Preparation and evaluation of hydrocalumite-iron oxide magnetic intercalated with dodecyl sulfate for removal of agrichemicals

Journal of Environmental Management 255 (2020) 109845

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Research article

Preparation and evaluation of hydrocalumite-iron oxide magnetic intercalated with dodecyl sulfate for removal of agrichemicals Jaderson Lopes Milagres a, Carlos Roberto Bellato a, *, Sukarno Olavo Ferreira b, ~es b Luciano de Moura Guimara a b

Department of Chemistry, Universidade Federal de Viçosa, Av. PH Holfs, s/n, 36570-900, Viçosa, Minas Gerais, Brazil Department of Physics, Universidade Federal de Viçosa, Av. PH Holfs, s/n, 36570-900, Viçosa, Minas Gerais, Brazil

A R T I C L E I N F O

A B S T R A C T

Keywords: Layered double hydroxides Hydrocalumite intercalated surfactants Adsorption isotherm Kinetics Magnetic separation Agrochemical removal

The magnetic adsorbent prepared with hydrocalumite-iron oxide (HC/Fe) modified with dodecyl sulfate (DS) was examined for the removal of the agrichemicals atrazine (ATZ) and chlorpyrifos (CPF) from aqueous solution. The adsorbent HC-DS/Fe was characterized by infrared spectroscopy (IR), Raman spectroscopy, X-ray diffrac­ tometry (XRD) and atomic absorption spectrometry. The effects of adsorbent dosage, contact time, pH and initial concentration of ATZ and CPF were evaluated. HC-DS/Fe presented a maximum adsorption capacity for ATZ of 4.5 mg g 1 (30 min) and for CPF of 72.9 mg g 1 (210 min) at 25 � C. HC-DS/Fe can be readily removed from the aqueous solution by magnetization because of its magnetic properties. The free energy variation for HC-DS/Fe during the adsorption of the ATZ was 48.78 to 53.91 kJ mol 1 and for the CPF of 55.79 to 59.28 kJ mol 1, suggesting the spontaneity of the adsorption process. The positive value of △H suggests an endothermic process for the interaction of ATZ and CPF by HC-DS/Fe. This adsorbent showed satisfactory results when used in the treatment of a sample of river water, fortified with the agrichemicals chlorpyrifos, atrazine, thiamethoxam and acetamiprid.

1. Introduction Insecticides and herbicides are high toxicity chemical compounds that act in agricultural production systems, in the control of insects and weeds (Hazer et al., 2017). The herbicide atrazine (ATZ), a type of triazine, is widely used in the control of weeds in the production of corn, sugarcane and sorghum (DENG et al., 2007; Souza et al., 2016). Has great potential for leaching and high chemical stability in soils and waters (Bia et al., 2017; Chen et al., 2009). In addition, it has a relatively high solubility in water (32 mg L 1), and its presence can cause toxic effects in humans and microorganisms (Nwani et al., 2010). Chlorpyrifos (CPF) is registered for the control of several insects, which attack different crops such as corn, soybean, wheat, sorghum, beans, coffee and ^ncia Sanita �ria, 2015). Chlorpyrifos, others (Ag^ encia Nacional de Vigila an organophosphate insecticide, can cause toxic effects when absorbed, because it acts on the nervous system causing nausea, dizziness, confusion and at very high exposures, respiratory paralysis and death. (USEPA, 2015). A large number of agrichemicals (atrazine, thiamethoxam,

acetamiprid and others) can be transported dissolved in water, contaminating surface and groundwater. Some agrichemicals such as chlorpyrifos have high affinity for soil organic matter, not being a po­ tential groundwater contaminant, but a surface water contaminant when transported superficially associated with soil organic matter (Dores and De-lamonica-freire, 2001). Several studies that involve the adsorption of agrichemicals to their � et al., water removal, use materials such as activated carbon (Llado 2015), organic waste, (Chaparadza and Hossenlopp, 2012; Mandal et al., 2017; Mandal and Singh, 2016), soil (Jeong and Selim, 2011; Liu et al., 2006; Yue et al., 2017), chemically modified minerals (Grundgeiger et al., 2015; Jain et al., 2017; Park et al., 2014), carbon nanotubes (Chen et al., 2009; Tang et al., 2012; Wei et al., 2017), among others, being an effective, easy to handle and efficient method. Layered double hydroxides (LDHs), such as hydrocalumite (HC), with a two-dimensional structure composed of Ca2þ, Al3þ and OH , can be obtained from the cement and refinery production of bauxite (Palmer et al., 2009; Xu et al., 2009). The HC allows the incorporation of anionic surfactants such as dodecyl sulfate (DS) in its interlayered space, making

* Corresponding author. E-mail address: [email protected] (C.R. Bellato). https://doi.org/10.1016/j.jenvman.2019.109845 Received 27 June 2019; Received in revised form 4 October 2019; Accepted 7 November 2019 Available online 25 November 2019 0301-4797/© 2019 Elsevier Ltd. All rights reserved.

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Journal of Environmental Management 255 (2020) 109845

it an organocomposite (Miranda et al., 2014; Zhang et al., 2015). The hydrophobic nature and the accessibility of the interlamellar region of the organocomposites make these candidate materials promising for the adsorption of the agrichemicals of the solution (Bruna et al., 2012; Jain et al., 2017; Miranda et al., 2014). In addition, the incorporation of iron oxide in LDH ensures the easy removal of the adsorbent from aqueous solution by the application of a magnetic field, which reduces the costs and time spent for the recovery of the adsorbent material (Marques Neto et al., 2017). In this work the hydrocalumite (HC) organocomposite intercalated with the surfactant dodecyl sulfate (DS) was prepared. In the HC-DS was deposited iron oxide magnetic (HC-DS/Fe) allowing its removal of the aqueous solution. To the best of our knowledge, the adsorbent HC-DS/Fe synthesized in this work has not been reported in the literature, as well as its use in the adsorption of water agrichemicals. In the literature it is scarce the use of LDHs for the removal of agrichemicals, mainly when associated with magnetic properties. Thus, the following steps were evaluated in this study: (1) to synthesize the organocomposite with dodecyl sulfate surfactant (DS) intercalated in HC, which contains the magnetic properties of iron oxide, (2) to propose a possible mechanism of interaction between the ATZ and CPF and the HC-DS/Fe and (3) to evaluate the adsorption performance of HC-DS/Fe in removing different groups of agrichemicals of a river water sample, i.e., the ATZ (triazine) and CPF (organophosphate) with neonicotinoids, thiamethoxam (TMT) and acetamiprid (ACM)).

and 0.0554 g of iron oxide under stirring. After this period, the formed precipitate remained under stirring for 18 h and then filtered, kept in an oven at 70 � C for 12 h, macerated and passed through a 200 mesh sieve (0.074 mm). 2.2.3. Characterization of HC-DS/Fe The samples were characterized by infrared spectroscopy (Varian 660-IR) in the region of 400–4000 cm 1, with attenuated reflectance accessory PikeGladiATR. In the Raman scattering analyzes, the Renishaw InVia micro Raman spectrometer was used, argon laser (785.0 nm) and 50� objective (NA ¼ 0.75), which corresponds to a spot of approximately 1 μm in diameter and 1 cm 1 spectral resolution. Due to the effect of fluorescence, the powers used in the Raman scatterings did not exceed 1.6 mW. In X-ray diffraction (D8 DISCOVER (BRUKER)) Cukα radiation (λ ¼ 1.5418 Å) with angular variation of 1–50� (2θ) was used. To determine the calcium, aluminum and iron content in the ad­ sorbents, 12 mL of aqua regia, HNO3: HCl (1:3 v/v), were added to samples of 0.100 g of each material (HC, HC-DS and HC-DS/Fe). Sub­ sequently, the samples were submitted to digestion in an industrial microwave oven (Milestone) in two stages of heating, the first with a heating slope of 10 min–220 � C (1200 W) and the second stage main­ taining the same temperature for 20 min (1200 W). Thereafter, the digested samples were diluted and the concentration of the metal determined by atomic absorption spectrometry. The agrichemicals were analyzed in an AGILENT liquid chromato­ graph, model 1260 (infinity), equipped with linear array detector (HPLC-DAD) at the wavelength of 200, 222, 245 and 252 nm for CPF, ATZ, ACM and TMT, respectively. The column used was a Zorbax Eclipse Plus® C18 (4.6 � 150 mm, 5.0 μm) reverse phase. The run conditions were in the proportion of water:acetonitrile (40:60) (v/v) solvent to the ATZ, with retention time of 5.3 min; water:acetonitrile (20:80) (v/v) for CPF, with retention time of 9.9 min and water:methanol (45:55) (v/v) for ACM and TMT, with retention time of 4.1 and 3.2, respectively. The column temperature was 30 � C, mobile phase velocity of 1.0 mL min 1 and the injection volume was 20 μL. The linear working range was 0.050–2.000 mg L 1 for all agrichemicals with an R2 � 0.998 (Figure S1 in the supplemental material). The limit of detection (LD) and quanti­ fication (LQ) was calculated according to the method based on param­ eters of the analytical curve, i.e., the standard deviation of the blank divided by the angular coefficient of the analytical curve multiplied by 3.3 for LD or 10 for LQ, respectively. The values found for LD and LQ were 0.4 and 1.4 μg L 1 for ATZ, 7.1 and 23.5 μg L 1 for CPF, 0.7 and 2.6 μg L 1 for ACM and 1.1 and 3.8 μg L 1 for TMT, respectively (Ribani et al., 2004).

2. Materials and methods 2.1. Materials All solutions were prepared with analytical grade reagents (NaOH, NaCl, CaCl2, AlCl3.6H2O, FeCl3.6H2O, FeSO4.7H2O, sodium dodecyl sulfate (C12H25NaO4S, Sigma Aldrich) in high purity deionized water produced by a Milli-Q® system (Millipore, Bedford, MA, USA). The agrichemicals used were Atrazine (C8H14ClN5, Sigma Aldrich), Chlor­ pyrifos (C9H11Cl3NO3PS, Sigma Aldrich), Acetamiprid (C10H11ClN4, Sigma Aldrich) and Thiamethoxam (C8H10ClN5O3S, Sigma Aldrich). Stock solution of Atrazine (1000 mg L 1) and Chlorpyrifos (1000 mg L 1) were prepared using acetone. Stock solution of Thiamethoxam (1000 mg L 1) and Acetamiprid (1000 mg L 1) were prepared in deionized water. All stock solutions were kept at 4 � C and protected from light to prevent agrichemical degradation. 2.2. Methods

2.2.4. Adsorption studies The adsorption studies of ATZ and CPF were performed in batch in a controlled temperature bath. The experiments were carried out in trip­ licate using 10.0 mL of solutions of 10 mg L 1 of ATZ or 25 mg L 1 of CPF in pH equal to 7. In the study of the molar ratio of calcium:dodecyl sulfate (Ca:DS) and iron oxide:calcium chloride (Fe:CaCl2) mass ratio, an adsorbent dosage of 4.0 g L 1 in the solutions of ATZ and 0.5 g L 1 in the solutions of CPF was used. The dose effect of the adsorbent was evalu­ ated by varying the amount of adsorbent mass from 10 to 100 mg for ATZ and from 1 to 40 mg for CPF. In the kinetic study, the optimum dosage of the adsorbent was used, and the samples containing ATZ and CPF were kept under agitation for different times (10–420 min). The isothermal studies were performed using solutions of ATZ at concen­ trations of 0.1 mg L 1 (4.7 � 10 4 mmol L 1) at 75.0 mg L 1 (3.5 � 10 1 mmol L 1) or CPF at concentrations of 0.1 mg L 1 (2.8 � 10 4 mmol L 1) at 100.0 mg L 1 (3.8 � 10 1 mmol L 1). In order to evaluate the effect of the temperature on the adsorption process, the isotherms were conducted for 4 h at temperatures of 25, 30, 35 and 40 � C. After obtaining the optimum conditions, the adsorbent (HC, 103-HC-DS or 103-HC-DS/Fe-5) was applied in a fortified river water sample with the 0.1 mg L 1 and 1 mg L 1 in mixture of each of the agrichemicals (CPF,

2.2.1. Preparation of iron oxide The iron oxide used in the synthesis of the organocomposite HC-DS/ Fe was synthesized according to the method described by Toledo and Bellato, 2011. A solution containing 1.6 L of water, 2.0 g of FeCl3.6H2O and 4.8 g FeSO4.7H2O was heated to 70 � C. Then, 120 mL of 5 mol L 1 of NaOH was added to precipitate the iron oxide. The solid obtained was washed with water to pH 7.0, then dried at 70 � C for 18 h. 2.2.2. Synthesis of HC-DS/Fe organocomposite The preparation of HC-DS/Fe was carried out by the co-precipitation method, in the molar ratio Ca:Al equal to 3:1, in the Ca:DS molar ratios of 10:0; 10:1; 10:2; 10:3; 10:4 and 10:5 and in the iron oxide mass:CaCl2 ratio of 2.5; 5.0; 10.0; 20.0 and 30.0%. The obtained adsorbent was labeled as X-HC-DS/Fe–Y, where X ¼ 100; 101; 102; 103, 104 and 105 represents the ratios of Ca:DS and Y ¼ 2.5; 5; 10; 20 and 30 represents the ratios of iron oxide:CaCl2. Thus, in the synthesis of 103-HC-DS/Fe-5, a solution containing 1.1099 g of CaCl2 and 0.8048 g of AlCl3.6H2O diluted in 100 mL of deionized water and slowly added by means of a peristaltic pump (Gil­ son®, model Minipuls 3) to a flow of 1 mL min 1 to 300 mL of a solution containing 1.2000 g of NaOH, 0.8652 g of sodium dodecyl sulfate (SDS) 2

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ATZ, TMT and ACM). 2.2.5. Desorption In the adsorption/desorption process of the adsorbent (103-HC-DS/ Fe-5) for the removal of ATZ and CPF, studies were performed with three consecutive cycles. In each cycle, 350 mg or 50 mg of the adsorbent was added in 50 mL of solutions containing 10 mg L 1 of ATZ or 25 mg L 1 of CPF, respectively, kept under stirring for 4 h. Then the adsorbent satu­ rated with ATZ or CPF was separated from the solution by magnetiza­ tion, washed with deionized water and placed in contact with 10 mL ethanol desorbing solution, and kept under stirring for 4 h. The con­ centration of ATZ and CPF was determined in each cycle by HPLC-DAD. After each desorption cycle, the adsorbent was washed with deionized water to provide reconditioning for the next cycle.

Fig. 2. Removal of the agrichemicals ATZ and CPF with 104-HC-DS-Fe-Y, where Y are the iron mass percentages. Experimental conditions: Agitation time of 7 h, solution in pH 7.0 and temperature 25 � C. ATZ: Concentration 10 mg L 1 and adsorbent dosage 4 g L 1; CPF: Concentration 25 mg L 1 and adsorbent dosage 0.5 g L 1.

3. Results and discussion 3.1. Effect of iron oxide

3.2. Effect dodecyl sulfate

In the diffractograms of Fig. 1, it can be seen that the peaks at 25.2 Å (001) and 12.5 Å (002) for the interlamellar distance of 104-HC-DS were maintained in all proportions of iron oxide studied (Kopka et al., 1988; Meyn et al., 1990). In the diffractogram, peaks of 2.9 Å (220) and 2.5 Å (311) are observed for the of iron oxide (Marques Neto et al., 2017). It is observed that the peaks related to iron oxide have their signal intensity increased with the increase in the amount of the iron oxide. Therefore, iron oxide did not alter the interlamellar distance of 104-HC-DS, and it can be concluded that its deposition may occur on the lamellae of HC. In Fig. 2 it is observed that the pure iron oxide presents low adsorption capacity, with values of 3.0 and 4.7% for ATZ and CPF, respectively. The increase in the amount of iron oxide up to the 5.0% ratio (104-HC-DS/Fe-5), allows a more pronounced adsorption gain for ATZ than for CPF, i.e., 8.4% and 63.9% in 104-HC-DS/Fe-0 to 43.3% and 79.2% in 104-HC-DS/Fe-5, respectively. Iron oxide present in larger amounts (104-HC-DS/Fe-10, 20 or 30) possibly obstructs the adsorption sites, reducing the adsorption capacity of the agrichemicals. Thus, in the later studies the proportion of 5.0% of iron oxide was used for the removal of the agrichemicals from the aqueous solution.

In the diffractograms of Fig. 3, is verified in the 100-HC-DS/Fe-5 (HC without DS) the presence of the diffraction peaks 7.9 Å (11.20� ), 3.9 Å (22.70� ) and 3.8 Å (23.20� ), referring to HC intercallated with chloride in its interlamellar space (Milagres et al., 2017). In the adsorbents 101-HC-DS/Fe-5 and 102-HC-DS/Fe-5, the presence of DS in HC de­ creases the intensity of the peak 7.90 Å (11.20� ) and increases the peak intensity 32.7 Å (2.70� ). This peak possibly refers to a DS bilayer distributed at a 40� orientation with respect to the HDL plane. The in­ crease of DS in the solution (103-HC-DS/Fe-5, 104-HC-DS/Fe-5 and 105-HC-DS/Fe-5) displaces peak 32.7 Å (2.70� ) to 25.2 Å (3.50� ), due to the formation of a possible DS mono-layer structure in a 90� orientation with respect to the HDL plane (Kopka et al., 1988; Meyn et al., 1990). In the synthesis of 105-HC-DS/Fe-5, where there is an excess of DS in so­ lution, the formation of calcium dodecyl sulfate (CaDS) occurs, which is verified in the diffractogram by peaks with distances of 30.5 Å (2.90� ), 15.2 Å (5.85� ) and 10.1 Å (8.80� ). (Dutta and Pramanik, 2013). In Fig. 4, it can be seen that from 100-HC-DS/Fe-5 to 103-HC-DS/Fe-

Fig. 3. X-ray diffractograms of X-HC-DS/Fe-5, where X are the molar ratios between Ca:DS. � Hydrocalumite intercalated with dodecyl sulfate (HC-DS); ● Calcium dodecyl sulfate (CaDS); ◈ Hydrocalumite intercalated with chloride (HC); ✸ Signal of the apparatus; ◆ Calcium carbonate (CaCO3).

Fig. 1. X-ray diffractograms of 104-HC-DS/Fe–Y, where Y are the mass per­ centages of iron oxide. � 104-HC-DS; ■ Iron Oxide. 3

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chain. In previous studies we have seen that adsorption of ATZ increases when iron oxide is added in HC-DS (103-HC-DS/Fe-5), which is due to the hydrogen bond interactions occurring between amino groups of the side chain (N-H) of ATZ with the Fe–OH group of iron oxide (Chappell et al., 2005). The presence of the band at the N-H-stretch of the amine groups of the ATZ was not observed in the region close to 3252 cm 1 in the spectrum of 103-HC-DS/Fe-5 with ATZ, because in this region there was a widening of the spectrum from the presence of water molecules in the adsorbent. – S– –O Fig. 5-B shows a shift of the band at 1195 cm 1 from the O– group (Lee et al., 2011) of 103-HC-DS/Fe-5 to 1201 cm 1 after adsorption of CPF. This indicates that a change occurred in the vibra­ tional mode of the –OSO-3 group of DS, after adsorption of CPF. This and other interactions between DS and CPF can also be found in studies performed by Raman spectroscopy in Fig. 6 and Fig. 7. The most intense peaks obtained in the Raman spectra (Fig. 6) are represented in Table S2 (supplementary material) with their respective vibrational modes, as described in the literature (Burrueco et al., 2013; Chaparadza and Hossenlopp, 2012; Jeong and Selim, 2011; Miranda et al., 2014; Nwani et al., 2010; Tette, 2016; Liu et al., 2016). Fig. 6A shows that between the Raman spectrum of 103-HC-DS and 103-HC-DS/Fe-5 differences occur in some of its signals. In these spectra we observe shifts of the primary peaks 1132 and 1297 cm 1 of the DS – O, and a displacement of that refer to the vibrational modes C–C and S– the band in 675 cm 1 of the pure iron oxide to 667 cm 1 of iron oxide in 103-HC-DS/Fe-5. This is due to the interactions that occurring between the iron oxide and the –OSO-3 group of the DS of the 103-HC-DS/Fe-5. In Fig. 6-A no changes in peak positions were observed after ATZ or CPF adsorption in 103-HC-DS/Fe-5. However, in Fig. 6-B it is observed that in the overlapping of the spectra 103-HC-DS/Fe-5 and 103-HC-DS/ Fe-5 with CPF, there is only an increase in the relative intensity of the peak referring to the C–C stretch of the DS. A further change in the signals of these spectra (103-HC-DS/Fe-5 and 103-HC-DS/Fe-5 with

Fig. 4. Removal of the agrichemicals ATZ and CPF with the X-HC-DS/Fe-5, where X are the molar ratios between Ca:DS. Experimental conditions: Agita­ tion time of 7 h, solution in pH 7.0 and temperature 25 � C. ATZ: Concentration 10 mg L 1 and adsorbent dosage 4 g L 1; CPF: Concentration 25 mg L 1 and adsorbent dosage 0.5 g L 1.

5 a gain occurs in adsorption of ATZ and CPF from the solution, i.e., 6.7% and 53.7% in 100-HC-DS/Fe-5 to 46.0% and 75.0% in 103-HC-DS/ Fe-5, respectively. For the adsorbent 105-HC-DS/Fe-5, removal values of 30.3% ATZ and 58.6% CPF were found, being lower than that found by 103-HC-DS/Fe-5. In the synthesis of 105-HC-DS/Fe-5 the formation of CaDS occurred, which provided the reduction in adsorption of ATZ and CPF. This is because CaDS does not adsorb the ATZ and CPF of aqueous solution. This shows us that DS when present in the interlamellar region of HC results in a significant improvement in the removal of the agri­ chemicals (ATZ and CPF) from the solution. 3.3. Characterization of material Table S1 (supplementary material) summarizes some elementary information of the adsorbents HC, 103-HC-DS and 103-HC-DS/Fe-5, which have the Ca:Al molar ratio of 2.85:1, 2.74:1 and 2.79:1, respec­ tively. The 103-HC-DS/Fe-5 showed that the presence of iron did not change Ca:Al molar ratio, also approaching the ratio of 3:1 of the pre­ cursor solutions. Fig. 5 shows the infrared spectra of the 103-HC-DS/Fe-5, ATZ and CPF separately and of the 103-HC-DS/Fe-5 with ATZ (Fig. 5-A) or CPF (Fig. 5-B) adsorbed. The chemical structures of ATZ and CPF are shown in Figure S2 in the supplementary material. Fig. 5-A shows that the band at 1540 cm 1 relative to the C¼N stretch of the ATZ triazine ring (Kumar et al., 2015) was shifted to 1580 cm 1 on the spectrum of 103-HC-DS/Fe-5 containing adsorbed ATZ. This displacement occurs due to a probable interaction of the C¼N of ATZ with the DS carbon

Fig. 6. (A) Raman spectrum of (a) 103-HC-DS, (b) Iron Oxide, (c) 103-HC-DS/ Fe-5, (d) CPF, (e) 103-HC-DS/Fe-5 with CPF; (f) 103-HC-DS/Fe-5 with ATZ; (B) Comparative Raman spectrum of 103-HC-DS/Fe-5 and 103-HC-DS/Fe-5 with CPF.

Fig. 5. Infrared spectrum of 103-HC-DS/Fe-5 and of the agrichemicals before and after the (A) Removal of ATZ and (B) Removal of CPF. 4

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CPF adsorption studies. The pH study on the removal of ATZ and CPF by 103-HC-DS/Fe-5 was evaluated in the pH range of 4 and 11 (Fig. 8). ATZ (weak base) with pKa ¼ 1.7 and CPF (very weak base) are in nonionic forms at pH values � 4. Therefore, ATZ and CPF agrichemicals in their nonionic forms are removed from the solution by interaction with 103-HC-DS/Fe5. In the pH range of 4 and 11 the removal of ATZ and CPF remained practically constant, being 73.5% and 99.0%, respectively. In the characterization by infrared and Raman, we observed that the adsorp­ tion process of ATZ and CPF with 103-HC-DS/Fe-5 occurs mainly by hydrophobic interaction with the DS carbon chain. Therefore, due to the hydrophobic character involved in the adsorption, the removal of ATZ and CPF did not change in the pH range of 4–11. 3.5. Adsorption kinetics Fig. 9-a shows that ATZ removal remains constant from 60 min for all concentrations studied, achieving a 60.0%–75.3% removal at concen­ trations of 1–25 mg L 1, respectively. In Fig. 9-b the CPF removal was kept constant from 60 min to 1 mg L 1 concentration and constant from 210 min to the concentrations of 5–25 mg L 1, obtaining a removal of about 99% for all concentrations studied. The adsorbent 103-HC-DS/Fe5 was efficient in the removal of ATZ and CPF agrichemicals, indepen­ dent of the concentration present in the aqueous solution. In this study, kinetic models were applied in the removal of ATZ and CPF agrichemicals at 1, 5, 10 and 25 mg L 1 concentration. The models used were pseudo-first order of Lagergren, pseudo-second order of Ho and McKay and pseudo-nth order. This kinetics models in non-linear form were applied using experimentally determined adsorption capac­ ity (qe exp), which can be better represented by the fraction of adsorption capacities (qt/qe exp), as shown in equations (1)–(3), respectively. Equations (1)–(3) should be used with the fraction of adsorption ca­ pacities (qt/qe exp) containing values below 1, i.e., with the kinetic data obtained before equilibrium (Simonin, 2016). Fig. 7. Deconvolution Raman spectrum of (a) 103-HC-DS/Fe-5, (b) 103-HCDS/Fe-5 dry, after be kept in aqueous solution by 7 hs; (c) CPF; (d) 103-HCDS/Fe-5 with CPF.

qt ¼1 qexp

expð k1 tÞ

qt k* t ¼ 2 qexp 1 þ k*2 t

CPF) can be seen in Fig. 7, where a more detailed analysis was made by means of the deconvolution Raman spectrum in the region of 950–1150 cm 1. In Fig. 7b and 7d it is found that after 103-HC-DS/Fe-5 is maintained in aqueous solution, a peak appears at 1085 cm-1 referent to the car­ bonate formed by the absorption of CO2 from the air and a displacement of the peak at 1076 cm 1 (Fig. 7a) relative to the S–O stretching of the DS to 1080 cm 1. This displacement is due to interactions occurring between the –OSO-3 group of DS and the adsorbed water molecules. In the adsorption of CPF on 103-HC-DS/Fe-5, it is verified that the peak – O is shifted from 1085 cm 1 (Figure 7a) to corresponding to the S– 1092 cm 1 (Fig. 7d), indicating an interaction between the –OSO-3 group of DS and the adsorbed CPF in 103-HC-DS/Fe-5. Therefore, the changes in DS signals after adsorption of CPF in 103-HC-DS/Fe-5, confirm that CPF is retained in the organocomposite by hydrophobic interaction with the DS carbon chain and also by interaction with the group –OSO-3 of DS.

qt ¼1 qexp

1 þ k*n t

(1) (2)

�1 1 n

(3)

1) where k2* ¼ k2qe; kn* ¼ (n-1)q(n kn; qt and qe exp (mg g 1) are e adsorbed amounts of agrichemical per unit mass at time t and obtained experimentally in equilibrium, respectively; k1, k2* and kn* (min 1) are the pseudo-first order, pseudo-second order and pseudo-nth order con­ stants; n is the order kinetic of the adsorption.

3.4. Effect of dosage and pH In the removal of ATZ and CPF agrichemicals different dosages of 103-HC-DS/Fe-5 were evaluated. In Figure S3 (supplementary material) a 75.5% removal of ATZ was observed for the 7.0 g L 1 dosage. Dosages greater than 7.0 g L 1 did not increase the percentage of removal, being the 7.0 g L 1 dose defined for subsequent ATZ adsorption studies. Figure S3 (supplementary material) shows also a removal of 99.0% CPF for the 1.0 g L 1 dose. Above 1.0 g L 1, the percentage of CPF removal remained constant, being the 1.0 g L 1 dosage defined for subsequent

Fig. 8. Effect of pH on the removal of the ATZ and CPF agrichemicals by 103HC-DS/Fe-5. Experimental conditions: Agitation time of 7 h and Temperature: 25 � C. ATZ: Concentration 10 mg L 1 and adsorbent dosage 7.0 g L 1; CPF: Concentration 25 mg L 1 and adsorbent dosage 1.0 g L 1. 5

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to 1.14, respectively. The adsorption kinetic order values (n) for ATZ decreased from 1 to 10 mg L 1, with values from 2.73 to 1.59, respec­ tively. When the concentration of ATZ increased from 10 mg L 1 to 25 mg L 1, the n-order model did not fit correctly which can be observed by increase of the value of the kinetic order (n). This shows that at low concentrations there is an increase in the rate of adsorption of the agrichemical by 103-HC-DS/Fe-5, as well in the constant kn* values, which indicates an increase in the rate of adsorption when the concen­ tration decreases. Figure S5 (supplementary material) shows that the graph of qt in function t0.5 has a multilinear characteristic, suggesting that the adsorption process occurs in three stages. The first stage occurred from 10 to 30 min being represented by a greater slope, which indicates a fast adsorption on the external surface of the adsorbent. The second stage from 30 to 60 min occurs a gradual adsorption of ATZ or CPF in the 103HC-DS/Fe-5, being the speed of this stage controlled by the process of intraparticle diffusion. In the latter step after 60 min the values of the adsorption rate decrease, indicating a reduction in the concentration gradient or a saturation of the adsorbent (Chen et al., 2016; Gokce and Aktas, 2014; Xiao et al., 2015; Zolgharnein et al., 2015). In Table 2, the value of 8.61 � 10 1 mg g 1 min 0.5 for ATZ and 2.50 mg g 1 min 0.5 for CPF was obtained for the constant C of the first stage of intraparticle diffusion. The value of C other than zero for the first stage, indicates the presence of other mechanisms involved in the rapid adsorption step. In the other stages, higher values were found for the constant C, due to a boundary layer resistant to the diffusion process, which provides a reduction in the rate of adsorption (Mandal et al., 2017; Toor and Jin, 2012; Xiao et al., 2015).

Fig. 9. Adsorption kinetics of removal of (a) ATZ at different concentrations and (b) CPF at different concentrations. Experimental conditions: Solution in pH 7.0 and temperature 25 � C. ATZ: adsorbent dosage 7.0 g L 1; CPF: adsorbent dosage 1.0 g L 1.

3.6. Adsorption isotherms

To better understand the reaction pathways and adsorption mecha­ nisms and predicting the rate-controlling step, the model of intraparticle diffusion of Weber and Morris (equation (4)) was used in the concen­ tration of 10 mg L 1 (Tran et al., 2017).

The adsorption isotherms of the ATZ and CPF agrichemicals can be represented by models of isotherms such as Langmuir and Freudlich, presented in equations (5) and (6), respectively (Limousin et al., 2007).

(4)

qt ¼ ki t0:5 þ C

qe ¼

where qt is adsorbed amount of agrichemical per unit mass at time t; ki (mg g 1 min 0.5) is the intraparticle diffusion constant and C is the boundary layer thickness of the adsorption. The kinetic models were applied for the removal of ATZ and CPF agrichemicals using the kinetic data obtained below 60 min (qt/qe exp <1), as shown in Figure S4. In Table 1 it can be observed that the kinetic models of pseudo-first order and pseudo-second order have determina­ tion coefficient (R2) greater than 0.92 for some agrichemical concen­ trations. Although these concentrations are well adjusted to R2, their residue distribution over time does not follow randomness and cannot properly explain the kinetic adsorption behavior. The pseudo-nth order model was the most appropriate to describe the ATZ and CPF adsorption by 103-HC-DS/Fe-5, presenting a good fit (R2 > 0.91) for all agri­ chemicals concentrations, with residues satisfactorily distributed over time. The adsorption kinetic order values (n) decreasing with increased concentration of CPF in the range of 1–25 mg L 1, with values from 1.77

qmax kL Ce 1 þ kL Ce

(5) (6)

qe ¼ kF Cne

Table 2 Kinetic parameters for the intra-particle diffusion of the adsorption of atrazine (ATZ) and chlorpyrifos (CPF) at concentration of the 10 mg L 1 (T ¼ 25 � C). kinetic model

Constants

Intra-particle diffusion

kd1/mg g C R12 kd2/mg g C R22 kd3/mg g C R23

ATZ 1

min

0.5

1

min

0.5

1

min

0.5

Table 1 Kinetic parameters for the adsorption of atrazine (ATZ) and chlorpyrifos (CPF) at concentrations of the 1, 5, 10 and 25 mg L Agrichemicals

Concentration/mg L

1

Pseudo-first order k1/min

ATZ

CPF

1.00 5.00 10.00 25.00 1.00 5.00 10.00 25.00

2.01 1.88 2.38 5.68 1.46 1.11 8.20 3.40

1

� 10 � 10 � 10 � 10 � 10 � 10 � 10 � 10

Pseudo-second order R2

1 1 1 2 1 1 2 2

k2*/min

2.14 0.73 0.75 0.64 0.55 0.71 0.83 0.99

6.72 � 6.11 � 1.19 1.21 � 4.32 � 2.77 � 1.86 � 5.84 �

6

1

10 10

1

10 10 10 10 10

1

1

1 1 1 2

1

3.98 � 10 8.61 � 10 0.98 1.90 � 10 1.06 0.99 2.00 � 10 1.08 0.93

CPF 2 1 3

4

1.13 2.50 0.99 2.60 � 10 7.32 0.99 1.63 � 10 9.60 0.90

1

2

(T ¼ 25 � C).

Pseudo-nth order R2

kn*/min

1

0.65 0.93 0.89 0.87 0.95 0.94 0.96 0.92

4.26 1.43 3.21 � 10 9.44 � 10 2.43 � 10 1.41 � 10 7.88 � 10 5.11 � 10

1 2 1 1 2 3

n

R2

2.73 2.34 1.59 1.86 1.77 1.70 1.60 1.14

0.91 0.99 0.96 0.84 0.97 0.96 0.99 0.99

J.L. Milagres et al.

Journal of Environmental Management 255 (2020) 109845

Table 4 Removal capacity of the agrichemicals by various materials and methods.

where, qe (mmol g 1) is the amount adsorbed at equilibrium; Ce (mmol L 1) the residual concentration at equilibrium; qmax (mmol g 1) is the maximum adsorption capacity; kL (L mmol 1) refers to the energy involved in the adsorption process; kF ((mmol g 1) (L mmol 1)1/n) is related to the adsorption capacity of the material; n refers to the het­ erogeneity of the energies of the adsorptive site. The experimental plot was obtained by plotting qe versus Ce and the values of the Langmuir and Freundlich constants were obtained by the non-linear regression method and presented in Table 3. In Table 3 the adsorption equilibrium data of ATZ and CPF by 103HC-DS/Fe-5 were adjusted to the two models studied, with the coeffi­ cient of determination (R2) greater than 0.98. The values of qmax ob­ tained in the Langmuir model were between 2.1 � 10 2 to 3.7 � 10 2 mmoL g-1 (4.53–7.98 mg g-1) for ATZ and 2.08 � 10 1 to 3.89 � 10 1 mmoL g-1 (72.92–136.38 mg g-1) for CPF, where the highest value was obtained at 40 � C, indicating that the adsorption of agrichemicals on 103-HC-DS/Fe-5 is more favorable at higher temperatures. The maximum adsorption capacities of these adsorbent presented satisfac­ tory performance for the removal of ATZ and CPF in comparison with other adsorbents (Table 4). (Liu et al., 2015; Mandal and Singh, 2016; Moradeeya et al., 2017; Narayanan et al., 2017; Park et al., 2014; Suciu and Capri, 2009; Wang et al., 2015; Zheng et al., 2019) In the adsorption process of ATZ and CPF the KL constant of the Langmuir model increased significantly with increasing temperature from 25 to 40 � C, obtaining values of 6.45–17.45 L mmol-1 for ATZ and 107.61–141.44 L mmol-1 for CPF, respectively. This indicates a gain in adsorbate-adsorbent binding energy with increasing solution tempera­ ture. For the Freundlich model, the temperature increase also provided an increase in KF values ranging from 4.00 � 10 2 to 6.20 � 10 2 for ATZ and from 5.68 � 10 1 to 3.42 for CPF. The values of n also increased with the temperature of 0.52–0.66 for ATZ and 0.40 to 0.60 for CPF, suggesting a heterogeneity in the energy of the adsorption sites of the adsorbent (Toledo et al., 2013).

Materials

Agrichemical removed

Removal capacity (mg g 1)

Ref.

Bark of Eucalyptus tereticornis L. Molecularly imprinted polymer Montmorillonitequaternary ammonium salts Carboxy methyl cellulose-nano organoclay 103-HC-DS/Fe-5 Biochars and low molecular weight organic acids Straw-derived biochar Nanocellulose

30.0

Imidacloprid; Atrazine

0.39; 0.94

4.0

Atrazine

0.39

Mandal and Singh (2016) Liu et al. (2015)

2.5–5.0

Atrazine; Imazaquin

2.61; 3.63

Park et al. (2014)

10.0

Imidacloprid; thiamethoxam; atrazine Atrazine Chlorpyrifos; Chlorpyrifosmethyl

2.00; 1.67; 1.43

Narayanan et al. (2017) This study Zheng et al. (2019)

–

Chlorpyrifos

16.6

2.0

Chlorpyrifos

12.32–7.25

Montmorillonitequaternary ammonium salts 103-HC-DS/Fe-5

5.0

Chlorpyrifos; Penconazole

8.32; 6.33

1.0

Chlopryrifos

72.90

ΔG∘ ¼ ΔH∘

ΔH ∘ RT

7.0 0.036–0.071

4.50 14.8; 50.5

Wang et al. (2015) Moradeeya et al. (2017) Suciu and Capri (2009) This study

(8)

TΔS∘

In Table 5 the positive values of △H indicate an endothermic adsorption process and values less than 20 kJ mol 1, as found for CPF (13.50 kJ mol 1), indicates that the adsorption process is physisorption, whereas for ATZ (53.04 kJ mol 1) the chemisorption process pre­ dominates (Miranda et al., 2014; Venugopal and Mohanty, 2011). The process of adsorption by physisorption of CPF by 103-HC-DS/Fe-5 is consistent with the characterizations obtained by infrared and Raman spectroscopy, which show that the CPF is retained in the DS carbon chain by hydrophobic interactions and by interactions with the –OSO-3 group of DS. ATZ is possibly adsorbed by hydrophobic interactions and hydrogen bonding interaction between the amino groups of its side chain (N–H) with the Fe–OH group of the iron oxide of the adsorbent. This may provide a strong interaction between ATZ and iron oxide, justifying the chemisorption involved in the adsorption process (Nasci­ mento et al., 2014; Yue et al., 2017). The positive value of △S suggests an increase in randomness at the liquid-solid interface. During the

The calculation of the thermodynamic parameters, such as free en­ ergy of Gibbs (△G), enthalpy variation (△H) and entropy variation (△S) were calculated from the values of the standard equilibrium constant k� obtained from the constant kL of the Langmuir isotherm at different temperatures. The constant k� is a dimensionless parameter, being necessary to correct the value of the kL (L mmol 1) constant of the Langmuir isotherm, multiplying its value by the factor (103 � 55.5) to obtain the thermodynamic adsorption parameters (△G, △H and △S) (Zhou and Zhou, 2014). Considering the Van Hoff equation, the values of △H and △S were determined from Equation (7). ΔS∘ R

Dosage (g L 1)

Gibbs variation, (△S (J mol 1 K 1) the entropy variation and △H (kJ mol 1) the enthalpy variation of the system. The relationship between △G, △H and △S is expressed by Equation (8).

3.7. Thermodynamic studies

lnk∘ ¼

Experimental conditions

(7)

Where k� is a dimensionless parameter, R is the gas constant (8.314 J mol 1 K 1), T is the temperature (K), △G (kJ mol 1) the free energy of

Table 3 Parameters calculated from isotherm models for the adsorption of atrazine (ATZ) and Chlorpyrif� os (CPF) in solution. Agrochemicals

Tem(K)

Langmuir constants qm�ax(mmol g 1)

ATZ

CPF

298 303 308 313 298 303 308 313

2.10 � 10 2.30 � 10 2.80 � 10 3.70 � 10 2.08 � 10 2.36 � 10 2.78 � 10 3.89 � 10

2 2 2 2 1 1 1 1

Freundlich constants kL(L mmol 6.45 8.77 13.50 17.45 107.61 121.40 127.61 141.44

7

1

)

R2

kF((mmol g 1) (L mmol 1)1/n)

0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99

4.00 � 4.20 � 4.80 � 6.20 � 5.68 � 7.64 � 1.15 3.42

10 10 10 10 10 10

2 2 2 2 1 1

n

R2

0.52 0.55 0.61 0.66 0.40 0.43 0.47 0.60

0.98 0.99 0.99 0.99 0.98 0.98 0.98 0.99

J.L. Milagres et al.

Journal of Environmental Management 255 (2020) 109845

Table 5 Thermodynamic parameters for Atrazine and Chlorpyrifos adsorption in 103-HC-DS/Fe-5. Agrichemical

CPF ATZ

△S (J mol

232.53 341.69

1

K

1

)

△H (kJ mol

1

)

△G (kJ mol

1

)

Temperature (K) 298 55.79 48.78

13.50 53.04

adsorption are displaced molecules of the solvent that gain more translational entropy than that lost by the adsorbed agrichemical, thus allowing prevail the randomness in the system (Helen Kalavathy and Miranda, 2010). The Gibbs energy variation for 103-HC-DS/Fe-5 during the adsorption of the CPF of 55.79 to 59.28 kJ mol 1 and for the ATZ was 48.78 to 53.91 kJ mol 1, suggesting the spontaneity of the adsorption process.

303 56.96 50.49

308 58.12 52.20

313 59.28 53.91

adsorbent for water treatment. 3.9. Application in water After evaluating the optimum adsorption conditions with ATZ and CPF, which belong to the triazine and organophosphate group, respec­ tively, the adsorbent (103-HC-DS/Fe-5) was applied in the simultaneous removal of four agrichemicals added in a river water sample. Thus, the sample was fortified with different groups of agrichemicals, being ATZ a triazine, CPF an organophosphate and thiamethoxam (TMT) and acet­ amiprid (ACM) both neonicotinoids. The chemical structures of ATZ, CPF, TMT and ACM are shown in Figure S2 in the supplementary material. The river water sample was fortified with a mixture of 0.1 mg L 1 or 1 mg L 1 of each of the agrichemicals (ATZ, CPF, TMT and ACM). The water sample was collected in Carmo River, located in the Iron Quad­ rangle - MG region. The sample was characterized physicochemically in situ by analyzes of temperature, dissolved oxygen, pH, electrical con­ ductivity, total dissolved solids and salinity, according to the procedure described by APHA (2005). In Table S3 (Supplementary material) con­ tains the physicochemical parameters obtained for the water sample. Fig. 11 shows the performance of HC, 103-HC-DS and 103-HC-DS/Fe-5 in the simultaneous removal of the agrichemicals contained in the river water sample. It is observed that the adsorbent HC allows to remove 20% or 32% of the CPF at concentrations 0.1 mg L 1 or 1.0 mg L 1, respectively. In Fig. 11, it is verified also that the removal of CPF was �100% for both adsorbents 103-HC-DS and 103-HC-DS/Fe-5, because CPF interacted by hydrophobic interaction with DS carbon chain and also by interaction with the group –OSO-3 of DS. In the removal of ATZ 0.1 mg L 1 (Fig. 11-a), it is observed that 103HC-DS and 103-HC-DS/Fe-5 removed 23% and 39%, respectively, i.e., a 16% increase in removal due to the presence of iron oxide. This increase

3.8. Reuse For the purpose of practical application, it is essential to evaluate the reusability and stability of the adsorbent. The HC-103-DS/Fe-5 after adsorption was placed in contact with 10 mL ethanol solution desorbing. Fig. 10-a shows that the adsorption efficiency of ATZ was 75% (7.5 mg L 1) in the first cycle, gradually decreasing to 43.7% (4.3 mg L 1) in the third cycle. Fig. 10-b shows that the adsorption efficiency of CPF was �100% (25 mg L 1) in the first cycle, gradually decreasing to 52.4% (13 mg L 1) in the third cycle. The integrity of the ATZ and CPF recovered was confirmed by the similarity of the HPLC-DAD and UV–Vis analyzes, with the standard solutions of these agrichemicals. Therefore, reuse studies show that 103-HC-DS/Fe-5 can be used repeatedly as an efficient

Fig. 11. Simultaneous adsorption of the different agrichemicals of river water sample by adsorbents (1) HC; (2) 103-HC-DS and (3) 103-HC-DS/Fe-5. Chlor­ pyrifos (CPF); Atrazine (ATZ); Thiamethoxam (TMT); Acetamiprid (ACM). Experimental conditions: Agitation time of 4 h, solution in pH 7.0 and tem­ perature 25 � C; Agrichemical concentration: (a) 0.1 mg L 1 and (b) 1.0 mg L 1; adsorbent dosage 7.0 g L 1.

Fig. 10. Adsorption/desorption cycles of the agrichemicals (a) ATZ and (b) CPF. Experimental conditions: Agitation time of 4 h, solution in pH 7.0 and temperature 25 � C. ATZ: Concentration 10 mg L 1 and adsorbent dosage 7.0 g L 1; CPF: Concentration 25 mg L 1 and adsorbent dosage 1.0 g L 1. 8

J.L. Milagres et al.

Journal of Environmental Management 255 (2020) 109845

occurs due to ATZ interacting with the DS carbon chain and the Fe–OH group of the iron oxide of the 103-HC-DS/Fe-5. It is observed (Fig. 11-a) also that TMT and ACM were not adsorbed by HC and showed similar adsorption behavior of 30% and 21% for 103-HC-DS and 35% and 23% for 103-HC-DS/Fe-5, respectively. The removal of the agrichemicals at concentration of 1 mg L 1 in the water samples (Fig. 11-b) by 103-HC-DS/Fe-5 was 61%, 50% and 31% for ATZ, TMT and ACM, respectively. It is observed that 103-HC-DS/Fe5 was more efficient in removing of the agrichemicals to the concen­ tration of 1 mg L 1 (Fig. 11-b) when compared to 0.1 mg L 1 (Fig. 11-a). When the adsorbent is used to remove lower concentrations of agri­ chemicals, possibly a competition of water molecules occurs by the adsorption sites of the adsorbent, reducing their removal capacity (Giles et al., 1960). The CPF presented a removal �100% for both concentra­ tions (0.1 and 1 mg L 1), because the hydrophobic interaction that oc­ curs with the carbon chain of the DS favors its removal when present at low concentrations. Thus, due to the magnetic characteristics, the 103-HC-DS/Fe-5 has the advantage of being easily removed from the aqueous solution by an external magnetic field, making it economically feasible for practical applications. The 103-HC-DS/Fe-5 was efficient in removing of the differents agrichemicals studied when present in a real water sample.

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4. Conclusions The magnetic adsorbent prepared with hydrocalumite, iron oxide and dodecyl sulfate (103-HC-DS/Fe-5) allowed the removal of the ag­ richemicals atrazine and chlorpyrifos with maximum efficiency in the pH range of 4–11. This result indicates that 103-HC-DS/Fe-5 can be used in the removal of atrazine and chlorpyrifos over a wide pH range. The maximum adsorption capacities calculated from the Langmuir model were 4.5 mg g 1 for ATZ and 72.9 mg g 1 for CPF at 25 � C. Thermo­ dynamic data indicate the spontaneity and endothermic nature of the adsorption process. The results of adsorption/desorption cycles showed a satisfactory removal in the third reuse cycle, i.e., 43.7% ATZ (10 mg L 1) and 52.4% CPF (25 mg L 1). The magnetic adsorbent can be removed from the aqueous solution by an external magnetic field, which makes it economically feasible in practical applications. The 103-HCDS/Fe-5 when applied in a sample of river water fortified with the 0.1 mg L 1 mixture of each of the agrichemicals chlorpyrifos (organo­ phosphate), atrazine (triazine), thiamethoxam and acetamiprid (neon­ icotinoids), removed �100%, 38%, 35% and 23%, respectively. These results showed that 103-HC-DS/Fe-5 can be used satisfactorily for the removal of the different agrichemicals when present in a sample of river water. Acknowledgements ~o The authors acknowledge the financial support of the Coordenaça de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) � Pesquisa do Estado de Minas Finance Code 001, Fundaç~ ao de Amparo a Gerais (FAPEMIG, Universal Demand, process number: APQ-00445-14) �gico and the Conselho Nacional de Desenvolvimento Científico e Tecnolo (CNPq). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jenvman.2019.109845. References Ag^ encia Nacional de Vigil^ ancia Sanit� aria, 2015. Resolution - RE n� 2.346 17. August, 2015. (APHA), 2005. American public health association/(AWWA), American water works association/(WEF), W.E.F. In: Clesceri, E., Eaton, Lenore S., Andrew, D. (Eds.),

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