The influence of pH and dissolved organic carbon on the ecotoxicity of ampicillin and clarithromycin

Qiyun Zhang; Kristof Demeestere; Karel A C De Schamphelaere

doi:10.1016/j.scitotenv.2023.166781

The influence of pH and dissolved organic carbon on the ecotoxicity of ampicillin and clarithromycin

Sci Total Environ. 2023 Dec 15:904:166781. doi: 10.1016/j.scitotenv.2023.166781. Epub 2023 Sep 4.

Authors

Qiyun Zhang¹, Kristof Demeestere², Karel A C De Schamphelaere³

Affiliations

¹ GhEnToxLab, Department of Animal Science and Aquatic Ecology, Ghent University, Ghent, Belgium; Research group EnVOC, Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium. Electronic address: qiyun.zhang@ugent.be.
² Research group EnVOC, Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
³ GhEnToxLab, Department of Animal Science and Aquatic Ecology, Ghent University, Ghent, Belgium.

PMID: 37666341
DOI: 10.1016/j.scitotenv.2023.166781

Abstract

The impacts of water chemistry properties including pH and dissolved organic carbon (DOC) on the ecotoxicity of active pharmaceutical ingredients (APIs) are increasingly evident. These impacts are a result of alterations in API bioavailability: pH regulates the bioavailability of many ionizable APIs via chemical speciation, whereas DOC interacts with several APIs to inhibit the APIs from traversing the membrane system of organisms. In this study, we examined the influences of pH and DOC on the bioavailability of ampicillin (AMP) and clarithromycin (CLA) with the help of a bioavailability model. The effects on bioavailability were quantified by ecotoxicity observed in cyanobacteria growth inhibition tests with Microcystis aeruginosa PCC7806. The median effect concentration (96 h-EC50_total) of AMP increased by 5-fold when pH raised from 7.4 to 9.0, suggesting the zwitterionic AMP^+/- species being higher in bioavailability than the negatively charged AMP^- species. CLA ecotoxicity showed no significant pH-dependency, suggesting CLA⁺ and CLA⁰ species to be equally bioavailable, albeit it correlated significantly with M. aeruginosa growth rate in negative controls. In addition, DOC demonstrated no significant effects on the ecotoxicity of AMP or CLA. Overall, together with earlier results on ciprofloxacin, our data show that bioavailability relations with pH and DOC are variable among different antibiotics. Factors other than chemical speciation alone could play a role in their bioavailability, such as their molecular size and polarity.

Keywords: Antibiotics; Bioavailability; Ecotoxicology; Ionizable compound.

MeSH terms

Ampicillin / toxicity
Carbon / chemistry
Clarithromycin* / toxicity
Dissolved Organic Matter
Hydrogen-Ion Concentration
Water Pollutants, Chemical* / analysis

Substances

Clarithromycin
Dissolved Organic Matter
Water Pollutants, Chemical
Ampicillin
Carbon