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(348) Baseline toxicity of mixtures: measuring and estimating TBR . Leslie, Heather1,2, Oosthoek, Annelies2, Busser, Frans1, Kraak, Michiel2, Hermens, Joop1, 1 2 ABSTRACT- In the aquatic environment, organisms are exposed to complex mixtures of organic contaminants which exhibit baseline toxicity. Biomimetic solid phase microextraction (SPME) is currently being developed as a tool for the risk assessment of contaminants with this mode of action. Applying this chemical partitioning method, a small amount (negligible depletion) of the freely dissolved ('bioavailable') fraction of organic chemicals in an aqueous sample is extracted by the polymer coating of an SPME fiber. Baseline toxicity resulting from these chemicals is dependent on the total internal concentration and concentration addition applies. Our goal was to determine if total body residues (TBRs) of contaminants in organisms can be estimated by determining concentrations in a surrogate phase, the SPME fibers. To investigate this, Lumbriculus variegatus worms, Chironomus riparius midge larvae and SPME fibers were exposed to mixtures of chlorinated benzenes. The SPME fibers accumulated the compounds in proportions similar to the invertebrates within the time frame of our toxicity tests. Acute mortality was scored and critical body residues (CBRs) were in the expected range of 30-160 mmol/kg lipid, although the worms survived somewhat higher concentrations than the midge larvae. Based on the results of biomimetic SPME and applying a conversion factor, we were able to make reliable estimates of the TBR, from which baseline toxicity can be predicted. Key words: mixtures, baseline toxicity, SPME, body residues |
