Relative sensitivity of duckweed Lemna minor and six algae to seven herbicides

We investigated the relative sensitivity of duckweed Lemna minor and six species of algae to seven herbicides, using an efficient high-throughput microplate-based toxicity assay. First, we assessed the sensitivity of L. minor to the seven herbicides, and then we compared its sensitivity to that of previously published data for six algal species based on EC₅₀ values. For five herbicides, the most sensitive species differed: L. minor was most sensitive to cyclosulfamuron: Raphidocelis subcapitata was most sensitive to pretilachlor and esprocarb: Desmodesmus subspicatus was most sensitive to pyraclonil; and Navicula pelliculosa was most sensitive to pyrazoxyfen. Simetryn was evenly toxic to all species, whereas 2,4-D was evenly less toxic, with only small differences in species sensitivity. These results suggested that a single algal species cannot represent the sensitivity of the primary producer assemblage to a given herbicide. Therefore, to assess the ecological effects of herbicides, aquatic plant and multispecies algal toxicity data sets are essential.     

The toxicity of herbicides to non-target aquatic plants and algae: assessment of predictive factors and hazard

Widely used herbicides sometimes inadvertently contaminate surface waters. In this study we evaluate the toxicity of herbicides to aquatic plants and algae and relate it to environmental herbicide concentrations and exposure scenarios, herbicide formulation and mode of action. This was done experimentally for ten herbicides, using the aquatic macrophyte Lemna minor L. and the green alga Pseudokirchneriella subcapitata (Korshikov) Hindak, supplemented with a database study comprising algae toxicity data for 146 herbicides. The laboratory study showed that herbicide formulations in general did not enhance herbicide efficacy in the aquatic environment. The Roundup formulation of glyphosate proved to be the only exception, decreasing the EC(50) of the technical product for both L. minor and P. subcapitata approximately fourfold. Comparison of the sensitivity of L. minor and P. subcapitata revealed up to 1000-fold higher sensitivity of L. minor for the herbicides categorized as weak acids (pK(a) < 5), emphasizing the importance of higher plants in hazard assessment. Database analyses showed that no herbicide group, categorized by site of action, was significantly more toxic than another. Synthetic auxins were the exception as they are virtually non-toxic to unicellular algae. There was no strong correlation between toxicity to algae and K(ow) of the herbicides, not even within groups having the same site of action. Evaluating all data, few herbicides were toxic at concentrations below 1 microg l(-1), which is the 99.9th percentile of the herbicide concentrations measured in the Danish surveillance programme. Joint action of several herbicides cannot however be excluded.     

Mode of action studies with mefenacet

The unicellular green alga Chlamydomonas reinhardtii was used as a model organism in studies of the mode of action of the oxyacetamide herbicide mefenacet. An algal strain with a decreased sensitivity towards mefenacet was obtained by successively increasing the herbicide concentration in the culture medium from 10 to 50 μM over 9 weeks. Similarly, a second strain was adapted to 10 μM metazachlor and a third one to 20 μM metolachlor. The resistance patterns of these three strains were studied with a selection of herbicides representing different modes of action. In the mefenacet- and metolachlor-adapted strains, clear cross-resistance was only obtained between the oxyacetamide mefenacet and the chloroacetanilides alachlor, butachlor, metazachlor and metolachlor. The resistance factors (I₅₀ in resistant/I₅₀ in sensitive algae) were between 4 and 50. Little or no resistance was obtained when herbicides with other modes of action were studied (resistance factors between 0.5 and 4). The situation was less clear in the metazachlor-adapted strain, but here also strong cross-resistance was seen with other chloroacetanilides and mefenacet (resistance factors between 25 and 40). This strain was, however, significantly cross-resistant to some herbicides with other modes of action. Investigations of the possible resistance mechanism in the mefenacet-adapted strain have shown that neither uptake nor metabolism can explain the observed resistance behaviour. The lipid composition and the pattern of soluble amino acids were unchanged. It is concluded that oxyacetamides and chloroacetanilides have the same site of herbicidal action.     

Communication to the Editor Degradation of Bromoxynil,Ioxynil, Dichlobenil and their Mixtures by Agrobacterium radiobacter 8/4

Degradation of three benzonitrile herbicides, bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), ioxynil (3,5-diiodo-4-hydroxybenzonitrile), dichlobenil (2,6-dichlorobenzonitrile), and their mixtures by the soil micro-organism Agrobacterium radiobacter 8/4 was studied in batch cultures. Bromoxynil was found to be most rapidly degraded, while dichlobenil had the lowest toxicity to our strain. All transformations of studied benzonitriles were performed by the nitrile hydratase which has been shown to act on a broad range of substituted aromatic nitriles. © 1997 SCI.     

A comparison of crop and non-crop plants as sensitive indicator species for regulatory testing

The effectiveness of regulatory non-target plant testing using crop species to predict the phytotoxicicity of herbicides to non-crop species was evaluated for eleven herbicides. These herbicides were representative of eight chemical classes and six modes of action. Data for non-crop plants from pre-emergence and post-emergence efficacy screening studies were compared with those for the most sensitive crop species defined by regulatory tests conducted to meet US EPA requirements. Testing under pre-emergence conditions for ten compounds indicated that for five of the compounds (K-815910, trifluralin, pyridyloxy A, pyridyloxy B and cyanazine), the most sensitive crop species was more sensitive than all the non-crop species evaluated. For metsulfuron-methyl, chlorimuron-ethyl, hexazinone and bromacil, only one of the non-crop species evaluated was more sensitive than the most sensitive crop species from regulatory tests. Data for the tenth compound, chloroacetamide, showed that four of 32 non-crop species tested in efficacy screens had at least one rate at which greater visual effects were observed than were observed for the most sensitive crop response in a regulatory test. The results of post-emergence exposure comparisons for five of the compounds (pyridyloxy A, cloransulam-methyl, chlorimuron-ethyl, cyanazine and hexazinone) indicated that the most sensitive crop species were more sensitive than all the non-crop species evaluated. Data for pyridyloxy B, metsulfuron-methyl and bromacil indicated that only one of the non-crop species evaluated was more sensitive than the most sensitive crop species. For trifluralin, three of the eight non-crop species were more sensitive than the most sensitive crop species. Data for K-815910 indicated that four of the fourteen non-crop species tested were marginally more sensitive than the most sensitive crop, but were within the same range of sensitivity. These results indicate that the current regulatory test batteries and methods using crop species effectively provide suitable sensitive indicator plants for the eleven diverse herbicides evaluated. This comparison indicates that crop species sensitivity to test substances is likely to be representative of non-crop herbaceous species response, regardless of chemical class, mode of action and magnitude or route of exposure.     

THE USE OF THREE SIMPLE,RAPID BIOASSAYS ON FORTY-TWO HERBICIDES*

Three rapid bioassays were tested on forty-two herbicides having several different modes of action. A 50% or greater inhibition of growth was found at 1 ppm with thirty-one herbicides in one or more of the bioassays. Of the remaining eleven herbicides, seven were detected at 10 ppm, two at 20 ppm and two at 30 ppm. The techniques used were a Chlorella bioassay, a root bioassay with sorghum, oat and cucumber and a shoot bioassay with sorghum and oat. The duration of the bioassays was 1, 2 and 4 days respectively. As a general rule, the Chlorella bioassay was especially sensitive to photosynthetic and respiratory inhibitors but not sensitive to herbicides with other modes of action, whereas the root and/or shoot bioassays were sensitive to most of the herbicides except the photosynthetic inhibitors. The use of the three bioassays simultaneously is suggested as a possible method for primary screening of herbicides.     

Localization of metabolic sites of action of herbicides

Time- and concentration-course studies were conducted to determine the effect of thirteen herbicides on photosynthesis, respiration, RNA synthesis, protein synthesis, and lipid synthesis using isolated single leaf cells. Each herbicide was from a different chemical class. Appropriate ¹⁴C-substrates and product purification procedures were used for each process prior to liquid scintillation counting. The most sensitive metabolic site of inhibition was photosynthesis for atrazine, bromacil, dichlobenil, monuron, and paraquat; RNA synthesis for dalapon and dinoseb; protein synthesis for chlorpropham; and lipid synthesis for CDAA, chloramben, 2,4-D, EPTC, and trifluralin. However, with several herbicides, one or more process was almost as sensitive as the one mentioned above. All herbicides inhibited more than one process, and the most sensitive site of inhibition may not be the same process that was inhibited the greatest at the maximum concentration and maximum exposure time used. Therefore, a concept of metabolic sites of action, rather than a primary site of action, appears to be more meaningful for herbicides.     

Studies on the effects of herbicides on soil nitrification,II

The effects of selected herbicides have been studied on the following parameters of soil nitrification processes: the rates of nitrate and nitrite formation from ammonia in freshly perfused soils and in soils previously saturated with nitrifying organisms in an improved perfusion apparatus; the rates of oxygen consumption and of oxidation of ammonia and nitrite in washed cell suspensions of Nitrosomonas europaea and Nitrobacter winogradskii, respectively; the rates of growth of those two organisms in newly established cultures; the rates of oxygen uptake by soil enriched in nitrifying organisms; the rates of proliferation of nitrifying populations in freshly perfused soil. ID50 values were computed for all parameters and herbicides studied. On average, the most sensitive parameters were the metabolism and growth of the two organisms in pure culture, while the least sensitive were the corresponding measures in the soil environment. Similarly, herbicides fell into four distinct groups. The most toxic were the formulated octanoates of bromoxynil and ioxynil (NPH1320 and Totril, respectively); next in order of toxicity were chlorbufam, phenmedipham, formulated oxadiazon, formulated legurame, ioxynil, formulated trifluralin, and bromoxynil; low toxicity was shown by terbacil, dicamba, and tricamba, whereas asulam and the related experimental herbicide MB9555 showed activity on some parameters at the very highest concentrations only. Comparisons of soil with pure-culture parameters showed that the relative toxicities of herbicides to Nitrosomonas in culture bore little relationship to those in soil. The inhibitions of Nitrobacter proliferations in soil on the other hand were correlated with the inhibitions of growth and metabolism in pure culture. Within these overall effects, individual herbicides showed marked differential actions on various parameters. Thus, the formulated octanoates of bromoxynil and ioxynil were extremely toxic to the growth of nitrifying organisms in culture, an action probably due to an unknown formulation component. Relative to other herbicides, bromoxynil and ioxynil were more effective on nitrification processes in the soil environment. Both in culture and in the soil, Nitrobacter is more sensitive than Nitrosomonas to these four herbicides. Legurame and oxadiazon are relatively more toxic to Nitrosomonas in culture, but this differential action is not demonstrable in the soil. Dicamba, tricamba, trifluralin, and chlorbufam are more toxic to Nitrobacter than to Nitrosomonas in the soil environment. Formulated trifluralin seems to exert a stimulating action on the growth of nitrifying organisms, but only in the soil; suppression of antagonistic organisms is suggested as a possible cause. Extrapolation of these results to the field situation suggests that the only herbicide which might cause small inhibitions of nitrification at field rates is terbacil, which is disproportionately toxic at low concentrations. At rates somewhat in excess of normal, the formulated octanoates of bromoxynil and ioxynil and possibly dicamba and oxadiazon could also cause small inhibitions.     

Effects of the herbicides benzoylpropethyl and flampropisopropyl on rat liver mitochondria: An alteration in membrane fluidity?

The action of the herbicides benzoylpropethyl and flampropisopropyl, and the corresponding unesterified acids was studied in rat liver mitochondria. The herbicides were found to (a) inhibit the mitochondrial electron transfer in complex III or at the level of ubiquinone (I₅₀ of 4 nmol mg protein^?1 for flampropisopropyl and 18 for benzoylpropethyl with succinate as a substrate); (b) have an additional (however less sensitive) site of inhibition near succinate dehydrogenase; and (c) interfere with energy transfer. Sensitivity was increased 2- (benzoylpropethyl) and 3.5-fold (flampropisopropyl) as the rats age increased from 12–13 weeks to 23–26 weeks. The free acids were far less effective. Since the herbicides benzoylpropethyl and flampropisopropyl are readily hydrolyzed by animals and since the free acids are less effective than the herbicides, it explains why these potentially harmful compounds have a low acute toxicity. Swelling studies in isoosmotic salts suggested that the two herbicides decrease membrane fluidity, an action which was assumed to be responsible for the electron transfer inhibition and, via inhibition of phosphate transport, the interference with energy transfer.     

360种农药制剂对斑马鱼的急性毒性研究

采用半静态法测定了360种常用农药制剂(包括135种有效成分)对斑马鱼的急性毒性,其中杀虫剂、杀菌剂、除草剂、植物生长调节剂等不同类别农药所占的比例分别为67.5%、16.1%、13.6%、2.8%。结果表明:49%的制剂对斑马鱼表现高毒或剧毒,涉及25种农药有效成分,主要为杀虫剂,杀菌剂和除草剂的毒性相对较低,微生物农药对斑马鱼的急性毒性较低,而部分植物源农药的急性毒性较高;相同有效成分的不同制剂之间由于有效成分含量、剂型及加工工艺的不同,会出现毒性存在差异的情况。     

酰胺类除草剂的研究和应用进展

酰胺类除草剂是目前世界使用最广泛的除草剂之一,适用作物种类和施用面积均居各类除草剂前列,其具有高效、低毒、经济等优点,因此备受人们的关注,本文系统的综述了此类除草剂的种类,作用机理及应用情况。     

Effects of various classes of herbicides on four species of algae

Chlorella pyrenoidosa, Chlorococcum sp., Lyngbya sp., and Anabaena variabilis were cultured in Bold's basal medium. They were treated with 0.1, 1.0, and 10 μM concentrations of 2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide (alachlor), 2-chloro-4-(ethylamino)-6-(tert-butyl-amino)-s-triazine (terbuthylazine), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 1,1-dimethyl-3-(α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine) (profluralin), 2, 4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Growth of all algal species tested was markedly reduced by the triazines. Alachlor, dinoseb, and fluometuron inhibited growth of some algae at higher concentrations while 2,4-D and profluralin did not inhibit growth at the concentrations tested. Photosynthesis was greatly inhibited by the triazines, even at the 0.1 μM concentration. Fluometuron was very toxic to the blue-green algae but had less effect on the green algae tested. Lyngbya was most susceptible to photosynthesis reduction by the herbicides. The concentrations of herbicides tested had little effect on respiration of the algae species. It appears that effects on algal growth were due primarily to inhibition of photosynthesis rather than to other metabolic processes.     

Rice paddy field herbicides and their effects on the environment and ecosystems

Paddy herbicides contribute to the reduction of weeding labor, however, there are concerns about their effects on the environment and ecosystems. The environmental burden of applied herbicides is heaviest in water systems such as irrigation channels and rivers. Herbicides are generally detected in rivers in concentrations in levels of ng/L for only 2 to 3 months after use. It is to be regretted that herbicides have been implicated in accidents involving fish, the impeded propagation of algae and other non‐target organisms. Therefore, it is necessary to assess the ecological risk, and the Environment Agency in Japan compiled an interim report on how pesticides' ecological effects should be assessed. Pesticides are separately examined for their toxicity (hazard assessment) and exposure (exposure analysis). However, to the environment and ecosystems there are many problems in assessing the ecological risk of pesticides, such as selection of geographic locations, methodology of assessing the impacts on ecosystems and monitoring the effect of pesticides. New herbicides are expected to have high selectivity and low toxicity. Decreasing herbicide toxicity requires high selectivity to distinguish target weeds from crops and non‐target organisms. New groups of compounds will be developed based on a biorational approach. Moreover, it is necessary to develop an environmentally low‐impact application method such as the use of granular types and sustained‐release formulation among others. It is important that integrated methods be used to control paddy weeds by combining ecological/agronomical, mechanical and biological control methods, instead of relying solely on chemical herbicides.     

Rapid chlorophyll fluorescence technique for the study of penetration of photosynthetically active herbicides into leaf tissue

A rapid and sensitive technique, involving analysis of chlorophyll a fluorescence induction kinetics, for the study of the penetration of photosynthetically active herbicides into leaves is described. A range of chlorophyll fluorescence parameters are examined for wheat leaves treated with diuron in order to determine the most appropriate parameter to use in herbicide penetration studies. The usefulness of the technique is demonstrated by examination of the effect of a range of commercially available additives on diuron penetration in wheat leaves.     

Corn poppy (Papaver rhoeas) cross-resistance to ALS-inhibiting herbicides

BACKGROUND: Papaver rhoeas (L.) has evolved resistance to tribenuron in winter wheat fields in northern Greece owing to multiple Pro₁₉₇ substitutions. Therefore, the cross‐resistance pattern to other sulfonylurea and non‐sulfonylurea ALS‐inhibiting herbicides of the tribenuron resistant (R) and susceptible (S) corn poppy populations was studied by using whole‐plant trials and in vitro ALS catalytic activity assays. RESULTS: The whole‐plant trials revealed that tribenuron R populations were also cross‐resistant to sulfonylureas mesosulfuron + iodosulfuron, chlorsulfuron and triasulfuron. The whole‐plant resistance factors (RFs) calculated for pyrithiobac, imazamox and florasulam ranged from 12.4 to > 88, from 1.5 to 28.3 and from 5.6 to 25.4, respectively, and were lower than the respective tribenuron RF values (137 to > 2400). The ALS activity assay showed higher resistance of the ALS enzyme to sulfonylurea herbicides (tribenuron > chlorsulfuron) and lower resistance to non‐sulfonylurea ALS‐inhibiting herbicides (pyrithiobac > florasulam ≈ imazamox). CONCLUSION: These findings indicate that Pro₁₉₇ substitution by Ala, Ser, Arg or Thr in corn poppy results in a less sensitive ALS enzyme to sulfonylurea herbicides than to other ALS‐inhibiting herbicides. The continued use of sulfonylurea herbicides led to cross‐resistance to all ALS‐inhibiting herbicides, making their use impossible in corn poppy resistance management programmes. Copyright © 2011 Society of Chemical Industry     

10种除草剂对斜生栅藻的生长抑制活性研究

本文采用吸光度法测定了10个除草剂对斜生栅藻的生长抑制活性,其中包括3个原药和7个制剂产品,涉及12种有效成分。结果表明有5个药剂对斜生栅藻表现高毒,2个药剂为中等毒性,仅3个药剂为低毒。总体上磺酰脲类除草剂以及敌草隆、酰苯胺类吡唑草胺和吡氟酰草胺对斜生栅藻的毒性均较高。     

Mode of action,crop selectivity,and soil relations of the sulfonylurea herbicides

The sulfonylurea herbicides are characterized by broad-spectrum weed control at very low use rates (c. 2–75 g ha^?1), good crop selectivity, and very low acute and chronic animal toxicity. This class of herbicides acts through inhibition of acetolactate synthase (EC 4.1.3.18; also known as acetohydroxyacid synthase), thereby blocking the biosynthesis of the branched-chain amino acids valine, leucine and isoleucine. This inhibition leads to the rapid cessation of plant cell division and growth. Crop-selective sulfonylurea herbicides have been commercialized for use in wheat, barley, rice, corn, soybeans and oilseed rape, with additional crop-selective compounds in cotton, potatoes, and sugarbeet having been noted. Crop selectivity results from rapid metabolic inactivation of the herbicide in the tolerant crop. Under growth-room conditions, metabolic half-lives in tolerant crop plants range from 1–5 h, while sensitive plant species metabolize these herbicides much more slowly, with half-lives > 20 h. Pathways by which sulfonylurea herbicides are inactivated among these plants include aryl and aliphatic hydroxylation followed by glucose conjugation, sulfonylurea bridge hydrolysis and sulfonamide bond cleavage, oxidative O-demethylation and direct conjugation with (homo)glutathione. Sulfonylurea herbicides degrade in soil through a combination of bridge hydrolysis and microbial degradation. Hydrolysis is significantly faster under acidic (pH 5) than alkaline (pH 8) conditions, allowing the use of soil pH as a predictor of soil residual activity. Chemical and microbial processes combine to give typical field dissipation half-lives of 1–6 weeks, depending on the soil type, location and compound. Very short residual sulfonylurea herbicides with enhanced susceptibility to hydrolysis (DPX-L5300) and microbial degradation (thifensulfuron-methyl) have been developed.     

Fourteenth International Congress of Entomology,Canberra, August 22–30, 1972

Abstract

An experimental herbicide, AC 92,553 has been developed by Cyanamid International to control most annual grasses and several small-seeded broad-leaved weeds, applied either pre- or post-seeding on a wide range of crops. The influence of soil and weather conditions on the effectiveness of the herbicide are discussed. Suggested combinations with other herbicides and rates of application are given. The results of toxicity studies are summarised.     

Effect of some herbicides on freshwater algae

The activity of 12 herbicides was tested against various freshwater algae found in Britain. Three of the most troublesome species, Cladophora glomerata L., Rhizoclonium hieroglyphicum Katz., and Vaucheria dichotoma Ag. were all susceptible to methylthio-1,3,5-triazines. Terbutryne and cyanatryn were the most active and both killed C. glomerata and R. hieroglyphicum at 0.05 mg/litre. The concentration of terbutryne had to be increased to 0.1 mg/litre to control V. dichotoma. Asulam and WSCP (2.0 mg/litre), metflurazone and HZ5914 (1.0 mg/litre), copper sulphate (1.0 mg copper ion/litre) and cutrine (2.0 mg copper ion/litre) had no visible effect on the algae. Diquat (1.0 mg cation/litre) did, however, control C. glomerata and R. hieroglyphicum although, in natural conditions, the algae quickly recovered after treatment. Success with diquat (2.0 mg/litre) against V. dichotoma in laboratory experiments was not achieved in a field experiment.     

Transformation of the herbicides propanil and chlorpropham by micro-algae

Two species of green algae and four of blue-green algae hydrolysed the acylanilide herbicide propanil to the aniline derivative, 3,4-dichloroaniline. Of the cultures tested, only the blue-green alga Anacystis nidulans was shown to be capable of converting the phenylcarbamate herbicides propham and chlorpropham to the corresponding anilines. The green alga Ulothrix fimbriata was apparently unable to hydrolyse propanil or chlorpropham.