Recommendations for the advancement of oil-in-water media and source oil characterization in aquatic toxicity test studies.

During toxicity testing, chemical analyses of oil and exposure media samples are needed to allow comparison of results between different tests as well as to assist with identification of the drivers and mechanisms for the toxic effects observed. However, to maximize the ability to compare results between different laboratories and biota, it has long been recognized that guidelines for standard protocols were needed. In 2005, the Chemical Response to Oil Spills: Ecological Effects Research Forum (CROSERF) protocol was developed with existing common analytical methods that described a standard method for reproducible preparation of exposure media as well as recommended specific analytical methods and analyte lists for comparative toxicity testing. At the time, the primary purpose for the data collected was to inform oil spill response and contingency planning. Since then, with improvements in both analytical equipment and methods, the use of toxicity data has expanded to include their integration into fate and effect models that aim to extend the applicability of lab-based study results to make predictions for field system-level impacts. This paper focuses on providing a summary of current chemical analyses for characterization of oil and exposure media used during aquatic toxicity testing and makes recommendations for the minimum analyses needed to allow for interpretation and modeling purposes.

High resolution Orbitrap mass spectrometry analysis of oxidized hydrocarbons found in freshwater following a simulated spill of crude oil.

Negative ion electrospray Orbitrap mass spectrometry was used to analyze water samples taken from a pilot-scale spill tank test of conventional crude oil on freshwater. A 56-day spill test was performed, and water samples were taken at regular intervals throughout the test to determine what changes in water chemistry occur with time. Orbitrap mass spectrometry was used to measure oxidized species in water samples, and oxidized species are analyzed by carbon number, double bond equivalent and hydrocarbon class. Emphasis is placed on changes with time over the course of the spill test, to examine changes by weathering processes that could occur naturally in a field spill scenario. Results demonstrate that while the concentrations of polycyclic aromatic hydrocarbons decrease in the water phase over time, the concentrations of total organic carbon and oxidized species in the water increase with time, where quantities of O2 and O3 species have the highest abundance. Measurement of increasing concentrations and changing relative abundances of these oxidized compounds can be used to assess how oil behaves in a freshwater aquatic environment after a spill.

Fate and Fathead Minnow Embryotoxicity of Weathering Crude Oil in a Pilot-Scale Spill Tank.

For several years now, the Natural Resources Canada research facility at CanmetENERGY Devon (AB, Canada) has been performing experiments in a pilot-scale spill tank using 1200 L of river water to examine the physical and chemical behaviors of various crude oil/water mixtures under varying water temperature regimes. Because oil toxicity can be modulated by weathering of the petroleum products, the present study aimed to assess changes in fish embryotoxicity to mixed sweet blend crude oil as it weathered at air and water temperatures of 14 °C and 15 °C, respectively, for 28 d. The physicochemical behavior of the oil was also monitored. Water samples were taken from the spill tank 5 times during the 28-d experiment on days 1, 6, 14, 21, and 28 and were used to perform toxicity exposures using fathead minnow embryos (Pimephales promelas). For each water sampling day, newly fertilized embryos were exposed to a serial dilution of the spill tank water, noncontaminated river water (used in the spill tank), and a reconstituted water laboratory control. Embryos were raised until hatching. Although mortality was not significantly altered by the oil contamination over the time period, malformation occurrence and severity showed concentration-dependent responses to all contaminated water collected. The results suggest that days 14, 21, and 28 were the most toxic time periods for the fish embryos, which corresponded to increasing concentrations of unidentified oxidized organic compounds detected by a quadropole-time-of-flight system. The present study highlights a novel area for oil research, which could help us to better understand the toxicity associated with oil weathering for aquatic species. Environ Toxicol Chem 2021;40:127-138. © 2020 Her Majesty the Queen in Right of Canada. Reproduced with the permission of the Minister of Natural Resources Canada.