Griseofulvin Inhibits Root Growth by Targeting Microtubule-Associated Proteins Rather Tubulins in Arabidopsis.

Griseofulvin was considered an effective agent for cancer therapy in past decades. Although the negative effects of griseofulvin on microtubule stability are known, the exact target and mechanism of action in plants remain unclear. Here, we used trifluralin, a well-known herbicide targeting microtubules, as a reference and revealed the differences in root tip morphology, reactive oxygen species production (ROS), microtubule dynamics, and transcriptome analysis between Arabidopsis treated with griseofulvin and trifluralin to elucidate the mechanism of root growth inhibition by griseofulvin. Like trifluralin, griseofulvin inhibited root growth and caused significant swelling of the root tip due to cell death induced by ROS. However, the presence of griseofulvin and trifluralin caused cell swelling in the transition zone (TZ) and meristematic zone (MZ) of root tips, respectively. Further observations revealed that griseofulvin first destroyed cortical microtubules in the cells of the TZ and early elongation zone (EZ) and then gradually affected the cells of other zones. The first target of trifluralin is the microtubules in the root MZ cells. Transcriptome analysis showed that griseofulvin mainly affected the expression of microtubule-associated protein (MAP) genes rather than tubulin genes, whereas trifluralin significantly suppressed the expression of αß-tubulin genes. Finally, it was proposed that griseofulvin could first reduce the expression of MAP genes, meanwhile increasing the expression of auxin and ethylene-related genes to disrupt microtubule alignment in root tip TZ and early EZ cells, induce dramatic ROS production, and cause severe cell death, eventually leading to cell swelling in the corresponding zones and inhibition of root growth.

The capacity of some newly bacteria and fungi for biodegradation of herbicide trifluralin under agiated culture media.

Bioremediation is the use of microorganisms to degrade environmental contaminants (pesticides, polyaromatic hydrocarbons etc.) into less toxic forms or compounds. In this study microbial biodegradation of trifluralin was performed in liquid media with 11 different types of identified fungi and bacteria cultures and their mixtures in agiated culture media. The isolated fungi and bacteria mixtures showed the highest degradation, reaching 93% in the chemical oxygen demand (COD) parameter in four days and 82% as trifluralin active ingredient in five days. Bacteria and fungi mixtures achieved 69% and 66% degradations of trifluralin active ingredient respectively. In the fungi studies, the best removal was achieved by M.Chlamydosporia at 80%, in the bacteria studies, the best removal was achieved by Bacillus simplex about 95% in five days. These different removal rates were due to the microbial differencies.

On-farm bioremediation of dimethazone and trifluralin residues in runoff water from an agricultural field.

Bioremediation is the use of living organisms, primarily microorganisms, to degrade environmental contaminants into less toxic forms. Nine biobeds (ground cavity filled with a mixture of composted organic matter, topsoil, and a surface grass) were established at Kentucky State University research farm (Franklin County, KY) to study the impact of this practice on reducing surface runoff water contamination by residues of dimethazone and trifluralin herbicides arising from an agricultural field. Biobed (biofilter) systems were installed at the bottom of the slope of specially designed runoff plots to examine herbicides retention and degradation before entering streams and rivers. In addition to biobed systems, three soil management practices: municipal sewage sludge (SS), SS mixed with yard waste compost (SS + YW), and no-mulch rototilled bare soil (NM used for comparison purposes) were used to monitor the impact of soil amendments on herbicide residues in soil following natural rainfall events. Organic amendments increased soil organic matter content and herbicide residues retained in soil following rainfall events. Biobeds installed in NM soil reduced dimethazone and trifluralin by 84 and 82%, respectively in runoff water that would have been transported down the land slope of agricultural fields and contaminated natural water resources. Biobeds installed in SS and SS+YW treatments reduced dimethazone by 65 and 46% and trifluralin by 52 and 79%, respectively. These findings indicated that biobeds are effective for treating dimethazone and trifluralin residues in runoff water.

Inhibition of leishmanias but not host macrophages by the antitubulin herbicide trifluralin.

The dinitroaniline herbicide trifluralin (alpha, alpha, alpha-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine), at micromolar concentrations, selectively inhibited both proliferation and differentiation of the parasitic protozoan Leishmania mexicana amazonensis. In vitro, radioactive trifluralin showed specific binding to leishmania tubulin but not to mammalian tubulin. Because herbicides such as trifluralin are economical and are considered safe for man and domesticated animals, they may serve as useful sources of potential antiparasitic agents.

Uptake and elimination kinetics of trifluralin and pendimethalin in Pheretima spp. and Eisenia spp.

The purpose of this study was to clarify the kinetic bioaccumulation potential of herbicides in the earthworm, Pheretima spp., the most common earthworms throughout Asia, and Eisenia spp., litter-feeding earthworms included in the test species recommended by the Organization for Economic Co-operation and Development. The kinetic bioaccumulation factors of trifluralin and pendimethalin were estimated from an uptake test for 10 or 12 days and from an elimination test for 10 days. The time required to reach a steady state following herbicide exposure was 7 days for both herbicides in Eisenia spp. and 1 day in Pheretima spp. The uptake rate constant (g-soil/g-worm/day) and elimination rate constant (per day) for trifluralin were 2.1 and 0.23 in Eisenia spp. and 0.42 and 0.45 in Pheretima spp., respectively, and those for pendimethalin were 1.5 and 0.26 in Eisenia spp. and 0.27 and 1.0 in Pheretima spp., respectively. Kinetic bioaccumulation factors of both herbicides were relatively close to bioaccumulation factors in steady state and were higher in Eisenia spp. (8.9 for trifluralin and 5.7 for pendimethalin) than in Pheretima spp. (0.95 and 0.26). These results demonstrated that the herbicide bioaccumulation risk is lower for Pheretima spp. than for Eisenia spp. because of the lower uptake rate and higher elimination rate in Pheretima spp.

Enhanced Trifluralin Metabolism Can Confer Resistance in Lolium rigidum.

Resistance to the pre-emergence herbicide trifluralin is increasing in Australian annual ryegrass ( Lolium rigidum) populations. Three L. rigidum populations (R1, R2, and R3) collected from Australian grain fields were identified with trifluralin resistance. Both target-site and nontarget-site resistance mechanisms were investigated. No target-site α-tubulin mutations were detected in populations R1 and R3, while an Arg-243-Lys mutation was found in R2. Compared with the three trifluralin-susceptible populations, enhanced [14C]-trifluralin metabolism, quantified by measuring the amount of [14C] label partitioning into the polar phase of a hexane:methanol system, was identified in all the three resistant populations. This is the first report of metabolic resistance to trifluralin. Coevolution of target-site and nontarget-site resistance to trifluralin is occurring, and metabolic resistance is not rare in L. rigidum populations in Australia. A method was established for trifluralin metabolic resistance detection, overcoming the difficulties of quantifying this highly volatile herbicide by chromatographic methods.

Effect of crop residues on interception and activity of prosulfocarb, pyroxasulfone, and trifluralin.

Crop residue retention on the soil surface in no-tillage system can intercept pre-emergent herbicides and reduce their efficacy. Three experiments were conducted to investigate the effect of crop residue amount (0, 1, 2 and 4 t ha-1), moisture (wet versus dry), type (wheat, barley, canola, chickpea and lupin) and age (fresh or aged for one year) on the interception and subsequent leaching of prosulfocarb, pyroxasulfone, and trifluralin from the residue into soil. Bioassays, using cucumber and annual ryegrass as indicator plants, were used to assess herbicide activity/availability in the soil and on the residue. Herbicide interception increased considerably as residue quantity increased from 2 to 4 t ha-1. After simulated rainfall, which washed herbicide into the soil, complete control of ryegrass occurred for trifluralin with 0 t ha-1 residue, for prosulfocarb with 0 and 1 t ha-1 residue, and for pyroxasulfone with all residue rates. Therefore, with rain or irrigation, pyroxasulfone was the herbicide least affected by high residue loads. Less chemical leached from the crop residue into the soil after rainfall, when prosulfocarb and trifluralin were applied to wet residue compared with dry residue, but the initial moisture condition had no effect on the leaching of pyroxasulfone from residue. If practically possible, farmers should minimise spraying prosulfocarb and trifluralin onto wet crop residue. Barley and wheat residues intercepted more herbicide than an equivalent mass of canola, chickpea or lupin residue, which was largely due to the increased ground cover with cereal residues. The effect of residue age on herbicide interception and leaching was relatively small and variable. Overall, more herbicide reached the soil when sprayed on one-year old residue than new residue, which was largely due to reduced ground cover with aged residue. A strong positive linear relationship existed between ground cover percentage and growth of bioassay species (r2 = 0.75). This means that there was little difference in the ability of residue to adsorb and retain herbicide between crop residue types and ages, such that farmers can simply use the ground cover of the crop residue to assess interception.

Uptake and modeling of pesticides by roots and shoots of parrotfeather (Myriophyllum aquaticum).

INTENTION, GOAL, SCOPE, BACKGROUND: Aquatic plants have a great potential to function as in situ, on-site biosinks and biofilters of pollutants. They are used for phytoremediation and phytotoxicity studies. Pesticide uptake studies are very important to predict contaminant accumulation, translocation, and transformation. There are a lot of models which have been developed for emergent plants, but there are not any existing models for submerged aquatic plants for assessing pesticide uptake. OBJECTIVE: In this study, uptake of selected pesticides in parrotfeather (Myriophyllum aquaticum) were studied and the results were modeled with the aid of Log Kow and the concentration of pesticides. At the end, the developed model was compared to other existing models. METHODS: The test was conducted with parrotfeather as a model plant. The bioassay and cultivation of this plant were examined. Pesticide uptake by roots and shoots was determined using 14C-radiolabeled materials. RESULTS AND DISCUSSION: The results were fitted with an equation that showed a relationship between uptake and lipophilicity of pesticides. The model was compared with other pesticide uptake models developed for other plants. Atrazine and cycloxidim were taken up more by roots than by shoots in comparison to other pesticides used. The total uptake, both in shoots and roots, was lower than for terbutryn and trifluralin. The best appropriate model was developed from the results against the other models seen in the literature. The concentration factors (Root Concentration Factor (RCF) and Submerged Shoot Concentration Factor (SSCF)) increased with a higher Kow of the substances. The Submerged Shoot Concentration Factor (SSCF) revealed a better relationship of the chemicals than did the Root Concentration Factor (RCF). CONCLUSIONS: In this study, an uptake model was developed for rooted, submerged aquatic plants. Further studies are necessary to develop and compare models with different plants and pesticides. RECOMMENDATION AND OUTLOOK: Such studies as this one may be extended to other environmental pollutants in the aquatic ecosystem and may be employed to evaluate the possibility of using different plants in phytoremediation studies.

Transdermal penetration of atrazine, alachlor, and trifluralin: effect of formulation.

Commercial formulations of herbicides contain surfactants and other compounds to increase absorption by targeted plants. These chemicals, however, are also potential penetration enhancers for mammalian skin. The effect of formulation on dermal absorption of the herbicides atrazine, alachlor, and trifluralin and their commercial formulations Aatrex, Lasso, and Treflan was determined. In vitro absorption studies were performed by placing hairless mouse skin in a Bronough flow-through diffusion system. Donor solution was spiked with (14)C-labeled herbicide, and its penetration through the skin was monitored in 90-min fractions. Results demonstrate that dermal penetration of commercially formulated compound was significantly greater (p < 0.05) than that of the pure compound at the same concentration. The physical properties of a herbicide predicted penetration (r(2) = 0.97-0.99) for commercial formulations but were not as effective at predicting absorption for the pure compounds (r(2) = 0.51-0.71). The solvents associated with the hydrophobic herbicide Treflan altered dermal penetration of the more hydrophilic herbicides Lasso and Aatrex. Furthermore, although the most hydrophobic compound had the least penetration, it accumulated in the stratum corneum at the greatest rate. These studies can have important implications on future experiments performed to predict percutaneous penetration of herbicides.

Environmental fate of trifluralin.

Trifluralin, a preemergence, soil-applied and soil-incorporated herbicide, has been in agricultural use since 1963. The environmental chemistry and fate of dinitroaniline herbicides, including trifluralin, has been studied extensively in agricultural soils. Probst et al. (1975) and Helling (1976) have summarized pre-1975 data on the mobility, persistence, and degradation or metabolism of dinitroaniline herbicides as a group. Since then, numerous studies have been carried out on the fate of dinitroanilines, especially trifluralin, in the environment to understand further their degradation in soil, potential for mobility and persistence, and environmental concentration in water and air. The present review, while summarizing briefly earlier data, concentrates primarily on the post-1975 data on degradation, mobility, and persistence of trifluralin in soils and its potential concentrations in water and air. Trifluralin is readily degraded under sunlight in all media, with half-lives (t1/2) of minutes to several months, depending on the substrate. In addition, other dissipation processes, such as microbial and chemical, are also operative in soils, water, and sediments. Several degradation products of trifluralin have been identified and characterized, both under photolysis and following aerobic and anaerobic metabolism in soils and water-sediment systems. The differences between various degradative pathways of trifluralin appear to be more quantitative than qualitative in nature, leading eventually to the same end products that are subject to binding or mineralization with time. The general lack of accumulation of the breakdown products of trifluralin suggests that these are also subject to the same degradative mechanisms as the parent compound. Trifluralin has low water solubility and is strongly bound to soil components; mean Koc values range from 4,000 to 13,000. Once applied and incorporated into the soil, trifluralin remains relatively immobile with minimal or no potential for contamination of groundwaters under or near the treated zones. Trifluralin residues in soil surface layers are subject to loss via transport in runoff water or volatilization into the air. Seasonal losses in surface runoff are consistently less than 0.5% of the amounts applied, with concentrations in edge-of-the-field run-off water typically < 1.0 microgram L-1. Consequently, trifluralin is infrequently detected in surface waters and, if present, usually occurs below levels of quantification. Seasonal trifluralin losses into the atmosphere can be as high as 25% of that applied. Maximum trifluralin residues in the air above treated fields are in the 2-3 micrograms m-3 range following application, decreasing to < 100 ng m-3 in ambient air of intensive use areas, indicating its rapid dissipation in air. Trifluralin residues at < 100 pg m-3 in the atmosphere of remote nonuse regions have been reported, suggesting its potential for long-range transport. However, there is a general lack of understanding of the mechanisms controlling its potential for long-distance transport, especially considering its rapid photodegradation in vapor and solution states. The persistence of trifluralin in agricultural soils following incorporation is highly variable, depending on several factors such as depth of incorporation, soil moisture, soil temperature, soil air, and soil organic matter content. Estimated half-lives under a variety of agronomic conditions range from 25 to > 201 d, thus categorizing its persistence from 'moderate' to 'persistent'. The estimated half-life data for trifluralin under agronomic conditions, however, cannot be extrapolated to other potential scenarios, such as its dissipation in nontarget areas where trifluralin residues, if any, are essentially deposited on surfaces. Surface deposits on nontarget areas, unlike soil-incorporated residues, would be subject to volatilization and photolysis and thus more short lived. (ABSTRACT TRUNCATED)

Influence of rhamnolipids and triton X-100 on the biodegradation of three pesticides in aqueous phase and soil slurries.

The effect of surfactants on the biodegradation of trifluralin and atrazine (by Streptomyces PS1/5) and coumaphos (by degrading consortia from a contaminated cattle dip) in liquid cultures and soil slurries was tested at different concentrations of a rhamnolipid mixture (Rh-mix) and Triton X-100 (TX-100). The extent of trifluralin biodegradation in liquid culture was improved at high concentrations of both surfactants. The extent of atrazine degradation dropped in the presence of either surfactant. Coumaphos biodegradation improved slightly at Rh-mix dosages >3000 microM; however, it was readily inhibited by TX-100 at amounts above the critical micelle concentration. In soil slurries, the extent of both trifluralin and atrazine biodegradation was higher in Hagerstown A (HTA) soil than in Hagerstown B (HTB) soil and was not significantly affected by the presence of either surfactant. The onset of trifluralin biodegradation was retarded at higher concentrations of surfactants. In the absence of surfactant, up to 98% of coumaphos in both soil slurries was transformed. At increasing dosages of Rh-mix, the onset of coumaphos biodegradation was retarded, but the removal efficiency of the pesticide increased. Rh-mix and TX-100 depletion was observed during Streptomyces PS1/5 growth in liquid cultures. Rh-mix concentration also decreased during coumaphos biodegradation, whereas TX-100 concentration was not affected. These results suggest that surfactants, added for the purpose of increasing the apparent water solubility of hydrophobic organic compounds, may have unintended effects on both the rate and extent of biodegradation of the target compounds if the surfactants can also be degraded by the microorganisms in the system.

Evidence of differences in the biotransformation of organic contaminants in three species of freshwater invertebrates.

Acute static bioassays were performed using three freshwater invertebrate species (the oligochaete Lumbriculus variegatus, the fingernail clam Sphaerium corneum and the larvae Chironomus riparius) exposed separately to a variety of 14C radiolabelled contaminants. The aim of this work was to investigate if the chemicals remained as parent compounds after the treatments. Chemicals used were 2,4-dichlorophenol; 2,4,5-trichlorophenol; pentachlorophenol; pyrene; Fenpropidin, and Trifluralin. Homogenates of the whole body tissue of each organism were prepared and total radioactivity was measured. Contaminants were then extracted into organic solvents and analysed by high-pressure liquid chromatography techniques. Chromatograms showed that most of the substances extracted were present as parent compounds in S. corneum and in L. variegatus. In contrast, for C. riparius a low proportion of the chemicals was recovered as parent compounds. These results suggest that different metabolic processes could take place in the different species.

Genes similar to naphthalene dioxygenase genes in trifluralin-degrading bacteria.

Trifluralin (alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) is a dinitroaniline compound which was first produced in the 1960s and has been used extensively as an agricultural herbicide. There are a few publications on the biodegradation of this xenobiotic compound, but to our knowledge nothing has been documented on the genetic aspects of its catabolism. In this article, we report the analysis of DNA isolated from bacteria previously shown to degrade trifluralin, using as probes the catabolic genes ndoB, todC, xyIX, catA and xyIE which encode the enzymes naphthalene 1,2-dioxygenase, toluene dioxygenase, toluate 1,2-dioxygenase, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase respectively. Using PCR and hybridization analysis, the strong hybridization of the ndoB gene with DNA extracted from four trifluralin-degrading isolates was demonstrated, although none of them was able to degrade naphthalene, as indicated by the 'clear zone' test. The results indicated the presence in these bacteria of a dioxygenase gene, whose product could act on trifluralin as its principal substrate, or fortuitously, by cometabolism. This is the first publication on genes in trifluralin-degrading bacteria.

Fluorescence studies on native and bound to trifluraline soy bean Lb"a" in the enhanced N2 fixation.

The differences in the tryptophan (Trp) fluorescence of native (control) Lb"a" and experimental substance isolated from nodules of the Williams' soy beans variety treated with trifluraline at a concentration of 2.1 x 10(-10) M have been studied. A positively charged environment has been proved for the tryptophans of the native Lb"a" and a negative one for the tryptophans of the experimental Lb"a". The difference in the tryptophan emission spectra at lambdaex = 280 and 300 nm may be assigned to conformational alterations occurring in the experimental Lb"a". This is also confirmed by the greater energy transfer from tyrosine to tryptophan in the experimental Lb"a"--30% compared to the 10% in the native Lb"a". The value of the constant of acrylamide quenching (Ksv = 2.77 M(-1)) shows that the tryptophans are buried more deeply in the experimental Lb"a" than in the native Lb"a" (Ksv = 4 M(-1)). They are substantially lower than Ksv of the standard compound N-Ac-Trp-NH2 (16.30 M(-1)). The activation energy (Ea) of the thermal quenching of tryptophan fluorescence is higher for the experimental Lb"a" (37 kJ mol(-1)) as compared to the standard compound N-Ac-Trp-NH2 (24 kJ mol(-1)) and the native Lb "a" (32 kJ mol(-1)). The dissociation constant of the complex of trifluraline with Lb "a" (6.32 x 10(-11) M) has been determined as well as the stoichiometric ratio trifluraline/Lb"a" (1:1). The estimated nitrogenase activity (microM/gfrw h) and the total Lb (mg/gfrw) for trifluraline are higher as compared to those for the control.

[Evaluation of the cytogenetic effect of the herbicide treflan and of a number of its metabolites on mammalian somatic cells]. / Otsenka tsitogeneticheskogo deistviia gerbitsida treflana i riada ego metabolitov na somaticheskikh kletkakh mlekopitaiushchikh.

Investigation of the cytogenetic effect of two samples of trifluralin, a herbicide, (chemically pure active ingredient and 25% emulsion concentrate) and its eight metabolites in the culture of human peripheral lymphocytes in vitro and in the bone marrow cells of mice in vivo has revealed that trifluralin itself does not induce chromosome aberrations both in vitro and in vivo, but some of its derivatives possess moderate (metabolites III and VII) or weak (metabolites II and XI) clastogenic activity. The results obtained should be taken into account for the hygienic regulation of trifluralin use allowing for the reality of entrance of its mutagenic derivatives into the human organism and for the degree of its genetic danger.

Investigation of the fate of trifluralin in shrimp.

Juvenile Pacific white shrimp (Litopenaeus vannamei) were exposed to trifluralin at 0.1 and 0.01 mg L(-1) for 72 h under controlled conditions. Samples of shrimp and tank water were collected at intervals up to 48 days after exposure. Analysis of the shrimp tissues by gas chromatography-mass spectrometry (GC-MS) and ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-qToF-MS) in combination with profiling and metabolite identification software (Agilent MET-ID and Mass Profiler Professional) detected the presence of parent trifluralin together with two main transformation products (TPs), 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole (TP1) and 2-amino-6-nitro-4-(trifluoromethyl)phenyl)propylamine (TP2). The highest concentration of trifluralin, determined by GC-MS, was 120 µg kg(-1) at 0 day withdrawal. Residues of trifluralin (CCα = 0.25 µg kg(-1), CCß = 0.42 µg kg(-1)) were detectable for up to 7 days after exposure. Similarly, the highest concentrations of TP1 and TP 2, determined by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS), were 14 and 18 µg kg(-1), respectively. Residues of TP1 (CCα = 0.05 µg kg(-1), CCß = 0.09 µg kg(-1)) and TP2 (CCα = 0.1 µg kg(-1), CCß = 0.17 µg kg(-1)) were detectable for up to 4 and 24 withdrawal days, respectively.

Current-use pesticides in inland lake waters, precipitation, and air from Ontario, Canada.

Concentrations of current-use pesticides (CUPs) in water, zooplankton, precipitation, and air samples as well as stereoisomer fractions (SF; herbicidally active/total stereoisomers) of metolachlor were determined in water samples collected from 10 remote inland lakes in Ontario, Canada, between 2003 and 2005. The most frequently detected chemicals in lake water, precipitation, and air were α-endosulfan, atrazine, metolachlor, chlorpyrifos, chlorothalonil, and trifluralin, and α-endosulfan and chlorpyrifos were the chemicals detected frequently in zooplankton. Air concentrations of these CUPs were within the range of previously reported values for background sites in the Great Lakes basin. High detection frequency of CUPs in lake water and precipitation was attributed to high usage amounts, but some CUPs such as ametryn and disulfoton that were not used in Ontario were also detected. Mean bioaccumulation factors (wet wt) in zooplankton for endosulfan ranged from 160 to 590 and from 20 to 60 for chlorpyrifos. The overall median SF of metolachlor in precipitation samples (0.846) was similar to that of the commercial S-metolachlor (0.882). However, the median SF of metolachlor in water from all sampled inland lakes (0.806) was significantly lower compared with Ontario rivers (0.873) but higher compared with previous measurements in the Great Lakes (0.710). Lakes with smaller watershed areas showed higher SFs, supporting the hypothesis of stereoselective processing of deposited metolachlor within the watersheds, followed by transport to the lakes.

Kinetics and mechanism of the degradation of two pesticides in aqueous solutions by ozonation.

This study evaluated the reaction kinetics and degradation mechanism of the pesticides bromoxynil and trifluralin during conventional ozonation. The second-order rate constants for the direct molecular ozone and hydroxyl radical reactions with bromoxynil and trifluralin were determined using a rapid-scan stopped-flow spectrophotometry, competition kinetics, and an organic substrate monitoring method. High reactivity toward ozone and hydroxyl radicals was observed for bromoxynil and trifluralin. The second-order rate constants for the reaction with ozone were about 10(2)M(-1)s(-1). The values of the second-order rate constants for the reaction between hydroxyl radicals and bromoxynil and trifluralin in ultrapure water at 20 degrees C were estimated to be around 8.4x10(9) and 7.5x10(9)M(-1)s(-1), respectively. The identification of oxidation by-products generated during ozonation was also addressed. It was found that hydroxylation and debromination were the primary pathways for the bromoxynil degradation, whereas hydroxylation and dealkylation were found to be the major mechanisms for trifluralin oxidation.