Acute toxicity and metabolism of pesticides in birds.

The median lethal dose of pesticide in acute oral toxicity, used as a conservative index in avian risk assessment, varies by the species with differences of less than one order of magnitude, depending on body size, feeding habit, and metabolic enzyme activity. The profiles of pesticide metabolism in birds with characteristic conjugations are basically common to those in mammals, but less information is available on their relevant enzymes. The higher toxicity of some pesticides in birds than in mammals is due to the lower activity of avian metabolic enzymes. The bioaccumulation in birds is limited for very hydrophobic pesticides resistant to metabolic degradation. Several in silico approaches using the descriptors of a pesticide molecule have recently been employed to estimate the profiles of acute oral toxicity and bioaccumulation.

Theoretical and organic chemical approaches to environmental behavior and metabolism of pesticides.

Investigation of the dissipation and transformation of pesticide through laboratory experiments, conducted in accordance with standard and newly developed designs, gives us valuable information to understand their environmental behavior. We have also been investigating the mechanisms of partition and transformation reactions of pesticides, not only through kinetic analyses, but also through theoretical approaches based on their molecular properties estimated using various spectroscopies and molecular orbital calculations. Furthermore, synthetic iron porphyrin with a peroxide was shown to be a good model to simulate the P450-catalyzed oxidation in the metabolism of pesticides. Through these investigations, the knowledge of surface water, soil, sediment, and plants, such as their properties and constituents, was found indispensable to a deep understanding of the mechanism in the hydrolysis, photolysis, and metabolism of pesticides.

In vitro metabolism of pesticides and industrial chemicals in fish.

Metabolism is one of the most important factors in controlling the toxicity and bioaccumulation of pesticides in fish. In vitro systems using subcellular fractions, cell lines, hepatocytes and tissues of a specific organ, each of which is characterized by usability, enzyme activity and chemical transport via membrane, have been applied to investigate the metabolic profiles of pesticides. Not only species and organs but also the fishkeeping conditions are known to greatly affect the in vitro metabolism of pesticides. A comparison of the metabolic profiles of pesticides and industrial chemicals taken under similar conditions has shown that in vitro systems using a subcellular S9 fraction and hepatocytes qualitatively reproduce many in vivo metabolic reactions. More investigation of these in vitro systems for pesticides is necessary to verify their applicability to the estimation of pesticide metabolism in fish.

Direct photolysis mechanism of pesticides in water.

Photodegradation is one of the most important abiotic transformations for pesticides in the aquatic environment, and the high energy of sunlight causes characteristic reactions such as bond scission, cyclization, and rearrangement, which are scarcely observed in hydrolysis and microbial degradation. This review deals with direct photolysis via excitation of a pesticide by absorbing natural or artificial sunlight in order to know its basic photochemistry, and indirect photolysis meaning either sensitization by dissolved organic matters or oxidation by reactive oxygen species is basically excluded. Several experimental approaches including spectroscopic techniques together with theoretical calculations are first discussed from the viewpoint of the reaction mechanisms in direct photolysis. Then, the typical photoreactions of pesticides are summarized by chemical classes and/or functional groups and discussed as far as possible in relation to their mechanisms.

Metabolism of the Strobilurin Fungicide Mandestrobin in Wheat.

The metabolic fate of a new fungicide, mandestrobin, labeled with 14C at the phenoxy or benzyl ring was examined in wheat after a single spray application at 300 g/ha. Mandestrobin penetrated into foliage over time, with both radiolabels showing similar 14C distribution in wheat, and 2.8-3.3% of the total radioactive residue remained on the surface of straw at the final harvest. In foliage, mandestrobin primarily underwent mono-oxidation at the phenoxy ring to produce 4-hydroxy or 2-/5-hydroxymethyl derivatives, followed by their subsequent formation of malonylglucose conjugates. In grain, the cleavage of its benzyl phenyl ether bond was the major metabolic reaction, releasing the corresponding alcohol derivative, while the counterpart 2,5-dimethylphenol was not detected. The constant RS enantiomeric ratio of mandestrobin showed its enantioselective metabolism to be unlikely on/in wheat.

Photodegradation of Strobilurin Fungicide Mandestrobin in Water.

Photodegradation of a new strobilurin fungicide, mandestrobin, was investigated in buffered aqueous solution and synthetic humic water (SHW) under continuous irradiation with artificial sunlight (λ > 290 nm). In both aquatic media, the direct photolysis preferentially proceeded via homolytic bond cleavage at the benzyl phenyl ether, and the subsequent recombination of geminate radicals in a solvent cage gave the photo-Claisen rearrangement products. A radical mechanism in the photochemical rearrangement was strongly supported by a radical-trapping technique using a novel nitroxide spin label combined with electron spin resonance (ESR) and liquid chromatography-mass spectrometry (LC-MS) analyses. Photosensitized generation of hydroxyl radical in SHW might significantly contribute to enhancing the formation of a benzyl alcohol derivative. The series of photolysis products steadily degraded and finally mineralized to carbon dioxide.

Bioconcentration and Metabolism of Pyriproxyfen in Tadpoles of African Clawed Frogs, Xenopus laevis.

Bioconcentration and metabolism of pyriproxyfen uniformly labeled with 14C at the phenoxyphenyl ring were studied using tadpoles of African clawed frog, Xenopus laevis, exposed to water at the nominal concentrations of 3 and 300 ppb for 22 days under the flow-through conditions, with a following 3 day depuration phase. Neither meaningful mortality nor abnormal behavior was observed in control and exposure groups throughout the study. After the rapid uptake to tadpoles, pyriproxyfen was extensively metabolized and excreted, and as a result, steady-state bioconcentration factors and depuration half-lives ranged from 550 to 610 and from 0.34 to 0.54 days, respectively. The metabolites were mostly distributed in the liver or gastrointestinal tract. The major metabolic reactions were hydroxylation at the 4' position of the phenoxyphenyl group and cleavage of the ether linkage, followed by sulfate conjugation.

Fate of Flumioxazin in Aquatic Plants: Two Algae (Pseudokirchneriella subcapitata, Synechococcus sp.), Duckweed (Lemna sp.), and Water Milfoil (Myriophyllum elatinoides).

Flumioxazin separately 14C-labeled at 1,2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was exposed to two algae and duckweed via the water layer and water milfoil via the water layer or bottom sediment for 14 days to investigate uptake and metabolic profiles in these aquatic plants. While 14C-flumioxazin received immediate hydrolysis through maleimide ring opening and amide bond cleavage with its hydrolytic half-life of <1 day in both water and sediment, the 14C-plant uptake was ≤4.7% of the applied radioactivity (%AR) with water exposure for all plants and 0.9%AR with sediment exposure for water milfoil. No 14C-translocation between shoot/leaves and roots occurred in water milfoil. The components of 14C residues in plants were common among the species, which were the above hydrolysates and their transformation products, that is, dicarboxylic acid derivative metabolized via hydroxylation at the double bond of the cyclohexene ring followed by sugar conjugation with its counterpart amine derivative via acid conjugations.

Behavior of cyphenothrin in aquatic environment.

The behavior of cyphenothrin (1) [(RS)-α-cyano-3-phenoxybenzyl (1RS)-cis-trans-2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylate] in an aquatic environment was investigated by using the 14C-labeled trans and cis isomers. In parallel with the rapid partition from water phase to bottom sediment, 1 was degraded with the first-order half-lives of 2.0 (trans-1) and 7.3 days (cis-1) in the water-sediment system under dark conditions. 1 underwent extensive microbial degradation via ester cleavage to form 3-phenoxybenzoic acid, finally forming bound residues and mineralizing to CO2. Aqueous photolysis significantly accelerated the degradation of 1 with a half-life of <1 day, mainly via photo-induced oxidation at the 2-methylprop-1-enyl group and ester cleavage without cis-trans isomerization. These results strongly suggest that 1 is unlikely to persist in the actual aquatic environment due to its rapid photolysis and extensive microbial degradation.

Metabolism, bioaccumulation, and toxicity of pesticides in aquatic insect larvae.

Aquatic insects having a high diversity are good biotic indicators for freshwater quality. Their larvae living in freshwater are sensitive to pesticides, and its impacts has been examined not only through laboratory toxicity studies using water and sediment exposure but also through higher-tier micro-/mesocosm studies and field monitoring. Many sophisticated statistical methods have been applied to assess the impacts of pesticides at levels from species to community, but their body burden has been studied much less, especially in relation to toxicity. We review the uptake, metabolism with relevant detoxifying enzymes, and depuration of pesticides in aquatic insect larvae, which determine their body burden and help to understand the toxicity profiles specific to each chemical class. We also discuss experimental conditions, environmental factors, and species sensitivity in relation to the bioconcentration/-accumulation and toxicity of pesticides.

Pesticide behavior in modified water-sediment systems.

The standardized laboratory water-sediment study in darkness is utilized as primary information on pesticide behavior to assess its ecotoxicological impacts in the edge-of-field water bodies. The half-lives of pesticide in water and sediment are key parameters to predict its environmental concentration, and its metabolic profiles help to avoid overlooking unexpected toxicological impacts from metabolites. However, no consideration of environmental factors such as sunlight and aquatic macrophytes is included, and this may lead to a conservative assessment. We review the experimental factors in the existing standardized design and then the effects of illumination and aquatic macrophytes introduced to the water-sediment system. The effects of temperature and the water-sediment ratio should be investigated in more detail and the pesticide behavior is possibly modified by illumination via photodegradation and/or metabolism in phototrophic microorganisms. Aquatic macrophytes play a major role as an additional sorption site and in further pesticide metabolism.

Uptake, Translocation, and Metabolism of Phenols by Submerged Rooted Macrophyte, Water Milfoil (Myriophyllum elatinoides).

Shoot and root uptakes of (14)C-labeled phenol (1), 4-nitrophenol (2), 4-cyanophenol (3), 4-hydroxybenzamide (4), and 4-hydroxybenzoic acid (5) by Myriophyllum elatinoides were individually examined with water or sediment treatments using the sequestered chamber. Shoot uptake of each (14)C-phenol dissolved in water amounted to 21.0% (1), 14.3% (2), 12.8% (3), 4.2% (4) and 41.7% (5) of the applied radioactivity (AR) after 96 h without significant (14)C translocation from shoot to root (≤0.9% AR), and the major metabolite produced was the glucose conjugate. On the other hand, root uptake of (14)C-phenols from sediment was much slower/smaller (≤6.6% AR), and (14)C transportation from root to shoot was scarcely observed, except for compound 5 (≤1.5% AR). For the water treatment, a kinetic analysis on uptake/metabolism was conducted using the assumed compartment. Good correlation was observed between lipophilicity and shoot uptake rate constants, and the electronic state of the hydroxyl group (σ, σ(-), or EHOMO(OH)) and the transformation rate constant of glucosidation.

Soil column leaching of pesticides.

In this review, I address the practical and theoretical aspects of pesticide soil mobility.I also address the methods used to measure mobility, and the factors that influence it, and I summarize the data that have been published on the column leaching of pesticides.Pesticides that enter the unsaturated soil profile are transported downwards by the water flux, and are adsorbed, desorbed, and/or degraded as they pass through the soil. The rate of passage of a pesticide through the soil depends on the properties of the pesticide, the properties of the soil and the prevailing environmental conditions.Because large amounts of many different pesticides are used around the world, they and their degradates may sometimes contaminate groundwater at unacceptable levels.It is for this reason that assessing the transport behavior and soil mobility of pesticides before they are sold into commerce is important and is one indispensable element that regulators use to assess probable pesticide safety. Both elementary soil column leaching and sophisticated outdoor lysimeter studies are performed to measure the leaching potential for pesticides; the latter approach more reliably reflects probable field behavior, but the former is useful to initially profile a pesticide for soil mobility potential.Soil is physically heterogeneous. The structure of soil varies both vertically and laterally, and this variability affects the complex flow of water through the soil profile, making it difficult to predict with accuracy. In addition, macropores exist in soils and further add to the complexity of how water flow occurs. The degree to which soil is tilled, the density of vegetation on the surface, and the type and amounts of organic soil amendments that are added to soil further affect the movement rate of water through soil, the character of soil adsorption sites and the microbial populations that exist in the soil. Parameters that most influence the rate of pesticide mobility in soil are persistence (DT50) of the pesticide, and its sorption/desorption(Koc) characteristics. These parameters may vary for the same pesticide from geographic site-to-site and with soil depth. The interactions that normally occur between pesticides and dissolved organic matter (DOM) or WDC are yet other factors that may complicate pesticide leaching behavior.The soil mobility of pesticides is normally tested both in the laboratory and in the field. Lab studies are initially performed to give researchers a preliminary appraisal of the relative mobility of a pesticide. Later, field lysimeter studies can be performed to provide more natural leaching conditions that emulate the actual field use pattern. Lysimeter studies give the most reliable information on the leaching behavior of a pesticide under field conditions, but these studies are time-consuming and expensive and cannot be performed everywhere. It is for this reason that the laboratory soil column leaching approach is commonly utilized to profile the mobility of a pesticide,and appraise how it behaves in different soils, and relative to other pesticides.Because the soil structure is chemically and physically heterogenous, different pesticide tests may produce variable DT50 and Koc values; therefore, initial pesticide mobility testing is undertaken in homogeneously packed columns that contain two or more soils and are eluted at constant flow rates. Such studies are done in duplicate and utilize a conservative tracer element. By fitting an appropriate mathematical model to the breakthrough curve of the conservative tracer selected,researchers determine key mobility parameters, such as pore water velocity, the column-specific dispersion coefficient, and the contribution of non equilibrium transport processes. Such parameters form the basis for estimating the probable transport and degradation rates that will be characteristic of the tested pesticide. Researchers also examine how a pesticide interacts with soil DOM and WDC, and what contribution from facilitated transport to mobility is made as a result of the effects of pH and ionic strength. Other methods are used to test how pesticides may interact with soil components to change mobility. Spectroscopic approaches are used to analyze the nature of soil pesticide complexes. These may provide insight into the mechanism by which interactions occur. Other studies may be performed to determine the effect of agricultural practices (e.g., tillage) on pesticide leaching under controlled conditions using intact soil cores from the field. When preferential flow is suspected to occur, dye staining is used to examine the contribution of macropores to pesticide transport. These methods and others are addressed in the text of this review.

Metabolism of the insecticide metofluthrin in cabbage (Brassica oleracea).

The metabolic fate of metofluthrin [2,3,5,6-tetrafluoro-4-(methoxymethyl)benzyl (E,Z)-(1R,3R)-2,2-dimethyl-3-(prop-1-enyl)cyclopropanecarboxylate] separately labeled with (14)C at the carbonyl carbon and the α-position of the 4-methoxymethylbenzyl ring was studied in cabbage ( Brassica oleracea ). An acetonitrile solution of (14)C-metofluthrin at 431 g ai ha(-1) was once applied topically to cabbage leaves at head-forming stage, and the plants were grown for up to 14 days. Each isomer of metofluthrin applied onto the leaf surface rapidly volatilized into the air and was scarcely translocated to the untreated portion. On the leaf surface, metofluthrin was primarily degraded through ozonolysis of the propenyl side chain to produce the secondary ozonide, which further decomposed to the corresponding aldehyde and carboxylic acid derivatives. In the leaf tissues, the 1R-trans-Z isomer was mainly metabolized to its dihydrodiol derivative probably via an epoxy intermediate followed by saccharide conjugation in parallel with the ester cleavage, whereas no specific metabolite was dominant for the 1R-trans-E isomer. Isomerization of metofluthrin at the cyclopropyl ring was negligible for both isomers. In this study, the chemical structure of each secondary ozonide derivative was fully elucidated by the various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy together with cochromatography with the synthetic standard, and their cis/trans configuration was examined by the nuclear Overhauser effect (NOE) difference NMR spectrum.

Environmental behavior of synthetic pyrethroids.

New experimental approaches together with recent progress in spectroscopic technologies have given useful information to understand better the environmental fate of synthetic pyrethroids. The successive transformation of intermediate free radicals by using spin-trapping reagents and fluorophores enables their easier detection in aqueous photolysis. Chiral chromatographic analyses have shown stereo-selective metabolism of pyrethroids in soil. The knowledge on relevant enzymes in soil and plant being involved in hydrolysis, oxidation, and glucose conjugation of pyrethroids has been accumulated. Utilization of either iron-porphyrin with an oxidant or isolated leaf cells as model systems can give more information on metabolism of pyrethroids.

Degradation of flumioxazin in illuminated water-sediment systems.

The aerobic aquatic metabolism of flumioxazin was studied in two water-sediment systems under illumination and in darkness to investigate its degradation profiles. (14)C-Flumioxazin separately labeled at the 1- and 2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was applied to a overlying water at a rate equivalent to 600 g ai/ha by assuming uniform distribution in the water layer to a depth of 100 cm. Flumioxazin was rapidly degraded at 20 °C in the overlying waters irrespective of irradiation with half-lives of 0.1-0.4 day. Both various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analyses showed four major degradates under irradiation. Two of them were formed via successive hydrolysis of the cyclic imide ring, and the others were 2-arizidinone derivatives via photoinduced rearrangement. The presence of sediment under illumination greatly reduced the formation of these degradates and accelerated their degradation. The partitions of flumioxazin and its degradates to the bottom sediment not only reduced their fractions in the water layer subjected to hydrolysis and photolysis but also enhanced their microbial degradation in the sediment. The illuminated water-sediment systems were considered to more adequately represent the behavior of flumioxazin and its degradates in the environment than the corresponding studies of aqueous photolysis and water-sediment in darkness.

Photoinduced oxidation of the insecticide phenothrin on soil surfaces.

Photodegradation profiles of the pyrethroid insecticide phenothrin on a moistened U.S. soil thin layer was investigated by using its predominant component, the 1R-trans-isomer (I), under continuous exposure to light at >290 nm from a xenon arc lamp. Its degradation was moderately accelerated by irradiation with half-lives of 5.7-5.9 days (dark control 21-24 days), mainly via successive oxidation of the 2-methylprop-1-enyl group and ester cleavage followed by mineralization to carbon dioxide. Spectroscopic and cochromatographic analyses showed that the major degradates were the alcohol and ketone derivatives of I formed via photoinduced oxidation of the 2-methylprop-1-enyl group by singlet oxygen. The photoinduced generation of singlet oxygen in/on the soil surface was confirmed by using chemical trapping reactions together with ESR spectroscopy.

Bioconcentration, bioaccumulation, and metabolism of pesticides in aquatic organisms.

The ecotoxicological assessment of pesticide effects in the aquatic environment should normally be based on a deep knowledge of not only the concentration of pesticides and metabolites found but also on the influence of key abiotic and biotic processes that effect rates of dissipation. Although the bioconcentration and bioaccumulation potentials of pesticides in aquatic organisms are conveniently estimated from their hydrophobicity (represented by log K(ow), it is still indispensable to factor in the effects of key abiotic and biotic processes on such pesticides to gain a more precise understanding of how they may have in the natural environment. Relying only on pesticide hydrophobicity may produce an erroneous environmental impact assessment. Several factors affect rates of pesticide dissipation and accumulation in the aquatic environment. Such factors include the amount and type of sediment present in the water and type of diet available to water-dwelling organisms. The particular physiological behavior profiles of aquatic organisms in water, such as capacity for uptake, metabolism, and elimination, are also compelling factors, as is the chemistry of the water. When evaluating pesticide uptake and bioconcentration processes, it is important to know the amount and nature of bottom sediments present and the propensity that the stuffed aquatic organisms have to absorb and process xenobiotics. Extremely hydrophobic pesticides such as the organochlorines and pyrethroids are susceptible to adsorb strongly to dissolved organic matter associated with bottom sediment. Such absorption reduces the bioavailable fraction of pesticide dissolved in the water column and reduces the probable ecotoxicological impact on aquatic organisms living the water. In contrast, sediment dweller may suffer from higher levels of direct exposure to a pesticide, unless it is rapidly degraded in sediment. Metabolism is important to bioconcentration and bioaccumulation processes, as is detoxification and bioactivation. Hydrophobic pesticides that are expected to be highly stored in tissues would not be bioconcentrated if susceptible to biotic transformation by aquatic organisms to more rapidly metabolized to hydrophilic entities are generally less toxic. By analogy, pesticides that are metabolized to similar entities by aquatic species surely are les ecotoxicologically significant. One feature of fish and other aquatic species that makes them more relevant as targets of environmental studies and of regulation is that they may not only become contaminated by pesticides or other chemicals, but that they constitute and important part of the human diet. In this chapter, we provide an overview of the enzymes that are capable of metabolizing or otherwise assisting in the removal of xenobiotics from aquatic species. Many studies have been performed on the enzymes that are responsible for metabolizing xenobiotics. In addition to the use of conventional biochemical methods, such studies on enzymes are increasingly being conducted using immunochemical methods and amino acid or gene sequences analysis. Such studies have been performed in algae, in some aquatic macrophytes, and in bivalva, but less information is available for other aquatic species such as crustacea, annelids, aquatic insecta, and other species. Although their catabolizing activity is often lower than in mammals, oxidases, especially cytochrome P450 enzymes, play a central role in transforming pesticides in aquatic organisms. Primary metabolites, formed from such initial enzymatic action, are further conjugated with natural components such as carbohydrates, and this aids removal form the organisms. The pesticides that are susceptible to abiotic hydrolysis are generally also biotically degraded by various esterases to from hydrophilic conjugates. Reductive transformation is the main metabolic pathway for organochlorine pesticides, but less information on reductive enzymology processes is available. The information on aquatic species, other than fish, that pertains to bioconcentration factors, metabolism, and elimination is rather limited in the literature. The kinds of basic information that is unavailable but is needed on important aquatic species includes biochemistry, physiology, position in food web, habitat, life cycle, etc. such information is very important to obtaining improved ecotoxicology risk assessments for many pesticides and other chemicals. More research attention on the behavior of pesticides in, and affect on many standard aquatic test species (e.g., daphnids, chironomids, oligochaetes and some bivalves) would particularly be welcome. In addition to improving ecotoxicology risk assessments on target species, such information would also assist in better delineating affects on species at higher trophic levels that are predaceous on the target species. There is also need for designing and employing more realistic approaches to measure bioconcentration and bioaccumulation, and ecotoxicology effects of pesticides in natural environment. The currently employed steady-state laboratory exposure studies are insufficient to deal with the complexity of parameters that control the contrasts to the abiotic processes of pesticide investigated under the strictly controlled conditions, each process is significantly affected in the natural environment not only by the site-specific chemistry of water and sediment but also by climate. From this viewpoint, ecotoxicological assessment should be conducted, together with the detailed analyses of abiotic processes, when higher-tier mesocosm studies are performed. Moreover, in-depth investigation is needed to better understand the relationship between pesticide residues in organisms and associated ecotoxicological endpoints. The usual exposure assessment is based on apparent (nominal) concentrations fo pesticides, and the residues of pesticides or their metabolites in the organisms are not considered in to the context of ecotoxicological endpoints. Therefore, more metabolic and tissue distribution information for terminal pesticide residues is needed for aquatic species both in laboratory settings and in higher-tier (microcosm, mesocosm) studies.

Application of separated leaf cell suspension to xenobiotic metabolism in plant.

Metabolic profiles of (14)C-labeled primary metabolites from several pesticides, 4-cyanophenol (1), 3-phenoxybenzoic acid (2), 3-phenoxybenzyl alcohol (3), 3,5-dichloroaniline (4), and (1RS)-trans-2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid (5), were examined by using enzymatically separated leaf cell suspension from seedlings of cabbage ( Brassica oleracea ) and tomato ( Lycopersicon esculentum ). After 1 day of incubation, the metabolites were extensively transformed in cabbage, whereas they were scarcely metabolized in tomato. The major metabolic pathways were the phase II reactions leading to a number of conjugates such as glucoside/malonylglucoside of 1-5, malate of 2, and glutamate of 4. The oxidation of 1 and 2 was observed as a minor reaction to produce 4-hydroxybezoic acid and 3-(4-hydroxyphenoxy)benzoic acid. The chemical identities of the secondary metabolites were determined by various spectrometric analyses (LC-MS, LC-MS/MS, and NMR) and/or HPLC cochromatography with the synthetic reference standards. As a result, this separated leaf cell suspension system was found to well reproduce the in vivo plant metabolism.

Novel fluorescence detection of free radicals generated in photolysis of fenvalerate.

Photoinduced decarboxylation via homolytic cleavage of the ester linkage generating two benzyl radicals being recoupled is known to be a major photolytic pathway of the insecticide fenvalerate in aqueous or organic solvents. A highly sensitive and selective fluorescence spectroscopic method was applied to detect these radicals generated under xenon lamp irradiation in organic solvents and aqueous acetonitrile solutions. The short-lived radicals were efficiently trapped by the nitroxide free radical having a primary amino group, and the resultant diamagnetic adducts were instantaneously derivatized with fluorescamine as a fluorescent probe. The highly fluorescent derivatives were successfully separated and detected by a reversed-phase high-performance liquid chromatography equipped with a fluorescence detector, and their structures were individually identified by liquid chromatography/mass spectrometry.