Preclinical toxicity evaluation of novel antibacterial contezolid acefosamil in rats and dogs.

Contezolid acefosamil (CZA) is an intravenous prodrug of oxazolidinone antibiotic contezolid (CZD). It is being developed to treat infections due to Gram-positive bacteria including multidrug-resistant pathogens, while addressing myelosuppression and neurotoxicity limitations associated with long-term use of this class of antibiotics. In vivo, CZA is rapidly deacylated into its first metabolite MRX-1352, which is then dephosphorylated to release active drug CZD. Four-week repeat-dose toxicity studies of intravenous CZA were conducted in Sprague-Dawley rats (40, 80, and 160/120 mg/kg/dose twice a day [BID]) and beagle dogs (25, 50, and 100/75 mg/kg/dose BID). The high doses administered to both rats and dogs were adjusted due to adverse effects including decreased body weight and food consumption. Additionally, a dose-dependent transient reduction in erythrocyte levels was recorded at the end of dosing phase. Importantly, no myelosuppressive reduction in platelet counts was observed, in contrast to the myelosuppression documented for standard-of-care oxazolidinone linezolid. The no-observed-adverse-effect level (NOAEL) of CZA was 80 and 25 mg/kg/dose BID in rats and dogs, respectively. Separately, 3-month neuropathological evaluation in Long-Evans rats (25, 37.5, and 50 mg/kg/dose, oral CZA, BID) demonstrated no neurotoxicity in the central, peripheral, and optical neurological systems. Toxicokinetic data from these studies revealed that CZD exposures at NOAELs were higher than or comparable with that for the intended clinical dose. These results confirm the favorable safety profile for CZA and support its clinical evaluation for long-term therapy of persistent Gram-positive infections, beyond the application for earlier oxazolidinones.

Invention of MK-8262, a Cholesteryl Ester Transfer Protein (CETP) Inhibitor Backup to Anacetrapib with Best-in-Class Properties.

Cholesteryl ester transfer protein (CETP) represents one of the key regulators of the homeostasis of lipid particles, including high-density lipoprotein (HDL) and low-density lipoprotein (LDL) particles. Epidemiological evidence correlates increased HDL and decreased LDL to coronary heart disease (CHD) risk reduction. This relationship is consistent with a clinical outcomes trial of a CETP inhibitor (anacetrapib) combined with standard of care (statin), which led to a 9% additional risk reduction compared to standard of care alone. We discuss here the discovery of MK-8262, a CETP inhibitor with the potential for being the best-in-class molecule. Novel in vitro and in vivo paradigms were integrated to drug discovery to guide optimization informed by a critical understanding of key clinical adverse effect profiles. We present preclinical and clinical evidence of MK-8262 safety and efficacy by means of HDL increase and LDL reduction as biomarkers for reduced CHD risk.

Residues and dietary intake risk assessments of clomazone, fomesafen, haloxyfop-methyl and its metabolite haloxyfop in spring soybean field ecosystem.

Soybean is an important oilseed crop, but weed can have a significant effect on soybean yield. Clomazone, fomesafen, and haloxyfop-methyl are high-efficacy herbicides, and the combination of these herbicides shows an ideal effect on weed control. However, the residues of these herbicides and their impacts on human health are still largely unknown. In the current study, a rapid, sensitive, and selective method using modified QuECHERS procedure combined with HPLC-MS/MS was established to detect these herbicides in soybean matrices. The limits of quantification were 0.01, 0.01 and 0.025 mg/kg for haloxyfop-methyl, haloxyfop and fomesafen, and 0.005, 0.005 and 0.0125 mg/kg for clomazone in green soybean, soybean grain, and straw, with the average recoveries ranging from 80% to 107%. The terminal residues of the target compounds were all below the corresponding limits of quantification. The dietary risk assessment showed that the risk quotient values were far below the acceptable human consumption levels.

Morphoanatomical injuries in Pistia stratiotes L. (Araceae) as a result of exposure to clomazone in water.

Contamination of water sources due to herbicide is of great concern. Clomazone is a pesticide with a high contamination potential which could possibility lixiviate to water streams. Changes caused by residual herbicide include flora modifications which are generally detrimental for some species. The lack of morphological studies performed in aquatic plants exposed to herbicide-contaminated environments has encouraged the development of our research. For the first time, we present a study that aimed to evaluate leaf injuries visible to the naked eye as well as microscopical effects which may be caused by clomazone on Pistia stratiotes. Pistia stratiotes was subjected to five concentrations of clomazone. Our analysis showed leaf injuries, especially after 15 days of clomazone application. Hormesis was observed when the water lettuce was subjected to the lower concentrations. Total leaf area showed increase following by reduction while injured until reaching the highest concentration. Although the concentrations of clomazone tested in our study are not lethal to water lettuce, such herbicide have still caused morphoanatomical damages on leaves which advocates for the use of P. stratiotes as a bioindicator of the presence of herbicides such as clomazone in water.

Simultaneous Analysis and Dietary Exposure Risk Assessment of Fomesafen, Clomazone, Clethodim and Its Two Metabolites in Soybean Ecosystem.

A commercial formulation, 37% dispersible oil suspension (DOS) (fomesafen, clomazone, and clethodim), is being registered in China to control annual or perennial weeds in soybean fields. In this paper, a liquid chromatography tandem mass spectrometry method with QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation was developed for the simultaneous determination of fomesafen, clomazone, clethodim, and its two metabolites (CSO and CSO2) in soybean, green soybean, and soybean straw samples. The mean recoveries of our developed method for the five analytes in three matrices were ranged from 71% to 116% with relative standard deviations (RSDs) less than 12.6%. The limits of quantification (LOQs) were 0.01 mg/kg in soybean, 0.01 mg/kg in green soybean, and 0.02 mg/kg in soybean straw while the limits of detection (LODs) ranged from 0.018 to 0.125 µg/kg for these five analytes. The highest final residual amount of CSO2 in green soybean samples (0.015 mg/kg) appeared in Anhui, and the highest in soybean straw samples was 0.029 mg/kg in Guangxi, whilst the terminal residues of fomesafen, clomazone, clethodim and CSO were lower than LOQs (0.01 mg/kg) in all samples. Furthermore, these terminal residues were all lower than the maximum residue limits (MRLs) set by China (0.1 mg/kg for fomesafen and clethodim, 0.05 mg/kg for clomazone) at harvest. Additional chronic dietary risk was evaluated using a risk quotients (RQs) method based on Chinese dietary habits. The chronic dietary exposure risk quotients were 4.3 for fomesafen, 0.12 for clomazone, and 19.3 for clethodim, respectively, which were significantly lower than 100. These results demonstrated that the dietary exposure risk of fomesafen, clomazone, and clethodim used in soybean according to good agricultural practices (GAP) was acceptable and would not pose an unacceptable health risk to Chinese consumers. These results not only offer insight with respect to the analytes, but also contribute to environmental protection and food safety.

Monoamine oxidase A inhibition by toxic concentrations of metaxalone.

Context: Serotonin toxicity is a reported complication associated with both therapeutic use and overdose of metaxalone while on therapeutic doses of serotonergic drugs such as serotonin reuptake inhibitors. Monoamine oxidase A (MAO-A) inhibition by metaxalone has been proposed as the etiology of this toxicity. Metaxalone concentrations reported with cases of serotonin toxicity range from 31 to 61 mcg/ml (140-276 µM). We investigated the effect of metaxalone on MAO-A activity using an in vitro model.Methods: Metaxalone at concentrations ranging from 1.56 to 400 µM were incubated with a proprietary MAO substrate and recombinant human MAO-A for 1 h. After that, an esterase and luciferase were added and luminescence measured. Clorgyline, a known MAO-A inhibitor, was used as a positive control. Luminescence was measured using a Biotek Synergy HT microplate reader.Results: Metaxalone demonstrated significant dose-related inhibition of MAO-A activity. Four-parameter logistic regression analysis demonstrated a strong dose-response relationship at increasing concentrations.Conclusions: Our in vitro model shows that at toxic concentrations similar to those reported in case reports metaxalone shows significant MAO-A inhibition. Clinicians should be aware of this mechanism and understand the potentially lethal interactions metaxalone can have when prescribed with other serotonergic drugs and consider this as a potential cause of serotonin toxicity, especially in overdose scenarios.

Prolonged inhibition and incomplete recovery of mitochondrial function in oxazolidinone-treated megakaryoblastic cell lines.

Thrombocytopenia is commonly seen in patients receiving linezolid for >14 days. Linezolid is a reversible inhibitor of mitochondrial function in various cell types. This study investigated the inhibitory effects of linezolid and tedizolid, and their potential recovery on (i) CYTox I expression (subunit I of cytochrome c-oxidase; encoded by the mitochondrial genome), (ii) cytochrome c-oxidase activity and (iii) mitochondrial respiration (Seahorse bioanalysis) in two megakaryocytic cell lines [UT-7 WT (human acute megakaryoblastic leukaemia cells) and UT-7 MPL (transduced to express the thrombopoietin receptor)]. Cells were exposed to linezolid (0.5-25 mg/L) or tedizolid (0.1-5 mg/L) for up to 5 days and recovery followed after drug removal. Both oxazolidinones caused concentration- and time-dependent inhibition of CYTox I expression, cytochrome c-oxidase activity and mitochondrial spare capacity. On electron microscopy, mitochondria appeared dilated with a loss of cristae. Globally, tedizolid exerted stronger effects than linezolid. While CYTox I expression recovered completely after 6 days of drug washout, only partial (linezolid) or no (tedizolid) recovery of cytochrome c-oxidase activity, and no rescue of mitochondrial spare capacity (after 3 days) was observed. Thus, and in contrast to previous studies using a variety of cell lines unrelated to megakaryocytic lineages, the inhibitory effects exerted by oxazolidinones on the mitochondrial function of megakaryoblastic cells appear to be particularly protracted. Given the dynamics of platelet production and destruction, these results may explain why oxazolidinone-induced thrombocytopenia is one of the most common side effects in patients exposed to these antibiotics.

Clomazone influence soil microbial community and soil nitrogen cycling.

We designed an indoor mesocosm experiment to investigate the long-term effects of exposure to clomazone, a widely used herbicide, on soil microbial communities and their nitrogen (N) cycling functions. Clomazone was applied to two typical soils from China at three concentrations: 0.8 (the recommended dosage), 8 and 80 mg kg-1 soil dry weight, and the mix was incubated for 90 days. Samples were removed periodically for assay with several techniques. The half-lives of clomazone in this experiment were 11-126 d. Results were significant only for the highest clomazone concentration. Next-generation sequencing of the 16S and 18S rDNA genes revealed that bacterial diversity significantly decreased whereas fungal abundance increased after day 60 but with no detectable effect on the microbial community. Hierarchical cluster and principal coordinates analysis revealed that the bacterial community structure was negatively impacted. Linear discriminant analysis of effect size identified Sphingomonas and Arthrobacter as the predominant bacterial species. Finally, we measured soil NH4+ and NO3- concentrations and used real-time PCR to analyze the abundance of the N-cycling genes, nifH and amoA. In the first 30 days, the NO3--N content and the number of ammonia-oxidizing bacteria increased. N2-fixing bacteria were inhibited after 60 days, but the NH4+-N concentration remained unchanged and was likely provided by ammoniation.

Responses of macroinvertebrate communities to pesticide application in irrigated rice fields.

The ability to recover to original states after disturbances makes macroinvertebrates useful tools for assessing the impacts of pesticides. Many studies showed that direct exposure to pesticides decreases macroinvertebrate richness and alters their composition. The main objective of this study was to assess recovery patterns in macroinvertebrate communities after pesticide application in irrigated rice fields. We analyzed short-term temporal dynamics of macroinvertebrate communities after application of the herbicides bispyribac-sodium and clomazone and the insecticide chlorantraniliprole, over the rice-growing season in southern Brazil. We selected three conventional rice fields and the recovery of macroinvertebrate communities was also compared with three adjacent natural ponds. The study was developed from November 2011 to February 2012 (rice-growing season). Five macroinvertebrate collections were carried out 3, 7, 14, 38, and 60 days after pesticide application (November 25). Rice fields showed lower richness and abundance than ponds in the period immediately after pesticide application, and recovery rates in the richness of macroinvertebrate communities were more conspicuous as pesticide residuals dissipated from the fields. Macroinvertebrate community structure in rice fields also became more similar to natural ponds as pesticide traces were scarcer. However, macroinvertebrate abundance patterns were not related to pesticide concentrations in the fields. Our results supported the general hypothesis on the negative effects of pesticide application on macroinvertebrate community in irrigated rice fields, although other environmental features (e.g., length of the flooded period) also contributed to explain temporal dynamics in the macroinvertebrate communities from irrigated rice fields.

Combined effects of temperature and clomazone (Gamit®) on oxidative stress responses and B-esterase activity of Physalaemus nattereri (Leiuperidae) and Rhinella schneideri (Bufonidae) tadpoles.

Temperature is an important factor influencing the toxicity of chemicals in aquatic environments. Neotropical tadpoles experience large temperature fluctuations in their habitats and many species are distributed in areas impacted by agriculture. This study evaluated the effects caused by the exposure to clomazone (Gamit®) at different temperatures (28, 32 and 36 °C) on biochemical stress responses and esterase activities in Physalaemus nattereri and Rhinella schneideri tadpoles. Results evidenced that temperature modulates the effects of clomazone on biochemical response of tadpoles. Antioxidant enzymes, including catalase, superoxide dismutase (SOD), and glucose-6-phosphate dehydrogenase had their activities increased by clomazone in P. nattereri treated at higher temperatures. The biotransformation enzyme glutathione-S-transferase (GST) was also induced by clomazone at 32 and 36 °C. In R. schneideri, clomazone failed to alter antioxidant enzymes at 28 °C, but SOD and GST were increased by clomazone at higher temperatures after three days. All enzymes had their activities returned to the control levels after eight days in R. schneideri. Lipid peroxidation was induced in both species exposed to clomazone at 32 and 36 °C, but not at 28 °C. Acetylcholinesterase was not sensitive to clomazone and temperature, while most treatments impaired carboxylesterase activity. Integrated biomarker response (IBR) was notably induced by temperature in both species, and a synergic effect of temperature and clomazone was mostly observed after three days of exposure. These findings imply that tadpoles from tropical areas may present differential responses in their physiological mechanism linked to antioxidant defense to deal with temperature fluctuations and agrochemicals presence in their habitats.

Toxicity of clomazone and its formulations to zebrafish embryos (Danio rerio).

Herbicides are the most widely used group of pesticides but after reaching water bodies they are able to cause adverse effects on non-target organisms. Different formulations using the same active ingredient are frequently available, which raises the issue of potential influence of different formulation types on herbicide toxicity. The present study evaluated the toxicity and teratogenic effects of the active ingredient clomazone and its two formulations (Rampa® EC and GAT Cenit 36 CS, both containing 360g a.i./l of clomazone) on zebrafish embryos. The crucial difference between the two formulation types is the way of active substance release. This investigation is the first report on zebrafish embryotoxicity of both clomazone and its formulations. The technical active ingredient and formulations caused mortality and diverse teratogenic effects, showing different levels of toxicity. The LC50 values for the technical ingredient, Rampa® EC and GAT Cenit 36 CS were 61.4, 9.6 and 92.5mg a.i./l, respectively. Spontaneous movements in 22 hpf embryos decreased under exposure to both the technical ingredient and formulations. A significant number of underdeveloped embryos was detected after exposure to clomazone and Rampa® EC, while no underdevelopment was noted in embryos exposed to GAT Cenit 36 CS. Exposure to the technical ingredient and formulations led also to a series of morphological changes and interfered with the growth of zebrafish embryos. The EC50 based on detection of edemas, spine and tail tip deformations and gas bladder absence (120hpf) was 12.1, 10.1 and 24.1mg/l for technical clomazone, Rampa® EC and GAT Cenit 36 CS, while teratogenicity index (TI) based on LC50/EC50 ratio was 5.1, 1 and 3.8, respectively. The data in this study showed that the emulsifiable concentrate formulation (Rampa® EC) caused statistically significantly higher toxicity, and the aqueous capsule suspension (GAT Cenit 36 CS) lower toxicity than technical clomazone. It indicates that different formulations with the same active ingredient may have different environmental impacts, which is why risk assessment based only on active ingredient toxicity might not be sufficient in terms of preventing formulation effects on the environment.

Anacetrapib, but not evacetrapib, impairs endothelial function in CETP-transgenic mice in spite of marked HDL-C increase.

BACKGROUND AND AIMS: High-density lipoprotein cholesterol (HDL-C) is inversely related to cardiovascular risk. HDL-C raising ester transfer protein (CETP) inhibitors, are novel therapeutics. We studied the effects of CETP inhibitors anacetrapib and evacetrapib on triglycerides, cholesterol and lipoproteins, cholesterol efflux, paraoxonase activity (PON-1), reactive oxygen species (ROS), and endothelial function in E3L and E3L.CETP mice. METHODS: Triglycerides and cholesterol were measured at weeks 5, 14 and 21 in E3L.CETP mice on high cholesterol diet and treated with anacetrapib (3 mg/kg/day), evacetrapib (3 mg/kg/day) or placebo. Cholesterol efflux was assessed ex-vivo in mice treated with CETP inhibitors for 3 weeks on a normal chow diet. Endothelial function was analyzed at week 21 in isolated aortic rings, and serum lipoproteins assessed by fast-performance liquid chromatography. RESULTS: Anacetrapib and evacetrapib increased HDL-C levels (5- and 3.4-fold, resp.) and reduced triglycerides (-39% vs. placebo, p = 0.0174). Total cholesterol levels were reduced only in anacetrapib-treated mice (-32%, p = 0.0386). Cholesterol efflux and PON-1 activity (+45% and +35% vs. control, p < 0.005, resp.) were increased, while aortic ROS production was reduced with evacetrapib (-49% vs. control, p = 0.020). Anacetrapib, but not evacetrapib, impaired endothelium dependent vasorelaxation (p < 0.05). In contrast, no such effects were observed in E3L mice for all parameters tested. CONCLUSIONS: Notwithstanding a marked rise in HDL-C, evacetrapib did not improve endothelial function, while anacetrapib impaired it, suggesting that CETP inhibition does not provide vascular protection. Anacetrapib exerts unfavorable endothelial effects beyond CETP inhibition, which may explain the neutral results of large clinical trials in spite of increased HDL-C.

Can herbicide safeners allow selective control of weedy rice infesting rice crops?

BACKGROUND: Rice is a major field crop of paramount importance for global food security. However, the increased adoption of more profitable and resource-efficient direct-seeded rice (DSR) systems has contributed to greater weed infestations, including weedy rice, which has become a severe problem in several Asian regions. In this study we have developed a conceptually novel method to protect rice plants at high doses of clomazone and triallate. RESULTS: The insecticide phorate applied to rice seeds provided a substantial level of protection against the herbicides clomazone or triallate. A quantity of 15 kg phorate ha-1 significantly increased the LD50 values, which were more than twofold greater than for rice plants treated only with clomazone. A quantity of 20 kg phorate ha-1 in combination with 2000 g triallate ha-1 safened rice plants (80% survival) with LD50 >3.4-fold greater than in phorate-untreated rice. Weed control efficacy was not lowered by the presence of phorate-treated rice seeds. CONCLUSION: Weedy rice is one of the most damaging global weeds and a major threat to DSR systems. In this study we have developed a proof-of-concept method to allow selective weedy rice control in rice crops. We call for herbicide discovery programmes and research to identify candidate safener and herbicide combinations to achieve selective herbicide control of weedy rice and alleviate weed infestations in global rice crops. © 2016 Society of Chemical Industry.

Hepatic effects of the clomazone herbicide in both its free form and associated with chitosan-alginate nanoparticles in bullfrog tadpoles.

The use of agrochemicals in agriculture is intense and most of them could be carried out to aquatic environment. Nevertheless, there are only few studies that assess the effects of these xenobiotics on amphibians. Clomazone is an herbicide widely used in rice fields, where amphibian species live. Thus, those species may be threatened by non-target exposure. However, nanoparticles are being developed to be used as a carrier system for the agrochemicals. Such nanoparticles release the herbicide in a modified way, and are considered to be more efficient and less harmful to the environment. The aim of this study was to comparatively evaluate the effect of clomazone in its free form and associated with nanoparticles, in the liver of bullfrog tadpoles (Lithobates catesbeianus) when submitted to acute exposure for 96 h. According to semi-quantitative analysis, there was an increase in the frequency of melanomacrophage centres, in the accumulation of eosinophils and in lipidosis in the liver of experimental groups exposed to clomazone - in its free form and associated with nanoparticles - in comparison with the control group, and the nanotoxicity of chitosan-alginate nanoparticles. The increase of melanomacrophage centres in all exposed groups was significant (P < 0.0001) in comparison to control group. Therefore, the results of this research have shown that exposure to sublethal doses of the herbicide and nanoparticles triggered hepatic responses. Moreover, these results provided important data about the effect of the clomazone herbicide and organic nanoparticles, which act as carriers of agrochemicals, on the bullfrog tadpole liver.

Bioaccumulation and Elimination of the Herbicide Clomazone in the Earthworms Eisenia fetida.

Acute toxicity, bioaccumulation, and elimination of herbicide clomazone in the earthworm Eisenia fetida were investigated in the different exposure systems. The LC50 values of clomazone on earthworms were 5.6 µg cm(-2) in the contact filter paper test (48 h), 174.9 mg kg(-1) (7 days) and 123.4 mg kg(-1) (14 days) in artificial soil test, respectively. Clomazone could rapidly bioaccumulate in earthworms and reached the highest concentration after 3 days exposure, with the maximum concentrations of 9.0, 35.3 and 142.3 mg kg(-1) at 10.0, 40.0 and 160.0 mg kg(-1) of clomazone, respectively. Clomazone uptake showed a good correlation with exposure concentration. After the 14th day, clomazone declined to minimum value. About 74%-80% of accumulated clomazone was eliminated within 1 day after exposed to clomazone-free soil. However, a trace amount of clomazone persisted for a relatively long time in earthworms.

Alternation of light/dark period priming enhances clomazone tolerance by increasing the levels of ascorbate and phenolic compounds and ROS detoxification in tobacco (Nicotiana tabacum L.) plantlets.

The effect of the alternation of light/dark periods (AL) (16/8 min light/dark cycles and a photosynthetic photon flux density (PPFD) of 50 µmol photons m(-2) s(-1) for three days) to clarify the mechanisms involved in the clomazone tolerance of tobacco plantlets primed with AL was studied. Clomazone decreased PSII activity, the net photosynthetic rate (Pn), and the ascorbate and total polyphenol contents and increased H2O2 and starch grain accumulation and the number of the cells that underwent programmed cell death (PCD). The pretreatment with AL reduced the inhibitory effect of clomazone on the PSII activity and photosynthesis, as indicated by the decreases in the H2O2 and starch grain accumulation and the PCD levels, and increased the content of ascorbate and certain phenolic compounds, such as chlorogenic acid, neochlorogenic acid and rutin. The AL treatment could promote photorespiration via post-illumination burst (PIB) effects. This alternative photorespiratory electron pathway may reduce H2O2 generation via the consumption of photochemical energy, such as NADH+H(+). At 10 days (D10) of AL treatment, this process induced moderate stress which stimulates H2O2 detoxification systems by increasing the activity of antioxidant enzymes and the biosynthesis of antioxidant components. Therefore, the PCD levels provoked by clomazone were noticeably decreased.

Integrated assessment of biomarker response in carp (Cyprinus carpio) and silver catfish (Rhamdia quelen) exposed to clomazone.

Clomazone is considered a potential contaminant of groundwater and is persistent in the environment. To verify the effects of clomazone in Cyprinus carpio and Rhamdia quelen, a method that combines biomarker responses into an index of "integrated biomarker response" (IBR) was used for observed biological alterations in these species. Thiobarbituric acid-reactive substances in liver of carp and silver catfish decreased at both concentrations tested. However, in muscle it increased in carp at 3 mg/L and silver catfish at 6 mg/L. Protein carbonyl increased in liver (3 and 6 mg/L) and muscle (6 mg/L) of carp. In carp, superoxide dismutase (SOD) increased at 3 mg/L and catalase at 6 mg/L. In silver catfish, SOD in liver decreased at 3 mg/L. Glutathione-S-transferase increased at 3 mg/L in muscle of carp. Nonprotein thiol levels decreased at both concentrations in liver of silver catfish and muscle of carp. In silver catfish, acetylcholinesterase (AChE) decreased in brain at 6 mg/L. Nevertheless, AChE in muscle of both species increased at 3 and 6 mg/L. IBR was standardized scores of biomarker responses and was visualized using star plots. The IBR values shown that in carp there was predominantly an induction of parameters, whereas in silver catfish there was inhibition of these responses. In this way, IBR may be a practical tool for the identification of biological alterations in fish exposed to pesticides. In the present study, IBR was efficient for comparisons of fish species using clomazone. This study may serve as a base for evaluation of other pesticides in the rice field, environment, or laboratory experiment.

Pretreatment with alternation of light/dark periods improves the tolerance of tobacco (Nicotiana tabacum) to clomazone herbicide.

This work analyses the effects of alternation of light/dark periods pretreatment (AL) in tobacco plantlets (Nicotiana tabacum L. cv.Virginie vk51) growing in solution with low concentration of the clomazone herbicide. The experimentation has been carried out by exposing the plantlets to successive and regulated periods of light (16min light/8min dark cycles, PAR 50µmolm(-2)s(-1)) for three days. The photosynthesis efficiency was determined by mean of the chlorophyll fluorescence and JIP-test. The AL pretreatment improved the clomazone tolerance; this has been observed by the increase in the leaf area of the plant, the maximal photochemical quantum efficiency of PSII (Fv/Fm), the actual PSII efficiency (ФPSII), the performance index (PIabs), the electron flux beyond Quinone A (1-VJ), and also by the diminution of the energy dissipating into heat (DI0/RC). Furthermore, AL pretreatment led to low accumulation of hydrogen peroxide (H2O2) which proves that the scavenging enzymatic system have been activated before clomazone treatment. In the plantlets pretreated with AL, with regard to the ascorbate content, some of antioxidant enzyme whose function is associated with it have continued to scavenge reactive oxygen species (ROS) induced by clomazone, such as ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). So, the observed photooxidative damages induced by clomazone herbicide were noticeably reduced.

Herbicide clomazone effects on δ-aminolevulinic acid activity and metabolic parameters in Cyprinus carpio.

The objective of this study was to investigate δ-aminolevulinic acid (δ-ALA-D) activity and metabolic parameters of Cyprinus carpio exposed to clomazone herbicide. Fish were exposed 2.5, 5, 10 and 20 mg L(-1) of clomazone for 192 h. Results indicated that δ-ALA-D activity was decreased in the gills at concentrations of 5 and 10 mg L(-1). Liver glycogen increased, while muscle and gill glycogen levels decreased at 5, 10 and 20 mg L(-1). Glucose was increased in the gills and plasma. Lactate decreased in the gills and liver and increased in the muscle. Protein and amino acids levels increased in the liver and gills and decreased in the muscle. At a clomazone concentration of 20 mg L(-1), ammonia increased in the gills and muscle and decreased in the liver. The results indicated that the metabolic parameters of glycogen, lactate, protein and amino acids in liver, muscle and gills, blood glucose levels, and the enzyme δ-ALA-D in gills may be useful indicators of clomazone toxicity in carp.

Environmental fate and toxicology of clomazone.

Clomazone, an isoxazolane herbicide, was first registered for use in 1986 for pest grasses and broad leaf weeds. Although the exact mode of action is still unclear, it is well documented that clomazone causes bleaching of foliar structures; the clomazone metabolite 5-ketoclomazone is regarded to cause the bleaching and to be the ultimate plant toxicant. Although clomazone exhibits low mammalian toxicity and is selective towards certain plant species, studies have shown that it does inhibit AChE and catalase activities. In addition, it has been found to be highly toxic to aquatic invertebrates, in particular mysid shrimp.Clomazone has a low Henry's law constant and moderate vapor pressure, and thus may volatilize from dry soils. Photolysis represents a minor dissipationpathway; however, clomazone can be photolytically degraded under both direct and indirect conditions. Clomazone has high water solubility, and it is often assumed to undergo hydrolysis easily; unfortunately, this is not the case. Clomazone is stable over a wide pH range and does not hydrolyze. Clomazone has a weak to moderates oil adsorption coefficient; therefore, its affinity to sorb to soil is minimal, rendering it a potential threat to groundwater supplies.Microbial metabolism is the major degradation pathway, resulting in products such as 5-hydroxyclomazone, hydroxymethylclomazone, 2-chlorobenzyl alcohol and 3'-hydroxyclomazone. Although clomazone has not been shown to degrade viahydrolysis, it nonetheless represents a potential threat to aquatic organisms. With this in mind, caution should be taken when applying clomazone or when draining fields that have detectable clomazone residues.