Integrated approach for submerged oil survey: Experience from Hebei Spirit Oil Spill

Abstract

Three kinds of Middle East crude oil were released from the Hebei Spirit oil spill in December 2007. The specific gravity of the oils ranged 0.85 ~ 0.87 which will naturally float on the water but a conflict of opinions arose over the submerged oil as the weathering and oil cleanup can alter the density of the spilled oil. The surveys for the submerged oil had been performed continuously since the spill incident using sediment grab sampling, SCUBA diving, underwater pumping, and trawling, because their possible existence on the seafloor may confer great impact on the marine environment and ecosystem. In Jun 2009, existence of submerged oil was extensively surveyed using the V-SORS (vessel-submerged oil recovery systems) and dredged net system focusing on the most concerned regions. A small amount of submerged oil was detected by the V-SORS method, mostly in a form of small spot of tar, less than 1 cm in diameter at 41% of the sections surveyed. PAH concentrations in biota collected by dredged net were similar to background levels, except relatively high PAH levels in ark shells (Scapharca broughtonii). The health risks of consuming the fishes and bivalves from the survey area were calculated to be much lower than the criteria for safe consumption.