The bioavailability of organic compounds is dependent on the aquatic environment characteristics. In particular, organic compounds may be bounded by dissolved organic matter (DOM) making them more mobile and less biodegradable by biological/chemical processes. The presence of DOMs also usually reduces the bioavailability of organic compounds. The generally accepted assumption is that pollutants that are bound to DOM are too large to cross biological membranes. An artificial device (Semi-Permeable Membrane Device (SPMD)) has been developed to evaluate bioavailable fractions of hydrophobic organic compounds [1,2]. It is a long, flat, polyethylene (PET) tube containing lipid (triolein). The 10 Å pore diameter of PET allows contaminants to pass through, in the same way as the membranes of animal cells and the triolein was chosen to be like lipids in biological tissues. To evaluate the representativity of the SPMD sampling, we have compared SPMD-available fraction with Daphnia-available fraction of benzo(a)pyrene (BaP) in controlled solutions with various natural or commercial DOMs characterised by different molecular sizes and binding capacities. Natural DOMs were previously extracted from rivers onto XAD resins. Our results showed that in most cases, SPMDs are good surrogates for living organisms when considering the BaP fraction accumulated.