Characteristics and source analysis of PAHs pollution in sediments based on different closing times of oil well

In order to evaluate the ecological environment of the oil well closed clearance area in the coastal wetland of the northern part of the Yellow River Delta and compare the ecological environment effect between area at different closing times, the oil well clearance areas that closed in 2002, 2012 and 2018 were selected. The pollution characteristics of polycyclic aromatic hydrocarbons (PAHs) in surface sediments were analyzed, the source was analyzed by characteristic ratio method and positive matrix factorization (PMF), and the ecological risk was evaluated by toxic equivalent quantity (TEQ) and mean effects range median (M-ERM-Q) methods. The results show that the average content in total sediments ΣPAHs is 791.691 ng/g, which is moderately polluted, mainly with 4 to 5 rings. The average content of ΣPAHs in the sediments in 2002, 2012 and 2018 are 587.29, 135.36 and 1 652.41 ng/g respectively, which are slightly polluted, unpolluted and severely polluted, and the main number of rings are 4~5,2 and 4~5 rings respectively. Total sediments PAHs are mainly affected by the oil spill, supplemented by the effects of vehicle emissions, sall, and coal combustion. The main sources in 2002 and 2012 contains oil leaks, vehicle emissions, coal combustion, and 2002 contains fuelwood burning, and in 2018 contains fuel wood combustion and vehicle emissions. The average TEQ of total sediments ΣPAHs is 193.53 ng/g, which falls within the safety range of environmental and human health. The average M-ERM-Q of sediments ΣPAHs in different years are less than 0.1, with low ecological risk, but there is a 30% probability of toxicity at individual points in the closed area in 2018. The restoration effect of the closed well was generally good, but the individual points had high pollution and low ecological risk, so further researches and ecological restoration projects were needed.