The occurrence and the partitioning of Polycyclic Aromatic Hydrocarbons (PAHs) and trace metals were investigated in conventional activated sludge wastewater treatment plants. Concentrations of labile, total dissolved and particulate contaminants were determined in wastewater at several points across the treatment system. Labile (i.e. truly dissolved) PAHs were sampled by means of Semipermeable Membrane Devices. Labile (inorganic and weakly complexed) dissolved metals were sampled using the Diffusive Gradient in Thin film technique. Total dissolved and particulate contaminants were analyzed in grab samples. All contaminant concentrations decreased in wastewater along the treatment, although dissolved and labile concentrations sometimes increased for substances with less affinity with organic matter. Partitioning of contaminants between particles and the water phase was strongly related to suspended solid concentrations. Conversely, poorly significant relationships were observed between dissolved organic matter and labile fractions of substances in filtered wastewater.