Journal of Hazardous Materials 172 (2009) 13031310

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Journal of Hazardous Materials

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Photoc inZnO un

S. Navarra Departament cia. Cab Departament grario30150 Murcia,c Facultad de C os, s/

a r t i c l

Article history:Received 29 AReceived in reAccepted 30 JuAvailable onlin

Keywords:AgrochemicalsGroundwater pollutionPhotooxidationSemiconductorSunlight irradiation

n leacpouneppeconazmideationf pho

comparisonwith photolytic tests; signicantly increasing the reaction rates. The use of Na2S2O8 implies asignicant reduction in treatment time showing a quicker reaction time than ZnO alone. On the contrary,the addition of H2O2 into illuminated ZnO suspensions does not improve the rate of photooxidation. Thedisappearance of the pesticides followed rst-order kinetics according to LangmuirHinshelwood modeland complete degradation occurs from 60 to 120min. The disappearance time (DT75), referred to thenormalized illumination time (t ) was lower than 3min in all cases.

1. Introdu

The envmobility inmental commove pestimovementpesticides treceiving in

In the leagrochemicorganic maThe displacon the exteally accepterelated to tproperty [4demonstrattent and thecommon an

CorresponE-mail add

0304-3894/$ doi:10.1016/j.30W

2009 Elsevier B.V. All rights reserved.

ction

ironmental fate of pesticides depends a lot on theirsoils and their tendency to partition into other environ-partments, such as air and water. Transfer processescides in the environment. Concretely, leaching (theof water and dissolved chemicals through the soil) ofhrough the soil prole from agricultural practices iscreasing attention [1].aching process, the physicochemical properties of theals used aswell as soil properties (texture, clay content,tter content and permeability) play a decisive role [2].ement of pesticides from soil to water mostly dependsnt to which they are retained in soils [3]. It is gener-d that adsorption of pesticides by soils is more closelyhe soil organic matter content than any other single]. Many papers published in the last four decades haveed a high correlation between the organic matter con-distribution coefcientKd in a variety of soils. Themostd today generally accepted quantitative measure of the

ding author. Tel.: +34 968 367477; fax: +34 968 364148.ress: snavarro@um.es (S. Navarro).

sorption of organic pollutants by soils from aqueous solutions isthe soil organic adsorption coefcient (KOC). This chemical specicparameter plays a signicant role in the fate of pesticides in aque-ous/soil environment, like bioaccumulation and leaching ability,which is dened as: KOC =Kd/FOC, where FOC is the organic carbonfraction of the soil and Kd is the distribution coefcient.

KOC values are universally used as measures of the relativepotential mobility of pesticides in soils and in fugacity modelsdescribing the partitioning of pesticides in soil/water/atmospheresystems [5]. In general, compounds with higher logKOC valueswill be less mobile than those with lower values. Especially forthe hydrophobic pesticides (KOW 2), their mobility, and thereforethe risk of their leaching into groundwater, has been correlatedwith weak sorption on the soil, as quantied by KOC [6]. Gener-ally, pesticides with logKOC 3 are potentially leacher compoundsalthough pesticideswith logKOC 3 have been nd in groundwaterand drainage water [7].

The worlds tremendous output of pollutants challenges thecapacity of waterways to assimilate or ush away pollution.Concretely, Europe confronts enormous groundwater pollutionproblems being Agriculture the biggest polluter, even more so thanindustries and municipalities. European Union (EU) recent esti-mates reveal that about 1.5 million industrial and waste disposalsites exist which could have the potential to negatively inuence

see front matter 2009 Elsevier B.V. All rights reserved.jhazmat.2009.07.137atalytic degradation of eight pesticidesder natural sunlight

oa,, J. Fenollb, N. Velac, E. Ruizb, G. Navarroa

o de Qumica Agrcola, Geologa y Edafologa. Facultad de Qumica. Universidad de Muro de Calidad y Garanta Alimentaria. Instituto Murciano de Investigacin y Desarrollo ASpainiencias de la Salud. Universidad Catlica San Antonio de Murcia. Campus de Los Jernim

e i n f o

pril 2009vised form 30 July 2009ly 2009e 8 August 2009

a b s t r a c t

Photodegradation of eight pesticides ias photosensitizer/oxidant and comThe pesticides, habitually used on pazoxyxtrobin, kresoxim-methyl, hexaprimicarb (insecticide), and propyzator used at 150mgL1 on the degradexperiments show that the addition o/ locate / jhazmat

leaching water by use of

mpus Universitario de Espinardo. 30100 Murcia, Spainy Alimentario (IMIDA). C/ Mayor s/n. La Alberca,

n. Guadalupe, 30107 Murcia, Spain

hingwater at pilot plant scale using the tandemZnO/Na2S2O8d parabolic collectors under natural sunlight is reported.r culture and belonging to different chemical groups wereole, tebuconazole, triadimenol, andpyrimethanil (fungicides),(herbicide). As expected, the inuence of the semiconduc-of pesticides was very signicant in all cases. Photocatalytictosensitizer strongly improves the elimination of pesticides in

1304 S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310

soil and groundwater, the later being the major source for drinkingwater [8]. The consumption of pesticides by weight is decreasing,but it is the toxicity of an individual pesticide, not necessarily theamount used, which determines its potential for environmentaldamage. A fstorage of pcountries inawarenessincreasingAccession cter impactsstandards iresources isber 2000, twas adopteCommissiogroundwatewhoseAnneare listed.

Under cewater fromliterature cbehaviour iand practicgroundwateexceed theDirective (9water not tfor total pehealth of hbut also canused for irr

Unfortunnon-biodegprocess andoxidation tof pollutedpesticides t

Photolysing the fateenergy emptocatalysisto play andother contamediates, moxidant (E

oxides is anpollutedwaareas, whercess quite atitanium dicatalyst and[20], althoulike zinc oxwide bandgap, large eThe band garesponds toUV light withe electron(e/h+) paiagents. Intrwhile extriimpurity atof the mainis the difc

n-type is easily realized via excess Zn or with Al, Ga or In doping[21].

Although new management practices as integrated crop man-agement (ICM) have evolved in the last years as response to the

o redverytionay dr

direuringas wlisheotosdes, cnatu

erim

sticid

ticidGm

Theloresaretiescoefs soquityse (Pe sizAlfalone,cetatlone,cks soed innd stepar102ponstionon (L0.3

achin

watlysimlocat.7 anbyittere wa547) water wient

lar p

expSpat irrinteturthermajor threat to groundwater is the inappropriateesticides. Although a lot of effort is being made by EUinvestigating the situation of pesticide pollution, the

of pesticides causing problems in groundwater is stillas indicated in their State of Environment reports [9].ountries face similar or even more serious groundwa-and are supposed to follow EU environmental quality

n the near future [10]. The protection of groundwatera priority of EU environmental policy. Thus, on Octo-

he EU Water Framework Directive (WFD, 2000/60/EC)d and 3 years later, on September 2003, the Europeann adopted a proposal for a new Directive to protectr from pollution and deterioration (2006/118/EC) inx I, the quality standards for pesticides andmetabolites

rtain conditions, some pesticides may leach to ground-normal eld applications [6]. Although there is large

oncerning groundwater pollution, predicting pesticiden subsurface geosystems remains a complex scientical problem. Pesticide residues have been retrieved inr bodies all over the world and their levels frequently

drinking water limit set by the EU. The Drinking Water8/83/EC) requires pesticide concentration in drinkingo exceed 0.1g L1 for a single pesticide and 0.5g L1

sticides. Groundwater pollution not only affects theumans being as it is being used for drinking purpose,act as a source of contamination for food chain, when

igation.ately, a great number of pesticides are bio-recalcitrant,radable. Therefore, biological process is not the idealother more effective technologies such as advanced

echnologies (AOTs) have been proposed for treatmentwater by pesticides [1113]. These technologies allowo be removed by mineralization.is is one of the major transformation processes affect-of pesticides in the aquatic environment. If the excitingloyed is from the sun, the process is called solar pho-[14]. Sunlight photoalteration processes are well nowimportant role in the degradation of pesticides and

minants in water by generation of highly reactive inter-ainly hydroxyl radical (OH), a powerful non-specic=2.8V). Photocatalytic oxidation by semiconductorarea of environmental interest for the treatment of

ter, particularly relevant forMediterraneanagriculturale solar irradiation is highly available making this pro-ttractive [1519]. Due to its stability and non-toxicity,oxide (TiO2) has been demonstrated to be an excellentits behaviour is very well documented in the literaturegh the photocatalytic effect of other semiconductorside (ZnO) is not so well known. ZnO is a very interestinggap semiconductor material, because of its direct bandxcitation binding energy, and piezoelectric properties.p of this semiconductormaterial is ca. 3.2 eVwhich cor-radiation of wavelength around 390nm. Therefore, an

th wavelength shorter than 380nm is needed to excites in valenceband to conductionband. The electron/holers thus generated serve as the oxidizing and reducinginsic ZnO is essentially pure semiconductor materialnsic ZnO can be formed from intrinsic ZnO by addedoms to the crystal in a process known as doping. Oneremaining obstacles, limiting the development of ZnO,ulty in achieving p-type doping of this material while

need tis stillcultivaby sprrain orused dprole(unpubthe phpesticiunder

2. Exp

2.1. Pe

Pesstorferpure.Fitododientspropertitionaqueouter UbiDataBaparticlfrom(Barceethyl a(Barce

Stopreparlight awas prtion ofof 0.05tor rescorrelaticati0.01 to

2.2. Le

Thefrom 8house(pH=84 daysper emter. ThNO3 =(1000Lthe waat amb

2.3. So

Thecia, SEsunlighphotosuce dependence of pesticides, the use of agrochemicalsimportant in many areas. Concretely, during peppermany pesticides can be deposited on the soil surfaceift after pesticide application, wash-off from plants byct treatment to the soil. Some pesticides commonlythe crop development can be leached through the soile have observed under laboratory and eld conditionsd data). For this reason in this work we have studied

ensitization effect of ZnO on the degradation of eightommonly used for pepper protection, in leachingwater

ral sunlight.

ental

es and reagents

e analytical standards were obtained from Dr. Ehren-bH (Augsburg, Germany). They were higher than 98%commercial formulations used were purchased fromSL (Murcia, Spain). The structures of the active ingre-shown in Fig. 1 and their main physicalchemicalin Table 1. Experimental values of octanol/water par-cient (KOW), soil/organic partition coefcient (KOC),

lubility (SW), aqueous hydrolysis, and GUS (Groundwa-Score) index were taken from The Pesticide PropertiesPDB) [22]. Zinc oxide (99.9%, metals basis; 0.99 and the limits of quan-OQ, obtained at signal-to-noise ratio 10) ranged fromgL1.

g water

er used in the photodegradation studies was obtainedeters (3.5m4m1m) from an experimental green-

ed in Campo de Cartagena (SE Spain). A clayloam soild OM=0.22%) was used. The soil was irrigated everythree dripperlines (45min per day and 50mLmin1

). About 8 L per day were collected from each lysime-ter had pH=8.41, EC=4.32dSm1, TOC=130mgL1,mgL1, and NO2 =0.12mgL1. The leaching waters collected and transported to the storage tank. Finally,as spiked with commercial products and stored in darktemperature for 1 week.

hotocatalysis experiment

eriment was carried out in a pilot plant placed in Mur-in (latitude 3759N, longitude 108W) using naturaladiation during July, 2008. The values (mean SD) ofically active (400700nm),UVA(315400nm)andUVB

S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310 1305

Fig. 1. Chemi strobmethyl [14339 thanil[55219653]

(280315ndiometer DThe mean v26.12.4,100,7505(n=6) recor

To faciliments, the of expositiothe followin

t30W,n = t30

tn = tn t

Table 1Physicalchem

Commercial

Ortiva 25% (Daltonex 3%Stroby 50% WAphox 50% WKerb Flo 40%Scala 40% (wFolicur ME 1Baydan 25%

a F: fungicidb Water soluc DT50 (daysd Groundwacal structures of the active ingredients used (CAS RN are in brackets): (1) azoxy0890], (4) pirimicarb [23103982], (5) propyzamide [23950585], (6) pyrime

.

m) radiation were recovered with a portable photora-elta Ohm HD 2102.2 (Caseelle di Selvazzano, Italy).alues of PA, UVA and UVB at 14h were 901.252.3,and 1.830.16 (all in Wm2), respectively while794 lx were recorded. Fig. 2 shows the mean valuesded from UV radiation during the sampling.tate the comparison with other photocatalytic experi-normalized illumination time (t30W) was used insteadn time (t). The t30W has been calculated according tog equation:

W,n1 + tn (UV/30)(

ViVT

)

n1

where tn issolar ultravatedvolumunilluminaing on this t30Wm2, tnoon.

(a) Solar phexperimtechnolactor mlengthreecto

ical characteristics of the pesticides used in this study.

names Active ingredienta Molecular formula Molecularweight

L

w/v), SC (Syngenta) AzoxystrobinF C22H17N3O5 403.4 2WG (Nufarm) Hexaconazole()F C14H17Cl2N3O 314.2 3G (BASF) Kresoxim-methylF C18H19NO4 313.4 3G (Syngenta) PirimicarbI C11H18N4O2 238.3 1(w/v) SC (Dow) PropyzamideH C12H11Cl2NO 256.1 3/v) SC (BASF) PyrimethanilF C12H13N3 199.3 20% WG (Bayer) Tebuconazole()F C16H22ClN3O 307.8 3(w/v) EC (Bayer) Triadimenol(A+B)F C14H18ClN3O2 295.8 3

e; H: herbicide; I: insecticide.bility (mgL1).) at 20 C and pH=7.ter Ubiquity Score (GUS) Index.in [131860338], (2) hexaconazole [79983714], (3) kresoxim-[53112280], (7) tebuconazole [107534963], and (8) triadimenolthe exposition time for each sample, UV the averageiolet radiation measured during t, Vi the total irradi-e, andVT the total volumeof the reactor (illuminatedandted). In this expression, used by several authors work-opic [17,18], time refers to a constant solar UV power ofypical solar UV power on a perfectly sunny day around

otocatalytic plant. The solar pilot plant used in thisent is based on compound parabolic collector (CPC)

ogy [23]. This small prototype consists of one photore-odule (1.27m2) with ve borosilicate tubes (200 cm4cm i.d.) mounted on a curved polished aluminium

rs (0.9 cm radius of curvature) running in the East-West

ogKOW SWb Aqueoushydrolysisc

Soil sorptionlogKOC

GUS indexd

.5 7 Stable 2.6 2.5

.9 18 Stable 3.0 2.0

.4 2 34 2.5 1.8

.7 3100 Stable 1.9 4.0

.1 9 Stable 3.3 1.8

.8 121 Stable 2.5 2.6

.7 36 Stable 2.9 2.0

.2 72 Stable 2.4 3.7

1306 S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310

Fig. 2. Mean values (n=6) for UVA and UVB radiation in the different sample pointsof the photoperiod (480min).

line. The water ows directly from one to another tube con-nected in series and nally to the reservoir tank (250 L) and acentrifugal pump (0.55kw) then returns the water (45 Lmin1)to the collector tubes in a closed circuit. The reaction systemwascontinuously stirred to achieve a homogeneous suspension andthermostated by circulating water to keep the temperature at252 C. The illuminated volumewas 12.55 L and the dead vol-ume of PVC tubes about 6.5 L. Storage tank, owmeter, sensors(pH, O2 and T), pipes, and ttings complete the installation. Ascheme of the pilot plant used is shown in Fig. 3.

(b) Photocatalysis design. At the beginning of the assay, the leach-ingwater (150 L)wasmixedwithcommercialproducts (Table1)to reach a spiking level of about 0.5mgL1 of each one homog-enizing the mixture for 20min to constant concentration in the

darkwith collectors coveredby a black awning. Finally, the pho-tosensitizer (ZnO) and oxidant (Na2S2O8) were added at 150and 100mgL1 and the cover removed after 15min. Severalsamples (0, 15, 30, 60, 120, 240, and 480min) were taken dur-ing the photoperiod (8h), from 10 to 18h. Periodically, air wasinjected in the tank. A parallel blank assay, without ZnO andNa2S2O8 (photolysis experiment),wascarriedout. Inbothcases,assays were replicated 3 times.

(c) Photocatalytic kinetics. As reviewed by Konstantinou andAlbanis [20], the photocatalytic oxidation of several organicpollutants-including pesticides over illuminated catalyst ttedthe LangmuirHinshelwood (LH) kinetics given by the follow-ing equation:

r = dCdt

= kKC2

+ KC

where r is the mineralization rate of pesticide, C is the con-centration of the pesticide, k is the rate constant, and K theadsorption coefcient of the pesticide. When the initial con-centration C0 is small (ppbppm range), many researchers hasapproximated the LH kinetics to rst-order expression justto easily obtain the parameter involved in the LH equationaccording to the following equation:

r = dCdt

= kC = kKC

Its integration results in the following equations:

Ct = C0ekt or ln

(C0C

)= kKt = kt

where k (in units of time1) is the apparent rst-order rateconstant.Fig. 3. Scheme of the pilot plant used for the photocatalytic experiments.

S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310 1307

The half-life time given by the equation t1/2 = (1/k)ln 2 is theamount of time required for 50% of the initial pesticide concentra-tion to dissipate. Unlike the half-life, the dissipation time does notassume a specic degradation model (e.g., rst-order degradation).

2.4. Analyti

(a) GC/MSgas chroeter andoperateing eneper scaquadrupvoltagedelay oflary colusuppliedtemperagramme3 C/minand helin splitlmonitortarget aof indivgraphicrangingtheir retions, antion timqualieritive condetermifound fotion.

(b) Extractiples weliquidllation osonicatiture solGC/MS iditions,76.5 toin the m

(c) Total or(Kyoto,bustionand accu

3. Results

3.1. Prelimi

Laboratodetermine tdisturbed cloffer good ptute closedthe soil. Allguidelines [to 150g of0.01M CaCtion which

umul. Erro

periticids cann. T

iadimtheresonazont prUbiqotallimitg Lcorr

the oo thedosunpacitadatimentweratalyysisysis w

otolysis and photocatalysis kinetics

vious to the beginning of each assay the collectors wered and water circulated during 15min to homogenise then. The initial pesticide concentrations ranged from 0.33 tog L1. Fig. 5 shows the comparative degradation of pesticideshing water by use (photocatalysis) or not (photolysis) of thed photosensitizer (ZnO) during the studied photoperiod.diation of water in the absence of ZnO shows that photolyticposition of the pesticides occurs at a much slower rate withtages remaining at the end of the experiment ranged from0% of the initial amount. Furthermore, blank experimentsd that the addition of the catalyst without solar radiationegligible effect on pesticide degradation.

s small fall in pesticide concentration can be possibly duepresence of some ions in leaching water such as nitriteg L1) and mainly nitrate (547mgL1). The presence ofther enhances or decreases the reaction rate depending oncal determinations

analysis. An Agilent (Waldbronn, Germany) HP 6890matograph equipped with a 5973N mass spectrom-automatic splitsplitless injector Agilent 7683 was

d in electron impact ionization mode with an ioniz-rgy of 70eV, scanning from m/z 50 to 500 at 3.21 sn. The ion source temperature was 230 C, and theole temperature was 150 C. The electron multiplier(EM voltage) was maintained at 1300V, and a solvent4.5min was employed. An HP-5MSI fused silica capil-mn (30m0.25mm i.d.) and 0.25m lm thickness,by Agilent Technologies, was employed. The column

ture was maintained at 70 C for 2min and then pro-d at 25 C/min to 150 C, increased to 200 C at a rate of, followed by a nal ramp to 280 C at a rate of 8 C/min,

d for 10min. One microliter of samples was injectedess mode. Analysis was performed with selected ioning (SIM) mode using primary and secondary ions. Thend qualier abundances were determined by injectionidual pesticide standards under the same chromato-conditions using full scan with the mass/charge ratiofrom m/z 50 to 500. Pesticides were conrmed byention times, the identication of target and qualierd the determination of qualier-to-target ratios. Reten-es had to be within 0.1min of the expected time, and-to-target ratios had to be within a 10% range for pos-rmation. The concentration of each compound was

ned by comparing the peak areas in the sample to thoser mixtures of pesticide standards of known concentra-

on procedure. To remove ZnO particles the water sam-re ltered through a funnel of porous plate No. 4. Aiquid (LL) microextraction method was used for the iso-f pesticides. Water samples (20mL) were extracted byon with 40mL of n-hexanedichloromethane 1:1 mix-vent. Finally, pesticide residues were determined byn SIM mode as previously specied. Under these con-the recoveries obtained for the pesticide ranged from106% with a relative standard deviation lower than 7%ost unfavourable case.ganic carbon (TOC). An Analyzer Shimadzu TOC VcshJapan) provided with an NDIR detector (680 C com-catalytic oxidation technique)was used (LOD=4g L1

racy

1308 S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310

Fig. 5. Disappearance kinetics of the studied pesticides by photolysis () and photocatalysis () with ZnO during the photoperiod (as t30W). Error bars denote standarddeviation. Observed versus predicted kinetics according to a rst-order model for photocatalysis experiments are shown in the inserted graphics (vertical dash lines showDT75).

S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310 1309

the mechanism. Most of the anions and cations in leaching watersuch as chloride 446 (mgL1), sulphate (1.498mgL1), sodium(344mgL1) or potassium (165mgL1) are transparent to solarirradiation. However, some metal cations, nitrate and nitrite showany absorbance. Nitrite (max =355) andnitrate (max =303) absorblight and undergo homolysis to produce OH radicals and nitro-gen reactive species (NO, NO2, N2O3, and N2O4) leading to thedegradation of pesticides [2629], although OH may further bescavenged by NO2 to form NO2 [30]. Also, the presence of otherions such as calcium (460mgL1) andmagnesium (157mgL1) canaccelerate de photodegradation as reported by Larson and Weber[27], and the presence of some traces of Fe2+ in leaching watercan contribute to the degradation following photo-Fenton reaction[31]. Although only traces of manganese (0.02mgL1) and copper(0.04mgL1) were found in leaching water those small amounts ofMn2+ and Cu2+ ions could have catalytic effect in the degradationof the pesticides by trapping photogenerated electrons and therebyreducing e/h+ recombination [15].

On the other hand, it is known that humic substances (HS),the recalcitphotocatalyment. Totalassay. The massays wasbe done witthe reactorexperimentwhich it isphotosensiting water awater (initisolved orgasunlight abschemicals rby HS whicfree radicalpesticide phden by theof the impoundergo phquickly reatects pesticby migratiopenetrate, oconstituent

The rolewithout beithe type anof pollutan150mgL1.the process

more than75%of thepesticides amount initially present in leachingwater was degraded after 1h of illumination (t30W 3min).

Knowledge of kinetics is required to assess the efciency ofsystems used for the photooxidation of pesticides. The photoly-sis kinetic parameters of pesticides are shown in Table 2 whereapparent rate constants and half-lives are listed. In all cases, thekinetics of dissipation followed an apparent rst-order degrada-tion curve with R2 ranging from 0.981 to 0.995 and standard errorof estimate lower than 6.5 in the most unfavourable case. The car-bamic insecticide pirimicarb was quickly degraded. The amountof time required for 50% of its initial pesticide concentration todissipate was about 10min (t30W =0.47min). Similar behaviourwas observed for pyrimethanil (anilinopyrimidine) and propyza-mide (benzamide) where 20min (t30W =1min) were necessary todissipate 50%. The half-lives for strobilurin compounds (azoxys-trobin and kresosim-methyl) were about 24min (t30W =1.2min)while for triazole fungicides, the calculated values ranged from 25to 35min (t30W =1.21.8min) for tebuconazole and triadimenol,respectively. Obviously, the high rate degradation of all pesticides

presy.abil

y to eattrid vainat

ole ps canceptpeddparte thTiOsencrposntainplayal rot as act assorptt eart imimpodes iof tout

ocests). Ass forO can

Table 2Kinetic param pesti

Pesticide

AzoxystrobiHexaconazoKresoxim-mPirimicarbPropyzamidPyrimethaniTebuconazoTriadimenol

a Standard eb Referred torant constituents of natural organic matter, can exhibittic effect to pesticide residues in aqueous environ-organic carbon (TOC) was measured at the end of eachean TOC value recorded at that time for photocatalysis397mgL1. The initial TOC concentration could noth precision, as some of the pesticides usually adhere towalls due to hydrophobic components. For photolysis, after 480min 10212mgL1 of TOC were measuredindicative of a slow mineralization in absence of theizer. In a previous study [32]we have veried for leach-quick degradation (3) in comparison with drinkingal TOC=1.1mgL1). The photocatalytic effect of dis-nic matter (DOM) is contradictory in the literature. Theorbance by DOM could provide a rich variety of photo-eactions resulting reactive transients produced mainlyh could participate in energy and electron transfer andgeneration [33]. On the contrary, HS can reduce theotodegradation because the sensitization effect is hid-strong lter effect (quenching). They could act as onertant sunlight-absorbing (especially on UV range), theyotolysis under incident UVVIS light and they can alsoct with OH radicals [34]. Additionally, sorption pro-ides from photolysis by competitive light attenuation,n of the pesticide into regions where light does notr by quenching of the excited states of substrates bys of the particles [27].of photocatalyst is to accelerate the rate of the reactionng consumed in it. The amount of catalyst depends ond dimensions of the photoreactor used and the kindts to degrade [15]. In our case the optimal dose wasHigher dose did not signicantly increase the yield of

. As can be seen in Fig. 4, for photocatalysis experiment

in theactivit

Thequentlcan beby lleis illumtron/hspecietron acor trapchargepromoZnO orthe prethis puto maioxygenprincipis to acit can ahas abtrum awas no

Anpesticichargecarriedtion pr0.6unitivenepH, Zn

eters (rate constants and half-lives) for photocatalysis and photolysis of the studied

C0 (%)a K (min1)a

Photocatalysis Photolysis Photocatalysis

n 100.59 (3.26) 99.99 (1.21) 0.6014 (0.0460)le 97.47 (4.37) 98.74 (1.58) 0.4762 (0.0550)ethyl 100.35 (3.26) 100.59 (1.91) 0.5862 (0.0451)

98.93 (5.39) 95.51 (2.10) 1.4727 (0.1931)e 98.10 (3.31) 97.27 (1.57) 0.7019 (0.0547)l 99.14 (3.72) 96.95 (2.22) 0.7370 (0.0636)le 98.69 (4.32) 98.23 (2.06) 0.5475 (0.0647)

96.21 (4.01) 97.43 (2.03) 0.3885 (0.0418)

rror in parenthesis.t30W (calculated according Section 2.3).ence of ZnO can clearly be ascribed to the catalysts

ity of the semiconductor to act as sensitizer and conse-nhance the photodegradation of the pesticides studiedbuted to its electronic structure which is characterizedlence band and an empty conduction band. When ZnOed with energy higher than its bandgap energy, elec-airs are produced: ZnO+hv(

1310 S. Navarro et al. / Journal of Hazardous Materials 172 (2009) 13031310

at alkalic pH, it can react with a base to form some complexes. Theresult is the dissolution and photodissolution of ZnO in those casesand in consequence a decrease in the reaction rates.

The use of other electron acceptors, such as hydrogen peroxide(H2O2) and inorganic peroxides (S2O82) has been demonstratedto notably enhance the rate of degradation of several organic pol-lutants [13] because they trap the photogenerated electrons moreefciently than molecular oxygen. However, preliminary studiescarried out by us using H2O2 in combination with ZnO show thatthe addition of peroxide does not improve the result or even, itcan have a negative effect if an excess of peroxide because it canact as OH scavenger. Similar ndings were found by Evgenidouet al. [36] fthe additiobecause theticides.No swhen increH2O2, hightal to the rperoxydisuof electronsthe photogebination (mthe positivestrong oxidThis implie6 times fast

4. Conclus

Theuse otizer constiteliminationtic effect wainto illuminprocess. Theconcentratitions (equivwas achieve

Bearingraneanagriphotocatalyventional msource of emainly in sof sunlight

Acknowled

The autNacional deof Spain, re

References

[1] M. VancloGottesb119.

[2] S. Navarro, N. Vela, G. Navarro, Spanish J. Agric. Res. 5 (2007) 357375.[3] R.D. Wauchope, S. Yeh, J. Linders, R. Kloskowski, K. Tanaka, B. Rubin, A.

Katayama, W. Krdel, Z. Gerstl, M. Lane, J.B. Unsworth, Pest Manage. Sci. 58(2002) 419445.

[4] C.E. Clapp, M.H.B. Hayes, N. Senesi, N.P.R. Bloom, P.M. Jardin, Humic Substancesand Chemical Contaminants, Soil Science Society of America, Madison, WI,2001, pp. 502.

[5] D. Mackay, S. Paterson, Environ. Sci. Technol. 25 (1991) 427.[6] M. Arias-Estvez, E. Lpez-Periago, E. Martnez-Carballo, J. Simal-Gndara, J.C.

Mejuto, L. Garca-Ro, Agric. Ecosys. Environ. 123 (2008) 247260.[7] J.A. Elliott, A.J. Cessna, K.B. Best,W. Nicholaichuk, L.C. Tollefson, J. Environ. Qual.

29 (2000) 16501656.[8] EEA, Environmental Signals 2001. Environmental Assessment Report

No. 8 (European Environment Agency, Copenhagen, Denmark, 2001).http://reports.eea.eu.int/signals-2001.

[9] EEA, Pesticides in Groundwater. Indicator WHS1a (Euro-n Environment Agency, Copenhagen, Denmark, 2004).p://theSchamntriesPerspelizzeof or

SchiavTO AS. Herm

Blanltp://walato

Kabra376Evgen89.Hincalesterller, Wlato, J. Maldlato, JKonstPeartolou, F3.icultu

ofp://ww

alato5.D. Orting oGustaarne

. Larsoy, CRCorren

. Technack, J. Sha114. Lars720

enoll,th Euhe EnticideKons130. Lindhirayvgeni05) 29Hincaer, W.or the photooxidation of dimethoate. On the contrary,n of Na2S2O8 (100mgL1) to the tank was benecialoxidant strongly enhances the reaction rate for all pes-ignicantdifferenceswereobserved in the reaction rateasing the concentration of the oxidant although unlikeconcentrations of peroxydisulfate were not detrimen-eaction rate. As pointed by some authors [36,37], thelfate enhancement effect is related to both scavengingand production of additional oxidising species. It trapsnerated electron and reduces the probability of recom-ayor cause of ZnO photocatalysis quantum yield) withhole, generating SO4 radicals, which are also a veryizing species (E =2.6V) and more hydroxyl radicals.s a signicant reduction in treatment time, from 4 toer than ZnO alone.

ions

f solar photocatalysis in presence of ZnOasphotosensi-utes a very effectivemethod for the reduction and evenof the selected pesticides in leachingwater. A synergis-s observed with the addition of the oxidant (Na2S2O8)atedZnOsuspensionsbyenhancing the efciencyof theamount of time required for 50% of the initial pesticide

on to dissipate ranged from 10 to 35min in our condi-alent to t30W =0.52min) and complete mineralizationd after 2h of treatment.

inmind the extensive use of pesticides in someMediter-cultural areas, and the groundwater pollutionproblems,sis offers a good technology as substitute to other con-ethods for water remediation by using a renewablenergy, inexhaustible and pollution-free, like sunlightome areas as SE of Spain receiving more than 3000hper year.

gements

hors acknowledge nancial support from InstitutoInvestigacinyTecnologaAgraria yAlimentaria (INIA),search project number RTA2005-00127-00-00.

oster, J.J.T.I. Boesten, M. Trevisan, C.D. Brown, E. Capri, O.M. Eklo, B.ren, V. Gouy, A.M.A. van der Linden, Agric. Water Manage. 44 (2000)

peahtt

[10] M.couand

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[14] S. M[15] K.

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Ma[20] I.K.[21] S.J.

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[23] S. M11

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[25] D.I.[26] P. W[27] R.A

istr[28] A. T

Sci[29] J. M[30] M.V

146[31] R.A

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[33] I.K.121

[34] M.E[35] H. S[36] E. E

(20[37] M.

Ollmes.eea.europa.eu/Specic media/water/indicators/WHS01a%2C2004.05.ann, P. Menger, G. Prokop, Contaminated sites management in CEE, in: Remediation of Polluted Sites in CEE Countries: Current Statusectives, ICS-UNIDO, Trieste, Italy, 2002.tti, E. Pramauro, C. Minero, N. Serpone, E. Borgarello, Photodegrada-ganic pollutants in aquatic systems catalyzed by semiconductors, in:ello (Ed.), Photocatalysis and Environment Trends and Applications,I Series, Kluiver, Dordrecht, The Netherlands, 1988.ann, Catal. Today 53 (1999) 115129.co, S. Malato, Solar Detoxication. UNESCO, Nat-Sciences, World Solar Programme 19962005ww.unesco.org/science/wsp/publications/solar.htm), 2001., J. Blanco, J.M. Herrman, Catal. Today 54 (1999) 191377., R. Chaudhary, R.L. Sawhney, Ind. Eng. Chem. Res. 43 (2004)96.idou, K. Fytianos, I. Poulios, Appl. Catal. B: Environ. 59 (2005)

pi, M.I. Maldonado, I. Oller, W. Gernjak, J.A. Snchez-Prez, M.M.os, S. Malato, Catal. Today 101 (2005) 203210.. Gernjak, M.I. Maldonado, L.A. Prez-E strada, J.A. Snchez-Prez, S.

. Hazard. Mater. B138 (2006) 507517.onado, P.C. Passarinho, I. Oller, W. Gernjak, P. Fernndez, J. Blanco, S.. Photochem. Photobiol. A: Chem. 185 (2007) 354363.antinou, T.A. Albanis, Appl. Catal. B: Environ. 42 (2003) 319335.n, C.R. Abernathy, M.E. Overbeg, G.T. Thaler, D.P. Norton, N. Theodor-. Hebard, Y.D. Park, F. Ren, J. Kim, L.A. Boatner, J. Appl. Phys. 93 (2003)

re & Environment Research Unit (AERU) at the Univer-Hertfordshire, The Pesticide Properties DataBase (PPDB).w.herts.ac.uk/aeru/footprint, 2009., J. Blanco, A. Vidal, C. Richter, Appl. Catal. B: Environ. 37 (2002)

ganisation for Economic Cooperation andDevelopmentGuidelines forf Chemicals. No. 312, Leaching in Soil Columns. Paris, 2007.fson, Environ. Toxicol. Chem. 8 (1989) 339357.ck, C. Wurzinger, J. Phys. Chem. 92 (1988) 62786283.n, E.J.Weber, ReactionsMechanisms inEnvironmentalOrganicChem-Press, Boca Raton, FL, 1994.

ts, B.G. Anderson, S. Bilboulian, W.E. Johnson, C.J. Hapeman, Environ.ol. 31 (1997) 14761482.

.R. Bolton, J. Photochem. Photobiol. A 128 (1999) 113.nkar, S. Nlieu, L. Kerhoas, J. Einhorn, Chemosphere 71 (2008)68.on, M.B. Schlauch, K.A. Marley, J. Agric. Food Chem. 39 (1991)62.N. Vela, E. Ruiz, P. Flores, G. Navarro, P. Helln, S. Navarro, Presentedropean Conference on Pesticides and Related Organic Micropollutansvironment and 11th Symposium on Chemistry and Fate of Moderns. Marseille, France, 2008 (unpublished data).tantinou, A.K. Zarkadis, T.A. Albanis, J. Environ. Qual. 30 (2001).say, M.A. Tarr, Environ. Sci. Technol. 34 (2000) 444449.ama, Y. Tobezo, S. Taguchi, Water Res. 35 (2001) 19411950.dou, K. Fytianos, I. Poulios, J. Photochem. Photobiol. A: Chem. 17538.pi, G. Penuela, M.I. Maldonado, O. Malato, P. Fernndez-Ibanez, I.Gernjak, S. Malato, Appl. Catal. B: Environ. 64 (2006) 272281.

Photocatalytic degradation of eight pesticides in leaching water by use of ZnO under natural sunlightIntroductionExperimentalPesticides and reagentsLeaching waterSolar photocatalysis experimentAnalytical determinations

Results and discussionPreliminary studiesPhotolysis and photocatalysis kinetics

ConclusionsAcknowledgementsReferences