Interfaces in aquatic ecosystems: Implications for transport and impact of anthropogenic compounds

Abstract: Mechanisms that govern transport, accumulation and toxicity of persistent pollutants at interfaces in aquatic ecosystems are the foci of this thesis. Specific attention is paid to humic substances, their occurrence, composition, and role in exchange processes across interfaces. It was concluded that: Composition of humic substances in aquatic surface microlayers is different from that of the subsurface water and terrestrial humic material. Levels of dissolved organic carbon (DOC) in the aquatic surface microlayer reflect the DOC levels in the subsurface water. While the levels and enrichment of DOC in the aquatic surface microlayer generally show small variations, the levels and enrichment of particulate organic carbon (POC) vary to a great extent. Similarities exist between aquatic surface films, artificial semi-permeable and biological membranes with regard to their structure and functioning. Acidifcation and liming of fresh-water ecosystems affect DOC:POC ratio and humic composition of the surface film, thus influencing the partitioning of pollutants across interfaces. Properties of lake catchment areas extensively govern DOC:POC ratio both in the surface film and the subsurface water. Increased UV-B irradiation changes the DOC:POC ratio in the surface film and thus affects transfer of matter across the interface. Transport of lipophilic, persistent organic pollutants across semi-permeable membranes is influenced by the organic composition of the solute. Significant passive, diffusion mediated transport of lipophilic, organic pollutants across interfaces in aquatic ecosystems exists.