Dispersant effectiveness on oil spills – impact of salinity

When a dispersant is applied to an oil slick, its effectiveness in dispersing the spilled oil depends on factors such as oil properties, wave-mixing energy, temperature, and salinity of the water. Estuaries represent water with varying salinity, so in this study, three salinity values in the range 10–34 psu were investigated, representing potential salinity concentrations found in typical estuaries. Three oils were chosen to represent light refined oil, light crude oil, and medium crude oil. Each was tested at three weathering levels to represent maximum, medium, and zero weathering. Two dispersants were chosen for evaluation. A modified trypsinizing flask termed a baffled flask was used to conduct the experimental runs. A full factorial experiment was conducted for each oil. The interactions between the effects of salinity and three environmental factors, temperature, oil weathering, and mixing energy, on dispersion effectiveness were investigated. Each experiment was replicated four times in order to evaluate the accuracy of the test. Statistical analyses of the experimental data were performed for each of the three oils independently for each dispersant treatment (two dispersants and oil controls). A linear regression model representing the main factors (salinity, temperature, oil weathering, flask speed) and second-order interactions among the factors was fitted to the experimental data. Salinity played an important role in determining the significance of temperature and mixing energy on dispersant effectiveness for almost all the oil–dispersant combinations. The impact of salinity at different weathering was only significant for light crude oil with dispersant A.