Understanding the effects of mineral water matrix on degradation of several pharmaceuticals by ultrasound: Influence of chemical structure and concentration of the pollutants

Abstract

Degradation of seven relevant pharmaceuticals with different chemical structures and properties: acetaminophen (ACE), cloxacillin (CXL), diclofenac (DCF), naproxen (NPX), piroxicam (PXC), sulfacetamide (SAM) and cefadroxil (CDX), in distilled water and mineral water by ultrasound was studied herein. Firstly, proper conditions of frequency and acoustic power were determined based on the degradation ability of the system and the accumulation of sonogenerated hydrogen peroxide (24.4 W and 375 kHz were found as the suitable conditions for the sonochemical treatment of the pharmaceuticals). Under such conditions, the pharmaceuticals degradation order in distilled water was: PXC > DCF ~ NPX > CXL > ACE > SAM > CDX. In fact, the initial degradation rate showed a good correlation with the Log P parameter, most hydrophobic compounds were eliminated faster than the hydrophilic ones. Interestingly, in mineral water, the degradation of those hydrophilic compounds (i.e., ACE, SAM and CDX) was accelerated, which was attributed to the presence of bicarbonate ions. Afterwards, mineral water containing six different initial concentrations (i.e., 0.331, 0.662, 3.31, 16.55, 33.1, and 331 µM) of selected pharmaceuticals was sonicated, the lowest concentration (0.331 µM) always gave the highest degradation of the pollutants. This result highlights the great ability of the sonochemical process to treat bicarbonate-rich waters containing pollutants at trace levels, as pharmaceuticals. Finally, the addition of ferrous ions to the sonochemical system to generate a sono-Fenton process resulted in an acceleration of degradation in distilled water but not in mineral water. This was attributed to the scavenging of sonogenerated HO• by bicarbonate anion, which decreases H₂O₂ accumulation, thus limiting the Fenton reaction.

Keywords: Bicarbonate effect; Carbonate radical; Mineral water; Pharmaceuticals; Sonochemistry.

Graphical abstract

Fig. 1

Diclofenac (DCF) evolution under different sonolysis frequencies. Inset: H₂O₂ accumulation rate (Ra, µM min⁻¹) during DFC degradation. Conditions: initial DCF concentration: 3.31 µM, pH: 7.2 ± 0.1, acoustic power: 24.4 W, temperature: 20 °C and volume: 250 mL.

Fig. 2

DCF evolution under different acoustic powers. Inset: H₂O₂ accumulation rate (Ra, in µM min⁻¹) during DCF degradation. Experimental conditions: Initial DCF concentration: 3.31 µM, pH: 7.2 ± 0.1, frequency: 375 kHz, temperature: 20 °C and volume: 250 mL.

Fig. 3

Pharmaceuticals evolution during the sonochemical treatment in distilled water. Inset: H₂O₂ accumulation rate (Ra, µM min⁻¹). Experimental conditions: Initial pollutant concentration: 3.31 µM, initial pH: 7.2 ± 0.1, Frequency: 375 kHz, Acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.

Fig. 4

Relationship between the initial degradation rate (Rd, µM min⁻¹) and different physicochemical parameters of pharmaceutical. A. Reaction rate constant with HO•, B. Henry’s Law constant, C. Topological Polar Surface Area (TPSA), D. Water solubility, and E. Octanol/water partition coefficient (Log P). Conditions: Initial pollutant concentration: 3.31 µM, initial pH: 7.2 ± 0.1, Frequency: 375 kHz, Acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL. Note: The values of k_(HO), Log (P), S_W, TPSA, k_H were taken from references, , , , , , , , , .

Fig. 5

Degradation of the target pollutants in mineral water. A. Pharmaceuticals evolution. B. Ratio between the initial degradation rate in mineral water and distilled water. Conditions: Initial pollutant concentration: 3.31 µM, initial pH: 7.2 ± 0.1, Frequency: 375 kHz, acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.

Fig. 6

Relationship between the initial degradation rate of the pharmaceuticals (Rd, µM min⁻¹) in mineral water and octanol/water partition coefficient (A), water solubility (B). Initial pollutant concentration: 3.31 µM, initial pH: 7.2 ± 0.1, Frequency: 375 kHz, Acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.

Fig. 7

Sulfacetamide (SAM) removal in the presence of individual components of mineral water constituents. Inset: Effect of ionic constituents on the H₂O₂ accumulation. Conditions: Initial pharmaceutical concentration: 3.31 µM, initial pH: 7.2 ± 0.1, Frequency: 375 kHz, Acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.

Fig. 8

Effect of pharmaceuticals concentration on the degradation in mineral water. RdMW/RdDW: Relationship between the initial degradation rate in mineral water and in distilled water for different concentrations. A. SAM, B. CXL, and C. CDX. Conditions: initial pH: 7.2 ± 0.1, Frequency: 375 kHz, Acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.

Fig. 9

Removal of CDX through sono-Fenton (SF) process in distilled water. Inset: comparison of H₂O₂ accumulation rates (in µM min⁻¹) for individual sonolysis, sono-Fenton (Fe²⁺= 1.0 mg L⁻¹) and sono-Fenton (Fe²⁺= 5.0 mg L⁻¹). Conditions: initial CDX concentration: 3.31 µM, pH: 7.2 ± 0.1, frequency: 375 kHz, acoustic power: 24.4 W, temperature: 20 °C and volume: 250 mL.

Fig. 10

Degradation of CDX in mineral water by the sono-Fenton process. Conditions: Initial pharmaceutical concentration: 3.31 µM, pH: 7.2 ± 0.1, Frequency: 375 kHz, acoustic power: 24.4 W, Temperature: 20 °C and Volume: 250 mL.