Degradation of the herbicide paraquat by photo-fenton process: optimization by experimental design and toxicity assessment

ARTICLE

Degradation of the herbicide paraquat by photo-fenton process: optimization by experimental design and toxicity assessment

Alam G. Trovó^I,*; Oswaldo Gomes Junior^I; Antonio E. H. Machado^I; Waldomiro Borges Neto^I; Jader O. Silva^II

^IInstituto de Química, Universidade Federal de Uberlândia (UFU), CP 593, 38400-902 Uberlândia-MG, Brazil

^IIDepartamento Municipal de Água e Esgoto de Uberlândia (DMAE), 38400-606 Uberlândia-MG, Brazil

ABSTRACT

This study describes the influence and optimization of Fenton's reagent (concentration of Fe²⁺ and H₂O₂ ) on the efficiency of mineralization of the herbicide paraquat (PQT, 50 mg L^-1) in water, after 60 min (equivalent to 642 kJ L^–1 of accumulated UVA radiation) treatment by photo-Fenton process in laboratory scale, using central composite design (CCD). Under optimized conditions, kinetic experiments were done, evaluating the PQT removal, its mineralization and toxicity in laboratory scale, using artificial irradiation, and in a pilot plant under solar irradiation. The same removal efficiency and mineralization of PQT were obtained in both reactors. The toxicity of the samples, estimated in terms of mortality of Artemia salina, decreases simultaneously with the decay of concentration of PQT, suggesting the formation of intermediates of lower toxicity. In this way, the solar photo-Fenton process can be considered as a viable alternative for the treatment of wastewater containing PQT.

Keywords: pesticides, detoxification, pilot plant, wastewater treatment, solar light intensity

RESUMO

Este trabalho descreve a influência e otimização dos reagentes de Fenton (concentração de Fe²⁺ e H₂O₂) na eficiência da mineralização do herbicida paraquat (PQT, 50 mg L^–1) em água, após 60 min (equivalendo a 642 kJ L^–1 de radiação UVA acumulada) de tratamento por processo foto-Fenton em escala de laboratório, usando planejamento composto central (CCD). Sob condições otimizadas, experimentos cinéticos foram feitos, avaliando a remoção do PQT, sua mineralização e toxicidade em escala de laboratório, usando irradiação artificial, e em planta piloto sob irradiação solar. A mesma eficiência de remoção e mineralização do PQT foram obtidas em ambos os reatores utilizados. A toxicidade das amostras, estimada em termos de mortalidade de Artemia salina, diminui simultaneamente com o decaimento da concentração de PQT, sugerindo a formação de intermediários de menor toxicidade. Dessa maneira, o processo foto-Fenton/solar pode ser considerado uma alternativa viável para o tratamento de águas residuais contendo PQT.

Introduction

Since 2008 Brazil has overtaken the United States in pesticides consumption, becoming the largest consumer.¹ The herbicide paraquat dichloride (PQT, Figure 1) has been widely used for application in post-emergence of weeds and also as desiccant.² Its residence time in soils can vary from 1.4 to 7.2 years depending on the concentration, soil characteristics (organic matter), temperature and rainfall.³ In river water samples, it has been observed that PQT is not easily microbiologically degraded, since, even after 56 days of incubation, more than 80% of the initial concentration remains unchanged, suggesting to PQT considerable recalcitrance.⁴ In addition, PQT is polar, showing high solubility in water, as well as a low octanol-water partition coefficient (log K_ow = –4.5), which provides a great mobility in some soils, arriving easily until the next water supplies.⁵ It has been found in the range of 2-12 µg L^–1 in groundwater,⁶ and, for example, at average concentration of 0.78 µg L^–1 in surface waters in Spain.⁷

In acute toxicity studies performed by US Environmental Protection Agency using laboratory animals, PQT has been shown to be highly toxic by inhalation route, having been classified in toxicity category I (the highest of four levels). The high toxicity of this compound has also been observed in studies involving the use of bacteria, small crustaceans, algae and aquatic plants.^8-12 Thus, its presence in the environment can cause adverse effects in aquatic and terrestrial organisms. Therefore, it is desirable for the development and optimization of viable technologies with a focus on disposal of such waste.

Since the traditional biological treatments are not effective in the PQT removing, an alternative can be the use of advanced oxidation processes (AOPs) due to their recognized efficiency in the treatment of recalcitrant organic matter, through the efficient generation of HO^· radicals.^13-15 From the variety of existing AOPs, particular attention has been given to photo-Fenton process and heterogeneous photocatalysis due to the possibility of use of solar radiation,¹⁶ reducing the energetic costs. The photo-Fenton process has the advantage to be a homogeneous process, avoiding an additional step of removal of catalyst, usual when dealing with a heterogeneous process. Another advantage is the fact that homogeneous processes favor a greater contact between reagent species, with favorable implications for process performance.

The use of different AOPs for degradation of PQT has been reported, such as immobilized TiO₂ and/or in suspension, combined with UV irradiation,^17-21 UV-ozonation,^22,23 Fenton's reaction,²⁴ activated carbon modified with iron and combined with hydrogen peroxide, and electrochemical methods.^25,26 However, a study by applying experimental design and response surface methodology that provides conclusions which result in the optimization of Fenton's reagents for PQT degradation was not reported until now. In addition, a kinetic study on the degradation of PQT by photo-Fenton process and toxicity assessment was also not published. Therefore, the aim of the present work was to evaluate the role of each variable (Fe²⁺ and H₂O₂ concentration) on the percentage of mineralization of a commercial formulation of PQT (Helmoxone^TM) at lab-scale, and, under optimized conditions, monitor the kinetic of PQT removal, mineralization, toxicity and the carbon oxidation state (COS) during photo-Fenton treatment not only at lab-scale but also in a solar pilot plant.

Experimental

Reagents

All solutions were prepared using ultrapure water. FeSO₄.7H₂O (Vetec) was used to prepare aqueous 0.25 mol L^–1 Fe²⁺ stock solution; H₂O₂ (30% m/m), H₂SO₄, NaOH and Na₂SO₃, all from Vetec, were used as received. A solution of ammonium metavanadate (Vetec) was prepared at a concentration of 0.060 mol L^–1 in 0.36 mol L^–1 H₂SO₄ and used for H₂O₂ quantification.

All experiments were carried out using the commercial formulation (276 g L^–1 of PQT, C₁₂H₁₄Cl₂N₂ = 257 g mol^–1), diluted to obtain 50 mg L^–1 PQT in solution. Although the PQT concentration is higher than that found in aquatic environments, it was chosen to permit an adequate evaluation of the toxicity. An analytical standard of PQT for chromatographic analysis was purchased from Sigma-Aldrich. High performance liquid chromatography (HPLC) analyses were done using HPLC grade methanol (Vetec).

Experimental design

The central composite design (CCD) was applied to optimize the concentration of the variables (Fe²⁺ and H₂O₂), able to induce a high percentage of mineralization of commercial formulation by the photo-Fenton process, as well as to evaluate the interactions among these two variables. The percentage of mineralization, measured by total organic carbon (TOC) decay after 60 min of reaction in relation to the initial TOC value, was chosen as the response factor of the photo-Fenton process. CCD is a star type project that consists of three series of experiments: (i) a 2^k factorial design (all possible combinations of codified values between +1.0 and –1.0) for k = 2 variables consists of four experiments; (ii) axial or star points (+1.4 and –1.4), and 0 for two variables (four experiments); and (iii) replicates of the central point (0) (five experiments). Thus, for this design, it was necessary to do thirteen experiments, in which the two variables were codified in five levels, varying within the following ranges: Fe²⁺ (7.2-12.8 mg L^–1) and H₂O₂ (39.8-232.2 mg L^–1). The ranges of the variables were chosen according to previous studies.^27-30 For CCD, the equations used to quantitatively describe each system and draw the response surface and contour plots were built using STATISTICA 6.0 software. Statistical validation was obtained using the analysis of variance (ANOVA) test at 95% confidence level.

Photodegradation procedures

Lab-scale experiments

The photodegradation experiments were performed in lab-scale using a 400 W high pressure mercury vapor lamp as irradiation source. The photocatalytic reactor consists of an annular recipient of borosilicate glass with an irradiated surface of 3.89 × 10^–2 m². The lamp was positioned at the center of the reactor, as described and schematically presented by Oliveira et al.³¹ The average irradiance of UVA radiation measured for the lamp³² is 1100 W m^–2, which presents a photonic flux of 3.3 × 10^-6 einstein s^–1 between 295 and 710 nm.³³ The measurements were done using a Solar Light PMA 2100 photometer/radiometer, equipped with an UVA detector (320-400 nm) and a radiometric/photometric setup,³³ built with components furnished by Ocean Optics, Inc.

The irradiated volume of the reactor was 0.280 L and a total volume of 4 L of commercial formulation was recirculated, by pumping at a flow rate of 2.14 L min^–1 after the addition of iron solution, pH adjustment between 2.5 and 2.8 (the optimum pH range for the Fenton reaction) and addition of H₂O₂. The lamp was only turned on when the reactor was filled with solution.

For CCD experiments, aliquots of the photolyzed solutions (20 mL) were collected only after 60 min of reaction, while for the kinetic experiment, samples (70 mL) were collected at 20 min intervals up to 120 min. The initial conditions used in CCD design are described in the section of the experimental design.

The kinetic experiments were carried out using initially 50.0 mg L^–1 PQT, 11.8 mg L^–1 Fe²⁺ and 188.1 mg L^–1 H₂O₂, the last replaced in 60 and 100 min of reaction due to its consumption. After sampling and before analysis, a calculated volume of 2.0 mol L^–1 Na₂SO₃ solution was added to the samples, according to the stoichiometry between H₂O₂ and Na₂SO₃, and H₂O₂ concentration. This procedure ensures the removal of the remaining H₂O₂, interrupting the Fenton reaction. Also, it eliminates the interference caused by traces of H₂O₂ in toxicity assays and avoids the sulfite interference on the chemical oxidation demand (COD) measurements.³⁴

For the toxicity assays, the pH value was adjusted in the range between 6 and 8 after adding the Na₂SO₃ solution. The solution temperature was controlled using a thermostatic bath (Tecnal TE-184), keeping close to 25 ± 2 ºC. Control experiments were performed using the same experimental setup previously described for the kinetic photo-Fenton experiments.

Experiments in a pilot plant: use of solar radiation

Experiments using solar radiation were carried out during Autumn, under clear sky conditions, using a solar pilot plant. The solar irradiance was measured using a radiometer (PMA 2100, Solar Light, Co.) in the UVA region (320-400 nm), with the sensor attached with the same inclination of the reflective surface of the reactor.³⁵ Under this condition, an average solar irradiance of 36.4 ± 5.4 W m^–2 was obtained between 9:45 and 11:45 am in May/2012.

The solar reactor is a compound parabolic collector (CPC) with an irradiated surface of 1.62 m² (irradiated volume: 12 L) and a reservoir with maximum capacity of 120 L.³⁵ A volume of 50 L of the PQT solution was circulated under turbulent flow (33.3 L min^–1) into the CPC absorber tubes in a closed recirculating system. The photoreactor hydraulic circuit consists of a continuously stirred tank and a 0.50 HP centrifugal pump. At the beginning of the experiment, with the collectors covered, the same initial conditions defined for the reagents in kinetic experiments using lab-scale reactor were used. The cover was then removed and samples were collected at intervals of 20 min up to 120 min. The same treatment previously described, using Na₂SO₃ solution, was done to stop the Fenton reaction.

In this experiment, new additions of H₂O₂ were done at 60, 80 and 100 min of reaction.

Measurements of the accumulated UVA energy

It is important to mention that due the differences of the reactors, like as the average irradiance, surface area, total volume of solution, the accumulated UVA energy (Q_UVA,n, kJ L^–1) was calculated for each time of sampling in each reactor to allow a good comparison of the results. Equation 1 allows to estimate the amount of accumulated UVA energy (Q_UVA,n) received on any surface per unit of volume, for a solution inside the reactor, in a time interval Δt.³⁶

where t_n is the sampling time, V_t is the total reactor volume, A_r the illuminated collector surface area and UVA_G,n the average solar or artificial UVA radiation, measured during the period Δt_n (t_n – t_n-1).

Table 1 presents the accumulated UVA energy for each reactor corresponding to the sampling times of 20, 40, 60, 80, 100 and 120 min. A significant difference in the accumulated UVA energy was obtained for both reactors. An accumulated UVA energy 10 times higher than that provided by solar radiation to the pilot plant is provided by the mercury lamp to the lab-scale reactor. In the X-axis of Figures 3 and 4, the sampling time was maintained for comparison with control experiments done in the dark, in function of the reaction time.

Analysis

Before chemical analyses, except for TOC determination, the samples were filtered through membranes with pore diameter of 0.45 µm. Mineralization, conversion of the organic matter to carbon dioxide and water, of PQT present in a commercial formulation was followed measuring the TOC decay using a TOC analyzer (Shimadzu TOC-VCPH/CPN) equipped with an ASI-V auto sampler. The determination consists of two analyses: first the total carbon (TC) of the sample is determined after catalytic oxidation at high temperature, while the total inorganic carbon (TIC) is determined by equilibrium shift after addition of phosphoric acid to the sample. In both analyses, the CO₂ released is determined by infrared spectroscopy.

The TOC concentration includes the carbon content of the target compound, the intermediates generated during the experiment and the excipient of the commercial product. It is calculated by the difference between TC and TIC. Hydrogen peroxide was quantified spectrophotometrically using ammonium metavanadate, monitoring the absorption of the red-orange peroxovanadium cation, at 450 nm (equation 2).³⁷

Kinetic experiments were also carried out by HPLC analyses aiming to evaluate the PQT removal, as well as the toxicity and COS. The PQT concentrations were determined by reversed phase HPLC, using a VWR-Hitachi L-2130 chromatograph with UV-Vis detector (Merck-Hitachi L-4250) and a C₁₈ column (Lychrispher, 5 µm, 250 × 4.6 mm). The separation occurred using a mixture of 3 mmol L^-1 HCl and methanol (25:75, v/v) in isocratic mode, at a flow rate of 1 mL min^–1. The detection was performed by UV absorption at 257 nm. The injection volume was 20 µL. Under these conditions, the retention time for PQT was between 2.6 and 2.8 min, with a limit of quantitation of 1.0 mg L^–1.

COD, quantity of oxygen required to chemically oxidize organic matter without the intervention of microorganisms, was estimated by absorbance measurement at 420 nm by means a standard photometric method (5220 D).³⁸ This parameter was determined after digestion of the organic matter with dichromate solution in closed reflux vessels at 150 ºC for 2 h.

COS of the solutions treated by photo-Fenton process was estimated according to equation 3, where TOC and COD are expressed in mg C L^–1 and mg O₂ L^–1, respectively. COS is between +4 for CO₂, the most oxidized state of C, and –4 for CH₄, the most reduced state of C.³⁴

The toxicity tests were done evaluating the immobilization of Artemia salina, as described by Trovóet al.³⁰

Results and Discussion

Optimization of Fenton's reagents for the mineralization of PQT in a commercial formulation using experimental design

Before evaluating the degradation kinetics of PQT, CCD was held with the purpose of evaluating the role of each reagent, optimizing their concentration, so as to ensure maximum efficiency for photo-Fenton reaction. Table 2 shows the experimental planning in CCD as well as the response obtained in each experiment in terms of mineralization of PQT present in a commercial formulation.

Equation 4 was obtained using statistical analysis of the experimental data presented in Table 2.

The effect of each process independent variable can be directly correlated to its coefficient.^27,30

From equation 4, although negative quadratic coefficients have been obtained for Fe²⁺ (–2.30) and H₂O₂ (–0.002), the expressive positive linear coefficients for Fe²⁺ (+44.01) and H₂O₂ (+0.20), and the positive coefficient found for the interaction between Fe²⁺ and H₂O₂ (+0.05), suggest that the mineralization is favored increasing their concentrations. The overall effect can be observed in Figure 2, that presents a diagram that represents the polynomials related to photo-Fenton reaction, constructed from the results presented in Table 2. An analysis of the surface (Figure 2) suggests that a high percentage of mineralization can be obtained using 11.8 mg L^–1 Fe²⁺ and 188.1 mg L^–1 H₂O₂.

An experiment was performed in order to check the optimized values, predicted by the mathematical model. The theoretical result, calculated using equation 4, shows a very good agreement with the experimental results obtained for the optimal concentration of Fe²⁺ and H₂O₂ (Table 3), assuming a standard deviation of ± 3.1% for mineralization (value obtained from five replicates in the central point of CCD). This demonstrates that the surface response methodology can be useful as a tool to optimize the degradation of organic matter in reactions mediated by photo-Fenton process.

Kinetics of PQT degradation and toxicity assessment

Using the optimized conditions defined by the analysis of the response surface from the results obtained at lab-scale, the degradation profile of PQT and its mineralization in a commercial formulation (Figure 3), as well as assessment of the toxicity and COS (Figure 4) during photo-Fenton process at lab-scale and in a solar pilot plant was obtained.

The PQT concentration reached the limit of quantitation (1.0 mg L^–1) at lab-scale after 20 min (214 kJ L^–1 of UVA radiation) while 40 min (42.8 kJ L^–1 of UVA radiation) were necessary when the solar pilot plant was used (Figure 3a). Similar behavior was also observed during the mineralization of PQT by photo-Fenton treatment (Figure 3b). A rapid decay of mineralization at lab-scale was obtained in relation to the solar pilot plant. This can be attributed to the higher accumulated UVA energy at lab-scale (Table 1). However, after 120 min of photo-Fenton treatment, a similar efficiency was reached for both reactors (89.4 at lab-scale and 84.1% at solar pilot plant), even assuming a standard deviation of ± 3.1% for mineralization (Table 2). In addition, a lower accumulated UV energy at solar pilot plant (146.9 kJ L^–1 of UVA radiation) was necessary to obtain the same efficiency in relation lab-scale (1284 kJ L^–1 of UVA radiation). Nogueira et al.³⁹ evaluated the influence of the solar light intensity on the TOC removal and observed that the degradation rate increases linearly with the light intensity for values up to 15 W m^–2, but above this value, the degradation is best described by a square root relationship, which justifies the results obtained in this work. Although a 400 W high pressure mercury vapor lamp (average irradiance of 1100 W m^–2) was used as irradiation source at lab-scale, the same efficiency was obtained in a solar pilot plant with an average solar irradiance of 36.4 ± 5.4 W m^–2. The consumption of hydrogen peroxide agrees with the results of mineralization (Figure 3b). After 120 min (146.9 and 1284 kJ L^–1 of UVA radiation, respectively under solar irradiation and in lab-scale) of photo-Fenton treatment, 565 and 591 mg L^–1 of H₂O₂ were consumed at lab-scale and solar pilot plant experiments, respectively (Figure 3b). The H₂O₂ consumption profile shows a linear correlation with the reaction time (α = 4.7 and 4.9 mg H₂O₂ min^–1 at lab-scale and in a solar pilot plant, respectively). For this same sequence, under the operating conditions, 10.8 and 12.4 mg H₂O₂ were consumed for each mg of TOC mineralized (Figure 3b).

Control experiments at lab-scale were also performed for an initial PQT concentration equal to 50 mg L^–1 in the: (i) absence of Fe²⁺ and H₂O₂ (direct photolysis at pH 6.3, natural pH of the solution); (ii) dark, without Fe²⁺ and in the presence of H₂O₂ (188.1 mg L^–1); (iii) presence of UV irradiation and 188.1 mg L^–1 H₂O₂ at pH 6.3, without Fe²⁺; (iv) hydrolysis at pH 2.5; (v) presence of UV irradiation and 11.8 mg L^–1 Fe²⁺ at pH 2.5, without H₂O₂; and (vi) presence of 11.8 mg L^–1 Fe²⁺ and 188.1 mg L^–1 H₂O₂ in the dark (Figure 3). A lower removal of PQT and mineralization was obtained for all control experiments, when compared to the photo-Fenton process, evidencing its high efficiency and assuring that the results found are consistent and not due to hydrolysis, thermal Fenton process, and/or direct or due to hydrogen peroxide photolysis (Figure 3).

COSs for the samples in reactions mediated at lab-scale, and toxicity at lab-scale and using a solar pilot plant, were also analyzed during PQT degradation aiming to evaluate the toxicity behavior and COS variation during application of the photo-Fenton process under optimum conditions. The assessment of the toxicity during the degradation of pesticides is critical when a process is studied as an alternative to wastewater treatment, or when this same process is regarded as the first stage in a treatment process coupled to a subsequent biological process.⁴⁰

The solution containing 50 mg L^–1 of PQT showed a high value of COS (+ 3.44), suggesting that the compound has a high COS (Figure 4). However, this value does not show correspondence with the theoretical value. The experimental COD value obtained for the experimental TOC initial concentration of commercial formulation is equivalent to only 14.0% of the theoretical value (157 mg O₂ L^–1). This low experimental COD value obtained in relation the experimental initial TOC (59 mg C L^–1) contributes to generate a high experimental COS (equation 3), higher than the theoretical value (COS = 0.0008). This lower value measured for COD is probably due to the presence of two pyridine rings on PQT structure, a refractory species to APHA method for determination of COD.³⁴

Applying the photo-Fenton process at lab-scale, the PQT concentration reached the limit of quantitation (1.0 mg L^–1) with 18% of TOC removal (Figure 3) and an increase in COS from +3.44 to +3.84 (Figure 4), in only 20 min of reaction (214 kJ L^–1 of UVA radiation), after consumption of 78 mg L^–1 H₂O₂. In this same period, the acute toxicity, calculated by the inhibition of mobility of A. salina, decreased from 87 to 33% (Figure 4), which is related with the PQT concentration reduction (Figure 3a). With the increase of the reaction time up to 40 min (428 kJ L^–1 of UVA radiation), a consumption of 174 mg L^–1 H₂O₂, a TOC removal of 50% (Figure 3b), the same COS value of +3.84 and a decrease in the toxicity from 33 to 10% (Figure 4) were reached. Although the COS values obtained do not show correspondence with the theoretical data, the application of photo-Fenton process contributed to the formation of intermediates more oxidized and a lower toxicity than the verified for the initial sample containing only PQT. After 60 min (642 kJ L^–1 of UVA radiation) of reaction and consumption of 213 mg L^–1 H₂O₂, 69% of TOC removal (Figure 3b) and a toxicity of 13% (Figure 4) were obtained. It was not possible to calculate the COS value after 60 min (642 kJ L^–1 of UVA radiation) of reaction, once that the COD values obtained were null. For an irradiation time up to 120 min (1284 kJ L^–1 of UVA radiation) and consumption of 565 mg L^–1 H₂O₂, 89% of TOC removal (Figure 3b) and a toxicity of 20% were reached (Figure 4). Similar behavior was obtained to toxicity when the experiment was carried out in a solar pilot plant, however with a lower accumulated UVA energy (Figure 4 and Table 1). The residual toxicity, between 10-20% in both reactors (Figure 4) is probably due the formation of carboxylic acids, as already observed for Daphnia magna and Vibrio fischeri during degradation of sulfamethoxazole and amoxicillin.^41,42

On the other hand, Santos et al.²⁴ observed a decrease in the biodegradability and no toxicity reduction during PQT degradation by the Fenton's process after 25 h using the initial conditions: 100 mg L^–1 PQT, 28 mg L^–1 Fe²⁺ and 221 mg L^–1 H₂O₂. Probably this difference, compared to our best results, may be due to different initial concentration of PQT and reagents, the removal of TOC reached and/or the concentration of intermediates generated in solution.

In general, it can be observed that after short periods of photo-Fenton process (between 20 and 40 min), the toxicity tends to decrease with the PQT concentration reduction and intermediates more oxidized were obtained (Figure 4). So, after these times, probably a biological process could be coupled with the photo-Fenton one, reducing the operational costs of the oxidative treatment. Similar behavior has been observed for other compounds/wastewaters, during the application of Fenton and photo-Fenton processes.^43-46

Conclusions

Based on the experimental results obtained, it is possible to conclude that experimental design and response surface methodology are powerful tools to optimize, in a short set of experiments, the concentration of Fenton reagents, obtaining a high percentage of mineralization of PQT in a commercial formulation. Under optimized conditions, the same efficiency was obtained for both reactors. These results demonstrates that the photo-Fenton process can be applied as an alternative to the wastewater treatment containing this herbicide in large scale and using solar radiation, once that the toxicity decreased significantly with the paraquat concentration reduction and intermediates more oxidized were obtained. In addition, the use of solar radiation is completely advantageous, mainly in tropical countries like Brazil since the energetic costs of the process are reduced to zero.

Acknowledgments

The authors thank CNPq (Project No. 2011-EXA022) for the scholarship to O. Gomes Junior, and FAPEMIG (CEX-APQ-00915-11, CEX-APQ-01798-11 and CEX-APQ-02425-10), CAPES, CNPq (300.587/2008-2 and 304.576/2011-5) for the financial support of this work. A. E. H. Machado is particularly indebted to CNPq and CAPES for his research grants. The authors also thank to Dr. R. Ruggiero for providing access and use of the HPLC/UV equipment.

References

1. http://portal.anvisa.gov.br/wps/content/anvisa+portal/anvisa/sala+de+imprensa/menu+-+noticias+anos/2012+noticias/seminario+volta+a+discutir+mercado+de+agrotoxicos+em+2012 acessed in November 2012.

2. http://portal.anvisa.gov.br/wps/wcm/connect/7bfd7800474594009b90df3fbc4c6735/P01++Paraquate.pdf?MOD=AJPERES accessed in November 2012

3. Cheah, U-B.; Kirkwood, R. C.; Lum, K.-Y.; J. Agric. Food Chem. 1998, 46, 1217.

4. Wang, Y.; Yen, J.; Hsien, Y.; Chen, Y.; Water, Air, Soil Pollut. 1994, 72, 1.

5. Tomlim, C. D. S.; The Pesticide Manual, 12^th ed.; British Crop Protection Council: UK, 2000.

6. Vidal, J. L. M.; Vega, A. B.; López, F. J. S.; Frenich, A. G.; J. Chromatogr., A 2004, 1050, 179.

7. Fernández, M.; Ibáñez, M.; Picó, Y.; Mañes, J.; Arch. Environ. Contam. Toxicol. 1998, 35, 377.

8. Alberdi, J. L.; Saenz, M. E.; DiMarzio, W. D.; Tortorelli, M. C.; Bull. Environ. Contam. Toxicol. 1996, 57, 229.

9. Ruiz, M. J.; López-Jaramillo, L.; Redondo, M. J.; Font, G.; Bull. Environ. Contam. Toxicol. 1997, 59, 619.

10. Qian, H. F.; Chen, W.; Sun, L. W.; Jin, Y. X.; Liu, W. P.; Fu, Z. W.; Ecotoxicology 2009, 18, 537.

11. Mohammad, M.; Itoh, K.; Suyama, K.; Arch. Environ. Contam. Toxicol. 2010, 58, 605.

12. Jamers, A.; De Coen, W.; Environ. Toxicol. Chem. 2010, 29, 893.

13. Malato, S.; Fernández-Ibáñez, P.; Maldonado, M. I.; Blanco, J.; Gernjak, W.; Catal. Today 2009, 147, 1.

14. Zapata A.; Oller, I.; Sirtori, C.; Rodríguez, A.; Sánchez-Pérez, J. A.; López, A.; Mezcua, M.; Malato, S.; Chem. Eng. J. 2010, 160, 447.

15. Pintor, A. M. A.; Vilar, V. J. P.; Boaventura, R. A. R.; Sol. Energy 2011, 85, 579.

16. Safarzadeh-Amiri, A.; Bolton, J. R.; Carter, S. R.; J. Adv. Oxid. Technol. 1996, 1, 8.

17. Tennakone, K.; Kottegoda, I. R. M.; J. Photochem. Photobiol., A 1996, 93, 79.

18. Moctezuma, E.; Leyva E.; Monreal, E.; Villegas, N.; Infante, D.; Chemosphere 1999, 39, 511.

19. Lee, J. C.; Kim, M. S.; Kim, C. K.; Chung, C. H.; Cho, S. M.; Han, G. Y.; Yoon, K. J.; Kim, B. W.; Korean J. Chem. Eng. 2003, 20, 862.

20. Lee, J-C.; Kim, M-S.; Kim, B-W.; Water Res. 2002, 36, 1776.

21. Florencio, M. H.; Pires, E.; Castro, A. L.; Nunes, M. R.; Borges, C.; Costa, F. M.; Chemosphere 2004, 55, 345.

22. Ruth, J. M.; Kearney, P. C.; Zeng, Q.; Chemosphere 1985, 14, 1181.

23. Kearney, P. C.; Ruth, J. M.; Zeng, Q.; Mazzocchi, P.; J. Agric. Food Chem. 1985, 33, 953.

24. Santos, M. S. F.; Alves, A.; Madeira, L. M.; Chem. Eng. J. 2011, 175, 279.

25. Dhaouadi, A.; Adhoum, N.; J. Electroanal. Chem. 2009, 637, 33.

26. Dhaouadi, A.; Adhoum, N.; Appl. Catal., B 2010, 97, 227.

27. Trovó, A. G.; Paterlini, W. C.; Nogueira, R. F. P.; J. Hazard. Mater. 2006, 137, 1577.

28. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Sirtori, C.; Malato, S.; Water Res. 2009, 43, 3922.

29. Trovó, A. G.; Nogueira, R. F. P.; J. Braz. Chem. Soc. 2011, 22, 1033.

30. Trovó, A. G.; Silva, T. F. S.; Gomes Jr., O.; Machado, A. E. H.; Borges Neto, W.; Muller Jr., P. S.; Daniel, D.; Chemosphere, 2013, 90, 170.

31. Oliveira, D. F. M.; Batista, P. S.; Muller Jr., P. S.; Velani, V.; França, M. D.; de Souza, D. R.; Machado, A. E. H.; Dyes Pigm. 2012, 92, 563.

32. Machado, A. E. H.; de Miranda, J. A.; de Freitas, R. F.; Mendonça-Duarte, E. T. F.; Ferreira, L. F.; Albuquerque, Y. D. T.; Ruggiero, R.; Sattler, C.; de Oliveira, L.; J. Photochem. Photobiol., A 2003, 155, 231.

33. Machado, A. E. H.; França, M. D.; Velani, V.; Magnino, G. A.; Velani, H. M. M.; Freitas, F. S.; Müller Jr.; P. S.; Sattler, C.; Schmücker, M.; Int. J. Photoenergy 2008, DOI 10.1155/2008/482373

34. Vogel, F.; Harf, J.; Hug, A.; Von Rohr, P. R.; Water Res. 2000, 34, 2689.

35. Duarte, E. T. F. M.; Xavier, T. P.; de Souza, D. R.; de Miranda, J. A.; Machado, A. E. H.; Jung, C.; de Oliveira, L.; Sattler, C; Quim. Nova 2005, 28, 921.

36. Malato, S.; Blanco, J.; Vidal, A.; Richter, C.; Appl. Catal., B. 2002, 37, 1.

37. Nogueira, R. F. P.; Oliveira, M. C.; Paterlini, W. C.; Talanta 2005, 66, 86.

38. American Public Health Association (APHA); Standard Methods for the Examination of Water and Wastewater, 16^th ed.; APHA: Washington: USA, 1985.

39. Nogueira, R. F. P.; Trovó, A. G.; Modé, D. F.; Chemosphere 2002, 48, 385.

40. Zapata, A.; Velegraki, T.; Sánchez-Pérez, J. A.; Mantzavinos, D.; Maldonado, M. I.; Malato, S.; Appl. Catal., B 2009, 88, 448.

41. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Sirtori, C.; Malato, S.; Water Res. 2009, 43, 3922.

42. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Malato, S.; Water Res. 2011, 45, 1394.

43. Cassano, D.; Zapata, A.; Brunetti, G.; Del Moro, G.; Di laconi, C.; Oller, I.; Malato, S.; Mascolo, G.; Chem. Eng. J. 2011, 172, 250.

44. Wang, C. W.; Fu, H. X.; Lu, Y.; Zhao, X. F.; Environ. Eng. Sci. 2012, 29, 248.

45. Keskin, T.; Tutuk, F.; Azbar, N.; Chem. Biochem. Eng. Q. 2012, 26, 23.

46. Elmolla, E. S.; Chaudhuri, M.; Desalination 2012, 285, 14.

Submitted: September 23, 2012

Published online: February 7, 2013

• ¹
  http://portal.anvisa.gov.br/wps/content/anvisa+portal/anvisa/sala+de+imprensa/menu+-+noticias+anos/2012+noticias/seminario+volta+a+discutir+mercado+de+agrotoxicos+em+2012 acessed in November 2012.
  » link
• ²
  http://portal.anvisa.gov.br/wps/wcm/connect/7bfd7800474594009b90df3fbc4c6735/P01++Paraquate.pdf?MOD=AJPERES accessed in November 2012
  » link
• 3. Cheah, U-B.; Kirkwood, R. C.; Lum, K.-Y.; J. Agric. Food Chem. 1998, 46, 1217.
• 4. Wang, Y.; Yen, J.; Hsien, Y.; Chen, Y.; Water, Air, Soil Pollut. 1994, 72, 1.
• 5. Tomlim, C. D. S.; The Pesticide Manual, 12^th ed.; British Crop Protection Council: UK, 2000.
• 6. Vidal, J. L. M.; Vega, A. B.; López, F. J. S.; Frenich, A. G.; J. Chromatogr., A 2004, 1050, 179.
• 7. Fernández, M.; Ibáñez, M.; Picó, Y.; Mañes, J.; Arch. Environ. Contam. Toxicol. 1998, 35, 377.
• 8. Alberdi, J. L.; Saenz, M. E.; DiMarzio, W. D.; Tortorelli, M. C.; Bull. Environ. Contam. Toxicol. 1996, 57, 229.
• 9. Ruiz, M. J.; López-Jaramillo, L.; Redondo, M. J.; Font, G.; Bull. Environ. Contam. Toxicol. 1997, 59, 619.
• 10. Qian, H. F.; Chen, W.; Sun, L. W.; Jin, Y. X.; Liu, W. P.; Fu, Z. W.; Ecotoxicology 2009, 18, 537.
• 11. Mohammad, M.; Itoh, K.; Suyama, K.; Arch. Environ. Contam. Toxicol. 2010, 58, 605.
• 12. Jamers, A.; De Coen, W.; Environ. Toxicol. Chem. 2010, 29, 893.
• 13. Malato, S.; Fernández-Ibáñez, P.; Maldonado, M. I.; Blanco, J.; Gernjak, W.; Catal. Today 2009, 147, 1.
• 14. Zapata A.; Oller, I.; Sirtori, C.; Rodríguez, A.; Sánchez-Pérez, J. A.; López, A.; Mezcua, M.; Malato, S.; Chem. Eng. J. 2010, 160, 447.
• 15. Pintor, A. M. A.; Vilar, V. J. P.; Boaventura, R. A. R.; Sol. Energy 2011, 85, 579.
• 16. Safarzadeh-Amiri, A.; Bolton, J. R.; Carter, S. R.; J. Adv. Oxid. Technol. 1996, 1, 8.
• 17. Tennakone, K.; Kottegoda, I. R. M.; J. Photochem. Photobiol., A 1996, 93, 79.
• 18. Moctezuma, E.; Leyva E.; Monreal, E.; Villegas, N.; Infante, D.; Chemosphere 1999, 39, 511.
• 19. Lee, J. C.; Kim, M. S.; Kim, C. K.; Chung, C. H.; Cho, S. M.; Han, G. Y.; Yoon, K. J.; Kim, B. W.; Korean J. Chem. Eng. 2003, 20, 862.
• 20. Lee, J-C.; Kim, M-S.; Kim, B-W.; Water Res. 2002, 36, 1776.
• 21. Florencio, M. H.; Pires, E.; Castro, A. L.; Nunes, M. R.; Borges, C.; Costa, F. M.; Chemosphere 2004, 55, 345.
• 22. Ruth, J. M.; Kearney, P. C.; Zeng, Q.; Chemosphere 1985, 14, 1181.
• 23. Kearney, P. C.; Ruth, J. M.; Zeng, Q.; Mazzocchi, P.; J. Agric. Food Chem. 1985, 33, 953.
• 24. Santos, M. S. F.; Alves, A.; Madeira, L. M.; Chem. Eng. J. 2011, 175, 279.
• 25. Dhaouadi, A.; Adhoum, N.; J. Electroanal. Chem. 2009, 637, 33.
• 26. Dhaouadi, A.; Adhoum, N.; Appl. Catal., B 2010, 97, 227.
• 27. Trovó, A. G.; Paterlini, W. C.; Nogueira, R. F. P.; J. Hazard. Mater. 2006, 137, 1577.
• 28. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Sirtori, C.; Malato, S.; Water Res. 2009, 43, 3922.
• 29. Trovó, A. G.; Nogueira, R. F. P.; J. Braz. Chem. Soc. 2011, 22, 1033.
• 30. Trovó, A. G.; Silva, T. F. S.; Gomes Jr., O.; Machado, A. E. H.; Borges Neto, W.; Muller Jr., P. S.; Daniel, D.; Chemosphere, 2013, 90, 170.
• 31. Oliveira, D. F. M.; Batista, P. S.; Muller Jr., P. S.; Velani, V.; França, M. D.; de Souza, D. R.; Machado, A. E. H.; Dyes Pigm. 2012, 92, 563.
• 32. Machado, A. E. H.; de Miranda, J. A.; de Freitas, R. F.; Mendonça-Duarte, E. T. F.; Ferreira, L. F.; Albuquerque, Y. D. T.; Ruggiero, R.; Sattler, C.; de Oliveira, L.; J. Photochem. Photobiol., A 2003, 155, 231.
• 33. Machado, A. E. H.; França, M. D.; Velani, V.; Magnino, G. A.; Velani, H. M. M.; Freitas, F. S.; Müller Jr.; P. S.; Sattler, C.; Schmücker, M.; Int. J. Photoenergy 2008, DOI 10.1155/2008/482373
• 34. Vogel, F.; Harf, J.; Hug, A.; Von Rohr, P. R.; Water Res. 2000, 34, 2689.
• 35. Duarte, E. T. F. M.; Xavier, T. P.; de Souza, D. R.; de Miranda, J. A.; Machado, A. E. H.; Jung, C.; de Oliveira, L.; Sattler, C; Quim. Nova 2005, 28, 921.
• 36. Malato, S.; Blanco, J.; Vidal, A.; Richter, C.; Appl. Catal., B. 2002, 37, 1.
• 37. Nogueira, R. F. P.; Oliveira, M. C.; Paterlini, W. C.; Talanta 2005, 66, 86.
• 39. Nogueira, R. F. P.; Trovó, A. G.; Modé, D. F.; Chemosphere 2002, 48, 385.
• 40. Zapata, A.; Velegraki, T.; Sánchez-Pérez, J. A.; Mantzavinos, D.; Maldonado, M. I.; Malato, S.; Appl. Catal., B 2009, 88, 448.
• 41. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Sirtori, C.; Malato, S.; Water Res 2009, 43, 3922.
• 42. Trovó, A. G.; Nogueira, R. F. P.; Aguera, A.; Fernandez-Alba, A. R.; Malato, S.; Water Res 2011, 45, 1394.
• 43. Cassano, D.; Zapata, A.; Brunetti, G.; Del Moro, G.; Di laconi, C.; Oller, I.; Malato, S.; Mascolo, G.; Chem. Eng. J. 2011, 172, 250.
• 44. Wang, C. W.; Fu, H. X.; Lu, Y.; Zhao, X. F.; Environ. Eng. Sci. 2012, 29, 248.
• 45. Keskin, T.; Tutuk, F.; Azbar, N.; Chem. Biochem. Eng. Q. 2012, 26, 23.
• 46. Elmolla, E. S.; Chaudhuri, M.; Desalination 2012, 285, 14.

Publication Dates

• Publication in this collection
  28 Feb 2013
• Date of issue
  Jan 2013

History

• Received
  23 Sept 2012
• Accepted
  07 Feb 2013