Predicting herbicides concentrations in paddy water and runoff to the river basin

Journal of Enironmental Sciences Vol. 17 ,No.4,pp.631- -636,2005CNII- 2629/1Article ID: 1001-0742(2005)04-0631-06CLC number: X131.2Document code: APredicting herbicides concentrations in paddy water and runoff to the riverbasinPARVEEN Sultana'*，KOHGUCHI Testuyuki?，BISWAS Moloy'，NAKAGOSHI Nobukazu'(1.Graduate School for International Development and Cooperation (IDEC)，Hiroshima Univrsity, Kagamiyama 1-5-1, Higashi Hiroshima 739 8529 ,Japan. E- mail: parveen_ sultana04 @ yahoo . com; 2. Hiroshina Prefecture Agriculture Research Center, Hara， Hachihonmatu, Higashi Hiroshima739-0151，Japan; 3. Department of Enironmental Studies, IDEC, Hiroshima University, Higashi Hiroshima, Japan 739 8529)Abstract: This study was conducted to investigate the dissipation pattem and runoff of herbicides to the river basin from the paddy fields.Pesticide paddy field model( PADDY) was applied to predict herbicide concentration in paddy fields. A field study was conducted in a paddyfam of Higashi Hiroshima City, Hiroshima Prefecture, Japan in the year of 2003 paddy season. The herbicides were mefenacet,thiobencarb, and bensulfuron methyI. The sample water was analyzed by using gas chromatography and HPLC atter solid phaseextraction. Predicted dissipation rate of thiobencarb in paddy water was higher( DTso = 4.36) than that measured, with a lower k value( -0.069). Two weeks after application no thiobencarb was detected in the drainage channel and down stream. In the down stream,thiobencarb was detected until 3 d after application, with a range of 0.02% to 0.08% of applied herbicide. The predicted dissipation rate(k) and hl-life( DTs) of mefenacet was not significanty diferent from that of measured. In the drainage channel, upstream anddownstream mefenacet was found during the whole study period. In downstream, the maximum concentration of mefenacet was present0.61% of applied in the paddy field on 3DAH. The dissipation rate( k) of BSM varied from -0.0860 to -0. 1059 to with half-lf( DTg) 3.5and 2.84 d. In upstream water , no BSM was detected except trace amounts(0.01 ug/L) at 3 d after application. However, in the drainagechannel 8%，6% and 1.58% of applied BSM was present at0, 1 and 3 d atter application respectively. In the down stream, the highestconcentration was 1 .06%，shortly after application.Keywords: paddy field; pesticide paddy field model( PADDY) ; herbicide; dissipation; runofffrom place to place and year to year, intensive long- termIntroductionstudies are needed. Such studies will be useful in analyzingPublie concerm has recently been growing over the runoffthe long term effcts on the environment and to assess theof pesticides applied to agricultural land and the potentialpotential risks to aquatic ecosystems. In addition, knowledgecontamination of drinking water and adverse effects on aquaticof movement and degradation of an herbicide can helpecosystems. In Japan, more than half of all agricultural landagricultural scientists design management practices that willis paddy fields, from which pesticides can easily flow outresult in protection of offsite areas from herbicidethrough drainage into public water areas such as rivers andcontamination .lakes ( Inao， 2003 ). Many researchers have measuredIn Japan, in rice- producing areas river water is the mainpesticide losses from small paddy fields in Japan ( Izuka,source for irrigation( about 88% of total water use)，and this1982; Hori， 1982; Nakamura， 1982; Tsukamoto, 1983;is introduced to a main canal by weirs and then diverted toMikuriya, 1983; Numabe, 1992; Ebise, 1993; Nohara，branch canals( Hasegawa, 1995) . Drainage water from paddy1996; Sasagawa， 1996). Most of them reported that thefields is used repeatedly in other paddy fields of downstream.maximum concentrations during observation periods rangedThe flow of imigation and drainage water in rice paddies canfrom 10 to 100 mg/L for berbicides, and 1 to 10 mg/L forbe classified as three major scales, such as field level, farmfungicides and insecticides . The transportation of pesticideslevel and river basin. The behaviour and concentration offrom larger land areas has also been examined. In the USA,pesticides in surface water can be conceptualized based onWillfred et al. (Willfred, 1993) investigated the Missisippithe three points.River and its tributaries in July and August 1991 . MolinateIn this study， dissipation pattem and runoff ofand thiobencarb were found in the tributaries with maximumherbicides to the river basin from the paddy fields wasconcentrations of 2.6 and 0.06 mg/L， respectively, in theinvestigated. Pesticide paddy field model ( PADDY ) wasdissolved phase. In Greece, Albanis et al . ( Albanis, 1994)applied to predict and validate the herbicide runof potentialestimated the percentages of the total amount of molinateto the drainage channel and river system.released by rivers into the Thermaikos Gulf as 0.8% and1 Materials and methods0.25% for the years of 1992 and 1993，respectively .Important factors that determine the distribution of1.1 Pesticide paddy field model( PADDY)pesticides include their mobility from soil to water and theirThe pesticide paddy field model(PADDY) for predictinglife span in soil and water. Problems may occur due to ofsitepesticide concentration in water and soil of paddy fields andmovement with drift to sensitive crops ，runoff with rainfall,the runi was first developed andor leaching into soil if rainfall occurs soon after application.evaluate中国煤化工，199) This modelOther factors include the extent of pesticide contamination,vas focu:YC N M H Gridely used herbicidesrelated to the amount and frequency of their application, ason paddy nelas In Japan. Intually tnus model was applied towell as to climatic and imigation conditions( Landon, 1994;paddy field plots to predict the concentration of molinate andClay, 1998). Because these factors may differ significantlysimetryn. Later on，it was applied for a wide range of* Crspd5弓数据Vol.17PARVEEN Sultana et al .herbicides, and in filed level landscape level, such as blockand district level ( Inao, 2001; 2003). Many models have, Upstreambeen developed and aplied to predict the pesticide runoff, andand degradation in soil and aquatic environment( surfaceground water). However, the PADDY field model is basedon paddy fields, and so it is particularly well suited to thePaddiesherbicides used in paddy farming.The herbicide applied in paddy fields can be quantifiedby considering the main pesses: dslutioun of herbieide"Downstreamfrom ganules into water, adsoption and desoption, run of,leaching, vlaizaion and degradaio. Herbicide upook byKurose Riverplants was not considered in this model.a Sampling site1.2Equation for herbicide concentration of watersurface in the paddy feldImigationThe herbicide concentration in paddy field water wascalculated using the fllowing Equation:FieldIVd.c /di= V.k. (C.-C.)-Q.C. Qc.-M.kan(KC.C.)-K. AC..-V。kan C..Field2Where, V。 is the volume of paddy feld water; C。isDrainagethe pesticide concentration in paddy field(mg/L); k, is theb. Water movementdesolution rate constant; C.. is the water solubility ofpesticeide; Q. is the outlow rate of water; Q; is theFig.1 Map of sampling lcations in the study sitepenetration rate of water; M。 is the weight of suface soila. sampling site; b. water movementsolid; K, is the freundich adsorption cofficient; K is thefarm(Fig.1).overall mass transfer cofficient; A is the area of paddy field;ke is the first order degradation rate constant .Water samples were collected from the upstream, threeThe volumetrie flow rate into and out of paddy fields ispaddy fields, downstream and oulet to the downstream. Theconstant(i.e., inflow rate = outlow rate + penetration ratesampling was made at or around0, 1,3, 7, 14, 21, 28 and+ evaporation rate = constant), and the volume of paddy35 d after herbicide application using glass bttles. Samplesfield water is also constant .were taken from random spots in each of the paddy fields.1.3 Study areaFrom each of the sampling point 1000 ml samples wereThe study of herbicide dissipation and runoff was carriedcollected during the whole study period. The water samplesout in a rice producing area Higashi Hiroshima City in thewere brought to the laboratory immediately and analyzed usingKurose Basin, Hiroshima Prefecture, Japan. The city area isgas chromatography and HPLC after solid phase extraction.288.25 km', of which about 12% is agricultural land, andThe method used for the residue analysis was developed at theabout 95% of that agriculural land is under paddyPesticide AnalysisLaboratory of Hroshima Prefectureculivation. The altitude is approximately 200 m above seaAgriculture Experiment Center.level and the eity is located in the Saijo basin under the1.5 Analysis of the samplesKurose watershed, which is surounded by mountains of aboutA Sep-Pak Caridge Rack(Nippon Milipore Co.) was500 m abore sea level. The study area is regarded as aused for solid phase extraction and elution. Herbicides andtypical paddy culivating area in Japan. A small river(Nukuiother reagents were purchased from Kanto Chemicals(Japan) .River) flowing over the study site is used athe mainAll solvents used were of pesticide residue-grade. Waterimigation channel and termed as “ upstream'。Rice peaddysamples were filtered through the No.7 filter paper of4 pm-fields are spread along the basin of the river. The river bankspore size with Hylo-Super-Cel( Kiriyama, Japan) to removeon both sides are protected by concrete blocks. In the area,the particles. Sep Pak-PS2(C18) cartridge( Waters, Ireland)water was distributed to individual farms by pump and then2 per sample, were preconditioned by washing with 10 mlfrom one field to another as shown in Fig.1. The drainageacetonirile and 30 ml dstilled water, and dried with a watercanal of the farm flows through the river, which ultimatelyaspirator. A 200 ml volume of filtered water with 2 repetitionsflows to the main river, which is termed as "downstream".of each sample was passed through the cattidge at a flow rateIn the monitored farm, rice was transplanted at the endof 10 m/min_ The harhinidee tranned on the cartnidge wereof May and one-shot herbicide Ulfues 1 kg granuleseluted中国煤化工The elutes were passed(mefenacet 3.0% , thiobencarb 15% and bensulfuron methylthrouMHC N M H Garators siline treated0.51%) was applied at a rate of 10 kg/hm2 under floodedfilter papen 1J.U cu uaeter, w natman) to remove water.conditions for 5 d afer transplanting on June 2, 2003, whenElutes were then concentrated to 1 ml by using a rotaryalmost all others farm has completed transplanting within theevaporator，followed by nitrogen gas concentration untilmonth of May. Therefore, the chance of herbicide residuedried. The extracts were then rdissolved in 1 ml acetone andreing carried out by imigation water was minimal. Thehe resuling solution was analyzed by using a gasimigation再妨频据ge water was used for two fields of thechromatograph and HPLC.No.4Predicting herbicides concentrations in paddy water and runoff to the river basin633A Shimadzu GC-14A gas chromatograph with FTD-8Table 1 Model ioput parameters for mefenacent and thiobencarb( Flame thermionic detector) was used for the analysis. ThValueParameterlass column was a chromosorb(w) HP(i.d. 3 mm andMefenacetThiobencarblength 1.0 m) with 1.5% silicone 0V-17 and 1.95%Molecular weight, g/mol298.4257.8silicone DC QF-1. The column temperature was 190 for 4Water solubility( C.)，mg/L4(20C )30(20C)min, with an increase of 30C/ min and the final temperatureVapor pressure, mmHg4.8x0-(20) 2.2x 10*(20C)was 230C for 11 min， with an injection temperature ofEquilibrium conslants250C，and a detector temperature of 280. The GC wasHenry constants( - )2.0x 10H0o2.7x 107日equipped with an automatic sampler with the injection volumestant related to1000b1380bset to2 μ. The temperature program was the same for all theAdorption eofftciecn( Kg) ,1kg26herbicides. The recovery for thiobencarb was 96.5%( SD =Freundich exponent(1/n)3.6,n=3) and 93.1 % for mefenacet( SD =4.3,n=3).Rate constantsBensulfuron methylwasanalysed using HighDissolution( k),1/d3.0x 10~143.4x 10-7d8Performance Liquid Chromatography (HPLC)， using an ODS4.0x 10-205.1x 10-1。column with a UV detector. Limit of detection was 0.01 μg/L4.0x 10-21Volatization( K[) ,m/d3.5x 10-85.0Sx 10-28and recoveriesof BSM ranged 75%-100% at the level ofDegradation in water( kdw) ,1/d2.8x 10-2h2.3x10-211.0 ug/L.Degradation in sediment soildThe stream flow and stream width of the upstream and(ka),1/d2.8x10-212.3x 10-2日downstream were recorded on each sampling date .1.6 Data analysis(1996); 。estimated from Ke with organic carbon content in soilDissipation rates were calculated using simple first order(1. 89%); d meaured value; 。asumed to be equal to kae; ' obtainedkinetics(SFOK). The equation C= Cge-" was used for thefrom Inao et al .( 999;“calculated value; . calculated by the Liss andSlater method( Ref. Liss and Slater, 1974);”assumed to be equal to kde ;“first order kinetics, where C is the amount of herbicide( mg/Lcalculated valuewater) at time t; C。is the amount of herbicide( mg/L water)只50厂at time0; h is the rate constant(d') and t is the time(d).50- aInitial concentrations of herbicide( Co) were calculated on the9basis of the total amount of water(in L) in the paddy field at40一the time of application and the total amount of herbicide0active ingredient(g) applied, assuming that 100% of active20 tingredient had been dissolved in the water. The dissipation0上rate constant( k) was calculated by linear regression from theoLl|ltransformed first order rate equation, InC = In Co- kt . Half-/2 6/3 6/5 6/9 6/16 6/23 6/30 7/life( DT,o) was calculated using the equation -log (2)/kDate( Kohno, 1986). Data were analyzed using SPSS 11.0 for45厂40 FWindows.35十30 FThe measured concentration of herbicides mefenacet andthiobencarb in the farm paddy field were compared with the25 F20 Fconcentrations predicted by the model using input parameters15 F(Table 1). The predicted concentration of BSM was not0Fcalculated .2 Results and discussion6/1 6/4 6/7 6/106/13 6/16 6/19 6/22 6/25 6/28 7/1 7/4 7172.1 Environmental conditions of the study siteFig.2 Changes in environmental conditionIn the study area, the surface layer of the paddy fieldsa. volumetric flow rate in down stream; b. pecipitationcomprised of alluvial soil， classified as sandy loam withDissipation pattemn of thiobencarb was similar in15.5% clay content and 1.89% humus， bulk density ofpredicted and measured concentration ( Fig.3a). Measured0.75 g/ml， and porosity of 0.72. The cation exchangeconcentration of thiobencarb in paddy fields reached peak at 3capacity( CEC) varies from 8.6 to 11 .0 meq/100g soil. Thewater pH of the study paddy fields were acidic at the earlyd after herbicide application, degraded fast, and decreased tostage and acidic to neutral at the later stage varying from 6.2trace levels after one month of application showing normalto 7.5. The mean annual rainfall of this area was 1071 mm indistribution curve. The measured concentration of thiobencarb2003，the corresponding mean annual temperature rangedin paddy water was slightly higher than the predicted, but thefrom 3.39 in January to 26.4C in July. Minimumtrend中国煤化工iod(Fig .4a). During thewhole-centration was higher intemperature of paddy water was 18.2C at early May and rosepaddyYHC N M H Gically was not sgificantup to 32.5C at early June. However, precipitation and(Table 2). The reason might be that with the imigation waterwater flow in downstream are shown in Fig.2. There was noherbicide runoff to the field 2. Except one day after herbicidesignificant rainfall event until two weeks after herbicideapplication, thiobencarb concentration in the drainage channelapplication .2.2 Thiobencarb concentration in paddy and otherwas similar to that of the paddy fields . However, 2 weeks afterapplication no thiobencarb was detected in drainage channelsurface啊方数据634PARVEEN Sultana et al .Vol.17and in down stream. In down stream， thiobencarb was+ Paddy field 1+ Paddy field 2detected until 3 days after application, with a range of 0.02%士Drainage chanel, Upstream母Downstreamto 0.08 % of the applied herbicide.1000 [1001000Mesurca0.1 t010.0010.1|b]0.010.001000).1 f昌0.01c]00 t10一4212835Days after herbicide application, dsimulated andmeasured concentrations 014212835herbicides in paddy watera. thiobencarb; b. mefenacetThe rate of dissipation(k) and the half-life( DTso) ofFig.4 Measured concentration of herbicides detcted in the dfferent samplingthiobencarb in the two paddy fields were quite similar, 3 andpoints2.95 days in field 1 and field 2 respectively ( Table 3 ).a. thiobencarb; b. mefenacet; e. bensulfuron methylTable 2 Measured concentratons( pg/L)o thiobencarb in paddy and surface waterDays afterSampling sitePercentage of pplied in paddy fieldDateherbieidePaddyPaddDrainageDruinageUpstreamDownstreamapplicationfield 2channelJune 2,2003313.28320. 16318.430.521.796.370.04June 3 ,2003286.80 .313.66243.13n1.04.860.02June s, 20030461.8534.58nd.080.69 .0.08June 9,200339.6546.5346.292.60d0.93June 16,2003145.637.355.430.11June 23 ,20030.911.090.78noJune 30,200328July 7,200335< 0.01<0.01ncNote: nd = not detectedHowever, the predicted dissipation rate of thiobencarb inTable3 Halr.Hie( DTs), dispation rate and R2 values of the studypaddy water using the PADDY field model was higher( DTsoherbicides=.4.36) than that measured for both the paddy fields, withHerbicideRDTsoa lower h value(-0.069). Quick disipation and shorter half-Measured:life of thiobencarb could be anticipated from its higher waterField 1 Thiobencarb- 0.10030.9388(p < 0.001) 3solubility(20 mg/L) and lower adsorption cofficient( K。=Mefenacet- 0.0480.8279(p=0.002) 6.2713.6).Bensulfuron methyl - 0.10590.804(p=0.01) 2.842.3Mefenacet concentration in paddy and otherField 2 Thiobencarb-0.1022 0.9522(p<0.001) 2.95surface water- 0.05490.8423(p=0.001) 5.48The simulated and measured concentration of mefenacet中国煤化工.8353(ρ=0.01) 3.sin paddy field was larger on one and three days afterDrainagcanYHCN M H G0.82(ρ=0.04) 4.04 .application (Fig. 3b) . Mefenacet was detected in the paddywater until 35 days after herbicide application ( Fig. 4b).Melenacet-0.1170.930(p=0.02) 2.57Bensulfuron mebyl - 0.05090.750(p=0.08) 5.9There were no significant diferences between concentrationsPredicted: Thiobenearb-0.069 0. 8658(p=0.001) 4.36of the two paddy fields. Mefenacet was found during th-0.05825 0.8720(p=0.00) 5.17whole study period in the drainage channel, upstream andNoles: DTxo = hal lie(in days) ; computed using the equation -Log(2)/k;k=downstream方別数糖. In down stream , the highest amountisipation rate; slope of the rgression linesNo.4Predicting herbicides concentrations in paddy water and runoff to the river basin635of mefenacet(6.08 ug/L) was detected on three days afterhigher adsorption coefficient( K。= 24.07)，and for thisapplication，which corresponds with the upstream andreason much of its residues could have been adsorbed by thedrainage channel concentrations . The underlying cause mightoil， leaving only a small portion in water which may againbe that, mefenacet has lower water solubility(4 mg/L) anddesorbed in water( Ferdinand, 2000).Table 4 Measured concentrations( pg/L) of mefenacet in paddy and surface waterDays afterSampling sitePercentage of applied in paddy fieldDateherbieidePaddyDrainageUpstreamDown streamDownstreamapplicationfreld1field 2channelJune 2,200349.7648.8143.510.170.424.350.04June 3,2003178.56125 .01108.230.750.910.820.09June 5,2003233.27248.47121.0110.65 .6.0812.100.61 .June 9,200323.0520.645.081.27I .430.510.14June 16,20034.54 .33.863.072.530.270.310.03June 23 ,200321.503.71< 0.010.0.370.00June 30,2003280.520.252.80.020.28July 7,2003350.13.0.44<0.010.01The dissipation rate ( k) and half-life ( DTso) of24.57，10.37, 4.63, 2.28 and 0.98 pug/L in field 1. In .mefenacet predicted by applying the PADDY field model, wasfield 2，concentrations were slightly higher as， 40.73,not significantly different from that of measured ( Table 5).16.81, 5.21, 2.85 and 1.29 ug/Lon1, 3, 7, 14 and21 dThe dissipation rate of field 1 was -0.048(k) with longerafter application respectively. Three weeks after herbicidehalf-life(DTso= 6.27 d)，whereas in field 2，k and DTsoapplication, BSM in the treated paddy water had decreased towere -0.0549 and 5. 48 respectively, compared to predictedtrace levels. This is in agreement with previous studies- 0.0582(k) and5.17 d (DT3).demonstrating similar dissipation pattemns ( Okamoto, 1998 ) .2.4 Bensulfuron methy| concentration in paddy and21 d after application, no BSM was detected in the drainagechannel and downstream. In upstream water, no BSM wasother surface waterDissipation of BSM in the paddy field water ，drainagedetected except trace amounts (0.01 pg/L) at 3 d afterchannel, upstream and downstream is shown in Fig. 4c.application. However, in the drainage channel 8，6 andObserved peak concentration was 139 .97 and 162.65 μg/L in1.58% of applied BSM was present at 0, 1 and 3 d afterfield 1 and in field 2 respectively(Table 5). This occurredapplication respectively. In the down stream， the highestshortly afer application(0 d). On 1, 3, 7，14 and 21 dconcentration was 1 .06 %，shortly after application .The dissipation rate of BSM in field 1 was faster( k =after application, the concentration had dropped rapidly toTable 5 Measured conentrations( pag/L)of bensulfuron methyl in paddy and surface waterherbicideUpstrean Downstreamfield 10139.97162.6541.54ne5.398.151.0624.5740.7331.94nc1.666.260.3210.3716.818.060.701.58June 9.20034.635.213.650.390.720.08 .42.282.850.66nd0.130.05June 23,20030.981.29id_nd一0. 1059) with shorter hal-life( DTso = 2.84 d). The .L of thiobencarb, and pesticide losses ranged from 0.26%dissipation rate(k) in field 2 was -0.0860 and half-life wasfor chlomethoxyfen to 12% for simetryn. Fukushima, et al.3.5 d(Table 5).( Fukushima, 1995 ) reported that the highest concentration ofThe herbicides concentrations found in the downstream20 mg/L for isoprothiolane, diazinon, molinate , and simetrynwere much lower than in previous studies. Study ( Maru,and over 1 mg/L for thiobencarb, in April 1990 and August1985) found maximum concentrations of 52.6, 58.0 and1994，in the Yodo River basin. The average concentrations14.1 mg/L for molinate， simetryn, and thiobencarb in thein the Seta River monitored in Apil 1990 and August 1994,main river in Chiba Prefecture and estimated that the中国煤化工ate，simetryn andexportation rate of these pesticides to be, 11.3%，6.7%,thiobencTYHCior isoprothiolane, lessand 2.2% respectively of the applied amounts in 1981, andthan 0.CNM H G. than 0.01 mng/L for6.0%，5.7% and 1.4% in 1984. Yamaguchi， et al.diazinon and fenitrothion ( Fukushima，1995 ). Monthly( Yamaguchi, 1999) surveyed pesticide pollution in the Yodoobservations showed that the loads of simazine, iprofenfos andRiver basin and about 30 pesticides were detected ，with meanfenitrothion from the Lake Biwa basin from April to Decemberconcentrations ranging from 0.3 ng/L of quintozene to 300 ng/in 1990 to be 130，250 and 21 kg, respectively, accounting.636PARVEEN Sultana et al .Vol. 17for 52%，30% and 5% of the downstream loading of theScience, 25(2): 94- -100.Yodo River( Yamaguchi, 1999). In addition, the maximumFukushima M, Yamnguchipollution in river water a a sourcee of potable water[R]. IWSA Specializedconcentration in the Seta River which flows into Lake BiwaConference on Advanced Treatment and Integrated Water System Mangementwas about 20 mg/L for molinate, 10 mg/L for simetryn andinto the 21th Century. 1:less than 5 mg/L for oxadiazon, as reported by Sasagawa, eHasegawa s, Tabuchi T, 1995. Well failiated paddy fields in Japen[M]. In:al. (Sasagawa, 1996) .Paddy fields in the world(Tabuchi T, Hasegawa s. ed.). Japan Tokyo:The Japanese Society of Irigation, Drainage and Reclamation EngineeringOne reason behind the lower herbicide concentration in(JSIDRE). 103-124.downstream and upstream might be having no to lowHori K, Nakaji M，1982. Pesticides plluion of natural waters in Kunamotoprecipitation during the first two weeks after herbicidePrefocture[J]. Ecol Chem, 5(2): 3-13.Inao K, Ishi Y, Kobara Y et al., 2003. Landscape scale simulation of pesticideapplication( Fig.2). The rainfall immediate after herbicidebehavior in river besin due to runoff from paddy fields using Pesticide Paddyapplication is an important factor for efective runoff. LowerField Model (PADDY)[J].icide Science,28(1):24- -32concentration of herbicides in the entry route was due to thatInao K, Ishi Y, Kobern Y et al.. 2001. Predicton of pesticide beharvior in paddyfield by water balance on the water management using Pesticide Paddy Fieldthe precipitations were lower at the early stage of herbicideModel( PADDY)[J]. Joumal of Pesticide Science, 26(3): 229- 235.application. The field runoff can only be observed whenInao K, Kitemurn Y, 999. Pesticide Paddy Field Mode(PADDY) for predicingprecipitation exceeded 10 mn/d and at least 2% of thepesticide concentraion in water and soil paddy felds[J]. Journal of Pesticideprecipitations become field runoff ( Neumann, 2002). LateSeience, 55: 38- -46.transplanting of the study paddy fields', when transplantationIzuka H, Iwanada s, 1982. Pesticide contamnination of river water from paddyfield[J]. J Water Waste, 24(6): 629- -635of other farms had been completed in the study area, may beKohno K，1986. Calculation of half-life, cllection of experimental data[J].another reason. Soil adsorption is one mechanism thatSpecial Bulletin of Kyushu Agricultural Experiment Station, 68:1- 7. .accounts for thedissipation of herbicides in paddy water.Landon M，Jacobsen J, Johnson G, 1994. Pesticide Managerment for Wate. M，JacobsenJ;1 MontanoOnce the herbicides adsorbed to soil, with the passing of timeQualityProtection [ Z]. Montana State University Extension. PesticideManagement Extension Bulletin. Montana State University， Bozeman ,the chance of desorption into the water is least ( Okamoto,1998).Maru S, 1985. Mornitoring survey of pesticides in river water within ChibaMonitoring and fate of herbicides in paddy water,Pefecture[J]. Ecol Chem, 8(3): 3- 10.drainage canal and streams provides an effective means forMikuriya R, Miyahura K, 1983. Pllution of creek waters in Saga Pref. bypesticides applied in paddy fields[J]. Ecol Chem, 6(2): 23- -33 .assessing the flow of herbicides in to and through publicNakamura K, 1982. Fale of herbicide around paddy field[J]. 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