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Dioxins in Clays

Compounds :
Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are tricyclic aromatic compounds with similar chemical and physical properties. They are ubiquitous in the environment and usually do not occur naturally.There are 75 positional isomers of PCDDs and 135 isomers of PCDFs. 2,3,7,8-TCDD (TCDD) is the most toxic isomer, and the estimated toxic risk in humans is calculated in terms of "TCDD equivalents".
For exemple, the toxic effect of different isomers is calculated in terms of the amount that would cause the same degree of toxicity as TCDD.
Octachloro-dibenzo-p-dioxine, produced during the synthesis of pentachlorophenol (Norback et al. 1975), is quite less toxic than TCDD produced during the synthesis of the herbicide 2,4,5-T.TCDD is one of a family of componds known effectively as dioxins which comprises PCDDs, PCDFs, and PCBs (polychlorinated biphenyls). There are 7 PCDDs, 10 PCDFs, and 12 PCBs considered to give dioxin-like activity among a total of 419 congeners (compounds).
Sources :
-Contaminated products such as chlorinated phenols and their derivatives.
-Polychlorinated biphenyls (PCBs).
-Incineration of municipal, hazardous, and hospital wastes.
-Sewage sludge.
-Automobile operations.
-Fossil fuel combustion.
-Emissions from fire involving PCBs.
-Production of chlorophenols and their derivatives.
-Chlorophenol wood treatment.
-Chlorine bleaching in the pulp industry.
- Production and handling of iron, steel, and other metals, such as aluminium.
-Exposure has occurred from herbicide use and from industrial and transportation incidents.
-In occupational settings, exposure has occurred in chemical manufacturing processes and from handling the wastes from these processes.
-American ball clays.
-One german china clay deposit.
-Other materials including montmorillonite, bentonite, ground clay, bulk clay, Al-Ca-silicate and lime.
-Dioxins, in small amounts, are also produced naturally by volcanoes and forest fires.
Of the 23 categories of dioxin sources throughout North America, the biggest are :
-municipal waste incinerators (25 percent),
-backyard trash burning (22 percent),
-cement kilns burning hazardous waste (18 percent),
-medical waste incinerators (11 percent),
-secondary copper smelters (8 percent),
-iron sintering plants (7 percent)
Exposure :
Ingestion, inhalation, and dermal absorption are all thought to be routes of exposure to PCDDs and PCDFs. However, exposure for most individuals will be small and will come through a variety of sources.
It is generally accepted that about 95% of human exposure comes from food.
The major environmental exposure hazard for humans is with fish consumption.
Anthropogenic production of dioxin has decreased a lot during the past two decades.
Current herbicide manufacturing processes are designed to remove dioxin contaminants.
Toxicology :
Dioxins are insoluble in water but lipophilic (soluble in fats) and other hydrophobic materials, and bind to solid material such as soil and fly ash. They have a low rate of metabolic breakdown, they preferentially accumulate in adipose tissue, skin, liver, and breast milk in mammals. The amount of dioxins expressed as TCDD equivalents in breast milk of lactating women often exceeds the tolerated Swedish daily intake of 5 pg/kg body weight by a factor of 20 to 30.
In soil TCDD has an extremely long half-life time, greater than 10 years.
The biologic half-life in humans has been measured to be in the range of 5 to 8 years.
TCDD represents one of the most toxic synthetic compounds known.
When heated to decomposition it emits toxic fumes of CL-.
A-Acute intoxication :
In humans, the acute toxicity of TCDD is known from accidental release due to runaway reactions or explosions.
Essentials of diagnosis are :
-eye and respiratory irritation,
-skin rash, chloracne,
-fatigue,nervousness, irritability.
A process accident in 1949 was followed by :
-acute skin, eye, and respiratory tract irritation,
-headache, dizzines, and nausea.
These symptoms subsided within 1-2 weeks and were followed by :
-acneiform eruption,
-severe muscle pain in the extremities, thorax, and shoulders,
-fatigue, nervousness, and irritability,
-complaints of decreased libido,
-intolerance to cold.
Workers also exhibited :
-severe chloracne,
-hepatic enlargement;
-peripheral neuritis;
-delayed prothrombin time;
-increased total serum lipid levels.
A follow-up study 30 years later found persistance of chloracne in 55% of the workers.
B-Chronic intoxication :
Essentials of diagnosis are :
-soft tissue sarcoma,
- non-Hodgkin's lymphoma,
-Hodgkin's disease.
Chloracne can result within several weeks after exposure to TCDD and can persist for decades, the severity of chloracne is related to the degree of exposure.
In some workplaces, exposed persons had chloracne but no systemic illnesses.
In others, workers experienced :
-weight loss,
-decrease libido.
The liver has become enlarged and tender; and sensory changes particularly in the lower extremities.
In exposed production workers, systemic symptoms, except for chloracne, have not persisted after exposures ceased.
The American Air Force has found a "significant and potentially meaningful" relationship between diabetes and bloodstream levels of chemical dioxin in its ongoing study of people who worked with Agent Orange.
It acts as a complete carcinogen in several species.
Rats, mice, and hamsters exposed to TCDD have developed histiocytic lymphomas, fibrosarcomas, and tumors of liver, skin, lung, thyroid, tongue, hard palate, and nasal turbinates.Initiating or promoting carcinogenesis may be functions of TCDD.
It has been concluded, TCDD is among the most potent identified chemical carcinogens. It is transspecies, transstrain, transsex, multisite, and complete carcinogen.
By now, an increased risk for all cancer sites combined has been shown in cohort studies on TCDD-exposed subjects, with an especially high risk for soft-tissue sarcoma (STS). TCDD has also been associated with Hodgkin's disease and non-Hodgkin's.
In Seveso, Italy, area with TCDD soil contamination, excess numbers of tumors have been found, including lymphomas and STS.
Immunotoxicity and Reproduction :
Immunotoxic and reproductive effects appear to be among the most sensitive indicators of dioxin toxicity.
In animals TCDD is a teratogen and toxic to the fœtus.
A variety of immunologic effects have been seen in animals.
Dioxin produces adverse developmental and reproductive effects in fish, birds, and mammals.
Laboratory studies in animals suggest that dioxin-like compounds cause altered development (low birth weight, spontaneous abortions, congenital malformations) adverse changes in reproductive health ( fertility, sex organ development, reproductive
For humans, the immunotoxic effects by dioxins are probably at least as serious as the carcinogenic properties.
Little is still understood about the potential effects on fertility and the developing nervous system in children by dioxins and related chlorinated compounds.
TCDD may be transferred trans-placentally and via breast milk, and elevated levels of TCDD have been detected in adult children of female production workers exposed to dioxins.
Human studies have shown alteration in delayed-type hypersensitivity after exposure to dioxins.
Exposure limits :
NIOSH recommends that TCDD be treated as a potential human carcinogen.
NIOSH REL (Dioxin) : Reduce to lowest feasible level.
Laboratory findings :
1-Abnormalities reported most consistently are :
-elevated liver enzymes
-prolonged prothrombin time
-elevated cholesterol and triglycerides levels
2-Urinary porphyrins may be elevated
3- 2,3,7,8-TCDD may be measured in :
-serum (body burden)
-blood lipids
-adipose tissue
-breast milk.
Differential diagnosis :
Known causes of an acneiform eruption in the workplace include :
-petroleum cutting oils,
-coal tar,
-chlorinated aromatic compounds.
With systemic complaints, such as weight loss, headache, myalgias, and irritability, other underlying medical illnesses should be ruled out before attributing the disorder to TCDD.
Conclusion :
Not knowing the exact exposure of ceramicists to the different isomers( different levels of toxicity) identified in kaolins and ball clays, it is very difficult to discuss this problem properly.
For obvious reasons, we should be more worried about employees working in mining and processing these dioxin-containing clays, and by pottery factory employees than by studio potters, hobbyists, teachers and their students.
The use of clays made without ball clays could be recommended for those more worried while awaiting more information.
However, in Ceramics Monthly, January 2001, page 8, Dr. David Cleverly of EPA in Washington DC. is cited as having written the following to a potter :
" The good news is that once the ball clay has been commercially processed in a kiln before it is sold to potters, all the dioxin is removed. We have verified this in EPA's laboratories. So you can rest easy and continue making great art out of ball clay "
Still, it would be good practice to proceed to good housekeeping of workshops, to avoid unnecessary dusty operations and to use an appropriate dust mask to prevent hazardous exposure.
References :
1-Occupational Medicine, Carl Zenz, last edition.
2-Sax's Dangerous Properties of Industrial Materials, last edition
3-Occupational & Environmental Medicine, Ladoue J., last edition.
4- Clinical Environmental Health and Toxic Exposures, Sullivan & Krieger, last edition.
5-Toxicologie Industrielle et Intoxications Professionnelles, Lauwerys R., last edition.
6-Summary of Evidence for the Possible Natural Formation of Dioxins in Mined Clay Products, Ferrario J, Byrne C, Cleverly D.
7-Ceramics Monthly, January 2001, page 8.
8-R&H Hall Technical Bulletin Issue No.1~2000, Dr. Mark McGee, Technical Executive.

Related Information


Typecodes Article by Edouard Bastarache
Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.
Materials Ball Clay
Hazards Ball Clay

By Edouard Bastarache

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