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Mechanisms of Oil Toxicity and Adverse Outcome Pathways of Petroleum Hydrocarbons
Citation:
Barron, M. Mechanisms of Oil Toxicity and Adverse Outcome Pathways of Petroleum Hydrocarbons. SETAC SE Regional Chapter Meeting, Pensacola Beach, FL, September 12 - 13, 2019.
Impact/Purpose:
The purpose of this presentation is to summarize the historical context and state of the science on the mechanisms of action of toxic components of oil. The presentation will provide conference participants a succinct overview of mechanisms of toxicity, which are not widely understood or appreciated. The impact of this presentation is three fold: (1) It will communicate that dogma concerning a single minimal toxicity mechanism is not sufficient in assessing the impacts of oil spills. (2) It will show that EPA scientists are leaders in the field of oil toxicology, which is significant for future testimony as an expert witness. (3) It provides an opportunity to interact with other scientists and exchange information.
Description:
Alkyl homologs of the two ring PAH naphthalene and single ring aromatics were identified as primary chemicals of concern in spilled oil in early studies of petrogenic PAHs because of their relatively high abundance, water solubility, and rapid partitioning into aquatic organisms. These compounds were observed to cause toxicity through a narcosis mode of action similar to the reversible anesthetic-like effects seen with solvents and other chemicals of moderate polarity. Beginning in the 1980s, research showed that PAHs with specific structural conformations could cause toxicity through a unique mode of action known as photoenhanced toxicity resulting from the interaction of a PAH with ultraviolet radiation present in sunlight. Multiple studies then determined that specific PAHs and multiple oil products can have significantly increased toxicity at levels of sunlight in many aquatic environments. Following the Exxon Valdez oil spill, species of salmon and herring exhibited a syndrome of edema and skeletal malformations similar to what is observed with dioxin toxicity. Subsequent research identified specific three ring and larger PAHs and heterocyclic compounds as causing a characteristic suite of cardiotoxicity and other embryotoxic effects in multiple species of freshwater and marine fish exposed to crude or heavy oils. This body of research shows that petrogenic PAH toxicity in early life stages of aquatic organisms can act through distinct toxicity mechanisms and yield differing organismal-level outcomes. Considering these the mechanisms and pathways to adverse outcomes can lead to a better understanding of concentrations of concern and life stages and organisms at risk relevant to impact assessments and spill response.