Effects of sediment homogenization on interstitial water PCB geochemistry

Sediment homogenization is a common practice in many contaminated sediment toxicity testing and chemical analysis protocols. A primary goal of sediment homogenization is to reduce inter-replicate variability. In this study, the geochemical effects of sediment homogenization were evaluated by measuring the concentration and distribution of polychlorinated biphenyls (PCBs) in environmentally contaminated marine sediment interstitial waters. Sediment homogenization, prior to isolation of interstitial waters, was found to significantly increase the concentration of PCBs in the dissolved and colloidal phases-generally by a factor of two. Long-term storage (i.e., several months) of sediments following mixing appeared to allow interstitial water distributions of PCBs to return to "normal," although a storage artifact may also be present. This study indicates that homogenization results in significant changes in the concentration of PCBs in environmentally contaminated sediment interstitial waters. Consequences of these changes on inferences made based on toxicity tests or chemical analyses using homogenized sediments need to be considered and studied further.