Origin of PCDDs in Ball Clay Assessed with Compound-Specific Chlorine Isotope Analysis and Radiocarbon Dating

• Published in: Environmental science & technology 2006-06, Vol.40 (12), p.3730-3735
• Main Authors: Holmstrand, Henry, Gadomski, Damien, Mandalakis, Manolis, Tysklind, Mats, Irvine, Robert, Andersson, Per, Gustafsson, Örjan
• Format: Article
• Language: English
• Subjects: Aluminum Silicates - chemistry; Applied sciences; Carbon Radioisotopes - analysis; Carbon Radioisotopes - metabolism; Carbon Radioisotopes/analysis/metabolism; Chlorine - analysis; Chlorine - metabolism; Chlorine/analysis/metabolism; Clay; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Isotopes - analysis; Isotopes - metabolism; Isotopes/analysis/metabolism; Kentucky; Pollution; Pollution sources. Measurement results; Pollution, environment geology; Polychlorinated Dibenzodioxins - analogs & derivatives; Polychlorinated Dibenzodioxins - analysis; Polychlorinated Dibenzodioxins - chemistry; Polychlorinated Dibenzodioxins - metabolism; Rivers; Soil and sediments pollution; Soil Pollutants - analysis; Soil Pollutants - metabolism; Soil Pollutants/analysis/metabolism; Tennessee; Tetrachlorodibenzodioxin/analogs & derivatives/analysis/chemistry/metabolism
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es0602142

Polychlorinated dibenzo-p-dioxins (PCDDs) of high concentrations in a ball clay deposit from the Mississippi Embayment were found to be consistent with a natural abiotic and non-pyrogenic origin by investigation with bulk radiocarbon analysis, compound-specific chlorine isotope analysis (CSIA-δ37Cl) of octachlorodibenzo-p-dioxin (OCDD), and black carbon (BC) analysis. The conventional radiocarbon date of total organic carbon from a depth of approximately 10 m in three parallel cores ranged from 14 700 years to >48 000 years, indicating that the strata with elevated levels of PCDDs have remained isolated from recent anthropogenic input in these >40 Ma old clay sediments. The CSIA-δ37Cl of OCDD yielded a δ37Cl of −0.2‰, which is significantly higher than the postulated range for biotic chlorination by chloroperoxidase enzymes, −11 to −10‰, and falls within the known range for abiotic organochlorines, −6 to +3‰. The absence of correlations between concentrations of PCDDs and corresponding pyrogenic black carbon (BC), together with estimations of BC sorptive loadings and the absence of polychlorinated dibenzofurans (PCDFs), suggest that vegetation fires did not form these ball-clay PCDDs. Results from this study indicate that the high levels of the toxic and carcinogenic PCDDs found in kaolinite-bearing clays may result from natural abiotic formation via in situ surface-promoted reactions on the clay mineral, including a so-far unknown organic precursor, rather than being the result of anthropogenic contamination.