INTRODUCTION The American Society for Testing and Materials (ASTM) task group (F-20) has proposed two draft procedures for the evaluation of acute toxicity of chemically-dispersed oil on marine organisms (ASTM@ 1981). The proposed procedures provide for 1) the use of a continuous flow-through bioassay system for the determination of an LC50 value@ and 2) a decreasing concentration bioassay for determination of a toxicity index value proposed by Anderson et al. (1980). The LC50 value as used herein is generated by the exposure of test organisms to constant concentrations of an oil/dispersant mixture in a continuous flow of seawater. The Toxicity Index (TI) is determined by the exposure of test organisms to a uniformly decreasing concentration of oil/dispersant mixture in a continuous flow of seawater. With both tests the toxicity is indicated by 50% mortality of the test organisms. It appears that the use of the decreasing concentration bioassay procedure may provide a laboratory toxicity test method that more closely simulates environmental conditions than previously available laboratory test methods. The exposure of marine organisms to oil/dispersant mixtures at constant concentrations over some defined period of time in the constant concentration procedure does not simulate actual field conditions following the application of a dispersant to spilled oil in marine waters. Therefore@ it is desirable to establish differences and similarities in toxicity test results when determined by the two methods. An understanding of the relationships between toxicity data derived from the two procedures may lead to the acceptance of a more realistic bioassay method by regulatory officials. To date@ neither the flow-through constant concentration nor the decreasing concentration bioassay methods have been tested and critiqued by commercial laboratories. Such laboratories have routinely used the EPA approved@ static system approach to obtain LC50 values for oil/dispersant mixtures in seawater. In order to evaluate the two bioassay protocols described above@ Pacific Environmental Laboratory identified the following objectives for the study: 1. Evaluate the precision and repeatability of the decreasing concentration bioassay as proposed by ASTM using two different dispersants with one oil on the coon-stripe shrimp@ Pandalus danae. 2. Evaluate the proposed ASTM continuous flow-through constant concentration bioassay procedure with two dispersants and one oil on the coon-stripe shrimp@ Pandalus danae. 3. Compare the results from objectives 1 and 2@ i.e.@ the LC50 and the decreasing concentration values obtained from exposing Pandalus danae to chemically-dispersed oil under the same laboratory conditions.
API DR169-1984 history
1984API DR169-1984 Final Report Interlaboratory Testing: Acute Toxicity Bioassay Method for Chemically-Dispersed Oils