Predicting the synergy of multiple stress effects.

Matthias Liess,Ralf B Schäfer,Hans-Dieter Liess,Saskia Knillmann,Kaarina Foit

doi:10.1038/srep32965

Abstract

Toxicants and other, non-chemical environmental stressors contribute to the global biodiversity crisis. Examples include the loss of bees and the reduction of aquatic biodiversity. Although non-compliance with regulations might be contributing, the widespread existence of these impacts suggests that for example the current approach of pesticide risk assessment fails to protect biodiversity when multiple stressors concurrently affect organisms. To quantify such multiple stress effects, we analysed all applicable aquatic studies and found that the presence of environmental stressors increases individual sensitivity to toxicants (pesticides, trace metals) by a factor of up to 100. To predict this dependence, we developed the “Stress Addition Model” (SAM). With the SAM, we assume that each individual has a general stress capacity towards all types of specific stress that should not be exhausted. Experimental stress levels are transferred into general stress levels of the SAM using the stress-related mortality as a common link. These general stress levels of independent stressors are additive, with the sum determining the total stress exerted on a population. With this approach, we provide a tool that quantitatively predicts the highly synergistic direct effects of independent stressor combinations.

Highlights

Toxicants and other, non-chemical environmental stressors contribute to the global biodiversity crisis
Examples include (i) wild bee populations and honey bee colonies, which have declined in response to the combined effects of pesticides and environmental stressors, such as parasites[9], reduced floral abundance or weather[8,10]; (ii) marine crustaceans, which have exhibited an increased sensitivity to the combination of copper and ultraviolet radiation[11]; (iii) amphibians, which have been negatively affected by the interaction between agrochemicals and parasites[12]; and (iv) human populations, for which heat stress exacerbates the toxicity of many air pollutants, insecticides, and other toxic chemicals[13]
The key challenge to predict multiple stress effects is to identify a “common currency” to quantify and join different independent stressors[16]. We solved this problem by assuming a universal capacity towards all types of stress, the general stress capacity within the Stress Addition Model” (SAM) framework. This idea of a general stress capacity enabled us to transform all specific stressors into general stress levels

Summary

Introduction

Non-chemical environmental stressors contribute to the global biodiversity crisis. Non-compliance with regulations might be contributing, the widespread existence of these impacts suggests that for example the current approach of pesticide risk assessment fails to protect biodiversity when multiple stressors concurrently affect organisms. To quantify such multiple stress effects, we analysed all applicable aquatic studies and found that the presence of environmental stressors increases individual sensitivity to toxicants (pesticides, trace metals) by a factor of up to 100. In global surface waters insecticide contamination is generally present and frequently exceeds the regulatory threshold levels[2] This toxic pressure results in large-scale community alterations first identified in central Europe[3], confirmed in several global regions[4] and induce a reduction of aquatic biodiversity[5]. The challenge of quantitatively predicting the combined impacts of stressors remains a fundamental issue in the medical and ecological sciences

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Conclusion