Toxicity of oil sands process-affected water to early life stage rainbow trout ( <i>Oncorhynchus mykiss</i> )

To provide insights into the potential impacts of releases of oil sands process affected water (OSPW) into the environment, chronic toxicity tests on early-life stage rainbow trout (ELS-RBT) were conducted. The objective of the testing was to better characterize the effects of OSPW from the Alberta Oil sands on swim-up fry mortality, development (fish length and width, yolk sac development), and deformities (skeletal, craniofacial, finfold, and edemas) as a function of OSPW dilution (%) and ∑O2-naphthenic acid concentrations. More than 95% mortality in ELS-RBT was observed in the range of 22 to 100% OSPW. Lethal concentrations of 50% of the test population (LC50) values expressed in terms of OSPW dilutions were 13.7 (SE 0.7), 10.6 (SE 0.5), and 12.7 (SE 0.5) % for OSPW collected in 2019, 2021, and 2022, respectively. Corresponding LC50 values for ∑O2-naphthenic acids concentrations were 2.8 (SE 0.14), 2.0 (SE 0.11), and 2.2 (SE 0.09) mg/L, respectively. Primary sublethal effects included delayed development, craniofacial defects, and evidence of cardiovascular toxicity, including pericardial and yolk sac edema and hemorrhaging. Evidence of sublethal developmental effects was observed at OSPW dilutions above 10% and corresponding ∑O2-naphthenic acid concentrations above 1.69 mg/L. The only exception was for 17.1 (SE 3.3) % craniofacial deformities at OSPW concentrations of 3.2% and corresponding ∑O2-naphthenic acid concentrations of 0.66 mg/L, but only for OSPW collected in 2019. The results from this indicate that a 20-fold or greater dilution (or a corresponding removal of OSPW) of the tested OSPW from the Kearl site is sufficient to negate the chronic toxicity in Rainbow trout investigated in this study.