Modelling the effects of binary mixtures on survival in time
Baas, J., Houte, B. P. P. van, Gestel, C. A. M. van and Kooijman, S. A. L. M.
2007.
Modelling the effects of binary mixtures on survival in time.
Environmental Toxicology & Chemistry : to appear
Abstract
In general effects of mixtures are difficult to describe, and most
of the models in use are descriptive in nature and lack a strong
mechanistic basis. The aim of this experiment was to develop a
process-based model for the interpretation of mixture toxicity
measurements, with effects of binary mixtures on survival as a
starting point. The survival of Folsomia candida was monitored
daily for 21 d during the exposure to six binary mixtures of
cadmium, copper, lead, and zinc in a loamy sand soil. The
measurements were used to develop a model to describe survival in
time. The model consists of two parts: A one compartment model that
describes uptake and elimination of the compounds, and a hazard
model describing survival. The model was very successful in
describing the data and at finding possible interactions. The
mixture of copper and lead showed a slight antagonistic effect, the
other mixtures showed no interaction. The model is straightforward
in its biological assumptions and does not require an a priori
choice of mode of action of the mixture that might influence the
modeled interaction of the components in the mixture. The model
requires measurements at intermediate time points, but runs with
relatively few parameters and is robust in finding
interactions. When mixture effects are considered at only one time
point, care should be taken with the assignment of interactions as
these may be different for different points during the time course
of the experiments.