Degradation of Benthiocarb Herbicide in Soil*

J. Pesticide Sci. 1, 49-57 (1976)

Kanjl ISHIKAWA,** Yasuo NAKAMURAand Shozo KUWATSUKA

Life Science Research Institute, Kumiai Chem. Ind. Co., Ltd., Kikugawa-cho, Ogasa-gun, Shizuoka-ken 439, Japan

(Received October 10, 1975)

Laboratory experiments were conducted on the persistence and the degradation products of benthiocarb (4-chrolobenzyl N, N diethylthiolcarbamate) in soil, using 14C-labeled and unlabeled benthiocarb. The radioactive substances extracted with organic solvents from soil consisted mainly of parent benthiocarb with small amounts of degradation products. About 20 radioactive spots were detected by thin layer chromatography. Desethyl benthiocarb, benthiocarb sulfoxide, 4-chlorobenzoic acid, 2-hydroxy Benthiocarb and 4- chlorobenzyl methyl sulfone were identified as relatively major products, and 4-chlorobenzyl methyl sulfoxide and 4-chlorobenzyl alcohol, as minor ones. The degradation rates of benthiocarb and six related compounds in soil were also compared.

was synthesized by International Minerals & INTRODUCTION Chemical Corp. and supplied by Kumiai Benthiocarb, 4-chlorobenzyl N, N diethyl- Chemical Ind. Co., Ltd. The specific radio- thiolcarbamate, alone or in combination with activity was 3.21 m Ci/mmole and radioactive simetryne, prometryne and CNP, is now purity was about 990. extensively used to control weeds in paddy 2. Chemicals and upland fields. The herbicide is applied Benthiocarb, the 4-chlorobenzyl esters of mainly to the surface water of paddy fields N, NVdimethylthiolcarbamic, N, NVdiisopro- or to the soil of upland fields. In the fields, pylthiolcarbamic, N, N diethylcarbamic and a part of the herbicide is degraded photo- N, N diethyldithiocarbamic acids, and the l- chemically by sunlight, a part is absorbed and 3-chlorobenzyl esters of N, NVdiethyl- by the plants, while the major part penetrates thiolcarbamic acid were described previous- into the soil. Investigations on the fate and ly." 2-Hydroxy benthiocarb (mp 110-111C), behavior of the herbicide in soil are impor- 4-chlorobenzyl methyl sulf oxide (mp 101- tant. Studies on the metabolism of benthio- 102C) and its sulfone (mp 121-122C), bis(4- carb in mice" and in plants,Z and its photo- chlorobenzyl) sulfoxide (mp 164-164.5C) and degradation and volatility in aqueous solu- its sulfone (mp 241-242.5C), 4-chlorobenzyl tion3 have been reported. This paper deals methyl sulfide (bp 110-112C/10 mmHg), and with studies on the degradation of benthio- benthiocarb sulfoxide (bp>140C/008mmHg) carb in soil, with emphasis on the degradation were supplied by the Chemical Institute of pathways. The degradation rates of related Kumiai Chemical Ind. Co., Ltd. Other re- compounds are also compared. ference compounds were described in the MATERIALS AND METHODS previous paper." 3. Soil Sample 1. Radioactive Benthiocarb 14C-Benthiocarb labeled at the benzene ring Soil was taken from furrow slices of the paddy field at the Pref ectural Agricultural * Studies on the Metabolism of Benthiocarb. Part Experiment Station in Anjo, Aichi Prefecture III. See Ref. 1). ** Present address: Laboratory of Soil Science, in winter. The soil was crushed and passed Faculty of Agriculture, Nagoya University, through a 2 mm sieve. The physico-chemical Furo-cho, Chikusa-ku, Nagoya, 464, Japan. properties of the soil sample were as follows: 50 日本農薬学会誌第1巻第1号昭和51年2月

clay mineral: kaolin; texture: sandy clay 6. Extraction and Separation of Radioactive loam; clay content: 23.1%; pH (H20): 5.83; Compounds total carbon: 1.93%; C.E.C.: 13.6 me/100 g; The incubated soil was transferred into a free iron: 1.25%; available phosphorus: centrifuge tube. 100 ml of acetone was added 10.3mg%; phosphate absorption coefficient: (in unflooded soil, 40 ml of water was also 504mg (P205). added), the tube was capped, shaken 400 4. Soil Conditioning (pre-incubation) times per min for 30 min, and centrifuged (A) Flooded conditions: Fifty grams (oven- at 3000 rpm for 10 min. The supernatant was dried weight basis) of the soil sample in a collected. The sedimented soil was extracted 300 ml reagent bottle was flooded with water repeatedly with a mixture of 20 ml of water up to 1 cm deep. The soil was incubated at and 100 ml of acetone by the same procedure. 30C in the dark for 2 weeks. (B) Upland The supernatant solutions were combined conditions: Fifty grams of the soil sample and concentrated under reduced pressure to was placed in a 100 ml Erlenmeyer flask. distil off acetone. The residual water was Water was added to adjust the soil moisture extracted three times, each with 70 ml of to 600 of the maximum water holding n-hexane. These extract solutions were capacity and the soil was incubated in the radioassayed. The residual soil was air-dried same way as the flooded sample. and a small portion was oxidized to 14C- 5. Application of 14C-benthiocarb and Incuba- carbon dioxide using a Sample Oxidizer tion (Packard. Tri-Carb model 306) and the 14C-Benthiocarb (25.8 x 105 dpm) dissolved carbon dioxide evolved was trapped in in a small amount of acetone (0.5 ml) was scintillation liquid and radioassayed. mixed well with the pre-incubated soil in a 7. Radioassay flask at a concentration of 10 ppm on dry A liquid scintillation spectrometer was used soil basis. The soil was incubated under to measure the radioactivity. Samples were the same conditions as above, for 10, 20, 40 counted in 10 ml of dioxane liquid scintil- and 80 days. The moisture content was lator.l The amount of quenching was maintained at the initial level by the addi- determined by the use of an external standard tion of water once a week to replace the and comparison with a standardized quench- water lost by evaporation. ing curve. The radioactivity is expressed as

Table 1 Rf values of benthiocarb and the reference compounds.

A: benzene-ethyl acetate (10:1), B: chloroform-diisopropyl ether-n-hexane-acetic acid (10:10:10:1), C: benzene-ethyl alcohol-acetic acid (40:1:2), D: n-hexane-diisopropyl ether-diethylamine (20:20:1), E: benzene-methyl alcohol-formic acid (100: 20: 1), F: n-hexane Journal of Pesticide Science 1 (1), February 1976 51 dpm. Table 2 Relative retention times of compounds 8. Thin layer chromatography related to benthiocarb. n-Hexane extracts from the soil were dried with anhydrous sodium sulfate and concentrated. An aliquot of each concentrate was spotted on silicagel plates (Merck 60 F254, precoated, 0.25 mm thick, 20 x 20 cm) and an aliquot of the acetone solution containing reference compounds was spotted over this. Plates were developed mainly in two di- mensions with benzene-ethyl acetate (10:1) for the first development and chloroform-n- hexane-diisopropyl ether-acetic acid (10: 10: 10: 1) for the second one. Four other solvent systems, benzene-ethyl alcohol-acetic acid (40: 1: 2), n-hexane-diisopropyl ether-diethylamine (20:20:1), benzene-methyl alcohol- formic acid (100: 20: 1) and n-hexane were used, if necessary. Rf values of the refer- A Hitachi 063 gas chromatograph and 3 mm (i.d.) x 200 cm stainless steel column packed with 3% ence compounds are shown in Table 1. Silicone SE-30 on 60-80 mesh Chromosorb W Spots of the reference compounds were (AW. DMCS.) were used. The relative retention detected by irradiation of ultraviolet rays times were calculated from the retention time of (254 nm), and the radioactive ones, by radio- benzyl N, N-diisopropyldithiocarbamate. autograms on X-ray films. 9. Degradation of Benthiocarb and its Related pressure to a final volume of 1 ml. An ali- Compounds quot of the concentrate was injected into a Benthiocarb, 4-chlorobenzyl esters of N, N gas chromatograph. The gas chromatograph dimethylthiolcarbamic, N, Ndiisopropylthiol- and the operating conditions were described carbamic, N, Ndiethylcarbamic and N, N previously. Relative retention times of the diethyldithiocarbamic acids, and the 2- and compounds are shown in Table 2. The re- 3-chlorobenzyl esters of N, Ndiethylthiol- coveries of these compounds 30 min after carbamic acid were degraded in Anjo soil their addition into the soil were in the range under flooded conditions. The soil sample of 1000. was pre-incubated under flooded conditions for 2 weeks and each of these compounds RESULTS was mixed well with the soil at a concent- The rates of change in the levels of radio- ration of 30 ppm on dry soil basis. The activity present in acetone extracts of in- mixtures were incubated at 30C in the dark cubated Anjo soil sample and in the soil for 2, 4, 8, 16, 32 and 64 days. The analy- residue are shown in Fig. 1. The amount tical procedures employed were as follows: of radioactivity released from the soil sys- The incubated soil was transferred into a tems are also shown in the figure. One hour centrifuge tube, and 1 ml of 15N sodium after the addition of the radioactive chemical, hydroxide and 250 ml of n-hexane were about 1000 of the radioactivity was recovered added. The tube was capped air-tight, from the soil under both flooded and upland shaken 400 times per min for 25 min, and conditions using the acetone-water extrac- centrifuged at 3000 rpm for 10 min. Into 50m1 tant. However, the extractable radioactivity of the supernatant n-hexane solution, 1 or gradually decreased with time, and the 3 ml of benzyl N, Ndiisopropyldithiocarba- amount of radioactivity in the soil residue, mate in n-hexane (100 ppm) was added as as well as the amount released from soil, the internal standard substance, and the increased. The rate of change was lower solution was concentrated under reduced under flooded conditions than under upland 52 日本農薬学会誌第1巻第1号昭和51年2月

Flooded conditions Upland conditions

Fig. 1 Radioactivity extracted from Anjo soil Fig. 3 Percent of acetone-extractable (% of applied SC). benthiocarb applied at 10 ppm to acetone extracts (s), soil residue (A), loss (s). Anjo soil. flooded conditions (o) and upland conditions (A) conditions. even after 80 days. On thin layer chromato- Acetone extracts were concentrated, and grams of n-hexane extracts, about 20 radio- the remaining water solutions were parti- active spots were detected, as shown in Fig. tioned with n-hexane. Most of the radio- 2. The radioactivity in the n-hexane frac- activity appeared in the n-hexane extracts, tion was largely due to benthiocarb and the and only a small portion, less than 1.5% of degradation products were minor. the applied radioactivity, remained in water Fig. 3 shows the change in the amount of benthiocarb extracted with acetone-water from Anjo paddy soil. As shown in the figure, the degradation rate of benthiocarb in soil was higher under upland conditions than under flooded conditions. Half-life periods were about 45 days in the former and about 100 days in the latter. Five relatively major degradation products were identified by cochromatography (Fig. 2) as 2-hydroxybenthiocarb (spot 3), desethyl benthiocarb (spot 4), 4-chlorobenzoic acid (spot 10), benthiocarb sulfoxide (spot 15) and 4-chlorobenzyl methyl sulfone (spot 13). 4- Chlorobenzyl alcohol (spot 11) and 4-chlorobenzyl methyl sulfoxide (spot 16) were also identified as minor products. Their time- 2nd. C6Hi4-CHCI3-(iPr)20-AcOH (10:10:10:1) courses are shown in Table 3. As shown in Authentic samples the table, none of these products were present in amounts over 3% of the applied radioactivity. All of the degradation products showed no tendency to accumulate. If they increased once, they rapidly decreased later. Only a small amount of the radioactivity remained in the water fraction after extrac- Fig. 2 Thin layer chromatogram of n-hexane tion with n-hexane. Benthiocarb sulfoxide, extracts. 4-chlorobenzyl methyl sulfoxide and the sul- Jonrnal of Pesticide Science 1 (1), February 1976 53

Table 3 Time courses of the degradation products in acetone-extractable fraction. (% of applied 14c)

tr.: trace amounts (less than 0.1%)

Flooded conditions Upland conditions

Fig. 4 Procedures followed for the fractionation and determination of radioactivity in soil residue (80 days after treatment). fone were identified by thin layer chromato- acetone solution, as shown in Fig. 4. The graphy as the principal substances in the extracted substances consisted mostly of water fraction. undegraded benthiocarb. The degradation products identified were The degradation rates of seven carbamate the same for both flooded and upland soil and sulfur-containing carbamate compounds conditions. The total amounts of the de- related to benthiocarb were compared. The gradation products were somewhat larger results obtained are shown in Fig. 5. There under upland conditions than under flooded were no remarkable differences in degrada- conditions. tion rates amoung the chloro isomers. The The amount of acetone-unextractable degradation rates of NValkyl derivatives radioactive material increased gradually with decreased in the order of methyl, ethyl and time, as shown in Fig. 1. At 80 days after isopropyl. Both the carbamate and dithio- treatment, the unextractable radioactivity carbamate derivatives of benthiocarb dis- remaining in the soil was 9% under flooded sappeared more rapidly than benthiocarb. canditions and 23% under upland conditions. Their half-life periods are as follows: 35 Most of the radioactivity remaining in the days for benthiocarb, 45 days for the 2- soil was extracted by shaking with 10 ml of or 3-chloro isomers, 20 days for both the 1.25 N sodium hydroxide and 50 ml of acetone N, NVdimethyl and the dithiocarbamate deri- or 10 ml of 2 N sulfuric acid and 50 ml of vatives, 10 days for the carbamate derivative 54 日本農薬学会誌第1巻第1号昭和51年2月

Table 4 Degree of hydrolysis of related compounds after 3 hrs with 1N-KOH.

Solution (1N-KOH ethanol 10: 1) of each compound Fig. 5 Degradation rates of benthiocarb and (10-12 ppm) was heated at 78-79C for 3 hrs. related compounds. 5ml aliquots were extracted with 5-15 ml of ethyl A: 4-chlorobenzyl N, N-diethylthiolcarbamate acetate. The ethyl acetate extract was concent- B: 2-chlorobenzyl N, NVdiethylthiolcarbamate rated after drying with anhydrous sodium sulfate. C: 3-chlorobenzyl N, N-diethylthiolcarbamate An aliquot of the concentrate was injected into D: 4-chlorobenzyl N, N-dimethylthiolcarbamate the gas chromatograph to determine the amounts E: 4-chlorobenzyl N, N-diisopropylthiolcarbamate of undegraded compound. F: 4-chlorobenzyl N, N-diethylcarbamate G: 4-chlorobenzyl N, N diethyldithiocarbamate degradation products were detected by thin layer chromatography in the acetone extracts and 100 days for the diisopropyl derivative. from soils. Their amounts, however, were The rates of hydrolysis of benthiocarb and very small compared with undegraded ben- its related compounds in 1N potassium hy- thiocarb. They were not believed to be the droxide at 78-79C for 3 hrs are shown in terminal residual compounds, because none Table 4. As shown in the table, the rates of them accumulated in the run of experi- of hydrolysis of the different chloro isomers ments. were almost similar. N, N-dimethylthiol- On the other hand, the total radioactivity carbamate and N, NVdiethyldithiocarbamate in the soil system decreased with time, es- were obviously hydrolyzed more rapidly than pecially in soils under upland conditions, benthiocarb. The rates for isopropyl deriv- which means that the radioactivity was re- ative and N, N-diethylcarbamate, on the leased from the soil system during incuba- other hand, lie between those of methyl and tion. Most thiocabamate herbicides are well ethyl derivatives. known to volatilize from soil easily.4 Ben- thiocarb was also observed to volatilize DISCUSSIONS readily from its aqueous solution when ex- The persistence of benthiocarb in a soil posed to the sun. The volatilization process, under flooded and upland conditions and the however, was retarded by the addition of degradation products of the herbicide were soil into the solution. Furthermore, very investigated. The propaties of this soil are little volatilization occurred from soils into most common among the rice field in Japan. which the chemical was incorporated.3 The degradation rate of the herbicide was Therefore, the disappearance of the radio- higher under upland than under flooded activity from the soil system was thought conditions. In both cases, more than 20 to be due to the release of 14C-carbon dioxide. Journal of Pesticide Science 1 (1), February 1976 55

not describe the dealkylation process prior to hydrolysis. At least with respect to benthiocarb, deethylation is observed to be one of the degradation processes. On the other hand, the mercaptan was perhaps methylated and subsequently oxidized. The mercaptan itself and the methylated derivative were not detected, but the sul- f oxide and the sulf one of the methylated compound were detected. These results suggest that the methylation of the mercaptan and the successive sulfoxidation occur very rapidly. Thus, these products do not accumulate in detectable quanti- ties. The other possibility is Fig. 6 Possible degradation pathways of benthiocarb in soil. that the sulfoxide was directly formed from benthiocarb sul- This evolution was ascertained by separate foxide by transmethylation. No proofs to experiments.5 establish these routes are available at pre- In general, the degradation pathways of sent. But the methylation process from the thiocarbamate herbicides such as EPTC, mercaptan seems to occur, considering data vernolate and diallate in soil have not been from the hydrolysis and methylation8' of clarified, although it was observed that 14C- many compounds in soils. carbon dioxide was liberated from 14C-EPTC The second possible degradation route in the soil and by microorganisms.67 Kauf- involves sulfoxidation to benthiocarb sul- man suggested the possible degradation foxide. The process is reversible under pathway.7 From the results of the present light.9 The fate of the sulfoxide in the soil investigation, a possible degradation pathway was not investigated, but it is possible that of benthiocarb in the soil is proposed (Fig. the sulf oxide is oxidized into the sulfone, 6). It is presumed that the degradation of which may be hydrolyzed to form 4-chloro- the benthiocarb molecule is initiated at any benzyl sulfonic acid. Benthiocarb sulfoxide of three possible sites of attack. The first was first synthesized by Casida, et al.,10 who proposed pathway involves deethylation to investigated its metabolism in mice. It was produce desethyl benthiocarb which is sub- also identified as one of the photodegradation sequently dethylated to 4-chlorobenzyl thiol- products of benthiocarb.9 The experimental carbamate. Then, 4-chlorobenzyl mercaptan conditions employed in this study precluded is formed upon hydrolysis of these deethy- any reaction of the chemical with light. lated compounds and/or direct hydrolysis of Furthermore, if this sulf oxide had been the parent benthiocarb. The mercaptan formed in the course of the experiment, as then eliminates the sulf hydryl group to form in the extraction or concentration process, 4-chlorobenzyl alcohol, which is oxidized it should have been detected in the plant further in a stepwise manner to the aldehyde metabolism study, where similar procedures and the acid. This route is nearly the same were used. However, it was not detected in as Kaufman's proposed metabolic pathway the plant metabolism study. Therefore, it for EPTC and other thiocarbamate herbicides can be assumed that the sulfoxide was pro- in animals and plants.7 However, he did duced in the soil. Several organophosphorus 56 日本農薬学会誌第1巻第1号昭和51年2月 insecticides in soil are known to undergo thiocarb is much by moisture content in the oxidation of thioether linkages to the sul- soil, but is largely affected by the moisture foxide and sulfone.ll 2 state, probably the oxidation-reduction state, The third route involves hydroxylation of of the soil. the benzene ring to form 2-hydroxybenthio- Compounds related to benthiocarb are carb, which is perhaps hydrolyzed in the thought to be degraded in a similar manner. form of the desethyl analogue and/or the Their degradation rates in soil (Fig. 5) are compound itself and then oxidized subse- relatively in accordance with their stability quently in the same processes as those of to alkaline hydrolysis (Table 4). the first pathway described. The presence or absence of the chlorine The total radioactivity in the system de- atom, and its position in the benzene ring creased with time, and most part of the had little effect on the rate of degradation radioactive substances remaining in the both in the soil and in the alkaline solution. system was 14C-benthiocarb. Moreover, the These facts suggest that the hydrolytic released radioactive substances consisted cleavage of carbamate bond of benthiocarb mainly of 14C02. Details of the experiments related compounds and/or their dealkylated will be reported in a subsequent paper.5' derivatives constitute the important proces- The first degradation route described ses in the degradation in soil, and the above was the same route as that confirmed hydroxylation of benzene ring is not very in mice metabolism. In mice, the route important. leading to 4-chlorobenzoic acid was thought On the contrary, the kind of alkyl group to be the main one and that leading to 4- attached to the nitrogen atom and the chlorobenzyl methyl sulfoxide and the sulfone number of sulfur or oxygen atom attached was believed to be a minor route.l3 How- to the carbon of carbonyl or thiocarbonyl ever, in carp, the methylation and succes- largely affected the degradation rate. The sive sulfoxidation was the dominant meta- V methyl derivative and dithiocarbamate bolic pathway.14 The second sulfoxidation were degraded more rapidly in soil as well of benthiocarb was suggested as a possible as in alkaline solution. The 1V isopropyl route in mice metabolism by Casida, et al. derivative was relatively stable in the soil, This sulfoxide was fairly detected in the but it was hydrolyzed comparably rapidly in photodegradation of benthiocarb.3 In this the alkaline solution. This difference sug- study, the first pathway, leading to 4-chloro- gests that the hydrolytic cleavage or dealky- benzaldehyde, was ascertained to be the lation in soil is mainly due to microbial major route, considering that the metabolites action, but not due to chemical hydrolysis. of this pathway were formed in large The degradation of benthiocarb in the amounts. The minor route was clarified as sterilized soil will be reported in a subse- that involving a series of analogues sub- quent paper.5 stituted at the para-position of the chlorine The degradation under different water- atom by the hydroxyl group. The first and conditions was compared among several soils. the third routes in soil were also observed The behavior and degradation products were as the two major routes in plant metabo- almost same among these soils. The details lism.2 The benzene ring of benthiocarb will be also reported in the subsequent was cleaved and oxidized into carbon dioxide paper.5 in soil.5 The degradation products extracted with ACKNOWLEDGEMENTS acetone-water were nearly the some under This study was largely supported a research grant both flooded and upland conditions, although from Kumiai Chemical Ind. Co., Ltd., which also the degradation rates of benthiocarb were supplied the radioactive benthiocarb and many non- considerably different. This result indicates radioactive synthetic chemicals. The authors wish that the degradation process is the same in to express their thanks to the Company for their both cases and that the degradation of ben- support. Thanks are also due to Professor K. Journal of Pesticide Science 1 (1), February 1976 57

Kumada in the authors laboratory for his valuable advice and encouragement during the course of REFERENCES this study. The authors also express their thanks 1) K. Ishikawa, I. Okuda & S. Kuwatsuka: Agr. to Dr. A. Nakanishi of the Pref ectural Agricultural Biol. Chem. 37, 165 (1973) Experiment Station of Aichi for the soil sample, 2) Y. Nakamura, K. Ishikawa & S. Kuwatsuka: and to the members of the authors laboratory for Ann. Meeting of Agr. Chem. Soc. of Japan, the analysis of properties of the soil sample. This Abstract p. 443, 1974, Agr. Biol. Chem, under study was also supported in part by research grants preparation. from the Ministry of Education and the Ministry 3) K. Ishikawa, Y. Nakamura, Y. Niki & S. of Agriculture and Forestry. Kuwatsuka: ibid. p. 443, 1974 4) E. Koren, C. L. Foy & F.M. Ashton: Weeds, 17, 148 (1969) 要約 5) Y. Nakamura, K. Ishikawa & S. Kuwatsuka: ベンチオカーブのベンゼン環を14Cで標識した化合物 Ann. Meeting of Agr. Chem. Soc. of Japan,

および無標識の化合物を用い, 土壌中における安定性と Abstract p. 24, 1975. This Journal, under preparation. その分解生成物にっいて室内実験により検討した. ベン 6) I.C. MacRae & H. Alexander: J. Agr. Food チオカーブの分解は湛水条件よりも畑地条件で速やかで Chem. 13, 72 (1965) あった. 土壌中の全放射能も時間とともに減少したが, 7) D.D. Kaufman: ibid. 15, 582 (1967) 8) CS. Helling, P.C. Kearney & M. Alexander: 畑地条件のほうが速やかに減少した. 土壌中に残った放 "Advances in Agronomy," Vol. XXIII, p. 147, 射能の大部分は有機溶媒で抽出され, さらに抽出された 1971 放射能の大部分は未分解のベンチオカーブであった. 約 9) Y. Nakamura, K. Ishikawa & S. Kuwatsuka: 20の分解生成物が検出され, その中でdesethyl benthio- unpublished data. carb, benthiocarb sulfoxide, 4-chlorobenzoic acid, 2- 10) J. E. Casida, R. A. Gray & H. Tilles: Science hydroxy benthiocarbおよび4-chlorobenzyl methyl sul- 184, 573 (1974) 11) I. Takase, H. Tsuda & Y. Yoshimoto: Jap. J. foneが比較的主要な分解物として同定され, ほかに4- appl. Ent. Zool. 15, 63 (1971) chlorobenzyl alcohol および4-chlorobenzyl methyl sul- 12) L.W. Getzen & R.K. Chapman: J. Econ. Ento- foxide などが同定された. いずれの分解物も施用量の mol. 53, 47 (1960) 13) K. Ishikawa & S. Kuwatsuka: unpublished 3%を越えなかった. また, ベンチオカーブと6種類の data. 関連化合物の土壌中における分解速度を比較して化学構 14) R. Shinohara, S. Watari, K. Kojima & M. 造と分解との関係を検討し, さらにアルカリ水溶液中の Shimizu: Abstracts of Autumn Meeting of 加水分解との関連を調べた. Nippon Suisangakkai, Oct. 1973, p. 223