title: Isomer-specific investigation of PCDD/F mobility and other fate processes in deep soil cores.
abstract: Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are highly hydrophobic compounds with low migration potential in soil-water. Nevertheless, they have been occasionally reported in subsurface soils hypothesised as the result of facilitated transport processes with colloids or surfactants, or yet unidentified in-situ formation processes. To date, however, the prevalence of deep soil contamination, involved processes and their kinetics remain poorly understood. This study investigated PCDD/F concentrations and isomer profiles through deep soil cores (to 20 m) from agricultural, industrial and urban sites in Queensland, Australia. Based on isomer profiles, a unique source common to all core soils (regardless of depth) was identified, dominated by octachlorodibenzo-p-dioxin (OCDD). The source was consistent with contamination resulting from pesticide impurities. Elevated PCDD concentrations (μg/kg range) to depths up to ∼4-17 m and a continuous increase of peri-chlorinated (1,4,6,9-substituted) isomers through the cores suggested that vertical transport and lateral dechlorination were key post-depositional processes at these sites. The mobility of PCDDs in the present study is far greater than previously reported in soils in general. High estimated mass transport rates for OCDD in four agricultural cores (3.0-6.2% year(-1)) likely reflect significant levels of facilitating species, including surfactants, and intensive rainfall at these sites. The implications of such extensive subsurface transport of PCDD/Fs for groundwater contamination and load estimates may be significant. If the cores of the present study are assumed representative of the region, a total PCDD/F load in the order of 800 tonnes (1.6 tonnes TEQ) could be present in subsurface Queensland coastal soils.
authors.affiliation: The University of Queensland, National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia. Electronic address: s.grant@uq.edu.au.
authors.forename: Sharon
authors.initials: S
authors.lastname: Grant
authors.affiliation: National Measurement Institute, Dioxin Analysis Unit, North Ryde, NSW 1670, Australia.
authors.forename: Gavin
authors.initials: G
authors.lastname: Stevenson
authors.affiliation: Department of Science, IT, Innovation and the Arts, 41 Boggo Road, Dutton Park, QLD 4102, Australia.
authors.forename: Don
authors.initials: D
authors.lastname: Malcolm
authors.affiliation: Empa, Laboratory for Advanced Analytical Technologies, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Zennegg
authors.affiliation: The University of Queensland, National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia.
authors.forename: Caroline
authors.initials: C
authors.lastname: Gaus
mesh_terms: D000383:Agriculture; D001572:Benzofurans / Q000032:analysis* / Q000737:chemistry; D000072338:Dibenzofurans, Polychlorinated; D004784:Environmental Monitoring / Q000379:methods*; D004787:Environmental Pollution / Q000032:analysis* / Q000517:prevention & control; D007221:Industry; D007536:Isomerism; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D011793:Queensland; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D014507:Urbanization
chemical_list: D001572:Benzofurans; D000072338:Dibenzofurans, Polychlorinated; D000072317:Polychlorinated Dibenzodioxins; D012987:Soil; D012989:Soil Pollutants
keywords: Degradation; Dioxins; Facilitated transport; Isomer profile; Mobility; Soil core