Toxicological exposure of bound recalcitrant compounds - Bioremediation of Recalcitrant Compounds - page 14

2000). That is, field reference-derived BSAFs were substituted for AFs in the
original TBP equation. Clarke and McFarland (2000) concluded that TBP was
a useful screening tool for eliminating sediments with negligible likelihood
of causing unacceptable bioaccumulation from further testing and tended
to generally overestimate recalcitrant compounds' bioaccumulation from
sediment.

2.3 Equilibrium partitioning and sediment quality
guidelines
In the absence of site-specific information, environmental managers must
use the best available information, and this often entails the use of model
predictions to support sediment management decisions. To this end, the logic
of Karickhoff's fugacity-based model of recalcitrant compounds-sediment
partition coefficients K p normalized to organic carbon content K oc has been
combined with that of TBP to predict benthic marcofauna exposure levels
(Figure 2.1). Predicted exposure levels are subsequently interpreted in the
context of aquatic toxicity databases. This equilibrium partitioning
(EqP)-based logic is the basis for deriving sediment quality criteria as pro-
posed by DiToro et al. (1991).
TBP predictions of bioaccumulation potentials and EqP estimates of
exposure potentials are both derived from K oc . The accuracy, precision, and
general applicability of predictions made on the basis of K oc -predicted recal-
citrant compounds-sediment-pore water equilibrium partitioning have been
debated in the technical literature since it was first proposed. The practical
ecological and economic consequences of this issue have escalated as appli-
cations of the K oc model have expanded beyond that of a sediment screening

Biota

Sediment
Carbon

Pore
Water

K oc

Figure 2.1 Equilibrium partitioning (EqP) as described by DiToro et al. (1991) is
predicated on a model that assumes that equilibrium exists between the contaminant
sorbed to sediment organic carbon, pore water, and lipid of benthic biota. The par-
titioning of recalcitrant compounds between sediment organic matter and pore water
is predicted from K oc (Karickhoff, 1981).