Compound-Specific Carbon and Hydrogen Isotope Fingerprinting Resolves Dominant PAH Sources in Sediments from a Major Shipyard Harbor

Abstract

Accurate source discrimination of polycyclic aromatic hydrocarbons (PAHs) in industrialized coastal sediments remains challenging because multiple pyrogenic sources often exhibit overlapping molecular signatures. Despite frequent elevated PAH contamination in sediments near shipyards, the dominant sources remain poorly constrained. In this study, compound-specific dual isotope analysis (δ13C and δ2H) was applied to surface sediments from Okpo Harbor, a major shipbuilding center in South Korea. PAH concentrations ranged from tens to >2000 ng g–1 dry weight (dw), with contamination hotspots concentrated in the inner shipyard area. Elevated benzo[a]anthracene and chrysene ratios [BaA/(BaA + Chr)] indicated substantial contributions from coal tar in addition to mixed pyrogenic sources. Intercompound isotopic variations may reflect differences in PAH formation pathways, potentially including hydrogen abstraction–acetylene addition. In particular, markedly depleted δ2H values of BaA may be associated with differences in its formation pathway, although this interpretation remains a working hypothesis requiring experimental validation. Principal component analysis resolved three major source groups, including coal tar, liquid fuel leakage, and background (i.e., coal combustion), which were subsequently quantified using a Bayesian isotope mixing model. Coal tar-derived PAHs accounted for 65.7% of the total PAH inventory despite their limited spatial extent, reflecting highly concentrated shipyard-associated point-source contamination. In contrast, liquid fuel-derived PAHs accounted for 17.9% of the total inventory and exhibited a geographically distinct hotspot pattern. These findings highlight distinct compound-specific carbon and hydrogen isotope behaviors among PAHs, providing insights into potential links between molecular formation processes and their isotopic signatures. When integrated with spatial patterns and Bayesian mixing, these compound-specific isotope characteristics provide complementary constraints for discriminating and quantifying PAH sources in complex industrial harbor environments.