Persistence and metabolism of dinitroaniline herbicides in soils

The persistence, binding, and metabolism of six dinitroaniline herbicides, including trifluralin, profluralin, dinitramine, butralin, fluchloralin, and chlornidine, added to Matapeake silt loam were determined after 3, 5, and 7 months. Dinitramine was rapidly degraded during the first 5 months, while butralin and chlornidine were less persistent than fluchloralin, profluralin, and trifluralin after 7 months. The latter three herbicides were similar in persistence and binding properties. The parent herbicide was the major extractable product detected in soil at each sampling time. Degradation products were identified by cochromatography on thin-layer plates, retention times on gas-liquid and high-pressure liquid chromatography, and mass spectral analysis. Dealkylated and cyclic derivatives of the parent herbicide were detected as metabolites. The cyclic products included benzimidazole derivatives of dinitramine, trifluralin, and fluchloralin; a morpholine derivative of chlornidine; and a quinoxaline derivative of fluchloralin. A unique metabolite of butralin was derived from the parent material by the loss of one nitro substituent.     

Distribution and isolation of radioactivity from 74As-arsenate and 14C-methanearsonic acid in an aquatic model ecosystem

A model aquatic ecosystem was used to measure the bioaccumulation and distribution of ⁷⁴As-arsenate and ¹⁴C-methanearsonic acid in the following aquatic organisms: algae, Oedogonium cardiacum; daphnids, Daphnia magna; fish, Gambusia affins and catfish, Ictalurus punctatus; and crayfish, Procambarus clarkii, Procambarus sp. Bioaccumulation ratios (BR) for ⁷⁴As ranged from 80 to 480 and 4 to 7, for crayfish, and catfish, respectively, in Experiment I. Bioaccumulation ratios were 5, 127, 34, and 5 for daphnids, Gambusia, algae, and crayfish in Experiment II. Values declined for both crayfish and catfish after they were removed to untreated water. Homogenates of all organisms were extracted sequentially with cold 5% trichloroacetic acid, 75% EtOH, and hot 5% TCA. Distribution of the two arsenicals differed with extractant and biological species. The cold acid extracts of algae, daphnids, and crayfish contained the highest levels of ⁷⁴As. Generally, ¹⁴C was distributed more uniformly among the four fractions and was found at a higher percentage in the residue than was arsenate. By gel filtration chromatography, several compounds were separated from extracts of algae, daphnids, Gambusia, and crayfish treated with ⁷⁴As. These compounds were not arsenate, MSMA, or cacodylic acid. Extracts of MSMA-exposed organisms had one major compound which had the same retention volume (about the same molecular weight) as authentic MSMA. High-molecular-weight material (> 5000) was formed in Gambusia and algae treated with MSMA.     

Phytotoxicity of trifluoromethyl- and methyl-substituted dinitroaniline herbicides on resistant and susceptible populations of black-grass (Alopecurus myosuroides)

A Petri-dish assay was used to determine the phytotoxicities of the dinitroaniline herbicides pendimethalin, trifluralin, benfluralin and ethalfluralin, and the methyl-substituted analogues of the last three herbicides, on susceptible (Rothamsted) and multiple-herbicide resistant (Peldon) populations of blackgrass Alopecurus myosuroides Huds. The Peldon population showed a high degree of resistance to pendimethalin, which possesses a 3,4-dimethyl substitution. The two populations were equally sensitive to trifluralin, benfluralin and ethalfluralin which do not possess ring-methyl groups but contain a 4-trifluoromethyl group. Substitution of the 4-trifluoromethyl with a methyl group, as demonstrated by the analogues, reduced phytotoxicity, but to a much greater degree in Peldon than in the Rothamsted population. The study indicates that resistance to pendimethalin in the Peldon population is attributable to an oxidative degradation of the 4-methyl group, analogous to that which occurs with resistance to chlorotoluron. The lack of cross-resistance to the other dinitroaniline herbicides appears to be due to the absence of ring-methyl or other groups which are vulnerable to oxidative degradation, trifluoromethyl groups being particularly resistant to this form of reaction.     

Enhanced degradation of some soil-applied herbicides

In a field experiment involving repeated herbicide application, persistence of simazine was not affected by up to three previous doses of the herbicide. With propyzamide, there was a trend to more rapid rates of degradation with increasing number of previous treatments. Persistence of linuron and alachlor was affected only slightly by prior applications. In a laboratory incubation with soil from the field that had received four doses of the appropriate herbicide over a 12–month period, there was again no effect from simazine pretreatments on rates of loss. However, propyzamide, linuron and alachlor all degraded more rapidly in the previously treated than in similar untreated soil samples. Propyzamide, linuron, alachlor and napropamide degradation rates were all enhanced by a single pretreatment of soil in laboratory incubations, whereas degradation rates of isoproturon, metazachlor, atrazine and simazine were the same in pretreated and control soil samples.     

典型咪唑啉酮类除草剂的微生物降解研究进展

咪唑啉酮类除草剂是中国广泛应用的除草剂,具有杀草谱广、活性高、选择性强等优点,但其在土壤中残留期长,影响后茬作物.本文综述了典型的咪唑啉酮类除草剂甲氧咪草烟、咪唑乙烟酸和甲咪唑烟酸残留对后茬作物的影响,探究了降解部分咪唑啉酮类除草剂(甲氧咪草烟、咪唑乙烟酸和咪唑烟酸)的微生物所属类群及降解途径,分析了影响微生物降解咪唑...     

微生物降解二苯醚类除草剂的研究进展

本文概述了降解二苯醚类除草剂的微生物种类、降解机理及影响微生物降解二苯醚类除草剂的因素,指出利用微生物修复土壤中二苯醚类除草剂残留是一个有效的手段; 同时指出二苯醚类除草剂微生物降解过程中起关键作用的酶及基因有待于进一步研究。     

Adsorption and degradation of four acidic herbicides in soils from southern Spain

BACKGROUND: Pesticide degradation and adsorption in soils are key processes determining whether pesticide use will have any impact on environmental quality. Pesticide degradation in soil generally results in a reduction in toxicity, but some pesticides have breakdown products that are more toxic than the parent compound. Adsorption to soil particles ensures that herbicide is retained in the place where its biological activity is expressed and also determines potential for transportation away from the site of action. Degradation and adsorption are complex processes, and shortcomings in understanding them still restrict the ability to predict the fate and behaviour of ionisable pesticides. This paper reports the sorption and degradation behaviour of four acidic pesticides in five soils from southern Spain. Results are used to investigate the influence of soil and pesticide properties on adsorption and degradation as well as the potential link between the two processes. RESULTS: Adsorption and degradation of four acidic pesticides were measured in four soils from Spain characterised by small organic matter (OM) contents (0.3-1.0%) and varying clay contents (3-66%). In general, sorption increased in the order dicamba < metsulfuron-methyl < 2,4-D < flupyrsulfuron-methyl-sodium. Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for these soils. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. A clear positive correlation was observed for degradation rate with clay and OM content (P < 0.01), and a negative correlation was observed with pH (P < 0.01). The exception was metsulfuron-methyl, for which degradation was found to be significantly correlated only with soil bioactivity (P < 0.05). CONCLUSIONS: Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for soils of this type. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. The contrasting behaviour shown for these four acidic pesticides indicates that chemical degradation in soil is more difficult to predict than adsorption. Most of the variables measured were interrelated, and different behaviours were observed even for compounds from the same chemical class and with similar structures.     

Methods for assessing the toxicity of herbicides to submersed aquatic plants

A new test design for the non-axenic submergent aquatic macrophytes Elodea canadensis Michx. and Myriophyllum spicatum L. has been developed for potential use in herbicide toxicity testing. For the non-axenic cultures, the best growth conditions were observed in the Elendt-M4 medium in which no growth of algae or bacteria was observed. Cuttings were placed in beakers containing only the artificial M4 medium or were planted in small beakers containing OECD (Organisation for Economic Cooperation and Development) sediment (5% peat, 75% sand, 20% kaolinite), which were then placed in larger vessels with the M4 medium. The plants were observed for main and secondary shoot length, biomass and root formation within 2-3 weeks of planting. Growth rates were calculated for total plant length and biomass. The variance between the replicates was low throughout the experiment [coefficient of variation (CV) < 26% for total plant length, and between 16 and 40% for biomass]. Relative growth rates based on total plant length were determined as 0.028 and 0.050 per day for M. spicatum in the systems containing M4 medium only and medium plus sediment respectively. Similar results were observed for E. canadensis, with relative growth rates of 0.26 and 0.073 per day in the two test systems. The root-shoot ratio at harvest was greater by a factor of 2-3 for E. canadensis in the M4 medium than in the system containing sediment. However, comparable ratios were observed for M. spicatum in the two test systems. Both growth in total plant length and growth in biomass of the two species have potential as measures of toxicity.     

Accelerated degradation of thiocarbamate herbicides in Israeli soils following repeated use of vernolate

Accelerated degradation of vernolate, EPTC and butylate but not of cycloate was detected in soils from three locations in Israel which were treated annually with vernolate. Repeated application of EPTC to soils with and without a history of vernolate application, under laboratory conditions, resulted in a progressive increase in its rate of dissipation with each application. Accelerated degradation of EPTC was also rapidly induced by mixing small amounts (5%) of soil with a history of vernolate treatment with soil that had never received vernolate. Liberation of ¹⁴CO₂ from [¹⁴C]EPTC was more rapid in vernolate-treated soils than in untreated soils, indicating a development of microbial populations in soil capable of rapidly degrading the EPTC. Degradation of [¹⁴C]EPTC was faster in soil previously cropped with maize than in non-cropped soil, but slower in soils cropped with cotton or peanuts.     

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.     

Catalytic effect of dissolved humic acids on the chemical degradation of phenylurea herbicides

BACKGROUND: Although biodegradation seems to be the main cause of herbicide degradation, abiotic degradation can also be important for chemicals such as phenylureas, which are subject to catalysed soil reactions. The aim of this work is to investigate the effect of dissolved humic acids (HAs), normally present in natural waters, on the hydrolysis of phenylurea herbicides, and it presents a kinetic model that takes into account the role of adsorption. RESULTS: The linearity of the adsorption isotherms indicates that phenylurea-humic acid interaction can be considered in terms of a repartition-like equilibrium of phenylurea between water and HAs. Kinetic experiments show that the degradation rates of phenylureas increase with HA concentration. CONCLUSION: The kinetic equation adopted adequately describes the experimental data trend, allowing the evaluation of the catalytic effect of HAs on the chemical degradation of phenylureas. Carboxyl groups of HAs seem to play a leading role in the catalysis. The kinetic equation derived in this work could be helpful in predicting the persistence of phenylureas and of related compounds in natural water.     

Risks to the aquatic ecosystem from the application of Metarhizium anisopliae for locust control in Australia

Laboratory tests of Metarhizium anisopliae var acridum Driver & Milner, at a dose of 1.3 x 10(6) conidia ml-1, had no adverse effects on nymphs of mayfly, Ulmerophlebia sp or 8-week-old fry of the rainbow fish, Melanotaenia duboulayi Castelnau. This dose was toxic to the cladoceran, Ceriodaphnia dubia Richard, causing 100% mortality in 48 h. When this test was repeated at doses of up to 6.7 x 10(3) conidia ml-1, there was only 5% mortality after 192 h. Spraying of artificial water sources with a very high dose of the fungus as an aqueous spray resulted in 80-130 conidia ml-1 at 15 cm depth in the first 24 h after spraying. The conidia rapidly settled out and were absent from the top 15 cm layer of water after about 50 h. A similar experiment using the oil formulation as used in field control resulted in a 2- to 20-fold lower level of conidia in the water. Finally, sampling actual water sources in spray areas revealed a very low level of contamination of the water, with a maximum mean level of 29 conidia ml-1 in the first 24 h after treatment. Thus the level of conidia likely to enter water during control campaigns is a small fraction of that required to kill cladocerans, the only sensitive non-target organism tested. It is concluded that the biopesticide is very unlikely to pose any hazard to aquatic organisms.     

Residues of diuron and phytotoxic degradation products in aquatic situations. II. Diuron in irrigation water

When diuron is used as a soil-residual herbicide in irrigation canals, water quality is protected in standard practice by ‘flushing’–the diversion of the first discharge of water to the drainage system before irrigation is resumed. In three canals treated with diuron at about 40–45 kg ha^?1, flushing for 4 h was relatively inefficient, removing 15% or less of the residual diuron in the sediment. In one other canal approximately 40% was removed during flushing. Cumulative loss of diuron was proportional to the square root of the time of water discharge. The effect of the time interval between treatment and flushing was investigated in trials on soils of typically heavy texture. When flushing closely followed treatment about 6 kg diuron ha^?1 was removed but in three trials, for a range of times from treatment of 5–15 weeks, losses were similar and about 2.5 kg ha^?1, suggesting that a restriction of longer than 5 weeks is unlikely to reduce contamination. In a contrasting soil of sandier texture greater movement of diuron away from the sediment surface probably contributed to a five-fold reduction of diuron extracted in flushing. These data were used to calculate the effects of flushing time on both the concentrations of diuron in water discharged to drains for subsequent re-use and the concentrations in the irrigation water, to aid assessment of hazard to crops. Flushing times required for residues in water to reach 0.1 μg ml^?1, calculated by extrapolation, were in the order of days so that it may be necessary to restrict the use of diuron to farms which can retain the discharge water within their own boundaries, or to areas where dilution in receiving waters can be shown to be adequate.     

Residues of diuron and phytotoxic degradation products in aquatic situations. I. Analytical methods for soil and water

Thin-layer and gas-liquid chromatography, ultraviolet analysis and bioassay with Chlorella spp. have been used to investigate the pathway of degradation of diuron to phytotoxic derivatives when diuron was used as a soil-residual herbicide in irrigation canals. Observations suggest that 1-(3,4-dichlorophenyl)-3-methylurea and 1-(3,4-dichlorophenyl)urea make a contribution to total residues equivalent to a maximum of about 40 and 55%, respectively, of diuron concentrations. Application of a phyto-toxicity rating suggests that in this environment, measurement of diuron specifically would underestimate the total phytotoxicity of residues by a maximum of about 7%.     

杀虫剂和除草剂的植物修复研究进展

随着农药施用量的增加,农药污染土壤给生态环境造成了极大的危害,并引起了人们的普遍关注。传统的修复方法因其价格昂贵而不能普遍采用,植物修复是近年来兴起的一种利用植物积累、吸收、降解等去除土壤、水和沉积物中污染物的新方法。本文主要介绍了植物修复的机制和方式,对近年来杀虫剂和除草剂的植物修复研究进展进行综述,指出了植物修复的不足和今后的发展方向。     

Cross-resistance pattern and alternative herbicides for Cyperus difformis resistant to sulfonylurea herbicides in Korea

A Cyperus difformis L accession from Chonnam province, Korea was tested for resistance to the sulfonylurea herbicide, imazosulfuron. The accession was confirmed to be resistant (R) and was cross-resistant to other sulfonylurea herbicides, bensulfuron-methyl, cyclosulfamuron and pyrazosulfuron-ethyl, the pyrimidinyl thiobenzoate herbicide, bispyribac-sodium, and the imidazolinone herbicide imazapyr, but not to imazaquin. Multiple resistance was tested using twelve herbicides with target sites other than acetolactate synthase (ALS). The R biotype could be controlled by other herbicides with different modes of action such as butachlor, carfentrazone-ethyl, clomeprop, dithiopyr, esprocarb, mefenacet, oxadiazon, pretilachlor, pyrazolate and thiobencarb, applied to soil at recommended rates. Several sulfonylurea herbicide-based mixtures can control both the R and S biotypes of C difformis, except sulfonylurea plus dimepiperate, molinate or pyriftalid, and pyrazolate plus butachlor. Although mixtures of sulfonylurea herbicides might be more effective, they should be avoided and used only in special cases. In terms of in vitro ALS activity, the R biotype was 1139-, 3583-, 1482-, 416-, 5- and 9-fold more resistant to bensulfuron-methyl, cyclosulfamuron, imazosulfuron, pyrazosulfuron-ethyl, bispyribac-sodium and imazapyr, respectively, than the S biotype. The in vivo ALS activity of the R biotype was also less affected by the sulfonylurea herbicides, imazosulfuron and pyrazosulfuron-ethyl, than the S biotype. Results of in vitro and in vivo ALS assays indicated that the resistance mechanism of C difformis to ALS inhibitor herbicides was primarily due to an alteration in the target enzyme, ALS. Greenhouse experiments showed delayed flowering and reduced seed production of the R biotype, which could possibly result in reduced fitness. This unusual observation needs to be confirmed in field situations.     

Metabolism and selectivity of rice herbicides in plants

Chemical weed control with effective and highly active herbicides has been very useful and convenient means. It has contributed to stable crop production and is labor saving. Recent herbicides have had characteristics such as high effectiveness without causing environmental pollution or harmful effects, and appropriate herbicides having high activity, low toxicity, high selectivity and being non-persistent have been developed. The metabolism of rice herbicides used mainly in Japan, such as sulfonylurea, chloroacetamide, acylamide, urea, thiocarbamate, pyrazole, triazine, diphenyl ether, phthalimide, phenoxy, aryloxyphenoxypropionate, etc., is reviewed, and its involvement in selectivity is also discussed. The metabolism of herbicides is closely related to their activity and selectivity. Differential herbicide metabolism in plants is a contributing factor of selectivity between crops and weeds. Chemicals that are more detoxified in crops and/or more activated or less detoxified in weeds are considered as being effective and selective herbicides. The metabolism of various types of rice herbicides includes: oxidative reaction (ring and chain hydroxylation, O - and N -dealkylation), hydrolysis and subsequent glucose conjugation, and glutathione conjugation in rice. These detoxicative activities are much higher in rice than weeds in paddies, and this leads to the selectivity of herbicides. Enzymes, oxidase, P-450 mono-oxygenase, esterase, acylamidase, glucosyl transferase, glutathione transferase, etc., play important roles in herbicide metabolism and selectivity.     

Split application of herbicides in peas

The efficacy of split application of herbicides in peas compared to a single treatment with the same total dosage was investigated in field trials. The results of four efficacy trials and two tolerance trials, employing some of the commonly used tank mixtures of herbicides, are described. The tank mixtures consisted of cyanazine or pendimethalin in mixture with bentazone, bentazone/MCPA, MCPB or MCPA. Split application enhanced the weed control compared to the efficacy of a single application at the same total dosage. The improved weed control was considered to be mainly due to the fact that sequential use makes it possible to target a larger proportion of the weeds at the sensitive cotyledon stage than is possible with a single application, which must be delayed until the majority of the weeds have emerged. The use of split application increased the reliability of the weed control, as the efficacy remained high if just one of the treatments was carried out at a favourable time for the efficacy of the tank mixture. The tolerance trials showed that, when a single application treatment at the optimal time for efficacy was compared to split application, then there was a tendency for there to be a higher yield after the split application treatment, caused by greater crop damage after the single-dose application. Applications fractionnees d'herbicides en cultures de pois L'efficacité d'une application fractionnée d'herbicides en cultures de pois a étéétudiée en essais de plein champ, en comparaison d'une application simple apportant la même dose totale. Les résultats obtenus dans 4 essais d'efficacité et 2 de sélectivité, avec quelques uns des mélanges d'herbicides communément pratiqués sont décrits. Les mélanges étaient à base de cyanazine ou de pendimethaline avec de la bentazone, de la bentazone/MCPA, du MCPB ou du MCPA. Les applications fractionnées ont augmenté l'efficacité herbicide en comparaison d'une simple application à la même dose globale. L'amélioration de l'activité herbicide est supposée être due par le fait qu'une utilisation séquentielle fait qu'il est possible d'atteindre une plus grande proportion de mauvaises herbes au stade cotylédonnaire sensible, que celle qu'il est possible d'atteindre avec une application unique qui doit attendre que la majorité des adventices soit levée. L'utilisation des applications fractionnées a augmenté la régularité du desherbage attendu que l'efficacité est demeurée élevée quand seulement un des traitements avait été appliqué au moment favorable pour l'efficacité du mélange. Les essais de sélectivité ont montré que pour une simple application appliquée au moment optimal pour l'efficacité comparée à une application fractionnée on avait tendance à avoir un rendement moins élevé, ceci étant liéà une phytotoxicité plus grande liée aux simples applications. Geteilte Anwendungen von Herbiziden in Erbsen Die Wirkung geteilter Anwendungen von Herbiziden in Erbsen wurden im Freiland im Vergleich zu Einzel-Behandlungen mit derselben Gesamtdosis untersucht. Die Ergebnisse von 4 Wirkungs- und 2 Toleranzversuchen mit einigen häufig vorgenommenen Tankmischungen werden beschrieben. Die Tankmischungen bestanden aus Cyanazin und Pendimethalin in Mischung mit Bentazon, Bentazon/MCPA, MCPB oder MCPA. Die geteilte Anwendung verstärkte die Unkrautbekämpfung. Diese Verbesserung war vermutlich vorrangig darauf zurückzuführen, daß man mit den aufeinander folgenden Teilanwendungen einen größeren Teil der Unkräuter im empfindlichen Keimblattstadium trifft, im Gegensatz zur Einzel-Behandlung, bei der man die Hauptkeimwelle der Unkräuter abwarten muß. Durch geteilte Anwendungen wurde die Unkrautbekämpfung verläßlicher, weil die Wirkung auch dann groß blieb, wenn nur eine der Behandlungen zu einem günstigen Zeitpunkt stattfand. Im Toleranzversuch erwies sich das Verfahren der Teilanwendungen verträglicher und tendierte zu höheren Erträgen, denn bei den Einzel-Behandlungen zum Zeitpunkt optimaler Wirkung traten größere Schäden an den Kulturpflanzen auf.