Examination of impact assessment of the oil spill using n-hexane extracts gravimetric method on Kesennuma Bay sediment after the Great East Japan Earthquake
2016
Kono, E. (IDEA Consultants, Inc., Yokohama, Kanagawa (Japan). Institute of Environmental Informatics) | Yumiki, M. | Shimada, K. | Yokoyama, K. | Yoshinaga, I.
Kesennuma port is the largest fishing port in northeast Japan. Twenty-two oil tanks stipulated to refuel fishing vessels in this port were destroyed by the tsunami that occurred on March 11, 2011. This resulted in a massive oil spill of 11,500 cubic m accompanied by a massive fire in Kesennuma Bay. The distribution of spilled oil in the sediments of the bay was investigated in the present study. Surface sediments were sampled in May 2011, and the sediment core was sampled in May and November of 2012. The concentration of n-hexane extracts (nHE) was compared with that of mineral oil, in order to serve as another indicator of oil content of the sediments. The nHE concentration was 10 times higher than the mineral oil concentration. The nHE concentration overestimated the amount of oil present in Kesennuma Bay, because the nHE contained not only mineral oil but also sulfur compound and chlorophyll pigment. Hence, it was proposed that the mineral oil must be analyzed independently, in order to understand the extent of oil pollution in the marine sediments. A vertical core study revealed that several centimeters of the surface deposit were made up of new phytoplankton detritus and that the mineral oil concentration increased at depths of 5-10 cm. Since the sediment surface was covered with newly formed deposits and the maximum concentration of mineral oil was 1.2 mg/g, it was inferred that the influence of oil odorant of the marine products by oil spill in Kesennuma Bay was low.
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