Fathead Minnows Exposed to Organic Compounds from Oil Sands Tailings as Embryos Have Reduced Survival, Impaired Development, and Altered Behaviors That Persist into Larval Stages

Abstract

Our study evaluated whether exposure to naphthenic acid fraction compounds (NAFCs) extracted from oil sands process-affected waters (OSPW) has adverse effects on fish embryos that persist into later life. We exposed fathead minnow (Pimephales promelas) embryos to concentrations of NAFCs found in OSPW (2.5-54 mg/L) for 7 days (1 day postfertilization to hatch), then raised surviving larvae in outdoor mesocosms of uncontaminated lake water for 1 month. Embryos exposed to NAFCs were more likely to exhibit malformations (by up to 8-fold) and had slower heart rates (by up to 24%) compared to controls. Fish raised in uncontaminated lake water following exposure to NAFCs as embryos, were 2.5-fold less likely to survive during the larval stage than control fish. These fish also showed up to a 45% decrease in swim activity and a 36% increase in swim burst events during behavioral tests relative to controls. We conclude that exposure to NAFCs during the embryonic stage can have lasting effects on fish survival, physiology, and behavior that persist at least through the larval stage. These findings of delayed mortalities and persistent sublethal effects of embryonic NAFC exposure are relevant to informing the development of regulations on treated OSPW releases from mining operations. Environ Toxicol Chem 2022;41:1319-1332. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Keywords: Aquatic toxicology; Behavioral toxicology; Ecotoxicology; Exposure-response modeling; Industrial effluents.

Figure 1

Chemical analysis of naphthenic acid fraction compounds (NAFCs) measured in seminatural exposure vessels during the 7‐day embryonic exposure. Percentage abundance of compounds by size for a representative NAFC sample from the highest‐concentration NAFC solution (A, nominal 54 mg/L NAFCs) and the control (B, filtered lake water). The size of compounds is represented as the number of double‐bond equivalents (1.5–8.5) and the number of carbons present (7–20). Samples shown were collected on the first day of exposure, which did not change in abundance by more than ±0.3% in all samples by the end of exposure. Relationship between nominal and measured NAFC concentrations in exposure vessels throughout the exposure period (C); diagonal dashed line indicates 1:1 relationship compared to the line of best fit for measured versus nominal NAFC concentrations (y = 0.38x + 0.74). Temporal trends in NAFC concentrations (D), with vertical dashed lines indicating dates when NAFC solution was added to exposure vessels.

Figure 2

Embryonic mortality (A), hatch viability (B), heart rate at 96 h postfertilization (C), body twitching rate at hatch (D), and mass at hatch (E) in fathead minnows (Pimephales promelas) as functions of exposure to nominal concentrations of naphthenic acid fraction compounds (NAFCs). Solid lines represent the line of best fit, gray‐shaded areas are the ±95% confidence intervals, and each circle represents one replicate exposure vessel. Exposure to NAFCs significantly increased embryo mortality and decreased hatch viability (generalized linear mixed‐effects model [GLMM], Wald's Chi‐squared (1,18) = 84.7, p < 0.0001), decreased heart rate (linear mixed‐effects model [LME] F(1,18.1) = 32.9, p < 0.001), increased twitching rate (LME, F(1,17.3) = 17.5, p < 0.001), and a trend towards increased mass at hatch (GLM, F(1,24) = 3.13, P = 0.089).

Figure 3

Percent malformations at hatch in fathead minnows (Pimephales promelas) following a 7‐day exposure to nominal concentrations of naphthenic acid fraction compounds (NAFCs). Total (A); cardiovascular, including pericardial edema and hemorrhaging (B); myoskeletal, specifically spinal curvatures (C); craniofacial, including altered head, eye, and jaw development (D); and peritoneal, specifically yolk sac edema (E) malformations. Malformations for each index are further categorized as mild, moderate, or severe, based on the severity of the malformation. Images show representations of each malformation, scored from 0 (no malformation) to 3 (severe malformations). Data and images from high treatments (>21 mg/L NAFCs) were excluded because of high rates of mortality. The prevalence and severity of malformations increased significantly as a function of increasing NAFC concentrations (generalized linear model, GLM, F(1,16) = 13.9, p < 0.01).

Figure 4

Postembryonic exposure–phase larval mortality in fathead minnows (Pimephales promelas; A; gray areas represent ±95% confidence intervals, each point represents one replicate exposure vessel) and behavioral responses to a food stimulus, including burst events (B), swim duration (C), and duration in the middle of the arena (D), as functions of nominal concentrations of naphthenic acid fraction components (NAFCs). Points and error bars (B–D) are means ± standard deviation. Embryonic exposure to NAFCs significantly increased larval mortality GLMM, Wald's Chi‐squared(1,12) = 9.06, p < 0.01 and frequency of burst swims LME, F(1,16) = 6.47, p = 0.022 Swimming duration LME, F(1,16) = 2.66, p = 0.12 and duration in the middle of the arena LME, F(1,16) = 2.7, P = 0.12 did not vary significantly between treatment groups.