Drilling mud follow up study - Input data and validation experiments for ERMS

Discharges from drilling operations during exploration and production of oil and gas in the North Sea spread over large areas and remain in the water column for a long time. Potential impacts on marine organisms need to be elucidated to clearly establish what actions, if any, are needed to comply with the "no harmful environmental effects" goal stated by the Norwegian petroleum industry and the Norwegian State Pollution Authorities. In our ongoing PROOF project (159183) effects of barite and used water ba sed drilling mud with barite were detected in cod, mussels and scallops. Increased metal concentrations were detected in the tissues of exposed animals. In order to model fate and effects of drilling mud discharges, it is important to know if metal toxici ty contribute significantly to the effects observed in barite exposed animals. In this project, mussels will be exposed to barite with high and low metal content. Metal concentrations and effects will be studied in different mussel tissues. Recovery will be included to see if observed effects are reversible. Comparison of metal accumulation and effects in cod following direct exposure to barite and dietary exposure will be done by feeding the cod with mussels exposed to barite. Because of its lower metal content ilmenite is considered to be a more environmentally friendly weighting material in drilling mud than barite. Adult scallops and mussel larvae will be exposed to ilmenite and used drilling mud with ilmenite. We will test if ilmenite cause less effe cts than barite, and if the potential effects of ilmenite are reversible. The concentrations of metals in tissues of scallops exposed to barite and to ilmenite will be compared. The plan is to collaborate with an externally financed PhD student working on the effects of drilling mud on other species and other parameters, increasing the total output of the project.