Dioxins in Primary Kaolin and Secondary Kaolinitic Clays

Abstract

Since 1996 dioxins have been repeatedly detected worldwide in Tertiary ball clays used as anticaking agent in the production of animal feed and a variety of other applications. The dioxins of these natural clays are very unlikely of anthropogenic source, but no model of dioxin enrichment has been established. A hypothetical model is presented which explains the highly variable dioxin loadings of the Tertiary kaolinitic clays by natural addition during clay-sedimentation. To prove this hypothesis, Tertiary primary nonsedimentary kaolin and sedimentary kaolinitic clays were collected at three profiles in Europe and analyzed for mineralogy, chemistry, organic carbon, and polychlorinated dibenzo-p-dioxins/-furans (PCDD/F). Primary kaolin, kaolinitic, and lignitic clays contained almost no PCDFs. PCDD concentration differed markedly between primary kaolin (3-91 pg/g) and secondary kaolinitic clay (711-45935 pg/g), respectively, lignitic clays (13513-1191120 pg/g). The dioxin loading of secondary kaolinitic and lignitic clays is approximately 10 to a few thousand times higher than in the primary kaolin or recent environmental settings. The dioxin concentrations decrease from octachlorodibenzo-p-dioxin to the tetrachlorodibenzo-p-dioxins and exhibit the "natural formation pattern". No correlation between PCDD/F concentration and bulk composition of clays was found. These findings support the hypothesis of the enrichment of dioxin in clays during sedimentation.

Evaluation of PCDD/Fs emissions during ceramic production: A laboratory study

“…PCDFs were not detected or were found at the ultra trace level in the samples. These results were very similar to previous studies that reported PCDD/Fs in kaolinitic clays were characterized by congener profiles dominated by OCDD and HpCDDs and trace levels of PCDFs [1,2,5,13].…”

“…Schmitz et al [5] collected and analyzed Tertiary primary nonsedimentary kaolin and sedimentary kaolinitic clays in Europe. The results showed that the PCDD concentrations were in the range of 3-91 pg/g, 711-45,935 pg/g, and 13,513-1,191,120 pg/g, in primary kaolin, secondary kaolinitic clay, and lignitic clays, respectively.…”

Isomer-specific investigation of PCDD/F mobility and other fate processes in deep soil cores

“…The two notable land-uses are rice paddy soils in Japan impacted by contaminated pesticides (mainly PCP and CNP) (Kiguchi et al, 2007) and deep kaolinitic and lignitic clays from the US and Europe (Ferrario et al, 2000;Gadomski et al, 2004;Schmitz et al, 2011). Here we used PCA to compare the PCDD/F profiles in surface soil and deep soil layers among these studies to establish whether a common source was likely.…”

“…Preferential removal of lateral (2,3,7,8-substituted) profiles for tetra-to hepta-PCDDs (normalised to homologue totals) to compare global soils with similar OCDD-dominated PCDD/F profiles. Kaolinitic/lignitic clays (circles) are sourced from (Prange, 2003;Gadomski et al, 2004;Schmitz et al, 2011); rice paddy soils (squares) from Kiguchi et al (2007); Queensland agricultural, urban and industrial surface soils (triangles) from (Gaus et al, 2001;Prange, 2003;Müller et al, 2004;Gaus et al, 2009;Grant et al, 2011). Isomer groups for PCA (B) are defined in Table S4-SI, and groups that include 1,4,6,9-substituted isomers are highlighted in the loading plot (B) in blue.…”

“…Based on 2,3,7,8-congener and homologue profiles, however, the source and mobility of PCDD/Fs at this site could not be elucidated (Prange, 2003). Similarities in profiles between Queensland soils and deep soils dominated by kaolinitic and lignitic clays in the USA and Europe have further led to suggestions of a common PCDD/F source (Ferrario et al, 2000;Gadomski et al, 2004;Schmitz et al, 2011). Elevated PCDD levels in these clays up to 27 m depth were considered unlikely to result from vertical transport processes and an in-situ, non-anthropogenic formation process was hypothesised for these areas (Ferrario et al, 2000).…”