Unraveling combined toxicity of microplastics and antibiotics on aquatic ecosystems: A case study in the Beiluo river, China

Microplastics (MPs) can adsorb antibiotics to form complex pollutants that seriously threaten the health of freshwater ecosystems. However, few studies have examined the combined ecotoxicity of MPs and multiple antibiotics in natural aquatic environments. In this study, we examined the effects of combined exposure to antibiotics and MPs on aquatic community structure in natural settings in the Beiluo River using eDNA analysis. The results revealed that antibiotic pollution in the Beiluo River mainly originates from animal husbandry and agriculture, whereas MPs mainly originate from agriculture and urban sewage. The community structure of aquatic organisms was significantly correlated with the concentrations of antibiotics and MPs (Mantel's test r ​= ​−0.58 to 0.90, p ​< ​0.05). The combined effects of antibiotics and MPs explained 24.36 ​% and 45.14 ​% of the variation in cyanobacteria and phytoplankton (VPA). Key antibiotics including tetracycline hydrochloride ( r ​= ​0.89), OTC hydrochloride ( r ​= ​0.87), and lincomycin hydrochloride ( r ​= ​0.90) showed particularly strong associations with phytoplankton communities. The effect of MPs on antibiotic toxicity was highly dependent on the antibiotic type and MP particle size. Small-particle-size MPs (<500 ​μm) mainly affected planktonic communities, while large-particle-size MPs (>500 ​μm) predominantly impacted zoobenthos. The results of this study enhance our understanding of the complex combined effects of MPs and antibiotics on aquatic organisms, emphasizing the necessity of informed scientific management of these emerging contaminants. • Multiple antibiotics were detected in surface water of the Beiluo River. • The effects of antibiotics on aquatic communities vary depending on the antibiotic. • The combined toxicity had significant effects on cyanobacteria and phytoplankton. • Small-particle-size microplastics and antibiotics have synergistic toxicity.