Trophic dilution of PAHs through benthic food web in tidal flat

Polycyclic aromatic hydrocarbons (PAHs) are anthropogenic and ubiquitous substances in coastal environments. They are also known to have relatively hydrophobic and potent toxicity such as carcinogenicity and mutagenicity. Therefore, it is important to understand trophic transfer of PAHs for the better understanding of contamination by anthropogenic compounds through food web. The objective of this research is to reveal biomagnification of PAHs in lower level of the benthic food web using carbon and nitrogen stable isotope ratios in the selected tidal flats near river mouth surrounded by reed marsh. The concentrations of PAHs in potential food sources were 14-67 times higher than those of macroinvertebrates. The PAH compositions in potential food sources were dominated by five to six ring PAHs with higher molecular weight and the level of two to three ring PAHs was relatively low. Significant negative relationships were found between the nitrogen stable isotope ratios and lipid concentrations of 8 PAHs (fluorine, phenanthrene, fluoranthene, pyrene, chrysene, benzo(a)pyrene, benzo(κ)fluoranthene and benzo(b)fluoranthene). Trophic Magnification Factor tended to decrease with increasing logK_ow and molecular weight of PAHs, which suggests that low molecular weight PAHs tends to remain in macroinvertebrates. These results confirm the trophic dilution of PAHs in lower trophic level of the benthic food web.