The influence of sediment and feeding on the elimination of polycyclic aromatic hydrocarbons in the freshwater amphipod, Diporeia spp.

The elimination of non-polar organic contaminants from sediment dwelling aquatic invertebrates was thought to be dominated by fecal elimination. This was particularly thought to be the case for the amphipod, Diporeia spp. that encapsulates the fecal material in a peritrophic membrane. The elimination of selected PAH congeners by Diporeia spp. was determined in the presence of three solid substrates and under water only conditions. The elimination was generally enhanced by the presence of a solid substrate whether or not the organism employed the material as a food source. The greater the sorptive capacity of the substrate, the greater its influence on the elimination process. Elimination via the fecal route was generally insignificant except for the elimination of BaP in the presence of sediment. In this case, the fecal elimination accounted for up to 40% of the total elimination, and the extent of elimination via the fecal route increased with the amount of fecal material produced. Thus, it is clear from the above effort that the main mechanism for elimination of contaminants in the presence of a substrate is primarily via passive diffusion from the organism with subsequent sorption to the solid substrate, which maintains the chemical activity gradient between the organism and the water. This effort refutes the earlier hypothesis that fecal elimination is the dominant route of elimination for Diporeia spp., and that the peritrophic membrane plays any substantial role in the elimination process.