Effects of six antibiotics and their binary mixtures on growth of Pseudokirchneriella subcapitata

Area of Science:

• Environmental toxicology
• Aquatic ecology
• Pharmaceutical science

Background:

• Antibiotics are emerging environmental contaminants.
• Non-target aquatic organisms can be affected by pharmaceutical pollution.
• Mixture toxicity is complex and difficult to predict.

Purpose of the Study:

• To assess the individual and combined toxicity of six antibiotics on the green alga Pseudokichneriella subcapitata.
• To compare experimental mixture toxicity with predictions from concentration addition (CA) and independent action (IA) models.
• To evaluate the ecological risk of these antibiotics in hospital effluents.

Main Methods:

• Testing the toxicity of ampicillin, amoxicillin, cephalotin, ciprofloxacin, gentamycin, and vancomycin individually and in binary mixtures on Pseudokichneriella subcapitata.
• Using algal growth inhibition assays to determine EC50 values.
• Applying CA and IA models to predict mixture toxicity and comparing with experimental results.
• Conducting a risk assessment using predicted environmental concentrations (PEC) and predicted no-effect concentrations (PNEC).

Main Results:

• Ciprofloxacin and gentamycin were the most toxic antibiotics individually.
• Ampicillin and amoxicillin showed no significant toxicity.
• Binary mixtures exhibited clear synergistic effects, with experimental toxicity exceeding predictions from CA and IA models.
• Most antibiotics, except gentamycin, posed a potential ecological risk based on hospital effluent data, with risks amplified in mixtures.

Conclusions:

• Single antibiotic toxicity data are insufficient for predicting the ecological risks of antibiotic mixtures.
• Synergistic interactions significantly increase the toxicity of antibiotic mixtures in aquatic environments.
• Hospital effluents containing antibiotics pose a considerable ecological risk to aquatic organisms like Pseudokichneriella subcapitata.