Progress in the development of short term chronic toxicity testing methods for crude oil and commercial bioremediation agents

Proposed modifications to the National Oil and Hazardous Substance Pollution Contingency Plan (NCP) have prompted examinations of the methodology used in toxicity testing of the water soluble fraction of oil, commercial bioremediation agents (CBA), and a combination of the two. The specific concerns addressed by this research are the use of unweathered Alaska North Slope (ANS) crude oil instead of the more expensive, less environmentally realistic distillate ANS-521, and the appropriate laboratory preparation methodology for the water soluble fraction (WSF) used in testing. Seven-day chronic tests exposing the inland silverside (Menidia beryllina) and estuarine mysid (Mysidopsis bahia) to the water soluble fraction of unweathered ANS and ANS-521 showed that mysids responded similarly to the two types of oils while silversides were more sensitive to unweathered ANS. In the presence of a CBA and WSF, the mortality of the organisms and the mysid growth were similar in both types of oil. The NOEC for silverside growth, however, was lower in the combined exposure of a CBA with ANS-521 WSF than it was in the CBA-WSF unweathered ANS. Testing is underway to determine if the stirring time length effects the toxicity of the WSF, or the WSF and CBA combination. In chronic tests using both the silverside and mysid there were no differences in growth and mortality of the organisms tested in WSF prepared from 10 and 20 hours of stirring, however, the 5 hour stirring exposure is less toxic to both organisms