Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species in Oil Spill Toxicology

Abstract

The response to the 2010 Deepwater Horizon (DWH) oil spill lead to a number of peer-reviewed publications examining the effects of the released oil and dispersant on fish species found in the northern Gulf of Mexico (GoM). Many of these papers, for very good reasons, focused on assessing toxicity by defining lethality through identification of dose-response curves that were specific to a given species, age class, exposure type, oil preparation method, and many other factors. Often those dose-response curves were used to predict LC or EC50 concentrations – amounts of oil that produced an effect on 50% of the exposed organisms. The advantage of this approach is obvious, in that it provides a single point estimate and variance of a concentration required to produce a given effect. This point estimate can then be compared across different exposure regimes to compare susceptibilities. Relevant LC/EC50 data is summarized and discussed in A synthesis of DWH oil, chemical dispersant and chemically dispersed oil aquatic standard laboratory acute and chronic toxicity studies (see Mitchelmore et al. A synthesis of Deepwater Horizon oil, chemical dispersant and chemically dispersed oil aquatic standard laboratory acute and chronic toxicity studies (Chap. 28). In: Murawski SA, Ainsworth C, Gilbert S, Hollander D, Paris CB, Schlüter M, Wetzel D (Eds.) Deep oil spills – facts, fate and effects. Springer; 2020). By constraining toxicity to this point estimate (often of lethality), however, researchers run the risk of missing effects that evince more subtle effects that do not manifest themselves as overt mortality in the short term. In the present chapter, we focus exclusively on fish and explore some of these endpoints, many of which were successfully used in recent years to assess sublethal health impacts on marine fish as part of the response to the DWH spill. We compare what is known about differences in sensitivity, among species, and between age classes within species, examining both organismal and molecular endpoints. Developmental impacts on cardiac health, swim performance, and sensory systems have been widely studied. We discuss what is known about effects on fish immune and endocrine function, the microbiome of the intestine and gill, and intracellular effects such as altered gene expression, oxidative stress, and DNA damage. In conclusion, we attempt to compare the endpoints, assess the sensitivity and utility, and link molecular- and individual-level impacts to larger population and community-level effects.