Origin of Polycyclic Aromatic Hydrocarbons in Reduced Mud in the Yoro Tidal Flat, Japan

Reduced mud in the Yoro tidal flat (inner part of Tokyo Bay, Japan) consists of black and highly viscous sediment containing high levels of polycyclic aromatic hydrocarbons (PAHs). The mud is formed through the decomposition of terrestrial plants washed up on the tidal flat; however, the origin of PAHs within the mud has remained unclear. To investigate the origin of PAHs in the mud, we analyzed PAHs in the mud and fragments of terrestrial plants using gas chromatography–mass spectrometry. The total PAH concentrations except for perylene were comparable between the mud (336 ± 58 μg kg-dry−1) and the fragments of plants (247 ± 77–435 ± 235 μg kg-dry−1), and their compositional patterns were also similar. These results indicate that the high levels of PAHs in the mud primarily originated from the fragments of plants that composed the mud. Furthermore, the perylene (Pery) concentrations in the fragments of plants were the same as or higher than those in the mud, suggesting that the formation of Pery begins in the plant tissues even before the mud was formed. These findings reveal a previously unrecognized pathway by which terrestrial plants introduce PAHs into tidal flat environments.