Advective pore-water transport of hydrocarbons in North East Scotland coastal sands

Oil spills in the marine environment can cause ecosystem-level impacts. Dispersant application as an oil spill response measure leads to the widespread distribution of hydrocarbons in the water column and marine sediments. The North Sea is an area of intense hydrocarbon production and is at risk of oil spills, which are of concern to its benthic ecosystem due to its sediments’ high permeability. Here, entrainment of hydrocarbons via pore-water advection into permeable North Sea sands and the associated effect of Superdispersant-25, a commercial oil dispersant, were evaluated in a laboratory. Centrally stirred chambers that induce advective pore-water fluxes in sediments were filled with sediment, seawater and mixtures of oil and Superdispersant-25. Dispersant application had contrasting effects on hydrocarbon interactions with sediment: (1) it reduced accumulation of hydrocarbons in surface sediments and (2) facilitated the entrainment of hydrocarbons up to 8 cm deep into sediments by increasing hydrocarbon solubility in seawater and its subsequent washout or pumping into sediment by pore-water movement. Results here show that dispersant application can have counter-intuitive effects on hydrocarbon interactions with marine sediments and highlight the need for further research in this area to make better informed decision in an oil spill response scenario.