Humic Acid Polymer Research Articles

Improvements on physical conditions of bauxite residue following application of organic materials

Soil formation and ecological rehabilitation is the most promising strategy to eliminate environmental risks of bauxite residue disposal areas. Its poor physical structure is nevertheless a major limitation to plant growth. Organic materials were demonstrated as effective ameliorants to improve the physical conditions of bauxite residue. In this study, three different organic materials including straw (5% W/W), humic acid (5% W/W), and humic acid-acrylamide polymer (0.2% and 0.4%, W/W) were selected to evaluate their effects on physical conditions of bauxite residue pretreated by phosphogypsum following a 120-day incubation experiment. The proportion of 2-1 mm macro-aggregates, mean weight diameter (MWD) and geometric mean diameter (GWD) increased following organic materials addition, which indicated that organic materials could enhance aggregate stability. Compared with straw, and humic acid, humic acid-acrylamide polymer application had improved effects on the formation of water-stable aggregates in the residues. Furthermore, organic materials increased the total porosity, total pore volume and average pore diameter, and reduced the micropore content according to nitrogen gas adsorption (NA) and mercury intrusion porosimetry (MIP) analysis, whilst enhancing water retention of the residues based on water characteristic curves. Compared with traditional organic wastes, humic acid-acrylamide polymer could be regarded as a candidate according to the comprehensive consideration of the additive amount and the effects on physical conditions of bauxite residue. These findings could provide a novel application to both Ca-contained acid solid waste and high-molecular polymers on ecological rehabilitation at disposal areas.

Influence of Super Absorbent Polymer and Humic Acid on Maize Yield and Nutrient Uptake on Rainfed Alfisols

The advances and development in agriculture depend not only on mechanization and new hybrid seeds but also on the improvement of soil physical and chemical properties which in turn help to increase crop productivity in dry land soils. A field study was carried out to study the influence of superabsorbent polymer at 2.5 and 4.5 kg ha-1and humic acid at 15 and 30 kg ha-1 alone and their combinations with recommended 100% fertilizers on yield, uptake, and photosynthetic pigments of maize grown on rainfed alfisols at Regional Agricultural Research Station, Palem, Telangana. The experiment was laid out in randomized block design with three replications, consisting of nine treatments. Further, results showed that conjoint application of hydrogel@4.5 kg ha-1 + humic acid@30 kg ha-1 along with 100% RDF package significantly increased the pooled grain and stover yield (7136 and 8457 kg ha-1) of maize. Irrespective level of hydrogel and humic acid combinations with 100% RDF increased the macronutrient uptake by grain and stover, which further build up the total uptake. A similar pattern was also observed in corresponding to grain and stover yield.The chlorophyll “a”, “b” and total chlorophyll content (1.81, 1.69 1.54; 0.69, 0.62, 0.55 and 2.65, 2.46 and 2.24 mg g-1 in fresh plant weight at 30, 60 and 90 DAS) significantly influenced by application of hydrogel@4.5 kg ha-1+ humic acid@30 kg ha-1. In conclusion, the present investigation indicates the positive interaction between humic acid and super absorbent polymer which improved nutrient uptake and maize yield.

Responses of Low-Quality Soil Microbial Community Structure and Activities to Application of a Mixed Material of Humic Acid, Biochar, and Super Absorbent Polymer.

Low-quality soil for land reuse is a crucial problem in vegetation quality and especially to waste disposal sites in mining areas. It is necessary to find suitable materials to improve the soil quality and especially to increase soil microbial diversity and activity. In this study, pot experiments were conducted to investigate the effect of a mixed material of humic acid, super absorbent polymer and biochar on low-quality soil indexes and the microbial community response. The indexes included soil physicochemical properties and the corresponding plant growth. The results showed that the mixed material could improve chemical properties and physical structure of soil by increasing the bulk density, porosity, macro aggregate, and promote the mineralization of nutrient elements in soil. The best performance was achieved by adding 3 g·kg-1 super absorbent polymer, 3 g·kg-1 humic acid, and 10 g·kg-1 biochar to soil with plant total nitrogen, dry weight and height increased by 85.18%, 266.41% and 74.06%, respectively. Physicochemical properties caused changes in soil microbial diversity. Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Nitrospirae, Planctomycetes, and Proteobacteria were significantly positively correlated with most of the physical, chemical and plant indicators. Actinobacteria and Armatimonadetes were significantly negatively correlated with most measurement factors. Therefore, this study can contribute to improving the understanding of low-quality soil and how it affects soil microbial functions and sustainability.

EFFECT OF SOME SOIL CONDITIONERS ON PHYSICAL AND CHEMICAL PROPERTIES OF NORTH SINAI SANDY SOILS

A pot experiment was carried out during the early winter of 2016-2017 at the Experimental Farm of Faculty of Environmental Agricultural Sciences, Arish University, to evaluate the use of some soil conditioners on physical and chemical properties of Arish sandy soil, Wheat (Triticum aestivum L.,CV Sakha 94) plants were grown in pots, A surface sandy soil sample (0-15cm) from the Experimental Farm of the Faculty was used in the study. Each conditioner was homogenously distributed on the soil surface and then were mixed with the upper 15 cm of soil surface. Grains of wheat were sown in each pot containing 20 Kg soil. NPK fertilizers were added as recommended. Vinasse, humic acid and polyacrylamide were added at three rates (0.5,1.0 and1.5(W/W)). The experimental design was complete randomized with four replicates for each treatment. Results of pH showed that the effect of applied both vinasse and humic acid to the soil in different rates led to slightly decrease on pH values gradually by increasing the rate of application. The result of acrylamide polymer show that the effect of the application to the soil led to increase pH values gradually by increasing the rate of application. Results of EC in soil show that the effect of applied vinasse, humic acid and acrylamide polymer to the soil in different rates led to increase on EC values gradually by increasing the rate of application. Also, data showed an increase in available N, P and K at all application, the higher value of N observed on application of vinasse on rates of V2 at the initial soil sampling periods, V3 at the mid-season and harvesting soil sampling periods. The higher value of P observed on application of vinasse on rates V3 at the initial soil sampling periods and HA3 at the mid-season and harvesting soil sampling periods and the higher value of K observed with application of V3 at all experiment periods. Except vinasse treatments, the mean values of organic matter, significantly increased with increasing the rates of the application the higher value HA3. Also, data indicate that for all studied levels of vinasse significantly increase soil organic matter values comparing to control treatments, HA3 achieve the highest increasing values of OM while application of PAM3 treatment was the superior for increasing soil OM. All studied levels of vinasse significantly increased soil bulk density. Apparently, HA2 and HA3 achieved the highest reducing values of BD. Such decreases represent about 8.05% and 7.89% lower than control treatment for the previously mentioned two HA rates and PAM3 treatment was the superior to other PAM3 for reducing soil BD, such decrease was 0.13 Mg m-3at the development stage of soil sampling and represent about 8.87% lower than control treatment. Results also revealed that there was a pronounced decreasing in soil Ks at the Initial period of soil sampling. Soil moisture content in both field capacity and witting point were increase along most of the studied soil sampling stages. The highest N, P and K content in grains was found for addition V3. Also, the highest grains yield was found for addition (vinasse)V3 while the control treatment had the lowest values.

The effect of humic acid and water super absorbent polymer application on sesame in an ecological cropping system: a new employment of structural equation modeling in agriculture

BackgroundThe current knowledge does not prepare a precise scientific tool for quantifying the effects of inputs particularly ecofriendly inputs such as superabsorbent polymer (SAP) and humic acid (HA) are being used to increase soil fertility, improve crop performance and finally food production. This study was designed and conducted aimed to suggest an innovative approach not only to identify and quantify the effects of these inputs but also to determine the efficient path among underground/aboveground relationships associated with sesame oil production. Two experiments were conducted at the Research Farm of Ferdowsi University of Mashhad using randomized complete block design with split strip plot arrangement and three replications in two successive cropping years (2015–2016) to evaluate the effects of SAP and HA on Sesamum indicum L. growth characteristics and oil production under two different irrigation levels including: supplying 50 and 100% of the sesame water requirement were allocated to the main plots. Applying of SAP (80 kg ha−1) into the soil and control (no applying SAP) were allocated to the subplots. Foliar application of HA (6 kg ha−1) and control (not applying HA) were allocated to the strip plots. The analysis of variance revealed that the effects of HA and SAP on many sesame traits also soil properties were significant.ResultThe fitted structural equation model suggests a direct strong-positive effect of leaf area index (LAI), plant height (PlantH) and water-use efficiency (WUE) on plant architecture construct (PlantArchitecture), soil nitrogen content (SoilN), soil electrical conductivity (SoilEC), and on soil properties construct (SoilProperties), which finally increase the sesame qualitative yield production. The calculation of the standard regression coefficients of the model’s variables revealed that variables including: LAI, WUE and PlantPhysiology have had the most causal effect to defining the yield of sesame oil under the field condition of SAP and HA application. The findings in our study suggest that the direct advantages of SAP and HA application is to increase PlantPhysiology, PlantArchitecture and SoilProperties by 65, 50 and 17 percent, respectively, through contributing to the respective processes.ConclusionGenerally, the coefficient of determination of the suggested model (R2= 0.44) indicates that the model explains 44% of the variations in the sesame qualitative yield. The present study suggests employing the structural equation modeling could be best taken as a precise and practical quantitative modeling approach rather than a specific statistical technique, not only to quantify the effects of inputs and management operations but also helps to profound our understanding to identify the most efficient paths involved to certain process which in turn prepare options to reduce production costs beside to produce healthy food and products.

Nitrogen fertility and abiotic stresses management in cotton crop: a review.

This review outlines nitrogen (N) responses in crop production and potential management decisions to ameliorate abiotic stresses for better crop production. N is a primary constituent of the nucleotides and proteins that are essential for life. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment. Therefore, increasing plant N use efficiency (NUE) is important for the development of sustainable agriculture. NUE has a key role in crop yield and can be enhanced by controlling loss of fertilizers by application of humic acid and natural polymers (hydrogels), having high water-holding capacity which can improve plant performance under field conditions. Abiotic stresses such as waterlogging, drought, heat, and salinity are the major limitations for successful crop production. Therefore, integrated management approaches such as addition of aminoethoxyvinylglycine (AVG), the film antitranspirant (di-1-p-menthene and pinolene) nutrients, hydrogels, and phytohormones may provide novel approaches to improve plant tolerance against abiotic stress-induced damage. Moreover, for plant breeders and molecular biologists, it is a challenge to develop cotton cultivars that can tolerate plant abiotic stresses while having high potential NUE for the future.

Melanin and humic acid-like polymer complex from olive mill waste waters. Part I. Isolation and characterization

A water soluble humic acid and melanin-like polymer complex (OMWW–ASP) was isolated from olive mill waste waters (OMWW) by ammonium sulfate fractionation to be used as natural additive in food preparations. The dark polymer complex was further characterized by a variety of biochemical, physicochemical and spectroscopic techniques. OMWW–ASP is composed mainly of proteins associated with polyphenols and carbohydrates and the distribution of its relative molecular size was determined between about 5 and 190kDa. SDS–PAGE shows the presence of a well separated protein band of 21.3kDa and a low molecular weight peptide. The OMWW–ASP complex exhibits a monotonically increasing UV–Vis absorption spectrum and it contains stable radicals. Antioxidant activity measurements reveal the ability of the OMWW protein fraction to scavenge both the cationic 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical, as well as the stable nitroxide free radical 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL).

A new humic acid remedy with addition of silver nanoparticles

Previously known biogenic stimulator humic acid (HA) was the subject of this current study and HA based new remediation was developed by addition of silver (Ag) nanoparticles in its macromolecule. Extracted HA from a healing mud was characterized and used as reducing agent for Ag ion as well as a stabilizer for the formed Ag nanoparticles. The properties of the obtained hybrid composite were examined by XRD, UV and FTIR spectroscopic techniques. The diameter of the nanoparticles in the HA polymer was up to 8.6 nm and they were identified to be metallic Ag.DOI: http://dx.doi.org/10.5564/mjc.v13i0.151 Mongolian Journal of Chemistry Vol.13 2012: 7-11

Synthesis and Characterization of Substituted-Ammonium Humic Acid Fluid Loss Additive for Oil-Based Drilling Fluids

Using widely distributed and cheap lignite as starting material, humic acid was modified by octadecylamine, and a new kind of humic acid acetamide was prepared. The optimal reaction conditions of the humic acid acetamide polymer were obtained through laboratory tests as follow: the ratio of of humic acid and octadecylamine was 1:1.5, the reaction temperature was 150 °C, and the reaction time was 16~18 h. The new product was characterized by IR, and the results showed that this substituted-ammonium humic acid was successfully prepared by reacting parts of carboxyl group of humic acid with octadecylamine. HTHP filtration experiments demonstrated that the substituted-ammonium humic acid had good fluid loss properties. As a result, this substituted-ammonium humic acid polymer is an excellent fluid loss additive, and it could meet the requirement of drilling operation under extreme condition.

Effect and mechanism of manganate preoxidation for organics removal

The performance and mechanism of manganate preoxidation process for organics removal were investigated in the present paper. The results showed that manganate was a potentially powerful oxidizing agent and could make the natural organic matter (NOM) concentration of sample solution increase. The process of manganate in combination with ferrous sulphate (FeMnO) was effective for organics removal and with the highest removal rate of 89% when the FeMnO dose was 0.18 mmol/L. The fluorescence analysis showed that the fluorescence intensity values related to hydrophobic acids and model humic acid polymers were the highest and the relative position of the main peak fluorescence intensity was shifted towards lower emission wavelengths, which indicated the reduction in the degree of aromaticity of residual organic matter fraction.

A comprehensive study on enhanced characteristics of modified polylactic acid based versatile biopolymer

Now a days, polylactic acid (PLA) and its derivatives are receiving significant attention due to its versatile applications. The present study provides a deep insight on major structural and functional properties of novel PLA–HA polymer synthesized by incorporating humic acid (HA) in PLA. Topographical features of both pure and modified PLA have been studied using SEM and AFM to analyze their comparative surface microstructures. Incorporation of HA was found to enhance slightly the thermal stability profile of the polymer. However, reduction of Tg, Tm and degree of crystallinity has also been noticed, which in turn resulted in enhanced ductility and higher elongation at break. Moreover, improvement in radical scavenging properties, total available phenolics (0.075 μmole GAE/g film) and water absorption capacity (90.65%) has been observed which essentially suggested introduction as well as enhancement of several utility features, originally absent in pure PLA. The study thus predicts multifaceted applications of PLA–HA polymer, from industrial packaging to fabrication of biomedical devices depending on its superior characteristics as compared to pure PLA.

Interaction of oil sands tailings particles with polymers and microbial cells: First steps toward reclamation to soil

Production of bitumen by surface mining of Alberta's oil sands has given rise to tailings ponds, containing large volumes of finely dispersed clays (10(8) m(3)), which settle only slowly. The mature fine tailings (MFT) in these ponds are operationally defined as consisting of particles smaller than 44 μm with a solids content in excess of 30% (w/w). Increasing the rate of densification of MFT is a rate-limiting step in tailings pond reclamation. Accelerated densification has been achieved through mixing of MFT with sand in the presence of calcium sulfate as a binding agent to generate consolidated tailings. Addition of negatively charged polymer, together with either calcium or magnesium ions, is similarly effective. Although toxic to higher aquatic life, tailings ponds harbour a wide variety of mainly anaerobic microbes. These convert residual hydrocarbon, causing methane emissions of up to 10(4) m(3) day(-1). Interestingly, anaerobic microbial activity also accelerates tailings pond densification. Hence, many technologies designed to accelerate densification move tailings, at least conceptually, towards soil in which sand and clay particles are linked by large amounts of humic and fulvic acid polymers supporting large numbers of microbes in a mechanically stable structure.

Isotherm modeling of organic activated bentonite and humic acid polymer used as mycotoxin adsorbents

The aim of the current study was to evaluate and compare two representative samples of different classes of adsorbents intended for use as feed additives in the prevention or reduction of the adverse effects exerted by mycotoxins, specifically ochratoxin A (OTA) and zearalenone (ZEN). The adsorbents, an organically activated bentonite (OAB) and a humic acid polymer (HAP), were tested in a common in vitro model with a pH course comparing the maximum pH changes that can be expected in the digestive system of a monogastric animal, i.e. pH 7.4 for the oral cavity, pH 3.0 for the stomach, and pH 8.4 for the intestines. In the first experiment, the concentration-dependent adsorbent capacity of OAB and HAB were tested using a fixed concentration of either mycotoxin. Thereafter, adsorption was evaluated applying different isotherms models, such as Freundlich, Langmuir, Brunauer–Emmett–Teller (BET) and Redlich–Peterson, to characterize the adsorption process as being either homo- or heterogeneous and representing either mono- or multilayer binding. At the recommended statutory level for the mycotoxins of 0.1 mg kg−1 OTA and 0.5 mg kg−1 ZEN, OAB showed an adsorbed capacity of >96% towards both mycotoxins, regardless of the pH. The HAP product was also able to absorb >96% of both mycotoxins at pH 3.0, but extensive desorption occurred at pH 8.4. Based on χ-square (χ2) values, Langmuir and Redlich–Peterson equations proved to be the best models to predict monolayer equilibrium sorption of OTA and ZEN onto the organically activated bentonite and the humic acid polymer. The applied methodology has a sufficient robustness to facilitate further comparative studies with different mycotoxin-adsorbing agents.

The interaction of triazine herbicides with humic acids

Although the binding of pesticides to organic carbon in soil, especially to humic acid (HA), is well recognized, the mechanisms have not been completely explained. This publication deals with adsorption of atrazine and terbuthylazine by humic acid under different experimental conditions, including adsorption times longer than those used hitherto. Direct HPLC analysis of HA suspensions is assessed as an alternative to more complicated techniques for estimation of free triazines, and compared with combined solid-phase extraction and HPLC. Experimental conditions such as time of exposure, addition of neutral salt, pH of the suspension, and HA concentration have a significant impact on the extent of triazine adsorption. At alkaline pH, triazines become partitioned in the HA fraction because of its hydrophobicity, whereas at acidic pH hydrogen-bonding probably occurs between triazine molecules and humic acid polymers.

Humic acid reduces protein‐C‐activating cofactor activity of thrombomodulin of human umbilical vein endothelial cells

Humic acid in the drinking water of blackfoot disease endemic areas in Taiwan has been implicated as one of the aetiological factors of the disease. For this report we examined the effects of humic acid on the expression of thrombomodulin (TM) cofactor activity by cultured human umbilical vein endothelial cells (HUVEC). Incubation of HUVEC with humic acid (HA) isolated from the drinking water, as a synthetic humic acid polymer (SHA) or with commercial HA, resulted in a dose-dependent reduction of cell surface thrombomodulin activity. Characterization of the mechanism by which humic acid reduced the protein C activation indicated that inhibition was not caused by production or release of a protein C inhibitor. Kinetic analysis showed that binding affinities of TM to thrombin and of TM-thrombin complex to protein C was unchanged upon humic acid treatment. However, the cell surface TM activity was reduced by humic acid, which functions as an irreversible noncompetitive inhibitor of thrombin binding. Down-regulation of TM was inhibited by non-selective protein kinase C inhibitors and a selective inhibitor. These results suggest that protein kinase C is intricately involved in HA-induced TM down-regulation. Down-regulation of TM was also inhibited by free radical scavengers. All these changes occurred in the absence of significant cytotoxic effect. In conclusion, our results suggest that HA induces down-regulation of TM by directly increasing permeability of the cell membrane, thus causing elevation in [Ca2+]i. This species functions as a second messenger to activate protein kinase C, and/or Ca-dependent enzymes eventually inducing down-regulation of TM. Attenuation of vascular endothelial cell TM cofactor activity by humic acid may play a role in the humic acid-induced thrombotic vascular disorders of blackfoot disease.

Influence of Salinity and Dissolved Humic Acids on Pesticides Extraction from Water Using Solid-Phase Extraction Disks

The influence of water salinity and dissolved organic matter (DOM) on pesticide extraction recoveries using solid phase extraction disks was investigated. Eleven selected pesticides, belonging to different chemical groups were spiked at 1–5 μg/L in 500 ml distilled water containing sodium chlorine at 0, 5, 10, 15, 20, 25, 30 and 35 ‰ or humic acids at either 0, 1, 5, 10, 25, 50 and 100 mg/L dissolved organic carbon (DOC). Samples were prefiltered and their extraction was done by using C18 Empore solid phase extraction disks and filter aid glass beads. The pesticides eluted from the disks were analysed by gas chromatography with flame thermoionic detector (FTD) and mass selected detector (MSD) in the selected ion monitoring (SIM) mode. Higher recoveries of most pesticides were obtained as the water salinity increased from 0 to 35 ‰. Concentrations of DOC in humic acid had less effect on extraction efficiency, which was probably due to greater nonpolar interactions of pesticides to the charge-neutralized humic acid polymer.

The role of selected cations in the formation of pseudomicelles in aqueous humic acid

The fluorescence intensity enhancement of a pyrene probe in aqueous humic acid solutions was assessed in terms of added lanthanide and thorium cations. Among the trivalent ions it was found that size played a role, with the small Lu 3+ ion producing the greatest increase in pyrene emission. This was attributed to its superior ability to cause pseudomicellization in the humic acid polymer. Slow kinetic effects were observed, leading to substantial fluorescence enhancement over a period of 7 h. This was ascribed to a continuous aggregation process in aqueous humic acid, leading to ever more viscous microenvironments for the probe molecule.

Influence of Dissolved Humic Acid and Ca-Montmorillonite Clay on Pesticide Extraction Efficiency from Water Using Solid-Phase Extraction Disks

Intermittent rain can influence the sediment load in surface runofffrom agricultural fields, thereby causing variability in amounts of sediment and dissolved organic matter (DOM) in the water that could adversely affect extraction efficiency and ultimately the method sensitivity of pesticide analyses in water monitoring studies. Therefore, a study was conducted to determine the effect of purified sediment components, Ca-montmorillinite clay and commercial humic acid, on extraction efficiency of 12 pesticides from water using solid-phase extraction (SPE) disks. Batches of water at pH 6.0 and 8.0 were prepared at an ionic strength of 3 x 10 -3 M. Individual water samples (250 mL) at each pH containing 20 μg L -1 each pesticide were amended with all possible combinations of (a) commercial humic acid at either 0, 5, 10, or 25 mg L -1 dissolved organic carbon (DOC) and (b) Ca-montmorillinite amounts of either 0, 0.01, 0.1, or 1 g. Samples were prefiltered to remove clay and then extracted using solid-phase extraction (SPE) disks. Pesticides eluted from disks were analyzed by gas chromatography/mass spectroscopy (GC/MS). Pesticides within chemical families reacted similarly to treatments of pH, Ca-montmorillinite, and humic acid. The effects of Ca-montmorillinite and humic acid were generally pH-dependent and acted independently in affecting extraction efficiency. Lower recovery of most pesticides was observed at pH 8 when Ca-montmorillinite was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area, and subsequent adsorption. Concentrations of DOC in humic acid had less effect on extraction efficiency when water was at pH 8 compared to water at pH 6, which was probably due to greater nonpolar interactions of pesticides to the charge-neutralized humic acid polymer.

Humic Acid Induces Expression of Tissue Factor by Cultured Endothelial Cells: Regulation by Cytosolic Calcium and Protein Kinase C

Blackfoot disease is a thrombotic peripheral vascular disease causally related to the fluorescent humic acid (HA) found in the drinking water of wells in endemic areas in Taiwan. In this study we examined the effect of HA on tissue factor (TF) expression by vascular endothelial cells. Incubation of cultured human umbilical vein endothelial cells (HUVEC) with HA isolated from endemic area drinking water or with a synthetic humic acid polymer (SHA), resulted in enhanced cell surface expression of TF activity by HUVEC. The intracellular calcium level ([Ca2+]i) was measured using a calcium-specific fluorescent probe, fura 2. Changes in [Ca2+]i level were followed and quantitatively analyzed by spectrofluorometric microscopy, after incubation of the fura 2-loaded HUVEC with HA or SHA in a medium containing 1.8 mM CaCl2. Both HA and SHA increased [Ca2+]i in the presence of extracellular calcium ions, but not in their absence, indicating that influx of extracellular Ca2+ occurred during incubation of HUVEC with HA or SHA. Verapamil, a potent calcium channel blocker, did not abolish the enhancement of [Ca2+]i induced by HA or SHA, indicating that specific calcium channels may not be involved in the HA/SHA-induced elevation of [Ca2+]i. The elevated [Ca2+]i level induced by HA or SHA returned to basal level following removal of HA or SHA and incubation of the washed cells in medium containing 1.8 mM CaCl2. All these changes occurred in the absence of significant cytotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Microbial Release and Degradation of Catechol and Chlorophenols Bound to Synthetic Humic Acid

AbstractThe binding of xenobiotics of humus occurs continuously in nature, and it is possible that this reaction can also be used for decontamination of the environment. It is not yet clear, however, to what extent the release of xenobiotics from humus may cause a delayed pollution problem. To evaluate this question, 14C‐labeled catechol (o‐dihydroxybenzene), 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,5‐trichlorophenol, and pentachlorophenol bound to synthetic humic acid polymer were incubated with microbial soil populations, and the evolution of 14CO2 and release of radioactive compounds into the medium was monitored. The quantity of 14CO2 evolved varied with the source of the inocula and the chemical structure of the compound under investigation. After 13 wk of incubation, 14CO2 evolution ranged from 1.2 to 10.0% of the initially bound radioactivity. Radioactive substances, which were released into the media mostly in the form of the unchanged compound, varied from 0.4 to 12.4% of the initially bound radioactivity. Most radioactivity (54.7–88.9%) remained bound to the synthetic humic acid, suggesting that once chlorophenols are incorporated into humus their release is very slow and unlikely to adversely affect the environment.