PAH contaminations and recoveries in the sandy versus muddy sediment coastlines after the Hebei Spirit oil spill

Abstract

After the collision between the oil tanker Hebei Spirit and a barge carrying a crane, approximately 10,900 tons of Middle East crude oil was released 10 km off the west coast of Korea in December 2007. Total 438 sediment samples were collected to assess the spatiotemporal trends of PAH contaminations and its recoveries, from December of 2007 through May of 2016. PAH concentrations in sediments measured immediately after the spill ranged from 3.2 ng g-1 to 71,200 ng g-1, with an average of 3,800 ng g-1. Increases in PAH concentrations were observed at stations 7 through 23, which were heavily oiled due to tidal currents and northwesterly wind that transported the spilled oil to these locations. Mean and maximum PAH concentrations decreased drastically from 3,800 to 88.5 ng g-1 and 71,200 to 1,700 ng g-1, respectively, four months after the spill. PAH concentrations highly fluctuated for the first one year after the spill and then decreased slowly to background levels. Reduction rate of PAH concentration was much faster at the sandy beaches (half-life = 43.3 d) than in the muddy sites (half-life = 693 d). In muddy sediments, low attenuation due to low flushing rate in the mostly anaerobic sediment possibly contributed the persistence of PAHs. By May of 2016 (~8.5 yrs after the spill), mean and maximum PAH concentrations decreased by ~ 50 and 500 times, respectively, compared to the initial contamination levels. Composited to assess the spatiotemporal trends of PAH contaminations and its recoveries, from December of 2007 through May of 2016. PAH concentrations in sediments measured immediately after the spill ranged from 3.2 ng g-1 to 71,200 ng g-1, with an average of 3,800 ng g-1. Increases in PAH concentrations were observed at stations 7 through 23, which were heavily oiled due to tidal currents and northwesterly wind that transported the spilled oil to these locations. Mean and maximum PAH concentrations decreased drastically from 3,800 to 88.5 ng g-1 and 71,200 to 1,700 ng g-1, respectively, four months after the spill. PAH concentrations highly fluctuated for the first one year after the spill and then decreased slowly to background levels. Reduction rate of PAH concentration was much faster at the sandy beaches (half-life = 43.3 d) than in the muddy sites (half-life = 693 d). In muddy sediments, low attenuation due to low flushing rate in the mostly anaerobic sediment possibly contributed the persistence of PAHs. By May of 2016 (~8.5 yrs after the spill), mean and maximum PAH concentrations decreased by ~ 50 and 500 times, respectively, compared to the initial contamination levels. Composi