Persistence of trace metals in shallow arctic marine sediments contaminated by drilling effluents

Offshore oil exploration activity usually requires the discharge of drilling muds and formation cuttings into adjacent waters or on ice above these waters. Although dispersal of these muds is well documented in marine environments of moderate to high energy, the fate of drilling muds in shallow, low-energy Arctic environments has received little attention. This study focused on three drilling effluent disposal sites around Stefansson Sound in the Alaskan Beaufort Sea. All sites were in shallow (less than 5 m), low-energy marine environments. Sediment concentrations of six metals often present in drilling effluents (aluminum, arsenic, barium, chromium, lead and zinc) were examined. Metal concentrations obtained from replicate grab samples along 100 m transects were compared with those taken at four shallow-water offshore island control sites, and with data from other studies.

The results indicate persistence of barium, chromium, lead and zinc at certain stations at all three discharge sites, and elevated concentrations of aluminum at one of the three sites when sampled 2–4 years after the discharges. Metal concentrations, when elevated, were typically highest near the discharge points, continued in the direction of wind-induced longshore transport, and generally diminished with distance from the discharge site. However, distributions displayed some patchiness indicative of in place melting of ice-rafted muds or reworking of sediments by currents or icegouging.

Further work will be needed to evaluate the biological impacts of drilling effluents. However, the slow dispersal of these materials suggests there is a need for closer evaluation of drilling effluent persistence problems at shallow, lowenergy locations in the Beaufort Sea.