Residues of 15 pesticides in rainwater were investigated monthly from July 1999 to July 2000 at five sampling sites in Utsunomiya, eastern Japan. Additionally, the residues for each precipitation were measured at one site. Among pesticides applied mostly as granular formulations to paddy fields, simetryn, pretilachlor, mefenacet and iprobenfos with small Henry’s law constants were infrequently detected. In contrast, the herbicides thiobencarb and esprocarb with large Henry’s law constants were frequently detected outside of the application periods, suggesting that the volatilization from water and soil surfaces had continued for a long time. The annual (July 1999-June 2000) deposited amount as an average value among the sampling sites was largest for fenitrothion at 546 μg/m2, followed by thiobencarb at 196 μg/m2, esprocarb at 109 μg/m2, and fenobucarb, diazinon and phthalide at about 40 μg/m2 each. The relative standard deviations of the deposited amounts among the sampling sites were 30% or less. Fenitrothion, fenobucarb and phthalide were applied mostly as wettable powder, emulsifiable concentrate and dust formulations, allowing the pesticides to easily enter the atmosphere during the spraying or dusting process. The less variable distribution of these three pesticides is ascribable in part to the application of the above three formulations in large quantities. The annual deposited amounts of the other pesticides were about 20 μg/m2 or less, with marked variation among the sampling sites.
Compounds in which two methyl groups of acetamiprid are replaced with a set of substituents were prepared and the presence of the two rotamers was confirmed from NMR spectra. The insecticidal activities against American cockroaches and houseflies were measured by injection methods with or without metabolic inhibitors. The modified compounds were weaker than acetamiprid in their insecticidal activities against both species. A metabolic inhibitor, piperonyl butoxide, increased the insecticidal activities and in combination with NIA 16388 enlarged the rates of increase. The neuroblocking activity of the compounds was measured with excised central nerve cord of the cockroach. Here also the substitution with bulky groups at the terminal site or on the amino nitrogen atom lowered the neuroactivity, the lowering rate being greater in the former. The insecticidal potency for the cockroach with both metabolic inhibitors correlated well with the neuroblocking activity when the hydrophobicity factor of compounds was calculated separately.
The effect of light on quinclorac (3,7-dichloro-8-quinolinecarboxylic acid)-induced phytotoxicity and on 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity in intact maize (Zea mays L. cv. Honey Bantam) seedlings was investigated. The root-treatment of intact seedlings with quinclorac significantly reduced the FW of the plants, and water and chlorophyll contents of the first leaves under illumination, but not in the dark. Quinclorac (50 μM)-treated seedlings produced approximately two-fold larger amounts of ethylene in the light than in the dark. 2,5-Norbornadiene (NBD), a competitive inhibitor of ethylene, significantly recovered the quinclorac-induced decrease in water and chlorophyll. For determining ACC synthase activity, the seedlings were treated with quinclorac (50 μM) for 12 hr in the dark, and then transferred to light or kept in darkness. Quinclorac significantly enhanced ACC synthase activity in the shoot 6 hr after exposure to light, while no significant activation was observed in the dark. These results suggest that light is involved in the phytotoxic action of quinclorac in intact maize seedlings through an enhancement of ethylene biosynthesis, and that the generation of unknown light-regulated factor(s) might be responsible for the induction of ACC synthase activity following quinclorac treatment.
A landscape-scale simulation model (PADDY-Large) based on PADDY was developed for predicting pesticide concentrations in drainage canals and rivers due to runoff from paddy fields. Based on the irrigation systems used in agrohydrology, a rice-producing area was classified into a “field plot”, “farm block”, “district”, and “river basin” and pesticide behavior was estimated focusing on the main drainage canals in the “district” area. To validate the model, a surveillance of pesticide residues was carried out in a rice-producing area. Herbicide concentrations in a main drainage canal in the area increased in early May, reached a maximum in mid May, and declined to below detection limits by early July. The correlation between simulated and observed concentrations of a herbicide mefenacet in the main canal were obtained by considering actual pesticide use and environmental conditions in the rice-producing area.
Culture broths of fungal strains were screened for novel insect chitinase inhibitors using the Spodoptera litura chitinase inhibitory assay. The culture filtrates of 5 strains showed potent and specific inhibitory activity against the insect chitinase. Partial characterization showed that the active compounds produced by these strains were water-soluble macromolecular compounds which had not been hitherto reported as chitinase inhibitors. These novel chitinase inhibitors are, therefore, expected to be potential agents for insect control.
In the course of study to develop new herbicidal compounds, we found that some 4-thiazolone derivatives possessed herbicidal activity against several paddy weeds. As a result of a structure-activity relation study, 5-(2-chloroethyl)-5-methyl-2-(3-methyl-2,3-dihydro-1,4-benzoxazin-4-yl)-4-thiazolone (CMT) was selected as one of the potential herbicides for rice. CMT showed potent herbicidal activity against paddy weeds, especially barnyardgrass (Echinochloa oryzicola) and three-square grass (Scirpus juncoides). The herbicidal activity of CMT appeared to be caused by specific inhibition in the growing tissues. Electron microscopic observations of CMT-treated barnyardgrass revealed that exposure to 10 μM CMT for 4 hr caused swelling of the endoplasmic reticulum (ER) and Golgi apparatus, the separation of plasma membranes from cell walls, and an accumulation of small vesicles in the plasma membrane-cell wall interspace. These findings suggest that CMT acts primarily as an inhibitor of the secretory pathway, resulting in a dysfunction of cell wall biosynthesis.
Hydrolysis of the N-phenylimide herbicide flumioxazin was studied at pH 2.5-9.0 and 25±1°C by directly analyzing a buffered aqueous solution with column-switching high performance liquid chromatography. Flumioxazin was hydrolyzed via a base-catalyzed opening of the cyclic imide moiety with half-lives of 4.1 days, 16.1 hr and 17.5 min at pH 5.0, 7.0 and 9.0, respectively. The primary hydrolysis product was the anilic acid derivative which was subsequently degraded to the corresponding aniline and dicarboxylic acid via cleavage of the amide linkage under acidic and neutral conditions, along with a partial recyclization to flumioxazin. Kinetic analysis of the pH dependency of each reaction path showed that the acid-catalyzed cleavage of the amide bond in the anilic acid was an intramolecular reaction where the undissociated form of the carboxyl group participated.
The effect of a herbicide Zark D51 (ZD, 4.5% daimuron and 0.51% bensulfuron methyl) powder and a fungicide Fuji-One Moncut (MC, 12.0% isoprothiolane and 7.0% flutolanil) powder on microbial communities in a paddy soil was examined in laboratory experiments using Biolog GN plates. ZD had little effect on the soil microbial communities at the recommended and 50 times the recommended rate. MC showed no significant effect at the recommended rate, however, the 50-fold application caused changes in the microbial communities for at least four weeks although the activity to utilize carbon as substrate determined by color development in the Biolog plate had recovered by that time. For assessing the significance of the change in microbial communities, the magnitude of the change caused by MC was compared with that caused by soil flooding which had been shown to be the most influential environmental parameter acting on the microbial communities in paddy soils. At one week after the application of 10 times the recommended dose of MC, the microbial communities could be differentiated by the soil flooding, but not the application of MC. On the other hand, at four weeks after the application, the microbial communities could be distinctly separated by the MC application beyond the magnitude caused by the flooding. A reasonable approach is proposed for assessing the effects of pesticide on soil microbial communities.
The model to predict concentration of pesticides in the atmosphere after application on the paddy field was investigated using the Gaussian plume equation as an atmospheric diffusion model. The model was on the assumption that the pesticide was constantly discharged from the emission source, the sprayed area was topographically flat, the wind direction and the wind speed were constant. The area source was combined by 50 m square of mesh, and a point source was located in the center of the mesh. The emission rate was derived from the observed concentration inside the sprayed area, and it was observed that the emission rate decreased with elapsed time and the emission rate had a positive correlation with vapor pressure. The emission rate was estimated by vapor pressure, a temperature and elapsed time after application, then an emission rate, a plume height and a meteorological and geographical conditions were input into the area source plume equation, a predicted concentration was calculated. As a result, the predicted concentration showed significant correlation with the observed concentration (p<0.01). The predicted concentrations generally ranged from l/10 to l0 times the observed concentrations. Therefore, this model is useful for predicting pesticide concentrations.
An investigation into the leaching of 6 organophosphorus pesticides applied to an experimental putting green and their fate in a reservoir was conducted. Analyses were carried out by GC (FPD). Leaching was observed in highly water soluble trichlorfon, but the leaching ratio was only 0.014% with 40 mm/hr of sprinkle water. The other 5 pesticides were rarely found. The residual concentration of pesticides in pond water decreased with time and half-lives were longest at 17 hr for fenitrothion and diazinon, followed by chlorpyrifos > butamifos = prothiofos > trichlorfon. Although prothiofos and chlorpyrifos disappeared from the water, they persisted in the sediment. The fates of pesticides in a water-sediment system were also investigated in laboratory tests. When pesticides were applied to the water, significant differences in their half-lives were observed between field and laboratory tests, but their degradation patterns were similar. The low water soluble pesticides, prothiofos and chlorpyrifos, were rapidly and easily adsorbed by sediment with more than 40% of the applied amount take up at 3 days after application. Generally, a correlation with the solubility in water was found and a correlation (r=0.8624) between the value of octanol-water partition coefficients and adsorption in the sediment was recognized.