Association with sediments is of major importance for fate and effects of trace contaminants in aquatic systems. Sediments serve as a sink for various environmental pollutants, especially hydrophobic organic contaminants (HOCs) including many persistent organic compounds (POPs), due to their highly hydrophobic nature and low aqueous solubility. Hydrophobicity is important namely for the catchment of the nonpolar organic pollutants including polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), polychlorinated naphthalenes (PCNs) and polybrominated diphenylethers (PBDEs). POPs in the river ecosystem are transported as dissolved, or bound to different-sized particles. But due to their overall low solubility POPs tend to appear mainly in association with particulate matter.