Phenylurea pesticides

V. Pichon, F. Chen and M.-C. Hennion, On-line preconcenti ation and liquid cliromato-graphic analysis of phenylurea pesticides in environmental water using a silica-based immunosorbent , Aim/. Chim. Acta 311 429-436 (1995). 

Lord and Pawliszyn" developed a related technique called in-tube SPME in which analytes partition into a polymer coated on the inside of a fused-silica capillary. In automated SPME/HPLC the sample is injected directly into the SPME tube and the analyte is selectively eluted with either the mobile phase or a desorption solution of choice. A mixture of six phenylurea pesticides and eight carbamate pesticides was analyzed using this technique. Lee etal. utilized a novel technique of diazomethane gas-phase methylation post-SPE for the determination of acidic herbicides in water, and Nilsson et al. used SPME post-derivatization to extract benzyl ester herbicides. The successful analysis of volatile analytes indicates a potential for the analysis of fumigant pesticides such as formaldehyde, methyl bromide and phosphine. 

Figure 3. Proposed chemical reactions leading to stabilization of phenylamide, phenylcarbamate and phenylurea pesticides In soils. (From ACS Symposium Series No. 29, 1976) (173).

Pesticides Triazines, phenylureas, OPs, chloroacetanilides, thiocarbamates River water Online SPE... 

A Cis disk has been used to remove chlorotriazine, atrazine, metabolites, organophosphorus compounds, phenylurea, and carbamate pesticides from seawater prior to analysis by HPLC [392],... 

Analysis of pesticides in water was performed by fully automated online solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS/ MS) [25, 31]. These pesticides (a total of 22 belonging to the classes of triazines, OP, chloroacetanilides, phenylureas, thiocarbamates, acid herbicides, and anilides) were selected on the basis of previously published studies [20, 25], information gathered from the water authorities, and known use in rice crops. 

Pesticides arrive in the Ebro River at least from two main sources. Chlorinated pesticides (DDT, HCHs, etc.), currently limited or banned in Europe, are or have been produced by different factories in Monzon and Flix, along with its subproduct HCB. These compounds are present not only in the Flix residues, but also in sediments and fauna all along the low Ebro River. In addition, modem, more sophisticated pesticides, including triazines, phenylureas, anilines, and organopho-sphates, are currently used in the intensive agricultural practices currently common in the Ebro Delta [6, 7, 10]. 

Two of the most commonly used types of pesticides in Britain are herbicides, of the carboxyacid and phenylurea groups, applied to cereal growing land (Table 16.4). 

Pesticides containing methyl or other alkyl substituents maybe linked to N or 0 (i.e., N- or O-alkyl substitution). An N- or O-dealkylation catalyzed by microorganisms frequently results in loss of the pesticide activity. Phenylurea (see Chap. 1) becomes less active when microorganisms AT-demethylate the molecules (e. g., the conversion of Diuron to the normethyl derivative, Fig. 7). The subsequent removal of the second AT-methyl group renders the molecule fully nontoxic [169]. On the other hand, the microbial O-demethylation of Chloroneb creates the non-toxic product 2,5-dichloro-4-methoxyphenol (Fig. 7). 

Carbamates and ureas constitute important groups of pesticides that are used as herbicides (phenylureas, sulfonylureas, phenylcarbamates, and alkylthiocarbamates), insecticides (ben-zoylureas, methylcarbamates, and oximemethylcarbamates), or fungicides (dithiocarbamates, alkylenebisdithiocarbamates, and benzimidazolecarbamates) in different crops to control various weeds, pests, and diseases. 

Several cleanup methods have been developed for the determination of urea pesticides, involving different basic procedures, such as liquid-liquid partition (30-32,34,36,37), steam distillation (31), and liquid-solid chromatography (9,30,32,34,36,38,56-58). Different factors, e.g., water solubility, ionic and polarity properties, thermal stability, and the molecular weight of the compounds, determine the choice of the cleanup method. Moreover, micro-cleanup procedures and online enrichment techniques have been introduced for the automated determination of phenylureas (60). Table 6 summarizes the use of the different cleanup procedures in the determination of urea pesticides. 

JM Finocchiaro, WR Benson. Thin layer chromatography of some carbamate and phenylurea pesticides. J Assoc Off Anal Chem 50 888-895, 1967. 

Liquid chromatography -APCI-MS is applicable to many different types of pesticide structures, such as triazines, phenylurea herbicides, acetanilides, and OPPs. A study of 12 pesticides and pesticide degradation products demonstrated the sensitivity of the technique for OPP determination, with detection limits for water samples of about 0.001-0.005 /zg/L (32). 

Phenylcarbamate, phenylurea and many amide herbicides which yield anilines on hydrolysis can be detected after TLC by spraying with fluorescamine [100]. The limits of detection of a number of anilines separated by TLC and detected with fluorescamine are given in Table 4.16. A number of pesticides which yield anilines on hydrolysis or degradation is listed in Table 4.28. The analysis of anilines by this technique is described in Section 4.2.1.2.3. 

Pussemier, L., R. DeBorger, P. Cloos, and R. VanBladel. 1989. Relation between the molecular structure and the adsorption of arylcarbamate, phenylurea and anilide pesticides in soil and model organic adsorbents. Chemosphere 18(9/10) 1871-1882. 

Pichon, V., L. Chen, N. Durand, F. Le Groffic, and M.C. Hennion (1996). Selective trace enrichment on immunosorbents for the multiresidue analysis of phenylurea and triazine pesticides. J. Chromatogr. A, 725 107-119. 

Batard, Y., Robineau, T., Durst, F., Werck-Reichart, D., and Didierjean, L., Use of Helianthus tuberosus Cytochrome P450 Protein CYP76B1 for Improved Resistance to Phenylurea Herbicides and Pesticides in Transgenic Plants and for Soil and groundwater bioremediation, U.S. Patent 6376753, 2002. 

Substituted phenylurea derivatives form an important group of pesticides [6]. As mentioned in the Introduction, their photochemistry has been described in detail in a recent review article, which also covers the older literature [9]. This allows us to be more brief here readers are referred to this publication concerning detailed reaction mechanisms. In line with the topic of our review, we will concentrate on halogenated phenylureas, but also include some related compounds. 

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