Analysis of bioassays with time-varying concentrations
Péry, A. R. R., Bedaux, J. J. M., Zonneveld, C. and
Kooijman, S. A. L. M. 2001. Analysis of bioassays with time-varying
concentrations. Water Research, 35: 3825 - 3832.
Abstract
In the analysis of ecotoxicological bioassays the concentration of the
test compounds is assumed to be constant. In many situations this
assumption is questionable, as various processes may cause a
substantial decline in the concentration during exposure. This leads to
difficulties in the estimation of parameters that characterise the
toxicity of the test compound. As a solution to this problem,time-
varying concentrations are often replaced by their mean values for the
estimation of toxicity parameters. However, Monte-Carlo simulations
show that this approach results in biased estimates of the toxicity
parameters. As an alternative approach, we propose models to estimate
one important toxicity parameter, the no-effect concentration, in
situations where the concentration of the compound varies in
time. These models are extensions of the DEBtox model (Kooijman and
Bedaux, 1996) which is based on biological assumptions about
toxicokinetics and toxic effects. We also propose a new approach for
the estimation of toxicity parameters for strongly accumulating
non-metabolisable compounds. This approach does not require any
kinetic assumption. Computer simulation and experimental data confirm
the relevance of the different proposals.