PARENT SESSION
3G Environmental partitioning processes
9:00 AM to 7:00 PM, Tuesday, 08 May 2001

(T/MF151) Bioaccumulation of Organic Chemicals in Aquatic & Terrestrial Food-chains: The Case for a New Bioaccumulation Paradigm & QSAR .

Gobas, Frank¹, Arnot, Jon¹, Kelly, Barry¹, ¹

ABSTRACT- Various countries in Europe, the US and Canada and several international organization are evaluating large numbers of chemical substances on their potential to be Persistent, Bioaccumulative and Toxic in the environment. Since empirical data that can be used to assess the PBT properties of these chemical substances are largely absent, the properties of the majority of the chemical substances will be assessed by using QSARs. We will review and analyze the predictability of QSARs that are used worldwide to assess the bioaccumulation potential of organic substances in aquatic food-chains. This analysis consists of a comparison of the QSAR predictions and empirical data on laboratory based bioconcentration factors and field based bioaccumulation factors. It is concluded that (1) octanol-water partition coefficient (Kow) is an appropriate paradigm for bioaccumulation in aquatic food-chains, (2) certain Kow based QSARs are adequate in assessing the bioaccumulation potential of organic chemicals in aquatic food-chains and (3) a generic BAF-QSAR is proposed and discussed. We further demonstrate that Kow-based QSARs are not adequate methods for the assessment of the bioaccumulation potential of organic chemicals in terrestrial food-chains. We will present an analysis of the biomagnification factors of a range of hydrophobic organic substances in terrestrial food-chains. The analysis shows that the BMF follows a stronger relationship with the octanol-air partition coefficient (Koa) than with Kow. A mechanistic explanation will be presented.The analysis also demonstrates that chemicals wih high Koa are subject to biomagnification in the food-chain even if the Kow is low. Examples will be presented illustrating that chemicals with a log Kow of less than 4 biomagnify in terrestrial and marine mammal food-chains. It will be concluded that current PBT management policies that consider only chemicals with log Kow > 5 or 4 to be bioaccumulative substances, fail to identify substances that have the potential to biomagnify in certain terrestrial food-chains. A QSAR that can be used to assess the biomagnification potential of unmetabolizable organic substances in non-aquatic food-chains will be proposed.

Key words: Bioaccumulation, Aquatic, Terrestrial, Marine