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. Dat a from each bog show occasional low levels of 2,3,7,8-substituted tetr a-through octachloro dioxins and furans. Mono-through trichlorodioxins and furans have also been identified. A consistent pattern was observ ed among the TCDD's and TCDF's which was reproducible across all peat samples analyzed. A single TCDF isomer (2468-TCDF) predominates over a ll other isomers whereas two isomers of TCDD were prominent (1,3,6,8-T CDD 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 s ources of PCDD/DF's (eg. fly ash, pulp and paper effluent etc). The pa ttern is replicated with in vitro oxidative coupling of 2,4-dichloroph enol at pH 2.9 using a commercially available chloroperoxidase from th e fungus Caldariomyces fumago. Significant incorporation of Cl-36(-) o ccurred in peat. Autoclaving decreased incorporation while adding case in hydrolysate increased it. The incorporation mirrored the metabolic activity (CO2 production) of samples consistent with organochlorine sy nthesis being due to biological activity. Total Organic Halide (TOX) l evels 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 a ll depths and, since the topography probably excludes leaching from su rrounding areas: a local origin of organochlorines is suggested. Chlor oform and a range of chlorinated aromatic compounds (chlorophenols, ch lorophenoxy and chlorobenzoic acid derivatives) have also been identif ied in peat. Our findings to date are consistent with the hypothesis f or a biogenic origin for at least some of the organochlorine compounds , including some of the PCDD/DF's, found in peat bogs. (C) 1997 Elsevi er Science Ltd.