Combined impacts of chlorine and pharmaceutical discharge on river periphyton and zoobenthos

Abstract

Following the COVID-19 outbreak, a vast array of chlorine disinfectants was used to eliminate the virus, leading to inevitable discharge into aquatic ecosystems. These environments also contain various anthropogenic micropollutants, such as pharmaceuticals, which pose threats to the survival and activities of biological communities. Consequently, the presence of discharged chlorine disinfectants and pharmaceuticals can simultaneously impact the structure and function of aquatic ecosystems. To investigate the combined effects of chlorine disinfectants and pharmaceuticals on the periphyton and zoobenthos (Limnodrilus hoffmeisteri) community composition and function, we conducted a 12-flume reactor experiment using sodium hypochlorite and representative pharmaceuticals (abundant in the Yangtze River) as influents. Results demonstrated that the discharge of chlorine disinfectants further altered the composition of river prokaryotic communities. Eukaryotic organisms within the periphyton exhibited greater resilience to chlorine exposure compared to prokaryotic communities. Metagenomic analysis revealed that prokaryotic communities with different compositions can execute similar functions, while RNA sequencing indicated that co-exposure promoted biological processes such as focal adhesion and ribosome synthesis, but inhibited activities related to nitrogen metabolism and resistance to folate antimicrobials. Additionally, co-exposure induced oxidative stress in L. hoffmeisteri, leading to stronger environmental adaptation.