COMPARISON OF TECHNIQUES FOR THE ISOLATION OF SEDIMENT PORE-WATER FORTOXICITY TESTING

The objective of this study was to define an interstitial (pore) water isolation technique suitable for sediment toxicity testing and toxici ty identification evaluation (TIE) research. Pore water was prepared f rom sediments collected at two freshwater sites (Saginaw River, Keween aw Waterway) using four or five different techniques, and the samples were compared with respect to toxicity to Ceriodaphnia dubia and sever al inorganic chemical parameters. Methods evaluated were: high speed(1 0,000 x g) and low speed (2,500 x g) centrifugation, syringe extractio n, compression,and dialysis. Both high speed and low speed centrifugat ion resulted in adequate volumes of pore water for routine testing wit h relatively minimal effort, while the other three techniques were lab or intensive and/or yielded small quantities of pore water. Filtration of samples either during preparation (syringe-extraction, compression ) or subsequent to initial isolation (centrifuged samples) resulted in significant losses of toxicity, apparently due to the adsorption of c ontaminants onto the filter or particles retained by the filter. Low s peed centrifugation generally resulted in much higher metal concentrat ions than the other four techniques. However, compared to samples prep ared by high speed centrifugation or dialysis, a relatively high propo rtion of the metals in pore water isolated by low speed centrifugation were biologically unavailable, as inferred from the results of the to xicity tests. Based on these studies, as well as the work of others, w e recommend that sediment pore water for toxicity testing and/or TIE a nalyses be prepared by centrifugation (preferably at 10,000 x g) witho ut subsequent filtration.