Modelling the impact of the environmental scenario on population recovery from chemical stress exposure: A case study using Daphnia magna

• We model the impact of biotic interactions on population recovery from toxic stress.
• Time to recovery strongly depended on the environmental scenario.
• Biological interactions fostered or delayed recovery from the same chemical.
• Ecological models are useful to test many combinations of relevant exposure scenarios.
• Ecological models should be used as valuable tools in risk assessment of chemicals.

Recovery of organisms is an important attribute for evaluating the acceptability of chemicals’ effects in ecological risk assessment in Europe. Recovery in the field does not depend on the chemical's properties and type of exposure only, but it is strongly linked to important environmental variables and biological interactions as well. Yet, these remain only marginally considered in the European risk assessment of chemicals. Here, we use individual-based modelling to investigate how the environmental scenario affects Daphnia magna population recovery from chemical exposure. Simulation experiments were performed for chemicals with lethality levels ranging from 40% to 90% at different food and temperature conditions. The same toxicity levels were then tested in combination with biological interactions including predation or competition. Results show that for the same chemical effect strength, populations often exhibited different recovery times in a different environmental context. The interactions between the chemical and the environmental variables were the strongest determinants of population recovery. Most important, biotic interactions even induced opposite effects on recovery at low and at high mortality levels. Results of this study infer that no specific role can be attributed to any abiotic or biotic variable in isolation. We conclude that unless the complex interactive mechanisms between the different factors constituting the full environmental scenario are taken into account in risk assessment, we cannot achieve a complete understanding of recovery processes from chemical effects.