Effects of Surfactants on the Degradation of Diclofenac by Manganese Oxide.

Wen-Hui Kuan,Ching-Yao Hu,Yu-Jung Liu

doi:10.3390/ijerph17124513

Abstract

Amine-containing pharmaceuticals are the most often detected pharmaceuticals in wastewater and ambient aquatic environments. They can usually be degraded by manganese oxide (MnO2), which is a common natural oxidant in soils. Surfactants often coexist with pharmaceuticals in wastewater. Some amine-containing pharmaceuticals, such as diclofenac (DIC), are acidic and are thus ionic compounds in neutral conditions. These compounds, therefore, have similar properties to surfactants. Surfactants, thus, may influence the adsorption and degradation processes of DIC by MnO2. The effect of the type of surfactant on the degradation of DIC by MnO2 was investigated in this study with the addition of two common biodegradable surfactants (cetyltrimethyl-ammonium bromide (CTAB) and sodium dodecylsulfate (SDS)). The results indicated that the cationic surfactant (CTAB) significantly increased the degradation rate in neutral and alkaline conditions. On the other hand, the anionic surfactant (SDS) slightly increased the DIC removal rate in an acidic condition but significantly decreased the removal in neutral and alkaline conditions. Coexisting cationic surfactants not only influenced the kinetics but also altered the transformation mechanism of DIC by MnO2. Decarboxylation is the main transformation mechanism of DIC in the presence of CTAB, while both decarboxylation and hydroxylation are the main transformation mechanisms in the absence of CTAB.

Highlights

Diclofenac (2-((2,6-dichlorophenyl) amino) phenylacetic acid, DIC) is one of the most widely used non-steroidal anti-inflammatory drugs (NSADs) in the world
It is notable that the addition of a cationic surfactant (CTAB) significantly improved the removal of DIC at all pH values
When cationic surfactant molecules are adsorbed onto the surface of a metal oxide, the anionic DIC ions can be adsorbed because of attractive forces between the hydrophobic tails of the two molecules

Summary

Introduction

Diclofenac (2-((2,6-dichlorophenyl) amino) phenylacetic acid, DIC) is one of the most widely used non-steroidal anti-inflammatory drugs (NSADs) in the world. It is an amine-containing pharmaceutical and can evade wastewater treatment because of its high hydrophilic nature [1]. It is found in many aquatic environments [3,4]. It may be toxic to aquatic organisms and harmful to embryos, infants, children, and adults with weak constitutions and those who are sensitive to pharmaceuticals [5,6,7,8]. Continuous exposure to low concentrations of the pharmaceutical may cause unexpected health risks to humans and other organisms. The bioaccumulation and sublethal effects of DIC were observed in rainbow trout with the lowest observed effect concentration (LOEC/28 days of 1.0 μg L−1 ) in the range of discharge levels [9,10]

Methods

Results

Conclusion