Microplastics (MPs) are widely recognized as emerging pollutants in aquatic environments, including estuarine and brackish water systems. These tiny plastic particles not only persist in the environment but also act as carriers for various chemical pollutants, including antibiotics. Due to human activities, antibiotics are frequently detected in aquatic systems and can adsorb onto MPs, influencing their transport, bioavailability, and potential ecological risks. In estuarine environments, where freshwater and seawater mix, fluctuations in salinity, organic matter content, and microbial communities further complicate the interactions between MPs and antibiotics. While previous studies have investigated the adsorption-desorption behavior of MPs with pollutants in freshwater and marine systems, research on these processes in estuarine conditions remains limited. Additionally, the potential effects of MP-antibiotic complexes on microbial communities are not yet well understood. Given the ecological significance of estuaries as biodiversity hotspots and key nurseries for marine life, a deeper understanding of these interactions is essential. This study aims to examine the adsorption-desorption behavior of antibiotics on MPs in estuarine waters and evaluate their impact on microbial communities, providing critical insights into environmental risks and pollution management strategies.
　　The experiment consists of two stages: (1) In the first stage, antibiotic-MP mixtures will be dispersed in simulated brackish water with varying salinities. Over at least four days, the concentration and composition of antibiotics in both the water phase and on MP surfaces will be periodically measured to establish desorption curves under different salinity conditions. (2) In the second stage, the antibiotic-MP mixtures will be introduced into a microbial experimental ecosystem designed to simulate a typical Japanese brackish water environment, specifically Lake Hamana, for a period of more than 20 days. During this time, biochemical analyses of water samples and sediment leachates will be conducted to assess the ecological risks of these combined pollutants. These analyses will evaluate microbial community activity and changes in biogeochemical cycling in both the water column and sediments.