Assessing the Toxicity of Individual Aromatic Compounds and Mixtures to American Lobster (Homarus americanus) Larvae Using a Passive Dosing System

Abstract

Aquatic exposures to aromatic compounds (ACs) may be important contributors to biological effects of oil spills. The present study examined the acute toxicity of 11 ACs and 3 binary AC mixtures on stage 1 American lobster larvae using a passive dosing test design. The ACs investigated covered a range of classes and log octanol-water partition coefficient values (K_OW ; 2.5-5.5). Silicone O-rings were used to partition ACs into seawater and maintain stable exposures. Exposed lobster larvae were assessed for mobility and survival at 3, 6, 12, 24, 36, and 48 h. Fluorometry and gas chromatography-mass spectrometry measurements confirmed well-defined substance exposures. Expressing lethality in terms of chemical activities yielded values between 0.01 and 0.1, consistent with a baseline mode of action. Analysis of time-dependent median lethal/effect concentration (L/EC50) values were used to determine incipient values. An expected linear relationship between the incipient log L/EC50 and log K_OW was fit to the empirical toxicity data to derive critical target lipid body burdens for immobilization and lethality endpoints. These values indicate that American lobster larvae fall on the sensitive end of the acute species sensitivity distribution. We used AC toxicity data to successfully predict toxicity of binary mixtures assuming additive toxicity. The observed time-dependent toxicity was inversely related to log K_OW and occurred more quickly than reported previously. The results contribute to improving models for predicting oil spill impacts on American lobster larvae populations. Environ Toxicol Chem 2021;40:1379-1388. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Keywords: Dose-response modeling; Marine toxicity tests; Oil spills; Polycyclic aromatic hydrocarbons; Quantitative structure-activity relationships.

Figure 1

Dose–response curve (DRC) models used to calculate the median lethal concentration values at each time point for all 9 polycyclic aromatic compounds that caused biological effects. Mortality was observed at various assessment points for (A) toluene, (B) naphthalene, (C) phenanthrene, (D) fluorene, (E) methylnaphthalene, (F) methylanthracene, (G) acridine, (H) dibenzofuran, and (I) dibenzothiophene. The model chosen for each DRC was chosen based on the model fit function in R.

Figure 2

Regression analysis for describing the empirically derived $\mathrm{\epsilon }$ _LC50 estimates for describing the time course of mortality using log octanol–water partition coefficient for the aromatic hydrocarbons reported in Table 3. For comparison, the $\mathrm{\epsilon }$ _LC50 estimate for acridine is also plotted. The solid black line denotes the equation reported by French‐McCay (2002) using the study temperature of 15 °C. K _OW = octanol–water partition coefficient; LC50 = median lethal concentration.

Figure 3

Class‐corrected incipient median lethal concentration (A) and median effect concentration (B) values plotted against the log octanol–water partition coefficient values for aromatic hydrocarbons and heterocyclic aromatic hydrocarbons. EC50 = median effect concentration; K _OW = octanol–water partition coefficient; LC50 = median lethal concentration.

Figure 4

Acute immobilization (first row) and lethality (second row) of aromatic compound mixtures to stage 1 American lobster larvae at 24, 36, and 48 h of exposure. Toxic units (toxic units) were calculated using the median lethal/effect concentration values for the individual polycyclic aromatic compounds reported in Tables 1 and 2. Dashed black lines represent the 0.5 to 2 toxic unit window.