Distribution of hydrocarbons in seabed sediments derived from tsunami-spilled oil in Kesennuma Bay, Japan

As a result of the 2011 Great East Japan earthquake, about 11,000 kL of fuel oil was spilled into Kesennuma Bay, Miyagi Prefecture. This oil either accumulated in seabed sediments or was burned in a marine fire on the sea surface. We investigated spatial and temporal variations in the concentrations of oil and hydrocarbons. The maximum concentrations of n-hexane extract (NHE), total petroleum hydrocarbon (TPH), and polycyclic aromatic hydrocarbons (PAHs) in the sediments in 2012 were 8000, 1200, and 16.2 mg/kg (DW), respectively. NHE and TPH concentrations were high in the inner and west bay, and PAHs concentrations were high in the east bay. NHE and PAH concentrations didn't change; however, TPH concentrations decreased significantly with time. The total NHE in the sediment across the whole bay was estimated at 1685 kL and there was still about 13% of the original amount in the sediment in December 2014.