A Bioavailability Model to Predict the Impact of pH and Dissolved Organic Carbon on Ciprofloxacin Ecotoxicity to the Cyanobacterium Microcystis aeruginosa

Abstract

Ciprofloxacin (CIP) is a pseudopersistent antibiotic detected in freshwater worldwide. As an ionizable chemical, its fate in freshwater is influenced by water chemistry factors such as pH, hardness, and dissolved organic carbon (DOC) content. We investigated the effect of pH, DOC, and Ca 2+ levels on the toxicity of CIP to Microcystis aeruginosa and developed a bioavailability model on the basis of these experimental results. We found that the zwitterion (CIP +/− ) is the most bioavailable species of CIP to M. aeruginosa, whereas DOC is the most dominant factor reducing CIP toxicity, possibly via binding of both CIP +/− and CIP + to DOC. pH likely also regulates CIP-DOC binding indirectly through its influence on CIP speciation. In addition, higher tolerance to CIP by M. aeruginosa was observed at pH < 7.2, but the underlying mechanism is yet unclear. Calcium was identified as an insignificant factor in CIP bioavailability. When parameterized with the data obtained from toxicity experiments, our bioavailability model is able to provide accurate predictions of CIP toxicity because the observed and predicted total median effective concentrations deviated by <28% from each other. Our model predicts that changes in pH and DOC conditions can affect CIP toxicity by up to 10-fold, suggesting that CIP in many natural environments is likely less toxic than in standard laboratory toxicity experiments.

Occurrence, Bioaccumulation, Metabolism and Ecotoxicity of Fluoroquinolones in the Aquatic Environment: A Review

“…Similarly, Jia et al [ 185 ] observed that co-exposure to heavy metals (Cu and Cd) and FQs (ENR and CIP) exacerbated inflammation in D. rerio embryos. Furthermore, Zhang et al [ 204 ] noted that variations in water pH and dissolved organic carbon (DOC) significantly affected the toxicity of CIP to M. aeruginosa , revealing potential differences in cell toxicity of up to 10-fold under different water conditions. These findings indicate that changes in environmental factors can significantly influence the cellular toxicity of FQs.…”

Water Brownness Regulates the Bioavailability of a Fluoroquinolone Antibiotic: UV-Absorbance as a Predictor of Ciprofloxacin Ecotoxicity

“…After adjusting the pH of the samples to 3.0, the samples were extracted with OASIS HLB cartridges (6 mL, 200 mg sorbent) as described in Zhang et al 10 . The extracts were dried under N2 flux and dissolved again in 1.0 mL reconstitute solvent made of methanol/water (10/90, v/v %) containing 0.1% formic acid and 0.1 g L -1…”

“…The relationship between the bioavailability of CIP and DOC was simulated using the bioavailability model developed by Zhang et al 10 . The CIP-DOC interaction is simulated as a simple binding process (Eq.…”

“…Recently, DOC was found to affect the bioavailability of ciprofloxacin (CIP), an antibiotic pharmaceutical with relatively low hydrophobicity 10 . As a widely applied human and veterinary medicine, CIP has been detected in surface water worldwide, which raises concerns about its potential to trigger adverse effects on aquatic organisms and about antimicrobial resistance (AMR) selection 11,12 .…”

“…Using toxicity experiments, it is impractical to test all the possible conditions of the different waters. Using a bioavailability model, as suggested by Zhang et al 10 , could be an efficient method to simulate the impact of the dynamics in the DOC, but it is yet unclear whether and which properties of DOC might determine the impact of DOC on CIP bioavailability.…”