Adsorption of antibiotics on different microplastics (MPs): Behavior and mechanism

Area of Science:

• Environmental Chemistry
• Materials Science
• Environmental Science

Background:

• Microplastics (MPs) are emerging contaminants in aquatic environments.
• MPs can adsorb and accumulate pharmaceuticals, including antibiotics, posing ecological risks.
• Understanding the adsorption behavior of antibiotics on various MPs is crucial for risk assessment.

Purpose of the Study:

• To investigate the adsorption behavior and mechanisms of amoxicillin (AMX), ciprofloxacin (CIP), and tetracycline (TC) on four common MPs: polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), and polyethylene (PE).
• To evaluate the influence of environmental factors such as salinity, pH, humic acid (HA), and sodium alginate (SA) on the adsorption process.

Main Methods:

• Batch adsorption experiments were conducted to study the kinetics and isotherms of antibiotic adsorption onto MPs.
• Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) were used to analyze adsorption mechanisms.
• The effects of varying concentrations of NaCl, pH, HA, and SA on adsorption capacity were systematically examined.

Main Results:

• Antibiotic adsorption onto MPs followed pseudo-second-order kinetics and Freundlich isotherm models, indicating multilayer chemical adsorption.
• Adsorption was influenced by both physical and chemical processes, as confirmed by spectroscopic and microscopic analyses.
• Salinity (NaCl), extreme pH values (3 and 9), and the presence of humic acid and sodium alginate generally inhibited antibiotic adsorption, with varying effects depending on the specific antibiotic and co-contaminant concentration.

Conclusions:

• The adsorption of AMX, CIP, and TC onto PVC, PS, PP, and PE is a complex process governed by chemical and physical interactions.
• Environmental factors like salinity, pH, humic acid, and sodium alginate significantly modulate the adsorption efficiency, often leading to inhibition.
• These findings highlight the critical role of MPs in the environmental fate of antibiotics and underscore the need to consider co-contaminants in risk assessments.