Environmental fate of 1,2,3,4,7-pentachlorodibenzo-p-dioxin in a Canadian prairie soil

The fate of 1,2,3,4,7-pentachlorodibenzo-p-dioxin (P 5 CDD) was studied in a Canadian prairie soil under field conditions by applying 14 C-labelled P 5 CDD to a series of soil microplots and sampling the 0-2 and 2-5 cm depths over a period of 2 years. Analysis by HPLC-LSC revealed that, although P 5 CDD dissipated from the plots with a half-life of approximately 1.1 y, leaching and biodegradation were unable to account for the observed losses. Only 1.3% of the applied 14 C-P 5 CDD appeared in the 2-5 cm depth at 639 days indicating minimal leaching during the course of the experiment. Furthermore, since only 0.9% of the applied radiolabel appeared as extractable degradation products at day 639, biodegradation was not an important loss pathway for P 5 CDD in soil. Nonextractable 14 C, representing an irreversibly bound fraction of P 5 CDD, stabilized at approximately 10% leaving roughly 70% of the radiolabel unaccounted for at day 639. The observed losses are attributed to volatilization of parent P 5 CDD from the soil plots.