Degradation and sorption of atrazine, hexazinone and procymidone in coastal sand aquifer media

The degradation, sorption and transport of atrazine, hexazinone and procymidone in saturated coastal sand aquifer media were investigated in batch and column experiments. The pesticides were incubated with sterilised and non-sterilised groundwater or a mixture of groundwater and the aquifer material in the dark at 15 degrees C for 120 days. The estimated half-lives of the pesticides (and their ranges) in the mixture of groundwater and aquifer sand were 36 (31-40), 54 (40-77) and 84 (46-260) days for atrazine, procymidone and hexazinone, respectively. Compared with the relevant results for the groundwater-sand mixture phase, the estimated half-life of pesticides in the groundwater phase alone was shorter for procymidone (21 days) but longer for hexazinone (134 days); atrazine was not degraded in the groundwater phase. Chemical degradation appeared to have played the predominant role in the degradation of hexazinone and procymidone in the aquifer system, while both chemical and biological processes seemed to be important for the degradation of atrazine. Batch isothermal experiments were carried out at pH 4.6-4.7 to obtain sorption coefficients under equilibrium conditions. The isothermal data of the pesticides fitted well with the non-linear Freundlich function with an exponent of sorption coefficient that was greater than one. Contrary to reports in the literature, sorption of atrazine was the greatest, and procymidone was slightly more sorbed than hexazinone. A column experiment was conducted at a typical field-flow velocity of 0.5 m day(-1) over 60 days to study pesticide attenuation and transport in flow dynamic conditions. Retardation factors, R, derived from a two-site sorption/desorption model were 8.22, 1.76 and 1.63 for atrazine, procymidone and hexazinone, respectively. Atrazine displayed the lowest mobility and the mobility of procymidone was only slightly less than that of hexazinone, which is consistent with observations in the batch experiment. A possible explanation for these observations is that ionic atrazine is bound to oppositely charged ionic oxides, and ionic oxides have less effect on the sorption of the non-ionic procymidone. The significant tailing in the pesticide breakthrough curves (BTCs) in comparison with the bromide BTC, together with model-simulated results, suggests that the transport of the pesticides was under chemical non-equilibrium conditions with R values that were less than their equivalent values predicted using the batch equilibrium isothermal data. As a result of non-linear kinetic sorption, retardation factors of the pesticides in groundwater systems would not be constant and will decrease with decreasing pesticide concentrations and increasing flow velocities. Hence, the use of equilibrium isotherm data will probably over-predict the sorption of pesticides in groundwater systems. Rhodamine WT, a commonly used groundwater tracer, was significantly retarded (R = 5.48) and its BTC was much more spread out than the bromide BTC. Therefore, it would not be a good tracer for the indication of groundwater flow velocity and dispersion for the coastal sand aquifer system. In contrast to some aquifer media, the dye tracer was unsuitable as a marker of the appearance of atrazine in a coastal sand aquifer system.     

Behaviour of the insecticides ethoprophos and carbofuran during soil—water transport

The movement of the organophosphate nematicide-insecticide ethoprophos (ethoprop; O-ethyl S,S-dipropyl phosphorodithioate) and the carbamate insecticide-nematicide carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yI methylcarbamate) was studied under steady-state flow in small-scale laboratory soil columns. Miscible displacement column experiments, mass balance calculations, and batch incubation studies furnished information on insecticide sorption and degradation processes that occur during transport through soil. Miscible displacement studies demonstrated that ethoprophos degradation could be described as first-order and that both insecticides exhibited non-equilibrium sorption. Both batch and miscible displacement results showed ethoprophos to be more strongly sorbed by soil than carbofuran. Measured equilibrium sorption coefficients were 1.29 cm³ g^?1 for ethoprophos and 0.29 cm³ g^?1 for carbofuran on a Riverhead soil (0.011 organic carbon fraction); 035 cm³ g^?1 for carbofuran on Valois soil (0.016 organic carbon fraction); and 2.38 cm³ g^?1 for ethoprophos on Rhinebeck soil (0.031 organic carbon fraction). Two solutions to the convection-dispersion equation, one that incorporated equilibrium sorption and another (bicontinuum model) that included a non-equilibrium sorption term, allowed quantitative evaluation of transport processes. The bicontinuum model used in conjunction with experimental batch and mass balance techniques provided estimates of insecticide sorption and degradation parameters.     

Sorption of atrazine and dicamba in Delaware coastal plain soils: a comparison of soil thin layer and batch equilibrium results

The mobility and retention of atrazine and dicamba in six Atlantic Coastal Plain soils were estimated by soil thin-layer chromatography (soil-TLC). The soils studied were representative of the major agricultural regions in Delaware and were sampled, by horizon, to the water table. Four horizons from each profile were leached simultaneously with distilled water on one soil-TLC plate. Two values were obtained from each plate: the ratio of the distance traveled by the herbicide center of mass over that traveled by the solvent front (R_m), and a sorption distribution coefficient (K_d). The R_m values ranged from 0·06 to 0·94 for atrazine and from 0·80 to 0·94 for dicamba. Herbicide mobility was found to be greatest in coarse-textured soil horizons that contained low levels of organic matter, clay, and Fe and Al oxides. Correlation analysis indicated that effective cation exchange capacity, exchangeable acidity, exchangeable aluminum, and clay were useful predictive variables or both atrazine mobility and sorption. Organic matter was not useful for predicting soil-TLC derived sorption estimates; however, it was correlated to K_d-batch estimates. Distribution coefficients calculated from soil-TLC data were found to be in general agreement with K_d values obtained for the same soils by batch equilibrium techniques. The average K_d-soil-TLC values for atrazine and dicamba were 2·09(±2·24) and 0·03(±0·02), respectively. The ratio of the batch K_d to the soil-TLC K_d ranged from 0·1 to 19 (x̄=1·6, SD=3·8) for atrazine and from 2·9 to 38 (x̄=12·6, SD=8·7) for dicamba. Thus, although for some horizons agreement between the two methods was good, for other horizons significant discrepancies existed. It is suggested that the soil-TLC gives results under non-equilibrium conditions, whereas the batch procedure is, by definition, at quasi-equilibrium. These fundamental differences may account for the observed differences between the two methods. It is also suggested that, due to this difference, the soil-TLC procedure can provide additional information relevant to herbicide partitioning in the field environment that is not provided by traditional batch equilibrium techniques. © 1998 Society of Chemical Industry     

Kinetics of Uptake and Metabolism of Atrazine in Model Plant Systems

The present work concerns atrazine absorption and metabolism by corn (Zea mays.) seedlings immersed in an aqueous medium in comparison with Acer pseudoplatanus cell cultures. At the point of equilibrium, the apparent concentration inside the A. pseudoplatanus cells (with a moderate lipid content: 0·17% of dry weight) was about twice that of the medium. This equilibrium was probably due to a simple partition process; part of the atrazine was dissolved in the cell water and reached the same concentration as in the external medium while the rest was concentrated inside the cellular lipids. The theoretical calculation of the lipid/water partition, taking into account the value of log P measured not with the lipids but with octanol (log P=2·5), gave a value of 1·5 for concentration inside the plant material. Such an equilibrium, resulting from a partition process between water and lipids, was also obtained in non-living corn seedlings. In living seedlings, an over-concentration of radioactivity due to [¹⁴C]atrazine derivatives was rapidly obtained inside roots and shoots giving concentrations respectively 7- and 12-fold higher than that of atrazine in the external medium. This was due to very rapid chemical transformation of atrazine into its hydroxy derivatives, especially hydroxyatrazine. This hydrolysis of atrazine in corn was due to the presence of high levels of benzoxazinone derivatives in corn seedling cells. The hydroxylated metabolites were able to concentrate in the cells very rapidly and were unable to diffuse freely into the external medium. As a consequence, this process facilitated the penetration of large quantities of atrazine which became rapidly hydroxylated, allowing therefore the passive penetration of atrazine to be further improved, since the concentration C₁ in the receiver compartment was always close to zero. The passive transfer of atrazine, following Fick's law: dq/dt=-Pa (C₀–C₁), was therefore optimized. © 1997 SCI.     

Influence of pesticides on the activity and kinetics of invertase,urease and acid phosphatase enzymes

The effects of four pesticides (three herbicides, atrazine, paraquat, glyphosate, and an insecticide, carbaryl) on the activity and kinetics of an invertase (from yeast), a urease (from jack bean) and an acid phosphatase (from potato) were investigated. Glyphosate and paraquat showed a marked activation effect on invertase activity. From the dependence of V_max and K_m parameters on pesticide concentrations, a mixed-type activation mechanism was suggested. The kinetic behaviour of urease and acid phosphatase appeared to be uninfluenced by both pesticides. Methanol, used as solvent for both carbaryl and atrazine, inhibited invertase, urease and acid phosphatase with, respectively, competitive, non-competitive and uncompetitive mechanisms. The extent of the inhibition was different, as estimated by the values of the inhibition constant K₁. An additional inhibition effect of urease and invertase activities was achieved in the presence of carbaryl, whereas no influence was detected on the activity and kinetics of acid phosphatase. Finally, atrazine was shown to alter the kinetics of the enzymes only at higher concentrations.     

Field strains of Stemphylium vesicarium with a resistance to dicarboximide fungicides correlated with changes in a two-component histidine kinase

In Stemphylium vesicarium, four phenotypes were recognized according to their in vitro responses to dicarboximide fungicides: S (sensitive), S₊ (low resistant to iprodione and procymidone but moderately resistant to vinclozolin), R₁ (moderately resistant to iprodione and vinclozolin but highly resistant to procymidone), R₂ (highly resistant to all dicarboximides). Cross-resistance was observed between dicarboximides and aromatic hydrocarbon fungicides in all cases while cross-resistance to phenylpyrroles was only detected in R₂ phenotype. Moreover, no changes were noted in sensitivity to oxidative and osmotic stress inducers. An osmosensing histidine kinase gene, homologous to OS1 from Neurospora crassa, was sequenced from several field isolates of Stemphylium vesicarium. This gene is predicted to encode a 1,329 amino acid protein, comprising a conserved histidine-kinase domain in the C-terminal region and six tandem repeats of about 90 amino acids at the N-terminal end. In S₊ and R₁ phenotype isolates, a single amino acid substitution was observed in the first amino acid repeat; F267L and L290S respectively. For the R₂ isolates, the exchanges T765R or Q777R were located within the histidine-kinase domain.     

A field tracer study of attenuation of atrazine,hexazinone and procymidone in a pumice sand aquifer

A field tracer experiment, simulating point source contamination, was conducted to investigate attenuation and transport of atrazine, hexazinone and procymidone in a volcanic pumice sand aquifer. Preliminary laboratory incubation tests were also carried out to determine degradation rates. Field transport of the pesticides was observed to be significant under non‐equilibrium conditions. Therefore, a two‐region/two‐site non‐equilibrium transport model, N3DADE, was used for analysis of the field data. A lump reduction rate constant was used in this paper to encompass all the irreversible reduction processes (eg degradation, irreversible adsorption, complexation and filtration for the pesticides adsorbed into particles and colloids) which are assumed to follow a first‐order rate law. Results from the field experiment suggest that (a) hexazinone was the most mobile (retardation factor R = 1.4) and underwent least mass reduction; (b) procymidone was the least mobile (R = 9.26) and underwent the greatest mass reduction; (c) the mobility of atrazine (R = 4.45) was similar to that of rhodamine WT (R = 4.10). Hence, rhodamine WT can be used to delimit the appearance of atrazine in pumice sand groundwater. Results from the incubation tests suggest that (a) hexazinone was degraded only in the mixture of groundwater and aquifer material (degradation rate constant = 4.36 × 10^?3 day^?1); (b) procymidone was degraded not only in the mixture of groundwater and aquifer material (rate constant = 1.12 × 10^?2 day^?1) but also in the groundwater alone (rate constant = 2.79 × 10^?2 day^?1); (c) atrazine was not degraded over 57 days incubation in either the mixture of aquifer material and groundwater or the groundwater alone. Degradation rates measured in the batch tests were much lower than the total reduction rates. This suggests that not only degradation but also other irreversible processes are important in attenuating pesticides under field conditions. Hence, the use of laboratory‐determined degradation rates could underestimate reduction of pesticides in field conditions. © 2001 Society of Chemical Industry     

Resistance of barnyardgrass (Echinochloa crus-galli) to atrazine and quinclorac

Two populations of Echinochloa crus-galli (R and I) exhibited resistance to quinclorac. Another population (X) exhibited resistance to quinclorac and atrazine. The R and I populations were collected from monocultures of rice in southern Spain. The X population was collected from maize fields subjected to the application of atrazine over several years. The susceptible (S) population of the same genus was collected from locations which had never been treated with herbicides. The quinclorac ED₅₀ value (dose causing 50% reduction in shoot fresh weight) for the R and I biotypes were 26- and 6-fold greater than for the S biotype. The X biotype was 10 times more tolerant to quinclorac than the S biotype and also showed cross-resistance to atrazine, being 82-fold more resistant to atrazine than the R, I and S biotypes. Chlorophyll fluorescence and Hill reaction analysis supported the view that the mechanism of resistance to atrazine in the X biotype was modification of the target site, the DI protein. Quinclorac at 20 mg litre^-1 did not inhibit photosynthetic electron transport in any of the test biotypes. The quinclorac I₅₀ values (herbicide dose needed for 50% Hill reaction reduction) of the S population was over 50000-fold higher than the atrazine I₅₀ value for the same S population, indicating that quinclorac is not a PS II inhibiting herbicide. Propanil at doses greater than 0·5 kg ha^-1 controlled all the biotypes. © 1997 SCI     

Modelling the kinetics of ethyl formate sorption by wheat using batch experiments

BACKGROUND: Ethyl formate formulations are being considered to replace methyl bromide for fast grain disinfestation. Grain adsorbs ethyl formate rapidly, which can result in inadequate fumigation concentrations and unacceptable grain residues. A model of ethyl formate sorption kinetics will enable fumigation approaches to be determined that meet disinfestation and food safety requirements. RESULTS: This paper identifies all mass transport processes involved in ethyl formate sorption by wheat from published and experimental evidence. The model accounts for reaction losses of ethyl formate in air and grain using first‐order kinetics, transport in the gas and solid phases with linear mass transfer coefficients and uses a linear partition relationship representation of sorption equilibrium. Batch experimental data were measured to determine model coefficients. Novel gaseous breakdown data for ethyl formate in air were measured, and first‐order kinetics was demonstrated, although the specific reactions involved were not identified. CONCLUSION: The model predicts air and grain fumigant concentrations relevant for grain disinfestation and food residue contamination successfully. The form of the model should be applicable to all fumigant–grain systems, as it accounts for the diffusion and reaction influences known to occur with all modern fumigants under concentration and exposure conditions relevant to industry. Copyright © 2009 CSIRO, Australia. Published by John Wiley & Sons, Ltd.     

异噁唑草酮在土壤表面光解及在土壤中的降解和淋溶特性

为合理评估除草剂异唑草酮的环境风险,在实验室模拟条件下,研究了异唑草酮在土壤 (红壤土)表面光解以及在不同质地土壤 (潮土、水稻土和红壤土) 中的降解和淋溶特性。结果表明:异唑草酮在土壤表面的光解遵循一级反应动力学方程c_t = 4.23e–0.008t (r = 0.937),半衰期为82.5 h;其在潮土、水稻土和红壤土中的降解均符合一级动力学方程,好氧条件下,异唑草酮在3种土壤中的降解半衰期分别为10.5、43.3和139 h,厌氧条件下的降解半衰期分别为19.4、18.4和158 h;其在潮土、水稻土和红壤土中的淋溶系数 (R_f) 分别为0.417 0、0.083 3和0.083 3。研究表明:异唑草酮在土壤表面光解速率较慢,而在土壤中好氧及厌氧条件下降解速率均较快,残留期短;其在土壤中淋溶性较弱,不易对周围环境及地下水造成污染风险。     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. II. Prognose möglicher Folgekulturen bei Atrazinrükständen im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. II. Prediction of the phytotoxicity of atrazine residues to following crops Total and plant-available atrazine residues in the top 10 cm soil were measured 120 days after application of 3 kg ai ha^?1 to maize (Zea mays L.) at three sites in Rumania. At one site, similar measurements were made 3?5 years after application of 100 kg ai ha^?1. Plant-available atrazine residues were estimated by extraction of soil samples with water, and by bioassay using Brassica rapa as the test plant. It was calculated that between 30 and 120μg atrazine 1^?1 was potentially available to plants in the different soils. Dose-response relationships for atrazine and the most important rotational crops with maize in Rumania—sunflower, winter wheat, soybean and flax—were determined in hydroponic culture using herbicide concentrations corresponding with the plant-available fractions measured in the different soils. ED₅₀ values were determined by probit analysis and the results showed that sunflower (ED₅₀, 22μg 1^?1) was the most sensitive crop, and soybean (ED₅₀, 78μg 1^?1) was the least. The residual phytotoxicity of atrazine to succeeding crops in the different soils was predicted using the appropriate availability and phytotoxicity data, and the results showed good agreement with those observed. The results suggest that measurements of plant-available herbicide residues afford a rapid method of assessing possible phytotoxicity to following crops.     

Characterization of triadimefon sorption in soils using supercritical fluid (SFE) and accelerated solvent (ASE) extraction techniques

Sorption–desorption of the fungicide triadimefon in field‐moist silt loam and sandy loam soils were determined using low‐density supercritical fluid extraction (SFE). The selectivity of SFE enables extraction of triadimefon from the soil water phase only, thus allowing calculation of sorption coefficients (K_d) at field‐moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature; sorption increased with increased moisture content up to saturation, and decreased with increased temperature. For instance, K_d values for triadimefon on the silt loam and the sandy loam soils at 40 °C and 10% water content were 1.9 and 2.5 ml g⁻¹, respectively, and at 18% water content, 3.3 and 6.4 ml g⁻¹, respectively. Isosteric heats of sorption (ΔH_i) were −42 and −7 kJ mol⁻¹ for the silt loam and sandy loam soils, respectively. Sorption–desorption was also determined using an automated accelerated solvent extraction system (ASE), in which triadimefon was extracted from silt loam soil by 0.01 M CaCl₂. Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a similar ΔH_i value (−29 kJ mol⁻¹) for the silt loam soil (K_f = 27 µg^{1 − 1/n} ml^1/n g⁻¹). In order to predict transport of pesticides through the soil profile more accurately on the basis of these data, information is needed on sorption as a function of soil water content. © 2000 Society of Chemical Industry     

Measurement and simulation of the movement of thiazafluron, clopyralid and metamitron in soil columns

Adsorption and leaching of the herbicides thiazafluron (1,3-dimethyl-1(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)urea), metamitron (4-amino-4,5-dihydro-3-methyl-6-phenyl-1,2,4-tri azin-5-one) and clopyralid (3,6-dichloropicolinic acid) were studied in one sandy and two silty-clay soils. Equilibrium adsorption coefficients (K_d) were measured using a batch equilibration procedure, and mobility was studied in repacked columns of the soils under fluctuating saturated/unsaturated flow conditions. Breakthrough curves (BTCs) were consistent with an inverse relationship between leaching and adsorption with greater mobility of the weakly-adsorbed clopyralid than the more strongly adsorbed thiazafluron or metamitron. The BTC data were used to evaluate the LEACHP simulation model. Following model calibration with respect to hydrological parameters and some of the herbicide degradation rates, the best fits between predicted and observed data were with the less adsorptive and highly mobile clopyralid. In general, the model gave acceptable predictions of the timing of the concentration maxima and the shapes of the BTCs, although earlier breakthrough than that observed was predicted with the less mobile herbicides, thiazafluron and metamitron, in the silty-clay soils. For metamitron, the total amounts leached were not predicted accurately, suggesting more rapid degradation of the herbicide in the soil columns than in the kinetic studies performed in a 1:1 soil:solution ratio shaken system.     

Sorption of isoxaflutole by five different soils varying in physical and chemical properties

Isoxaflutole is a new pre-emergence corn herbicide which controls both grass and broadleaf weeds. Experiments were performed in the laboratory to study the sorption of isoxaflutole in five different soils (Moorhead, MN; East Monroe, CO; Ellendale, MN; South Deerfield, MA; and Chelsea, MI) using the batch equilibration technique. Total initial isoxaflutole solution concentrations for each soil were 0.05, 0.15, 0.3. 0.8, 1.5, 2.0 and 4.0 mg litre⁻¹. Analysis of [ring-¹⁴C] isoxaflutole was performed using liquid scintillation counting, and sorption data were fitted with the Freundlich model. Isotherms of isoxaflutole in all the soils were non-linear as depicted by the exponent (n < 1.0), indicating differential distribution of sorption site energies in various soils. Since the isotherms were non-linear the data fit Freundlich's isotherm well, as was indicated by high values of the regression coefficient (r²). The Freundlich sorption coefficient ranged from 0.555 to 50.0 (litre ⁿmg ^l−nkg⁻¹). Multiple regression of the sorption constant, K_F against selected soil properties indicated that organic matter content was the best single predictor of isoxaflutole sorption (r² = 0.999) followed by soil pH (r² = 0.954). Clay content of the soils did not have a high correlation with K_F values (r² = 0.453), while the sorption of isoxaflutole was not influenced by the Ca²⁺ concentration in the soil solution. Isoxaflutole sorption increased with an increase in organic matter content of soils. Sorption of isoxaflutole decreased as the soil pH increased from 4.5 to 8.5, which was depicted by the reduction of K_F values. Sorption of isoxaflutole to the soils varied with differences in binding energies. At a particular net energy value (E*), the corresponding site energy distribution [F(E*)] values followed the order, Chelsea, MI > Moorhead, MN > East Monroe, CO > South Deerfield, MA > Ellendale, MN. The negative magnitude of Gibbs free energy of sorption (ΔG ^x) indicates the spontaneity of the given sorption process in the soils from Moorhead, MN; East Monroe, CO and Chelsea, MI. © 1999 Society of Chemical Industry     

Modelling uptake into roots and subsequent translocation of neutral and ionisable organic compounds

A study on uptake of neutral and dissociating organic compounds from soil solution into roots, and their subsequent translocation, was undertaken using model simulations. The model approach combines the processes of lipophilic sorption, electrochemical interactions, ion trap, advection in xylem and dilution by growth. It needs as input data, apart from plant properties, log K_OW, pK_a and the valency number of the compound, and pH and chemical concentration in the soil solution. Equilibrium and dynamic (steady‐state) models were tested against measured data from several authors, including non‐electrolytes as well as weakly acidic and weakly basic compounds. Deviations from the measured values led to further development of the model approach: sorption in the central cylinder may explain the small transpiration stream concentration factor of lipophilic compounds. For non‐electrolytes, the model predicted uptake and translocation with high accuracy. For acids and bases, the tendency of the results was satisfactory. The dynamic model and the equilibrium approach gave similar results for the root concentration factor. The calculation of the transpiration stream concentration factor was more accurate with the dynamic model, but still gave deviations up to factor of ten or more. The dominating process for monovalent weak electrolytes was found to be the ion trap effect. © 2000 Society of Chemical Industry     

Degradation of dicarboximidic fungicides in wine

The degradation of some dicarboximidic fungicides (chlozolinate, iprodione, procymidone and vinclozolin) has been studied in wine at pH values of 3.0 and 4.0, at 30°. The kinetic data obtained by observing the disappearance of the active ingredient (3.0 mg kg^?1) showed the pseudo first-order rate constants to be higher at pH 4.0 than at 3.0, with a trend for the values to be in the order: chlozolinate > vinclozolin > procymidone > iprodione. 3, 5-Dichloroaniline was not detected as a degradation product of any of the compounds. Chlozolinate and vinclozolin in wine each yielded a major metabolite, the structures of which are proposed.     

Variations among field isolates of Botrytis cinerea in their sensitivity to antifungal compounds

Seventeen field isolates of Botrytis cinerea were compared by determining their radial growth on synthetic media containing various amounts of 21 antifungal compounds. Twelve of these compounds were fungicides that are recommended for the control of Botrytis infections. There were marked differences between the isolates in their sensitivity to the compounds. Individual isolates displayed high levels of resistance to some of the fungicides, including benomyl, carbendazim, iprodione, thiabendazole, thiophanate-methyl, vinclozolin and zineb. The most potent growth inhibitors were benomyl and carbendazim (ED₉₅ values for most isolates <0.1 μg fungicide ml^?1 media), dichlofluanid, iprodione, nystatin, thiabendazole, thiophanatemethyl and vinclozolin (ED₉₅ values for most isolates < 1.0 μg ml^?1), and captan, chlorothalonil, dicloran and thiram (ED₉₅ values for most isolates < 6.0 μg ml^?1). Zineb was much less potent than the other recommended anti-Botrytis fungicides; it was no more effective than carboxin, dinocap and mancozeb (ED₉₅ values for most isolates > 25 μg ml^?1).     

In-vivo effects of 2,4-D and atrazine on cytochrome P-450 and insecticide toxicity in southern armyworm (Spodoptera eridania) larvae

After feeding 2,4-D or atrazine in a diet to southern armyworm (Spodoptera eridania Cram.) larvae for three days, the effect on total content and activities of cytochrome P450 and on insecticide toxicity were determined. Both 2,4-D and atrazine induced cytochrome P450-catalyzed aldrin epoxidation (AE) and methoxyresorufin O-demethylatin (MROD). The 2,4-D was a more potent inducer for total cytochrome P450 content, whereas atrazine disproportionately increased AE. Both compounds increased MROD significantly. The apparent kinetic characteristics of AE indicates that 2,4-D and atrazine induced similar P450 isozymes (K_m 8.78 and 7.80 μM, respectively), which may differ from the constitutive isozyme (K_m 3.14 μM). The 2,4-D-induced cytochrome P450 contributed to decreased carbaryl and permethrin toxicity, whereas the atrazine-induced cytochrome P450 caused decreased parathion and permethrin toxicity. The carbaryl toxicity correlated directly with 2,4-D-induced total P450 content and activities but not with atrazine-induced changes. The 2,4-D and atrazine also induced nonspecific esterase activity which may contribute to permethrin detoxification.