Unravelling the combined effects of toxicants and environmental conditions
using a process-based analysis

Tjalling Jager, Olga Alda Alvarez, Evelyn Heugens, Bas Kooijman

The apparent toxicity of a chemical depends on the value of environmental 
conditions such as temperature and food availability. These environmental 
conditions affect the uptake of the toxicant into the body, the life-history
 characteristics of the organism, and they also may affect the intrinsic 
sensitivity of the organism. However, using descriptive dose-response curves 
(as used to derive ECx) does not allow distinguishing between these three 
contributions to the toxic response. The same intrinsic sensitivity (the 
relationship between the body residue and the internal target parameter) may 
lead to radically different responses on growth, reproduction and survival 
under different environmental circumstances. For example, chemicals that 
affect feeding or maintenance rates will show a larger effect on growth and 
reproduction at limiting food levels because of the way resources allocation 
depends on food availability. To properly distinguish between the various 
effects of environmental conditions on the toxic response, we apply a process-
based approach (DEBtox). Several examples for nematodes and daphnids will be 
shown.

Keywords: DEBtox, multi stress, life-history, energy budgets
Platform presentation
session: “Multiple stress: How relevant is chemical stress compared to other 
stress? (ES2)”