Warming fluctuating temperature shifts the BPA-damage threshold of a freshwater microplankton community

The increasing production of plastics worldwide is a growing source of emerging contaminants, particularly bisphenol A (BPA), a major chemical additive in plastics that, as waste, ends up polluting aquatic ecosystems. This study investigated the combined effects of environmentally relevant BPA concentrations (0-5 µg L^-1) and warming fluctuating temperature (WF, 19-24 °C) under environmentally realistic conditions on a freshwater microplankton community in Charca de Suárez (Motril, Spain). A 2 × 6 factorial experiment measured photochemical efficiency, chlorophyll a, primary production, community respiration, and metabolic balance over seven incubation days. Contrary to expectations, WF did not consistently accentuate BPA toxicity. Instead, BPA produced concentration-dependent, non-linear responses modulated by WF, leading to antagonistic interactions that varied across physiological traits. Photochemical efficiency remained within a physiologically normal range, showing only a slight increase at low-intermediate BPA under constant temperature that was attenuated under WF. Net primary production, chlorophyll a, and community respiration displayed U-shaped responses along the BPA gradient, with WF partially mitigating inhibitory effects on production but enhancing community respiration. Metabolic balance remained net autotrophic, though altered under WF. BPA removal rate was high (>95%), with efficiency influenced by BPA concentration, biomass, and temperature regime. Overall, interactions between BPA concentration and thermal variability were predominantly antagonistic and trait-specific. These findings underscore the need to incorporate realistic chemical and temperature dynamics when evaluating the ecological risks of emerging contaminants under global warming. They reveal how these factors shape the metabolic activity of microplankton, providing valuable insights into the potential ecological consequences of contaminant exposure in a warming world.