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

Area of Science:

• Environmental Chemistry
• Environmental Science
• Geochemistry

Background:

• Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/DFs) are persistent organic pollutants.
• The Great Hanshin-Awaji earthquake caused large-scale fires, raising concerns about environmental contamination.

Purpose of the Study:

• To investigate the impact of fires from the Great Hanshin-Awaji earthquake on PCDDs/DFs concentrations in Kobe coastal sediments.
• To estimate the total amount of PCDDs/DFs released by the fires and determine their transport pathways.

Main Methods:

• Sediment core and surface sediment sampling in Kobe coastal area.
• Estimation of total PCDDs/DFs released from fires.
• Utilizing an air diffusion model to assess transport routes (air vs. water).

Main Results:

• Significant increases in PCDDs/DFs concentrations were observed in the upper sediment layers.
• Estimated total release of 2000 g-total PCDDs/DFs (22 g-TEQ) from the fires.
• Water transport was identified as the principal pathway for fire-generated PCDDs/DFs to reach sediments, exceeding air transport.

Conclusions:

• Fires associated with the Great Hanshin-Awaji earthquake were a major source of PCDDs/DFs contamination in Kobe coastal sediments.
• Waterborne transport played a more significant role than airborne transport in sediment deposition of these pollutants.
• A relatively small fraction (20%) of fire-generated PCDDs/DFs entering water could account for the observed sediment contamination.