Large-scale fires and time trends of PCDDs/DFs in sediments

Drastic increases in PCDDs/DFs concentrations were identified in the uppermost layers of a sediment core sample taken from the coastal area of Kobe City. As large-scale fires caused by the Great Hanshin–Awaji earthquake were deemed to be a possible cause, we performed additional sampling of sediment cores and surface sediment samples, estimating the total amount of PCDDs/DFs released from fires and presuming the load to sediments by individual transport routes, such as air and water, using an air diffusion model to investigate the influence of fires. The total amount of PCDDs/DFs released from fires was estimated at 2000 g-total PCDDs/DFs, 22 g-TEQ. Increases in PCDDs/DFs generated in fires were principally transported through water rather than air. If 20% of the total PCDDs/DFs formed in fires had entered water, it would correspond to the entire increase of PCDDs/DFs concentration in sediment cores.