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At least 847 records · Page 47Linked to original sources
PubMed2006

Evaluation of the bioavailability of the herbicide prosulfocarb through adsorption on soils and model soil colloids, and through a simple bioassay.

Adsorption isotherms of prosulfocarb were determined on soils with different physicochemical properties. The extent of adsorption increased with the organic carbon content, but the results also suggested the involvement of some inorganic soil surfaces. In order better to understand the role of each soil surface, adsorption-desorption isotherms were determined on model soil colloids consisting of a soil humic acid, a montmorillonite, a synthetic aluminium hydroxide and their associations. The highest adsorption was observed on the humic acid, but it was also confirmed that the montmorillonite interacted with prosulfocarb. In contrast, the aluminium hydroxide was not active and its association with montmorillonite provoked a decrease in adsorption compared with montmorillonite alone. Except for humic acid, the highest adsorption took place on the ternary association montmorillonite-aluminium hydroxide-humic acid. On each surface tested, the adsorption was largely reversible and decreased at increasing pH. The herbicidal activity of prosulfocarb was tested by the determination of the germination and growth of a typical weed, Lolium multiflorum Lam, in contact with prosulfocarb solutions at different concentrations. The herbicide did not prevent the germination of the seeds but inhibited the growth of the roots and leaves. The same test was performed in the presence of the ternary system to evaluate the influence of adsorption on the plant bioavailability. It was concluded that the presence of an adsorptive surface reduced the herbicidal activity and that the simple bioassay proposed could be useful in predicting the extent of adsorption in a given soil.

Adsorption↗
PubMed2001

Rate of bentazone transformation in four layers of a humic sandy soil profile with fluctuating water table.

The rate of transformation of a pesticide as a function of the depth in the soil is needed as an input into computations on the risk of residues leaching to groundwater. The herbicide bentazone was incubated at 15 degrees C in soil materials derived from four layers at depths of up to 2.5 m in a humic sandy soil profile with a fluctuating water table (0.8 to 1.4 m), while simulating the redox conditions existing in the field. Gamma-irradiation experiments indicated that bentazone is mainly transformed by microbial activity in the soil. The rate constant for transformation was highest in the humic sandy top layer; it decreased with depth in the sandy vadose subsoil. However, material from the top of the phreatic aquifer had a higher rate constant than that from the layers just above. The presence of fossil organic material in the fluviatile water-saturated sediment probably stimulated microbial activity and bentazone transformation. The changes in the transformation rate constant with depth showed the same trend as those in some soil factors, viz organic carbon content, water-extractable phosphorus and microbial density as measured by fluorescence counts. However, the (low) concentration of dissolved organic carbon (DOC) in the top of the aquifer did not fit the trend. The rate constant for bentazone transformation in the layers was higher at lower initial contents of the herbicide.

Benzothiadiazines↗
PubMed2002

Photodegradation of diafenthiuron in water.

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

2-Propanol↗
PubMed2002

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

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

Adsorption↗
PubMed2004

Determination of molecular formulas and structural regularities of low molecular weight fulvic acids by size-exclusion chromatography with electrospray ionization quadrupole time-of-flight mass spectrometry.

Size-exclusion chromatography was coupled to a quadrupole time-of-flight mass spectrometer using electrospray ionization in the negative ion mode to analyze Suwannee River fulvic acid. About 220 exact masses of low molecular weight fulvic acids (FAs) were measured in the range from m/z 190 to 350, and molecular formulas could be deduced for all these molecular masses. All molecular formulas can be described by the superimposition of three homologous series in the FA mixture: (a) a series of hydrogen homologs constituted of five to six members for a given number of carbons and oxygens; (b) a series of alkyl chain homologs with stepwise addition of one methylene group; and (c) isobaric compounds that differ by the formal replacement of an oxygen atom by a methane group. Product ion spectra of the FA species reflect the repeated parallel losses of carbon dioxide and water. The minimum number of carboxylate groups and the maximum number of hydroxy moieties could be determined from the product ion spectra. Furthermore, it was obvious that the structural differences between homologs in the three series are located in the carbon backbone of the FA rather than in its extremities that are expelled as neutral fragments. These structural regularities reduce the complexity of FA mixtures to a certain set of yet unknown basic structures.

Benzopyrans↗
PubMed2001

Characterisation of dissolved combined amino acids in marine waters.

Dissolved combined amino acids (DCAA) are important constituents of the dissolved organic nitrogen (DON) pool in marine environments, although little is known about their sources, dynamics and sinks. The DCAA pool consists of various compounds including proteins and peptides, proteins linked to sugars and amino acids adsorbed to humic and fulvic acids, clays and other materials. The proportions of each of these components and the extent to which they are used by microplankton living within the photic zone are not known. An investigation was carried out, using (15)N isotope dilution techniques, to determine the concentration and composition of dissolved amino acid pools in the marine environment. A near-shore seawater sample was collected and split into fractions to determine the concentrations of dissolved free amino acids (DFAA), DCAA and a <3 kDa dissolved peptide fraction (DPEP; obtained by ultrafiltration). DCAA and DPEP fractions were hydrolysed to yield free amino acids and all samples were analysed by gas chromatography/mass spectrometry (GC/MS) as isobutyloxycarbonyl/tert-butyldimethylsilyl derivatives. The DFAA was the smallest fraction representing approximately 1% of total dissolved amino acids. The majority of DCAA was contained in the low molecular weight DPEP fraction (90%) and was probably as a result of release from phytoplankton and degradation by heterotrophic bacteria.

Algorithms↗
PubMed2003

Automated quantitative and isotopic (13C) analysis of dissolved inorganic carbon and dissolved organic carbon in continuous-flow using a total organic carbon analyser.

A method for the automated (13)C analysis of dissolved inorganic and organic carbon species has been developed to operate on a continuous-flow isotope ratio mass spectrometer (CF-IRMS). For natural and anthropogenic carbon species, the (13)C stable isotope has proven to be an excellent environmental tracer. Analytical performance tests were carried out on various organic compounds from easily oxidisable (sugar) to difficult (humic acid). A set of natural samples was also analysed to confirm the flexibility of the system. Analytical precision (2sigma) is typically <0.20 per thousand with sample reproducibility from 0.10-0.35 per thousand depending on reactivity of material. We believe this to be the first successful use of a total organic carbon (TOC) analyser for both dissolved inorganic and, specifically, dissolved organic species for (13)C stable isotope analysis in an automated CF-IRMS system. Routine analysis is achieved fairly quickly, is relatively simple with little or no sample manipulation, and will allow new and exciting studies for stable isotope research in both natural abundance and organic tracer studies not easily achieved before.

Carbon↗
PubMed2006

Attenuating effects of natural organic matter on microcystin toxicity in zebra fish (Danio rerio) embryos -- benefits and costs of microcystin detoxication.

To contribute to the understanding of joined factors in the environment, impact of pure microcystins (-RR and -LF) on zebra fish (Danio rerio) embryos were investigated individually and in combination with a natural organic matter (NOM). The applied NOM was a reverse osmosis isolate from Lake Schwarzer See (i.e., Black Lake, BL-NOM). Teratogenic effects were evaluated through changes in embryonic development within 48 h of exposure. Detoxication activities were assessed by the activities of phase II biotransformation enzymes, soluble and microsomal glutathione S-transferase (s, mGST). Oxidative stress was assessed by determining both the production of hydrogen peroxide and by analyzing the activities of the antioxidative enzymes, guajacol peroxidase (POD), catalase (CAT), glutathione peroxidase (GPx), and the glutathione restoring enzyme glutathione reductase (GR). Energetic costs were evaluated by determining contents of fat, carbohydrates, and proteins in both exposed and control embryos. BL-NOM attenuated toxic effects of MC-LF and MC-RR verified by less pronounced teratological effects within 24 h, in particular, as well as less rise in the activity of s-GST, when compared with embryos exposed to either pure toxins or in combination with organic matter. BL-NOM also diminished oxidative effects caused by MC-LF; however, it failed to attenuate oxidative stress caused by MC-RR. Content of lipids was significantly reduced in exposed embryos following a trend similar to that obtained with teratological and enzymatic assays confirming the attenuating effect of BL-NOM. Physiological responses to microcystins and NOM required energetic costs, which were compensated to the expense of the energy resources of the yolk, which in turn might affect the normal development of embryos.

Animals↗
PubMed2001

Induction of oxidative stress by humic acid through increasing intracellular iron: a possible mechanism leading to atherothrombotic vascular disorder in blackfoot disease.

Humic acid (HA), a potential toxin that has penetrated the drinking well water of blackfoot disease-endemic areas in Taiwan, has been implicated as an etiological factor of this disease. In this study, we investigated the effects of HA on the generation of reactive oxygen species (ROS) in cultured human umbilical vein endothelial cells (HUVECs). The generation of ROS was monitored by flow cytometry. Pretreatment of HUVECs with HA induced reactive oxygen species in a dose- and time-dependent manner. Xanthine oxidase inhibitor (Allopurinol), NADPH oxidase inhibitor (diphenylene iodomium) and calcium chelator (BAPTA) could not reduce the generation of ROS. Protein kinase C inhibitor (H7) could reduce the generation of ROS slightly, but the intracellular antioxidant glutathione monoethyl ester and the iron chelator desferrioxamine (DFO) could inhibit the generation of ROS completely. HA also enhanced the expression of ferritin and induced intracellular chelatable iron; however, HA reduced the expression of transferrin receptor. Pretreatment with DFO inhibited HA-mediated increases of ferritin synthesis and intracellular chelatable iron, but caused recovery of the inhibitory effect on transferrin receptor. Cotreatment with iron and HA induced more ROS and intracellular chelatable iron than iron or HA treatment alone. Furthermore, HA enhanced the accumulation of iron in endothelial cells. These data demonstrate that HA can increase the generation of ROS through enhancing the accumulation of intracellular iron. Taken together, our findings suggest that iron mediates HA-associated oxidative stress in endothelial cells, which may be a possible mechanism leading to atherothrombotic vascular injury observed for patients with blackfoot disease.

Arterial Occlusive Diseases↗
PubMed1996

Deltamethrin lethal multifactorial activity toward carp larva related to pH, calcium, and humic acid concentrations.

Acute 24-hr embryotoxicity of the pyrethroid insecticide delta-methrin toward carp larvae was tested in multifactorial combinations of three pHs (6.9, 7.8, 9.0), two calcium concentrations ([Ca] = 2 x 10(-4) and 2 x 10(-2) M), and three humic acids concentrations ([HA] = 0, 5, and 100 mg/liter). Lethal effects were determined and compared to the distribution and hexane extractibility of radiolabeled deltamethrin in the solution and on the vessel walls, either in the presence or in the absence of the larvae. As a function of the three combined factors tested, the no observed effect concentrations (NOECs) differed to a maximum by a factor of 8, while they differed by only a factor of 2 with pH alone, and by a factor of 4 with calcium or humic acids alone. No contact toxicity was observed with adsorbed deltamethrin on the vessel walls, on which adsorption and hexane extractibility was increased in the presence of larvae. The most plausible interpretation for the toxicological influence of the physicochemical factors tested on deltamethrin toxicity deals with the deltamethrin distribution in the medium for humic acids, changes in biological targets for calcium influence, and, for pH influence, degradation speed or one of the two other explanations.

Adsorption↗
PubMed1996

Deltamethrin multifactorial activity toward carp larva mobility related to calcium, humic acids, and pH.

The toxicity of pyrethroid insecticide deltamethrin was assessed by the "escaping capability" of carp larvae out of a trap. Mobility was tested after 1, 4, and 12 hr exposure to eight deltamethrin concentrations in standard water and after 24 hr exposure to seven deltamethrin concentrations in 18 media derived from the combinations of pH levels of 6.9, 7.8, 9.0, calcium concentrations of 2 . 10(-4) and 2 . 10(-2) M, and humic acid concentrations on 0, 5 and 100 mg/liter. In standard water, a 1-hr exposure at 4 microg/liter deltamethrin increased the mobility, while a 4-hr 32 microg/liter exposure decreased it. After 24 hr without deltamethrin, mobility was reduced at pH 6.9 and 7.8 and 2 . 10(-4) M calcium. It was also reduced in 100 mg/liter humic acids, especially when the former pH and calcium conditions were used. Humic acid effects could partly result from a calcium concentration reduction in water, and darkness due to humic acid coloration could play a minor role. Increasing humic acid concentration, calcium concentration, and pH reduced deltamethrin activity. In 0 or 5 mg/liter humic acids the No Observed Effect Concentration was 1 microg/liter, and in 100 mg/liter humic acid it was 2 microg/liter. Compared to previous results on deltamethrin-induced lethality, the escape test appeared less reproducible, but was 2 or 4 times more sensitive.

Absorption↗
PubMed1998

Amelioration of the photo-induced toxicity of polycyclic aromatic hydrocarbons by a commercial humic acid.

The ability of a commercial (Aldrich Chemical Co.) humic acid (AHA) to ameliorate the photo-induced toxicity of polycyclic aromatic hydrocarbons (PAHs) was examined using Lemna gibba L. (G3). Plants were exposed to anthracene and benzo(a)pyrene both with and without AHA and grown under visible light as well as lighting that simulates relative abundances of UV-A and UV-B in natural sunlight (SSR). Modest additions of 1.6 mg.L-1 AHA were sufficient to ameliorate the photo-induced toxicity of 2 mg.L-1 anthracene by improving growth rates to nearly 50% of controls and inducing minor recovery from complete chlorosis in the most highly affected plants. Benzo(a)pyrene induced minor, but significant, chlorosis under SSR, and AHA additions always increased growth rate and chlorophyll content, although to less of a degree than anthracene toxicity under SSR. The protective effects of AHA on anthracene toxicity increased linearly with increases in AHA concentrations up to 6.2 mg.L-1. Slopes of these relationships changed in the presence of UV light relative to visible light treatments; thus UV changed the extent to which AHA mediates PAH toxicity. However, the net effect was still for AHA to ameliorate PAH photo-induced toxicity even though UV has the potential to photooxidize AHA and enhance the production of potentially toxic reactive oxygen species from AHA photosensitization.

Anthracenes↗
PubMed1998

Influence of an aquatic humic acid on the bioconcentration of selected compounds in Daphnia magna.

Several chemicals covering a wide range of octanol-water partition coefficients were assayed for their bioconcentration in Daphnia magna in the presence of an aquatic humic acid. Assuming the properties of the humic acid used were similar to those known for organic matter from soils, the influence of the aquatic humic acid on physicochemical moderation of bioconcentration could not be demonstrated experimentally in a log Kow range of the chemicals between 2 and 6. Thus, the lipophilic character of the aquatic humic acid and the related effect of solubilization of the chemicals in the aqueous phase are much less than expected. This result is confirmed by determining the octanol-water partition coefficient of the aquatic humic acid. Comparing this value with log Kow values of humic acids of terrestrial origin, it can be clearly demonstrated that the lipophilicity of the aquatic humic acid is lower by a factor of 50.

1-Octanol↗
PubMed1999

Effect of natural dissolved humic material on bioavailability and acute toxicity of fenpropathrin to the grass carp, Ctenopharyngodon idellus.

The effects of aquatic humic acids on the bioconcentration and acute toxicity of fenpropathrin were evaluated using grass carp, Ctenopharyngodon idellus, in laboratory freshwater systems. The results demonstrated that both bioavailability and acute toxicity decreased in the presence of aquatic humic acid 5 and 10 mg/liter. In addition, the extent of influence increased with increasing concentration of aquatic humic acid.

Animals↗
PubMed2000

Stability constants of metal-humic acid complexes and its role in environmental detoxification.

Humic acid with hydroxyl-, phenoxyl-, and carboxyl-reactive groups can form coordination compounds with metals. The ion-exchange 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 microg ( approximately 3x10(-5)-15x10(-5) mol/liter) and metal salts solution 200 microg at pH 3.5. The stability constant (log K) for different 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 affecting the stability constants such as cation exchange capacity of humus soil, molecular radius, and molecular surface area of humic molecules were also estimated. The significance of the data to predict the behavior of these complexes in the environment is discussed.

Algorithms↗
PubMed2002

The effects of humic acid-arsenate complexes on human red blood cells.

Humic acid (HA) has been proposed as factor in the cause of Blackfoot disease (BFD) among individuals who live along the southwest coast of Taiwan. In this study, the interaction of the synthetic humic acid, made from catechol, with sodium arsenate (As(V)) was investigated and assessed with respect to damage to human red blood cells. HA is characterized as phenolic and phenolic carboxylic polymer structures containing both -COOH and -OH as their main functional groups. HA and As(V) alone are able to hemolyze 60-100 and 5-20% human red blood cells at concentrations of 50-300 microg/ml and 5-100 mM, respectively, after 6 h. HA is shown to be relatively ineffective in causing ATP depletion of red blood cells. For organometallic complexes composed of HA-As(V) the inhibition effect of EDTA was completely abolished and the use of the triple complex HA-As(V)-EDTA resulted in an enhancement of hemolysis. HA caused lipid peroxidation in a concentration- and time-dependent manner. However, HA-As(V) and As(V) decreased lipid peroxidation. These results indicated that HA initiates oxidative stress on red blood cells and this results in their dysfunction. HA-chelated high-concentration metal complexes inhibited the structures containing the main functional groups involved in decreasing hemolysis, and, thus, HA may be a significant factor in the etiology of BFD.

Arsenates↗
PubMed2000

Humic acid suppresses the LPS-induced expression of cell-surface adhesion proteins through the inhibition of NF-kappaB activation.

Humic acid (HA), a potential toxin when penetrating the drinking well water of blackfoot disease-endemic areas in Taiwan, has been implicated as one of the etiological factors of this disease. In this study, we investigated the effects of HA on the expression of human vascular endothelial-leukocyte adhesion molecules and the activation of nuclear factor kappa B (NF-kappaB) in cultured human umbilical vein endothelial cells (HUVECs). The expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin was monitored by flow cytometry. Pretreatment of HUVECs with HA inhibited the lipopolysaccharide (LPS)-induced expression of these three adhesion molecules in a dose- and time-dependent manner. Since NF-kappaB can regulate the expression of these adhesion molecules, NF-kappaB activation was assessed by electrophoretic mobility shift assay (EMSA). Our results reveal that the activation of NF-kappaB by LPS is suppressed by HA in a dose- and time-dependent manner. Furthermore, HA reduces NF-kappaB binding to DNA slightly, but completely inhibits the degradation of IkappaBalpha at a concentration of 100 microg/ml. Thus, all our data demonstrate that HA can inhibit the LPS-induced expression of adhesion molecules through the inhibition of NF-kappaB activation. HA may also suppress the immune or inflammatory reaction of HUVECs responsible for endotoxin, which could be one possible explanation for the causes of the infection and inflammation observed for patients with blackfoot disease. Our results also suggest that immune or inflammatory disturbance occurs for patients with blackfoot disease and that NF-kappaB may be a critical molecule in the pathogenesis of this disease.

Cell Adhesion↗