Integrative approaches in ecotoxicological testing: Implications for biomarker development and application

Sammanfattning: Ecotoxicology aims to understand toxic effects of chemicals in the environment. Effects can be observed at different levels of the biological organization, from molecular to ecosystem level. Biomarkers on molecular and biochemical levels are used in ecotoxicology as early warning signals of chemical exposure, possible toxic effects and underlying mechanisms. As methods and technologies improve, more biomarkers are being implemented in ecotoxicological studies, due to the general interest in early detection and thus efficient prevention of environmental risks. However, to be of value in ecotoxicological assessment, a connection between biomarker response and effects at higher levels of biological organization should be established. Also, baseline variability for the biomarker in question as well as response to natural fluctuations of environmental factors should be evaluated.The aim of this thesis was to increase value and understanding of biomarkers in ecotoxicological assessment by (1) linking responses across different levels of biological organization, and (2) gaining better understanding of the relative importance of ecological and physiological factors affecting oxidative biomarkers.Paper I is focused on evolutionary conserved drug targets and the toxicity of pharmaceuticals for non-target organisms. The main conclusion from this study is that pharmaceuticals with conserved drug targets in non-target organisms have a higher toxicity than pharmaceuticals for which drug-targets have not been identified in the species. The effects were evaluated using end points at molecular, biochemical and individual levels. Consistent with the expected higher sensitivity of molecular and biochemical end points, the effects on the low-level biomarkers were observed at lower concentrations than at the individual level.  Paper II is focused on delineating effects of feeding and toxic exposure on oxidative biomarkers commonly used in ecotoxicology. The results are in agreement with the theory of caloric restriction that links enhanced caloric intake to increased pro-oxidative processes in animals. In our experiments with the cladoceran Daphnia magna, we observed positive effects for both antioxidant capacity and oxidized lipids in response to enhanced feeding rates. This have implications for the use of oxidative stress biomarkers in ecotoxicology as many substances have inhibitory effects on feeding rate and thus, changes in oxidative biomarkers can result from the altered feeding rate rather than other toxic mechanisms. Therefore, possible changes in feeding rate should be assessed when conducting exposure experiments or interpreting field data in studies employing oxidative stress biomarkers. However, it was concluded that the ratio between antioxidative capacity and protein content was independent of feeding rate. Thus, this biomarker is suitable for xenobiotic exposure in D. magna. This thesis have contributed to better understanding of molecular and biochemical biomarkers in ecotoxicological studies in regard to the connections between effects at different biological levels and confounding factors in biomarker response.