This study utilizes sediment cores as valuable natural archives to reconstruct historical trends of polycyclic aromatic hydrocarbons (PAHs) in Rayong Bay, Thailand, a coastal ecosystem facing significant anthropogenic pressures. Sediments are crucial sinks for these persistent contaminants, reflecting past pollution events.

An increasing trend in PAH concentrations since the 1950s and 1960s was observed. This rise can be attributed to intensified industrialization, and motorization, as well as broader urbanization. Notably, unlike industrialized nations where PAH levels decreased after the 1960s, inputs to Thailand’s coastal environments have not shown a similar decline, indicating ongoing development impacts.

Specifically for Rayong Bay, post-1987 data from sediment cores, coinciding with the development of the Map Ta Phut Industrial Estate (MTPIE), show a distinct upward trend in ∑16PAHs concentrations. This period is characterized by an elevated accumulation of pyrogenic high-molecular-weight (HMW) PAHs, possibly originating from industrial fossil fuel combustion, atmospheric deposition, and shipping emissions. Episodic peaks of low-molecular-weight (LMW) PAHs are also observed, linked to acute, unburned petrogenic spills from intensive maritime traffic. Crucially, this PAH enrichment persists despite dilution effects from land reclamation and coarser modern sediments, underscoring the immense magnitude of anthropogenic PAH inputs.

While current PAH concentrations in these core samples remain below established Thai and international sediment quality guidelines, suggesting unlikely acute biological effects, the documented historical increase and shift in PAH profiles provide clear evidence of long-term anthropogenic impact on Rayong Bay's coastal ecosystem. This necessitates continuous monitoring to understand temporal variations and inform management strategies.

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