We use monitoring data of petroleum hydrocarbons (PHs) after ten years as indicators to assess the long-term environmental impact of the Dalian "7.16" Oil Spill on seawater and sediments. Compared with the values measured ten years ago, the monitoring PHs concentrations in water and sediment have decreased 91.1% and 69.2%. Although oil has been eliminated from the surface, the long-term environmental impacts are confined to the sea beds where PHs levels in sediment exceeding 1000 mg/kg. High levels of PHs are primarily concentrated in industrial area far away from spill site, indicating that the PHs in seawater is mainly from on-going sewage outfalls rather than the spill event. Unless external loading levels of PHs are suppressed, the sediment quality is expected to recover slowly.
Spilled oil has long been recognized as a problem for the oceans: it pollutes both beaches and sea surface; and is consumed by fish, seabirds, and other creatures. The Dalian "7.16" oil spill happened on July 16, 2010, and released approximate 35,000 tonnes of crude oil into the coastal water (Xu et al., 2012; Guo et al., 2014). Oil leakage contaminated the surrounding area and the Yellow Sea in China, causing 100 square kilometers of sea surface covered by oil slicks (Liu et al., 2013). An area of approximately 10 square kilometers was heavily polluted (Liu, 2016). Oil spills were cleaned up using physical methods such as oil absorbent felt within a month. In addition, 30 tons of oil abatement agents were also sprayed in the contaminated area in order to break down and dissolve the crude oil (Hong et al., 2020). A large extent of the shoreline in Dalian was also heavily polluted. The spilled oil had brought dramatic ecological impacts to the Dalian coastal ecosystem (Liu et al., 2013). Recent oil spills have shown that oil can persist in coastal sediment for several decades (Reddy et al., 2002; Peterson et al., 2003). An important indicator of water quality is the PH of seawater, which is also recognized as a key indicator of environmental pollution in China at the present time (Wu, 2018).
