scope:

The objectives of this report are to evaluate the inter-laboratory (between-laboratory) and intralaboratory (within-laboratory) variability that is inherent in the draft toxicity-test (bioassay) protocol recommended by the American Petroleum Institute (API, 1983) for assessing the acute toxicity of the suspended particulate phase of drilling fluids to mysid shrimp (Mysidopsis bahia). The identification and reduction of confounding sources of variation in that toxicity test is of particular importance because of the use of the test (or slight variations thereof: e. g., Petrazzuolo, 1983) by several regions of the U. S. Environmental Protection Agency (EPA) to regulate the discharge of drilling fluids from offshore drilling rigs.

To achieve the above-stated objectives, the API selected ERCO as the prime consultant; and further specified that three commercial aquatic toxicology laboratories, each representing a different coastal region of the united States, participate in the interlaboratory and intralaboratory testing. The specified laboratories were ERCO, Cambridge, Massachusetts (Atlantic coast); Marine Bioassay Laboratories, Watsonville, California (Pacific coast); and Espey, Huston and Associates, Galveston, Texas (Gulf of Mexico). The API and ERCO concurred that, to minimize bias in the investigation, the principal investigator for the study (Dr. Curt Rose of ERCO) would have no more or no less communications regarding the study with his laboratory than with the other participating laboratories.