< Back to previous page

Project

High resolution LC tandem for MS for the identification of unknown polar oxidation products of pyralozone pharmaceuticals, their metabolites and biotransformation products

In this thesis, the issue of the contamination of the aquatic environment by pyrazolone type pharmaceuticals and metabolites and two oxidative processes of remediation was studied. 

 

Several pyrazolone type compounds were studied. Dipyrone - also named metamizole - is one of the most widely used analgesic pharmaceuticals. Completely metabolized in the human body, it produces 4-acetamidoantipyrine (AAA) and 4-formylaminoantipyrine (FAA) that can be found in water streams in levels in the ng/L to μg/L range. Next to those, phenazone and propyphenazone, also analgesics, were selected to bring the total of studied compounds to four. An analytical method for the determination of these four compounds was developed and validated. It was applied on environmental water samples from Germany and Brazil, where dipyrone is available on prescription and over the counter, respectively. The difference in concentration measured showed an impact of the over the counter availability, although this difference was not considered to be large. The samples from Brazil demonstrated that the contamination of the aquatic environment by these molecules is large with levels of AAA exiting WWTP in the μg/L range and further detection in surface waters, water reservoirs and drinking water.

 

Closed-loop bottle tests were used to mimic microbial degradation and study the formed by-products. Degradation of AAA was only observed when AAA was solely present in the solution. As soon as another carbon source was available, the level of AAA remained stable. Our study unveiled four degradation products being formed, the major one being 4-aminoantipyrine (AA) by a deacetylation mechanism. The other observed degradation mechanism was a combination of oxidation of a C=C double-bond and denitrification. A grab sample study at a wastewater plant revealed levels of all degradation products at different stages of the wastewater process. Contrary to AAA, FAA has been shown in literature, to be resilient to biological treatment. 

 

Additionally, phenazone, propyphenazone, AAA and FAA were treated with ozone under laboratory conditions and 17 degradation products were identified by an elucidation approach based on high-resolution mass spectrometry (LTQ Orbitrap). Typical oxidation of carbon-carbon double bonds by ozone was observed among other mechanisms of ring opening. It was demonstrated that the reactivity of these compounds with ozone is high (rate constants kO3 ranging from 6.5×104 to 2.4×106 M-1s-1).

 

The degradation of phenazone, propyphenazone, acetamido antipyrine and formyl aminoantipyrine by UV radiation was investigated as well under laboratory conditions. An elucidation approach based on high-resolution mass spectrometry resulted in the identification of 11 degradation products. A mechanism of ring opening via the oxidation of the N-N bond of the pyrazolone ring was observed as well as the more typical oxidation of carbon-carbon double bonds. Aside from the degradation products, the capacity of formyl aminoantipyrine to produce trimers and dimers was demonstrated. The dimers were shown to be persistent despite continuous UV radiation.

 

The toxicity of the formed degradation products was estimated by quantitative structure-activity relationships (QSAR). It was shown that, when the carbon-carbon double bond is partially oxidized to an epoxy, the toxicity towards fish and daphnids is higher than that of the parent compound. By further oxidizing the molecules, a common degradation product – 1-acetyl-1-methyl-2-phenylhydrazide (AMPH) – was also found to be more toxic than its parent compounds, which is of concern since this compound has previously been reported in environmental waters. 


    Overall, this class of compounds is present in high levels in wastewater and is prone to transformation during the oxidative processes used as tertiary treatment steps. It is considered that removal should not only be assessed for the parent compounds but also for their degradation products. The task at hand is still large on this side given the number of different possible pharmaceutical compounds present in WWTP effluents. However, improvements in analytical techniques, as well as their combination with in-silico methods, could provide the knowledge needed to optimize oxidative treatment processes.

Date:1 Sep 2013 →  9 Oct 2019
Keywords:pharmaceuticals in the environment
Disciplines:Biomarker discovery and evaluation, Drug discovery and development, Medicinal products, Pharmaceutics, Pharmacognosy and phytochemistry, Pharmacology, Pharmacotherapy, Toxicology and toxinology, Other pharmaceutical sciences, Analytical chemistry, Pharmaceutical analysis and quality assurance, Chemical product design and formulation, Biomaterials engineering
Project type:PhD project