2,3,7,8-Dibenzo-p-dioxins in Mined Clay Products from the United States:  Evidence for Possible Natural Origin

Abstract

Ball clay was the source of dioxin contamination discovered in selected chickens analyzed as part of a joint U.S. Department of Agriculture/U.S. Environmental Protection Agency national survey of the U.S. poultry supply conducted in 1997. The affected animals, which had been raised in the southern United States, represented approximately 5% of the national poultry production. All of these chickens and other animal food sources (i.e., farmraised catfish), similarly contaminated, were fed a diet of animal feed containing ball clay as an anti-caking additive. The clay was mined in northwestern Mississippi within a geological formation referred to as the Mississippi Embayment. Individual raw and processed ball clay samples were analyzed for the presence of the 2,3,7,8-PCDDs/ -PCDFs. The average toxic equivalents (TEQs) for the raw and processed samples were 1513 and 966 ppt dw, respectively. Other mined clay-based products used in animal feeds revealed lower TEQs. All of the products exhibited either an absence of detectable concentrations of 2,3,7,8-PCDFs or concentrations 2-3 orders of magnitude lower than the PCDDs. The isomer distribution, specific isomer identification, and congener profile of the PCDDs in the clay were established and compared to known sources of dioxin contamination. Several unique features of this isomer distribution are characteristic of the clays and are distinguishable from those of other known sources. These characteristics found in prehistoric clay deposits in the United States and Germany have led to speculation attributing their presence to natural geologic processes.

Fate and Distribution of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in a Woodchip-fuelled Boiler

“…OCDD is the most prominent congener in the woodchip samples. The PCDD/F congener profile of the stack flue gases is more dominant with OCDD (> 30%) followed by 2,3,7,2,3,4,6,7,showing close similarity with that of the other woodchip-fuelled boiler , and that of burning of the tree bark samples (Ferrario et al, 2000). The PCDD/F congener profiles of the ash samples are generally similar to that of the stack flue gases, especially for bottom residues, but with the increase of PCDD/F contents, 2,3,7,8-TeCDF possesses higher fraction.…”

Unsanitary Landfill Fires as a Source of a PCDD/Fs Contamination

“…Correlation of congener distribution, especially between the air sample collected during the fire and the soil from the landfill point to the landfill fire as the origin of the PCDD/Fs (Figure 4). Further on, dominant congeners of "natural pattern" [10,36] are not matching the one from the analysed samples, which diminish the possibility of natural origin for PCDD/Fs. The increase of some congener mass fractions in the lake sediment from the year 2008 to the year 2010 reflected the profile and concentrations of PCDD/Fs congeners in the air collected in the time of fire.…”

“…Muscovite and kaolinite were determined in very small amounts. Such mineral composition can be compared with limestone analysed for PCDD/Fs mass fractions and congener pattern by Ferrario et al [36] The dominant congener in limestone was octa-CDD (OCDD), and the PCDD/Fs pattern found was considered as typical "natural pattern" for limestone. The compound OCDD was detected in both Lake Vrana sediment samples, S 2008 and S 2010.…”

Abiotic Formation of Organohalogens During Early Diagenetic Processes

“…Recent findings of elevated dioxin concentrations in clays mined from deposits reported to be millions of years old (up to 40 million years) in disparate regions in the United States [44] and in Germany [45] with distinct unprecedented isomer patterns point to a common natural geologic mechanism to account for their origin. Indeed, there are similarities of the isomeric patterns pointing to biogenic sources [33,41] as Rappe et al [46][47] stated.…”