Phenylurea Herbicides Diuron Research Articles

Rapid Mineralization of the Phenylurea Herbicide Diuron by Variovorax sp. Strain SRS16 in Pure Culture and within a Two-Member Consortium

The phenylurea herbicide diuron [N-(3,4-dichlorophenyl)-N,N-dimethylurea] is widely used in a broad range of herbicide formulations, and consequently, it is frequently detected as a major water contaminant in areas where there is extensive use. We constructed a linuron [N-(3,4-dichlorophenyl)-N-methoxy-N-methylurea]- and diuron-mineralizing two-member consortium by combining the cooperative degradation capacities of the diuron-degrading organism Arthrobacter globiformis strain D47 and the linuron-mineralizing organism Variovorax sp. strain SRS16. Neither of the strains mineralized diuron alone in a mineral medium, but combined, the two strains mineralized 31 to 62% of the added [ring-U-(14)C]diuron to (14)CO(2), depending on the initial diuron concentration and the cultivation conditions. The constructed consortium was used to initiate the degradation and mineralization of diuron in soil without natural attenuation potential. This approach led to the unexpected finding that Variovorax sp. strain SRS16 was able to mineralize diuron in a pure culture when it was supplemented with appropriate growth substrates, making this strain the first known bacterium capable of mineralizing diuron and representatives of both the N,N-dimethyl- and N-methoxy-N-methyl-substituted phenylurea herbicides. The ability of the coculture to mineralize microgram-per-liter levels of diuron was compared to the ability of strain SRS16 alone, which revealed the greater extent of mineralization by the two-member consortium (31 to 33% of the added [ring-U-(14)C]diuron was mineralized to (14)CO(2) when 15.5 to 38.9 mug liter(-1) diuron was used). These results suggest that the consortium consisting of strains SRS16 and D47 could be a promising candidate for remediation of soil and water contaminated with diuron and linuron and their shared metabolite 3,4-dichloroaniline.

NDMA Formation during Chlorination and Chloramination of Aqueous Diuron Solutions

Formation of the potent carcinogen N-nitrosodimethylamine (NDMA) during chlorine disinfection of water containing secondary amines is now generally acknowledged. The phenylurea herbicide diuron is one of the most widely used herbicides in California, has been frequently detected in California's water sources with a transient nature of appearance, and has a structure that suggests it might be an NDMA precursor. This study sought to quantify the potential for NDMA formation from aqueous diuron solutions under varied chlorine and chloramine conditions. NDMA formation was consistently observed even in the absence of added ammonia, which has usually been the source of the nitroso-nitrogen during chloramination of other precursors. It appears that both nitrogen atoms in NDMA are donated by diuron during chlorination in the absence of added ammonia. For a given chlorine and diuron dose, NDMA formation increased in the order OCl- < NH2Cl < NHCl2, a result consistentwith previous NDMAformation studies. Significant quantities of NDMA (170 ng/L) were produced during dichloramination of diuron using a low dichloramine concentration and a diuron concentration at the upper end of typically detected concentrations in California (20 microg/L), suggesting a need for further investigation to accurately assess the human health risks posed by diuron with respect to NDMA formation potential. A reaction pathway is proposed to provide a possible explanation for NDMA formation from diuron during chlorination or chloramination. The findings in this study identify a specific potential precursor of NDMA formation, one that arises from nonpoint sources. This further highlights the difficulties associated with determining the environmental safety of chemicals and their associated byproducts.

Effects of the phenylurea herbicide diuron on natural riverine microbial communities in an experimental study

The effects of the phenylurea herbicide diuron (10 μg l −1) on natural riverine microbial communities were investigated using a three-week laboratory microcosm study. During the first six days, a latency period was observed both in the algal and the bacterial communities despite favorable abiotic conditions and independently of diuron exposure. From the second week, an intense algal bloom (chlorophyll a concentrations and cell abundances) was observed in the uncontaminated microcosms but not in the treated microcosms. The bloom stimulated the bacterial community and led to an increase in heterotrophic bacterial production ([ 3H]thymidine incorporation), activity (CTC reduction) and cell abundance. In parallel, shifts in bacterial community composition were recorded by polymerase chain reaction (PCR)–temporal temperature gradient gel electrophoresis (TTGE) analysis, whereas no major variation was detected using the fluorescent in situ hybridization (FISH) method. In the treated microcosms, the diuron acted not by damaging the initial communities but by inhibiting the algal bloom and indirectly maintaining constant bacterial conditions throughout the experiment. These inhibitory effects, which were recorded in terms of abundance, activity and diversity, suggest that exposure to diuron can decrease the recovery capacities of microbial communities and delay the resumption of an efficient microbial food web despite favorable environmental conditions.

Fate of Diuron and Linuron in a Field Lysimeter Experiment

The environmental fate of herbicides can be studied at different levels: in the lab with disturbed or undisturbed soil columns or in the field with suction cup lysimeters or soil enclosure lysimeters. A field lysimeter experiment with 10 soil enclosures was performed to evaluate the mass balance in different environmental compartments of the phenylurea herbicides diuron [3-(3,4-diclorophenyl)-1,1-dimethyl-urea] and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea]. After application on the agricultural soil, the herbicides were searched for in soil, pore water, and air samples. Soil and water samples were collected at different depths of the soil profile and analyzed to determine residual concentrations of both the parent compounds and of their main transformation products, to verify their persistence and their leaching capacity. Air volatilization was calculated using the theoretical profile shape method. The herbicides were detected only in the surface layer (0-10 cm) of soil. In this layer, diuron was reduced to 50% of its initial concentration at the end of the experiment, while linuron was still 70% present after 245 d. The main metabolites detected were DCPMU [3-(3,4-dichlorophenyl)-1-methylurea] and DCA (3,4-dichloroaniline). In soil pore water, diuron and linuron were detected at depths of 20 and 40 cm, although in very low concentrations. Therefore the leaching of these herbicides was quite low in this experiment. Moreover, volatilization losses were inconsequential. The calculated total mass balance showed a high persistence of linuron and diuron in the soil, a low mobility in soil pore water (less than 0.5% in leachate water), and a negligible volatilization effect. The application of the Pesticide Leaching Model (PELMO) showed similar low mobility of the chemicals in soil and water, but overestimated their volatilization and their degradation to the metabolite DCPMU. In conclusion, the use of soil enclosure lysimeters proved to be a good experimental design for studying mobility and transport processes of herbicides in field conditions.

Time-Dependent Absorption Evidence of Phenylurea-Derived Herbicides on Model Biomembranes: A DSC Study

Environmental Context. The need to improve the quality of agricultural cultivation and to control the weed growth of non-cultivated area has brought herbicides to wide-scale use. Unfortunately, these compounds have been proved to be toxic for many organisms, humans included. With an aim to a better knowledge of the mobility and fate of environmental pollutants, it becomes very important to have an exact knowledge of the role that the medium in which these products are dissolved or dispersed plays on the absorption of these products by biological membranes as a complement to information on the interaction between these compounds and cells. Abstract. Phenylurea derivatives are used as herbicides that inhibit photosynthesis. These materials enter plants via their roots and are employed for selective control of germinating grass and broad-leaved weeds in many crops as well as for total weed control of non-cultivated areas such as roads, railways, and parks. The study of the interaction between the herbicide and lipid membrane is interesting in assessing the relevance of the dispersing medium in the absorption processes. Differential scanning calorimetry (DSC), which detects the effect of foreign molecules on the phase transition from an ordered to a disordered lipid structure when submitted to heating, was employed to study such an interaction. Effects exerted by four phenylurea herbicides (difenoxuron, diuron, metoxuron, and linuron) on the thermotropic behavior of model membranes were here investigated. Aqueous dispersions of dimyristoylphosphatidylcholine (DMPC) were used as model membranes to study herbicide–membrane interactions. Experiments carried out by leaving herbicides, in a powdered form, in contact with DMPC-based multilamellar or unilamellar vesicles show that all the examined herbicides are able, but in different ways, to migrate through the aqueous medium and interact with model membranes. Experiments on herbicide-loaded liposomes in contact with empty ones indicate that the compounds are able to migrate from a loaded membrane to an empty one. The obtained data seem to validate the use of the DSC in demonstrating that bioactive and potentially toxic compounds not only to interact with biological membranes but also adsorb into a cell when dispersed in a lipophilic medium.

Kinetics of photocatalytic degradation of diuron in aqueous colloidal solutions of Q-TiO 2 particles

Kinetics of the photocatalytic degradation of a phenylurea herbicide diuron in aqueous colloidal solutions of Q-TiO 2 nanoparticles was analyzed in detail applying a model of parallel consecutive reactions of the first-order. The found mechanism was compared with the reaction pathways of electrochemically assisted photoprocesses on illuminated TiO 2 layers, polarized by external voltage, in various solvents. While a reductive dechlorination on benzene ring of diuron represented the major pathway in acetonitrile, a consecutive oxidative demethylation on the aliphatic side chain was mainly observed in water.

Determination of phenylurea herbicides in drinking water

The phenylurea herbicides chlortoluron, diuron, fluometuron, isoproturon, linuron, methabenzthiazuron, and neburon have been separated by use of three different thin-layer chromatographic systems and quantified densitometrically at nanogram levels. Calibration plots were linear between 50 and 2500 ng for all the herbicides; correlation coefficients, r , were between 0.9962 and 0.9999. For determination of the herbicides in drinking water the substances were enriched from water samples by solid phase extraction (SPE) on C 18 cartridges. Recovery rates were between 91 and 102% except for methabenzthiazuron (87%); relative standard deviations were ±1.2–2.9%. A rapid fluorodensitometric screening method, involving thermal hydrolysis and subsequent derivatization with fluorescamine, was also developed for the phenylureas. This improved the limit of detection 25-fold.

Development of Robust, Environmental, Immunoassay Formats for the Quantification of Pesticides in Soil

The use of antibodies, or more specifically recombinant antibody fragments (scAbs), for the immunodetection of pesticides, could provide a rapid, reliable, and robust method of environmental analysis. The inherent instability of some antibody structures in nonphysiological conditions, however, limits the utility of this approach. We have developed a generic strategy for the stabilization of scAbs in polar and nonpolar solvents, and in a range of other denaturing environments, by the introduction of an interdomain disulfide bond, generating stabilized antibody fragments or stAbs. StAbs specific for the phenoxyacid herbicide mecoprop and the phenylurea herbicide diuron were fully functional when compared to their equivalent unmodified scAbs but significantly more stable in nonphysiological conditions associated with the extraction of organics from environmental samples. Antiatrazine, mecoprop, diuron, and paraquat stAbs were successfully used to accurately identify and quantify pesticides present in solvent and aqueous extracted soil samples. Immunoassay data were validated by HPLC. Recombinant stAbs can be produced readily, cost-effectively, and in quantity from Escherichia coli expression systems and provide robust reagents for immunoassay detection of pollutants present in complex environmental matrices.

Determination of the rodenticides warfarin, diphenadione and chlorophacinone in soil samples by HPLC-DAD

A HPLC-DAD method is described for the analysis of the rodenticides warfarin, diphenadione and chlorophacinone, together with the phenylurea herbicides isoproturon and diuron, in soil samples. The HPLC parameters have been optimised to provide baseline separation with symmetrical peakshapes in short analysis times. The sample preparation consists of Soxhlet extraction followed by SPE clean-up on cyanopropyl silica.

Derivation and Properties of Recombinant Fab Antibodies to the Phenylurea Herbicide Diuron

The Fab domain sequences from messenger RNA of a mouse hybridoma cell line secreting a monoclonal antibody (MAb) specific for the phenylurea herbicide diuron were amplified and inserted into the M13 phagemid vector pComb8. Phage displaying diuron-specific Fab fragments were selected by binding to magnetic beads coated with diuron hapten conjugates, and eluted with diuron. Soluble rFab in E. coli lysates bound diuron with half-maximal inhibition (I50) of 1.6−12 ppb (ng/mL) in indirect and direct competition enzyme immunoassays (EIAs). The optimal competing hapten was different for indirect EIAs with proteolytic or recombinant Fabs and the intact MAb. Selectivity of rFabs for phenylureas was similar to that of the original MAb and its proteolytic Fab fragment and was not significantly affected by exchange of heavy and light chains among rFab clones, indicating that a single antibody species had been cloned. Keywords: Immunoassay; recombinant antibodies; monoclonal antibodies; diuron; herbicide; phenylurea; arylurea

Sequences of the cDNAs encoding the heavy- and light-chain Fab region of an antibody to the phenylurea herbicide diuron

The cDNAs from a hybridoma (mAb 481.1) specific for diuron, a widely used phenylurea herbicide, were cloned into the phage display vector pComb8. Antigen-binding clones were selected by panning on diuron-hapten-BSA conjugates. The nucleotide and deduced amino-acid sequences encoding the Fab regions of the light (κ) and heavy (γ) chains were determined. The light chain was from mouse κ chain subgroup III and the heavy chain was a member of the mouse H chain subgroup III(d).

Synthesis of Haptens and Derivation of Monoclonal Antibodies for Immunoassay of the Phenylurea Herbicide Diuron

Diuron and related phenylurea herbicides and their metabolites are important candidates for sensitive and specific immunodetection. This paper describes a scheme for the synthesis of two different types of phenylurea haptens for immunization and use as detecting conjugates in enzyme immunoassays (EIAs). The haptens were used to develop indirect and direct EIAs and to derive a panel of monoclonal antibodies (MAbs) with different specificities for diuron and its analogs. One of six possible combinations of hapten-spacer arm conjugates tested as immunizing and screening antigens resulted in an indirect competition EIA that was 100-2000-fold more sensitive than the others. The eight most sensitive MAbs had 160 values of 2-20 ppb for diuron. These MAbs gave two different patterns of cross-reactivities with monuron and linuron and negligible recognition of other arylurea herbicides. These MAbs and EIAs are potentially suitable for identification as well as detection of diuron, monuron, and linuron.

Liquid chromatographic determination of the herbicide diuron and its metabolite 3,4-dichloroaniline in asparagus.

A liquid chromatographic method is presented for the determination of the phenylurea herbicide diuron and its major metabolite, 3,4-dichloroaniline in asparagus. The method involves a simple isolation step using dichloromethane extraction, followed by reversed phase chromatography on a C18 column, using a basic aqueous-organic eluent and UV detection at 254 nm. The limit of determination is 0.02 mg/kg for both analytes.