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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

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

-Chlorophenol wood treatment.

-Chlorine bleaching in the pulp

- 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

-backyard trash burning (22

-cement kilns burning hazardous waste
(18 percent),

-medical waste incinerators (11

-secondary copper smelters (8

-iron sintering plants (7


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


Essentials of diagnosis are

-eye and respiratory irritation,

-skin rash, chloracne,



A process accident in 1949 was
followed by :

-acute skin, eye, and respiratory tract

-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

-complaints of decreased libido,

-intolerance to cold.


Workers also exhibited :

-severe chloracne,

-hepatic enlargement;

-peripheral neuritis;

-delayed prothrombin time;

-increased total serum lipid


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

In exposed production workers, systemic
symptoms, except for chloracne, have not persisted after exposures


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

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

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,



For humans, the immunotoxic effects by
dioxins are probably at least as serious as the carcinogenic

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


2-Urinary porphyrins may be


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


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

5-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R., last

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.


By Edouard Bastarache

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
A fine particled highly plastic secondary clay used mainly to impart plasticity to clay and porcelain bodies and to suspend glaze, slips and engobe slurries.
Hazards Ball Clay

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