Biomarker analysis of combined oxytetracycline and zinc pollution in earthworms (Eisenia fetida)

• Antagonistic effects of OTC and Zn2+ exposure were proofed compared to Zn2+ alone.
• A mechanism involving complexation of Zn2+ and OTC at alkaline pH is proposed.
• Lysosomal membrane stability and coelomocyte apoptosis are sensitive biomarkers.

To determine the interactive action of antibiotics and heavy metals, this study assessed pollutant-induced responses of cellular biomarkers in earthworms (Eisenia fetida) exposed to zinc (Zn2+) and oxytetracycline (OTC) in soil. Lysosomal membranes were damaged and coelomocyte apoptosis occurred with exposure to the individual and combined pollutants. Compared with Zn2+ alone, lysosomal membrane stability and coelomocyte apoptosis decreased in the Zn2+–OTC combined treatment, possibly as a result of complexation of Zn2+ and OTC at alkaline pH. Such complexation could reduce the toxicity of the pollutants. Lysosomal membrane stability and coelomocyte apoptosis are sensitive biomarkers and could be economical and rapid tools for the monitoring and assessment of a variety of pollutants.