Efficient degradation of butylparaben by gamma radiolysis

Author’s Accepted Manuscript Efficient Degradation of Butylparaben by Gamma Radiolysis Jhimli Paul Guin, Y.K. Bhardwaj, Lalit Varshney

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To appear in: Applied Radiation and Isotopes Received date: 2 April 2016 Revised date: 1 September 2016 Accepted date: 18 December 2016 Cite this article as: Jhimli Paul Guin, Y.K. Bhardwaj and Lalit Varshney, Efficient Degradation of Butylparaben by Gamma Radiolysis, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2016.12.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Efficient Degradation of Butylparaben by Gamma Radiolysis Jhimli Paul Guin, Y. K. Bhardwaj and Lalit Varshney Radiation Technology Development Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India 

Corresponding author

[E-mail: [email protected]; Tel.: +91 22 2559 0175; Fax: +91 22 2550 5151] Abstract Gamma radiolysis and ozonolysis are two competitive advanced oxidation processes for degradation of organic pollutants present in the ground water. In this paper, the gamma radiolytic degradation of an emerging organic pollutant Butylparaben (BP) in aqueous solution has been investigated for the first time at different absorbed doses. The effect of the absorbed dose rate in the degradation and mineralization of BP has been investigated. About 65 % mineralization of BP was observed at absorbed dose of 70 kGy and dose rate of 0.7 kGy h-1. Interestingly, turbidity appeared in the solution during radiolysis at doses higher than 2 kGy, which disappeared again at very higher dose (~90 kGy) making the solution again transparent. At lower dose rate of 0.175 kGy h-1 the turbidity was appeared at much lower dose about 1 kGy. However, the dose rate showed no effect in the dose of the disappearance of the turbidity. The hydrophobic fragments insoluble in water were generated during the initial stage of gamma radiolysis and those were completely mineralized to CO2 and H2O by direct absorption of gamma radiation. About 90 kGy dose was required to achieve ~90% mineralization of BP. On the contrary, maximum 50% 1

mineralization was achieved after 5 h of ozonation at the O3 flow rate of 0.5 L min-1 at pH 7.5 and it remained even constant upon prolonged ozonation. The oxygen-equivalent-chemicaloxidation-capacity (OCC) was used as the parameter to compare the % mineralization efficiencies of the two oxidative processes studied here and the gamma radiolysis was found to be more efficient between those processes. The phytotoxicity of the treated BP solution to agricultural seeds showed that the radiolytically generated fragments were less toxic compared to ozonolytically generated fragments. Thus gamma radiolysis is effective in significantly reducing the organic burden and the toxicity of water polluted with emerging pollutants like BP. Key words: Butylparaben; Radiolysis; Mineralization; Ozonolysis; Advanced oxidation process 1.

Introduction Fresh water availability in India has deteriorated significantly and it has raised the alarm

for judicial use of the available surface and ground water. Pollution of ground water with hazardous pollutants is one of the major causes for the water stress and water crisis in the developing countries like India. It creates a serious impact on agricultural yield because 89% of the ground water is used for the field irrigation (Annual Report of Ministry of Water Resources). Worldwide the existence of emerging pollutants in various aquatic streams has become a primary concern for environment (Gao et al., 2016). The emerging organic pollutants like parabens are enormously used in the food, cosmetics and pharmaceutical industries as antibacterial/antifungal and antioxidants and also used in varnishes, cigarettes, glues and healthcare products (Wang and Kannan, 2016). By the virtue of the heavy usage, these compounds are continuously getting released into the aquatic environment through domestic and industrial waste. Among all the parabens, butylparaben (BP) imposes greater potential threat to the aquatic system even at very 2

low concentration (Gryglik et al., 2009; Goswami and Kalita, 2013; Dhagrir et al., 2014). Therefore, removal of BP form the polluted water has become a major challenge to make water reusable. BP degradation by conventional biological treatment is not adequate due to the inefficient and incomplete microbial degradation (Leal et al., 2010). Therefore advanced oxidation processes have been investigated to establish an efficient technology for the fast and effective degradation of the organic pollutants. Various AOPs viz., photochemical, photosonochemical and ozonolytic degradation of BP have been reported (Dhagrir et al., 2014; Gmurek el., 2015). Among AOPs, radiolysis of water in situ produces strong oxidants without any added chemical. In addition to this the gamma radiation can be applied to real ground water as it is insignificantly affected by the presence of suspended solids. A low dose radiation pretreatment can enhance the biodegradability of the organic compounds (Paul et al., 2011; Paul et al., 2013). Recently, it has been shown that gamma radiolysis can efficiently degrade organic components in aqueous solution compared to other AOPs (Paul Guin et al., 2014a; Paul Guin et al., 2014b). Ozonation is also proven to be a promising technique for efficient disinfection and degradation of chemicals at reasonable cost and throughput (Wu et al., 2008; Tay et al., 2010a). Ozonolytic mineralization of BP solution was reported earlier by Tay et al. (Tay et al., 2010a; Tay et al., 2010b). The gamma radiolytic degradation of BP in aqueous solution is still unexplored. Further, no result is available to compare the efficiency of gamma radiolysis with the ozonolysis for the mineralization of BP. Therefore, in this maiden study, gamma radiolytic mineralization of BP in aqueous solution has been investigated. A comparative study on mineralization of aqueous BP solution by radiolysis and ozonolysis in terms of OCCs was carried out. The extent of phytotoxicity of the treated BP solution was also evaluated for the plant growth and seed germination. 3

2. Experimental 2.1. Materials and Methods Butylparaben (BP) of purity >99.9% from Sigma Aldrich was used without any further purification. Gamma radiolysis of the aqueous solution of 1 mM BP was carried out at a dose rate of 0.7 kGy h-1 using

60

Co GC-5000 gamma radiation chamber provided by BRIT, India.

Ozone (O3) was generated from the flow of pure oxygen at the rate of 0.5 L min-1 using Faraday Ozone Generator (Model L10) with maximum O3 dose of 10 g h-1. The mineralization extents of BP were expressed in terms of chemical oxygen demand (COD), which was measured by Spectroquant®Pharo 300 COD analyzer. Reverse phase HPLC experiments were performed using HPLC from Waters (Model 2690) through C-18 column with two gradient solvents of compositions, 0.1% TFA in H2O (A) and 60% acetonitrile with 0.09% TFA in H2O (B). The flowing sequence of the solvent through the column was optimized as follows: 5% B to 95% B in 30 min, followed by 95% B for 10 min, next 95% B to 5% B in 2 min, then 5% B for 10 min. The wavelength of the UV detector was fixed at 254 nm. 2.2. Phyto-toxicity study on the treated BP solution The phyto-toxicity of the treated BP solution was investigated at room temperature with the bench mark agricultural seed viz. Phaseolus mungo. The germination as well as the radicle length of the exposed seeds was measured after 3 days. The reported values are the average of a set of 5 seeds. The extent of germination of seeds exposed to untreated BP solution, treated BP solution and to tap water for the same time was also studied. 3. Results and discussion 4

3.1. Radiolytic mineralization of BP Fig. 1(A) shows the mineralization extent of aqueous 1 mM BP as a function of absorbed dose. It can be seen from the figure that the mineralization increases with increasing dose at a fixed dose rate of 0.7 kGy h-1. About 20 % and 65 % mineralizations were observed at doses of 35 and 70 kGy, respectively. The changes in the COD of the irradiated BP solution are shown in the Table 1 (A). However, turbidity appeared in the solution during the radiolysis at dose higher than 2 kGy and it became more prominent at moderate doses {Fig. 1B(a)}. At very higher dose than about 70 kGy the turbidity started disappearing {Fig. 1B(b)} and interestingly, at about 90 kGy the solution became again transparent {Fig. 1B(c)}. The BP solution was about 90% mineralized at 90 kGy {Fig. 1(A)}. Therefore, it could be anticipated that some water insoluble hydrophobic fragments were generated during the initial stage of gamma radiolysis and those got again fragmented to CO2 and H2O at higher doses. In order to understand the cause of the turbidity of the BP solution during the radiolysis, the BP solution irradiated in the dose range 0-16 kGy were analysed by HPLC and the chromatograms are shown in the Fig. 2. The retention time of unirradiated BP was observed at 29.7 min {Fig. 2(A)}. It can be clearly seen from Fig. 2(B) that radiolysis to a dose of 5 kGy resulted in generation of hydrophilic components eluting at the times 14.5 min, 19.7 min and 20.3 min as well as the relatively hydrophobic components with respect to BP eluting at the time scale 31.3 min, 32.6 min, 34 min and 35.9 min. Although the hydrophilic components were not observed, but the proportion of the hydrophobic components increased in the chromatogram of BP solution irradiated to a dose of 16 kGy {Fig. 2(C)}. Some overlapped peaks of low intensities were observed at retention time longer than 40 min in addition to the peaks observed earlier. It 5

indicates that the hydrophilic components were mineralized to CO2 and H2O at 16 kGy dose resulting in ~10% decrease in the COD of the solution and BP got fragmented into more hydrophobic components at higher doses. During radiolysis of aqueous BP solution, most of the radiation energy is deposited in water as it is the major component of the solution. Therefore, the role of the radiolytic products of water in the indirect radiolysis of BP is important to understand. Water radiolysis generates three major reactive transients viz. hydroxyl radical (•OH), hydrated electron (e-aq) and hydrogen atom (•H), which can react with BP. The G-values [in μM J-1] of the reactive transients are given below (Getoff, 2002). G(e-aq) = 0.28; G(•OH) = 0.28; G(•H) = 0.06 Under the discussed radiolysis conditions, part of •H and e-aq react with the dissolved oxygen present in the solution producing perhydroxyl radical (HO2•) and superoxide radical anion (O2•-), respectively. The addition of e-aq to the C=O (electrophilic centre) of the ester chain of BP and subsequent protonation would result in the reduction of BP (Scheme 1).

Scheme 1

6

However, the reaction of •OH radical with BP could lead to the formation of the polyhydroxy phenyl ring (I) as well as hydroxylatedester chain (II) (Scheme 2) along with many other fragments as reported earlier (Dhagrir et al., 2014 and Gao et al., 2014).

Scheme 2 Moreover, the hydrogen abstraction reaction from the BP alkyl chain by •H and/or •OH radicals and subsequent cleavage of C-C bond might have led to the production of water insoluble hydrophobic alkyl chains. This micro-phase separation caused turbidity in the irradiated BP solution. The insoluble fragments present in a different phase, would no longer be able to react with the reactive transients produced from water radiolysis. However, at very high absorbed dose, the insoluble compounds would have fragmented to smaller units by the direct absorption of the radiation. Therefore, the turbidity disappeared and subsequently the COD decreased at very high dose. This may be attributed to the ultimate fragmentation of the water insoluble components by the direct absorption of radiation. Fig. 3 shows the mineralization of BP at different dose rates for a fixed dose of 70 kGy and the changes in COD of the irradiated BP solution at different dose rates are shown in Table 7

1(B). It can be seen from the figure that the mineralization extent increases with decrease in the dose rate which is in agreement with the earlier report (Dessouki et al., 1998). The solution became turbid at 2 kGy at dose rate of 0.7 kGy h-1, but the turbidity appeared at lower dose (~1 kGy) at dose rate of 0.175 kGy h-1. However, the turbidity disappeared at almost same dose of ~90 kGy in all cases irrespective of the dose rate. The probability of the formation of molecular products increases at higher dose rates because of the inter-radical reactions. Thus at higher dose rates, comparatively less radicals are available for reaction with BP leading to its lesser extent of mineralization. Irradiation to higher dose (90 kGy) is required for complete mineralization through direct absorption of radiation by the hydrophobic fragments of BP at all dose rates. 3.2. Ozonolytic mineralization of BP 3.2.1. Effect of O3 flow rate on the mineralization of BP Ozonolytic mineralization of aqueous 1 mM BP solution was investigated for 0.5 h with varying O3 flow rates ranging from 0.5 L min-1 to 5 L min-1. The results of this study are shown in Fig. 4(A) and Table 1(C). It can be clearly seen that ozonolysis of BP solution at O3 flow rate of 0.5 L min-1 for 30 min resulted in about 40% mineralization. However, mineralization extent decreased by ~20% for higher flow rates. Lower mineralization extent at high flow rates may be attributed to rapid establishment of saturation concentration of O3, along with decrease in its residence time in solution. Therefore, lesser effective time of interaction of O3 with the organic fragments at higher flow rate would lead to the decrease in the extent of mineralization. Hence, the flow rate of O3 into the solution was fixed at 0.5 L min-1 for further studies to minimize the O3 loss and to maximize the mineralization of BP.

8

3.2.2. Duration of ozonolysis for mineralization of BP O3 (Eo = 2.1 V) slowly but selectively reacts with the π-bonds of the molecule causing its oxidation. However, O3 produces stronger oxidant •OH (Eo= 2.7 V) by decomposition at alkaline pH (Kasprzyk-Hordern et al., 2003). The pH of the solution governs the formation kinetics of •

OH radical (Mandavgane and Yenkie, 2011). Hence, at pH ~7.5, BP can be oxidized by the

parallel reactions of both the oxidants O3 and •OH (Hoigne and Bader, 1976; Kusvuran, 2013). Ozonolytic mineralization of aqueous 1 mM BP was studied for various time of ozonation at optimized O3 flow rate of 0.5 L min-1 {Fig. 4(B)}. The changes in COD of the ozonolyzed BP solution are shown in Table 1(D). It is clear from the figure that the extent of mineralization was increased rapidly up to 30 min of ozonation, though it changed insignificantly with further increase in the duration of ozonation up to ~5 h. Unlike radiolysis, apparently no turbidity appeared during ozonolysis of BP. Hence, HPLC analysis was carried out to understand the nature of the products generated from ozonolytically treated BPs {Fig. 4(C)} in comparison to the radiolytically treated BPs {Fig. 2(C)} for the same extent of mineralization (i.e. ~10%). Fig. 4(C) shows additional peaks at lower retention time scale specifically at 6.5 min, 8.1 min, 18.7 min, 19.2 min and 25.6 min as compared to the chromatogram of radiolytically treated BPs {Fig. 2(C)}. This clearly indicates that higher amounts of hydrophilic components are generated during the ozonolysis of BP. Some hydrophobic fragments may also have been generated during the ozonolysis of BP, but their amount is quite low to induce any turbidity in the solution. 3.3. Comparison of the process efficiencies of gamma radiolysis and ozonolysis In the earlier section, mineralization extent of 1 mM BP was investigated by both gamma radiolysis and ozonolysis by introducing two different experimental parameter, viz., radiation 9

dose and time of ozonation, respectively. Therefore, it has an immense importance to compare the oxidative mineralization efficiencies of afore described two mineralization processes through a commonly accepted parameter, namely the oxygen-equivalent-chemical-oxidation-capacity (OCC). The OCC is expressed as the amount of oxidant in terms of kg equivalent of O2 utilized for the treatment of 1 m3 of solution (Canizares et al., 2009). Fig. 5 shows that the OCC for gamma radiolysis and ozonolysis with varying extent of mineralizations. Although maximum 90% mineralization of BP could be achieved by gamma radiolysis, maximum only 50% mineralization of the same solution was found for ozonolysis. The OCC for 50% mineralization of aqueous 1 mM BP solution was calculated as 0.133 kg equiv. O2 m-3 for gamma radiolysis compared to 105.12 kg equiv. O2 m-3 for ozonolysis. These results show that same mineralization extent could be obtained with less amount of oxidants generated through gamma radiolysis and thus gamma radiolysis of BP is more efficient AOP in comparison to ozonolysis. 3.4. Phytotoxicity study The irrigation of the crops requires huge amount of water. Therefore to meet the water demand for irrigation, waste water can be treated and used for the purpose (Garg and Kaushik, 2008). This specific requirement mandates the evaluation of the phytotoxicity of the treated effluent for plant growth and seed germination (Garg and Kaushik, 2008). The phytotoxicity of the radiolytically and ozonolytically treated aqueous BP solution was studied by monitoring the extent of germination as well as the radicle growth of a bench-mark seed Phaseolus mungo. Fig. 6 shows the digital images of the seeds treated with (a) tap water, (b) 1 mM aqueous solution of BP (c) 10% radiolytically mineralized solution of 1 mM BP and (d) 10% ozonolytically mineralized solution of 1 mM BP. Other details regarding the seed germination and radicle 10

growth on exposure to 10% and highest possible mineralized BP by the two processes are listed in Table 2. No seed germination was observed in 1 mM BP solution as compared to the control (tap water). Therefore, it can be said that BP contaminated water is not suitable for irrigation. Interestingly, no suppression in the seed germination was observed for seeds immersed in the radiolytically treated BP solution (10% mineralized), although a decrease in the radicle length (by about 11%) was observed compared to the control. On the other hand, although seed germination did not show any dependency on the extent of ozonolytically mineralized BP, but the radicle length was suppressed by ~70% and ~55% for the 10% and 50% ozonolytically mineralized BP solution, respectively. Hence, it can be concluded that the chemical species generated by radiolysis of aqueous solution of BP are less toxic as compared to the ozonolysis of the same solution. 4. Conclusion The results of the present study indicate that gamma radiolysis could be employed for the efficient treatment of the polluted water with BP. Although maximum 90% mineralization of BP could be achieved by gamma radiolysis, maximum only 50% mineralization of the same solution was found for ozonolysis. The treatment efficiencies of gamma radiolysis and ozonolysis were systematically compared for the mineralization of BP through a commonly accepted parameter. The OCC of 50% mineralization of aqueous BP solution was calculated as 0.133 kg equiv. O2 m3

for gamma radiolysis compared to 105.12 kg equiv. O2 m-3 for ozonolysis proving gamma

radiolysis as the more efficient process for mineralization of BP. Toxicity of BP solution decreased in different extents for radiolysis and ozonolysis. The reduced toxicity of the treated water was clearly evident through the better growth of seed radicle exposed into radiolytically 11

mineralized BP solution. Hence, it can be concluded that the chemical species generated by the radiolysis of aqueous solution of BP are less toxic as compared to the ozonolysis of the same solution. The results indicate that judiciously chosen AOP treatment process can be effective in reducing the organic burden and the toxicity of water polluted with emerging pollutants like BP to a significant extent. Acknowledgement Authors sincerely acknowledge Dr. Dibakar Goswami for his contribution in the HPLC analysis of the test solutions. References Annual report 2013-14, Ministry of water resources, river development and ganga rejuvenation, http://wrmin.nic.in/writereaddata/AR_2013-14.pdf. Canizares, P., Paz, R., Saez, C., Radrigo, M.A., 2009. Costs of the electrochemical oxidation of wastewaters: A comparison with ozonation and Fenton oxidation processes, J. Environ. Manage. 90, 410-420. Daghrir, R., Dimboukou-Mpira, A., Seyhi, B., 2014. Photosonochemical degradation of butylparaben: Optimization, toxicity and kinetic studies. Science of the total environment, 490, 223234. Dessouki, A.M., Abdel-Al, S.E., 1988. Radiation degradation of some commercial dyes in wastewater. International Conference on hazardous waste: Sources, Effects and Management. 12-16 Decemher. Cairo-Eevpt.

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Gao, Y., An, T., Fang, H., Ji, Y., Li, G., 2014. Computational consideration on advanced oxidation degradation of phenolic preservative, methylparaben, in water: mechanisms, kinetics, and toxicity assessments. J. Hazard. Mater. 278, 417-425. Gao, Y., Ji, Y., Li, G., An, T., 2016. Theoretical investigation on the kinetics and mechanisms of hydroxyl radical-induced transformation of parabens and its consequences for toxicity: Influence of alkyl-chain length. Water Research, 91, 77-85. Garg, V.K., Kaushik, P., 2008. Influence of textile mill wastewater irrigation on the growth of sorghum cultivars. Appl. Ecol. Environ. Res. 6, 1-12. Getoff, N., 2002. Factors influencing the efficiency of radiation-induced degradation of water pollutants. Radiat. Phys. Chem. 65, 2002, 437-446. Gmurek, M., Rossi, A.F., Martins, R.C., Quinta-Ferreira, R.M., Ledakowicz, S., 2015. Photodegradation of single and mixture of parabens – Kinetic, by-products identification and cost-efficiency analysis. Chemical Engineering Journal 276, 303-314. Goswami, P., Kalita, J.C., 2013. Endocrine disrupting effect of butyl paraben: a review. IRJP, 4, 13-14. Gryglik, D., Lach, M., Miller, J.S., 2009. The aqueous photosensitized degradation of butylparaben. Photochem Photobiol Sci, 8, 549-555. Hoigne, J., Bader, H., 1976. The role of hydroxyl radical reactions in ozonation processes in aqueous solutions, Water Res. 10, 377-386. Kasprzyk-Hordern, B., Ziolek, M., Nawrocki, J., 2003. Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment. Appl. Catal., B., 46, 639-669.

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Kusvuran, E., Yildirim, D., 2013. Degradation of bisphenol A by ozonation and determination of degradation

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chromatography–mass spectrometry. Chemical Engineering Journal, 220, 6-14. Leal, L.H., Vieno, N., Temmink, H., Zeeman, G., Buisman, C.J.N., 2010. Occurence of xenobiotics in gray water and removal in three biological treatment systems. Environ, Sci. Technol. 44, 6835-6842. Mandavgane, S.A., Yenkie, M. K. N., 2011. Effect of pH of the medium on degradation of aqueous ozone. Rasayan, J. Chem. 3, 544-547. Paul, J., Rawat, K. P., Sarma, K. S. S., Sabharwal, S., 2011. Decoloration and degradation of Reactive Red-120 dye by electron beam irradiation in aqueous solution, Appl. Radiat. Isotop. 69, 982-987. Paul, J., A. A. Kadam, S. P. Govindwar, Kumar, P., Varshney, L., 2013. An insight into the influence of low dose irradiation pretreatment on the microbial decolouration and degradation of Reactive Red - 120 dye; Chemosphere, 90, 1348-1358. Paul Guin, J., Naik, D. B., Bhardwaj, Y. K., Varshney, L., 2014a. An insight into the effective advanced oxidation process for treatment of simulated textile dye waste water, RSC Adv. 4, 39941-39947. Paul Guin, J., Bhardwaj, Y. K., Naik, D. B., Varshney, L., 2014b. Evaluation of efficiencies of radiolysis, photocatalysis and ozonolysis of simulated textile dye waste water, RSC Adv. 4, 53921-53926. Tay, K.S., Rahman, N.A., Abas, M.R.B., 2010a. Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation. Environ Chem Lett, 8, 331–337.

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Tay, K.S., Rahman, N.A., Abas, M.R.B., 2010b. Ozonation of parabens in aqueous solution: Kinetics and mechanism of degradation. Chemosphere, 81, 1446-1453. Wang, W., Kannan, K., 2016. Fate of Parabens and Their Metabolites in Two Wastewater Treatment Plants in New York State, United States. Environ. Sci. Technol. 50, 1174-1181. Wu, C.H., 2008. Decolorization of C.I. Reactive Red 2 in O3, Fenton-like and O3/Fentonlike hybrid systems, Dyes Pigment 76, 187-194.

Figure captions Fig. 1 (A) The % mineralization calculated from the % changes in the COD of 1 mM aqueous BP solution during the progress of radiolysis at dose rate of 0.7 kGy h-1. The statistical variation of each data point is shown in by the error bars. (B) The digital image of the change in turbidity of the gamma irradiated 1 mM BP solution at different doses (a) 16 kGy (b) 70 kGy and (c) 90 kGy. Fig. 2 HPLC chromatograms of 1 mM BP solution after gamma radiolysis at (A) 0 kGy, (B) 5 kGy and (C) 16 kGy. Fig. 3 The effect of the dose rate in the mineralization of 1 mM aqueous BP solution for fixed absorbed dose of 70 kGy at the rate of (a) 0.175 kGy h-1, (b) 0.35 kGy h-1 and (c) 0.7 kGy h-1. Fig. 4 (A) Effect of O3 flow rate on the mineralization of 1 mM BP solution at pH 7.5 (B) Mineralization of 1 mM BP at pH 7.5 as function of time of ozonation; O3 flow rate = 0.5 L min1

(C) HPLC chromatogram of ozonolytically mineralized (10%) aqueous 1 mM BP solution. 15

Fig. 5 The change in OCC during the mineralization of 1 mM aqueous BP solution through (a) gamma radiolysis (b) ozonolysis. The inset shows the enlarged image of (a). Fig. 6 The digital image of germination and growth of Phaseolus mungo in (a) control (tap water) (b) 1 mM aqueous BP solution (c) 10% radiolytically mineralized 1 mM BP solution (d) 10% ozonolytically mineralized 1 mM BP solution.

Scheme 1 The general scheme of the reaction of e-aq with the C=O (electrophilic centre) of the ester chain of BP followed by subsequent protonation. Scheme 2 The general scheme of the reaction of •OH radical with BP forming poly-hydroxy phenyl ring (I) as well as hydroxylatedester chain (II) along with many other fragments as reported earlier (Dhagrir et al., 2014 and Gao et al., 2014).

Highlights: 

First report on the gamma radiolytic mineralization of butyl paraben.



The gamma radiolysis showed better efficacy for the mineralization of BP solution consuming minimum amount of oxidant compared to the same for ozonolysis.

16



The radiolytically treated solution was proved to be lesser toxic compared to ozonolytically treated solution for the same extent of mineralization.

Tables Table 1 (A) The COD values and the changes in COD of aqueous BP solution during gamma radiolysis at different doses at dose rate 0.7 kGy h-1; (B) The COD values and the changes in

A

B

C

D

Dos e, kGy

CO D, ppm

Chang es in COD, ppm

Dos e rate s, kGy h-1

CO D, ppm

Chang es in COD, ppm

Tim e, min

CO D, ppm

Chang es in COD, ppm

Tim e, min

CO D, ppm

Chang es in COD, ppm

0

460

0

0

460

0

0

460

0

0

460

0

5

454

6

0.17 5

60

400

0.5

278

182

2

421

39

16

414

46

0.35

110

350

2

362

98

4

391

69

35

363

97

0.7

160

300

3.5

368

92

10

326

134

50

290

170

4

367

93

20

303

157

70

161

299

5

366

94

30

285

175

90

46

414

60

276

184

90

271

189

120

257

203

150

257

203

300

243

217

COD of aqueous BP solution during the gamma radiolysis at fixed dose of 70 kGy with different dose rates; (C) The COD values and the changes in COD of aqueous BP solution during 17

ozonolysis at different flow rates of O3 at pH 7.5; (D) The COD values and the changes in COD of aqueous BP solution during ozonolysis at different time of ozonation at pH 7.5 and O3 flow

Radiolytically Radiolytically Ozonolytically Ozonolytically Parameters 10% 90% 10% 50% Water BP studied mineralized mineralized mineralized mineralized BP BP BP BP Germination (%)

100

-

100

100

80

80

Radicle length (cm)

4.5 ± 0.1

-

4.0 ± 0.3

4.5 ± 0.3

1.4 ± 0.2

2 ± 0.2

rate = 0.5 L min-1. The initial concentration of BP for all is 1 mM. Table 2 Phytotoxicity studies of 1 mM BP and chemical species generated from radiolysis and ozonolysis.

Figures

% Mineralization

100

(A)

80 60 40 20 0

18

0

20

40 60 Dose, kGy

80

100

19

100

Normalised intensity, %

(A)

80 60 40 20 0

10

20 30 40 Retention time, min

100

50

(B)

80 60 40 20 0

0

Normalised intensity, %

Normalised intensity, %

100

0

10

20 30 40 Retention time, min

50

(C)

80 60 40 20 0

0

10

20 30 40 Retention time, min

50

20

100

% Mineralization

80 60

(a) (b) (c)

40 20 0 0.0

0.2 0.4 0.6 -1 Dose Rate, kGy h

0.8

21

100

(A)

60 40 20 0

0

1 2 3 4 -1 Flow rate (L min )

(B)

80

% Mineralization

80

60 40 20 0

5

0

100 200 Time of ozonation, min

100

Normalised intensity, %

% Mineralization

100

300

(C)

80 60 40 20 0

0

10

20

30

40

50

Retention time, min

22

100

100

(a)

(a)

80

% Mineralization

% Mineralization

80

60

60

40

20

0 0.00

0.05

0.10

0.15

0.20

OCC (kg equiv. O2 m-3)

40

(b) 20

0 0

20

40

60

OCC (kg equiv. O2 m-3)

80

100

23

24