Evaluation of dissipation kinetic models to describe trifluralin degradation in soil and assessing the uncertainty of the half-life estimate.

In Australia, trifluralin is one of the commonly used herbicides to manage annual grasses and some broadleaf weeds. However, it may have some ecosystem impacts such as high toxicity to terrestrial and aquatic life, so it is vital to monitor the degradation of trifluralin for a considerable period for environmental safety. For risk assessment purposes, it is necessary to estimate the half-life of trifluralin, which is often evaluated using derived mathematical dissipation models. In the literature, bi-exponential (BEXP) and gamma models were suggested for modelling the dissipation of trifluralin in soil. Both models provide the half-life estimate without discussing the uncertainty of the estimate, which is a shortcoming in the literature. In this paper, we used simulation to illustrate the importance of estimate's uncertainty (standard error) and demonstrated a method to compute the standard error for the half-life estimate mathematically for kinetic dissipation models. Later, we evaluated the performance of the two suggested models using statistical indices. The computation of the half-life and the standard error of the half-life estimate were discussed. This allows us to describe the inference of the half-life parameter and determine whether the half-life estimates are significantly different against the co-variate (moisture) levels. We demonstrated the method to calculate the standard error of the half-life of trifluralin, which allows us to determine the statistical difference between the estimates. In this study, we found that the half-life of trifluralin in soil tends to increase with increasing moisture levels, and the half-life of trifluralin in soil with 100% moisture level is significantly greater than 40% and 70% moisture levels. Our findings suggest that soil moisture levels should be carefully considered before trifluralin application to minimize the non-target environmental damage.

Dinitroaniline herbicides: a comprehensive review of toxicity and side effects on animal non-target organisms.

The widespread use of herbicides has increased concern about the hazards and risks to animals living in terrestrial and aquatic ecosystems. A comprehensive understanding of their effective action at different levels of biological organization is critical for establishing guidelines to protect ecosystems and human health. Dinitroanilines are broad-spectrum pre-emergence herbicides currently used for weed control in the conventional agriculture. They are considered extremely safe agrochemicals because they act specifically on tubulin proteins and inhibit shoot and root growth of plants. However, there is a lack of toxicity information regarding the potential risk of exposure to non-target organisms. The aim of the present review is to focus on side effects of the most commonly used active ingredients, e.g. pendimethalin, oryzalin, trifluralin and benfluralin, on animal non-target cells of invertebrates and vertebrates. Acute toxicity varies from slightly to high in terrestrial and aquatic species (i.e. nematodes, earthworms, snails, insects, crustaceans, fish and mammals) depending on the species-specific ability of tested organisms to adsorb and discharge toxicants. Cytotoxicity, genotoxicity and activation of oxidative stress pathways as well as alterations of physiological, metabolic, morphological, developmental and behavioural traits, reviewed here, indicate that exposure to sublethal concentrations of active ingredients poses a clear hazard to animals and humans. Further research is required to evaluate the molecular mechanisms of action of these herbicides in the animal cell and on biological functions at multiple levels, from organisms to communities, including the effects of commercial formulations.

Atmospheric OH oxidation chemistry of trifluralin and acetochlor.

Trifluralin and acetochlor are two nitrogen-containing current use herbicides. While both herbicides have been observed in the atmosphere and have the potential to undergo atmospheric oxidation before deposition to off-target areas, the atmospheric photooxidation chemistry of these species is poorly understood. We use an oxidative flow reactor to expose the two herbicides to increasing concentrations of OH radicals, detecting pesticides and products using an iodide chemical ionization mass spectrometer. We identify new oxidation products and propose photooxidation mechanisms for trifluralin and acetochlor. Both herbicides contain reduced organic nitrogen atoms, and their OH oxidation produces isocyanic acid. While aerosol was observed in the flow reactor only for acetochlor, our results indicate that OH oxidation of neither herbicide would contribute to secondary organic aerosol formation under typical ambient atmospheric conditions. However, high wall losses of both pesticides in the flow reactor suggests that partitioning to pre-existing aerosol may occur and enable subsequent transport in the atmosphere.

Photo-assisted electrochemical abatement of trifluralin using a cathode containing a C60-carbon nanotubes composite.

This work reports the potential application of modified gas-diffusion electrode (GDE) with C60-CNT composite, as a stable and efficient cathode material for degradation of trifluralin (TRL) pesticide by photo-assisted electrochemical (PE) process. C60-CNT composite was prepared and characterized. Subsequently, a novel C60-CNT composite modified GDE cathode was developed and the electrochemical and physical characteristics of the modified GDEs were studied. C60-CNT composite/GDE showed great efficiencies for electro-generating H2O2, owing to huge surface area and high conductivity. Afterwards, a comparative study of TRL oxidation via photolysis, anodic oxidation (AO) and PE processes using C60-CNT composite/GDE revealed the degradation percentages of 42.2, 48.5 and 93.4%, respectively, after 180 min of treatment. The TRL degradation followed a pseudo-first-order kinetics, being faster in the order: photolysis < AO < PE. The effects of various operational conditions were assessed on the degradation of TRL. From the results, PE process using C60-CNT composite/GDE exhibited great performance for the degradation of TRL (20 mg L-1) under its original pH, Na2SO4 electrolyte concentration of 0.05 mol L-1, applied current intensity of 300 mA, and flow rate of 12.5 L h-1. TOC results displayed that 92.8% of TRL was mineralized after 8 h of PE process. In addition, a plausible pathway for mineralization of TRL was proposed according to the identified by-products detected by means of gas chromatography-mass spectroscopy (GC-MS), High-performance liquid chromatography (HPLC) and ion chromatography analyses.

Fifty years of herbicide research: comparing the discovery of trifluralin and halauxifen-methyl.

Fifty years separate the commercialization of the herbicides trifluralin and halauxifen-methyl. Despite the vast degree of technological change that occurred over that time frame, some aspects of their discovery stories are remarkably similar. For example, both herbicides were prepared very early in the iterative discovery process and both were developed from known lead compound structures by hypothesis-driven research efforts without the use of in vitro assays or computer-aided molecular design. However, there are aspects of the halauxifen-methyl and trifluralin discovery stories that are substantially different. For example, the chemical technology required for the cost-effective production of halauxifen-methyl simply did not exist just two decades prior to its commercial launch. By contrast, the chemical technology required for the cost-effective production of trifluralin was reported in the chemical literature more than two decades prior to its commercial launch. In addition, changes in regulatory environment since the early 1960s ensured that their respective discovery to commercial launch stories would also differ in substantial ways. Ultimately, the time and cost required to develop and register halauxifen-methyl demanded a global initial business case while the lower registration hurdles that trifluralin cleared enabled a narrow initial business case mainly focused on the USA. © 2017 Society of Chemical Industry.

The herbicides trifluralin and tebuthiuron have no genotoxic or mutagenic potential as evidenced by genetic tests.

Brazil has been the largest world consumer of pesticides since 2008, followed by the USA. The herbicides trifluralin and tebuthiuron have been widely applied in agriculture. These herbicides are selective for some plant species, and their use brings various benefits. However, the genotoxic and mutagenic effects of tebuthiuron on non-target organisms are poorly known, and in addition, the effects of trifluralin must be better investigated. Therefore, this study employed genetic tests including the comet assay and micronucleus test to evaluate the genotoxic effects of trifluralin and tebuthiuron on HepG2 cells. In addition, we have used the Ames test to assess the mutagenic effects of the herbicides on the TA97a, TA98, TA100, and TA1535 strains of Salmonella typhimurium. On the basis of the comet assay and the micronucleus test, trifluralin did not cause genetic damage to HepG2 cells. In addition, trifluralin did not impact the tested S. typhimurium strains. Regarding tebuthiuron, literature has shown that this herbicide damaged DNA in Oreochromis niloticus. Nevertheless, we have found that tebuthiuron was not genotoxic to either HepG2 cells or the S. typhimurium strains. Therefore, neither trifluralin nor tebuthiuron exerted genotoxic or mutagenic potential at the tested conditions.

Herbicide oryzalin inhibits human carbonic anhydrases in vitro.

Herbicides of the dinitroaniline chemical class, widely used oryzalin and trifluralin, and also nitralin were tested as inhibitors of recombinant human carbonic anhydrases (CAs). Oryzalin bound and inhibited 11 out of 12 catalytically active CA isoforms present in the human body with the affinities in the same range as clinically used CA drugs, while no effect was detected for the other two compounds. Binding of all three herbicides was examined by fluorescence-based thermal shift assay, isothermal titration calorimetry, and the inhibition of carbon dioxide hydratase activity. During the last decade, dinitroaniline compound-based therapies against protozoan diseases are being developed. Therefore, it is important to investigate their potential off-target effects, including human CAs.

Abiotic reduction of trifluralin and pendimethalin by sulfides in black-carbon-amended coastal sediments.

Dinitroaniline herbicides such as trifluralin and pendimethalin are persistent bioaccumulative toxins to aquatic organisms. Thus, in-situ remediation of contaminated sediments is desired. This study investigated whether black carbons (BCs), including apple wood charcoal (BC1), rice straw biochar (BC2), and activated carbon (BC3), could facilitate abiotic reduction of trifluralin and pendimethalin by sulfides of environmentally-relevant concentrations in anoxic coastal sediments. The reduction rates of trifluralin and pendimethalin increased substantially with increasing BC dosages in the sediments. This enhancing effect was dependent on BC type with the greatest for BC3 followed by BC1 and BC2, which well correlated with their specific surface area. The pseudo-first order reduction rate constants (kobs) for BC3-amended sediment (2%) were 13- and 14 times the rate constants in the BC-free sediment. The reduction rates increased with increasing temperature from 8 to 25°C in the BC-amended sediment, following the Arrhenius relationship. Finally, through molecular modeling by density functional theory and reaction species identification from mass spectra, molecular pathways of trifluralin and pendimethalin reduction were elucidated. In contrary to the separate sequential reduction of each nitro group to amine group, both nitro groups, first reduced to nitroso, then eventually to amine groups.

Products and mechanisms of the heterogeneous reaction of three suspended herbicide particles with NO3 radicals.

Over 60% of herbicides are capable of disrupting the endocrine and/or reproductive systems of animals. These herbicides may be released into the atmosphere in both gas and particulate phases, but most of their degradation processes in the atmosphere are not well known. In this study, the heterogeneous reactions of suspended isopropalin, trifluralin, and alachlor particles with NO3 radicals were investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. The reaction products for the three herbicides were determined by the assistance of the gas chromatography-mass spectrometer analysis. Mono-dealkylated derivatives were detected as the main reaction products of isopropalin and trifluralin. In addition, an α-amino alcohol product was detected for isopropalin. The carbonylation derivative and the nitro-substituted derivative were the main reaction products observed for alachlor. The reaction mechanism of NO3 radical-induced N-dealkylation for isopropalin was clarified by density functional theory calculations. It began with the H-abstraction from the N-propyl group, followed by the formation of the α-peroxypropyl radical, α-propyloxy radical, and α-amino alcohol, as well as by the collapse of the α-amino alcohol. The oxidation mechanism for trifluralin is similar to that of isopropalin, whereas the mechanism for alachlor involves carbonylation and nitro-substitution. These results provided insights on the chemical transformation of these herbicides in the atmosphere. The data generated from this study can be used as fundamental information for future studies on their toxic effects to the environment.

Partitioning of the pesticide trifluralin between dissolved organic matter and water using automated SPME-GC/MS.

Solid-phase microextraction (SPME) was used to determine the equilibrium association constant for a pesticide, trifluralin (TFR), with dissolved organic matter (DOM). After optimization of the SPME method for the analysis of TFR, partition coefficients (K DOM) with three different sources of DOM were determined in buffered solutions at pH 7. Commercial humic acids and DOM fractions isolated from two surface waters were used. The values of log K DOM varied from 4.3 to 5.8, depending on the nature of the organic material. A good correlation was established between log K DOM and DOM properties (as measured with the H/O atomic ratio and UV absorbance), in agreement with literature data. This is consistent with the effect of polarity and aromaticity for governing DOM-pollutant associations, regardless of the origin of DOM. This association phenomenon is relevant to better understand the behavior of pesticides in the environment since it controls part of pesticide leaching and fate in aquatic systems.

Catalytic strategy for efficient degradation of nitroaromatic pesticides by using gold nanoflower.

In this contribution, we report a new type of Au nanoflower-based nitroaromatic pesticide degradation platform that is fast, efficient, and simple. We found a straightforward, economically viable, and "green" approach for the synthesis and stabilization of relatively monodisperse Au nanoflowers by using nontoxic chemical of hydroxylamine (NH2OH) without stabilizer and the adjustment of the pH environment. This experiment shows that these Au nanoflowers function as effective catalyst for the reduction of pendimethalin in the presence of NaBH4 (otherwise unfeasible if NaBH4 is the only agent employed), which was reflected by the UV/vis spectra of the catalytic reaction kinetics. Importantly, the novel degradation platform could be put in use in two different practical soil samples with satisfactory results under laboratory conditions. To demonstrate the feasibility and universality of our design, two other nitroaromatic pesticides, trifluralin, and p-nitrophenol, were selected and were successfully degraded using this degradation platform.

Modeling pesticide volatilization: testing the additional effect of gaseous adsorption on soil solid surfaces.

Pesticide volatilization from bare soil exhibits usually a diurnal cycle with a potentially large decrease when the soil surface dries. We assume here that this decrease may be due to the increase in adsorption of gaseous pesticides to soil under dry conditions. Thus, a precise description of the change with time of water content of the soil surface and of additional process such as gaseous adsorption is required. We used the Volt'Air model: we first extended the van Genuchten curve to drier conditions and then inserted a partitioning coefficient of the pesticide between the air-filled pore space and the soil constituents. This coefficient was calculated by a quantum-chemistry-based method with a dependence on the Specific Surface Area of the soil (SSA) and Relative Humidity (RH) of the air-filled pore space. These developments were assessed by comparing with two data sets on volatilization of trifluralin applied to bare soil. The updated Volt'Air model allowed a better description of the volatilization dynamics on a diurnal cycle (increasing efficiency factor from 0.85 to 0.96 and -2.73 to 0.17 and decreasing RMSE from 146 to 78 and 353 to 168 for both scenarios) as well as the effect of a rewetting situation. Recommendations are made for further refining the description of this process together with the soil water conditions.

Gas-phase degradation of the herbicide ethalfluralin under atmospheric conditions.

The gas-phase degradation of ethalfluralin, N-ethyl-α,α,α-trifluoro-N-(2-methylallyl)-2,6-dinitro-p-toluidine, a widely used herbicide, was investigated under atmospheric conditions at the large outdoor European simulation chamber (EUPHORE) in Valencia, Spain. The photolysis of ethalfluralin was investigated under solar radiation and the mean photolysis rate coefficient was determined: J(ethalfluralin)=(1.3±0.2)×10(-3) s(-1) (JNO2=8×10(-3) s(-1)). The rate coefficients for the reactions of hydroxyl radicals and ozone with ethalfluralin in the dark were also measured under atmospheric conditions using the relative rate and the absolute rate technique, respectively. The rate coefficients values for the reactions of kOH(ethalfluralin)=(3.5±0.9)×10(-11)cm(3)molecule(-1)s(-1), and kO3(ethalfluralin)=(1.6±0.4)×10(-17) cm(3) molecule(-1) s(-1) were determined at 300±5 K and atmospheric pressure. The results show that removal of ethalfluralin from the atmosphere by reactions with OH radicals (τ ~ 4 h) or ozone (τ ~ 25 h) is slow compared to loss by photolysis. The available kinetic data suggest that the gas-phase tropospheric degradation of ethalfluralin will be controlled mainly by photolysis and provide an estimate for the tropospheric lifetime of approximately 12 min. The atmospheric implications of using ethalfluralin as a herbicide are discussed.

A novel alkyl phosphocholine-dinitroaniline hybrid molecule exhibits biological activity in vitro against Leishmania amazonensis.

Parasitic protozoa of the Leishmania genus cause leishmaniasis, an important complex of tropical diseases that affect about 12 million people around the world. The drugs used to treat leishmaniasis are pentavalent antimonials, miltefosine, amphotericin B and pentamidine. In the present study, we evaluated the effect of a novel alkyl phosphocholine-dinitroaniline hybrid molecule, TC95, against Leishmania amazonensis promastigotes and intracellular amastigotes. Antiproliferative assays indicated that TC95 is a potent inhibitor of promastigotes and intracellular amastigotes with IC50 values of 2.6 and 1.2 µM, respectively. Fluorescence microscopy with anti-α-tubulin antibody revealed changes in the cytoskeleton, whilst scanning electron microscopy showed alterations in the shape, plasma membrane, length of the flagellum, and cell cycle. Flow cytometry confirmed the cell cycle arrest mainly in G1 phase, however a significant population appeared in sub G0/G1 and super-G2. The alterations in the plasma membrane integrity were confirmed by fluorometric analysis using Sytox Blue. Transmission electron microscopy also revealed an accumulation of lipid bodies, confirmed by fluorescence microscopy and fluorometric analysis using Nile Red. Important lesions were also observed in organelles such as mitochondrion, endoplasmic reticulum and Golgi complex. In summary, our study suggests that TC95, an alkyl phosphocholine-trifluralin hybrid molecule, is a promising novel compound against L. amazonensis.

Biochar-mediated reductive transformation of nitro herbicides and explosives.

Biochar, a subset of black carbon produced via pyrolysis of biomass, has received much attention in recent years due to its potential to address many important issues, from energy and climate to agriculture and environmental quality. Biochar is known to influence the fate and transport of organic contaminants, although its role has been generally assumed to be as an adsorbent. In this study, the authors investigated the ability of biochar to catalyze the reductive reactions of nitro herbicides and explosives. Two biochars, derived from poultry litter and wastewater biosolids, were found to promote the reductive removal of the dinitro herbicides pendimethalin and trifluralin and the explosives 2,4-dinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by dithiothreitol. Parallel experiments using another black carbon material, graphite powder or granular activated carbon, in place of a biochar resulted in comparable rate enhancement to show reduction products, such as 2,4-diaminotoluene and formaldehyde. A cyclization product of trifluralin and reduction products of dinitrotoluene and RDX were detected only when biochar and dithiothreitol were both present, supporting the ability of biochar to promote redox reactions. Three possible catalysts, including graphene moieties, surface functional groups, and redox-active metals, in biochar may be responsible for the biochar-mediated reactions. The environmental significance, implications, and applications of this previously unrecognized role of biochar are discussed.

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.

Volatilization modeling of two herbicides from soil in a wind tunnel experiment under varying humidity conditions.

Volatilization of pesticides from the bare soil surface is drastically reduced when the soil is under dry conditions (i.e., water content lower than the permanent wilting point). This effect is caused by the hydrated mineral surfaces that become available as additional sorption sites under dry conditions. However, established volatilization models do not explicitly consider the hydrated mineral surfaces as an independent sorption compartment and cannot correctly cover the moisture effect on volatilization. Here we integrated the existing mechanistic understanding of sorption of organic compounds to mineral surfaces and its dependence on the hydration status into a simple volatilization model. The resulting model was tested with reported experimental data for two herbicides from a wind tunnel experiment under various well-defined humidity conditions. The required equilibrium sorption coefficients of triallate and trifluralin to the mineral surfaces, K(min/air), at 60% relative humidity were fitted to experimental data and extrapolated to other humidity conditions. The model captures the general trend of the volatilization in different humidity scenarios. The results reveal that it is essential to have high quality input data for K(min/air), the available specific surface area (SSA), the penetration depth of the applied pesticide solution, and the humidity conditions in the soil. The model approach presented here in combination with an improved description of the humidity conditions under dry conditions can be integrated into existing volatilization models that already work well for humid conditions but still lack the mechanistically based description of the volatilization process under dry conditions.

Poor efficacy of herbicides in biochar-amended soils as affected by their chemistry and mode of action.

We evaluated wheat straw biochar produced at 450°C for its ability to influence bioavailability and persistence of two commonly used herbicides (atrazine and trifluralin) with different modes of action (photosynthesis versus root tip mitosis inhibitors) in two contrasting soils. The biochar was added to soils at 0%, 0.5% and 1.0% (w/w) and the herbicides were applied to those soil-biochar mixes at nil, half, full, two times, and four times, the recommended dosage (H(4)). Annual ryegrass (Lolium rigidum) was grown in biochar amended soils for 1 month. Biochar had a positive impact on ryegrass survival rate and above-ground biomass at most of the application rates, and particularly at H(4). Within any given biochar treatment, increasing herbicide application decreased the survival rate and fresh weight of above-ground biomass. Biomass production across the biochar treatment gradient significantly differed (p<0.01) and was more pronounced in the case of atrazine than trifluralin. For example, the dose-response analysis showed that in the presence of 1% biochar in soil, the value of GR(50) (i.e. the dose required to reduce weed biomass by 50%) for atrazine increased by 3.5 times, whereas it increased only by a factor of 1.6 in the case of trifluralin. The combination of the chemical properties and the mode of action governed the extent of biochar-induced reduction in bioavailability of herbicides. The greater biomass of ryegrass in the soil containing the highest biochar (despite having the highest herbicide residues) demonstrates decreased bioavailability of the chemicals caused by the wheat straw biochar. This work clearly demonstrates decreased efficacy of herbicides in biochar amended soils. The role played by herbicide chemistry and mode of action will have major implications in choosing the appropriate application rates for biochar amended soils.

Oxidation kinetics of two pesticides in natural waters by ozonation and ozone combined with hydrogen peroxide.

The oxidation of bromoxynil and trifluralin was investigated using ozone (O(3)) and O(3) combined with hydrogen peroxide (H(2)O(2)) in natural waters using batch reactors. The results indicated that these pesticides could not be completely degraded during ozonation, achieving degradation levels lower than 50%. An enhancement of the level of degradation was observed using O(3)/H(2)O(2) process. A biphasic behaviour of O(3) was also observed. Depending on the experimental conditions, the rate constant for O(3) decomposition was estimated to be between 7.4 × 10(-4) s(-1) to 5.8 × 10(-2) s(-1), and 3.2 × 10(-3) s(-1) to 4.2 × 10(-2) s(-1) for bromoxynil and trifluralin samples, respectively. Acute toxicity analysis performed using Microtox(®) showed a decrease in the toxic effects of the samples on the luminescent bacteria during the first few minutes of treatment, followed by an increase of the toxic effects at the end of the reaction for both pesticides. The quantification of oxidation by-products generated during treatment was also addressed. The total molar balances of the degradation by-products versus the initial pesticide concentrations ranged from 60 to 103% under different experimental conditions.