Release of native and mass labelled PCDD/PCDF from soil heated to simulate bushfires

Soil is an important reservoir of PCDD/PCDF, which can be released when environmental conditions change. Fire is an extreme event that can increase the surface temperatures of soil substantially, yet little is known of the role soil plays in the emission of PCDD/PCDF. Soil containing native PCDD/PCDF was fortified with a mixture of mass labelled PCDD/PCDF and heated between 150 °C and 400 °C. Both native and mass labelled PCDD/PCDF were released from the soil beyond 200 °C. Release of the mass labelled compounds was linearly related to temperature with up to 9 % found in the air stream at 400 °C. The release of some native PCDD/PCDF was much greater. At 400 °C, emission of 1,2,3,7,8-Cl5DD was 300% compared to pre-experimental soil. Emission of PCDD/PCDF from soil during bushfires is a relevant process and may originate from both volatilization and formation via de novo or precursor pathways, or dechlorination.

► We fortified soil with mass labelled PCDD/PCDF.
► We heated the soil in a furnace and measured emissions of PCDD/PCDF.
► We found mass labelled and native PCDD/PCDF in the air stream.
► Formation of some native congeners occurred probably due to dechlorination of Cl8DD.
► We conclude that soil emits PCDD/PCDF when heated to temperatures found in bushfires.