title: Behavioural alterations from exposure to Cu, phenanthrene, and Cu-phenanthrene mixtures: linking behaviour to acute toxic mechanisms in the aquatic amphipod, Hyalella azteca.
abstract: Phenanthrene (PHE) and Cu are two contaminants commonly co-occurring in marine and freshwater environments. Mixtures of PHE and Cu have been reported to induce more-than-additive lethality in the amphipod, Hyalella azteca, a keystone aquatic invertebrate, yet little is understood regarding the interactive toxic mechanisms that mediate more-than-additive toxicity. Understanding the interactions among toxic mechanisms among Cu and PHE will allow for better predictive power in assessing the ecological risks of Cu-PHE mixtures in aquatic environments. Here we use behavioural impairment to help understand the toxic mechanisms of Cu, PHE, and Cu-PHE mixture toxicity in the aquatic amphipod crustacean, Hyalella azteca. Our principal objective was to link alterations in activity and ventilation with respiratory rates, oxidative stress, and neurotoxicity in adult H. azteca. Adult amphipods were used for all toxicity tests. Amphipods were tested at sublethal exposures of 91.8- and 195-μgL(-1) Cu and PHE, respectively, and a Cu-PHE mixture at the same concentrations for 24h. Neurotoxicity was measured as acetylcholinesterase (AChE) activity, where malathion was used as a positive control. Oxidative stress was measured as reactive oxygen species (ROS) production. Phenanthrene-exposed amphipods exhibited severe behavioural impairment, being hyperstimulated to the extent that they were incapable of coordinating muscle movements. In addition, respiration and AChE activity in PHE-exposed amphipods were increased and reduced by 51% and 23% respectively. However, ROS did not increase following exposure to phenanthrene. In contrast, Cu had no effect on amphipod behaviour, respiration or AChE activity, but did lead to an increase in ROS. However, co-exposure to Cu antagonized the PHE-induced reduction in ventilation and negated any increase in respiration. The results suggest that PHE acts like an organophosphate pesticide (e.g., malathion) in H. azteca following 24h sublethal exposures, and that AChE inhibition is the likely mechanism by which PHE alters H. azteca behaviour. However, interactive aspects of neurotoxicity do not account for the previously observed more-than-additive mortality in H. azteca following exposure to Cu-PHE mixtures.
authors.affiliation: Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada. Electronic address: pgauthi1@lakeheadu.ca.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Gauthier
authors.affiliation: Aquatic Contaminants Research Division, Environment Canada, Burlington, Ontario L7R 4A6, Canada.
authors.forename: Warren P
authors.initials: WP
authors.lastname: Norwood
authors.affiliation: Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada.
authors.forename: Ellie E
authors.initials: EE
authors.lastname: Prepas
authors.affiliation: Department of Biological Sciences, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada.
authors.forename: Greg G
authors.initials: GG
authors.lastname: Pyle
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D033304:Amphipoda / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001921:Brain / Q000201:enzymology; D056831:Coordination Complexes / Q000737:chemistry / Q000633:toxicity*; D003300:Copper / Q000737:chemistry / Q000633:toxicity*; D007306:Insecticides / Q000737:chemistry / Q000633:toxicity*; D010616:Phenanthrenes / Q000737:chemistry / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000378:metabolism; D056152:Respiratory Rate / Q000187:drug effects; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D056831:Coordination Complexes; D007306:Insecticides; D010616:Phenanthrenes; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; C031181:phenanthrene; D003300:Copper; D000110:Acetylcholinesterase
keywords: Behaviour; Copper; Mechanisms; Mixture toxicity; Neurotoxicity; Phenanthrene