Using the Tea Bag Index to unravel how interactions between an antibiotic (Trimethoprim) and endocrine disruptor (17a-estradiol) affect aquatic microbial activity.

The constant release of complex mixture of pharmaceuticals, including antimicrobials and endocrine disruptors, into the aquaticenvironment. These have the potential to affect aquatic microbial metabolismand alter biogeochemical cyclingof carbon and nutrients. Here we advance the Tea Bag Index (TBI) for decomposition by using it in a series of contaminant exposure experiments to test how interactions between an antibiotic ( trimethoprim) and endocrine disruptor(17a-estradiol) affects microbial activity in an aquaticsystem. The TBI is a citizen sciencetool used to test microbial activity by measuring the differential degradation of green and rooibos tea as proxies for labileand recalcitrant organic matterdecomposition. Exposure to trimethoprimand 17a-estradiol had significant independent negative effects upon decomposition of labile organic matter(green tea), suggesting additive effects upon microbial activity. Exposure to 17a-estradiol alone negatively affected the degradation of more recalcitrant organic matter(rooibos tea). Consequently, trimethoprimand 17a-estradiol stabilized labile organic matteragainst microbial degradation and restricted degradation rates. We propose that the method outlined could provide a powerful tool for testing the impacts of multiple interacting pollutants upon microbial activity, at a range of scales, across aquaticsystems and over biogeochemically relevant time scales.