Characterization of Miscellaneous Effluent Discharges from a Mobile Offshore Drilling Unit to the Marine Environment

A study was performed to evaluate the potential biological impacts from 8 different miscellaneous discharges from an oil and gas mobile offshore drilling unit (MODU) including deck drainage, desalination unit waste, boiler blowdown, fire control system test water, noncontact cooling water, and bilge water. Samples were evaluated for toxicity using a rapid (<1 h) initial screening test (echinoderm [Dendraster excentricus] fertilization test), and if toxicity was found, further testing was conducted using 3 chronic whole-effluent toxicity tests. This additional testing included the embryo larval development 72-h echinoderm (D. excentricus); 7-d mysid (Americamysis bahia) survival, growth, and fecundity invertebrate test; and 7-d topsmelt (Atherinops affinis) survival and growth fish test. Toxicity identification evaluations were performed on 3 discharges that consistently elicited a toxic response during whole-effluent toxicity testing. To place the results of the toxicity testing into the context of environmental risk, the spatial extent of potential biological effects was investigated using the CORMIX mixing zone model. The output of the modeling indicated that discharge of selected effluents did not result in concentrations, or duration of exposure, that would elicit toxic effects to organisms living in the surrounding environment. The present study provides a comprehensive data set that was used to characterize potential toxicity and environmental risk of MODU "miscellaneous discharges" which could help inform future risk assessments of these discharges. Environ Toxicol Chem 2019;38:2811-2823. © 2019 SETAC.