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1 Chemosphere 88 (212) Contents lists ville t SiVerse SieneDiret Chemosphere journl homepge: Tehnil Note Chlorpyrifos degrdtion in iomixture of ioed t different mturity stges G.R. Tortell,, O. Ruilr, M.d.P. Cstillo, M. Ce, R. Mell-Herrer, M.C. Diez Nuleo Científio Tenológio en Bioreursos, Universidd de L Fronter, Csill 54-D, Temuo, Chile JTI Swedish Institute of Agriulturl nd Environmentl Engineering, Uppsl, Sweden rtile info strt Artile history: Reeived 22 Novemer 211 Reeived in revised form 23 Ferury 212 Aepted 25 Ferury 212 Aville online 21 Mrh 212 Keywords: Bioeds Mturity stge Chlorpyrifos Biologil tivity The iomixture is prinipl element ontrolling the degrdtion effiy of the ioed. The mturity of the iomixture used in the ioed ffets its overll performne of the ioed, ut this is not well studied yet. The im of this reserh ws to evlute the effet of using typil omposition of Swedish iomixture t different mturity stges on the degrdtion of hlorpyrifos. Tests were mde using iomixture t three mturity stges: d (BC), (BC15) nd 3 d (BC3); hlorpyrifos ws dded to the ioeds t finl onentrtion of 2, 32 nd 48 mg kg 1. Chlorpyrifos degrdtion in the iomixture ws monitored over time. Formtion of TCP (3,5,6-trihloro-2-pyrinidol) ws lso quntified, nd hydrolyti nd phenoloxidse tivities mesured. The iomixture effiiently degrded hlorpyrifos (degrdtion effiieny >5%) in ll the evluted mturity stges. However, hlorpyrifos degrdtion deresed with inresing onentrtions of the pestiide. TCP formtion ourred in ll iomixtures, ut mjor umultion ws oserved in BC3. Signifint differenes were found in oth phenoloxidse nd hydrolyti tivities in the three mturity stges of iomixture evluted. Also, these two iologil tivities were ffeted y the inrese in pestiide onentrtion. In onlusion, our results demonstrted tht hlorpyrifos n e degrded effiiently in ll the evluted mturity stges. Ó 212 Elsevier Ltd. All rights reserved. 1. Introdution Corresponding uthor. Tel.: ; fx: E-mil ddress: gtortell@ufro.l (G.R. Tortell). Pestiides ply n importnt role in the suess of modern frming nd food prodution. However, surfe nd groundwter n e ontminted with pestiides due to their indequte mngement. Point soures suh s identl spillges during tnk filling or lening the sprying equipment hve een identified s the mjor ontmintion risks (Müller et l., 22). Pestiide ontmintion is extremely hrmful for the environment nd onstitutes n importnt puli topi t world level. It is importnt to develop novel proesses for the ontrol nd tretment of this type of pollution, nmely y tking prt of the tlyti potentil of iologil systems tht n e used to redue pestiide ontmintion. Bioeds re iologil systems developed in Sweden nd hd een suessfully used to redue point soure ontmintion y pestiides (Torstensson nd Cstillo, 1997; Torstensson, 2; Vishetti et l., 24). The prinipl omponent of the ioed systems is the iomixture. The typil iomixture is omposed y strw:pet:soil in the proportions 5:25:25 vol.% (Cstillo et l., 28). Biomixture effiieny is sed on the ility to retin nd degrde pestiides nd, therefore, good iomixture must hve good dsorption pity nd high iologil tlyti tivity for pestiide degrdtion (Cstillo et l., 28). There re severl ftors tht n ffet iomixture effiieny, suh s temperture, omposition, moisture, nd mturity (ge) of the iomixture (Cstillo et l., 28). Most of these ftors hve een evluted in the iomixture (Fogg et l., 23,; Fogg nd Boxll, 24), ut the influene of using iomixtures t different mturity stges hs not een extensively studied thus fr. Cstillo et l. (28) reported tht iomixture ge is importnt euse the progressive iodegrdtion of the omponent llows series of miroil retions nd enzymti tivities tht enle n effiient degrdtion of pestiides nd void metolite umultion. Cstillo nd Torstensson (27) suggested tht good prtie to e omplished is preompost the iomixture efore pestiide ontmintion. In this sme sense, Cstillo et l. (28) reported tht more reserh is needed to evlute hnges in pestiide degrdtion during mturtion of the iomixture. Fogg et l. (23) reported tht isoproturon nd hlorotlonil were degrded (>9%) in iomix preomposted for 8 1 d. However, omprisons etween different mturity times were never performed. Chlorpyrifos [O,O-diethyl O(3,5,6-trihloro-2-pyridyl) phosphorothite] is rod-spetrum orgnophosphorus insetiide widely used throughout the world. It hs low wter soluility (1.4 mg L 1 ) nd high ffinity for soil orgni ron (K o = 8.5 L g 1 )(Rke et l., 1996). Redution in the undne of miroil ommunities in soil hs een oserved fter ontmintions with hlorpyrifos (Chu et l., 28). Also, hlorpyrifos ounds to soil onstituents tht my e introdued into rivers y surfe runoff from griulturl lnds (Wu nd Lird, 24) /$ - see front mtter Ó 212 Elsevier Ltd. All rights reserved. doi:1.116/j.hemosphere

2 G.R. Tortell et l. / Chemosphere 88 (212) Degrdtion of hlorpyrifos leds to the formtion of mjor metolite tht hs een identified s 3,5,6-trihloro-2-pyrinidol (TCP). This metolite presents ntimiroil properties due to the presene of the hlorine toms in its struture, whih, when removed from the struture, n e toxi to hlorpyrifos-degrding miroflor (Singh et l., 23). It hs lso een reported tht TCP in soil n dely hlorpyrifos degrdtion (Rke et l., 199). The influene of iomixture mturity in pestiide degrdtion is not extensively studied. This is importnt for defining dequte onditions for the initil estlishment nd orret preprtion of iomixture. Therefore, the im of this study hs een to evlute three stges of mturity of the iomixture nd their effet on pestiide degrdtion nd iologil tivities. 2. Mterils nd methods 2.1. Chemils Anlyti-grde (99% purity) hlorpyrifos nd TCP were purhsed from Sigm Aldrih. Formulted hlorpyrifos (Clorpirifos S48) of 48% w/v ws purhsed from ASP Chile. MBTH (3- methyl-2-enzothizolinone hydrzone), DMAB (3-(dimethylmino) enzoi id) were purhsed from Aldrih. All others hemils nd solvents were of nlytil regent grde nd were purhsed from Equil nd Merk Chile Preprtion of the iomixture nd mturity onditions The iomixture ws prepred y mixing n Andisol top soil without hlorpyrifos pplition history (37.1% snd, 34.2% silt, 28.7% ly, orgni mtter 12%, ph 5.9), ommeril pet (orgni ron 39.67%) nd winter whet strw (orgni ron 43%) in the volumetri proportions of 1:1:2 respetively, in the sme form of the trditionl Swedish iomixture. The strw ws ut using food proessor to otin smll frgment (3 mm pproximtely) to otin homogeneous iomixture ording to Cstillo et l. (28) nd mixed with top soil nd pet. Soil nd pet were lso sieved to homogenize (3 mm). The iomixture ws put in polypropylene gs for the mturtion proess, moisture ontent ws djusted with distilled wter to 6% of their wter holding pity nd stored in drk t 2 C ± 2. Polypropylene gs were mintined under these ondition during the following time of mturtion: d (fresh iomixture), 15 nd 3 d, nmely BC, BC15 nd BC3 respetively, prior to eing used in the hlorpyrifos experiments. The mjor hemil properties of the iomixture in the three different times ompost re shown in Tle Degrdtion studies Formulted hlorpyrifos ontining the tive ingredient (Clorpirifos S48) ws used in the degrdtion studies. One ulk smple of iomixture (25 g dw) of BC, BC15 nd BC3 ws seprted into 84 su-smples (25 g) nd pled in glss flsk (25 ml). 63 su-smples were individully treted with formulted hlorpyrifos t n pplition rte of 2, 32 nd 48 mg kg 1 of tive ingredient hlorpyrifos pproximtely. 21 su-smples per eh onentrtion were estlished nd 21 su-smples were used for ontrol purposes in iologil ssys to BC, BC15 nd BC3. The three onentrtions used were to simulte n identl spill of pestiide. After mixing, the flsks were inuted in the drk for 4 d t 2 ± 2 C. The iomix moisture level ws mintined through periodi pplition of distilled wter. Immeditely fter mixing, treted smples nd ontrol smples were removed nd stored t 2 C until their nlysis. Chlorpyrifos residues nd TCP were extrted from iomixture (5 g) y shking (35 rpm, Tle 1 Chemil hrteriztion of the iomixture in the three different stges (d) of mturity evluted. Prmeter d 3 d N (mg kg 1 ) P (mg kg 1 ) K (mg kg 1 ) ph (wter) Orgni mtter (%) N (mol + kg 1 ) C (mol + kg 1 ) Mg (mol + kg 1 ) Al (mol + kg 1 ) Ction exhnge pity (CEC) (mol + kg 1 ) Sum of ses (mol + kg 1 ) h) nd ultrsonition (3 min) with 6 ml of idified etone (etone + wter + onentrted phosphori id, 98:1:1 y volume) per grm of sustrte (Coppol et l., 27). Lter, the smples were entrifuged t 1 rpm nd the superntnt (5 ml) ws filtered with PTFE memrne (.2 lm pore size; Millipore) nd nlyzed y liquid hromtogrphy (HPLC) s is desried elow Determintion of iologil tivities in the iomixture Phenoloxidse tivity ws determined in ll degrdtion ssys nd ws performed using MBTH/DMAB (Cstillo et l., 1994). Briefly, smples (1 g) of the iomixture were gitted (15 rpm, 2 h) with 25 ml of 1 mm suinte ltte uffer (ph 4.5). Smples were entrifuged (4 rpm, 2 min). The superntnt of eh smple ws olleted, filtered through.45 lm memrne (Ntionl Sientifis filter unit) nd mesured immeditely. The retion mixture ontined 3 ll of 6.6 mm DMAB, 1 ll of 1.4 mm MBTH, 3 ll of 2 mm MnSO 4, 156 ll of the filtered smple nd, the retion is initited with the ddition of 1 llof1mmh 2 O 2. The retion is followed in spetrophotometer Spetroni Genesis 2PC t 59 nm (e =.53 lm 1 m 1 ). Beuse no orretion ws mde for the possile presene of lignin peroxidse (LiP) nd lse (L) tivity, this mesurement my represent the sum of mngnese peroxidse, LiP nd L (Cstillo nd Torstensson, 27) nd is expressed s phenoloxidse tivity. Hydrolyti tivity ws determined in ll degrdtion ssys nd mesured y monitoring fluoresein diette hydrolysis (FDA) ording to Shnürer nd Rosswll (1982) with slight modifitions. Briefly, 1 g of iomixture ws inuted in 3 ml onil flsk with 9.9 ml of sterile 6 mm sodium phosphte uffer, ph 7.8. The retion ws strted y dding.1 ml of FDA solution (2. mg ml 1 ). After 1 h of inution t 25 ± 1 C, 1 ml of etone ws dded to stop the retion. A 49 ws mesured in spetrophotometrilly fter removl of the iomixture y entrifugtion nd filtrtion. The onentrtion of the relesed fluoresein ws lulted y lirtion urve with stndrd quntities of FDA nd the results were expressed s lg FDA g 1 h Pestiide nlysis For pestiide nlysis the smples were injeted with Rheodyne 7725 injetor with 2 ll loop in Merk Hithi HPLC system equipped with L-71 pump, nd n L-7455 diode rry detetor. The detetor ws set t 29 nm nd the olumn ws C18 olumn (Superspher RP-C18, 5 lm mm). The moile phse onsisted of 6% CH 3 CN nd 4% wter/eti id (95.3/ 4.3 v/v) with flow rte of 1 ml min 1 t 25 C. The hlorpyrifos nd TCP reovery ws >85% in the iomixture. The retention times

3 226 G.R. Tortell et l. / Chemosphere 88 (212) were 3.7 min for TCP nd 23 min for hlorpyrifos, the detetion limits were.2 nd.1 mg L 1 in the queous phse for TCP nd hlorpyrifos, respetively Sttistil nlysis of dt Experiments were onduted using three independent replites. Dt were sujeted to nlysis of vrine (one-wy ANO- VA) nd the verges were ompred y Dunn multiple rnge test t p < Results nd disussion 3.1. Chlorpyrifos degrdtion in the iomixture t different mturity stges Chlorpyrifos degrdtion in the iomixture t different mturity stges is shown in Fig. 1. A high degrdtion in the iomixture ontminted with 2 mg kg 1 ws found in the three mturity stges evluted (Fig. 1). After 4 d of inution 85% of hlorpyrifos hs een degrded in BC15, while in BC nd BC3 pproximtely 7% of initil onentrtion of hlorpyrifos ws degrded. When the iomixture ws treted with 32 mg kg 1 of hlorpyrifos, nd fter 4 d of inution, degrdtion in BC15 ws of 7%, wheres in BC nd BC3 ws of pproximtely 6% (Fig. 1). Similr results were found when the iomixture ws treted with 48 mg kg 1 (Fig. 1). In this ssy, 6% of the initil hlorpyrifos dded ws degrded fter 4 d of inution in BC15, while only 56% of pestiide ws degrded in BC nd BC3, respetively. Aording to these results degrdtion of hlorpyrifos ws signifintly higher (p <.5) in BC15 ontminted with 2 nd 32 mg kg 1, when ompred with BC nd BC3. However, no signifint differenes (p <.5) were found in the three stges of mturity when the iomixture ws ontminted with 48 mg kg 1 of hlorpyrifos. A derese on the effiieny of degrdtion ws oserved with the inrese in the onentrtion of pestiide. Similr results were reported y Vishetti et l. (28), who found tht the degrdtion rte of hlorpyrifos deresed with inresing onentrtion of this pestiide in the iomixture. One possile explntion to this is the high umultion of TCP in the iomixture with higher pestiide ontmintion, whih n use n inhiition of hlorpyrifos degrding teri due to ntimiroil properties of TCP. Severl studies refer to the ntimiroil properties of TCP in soil (Rke et l., 199; Singh et l., 23). Formtion of TCP in the iomixture ws deteted in ll mturity stges (BC, BC15 nd BC3) nd in the three onentrtions of Pestiide onentrtion (mg kg -1 ) () d 3 d (d) d 3 d Pestiide onentrtion (mg kg -1 ) () (e) Pestiide onentrtion (mg kg -1 ) () Time (d) (f) Time (d) Fig. 1. Chlorpyrifos degrdtion in three different time ompost (, 15 nd 3 d) t 2 mg kg 1 (), 32 mg kg 1 (), 48 mg kg 1 () of iomixture of ioed nd TCP formtion (mg kg 1 ) in 2 mg kg 1 (d), 32 mg kg 1 (e) nd 48 mg kg 1 (f) fter 4 d of tretment t 2 C. Different letters refer to signifint differenes etween men vlues (n = 3) with Dunn Test (p <.5).

4 G.R. Tortell et l. / Chemosphere 88 (212) hlorpyrifos evluted, s showed in Fig. 1d f. In generl, n umultion of this metolite ws oserved minly during the first of inution. Degrdtion of this metolite ws hieved fter this time in ll mturity stges evluted, priniplly in the iomixtures ontminted with 2 nd 32 mg kg 1 of hlorpyrifos, s shown in Fig. 1d e. In generl, greter umultion of TCP ws oserved in BC3 for ll onentrtions tested (Fig. 1d f) nd signifint differenes (p <.5) were found etween BC3 nd the others two mturity stges evluted (BC nd BC15). The high vlues of TCP onentrtion in BC3 my e due to the inresed ph in the iomixture, s results of the higher mounts of K, C nd Mg (Tle 1) whih my inrese the se sturtion of the iomixture nd lso y degrdtion produts of the orgni sustrtes (whet nd pet), s ws desried y Shen nd Shen (21). Therefore, promoting the ioti degrdtion of hlorpyrifos nd onomitnt formtion of TCP in the BC3 (Rke et l., 1996). The soil used in this study ontins 12% of orgni mtter, whih ould inrese the hlorpyrifos dsorption nd to llow further degrdtion. Also, the soils with high orgni mtter ontent ould promote the development of rih teril ommunities nd enle more effiient hlorpyrifos degrdtion. However, moleulr iology studies of the iomixture re neessry to e onlusive Determintion of iologil tivities in the iomixture Results for phenoloxidse tivity re showed in the Fig. 2. In generl, phenoloxidse tivity ws higher in BC15 for ll the onentrtions of hlorpyrifos evluted; signifint differenes (p <.5) etween this stge of mturity nd BC nd BC3 were found. It is interesting to note tht, in generl, the presene of hlorpyrifos used n inrese in the vlues of phenoloxidse tivity in ll the ssys nd t the three time points evluted, Phenoloxidse Ativity (U kg -1 ) Fluoresein relesed (µg g -1 h -1 ) () () ontrol Tretment (mg i. kg -1 ) d 3 d Fig. 2. Fluoresein diette hydrolysis (FDA) () nd lignilolyti tivity () in three different time ompost (, 15 nd 3 d) t 2 mg kg 1 (), 32 mg kg 1 (), 48 mg kg 1 () of iomixture of ioed fter 4 d of tretment t 2 C. Different letters refer to signifint differenes etween men vlues (n = 3) with Dunn Test (p <.5). when ompred with the ontrol (Fig. 2). However, in the three mturity stges evluted signifint inrese (p <.5) ws found in the iomixture ontminted with 2 mg kg 1 of hlorpyrifos. In our ssys, phenoloxidse tivity in the iomixture ws negtively ffeted y the presene of hlorpyrifos in high onentrtion (32 nd 48 mg kg 1 ). However, positive effets were found with respet to the ontrol, demonstrting tht the iomixture in ll the evluted mturity stges hd higher pity to mintin metoli miroil tivity when hlorpyrifos is dded t higher mounts. Hydrolyti tivity in the three different mturity stges of iomixtures (BC, BC15 nd BC3) showed signifint differenes (p <.5), when ompred to the ontrol test (Fig. 2). FDA hydrolysis ws higher in BC15 for ll the onentrtions of hlorpyrifos evluted. Signifint differenes etween BC nd BC15 were found only in the ontrol nd t the lowest hlorpyrifos onentrtion (2 mg kg 1 )(Fig. 2). Interestingly, oth ontrol nd tretment showed n inresed hydrolyti tivity in BC nd BC15, ut in BC3 hydrolyti tivity delined. This might e due to instility of the iomixture in BC3 nd likely not euse of the pestiide. Nevertheless, hydrolyti tivity ws ffeted y higher onentrtions of hlorpyrifos. Vishetti et l. (28) showed tht hlorpyrifos hd negtive effet on the miroil iomss in the iomixture of ioed, ut only t the first stge, fter tht new metoli equilirium ws oserved tht resulted in enhning hlorpyrifos degrdtion. On the other hnd, Dutt et l. (21) desried tht when hlorpyrifos ws dded to the soil t field rte of.5 mg kg 1, soil miroil iomss ws inresed nd FDA hydrolysis ws not negtively ffeted, wheres t higher dosge (5 mg kg 1 ) FDA hydrolysis deresed signifintly. Monitoring the FDA nd ligninolyti tivity in the iomix of ioeds is only one pproh to the effets of pestiides on iologil tivity, given tht the iodegrdtion of pestiides in the iomixture or soil is series of physil, hemil nd iologil intertions. Moreover, it hs een demonstrted tht severl enzymes n t in pestiide degrdtion in soil, suh s phosphtses (Hsn, 1999), hydrolses nd roxylesterses (Ln et l., 25). 4. Conlusions The iomixture is the prinipl omponent in the ioed, nd its orret preprtion is essentil for good performne. This study provides first evidene out pestiide degrdtion in different mturity stges of the iomixture. Our investigtion showed tht hlorpyrifos ws degrded effiiently (>5%) in ll mturity stges evluted. However, the iomixture with 3 d of mturity (BC3) ws less effiient in the hlorpyrifos degrdtion ompred with fresh iomixture ( d) nd with of mturity (BC15). Moreover, hlorpyrifos degrdtion ws ffeted y the initil onentrtion of pestiide dded in ll mturity stges evluted. On the other hnd, when the time of mturity of the iomixture inresed there ws greter umultion of the metolite TCP, whih n e due to instility of the iomixture in the short time. Neverless, this ompound lso ws degrded in the iomixture in ll mturity stges evluted. Therefore, lthough our results demonstrted tht hlorpyrifos n e degrded in ll mturity stges evluted, re neessry further studies with longer times of mturtion, to evlute the stility of the iomixture nd thus to void the TCP umultion. Aknowledgment This study ws finned y Fondef Projet D9R16 nd Fondeyt Projet No 3949.

5 228 G.R. Tortell et l. / Chemosphere 88 (212) Referenes Cstillo, M.d.P., Stenström, J., Ander, P., Determintion of mngnese peroxidse tivity with 3-methyl-2-enzothizolinone hydrsone nd 3-(dimethylmino) enzoi id. Anl Biohem. 218, Cstillo, M.d.P., Torstensson, L., 27. Effet of ioed omposition moisture, nd temperture on the degrdtion of pestiides. J. Agri. Food Chem. 55, Cstillo, M.d.P., Torstensson, L., Stenström, J., 28. Bioeds for environmentl protetion from pestiide use review. J. Agri. Food Chem. 56, Chu, X.Q., Fng, H., Pn, X.D., Wng, X., Shn, M., Feng, B., Yu, Y.L., 28. Degrdtion of hlorpyrifos lone nd in omintion with hlorothlonil nd their effets on soil miroil popultions. J. Environ. Si. 2, Coppol, L., Cstillo, M.d.P., Moni, E., Vishetti, C., 27. Adpttion of the ioed omposition for hlorpyrifos degrdtion to southern Europe onditions. J. Agri. Food Chem. 55, Dutt, M., Srdr, D., Pl, R., Kole, R., 21. Effet of hlorpyrifos on miroil iomss nd tivities in tropil ly lom soil. Environ. Monit. Assess. 16, Fogg, P., Boxll, A.B.A., 24. Degrdtion of pestiides in ioeds. J. Agri. Food Chem. 52, Fogg, P., Boxll, A.B.A., Wlker, A., 23. Degrdtion of pestiides in ioeds, the effet of onentrtion nd pestiide mixtures. J. Agri. Food Chem. 51, Fogg, P., Boxll, A.B.A., Wlker, A., Jukes, A.A., 23. Pestiide degrdtion in ioed omposting sustrte. Pest Mnge. Si. 59, Hsn, H., Fungl utiliztion of orgnophosphte pestiides nd their degrdtion y Aspergillus flvus nd A. sydowii in soil. Foli Miroiol. 44, Ln, W.S., Cong, J., Jing, H., Gu, B.G., Qio, C.L., 25. Biodegrdtion of pestiide pollutnts y two kinds of enzymes oexpressed in genetilly engineered teri. Bull. Environ. Contm. Toxiol. 75, Müller, K., Bh, M., Hrtmnn, H., Spiteller, M., Frede, H., 22. Point- nd nonpoint-soure pestiide ontmintion in the Zwester Ohm Cthment. Germny. J. Environ. Qul. 31, Rke, K.D., Lskowski, D.A., Shultz, M.R., 199. Resistne of hlorpyrifos to enhned iodegrdtion in soil. J. Agri. Food Chem. 38, Rke, K.D., Steele, K.P., Yoder, R.N., Dik, W.A., Avidov, E., Ftors ffeting the hydrolyti degrdtion of hlorpyrifos in soil. J. Agri. Food Chem. 44, Shnürer, J., Rosswll, T., Fluoresein diette hydrolysis s mesure of totl miroil tivity in soil nd litter. Appl. Environ. Miroiol. 6, Shen, Q.R., Shen, Z.G., 21. Effets of pig mnure nd whet strw on growth of mung en seedlings grown in luminium toxiity soil. Bioresour. Tehnol. 76, Singh, B.K., Wlker, A., Morgn, A.J.W., Wright, D.J., 23. Effets of soil ph on the iodegrdtion of hlorpyrifos nd isoltion of hlorpyrifos-degrding teriumñ. Appl. Environ. Miroiol. 69, Torstensson, L., 2. Experienes of ioeds in prtil use in Sweden. Pesti. Outlook 11, Torstensson, L., Cstillo, M.d.P., Use of ioeds in Sweden to minimize environmentl spillges from griulturl sprying equipment. Pesti. Outlook 8, Vishetti, C., Cpri, E., Trevisn, M., Csui, C., Perui, P., 24. Biomssed, iologil system to redue pestiide point ontmintion t frm level. Chemosphere 55, Vishetti, C., Moni, E., Crdinli, A., Csui, C., Perui, P., 28. The effet of initil onentrtion, o-pplition nd repeted pplitions on pestiide degrdtion in ioed mixture. Chemosphere 72, Wu, J., Lird, D.A., 24. Intertions of hlorpyrifos with olloidl mterils in queous systems. J. Environ. Qul. 33,