Distribution, Characteristics, and Worldwide Inventory of Dioxins in Kaolin Ball Clays

Abstract

Distribution, characteristics, and global inventory of dioxins (polychlorinated dibenzo-p-dioxins [PCDDs] and dibenzofurans [PCDFs] and dioxin like polychlorinated biphenyls) in kaolin clays collected from 10 countries were investigated. Dioxins were found in all kaolin clay samples analyzed, at total concentrations ranging from 1.2 pg/g (Brazil) to 520,000 pg/g (USA). Dioxin concentrations in kaolin clays from a few countries (e.g., Brazil and UK) were lower than those reported for background soils in Japan. Dioxin profiles in kaolin clays were characterized by the domination of the congener octachlorodibenzo-p-dioxin (OCDD), and the concentrations of other congeners decreased in the order of reduction in the levels of chlorination. Furthermore, specific distribution of congeners, with predominant proportions of 1,4,6,9-substituted PCDDs within each homologue group, was found in most clay samples. The ratios of concentrations of PCDD to PCDF and 1,2,3,7,8,9-HxCDD to 1,2,3,6,7,8-HxCDD indicated differences in the profiles found for anthropogenic sources (including pentachlorophenol) and kaolin clays. Concentrations of PCDD/Fs in kaolin clays, except for American ball clays, did not exceed the environmental criteria set by the Law Concerning Special Measures against Dioxins in Japan. Based on the average concentrations measured in our study, inventories of PCDD/Fs from the production/usage of ball clays on a global scale were estimated to be 650 kg/yr; the corresponding value on a TEQ basis is 2400 g-TEQ/yr. More than 480 kg of OCDD is estimated to be released annually from the production of kaolin clays worldwide, suggesting that kaolin clays can be a major contributor for additional source of dioxins, especially OCDD, in the environment.

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].…”

“…The samples were extracted using toluene for 24 h in a Soxhlet apparatus, and the extracts were concentrated on a rotary evaporator. The extracts were then sequentially purified using acidic silica-gel columns (44 wt.% sulfuric acid-impregnated silica gel) and 10 wt.% silver nitrate-impregnated silica gel [2,7]. The analyte was fractionated using an active carbon column (50 wt.% active carbon-blended silica gel and 50 wt.% active carbon dispersed silica gel).…”

“…Since then, many studies confirmed that numerous Tertiary clays, specified as kaolin or ball clay, in North and South Americas, Europe, South Pacific, and Asia also contain PCDD/Fs [2].…”

“…Horii et al [2] investigated the distributions and characteristics of PCDD/Fs in kaolin clays collected from ten countries. The results demonstrated that PCDD/Fs were ubiquitous in all kaolins analyzed, at total concentrations ranging from 1.2 pg/g (Brazil) to 520,000 pg/g (the U.S.).…”

Predictors of serum polychlorinated biphenyl concentrations in Anniston residents

“…A 1976 study of PCB adsorption on soils showed that illite (a clay mineral) was highly adsorptive for the three congeners tested, with higher adsorption for highly chlorinated congeners (Haque and Schmedding, 1976). PCBs and PCDD/Fs have been detected in types of clay that are often eaten (Horii et al, 2011; Reeuwijk et al, 2013), but we had no information on PCB concentrations in local clay.…”