Embryonic Development Effects of Basagran® Herbicide in Danio Rerio: A Preliminary Study

Bentazon (Basagran®) belongs to the chemical group of benzothiadiazinones. Thus, this study aimed to estimate the influence of herbicide bentazon (3 µg.L-1, 6 µg.L-1, 12 µg.L-1, 300 µg.L-1) in Danio rerio embryos development. The study tested environmental relevant concentrations of bentazon as well as the limit established for drinking water (300 µg.L-1) in Brazil. We performed behavioral and developmental analyzes during 96 h of exposure. The bentazon measurements after experimental period showed reduction ranging from 5.0 to 18.93% between exposed groups. Our results showed significant differences in the heart rate, which was significantly higher in groups exposed to all bentazon concentrations compared to control groups. The absence of alterations in the behavioral parameters showing that the herbicide bentazon at the concentrations tested had few adverse effects on the development and behavior of the Danio rerio embryos. Considering the toxic point of view, there is a chance that bentazon acts together with other environmental contaminants as an additive or synergistic way.

Coordinated downregulation of KCC2 and GABAA receptor contributes to inhibitory dysfunction during seizure induction

The GABAA receptor (GABAAR) is the main inhibitory receptor in the adult mammalian brain. GABAAR function is dependent on its expression, distribution, and the chloride (Cl-) transmembrane gradient, which is determined by the potassium-chloride cotransporter 2 (KCC2) in the adult brain. KCC2 and GABAAR are downregulated in an activity-dependent manner during seizure induction. Functionally, KCC2 and GABAAR are closely related membrane proteins which modulate GABAergic inhibition. However, it remains unclear how their downregulation during seizure induction is coordinated. This study aimed to assess this interaction. Our results revealed that KCC2 and GABAAR were simultaneously downregulated in both in vivo and in vitro seizure models induced by the convulsant cyclothazide (CTZ), which was at least partly due to structural coupling in hippocampal neuronal membranes. Immunohistochemistry revealed colocalization of gephyrin with KCC2 and co-immunoprecipitation exhibited a direct coupling between GABAAR α1-subunit and KCC2 protein in hippocampal cell membranes. KCC2 specific short hairpin RNA (KCC2-shRNA) was employed to specifically reduce the expression of KCC2 in cultured hippocampal neurons. This resulted in a significant reduction in KCC2-independent GABAergic miniature inhibitory post-synaptic current (mIPSC) amplitude in shKCC2-transfected neurons. Further, pre-treatment with furosemide, a KCC2 inhibitor, during CTZ stimulation followed by washout significantly prevented convulsant stimulation-induced membrane KCC2 downregulation and significantly attenuated GABAAR downregulation concomitant with recovery of suppressed KCC2-independent GABAergic mIPSC amplitude. Our results suggest that the coordinated downregulation of KCC2 and GABAAR during seizure induction exerts a strong functional impact on GABAAR, highlighting an important regulatory mechanism in epilepsy.

Oxidative degradation and mineralization of bentazone from water

Bentazone degradation efficiency and mineralization in water solutions using chlorine dioxide treatment were evaluated. Double distilled water and a river water sample spiked with bentazone were studied and compared after chlorine dioxide treatment. Degradation efficiency was determined using high-performance liquid chromatography (HPLC). Daphnia magna toxicity testing and total organic carbon (TOC) analysis were used to ascertain the toxicity of the degraded solutions and mineralization degree. Bentazone degradation products were identified using gas chromatography with a triple quadrupole mass detector (GC-MS-MS). A simple mechanistic scheme for oxidative degradation of bentazone was proposed based on the degradation products that were identified. Decrease in D. magna mortality, high degradation efficiency and partial bentazone mineralization were achieved by waters containing bentazone degradation products, which indicate the formation of less toxic compounds than the parent bentazone and effective removal of bentazone from the waters. Bentazone degraded into four main degradation products. Humic acid from Sava River water influenced bentazone degradation, resulting in a lower degradation efficiency in this matrix (about 10% lower than in distilled water). Chlorine dioxide treatment of water to degrade bentazone is efficient and offers a novel approach in the development of new technology for removal of this herbicide from contaminated water.

Herbicide Toxicity to Soybean-Rhizobium Symbiosis as Affected by Soil pH

The current study examined whether soil pH could influence the toxicity of herbicides to soybean-rhizobium symbiosis. This can be useful for farmers to minimize the toxicity of them to crop-rhizobium symbiosis via applying their reduced doses. The toxicity of bentazon, metribuzin, and trifluralin to soybean-rhizobium symbiosis was investigated in pH 6.4, 7.2, and 8 soils. Seed inoculation decreased shoot:root (S:R) ratio but increased height, shoot dry weight (SDW), root dry weight (RDW), shoot nitrogen content (SNC), root nitrogen content (RNC), and nitrogen fixation effectiveness (NFE) in the pH 7.2 soil without herbicide application. All herbicides decreased NFE in all soil pH regimes except metribuzin in the pH 6.4 soil. Unlike trifluralin, the toxicity of bentazon and metribuzin to soybean-rhizobium symbiosis was influenced by the soil pH. It can be concluded that soil acidification and alkalization, which can rapidly occur in agroecosystems, can decrease and increase the toxicity of bentazon and metribuzin to soybean-rhizobium symbiosis, respectively.

Basagran® induces developmental malformations and changes the bacterial community of zebrafish embryos

This study aimed to assess the effects of Basagran^® on zebrafish (Danio rerio) embryos. The embryos were exposed to Basagran^® at concentrations ranging from 120.0 to 480.6 mg/L, and the effects on embryo development (up to 96 h) and bacterial communities of 96 h-larvae were assessed. The embryo development response was time-dependent and concentration-dependent (106.35 < EC₅₀ < 421.58 mg/L). The sensitivity of embryo-related endpoints decreased as follows: blood clotting in the head and/or around the yolk sac > delay or anomaly in yolk sac absorption > change in swimming equilibrium > development of pericardial and/or yolk sac oedema > scoliosis. A PCR-DGGE analysis was used to evaluate changes in the structure, richness, evenness and diversity of bacterial communities after herbicide exposure. A herbicide-induced structural adjustment of bacterial community was observed. In this study, it was successfully demonstrated that Basagran^® affected zebrafish embryos and associated bacterial communities, showing time-dependent and concentration-dependent embryos' developmental response and structural changes in bacterial community. Thus, this work provides for the first time a complementary approach, which is useful to derive robust toxicity thresholds considering the embryo-microbiota system as a whole. The aquatic hazard assessment will be strengthened by combining current ecotoxicological tests with molecular microbiology tools.

Subacute and subchronic toxicity of Avalon(®) mixture (bentazone+dicamba) to rats

Subacute and subchronic toxicity of the herbicide Avalon(®), a mixture of bentazone and dicamba, were tested on rats. Avalon(®) was administered at dose levels of 250, 500 and 1000mg/kg body weight/day for 28 and 90 days. Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) activities were monitored together with biochemistry parameters. The results showed that the mixture caused increases in the activities of ALT, AST and ALP, elevated concentrations of sodium, albumin and albumin/globulin ratio in males. In females, ALT activity, cholesterol and phosphate levels were increased. The changes generally were dose related and, in most cases, females exhibited lower susceptibility than males. The effects of a mixture are, in the most cases, different from the effects of the individual substances. The effects of bentazone were not prevalent which would be expected taking the composition of the mixture into account.

Evaluation of the partial renewal of in situ phytoplankton microcosms and application to the impact assessment of bentazon and dimethenamid

Microcosms, each consisting of 2L natural surface seawater maintained in 2.3-L glass bottles, were immersed at a depth of 6m. The renewal of 10% of microcosm volumes was carried out every other day. Phytoplankton-containing seawater was used for renewal (previously filtered through 25-, 50- or 200-μm cut-off). Phytoplankton community pigment analysis (by HPLC) and flow cytometry analysis were performed. After 13 days, data exhibited phytoplankton characteristics in microcosms in the same range as that of the natural surrounding sea water over the same period. Furthermore, in these microcosms, a negative correlation was observed between the filtration cut-off used for renewal water, and the total cell count. Herbicides were tested as commercial mixtures at 1, 10 and 100 μgL(-1) active substance. Both Frontier® (dimethenamid) and Basamais® (bentazon) induced significant modifications of the phytoplankton populations at every concentration tested. Such results suggest a possible disturbance in polluted coastal areas.

Toxicological effect of herbicides (diuron and bentazon) on snake venom and electric eel acetylcholinesterase

The toxicological effects of the active ingredients of the herbicides diuron and bentazon on the activity of acetylcholinesterase (AChE) of krait (Bungarus sindanus) venom and electric eel (Electrophorus electricus) were studied. The diuron and entazon caused non-competitive inhibition of AChE from both species. For the venom AChE, the calculated IC50 for diuron and bentazon were found to be 3.25 and 0.14 μM, while for eel AChE, the respective IC50 values were 3.6 and 0.135 μM. In comparison, bentazon was a more potent inhibitor than diuron of AChE from both species. The insecticide lindane did not have any inhibitory effect on AChE activity in either species, even when tested at high concentrations (200-800 μM).

Cyclothiazide induces seizure behavior in freely moving rats

We have previously demonstrated that cyclothiazide (CTZ) is a potent convulsant drug inducing robust epileptiform activity in hippocampal neurons both in vitro and in vivo. Here we further establish an animal model for CTZ-induced behavioral seizures in freely moving rats. Microinjection of CTZ into the left ventricle dose-dependently induced robust seizure behaviors within 3h after administration. At a dose of 0.75 μmol, CTZ induced Racine score IV-V seizure behaviors in 71% (n=14) of the rats were tested. In addition, CTZ also induced epileptiform EEG activity accompanying behavioral seizures. The convulsant action of CTZ on both behavior and EEG was blocked by pretreatment with clinical anticonvulsant drug diazepam (n=5). In conclusion, our results demonstrate that CTZ is capable of inducing behavioral seizures in intact animals. Since CTZ acts on both GABAergic and glutamatergic systems, this new animal epilepsy model will be useful for anticonvulsant drug testing and general epilepsy research.

Bentazon triggers the promotion of oxidative damage in the Portuguese ricefield cyanobacterium Anabaena cylindrica: response of the antioxidant system

Rice fields are frequently exposed to environmental contamination by herbicides and cyanobacteria, as primary producers of these aquatic ecosystems, are adversely affected. Anabaena cylindrica is a cyanobacterium with a significantly widespread occurrence in Portuguese rice fields. This strain was studied throughout 72 h in laboratory conditions for its stress responses to sublethal concentrations (0.75-2 mM) of bentazon, a selective postemergence herbicide recommended for integrated weed management in rice, with special reference to oxidative stress, role of proline and intracellular antioxidant enzymes in herbicide-induced free radicals detoxification. Activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione S-transferase (GST) increased in a time- and herbicide dose-response manner and were higher than those in the control samples after 72 h. A time- and concentration-dependent increase of malondialdehyde (MDA) levels and the enhanced cell membrane leakage following bentazon exposure are indicative of lipid peroxidation, free radicals formation, and oxidative damage, while increased amounts of SOD, CAT, APX, GST, and proline indicated their involvement in free radical scavenging mechanisms. The appreciable decline in the reduced glutathione (GSH) pool after 72 h at higher bentazon concentrations could be explained by the reduction of the NADPH-dependent glutathione reductase (GR) activity. The obtained results suggested that the alterations of antioxidant systems in A. cylindrica might be useful biomarkers of bentazon exposure. As the toxic mechanism of bentazon is a complex phenomenon, this study also adds relevant findings to explain the oxidative stress pathways of bentazon promoting oxidative stress in cyanobacteria.

Comparative toxicity of bentazon and molinate on growth, photosynthetic pigments, photosynthesis, and respiration of the Portuguese ricefield cyanobacterium Nostoc muscorum

Bentazon and molinate are selective herbicides recommended for integrated weed management in rice. Their toxicity on growth and some biochemical and physiological parameters of Nostoc muscorum, an abundant cyanobacterium in Portuguese rice fields, was evaluated under laboratory conditions during time- and concentration-dependent exposure for 72 h. Results showed that toxic concentrations (0.75-2 mM) of both herbicides have pleiotropic effects on the cyanobacterium. Molinate was more toxic than bentazon to growth, respiration, chlorophyll-a, carotenoids, and phycobiliproteins contents. Protein content was increased by both herbicides although the effect was particularly evident with higher concentrations of molinate (1.5-2 mM). The herbicides had contrasting effects on carbohydrates content: molinate increased this organic fraction whereas bentazon decreased it. Photosynthesis and respiration were inhibited by both herbicides.

In-situ microcosms, a tool for assessment of pesticide impacts on oyster spat (Crassostrea gigas)

Effects of the herbicide Basamaïs (bentazon) and the fungicide Opus (epoxiconazole) on oyster spat (Crassostrea gigas) were assessed using in-situ microcosms in a field experiment lasting 13 days. Six-week-old hatchery spat (mean size 1.1 mm), previously collected on PVC plates, was immersed in glass bottles filled with 200 mum filtered seawater. Bottles were maintained underwater at 6 m depth and their water content changed every other day. Growth, measured as shell area index increase, was 126 +/- 4% in the control bottles. While no growth differences were observed between control and individual pesticide treatments at 10 microg l(-1), oysters treated with a mix of 10 microg l(-1) Opus and 10 microg l(-1) Basamaïs showed a 50% growth reduction compared with the control (P < 0.0001), suggesting a synergistic effect of these contaminants. Laboratory controls in microcosms maintained in a water bath with filtered natural light, were not significantly different from in-situ microcosm controls in the field, for organic weight content or growth. This in-situ experiment in microcosms allowed us to conclude that: (1) oyster spat can achieve significant growth in bottles immersed in situ without supplementary food; (2) this microcosm system is reliable and easy to use for environmental toxicity tests with C. gigas spat; (3) such microcosm systems can also be run in a laboratory water bath instead of more technically difficult immersed field experiments; (4) the synergistic effect observed here, at a concentration simulating a peak agricultural runoff event, suggests that the impacts of pesticides could be a real threat for oysters in estuarine areas.

The use of physiological characteristics for comparison of organic compounds phytotoxicity

The influence of intact (FLT) and photomodified (phFLT) fluoranthene (0.05, 0.5 and 5 micromol l(-1)) and herbicide Basagran (5, 20, 35 and 50 nmol l(-1)) on the germination, growth of seedlings and photosynthetic processes in pea plants (Pisum sativum L., cv. Garde) was investigated. The germination was significantly inhibited already by the lowest concentration (0.05 micromol l(-1)) of FLT and phFLT, while Basagran caused inhibition only in higher concentrations (35 and 50 nmol l(-1)). The growth of roots was significantly inhibited by higher concentration 5 micromol l(-1) of both FLT and phFLT and the shoot of seedlings was significantly influenced only by photomodified form. The length of root and shoot was inhibited already by concentration 5 nmol l(-1) of Basagran. Organic compounds applied on chloroplasts suspension influenced primary photochemical processes of photosynthesis. In chlorophyll fluorescence parameters, the significant increase of F(0) values and the decrease of F(V)/F(M) and Phi(II) values by application of FLT (0.5 and 5 micromol l(-1)) and phFLT (0.05, 0.5 and 5 micromol l(-1)) was recorded. The maximum capacity of PSII (F(V)/F(M)) was influenced by the highest (50 nmol l(-1)) and the effective quantum yield of PSII (Phi(II)) already by the lowest (5 nmol l(-1)) concentration of Basagran. Hill reaction activity decreased and was significantly inhibited by higher concentration (0.5 and 5 micromol l(-1)) of FLT and phFLT and already by the lowest concentration (5 nmol l(-1)) of Basagran.

Investigation of cancer occurrences associated with an herbicide manufacturing facility

This study evaluated cancer incidence and mortality among 251 employees of a facility that synthesized a benzothiadiazin herbicide between 1979-1987. It was initiated in response to a perceived cancer cluster. Cancers were identified mainly by review of occupational medical records and personal interviews. Standardized incidence ratios (SIRs) were computed using comparison data provided by the Louisiana Tumor Registry. Overall mortality was less than expected and did not vary by job type or duration of assignment in the facility. Total cancer incidence was marginally elevated [SIR = 1.4; 95% Confidence Interval (CI): 0.9-1.9] and was highest among men assigned to the unit during 1979 [SIR = 2.1; 95% CI: 1.3-3.3]. Thirteen of 20 cancers among these men were either prostate (9) or digestive system (4) cancers. Increased medical examinations and cancer awareness may have contributed to the detection of cancers at earlier ages than would be seen in a general population. No specific workplace agents were identified to account for the findings although a workplace role cannot be ruled out.

Map-based cloning of a novel rice cytochrome P450 gene CYP81A6 that confers resistance to two different classes of herbicides

Development of hybrid rice has greatly contributed to increased yields during the past three decades. Two bentazon-lethal mutants 8077S and Norin8m are being utilized in developing new hybrid rice systems. When the male sterile lines are developed in such a mutant background, the problem of F1 seed contamination by self-seeds from the sterile lines can be solved by spraying bentazon at seedling stage. We first determined the sensitivity of the mutant plants to bentazon. Both mutants showed symptoms to bentazon starting from 100 mg/l, which was about 60-fold, lower than the sensitivity threshold of their wild-type controls. In addition, both mutants were sensitive to sulfonylurea-type herbicides. The locus for the mutant phenotype is bel for 8077S and bsl for Norin8m. Tests showed that the two loci are allelic to each other. The two genes were cloned by map-based cloning. Interestingly, both mutant alleles had a single-base deletion, which was confirmed by PCR-RFLP. The two loci are renamed bel ( a ) (for bel) and bel ( b ) (for bsl). The wild-type Bel gene encodes a novel cytochrome P450 monooxgenase, named CYP81A6. Analysis of the mutant protein sequence also revealed the reason for bel ( a ) being slightly tolerant than bel ( b ). Introduction of the wild-type Bel gene rescued the bentazon- and sulfonylurea-sensitive phenotype of bel ( a ) mutant. On the other hand, expression of antisense Bel in W6154S induced a mutant phenotype. Based on these results we conclude that the novel cytochrome P450 monooxygenase CYP81A6 encoded by Bel confers resistance to two different classes of herbicides.

Effects of a low dose of bentazon on spermatogenesis of mice exposed during foetal, postnatal and adult life

Bentazon is a herbicide used to control many broadleaf weeds and sedges. Its use has improved rice production in paddy fields in Northern Italy, but as a negative consequence it is found in groundwater, the major source of drinking water. To determine whether low doses of bentazon affect spermatogenesis, it was dissolved in water at the concentration of 30 microg/L. Bentazon was administered through drinking water to: (1) adult mice for 100 days and (2) mice exposed in utero, during lactation and for 100 days after birth. The histopathological analysis of testes of treated animals showed that the frequency of defective tubules was comparable to that found in control groups. The cell associations of the 12 stages of the seminiferous epithelium were correct as well as the architecture of the epithelium. The spermatocytes/spermatids ratio was the same as in controls. However, the frequency of stages VII, IX and XII of the cycle of the seminiferous epithelium of adult mice and of stages I, III and VII of mice exposed in utero and for 100 days after birth was different when compared to that of control mice. Sperm number and morphology were not affected by the treatment. The potential genotoxic effects were evaluated on spermatozoa (Comet assay), in pachytene spermatocytes (analysis of the synaptonemal complex) and in bone marrow cells (frequency of micronuclei). None of these analyses evidenced genotoxic effects of bentazon. Although our results show that the administration of a low dose of bentazon does not impair spermatogenesis, we found alterations of the frequency of some stages of the cycle of the seminiferous epithelium in both experimental groups.

Testosterone amplifies excitotoxic damage of cultured oligodendrocytes

An overactivation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptors has been implicated in the pathophysiology of oligodendrocyte damage in demyelinating disorders of the CNS. We decided to examine the effect of testosterone on excitotoxic death of oligodendrocytes because a gender difference exists in the incidence and disease course of multiple sclerosis. Short-term pure cultures of oligodendrocytes (4 days in vitro) were exposed to a brief pulse with kainate or AMPA + cyclothiazide for the induction of excitotoxicity. Exposure to testosterone enantate was slightly toxic per se and amplified both AMPA and kainate toxicity. Testosterone treatment induced all gene targets of p53, and amplified the induction of these genes induced by kainate. The effect of testosterone was mediated by the activation of androgen receptors and was resistant to the aromatase inhibitors, dl-aminoglutethimide and 4-hydroxyandrost-4-ene-3,17-dione. Testosterone treatment also potentiated the stimulation of 45Ca2+ influx induced by AMPA + cyclothiazide or kainate without changing the expression of the glutamate receptor (GluR) 1, -2/3, and -4 subunits of AMPA receptors or the GluR6/7 subunits of kainate receptors. We conclude that testosterone amplifies excitotoxic damage of oligodendrocytes acting at an early step of the death cascade triggered by AMPA/kainate receptors.

Evaluation of herbicide combinations for livid amaranth (Amaranthus blitum) control in tuberous begonia (Begonia x tuberhybrida)

In the past years livid amaranth (Amaranthus blitum) is observed increasingly in begonia production fields. Control of weeds in begonia is generally done by a combined application of the soil herbicides isoxaben + simazin followed 10 days later by application of the contact herbicide bentazone. This treatment usually controls the weed population sufficiently with exception of amaranth. In 2003 a field trial was conducted to evaluate control of livid amaranth in tuberous begonia with isoxaben, simazin. S-metolachloor, phenmedipham + desmedipham and bentazone. These herbicides were used as combinations of soil treatment and contact herbicides. The results suggest that a soil treatment of isoxaben + S-metolachloor significantly reduces livid amaranth compared to isoxaben + simazin, without a pronounced negative effect on tuber yield. Application of phenmedipham + desmedipham however did not improve control of livid amaranth compared to bentazone.

Evaluation of the genotoxicity of four herbicides in the wing spot test of Drosophila melanogaster using two different strains

In the present study, the herbicides bentazone, molinate, thiobencarb and trifluralin were evaluated for mutagenic and recombinagenic effects using the wing spot test of Drosophila melanogaster (somatic mutation and recombination test, SMART). Both standard (ST) and high-bioactivation (HB) fly crosses were used, the latter cross is characterised by a high sensitivity to promutagens and procarcinogens. Three-day-old larvae, transheterozygous for the multiple wing hairs (mwh, 3-0.3) and flare-3 (flr(3), 3-38.8) genes, were chronically fed with six different concentrations of each herbicide. Feeding ended with pupation of the surviving larvae and the genetic changes induced in somatic cells of the wing's imaginal discs lead to the formation of mutant clones on the wing blade. Point mutation, chromosome breakage and mitotic recombination produce single spots; while twin spots are produced only by mitotic recombination. Bentazone, usually considered as a non-mutagen, gave positive results in the wing spot test with the high-bioactivation cross. Molinate, about which information on mutagenic effects is inconclusive, gave positive responses in both the standard and the high-bioactivation crosses, while the other thiocarbamate, thiobencarb, gave positive results only in the standard cross and at the highest concentration tested (10 mM). Finally, trifluralin, one of the most widely studied herbicides for genotoxic effects, gave positive results in the wing spot test with both crosses. Apart from the interest of the results found in the genotoxic evaluation of the four selected herbicides, our results also contribute to extend the existing database on the Drosophila wing spot test, and corroborate the utility of the use of high-bioactivation strains for the genotoxic evaluation of xenobiotics.

Linking fluorescence induction curve and biomass in herbicide screening

A suite of dose-response bioassays with white mustard (Sinapis alba L) and sugar beet (Beta vulgaris L) in the greenhouse and with three herbicides was used to analyse how the fluorescence induction curves (Kautsky curves) were affected by the herbicides. Bentazone, a photosystem II (PSII) inhibitor, completely blocked the normal fluorescence decay after the P-step. In contrast, fluorescence decay was still obvious for flurochloridone, a PDS inhibitor, and glyphosate, an EPSP inhibitor, which indicated that PSII inhibition was incomplete. From the numerous parameters that can be derived from OJIP-steps of the Kautsky curve the relative changes at the J-step [Fvj = (Fm - Fj)/Fm] was selected to be a common response parameter for the herbicides and yielded consistent dose-response relationships. Four hours after treatment, the response Fvj on the doses of bentazone and flurochloridone could be measured. For glyphosate, the changes of the Kautsky curve could similarly be detected 4 h after treatment in sugar beet, but only after 24 hs in S alba. The best prediction of biomass in relation to Fvj was found for bentazone. The experiments were conducted between May and August 2002 and showed that the ambient temperature and solar radiation in the greenhouse could affect dose-response relationships. If the Kautsky curve parameters should be used to predict the outcome of herbicide screening experiments in the greenhouse, where ambient radiation and temperature can only partly be controlled, it is imperative that the chosen fluorescence parameters can be used to predict accurately the resulting biomass used in classical bioassays.

Bioaccumulation and toxicity of sediment associated herbicides (ioxynil, pendimethalin, and bentazone) in Lumbriculus variegatus (Oligochaeta) and Chironomus riparius (Insecta)

The benthic macroinvertebrates Lumbriculus variegatus and Chironomus riparius were used in toxicity and bioaccumulation tests to determine the toxic concentrations and accumulation potential of sediment associated herbicides. The tested chemicals were ioxynil, bentazone, and pendimethalin. The bioaccumulation tests with L. variegatus were performed in four different sediments, each having different characteristics. Water-only LC(50) tests were performed with both L. variegatus and C. riparius. A sublethal effect of model compounds in sediments was assessed by a C. riparius larvae growth-inhibition test. Of the model compounds, ioxynil appeared to be the most toxic, with LC(50) values 1.79 and 2.79 mgL(-1) for L. variegatus and C. riparius, respectively. The LC(50) water concentrations for bentazone were 79.11 and 62.31 mgL(-1) for L. variegatus and C. riparius, respectively. Similarly, ioxynil revealed the highest bioaccumulation potential in bioaccumulation tests. The most important characters affecting chemical fate in the sediment seemed to be the organic matter content and the particle size fraction. The sediments with low organic material and coarse particle size consistently showed high bioaccumulation potential and vice versa. In C. riparius growth tests bentazone had a statistically significant effect on larval growth at sediment concentrations of 1160 and 4650 mgkg(-1) (P<0.05). It is noteworthy that standard deviations tend to be greater at high chemical concentrations, which addresses the fact that part of the individuals started to suffer. Ioxynil had an effect on the larval growth in other test sediment at the highest concentration (15.46 mgkg(-1)dw), in which head capsule length correlated with larval weight, decreasing toward higher exposure concentrations. The current results show the importance of sediment organic matter as a binding site of xenobiotics.

Induction and inactivation of a cytochrome P450 confering herbicide resistance in wheat seedlings

Cytochrome P450-dependent enzymes from wheat catalyze the oxidation of endogenous compounds (lauric and oleic acids) and of several herbicides (diclofop, chlortoluron, bentazon). Treatment of wheat seedlings with the safener, naphthalic anhydride and with phenobarbital increases dramatically several P450-dependent enzyme activities including diclofop and lauric acid hydroxylation. The parallel induction of lauric acid (omega-1)-hydroxylase and diclofop hydroxylase activities suggests that both compounds proceeds from the same or very similar forms of P450. To test whether either one or multiple P450 forms are involved in these oxidations, we have designed selective irreversible inhibitors of lauric acid (omega-1)-hydroxylase. Results of in vivo and in vitro experiments with acetylenic analogs of lauric acid (10- and 11-dodecynoic acids) strongly suggest that a single P450 catalyzes both laurate and diclofop hydroxylation. Treatment of wheat seedlings with these acetylenes results in a strong inhibition of the in vivo metabolism of diclofop although oxidation of chlortoluron and bentazon are not affected. Our results suggest that at least three distinct P450 forms are involved in the detoxification process of the three herbicides. Interestingly, we also demonstrate that herbicides themselves are potent inducers of the amount of total P450 and laurate/diclofop hydroxylase activies. This increased capacity of wheat to detoxify the herbicide through the induction of P450 enzymes seems to be for a large extend the mechanism which confers a tolerance on various herbicides.

Nonnucleoside human cytomegalovirus inhibitors: synthesis and antiviral evaluation of (chlorophenylmethyl)benzothiadiazine dioxide derivatives

A second generation of benzothiadiazine dioxide (BTD) derivatives was synthesized employing benzylation reactions mainly. The chlorophenylmethyl BTD derivatives showed activity against human cytomegalovirus (HCMV) with IC(50) values ranging from 3 to 10 microM. Their 50% cytotoxic concentrations were often >200 microM to lung fibroblast HEL cell proliferation and between 20 and 35 microM for lymphocyte CME cell growth. When cytotoxicity for cell morphology was considered, the minimum cytotoxic concentration for the different BTD derivatives varied between 5 and 200 microM. Some of the anti-HCMV compounds also showed activity against HIV-1 and HIV-2. The chlorophenylmethyl derivative 21 was active against a variety of HCMV clinical isolates from patients with different clinical manifestations and fully maintained its activity against a ganciclovir-resistant HCMV strain. The dibenzyl BTD derivatives did not inhibit HCMV protease, and preliminary pharmacological experiments revealed that their anti-HCMV action stems from interference with an early stage of the viral replicative cycle.

The AMPA-receptor antagonist YM90K reduces AMPA receptor-mediated excitotoxicity in rat hippocampal cultures

The effects of YM90K on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated excitotoxicity were investigated using kainate, AMPA and cyclothiazide in rat hippocampal cultures. YM90K had neuroprotective actions against both kainate toxicity and cyclothiazide-enhanced AMPA toxicity. YM90K induced a parallel and rightward shift of both kainate and AMPA dose-response curves. The application of YM90K even 3 hr after the start of kainate exposure significantly reduced kainate toxicity. These results indicate that YM90K protects neurons against AMPA receptor-mediated toxicity at an agonist site on the AMPA receptor and that YM90K protects against AMPA receptor-mediated toxicity even if applied after neurotoxic insult.

7-Chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine S,S-dioxide: a partial modulator of AMPA receptor desensitization devoid of neurotoxicity

In cerebellar granule neurons of neonatal rats micromolar concentrations of 7-chloro-3-methyl-3,4-dihydro-2H-1,2, 4-benzothiadiazine S,S-dioxide (IDRA-21) and cyclothiazide, two negative modulators of the spontaneous agonist-dependent rapid desensitization of alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA)-gated ion channels, facilitate AMPA receptor function by increasing the content of free cytosolic Ca2+ as measured by single-cell fura-2 acetoxymethyl ester (Fura-2) Ca2+-dependent fluorescence and intracellular Na+ measured with the sodium-binding bezofuran isophthalate acetoxymethyl ester fluorescence indicator. IDRA-21 increases intracellular Na+ transient with a threshold (5 microM) that is approximately 10 times higher and has an intrinsic activity significantly lower than that of cyclothiazide. By virtue of its low intrinsic activity, IDRA-21 elicits a free cytosolic Ca2+ transient increase that is shorter lasting than that elicited by cyclothiazide even when the drug is left in contact with cultured granule cells for several minutes. Additionally, while dose dependently, 5-25 microM cyclothiazide in the presence of AMPA is highly neurotoxic, IDRA-21 (up to 100 microM) is devoid of neurotoxicity. The neurotoxicity elicited by cyclothiazide persists in the presence of dizocilpine (an antagonist of N-methyl-D-aspartate-selective glutamate receptors) but is blocked by 2,3-dihydroxy-6-nitrosulfamoylbenzo[f]quinoxaline (a competitive AMPA receptor antagonist) and the 1-(aminophenyl)-4-methyl-7, 8-methylendioxy-5H-2,3-benzodiazepine (GYKI 52466; a noncompetitive AMPA receptor antagonist). Since the doses of IDRA-21 that enhance cognitive processes in rats and monkeys are several orders of magnitude lower than those required to elicit marginal neurotoxicity in cultured neurons, it can be surmised that IDRA-21 is a potent cognition-enhancing drug virtually devoid of neurotoxic liability because it acts as a partial negative allosteric modulator of AMPA receptor desensitization.

Rapid desensitization determines the pharmacology of glutamate neurotoxicity

Glutamate (Glu), the major excitatory neurotransmitter in the nervous system, is toxic to neurons when it accumulates at high concentrations in the extracellular space. Even though Glu is a mixed agonist, capable of activating N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors, in many preparations Glu neurotoxicity is prevented by selective blockade of NMDA receptors. In cultures of hippocampal neurons, treatment with 500 microM Glu for 30 min killed more than 90% of the neurons. The simultaneous addition of the selective NMDA agonist methyl-10,11-dihydro-5-H-dibenzocyclo-hepten-5,10-imine (MK-801) reduced the cell loss to less than 30%. However, when Glu was combined with either diazoxide or cyclothiazide, two thiazides which dramatically diminish rapid Glu desensitization, MK-801 was no longer very protective and neuronal loss exceeded 80%. However, the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), in combination with MK-801, was able to prevent most Glu neurotoxicity in the presence of these thiazides. These experiments show that there are circumstances under which Glu neurotoxicity is produced by overactivation of non-NMDA receptors. Our observations offer a possible explanation for the recent finding that blockade of non-NMDA receptors is much more beneficial than NMDA receptor blockade in protecting the brain in some in vivo models of global ischemia.

Environmental behavior of bentazon herbicide

Bentazon is a postemergence herbicide used in early spring to early summer in many crops, usually at application rates of 1.0 kg a.i./ha. Its selectivity is based on the ability of the crop plants to metabolize bentazon quickly to 6-OH- and 8-OH-bentazon and conjugate these with sugars, while weeds do not, so that photosynthesis is disrupted and the weeds die. Also, there is a further degradation to small fragments, which subsequently are incorporated into natural plant products. Residues in the raw agricultural commodities range from 0.1 to approximately 1.0 mg/kg (straw and other "leftover" plant parts). In the upper soil layer, bentazon is quickly degraded, microbially and aerobically, via the intermediary and instable products 6-OH-, 8-OH-bentazon, and AIBA. These are immediately bound biotically and abiotically to the mostly nonbioavailable soil organic matter fraction. Additionally, a considerable part (24-50%) is mineralized to CO2. Half-lives in field soils ranged from 3 to 21 d with an average of 12 d. Abiotic degradation processes predominantly involve photolyses on plant and soil surfaces and in surface water. The physical-chemical properties and soil column laboratory studies with bentazon would seem, at first glance, to predict a leaching potential. However, several field lysimeter studies unambiguously proved that it does not leach under field situations. Annual averages in the leachates were always < 0.1 microgram/L, also after the second year. Reasons for the favorable field behavior, in contrast to the laboratory studies, are discussed. Reports on bentazon findings in groundwater and drinking water were classified as resulting predominantly from former filtrate along Rhine banks. Since 1988, the bentazon levels in the Rhine River ranged below or near 0.1 microgram/L. Very few isolated point-source contaminations, arising from accidents and other reasons, are marked by sporadic findings of concentrations > 1 microgram/L. Nonvalidated findings at various locations are reported that lie below or near the determination limit. In such situations, it is highly recommended to identify bentazon with a "full" MS-spectrum. The ecotoxicological effects of bentazon lead to "no classification necessary." The small octanol/water partition coefficient precludes bioaccumulation. Bentazon is rapidly excreted by warm-blooded animals without any uptake of residues in edible tissues. Based on its toxicological properties, bentazon was classified as noncarcinogenic ("Group E") by the EPA. The ADI is set at 0.1 mg/kg body weight/d. The WHO drinking water guideline value, based on the toxicological profile of bentazon, was recently raised to 30 micrograms/L.(ABSTRACT TRUNCATED AT 400 WORDS)

The immune response of sheep to subclinical chronic exposure to the herbicide Bentazon TP

A study of the effect of the Czechoslovakian herbicide BENTAZON TP on cells of the sheep immune system was carried out over a 3-mo period. A temporary decline in the number of T-lymphocytes in the peripheral blood was seen after 6 w of daily feeding of the herbicide. Dose-dependent statistically significant changes in the leucocyte migration index (p < 0.05) were seen at daily doses of 1/10 the LD50 (195 mg/kg body weight) and 1/20 the LD50 (97.5 mg/kg body weight) the 8th and 10th w of feeding, respectively. Significant changes of phagocytic activity and in the phagocytic index were not observed.

Lethality, hexobarbital narcosis and behavior in rats exposed to atrazine, bentazon or molinate

Previous findings from our laboratory suggested a possible interaction of atrazine, bentazon and molinate with other environmental and/or occupational poisons. The aim of this research was to obtain further toxicological information by using phenobarbital-induced rats and to characterize the effects of these herbicides on the hepatic microsomal metabolism of xenobiotics. Acute experiments have shown that the LD50 is augmented by the barbiturate pretreatment when atrazine is used, remains unchanged in the case of bentazon, but is lowered when molinate is given. Recrystallized atrazine, in the absence of the wetting compounds, elicits the same acute toxicity found when animals are challenged with a commercial preparation. No significant sex-related differences have been observed. In long-term treatment with these toxicants, atrazine shortened the hexobarbital narcosis, but no effect was observed after administration of either bentazon or molinate. Further studies on hexobarbital sleeping time demonstrated that females are more susceptible than males to the narcotic effect of this compound. The induction-like effect of atrazine exposure has been confirmed, mainly in young animals. At the end of the sleeping time, the actual serum concentration of hexobarbital is practically the same, and is not related to the length of the sleeping time. The absence of behavioral alterations in the open field tests exclude possible neurological effects of the triazine herbicide. In conclusion, these data demonstrate that atrazine by itself induces the hepatic pharmacometabolic system, while its metabolites result less toxic than the parent compound. On the contrary, metabolic transformations render the toxic effects of bentazon more severe.

UV-A induced DNA nicking activities of skin photosensitive drugs: phenothiazines, benzothiadiazines and afloqualone

Plasmid pBR 322 was subjected to UV-A irradiation in the presence of photosensitive drugs, i.e., phenothiazines [chlorpromazine hydrochloride (CPZ), promethazine hydrochloride (PMZ) and mequitazine (MQZ)], benzothiadiazines [penflutizide (PFZ), hydrochlorothiazide (HCT) and methyclothiazide (MCT)] and afloqualone (AQ). The distribution of the closed-circular and the open-circular form of the plasmid DNA was analyzed by means of neutral agarose gel electrophoresis. All the drugs used induced more or less DNA nicking to yield the open-circular form. The nicking activities of the phenothiazines were in the order: CPZ greater than PMZ greater than MQZ. CPZ elicited extensive degradation of the DNA by photosensitization. The nicking activities of the benzothiadiazines and AQ were much weaker than CPZ and PMZ.