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82 J Adv Oxid Technol Vol 17 No 1 2014 ISSN 1203-8407 copy 2014 Science amp Technology Network Inc

Abamectin Degradation by Advanced Oxidation Processes Evaluation

of Toxicity Reduction Using Daphnia simil is

Joseacute Roberto Guimaratildees 1

Izabela Major Barbosa1 Milena Guedes Maniero

1 Susanne Rath

2

1School of Civil Engineering Architecture and Urbanism University of Campinas - UNICAMP PO Box 6021

CEP 13083-852 Campinas SP Brazil2Chemistry Institute University of Campinas mdash UNICAMP PO Box 6154 CEP 13084-971 Campinas SP

Brazil

AbstractThis work evaluated the toxicity reduction of abamectin in an aqueous solution (500 microg L -1) undergoing to

photolysis (UV) peroxidation (H2O2) peroxidation with ultraviolet radiation (UVH2O2) Fenton (Fe(II)H2O2)and photo-Fenton (Fe(II)UVH2O2) processes Toxicity trials were carried out using the microcrustacean Daphnia

similis Results were based on effective concentration EC50 48 h Using 10 mmol L-1

Fe (II) and 50 mmol L-1

H2O2 and a reaction time of 60 s the ranking of efficiency for the degradation of abamectin was as follows photo-Fenton gt Fenton gt UV = UV H2O2 gt H2O2 However after a reaction time of 300 s similar degradation wasobtained for photo-Fenton UV and UVH2O2 (more than 97) while the Fenton process degraded 80 of the

drug With the exception of peroxidation all of the processes evaluated were able to eliminate toxicity in 600 sof reaction (10 mmol L -1 Fe(II) and 50 mmol L-1 H2O2)

Keywords Daphnia similis Fenton photo-Fenton UVH2O2 veterinary drug

IntroductionAbamectin is a macrocyclic lactone in the

avermectin group It is active antihelmintics inseticides

and acaricides Avermectins has been widely employedin veterinary medicine to treat ecto- and endoparasitesand in agriculture because of these properties They

are produced by fermentation of an actomyceteStreptomyces avermitilis which is a naturally-occurring

soil bacterium (1) Abamectin is composed ofavermectin B1a (at least 80) (C48H72O14) and

avermectin B1b (no more than 20) (C47H70O14) Thetwo homologues B1a and B1b form a compound with a

high molar mass (87308 g mol-1

) It has low solubilityin water (lt 10 microg L-1) (2) and is soluble in organic

solvents (3)After abamectin is administered to animals a

significant amount of the non-metabolized drug isexcreted directly into the environment Much of thesubstance ends up in the soil and water According to

Tisler and Erzen (4) in the majority of cases up to98 of avermectins applied to cattle are excreted infeces unaltered or as an active metabolite Hernandoet al (5) and Tisler and Erzen (4) reported that

avermectins interfere in the reproduction and survivalof aquatic and terrestrial organisms that have importantroles in the food chain

Corresponding author E-mail address joroberfecunicampbr

An alternative to degrading organic compounds inwater is the use of Advanced Oxidation Processes(AOPs) These technologies are efficient at degradingand removal of recalcitrant organic compounds even atlow concentrations AOPs are based on the generationof hydroxyl radicals (HO) which are non-selective

and highly reductive speciesThe byproducts formed during degradation

processes can be as toxic as or even more toxic than theoriginal non-degraded substance (6) Even though AOPs

are very efficient at degrading organic compounds thetoxicity of the treated solutions must be evaluated

Species of genus Daphnia phylum Crustacea order

Cladocera play a large role in the zooplankton com-

munity and have been widely studied and characterizedin order to evaluate the toxicity of many substancesreleased into the environment Many authors havereported toxic effects of avermectins on some micro-crustaceans of Genus Daphnia (4 5 7-17) According

to Novelli et al (17) Daphnia similis is sensitive toavermectins Thus Daphnia similis is an appropriatemicrocrustacean for monitoring the toxicity of aqueousabamectin solution submitted to the degradation

processesThe objective of this study was to evaluate reduction

of toxicity of aqueous abamectin solutions that hadundergone photolysis peroxidation UVH2O2 Fenton

and photo-Fenton processes using the Daphnia similis microcrustacean as a test organism



J R Guimaratildees et al

J Adv Oxid Technol Vol 17 No 1 2014 83

Material and Methods

Chemical Reagents

Abamectin (gt97) was obtained from Fluka(Buchs Switzerland) and methanol (HPLC grade) fromJ T Baker (Xalostoc Mexico) while ferrous sulfate(FeSO47H2O) sulfuric acid and hydrogen peroxide

(30 mm) were obtained from Synth (DiademaBrazil) Ultra-pure water used in the tests was produced by a Milli-Q purification system from Millipore(Billerica USA)

Stock Solu tionThe abamectin stock solution (500 mg L-1) was

prepared in methanol The solution was stored in anamber flask which was protected from light and kept

at -10 degC The working solutions (500 microg L-1

) were prepared by diluting the stock solution with ultrapure

water

Experimental SystemThe photo-reactor was made up of a germicide

lamp (15 W λ max = 254 nm 20 cm diameter) covered by a quartz cylinder (50 cm diameter 520 cm long)inserted in the middle of a borosilicate tube (80 cm

diameter and 550 cm long) The sample volume used

in the reactor was 10 L The solution was homo-genized by a magnetic stirrer The tests were run in batches

Average irradiance was 383 mW cm-2 It wasmeasured by a model VLX 3 W Cole Parmer Series9811 radiometer calibrated to a 254 nm wavelengthThe radiation dose D (mJ cm-2) was calculated using

Equation (1)

(1)

in which D is the UV radiation dose (mJ cm-2) E is theirradiance (mW cm-2) and t is the exposure time (s)

For all of the processes evaluated reaction time

varied from 0 to 600 s Photolysis peroxidation and peroxidation with UV radiation trials were carried outat the natural pH of the sample (around 7) while

Fenton and photo-Fenton processes were carried outafter pH was adjusted to 285 Experiments carried outusing the Fenton reagent employed Fe(II) at concen-trations between 025 and 10 mmol L-1 and H2O2

between 10 and 100 mmol L-1

Fe(II) concentrationsgreater than H2O2 concentrations were not evaluated

because according to Neyens and Baeyens (18) themolar ratio of Fe(II)H2O2 must always be less than 1

In all of the tests carried out with hydrogen peroxide(peroxidation peroxidation assisted by ultraviolet

radiation Fenton and photo-Fenton) reactions werestopped and the residual H2O2 concentration was

destroyed by adding sodium bisulfite at a 11 molarratio with hydrogen peroxide (19)

Analytical Method

The concentration of abamectin in the aqueoussolutions was determined by high performance liquid

chromatography with UV detection Before quantitation

the samples were concentrated by solid phase extraction(SPE) using C18 cartridges (500 mg6 mL Varian) thathad been previously conditioned with methanol (6 mL)and water (6 mL) A liter of the solution percolated

through the cartridges at a flow rate of 10 mL min-1

The analytes were eluted with 4 mL of methanol Before

analyses the solutions were filtered through 022 micromMillipore membranes The extraction efficiencyevaluated through recovery tests ranged from 64 to99 for aqueous solutions containing abamectin with

concentrations ranging from 25 to 500 μg L

-1

Chromatographic analyses were carried out with a

Waters solvent delivery system (Waters 510) a tunableabsorbance detector (Waters 486) a Rheodyne 7725

injector with a sample loop of 20 microL and a Waters746 integrator Abamectin quantitation was performedat 245 nm The analytical column was a Waters

XBridgeTM

RP18 (250 mm x 46 mm 5 microm) and asmobile phase methanol and water (8515 vv) with a

flow rate of 1 mL min-1

was used The limit ofdetection (LOD) and limit of quantitation (LOQ) were

10 microg L-1

and 30 microg L-1

respectively considering aconcentration factor of 250

UV-Vis spectra were obtained using a UV-1601PCspectrophotometer (Shimadzu Japan) The initialsolution (500 μg L

-1 abamectin) and the samples

submitted to the degradation processes were concen-trated using SPE as described previously The analytewas eluted from the cartridge with methanol (4 mL)filtered and diluted 4 times before analysis Spectra

were registered from 200 to 350 nm since there wasno observed absorbance in the visible region of theeletromagnetic spectrum

Consumption of hydrogen peroxide was evaluated

based on the oxidation-reduction reaction betweenresidual H2O2 and metavanadate ions The vanadate

solution (which is yellow) turns red after the reactionwith H2O2 due to the formation of peroxovanadiumcations (Equation 2) which absorb at 450 nm (20)The limit of detection of the method (LOD) was 002mmol L-1

(2)Daphnia Simili s Toxicity Tr ials

Acute toxicity trials and cultivation of the organismswere carried out as specified by the Brazilian National




84 J Adv Oxid Technol Vol 17 No 1 2014

Standards Organization (NBR 12713) (21) Toevaluate the sensitivity of the organisms EC50 48 hwas determined for sodium chloride as described in NBR 12713 (21) All toxicity trials were followedwith blank samples which contained cultivation water

and neonate organisms and control samples whichcontained all of the reagents present in the sample to

be analyzed but not abamectin

The biological trials were carried out for all processes evaluated The samples were taken at the

beginning of the test and at 10 60 and 600 s Theywere diluted between 001 and 05 (vv) using thecultivating water as diluent Each dilution was evaluatedin four replicates each sample containing five neonateorganisms The organisms were incubated at 20 degC inthe dark After 48 h dead andor immobile Daphnia organisms were counted The dilution corresponding

to the effective median concentration (EC50 48 h) wasestimated by the Trimmed Spearman-Karber statisticalmethod (22) All of the trials were carried out intriplicate and the average values and standard deviations

were calculated Deviations of up to 20 wereconsidered acceptable (23)

Results and Discussion

Abamectin Degradation

In all cases in which abamectin was exposed to

UV radiation that is for the photolysis peroxidationwith UV radiation and photo-Fenton processes (Figure1) the degradation efficiencies were always higher

than 90 in the first 300 s of the reaction Theseresults agree with those reported by Escalada et al (24) who verified a high level of degradation of

abamectin by photolysis

At the very beginning of UV radiation exposure(60 s) (Figure 1a) at a dose of 2292 mJ cm-2

(Equation 1) approximately 70 of the substance wasdegraded After 600 s of UV radiation exposure at adose of 2292 mJ cm-2 (Equation 1) more than 95was degraded The photolytic process has already been

shown to be efficient at degrading various organiccompounds (25 26)

Degradation of abamectin by peroxidation using50 mmol L-1 H2O2 was less than 10 (Figure 1b)Increasing the H2O2 concentration from 025 to 100mmol L-1 did not result in an increase in the drug

degradation remaining below 10 this shows thatthe oxidant has little potential to oxidize abamectin

Similar results were obtained by Ay and Kargi (27)Catalkaya and Kargi (28) and Da Silva et al (25)who reported that peroxidation was ineffective atdegrading several drugs

Figure 1 Abamectin degradation by (a) UV (b) H2O2 (50 mmol

L-1 H2O2) (c) UVH2O2 (50 mmol L-1 H2O2) (d) Fenton (10 mmolL-1 Fe(II) and 50 mmol L-1 H2O2) and (e) photo-Fenton (10mmol L-1 Fe(II) and 50 mmol L-1 H2O2) Coabamectin = 500 μg L

-1

For the UVH2O2 process using 50 mmol L-1 H2O2 abamectin was reduced by 34 in 10 s ofreaction and in 300 s degradation was greater than

90 (Figure 1c) after this period there was no increasein degradation over time Comparing the UV and

UVH2O2 processes it is possible to verify that therewas no increase in the degradation rate of the drug

when H2O2 was added to the photolysis process(Figures 1a and 1c) In the UVH2O2 process (50mmol L-1) H2O2 consumption was only 140 mmol L-1

for degradation by peroxidation (50 mmol L-1) theoxidant was not consumed during the 600 s of reaction

timeFenton reagent (10 mmol L -1 Fe(II) and 50 mmol

L-1

H2O2) (Figure 1d) was efficient at degradingabamectin in the first 60 s of the experiment with

levels higher than 70 Similar results were obtained by Dal Bosco et al (29) which reported around 80degradation of ivermectin (another avermectin) in

aqueous solution by Fenton reagent using the same

conditions applied in this studyThe fastest degradation rate was verified for photo-

Fenton attaining degradation efficiencies greater than

90 in the first 60 s of reaction time (Figure 1e)Similar results were obtained for ivermectin by Dal

Bosco et al (29) using the photo-Fenton process andthe same initial concentrations of Fe(II) and H2O2 that

is 10 mmol L-1

Fe(II) and 50 mmol L-1

H2O2 It has been verified that the degradation rate of abamectin

was increased by adding UV radiation to the Fentonreagent (Figures 1d and 1e) The Fenton reaction

results in Fe(III) (Equation 3) and the increase in thedegradation rate by photo-Fenton is mainly due to

photo-reduction of Fe(III) formed in the Fenton process(Equations 4 and 5)

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

(a) (b) (c)

(d) (e)





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

025 mmol L-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

H2O2 + Fe(II) Fe(III) + HO

+-OH (3)

[Fe(III)

(OH)]2+

Fe(II) + HO

(4)

[Fe(III) (RCO2)]2+ Fe(II) + CO2 +

R (5)

For the photo-Fenton process H2O2 was quickly

consumed at all oxidant and catalyst concentrationsevaluated After 600 s of reaction molar concentrations

of H2O2 were near the methodrsquos detection limit (002mmol L-1) This was also reported by Dal Bosco et al (29) and Elmolla and Chaudhuri (30) who attribute thisto the fact that applied radiation quickly regenerates

Fe(III) to Fe(II) offering greater production of freehydroxyl radicals (Equations 3 to 5) consuming theoxidant (Equation 3)

Influence of Fe(II) and H 2O2 on the Fenton

ProcessWhen Fe(II) concentration was changed from 025

to 10 mmol L-1 with the H2O2 concentration kept at

50 mmol L-1 (Figure 2A) degradation increased from

40 to around 80 while for an H2O2 concentrationset at 100 mmol L-1 (Figure 2B) degradation rose

from 20 to 90 in 300 s of reactionIn the study carried out by Falmann et al (31) of

the degradation of various pesticides and abamectin by Fenton reagent the reaction rate increased with anincrease in the catalyst concentration in the first

minutes reaching a plateau after 50 minMolar ratios of ferrous ions to hydrogen peroxide

(Fe(II)H2O2) of 02510 02550 and 02510 werealso evaluated It was verified that an increase in

oxidant concentration results in a lower efficiency ofthe overall degradation process In 300 s a reductionfrom 80 to 20 using Fe(II)H2O2 from 02510 to02510 were achieved (Figure 3A) Lower abamectindegradation when greater concentrations of hydrogen peroxide were employed could be because the excess

of oxidant in the medium acts as a hydroxyl radicalscavenger (32-33) These results agree with those published previously in our research group by DalDosco et al (29) who verified a decrease in degradationof ivermectin as the oxidant concentration was increased

from 10 to 50 mmol L-1

maintaining the initial con-centration of Fe(II) (025 mmol L-1)

When the Fe(II) concentration was maintained at05 mmol L-1 (Figure 3B) an increase in abamectindegradation from 40 to 70 was verified whenoxidant concentration was increased from 10 to 100

mmol L-1 For 10 mmol L-1 Fe(II) (Figure 3C) thedegradation rate was greater in the first 10 s of theexperiment when the concentration of H2O2 wasincreased from 50 to 100 mmol L-1

Figure 2 Influence of Fe(II) concentration on abamectin degradation by Fenton reagent Coabamectin = 500 μg L-1 (A) CH2O2 = 50 mmolL-1 (B) CH2O2 = 100 mmol L-1

Abamectin degradation efficiency was around90 in 300 s of reaction using molar ratios of 02510and 1010 Fe(II)H2O2 and 65 for 05100 mmol L-1

Fe(II)H2O2 However in 10 s of reaction degradationrate was ranked in the following order 1010 gt 0510gt 02510 Fe(II) to H2O2 The efficiency at a ratio of

1010 was 77 for 0510 it was 53 and for 02510

it was 29 Therefore in order to achieve a high levelof efficiency of drug removal lower reagent concen-trations can be used with a longer reaction time or

larger concentrations of oxidant can be used withshorter test times

The concentration of abamectin reached a plateauin the Fenton process after a certain period of timewhich has also been observed by other authors (2935) This can take place due to inherent oxidant and

Fe(II) consumption in the process or due to thereaction between hydroxyl radicals and excess ferrous

ions resulting in ferric ions as shown in Equation 6Formation of organic compounds with smaller chains

reduces the activity of Fenton reagent and complexationof intermediaries formed with ferric cations resulting

h

h





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

025 mmol L-1 Fe(II) 10 mmol L

-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

A 025 mmol L-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2

O2

B

Figure 3 Influence of H2O2 concentration on abamectin degradation by Fenton reagent Coabamectin = 500 μg L-1 (A) CFe(II) = 025 mmol

L-1 (B) CFe(II) = 05 mmol L-1 (C) CFe(II) = 10 mmol L-1

in recalcitrant compounds could be the cause of the

stagnation of abamectin concentration It is also worthemphasizing that the Fenton reagent is not an advanced

oxidation process that yields a large amount of hydroxylradicals

HO

+ Fe(II) Fe(III) + -OH (6)

Figure 4 Influence of Fe(II) concentration on the efficiency of the

photo-Fenton process Coabamectin = 500 μg L-1 (A) CH2O2 = 50mmol L-1 (B) CH2O2 = 100 mmol L-1

Influence of Fe(II) Concentration on the Photo-

Fenton ProcessFor photo-Fenton an increase in Fe(II) concen-

tration from 025 to 10 mmol L-1 (Figure 4A and 4B)resulted in a higher abamectin degradation rate in the

first 10 s of exposure Degradation efficiency increased

from 50 to about 80 when 50 mmol L

-1

was used(Figure 4A) and from 30 to around 90 when 100mol L-1 was used (Figure 4B) However after 300 s of

reaction in all of the conditions evaluated the samedegradation efficiency was reached around 98 A

greater degradation efficiency of the target compoundwith the increased concentration of catalyst is the resultof a greater number of hydroxyl radicals in the mediumformed by the Fenton reaction (Equation 3) (36)

Influence of H 2O2 Concentration on the photo-

Fenton ProcessWhen the catalyst concentration was kept at 025

mmol L-1 an increase in oxidant concentration from 10

mmol L-1

to 100 mmol L-1

reduced the degradation of

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

C





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

025 mmol L-1 Fe(II)100 mmol L-1 H2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)

abamectin from 50 to 34 in 10 s and from 90 to77 in 60 s (Figure 5A) It was due to the scavengereffect of hydroxyl radicals by hydrogen peroxide whenlow Fe(II) concentrations are used

When the initial concentration of Fe(II) was

doubled to 05 mmol L-1 increasing the H2O2 level to100 mmol L

-1resulted in greater degradation efficiency

from 49 to 67 in 10 s of reaction (Figure 5B) ForFe(II) concentration of 10 mmol L-1 after 10 s ofreaction degradation increased from 77 to 88 withan increase in H2O2 concentration from 50 to 100

mmol L-1 after this time no difference was verified

between degradation for the two concentrations of

H2O2 (Figure 5C)

For tests carried out with Fenton reagent or withthe photo-Fenton process note that when catalyst andoxidant are used at concentration ratios of 025100

there was a reduction in degradation rate This may be because of the low concentration of the catalyst

compared to the oxidant or to the formation ofhydroperoxyl radicals (Equation 7) which are produced

in reactions with excess oxidant and are less reactiveand have less reduction potential (170 V) thanhydroxyl radicals (28 V) (37)

HO + H2O2 HO2 + H2O (7)

UV-Visible Spectrometry

The maximum absorbance of abamectin is at 245nm and the low-pressure mercury lamp emits a

maximum dose at 254 nm This property could havecontributed to the high degradation efficiency of

abamectin by the processes with added UV lightFigure 6 presents the UV-Vis spectra of abamectinsolutions submitted to peroxidation (Figure 6A)

photolysis (Figure 6B) peroxidation combined withUV radiation (Figure 6C) Fenton (Figure 6D) and

photo-Fenton (Figure 6E) processes

As degradation by UV radiation and UVH2O2 progressed a reduction at the 245 nm absorbance bandtook place (Figure 6B and 6C) showing that abamectinwas degraded over time In 600 s of reaction noabsorbance peak was seen showing that the parent

molecule was no longer in the solution Similar resultswere reported by Escalada et al (24) for abamectin

using an exposure time of 300 s of UV radiation at254 nm The authors attributed this to the opening ofrings by cleaving double bands mainly in carbons 3

14 and 22

The UV-spectra recorded for abamectin solutionsthat underwent the photo-Fenton process (Figure 6E)

showed a complete degradation of the molecule after600 s However when Fenton reagent was used a

Figure 5 Influence of H2O2 concentration on degradation ofabamectin by the photo-Fenton process Coabamectin= 500 μg L-1(A) CFe(II) = 025 mmol L-1 (B) CFe(II) = 05 mmol L-1 (C) CFe(II) =10 mmol L-1

reduction at the peak of the absorption band was onlyseen with an increase in reaction time (Figure 6D)

During the peroxidation trials there was noreduction in the characteristic peak of absorption ofabamectin at 245 nm (Figure 6A) proving that this process is not efficient at degrading this drug

Monitoring Toxicity ReductionThe Daphnia similis microcrustacean used as a

test organism in the toxicity trials meets the official





200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E

Figure 6 UV-Vis spectra of abamectin solutions submitted to (A) peroxidation (10 mmol L-1 H2O2) (B) photolysis (C) peroxidation

combined with UV radiation (10 mmol L-1 H2O2) (D) Fenton (025 mmol L-1 Fe(II) and 10 mmol L-1 H2O2) and (E) photo-Fenton (025mmol L-1 Fe(II) and 10 mmol L-1 H2O2)

requirements to be considered acceptable for trials asrecommended in NBR 127132009 (21) No sign ofimmobility of organisms was observed when theywere exposed to the control (which contained all of

the reagents present in the sample to be analyzed butnot abamectin) and blank solutions (which contained

cultivation water and neonate organisms) In additionthe average effective concentration for the reference

substance (sodium chloride) EC50 48 h was 268 g L-1 (n = 11) with variations of less than plusmn 2SD (twice the

standard deviation) as recommended in NBR127132009 (21)

Average EC50 48 h for Daphnia similis was 016μg L-1 (n = 4) with a confidence interval (95) between 015 and 020 μg L

-1 Authors such as Tisler

and Erzen (4) found EC50 48 h for abamectin of 025

μg L-1

in trials using Daphnia magna Ivermectin asynthetic derivative of abamectin was shown to be

more toxic than abamectin for different genera of Daphnia EC50 48 h of 70 ng L-1 for D similis (29) and

57 ng L-1 for D magna (11)Sensitivities of D magna and D similis can be

considered similar from the ecotoxicological point ofview with acceptable variance (a correlation coefficient





Table 1 Toxicity results for UV and UVH2O2 processes (Coabamectin = 500 μg L-1)

Process Time (s) Degradation ()Toxicity

reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic

of R 2 = 099) In toxicity studies with D magna and D

similis on industrial effluents and different chemicalcompounds such as phenol and potassium dichromate

it was concluded that the two species have similarsensitivity (38)

It is worth restating that there are frequentlydifferences in EC50 results because many of the

variables are linked to the trials such as reagents fromdifferent lots use of different solvents and the actual

handling by operators which can interfere in theuniformity of the results obtained

During the degradation of contaminants in water

it is very important to investigate the toxicity profilesince the intermediates generated might be more toxicthan the parent molecule For the degraded samplestoxicity results were expressed as toxicity reduction

The relationship between EC50 (dilution needed for50 of organisms to become motionless) and toxicityreduction is presented in Equations 8 and 9 Toxicityreduction was calculated from relative toxicity

according to Equation 8 Relative toxicity was calculatedusing Equation 9 in which EC500 is the dilution

needed for 50 of organisms to become motionless atthe beginning of the degradation test (t = 0 min) andEC50t is the dilution needed for 50 of organisms to

become motionless at 10 60 or 600 s

Toxicity reduction () = 100 ndash Relative toxicity ()

(8)

(9)

Toxicity Reduction During UVH 2O2 ProcessThe results presented on Table 1 referring to the

bioassays carried out using UV and UVH2O2 showthat abamectin concentration and toxicity decrease

over reaction time for both processes evaluated There

was a relationship between the toxicity parameter andthe abamectin degradation It might suggest that the

toxicity of the solution is directly related to the levelof abamectin present and the byproducts of degradation

are not highly toxic Therefore for the completedetoxification of abamectin solutions almost complete

degradation of the drug is necessaryFor UV and UVH2O2 (50 mmol L-1 H2O2)

processes in 600 s of reaction time the minimumnumber of immobilized organisms in the differentsolutions (varied dilutions) was not reached when

toxicity tests were carried out So it was impossible tocalculate the decrease in toxicity In these cases thesolutions were described as not toxic (NT) at least inthe experimental conditions used in this work

For photolysis the toxicity removal was 38 and67 at 10 s and 60 s respectively For the samereaction times the peroxidation combined with UVradiation was able to reduce 44 and 70 of the

toxicity Therefore both processes showed similarefficiency regarding toxicity removal

Toxicity Reduction During Fenton ProcessFenton reagent led to a reduction in toxicity that

was directly proportional to the removal of abamectinfrom the solution (Table 2) For example when the

best conditions were used (10 mmol L-1

Fe(II) and 50mmol L-1 H2O2) the values were statistically equalDal Bosco et al (29) got similar results in a study ofivermectin degradation by Fenton reagent They

reported a toxicity decrease of 78 and the ivermectindegradation of 81 using the same conditions applied

in the present workIt was verified that when low concentrations of

Fe(II) and H2O2 were used (Fe(II) 025 mmol L-1

andH2O2 10 mmol L-1 a molar ratio of 14) the reduction





Table 2 Toxicity results for the Fenton process (Coabamectin = 500 μg L-1)


reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic

Table 3 Toxicity results for the photo-Fenton process (Coabamectin = 500 μg L-1

)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic

in toxicity was different from the degradation efficiencyIn 600 s of reaction toxicity was reduced by 75while degradation of abamectin was 94 This mayoccurred due to the formation of toxic byproducts

In the assay using 025 mmol L

-1

Fe(II) and 50mmol L-1

H2O2 a molar ratio of 120 46 of the drugwas degraded in 600 s and toxicity was reduced by

around 29 The least efficient removal of the targetcompound as well as reduction of toxicity can be

attributed to the use of greater H2O2 concentrationswhich led to an excess of hydrogen peroxide in the

medium In excess H2O2 acts as an OH radicalscavenger (Equation 8)

Toxicity Reduction During Photo-Fenton Process

The data presented in Figure 6 and on Table 3shows that the photo-Fenton process was highly

efficient and abamectin was quickly degraded Clearlythis is due to the greater concentration of hydroxyl

radicals in the medium mainly resulting from the photo regeneration of Fe(III) to Fe(II) The toxicity ofthe solution reduced at the beginning of the trials(Table 3)

The greatest initial concentrations of catalyst andoxidant (10 mmol L-1 Fe(II) and 50 mmol L-1 H2O2)offered the greatest reduction in toxicity after 10 s ofexposure the solution was non-toxic to Daphnia similis When lower concentration of catalyst was used

(025 mmol L-1

Fe(II)) the toxicity reduction was 41and 47 in 10 s using 10 mmol L -1 and 50 mmol L-1

H2O2 respectively

In general from the results obtained in practically

all of the toxicity trials it is possible to suggest that allof the solutions formed by the target compound

(abamectin) and by the intermediates formed during thedegradation processes are less toxic to the Daphnia

similis microcrustacean than the original abamectinsolution







(30) Elmolla E Chaudhuri M J Hazard Mater 2009

172 1476-1481

(31) Fallmann H Krutzler T Bauer R Malato SBlanco J Catal Today 1999 54 309-319

(32) Fan C Tsui L Liao MC Chemosphere 2011 82

229-236

(33) Nogueira RFP Trovoacute AG Silva MRA Villa

RD Quim Nova 2007 30 400-408

(34) Klamerth N Rizzo L Malato RS MaldonadoMI Aguera A Feacuternandez-Alba AR Water Res2010 44 545-554

(35) Guimaratildees JR Gasparini MC Maniero MG

Mendes CGN J Braz Chem Soc 2012 23 1680-1687

(36) Lu LA Ma YS Kumar M Lin JG Chem Eng J 2011 166 150-156

(37) Legrini O Oliveros E Braun AM Chemosphere 1993 93 698-671

(38) Buratini SV Bertoletti E Zagatto PA Bull Environ Contam Toxicol 2004 73 878-882

Received for review May 20 2013 Revised manuscriptreceived November 6 2013 Accepted November 10 2013





Material and Methods

Chemical Reagents

Abamectin (gt97) was obtained from Fluka(Buchs Switzerland) and methanol (HPLC grade) fromJ T Baker (Xalostoc Mexico) while ferrous sulfate(FeSO47H2O) sulfuric acid and hydrogen peroxide

(30 mm) were obtained from Synth (DiademaBrazil) Ultra-pure water used in the tests was produced by a Milli-Q purification system from Millipore(Billerica USA)

Stock Solu tionThe abamectin stock solution (500 mg L-1) was

prepared in methanol The solution was stored in anamber flask which was protected from light and kept

at -10 degC The working solutions (500 microg L-1

) were prepared by diluting the stock solution with ultrapure

water

Experimental SystemThe photo-reactor was made up of a germicide

lamp (15 W λ max = 254 nm 20 cm diameter) covered by a quartz cylinder (50 cm diameter 520 cm long)inserted in the middle of a borosilicate tube (80 cm

diameter and 550 cm long) The sample volume used

in the reactor was 10 L The solution was homo-genized by a magnetic stirrer The tests were run in batches

Average irradiance was 383 mW cm-2 It wasmeasured by a model VLX 3 W Cole Parmer Series9811 radiometer calibrated to a 254 nm wavelengthThe radiation dose D (mJ cm-2) was calculated using

Equation (1)

(1)

in which D is the UV radiation dose (mJ cm-2) E is theirradiance (mW cm-2) and t is the exposure time (s)

For all of the processes evaluated reaction time

varied from 0 to 600 s Photolysis peroxidation and peroxidation with UV radiation trials were carried outat the natural pH of the sample (around 7) while

Fenton and photo-Fenton processes were carried outafter pH was adjusted to 285 Experiments carried outusing the Fenton reagent employed Fe(II) at concen-trations between 025 and 10 mmol L-1 and H2O2

between 10 and 100 mmol L-1

Fe(II) concentrationsgreater than H2O2 concentrations were not evaluated

because according to Neyens and Baeyens (18) themolar ratio of Fe(II)H2O2 must always be less than 1

In all of the tests carried out with hydrogen peroxide(peroxidation peroxidation assisted by ultraviolet

radiation Fenton and photo-Fenton) reactions werestopped and the residual H2O2 concentration was

destroyed by adding sodium bisulfite at a 11 molarratio with hydrogen peroxide (19)

Analytical Method

The concentration of abamectin in the aqueoussolutions was determined by high performance liquid

chromatography with UV detection Before quantitation

the samples were concentrated by solid phase extraction(SPE) using C18 cartridges (500 mg6 mL Varian) thathad been previously conditioned with methanol (6 mL)and water (6 mL) A liter of the solution percolated

through the cartridges at a flow rate of 10 mL min-1

The analytes were eluted with 4 mL of methanol Before

analyses the solutions were filtered through 022 micromMillipore membranes The extraction efficiencyevaluated through recovery tests ranged from 64 to99 for aqueous solutions containing abamectin with

concentrations ranging from 25 to 500 μg L

-1

Chromatographic analyses were carried out with a

Waters solvent delivery system (Waters 510) a tunableabsorbance detector (Waters 486) a Rheodyne 7725

injector with a sample loop of 20 microL and a Waters746 integrator Abamectin quantitation was performedat 245 nm The analytical column was a Waters

XBridgeTM

RP18 (250 mm x 46 mm 5 microm) and asmobile phase methanol and water (8515 vv) with a

flow rate of 1 mL min-1

was used The limit ofdetection (LOD) and limit of quantitation (LOQ) were

10 microg L-1

and 30 microg L-1

respectively considering aconcentration factor of 250

UV-Vis spectra were obtained using a UV-1601PCspectrophotometer (Shimadzu Japan) The initialsolution (500 μg L

-1 abamectin) and the samples

submitted to the degradation processes were concen-trated using SPE as described previously The analytewas eluted from the cartridge with methanol (4 mL)filtered and diluted 4 times before analysis Spectra

were registered from 200 to 350 nm since there wasno observed absorbance in the visible region of theeletromagnetic spectrum

Consumption of hydrogen peroxide was evaluated

based on the oxidation-reduction reaction betweenresidual H2O2 and metavanadate ions The vanadate

solution (which is yellow) turns red after the reactionwith H2O2 due to the formation of peroxovanadiumcations (Equation 2) which absorb at 450 nm (20)The limit of detection of the method (LOD) was 002mmol L-1

(2)Daphnia Simili s Toxicity Tr ials

Acute toxicity trials and cultivation of the organismswere carried out as specified by the Brazilian National


























-1







L-1








is 10 mmol L-1






0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

(a) (b) (c)

(d) (e)





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B


+-OH (3)

[Fe(III)

(OH)]2+

Fe(II) + HO

(4)


R (5)






























h

h





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2

O2

B






HO









-1







mmol L-1

to 100 mmol L-1


0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

C





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)








H2O2 (Figure 5C)





HO + H2O2 HO2 + H2O (7)










14 and 22












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408

































-1







L-1








is 10 mmol L-1






0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)

(a) (b) (c)

(d) (e)





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B


+-OH (3)

[Fe(III)

(OH)]2+

Fe(II) + HO

(4)


R (5)






























h

h





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2

O2

B






HO









-1







mmol L-1

to 100 mmol L-1


0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

C





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)








H2O2 (Figure 5C)





HO + H2O2 HO2 + H2O (7)










14 and 22












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408












0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B


+-OH (3)

[Fe(III)

(OH)]2+

Fe(II) + HO

(4)


R (5)






























h

h





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2

O2

B






HO









-1







mmol L-1

to 100 mmol L-1


0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

C





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)








H2O2 (Figure 5C)





HO + H2O2 HO2 + H2O (7)










14 and 22












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408












0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2

O2

B






HO









-1







mmol L-1

to 100 mmol L-1


0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2

C





0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)








H2O2 (Figure 5C)





HO + H2O2 HO2 + H2O (7)










14 and 22












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



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RD Quim Nova 2007 30 400-408












0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


2

A

0 100 200 300 400 500 60000

02

04

06

08

10

C C

o

Time (s)


-1 H

2O

2


-1 H

2O

2


-1 H

2O

2

B

0 100 200 300 400 500 60000

02

04

06

08

10 10 mmol L

-1 Fe(II)50 mmol L

-1 H

2O

2


-1 H

2O

2

C

C C

o

Time (s)








H2O2 (Figure 5C)





HO + H2O2 HO2 + H2O (7)










14 and 22












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408












200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 st = 60 st = 30 s

t = 10 st = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 st = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 st = 10 s

t = 0 s

A b s o r b

a n c e

(nm)

200 225 250 275 300 325 35000

02

04

06

08

10

12

14

t = 600 s

t = 300 s

t = 60 s

t = 30 s

t = 10 s

t = 0 s

A b s o r b a n c e

(nm)

A B

C D

E











μg L-1











reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408














reduction ()

Standard

deviation ()

UV

0 00 0 -

10 336 38 plusmn 9

60 681 67 plusmn 19

600 975 NT -

UVH2O2

(025 mmol L-1

)

0 00 0 -

10 325 59 plusmn 8

60 661 74 plusmn 5

600 986 89 plusmn 3

UVH2O2

(50 mmol L-1

)

0 00 0 -

10 347 44 plusmn 5

60 668 70 plusmn 5

600 991 NT -

NT ndash non-toxic














(8)

(9)


























reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408














reduction ()

Standard

deviation ()

Fenton

(10 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 641 65 plusmn 20

60 763 71 plusmn 9

600 890 NT -

Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 -

10 290 36 plusmn 12

60 672 55 plusmn 17

600 947 75 plusmn 10

Fenton

(025 mmol L-1

Fe(II)50 mmol L

-1 H2O2)

0 00 0 -

10 296 8 plusmn 7

60 346 27 plusmn 8

600 465 29 plusmn 10

NT ndash non-toxic


)

ProcessTime

(s)Degradation ()

Toxicity

reduction ()

Standard

deviation ()

photo-Fenton

(10 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 773 NT -

60 915 NT -

600 969 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

10 mmol L-1

H2O2)

0 00 0 0

10 496 41 plusmn 13

60 907 71 plusmn 14

600 986 NT -

photo-Fenton

(025 mmol L-1

Fe(II)

50 mmol L-1

H2O2)

0 00 0 0

10 521 47 plusmn 15

60 789 NT -

600 994 NT -

NT ndash non-toxic



-1











(025 mmol L-1


H2O2 respectively












172 1476-1481



229-236


RD Quim Nova 2007 30 400-408















172 1476-1481



229-236


RD Quim Nova 2007 30 400-408













172 1476-1481



229-236


RD Quim Nova 2007 30 400-408








Documents

Stress-strain modeling of 270 ksi low-relaxation prestressing strands