The potential for microbial dechlorination of the weathered polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) was determined in sediments with historical contamination by the chlorophenol wood preservative Ky-5 and its associated dimeric impurities. Sediments were collected from four sites of the Kymijoki River in South-Eastern Finland located at 0, 20, 30, and 60 km downstream from the source of contamination, and at a reference site. We examined the congener profiles of historical PCDD/Fs, including non-2,3,7,8-substituted congeners, and determined the dechlorination potential in sediments at the different sites of the river. The measured mean total concentrations for 2,3,7,8-PCDD/Fs were extremely high, 1200 mg/kg dw, at the most contaminated site, Kuusankoski. The mean concentrations for the predominant 2,3,7,8-congeners were 1,2,3,4,6,7,8-HpCDF 780 mg/kg dw, and for OCDF 380 mg/kg dw at Kuusankoski. At all other study sites of the river the mean total concentrations for 2,3,7,8-PCDD/Fs varied between 9 and 96 mg/kg dw, (6–80 mg/kg dw for 1,2,3,4,6,7,8-HpCDF, 3–13 mg/kg dw for OCDF). The sediment PCDD/F composition was similar to that of Ky-5, indicating that no or only minimal biodegradation of PCDD/F congeners has occurred in the river sediments over the last few decades since the contamination events. Microbes capable of PCDD/F dechlorination were present at all study sites based on Dehalococcoides-like Chloroflexi community determination and dechlorination of spiked 1,2,3,4-tetrachlorodibenzofuran. However, no substantial changes in the relative abundances of PCDD/Fs were observed over 2.5 years in laboratory microcosm studies, indicating that anaerobic dechlorination of weathered PCDD/Fs was limited over the course of the experiment. Therefore, concentrations of weathered PCDD/Fs in the sediments of the Kymijoki River are expected to remain at the same level for decades or centuries with further migration towards the Baltic Sea.
All Science Journal Classification (ASJC) codes
- Health, Toxicology and Mutagenesis