posted on 2015-10-20, 00:00authored byGuillaume Kon Kam
King, Marie Laure Delignette-Muller, Ben J. Kefford, Christophe Piscart, Sandrine Charles
Classical
species sensitivity distribution (SSD) is used to assess
the threat to ecological communities posed by a contaminant and derive
a safe concentration. It suffers from several well-documented weaknesses
regarding its ecological realism and statistical soundness. Criticism
includes that SSD does not take time-dependence of the data into account,
that safe concentrations obtained from SSD might not be entirely protective
of the target communities, and that there are issues of statistical
representativity and of uncertainty propagation from the experimental
data. We present a hierarchical toxico-dynamic (TD) model to simultaneously
address these weaknesses: TD models incorporate time-dependence and
allow improvement of the ecological relevance of safe concentrations,
while the hierarchical approach affords appropriate propagation of
uncertainty from the original data. We develop this model on a published
data set containing the salinity tolerance over 72 h of 217 macroinvertebrate
taxa, obtained through rapid toxicity testing (RTT). The shrinkage
properties of the hierarchical model prove particularly adequate for
modeling inhomogeneous RTT data. Taking into account the large variability
in the species response, the model fits the whole data set well. Moreover,
the model predicts a time-independent safe concentration below that
obtained with classical SSD at 72 h, demonstrating under-protectiveness
of the classical approach.