Evaluation of Degradation Efficiency of 2’-Ethylhexyl 4-(Dimethylamino)Benzoate under the Influence of Oxidizing Agents

The aim of the studies was to evaluate the effect of oxidizing agents on the degradation of 2-ethylhexyl 4-(dimethylamino)benzoate (ODPABA). The oxidation reaction was carried out in the presence of oxidizing agents used for disinfection of water and treatment of sewage containing organic pollutants. Oxidants, such as: sodium hypochlorite, hydrogen peroxide or ozone with UV radiation were applied. ODPABA degradation and analysis of products were performed using a gas chromatograph coupled with mass spectrometry detector. The use of sodium hypochlorite and UV radiation proved to be the most effective solutions. As a result, halogenoorganic products are formed. It is likely that the resulting by-products can be more toxic than the initial substrate. In the case of ozone and hydrogen peroxide, it was shown that these agents are characterized by weaker oxidative activity and therefore, fewer metabolites are formed.


INTRODUCTION
UV filters are chemical compounds the main purpose of which is to protect the skin against the negative effects of UV radiation [Dias-Cruz et al., 2008].UV filters are widely used in personal care products, i.e.: lipsticks, body lotions, hairsprays and also as an additive preventing the degradation of polymers and pigments [Negreira et al. 2008, Gackowska et al. 2014].Due to the wide use of UV-filters in various products, special attention was paid to their occurrence and impact on the environment [Dirtu et al. 2012].According to the literature data, ultraviolet filters can infiltrate into environment from direct and indirect sources [Dias-Cruz et al. 2012].The direct sources include the phenomena associated with the release of substances from the surface of the skin, e.g. during washing, bathing or swimming [la Farré et al. 2008].Particularly large consumption of UV-filters is observed during the summer time, which is caused by increased skin exposure to solar radiation [Zuloaga et al. 2012].Indirect sources of pollution are wastewater from households, which arise as a result of washing or rinsing but also from municipal and industrial wastes [Santos et al. 2013].
The stability of filters under the influence of external agents is a very important aspect for the producers of sunscreens, because it is connected with the loss of photo-protective properties of product [Dias-Cruz et al. 2008].The durability of UV filters is also an important problem for environment protection.It has been shown that sunscreens have the ability to accumulate in different matrices, which can result in the formation of undesirable products under the influence of external agents [Negreira et al. 2008].Due to their accumulation in the environment and lack of constant monitoring, they are considered as new pollutants -"emerging contaminations (ECs)" [Gomez et al. 2012].In order to learn about the processes of conversions that they can undergo in the aquatic environment, studies on the impact of various environmental agents on their behaviour are conducted.These studies are very important, because Giakos et al. [2007] have shown that UV filters in the aquatic environment can react with components of water matrix such as: dissolved organic matter, chlorides or nitrates.Stability can also be influenced by, for example: oxygen, peroxide radicals, hydroxyl groups, etc. [Santos et al.,2013].
One of the commonly used UV filters is 2'-ethylhexyl 4-(dimethylamino) benzoate (ODPABA).Among the current ODPABA durability studies, the effect of radiation has been examined, noting the reduction of the protective properties of the UV filter [Serpone et al. 2002 process involves substituting one hydrogen atom in the aromatic ring with chlorine or bromine.It was found that the rate of filter decomposition and the amount of halogen derivative by-products also depends on the pH of the system [Negreira et al., 2008].Due to the fact that ODPABA and other UV filters can undergo conversions in the environment, as a result of which by-products with much higher toxicity than the substrate can be formed, a trend of actions leading to the improvement of wastewater treatment methods by eliminating the radiation-protective compounds is observed.The aim of these activities is to eliminate the pollutants which, due to their properties (lipophilicity, poor biodegradability), after applying traditional methods of wastewater treatment, do not degrade and percolate into surface waters together with the treated wastewater.A promising solution can be advanced oxidation processes AOPs [Krzemińska et al. 2015;Kasih 2017].
The aim of the study was to evaluate the efficiency of degradation of 2'-ethylhexyl 4-(dimethylamino) benzoate in an aqueous matrix under the influence of oxidizing agents such as hydrogen peroxide, ozone, sodium hypochlorite in the presence of UV radiation.An attempt was also made to identify the by-products formed.

MATERIALS AND METHODS
Chemical filter 2-ethylhexyl 4-(dimethylamino)benzoate (ODPABA) 99%, CAS 21245-02-3, from Sigma Aldrich was used in our studies.Hydrogen peroxide (H 2 O 2 30%) and sodium chlorate (I) (NaOCl 100 g/L of free chlorine) purchased from POCH company were selected as the oxidizing agents.Another agent was ozone, which was produced by the DRP-30.7 VW generator, at the flow of 4 μl/min.
Aqueous solutions of 0.36 mM ODPABA were introduced into the Heraeus reactor and individual oxidants were added in the proportions given in Table 1.The studies on the additive effect of UV radiation were carried out using a medium-pressure mercury lamp with a range of 200-600 nm.The mercury lamp was placed in a water jacket to maintain a constant reaction temperature of 20ºC.The reactor was placed on a magnetic stirrer (200 rpm) to ensure uniform distribution of reagents in the solution.
The samples for qualitative and quantitative analysis were collected at various time intervals.From each test system, 100 ml of solution, after a specified time, was sampled and extracted with 20 ml of dichloromethane.The obtained extract was dried with anhydrous sodium sulfate and then concentrated in a vacuum evaporator to the volume of 1 ml.The change of ODPABA concentration in time under the influence of oxidizing agents and UV radiation as well as identification of degradation products was carried out using 5890 HEWLETT PACKARD gas chromatograph equipped with a MS detector and the ZB-5MS column (0.25 mm × 30 m × 0.25 μm).Temperature program was as follows: 80°C -10°C/1min -260°C -5°C/1min -300°C/2min.The injection volume was 1 μl.

RESULTS AND DISCUSSION
On the basis of our studies, it was found that ODPABA was unstable under the influence of oxidizing agents in the presence of UV radiation (Fig. 1).The fastest ODPABA degradation was observed in the system with sodium hypochlorite in the presence of UV radiation.In this system, the half-life decomposition of the filter was observed after 60 minutes and after 180 minutes, the filter loss was about 90%.In the case of O 3 /UV and H 2 O 2 /UV systems, the decomposition reactions ran more slowly than with NaOCl/UV.In both cases, the filter decomposition after 60 minutes was found to be about 40%, and after 180 minutes ODPABA was decomposed in 80%.In the presence of sole UV radiation, ODPABA degradation proceeded the slowest.The results confirm that the application of advanced oxidation processes contributes to improving the efficiency of removing the filter from water matrix.
While studying the influence of oxidizing agents (hydrogen peroxide, sodium hypochlorite, ozone and UV radiation) on another filter 2'-ethylhexyl 4-methoxycinnamate (EHMC), a different dependence concerning the effectiveness of oxidizing agents was observed.The oxidation system with ozone and UV radiation was the most effective [Studziński et al. 2017].By executing chlorination in swimming pools, Nakajima et al. [2009] revealed that ODPABA reacted with chlorine more rapidly than EHMC.The difference in reactivity is due to the presence of various substituents (methoxy and dimethylamino groups) in the benzene ring [Nakajima et al. 2009].
In search of the new methods for degradation of micro-pollutants with the use of oxidizing agents, scientists focus their attention on the As a result of sole ODPABA (1) water solution irradiation, three by-products were identified: 2'-ethylhexyl 4-aminobenzoate (3); 2-ethylhexan-1-ol ( 5); 2'-ethylhexyl 4-(methylamino) benzoate (8).The obtained results indicate that in presence of UV radiation, demethylation of the amino group takes place.
The solution generating the smallest amount of products in the ODPABA oxidation process is the ozonation in the presence of UV radiation.The reaction products identified in ODPABA/O 3 / UV system were 4-(methylamino) benzoic acid (4) and 2-ethylhexan-1-ol (5) (Fig. 4).
Increased awareness of the harmful effects of chloroorganic products used for disinfection of wa- Regardless of the type of oxidizing agent used, in the first stage of ODPABA degradation, the amine group is demethylated and then disintegration into lower molecular weight compounds occurs.The resulting products are at trace levels and are characterized by similar physicochemical properties.Their separation and isolation is arduous; hence, the assessment of a particular product on the environment is difficult.According to Nakajima et al. [2009] during disinfecting water with sodium hypochlorite, ODPABA forms mutagenic products.Therefore, according to the authors, development of research to assess the toxicity of all ODPABA conversion products can contribute not only to broadening of the knowledge about their properties, but will also be a valuable source of information in the context of assessment of the quality of water resources.

CONCLUSIONS
It was found that ODPABA was unstable under the influence of oxidizing agents, such as sodium hypochlorite, hydrogen peroxide and ozone.The process conducted with the participation of oxidizing agents in the presence of UV radiation accelerates the degradation of UV filter.
Our studies have shown that in each variant, the products which were formed could lead to secondary water pollution.The most effective solution was the use of sodium hypochlorite and UV radiation.However, this solution generated a large number of halogenorganic metabolites.It is likely that the resulting by-products can be more toxic than the initial substrate.
In the case of ozone and hydrogen peroxide, it has been shown that these agents exhibit weaker oxidative activity and cause formation of a smaller number of metabolites.The application of suitable oxidation processes can contribute to the degradation of micro-pollutants, and thus to an improvement of the water quality.
method effectiveness [Przywara 2017; Kuśmierek et al. 2015].During optimization of these methods, the efficiency of processes and the rate of pollutant degradation are checked [Lee et al. 2009; Hopkins et al. 2017].There is little literature data concerning the conversions and further fate of pollutants after the oxidation process [Hopkins et al., 2017].The products of conversions of micropollutants can cause secondary water contamination.Therefore, when assessing the method of ODPABA degradation of in water matrix, the analysis of metabolites formed in reaction with oxidizing agents was considered as well.The products of ODPABA conversions under the influence of NaOCl/UV, H 2 O 2 /UV and O 3 /UV oxidizing systems were presented in Figure 2.

Table 1 .
The reaction conditions and substrate proportions used in this study