The germination of rice and corn seeds within the graded moisture range between 11 and 15% was tested after they were fumigated with phosphine and methyl bromide at their different concentrations, exposure times and temperatures. The sorption of the fumigants by both seeds was also studied. The viability of rice seeds with 11 and 15% moisture was not impaired by phosphine with its concentration up to 200mg/l. Corn seeds were also tolerant to the fumigant when their moisture content remained 11%. With the 15% moisture their viability was affected drastically at both 30°C and 35°C. Rice seeds were more sensitive to methyl bromide than corn seeds. To maintain their reasonable viability when exposed to up to 5mg/l of methyl bromide at 25°C and 30°C for 5 days, moisture of the rice seeds should not be higher than 11%. Corn seeds were generally viable when exposed to up to 10mg/l of methyl bromide at 25°C and 30°C for 5 days when their moisture content was kept not higher than 13%. The rate of sorption was found to be related to the viability decline of both seeds. Rice seeds sorbed less phosphine than corn seeds and likewise were less affected. As for the methyl bromide sorption the reverse was true. The effects of seed moisture, exposure temperature and time, and types of sorption were also discussed in this paper.

View full abstract

The selectivity of naproanilide [2-(2-naphthoxy)propionanilide] in rice plants, broadleaf and cyperaceous weeds was studied through both pre- and post-emergence tests. Rice plants were found extensively tolerant to naproanilide, while Cyperus difformis L, , Monochoria vaginalis BURM, f., Rotala indica WILLD., Sagittaria pygmaea MIQ. and Scirpus juncoides ROXB. were very sensitive. The absorption rate of ¹⁴C-naproanilide in rice plants was much lower than in Sag. pygmaea. Moreover, in rice plants the translocation from root to upper portion was retarded, but in Sag. pygmaea, radioactivity was distributed uniformly in the shoot, tuber and root.

View full abstract

On single oral administrations of (RS)-(E)- and (RS)-(Z)-1-(2, 4-dichlorophenyl)-4, 4-dimethyl-2-(1, 2, 4-triazol-1-yl)-1-penten-3-ols [(RS)-8AE and (RS)-8AZ], both labeled with ¹⁴C at the phenyl or triazolyl carbon, to male rats at the rates of 5 and 125mg/kg b. w., ¹⁴C was eliminated rapidly in feces (major) and urine (minor) with 100% recovery within 7 days. Tissue residues on the 7th day after the administration at the rates of 5 and 125mg/kg b. w. were less than 29 and 400ng of parent compound equivalents/g tissue, respectively. Metabolic pathways of (RS)-8AE and (RS)-8AZ were established after identifying approximately 80% of the dosed ¹⁴C. Major metabolites were carboxylic acid and alcohol derivatives biotransformed by oxidation of the tert-butyl group, which amounted to 25-62% and 4-15% of the dosed ¹⁴C, respectively. Most of the metabolites were secreted into bile and underwent enterohepatic circulation. The amount of the carboxylic acid derivative excreted into feces was smaller in (RS)-8AZ-dosed rats than in (RS)-8AE-dosed rats. A smaller amount of a ketone derivative generated by oxidation at C₃ position was found only in bile of the rats dosed with (RS)-8AZ, whereas metabolites having methylthio and/or hydroxy groups on the benzene ring were detected only in feces of the rats dosed with (RS)-8AE.

View full abstract

The degradation of fenitrothion (I) and 3-methyl-4-nitrophenol (II), one of the major degradation products in soil, was studied, using ¹⁴C preparations labeled at the phenyl ring. In two kinds of aerobic upland soils, I and II degraded with an initial half-life of less than 7 days. A main degradation route of I was a cleavage of the P-O-aryl linkage, leading to the formation of II which underwent further metabolism to ¹⁴CO₂. In soils treated initially with II, a trace amount of 3-methyl-4-nitrocatechol was detected. When soils containing the bound ¹⁴C residues arising from I were mixed with fresh soil, 17.5 to 22.4% of the bound ¹⁴C was mineralized to ¹⁴CO₂ over 22-week period. In two kinds of submerged soils, I degraded mainly via reduction of the nitro group to the amino group with an initial half-life of less than 7 days. The resultant product was bound to the soils or metabolized further to the formylamino and acetylamino derivatives. In addition, a relatively large amount of ¹⁴CO₂ was evolved from the soils. When the conditions of the submerged soils were altered to those of aerobic upland by draining the flooded water, the bound ¹⁴C residues were partially mineralized to ¹⁴CO₂. Furthermore, the bound ¹⁴C residues in upland and submerged soils were hardly taken up by bean and rice plants, respectively.

View full abstract

The absorption, translocation and metabolism of [¹⁴C] benfuracarb or 2, 3-dihydro-2, 2-dimethyl-7-benzofuranyl N-[N-[2-(ethoxycarbonyl)ethyl]-N-isopropylsulfenamoyl]-N-methylcarbamate, a new sulfenylated methylcarbamate insecticide, was examined in cotton plants. The absorption and translocation of this material was also examined in the bean and corn plants. Topical application of radiolabeled benfuracarb to the base of the leaf resulted in translocation of radioactivity to all parts of the treated leaf including the stem and even movement in the root was observed. Stem injection of benfuracarb resulted in more rapid translocation of radioactivity to all parts of the plant including the root. In cotton plants, N-S bond cleavage occurred as the initial step in the metabolic pathway, giving rise to carbofuran which, in turn, was oxidized at the 3-position of the ring and the N-methyl group. These oxidized metabolites were then converted to plant conjugates. Major metabolites were carbofuran and 3-hydroxy-carbofuran.

View full abstract

In laboratory experiments, repeated applications of benthiocarb (thiobencarb, S-4-chlorobenzyl N, N-diethylthiocarbamate) to soil shortened the lag period of benthiocarb dechlorination and accelerated the dechlorination. This activity, however, decreased rapidly after complete disappearance of benthiocarb. When a small amount of soil activated by repeated applications of benthiocarb was inoculated into 16 different inactive soils, they showed different dechlorination activities due to the difference in their properties. The phosphate content was closely correlated to the activity. When the diluted suspension of activated soil was inoculated to autoclaved soil, the activity was stimulated. The inoculation to nonreactive soil also induced the high activity when the soil had been autoclaved. Dechlorinating microorganisms were hardly separable from soil particles. The dechlorination in soil was strongly inhibited by methoxyphenone and BNA-80, especially by BNA-80.

View full abstract

In a suspension of Ohshiro soil activated for dechlorination, benthiocarb (thiobencarb, S-4-chlorobenzyl N, N-diethylthiocarbamate) was dechlorinated after a lag period by amending with sugars, starch, cellulose, and ascorbate but not with several amino acids. The dechlorination activity was greatly affected by the concentration of organic additives, temperature, and pH of the suspension, and these factors worked within very narrow ranges. The optimum condition was 25°C-30°C and pH7. The reaction rate in the suspension was greater under N₂ than air. Even under aerobic conditions, the reaction did occur, although it started after a long lag period and proceeded slowly. Therefore, the dechlorinating microbes were suggested to be facultative anaerobes and the lag period for the dechlorination to be a time for proliferating dechlorinating microbes.

View full abstract

The behavior and disappearance of the herbicides chlomethoxynil and benthiocarb (thiobencarb) in soil and surface water were investigated using a model paddy field (an ordinary culture and a bare ground) under a controlled rate of drainage. The concentrations of chlomethoxynil in the effluent water were 4-6ppb at maximum and decreased gradually to 0.1ppb within 60 days after its application. A similar residue pattern of chlomethoxynil in water was observed both in ordinary culture and under bare ground conditions. A positive correlation (r=0.96) was observed between the concentration in soil and that in water. Benthiocarb concentration in the effluent water was 380ppb at maximum and decreased rapidly below the detection limit (1ppb) in 25-30 days after the application. The estimated half-life values of chlomethoxynil and benthiocarb in soil were 10-22 days and 10-30 days, respectively.

View full abstract

The metabolism of (±)-(2Z, 4E)-α-ionylideneacetic acid and its 1′-hydroxyl analog in plants such as tomato, soybean, oat and rice, was investigated. After incubation with the substrates for 12hr, the separated acidic metabolites were methylated with diazomethane and then analyzed by TLC and GLC. α-Ionylideneacetic acid was converted into 4′-oxo-α-ionylideneacetic acid in all the plants examined. (±)-(2Z, 4E)-1′-Hydroxy-α-ionylideneacetic acid was metabolized to (2Z, 4E)-dehydro-β-ionylideneacetic acid and (+)-abscisic acid in tomato plants.

View full abstract

Characteristics of the microbes which cause the dechlorination of benthiocarb (thiobencarb, S-4-chlorobenzyl N, N-diethylthiocarbamate) were studied using the highly diluted suspension of activated soil. The dechlorination in the suspension was accelerated by ascorbate. It did not start when the suspension was amended with inorganic reductants as well as thioglycolate. The reaction in the suspension containing starch was greatly promoted by NADPH and a little by ADP and ATP, but not by adenine and nicotinamide. In the experiment on the inhibition using various antibiotics, the dechlorination microorganisms were suggested to be gram-positive facultative anaerobic bacteria. The dechlorination was inhibited by methoxyphenone and BNA-80, especially by BNA-80 at extremely low concentrations. Of benthiocarb analogues, p-Cl-phenyl and m-Cl-phenyl derivatives, N, N-dimethyl-and N, N-dipropyl-substituted compounds and dithio derivatives were dechlorinated. The o-Cl-phenyl derivatives of benthiocarb as well as other groups of chlorinated compounds such as chlornitrofen, chlorpropham and γ-BHC were not dechlorinated. The findings suggest that the microbes can dechlorinate only limited compounds.

View full abstract

[in Japanese]

View full abstract

About forty bicyclic phosphates (BPs) and phosphorothionates (analogs of 2, 6, 7-trioxa-1-phosphabicyclo[2.2.2]octane) were synthesized to elucidate the mode of action of the cage convulsants. Some of them were highly toxic to the mouse and the housefly, although the former was more sensitive than the latter. The Hansch-Fujita analysis suggested that hydrophobic, steric and electronic interactions between the bridgehead substituent and putative binding site (s) in vivo played an important role in BP poisoning. Phosphorus compounds of this class were unique in that their anticholinesterase activity was extremely low despite their high reactivity under alkaline conditions. The bicyclic phosphates suppressed the miniature inhibitory junction potentials recorded from the longitudinal muscle of the earthworm. A specific binding site for toxic BPs was identified in the rat brain and was shown to be related to the γ-aminobutyric acid (GABA) receptor-ionophore complex by a ligand-receptor binding assay using 4-n-propyl[2, 3-³H]BP as a ligand. Interactions between BPs and the site of action were speculated by using cyclodextrin as a specific BP binding site model. Taken together, these findings indicate that the bridged bicyclic phosphorus esters antagonize the action of the neurotransmitter GABA by binding to a site linked to chloride ion channels in the postsynaptic membrane.

View full abstract

The design of new cyclic N-phenylimide fungicides was performed by using a QSAR technique, the Hansch-Fujita method. Furthermore, a computer program called PREHAC, which aids in the impartial selection of substituents for the synthesis of highly bioactive compounds among congeners based on the Hansch-Fujita method, was developed and used effectively for the above-mentioned fungicide design. 3, 5-Dihalo substituents on the benzene ring moiety enhance greatly the antifungal activity of cyclic N-phenylimides against Sclerotinia sclerotiorum, Botrytis cinerea, etc. The relationships between the chemical structure and antifungal activity against B. cinerea of a number of N-phenylsuccinimides and related N-phenyl-1, 2-dimethylcyclopropanedicarboximides having various benzene ring substituents were analyzed for the purpose of the clarification of the physicochemical meaning of 3, 5-dihalo substituents and the search for substitutes for them. The high antifungal activity of the cyclic N-(3, 5-dihalophenyl) imides was rationalized by the hydrophobicity and electron-withdrawing properties of halogen atoms. In addition, the steric bulk of one of the two halogen atoms was revealed to be unfavorable to this activity. It was concluded that 3, 5-dihalo substitutions were most desirable for high activity of this series of compounds. The antifungal activity of N-(3, 5-dichlorophenyl) succinimides and 3-(3, 5-dichlorophenyl)-2, 4-oxazolidinediones, having various substituents on the imido rings, against B. cinerea was related only with the hydrophobicity of the imido ring moieties including the substituents. The 1-isovaleroyl derivative of 3-(3, 5-dichlorophenyl)-2, 4-imidazolidinedione (isovaledione) was designed as a new fungicide against Alternaria diseases. The activity of 1-acyl-3-(3, 5-dichlorophenyl)-2, 4-imidazolidinediones against A. kikuchiana was related parabolically with both the hydrophobicity and steric bulkiness of the aryl moiety substituents. The higher the electroN-donating power of the substituents and the smaller their minimum width in the direction perpendicular to the bond axis, the greater was the activity.

View full abstract