Biodegradability of Dental Care Antimicrobial Agents Chlorhexidine and Octenidine by Ligninolytic Fungi.

Lucie Linhartová,Klára Michalíková,Kamila Šrédlová,Tomáš Cajthaml

doi:10.3390/molecules25020400

Abstract

Chlorhexidine (CHX) and octenidine (OCT), antimicrobial compounds used in oral care products (toothpastes and mouthwashes), were recently revealed to interfere with human sex hormone receptor pathways. Experiments employing model organisms—white-rot fungi Irpex lacteus and Pleurotus ostreatus—were carried out in order to investigate the biodegradability of these endocrine-disrupting compounds and the capability of the fungi and their extracellular enzyme apparatuses to biodegrade CHX and OCT. Up to 70% ± 6% of CHX was eliminated in comparison with a heat-killed control after 21 days of in vivo incubation. An additional in vitro experiment confirmed manganese-dependent peroxidase and laccase are partially responsible for the removal of CHX. Up to 48% ± 7% of OCT was removed in the same in vivo experiment, but the strong sorption of OCT on fungal biomass prevented a clear evaluation of the involvement of the fungi or extracellular enzymes. On the other hand, metabolites indicating the enzymatic transformation of both CHX and OCT were detected and their chemical structures were proposed by means of liquid chromatography–mass spectrometry. Complete biodegradation by the ligninolytic fungi was not achieved for any of the studied analytes, which emphasizes their recalcitrant character with low possibility to be removed from the environment.

Highlights

Antiseptics and disinfectants, whose worldwide consumption is increasing year by year, rank among the most intensively studied trace organic contaminants [1]
Quaternary ammonium compounds (QACs), such as hexadecylpyridinium chloride (HDP) and octenidine (OCT), phenolic derivatives, and biguadines belong among frequently used antiseptic compounds in toothpastes and mouthwashes and some of them were already detected in wastewater effluents [2,3]
The aim of this work was to investigate the biodegradability of CHX and OCT, which are used in oral care products and were identified in our previous research as endocrine disruptors, by two model ligninolytic fungal strains, I. lacteus and Pleurotus ostreatus, i.e., species with proven biodegradation capabilities

Summary

Introduction

Antiseptics and disinfectants, whose worldwide consumption is increasing year by year, rank among the most intensively studied trace organic contaminants [1]. The wide range of their usage in daily urban activities, including dental hygiene, contributes to the continual release of these biologically active compounds into the environment in amounts that lack any control or restrictions. The water solubility of these micropollutants has the potential to cause widespread contamination, usually at very low concentration levels (pg–μg/L). Due to the fact that wastewater treatment plant (WWTP) technologies are usually not designed for their removal, most disinfectants are not being eliminated [4,5]. Several studies demonstrated that antiseptics and disinfectants were released from

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