MA5 Novel Methods for Bioaccumulation Assessment
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() Relevance of free concentration measurements in biaccumulation and toxicity studies.

Hermens, Joop1, ter Laak, Thomas1, Heringa, Minne1, van der Wal, Leon2, 1 Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands2 University fo Umea, Umea, Sweden

ABSTRACT- Concentration measurements form the basis for the generation of numerous experimental parameters and many decisions are based on reported measured concentrations. Bioconcentration factors of highly hydrophobic compounds for example use aqueous concentrations in the denominator, although it is known that concentration measurements in aqueous solutions of hydrophobic chemicals are extremely difficult to perform and are often subject to systematic errors. Total concentrations in soil and sediment are still often used by regulatory agencies in risk assessment decisions, while differences in bioavailability may strongly affect a site-specific risk. Also in vitro systems often report a dose or a concentration at a certain biological effect. However, as the precise exposure in these systems is often not investigated, such data and also the conclusions based on these data are often highly uncertain. This is one of the reasons why quantitative in vitro assays are poor in predicting quantitative in vivo effects. In this presentation we advocate the use of measured freely dissolved concentrations as a more intrinsic concentration parameter. Experimental data show that bioconcentration factors in soil and sediment organisms, calculated via freely dissolved concentration, do not show the often observed non-linearity with octanol-water partition coefficients. We will show that effect concentrations based on freely dissolved concentrations represent the more intrinsic potency of chemicals in in vitro assays. These data provide unbiased input for computational methods, and can shed an entirely different light on the activity of chemicals. Finally, examples will be presented on measured free concentrations in relation to bioavailability in soil. Besides the focus on examples, also techniques for measuring freely dissolved concentrations will be briefly discussed with an emphasis on solid phase micro-extraction.

Key words: bioaccumulation, bioavailability, free concentrations, passive sampling methods

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