title: Time trends in sources and dechlorination pathways of dioxins in agrochemically contaminated sediments.
abstract: Although polychlorinated dibenzo-p-dioxins and dibezofurans (PCDD/Fs) are considered recalcitrant toward biotic and abiotic degradation processes, laboratory studies indicated lateral dechlorination pathways (removal of 2,3,7,8-substituted chlorines) as possible natural remediation strategies under highly reducing conditions prevailing in contaminated sediments. Previous principal component analysis (PCA) of PCDD/Fs in Japanese sediments left unidentified a factor characterized by penta- to octa- homologues fully chlorinated at 1,2,6,9-positions (1,2,6,9-pattern). In the present study, we reexamined PCDD/Fs in sediment cores from urban (Tokyo Bay) and remote (Lake Shinji) areas of Japan using positive matrix factorization (PMF) and revealed a lateral dechlorination fingerprint exhibiting the 1,2,6,9-pattern. Relative molar concentrations of putative lateral dechlorination products linearly increased with sediment depth, suggesting that decades of reaction resulted in the accumulation of hepta- and hexa- chlorinated lateral dechlorination products in the bottom sediment layers. Times required for in situ formation of dechlorination products were estimated to be at least 27.8 +/- 17.9 year(mole %)(-1) in Lake Shinji and 4.7 +/- 0.5 year(mole %)(-1) in Tokyo Bay (both for the formation of 1,2,3,4,6,7,9-HpCDD) and are significantly longer than the dechlorination pathways observed in the laboratory.
authors.affiliation: Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan. uchimiya@ynu.ac.jp
authors.forename: Minori
authors.initials: M
authors.lastname: Uchimiya
authors.forename: Shigeki
authors.initials: S
authors.lastname: Masunaga
mesh_terms: D016573:Agrochemicals / Q000737:chemistry*; D004147:Dioxins / Q000737:chemistry*; D005618:Fresh Water / Q000737:chemistry; D019015:Geologic Sediments; D007564:Japan; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D016573:Agrochemicals; D004147:Dioxins; D012989:Soil Pollutants