Humic Substances Research Papers - Academia.edu (original) (raw)

2007, Chemosphere

The low-cost, plant-based phytoextraction technique has often been described as a promising technique to remediate heavy metal contaminated agricultural land. The application of chelating agents has shown positive effects in increasing the solubility of heavy metals in soil and therefore in enhancing phytoextraction. This paper gives an overview of the chelating agents applied in recent studies. Various synthetic aminopolycarboxylic acids, such as ethylene diamine tetraacetic acid, and natural ones such as, ethylene diamine disuccinate and nitrilotriacetic acid, are described. Additionally, results of the application of natural low molecular weight organic acids, such as citric and tartaric acid are given. The effectiveness of these different chelating agents varies according to the plant and the heavy metals used. Furthermore, a focus is laid on the chelating agents fate after application and on its toxicity to plants and soil microorganisms, as well as it degradation. The rate of degradation is of great importance for the future of chelate assisted phytoextraction as it has a direct impact on the leaching probability. An effective prevention of leaching will be crucial for the acceptance and the economic breakthrough of enhanced phytoextraction, but a satisfactory solution to this key issue has so far not been found. Possibly further experiments in the field of enhanced phytoextraction will be able to solve this major problem, but over decades various greenhouse experiments and recently field experiments have resulted in different observations. Therefore, it is questionable if further research in this direction will lead to a promising solution. Phytoextraction has possibly reached a turning point in which it should distance itself from chelate assisted phytoextraction and focus on alternative options.

2004, Environment International

This study explores the modern history of Minoan culture and the myth of Minoan archaeology. Emerging from the cultural milieu of the late 19th and early 20th centuries, the genesis of this culture formed in the mind of Arthur Evans soon after he began excavations at Knossos in 1900. By 1930, he had transformed the site previously excavated by Minos Kalokairinos and earlier known as Tou Tseleve he Kephala and Ta Pitharia into the so-called Palace of Minos, and from poorly preserved ruins into a brightly painted, multi-storied, concrete vision of the past. After Evans's death, the restored palace became one of the most visited archaeological sites in the world and, in the process, the restoration assumed its own historical identity and became a major problem of conservation. Evans was the first not only to restore a monument to such an extent, but also to use actual archaeological remains as a medium of expression. Beyond giving posterity his vision of the past, Evans was to have a much greater influence on archaeological thought than is currently conceded. Evans viewed his Minoans as the first great European culture, but it was his disciple, V. Gordon Childe, who was to apply the concept of an archaeological culture systematically in his The Dawn of European Civilization (1925), thereby making it a working tool for all European archaeologists. At the brink of modernity, archaeology became entangled with a quest for European identity, and the legacy of that time continues to exert its influence on the present.

2008, Ecotoxicology

CITATIONS 248 READS 2,171 4 authors, including: Some of the authors of this publication are also working on these related projects: Nanomaterials -nanoparticles analysis and behaviours for different applications such as medical, biotechnology and environmental ones View project Potential ecological risk and human risk of heavy metal concentration in road dust from Rafsanjan View project

2000

Humic acid with hydroxyl-, phenoxyl-, and carboxyl-reactive groups can form coordination compounds with metals. The ionexchange equilibrium method using Dowex AG 50W-X8, 20-25 mesh Na ؉ form was used to determine stability constants of complexes formed between humic acid (isolated from the soil) 50+250 g (+3 ؋ 10 ؊ 5 +15 ؋ 10 ؊ 5 mol/liter) and metal salts solution 200 g at pH 3.5. The stability constant (log K) for di4erent metal+humic acid complexes indicated the following order of the stabilities of complexes formed between humic acid and metal ions: Cu > Fe > Pb > Ni > Co > Ca > Cd > Zn > Mn > Mg. The data on stability constants demonstrated substantial deviation from Irwing+Williams series reported for divalent ions. The molar humic acid/metal ratios were also calculated. Some of the factors a4ecting the stability constants such as cation exchange capacity of humus soil, molecular radius, and molecular surface area of humic molecules were also estimated. The signi5cance of the data to predict the behavior of these complexes in the environment is discussed.

2015, Chemosphere

State-of-the-art review of engineered nanoparticles and organic matter. Organic matter affects engineered nanoparticles stability and toxicity. The interaction of nanoparticles and organic matter is used for many purposes. Humic... more

2005, Chemosphere

The major limitation of soil application of sewage sludge compost is the total heavy metal contents and their bioavailability to the soil-plant system. This study was conducted to determine the heavy metal speciation and the influence of changing the physico-chemical properties of the medium in the course of composting on the concentrations, bioavailability or chemical forms of Cu, Zn, Pb and Ni in sewage sludge. Principal physical and chemical properties and FTIR spectroscopical characterization of sludge compost during treatment show the stability and maturity of end product. The total metal contents in the final compost were much lower than the limit values of composts to be used as good soil fertilizer. Furthermore, it was observed by using a sequential extraction procedure in sludge compost at different steps of treatment, that a large proportion of the heavy metals were associated to the residual fraction (70-80%) and more resistant fractions to extraction X-NaOH, X-EDTA, X-HNO 3 (12-29%). Less than 2% of metals bound to bioavailable fractions X-(KNO 3 + H 2 O). Heavy metal distribution and bioavailability show some changes during composting depending on the metal itself and the physico-chemical properties of the medium. Bioavailable fractions of all elements tend to decrease except Ni-H 2 O. Zn and mainly Cu present more affinity to organic and carbonate fractions. In contrast, Pb is usually preferentially bound to sulfide forms X-HNO 3 . Nickel shows a significant decrease of organic form. Significant degrees of correlation were found between heavy metal fractions and changes of some selected variables (e.g. pH, ash, organic matter, humic substance) during the course of composting. Mobile fractions of metals are poorly predictable from the total content. The R 2 value was significantly increased by the inclusion of other variables such as the amount of organic matter (OM) and pH.

The scientific understanding of the molecular size and shape of humic
substances (HS) is critically reviewed. The traditional view that HS are
polymers in soil is not substantiated by any direct evidence but is assumed
only on the basis of laboratory experiments with model molecules
and unwarranted results produced by incorrectly applying either analytical
procedures or mathematical treatments developed for purified and
undisputed biopolymers. A large body of evidence shows an alternative
understanding of the conformational nature of HS, which should be regarded
as supramolecular associations of self-assembling heterogeneous
and relatively small molecules deriving from the degradation and decomposition
of dead biological material. A major aspect of the humic
supramolecular conformation is that it is stabilized predominantly by
weak dispersive forces instead of covalent linkages. Hydrophobic (van
der Waals, -, CH-) and hydrogen bonds are responsible for the apparent
large molecular size of HS, the former becoming more important
with the increase of pH. This innovative understanding of the nature of
HS implies a further development of the science and technology for the
control of the chemistry and reactivity of natural organic matter in the
soil and the environment. (Soil Science 2001; 166:810–832)

2012, Chemosphere

a b s t r a c t Laccases (benzenediol: oxygen oxidoreductases, EC 1.10.3.2) are copper-containing enzymes that catalyze the oxidative conversion of a variety of chemicals, such as mono-, oligo-, and polyphenols and aromatic amines. Laccases have been proposed to participate in the transformation of organic matter and xenobiotics as well as microbial interactions. Several laccase assays have been proposed and used in soils. Here, we show that the optimal pH conditions for the laccase substrates 2,2 0 -azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS, pH 3-5), 2,6-dimethoxyphenol (4-5.5), L-3,4-dihydroxyphenylalanine (DOPA; 4-6), guaiacol (3.5-5), 4-methylcatechol (3.5-5), and syringaldazine (5.5-7.0) are similar between purified laccases from Trametes versicolor and Pyricularia sp. and soil extracts; the substrate affinities of purified enzymes (K M ) and soil extracts were also similar. The laccase assays showed specificity overlap with tyrosinase and ligninolytic peroxidases when hydrogen peroxide is present. The ABTS oxidation assay is able to reliably detect the presence of 13.5 pg mL À1 or 0.199 Â 10 À12 mol mL À1 of T. versicolor laccase, which is three times more sensitive than the 2,6-dimethoxyphenol-based assay and more than 40 times more sensitive than any of the other assays. The low molecular mass soil-derived compounds and the isolated fulvic and humic acids influence the laccase assays and should be removed from the soil extracts before measurements of the enzyme activity are performed.

2003, Journal of chromatography. A

Separation methods are widely used to isolate humic substances (HSs), to fractionate them before further investigation, and to obtain information about their structure and properties. Among the chromatographic methods, techniques based on a size-exclusion effect appear to be most useful, as they allow us to relate elution data to the molecular mass distribution of HSs. The limitations of this approach are discussed in this review. Gas chromatography with mass spectrometric detection is typically used to identify the products of pyrolysis or thermochemolysis of HSs; this technique is considered most important in the structural investigation of HSs. Electrophoretic methods (especially capillary zone electrophoresis) provide detailed characterization of HSs, but it is very difficult to relate the electrophoretic data to any specific subfraction, structure or properties of HSs. The electrophoretic patterns are often called ''fingerprints'' and can potentially be used for the identification and classification of HSs. This is limited, however, by the great diversity of the procedures employed and by the low degree of harmonization-no data on reproducibility and between-laboratory comparability are available. The same holds true, to a certain degree, for most methods utilized for the characterization of HSs. Separation methods play an important role in the examination of the interactions of HSs with heavy metals and other chemical pollutants. They allow us to determine binding constants and other data necessary to predict the mobility of chemical pollutants in the environment. 

Humic Substances (HS) occur naturally in our environment and are the remains of a process called humification, which is the biodegradation of biomass that then recombines and converts into dark colored complex compounds with no definite chemical structure. These are the end result of microbial degradation but resistant to further microbial degradation. It has a strong global presence as a dietary supplement and cosmetics applications for different beneficial uses. Till date its exploration as a pharmaceutical excipient has been limited to academic research only but the data being presented augurs a good commercial success.

2003, Journal of Hazardous Materials

In this study, the use of inductively coupled plasma/optical emission spectrometry (ICP/OES) to determine multi-metal binding to three biomasses, Sphagnum peat moss, humin and humic acids is reported. All the investigations were performed under part per billion (ppb) concentrations. Batch pH profile experiments were performed using multi-metal solutions of Cd(II), Cu(II), Pb(II), Ni(II), Cr(III) and Cr(VI). The results showed that at pH 2 and 3, the metal affinity of the three biomasses exposed to the multi-metal solution that included Cr(III) presented the following order: Cu(II), Pb(II) > Ni(II) > Cr(III) > Cd(II). On the other hand, when Cr(VI) was in the heavy metal mixture, Sphagnum peat moss and humin showed the following affinity: Cu(II), Pb(II) > Ni(II) > Cr(VI) > Cd(II); however, the affinity of the humic acids was: Cu(II) > Pb(II), Cr(VI) > Ni(II) > Cd(II). The results demonstrated that pH values of 4 and 5 were the most favorable for the heavy metal binding process. At pH 5, all the metals, except for Cr(VI), were bound between 90 and 100% to the three biomasses. However, the binding capacity of humic acids decreased at pH 6 in the presence of Cr(VI). The results showed that the ICP/OES permits the determination of heavy metal binding to organic matter at ppb concentration. These results will be very useful in understanding the role of humic substances in the fate and transport of heavy metals, and thus could provide information to develop new methodologies for the removal of low concentrations of toxic heavy metals from contaminated waters.

2014, Bioresource Technology

The semi-pilot scale SMABRs were operated on-site for a long-term. LMW organics responsible for biofouling of RO membrane were biodegraded. Biofouling reduction was validated with a rapid bioluminescence AOC measurement. Linear correlation between LMW organics and AOC concentration was observed. PAC helped to reduce fouling by coating on membrane without any damage.

2019

Application of biostimulation concept to direct action of humic substances on plants. Conference of CAC Shanghai 2019

2014, Science of The Total Environment

2009

Background, aim, and scope The novel system of ultraviolet light-emitting diodes (UV LEDs) was studied in water disinfection. Conventional UV lamps, like mercury vapor lamp, consume much energy and are considered to be problem waste after use. UV LEDs are energy efficient and free of toxicants. This study showed the suitability of LEDs in disinfection and provided information of the effect of two emitted wavelengths and different test mediums to Escherichia coli destruction. Materials and methods Common laboratory strain of E. coli (K12) was used and the effects of two emitted wavelengths (269 and 276 nm) were investigated with two photolytic batch reactors both including ten LEDs. The effects of test medium were examined with ultrapure water, nutrient and water, and nutrient and water with humic acids. Results Efficiency of reactors was almost the same even though the one emitting higher wavelength had doubled optical power compared to the other. Therefore, the effect of wavelength was evident and the radiation emitted at 269 nm was more powerful. Also, the impact of background was studied and noticed to have only slight deteriorating effect. In the 5-min experiment, the bacterial reduction of three to four log colony-forming units (CFU) per cubic centimeter was achieved, in all cases. Discussion When turbidity of the test medium was greater, part of the UV radiation was spent on the absorption and reactions with extra substances on liquid. Humic acids can also coat the bacteria reducing the sensitivity of the cells to UV light. The lower wavelength was distinctly more efficient when the optical power is considered, even though the difference of wavelengths was small. The reason presumably is the greater absorption of DNA causing more efficient bacterial breakage. Conclusions UV LEDs were efficient in E. coli destruction, even if LEDs were considered to have rather low optical power. The effect of wavelengths was noticeable but the test medium did not have much impact. Recommendations and perspectives This study found UV LEDs to be an optimal method for bacterial disinfection. The emitted wavelength was found to be an essential factor when using LEDs; thus, care should be taken in selecting the proper LED for maximum disinfection.

2011, Korean Journal of Chemical …

Methylene blue dye was adsorbed on an adsorbent prepared from cashew nut shell. A batch adsorption study was carried out with variable adsorbent amount, initial dye concentration, contact time and pH. Studies showed that the pH of aqueous solutions affected dye removal as a result of removal efficiency increased with increasing solution pH. The experimental data were analyzed by the Langmuir, Freundlich, Redlich-Peterson, Koble-Corrigan, Toth, Temkin, Sips and Dubinin-Radushkevich models of adsorption using MATLAB 7.1. The experimental data yielded excellent fits within the following isotherm order: Redlich-Peterson>Toth>Sips>Koble-Corrigan>Langmuir>Temkin>Dubinin-Radushkevich>Freundlich, based on its correlation coefficient values. Three simplified kinetic models including a pseudofirst-order, pseudo-second-order and intraparticle diffusion equations were selected to follow the adsorption process. It was shown that the adsorption of methylene blue could be described by the pseudo-second-order equation. The results indicate that cashew nut shell activated carbon could be employed as a low cost alternative to commercial activated carbon in the removal of dyes from wastewater.

2002, Pest Management Science

The soil sorption coef®cient K d and the soil organic carbon sorption coef®cient K OC 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. K OC 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.

2002, Environment International

Of the 2508 water samples analyzed in 10 districts of Bangladesh, 51%, on an average, contained arsenic levels of 0.05 to 2.50 mg/l. 95% of nail, 96% of hair, and 94% of urine samples contained arsenic above the normal level. Approximately 3.58 million people out of a total of 17.92 million who are drinking water containing arsenic levels > 0.20 mg/l are potentially exposed to high risk of health hazard. Eight thousand and five hundred arsenic patients are identified; they are suffering from various skin lesions, gangrene in leg, skin, lung, bladder, liver, and renal cancer. A big portion of the total population is highly vulnerable to various internal cancers. Lowest arsenic concentration in drinking water producing dermatological disease is found to be 0.103 mg/l. However, the exposure time to develop arsenicosis varies from case to case reflecting its dependence on arsenic level in drinking water and food, nutritional status, genetic variant of human being, and compounding factors. This study has determined the high intensity of fluorescent humic substances in drinking water containing elevated concentrations of arsenic and very low concentrations of heavy metals. The synergistic/antagonistic effect of fluorescent compounds present in drinking water may aggravate the toxicity of arsenic. Geochemical study suggests that arsenic may be released from both reductive dissolution of Fe and Mn (oxy)hydroxide and microbial oxidation of organic matter. D

2010, Chemosphere

Preparative high performance size-exclusion chromatography (HPSEC) was applied to humic acids (HA) extracted from vermicompost in order to separate humic matter of different molecular dimension and evaluate the relationship between chemical properties of size-fractions (SF) and their effects on plant root growth. Molecular dimensions of components in humic SF was further achieved by diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY-NMR) based on diffusion coefficients (D), while carbon distribution was evaluated by solid state (CP/MAS) 13 C NMR. Seedlings of maize and Arabidopsis were treated with different concentrations of SF to evaluate root growth. Six different SF were obtained and their carbohydrate-like content and alkyl chain length decreased with decreasing molecular size. Progressive reduction of aromatic carbon was also observed with decreasing molecular size of separated fractions. Diffusion-ordered spectroscopy (DOSY) spectra showed that SF were composed of complex mixtures of aliphatic, aromatic and carbohydrates constituents that could be separated on the basis of their diffusion. All SF promoted root growth in Arabidopsis and maize seedlings but the effects differed according to molecular size and plant species. In Arabidopsis seedlings, the bulk HA and its SF revealed a classical large auxin-like exogenous response, i.e.: shortened the principal root axis and induced lateral roots, while the effects in maize corresponded to low auxin-like levels, as suggested by enhanced principal axis length and induction of lateral roots. The reduction of humic heterogeneity obtained in HPSEC separated size-fractions suggested that their physiological influence on root growth and architecture was less an effect of their size than their content of specific bioactive molecules. However, these molecules may be dynamically released from humic superstructures and exert their bioactivity when weaker is the humic conformational stability as that obtained in the separated size-fractions.

2009, Water Research

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally contains suspended solids, dissolved inorganic ions and organic compounds (mainly humic substances) which may affect the efficacy of solar photocatalysis. In this work the photocatalytic and photolytic

2007, Planta

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H+ pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10−10 and 10−15 M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H+-ATPases and H+-pyrophosphatase. Further, the vacuolar H+-ATPase had a peak of stimulation in a range from 10−8 to 10−10 M IAA, whereas the H+-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10−3 to 10−15 M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H+ pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.

2005, Environmental Pollution

Solutions of natural humic acids appear to be a better choice for washing highly polluted soils.

1998, Analytical Biochemistry

with 50 ng/ml IGF-II, maximal expression of N-myc was observed after 30 min. The N-myc expression increased fourfold compared to serum-starved cells.

2002, Water Research

Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor. NDMA was formed from the reaction between DMA and monochloramine indicating that it should be considered a potential disinfection by-product. The formation of NDMA increased with increased monochloramine concentration and showed maximum in yield when DMA was varied at fixed monochloramine concentrations. The mass spectra of the NDMA formed from DMA and 15N isotope labeled monochloramine (15NH2Cl) showed that the source of one of the nitrogen atoms in the nitroso group in NDMA was from monochloramine. Addition of 0.05 and 0.5 mM of preformed monochloramine to a secondarily treated wastewater at pH 7.2 also resulted in the formation of 3.6 and 111 ng/L of NDMA, respectively, showing that this is indeed an environmentally relevant NDMA formation pathway. The proposed NDMA formation mechanism consists of (i) the formation of 1,1-dimethylhydrazine (UDMH) intermediate from the reaction of DMA with monochloramine followed by, (ii) the oxidation of UDMH by monochloramine to NDMA, and (iii) the reversible chlorine transfer reaction between monochloramine and DMA which is parallel to (i). We conclude that reactions involving monochloramine in addition to classical nitrosation reactions are potentially important pathways for NDMA formation.

2011, Journal of Chromatography A

Nanomaterials -nanoparticles analysis and behaviours for different applications such as medical, biotechnology and environmental ones View project Potential ecological risk and human risk of heavy metal concentration in road dust from... more

2012, Journal of Environmental Sciences

Accurate on-site determination of arsenic (As) concentration as well as its speciation presents a great environmental challenge especially to developing countries. To meet the need of routine field monitoring, we developed a rapid colorimetric method with a wide dynamic detection range and high precision. The novel application of KMnO 4 and CH 4 N 2 S as effective As(III) oxidant and As(V) reductant, respectively, in the formation of molybdenum blue complexes enabled the differentiation of As(III) and As(V). The detection limit of the method was 8 μg/L with a linear range (R 2 = 0.998) of four orders of magnitude in total As concentrations. The As speciation in groundwater samples determined with the colorimetric method in the field were consistent with the results using the high performance liquid chromatography atomic fluorescence spectrometry, as evidenced by a linear correlation in paired analysis with a slope of 0.9990-0.9997 (p < 0.0001, n = 28). The recovery of 96%-116% for total As, 85%-122% for As(III), and 88%-127% for As(V) were achieved for groundwater samples with a total As concentration range 100-800 μg/L. The colorimetric result showed that 3.61 g/L As(III) existed as the only As species in a real industrial wastewater, which was in good agreement with the HPLC-AFS result of 3.56 g/L As(III). No interference with the color development was observed in the presence of sulfate, phosphate, silicate, humic acid, and heavy metals from complex water matrix. This accurate, sensitive, and easy-to-use method is especially suitable for field As determination.

Journal of AOAC International

Increased use of humic substances in agriculture has generated intense interest among producers, consumers, and regulators for an accurate and reliable method to quantify humic acid (HA) and fulvic acid (FA) in raw ores and products. Here we present a thoroughly validated method, the new standardized method for determination of HA and FA contents in raw humate ores and in solid and liquid products produced from them. The methods used for preparation of HA and FA were adapted according to the guidelines of the International Humic Substances Society involving alkaline extraction followed by acidification to separate HA from the fulvic fraction. This is followed by separation of FA from the fulvic fraction by adsorption on a nonionic macroporous acrylic ester resin at acid pH. It differs from previous methods in that it determines HA and FA concentrations gravimetrically on an ash-free basis. Critical steps in the method, e.g., initial test portion mass, test portion to extract volume ...

2003, Environmental Research

Total concentration is not a reliable indicator of metal mobility or bioavailability in soils. The physicochemical form determines the behavior of metals in soils and hence the toxicity toward terrestrial biota. The main objectives of this study were the application and comparison of three approaches for the evaluation of cadmium behavior in soil samples. The mobility and bioavailability of cadmium in five selected soil samples were evaluated using equilibrium speciation (Windermere humic aqueous model (WHAM)), extraction procedures (Milli-Q water, DMSO, and DTPA), and a number of bioassays (Microtox, growth inhibition test, contact toxicity test, and respiration). The mobility, represented by the water-extractable fraction, corresponded well with the amount of cadmium in the soil solution, calculated using the WHAM (r 2 ¼ 0:96; Po0:001). The results of the ecotoxicological evaluation, which represent the bioavailable fraction of cadmium, correlated well with DTPA extractability and also with the concentration of free cadmium ion, which is recognized as the most bioavailable metal form. The results of the WHAM as well as the results of extraction experiments showed a strong binding of cadmium to organic matter and a weak sorption of cadmium to clay minerals. r

2004

Absorption and fluorescence spectroscopy and laser photobleaching experiments were employed to probe the origins of the optical properties of humic substances (HS). Luminescence quantum yields and the wavelengths of maximum emission were acquired for Suwannee River humic acid (SRHA) and fulvic acid (SRFA) at an extensive series of excitation wavelengths across the ultraviolet and visible. Laser irradiation at a series wavelength across the ultraviolet and visible was further employed to destroy selectively chromophores absorbing at specific wavelengths, using absorption spectroscopy to follow the absorption losses with irradiation time. The results provide unequivocal evidence that the absorption and emission spectra of these materials cannot result solely from a simple linear superposition of the spectra of numerous independent chromophores. Instead, the long wavelength absorption tail of HS (>350 nm) appears to arise from a continuum of coupled states. We propose that this behavior results from intramolecular charge-transfer interactions between hydroxy-aromatic donors and quinoid acceptors formed by the partial oxidation of lignin precursors. We further propose that these donor-acceptor interactions may be a common phenomenon, occurring within all natural hydroxy-or polyhydroxy-aromatic polymers that form appropriate acceptors upon partial oxidation. Examples of such species include lignin, polyphenols, tannins, and melanins.

2002, Environmental Science & Technology

Arsenite [As(III)] and arsenate [As(V)] are highly toxic aquatic contaminants. Since arsenite is more mobile in natural waters and less efficiently removed in adsorption/ coagulation processes than arsenate, the oxidation of arsenite to arsenate is desirable in water treatment. We performed the photocatalytic oxidation of arsenite in aqueous TiO 2 suspension and investigated the effects of pH, dissolved oxygen, humic acid (HA), and ferric ions on the kinetics and mechanisms of arsenite oxidation. Arsenite oxidation in UV-illuminated TiO 2 suspension was highly efficient in the presence of dissolved oxygen. Homogeneous photooxidation of arsenite in the absence of TiO 2 was negligibly slow. Since the addition of excess tert-butyl alcohol (OH radical scavenger) did not reduce the rate of arsenite oxidation, the OH radicals should not be responsible for As(III) oxidation. The addition of HA increased both arsenite oxidation and H 2 O 2 production at pH 3 under illumination, which could be ascribed to the enhanced superoxide generation through sensitization. We propose that the superoxide is the main oxidant of arsenite in the TiO 2 /UV process. The addition of ferric ions also significantly enhanced the arsenite photooxidation. In this case, the addition of tert-butyl alcohol reduced the arsenite oxidation rate, which implied that the OH radicalmediated oxidation path was operative in the presence of ferric ions. Since both Fe 3+ and HA that were often found with the arsenic in groundwater were beneficial to the photocatalytic oxidation of arsenite, the TiO 2 /UV process could be a viable pretreatment method. This can be as simple as exposing the arsenic-polluted water in a TiO 2 -coated trough to sunlight.

2012

Fouling mechanisms Alginate Humic acid a b s t r a c t Organic fouling remains a significant challenge in the application of ultrafiltration (UF) pretreatment systems in the desalination industry. In this study, the fouling potential of organic materials in seawater was investigated using model seawater solution containing humic acid and alginate. The buildup of organic fouling on UF membranes was studied after consecutive filtration cycles with periodical backwash. The effects of varying backwash conditions (duration, frequency, permeate/deionized water) on membrane performance were analysed. It was observed that the variation in filtration condition resulted in minor differences in membrane performance provided the total backwash volume applied remained constant. However, the substitution of permeate water backwash with deionized water improved fouling reversibility significantly. Furthermore, advanced characterisation of the membrane fouling layer after filtration revealed significant differences in foulant distribution due to the nature of the backwash solution. Deionized water backwash was found to be particularly effective in removing alginate from the membrane fouling layer, although the humic acid adsorbed onto the membrane surface were not significantly affected. However, permeability testing of the membranes after chemical cleaning revealed higher levels of irrecoverable fouling after deionized water backwash. From the data obtained in this study, a fouling mechanism is therefore proposed, in which the alginate fouling layer performs as a dynamic membrane, prefiltering smaller humic acid molecules and reducing adsorption on the membrane surface. ª journal h ome page: www.elsevier.com/loca te/watres w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 9 1 1 e9 2 1

2000, Toxicology and Applied Pharmacology

Toxic metals occur naturally at low concentrations throughout the environment, but are found in higher concentrations at many of the hazardous waste sites on the EPA Superfund list. As part of the Agency for Toxic Substances and Disease Registry (ATSDR) mandate to evaluate the toxicity of metals and mixtures, we chose four of the high-priority metal pollutants from ATSDR's HAZ-DAT list, including arsenic, cadmium, chromium, and lead, to test in a commercially developed assay system, CAT-Tox(L) (Xenometrix). This assay employs a battery of recombinant HepG2 cell lines to test the transcriptional activation capacity of xenobiotics in any of 13 different signal transduction pathways. Our specific aims were to identify metal-responsive promoters and determine whether the pattern of gene expression changed with a mixture of metals. Humic acid was used in all assays as a carrier to help solubilize the metals and, in all cases, the cells were exposed to the humic acid-metal mixture for 48 h. Humic acid alone, at 50 -100 M, showed moderate activation of the XRE promoter, but little other notable activity. As(V), at doses of 50 -250 M, produced a complex profile of activity showing significant dose-dependent induction of the hMTIIA, GST Ya, HSP70, FOS, XRE, NFBRE, GADD153, p53RE, and CRE promoters. Pb(II) showed doserelated induction of the GST Ya, XRE, hMTIIA, GRP78, and CYP IA1 promoters at doses in the range of 12-100 M. Cd(II), at 1.25-15 M, yielded significant dose-dependent induction of hMTIIA, XRE, CYP IA1, GST Ya, HSP70, NFBRE, and FOS. Whereas Cr(III) yielded small, though significant inductions of the CRE, FOS, GADD153, and XRE promoters only at the highest dose (750 M), Cr(VI) produced significant dose-related inductions of the p53RE, FOS, NFBRE, XRE, GADD45, HSP70, and CRE promoters at much lower doses, in the range of 5-10 M. Assays testing serial dilutions of a mixture comprising 7.5 M Cd(II), 750 M Cr(III), and 100 M Pb(II) (the combination of metals most frequently found at National Priority List sites) showed significant dose-dependent induction of the hMTIIA promoter, but failed to show dose-related induction of any other promoter and showed no evidence of synergistic activation of gene expression by the metals in this mixture. Our results thus show metal activation of gene expression through several previously unreported signal transduction pathways, including As(V) induction of GST Ya, FOS, XRE, NFkBRE, GADD153, p53RE, and CRE; Pb(II) induction of GST Ya, XRE, Cyp IA1, and GADD153; Cd(II) induction of NFkBRE, Cyp IA1, XRE, and GST Ya; and

The effect of additives on polysulfone membrane performance in peat water filtration was investigated. Polysulfone membrane was prepared by immersion precipitation from quarternary membrane systems containing N,N-dimethylacetamide (DMAc) as solvent, polyethylene glycol (PEG) and acetone as additives. The performance of membrane was evaluated by pure water flux and humic acid rejection. Results show that rejection of humic acid in peat water increased with the increase of acetone concentration. The maximum rejection was achieved at 8% wt acetone concentration. The presence of acetone contributed to the tight skin layer formation of polysulfone membrane. Other results suggest that membrane hydrophilicity can be improved by increasing of PEG concentration in membrane matrix, which was indicated by the increase of water flux around 127 LMH at the presence 25% wt of PEG. In high PEG concentration, the humic acid rejection was decreased which may be attributed to more open pore formed in the skin layer of the membrane and leads to a more severe irreversible fouling.

2006, Ecotoxicology and Environmental Safety

The effect of humic acids (HAs) on the toxicity of copper, zinc, and lead was investigated using the photobacterium Vibrio fischeri (Microtox test) as a test organism. The effects of HAs on metal toxicity were evaluated as functions of time and concentration in pure compound solutions. The toxicities of copper and lead were generally comparable, while the toxicity of zinc was lower than those of the other two metals. The toxicity of copper decreased with the addition of HAs, while the toxicity of zinc remained almost constant. On the other hand, the toxicity of lead increased, depending on the concentration of HAs. The interactive effects between copper and zinc and between lead and zinc were synergistic, while the interactive effect between copper and lead on the bioluminescence of V. fischeri was additive. The presence of HAs caused relatively high toxicity reduction in the binary mixtures of zinc and copper or zinc and lead, while the toxicity reduction in the case of the binary mixture of copper and lead was negligible. r

2010, Plant Signaling & Behavior

Available online xxxx Keywords: lignite humic acids cross-linking hydration DSC NMR relaxometry water molecule bridges

2014, TheScientificWorldJournal

The use of vermicompost (humified material) for treating wastewaters, remediating polluted soils, improving agricultural productivity, protecting crop production, and developing sensitive analytical methods is reviewed here, covering the past 17 years. The main advantages of vermicompost, considering all applications covered in this paper, comprise (i) easy acquisition, (ii) low costs, (iii) structural, chemical, and biological characteristics responsible for exceptional adsorptive capacities as well as pollutant degradation, and (iv) the promotion of biocontrol. Specifically, for wastewater decontamination, a considerable number of works have verified the adsorption of toxic metals, but the application of vermicompost is still scarce for the retention of organic compounds. Problems related to the final disposal of enriched vermicompost (after treatment steps) are often found, in spite of some successful destinations such as organic fertilizer. For decontaminating soils, the use of ...

We size fractionated a soil humic acid (HA) by preparative high performance size exclusion chromatography (HPSEC) and evaluated the analytical capacity of humeomics to isolate and identify humic molecular components in the separated size-fractions. HA and its three size-fractions were chemically fractionated to extract non-covalently bound organosoluble compounds (ORG1), weakly ester-bound organosoluble (ORG2) and hydrosoluble constituents (AQU2), strongly ester-bound organosoluble components (ORG3), and final unextractable residues (RES4). According to their solubility, the extracts were characterized by either GC–MS or on-line thermochemolysis/GC–MS techniques. The humeomic sequence showed that the analytical yields of identified compounds in either ORG or AQU extracts of size-fractions were invariably larger than for the unfractionated HA. This was attributed to a weaker conformational stability of humic suprastructures obtained by HPSEC fractionation, thereby enabling an improved separation and identification of single humic molecules. In line with the supramolecular understanding of humic substances , we found that hydrophobic compounds were mainly distributed in the largest size-fraction, while hydrophilic components were eluted in the smallest size-fraction. Furthermore, compounds with linear chains or stackable aromatic rings associated in regular structures were more abundant in the former fraction, whereas irregularly shaped compounds, that hindered association in larger size, were mostly found in the latter fraction. Thus the structural characteristics of single humic molecules determined their mutual association in humic suprastructures, as well as their conformational strength and shape. The lack of de novo synthesized macropolymers in the unfractionated soil humic matter was confirmed by the absence of RES4 fractions in the separated size-fractions. Our results indicate that humeomics capacity to reveal the complex molecular composition of humic suprastructures was significantly improved by subjecting humic matter to a preliminary HPSEC fractionation.

2014, Chemosphere

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabi...

2007, Chemical Geology

To predict metal-humic interactions in nature, experiments must be carried out using environmentally relevant concentrations of metal and humic substances (HS). Capillary electrophoresis coupled with ICP-MS (CE-ICP-MS) is a rapid and sensitive method to separate and detect metal species at trace-element concentrations. In this study CE-ICP-MS was used to measure partitioning of the rare earth elements (REE) between HS and a competing ligand (EDTA) under near environmental conditions (pH 6-10, 0.1 mol L − 1 NaNO 3 , 100 nmol L − 1 REE, 10 mg L − 1 HS). Conditional binding constants, K c,LnHS , were calculated for REE complexed with Elliot soil humic acid, Pahokee peat humic acid, Summit Hill soil humic acid, and Suwannee River natural organic matter and compared to existing data for REE complexation by Leonardite coal humic acid and Suwannee River fulvic acid. Results of these experiments show an increase in log K c,LnHS with decrease in ionic radius for REE-humic complexes (the lanthanide contraction effect), overall log K c,LnHS values ranging from 9 and 16 and indicating strong REE-HS binding, and a 2.7 log unit variation in K c,LnHS among humic sources. The inter-humic affinity for REE correlates with proton affinity and aromaticity of the HS sources.

2019

Landfill leachate consists mostly of a high content of refractory organic matter, ammonia and toxic compounds. All of these compounds, regardless of their nature, have a potential pollution effect on local ground and surface waters. In this context, the purpose of the present study was to evaluate a treatment process (coagulation-flocculation with lime coupled with nanofiltration) applied to landfill leachate from Seropédica, Rio de Janeiro (Brazil). Jar tests were conducted to determine the optimum dosage of lime (ranged from 0 to 10 g L-1) and, at optimum lime dose, ammonia nitrogen was removed during coagulation-flocculation process due to high pH. The process was settled for 6 h with slow stirring (50 rpm) to promote air entrainment and NH3-N stripping before using the final treatment step of nanofiltration at 8 bar. After ammonia stripping, NH3-N was reduced from 1236 mg.L-1 to 353 mg.L-1 (71% removal efficiency). At the end of the combined treatment, TOC (Total Organic Carbon), HS (Humic Substances) and COD (Chemical Oxygen Demand) removals were 89%, 80% and 94%, respectively. The results showed that the combined process was effective in the removal of recalcitrant compounds and NH3-N.

• Using humic acids and fulvic acids as chelating agents to improve EK efficiency. • HSs-enhanced EK efficiency was about 2–3 times greater than that in unenhanced EK. • Fulvic acids provided higher HMs removal than humic acids. • Results indicate the suitability of HSs-enhanced EK in real HMs contaminated soil. a b s t r a c t The effects of catholyte conditioning and the use of humic acids (HAs) and fulvic acids (FAs) as chelating agents to improve electrokinetic (EK) remediation efficiency were investigated using a real and highly contaminated soil. By applying a constant voltage (2.0 V/cm) to the soil, pH and current changes and heavy metals (HMs) concentration were investigated through a range of durations and positions. The observations demonstrated that both catholyte conditioning with 0.1 N HNO 3 and using humic substances (HSs) enhance remediation efficiency. After 20 days of EK treatment, the removal efficiency of HMs in HS-enhanced EK remediation was about 2.0–3.0 times greater than when unenhanced. The quantity of HMs moving toward the cathode exceeded the anode, from which it could be reasonably inferred that most negatively charged HM-HS complexes were moved by electroosmotic forces. Further, free HM cations and positively charged complexed HMs migrated to the catholyte compartment by electromigration. The results obtained in this study, demonstrate the suitability of HS-enhanced EK remediation in HMs contaminated soil.

2007, Environmental Pollution

Abstract This study examined the use of two composts derived from green waste and sewage sludge, amended with minerals (clinoptilolite or bentonite), for the remediation of metal-contaminated brownfield sites to transform them into greenspace. Soils contaminated with high or low levels of metals were mixed with the mineral-enhanced composts at different ratios and assessed by leaching tests, biomass production and metal accumulation of ryegrass (Lolium perenne L.). The results showed that the green waste compost reduced the leaching of Cd and Zn up to 48% whereas the composted sewage sludge doubled the leachate concentration of Zn. However, the same soil amended with composted sewage sludge showed an efficient reduction in plant concentrations of Cd, Cu, Pb or Zn by up to 80%. The results suggest that metal immobilisation and bioavailability are governed by the formation of complexes between the metals and organic matter. The amendment with minerals had only limited effects.

2000, Chemosphere

The aim of our study is to test the use of less time-consuming spectroscopic methods applied on original water samples in order to obtain information about DOM composition without any sample preparation. These results were directly compared with results from a conventional isolation and characterization procedure of dissolved humic substances (fulvic acids ± FA) isolated from the same water sample. FAs were characterized by UV-,¯uorescence-, FTIR spectroscopy and elemental composition. UV absorbance and¯uorescence behavior of FAs and original water samples follow the same pattern. A lower UV absorbance and a lower humi®cation index (derived from the synchronous¯uorescence spectra) of about 15% is typical for water samples compared to the FAs. We computed linear relationships between properties of the original water sample (UV-, synchronous¯uorescence spectra) and the isolated FA (IR absorption, C/N ratio). The application of synchronous¯uorescence and UV spectroscopy of aqueous samples has been proved to result in similar information about DOM composition as the characterization of isolated humic substances concerning the content of aromatic structures and the degree of humi®cation. Ó

Recently, ultrafiltration membrane technology is challenged to maintain their sustainability and favourable economics by improving their flux, selectivity and durability. Polysulfone membrane constitute the most extensively studied class of membrane materials due to its commercial availability, excellent chemical and thermal resistance, good mechanical properties and easy processing. However, polysulfone ultrafiltration membrane is susceptible to fouling and has low permeate flux due to hydrophobicity properties of the materials. Membrane modifications become unavoidable in order to reduce the fouling susceptibility. One simple and attractive method is blending polysulfone with additives. Previous studies show that the addition of additives in membrane solution could enhance membrane performances with higher porosity and flux. Meanwhile in surface water treatment application, humic substance has brought particular interest due to its nature which could produce some carcinogen substances that have negative effects on the human health in long term period. Therefore, the investigation to remove humic substances is considered as a sustainable solution in the field of surface water treatment. Many studies have been conducted with polysulfone based ultrafiltration membrane to remove humic substance from water, thus the factors that influenced humic substances fouling on polysulfone-based membrane and the effect of additive concentration on the improvement membrane performance for humic substance removal will be reviewed further in this paper.

2009, Environmental Science & Technology

The spectral dependencies of absorption and fluorescence emission (emission maxima (λ max ), quantum yields (φ), and mean lifetimes (τ m )) were acquired for a commercial lignin, Suwannee River humic (SRHA) and fulvic (SRFA) acids, and a series solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts). These parameters were compared with the relative average size and total lignin phenol content (TLP). TLP was strongly correlated with absorption at 280 and 355 nm for the MAB extracts, SRHA, and SRFA. The spectral dependence of λ max , φ, and τ m was very similar for all samples, suggesting a common photophysical and thus structural basis. A strong decrease of φ and τ m with increasing average size indicates thatintramolecularinteractionsmustbeimportant.Whencombined with previous work, the results lead us to conclude that the optical properties commonly associated with terrestrial humic substances and chromophoric dissolved organic matter arise primarily from an ensemble of partially oxidized lignins derived from vascular plant sources. They further provide additional support for an electronic interaction model in which intramolecular energy transfer, excited-state electron transfer, as well as charge transfer likely play important roles in producing the observed optical and photochemical properties of these materials.