Fate of selected pharmaceuticals in river waters

The aqueous environmental fate of two antibiotics, lincomycin and clarithromycin, and an antiepileptic drug, carbamazepine, was investigated by monitoring drugs decomposition and identifying intermediates in Po river water (North Italy). Initially, control experiments in the dark and under illumination were performed on river water spiked with drugs to simulate all possible transformation processes occurring in the aquatic system. Under illumination, these pharmaceuticals were degraded and transformed into numerous organic intermediate compounds. Several species were formed and characterised by analysing MS and MS(n) spectra and by comparison with parent molecule fragmentation pathways. River water was sampled at three sampling points in an urban area. The selected pharmaceuticals were detected in all samples. Eight transformation products identified in the laboratory simulation were found in natural river water from carbamazepine degradation, three from clarithromycin and two from lincomycin. Their transformation occurring in aquatic system mainly involved mono- and poly-hydroxylation followed by oxidation of the hydroxyl groups.

Identification of the unknown transformation products derived from clarithromycin and carbamazepine using liquid chromatography/high-resolution mass spectrometry

RATIONALE

A comprehensive study of the environmental fate of pollutants is more and more required, above all on new contaminants, i.e. pharmaceuticals. As high-resolution mass spectrometry (HRMS(n)) may be a suitable analytical approach for characterization of unknown compounds, its performance was evaluated in this study.

METHODS

The analyses were carried out using liquid chromatography (LC) (electrospray ionization (ESI) in positive mode) coupled with a LTQ-Orbitrap analyzer. High-resolution mass spectrometry was employed to assess the evolution of the drug transformation processes over time; accurate masses of protonated molecular ions and sequential product ions were reported with an error below 5 millimass units, which guarantee the correct assignment of their molecular formula in all cases, while their MS(2) and MS(3) spectra showed several structurally diagnostic ions that allowed characterization of the different transformation products (TPs) and to distinguish the isobaric species.

RESULTS

The simulation of phototransformation occurring in the aquatic environment and identification of biotic and abiotic transformation products of the two pharmaceuticals were carried out in heterogeneous photocatalysis using titanium dioxide, aimed to recreate conditions similar to those found in the environmental samples. Twenty-eight main species were identified after carbamazepine transformation and twenty-nine for clarithromycin.

CONCLUSIONS

This study demonstrates that HRMS, combined with LC, is a technique able to play a key role in the evaluation of the environmental fate of pollutants and allows elucidation of the transformation pathways followed by the two drugs.

Identification of the unknown transformation products derived from lincomycin using LC-HRMS technique

In this paper, a comprehensive study of the fate of an antibiotic, lincomycin, in the aquatic environment is presented. High-resolution mass spectrometry was employed to assess the evolution of the process over time. Formation of intermediate compounds was followed by high performance liquid chromatography-high resolution mass spectrometry (LC-HRMS); accurate mass-to-charge ratios of parent ions were reported with inaccuracy below 1 mmu, which guarantee the correct assignment of their molecular formula in all cases, while their MS(2) and MS(3) spectra showed several structural-diagnostic ions that allowed to characterize the different transformation products (TPs) and to discriminate the isobaric species. The simulation of phototransformation occurring in the aquatic environment and the identification of biotic and abiotic TPs of the pharmaceutical compound were carried out in different experimental conditions: dark experiments, homogeneous photolysis and heterogeneous photocatalysis using titanium dioxide, in order to recreate conditions similar to those found in the environment. Twenty-one main species were identified afterwards lincomycin transformation. Several isomeric species were formed and characterized by analyzing MS and MS(n) spectra and by comparison with parent molecule fragmentation pathways. The major transformation process for lincomycin is hydroxylation either at N-alkyl side chain or at the pyrrolidine moiety. In addition, oxidation/reduction, demethylation or cleavage of pyranose ring occurs. Based on this information and additional assessment of profiles over time of formation/disappearance of each species, it was possible to recognize the transformation pathways followed by the drug.