ACUTE EFFECTS OF FRESH VERSUS WEATHERED OIL TO MARINE ORGANISMS: CALIFORNIA FINDINGS

Abstract

ABSTRACT Early experiences with dispersants led to a widely accepted paradigm in the United States that chemically dispersing oil led to increased ecological damage. Since then, dispersant formulations have evolved significantly, leading many in the oil spill response community to revisit the question of whether or not dispersing oil can help achieve an overall net ecological benefit. Spill response must necessarily involve weighing the costs and benefits of both dispersant use and non-use to resources potentially at risk. The majority of comparative data on the toxicity of dispersed and undispersed oil in the literature to date is based on fresh oil. In most circumstances, however, mounting of dispersant operations requires hours to days, making the use of data based on fresh oil problematic. Laboratory-weathered oil has been used in the evaluation of dispersant effectiveness, but its use in toxicological investigations has been limited. Using standardized methods, the authors have compared the acute aquatic effects of untreated and chemically dispersed oil in both its fresh state, and artificially weathered to simulate approximately 1 day at sea. Oil weathering was done under controlled conditions using accepted, repeatable methods. Findings show that weathering significantly reduces the amount of low molecular weight hydrocarbons, and generally elicits reduced toxicity from both untreated and dispersed oil, compared to fresh oil. Based on actual hydrocarbon exposures, however, in several instances aqueous solutions from dispersed and undispersed oil (both fresh and weathered) were essentially equitoxic.