Loading of PES membrane. Efficient and uniform loading of the chemical on polymer material is a prerequisite step for the passive dosing approach. Because passive dosing would be particularly advantageous for long-chain BACs, the target substances were changed from C12-BAC to C14-, C16-and C18-BACs at this point. The actual mass of C14-, C16-and C18-BACs loaded on the PES membrane ranged from 70 to 148 % of the mass added initially to the loading solution (Figure ). Some BACs (1-30 %) remained in the loading solution, particularly when the BAC concentrations in the loading solution were high. The distribution between PES membrane and the loading solution followed the nonlinear Freundlich isotherm model (Figure ) with a Freundlich exponent of 0.23-0.43, indicating relatively weak sorption at high loading levels. C14-and C16-BACs on the glass beakers were less than 2 % of the added mass in the loading experiment (Figure ). In a preliminary loading experiment for two different exposure concentrations, the masses of C14-BAC in replicated loaded PES membranes were similar (Figure ), indicating uniform distribution to the PES membrane pieces in the loading step.