Increased amplitude of daily temperature fluctuation magnifies the acute toxicity of phenanthrene and upregulates molecular mechanisms of stress defense in Enchytraeus albidus (Oligochaeta)

Abstract

Climate change has resulted in a higher average temperature and increased temperature variability, which has severe consequences for organisms. Simultaneously, organisms are exposed to toxicants, such as polycyclic aromatic hydrocarbons, which are widely emitted by human activities and accumulate in soil. These two stressors may negatively influence terrestrial organisms through their interaction. In the present study, the potworm Enchytraeus albidus was exposed to a range of phenanthrene (PHE) concentrations (0, 20, 40, 80, 160, 320 mg kg^-1 dry soil) at various amplitudes of daily temperature fluctuation (DTF) (20 ± 0, 20 ± 2, 20 ± 5, 20 ± 7, 20 ± 8, 20 ± 9 and 20 ± 10 ºC) for 7 days. At the end of the experiment, the survival and the body concentration of PHE were measured for all treatments. Furthermore, the transcription of stress-related genes (heat shock protein 70, superoxide dismutase, catalase, cytochrome P450 4v2, glutathione-S-transferase, ABC transporter) was measured at the DTFs and the presence or absence of 40 mg PHE kg^-1 dry soil. The survival significantly decreased under increasing PHE concentration and temperature amplitudes, with a synergistic interaction between these stressors. The bioaccumulation of PHE was largely unaffected by temperature amplitude. The expression of the genes encoding superoxide dismutase and catalase was significantly elevated by both PHE exposure and increased temperature amplitude. These results show that higher temperature variability increases the effects of PHE in E. albidus in terms of mortality and expression of stress-responsive genes. Our findings highlight the importance of including temperature variability, such as that caused by heat waves, in the environmental risk assessment of lipophilic compounds.

Keywords: Gene expression; Multiple stressors; Polycyclic aromatic hydrocarbons; Survival; Temperature variability.