Simultaneous determination of 15 phenylurea herbicides in rice and corn using HPLC with fluorescence detection combined with UV decomposition and post-column derivatization

A method was developed for the simultaneous determination of 15 phenylurea herbicides (fenuron, tebuthiuron, metoxuron, monuron, chlortoluron, fluometuron, isoproturon, diuron, monolinuron, metobromuron, buturon, siduron, linuron, chlorbromuron, and neburon) in rice and corn samples by HPLC with fluorescence detection combined with UV decomposition and post-column derivatization. After extraction with acetonitrile and evaporation, the herbicides were redissolved in n-hexane and purified on a Florisil solid-phase extraction column. HPLC separation was carried out on a C18 column with water-acetonitrile gradient elution. UV decomposition was carried out under a 254-nm UV lamp. The method was evaluated in terms of the limits of detection and quantification. The linearity was satisfactory, with a correlation coefficient of >0.9980. Precision and recovery studies were evaluated at three concentration levels for each matrix. Good precision was obtained, with relative standard deviation in the range 1.5-9.6% for spiked rice samples and 0.9-9.9% for spiked corn samples. Recovery (n=6) ranged between 75.3% and 104.3% for rice and between 75.0% and 105.1% for corn. The intra-day precision (n=5) for the 15 herbicides in rice and corn samples spiked at an intermediate level was between 1.5% and 7.1%, and the inter-day precision over 10 days (n=10) was between 6.4% and 15.6%.     

Multi-Residue Analysis of Herbicides in Soil with an UPLC-ESI-MS Method

A rapid and sensitive method was developed for the determination of 51 herbicides in soil by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry (UPLC–ESI–MS). Using acetonitrile effectively extracted 22 kinds of triazine and other basic herbicides, and using 90:10 v/v acetonitrile-phosphate buffer (pH = 7.5) effectively extracted another 29 herbicides. The extract has not cleaned up further. Chromatographic separation was achieved within 10 min using gradient elution with acetonitrile–water as a mobile phase for 22 triazine and phenylurea herbicides, and with 5 mM ammonium acetate containing 0.1% formic acid aqueous solution–acetonitrile as a mobile phase for another 29 herbicides. The response was linear over two orders of magnitude with correlation coefficients (r²) higher than 0.99. The limits of quantification for the herbicides varied from 0.2 to 20 µg kg^?1. The intra- and inter-day precisions (relative standard deviation, RSD) were 2.2–9.3% and 5.7–17.1%, respectively. The average recovery varied from 61.6 to 112% with the RSD of 1.6–11.3%. Analyzing 51 soil samples from 17 counties formed the basis of this method. Three herbicide residues were found in four counties. Atrazine residue in soil for 17 counties was found; its content was 0.4–9.8 μg kg^?1. Nicosulfuron residue in soil for two counties was found, with a high up to 133 or 1317 μg kg^?1. Propazine (0.3 and 1.34 μg kg^?1), atratone (2.14 and 3.93 μg kg^?1), and cynanazine (0.34 μg kg^?1) in soils for some counties were also found. The validated method can ensure the rapid multi-class, multi-residue analysis at low μg kg^?1 level for 47 herbicides in soil. The developed method provides an effective analytical basis for controlling herbicide dosage, investigating their distribution and degradation, and evaluating their hazards on the environment and human health.     

LC-ESI-MS/MS determination of phenylurea and triazine herbicides and their dealkylated degradation products in oysters

A method was developed for the determination of several phenylurea and triazine herbicides and their transformation products in oysters at the low microg/kg level. Pressurised liquid extraction (PLE) of lyophilisated samples had required successive SPE combined with a liquid/liquid extraction to provide relatively clean extracts for the determination in LC-MS/MS. This procedure was validated according to the 2002/657/EC analytical decision. Efficiency of the analytical method led to confirmatory CCalpha values ranging from 0.1 to 14 microg/kg with an R.S.D. value ranging from 14% to 66% and a recovery yield ranging from 32% to 46% for phenylureas and from 29% to 75% for triazines.     

Class-specific molecularly imprinted polymers for the selective extraction and determination of sulfonylurea herbicides in maize samples by high-performance liquid chromatography–tandem mass spectrometry

A novel method based on the molecularly imprinted solid-phase extraction (MISPE) procedure has been developed for the simultaneous determination of concentrations of sulfonylurea herbicides such as chlorsulfuron (CS), monosulfuron (MNS), and thifensulfuron methyl (TFM) in maize samples by liquid chromatography–tandem quadrupole mass spectrometry (LC–MS/MS). The molecularly imprinted polymer (MIP) for sulfonylurea herbicides was synthesized by precipitation polymerization using chlorsulfuron as the template molecule, 2-(diethylamino)ethyl methacrylate (DEAMA) as the functional monomer, and trimethylolpropane trimethacrylate (TRIM) as the cross-linker. The selectivities of the chlorsulfuron template and its analogs on the molecularly imprinted polymer were evaluated by high-performance liquid chromatography (HPLC). The extraction and purification procedures for the solid-phase extraction (SPE) cartridge with a molecularly imprinted polymer as the adsorbent for the selected sulfonylurea herbicides were then established. A molecularly imprinted solid-phase extraction method followed by high-performance liquid chromatography–tandem mass spectrometry for the determination of chlorsulfuron, monosulfuron, and thifensulfuron methyl was also established. The mean recoveries of these compounds in maize were in the range 75–110% and the limits of detection (LOD) of chlorsulfuron, monosulfuron, and thifensulfuron methyl were 0.02, 0.75, and 1.45 μg kg⁻¹, respectively. It was demonstrated that the MISPE–HPLC–MS/MS method could be applied to the determination of chlorsulfuron, monosulfuron, and thifensulfuron methyl in maize samples.     

不同浓度下四种除草剂对福寿螺和坑螺的生态毒理效应

以化学除草剂应用为前提的水稻免耕抛秧栽培技术是近年来推广的节本栽培新技术。为更好地评价除草剂的环境风险,为防治除草剂的负效应提供科学依据,采用室内静水模拟实验研究了4种免耕稻田除草剂丁草胺、苄嘧磺隆、丁苄混剂和氯酸钾的3种浓度梯度下对典型水生动物福寿螺、坑螺的影响。结果表明,各除草剂对水生动物的代谢都有不同程度的影响, 氯酸钾和苄嘧磺隆对2种水生动物的呼吸作用影响不大,而丁草胺和丁苄混剂对3种水生动物的呼吸作用的影响有显著的抑制作用,且呈现一定的剂量效应;在本实验染毒剂量下, 丁草胺和丁苄混剂对2种水生动物的存活率影响很大,而氯酸钾和苄嘧磺隆对其存活率影响较小。丁草胺和丁苄混剂处理对福寿螺的氮代谢影响远远大于氯酸钾和苄嘧磺隆处理,而从水体总氮和总磷含量的影响来看,4种除草剂对其影响都较大。总之,从4种除草剂对实验用螺存活率和主要代谢生理指标的综合影响大小来看,丁草胺>丁苄混剂>苄嘧磺隆>氯酸钾。     

Sensitivity of Echinochloa muricata and Echinochloa crus-galli to HPPD- and ALS-inhibiting herbicides in corn

Until recently Echinochloa muricata var. microstachya Wiegand (rough barnyardgrass), an alien species native to North America, was completely overlooked in Belgium due to its close morphological resemblance to Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass). E. muricata var. microstachya has gradually spread and is now locally naturalized and abundant in and along maize fields. One of the possible reasons for its expansion in maize fields, besides e.g. the lack of crop rotation, might be a lower sensitivity to postemergence herbicides acting against panicoid grasses, in particular 4-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting herbicides and acetolactate synthase (ALS) inhibiting herbicides. Dose-response pot experiments were conducted in the greenhouse to evaluate the effectiveness of four HPPD-inhibitor herbicides [topramezone (ARIETTA), mesotrione (CALLISTO), tembotrione (LAUDIS), sulcotrione (MIKADO) and the ALS-inhibitor herbicide nicosulfuron (KELVIN) for controlling local populations of E. crus-galli and E. muricata. Pots were planted with 25 seeds, thinned afterwards to 5 plants (one week after sowing) and irrigated by overhead sprinklers. Herbicides were applied at the 3-4 leaf stage (BBCH stage 13-14). Fresh biomass was harvested 28 d after treatment. In another dose-response pot experiment, the influence of leaf stage at time of herbicide application on efficacy of topramezone for (rough) barnyardgrass control was evaluated. Sensitivity to HPPD-inhibitor herbicides topramezone and sulcotrione was significantly lower for E. muricata populations than for E. crus-galli populations. However, nicosulfuron sensitivity of both species was similar. Compared to E. crus-galli, sensitivity of E. muricata to topramezone was more dependent on leaf stage. Due to the intragenus variability in sensitivity to HPPD-inhibitor herbicides, higher awareness is required for presence of E. muricata plants in maize fields in order to avoid insufficient "barnyardgrass" control.     

Circadian response of annual weeds in a natural setting to high and low application rates of four herbicides with different modes of actions

Four herbicides [glyphosate (GLYT), an amino acid synthesis inhibitor; glufosinate (GLUF), a glutamine synthetase inhibitor; fomesafen (FOME), a protoporphyrinogen oxidase inhibitor; and chlorimuron ethyl (CLIM), an acetolactate synthase inhibitor] were used to examine the influence of time of day of application on the control of a variety of annual broadleaf weeds in field studies conducted in Minnesota (five studies on GLYT and GLUF, three studies on FOME and CLIM). All herbicides were applied with an adjuvant at recommended high and low (half or quarter strength) rates every 3h between 06:00 and 24:00h local time. Visual ratings of percent weed control evaluated at 14d were analyzed by herbicide and application rate for each study and across studies for time-of-day effect by analysis of variance (ANOVA) and single cosinor. A circadian response to each herbicide was found, with greatest weed control observed between 09:00 and 18:00h. Increasing the herbicide application rate did not overcome the time-of-day effect (ANOVA: p≤0.008 for time-of-day effect for each herbicide and application rate). The least-squares fit of a 24h cosine was significant (p≤0.001) for each herbicide and application rate, with double amplitudes of 18-82% (units=% visual control) and estimated peaks (acrophases) near midday between 12:40 and 13:35h. Analysis of residuals obtained from multiple regression that included weed height, herbicide rate, temperature, and relative humidity as independent factors also found a significant time-effect by both ANOVA and cosinor for each herbicide and rate, with acrophases advancing significantly by 3 to 7h for GLYT and GLUF, but not for FOME or CLIM. These results suggest that the four herbicides, while belonging to different families with different modes of action, may reveal different peak times of efficacy when adjusting for environmental factors. Nonetheless, each displays similar circadian patterns when influenced by these factors under natural seasonal field conditions. The within-day rhythmic differences found in weed control are large enough to warrant consideration of the practical financial and environmental importance of the time-of-day that these and other herbicides are applied.     

Drawing-up of pesticide selectivity lists to beneficial arthropods for IPM programmes in potato

In order to promote IPM programmes in potato, the toxicity of 19 fungicides, 4 herbicides and 11 insecticides commonly used in this crop in Belgium was assessed on three beneficial arthropods. These species were representative of the most important aphid specific natural enemies encountered in potatoes: a parasitic wasp--Aphidius rhopalosiphi (De Stefani-Perez) (Hym., Aphidiidae), a ladybird--Adalia bipunctata (L.) (Col., Coccinellidae) and a hoverfly--Episyrphus balteatus (Dipt., Syrphidae). In a first time, pesticides were tested on glass plates on A. rhopalosiphi adults and A. bipunctata and E. balteatus larvae. For each insect, products inducing corrected mortality (Mc) lower than 30% were directly classified in a positive list for harmless products (green list). The other compounds were further tested on plants and listed in toxicity classes according to mortalities induced during this extended laboratory test: harmless (Mc < 30%), slightly harmful (30% < Mc < 60%), moderately harmful (60% < Mc < 80%) and harmful (Mc > 80). A chemical determination of pesticides residues was also performed for each experiment in order to determine the exposure of beneficial arthropods to pesticide residues and to validate the application of chemicals on tested substrates. On the basis of the results of acute toxicity tests, the period of each pesticide use according to normal agricultural practices and the abundance and importance of the three different groups of aphid natural enemies at different periods of the year, four pesticides lists were built up. Each list corresponded to a different period of pesticides application: Period I--from seedling to beginning of June (based on A. rhopalosiphi tests), Period II--beginning to end of June (based on A. rhopalosiphi tests), Period III beginning to end of July (based on E. balteatus and A. bipunctata tests) and Period IV--August to harvest (no exposure of beneficials). Results showed that herbicides were not toxic to the three species and can be used according to normal agricultural practices without restrictions. All fungicides can also be used without restrictions at recommended rates. Only the mixture Metalaxyl-M + Fluazinam was slightly harmful to A. bipunctata but had no effects on A. rhopalosiphi and E. balteatus. Results were more contrasted for insecticides and none of them was totally selective for all the 3 beneficial arthropods. Therefore, they can only be used with restrictions at periods II and III, according to the beneficial species that need to be protected.     

Effects of pesticides on cyanobacterium Plectonema boryanum and cyanophage LPP-1.

Cyanobacterium Plectonema boryanum IU 594 and cyanophage LPP-1 were used as indicator organisms in a bioassay of 16 pesticides. Experiments such as spot tests, disk assays, growth curves, and one-step growth experiments were used to examine the effects of pesticides on the host and virus. Also, experiments were done in which host or virus was incubated in pesticide solutions and then assayed for PFU. P. boryanum was inhibited by four herbicides: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 1,1-dimethyl-3-(alpha, alpha,alpha-trifluoro-m-tolyl)urea ( Fluometeron ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (Atrazine), 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine ( Ametryn ). One insecticide, 2-methyl-2-(methylthio)-propionaldehyde O-( methylcarbamoyl )oxime (Aldicarb), also inhibited the cyanobacterium. Two insecticides inactivated LPP-1, O,O-dimethyl phosphorodithioate of diethyl mercaptosuccinate (malathion) and Isotox . Isotox is a mixture of three pesticides: S-[2-( ethylsulfinyl )ethyl]O,O-dimethyl phosphorothioate ( Metasystox -R), 1-naphthyl methylcarbamate ( Sevin ) and 4,4'-dichloro-alpha- (trichloromethyl) benzhydrom ( Kelthane ). Two pesticide-resistant strains of P. boryanum were isolated against DCMU and Atrazine. These mutants showed resistance to all four herbicides, which indicates a relationship between these phototoxic chemicals. The results indicate that P. boryanum may be a useful indicator species for phototoxic agents in bioassay procedures.     

Effects of pesticides on cyanobacterium Plectonema boryanum and cyanophage LPP-1

Cyanobacterium Plectonema boryanum IU 594 and cyanophage LPP-1 were used as indicator organisms in a bioassay of 16 pesticides. Experiments such as spot tests, disk assays, growth curves, and one-step growth experiments were used to examine the effects of pesticides on the host and virus. Also, experiments were done in which host or virus was incubated in pesticide solutions and then assayed for PFU. P. boryanum was inhibited by four herbicides: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 1,1-dimethyl-3-(alpha, alpha,alpha-trifluoro-m-tolyl)urea ( Fluometeron ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (Atrazine), 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine ( Ametryn ). One insecticide, 2-methyl-2-(methylthio)-propionaldehyde O-( methylcarbamoyl )oxime (Aldicarb), also inhibited the cyanobacterium. Two insecticides inactivated LPP-1, O,O-dimethyl phosphorodithioate of diethyl mercaptosuccinate (malathion) and Isotox . Isotox is a mixture of three pesticides: S-[2-( ethylsulfinyl )ethyl]O,O-dimethyl phosphorothioate ( Metasystox -R), 1-naphthyl methylcarbamate ( Sevin ) and 4,4'-dichloro-alpha- (trichloromethyl) benzhydrom ( Kelthane ). Two pesticide-resistant strains of P. boryanum were isolated against DCMU and Atrazine. These mutants showed resistance to all four herbicides, which indicates a relationship between these phototoxic chemicals. The results indicate that P. boryanum may be a useful indicator species for phototoxic agents in bioassay procedures.     

A multi-biosensor based on immobilized Photosystem II on screen-printed electrodes for the detection of herbicides in river water

A multi-biosensor for detection of herbicides and pollutants was constructed using various photosynthetic preparations as biosensing elements. The photosynthetic thylakoid from Spinacia oleracea L., Senecio vulgaris and its mutant resistant to atrazine were immobilized with (BSA-GA) on the surface of screen-printed sensors composed of a graphite-working electrode and Ag/AgCl reference electrode deposited on a polymeric substrate. The biosensor was composed of four flow cells with independent illumination of 650 nm to activate electron transfer in Photosystem II. The principle of the detection was based on the fact that herbicides selectively block electron transport activity in a concentration-dependent manner and that the four PSII biomediators show differential recognition activity toward herbicides. Changes of the activity were registered amperometrically as rate of photoreduction of the artificial electron acceptor DQ. The setup resulted in a reusable herbicide multibiosensor with a good stability (half-life of 16.7 h for spinach thylakoids) and limit of detection of about 10(-8) M for herbicides recovered in spring in river.     

Mechanism of Sulfonylurea Herbicide Resistance in the Broadleaf Weed, Kochia scoparia

Selection of kochia (Kochia scoparia) biotypes resistant to the sulfonylurea herbicide chlorsulfuron has occurred through the continued use of this herbicide in monoculture cereal-growing areas in the United States. The apparent sulfonylurea resistance observed in kochia was confirmed in greenhouse tests. Fresh and dry weight accumulation in the resistant kochia was 2- to >350-fold higher in the presence of four sulfonylurea herbicides as compared to the susceptible biotype. Acetolactate synthase (ALS) activity isolated from sulfonylurea-resistant kochia was less sensitive to inhibition by three classes of ALS-inhibiting herbicides, sulfonylureas, imidazolinones, and sulfonanilides. The decrease in ALS sensitivity to inhibition (as measured by the ratio of resistant I₅₀ to susceptible I₅₀) was 5- to 28-fold, 2- to 6-fold, and 20-fold for sulfonylurea herbicides, imidazolinone herbicides, and a sulfonanilide herbicide, respectively. No differences were observed in the ALS-specific activities or the rates of [¹⁴C]chlorsulfuron uptake, translocation, and metabolism between susceptible and resistant kochia biotypes. The K_m values for pyruvate using ALS from susceptible and resistant kochia were 2.13 and 1.74 mm, respectively. Based on these results, the mechanism of sulfonylurea resistance in this kochia biotype is due solely to a less sulfonylurea-sensitive ALS enzyme.     

Degradation of Chlorbromuron and Related Compounds by the Fungus Rhizoctonia solani

The ability of the soil fungus Rhizoctonia solani to degrade phenyl-substituted urea herbicides was investigated. The fungus was able to transform chlorbromuron [3-(3-chloro-4-bromophenyl)-1-methyl-1-methoxyurea] to the demethylated product [3-(3-chloro-4-bromophenyl)-1-methoxyurea], which was isolated and identified. Evidence was obtained that further degradation of chlorbromuron occurred. Several other phenylurea compounds (chloroxuron, diuron, fenuron, fluometuron, linuron, metobromuron, neburon, and siduron) were also metabolized by the fungus, indicating that R. solani may possess a generalized ability to attack this group of herbicides.     

Covalent binding of chloroacetamide herbicides to the active site cysteine of plant type III polyketide synthases

Chloroacetamide herbicides inhibit very-long-chain fatty acid elongase, and it has been suggested that covalent binding to the active site cysteine of the condensing enzyme is responsible [Pest Manage Sci 56 (2000), 497], but direct evidence was not available. The proposal implied that other condensing enzymes might also be targets, and therefore we have investigated four purified recombinant type III plant polyketide synthases. Chalcone synthase (CHS) revealed a high sensitivity to the chloroacetamide metazachlor, with 50% inhibition after a 10 min pre-incubation with 1-2 molecules per enzyme subunit, and the inactivation was irreversible. Stilbene synthase (STS) inactivation required 20-fold higher amounts, and 4-coumaroyltriacetic acid synthase and pyrone synthase revealed no response at the highest metazachlor concentrations tested. A similar spectrum of differential responses was detected with other herbicides that also inhibit fatty acid elongase (metolachlor and cafenstrole). The data indicate that type III polyketide synthases are potential targets of these herbicides, but each combination has to be investigated individually. The interaction of metazachlor with CHS was investigated by mass spectrometric peptide mapping, after incubation of the enzymes with the herbicides followed by tryptic digestion. A characteristic mass shift and MS/MS sequencing of the respective peptide showed that metazachlor was covalently bound to the cysteine of the active site, and the same was found with STS. This is the first direct evidence that the active site cysteine in condensing enzymes is the primary common target of these herbicides.     

High affinity ScFvs from a single rabbit immunized with multiple haptens

We report the generation of single-chain Fv (scFv) fragments with high affinities against four different hapten molecules from a single immunised rabbit. The rabbit was immunised with a mixture of protein conjugates of four different haptens, namely the herbicide mecoprop and derivatives of the herbicides atrazine, simazine, and isoproturon. An scFv phage display library was constructed, and several scFvs with high affinity against each hapten were isolated. For each hapten, a single binder was selected by k(off) ranking and used for affinity determination. The affinities were in sub-nanomolar range and the lowest K(d) value obtained was 6.75 x 10(-10) M. An unusual feature of one of the anti-isoproturon scFvs was its ability to retain binding activity at pH1.7. The utility and potential of using a single animal and immunisation with multiple antigens for the production of multiple, specific, high affinity scFvs by phage display is discussed.     

Competitive interaction of three peroxidizing herbicides with the binding of [3H]acifluorfen to corn etioplast membranes

The specific binding of the herbicide acifluorfen 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid to corn etioplast membranes is competitively inhibited by protoporphyrinogen IX, the substrate of protoporphyrinogen oxidase. Three other peroxidizing molecules, oxadiazon [5-terbutyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol -2-one], LS 82556 [(S)3-N-(methylbenzyl)carbamoyl-5-propionyl-2,6-lutidine], and M&B 39279 [5-amino-4-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazol], also compete with acifluorfen for its binding site. The four herbicides thus bind to the same site, or to closely located sites, on the enzyme protoporphyrinogen oxidase.     

Determination of nitrofuran metabolites in milk by liquid chromatography-electrospray ionization tandem mass spectrometry

An LC-ESI-MS-MS method for the analysis of metabolites of four nitrofurans (furazolidone, furaltadone, nitrofurazone and nitrofurantoin) in raw milk has been developed. The samples were achieved by hydrolysis of the protein-bound drug metabolites, derivatization with 2-nitrobenzaldehyd (2-NBA) and clean-up extraction liquid-liquid with ethyl acetate. LC separation was achieved by using a Phenomenex Luna C-18 column. The mass spectrometer operated in multiple reaction monitoring mode (MRM) with positive electro-spray interface (ESI). The method validation was done according to the criteria laid down in Commission Decision No. 2002/657 EC. The validation includes the determination of linearity, repeatability, within-laboratory reproducibility, accuracy, decision limit (CCalpha) and detection capability (CCbeta). The calibration curves were linear, with typical (R(2)) values higher than 0.991. The coefficient of variation (CV, %) was lower than 9.3% and the accuracy (RE, %) ranged from -9.0% to 7.0%. CV within-laboratory reproducibility was lower than 13%. The limits of decision (CCalpha) and detection capability (CCbeta) were 0.12-0.29 microg/kg and 0.15-0.37 microg/kg, thus below the minimum required performance limit (MRPL) set at 1 microg/kg by the UE. This validated method was successfully applied for the determination of nitrofuran metabolites in a large number of milk samples.     

Protoporphyrinogen oxidase as a molecular target for diphenyl ether herbicides.

Diphenyl ether herbicides induce an accumulation of protoporphyrin IX in plant tissues. By analogy to human porphyria, the accumulation could be attributed to decreased (Mg or Fe)-chelatase or protoporphyrinogen oxidase activities. Possible effects of acifluorfen-methyl on these enzymes were investigated in isolated corn (maize, Zea mays) etioplasts, potato (Solanum tuberosum) and mouse mitochondria, and yeast mitochondrial membranes. Acifluorfen-methyl was strongly inhibitory to protoporphyrinogen oxidase activities whatever their origins [concn. causing 50% inhibition (IC50) = 4 nM for the corn etioplast enzyme]. By contrast, it was roughly 100,000 times less active on (Mg or Fe)-chelatase activities (IC50 = 80-100 microM). Our results lead us to propose protoporphyrinogen oxidase as a cellular target for diphenyl ether herbicides.     

Quantitative structure—activity relationship study on the inhibitory effect of some herbicides on the growth of soil micro-organisms

The effect of eight herbicides on the growth of six soil bacteria and three microscopic fungi, and on the amylase, cellulase and dehydrogenase activity in a Hungarian soil was determined. Herbicide decomposition rate in the soil was also assessed. Qualitative structure-activity relationship (principal component analysis, spectral mapping technique and stepwise regression) analysis showed that the overwhelming majority (about 80%) of the effect of herbicides can be explained by one background variable showing the similarity between their mode of action. The two-dimensional non-linear map of principal component loadings and spectral map characteristics suggested that the number of substituents may be important in the determination of the toxic effects. The inhibition of bacterial growth, inhibition of fungal growth, and effects on enzyme activity and decomposition rate all formed different clusters on the maps indicating that herbicides influence these processes differently. Of the nine physicochemical parameters considered, only the electron withdrawing capacity of substituents significantly influenced the biological activity of herbicides, suggesting that electrostatic interactions between the herbicide molecules and micro-organisms is important.     

Response of multiple herbicide resistant strain of diazotrophic cyanobacterium, Anabaena variabilis, exposed to atrazine and DCMU

Effect of two photosynthetic inhibitor herbicides, atrazine (both purified and formulated) and [3-(3,4-dichlorophenyl)-1,1-dimethyl urea] (DCMU), on the growth, macromolecular contents, heterocyst frequency, photosynthetic O2 evolution and dark O2 uptake of wild type and multiple herbicide resistant (MHR) strain of diazotrophic cyanobacterium A. variabilis was studied. Cyanobacterial strains showed gradual inhibition in growth with increasing dosage of herbicides. Both wild type and MHR strain tolerated < 6.0 mg L(-1) of atrazine (purified), < 2.0 mg L(-1) of atrazine (formulated) and < 0.4 mg L(-1) of DCMU indicating similar level of herbicide tolerance. Atrazine (pure) (8.0 mg L(-1)) and 4.0 mg L(-1) of atrazine (formulated) were growth inhibitory concentrations (lethal) for both wild type and MHR strain indicating formulated atrazine was more toxic than the purified form. Comparatively lower concentrations of DCMU were found to be lethal for wild type and MHR strain, respectively. Thus, between the two herbicides tested DCMU was more growth toxic than atrazine. At sublethal dosages of herbicides, photosynthetic O2 evolution showed highest inhibition followed by chlorophyll a, phycobhiliproteins and heterocyst differentiation as compared to carotenoid, protein and respiratory O2 uptake.