Urea pesticides

Although most nonionic organic chemicals are subject to low energy bonding mechanisms, sorption of phenyl- and other substituted-urea pesticides such as diuron to sod or sod components has been attributed to a variety of mechanisms, depending on the sorbent. The mechanisms include hydrophobic interactions, cation bridging, van der Waals forces, and charge-transfer complexes. 

PHENYL UREA PESTICIDES, FLAMMABLE LIQUID, TOXIC, n.o.s.. 2768 ... 

Thust, R., Mendel, J., Schwarz, H. and Warzoki, R. (1980). Nitrosated urea pesticide metabolites and other nitrosamides. Activity in clastogenicity and SCE assays, and aberration kinetics in Chinese hamster V79-E cells. Mutation Res. 79 239-248. 

Additional methods considered for 304(h) rule making and the parameters measured are the following (the numbers in parentheses indicate the number of compounds included in the method) 622, organophosphorus pesticides (19) 623, 4,4 -methylene bis(2-chloroaniline) 626, acrolein and acrylonitrile (2) 627, dinitroaniline pesticides (5) 628, carbofuran 629, cyanazine 630, dithiocarbamates (15) 631, carbendazim and benomyl 632, carbamate and urea pesticides (7) and 633, organonitrogen pesticides (7). Most of these are... 

Tables 1 and 2 show the chemical name, molecular formula, water solubility, and vapor pressure of representative carbamate and urea pesticides.

The use of pesticides in agriculture has obvious advantages, such as an increase in the quantity and quality of food crops. Nevertheless, pesticides are toxic substances, and their residues can pose a risk to man and environment. Therefore, pesticide residues in food are regulated at the international and national levels according to the toxicity of the compound and the human intake of a particular crop. The acute oral toxicity for rats and the maximum residue levels (MRLs) of carbamate and urea pesticides are listed in Tables 1 and 2. 

Table 4 Extraction of Urea Pesticides from Foods...

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. 

Table 6 Cleanup Procedures for Sample Extracts Used in the Determination of Urea Pesticides...

Table 7 Derivatization Methods for HPLC Determination of Carbamate and Urea Pesticides...

Tables 8 and 9 summarize the separation conditions used in HPLC analysis of carbamate and urea pesticides.

Table 9 HPLC Determination of Urea Pesticides in Food Samples...

Determination of urea pesticides has been performed by gas chromatography (37,56,160, 161), a technique that has highly sensitive and selective detectors. Nevertheless, some substituted ureas are thermolabile and decompose during the analysis by GC (102). Therefore, direct determination of unchanged compounds by GC is possible only for some urea pesticides under determined chromatographic conditions (161). In other cases, a degradation product is quantified instead of the parent compound (29,162-164), or these substituted ureas must be derivatized before GC determination (37,102). 

Direct determination of urea pesticides by high-performance liquid chromatography has been widely reported in the literature (10,32-36,127-130). Ultraviolet detection has often been used (32,33,35,36,60,127) with usually acceptable sensitivity, although this detector is nonspecific and the sensibility is, in general, low. To overcome this problem, several techniques have been assayed, such as precolumn enrichment (60), postcolumn derivatization (34,10), and the use of other detection techniques such as the electrochemical (129), photoconductivity (128,130), and fluorescence detectors (9,10,34). Table 9 summarizes representative papers using these techniques in HPLC analysis. 

The successful combination of mass spectrometry with gas chromatography (GC-MS) and, subsequently, with liquid chromatography (HPLC-MS) allowed not only the determination of urea pesticides in food but also the identification of their residues at trace level. Mass spectrometry is a technique that can be used as a general detector, with cyclic scanning. The selectivity and sensibility of analysis can be enhanced using characteristic ions of the molecule, with selected ion monitoring (SIM). Urea pesticides have been determined by HPLC-MS directly (175-180), without the thermal instability problems of GC analysis. 

The application of immunoassays to the determination of various urea pesticides have been reported (181,182), and this technique has a great potential for residue analysis by using rapid, simple, and cost-effective tests (183,184). 

High-performance LC is the technique of choice for residue determination in foods of nonvolatile, thermally labile carbamate and urea pesticides. National programs for monitoring pesti-... 

Urea pesticides are structurally similar to carbamates. Some common pesticides of this class are listed in Table 2.19.2. These substances can be determined by reverse phase HPLC method. Aqueous samples can be analyzed by U.S. EPA Method 553 using a reverse phase HPLC column interfaced to a mass spectrometer with a particle beam interface. The outline of the method is described below. 

The precision and accuracy data are not available for all the urea pesticides listed in the Table 2.19.3. However, a matrix spike recovery between 70 and 130% and a RSD below 30% should be achieved for aqueous samples. Samples should be spiked with one or more surrogates. Compounds recommended as surrogates are benzidine-d8, 3,3-dichlorobenzidine-d6, and caffeine-15N2. Surrogate concentrations in samples or blank should be 50 to 100 pg/L. 

The frequent use of an aryl amine in urea pesticides is illustrated by the following compounds ... 

Carbamate and urea pesticides 632 WW Polynuclear aromatic hydrocarbon 8310 HW... 

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