Research Product

Proposed guidelines for BAT regulations that govern the discharge of drilling fluids from offshore oil and gas platforms include a requirement for conducting an acute toxicity test with mysids, (Mysidopsis bahia), a small shrimp-like crustacean. The purpose of the test is to obtain an indication of the potential effect of a drilling fluid on marine organisms and additional tests with other organisms may be required by EPA Regional Offices under section 403-c of the Clean Water Act. The data from the BAT-related toxicity test are used to calculate the 96-hour LC50, i.e., the concentration of the drilling fluid that is lethal to 50% of test organisms exposed for 96 hours. This test was chosen, in part, because it is relatively simple to perform, mysids are generally available to testing laboratories, and these crustaceans are sensitive to toxic materials. Additionally, there is a large body of historic data concerning mysid toxicology which is useful for comparative purposes and the method has been routinely subjected to quality assurance calibration. The manner in which results from the toxicity tests can contribute to the BAT approach is illustrated by data developed recently by the EPA Environmental Research Laboratory at Gulf Breeze, Florida. Samples of drilling fluids collected from active wells in the Gulf of Mexico were screened for toxicity according to the BAT procedure. Some of the drilling fluid samples were more toxic than expected and their toxicity correlated well with the amount of "diesel" present in the samples. As a result of the screening tests, other organisms were tested and the data confirmed the relationship between toxicity and diesel content. The data indicate that toxicity of these drilling fluids could have been diminished through product substitution, i.e., by the use of a less toxic lubricating agent in the drilling fluids.