Desorption kinetics and equilibrium. The desorption behavior of BACs from the PES membrane was examined to determine the pre-equilibration time. Dechlorinated tap water (hardness: ~80 mg-CaCO3/L) was selected as the exposure medium. Note that use of Elendt M4 synthetic medium resulted in lowering of the aqueous phase concentration of C14-BAC, likely due to degradation, and thus this medium was not used. In this desorption experiment, a loaded PES piece was placed in a 50 mL glass beaker, which received 50 mL of dechlorinated water and was shaken at 135 rpm, 25°C for 5 days (C14-BAC) and 7 days (C16-BAC). Note also that a piece of polyacrylate (PA) microfiber was put in the beaker for passive sampling but the results of this will be reported elsewhere. At desired time intervals, 0.5 mL water sample was taken with a glass pipette after five times aspirating and dispensing for pre-wetting of the pipette and was further diluted with 0.5 mL of acetonitrile (ACN) containing internal standard (100 µg/L) to measure the water concentration (Cw) of BACs. After the desorption test, the PES membranes were extracted two times with 0.1% formic acid/ACN at 150 rpm and 25°C for 24 h each. Then, all the dechlorinated water was replaced by 5 mL of 0.1% formic acid/ACN mixture to extract the wall of the glass beaker (2-3 h, 25°C, 150 rpm).