The effects of oil-based drill-muds in sediments on the settlement and development of biota in a 200-day tank test

Planktonic organisms from natural estuarine waters were allowed to settle in tanks floored with autoclaved natural sediment mixed with oil-based drill-muds to give an initial oil concentration of 1000 × the background total hydrocarbon content. Over the 200 days of the experiment, there was a marked difference between the biota developing in tanks containing oil-based drill-muds, and in the control tank, which received drill-mud solids only, without any oil. Differences in effect werefound between two drill-muds, based on alternative oils of moderate and low aromatic hydrocarbon content, but there was a greater difference between these two muds and a diesel-based mud. Biota developed, even in the diesel-mud tank, when surficial sediment oil concentrations fell, despite high oil concentrations remaining in the subsurface sediments.