Interactive effects of tyre wear particles and oxytetracycline on a marine polychaete-sediment ecosystem

Tyre wear particles (TWPs) and antibiotics are co-occurring contaminants in coastal sediments, yet their combined effects on polychaete-associated sediment processes remain under reported. This study provides new evidence on the joint effects of TWPs and oxytetracycline (OTC) on a polychaete-sediment ecosystem. Polychaete-sediment systems were exposed to TWPs (1% of sediment dry weight), OTC (2.0 mg·L^-1), and their combined treatment for 16 days. In polychaete-containing sediments, OTC-TWP co-exposure was associated with higher OM (1.74%) relative to the polychaete group, consistent with a reduced sediment-reworking effect. Co-exposure also altered inorganic nitrogen profiles and increased alkaline phosphatase activity to 184.37 nmol·g^-1. Microbial analysis showed that OTC-TWP co-exposure was associated with lower Chao1 and ACE indices, and Desulfobacterota showed a higher relative abundance in TWP groups. OTC and TWP co-exposure triggered oxidative stress and physiological alterations in P. aibuhitensis, reflected by increased MDA levels and changes in antioxidant responses. Moreover, exposure to these pollutants resulted in the suppression of AChE and LZM activities. Given the global occurrence of TWPs and antibiotics in coastal environments, this study provides insights into the ecological risks of emerging contaminant mixtures and highlights the need to incorporate particle-antibiotic co-pollution into sediment risk assessment.