posted on 2002-06-07, 00:00authored byJong-Hyeon Lee, Peter F. Landrum, Chul-Hwan Koh
The relationship between toxicokinetics and time-dependent
PAH toxicity to Hyalella azteca was examined to test
the constant critical body residue (CBR) model. A constant
CBR model is based on the assumption that the body
residue for 50% mortality is constant for each PAH across
exposure times. With a constant CBR, kinetic parameters
determined through kinetic experiments would be similar
to those estimated from time series toxicity data. Time-dependent toxicity was investigated using three types
of data: time series LC50 data, LT50(c), and CBR values
measured at multiple exposure times for live and dead
animals. Kinetic parameters were measured independently.
The constant CBR model did not predict the PAH toxicity
time course for H. azteca. Since a first-order kinetic model
predicted the bioaccumulation of the parent PAH except
for naphthalene, this result is not due to a failure to predict
the internal dose (body residue). The influence of
metabolites on toxicity was negligible except for naphthalene.
The LC50 values at multiple exposure times decreased to
an incipient lethal concentration after H. azteca reached
steady state. Measured CBR values also decreased with
increasing exposure time. Thus, the time course of PAH
toxicity is determined not only by the bioconcentration kinetics
but also by the cumulative toxicity with increasing
exposure time. Therefore, time-to-death or hazard models
must be developed as a complement to toxicokinetic
models to describe and predict the toxicity time course.