THE FATE AND EFFECTS OF DISPERSANT-TREATED COMPARED WITH UNTREATED CRUDE OIL, WITH PARTICULAR REFERENCE TO SHELTERED INTERTIDAL SEDIMENTS

Abstract

ABSTRACT Dispersant use is a factor that may partly determine the fate and effects of spilled oil. A series of quantitative field experiments has been initiated to simulate conditions following nearshore treatment of a floating oil slick or following the cleaning of a spill stranded on the shore. The basic experimental design is a series of treatments (Forties or Nigerian crude oil, BP 1100WD dispersant, or oil plus dispersant) applied to sets of experimental plots in a range of intertidal and subtidal communities. Biological recording includes frequency and density measurements of plants and animals, and hydrocarbon analysis is by capillary gas liquid chromatography and computerised gas chrornatography–mass spectrometry. Additionally, the effects of dispersant on the movement and fate of oil in different types of sediment is being investigated using a laboratory sediment column and controllable temperature seawater system. The columns have been successfully used in the modeling of low-energy sedimentary environments. Particular attention has been paid to the nature of water table fluctuations within the sediment, to grain size and sorting, to permeability, and also to the number of simulated “tides” that the columns experience after treatment. Hydrocarbon analysis is primarily by ultraviolet spectrophotometry, which has the advantage that the large number of samples generated by each experimental run can be quickly analysed. Gas liquid chromatography is used for checking selected samples. Preliminary results from the field and laboratory experiments indicate that some dispersant treatments increase penetration of oil, and that it may be retained below the sediment surface. Interacting factors include time of treatment in relation to tidal cycle and behaviour of the water table in the sediment.