Acute toxicity of the oil dispersant corexit 9500, and fresh and weathered Alaska North Slope crude oil to the Alaskan tanner crab (C. Bairdi), two standard test species, and V. fischeri (MICROTOX Assay)

Abstract

Toxicity assays of the oil dispersant Corexit 9500, and fresh and weathered Alaska North Slope (ANS) crude oil were conducted on Alaskan tanner crab larvae (Chionoecetes bairdi) under cold-region conditions, the reference species, Mysidopsis bahia and Menidia beryllina, and Vibrio fischeri (Microtox bioassay). Acute 96-hour toxicity data for C. bairdi were calculated using the response 'affected' (decreased phototactic response and ability to swim). C. bairdi were most sensitive to non-dispersed weathered oil (EC₅₀=0.4 mg/L), least to dispersant-only solutions (EC₅₀=1,267 mg/L), and were typically more sensitive than the reference species. Dispersant-only solutions were consistently least toxic for all species tested. Dispersed fresh oil was frequently more toxic than non-dispersed oil. Weathered oil data are greatly influenced by aqueous solubilities, indicating non-dispersed weathered oil was most toxic, although those solutions required the highest oil loading (25 g/L). Interpretations of toxicity data are dependent upon expression of solution concentrations.