphate on removal of humic substances by aluminum sulfate coagulant.

The presence of humic acid may change the way phosphate is absorbed or stabilized by soil and how it influences the growth of plants. The binding of phosphate with the humic substance requires bridging between phosphate ions and humic acid by metal ions, such as aluminum or iron ions. The bridging reaction can take place in peat and allophane soil under acidic conditions, altering the effectiveness of the phosphate in soil. Whether ternary phosphate-metal-HA complexes are actually formed has not yet been verified. This study considers variation in fluorescence intensity (FI) under various coagulation conditions to assess the mechanism by which humic acids and phosphate react with aluminum ions. A bond between the functional group of the humic acid and the electron-releasing group of the phosphate will enhance the florescent intensity of humic acids. Consequently the removal efficiency of humic acid, measured by florescence, declines as the phosphate concentration increases at low pH. This observation suggests that at low coagulation pH, the positively charged aluminum species can be used to bridge between the phosphate ion and the humic acid molecules.

Absorption↗

PubMed2002

Reactions of hydroxyl radical with humic substances: bleaching, mineralization, and production of bioavailable carbon substrates.

In this study, we examine the role of the hydroxyl (OH*) radical as a mechanism for the photodecomposition of chromophoric dissolved organic matter (CDOM) in sunlit surface waters. Using gamma-radiolysis of water, OH* was generated in solutions of standard humic substances in quantities comparable to those produced on time scales of days in sunlit surface waters. The second-order rate coefficients of OH* reaction with Suwannee River fulvic (SRFA; 2.7 x 10(4) s(-1) (mg of C/L)(-1)) and humic acids (SRHA; 1.9 x 10(4) s(-1) (mg of C/L)(-1)) are comparable to those observed for DOM in natural water samples and DOM isolates from other sources but decrease slightly with increasing OH* doses. OH* reactions with humic substances produced dissolved inorganic carbon (DIC) with a high efficiency of approximately 0.3 mol of CO2/mol of OH*. This efficiency stayed approximately constant from early phases of oxidation until complete mineralization of the DOM. Production rates of low molecular weight (LMW) acids including acetic, formic, malonic, and oxalic acids by reaction of SRFA and SRHA with OH* were measured using HPLC. Ratios of production rates of these acids to rates of DIC production for SRHA and for SRFA were similar to those observed upon photolysis of natural water samples. Bioassays indicated that OH* reactions with humic substances do not result in measurable formation of bioavailable carbon substrates other than the LMW acids. Bleaching of humic chromophores by OH* was relatively slow. Our results indicate that OH* reactions with humic substances are not likely to contribute significantly to observed rates of DOM photomineralization and LMW acid production in sunlit waters. They are also not likely to be a significant mechanism of photobleaching except in waters with very high OH* photoformation rates.

Biological Availability↗

PubMed2006

Photocatalytic oxidation of toxic organohalides with TiO2/UV: the effects of humic substances and organic mixtures.

TiO2/UV photocatalytic oxidation of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), 1,2,3-trichlorobenzene and 4-chlorophenol were examined in aqueous solution in the presence of humic substances and organic mixtures to study if the degradation rates were affected. Both commercial and natural humic substances were observed to retard the photodegradation rates, with a greater effect from the natural humic substances. Acetonitrile and isopropanol also caused significant retardation of 4-chlorophenol photodegradation. The overall retardation can be attributed to the combination of light attenuation, inhibition and competition effects. Moreover, the TiO2/UV system favors the decomposition of compounds that have stronger adsorption onto the TiO2 surface. To engineer effective treatment facilities that use the TiO2/UV system for the treatment of toxic substances in wastewater, the methodology must allow for concerns about adventitious species which are present.

2-Propanol↗

PubMed2004

Effect of low molecular size humic substances on nitrate uptake and expression of genes involved in nitrate transport in maize (Zea mays L.).

In this study, a detailed characterization of earthworm low molecular size humic substances (LMS) was performed and these substances were used to study their effect on the nitrate influx in roots, tissue nitrate content, and expression of maize genes putatively involved in nitrate uptake in maize (Zea mays L.). The results show that the humic fraction with low molecular size used in this study is endowed with the characteristic structural network described for most humic substances so far isolated and confirm the presence of IAA in this fraction. The results also show that the LMS fraction of humic substances stimulates the uptake of nitrate by roots and the accumulation of the anion at the leaf level. Moreover, the analysis of the expression of genes encoding two putative maize nitrate transporters (ZmNrt2.1 and ZmNrt1.1) and of two maize H(+)-ATPase isoforms (Mha1 and Mha2) show that these substances may exert direct effects on gene transcription in roots, as shown for the Mha2 gene, and long-distance effects in shoots, as observed for the ZmNrt2.1 gene.

Actins↗

PubMed1994

Determination of heavy metals in humic substances by instrumental photon activation analysis.

Photoactivation analysis is used for the determination of heavy metals in water and humic substances. Isolated humic acids serve as a carrier of environmental pollutants. The investigation of the drinking water catchment area in the middle German conurbation Leipzig/Halle shows it to be endangered from old neglected deposits of toxic wastes (chemical factory destroyed during World War II). Elevated concentrations of the elements zinc, cadmium, lead, and mercury in humic acids from surface waters were found.

Activation Analysis↗

PubMed2004

Involvement of humic substances in regrowth.

There appear to be interactions in the distribution system that complicate the ability to use AOC/BDOC as an independent assessment of regrowth potential. Two such complications are the limitation of the assays themselves and the potential interaction between the organic carbon concentration with the presence of disinfectants and pipe materials. To address these interactions, a series of experiments spanning several years have been conducted in model distribution systems at the Center for Biofilm Engineering (CBE) using soil-derived humics. When compared to easily utilized organics, humic substances supported the same order of magnitude of biofilm organisms. As carbon concentration was increased from 500 to 1000 to 2000 ppb, there was no increase in growth rate of the organisms, suggesting zero-order kinetics. If the system was chlorinated, there was less biomass, but growth rates were higher. In the presence of corrosion products, humic-fed systems supported more organisms than a control system fed biologically treated water. When free chlorine was maintained at a residual of about 0.2 mg/l, biofilm numbers on the surfaces were reduced. Phosphate alone did not result in fewer bacteria, while a combination of chorine and phosphate had the best results (lowest biofilm numbers). Adjustment to pH 9 was not effective. Recently completed work compared increasing levels of humic substances in the presence of free chlorine and monochloramine on biofilm growth on a number of surfaces (PVC, epoxy, cement, ductile iron). As the concentration of humic substances was increased from 0, 0.5 to 2 mg/l, there was an increase in biofilm numbers on all surfaces. This effect was the most pronounced on iron surfaces. These results illustrate that carbon compounds not measured by the BDOC or AOC tests may profoundly influence biofilm numbers. In addition, iron surfaces are at much higher risk for elevated biofilm counts in the presence of humic substances, even if disinfection is practiced. However, corrosion control may mitigate this interaction.

Bacteria↗

PubMed2005

Detection of PCBs in natural waters by front face fluorometry on solid sorbent on account of their fluorescence quantum yields and interaction with humic substances.

A method for the detection of PCBs in natural water, based on extraction/concentration with tab shaped elements cut from C18 fiber glass SPE disks coupled with a fluorescence detection has been evaluated. The potential of the method was estimated through the measurement of the fluorescence quantum yields in acetonitrile and limits of detection (LOD) of 11 PCBs congeners and Arochlors 1221 and 1242 in pure water. Most of the LOD values are within the range of PCB concentrations found in highly polluted waters (<1microg l(-1)) and thus confer some interest to the method. However, as expected, naturally present humic substances was shown to compete with the solid phase for PCBs adsorption thus reducing the capability of the method when applied to natural waters. A Stern-Volmer plot of the fluorescence signal reduction in the presence of various type of humic substances leads to apparent sorption coefficients (K(DOC)) significantly higher than the literature values determined for PCBs or for polycyclic aromatic hydrocarbons, indicating that besides complexing PCBs, humic substances may also block some of the adsorption sites at the sorbent surface. An increase of the pH up to 11 was shown to reduce the negative effect of humic substances but their preliminary total denaturation or destruction appears as a prerequisite condition for taking full advantage of the present method.

Adsorption↗

PubMed2002

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.

Anaerobiosis↗

PubMed2005

Competitive complexation of metal ions with humic substances.

The surface complexation model was applied to simulate the competitive complexation of Ni, Ca and Al with humic substances. The presence of two types of binding sites in humic acid, carboxylic and phenolic functional groups, were assumed at both low and high pH conditions. Potentiometric titrations were used to characterize the intrinsic acidity constants of the two binding sites and their concentrations. It was found that the diffuse-layer model (DLM) could fit the experimental data well under different experimental conditions. Ni and Ca ions strongly compete with each other for reactions with the humic acid but Al showed little influence on the complexation of either Ni or Ca due to its hydrolysis and precipitation at pH approximately 5. The surface complexation constants determined from the mono-element systems were compared with those obtained from the multiple-element system (a mixture of the three metal ions). Results indicate little changes in the intrinsic surface complexation constants. Modeling results also indicate that high concentrations of Ca in the contaminated groundwater could strongly inhibit the complexation of Ni ions whereas an increase in pH and the humic concentration could attenuate such competitive interactions. The present study suggests that the surface complexation model could be useful in predicting interactions of the metal ions with humic substances and potentially aid in the design of remediation strategies for metal-contaminated soil and groundwater.

Adsorption↗

PubMed1980

Effects of pollution on humic substances.

To assess effects of industrial and environmental pollution on analytical characteristics of humic substances, we isolated humic acids (HA's) and fulvic acids (FA's) from unpolluted and polluted soils and sediments. Following purification, the HA's and FA's were characterized by elemental (C, H, O, N, S) and functional group (CO2H, phenolic OH, total acidity) analyses, infrared (IR) spectrophotometry, differential thermal analysis (DTA) and by metal (Fe, Al, Cu, Mn, Pb, Ni, Co, Zn, Cr, Cd, Hg, Ca and Mg) analyses. Si was also determined in all samples. Polluted HA's and FA's contained more N and S but less O and were richer in all metals and Si than were unpolluted ones. IR spectra showed that polluted humic materials were enriched in COO- groups, secondary non-cyclic amides and possible also in SO3H groups. DTA curves indicated that polluted HA's and FA's were more thermostable than unpolluted HA's and FA's. Unusually high N, S, Cu, Cr, Zn and Hg contents of humic materials appear to be useful indicators of soil and sediment pollution.

Benzopyrans↗

PubMed1982

Reaction products of aquatic humic substances with chlorine.

A major concern of the chlorination of aquatic humic materials is the ubiquitous production of trihalomethanes. A large number of other chlorinated organic compounds, however, have been shown to be formed by chlorine's reaction with humic substances. In this study, humic material was concentrated from a coastal North Carolina lake and chlorinated at a chlorine to carbon mole ratio of 1.5 at pH 12. A high pH was necessary for complete dissolution of the humic material and for production of adequate quantities of oxidation and chlorination products for extraction, separation and mass spectrometric identification. After concentration in ether, samples were methylated, separated with a 50-m OV-17 glass capillary column or a 25 m SP-2100 fused-silica column and identified. A Hewlett-Packard 5710A gas chromatograph interfaced to a VG Micromass 7070F double-focusing mass spectrometer was used. Low resolution, accurate mass measurements were made with a combined EI-Cl source. The ability to do low resolution, accurate mass measurements made possible a rapid scan function necessary for capillary column gas chromatography. Accurate mass measurements allowed increased confidence in the identification of compounds, most of which are not available as standards. The products identified in these studies were chlorinated aliphatic straight-chain acids dominated by di- and trichloroacetic acid and the chlorinated dicarboxylic acids: succinic, fumaric and maleic acids. Chlorinated and unchlorinated aliphatic mono- and dicarboxylic acids and unchlorinated polycarboxylic aromatic acids comprise the remaining bulk of the compounds identified.

Chemical Phenomena↗

PubMed2002

Influence of dissolved humic substances on the leaching of MCPA in a soil column experiment.

The influence of dissolved humic substances on the transport of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in a sandy soil with a low organic carbon content was studied in a column experiment. Soil columns were eluted with aqueous solutions containing different fractions of humic substances. More than 70% of the applied compound was found in the leachate in all sandy soil experiments, but distinct differences were obtained depending on the composition of the eluent. The addition of both humic and fulvic acids to the eluent affected the leaching behaviour of MCPA. While the presence of humic acids increased and accelerated the movement of MCPA in the investigated sandy soil, fulvic acids caused the opposite effect: increased retention was observed relative to the control. We concluded that a possible carrier transport or retention strongly depends on the composition of the dissolved organic matter. Thus, changes in the composition of dissolved organic matter may affect MCPA movement into deeper soil layers.

2-Methyl-4-chlorophenoxyacetic Acid↗

PubMed2006

Differentiating ozone direct and indirect reactions on decomposition of humic substances.

The ozonation reaction is accomplished into two pathways: direct ozone oxidation and indirect free hydroxyl radical oxidation. Both reactions are proceeding simultaneously, thus, it is difficult to separate them and study their respective reaction mechanisms. Carbonate and bicarbonate react with free radicals that will effectively inhibit the indirect free radical oxidation without affecting the direct oxidation reaction. The feasibility of using these chemicals as scavengers to inhibit the hydroxyl radicals so that the direct ozone oxidation reaction and indirect free hydroxyl radical oxidation reaction can be differentiated is presented in this paper. The results will assist in achieving a better understanding of the ozone reaction mechanism in oxidizing organic substances. In this study, synthetic samples made of commercially available humic substance are used to carry out the inhibited and non-inhibited ozone oxidation experiments. The intersecting point of the ORP (oxidation reduction potential) time series curves of the inhibited and un-inhibited reactions, occurring at 120s after the onset of the oxidation reaction, marks the turning point at which all added scavenger chemicals have been completely exhausted. Based on the measured A(254) values, percentage distributions of direct ozone oxidation and indirect hydroxyl radical oxidation are estimated. The results indicate that the contribution of indirect reaction decreases with increasing amounts of inhibiting scavengers. The on-line ORP measurement results are simulated using a modified form of the Nernst equation expressed as ORP=11852-1196 pH+130 ln [(A(254,0)-A(254,t))(A(254,t))(-1)] with R(2) value of 0.99. In this equation, A(254) is the absorbance at 254 nm used to index the humic substance concentration while subscript 0 and t denote the initial and the final time, respectively.

Humic Substances↗

PubMed2006

Impact of humic substances on the aqueous solubility, uptake and bioaccumulation of platinum, palladium and rhodium in exposure studies with Dreissena polymorpha.

Zebra mussels (Dreissena polymorpha) were exposed to different types of water containing PGE salts (PtCl4, PdSO4, RhCl3) to investigate the influence of humic substances on the aqueous solubility, uptake and bioaccumulation of noble metals. The results showed a time dependent decrease of the aqueous PGE concentrations in tank water for all groups. This could mainly be related to non-biological processes. The aqueous solubility of Pd and Rh was higher in humic water compared with non-chlorinated tap water, whereas Pt showed opposing results. Highest metal uptake rates and highest bioaccumulation plateaus were found for Pd, followed by Pt and Rh. Pd uptake and bioaccumulation was significantly hampered by humic substances, whose presence appear to increase Pt uptake and bioaccumulation. No clear trend emerged for Rh. Differences in effects of humic matter among the PGE may be explained by formation of metal complexes with different fractions of humic substances.

Animals↗