Interactions between climatic and toxic stress – Studies with the freeze tolerant earthworm Dendrobaena octaedra

In traditional ecotoxicological studies, test organisms are usually exposed to a single chemical at increasing concentrations, performed under otherwise optimal conditions. However, in natural environments it is very likely that these organisms will also be exposed to other stressful factors, including climatic stressors as frost and drought. This means that traditional laboratory tests may underestimate the toxic effects of chemicals in natural environments. This PhD thesis examined the interaction between climatic and toxic stress, using the globally distributed freeze tolerant earthworm Dendrobaena octaedra as test organism. The physiological mechanisms known to affect the freeze tolerance of D. octaedra, including glucose production and adjustments in membrane phospholipid composition, was examined in worms exposed to copper, which is shown to interact synergistically with freezing temperatures. To test how general this phenomenon was, worms were furthermore exposed to a number of other chemicals with different modes of action in combination with freezing temperatures. In general, synergistic interactions seemed to occur mostly at high levels of climatic stress in combination with high concentrations of the chemical. It is suggested that it is important to include natural stressors as frost and drought in risk assessment, especially taken into consideration the predictions of future climate change. Layout: Tinna Christensen and Kathe Møgelvang Front page pictures: Asser Øllgaard and Brian Rasmussen ISBN: 978-87-7073-072-3 Printed by: The Repro Center – Faculty of Science, Aarhus University