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Behaviour of pesticides in Lake Kasumugaura, Japan
The Science of the Total Environment, 72 (1988) 29-42 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
29
B E H A V I O U R OF P E S T I C I D E S IN LAKE K A S U M I G A U R A , J A P A N
HIROAKI SHIRAISHI', FLUTRA PULA 2, AKIRA OTSUKI' and TOSHIO IWAKUMA 1
~National Institute for Environmental Studies, 16-20nogawa, Yatabe, Ibaraki 305 (Japan) eKomiteti Krahinor per Urbanizem, Rr. M. Tito 2, 38000 Prishtina (Yugoslavia) (Received September 19th, 1987; accepted October 22nd, 1987)
ABSTRACT Pesticides such as oxadiazon, isoprothiolane, diazinon, IBP, simetryne and benthiocarb, from surface runoff from rice paddy fields to Lake Kasumigaura, J a p a n were examined in order to determine seasonal changes in their concentrations in the lake water. The highest concentrations were observed near the river mouths during May to August, soon after pesticide application; hence they are transported mainly by surface runoff. Although these pesticides have been reported to be labile, concentrations of some of them, dispersed with the movement of the water, did not decrease rapidly in the natural aquatic environment. The highest concentrations, in 1985, of oxadiazon, isoprothiolane, diazinon, IBP, simetryne, benthiocarb and CSB were 0.66, 0.84, 0.16, 3.24, 3.23, 2.15 and 1.13 ppb, respectively. The relative order of persistence and mobility of pesticides in the lake water was estimated as: isoprothiolane, CSB, simetryne > IBP > diazinon >> oxadiazon > benthiocarb. INTRODUCTION
Organic chemicals such as pesticides (e.g. herbicides, insecticides, fungicides) are potentially hazardous to living organisms. Some pesticides, such as DDT and HCH, are persistent in the environment and accumulate in human tissue or other animals through the food chain, and their use has been banned. Consequently, new types of pesticides, such as organophosphorus and carbamate compounds, have been developed so as to reduce bioaccumulation and persistence in the environment, and toxicity to non-target organism. Although the new pesticides are more degradable than the organochlorines, their concentrations in river water draining from paddy fields are quite high directly after their application. Since the pesticides are applied directly to constantly overflowing paddy waters which drain to natural waters, aquatic organisms are exposed to pesticide-contaminated water. The degree of pesticide pollution is dependent upon dose rates and the manner of application. In J a p a n the use of organochloride pesticides in paddy fields is still increasing. Toxic effects to aquatic organisms caused by pesticide application have been reported (Suzuki, 1980). The concentrations of various pesticides in inland waters surrounded by paddy fields have been reported (Hori and Nakazaki, 1982; Nakamura, 1982; Suzuki, 1982; Mikuriya and Miyahara, 1983; Tsukamoto and Asaka, 1983; Ishii, 1984; Hankawa, 1985). Lake Kasumigaura, the second largest lake in Japan, is
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30 surrounded by many large paddy fields, but very little is known about pesticide residues in the lake water, which is an important source of water for drinking, agriculture, fisheries, and industry in southern Ibaraki prefecture. Therefore, inputs of toxic substances are undesirable and harmful. After a preliminary study in 1984, monitoring of pesticide levels in Lake Kasumigaura water was carried out from 1985 to 1986, and the results are reported here. EXPERIMENTAL
Field Description Lake Kasumigaura is located in the eastern part of the Kanto Plain, 50 km northeast of Tokyo. The lake has two large bays, Takahamairi and Tsuchiurairi. The lake basin is smooth and shallow with a surface area of 171 km 2, a mean depth of 4 m, and a maximum depth of 7.4 m near the mouth of Takahamairi Bay. The lake water surface is only l m above sea level.
Materials Hexane, benzene and methanol were pesticide grade (Wako Pure Chem. Ind., Ltd.) and required no further purification before use. Water was purified by distillation, and passage through a Milli-Q system (Millpore Corp.) and XAD-2 resin column before use. The following standard pesticides were used: 5-tertbutyl-3-(2,4-dichloro-5-isopropoxyphenyl)-l,3,4-oxadiazol-2(3H)-one (oxadiazon); diisopropyl 1,3-dithiolan-2-ylidene-malonate (isoprothiolane); O,O-diethyl O-2-isopropyl 6-methylpyrimidin-4-yl phosphorothioate (diazinon); S-benzyl O,O-diisopropyl-phosphorothioate (IBP); 2,4-bis(ethylamino-6methylthio-l,3,5-triazine (simetryne); and S-4-chlorobenzyldiethylthiocarbamate (benthiocarb); all were purchased from Wako Pure Chem. Ind., Ltd. 4-(Chloromethylsulfonyl)bromobenzene (CSB) was synthesized according to standard procedures.
Sampling Sampling stations in Lake Kasumigaura are shown in Fig. 1. Stations I 4 are located in Takahamairi Bay and Stations 6-8 in Tsuchiurairi Bay. Station 9 is in the centre of the lake and Stations 11 and 12 are near the outlet. Lake water (surface to 2m depth) was collected using a water column sampler. After mixing, the samples were stored in 11 glass bottles and transferred to the laboratory.
Extraction One liter of sampled water was dispensed to glass bottles, then immediately filtered through a Whatman GF/C glass filter. The weighed aliquot of water
31 Koise River
~
2
St.1 1 3 4
•
;,~..\ ~,st.3' "l TakahamairlWatershed , ~ ]
Fig. 1. Sampling stations of Lake Kasumigaura and Koise River. ( ~ I l) was mixed with the solvent (50 ml hexane) and shaken using an electric s h ak er for 10 min. The solvent phase was then separated from the water phase and the ex tr acti on was repeated once more with the same am ount of solvent (50 ml hexane). The hexane fractions were combined and frozen to remove any remaining water as ice. The e xt r act was c on cent rat ed by a r o t a r y e v a p o r a t o r to ~ 3 ml; this c o n c e n t r a t e was f ur t her c o n c e n t r a t e d under nitrogen gas flow at room t e m p e r a t u r e to 2 ml and t he n 3 gl aliquots of each concent rat ed ext ract was injected into a GC/ECD and GC/NPD. For GC/MS analysis it was furt her c o n c e n t r a t e d to 0.1 ml.
Determination CSB, oxadiazon and isoprothiolane were determined using a Hewlett P a c k a r d Model 5980A gas chr om at ogr a ph equipped with an ECD and fitted with a glass column (OV-17, 2m). The column was operated isothermally at 200°C, injector t e m p e r a t u r e 250°C and detector t em perat ure 300°C. Nitrogen was used as the car r i er gas at a flow rate of 5 0 m l m i n -~. Diazinon, IBP, simetryne and benthiocarb were determined using a Shimadzu GC-7A gas c h r o m a t o g r a p h equipped with a NPD and fitted with a capillary column (OV-1, 25 m). Helium was used as the car r i er gas at a flow rate of 2 ml min 1. The peak area of the pesticide signal in the gas chr o m at ogram was determined with a chromatographic data processor Model 7000 AS (SIC, Japan). The concentrations determined ( ngkg 1) by GC analysis using 11 of water were as follows: CSB (0.4), oxadiazon (2), isoprothiolane (2), CNP (2), diazinon (1), IBP (2), simetryne (24), benthiocarb (7), molinate (6), BPMC (8), MPP (10) and carbosulfan (10).
32
o >..
10"
1'2 " 14
" 1'6 " 1'8 " 2'0 " 2'2 " 2'4"
v~ m
216 ' 2'8 ' 310
rnin.
Fig. 2. R e c o n s t r u c t e d ion c h r o m a t o g r a m (RIC) of the h e x a n e e x t r a c t of Lake K a s u m i g a u r a water. TABLE1 List of compounds identified Compound a
RTh(min)
Diagnostic ions (rn/z) c
1 2 3 4 5 6 7 8 9 10 11 12 13 14
7/28 11130 16'48 18'00 20'20 21'54 22'08 23'10 23'48 24'22 24134 27'40 28'20 29~42
146([M]+), 148, 111, 113 128([M] ~ ), 127, 126 152([M] ~), 151, 150 126, 83, 98, 187([M] +)
p.Dichlorobenzene Naphthalene Acenaphthene Molinate p.sec-Butylphenol Diazinon Phenanthrene IBP CSB Simetryne Benthiocarb Oxadiazon Isoprothiolane Di-n-butylphthalate
121, 150([M] ~), 77 137, 179, 152, 304([M] + ), 151, 167 178([M1 ~ ) 113, 204, 91, 246, 288([M] ' ) 219, 157, 155, 76, 268([M] +) 213([M] ÷ ), 170, 198, 138, 185 100, 72, 257([M] ~ ), 259 175,177, 258, 302, 344([M] ~) 118, 162, 189, 290([M] ~ ), 231 57, 71, 43, 149([M]' ), 99
Peak n u m b e r refers to Fig. 2. hRT ~ r e t e n t i o n time. m / z is listed in t h e order of relative a b u n d a n c e of the ioas.
T h e pesticide identifications were confirmed by GC/MS using a Model DX300 double focusing mass s p e c t r o m e t e r (JEOL, J a p a n ) equipped with a H e w l e t t P a c k a r d Model 5700 GC, and JMA-3500 mass d a t a analysis system (JEOL). The c o l u m n (25m, OV-1701) was coupled d i r e c t l y to the mass spectrometer. The c o l u m n t e m p e r a t u r e was set at 60°C for 2 min, followed by an i n c r e a s e to 260°C at a r a t e of 8°C min 1, and t h e n held at 260°C. The i n j e c t o r t e m p e r a t u r e was 250°C and the h e a d p r e s s u r e of the c o l u m n was 0 . 6 k g c m -2. The mass spect r o m e t r i c c o n d i t i o n s were as follows: a c c e l e r a t i n g voltage, 3.0kV; ionizing
33 TABLE 2 List of physical properties of pesticides m.p. (melting point, °C); b.p. (boiling point, °C/mmHg); v.p. (vapor pressure, mmHg/°C); sol. (solubility in water, ppm/°C) Oxadiazon; 5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-l,3,4-oxadiazol-2(3H)-one (C,~Hls C12N203) m.p. 91; v.p. < 10 6/20; sol. 0.7/20 Benthiocarb; S-4-chlorobenzyldiethylthiocarbamate (C12H16C1NOS) m.p. 3.3; b.p. 12~129/8 × 10-3; v.p. 1.476 × 10 4/20; sol. 30/20 CSB; 4-(chloromethylsulfonyl)bromobenzene (CTH6BrSO2C1) m.p. 146; sol. 30 Simetryne; 2,4-bis(ethylamino)-6-methylthio-l,3,5-triazine m.p. 82 83; v.p. 7.1 × 10-7/20; sol. 450
(CsH15NsS)
IBP; S-benzyl O,O'-diisopropylphosphorothiolate (C,3H2103PS) m.p. 22.5-23.8; b.p. 126/0.04; sol. 1000 Diazinon; O,O'-diethyl-O~'-2-isopropyl-6-methylpyrimidin-4-phosphorothionate v.p. 1.4 × 10-4/20; b.p. 83-84/0.002; sol. 40
(C12H21N203PS)
Isoprothiolane; diisopropyl-l,3-dithiolan-2-ylidene-malonate (C12H~s04 S~) m.p. 54.5-55.0; b.p. 167-169/0.5; sol. 48/20 CNP; 2,4,6-trichlorophenyl-4-nitrophenyl ether (CI~H6C13NO3) m.p. 107 107.1; b.p. 210/~7; v.p. 0.35/109
c u r r e n t , 300/~A; i o n i z i n g v o l t a g e , 70 V; s c a n r a n g e m/z 10~400; m a s s r e s o l u t i o n , 500; s c a n i n t e r v a l 2 s. C h e m i c a l i o n i z a t i o n (CI) w a s p e r f o r m e d u s i n g i s o b u t a n e as t h e r e a g e n t gas.
Recovery test A n a c e t o n e s o l u t i o n (10 ttl) o f s t a n d a r d c o m p o u n d s w a s a d d e d to I 1 p u r i f i e d w a t e r , a n d t h e a q u e o u s p h a s e w a s e x t r a c t e d t w i c e w i t h 50 ml h e x a n e , a n d t h e solvent phase was then separated from the water phase, concentrated and a n a l y z e d as d e s c r i b e d a b o v e . T h e r e c o v e r y e x p e r i m e n t s w e r e p e r f o r m e d at 1 - 5 p p b levels. R e c o v e r i e s (%) w e r e as follows: d i a z i n o n (91), I B P (91), s i m e t r y n e (34), b e n t h i o c a r b (69), C S B (56), o x a d i a z o n (94), i s o p r o t h i o l a n e (72), B P M C (78), m o l i n a t e (100), M P P (100), b u t a c h l o r (100), c a r b o s u l f a n (100) a n d C N P (92). RESULTS AND DISCUSSION F i g u r e 2 s h o w s a r e c o n s t r u c t e d i o n c h r o m a t o g r a m (RIC) o f t h e e x t r a c t f r o m
34 TABLE 3 The amount of applied pesticides in rice paddy fieldsa and the month of application in Takahamairi Bay watershed in 1985 Pesticide
Month of application
Amount applied (kg)
1 2 3 4 5 6 7
Mid-May to early June Mid-July to early Aug Mid-May to early June Mid to late May Early May Early Aug Early May
2288 2531 42 483 173 105 1452
Benthiocarb IBP Diazinon Simetryne Oxadiazon Isoprothiolane CNP
aTotal area of rice paddy fields in the upper watershed of Takahamairi Bay is 1860ha. L a k e K a s u m i g a u r a w a t e r ( J u n e 1985, S t a t i o n 6); T a b l e 1 lists e a c h c o m p o u n d identified. All the l a r g e p e a k s in t h e RIC c h r o m a t o g r a m w e r e due to pesticides. A m o n g t h e o r g a n i c c o m p o u n d s listed in T a b l e 1, s e v e n pesticides, CSB, o x a d i a z o n , i s o p r o t h i o l a n e , diazinon, IBP, s i m e t r y n e a n d b e n t h i o c a r b w e r e m o n i t o r e d b e c a u s e of t h e i r wide use in p a d d y fields from 1985 to 1986. B P M C , m o l i n a t e , M P P , b u t a c h l o r a n d c a r b o s u l f a n w e r e m o n i t o r e d in 1986. T h e p h y s i c a l a n d c h e m i c a l c h a r a c t e r i s t i c s of the pesticides a r e s h o w n in T a b l e 2. T h e a m o u n t s of pesticides sold in the T a k a h a m a i r i w a t e r s h e d in 1985 w e r e o b t a i n e d f r o m a g r i c u l t u r a l c o o p e r a t i v e a s s o c i a t i o n s a n d a r e s u m m a r i z e d as a c t i v e c o m p o n e n t s in T a b l e 3. T h e m o n t h of t h e i r a p p l i c a t i o n in rice p a d d y fields is also shown. T h e s e v a l u e s could be u n d e r e s t i m a t e s , b e c a u s e of difficulties in i d e n t i f y i n g pesticide usage. T h e c h a n g e s in t h e c o n c e n t r a t i o n s of p e s t i c i d e s a t r i v e r m o u t h s ( S t a t i o n s 1 a n d 6) a n d the c e n t e r of t h e l a k e ( S t a t i o n 9) a r e s h o w n in Fig. 3. T h e a v e r a g e c o n c e n t r a t i o n s of t h e s e pesticides in L a k e K a s u m i g a u r a w a t e r from M a y 1985 to S e p t e m b e r 1986 a r e s h o w n in Fig. 4.
Oxadiazon T h e r e a r e m a n y r e p o r t s of t h e o c c u r r e n c e of o x a d i a z o n in s u r f a c e w a t e r s ( Y a m a t o et al., 1979; Y a m a t o a n d Suzuki, 1980; Ishii, 1984) a n d in fish ( I m a n a k a et al., 1981, 1985). O x a d i a z o n is applied before rice p l a n t i n g in liquid form, so it is r e s o n a b l e t h a t the h i g h e s t c o n c e n t r a t i o n s (0.66 #g kg-1 in 1985 a n d 0.78 #g kg-1 in 1986) a t S t a t i o n I w e r e f o u n d in May. D i r e c t a p p l i c a t i o n o f o x a d i a z o n in liquid form m a y r e s u l t in a r e l a t i v e l y r a p i d r u n o f f of this pesticide, despite its low s o l u b i l i t y in water. O x a d i a z o n was l e a c h e d c o n t i n u o u s l y f r o m t h e p a d d y fields to the l a k e d u r i n g t h e period from M a y to J u l y . A f t e r flowing into t h e lake, the c o n c e n t r a t i o n s in l a k e w a t e r d e c r e a s e d c o n s i d e r a b l y a n d the r e s i d u e levels r e m a i n e d low in the c e n t e r of t h e lake. T h e low c o n c e n t r a t i o n s o b s e r v e d m a y be due b o t h to its p e r s i s t e n c y a n d the a d s o r p t i o n of o x a d i a z o n on soil p a r t i c l e s Fig. 3. The changes in concentration of pesticides in Lake Kasumigaura water (Stations 1, 6 and 9) from April 1985 to September 1986.
35 OXADIAZON
ppb
~Sta. 1 ~Sta.6 -e-Sta.9
0"81
BENTHIOCARB
ppb 2.5"
Sta. 1 ~Sta.6 ~'-Sta. 9
2.0 0.6 1.5
i,ll
0.4
1.0 0.2
0.5
0
M J
J
A S 0 1985
ppb 1.5
0 A MJ
N D A M J J 1986
CSB Sta. 1 ~Sta.6 ~ - Sta. 9
J
ppb 5.0
AS 1985
. . . . ND
// - - _ MJ J A 1986
SIMETRYNE Sta.1 Sta.6 ~ - Sta.9
4.0-
0 I
3.0
/'~
2o
0.5
O
. . . . . . . .
A M J J A S 0 1985
ppb 5.0
r -~'I ~ N D A M J J 1986
JTM3
AS
IBP ~Sta.1 ~Sta.6 ~-Sta.9
ppb 0.5
4.0
o.4
3.0
o.3
DIAZINON
~Sta.1 Sta.6 ~ - Sta,9
i
0.2-
2.0
J A
1986
1985
1.0 O
M J J A ~ U M U 1985
ppb 1.5-
AM
m u19J86** o
ISOPROTHIOLANE ~ Sta. 1 Sta.6 -o- Sta.9
1.0
0,5
0
A
MJ J A s 0 N O#,i M J 5 i s 1985
1986
J
J A S 1985
0
N
D
M
JA 1986
36 ppb
2"5t 2.0
i [] Benthiocarb [] Dazinon I [] Oxadiazon
1.5 t
111111
[] Isoprothiolane / [] Simetryne
1.o
i
O'5l 0
.
.
.
.
.
.
.
.
.
.
1 2 3 4 6 7 8 9 11 12 (Sta.)
Fig. 4. The average concentrations of pesticides (from April 1985 to September 1986) in Lake Kasumigaura water. due to its low solubility in water. Taking into account the reported persistence of oxadiazon in soils (Ambrosi et al., 1977), it seems likely t hat oxadiazon is leached continuously and slowly from paddy fields. Oxadiazon would not be transported for long distances without fast flowing water, but would settle to the sediment with suspended particles. A slight increase in c o n c e n t r a t i o n was observed in October 1985, but the reason is not known. Benthiocarb Benthiocarb has been used extensively to control various weeds such as barn-yard-grass, slender and spikerush in both paddy and upland fields in Japan. The total production in 1985 was 5150 tons. Benthiocarb is applied to the surface water of paddy fields 3 20 days after transplanting rice seedlings. In Japan, benthiocarb has been one of the most commonly used herbicides in rice paddies in recent years. Its occurrence and concentrations in rivers and agricultural drainages have been reported (Suzuki et al., 1976; Nakamura, 1982; Ishii, 1984). The highest concentrations were oberved at Station 1 in J u n e 1985 (2.15pgkg 1), very soon after direct application of this herbicide. The conc e n t r a t i o n of benthiocarb then became very low, and decreased below the detection limit after September, except near river mouths. Benthiocarb was undetectable in the lake water very soon after entry, which agrees with studies on the photodegradation of benthiocarb herbicide and on its volatilization from aqueous solutions and soil (Ishikawa, et al., 1976, 1977a, b). In 1986, little benthiocarb is known to have been applied in Kasumigaura basin, hence low concentrations are expected. C SB There are a few reports on CSB; the environmental occurrence of this
37 compound has recently been reported (Shiraishi and Otsuki, 1987). CSB is used as one of the additives in benthiocarb. The highest concentrations of CSB residues were observed at Station 1 (1.13pgkg 1) in June, which correlates well with benthiocarb c o n c e n t r a t i o n s at Station 1; CSB levels at river mouths decreased with time and the lowest values were found in December (13 ng kg -1 , Station 1). While benthiocarb decomposes rapidly and could not be detected except at river mouths after September, CSB moved with the water mass and was dispersed over the whole lake. The highest c o n c e n t r a t i o n of CSB was observed 1 month after application at the center of the lake, and was t hen detected for several months over the whole lake. In 1986, CSB was undetectable in the lake water as a consequence of the much reduced application of benthiocarb. Taking into account t h a t the CSB content of benthiocarb is ~ 4% in commercial products, it was surprising t h a t CSB levels at Station 1 in June were similar to those of benthiocarb. This could be the result of a combination of factors: (i) CSB run-off was greater t h a n t hat for benthiocarb; (ii) benthiocarb decomposed faster t han CSB in both the paddy field and in the lake.
Simetryne Simetryne is a herbicide which is used in paddy fields to control various weeds. In June, the highest concent r a t i ons of simetryne (3.23 ttg kg-1 in 1985, and 4.84 gg kg ~in 1986) were observed at Station 1. The highest concent rat i ons at Station 6 were observed in J ul y (1.26 #g kg- ~in 1985 and 2.21 ttg kg- 1in 1986). The c o n c e n t r a t i o n in the lake center was at its highest 1 month after the entry of this herbicide into the lake. Although the reason was not clear, a slight increase in the c o n c e n t r a t i o n of this herbicide was observed in October 1985. The change in c o n c e n t r a t i o n of simetryne near the river mouth was very rapid, and was similar to t h a t of benthiocarb; but, the observed levels at the lake center were high, indicating t h a t this compound is relatively refract ory and is persistent in the quatic environment.
IBP The organophosphorus fungicide IBP is used against rice blast, and its annual production in 1985 was 3085 tons. The highest concent rat i ons of IBP (3.24 #g kg 1in 1985 and 4.63 ttg kg-1 in 1986) were observed at Station 1 in July, which correlates with the main season for application of IBP in paddy fields. The c o n c e n t r a t i o n decreased rapidly and was about one-tenth of its maximum value at river mouths after 1 month. It is transported by w at er flow and the highest c o n c e n t r a t i o n at the center of the lake was observed 1 month after application. These results indicate t h a t this fungicide is removed by runoff, and is not easily decomposed, which is expected because of its high solubility in water.
Diazinon The c o n c e n t r a t i o n s of diazinon in the lake were very low in comparison with
38 t h e o t h e r p e s t i c i d e s , b e c a u s e a p p l i c a t i o n o f t h i s p e s t i c i d e i n 1985 w a s v e r y low. The highest concentration observed at Station 1 occurred in June (0.16pg kg i n 1985 a n d 0 . 4 3 p g k g ~ i n 1986), w h e r e a s t h a t a t S t a t i o n 6 w a s i n J u l y ( 0 . 0 8 p g k g -1 i n 1985 a n d 0 . 1 9 # g k g -1 i n 1986). A l t h o u g h t h e a m o u n t o f t h i s p e s t i c i d e applied in paddy fields was estimated to be small, the concentration of diazinon a t S t a t i o n 1 w a s h i g h e r t h a n t h a t o f I B P (0.16 p g kg-1). T h i s c o i n c i d e s w i t h t h e report that diazinon has the tendency to remain in the surface water (Hughes e t al., 1980), w h e r e a s I B P is v o l a t i l e a n d h i g h e r c o n c e n t r a t i o n s a r e f o u n d i n r a i n w a t e r t h a n t h a t o f d i a z i n o n ( H o r i a n d N a k a z a k i , 1982).
Isoprothiolane T h e f u n g i c i d e i s o p r o t h i o l a n e is u s e d t o c o n t r o l r i c e b l a s t d i s e a s e c a u s e d b y
Pyricularia aryzae. T h e b e h a v i o r o f i s o p r o t h i o l a n e a n d i t s a n a l o g s i n t h e e n v i r o n m e n t h a s b e e n s t u d i e d e x p e r i m e n t a l l y ( C h o u , 1980; U c h i d a , 1984), b u t the occurrence of this fungicide in natural waters has not been reported. The highest concentration of isoprothiolane was observed at Station 6 ( 1 . 2 6 p g k g 1) i n A u g u s t , w h i c h a g r e e s w i t h t h e m o n t h o f a p p l i c a t i o n . T h e h i g h e s t c o n c e n t r a t i o n a t S t a t i o n 9 w a s 0 . 5 5 p g k g -1 i n S e p t e m b e r 1985. I t is worth noting that the highest concentration at the lake center was about o n e - h a l f o f t h a t a t t h e r i v e r m o u t h . T h i s r e d u c t i o n is s u r p r i s i n g l y s m a l l , c o n sidering that the water mass takes 1 month to move from Station 6 to Station 9; a l a r g e r d i l u t i o n w o u l d b e e x p e c t e d . I t h a s b e e n r e p o r t e d t h a t t h e h a l f - l i f e o f i s o p r o t h i o l a n e i n p a d d y w a t e r is 4 d a y s ( K a n a u c h i e t al. 1982), b u t o u r r e s u l t s i n d i c a t e a m u c h l o n g e r h a l f - l i f e . I s o p r o t h i o l a n e is a l w a y s p r e s e n t i n t h e l a k e water at background levels of several hundred ppt, and seems to be persistent and to have a high mobility in the aquatic environment. TABLE 4 The concentration ofpesticides in Koise River (KR1 8) and Takahamairi Bay (ST(~3') in June 1986 (#g kg 1) CNP MOL BPMC PROP MPP CARB BUTA OXA BEN SIM DIA IBP ISO KR2 KR3 KR4 KR5 KR6 KR8
ND 0.01 ND 0.01 0.02 0.05 0.04
ND ND ND 0.02 0.04 0.02 0.34
ND ND ND 1.49 0.73 1.26 1.10
ND ND ND 0.02 ND 0.08 0.07
ND ND ND 0.50 0.15 0.54 0.46
ND ND ND 0.02 0.03 0.03 0.14
ND ND ND 0.04 0.03 0.05 0.10
ND ND 0.02 0.33 0.20 0.19 0.29
ND ND ND 0.19 0.17 0.30 0.38
ND ND 0.02 0.20 0.23 0.78 0.88
ND ND ND 0.01 0.02 0.13 0.17
ND ND 0.01 1.30 1.75 5.05 5.59
ND ND ND 0.01 ND 0.16 0.25
ST0 ST1 ST2 ST3 ST3"
0.04 ND ND ND ND
0.36 0.23 0.15 0.01 0.01
1.15 0.33 0.08 0.05 0.07
0.02 0.07 0.07 0.03 0.03
0.46 0.14 0.02 ND ND
0.13 0.18 0.18 0.07 0.09
0.09 0.06 ND ND ND
0.30 0.28 0.18 0.08 0.10
0.41 0.31 0.16 ND 0.01
0.82 0.96 0.75 0.25 0.29
0.18 0.12 0.04 0.01 0.02
5.96 1.88 0.49 0.10 0.13
0.28 0.28 0.22 0.13 0.15
KR1
ND = not detected. MOL, molinate; PROP, propaphos; CARB, carbosulfane; BUTA, butachlor; OXA, oxadiazon; BEN, benthiocarb; SIM, simetryne; DIA, diazinon; ISO, isoprothiolane.
39 ppb 2.5~
r%l i nate
i lllSeptember ~:~August [J.ly
2o !
[]June [-.,
1.51.0-
•
0.5" I
Ei~ - . .
1
2
3
=_
4
6
ppb 0.5"
7
8
9
BPMC
11 12 (Sta.)
ISeptember []August []July []June []May
0.4' 0.3' 0.2 O.1. 0
1
2
3
4
ppb 0.6'
6
7
8
Carbosulran
0.5
9
11 12 (Sta.)
ISeptember []August []July []June []May
0.3. 0.4' I 0.2. 0.1.
o1 1
2
3
4
6
7
8
9 11 12 (Sta.)
Fig. 5. The changes in concentration of pesticides (molinate, BPMC, carbosulfan) in Lake Kasumigaura water from May to September, 1986.
CNP T h e c o n c e n t r a t i o n s of C N P a n d o t h e r p e s t i c i d e s in K o i s e R i v e r w a t e r in J u n e 1986 are s h o w n in T a b l e 4 ( s a m p l i n g p o i n t s a r e s h o w n in Fig. 1). C N P c o n c e n t r a t i o n s w e r e v e r y low; t h e h i g h e s t c o n c e n t r a t i o n in r i v e r w a t e r w a s 0.05 pg k g - 1, despite the l a r g e a m o u n t of C N P b e i n g applied to this w a t e r s h e d .
40 The c o n c e n t r a t i o n decreased rapidly near the river mouth, and CNP could not be detected in the lake water, which may be due to the insoluble n a t u r e of this pesticide. CNP may be transported with the river flow, but it seems t hat in the lake rapid settling out with the sediment occurs when the flow becomes very slow. CNP contamination of the Lake Kasumigaura basin has recently been reported (Ono and Nakanishi, 1987); CNP was seldom found in the lake water, but was found in the sediment near the river mouth at several hundred ppb. This observation agrees well with our results.
Other pesticides The co n cen tr a t i ons of molinate, BPMC, carbosulfan, MPP and butachlor in the lake water were monitored in 1986. The changes in the c o n c e n t r a t i o n of each pesticide are shown in Fig. 5; but achl or and MPP are not shown in the figure because they were only found at Station 1 in May and June, and their levels were < 0.1 ppb. The c o n c e n t r a t i o n of molinate was relatively high (1 ppb in J u n e and J u ly at Station 6), but then decreased rapidly. The c o n c e n t r a t i o n of carbosulfan was also high near the river mouths and could be detected at Station 9, so it seems t hat this compound is more persistent t han molinate in the lake water. The fact t ha t the spatial distribution of BPMC in the lake water was relatively uniform in J une and July, and it was not detected in September, indicates th at this pesticide has high mobility and is degradable in the lake.
Runoff property and persistency of the pesticides The ratio of the average c o n c e n t r a t i o n (see Fig. 4) of pesticides at river mouths (Stations I and 6) to average concentrations at the lake center (Station 9) should be related to the persistency of the pesticide in the lake water, because the water masses near the river mouths move to the lake center with time. For example, a pesticide which is easily removed from the water phase should have a higher ratio. Therefore, this value could be used as a relative measure of both the persistency and the mobility of each pesticide in the lake water. The calculated order was: isoprothiolane, CSB, simetryne (0.8) > IBP (0.6) > diazinon (0.5) >~ oxadiazon (0.3) > benthiocarb (0.1). This indicates t h at isoprothiolane, CSB and simetryne are persistent and are highly mobile in the water phase. Surface runoff tendency (SR) was estimated from the ratio of the maximum c o n c e n t r a t i o n at Station I to the total amount applied (Table 3). Larger values were expected for pesticides having higher runoff tendency. The calculated order was (the values are normalized to CSB): CSB (1) > isoprothiolane (0.65), diazinon (0.63), simetryne (0.62) >~ oxadiazon (0.31) > IBP (0.10) > benthiocarb (0.08) >> CNP (0). It is known that surface runoff tendency is highly correlated with the water solubility of the pesticide, and t h a t pesticides having a solubility > 10ppm are easily lost in runoff (Wauchope, 1978). Solubility (ppm) is as follows: IBP (1000) > simetryne (450) > isoprothiolane
41 (48) > d i a z i n o n (40) > CSB, b e n t h i o c a r b (30) > o x a d i a z o n (0.7). L o n g - t e r m l e a c h i n g t e n d e n c y (LT) was e s t i m a t e d from the r a t i o of the a v e r a g e c o n c e n t r a tion at S t a t i o n 1 to t o t a l applied a m o u n t s s h o w n in Table 3. The o r d e r is (the values are n o r m a l i z e d to CSB): i s o p r o t h i o l a n e (1.2) > CSB (1) > s i m e t r y n e (0.61), diazinon (0.6) > o x a d i a z o n (0.51) >> I B P (0.10) > b e n t h i o c a r b (0.09) >> C N P (0). The v a l u e s for i s o p r o t h i o l a n e a n d o x a d i a z o n are a f a c t o r of 2 g r e a t e r t h a n the c o r r e s p o n d i n g SR value, w h e r e a s the v a l u e s for the o t h e r pesticides are the same as the SR values, w h i c h i n d i c a t e s t h a t i s o p r o t h i o l a n e and o x a d i a z o n are r e l a t i v e l y stable in p a d d y fields, and are c o n t i n u o u s l y l e a c h e d to the lake t h r o u g h the r i v e r water. CONCLUSION G C / M S a n a l y s i s of h e x a n e e x t r a c t s of L a k e K a s u m i g a u r a w a t e r s i n d i c a t e s the p r e s e n c e of seven pesticides: oxadiazon, b e n t h i o c a r b , CSB, simetryne, i s o p r o t h i o l a n e , d i a z i n o n and IBP. The h i g h e s t c o n c e n t r a t i o n s of these pesticides were observed at S t a t i o n s 1 a n d 6 n e a r the r i v e r m o u t h s d u r i n g M a y to A u g u s t . It was c o n c l u d e d t h a t these pesticides were applied to p a d d y fields in the L a k e K a s u m i g a u r a w a t e r s h e d b e t w e e n April and A u g u s t to c o n t r o l v a r i o u s weeds a n d insects, and t h a t t h e y were t r a n s p o r t e d by r i v e r w a t e r into L a k e K a s u m i g a u r a . A l t h o u g h these pesticides h a v e been r e p o r t e d to be labile in the n a t u r a l a q u a t i c e n v i r o n m e n t , some of t h e i r residue levels in L a k e K a s u m i g a u r a were h i g h and did n o t decrease rapidly. ACKNOWLEDGMENT We t h a n k Dr K. T a k a m u r a and M r N. N o h a r a for t h e i r field work. One of the a u t h o r s (P.F.) also a c k n o w l e d g e s the J a p a n I n t e r n a t i o n a l C o o p e r a t i o n A g e n c y for the o p p o r t u n i t y to w o r k at NIES. REFERENCES Ambrosi, D., P.C. Kearney and J.A. Macchia, 1977. Persistence and metabolism of oxadiazon in soils. J. Agric. Food Chem., 25: 868~872. Chou, S-S., and M. Eto, 1980. Effects of paddy water and some photosensitizers on the photolysis of the fungicide isoprothiolane. J. Environ. Sci. Health, 2:135 146. Hankawa, Y. 1985. Behavior of molinate in paddy water and river water. J. Pestic. Sci., 10: 107-112. Hori, K. and M. Nakazaki, 1982. Pesticides pollution of natural waters in Kumamoto prefecture. Seitai Kagaku, 5:3-13 (in Japanese). Hughes, D., M. Boyer, M. Papst and C. Fowle, 1980. Persistence of three organophosphorus insecticides in artificial ponds and some biological implications. Environ. Sci. Technol., 8: 38-42. Imanaka, M., K. Matsunaga, A. Shigeta and T. Ishida, 1981. Oxadiazon residues in fish and shellfish. J. Pestic. Sci., 6: 41~417. Imanaka, M., S. Hino, K. Matsunaga and T. Ishida, 1985. Oxadiazon residues in surface water and crucian carp (Carassius cuvieri) of Lake Kojima. J. Pestic. Sci., 10: 12~134. Ishii, Y., 1984. Pollution by pesticides of estuaries in Aichi pref. and opinion on safe use of pesticides. Seitai Kagaku, 7:19-31 (in Japanese). Ishikawa, Y. Nakamura and S. Kuwatsuka, 1976. Degradation of benthiocarb herbicide in soil. J. Pestic. Sci., 1: 4~57.
42 Ishikawa, K., Y. N a k a m u r a and S. Kuwatsuka, 1977a Volatilization of benthiocarb herbicide from aqueous solution and soil. J. Pestic. Sci., 2:127 134. Ishikawa, K., Y. Nakamura, Y. Niki and S. Kuwatsuka, 1977b. Photodegradation of benthiocarb herbicide. J. Pestic. Sci., 2: 17-25. Kanauchi, M., M. Uchida and K. Tsuchiya, 1982. Persistence of isoprothiolane in paddy water and rice plants after submerged applications. J. Pestic. Sci., 7: 377-383. Mikuriya, H. and K. Miyahara, 1983. Pollution of creek waters in Saga pref. by pesticides applied in paddy fields. Seitai Kagaku, 6:23 33 (in Japanese). Nakamura, K., 1982. Fate of herbicide around paddy field. Shokubutu Boueki, 3 6 : 9 - 1 4 (in Japanese). Ono, H. and J. Nakanishi, 1987. Herbicide, CNP contamination in the Lake Kasumigaura basin. Water Res., 21: 669~75. Shiraishi, H. and A. Otsuki, 1987. Identification and determination of 4-(chloromethylsulfonyl) bromobenzene, a new herbicide additive, in lake water. Water Res., 21: 843-847. Suzuki, M., 1982. Pollution by pesticides of aquatic environment in the Kitakyushu district. Seitai Kagaku, 4:3-10 (in Japanese). Suzuki, M., Y. Yamato and T. Akiyama, 1976. Occurrence and determination of the herbicide benthiocarb in rivers and agricultural drainages. Water Res., 11: 27~279. Tsukamoto, R. and S. Asaka, 1983. Persistence of propaphos in inland water. Seitai Kagaku, 6: 17-22. Uchida, M. 1984. Behavior of isoprothiolane analogs in the envionment. J. Pestic. Sci., 9: 559-569. Wauchope, R.D., 1978. The pesticide content of surface water draining from agricultural fields. J. Environ. Qual., 4: 459~72. Yamato, Y. and M. Suzuki, 1980. Occurrence of herbicide oxadiazon in surface waters and tap water. Water Res., 14: 143h 1438. Yamato, Y., M. Suzuki and T. Watanabe, 1979. Field desorption mass spectrometric analyses of organic compound residues in the environment II - - Herbicides. Biomed. Mass Spectrom., 6: 205-207.
29
B E H A V I O U R OF P E S T I C I D E S IN LAKE K A S U M I G A U R A , J A P A N
HIROAKI SHIRAISHI', FLUTRA PULA 2, AKIRA OTSUKI' and TOSHIO IWAKUMA 1
~National Institute for Environmental Studies, 16-20nogawa, Yatabe, Ibaraki 305 (Japan) eKomiteti Krahinor per Urbanizem, Rr. M. Tito 2, 38000 Prishtina (Yugoslavia) (Received September 19th, 1987; accepted October 22nd, 1987)
ABSTRACT Pesticides such as oxadiazon, isoprothiolane, diazinon, IBP, simetryne and benthiocarb, from surface runoff from rice paddy fields to Lake Kasumigaura, J a p a n were examined in order to determine seasonal changes in their concentrations in the lake water. The highest concentrations were observed near the river mouths during May to August, soon after pesticide application; hence they are transported mainly by surface runoff. Although these pesticides have been reported to be labile, concentrations of some of them, dispersed with the movement of the water, did not decrease rapidly in the natural aquatic environment. The highest concentrations, in 1985, of oxadiazon, isoprothiolane, diazinon, IBP, simetryne, benthiocarb and CSB were 0.66, 0.84, 0.16, 3.24, 3.23, 2.15 and 1.13 ppb, respectively. The relative order of persistence and mobility of pesticides in the lake water was estimated as: isoprothiolane, CSB, simetryne > IBP > diazinon >> oxadiazon > benthiocarb. INTRODUCTION
Organic chemicals such as pesticides (e.g. herbicides, insecticides, fungicides) are potentially hazardous to living organisms. Some pesticides, such as DDT and HCH, are persistent in the environment and accumulate in human tissue or other animals through the food chain, and their use has been banned. Consequently, new types of pesticides, such as organophosphorus and carbamate compounds, have been developed so as to reduce bioaccumulation and persistence in the environment, and toxicity to non-target organism. Although the new pesticides are more degradable than the organochlorines, their concentrations in river water draining from paddy fields are quite high directly after their application. Since the pesticides are applied directly to constantly overflowing paddy waters which drain to natural waters, aquatic organisms are exposed to pesticide-contaminated water. The degree of pesticide pollution is dependent upon dose rates and the manner of application. In J a p a n the use of organochloride pesticides in paddy fields is still increasing. Toxic effects to aquatic organisms caused by pesticide application have been reported (Suzuki, 1980). The concentrations of various pesticides in inland waters surrounded by paddy fields have been reported (Hori and Nakazaki, 1982; Nakamura, 1982; Suzuki, 1982; Mikuriya and Miyahara, 1983; Tsukamoto and Asaka, 1983; Ishii, 1984; Hankawa, 1985). Lake Kasumigaura, the second largest lake in Japan, is
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30 surrounded by many large paddy fields, but very little is known about pesticide residues in the lake water, which is an important source of water for drinking, agriculture, fisheries, and industry in southern Ibaraki prefecture. Therefore, inputs of toxic substances are undesirable and harmful. After a preliminary study in 1984, monitoring of pesticide levels in Lake Kasumigaura water was carried out from 1985 to 1986, and the results are reported here. EXPERIMENTAL
Field Description Lake Kasumigaura is located in the eastern part of the Kanto Plain, 50 km northeast of Tokyo. The lake has two large bays, Takahamairi and Tsuchiurairi. The lake basin is smooth and shallow with a surface area of 171 km 2, a mean depth of 4 m, and a maximum depth of 7.4 m near the mouth of Takahamairi Bay. The lake water surface is only l m above sea level.
Materials Hexane, benzene and methanol were pesticide grade (Wako Pure Chem. Ind., Ltd.) and required no further purification before use. Water was purified by distillation, and passage through a Milli-Q system (Millpore Corp.) and XAD-2 resin column before use. The following standard pesticides were used: 5-tertbutyl-3-(2,4-dichloro-5-isopropoxyphenyl)-l,3,4-oxadiazol-2(3H)-one (oxadiazon); diisopropyl 1,3-dithiolan-2-ylidene-malonate (isoprothiolane); O,O-diethyl O-2-isopropyl 6-methylpyrimidin-4-yl phosphorothioate (diazinon); S-benzyl O,O-diisopropyl-phosphorothioate (IBP); 2,4-bis(ethylamino-6methylthio-l,3,5-triazine (simetryne); and S-4-chlorobenzyldiethylthiocarbamate (benthiocarb); all were purchased from Wako Pure Chem. Ind., Ltd. 4-(Chloromethylsulfonyl)bromobenzene (CSB) was synthesized according to standard procedures.
Sampling Sampling stations in Lake Kasumigaura are shown in Fig. 1. Stations I 4 are located in Takahamairi Bay and Stations 6-8 in Tsuchiurairi Bay. Station 9 is in the centre of the lake and Stations 11 and 12 are near the outlet. Lake water (surface to 2m depth) was collected using a water column sampler. After mixing, the samples were stored in 11 glass bottles and transferred to the laboratory.
Extraction One liter of sampled water was dispensed to glass bottles, then immediately filtered through a Whatman GF/C glass filter. The weighed aliquot of water
31 Koise River
~
2
St.1 1 3 4
•
;,~..\ ~,st.3' "l TakahamairlWatershed , ~ ]
Fig. 1. Sampling stations of Lake Kasumigaura and Koise River. ( ~ I l) was mixed with the solvent (50 ml hexane) and shaken using an electric s h ak er for 10 min. The solvent phase was then separated from the water phase and the ex tr acti on was repeated once more with the same am ount of solvent (50 ml hexane). The hexane fractions were combined and frozen to remove any remaining water as ice. The e xt r act was c on cent rat ed by a r o t a r y e v a p o r a t o r to ~ 3 ml; this c o n c e n t r a t e was f ur t her c o n c e n t r a t e d under nitrogen gas flow at room t e m p e r a t u r e to 2 ml and t he n 3 gl aliquots of each concent rat ed ext ract was injected into a GC/ECD and GC/NPD. For GC/MS analysis it was furt her c o n c e n t r a t e d to 0.1 ml.
Determination CSB, oxadiazon and isoprothiolane were determined using a Hewlett P a c k a r d Model 5980A gas chr om at ogr a ph equipped with an ECD and fitted with a glass column (OV-17, 2m). The column was operated isothermally at 200°C, injector t e m p e r a t u r e 250°C and detector t em perat ure 300°C. Nitrogen was used as the car r i er gas at a flow rate of 5 0 m l m i n -~. Diazinon, IBP, simetryne and benthiocarb were determined using a Shimadzu GC-7A gas c h r o m a t o g r a p h equipped with a NPD and fitted with a capillary column (OV-1, 25 m). Helium was used as the car r i er gas at a flow rate of 2 ml min 1. The peak area of the pesticide signal in the gas chr o m at ogram was determined with a chromatographic data processor Model 7000 AS (SIC, Japan). The concentrations determined ( ngkg 1) by GC analysis using 11 of water were as follows: CSB (0.4), oxadiazon (2), isoprothiolane (2), CNP (2), diazinon (1), IBP (2), simetryne (24), benthiocarb (7), molinate (6), BPMC (8), MPP (10) and carbosulfan (10).
32
o >..
10"
1'2 " 14
" 1'6 " 1'8 " 2'0 " 2'2 " 2'4"
v~ m
216 ' 2'8 ' 310
rnin.
Fig. 2. R e c o n s t r u c t e d ion c h r o m a t o g r a m (RIC) of the h e x a n e e x t r a c t of Lake K a s u m i g a u r a water. TABLE1 List of compounds identified Compound a
RTh(min)
Diagnostic ions (rn/z) c
1 2 3 4 5 6 7 8 9 10 11 12 13 14
7/28 11130 16'48 18'00 20'20 21'54 22'08 23'10 23'48 24'22 24134 27'40 28'20 29~42
146([M]+), 148, 111, 113 128([M] ~ ), 127, 126 152([M] ~), 151, 150 126, 83, 98, 187([M] +)
p.Dichlorobenzene Naphthalene Acenaphthene Molinate p.sec-Butylphenol Diazinon Phenanthrene IBP CSB Simetryne Benthiocarb Oxadiazon Isoprothiolane Di-n-butylphthalate
121, 150([M] ~), 77 137, 179, 152, 304([M] + ), 151, 167 178([M1 ~ ) 113, 204, 91, 246, 288([M] ' ) 219, 157, 155, 76, 268([M] +) 213([M] ÷ ), 170, 198, 138, 185 100, 72, 257([M] ~ ), 259 175,177, 258, 302, 344([M] ~) 118, 162, 189, 290([M] ~ ), 231 57, 71, 43, 149([M]' ), 99
Peak n u m b e r refers to Fig. 2. hRT ~ r e t e n t i o n time. m / z is listed in t h e order of relative a b u n d a n c e of the ioas.
T h e pesticide identifications were confirmed by GC/MS using a Model DX300 double focusing mass s p e c t r o m e t e r (JEOL, J a p a n ) equipped with a H e w l e t t P a c k a r d Model 5700 GC, and JMA-3500 mass d a t a analysis system (JEOL). The c o l u m n (25m, OV-1701) was coupled d i r e c t l y to the mass spectrometer. The c o l u m n t e m p e r a t u r e was set at 60°C for 2 min, followed by an i n c r e a s e to 260°C at a r a t e of 8°C min 1, and t h e n held at 260°C. The i n j e c t o r t e m p e r a t u r e was 250°C and the h e a d p r e s s u r e of the c o l u m n was 0 . 6 k g c m -2. The mass spect r o m e t r i c c o n d i t i o n s were as follows: a c c e l e r a t i n g voltage, 3.0kV; ionizing
33 TABLE 2 List of physical properties of pesticides m.p. (melting point, °C); b.p. (boiling point, °C/mmHg); v.p. (vapor pressure, mmHg/°C); sol. (solubility in water, ppm/°C) Oxadiazon; 5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-l,3,4-oxadiazol-2(3H)-one (C,~Hls C12N203) m.p. 91; v.p. < 10 6/20; sol. 0.7/20 Benthiocarb; S-4-chlorobenzyldiethylthiocarbamate (C12H16C1NOS) m.p. 3.3; b.p. 12~129/8 × 10-3; v.p. 1.476 × 10 4/20; sol. 30/20 CSB; 4-(chloromethylsulfonyl)bromobenzene (CTH6BrSO2C1) m.p. 146; sol. 30 Simetryne; 2,4-bis(ethylamino)-6-methylthio-l,3,5-triazine m.p. 82 83; v.p. 7.1 × 10-7/20; sol. 450
(CsH15NsS)
IBP; S-benzyl O,O'-diisopropylphosphorothiolate (C,3H2103PS) m.p. 22.5-23.8; b.p. 126/0.04; sol. 1000 Diazinon; O,O'-diethyl-O~'-2-isopropyl-6-methylpyrimidin-4-phosphorothionate v.p. 1.4 × 10-4/20; b.p. 83-84/0.002; sol. 40
(C12H21N203PS)
Isoprothiolane; diisopropyl-l,3-dithiolan-2-ylidene-malonate (C12H~s04 S~) m.p. 54.5-55.0; b.p. 167-169/0.5; sol. 48/20 CNP; 2,4,6-trichlorophenyl-4-nitrophenyl ether (CI~H6C13NO3) m.p. 107 107.1; b.p. 210/~7; v.p. 0.35/109
c u r r e n t , 300/~A; i o n i z i n g v o l t a g e , 70 V; s c a n r a n g e m/z 10~400; m a s s r e s o l u t i o n , 500; s c a n i n t e r v a l 2 s. C h e m i c a l i o n i z a t i o n (CI) w a s p e r f o r m e d u s i n g i s o b u t a n e as t h e r e a g e n t gas.
Recovery test A n a c e t o n e s o l u t i o n (10 ttl) o f s t a n d a r d c o m p o u n d s w a s a d d e d to I 1 p u r i f i e d w a t e r , a n d t h e a q u e o u s p h a s e w a s e x t r a c t e d t w i c e w i t h 50 ml h e x a n e , a n d t h e solvent phase was then separated from the water phase, concentrated and a n a l y z e d as d e s c r i b e d a b o v e . T h e r e c o v e r y e x p e r i m e n t s w e r e p e r f o r m e d at 1 - 5 p p b levels. R e c o v e r i e s (%) w e r e as follows: d i a z i n o n (91), I B P (91), s i m e t r y n e (34), b e n t h i o c a r b (69), C S B (56), o x a d i a z o n (94), i s o p r o t h i o l a n e (72), B P M C (78), m o l i n a t e (100), M P P (100), b u t a c h l o r (100), c a r b o s u l f a n (100) a n d C N P (92). RESULTS AND DISCUSSION F i g u r e 2 s h o w s a r e c o n s t r u c t e d i o n c h r o m a t o g r a m (RIC) o f t h e e x t r a c t f r o m
34 TABLE 3 The amount of applied pesticides in rice paddy fieldsa and the month of application in Takahamairi Bay watershed in 1985 Pesticide
Month of application
Amount applied (kg)
1 2 3 4 5 6 7
Mid-May to early June Mid-July to early Aug Mid-May to early June Mid to late May Early May Early Aug Early May
2288 2531 42 483 173 105 1452
Benthiocarb IBP Diazinon Simetryne Oxadiazon Isoprothiolane CNP
aTotal area of rice paddy fields in the upper watershed of Takahamairi Bay is 1860ha. L a k e K a s u m i g a u r a w a t e r ( J u n e 1985, S t a t i o n 6); T a b l e 1 lists e a c h c o m p o u n d identified. All the l a r g e p e a k s in t h e RIC c h r o m a t o g r a m w e r e due to pesticides. A m o n g t h e o r g a n i c c o m p o u n d s listed in T a b l e 1, s e v e n pesticides, CSB, o x a d i a z o n , i s o p r o t h i o l a n e , diazinon, IBP, s i m e t r y n e a n d b e n t h i o c a r b w e r e m o n i t o r e d b e c a u s e of t h e i r wide use in p a d d y fields from 1985 to 1986. B P M C , m o l i n a t e , M P P , b u t a c h l o r a n d c a r b o s u l f a n w e r e m o n i t o r e d in 1986. T h e p h y s i c a l a n d c h e m i c a l c h a r a c t e r i s t i c s of the pesticides a r e s h o w n in T a b l e 2. T h e a m o u n t s of pesticides sold in the T a k a h a m a i r i w a t e r s h e d in 1985 w e r e o b t a i n e d f r o m a g r i c u l t u r a l c o o p e r a t i v e a s s o c i a t i o n s a n d a r e s u m m a r i z e d as a c t i v e c o m p o n e n t s in T a b l e 3. T h e m o n t h of t h e i r a p p l i c a t i o n in rice p a d d y fields is also shown. T h e s e v a l u e s could be u n d e r e s t i m a t e s , b e c a u s e of difficulties in i d e n t i f y i n g pesticide usage. T h e c h a n g e s in t h e c o n c e n t r a t i o n s of p e s t i c i d e s a t r i v e r m o u t h s ( S t a t i o n s 1 a n d 6) a n d the c e n t e r of t h e l a k e ( S t a t i o n 9) a r e s h o w n in Fig. 3. T h e a v e r a g e c o n c e n t r a t i o n s of t h e s e pesticides in L a k e K a s u m i g a u r a w a t e r from M a y 1985 to S e p t e m b e r 1986 a r e s h o w n in Fig. 4.
Oxadiazon T h e r e a r e m a n y r e p o r t s of t h e o c c u r r e n c e of o x a d i a z o n in s u r f a c e w a t e r s ( Y a m a t o et al., 1979; Y a m a t o a n d Suzuki, 1980; Ishii, 1984) a n d in fish ( I m a n a k a et al., 1981, 1985). O x a d i a z o n is applied before rice p l a n t i n g in liquid form, so it is r e s o n a b l e t h a t the h i g h e s t c o n c e n t r a t i o n s (0.66 #g kg-1 in 1985 a n d 0.78 #g kg-1 in 1986) a t S t a t i o n I w e r e f o u n d in May. D i r e c t a p p l i c a t i o n o f o x a d i a z o n in liquid form m a y r e s u l t in a r e l a t i v e l y r a p i d r u n o f f of this pesticide, despite its low s o l u b i l i t y in water. O x a d i a z o n was l e a c h e d c o n t i n u o u s l y f r o m t h e p a d d y fields to the l a k e d u r i n g t h e period from M a y to J u l y . A f t e r flowing into t h e lake, the c o n c e n t r a t i o n s in l a k e w a t e r d e c r e a s e d c o n s i d e r a b l y a n d the r e s i d u e levels r e m a i n e d low in the c e n t e r of t h e lake. T h e low c o n c e n t r a t i o n s o b s e r v e d m a y be due b o t h to its p e r s i s t e n c y a n d the a d s o r p t i o n of o x a d i a z o n on soil p a r t i c l e s Fig. 3. The changes in concentration of pesticides in Lake Kasumigaura water (Stations 1, 6 and 9) from April 1985 to September 1986.
35 OXADIAZON
ppb
~Sta. 1 ~Sta.6 -e-Sta.9
0"81
BENTHIOCARB
ppb 2.5"
Sta. 1 ~Sta.6 ~'-Sta. 9
2.0 0.6 1.5
i,ll
0.4
1.0 0.2
0.5
0
M J
J
A S 0 1985
ppb 1.5
0 A MJ
N D A M J J 1986
CSB Sta. 1 ~Sta.6 ~ - Sta. 9
J
ppb 5.0
AS 1985
. . . . ND
// - - _ MJ J A 1986
SIMETRYNE Sta.1 Sta.6 ~ - Sta.9
4.0-
0 I
3.0
/'~
2o
0.5
O
. . . . . . . .
A M J J A S 0 1985
ppb 5.0
r -~'I ~ N D A M J J 1986
JTM3
AS
IBP ~Sta.1 ~Sta.6 ~-Sta.9
ppb 0.5
4.0
o.4
3.0
o.3
DIAZINON
~Sta.1 Sta.6 ~ - Sta,9
i
0.2-
2.0
J A
1986
1985
1.0 O
M J J A ~ U M U 1985
ppb 1.5-
AM
m u19J86** o
ISOPROTHIOLANE ~ Sta. 1 Sta.6 -o- Sta.9
1.0
0,5
0
A
MJ J A s 0 N O#,i M J 5 i s 1985
1986
J
J A S 1985
0
N
D
M
JA 1986
36 ppb
2"5t 2.0
i [] Benthiocarb [] Dazinon I [] Oxadiazon
1.5 t
111111
[] Isoprothiolane / [] Simetryne
1.o
i
O'5l 0
.
.
.
.
.
.
.
.
.
.
1 2 3 4 6 7 8 9 11 12 (Sta.)
Fig. 4. The average concentrations of pesticides (from April 1985 to September 1986) in Lake Kasumigaura water. due to its low solubility in water. Taking into account the reported persistence of oxadiazon in soils (Ambrosi et al., 1977), it seems likely t hat oxadiazon is leached continuously and slowly from paddy fields. Oxadiazon would not be transported for long distances without fast flowing water, but would settle to the sediment with suspended particles. A slight increase in c o n c e n t r a t i o n was observed in October 1985, but the reason is not known. Benthiocarb Benthiocarb has been used extensively to control various weeds such as barn-yard-grass, slender and spikerush in both paddy and upland fields in Japan. The total production in 1985 was 5150 tons. Benthiocarb is applied to the surface water of paddy fields 3 20 days after transplanting rice seedlings. In Japan, benthiocarb has been one of the most commonly used herbicides in rice paddies in recent years. Its occurrence and concentrations in rivers and agricultural drainages have been reported (Suzuki et al., 1976; Nakamura, 1982; Ishii, 1984). The highest concentrations were oberved at Station 1 in J u n e 1985 (2.15pgkg 1), very soon after direct application of this herbicide. The conc e n t r a t i o n of benthiocarb then became very low, and decreased below the detection limit after September, except near river mouths. Benthiocarb was undetectable in the lake water very soon after entry, which agrees with studies on the photodegradation of benthiocarb herbicide and on its volatilization from aqueous solutions and soil (Ishikawa, et al., 1976, 1977a, b). In 1986, little benthiocarb is known to have been applied in Kasumigaura basin, hence low concentrations are expected. C SB There are a few reports on CSB; the environmental occurrence of this
37 compound has recently been reported (Shiraishi and Otsuki, 1987). CSB is used as one of the additives in benthiocarb. The highest concentrations of CSB residues were observed at Station 1 (1.13pgkg 1) in June, which correlates well with benthiocarb c o n c e n t r a t i o n s at Station 1; CSB levels at river mouths decreased with time and the lowest values were found in December (13 ng kg -1 , Station 1). While benthiocarb decomposes rapidly and could not be detected except at river mouths after September, CSB moved with the water mass and was dispersed over the whole lake. The highest c o n c e n t r a t i o n of CSB was observed 1 month after application at the center of the lake, and was t hen detected for several months over the whole lake. In 1986, CSB was undetectable in the lake water as a consequence of the much reduced application of benthiocarb. Taking into account t h a t the CSB content of benthiocarb is ~ 4% in commercial products, it was surprising t h a t CSB levels at Station 1 in June were similar to those of benthiocarb. This could be the result of a combination of factors: (i) CSB run-off was greater t h a n t hat for benthiocarb; (ii) benthiocarb decomposed faster t han CSB in both the paddy field and in the lake.
Simetryne Simetryne is a herbicide which is used in paddy fields to control various weeds. In June, the highest concent r a t i ons of simetryne (3.23 ttg kg-1 in 1985, and 4.84 gg kg ~in 1986) were observed at Station 1. The highest concent rat i ons at Station 6 were observed in J ul y (1.26 #g kg- ~in 1985 and 2.21 ttg kg- 1in 1986). The c o n c e n t r a t i o n in the lake center was at its highest 1 month after the entry of this herbicide into the lake. Although the reason was not clear, a slight increase in the c o n c e n t r a t i o n of this herbicide was observed in October 1985. The change in c o n c e n t r a t i o n of simetryne near the river mouth was very rapid, and was similar to t h a t of benthiocarb; but, the observed levels at the lake center were high, indicating t h a t this compound is relatively refract ory and is persistent in the quatic environment.
IBP The organophosphorus fungicide IBP is used against rice blast, and its annual production in 1985 was 3085 tons. The highest concent rat i ons of IBP (3.24 #g kg 1in 1985 and 4.63 ttg kg-1 in 1986) were observed at Station 1 in July, which correlates with the main season for application of IBP in paddy fields. The c o n c e n t r a t i o n decreased rapidly and was about one-tenth of its maximum value at river mouths after 1 month. It is transported by w at er flow and the highest c o n c e n t r a t i o n at the center of the lake was observed 1 month after application. These results indicate t h a t this fungicide is removed by runoff, and is not easily decomposed, which is expected because of its high solubility in water.
Diazinon The c o n c e n t r a t i o n s of diazinon in the lake were very low in comparison with
38 t h e o t h e r p e s t i c i d e s , b e c a u s e a p p l i c a t i o n o f t h i s p e s t i c i d e i n 1985 w a s v e r y low. The highest concentration observed at Station 1 occurred in June (0.16pg kg i n 1985 a n d 0 . 4 3 p g k g ~ i n 1986), w h e r e a s t h a t a t S t a t i o n 6 w a s i n J u l y ( 0 . 0 8 p g k g -1 i n 1985 a n d 0 . 1 9 # g k g -1 i n 1986). A l t h o u g h t h e a m o u n t o f t h i s p e s t i c i d e applied in paddy fields was estimated to be small, the concentration of diazinon a t S t a t i o n 1 w a s h i g h e r t h a n t h a t o f I B P (0.16 p g kg-1). T h i s c o i n c i d e s w i t h t h e report that diazinon has the tendency to remain in the surface water (Hughes e t al., 1980), w h e r e a s I B P is v o l a t i l e a n d h i g h e r c o n c e n t r a t i o n s a r e f o u n d i n r a i n w a t e r t h a n t h a t o f d i a z i n o n ( H o r i a n d N a k a z a k i , 1982).
Isoprothiolane T h e f u n g i c i d e i s o p r o t h i o l a n e is u s e d t o c o n t r o l r i c e b l a s t d i s e a s e c a u s e d b y
Pyricularia aryzae. T h e b e h a v i o r o f i s o p r o t h i o l a n e a n d i t s a n a l o g s i n t h e e n v i r o n m e n t h a s b e e n s t u d i e d e x p e r i m e n t a l l y ( C h o u , 1980; U c h i d a , 1984), b u t the occurrence of this fungicide in natural waters has not been reported. The highest concentration of isoprothiolane was observed at Station 6 ( 1 . 2 6 p g k g 1) i n A u g u s t , w h i c h a g r e e s w i t h t h e m o n t h o f a p p l i c a t i o n . T h e h i g h e s t c o n c e n t r a t i o n a t S t a t i o n 9 w a s 0 . 5 5 p g k g -1 i n S e p t e m b e r 1985. I t is worth noting that the highest concentration at the lake center was about o n e - h a l f o f t h a t a t t h e r i v e r m o u t h . T h i s r e d u c t i o n is s u r p r i s i n g l y s m a l l , c o n sidering that the water mass takes 1 month to move from Station 6 to Station 9; a l a r g e r d i l u t i o n w o u l d b e e x p e c t e d . I t h a s b e e n r e p o r t e d t h a t t h e h a l f - l i f e o f i s o p r o t h i o l a n e i n p a d d y w a t e r is 4 d a y s ( K a n a u c h i e t al. 1982), b u t o u r r e s u l t s i n d i c a t e a m u c h l o n g e r h a l f - l i f e . I s o p r o t h i o l a n e is a l w a y s p r e s e n t i n t h e l a k e water at background levels of several hundred ppt, and seems to be persistent and to have a high mobility in the aquatic environment. TABLE 4 The concentration ofpesticides in Koise River (KR1 8) and Takahamairi Bay (ST(~3') in June 1986 (#g kg 1) CNP MOL BPMC PROP MPP CARB BUTA OXA BEN SIM DIA IBP ISO KR2 KR3 KR4 KR5 KR6 KR8
ND 0.01 ND 0.01 0.02 0.05 0.04
ND ND ND 0.02 0.04 0.02 0.34
ND ND ND 1.49 0.73 1.26 1.10
ND ND ND 0.02 ND 0.08 0.07
ND ND ND 0.50 0.15 0.54 0.46
ND ND ND 0.02 0.03 0.03 0.14
ND ND ND 0.04 0.03 0.05 0.10
ND ND 0.02 0.33 0.20 0.19 0.29
ND ND ND 0.19 0.17 0.30 0.38
ND ND 0.02 0.20 0.23 0.78 0.88
ND ND ND 0.01 0.02 0.13 0.17
ND ND 0.01 1.30 1.75 5.05 5.59
ND ND ND 0.01 ND 0.16 0.25
ST0 ST1 ST2 ST3 ST3"
0.04 ND ND ND ND
0.36 0.23 0.15 0.01 0.01
1.15 0.33 0.08 0.05 0.07
0.02 0.07 0.07 0.03 0.03
0.46 0.14 0.02 ND ND
0.13 0.18 0.18 0.07 0.09
0.09 0.06 ND ND ND
0.30 0.28 0.18 0.08 0.10
0.41 0.31 0.16 ND 0.01
0.82 0.96 0.75 0.25 0.29
0.18 0.12 0.04 0.01 0.02
5.96 1.88 0.49 0.10 0.13
0.28 0.28 0.22 0.13 0.15
KR1
ND = not detected. MOL, molinate; PROP, propaphos; CARB, carbosulfane; BUTA, butachlor; OXA, oxadiazon; BEN, benthiocarb; SIM, simetryne; DIA, diazinon; ISO, isoprothiolane.
39 ppb 2.5~
r%l i nate
i lllSeptember ~:~August [J.ly
2o !
[]June [-.,
1.51.0-
•
0.5" I
Ei~ - . .
1
2
3
=_
4
6
ppb 0.5"
7
8
9
BPMC
11 12 (Sta.)
ISeptember []August []July []June []May
0.4' 0.3' 0.2 O.1. 0
1
2
3
4
ppb 0.6'
6
7
8
Carbosulran
0.5
9
11 12 (Sta.)
ISeptember []August []July []June []May
0.3. 0.4' I 0.2. 0.1.
o1 1
2
3
4
6
7
8
9 11 12 (Sta.)
Fig. 5. The changes in concentration of pesticides (molinate, BPMC, carbosulfan) in Lake Kasumigaura water from May to September, 1986.
CNP T h e c o n c e n t r a t i o n s of C N P a n d o t h e r p e s t i c i d e s in K o i s e R i v e r w a t e r in J u n e 1986 are s h o w n in T a b l e 4 ( s a m p l i n g p o i n t s a r e s h o w n in Fig. 1). C N P c o n c e n t r a t i o n s w e r e v e r y low; t h e h i g h e s t c o n c e n t r a t i o n in r i v e r w a t e r w a s 0.05 pg k g - 1, despite the l a r g e a m o u n t of C N P b e i n g applied to this w a t e r s h e d .
40 The c o n c e n t r a t i o n decreased rapidly near the river mouth, and CNP could not be detected in the lake water, which may be due to the insoluble n a t u r e of this pesticide. CNP may be transported with the river flow, but it seems t hat in the lake rapid settling out with the sediment occurs when the flow becomes very slow. CNP contamination of the Lake Kasumigaura basin has recently been reported (Ono and Nakanishi, 1987); CNP was seldom found in the lake water, but was found in the sediment near the river mouth at several hundred ppb. This observation agrees well with our results.
Other pesticides The co n cen tr a t i ons of molinate, BPMC, carbosulfan, MPP and butachlor in the lake water were monitored in 1986. The changes in the c o n c e n t r a t i o n of each pesticide are shown in Fig. 5; but achl or and MPP are not shown in the figure because they were only found at Station 1 in May and June, and their levels were < 0.1 ppb. The c o n c e n t r a t i o n of molinate was relatively high (1 ppb in J u n e and J u ly at Station 6), but then decreased rapidly. The c o n c e n t r a t i o n of carbosulfan was also high near the river mouths and could be detected at Station 9, so it seems t hat this compound is more persistent t han molinate in the lake water. The fact t ha t the spatial distribution of BPMC in the lake water was relatively uniform in J une and July, and it was not detected in September, indicates th at this pesticide has high mobility and is degradable in the lake.
Runoff property and persistency of the pesticides The ratio of the average c o n c e n t r a t i o n (see Fig. 4) of pesticides at river mouths (Stations I and 6) to average concentrations at the lake center (Station 9) should be related to the persistency of the pesticide in the lake water, because the water masses near the river mouths move to the lake center with time. For example, a pesticide which is easily removed from the water phase should have a higher ratio. Therefore, this value could be used as a relative measure of both the persistency and the mobility of each pesticide in the lake water. The calculated order was: isoprothiolane, CSB, simetryne (0.8) > IBP (0.6) > diazinon (0.5) >~ oxadiazon (0.3) > benthiocarb (0.1). This indicates t h at isoprothiolane, CSB and simetryne are persistent and are highly mobile in the water phase. Surface runoff tendency (SR) was estimated from the ratio of the maximum c o n c e n t r a t i o n at Station I to the total amount applied (Table 3). Larger values were expected for pesticides having higher runoff tendency. The calculated order was (the values are normalized to CSB): CSB (1) > isoprothiolane (0.65), diazinon (0.63), simetryne (0.62) >~ oxadiazon (0.31) > IBP (0.10) > benthiocarb (0.08) >> CNP (0). It is known that surface runoff tendency is highly correlated with the water solubility of the pesticide, and t h a t pesticides having a solubility > 10ppm are easily lost in runoff (Wauchope, 1978). Solubility (ppm) is as follows: IBP (1000) > simetryne (450) > isoprothiolane
41 (48) > d i a z i n o n (40) > CSB, b e n t h i o c a r b (30) > o x a d i a z o n (0.7). L o n g - t e r m l e a c h i n g t e n d e n c y (LT) was e s t i m a t e d from the r a t i o of the a v e r a g e c o n c e n t r a tion at S t a t i o n 1 to t o t a l applied a m o u n t s s h o w n in Table 3. The o r d e r is (the values are n o r m a l i z e d to CSB): i s o p r o t h i o l a n e (1.2) > CSB (1) > s i m e t r y n e (0.61), diazinon (0.6) > o x a d i a z o n (0.51) >> I B P (0.10) > b e n t h i o c a r b (0.09) >> C N P (0). The v a l u e s for i s o p r o t h i o l a n e a n d o x a d i a z o n are a f a c t o r of 2 g r e a t e r t h a n the c o r r e s p o n d i n g SR value, w h e r e a s the v a l u e s for the o t h e r pesticides are the same as the SR values, w h i c h i n d i c a t e s t h a t i s o p r o t h i o l a n e and o x a d i a z o n are r e l a t i v e l y stable in p a d d y fields, and are c o n t i n u o u s l y l e a c h e d to the lake t h r o u g h the r i v e r water. CONCLUSION G C / M S a n a l y s i s of h e x a n e e x t r a c t s of L a k e K a s u m i g a u r a w a t e r s i n d i c a t e s the p r e s e n c e of seven pesticides: oxadiazon, b e n t h i o c a r b , CSB, simetryne, i s o p r o t h i o l a n e , d i a z i n o n and IBP. The h i g h e s t c o n c e n t r a t i o n s of these pesticides were observed at S t a t i o n s 1 a n d 6 n e a r the r i v e r m o u t h s d u r i n g M a y to A u g u s t . It was c o n c l u d e d t h a t these pesticides were applied to p a d d y fields in the L a k e K a s u m i g a u r a w a t e r s h e d b e t w e e n April and A u g u s t to c o n t r o l v a r i o u s weeds a n d insects, and t h a t t h e y were t r a n s p o r t e d by r i v e r w a t e r into L a k e K a s u m i g a u r a . A l t h o u g h these pesticides h a v e been r e p o r t e d to be labile in the n a t u r a l a q u a t i c e n v i r o n m e n t , some of t h e i r residue levels in L a k e K a s u m i g a u r a were h i g h and did n o t decrease rapidly. ACKNOWLEDGMENT We t h a n k Dr K. T a k a m u r a and M r N. N o h a r a for t h e i r field work. One of the a u t h o r s (P.F.) also a c k n o w l e d g e s the J a p a n I n t e r n a t i o n a l C o o p e r a t i o n A g e n c y for the o p p o r t u n i t y to w o r k at NIES. REFERENCES Ambrosi, D., P.C. Kearney and J.A. Macchia, 1977. Persistence and metabolism of oxadiazon in soils. J. Agric. Food Chem., 25: 868~872. Chou, S-S., and M. Eto, 1980. Effects of paddy water and some photosensitizers on the photolysis of the fungicide isoprothiolane. J. Environ. Sci. Health, 2:135 146. Hankawa, Y. 1985. Behavior of molinate in paddy water and river water. J. Pestic. Sci., 10: 107-112. Hori, K. and M. Nakazaki, 1982. Pesticides pollution of natural waters in Kumamoto prefecture. Seitai Kagaku, 5:3-13 (in Japanese). Hughes, D., M. Boyer, M. Papst and C. Fowle, 1980. Persistence of three organophosphorus insecticides in artificial ponds and some biological implications. Environ. Sci. Technol., 8: 38-42. Imanaka, M., K. Matsunaga, A. Shigeta and T. Ishida, 1981. Oxadiazon residues in fish and shellfish. J. Pestic. Sci., 6: 41~417. Imanaka, M., S. Hino, K. Matsunaga and T. Ishida, 1985. Oxadiazon residues in surface water and crucian carp (Carassius cuvieri) of Lake Kojima. J. Pestic. Sci., 10: 12~134. Ishii, Y., 1984. Pollution by pesticides of estuaries in Aichi pref. and opinion on safe use of pesticides. Seitai Kagaku, 7:19-31 (in Japanese). Ishikawa, Y. Nakamura and S. Kuwatsuka, 1976. Degradation of benthiocarb herbicide in soil. J. Pestic. Sci., 1: 4~57.
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