Acute and subacute toxicity of the polycyclic aromatic hydrocarbon 1-methylnaphthalene to the shallow-water coral Porites divaricata: Application of a novel exposure protocol

Abstract

Previous research evaluating hydrocarbon toxicity to corals and coral reefs has generally focused on community-level effects, and results often are not comparable between studies because of variability in hydrocarbon exposure characterization and evaluation of coral health and mortality during exposure. Toxicity of the polycyclic aromatic hydrocarbon 1-methylnaphthalene to the coral Porites divaricata was assessed in a constant exposure toxicity test utilizing a novel toxicity testing protocol uniquely applicable to shallow-water corals, which considered multiple assessment metrics and evaluated the potential for post-exposure mortality and/or recovery. Acute and subacute effects (gross morphological changes, photosynthetic efficiency, mortality, and histologic cellular changes) were evaluated during pre-exposure (4 wk), exposure (48 h), and post-exposure recovery (4 wk) periods. Coral condition scores were used to determine a 48-h median effective concentration of 7442 μg/L. Significant physical and histological changes resulted from exposure to 640 μg/L and 5427 μg/L 1-methylnaphthalene, with a 1-d to 3-d delay in photosynthetic efficiency effects (ΔF/Fm). Pigmented granular amoebocyte area was found to be a potentially useful sublethal endpoint for this species. Coral mortality was used to estimate a 48-h median lethal concentration of 12 123 μg/L. Environ Toxicol Chem 2017;36:212-219. © 2016 SETAC.

Short-term toxicity of 1-methylnaphthalene to Americamysis bahia and 5 deep-sea crustaceans

“…To determine lethal exposure thresholds in organisms exposed to individual high purity aromatic hydrocarbons, in this case 1‐MN, 48‐h constant exposure assays were carried out using a continuous‐flow exposure system as recommended by the Chemical Response to Oil Spills Ecological Effects Research Forum working group. This fits studies where organisms, such as corals, have been exposed to single hydrocarbons . The A. bahia test utilized 5 concentrations (nominally, 200, 400, 800, 1600, 3200 μg/L 1‐MN) and a seawater control, tested in replicates of 4, with 10 mysids, 4 to 5 d old, in each exposure chamber.…”

“…A key criterion for successful use of the passive dosing system is to ensure excess mass of hydrocarbon in both the loading solution and PDMS O‐ring reservoirs to prevent small amounts of depletion from affecting the target concentrations . The excessive amount of hydrocarbon loaded into the PDMS O‐rings has been proven to produce an accurate and precise constant aqueous concentration for the exposure duration, despite potential losses that occur in the test system .…”

“…An alternative to whole oils in toxicity studies is the use of individual hydrocarbons . Generally, the toxicity of specific oils results from the additive toxicity of constituent hydrocarbons, especially aromatics .…”

“…There are no such studies reporting concentrations that elicit mortality in 50% of the test animals (LC50) for deep‐sea organisms. The present laboratory experiments utilized a single compound, 1‐MN, and a passive dosing protocol to establish toxic threshold concentrations for use in the TLM.…”

Passive dosing yields dissolved aqueous exposures of crude oil comparable to the CROSERF (Chemical Response to Oil Spill: Ecological Effects Research Forum) water accommodated fraction method

“…A second passive dosing format involves application of silicone O‐rings. This approach has been used for dosing single hydrophobic compounds and defined mixtures (Smith et al ; Renegar et al ; Knap et al ; Stibany et al ) and has recently been extended to investigate the in vitro toxicity of selected fuels (Heger et al ).…”