Concentration and degradation behavior of persistent organic environmental pollutants via a polychaete <i>Marphysa</i> sp. (Annelida: Eunicidae) in tidal flats

Polycyclic aromatic hydrocarbons (PAHs) are persistent environmental pollutants generated by the combustion of fossil fuels, oil spills, and other anthropogenic and natural activities. Because some PAHs have carcinogenic and mutagenic properties, it is important to analyze their concentrations and behavior in the environment. In this review, we present our previous research findings on the concentration and degradation behavior of PAHs in the fecal pellets of Marphysa sp. E sensu Abe et al. 2019 (Annelida, Eunicidae), inhabiting the sediment of the Yoro tidal flat, which is located within Tokyo Bay, Ichihara, Chiba, Japan. Based on analyses of PAH concentrations, stable isotope ratios of carbon and nitrogen, total organic carbon, total nitrogen, and the particle size of fecal pellets of the worm and sediments (sand and reduced mud), we found that this worm ingested reduced muds (organics-rich silt and clay in a reductive state) containing high levels of PAHs. Furthermore, the PAH levels rapidly decreased in the fecal pellets after excretion. These results suggest that the feeding and excretion behaviors of the worm may play important roles in the purification of tidal flat environments. Additionally, we review previous studies on changes in PAH concentrations in tidal flat sediments caused by a fire at a neighboring oil refinery following the Great East Japan Earthquake in March 2011 as well as unpublished data on PAH concentrations in the sediment through 2022.