Applying an integrated ecotoxicological approach to assess stress from exposure to trace metals and UVB radiation

Abstract

Coastal marine organisms are impacted by combinations of chemical and nonchemical stressors, including exposure to metals and elevated UVB radiation. The impacts of chemical mixtures upon these are largely unknown, as are the links between exposure and biological effects. Regulatory guidelines are often based on single effect data and concentration addition (CA) modelling that assumes an additive response, thereby overlooking possible synergistic or antagonistic interactions. In this thesis, a harpacticoid copepod (Tisbe battagliai Volkmann-Rocco, 1972) and a chlorophyte microalga Tetraselmis suecica (Kylin) Butcher, 1959 were applied as models to characterise the toxicity and determine observed adverse effects of copper, nickel, and zinc chlorides (copepod and alga) or UVB (copepod only). An integrated toxicity characterisation for singular and combined metal exposures were conducted using endpoints across different levels of biological organisation, informed by metal concentrations previously determined from Kaldvellfjorden, Norway. For the combined studies, a form of resolution IV design (Definitive Screening Design, DSD) was implemented, using the EC20, EC50 and EC80 values from single exposure data. Additionally, CA and independent action (IA) models predict combined effects of mixtures. The UVBinduced effects were quantified using a cyclobutene pyrimidine dimer (CPD) DNA damage induced toxicity pathway, resulting in increased reactive oxygen species (ROS), CPD-DNA damage, short-term reproductive problems, developmental delays, and mortality. Single metal studies characterised toxicity along a metalinduced toxicity pathway that increased ROS production, oxidative DNA damage and apoptosis leading to reduced survival. T. battagliai survival was most impacted by copper (48h LC50 1.66 µM), followed by zinc (48h LC50 4.53 µM) and nickel (48h LC50 27.70 µM). All three metals were identified as significant effect drivers within the three-metal mixture, influencing survival after 24 and 48 hours. Significant interactions were found between the pairs copper and zinc, and copper and nickel after 24 hours. These mixtures were compared to CA (48h EC50 16.73 µM) and IA (48h EC50 23.32 µM) models that predicted copper would be the main risk driver at low mixture concentrations and zinc at high mixture concentrations. The observed mixtures were identified as having a noninteractive effect (additive) or an antagonistic interaction. T. suecica growth was most sensitive to zinc and copper after seven days of single exposure, but all three metals were significant effect drivers within the three-metal mixture. When comparing the two species sensitivity to these metals, T. battagliai was more sensitive to copper but less sensitive to nickel than T. suecica. This integrated ecotoxicological approach provides greater insight into how the interactions between metals influence mixture toxicity of copper, nickel, and zinc at different levels of biological organisation. Following stressor-specific toxicity pathways allowed stressor-specific endpoints to be developed and conducted. For some endpoints, the high variability in observed effects over time shows the complexity of interpreting toxicity from chemical and non-chemical stressors.