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PubMed1975

The effect of inhibitors on the electron flow triggering photo-phobic reactions in Cyanophyceae.

1. Since photo-phobic reactions in the blue green alga Phormidium uncinatum seem to be triggered by changes of electron flow rates into or out of an electron pool situated in the electron transport chain between photo-system II and I, the effect of inhibitors affecting the electron transport chain has been studied. 2. Dose response curves of the phobic reaction have been measured by varying the trap energy in double beam light trap experiments with constant pairs of monochromatic light. From these dose response curves the effects of the inhibitors on both types of phobic reactions, i.e. exit reactions and entrance reactions, have been calculated. 3. Dibromothymoquinone (DBMIB) inhibits the electron transport between the electron pool and photosystem I by preventing the reoxidation of plastoquinone. The phobic entrance reaction, which results in an emptying of the light trap, is triggered by changes in the electron flow out of the pool; thus it is more effected by DBMIB than the exit reaction, which is mediated by the electron transport into the pool. 4. The phobic exit reaction, which results in accumulations in the light trap, is triggered by changes in the electron flow into the electron pool via photosystem II. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibits the electron transport near photosystem II; thus it affects the exit reaction more than the entrance reaction.

Cell Movement↗
PubMed1995

Biological degradation of isoproturon, chlortoluron and fenitrothion.

For the purpose of biodegradation studies several microorganisms were isolated from soil and adapted under laboratory conditions in the presence of pesticides, with the following degradation results: isoproturon after 72 h-86%, chlortoluron after 72 h-93%, after 65 h-88% and fenitrothion after 72 h-66%. The cultures can be used for the biodegradation of pesticides in the lyophilized state with or without an organic carrier.

Bacteria↗
PubMed2002

Exploiting plant metabolism for the phytoremediation of persistent herbicides.

Weed control by herbicides has helped us to create the green revolution and to provide food for at least the majority of human beings living today. However, some herbicides remain in the environment and pose an ecological problem. The present review describes the properties and fate of four representative herbicides known to be presistent in ecosystems. Metabolic networks are depicted and it is concluded that removal of these compounds by the ecologically friendly technique of phytoremediation is possible. The largest problem is seen in the uptake of the compounds into suitable plants and the time needed for such an approach.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1994

A new glibenclamide-insensitive neuroselective hyperpolarizing agent.

We describe a novel compound, (-)-N-(2-ethoxyphenyl)-N'-(1,2,3-trimethylpropyl)-2-nitroethene-1, 1-diamine), Bay x9227, that demonstrates dose-dependent hyperpolarizing activity of remarkable potency (EC50 3 picomolar) and selectivity for CNS neurons and clonal neurotypic cells compared to smooth muscle cells. Single cell membrane potential measurements were obtained in physiologic buffer using the fluorescent probe, bisoxonol. Unlike K+ATP-channel activators including its (+)-enantiomer (Hoffman et al., 1993, Biochem. Biophys. Res. Commun. 190(2), 551), this activity was insensitive to glibenclamide antagonism. These data suggest a novel pharmacologic site for effecting neuroselective hyperpolarization.

Animals↗
PubMed2005

Validation and implementation of a liquid chromatography/tandem mass spectrometry assay to quantitate dimethyl benzoylphenylurea (BPU) and its five metabolites in human plasma and urine for clinical pharmacology studies.

A method has been developed for the quantitation of N-[4-(5-bromo-2-pyrimidinyloxy)-3-methylphenyl]-N'-(2-dimethylamino-benzoyl)urea (BPU) and its metabolites in human plasma and urine. BPU and metabolites were separated on a C18 column with acetonitrile-water mobile phase containing 0.1% formic acid using isocratic flow for 5 min. The analytes were monitored by tandem mass spectrometry. Calibration curves were generated over the range of 2.5-500 ng/mL for BPU, mmBPU, and aminoBPU in plasma; and 0.1-20, 0.1-20, 0.5-100, 10-2000, 1-200, and 3-600 ng/mL for BPU, mmBPU, aminoBPU, G280, G308, and G322 in urine, respectively. The method has been successfully applied to study the pharmacokinetics of BPU.

Calibration↗
PubMed2005

Correlation of epiphyllous bud differentiation with foliar senescence in crassulacean succulent Kalanchoe pinnata as revealed by thidiazuron and ethrel application.

Leaves of Kalanchoe pinnata have crenate margins with each notch bearing a dormant bud competent to develop into a healthy plantlet. Leaf detachment is a common signal for inducing two contrastingly different leaf-based processes, i.e. epiphyllous bud development into plantlet and foliar senescence. To investigate differentiation of bud and its correlation, if any, with foliar senescence, thidiazuron (TDZ), having cytokinin activity and ethrel (ETH), an ethylene releasing compound, were employed. The experimental system was comprised of marginal leaf discs, each harbouring an epiphyllous bud. Most of the growth characteristics of plantlet developing from the epiphyllous bud were significantly inhibited by TDZ but promoted by ETH. The two regulators modulated senescence in a manner different for leaf discs and plantlet leaves. Thus, TDZ caused a complete retention whereas ETH a complete loss of chlorophyll in the leaf discs. In contrast, the former resulted in a complete depletion of chlorophyll from the plantlet leaves producing an albino effect, while the latter reduced it by 50% only. In combined dispensation of the two regulators, the effect of TDZ was expressed in majority of responses studied. The results presented in this investigation clearly show that the foliar processes of epiphyllous bud differentiation and senescence are interlinked as TDZ that delayed senescence inhibited epiphyllous bud differentiation and ETH that hastened senescence promoted it. A working hypothesis to interpret responsiveness of the disc-bud composite on lines of a source-sink duo, has been proposed.

Dose-Response Relationship, Drug↗
PubMed1998

Investigation of photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography-electrospray ionization tandem mass spectrometry system. Application to trace and confirmatory analyses in food samples.

The photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography-electrospray ionization mass spectrometer (LC-hv-MS) was investigated. This paper describes the application of LC-hv-MS, in combination with tandem mass spectrometry (MS-MS), to identification of phototransformation products and to the establishment of possible photolytic pathways of pesticides. In addition, the applicability of LC-hv-MS as an alternative to LC-MS-MS, for trace and confirmatory multiresidue analysis in food samples was investigated. To demonstrate the potential of this technique, a series of N-heterocyclic compounds, phenylureas and carbamates, was studied. Several parameters, such as irradiation time and nature of photosensitizers, were investigated, and their impact on the photolytic transformation is presented here. The technique's versatility is also exhibited by using it for identification of triazine isomers, and for detection of pesticide residues in food sample extracts. Illustrative applications for analysis in lettuce and blueberry extracts are described.

Food Contamination↗
PubMed1999

Ultra-trace-level determination of polar pesticides and their transformation products in surface and estuarine water samples using column liquid chromatography-electrospray tandem mass spectrometry.

A method is developed for the determination of polar pesticides and their transformation products [atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachlor] in surface, estuarine and sea water samples at the low ng/l level. Solid-phase extraction is combined off-line with column liquid chromatography-electrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridges and graphitized carbon black extraction disks, is evaluated. The influence of the organic solvent used in gradient LC, as well as the amount of co-extracted humic material on the ESI process is studied. The eluotropic strength of the organic solvent was found to have a distinct effect on the sensitivity of ESI-MS if coupled with LC gradient separations. Methanol gave much better results than acetonitrile and phenylurea compounds are more susceptible to solvent changes than triazines. Co-extracted humic material causes signal suppression in ESI-MS-MS detection. The degree of suppression depends upon the sample pH and the nature of the samples, i.e., surface or estuarine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, with the exception of DPU (8 ng/l). The applicability of the procedure was demonstrated by analyzing surface and estuarine water.

Chromatography, Liquid↗
PubMed2001

By-products formation during degradation of isoproturon in aqueous solution. II: Chlorination.

After a previous study in which the considered oxidant was ozone (Part I), a laboratory investigation has been carried out to study the degradation of the herbicide isoproturon during its reaction with another oxidant, i.e. chlorine, in aqueous solution (Part II; this paper). The specific aim was to identify the by-products formed. The effects of pH and the presence of bromide ions were studied. Reactions have been carried out at room temperature, in phosphate buffered aqueous solutions, at four pHs (6, 7, 8 and 9). By-products identification was first performed using relatively high initial reagent concentrations which were analytically convenient ([isoproturon] = 40 mg/l, [HClO + ClO-] = 160 mg Cl/l, [Br-] = 80 mg/l). In follow-up studies, the by-products identified during this preliminary step were searched for when using concentration values closer to those actually encountered at real water treatment plants ([isoproturon] = 0.4 and 0.004 mg/l, [HClO + ClO-] = 1.6 mg Cl/l, [Br-] = 0.8 and 0.008 mg/l). Under all of the studied conditions, the results showed that isoproturon is completely degraded and that it decays much faster in the presence of bromide. The pH has a negligible influence when bromide ions are absent. On the contrary, if bromide ions are present, the isoproturon decay is slower at higher pH values. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses have led to the identification of several by-products as a result of simultaneous oxidation and substitution reactions, both occurring on the aromatic ring of the herbicide. However, the more abundant by-products are those resulting from the oxidation of the isoproturon aromatic ring. As far as halogenated by-products are concerned, the higher the bromide ion concentration the higher the ratio of brominated to chlorinated by-products. On the basis of the analytical results, a pathway for isoproturon degradation under the studied conditions is proposed.

Chlorine Compounds↗
PubMed2001

Formation of volatile halogenated by-products during chlorination of isoproturon aqueous solutions.

The present paper deals with the formation of volatile halogenated by-products (POX) during the chlorination (160 mg/l) of aqueous solutions of the herbicide isoproturon (40 mg/l). Chlorination reactions have been carried out over 48 h, at ambient temperature, at two pHs (6 and 9) and in the presence or not of bromide ions (80 mg/l). The main results obtained have been as follows: (1) in the presence of bromide, isoproturon degradation is rather fast and it results affected by pH, complete isoproturon degradation is achieved within 1 and 15 min at pH 6 and 9, respectively; (2) in the absence of bromide herbicide degradation is slow (complete degradation is achieved within 180 min) and it is not affected by pH; (3) at pH 6, regardless of the presence of bromide, the maximum amount of POX formed is low (approximately 15 micromol X-/l) and remains constant during the reaction; (4) at pH 9 the amount of POX formed is far greater and continuously increases during the reaction, reaching a value of about 110 micromol X-/l after 48 h; (5) two different groups of by-products have been identified by solid phase micro extraction (SPME)-gas chromatography (GC)-mass spectrometry (MS) for the reactions carried out with or without bromide; among them, aliphatic as well as aromatic by-products containing chlorine, bromine or both halogens are present even though the most abundant are halogenated-methane derivatives (haloforms); pH value affects the amount of these by-products but does not modify their chemical nature.

Chlorine↗
PubMed2003

Study of solubility of isoproturon by its complexation with beta-cyclodextrin.

The inclusion complexes of beta-cyclodextrin-isoproturon were prepared using techniques such as kneading, co-evaporation, and co-precipitation. These complexes were characterised for physical properties and spectral studies such as UV, FTIR, and 1HNMR spectroscopy. To investigate the stoichiometry of the complexes Phase solubility method was adopted. Most of the complexes showed an increase in the dissolution rate of the herbicide. The best results were obtained when inclusion complexes were prepared by co-precipitation and co-evaporation method. Findings of this paper will allow the rational use of isoproturon with increase in its efficacy.

Carcinogens↗
PubMed1997

Stability of isoproturon, bentazone, terbuthylazine and alachlor in natural groundwater, surface water and soil water samples stored under laboratory conditions.

The stability of isoproturon, bentazone, terbuthylazine and alachlor was investigated in groundwater (GrW), surface water (SuW) and soil water from the unsaturated zone (SoW). Samples fortified with a low spiking level (LSL) of about 0.3-0.5 microgram/L and a high spiking level (HSL) of about 0.9-1.3 micrograms/L were stored for 1, 2, 14 (GrW) and 30 days (SuW and SoW) at 4 degrees C in amber glass bottles without biological inhibition. The initial pesticide concentration played a significant role, the lowest concentrations being the least stable for all pesticides. Nevertheless, after 14 days of storage, no concentration had decreased significantly compared to day 0 values, except for bentazone LSL in the GrW and SuW. Significant losses of alachlor were observed only after 30 days. Terbuthylazine and isoproturon were stable for 30 days, except for a slight loss of terbuthylazine HSL in the SoW. The very poor recovery of bentazone from the SoW gave poor results for interpretation. Overall, the stability of the molecules was highest in the GrW and lowest in the SoW. For SoW, the variability of triplicate determinations at a given storage time was, in some cases, as great as the changes in mean concentrations observed over the total 30 day storage period.

Acetamides↗
PubMed1997

Evaluation of ELISA microtiter plate-based assays for the direct determination of isoproturon in water samples and soil extracts.

Trials were carried out on the commercially available Millipore isoproturon ELISA microtiter plate tests and on laboratory assays developed by Hirst as part of a Joint European Union research project (BIOPTICAS). The lowest detectable dose (LDD) was determined as three times the standard deviation of the blanks. Depending on the calibration curves obtained on different days with different plates, the LDD varied from 0.020 to 0.064 microgram/L for the Millipore test and from 0.080 to 0.329 microgram/L for the Hirst test. The mean coefficients of variation within a single plate for triplicate determinations of standard solutions in the 0.05 to 0.5 microgram/L range were 5.5 and 3.6% for Millipore and Hirst respectively. Cross-reactivity was studied for mono- and di-demethylated isoproturon, chlortoluron, diuron and linuron. The highest cross-reactivity with both tests was that of mono-demethylated isoproturon (22% for Millipore, 4% for Hirst). This molecule was the only one to show significant cross-reactivity in the Hirst test, whereas in the Millipore test, the di-demethylated isoproturon also cross-reacted (4%). Natural water samples, 19 ground-, 53 lysimetric plate and 47 suction cup water samples, and 32 soil samples were also analysed with the ELISA tests. HPLC with a diode array detector was used as a validated control technique for the natural samples. For each water type, ELISA concentrations of both tests were significantly correlated with the HPLC values (r > or = 0.937; p < 0.001). For the soil extracts, the correlations were also significant (p < 0.001), but the scatter in the data was greater. Overall, the Millipore correlation coefficients were higher than those of Hirst.

Antibodies↗
PubMed2000

Mobility of isoproturon from an alginate-bentonite controlled release formulation in layered soil.

The mobility of isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] from an alginate-based controlled release (CR) formulation was investigated by using soil columns. A layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil was used. The CR formulation was based on sodium alginate (1.87%), isoproturon (1.19%), natural bentonite (3.28%), and water (93.66%), and was compared to technical grade isoproturon. The use of the alginate-bentonite CR formulation produced less vertical mobility of the active ingredient as compared to the technical product. There was no presence of herbicide in the leachate when the alginate-bentonite CR formulation was used. However, 0.90% of isoproturon appeared when the treatment was carried out with technical grade material. Isoproturon mobility was modelled using the programme CMLS, which showed the peat layer to retard pesticide leaching. Analysis of the soil columns showed the highest isoproturon concentration in the peat layer.

Adsorption↗
PubMed2004

Seasonal changes in the sensitivity of river microalgae to atrazine and isoproturon along a contamination gradient.

A study was undertaken to investigate the environmental impact of herbicides on natural communities of freshwater periphyton and phytoplankton in the river Ozanne and in related nearby water reservoirs, including both pristine and pesticide- (atrazine and isoproturon) contaminated stations. The microalgal toxicity of both herbicides was investigated by short-term studies, using the in vivo fluorescence pattern to perform dose-effect experiments. The taxonomic composition of the communities sampled was assessed by microscopy and by HPLC pigment analysis. The EC50 (periphyton) or EC125 (phytoplankton) values, calculated using in vivo fluorescence endpoints, increased with the herbicide concentration found in the water. In contrast, the structure of the algal communities (periphyton) inhabiting the contaminated stations seemed to be permanently affected when compared to the reference community. A 'memory effect' could be detected, both in herbicide sensitivity and in the structure of periphytic communities that persisted even when peak contaminations had disappeared. This study shows that the response of algal communities is likely to reflect past selection pressures, and suggests that the function and structure of a community could both be modified by the persistent or repeated presence of microcontaminants in natural environments. We could use short-term ecotoxicological tests on freshwater microalgae to assess the effects of past temporary contaminations by agricultural pesticides, and combining this with diversity indices could make it possible to assess the ecotoxicological risk of herbicide contamination even when a complete chemical analysis of the contamination is not feasible.

Agriculture↗
PubMed2001

Penetration of herbicides to groundwater in an unconfined chalk aquifer following normal soil applications.

The persistence and penetration of the herbicides isoproturon and chlorotoluron in an unconfined chalk aquifer has been monitored over a 4-year period through soil sampling, shallow coring and groundwater monitoring. Chlorotoluron was applied on plots as a marker compound, having never been used previously on that, or surrounding fields. The fieldsite had a 5 degree slope with soil depths of 0.5 to 1.5 m and a water table between 20 and 5 m from the soil surface. Where the water table was deepest (9-20 m below surface (mbs)) little or no positive herbicide detections were made. However, where the water table was at only 4-5 mbs, a regular pesticide signal of around 0.1 microg/l for isoproturon and chlorotoluron could be distinguished. Over the winter recharge period automatic borehole samplers revealed a series of short-lived peaks of isoproturon and chlorotoluron reaching up to 0.8 microg/l. This is consistent with a preferential flow mechanism operating at this particular part of the field. Such peaks were occurring over 2 years after the last application of these compounds. Shallow coring failed to uncover any significant pesticide pulse moving through the deep unsaturated zone matrix at the fieldsite.

Environmental Monitoring↗
PubMed2001

Spatial variability in the degradation rate of isoproturon in soil.

Thirty samples of soil were taken at 50-m intersections on a grid pattern over an area of 250 x 200 m within a single field with nominally uniform soil characteristics. Incubations of isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) under standard conditions (15 degrees C; -33 kPa soil water potential) indicated considerable variation in degradation rate of the herbicide, with the time to 50% loss (DT50) varying from 6.5 to 30 days. The kinetics of degradation also varied between the sub-samples of soil. In many of them, there was an exponential decline in isoproturon residues; in others, exponential loss was followed by more rapid rates of decline; in a few soil samples, rapid rates of loss began shortly after the start of the incubations. In more detailed studies with soils from a smaller number of sub-sites (20), measurements were again made of isoproturon degradation rate, and the soils were analysed for organic matter content, pH, and nutrient status (N, P, K). Measurements were also made of isoproturon adsorption by the soils and of soil microbial biomass. Patterns of microbial metabolism were assessed using 95 substrates in Biolog GN plates. Soils showing rapid biodegradation were generally of higher pH and contained more available potassium than those showing slower degradation rates. They also had a larger microbial biomass and greater microbial metabolic diversity as determined by substrate utilisation on Biolog GN plates. The implications of the results for the efficacy and environmental behaviour of isoproturon are discussed.

Adsorption↗