Distribution, deposition flux and budget of polycyclic aromatic hydrocarbons in the Yangtze River estuarine-inner shelf of the East China Sea

The East China Sea (ECS) is a marginal sea greatly influenced by the Yangtze River. The drainage basin of the Yangtze is ~1.94×10⁶ km² accounting for ~20% of the area of the Chinese Mainland with 400 million inhabitants. The Yangtze estuarine-inner shelf is a scientifically unique and ideal site to study the source to sink of sediments and associated pollutants. In this work, surface sediments were obtained from a matrix of 76 sample sites coving an area of ~80,000 km² extending ~800 km from the mouth of the Yangtze River to the Min River in the inner shelf in the East China Sea (ECS) for a comprehensive study of the distribution, composition, deposition flux and fate of polycyclic aromatic hydrocarbons (PAHs). Principal component analysis (PCA) indicated that the 16 PAHs in the northern Yangtze estuarine mud area were mostly phenanthrene while shifting to high molecular weight PAHs in the southern Min-Zhe coastal mud area. The ECS is much influenced by ocean currents, and waves induced by the East Asian Monsoon, which in turn play important roles in the re-suspension and transport of the sediments at the Yangtze River Estuary. These conditions, together with the difference in the physical and chemical properties of the PAHs and the sediments, caused the partitioning of these compounds, i.e., the selective depletion of low molecular weight PAHs and the enrichment of low molecular weight PAHs from the north of the inner shelf to the south, as observed in the PCA and Positive matrix factorization model analyses. The total deposition flux of the 16 USEPA priority PAHs (16 PAHs) of the Yangtze estuarine-inner shelf was estimated to be 152 t/yr, accounting for ~38% of the total annual input of the 16 PAHs into the ECS. This indicates that the Yangtze estuarine- inner shelf is the largest reservoir of land-based PAHs in the East Asian marginal seas. The loss of LMW PAHs estimated during re-suspension and transport was 49 t/yr. This release of LMW PAHs could be an important PAH source for the water column in the ECS.