The acute toxicity test was performed for 48 h without shaking after a 24 or 48 h pre-equilibrium period to allow the passive dosing system to reach equilibrium. Water was sampled every 24 h starting from just before adding daphnids to the end of the exposure experiment to observe the stability of Cw throughout the test period. A beaker containing a PES membrane that experienced the same loading procedure but without the test chemical was prepared as a control sample. The loaded PES membranes were either immediately extracted before the toxicity test or used for the toxicity test, retrieved from the beaker after 48 h exposure, and extracted to check for loss of BACs from the PES membranes to the exposure system. Beaker wall extraction was also conducted for C14-, C16-and C18-BACs after the acute ecotoxicity test, following the procedure described above.