Sonochemical degradation of triclosan in water and wastewater

Sho Communica ion Sonochemical deg ada ion o iclosan in wa e and was ewa e Lucia Sanchez-P ado a , Ru h Ba o a , Ca men Ga cia-Ja es a , Ma ia Llompa a , Ma a Lo es a , Ch is os Pe akis b , Nicolas Kaloge akis c , Dionissios Man za inos c , Ele e ia Psillakis c,* a Depa men o Analy ical Chemis y, Nu i ion and B oma ology, Uni e si y o San iago de Compos ela, E-15782 San iago de Compos ela, Spain b Medi e anean Ag onomic Ins i u e o Chania (MAICh), P.O. Box 85, GR-73100 Chania, G eece c Depa men o En i onmen al Enginee ing, Technical Uni e si y o C e e, Poly echneioupolis, GR-73100 Chania, G eece Recei ed 6 Augus 2007; accep ed 21 Janua y 2008 A ailable online 2 Feb ua y 2008 Abs ac The sonochemical deg ada ion o 5 lgl 1 iclosan, a p io i y mic o-pollu an , in a ious en i onmen al samples (seawa e , u ban unoff and influen domes ic was ewa e ) as well as in model solu ions (pu e and saline wa e ) was in es iga ed. Expe imen s we e con- duc ed wi h a ho n- ype sonica o ope a ing a 80 kHz equency and a nominal applied powe o 135 W, while solid-phase mic oex ac- ion coupled wi h gas ch oma og aphy–elec on cap u e de ec o (SPME/GC–ECD) was employed o moni o iclosan deg ada ion. The la e ollowed pseudo-fi s o de kine ics wi h he a e cons an being (min 1 ): 0.2284 o seawa e > 0.1051 o 3.5% NaCl in deion- ised wa e > 0.0597 o cen i uged u ban unoff 0.0523 o un ea ed u ban unoff > 0.0272 o deionised wa e > 0.0063 o was ewa- e influen . SPME/GC–ECD and SPME coupled wi h gas ch oma og aphy–mass spec ome y (SPME/GC–MS) we e also used o check o he o ma ion o chlo ina ed and o he oxic by-p oduc s; a he condi ions in ques ion, he p esence o such compounds was no confi med. Ó2008 Else ie B.V. All igh s ese ed. Keywo ds: Deg ada ion; SPME; T iclosan; Ul asound; Wa e ma ix 1. In oduc ion T iclosan (5-chlo o-2-(2,4-dichlo ophenoxy)phenol) is an an imic obial agen lis ed by he 76/768/EEC Eu opean Union council di ec i e as a p ese a i e o cosme ic p oduc s. I s widesp ead use in consume p oduc s such as oo hpas es, an ipe spi an s, de e gen s, cosme ics, an imic obial c eams, lo ions and hand soaps is due o i s bac e ios a ic pe o mance agains a b oad spec um o mic oo ganisms as well as i s a ou able human sa e y p o- file. T iclosan is ypically anspo ed h ough a was e dis- posal con eyance sys em o a sewage ea men acili y. T ace le els o iclosan no emo ed du ing was ewa e ea men a e eleased o he ecei ing wa e s as pa o he effluen ma ix. Acco dingly, he p esence o iclosan in was ewa e , su ace wa e , seawa e and sedimen s has been equen ly epo ed in Eu ope and he Uni ed S a es and his is o conce n gi en he ac ha unde ce ain con- di ions (such as in p esence o hypochlo i e o due o pho- ochemical eac ions), he na i e species can be con e ed in o mo e oxic and pe sis en pola compounds, such as chlo ina ed phenols (mainly 2,4-dichlo o and 2,3,4- ichlo ophenol) polychlo ina ed biphenyl e he s and dihyd oxyla ed de i a i es as well as non-pola and bio- accumula i e species such as me hyl iclosan and polychlo- ina ed dibenzodioxins [1–6]. The use o high powe ul asound wi h equencies in he ange 20–1000 kHz induces he so-called acous ic ca i- a ion. In gene al, ca i a ion can be defined as he phenom- ena o he o ma ion, g ow h and subsequen collapse o mic obubbles o ca i ies occu ing in ex emely small 1350-4177/$ - see on ma e Ó2008 Else ie B.V. All igh s ese ed. doi:10.1016/j.ul sonch.2008.01.007 * Co esponding au ho . Tel.: +30 28210 37810; ax: +30 28210 37852. E-mail add ess: [email p o ec ed] (E. Psillakis). www.else ie .com/loca e/ul sonch A ailable online a www.sciencedi ec .com Ul asonics Sonochemis y 15 (2008) 689–694 in e als o ime and eleasing la ge magni udes o ene gy o e a e y small loca ion [7]. Today, he e a e se e al pub- lica ions epo ing he success ul emo al o a wide ange o o ganic pollu an s om ela i ely dilu e aqueous solu- ions [7,8]. Howe e and o he bes o ou knowledge, sonolysis o iclosan in wa e s and was ewa e s has no been epo ed be o e. Mo eo e , iclosan deg ada ion by ad anced oxida ion p ocesses o he han sonolysis has ecei ed me e a en ion. In ecen epo s, Yu e al. [9] s udied he TiO 2 -media ed pho oca aly ic deg ada ion in model aqueous solu ions, while Sua ez e al. [10] in es i- ga ed iclosan oxida ion be means o ozone. The aim o his wo k is o in es iga e o he fi s ime he sonolysis o iclosan, a p io i y mic o-pollu an , in aque- ous samples o en i onmen al impo ance. I is well known ha he p esence o ma ix componen s (such as sal , na u- al o ganic and pa icula e ma e ) may d ama ically al e he efficiency o sonochemical and o he ad anced oxida- ion p ocesses. Acco dingly, he p esen wo k in es iga es he effec o eal sample ma ix (seawa e , u ban unoff and influen domes ic was ewa e ) upon iclosan sonolysis. Fo he pu pose o he p esen in es iga ions solid-phase mic oex ac ion (SPME) was used as a iable analy ical ool o moni o ing he deg ada ion o iclosan as well as he possible o ma ion o chlo ina ed by-p oduc s. 2. Expe imen al 2.1. Chemicals and sample p epa a ion T iclosan (I gasan, 97%) was ob ained om Fluka, Sigma–Ald ich (S einheim, Ge many). Pes icide g ade me hanol and sodium chlo ide (>99.8% pu i y) we e ob ained om Me ck (Da ms ad , Ge many) and Riedel de Haen (Seelze, Ge many) espec i ely. Deionised wa e was p epa ed on a wa e pu ifica ion sys em om Lab- conco Wa e P o TM PS (Kansas Ci y, Missou i, USA). In hose cases whe e samples had o be cen i uged p io o sonica ion, his was done o 10 min a 4000 pm wi h a He aus Mega uge cen i uge. Fo sample p epa a ion, a 1000 mg l 1 s anda d s ock solu ion o iclosan was ini- ially p epa ed in me hanol. Spiked aqueous solu ions we e p epa ed daily by spiking wa e wi h he o ganic s ock solu ion o iclosan a he concen a ion le els o in e es . 2.2. Aqueous samples Sonica ion expe imen s we e conduc ed wi h model solu ions p epa ed in deionised wa e as well as wi h (i) sea- wa e collec ed om Chania, Wes e n C e e, G eece, (ii) u ban unoff collec ed om one o he exi s o he munici- pal s o mwa e d ain sys em o Chania discha ging in coas al wa e and (iii) was ewa e collec ed om he inle o he seconda y ea men o he domes ic was ewa e ea men plan o Chania. Real samples, whose p ope ies a e summa ised in Table 1, we e collec ed he day be o e he sonica ion expe imen was pe o med and we e ana- lysed o hei o al o ganic ca bon (TOC) con en using a Shimadzu TOC 5000A ins umen and o al dissol ed solids (TDS) d ied a 180 °C acco ding o he S anda d Me hod 2540 C [11]. pH and salini y we e measu ed using a po able ins umen (pH/Cond340i) supplied by WTW GmbH (Weilheim, Ge many). 2.3. SPME ex ac ion p ocedu e The SPME me hod used is desc ibed in de ail elsewhe e [12,13]. In b ie , a comme cially a ailable 100 lm poly- dime hylsiloxane SPME fib e, housed in a manual SPME holde (Supelco, Belle on e, PA, USA) was used o all ex ac ions. Each ime, aliquo s o wa e samples (5 ml) we e placed in 7 ml ials and di ec SPME was pe o med by exposing he fib e o he solu ion. The ex ac ion was ca ied ou o 30 min a oom empe a u e while s i ing a 1250 pm. 2.4. Gas ch oma og aphic analyses A Hewle –Packa d (HP 5890 Se ies II) gas ch oma og a- phy–elec on cap u e de ec o (GC–ECD) sys em equipped wi h a spli /spli less injec o was used o all analyses. The sys em was ope a ed by HP ChemS a ion A03.04 so wa e. Expe imen al condi ions we e column HP5-MS, 30 m  0.25 mm i.d. 0.25 lm film; o en empe a u e p og amme: 60 °C, hold 2 min, a e 15 °C min 1 o 210 °C hen 10 °C min 1 o 270 °C, hold 10 min. The injec o was main- ained a 280 °C and ope a ed in he spli less mode wi h he spli closed o 2 min (spli a io 50:1). The de ec o empe - a u e was 290 °C. Helium (>99.999 % pu i y) was used as he ca ie gas a a cons an head p essu e o 130 kPa. The lin- ea i y o he SPME me hod was e alua ed o iclosan con- cen a ions be ween 0.1 and 50 lgl 1 and was ound o be e y good ha ing a 0.996 co ela ion coefficien ( ). The me hod’s de ec ion limi was es ima ed o be 0.01 lgl 1 . Samples we e also analysed by means o SPME/GC–mass spec ome y (MS). These analyses we e ca ied ou on a Shi- madzu GC-17A, Ve sion 3, QP-5050A Gas Ch oma og aph/ Mass Spec ome e sys em (Shimadzu Co po a ion, Kyo o, Japan) equipped wi h he same capilla y column (HP5-MS, 30 m 0.25 mm i.d. 0.25 lm film) and ha ing iden ical injec o condi ions and o en empe a u e p og amme. The ioniza ion mode was elec on impac (70 eV), he in e ace empe a u e was se a 300 °C wi h 1.40 kV de ec o ol age Table 1 P ope ies o eal samples used in his s udy (measu ed a 20 °C) Sample Ini ial iclosan con amina ion (lgl 1 ) pH Salini y (% w: ) TDS (mg l 1 ) TOC (mg l 1 ) Seawa e <0.01 8 3.5 51 3.5 U ban unoff 0.07 7.7 0.018 397 6.7 Influen domes ic was ewa e 0.4 7.6 0.029 644 256 690 L. Sanchez-P ado e al. / Ul asonics Sonochemis y 15 (2008) 689–694 and he selec ed ion moni o ing (SIM) mode o ope a ion was used as a sensi i e analy ical ool. 2.5. Sonica ion expe imen s An Ul ason 250 (LabPlan , Hudde sfield, UK) ho n- ype sonica o capable o ope a ing ei he con inuously o in pulse mode a a fixed equency o 80 kHz and a a iable elec ic powe ou pu up o 150 W was used. Reac ions we e ca ied ou in a 250-ml ound-bo om cylind ical all-glass eac ion essel equipped wi h a cooling jacke , connec ed o a empe a u e con ol uni (Polys a cc2 model manu ac- u ed by Hube , Ge many). The eac ion essel was co e ed wi h aluminium oil, a oiding hus any pho ochemical eac- ions. In all cases, 200 ml solu ions con aining 5 lgl 1 o iclosan we e subjec ed o ul asonic i adia ion a a nom- inal powe ou pu o 135 W wi h he sonica o ope a ing in pulse mode (30 s ‘‘on”, 30 s ‘‘off”). I should be men ioned he e, ha he ex emely low me hanolic con en did no al e he physicochemical p ope ies o he syn he ic sam- ples. Resul s a e quo ed wi h espec o he ac ual sonica- ion ime (i.e. he ‘on’ pe iod o he du y cycle) a he han he o e all ea men ime (i.e. he ‘on’ and ‘off’ pe iod o he du y cycle) which was wice as much as he sonica ion ime. Pulse ope a ion was chosen o minimise hea dissipa- ion du ing sonica ion, hus acili a ing empe a u e con- ol. Mo eo e , p elimina y expe imen s we e conduc ed ei he lea ing he eac o ’s empe a u e uncon olled o keeping i cons an a 20 °C; in ei he case, iclosan deg a- da ion emained p ac ically unchanged. Hence, in all subse- quen expe imen s he empe a u e o he eac ion essel was le uncon olled. 3. Resul s and discussion Fig. 1 shows iclosan no malised concen a ion– ime p ofiles o he a ious samples subjec ed o ul asonic i a- dia ion. As seen, nea ly comple e iclosan emo al could be achie ed wi hin 120 min o i adia ion o all samples bu he influen domes ic was ewa e o which only 60% deg ada ion was eco ded a e 180 min o eac ion. Con- e sely, deg ada ion in seawa e p oceeded apidly yielding o e 95% con e sion in 15 min. Fo all samples, con ol expe imen s we e un, whe e 5 lgl 1 aqueous solu ions o iclosan we e le in he da k a ambien empe a u e o he same pe iod o ime and in he absence o ul asonic i adia ion, e ealing ha he dec ease in iclosan concen- a ion was due o he effec o sonica ion alone. Sonochemical deg ada ion o o ganic compounds a low concen a ions usually ollows pseudo-fi s o de kine ics ega ding subs a e concen a ion, i.e. dCi d ¼kCi() ln Ci;0 Ci  ¼k ð1Þ whe e kis an appa en eac ion a e cons an , and C i,0 and C i is he subs a e concen a ion a ime ze o and espec- i ely. I he da a o Fig. 1 a e plo ed in he o m o Eq. (1), s aigh lines passing h ough he o igin fi he expe imen al da a well and a e cons an s can be calcula ed om he slopes o he espec i e s aigh lines (plo s a e no shown o b e i y). The compu ed a e cons an s a e 0.0272 (0.983), 0.1051 (0.996), 0.2284 (0.944), 0.0523 (0.994), 0.0597 (0.997) and 0.0063 min 1 (0.982) o deion- ised wa e , 3.5% NaCl in deionised wa e , seawa e , 0 20 40 60 80 100 120 0 20 40 60 80 100 120 140 160 180 200 Sonica ion ime (min) C i /C o (%) Deionised Wa e Seawa e 3.5 % NaCl (w: ) U ban uno wa e Cen i uged u ban uno wa e In luen was ewa e Fig. 1. No malised concen a ion– ime p ofiles du ing sonica ion o a ious samples spiked wi h 5 lgl 1 iclosan. L. Sanchez-P ado e al. / Ul asonics Sonochemis y 15 (2008) 689–694 691 un ea ed u ban unoff, cen i uged u ban unoff and influ- en domes ic was ewa e espec i ely wi h numbe s in b acke s showing he co ela ion coefficien s ( ) o he lin- ea eg ession o he loga i hm o concen a ion agains ime. As clea ly seen, inc easing he ionic s eng h o he sam- ple had a beneficial effec on deg ada ion; a ou o eigh - old inc ease in he eac ion a e was eco ded when iclosan was ea ed in deionised wa e in he p esence o 3.5% NaCl o seawa e compa ed o he un wi hou sal . Seymou and Gup a [14] who in es iga ed he effec o sodium chlo ide addi ion upon he sonochemical deg ada- ion o aqueous solu ions o chlo obenzene, p-e hylphenol and phenol a 20 kHz ound ou ha he p esence o NaCl imp o ed subs an ially deg ada ion a es. The enhance- men in deg ada ion a es was a ibu ed o he sal ing- ou effec , whe e ewe wa e molecules a e a ailable o dissol ing he analy e molecules. The e o e, he solu e is expec ed o mig a e om he liquid bulk inside o nea he ca i a ion bubble whe e deg ada ion ia py olysis and/o hyd oxyl adical-induced eac ions is likely o occu as [15,16]. The ac ha deg ada ion in seawa e was as- e han in a ificial saline wa e may be associa ed wi h he wa e ma ix o he o me . Ino ganic and o ganic species can se e as ex a nuclei o ca i a ion as well as al e he gas and in e acial p ope ies o he ca i a ion bubble influ- encing hus he empe a u e, p essu e and chemical species p esen du ing he bubble collapse [17]. In u he uns, iclosan deg ada ion in u ban unoff wa e was s udied. Non-poin sou ce pollu ion, unlike pol- lu ion om indus ial and sewage ea men plan s, comes om many diffuse sou ces and is caused by ain all o snowmel mo ing o e and h ough he g ound. As he unoff mo es, i washes na u al and human-made pollu- an s, finally deposi ing hem in o lakes, i e s, we lands, coas al wa e s, o e en in unde g ound sou ces o d inking wa e . Acco ding o he USEPA, u ban unoff wa e s ep- esen one o he leading sou ces o wa e quali y impai - men . Indeed, in he unoff wa e samples in es iga ed he e, he p esence o iclosan was confi med (0.07 lgl 1 ). Sonochemical deg ada ion in u ban unoff was abou wice as as as ha in deionised wa e and o e 90% con e sion was eco ded in abou 60 min o eac ion. This can be explained in e ms o dissol ed solids acili a ing nuclea ion which appea s o be p edominan in he case o u ban un- off. Keck e al. [18] who in es iga ed he sonochemical deg- ada ion o a ious a oma ics in he p esence and absence o ine qua z pa icles in he ange 2–25 lm epo ed ha pe o mance was enhanced in he p esence o solids and his was asc ibed o solids al e ing he shape o bubbles om sphe ical o asymme ic, hus yielding la ge su aces a ailable o eac wi h mo e solu e molecules. Fo he pu - pose o he p esen s udies he expe imen was also epea ed wi h he unoff sample being cen i uged p io o iclosan con amina ion. As seen, he e was no signifi- can change in he a es o deg ada ion which we e in bo h cases as e han he one ound in deionised wa e . How- e e , when compa ing he aw unoff sample wi h he cen- i uged one, a sligh dec ease in a e (12%) was obse ed when he sample was no cen i uged ( aw) and i appea s ha al hough solid pa icles acili a ed nuclea ion o his ype o was ewa e , a second and mino effec akes place whe eby adso p ion o solu e molecules o pa icles is esponsible o he small dec ease in deg ada ion a e. Zhang and Hua [19] s udied he sonochemical deg ada ion o b omobenzene, b omophenola e ion, and 2,4,5- ichlo- obiphenyl in he p esence o 10 nm and 15 lm silica pa i- cles and 35 lm o ganic esin ( ep esen ing as he au ho s s a ed he ‘‘wo s case”) wi h he la e wo being sepa a ed om he solu ion by cen i uga ion. O e all, he au ho s ound ha he sonochemical decomposi ion a e cons an o b omobenzene was no significan ly impac ed by e y fine silica pa icles (10 nm) because hei diame e was much smalle han he sound wa eleng h and as such could no impac he sound field. In he p esence o he 15 lm sil- ica pa icles, esul s we e simila o he ones epo ed he e and sonica ion a es dec eased sligh ly (<7%) due o pa ial adso p ion o he solu e molecules o he solid pa icles. As expec ed he effec was mo e d ama ic when la ge pa icles such as o ganic esin (35 lm) we e p esen in he sonica ed mix u e [19]. Al hough la ge pa icles may se e as nuclei o bubble o ma ion, hey can also so b hyd ophobic chemicals mo e effec i ely impeding hus hei pa i ioning wi h he collapsing ca i a ion bubble [19,20]. This is in ag eemen wi h he esul s ob ained he e o he domes ic was ewa e sample whe e iclosan deg ada ion was ound o p oceed a subs an ially lowe a es han in any o he sample es ed. I is also possible ha su ac an s, ypically p esen in domes ic was ewa e , accumula e in he in e a- cial egion, hus educing he numbe o si es a ailable o iclosan deg ada ion [16,21]. The analy ical p o ocol used in his s udy was also capa- ble o checking o he chlo ina ed by-p oduc s a ising om iclosan deg ada ion as hese may ac ually be mo e oxic han iclosan i sel as well as be dioxins p ecu so s. Canosa e al. [2] de eloped a SPME-based me hod o de ec ing iclosan and i s me aboli es, namely me hyl iclosan, 2,4- dichlo ophenol and 2,3,4- ichlo ophenol in aqueous sam- ples (including influen and effluen was ewa e samples o an u ban sewage plan ). The use o SPME also enabled moni o ing he pho ochemical deg ada ion o iclosan in wa e and was ewa e when exposed o ul a iole (UV) o sunligh i adia ion [4,12,13]. These s udies confi med he iclosan o dioxin con e sion and he o ma ion o me aboli es such as chlo ina ed phenols, chlo ohyd oxydi- phenyl e he s, 2,8-dichlo odibenzo-p-dioxin and dichlo o- dibenzodioxin isome o dichlo ohyd oxydibenzo u an in a a ie y o en i onmen al ma ices. I has also been epo ed [9] ha he UV/TiO 2 -induced pho oca aly ic decomposi ion o iclosan was accompanied by he o ma- ion o 2,4-dichlo ophenol, a p io i y oxic pollu an which is known o be a dioxin p ecu so . In his wo k and unde he p esen expe imen al condi ions, none o he a o emen- ioned me aboli es was de ec ed in any o he samples 692 L. Sanchez-P ado e al. / Ul asonics Sonochemis y 15 (2008) 689–694 es ed. This is clea ly demons a ed in Fig. 2 whe e diffe en SPME/GC–ECD ch oma og ams ob ained be o e (Fig. 2b) and a e (Fig. 2c and d) sonica ion o he cen i uged u ban unoff sample a e shown. I should be men ioned he e ha simila ch oma og ams we e ob ained o he es o he samples ea ed he e. Compa ison be ween he ch oma o- g am co esponding o he o iginal, unspiked sample (Fig. 2a) and he ones ob ained a e spiking wi h 5 lgl 1 iclosan (Fig. 2b) o e en a e sonica ion (Fig. 2c and d) e eals ha he pa e n o he ex a peaks appea ing in he o iginal ch oma og am emains p ac ically unchanged. These ex a peaks appea ing in all ch oma og ams a e due o he ma ix and/o he use o SPME as a p econcen a ion me hod in which case he peaks a e commonly e e ed o as SPME con aminan s. The assump ion ha iclosan sono- chemical deg ada ion is no accompanied by he o ma ion o oxic by-p oduc s was also c oss-checked and confi med by means o SPME/GC–MS (SIM mode) analysis. The absence o chlo ina ed by-p oduc s in he eac ion mix u e may be asc ibed o he ac s ha (i) he hyd opho- bic iclosan (i s solubili y is abou 1 mg l 1 a oom em- pe a u e and he loga i hm o he oc anol–wa e pa i ion coefficien is 4.8 [22]), may be localised nea he ca i a ion bubble and unde go as he mal deg ada ion, hus mini- mising by-p oduc o ma ion and/o (ii) he a e o by- p oduc s o ma ion is lowe han he a e o hei sono- chemical deg ada ion and, consequen ly, hey do no accu- mula e in he eac ion mix u e. Fig. 2. SPME/GC–ECD ch oma og ams o he cen i uged u ban unoff sample (a) be o e spiking; (b) a e spiking wi h 5 lgl 1 iclosan and jus be o e sonica ion; (c) a e 15 min o sonica ion; (d) a e 120 min o sonica ion. L. Sanchez-P ado e al. / Ul asonics Sonochemis y 15 (2008) 689–694 693 4. Conclusions The low equency sonochemical deg ada ion o iclo- san in se e al model and ac ual samples o en i onmen al impo ance has been in es iga ed. In nea ly all cases, comple e con e sion can be achie ed a easonable ea - men imes; howe e , he a e o deg ada ion is e iden ly affec ed by he ma ix componen s p esen in he a ious samples. The effec may be an inc ease o dec ease depend- ing on he beha iou o he ma ix compound. O e all, deg ada ion dec eases in he o de : seawa e > 3.5% NaCl aqueous solu ion > cen i uged u ban unoff un ea ed u ban unoff > deionised wa e > was ewa e influen . A he expe imen al condi ions in ques ion, deg ada ion was no accompanied by he o ma ion o oxic me aboli es which commonly appea as by-p oduc s o iclosan na u- al a enua ion. Acknowledgemen s L.S.-P. and R.B. acknowledge he egional go e nmen Jun a de Galicia o hei doc o al and a el g an s. The au ho s would like o hank V. Koukou aki o conduc ing TOC measu emen s. Re e ences [1] K. A anami, J.W. Readman, Chemosphe e 66 (2007) 1052. [2] P. Canosa, I. Rod iguez, E. Rubı ´, R. Cela, J. Ch oma og . A 1072 (2005) 107. [3] D.E. La ch, J.L. Packe , B.L. S ende , J. VanO e beke, W.A. A nold, K. McNeill, En i on. Toxicol. Chem. 24 (2005) 517. [4] M. Lo es, M. Llompa , L. Sanchez-P ado, C. Ga cia-Ja es, R. Cela, Anal. Bioanal. Chem. 381 (2005) 1294. [5] M. Mezcua, M.J. Go ´mez, I. Fe e , A. Ague a, M.D. He nando, A.R. Fe na ´ndez-Alba, Anal. Chim. Ac a 524 (2004) 241. [6] H. Singe , S. Mu ¨lle , C. Tixie , L. Pillonel, En i on. Sci. Technol. 36 (2002) 4998. [7] Y.G. Adewuyi, Ind. Eng. Chem. Res. 40 (2001) 4681. [8] N.H. Ince, G. Tezcanli, R.K. Belen, I.G. Apikyan, Appl. Ca al. B: En i on. 29 (2001) 167. [9] J.C. Yu, T.Y. Kwong, Q. Luo, Z. Cai, Chemosphe e 65 (2006) 390. [10] S. Sua ez, M.C. Dodd, F. Omil, U. on Gun en, Wa e Res. 41 (2007) 2481. [11] L.S. Clesce i, A.E. G eenbe g, A.D. Ea on, S anda d Me hods o he Examina ion o Wa e and Was ewa e , 20 h ed., APHA, AWWA, WEF, Uni ed Book P ess Inc., Bal imo e, Ma yland, 1998. [12] L. Sanchez-P ado, M. Llompa , M. Lo es, M. Fe nandez-Al a ez, C. Ga cia-Ja es, R. Cela, Anal. Bioanal. Chem. 384 (2006) 1548. [13] L. Sanchez-P ado, M. Llompa , M. Lo es, C. Ga cia-Ja es, J.M. Bayona, R. Cela, Chemosphe e 65 (2006) 1338. [14] J.D. Seymou , R.B. Gup a, Ind. Eng. Chem. Res. 36 (1997) 3453. [15] N.N. Mahamuni, A.B. Pandi , Ul ason. Sonochem. 13 (2006) 165. [16] E. Manousaki, E. Psillakis, N. Kaloge akis, D. Man za inos, Wa e Res. 38 (2004) 3751. [17] O. K u ¨ge , T.L. Schulze, D. Pe e s, Ul ason. Sonochem. 6 (1999) 123. [18] A. Keck, E. Gilbe , R. Ko ¨s e , Ul asonics 40 (2002) 661. [19] G. Zhang, I. Hua, Chemosphe e 46 (2002) 59. [20] Z. Laugh ey, E. Bea , R. Jones, M.A. Ta , Ul ason. Sonochem. 8 (2001) 353. [21] B. Yim, H. Okuno, Y. Naga a, R. Nishimu a, Y. Maeda, Ul ason. Sonochem. 9 (2002) 209. [22] M.S. Duan, N. Zhao, I.B. O ¨ssu a do ´ i , T. Tho s einsson, T. Lo sson, In . J. Pha m. 297 (2005) 213. 694 L. Sanchez-P ado e al. / Ul asonics Sonochemis y 15 (2008) 689–694