Development of an Optical Detection System of Fuel Oil on Seabed Sediments

Abstract

Many oil tanks around coastal northeastern Japan were destroyed by the tsunami caused by the March 2011 earthquake. In Kesennuma Bay, Miyagi Prefecture, roughly 11,000 kL of fuel oil were flushed into the bay. Much of the oil was deposited on the seabed and mixed with sediment particles. Effective removal of the oil from seabed sediments requires a detailed understanding of its distribution throughout the seabed. Using ultraviolet (UV) fluorescence, we developed a new system of detecting oil in sediments and examined the effectiveness of the system. The in situ seabed sediments of Kesennuma Bay emitted fluorescence at a dominant wavelength of 550 nm under UV irradiation. The fluorescence was stronger in seabed sediments with higher concentrations of oil. The detection limit of oil in Kesennuma Bay occurred at a water depth of 6–7 m. Thus, the high turbidity and deep seabed in Kesennuma Bay prevent effective survey with the proposed system. In clear waters, however, the detection limit depth is estimated at 20–30 m, indicating that the system may be used to understand the distribution of oil in seabed sediments.