Investigating the toxicity of naphthenic acid fraction components from oil sands process-affected water to developing fathead minnow (Pimephales promelas)

Abstract

The extraction of bitumen from Alberta’s oil sands region generates large volumes of oil sands process-affected water (OSPW) that is stored in tailings ponds. Toxic constituents present in OSPW such as naphthenic acid fraction components (NAFCs) can cause adverse effects to aquatic life. Recent research has focused on the toxicity of NAFCs to highly vulnerable early life stages of fish. Here we examined the embryotoxicity of NAFCs (0-54 mg/L) extracted from OSPW to native fathead minnow (Pimephales promelas) from 1-day post-fertilization to hatch in a semi-natural setting at Queen’s University’s Biological Station. Embryo heart rate, mortality, prevalence and severity of malformations at hatch, post-hatch mass, and basal activity at hatch was examined. Embryo heart rates declined with increasing NAFC concentration, preceding pronounced exposure-response patterns of mortality and non-viable hatches. Visible malformations included cardiovascular (pericardial edema; present in 81.51% of non-viable hatches), craniofacial (reduced jaw and head size; 68.96%), myoskeletal (spinal curvatures; 60.90%), and peritoneal (yolk sac edema; 26.44%) malformations, that significantly increased in severity with increasing NAFC concentration. Fish that survived lethal concentrations displayed evidence of nervous system impairment including elevated patterns of erratic twitching. Post-hatch mass generally increased with increasing NAFC exposure, potentially as a compensatory-like response. Results of this work are the first to be reported in a semi-natural exposure setting and provide important toxicological information that will aid future policy directives for the management of OSPW in Alberta, Canada.