Black magic in the aquatic environment

Sorption to sediment controlsthe actual fate and risks ofhydrophobic organic contaminants (HOCs)in most aquatic environments. Sediment-bound HOCs are not readily available for uptake by organisms and degradation, and their mobility is drastically reduced as compared to dissolved chemicals. Sorption of HOCs to sediment is generally being considered as a simple linear equilibrium partitioning process between water and natural organic matter present in sediment. During the past few years, however, several observations have been reported that contradict this equilibrium partition theory (EPT). The first chapter of the present thesis shows some important examples of such observations for field sediments, which indicate that sorption of in particular HOCs with planar molecular structures may exceed EPT-predictions by a factor of 100-1000. This extremely strong sorption was attributed to the presence of sedimentary anthropogenic carbon phases (i.e., carbonaceous materials released into the environment as a result of human activities), such as soot. The remaining chapters focus on investigating sorption of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), as representative HOCs, to pure anthropogenic carbon phases (soot, (char)coal, and oil) and the effects these materials have on sorption to and bioaccumulation from sediment. As existing partition methods failed to quantify sorption to soot, anovel technique was developed first. Application of thisPolyoxymethylene Solid Phase Extraction (POM-SPE) method to ten different types of soot and soot-like materials showed extremely strong (highest ever reported) sorption of the chemicals, which often exceeded partitioning into natural organic matter by more than a factor of 1000. Furthermore, sorption was mostenhancedfor planar (most toxic) chemicals, which resulted in reduced uptake of such chemicals in aquatic worms during bioaccumulation experiments on sediments containing soot-like materials. Based on both POM-SPE sorption experiments and an extraction study with several organic solvents, large fractions of native soot- and coal-associated PAHs were concluded to be bound inside the solid matrixes in such a way that the chemicals were not available for desorption to the aqueous phase on time scales of probably years to decades. Finally, experiments with oils showed that weathering of oil-contaminated sediments resulted in the formation of weathered oil phases for which low-molecular-weight PAHs had extremely high affinities (exceeding affinities for most types of soot) and that were significantly less toxic than fresh oils. In addition, weathering of oil was found to stimulate PAH biodegradation. As current risk assessment procedures are all based on EPT and do not take enhanced sorption to ubiquitous anthropogenic carbon phases or reduced toxicity of weathered sediments into account, risks of contaminated sediments may often be overestimated.