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  • Photolysis of model emerging contaminants in ultra-pure water: kinetics, by-products formation and degradation pathways.

Photolysis of model emerging contaminants in ultra-pure water: kinetics, by-products formation and degradation pathways.

Water research (2012-12-12)
F Javier Benitez, Juan L Acero, Francisco J Real, Gloria Roldan, Elena Rodriguez
ABSTRACT

The photolysis of five frequent emerging contaminants (Benzotriazole, Chlorophene, N,N-diethyl-m-toluamide or DEET, Methylindole, and Nortriptyline HCl) was investigated in ultrapure water under monochromatic ultraviolet radiation at 254 nm and by a combination of UV and hydrogen peroxide. The results revealed that the photolysis rates followed first-order kinetics, with rate constant values depending on the nature of the specific compound, the pH, and the presence or absence of the scavenger tert-butanol. Quantum yields were also determined and values in the range of 53.8 × 10⁻³ - 9.4 × 10⁻³ mol E⁻¹ for Benzotriazole, 525 × 10⁻³ - 469 × 10⁻³ mol E⁻¹ for Chlorophene, 2.8 × 10⁻³ - 0.9 × 10⁻³ mol E⁻¹ for DEET, 108 × 10⁻³ - 165 × 10⁻³ mol E⁻¹ for Methylindole, and 13.8 × 10⁻³ - 15.0 × 10⁻³ mol E⁻¹ for Nortriptyline were obtained. The study also found that the UV/H₂O₂ process enhanced the oxidation rate in comparison to direct photolysis. High-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) technique was applied to the concentrations evaluation and further identification of the parent compounds and their by-products, which allowed the proposal of the degradation pathways for each compound. Finally, in order to assess the aquatic toxicity in the photodegradation of these compounds, the Vibrio fischeri acute toxicity test was used, and the results indicated an initial increase of this parameter in all cases, followed by a decrease in the specific case of Benzotriazole, DEET, Methylindole, and Chlorophene.

MATERIALS
Product Number
Brand
Product Description

Nortriptyline hydrochloride, European Pharmacopoeia (EP) Reference Standard
Sigma-Aldrich
Skatole, ≥98%
Sigma-Aldrich
N,N-Diethyl-3-methylbenzamide, 97%
Sigma-Aldrich
2-Benzyl-4-chlorophenol, 95%
Sigma-Aldrich
Bis(5-chloro-2-hydroxyphenyl)methane, 95%
Sigma-Aldrich
Nortriptyline hydrochloride, ≥98% (HPLC), powder
Sigma-Aldrich
tert-Butanol, anhydrous, ≥99.5%
Supelco
DEET, PESTANAL®, analytical standard
Sigma-Aldrich
3-Methylindole, 98%
Supelco
tert-Butanol, analytical standard
Sigma-Aldrich
tert-Butanol, SAJ special grade, ≥99.0%
Sigma-Aldrich
tert-Butanol, SAJ first grade, ≥98.0%
Supelco
Nortriptyline hydrochloride solution, 1.0 mg/mL in methanol (as free base), ampule of 1 mL, certified reference material, Cerilliant®
Sigma-Aldrich
tert-Butanol, ACS reagent, ≥99.0%
Sigma-Aldrich
tert-Butanol, puriss. p.a., ACS reagent, ≥99.7% (GC)
Sigma-Aldrich
tert-Butanol, TEBOL® 99, ≥99.3%
Sigma-Aldrich
tert-Butanol, ≥99% (GC)
Sigma-Aldrich
tert-Butanol, suitable for HPLC, ≥99.5%