title: Multiple stressor effects in Chlamydomonas reinhardtii--toward understanding mechanisms of interaction between effects of ultraviolet radiation and chemical pollutants.
abstract: The effects of chemical pollutants and environmental stressors, such as ultraviolet radiation (UVR), can interact when organisms are simultaneously exposed, resulting in higher (synergistic) or lower (antagonistic) multiple stressor effects than expected based on the effects of single stressors. Current understanding of interactive effects is limited due to a lack of mechanism-based multiple stressor studies. It has been hypothesized that effect interactions may generally occur if chemical and non-chemical stressors cause similar physiological effects in the organism. To test this hypothesis, we exposed the model green alga Chlamydomonas reinhardtii to combinations of UVR and single chemicals displaying modes of action (MOA) similar or dissimilar to the impact of UVR on photosynthesis. Stressor interactions were analyzed based on the independent action model. Effect interactions were found to depend on the MOA of the chemicals, and also on their concentrations, the exposure time and the measured endpoint. Indeed, only chemicals assumed to cause effects on photosynthesis similar to UVR showed interactions with UVR on photosynthetic yield: synergistic in case of Cd(II) and paraquat and antagonistic in case of diuron. No interaction on photosynthesis was observed for S-metolachlor, which acts dissimilarly to UVR. However, combined effects of S-metolachlor and UVR on algal reproduction were synergistic, highlighting the importance of considering additional MOA of UVR. Possible mechanisms of stressor effect interactions are discussed.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich, Switzerland.
authors.forename: Muris
authors.initials: M
authors.lastname: Korkaric
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf, Switzerland.
authors.forename: Renata
authors.initials: R
authors.lastname: Behra
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf, Switzerland.
authors.forename: Beat B
authors.initials: BB
authors.lastname: Fischer
authors.affiliation: Swiss Center for Applied Ecotoxicology Eawag-EPFL, 8600, Duebendorf, Switzerland.
authors.forename: Marion
authors.initials: M
authors.lastname: Junghans
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich, Switzerland. Electronic address: rik.eggen@eawag.ch.
authors.forename: Rik I L
authors.initials: RIL
authors.lastname: Eggen
mesh_terms: D000081:Acetamides / Q000633:toxicity; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000528:radiation effects*; D004237:Diuron / Q000633:toxicity; D010269:Paraquat / Q000633:toxicity; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects*; D012098:Reproduction / Q000187:drug effects; D013312:Stress, Physiological / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D000081:Acetamides; D014874:Water Pollutants, Chemical; D004237:Diuron; D010269:Paraquat; C051786:metolachlor
keywords: Chlamydomonas reinhardtii; Independent action; Mode of toxic action; Multiple stressor effects; Photosynthesis; Ultraviolet radiation