In most laboratory experiments used in risk assessment of chemicals, test organisms have typical optimal conditions regarding temperature, moisture, food etc. However, organisms in their natural environments will simultaneously be exposed to several stressful factors, and among these are sub-optimal and, occasionally, stressful environmental conditions. These stressful environmental conditions may significantly alter the tolerance towards a given contaminant (and vice versa). To be able to improve risk assessment, it therefore seems appropriate to supplement traditional ecotoxicological studies with investigations on how these natural stressors interact with chemical stressors. This has therefore been a long term research issue for the Section of Soil Fauna Ecology and Ecotoxicology. Not only are the classical ecotoxicological responses (which may be both synergistic and antagonistic) investigated, but the physiological and molecular mechanisms underlying these responses are investigated as well.
Using springtails and earthworms as models, researchers from The Section of Soil Fauna Ecology and Ecotoxicology have shown that toxicant like copper, detergents and polycyclic aromatic compounds (PACs) may have significant impacts on the drought tolerance of these organisms. For example, the viability of earthworm cocoons is not influenced by copper, however, when a subsequent cold stress is added significant synergistic effects appear due to the combination of the two stress types.
In the PhD-thesis by A.M. Bindesbøl the interactions between climatic and toxic stress were investigated using the globally distributed freeze tolerant earthworm Dendrobaena octaedra. The physiological mechanisms known to affect the freeze tolerance, including glucose production and adjustments in membrane phospholipid composition, were examined in worms exposed to copper, which is known to interact synergistically with freezing temperatures. To test how general this phenomenon is, worms were exposed to a number of other chemicals with different modes of action in combination with freezing temperatures. In general, synergistic interactions were found to occur mostly at high levels of climatic stress in combination with high concentrations of the chemical.