Using process-based analysis to extrapolate to populations under field conditions

Tjalling Jager, Olga Alda Alvarez, Bas Kooijman

Ecological risk assessment aims to protect field populations and systems, based on the 
results of laboratory toxicity tests. This involves extrapolation steps to cover the 
differences in toxic response going from lab to field species, lab to field conditions, 
short to long time scales, and from individuals to populations. The standard approach 
to extrapolation is to apply arbitrary assessment factors on the results of the laboratory 
tests (usually expressed as LC50, ECx or NOEC). This approach is hardly 
scientifically defensible, but a more intelligent extrapolation is hampered by the fact 
that, by applying descriptive dose-response curves, no attempt is made to estimate the 
processes underlying the toxic response. In this contribution we will demonstrate how 
a process-based analysis of the laboratory toxicity results (DEBtox) can be used to 
better understand the toxic effect, and make better underpinned extrapolations for risk 
assessment purposes. Our analysis allows for all kinds of straightforward 
extrapolations, such as from continuous exposure to any kind of time-varying 
exposure, and from individual to population responses at different temperatures and 
food levels.