The long-term status of petroleum hydrocarbons in both seawater and sediment contaminated by the Dalian New Port oil spill has been investigated since 2010. Seawater recovery is relatively swift and is complete within two years, while oil contamination persists in the coastal sediments for several years. Because of the slow degradation and low mobility in sediments, they serve as long-term reservoirs for residual oils. The erosion of sediments into the water column leads to an abrupt increase in hydrocarbons during storms. The cumulative results of hydrodynamic transport and ongoing industrial emissions lead to a spatial shift of hot spots with high petroleum hydrocarbon concentrations from the spill site to the inner corner of the bay. In addition to continuous petroleum hydrocarbon emissions from contiguous coastal outfalls, the regional oil contamination will persist indefinitely. The research provides comprehensive information for years to come to evaluate the long-term damage and multiphase medium impacts of a large oil spill.

Spatial–seasonal variations in dissolved heavy metals in surface seawater were analyzed based on surveys at 87 sampling sites and water samples from six rivers across Liaodong Bay. The concentrations of copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) had ranges of 0.20–40.00 (5.45 ± 5.67), 0.51–33.64 (4.68 ± 3.93), 0.03–13.47 (2.22 ± 2.01), and 0.50–80.09 μg/L (14.22 ± 16.32), respectively, throughout the four seasons of 2020. The trace metal concentration showed a spatial gradient of high to low from river to estuary and from inshore to offshore areas. A combination of pollution levels and marine sensitivity was employed to assess the pollution degree of the heavy metals. As a whole, the single pollution factors of trace metals in Liaodong Bay were ranged in the order Pb > Zn > Cu > Cd. The total pollution degree was relatively high in autumn and summer due to increased riverine inputs after the rainy season, while relatively low in spring and winter. These findings provide baseline data for future targeting policies to protect marine environments in Liaodong Bay.