Chapter 10. Sorption II: Partitioning to Living Media - Bioaccumulation and Baseline Toxicity

Summary

Bioaccumulation of organic chemicals such as DDT has inspired many people's concern for our environment. To understand such uptake, chemical partitioning into various key materials of which organisms consist (e.g., lipids, proteins, lignin, cutins) is examined in a manner analogous to organic solvent-water or organic solvent-air partitioning. Combining these medium-specific partitioning insights with compositional information for organisms or tissues of interest, values of the equilibrium distribution coefficients such as the biota-water distributions (Kbio) can be estimated. Further, for organisms simultaneously (a) exchanging organic pollutants with their surroundings via multiple processes involving respiration, food consumption, excretion and (b) influencing body burdens by metabolism and growth, the equilibrium distribution coefficients can be used in mass transfer formulations to assess bioaccumulation as a dynamic process. By using the equilibrium distribution coefficients as normalizing factors, both aquatic and terrestrial organisms can be examined for the fugacities (or chemical activities) of organic compounds of interest to determine the extent of disequilibrium between those organisms and the media to/from which they may exchange chemicals (e.g., fish versus water or nearby sediment beds) and whether chemical uptake truly reflects a biomagnification along food chains (e.g., grass to cows to humans). Finally, baseline toxicities (due to narcosis) and critical body burdens of organic chemicals can be understood using quantitative structure-activity relationships (QSARs) and parameters like lipid-water partition coefficients (Klip w) or organic solvent surrogates like Kow.