1 Department of Environmental Science - Environmental chemistry & toxicology, Department of Environmental Science, Science and Technology, Aarhus University2 ITM, Stockholm University3 University of Eastern Findland4 University of Eastern Finland5 Department of Environmental Science - Environmental chemistry & toxicology, Department of Environmental Science, Science and Technology, Aarhus University
Equilibrium sampling into various formats of the silicone polydimethylsiloxane (PDMS) is increasingly used to measure the exposure of hydrophobic organic chemicals in environmental matrices, and passive dosing from silicone is increasingly used to control and maintain their exposure in laboratory experiments. Both these equilibrium partitioning approaches are normally calibrated to freely dissolved aqueous concentrations (Cfree), which often are considered the effective concentration for partitioning, bioconcentration and toxicity. In the present studies we extend the calibration of such methods towards equilibrium partitioning concentrations in lipids (Clipid,partitioning). The first approach proceeds in two steps; (i) the concentration in the PDMS (CPDMS ) is determined and (ii) multiplied with recently determined lipid to PDMS partition ratios (Klipid,PDMS). The second approach applies external partitioning standards in vegetable or fish oil for the complete calibration of equilibrium sampling techniques without additional steps. Equilibrium in tissue sampling in three different fish yielded lipid based PCB concentrations in good agreement with those determined using total extraction and lipid normalization. These results support the validity of the in tissue sampling technique, while at the same time confirming that the fugacity capacity of these lipid-rich fish tissues for PCBs was dominated by the lipid fraction. Equilibrium sampling of PCB contaminated lake sediments with PDMS coated vials and with Head Space Solid Phase Microextraction (HS-SPME) yielded lipid based concentrations that were in good agreement with each other, but about a factor of two higher than measured lipid-normalized concentrations in the organisms. Passive dosing was applied to bioconcentration and toxicity studies of several PAHs with the terrestrial springtail Folsomia candida. Within the bioconcentration study, equilibrium partitioning concentrations in lipids served as a well defined reference for the evaluation of measured concentrations in the springtails. In the toxicity tests of naphthalene, phenanthrene and pyrene, lethal concentrations were determined also on a Clipid,partitioning basis and were in good agreement with the typical range of lipid membrane burdens for baseline toxicity (40-160 mM). This demonstrates that these new calibration principles also can be applied within a toxicological context.