Monitoring toxicity of polycyclic aromatic hydrocarbons in intertidal sediments for five years after the Hebei Spirit oil spill in Taean, Republic of Korea

•We monitored toxicity of intertidal sediments for 5years after Hebei Spirit oil spill.•Toxicity of sandy beaches decreased within 8months after the spill.•Sediment toxicity remained at heavily contaminated sites 5years after the spill.•Ecological impact and weathering process of residual oils are ongoing. Ecotoxicological monitoring of intertidal sediments was performed for 5years after the Hebei Spirit oil spill in Taean, Korea. Sediment toxicity was observed on most of the beaches 4months after the spill and later decreased rapidly to nontoxic levels 8months after the spill. The concentrations of total polycyclic aromatic hydrocarbons (TPAHs) in the sediments ranged from 2 to 530,000ng/g during the monitoring. More than half of the samples exhibited significant toxicity 5years after the Hebei Spirit oil spill. Using a logistic regression model, the median lethal concentration of TPAHs to amphipod Monocorophium uenoi was estimated to be 36,000ng/g. From the 63 chemistry and toxicity data, the effect range-low, effect range median, threshold effect level, and probable effect level were derived to be 3190, 54,100, 2480, and 29,000ng/g, respectively. The relative compositions of the PAH groups indicated that the weathering process is still ongoing.