Water brownness regulates the bioavailability of a fluoroquinolone antibiotic: UV-absorbance as a predictor of ciprofloxacin ecotoxicity

Qiyun Zhang; Kristof Demeestere; Karel A C De Schamphelaere

doi:10.1016/j.envpol.2023.122209

Water brownness regulates the bioavailability of a fluoroquinolone antibiotic: UV-absorbance as a predictor of ciprofloxacin ecotoxicity

Environ Pollut. 2023 Oct 1:334:122209. doi: 10.1016/j.envpol.2023.122209. Epub 2023 Jul 14.

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: 37454719
DOI: 10.1016/j.envpol.2023.122209

Abstract

Dissolved organic carbon (DOC) is a powerful regulator of the ecotoxicity of ciprofloxacin (CIP), a widely applied fluoroquinolone antibiotic. In this study, we investigated the impact of DOC from a variety of sources on CIP bioavailability, using a cyanobacteria growth inhibition test with Microcystis aeruginosa. We analyzed the impact from two perspectives: (1) DOC concentration, and (2) water brownness, defined in this work as the light absorbance of DOC solutions. The toxicity tests were conducted with (1) unprocessed freshwater DOC in the naturally occurring state, (2) DOC extracted from a freshwater stream (Schwarzbach stream, Küchelscheid, Belgium), and (3) the commercial DOC product Suwannee River organic matter. Across all DOC sources investigated, a strong negative correlation was observed between CIP ecotoxicity and light absorbance at four wavelengths across the ultraviolet-visible range (e.g., A₃₅₀), whereas CIP ecotoxicity correlated poorly with the DOC concentration. In addition, the interactions between CIP and DOC were modelled as a CIP-DOC binding process to allow the quantification of the inhibitory effects of DOC on CIP toxicity via binding constants (K_d,CIP^x, with x being the ionic charge + or +/-, L g^-1). Processed DOC sources showed higher binding potency than most of the unprocessed DOC sources, suggesting that toxicity tests employing only processed DOC potentially overestimates the impact of DOC in natural environments. Nonetheless, the light absorption coefficient (i.e., ε₃₅₀) appeared a reliable predictor of the K_d,CIP^+/- (and thus of the potential of the DOC source to reduce ecotoxicity of CIP) of both processed and unprocessed DOC. The relationship can be further incorporated into model simulations to estimate CIP bioavailability in dynamic environments. It is concluded that the brownness of water is a better predictor of the impact of DOC on CIP bioavailability than the DOC concentration itself.

Keywords: Antimicrobial; Bioavailability; Ciprofloxacin; Dissolved organic carbon; Environmental risk assessment; Pharmaceutical.

MeSH terms

Anti-Bacterial Agents
Biological Availability
Carbon
Ciprofloxacin / toxicity
Rivers
Water Pollutants, Chemical* / analysis
Water*

Substances

Water
Ciprofloxacin
Water Pollutants, Chemical
Anti-Bacterial Agents
Carbon