Evidence of natural organochlorine formation in peat bogs

Peat samples from four ombrotrophic and two minerotrophic peat bogs in New Brunswick, Canada, have been analyzed for polychlorinated dioxins and furans (PCDD/DF's) as well as other organochlorine compounds. Data from each bog show occasional low levels of 2,3,7,8-substituted tetra-through octachloro dioxins and furans. Mono-through trichlorodioxins and furans have also been identified.

A consistent pattern was observed among the TCDD's and TCDF's which was reproducible across all peat samples analyzed. A single TCDF isomer (2468-TCDF) predominates over all other isomers whereas two isomers of TCDD were prominent (1,3,6,8-TCDD and 1,3,7,9-TCDD). This distinct isomer pattern is present at all depths and is different from that of atmospheric deposition or known sources of PCDD/DF's (eg. fly ash, pulp and paper effluent etc). The pattern is replicated with in vitro oxidative coupling of 2,4-dichlorophenol at pH 2.9 using a commercially available chloroperoxidase from the fungus Caldariomyces fumago.

Significant incorporation of ³⁶Cl-occurred in peat. Autoclaving decreased incorporation while adding casein hydrolysate increased it. The incorporation mirrored the metabolic activity (CO₂ production) of samples consistent with organochlorine synthesis being due to biological activity.

Total Organic Halide (TOX) levels in peat show a wide range in values reaching ca. 1000 ppm at mid-depth in the ombrotrophic Kelly's Bog. TOX in Kelly's Bog occurs at all depths and, since the topography probably excludes leaching from surrounding areas, a local origin of organochlorines is suggested.

Chloroform and a range of chlorinated aromatic compounds (chlorophenols, chlorophenoxy and chlorobenzoic acid derivatives) have also been identified in peat.

Our findings to date are consistent with hypothesis for a biogenic origin for at least some of the organochlorine compounds, including some of the PCDD/DF's, found in peat bogs.