- On this page :
(French version), Dioxins in clays
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.
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
- -Contaminated products such
as chlorinated phenols and their derivatives.
- -Polychlorinated biphenyls
- -Incineration of municipal,
hazardous, and hospital wastes.
- -Sewage sludge.
- -Fossil fuel combustion.
- -Emissions from fire
- -Production of chlorophenols
and their derivatives.
- -Chlorophenol wood
- -Chlorine bleaching in the
- - Production and handling of
iron, steel, and other metals, such as
- -Exposure has occurred from
herbicide use and from industrial and transportation
- -In occupational settings,
exposure has occurred in chemical manufacturing
processes and from handling the wastes from these
- -American ball
- -One german china clay
- -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
- Of the 23 categories of
dioxin sources throughout North America, the biggest
- -municipal waste
incinerators (25 percent),
- -backyard trash burning (22
- -cement kilns burning
hazardous waste (18 percent),
- -medical waste incinerators
- -secondary copper smelters
- -iron sintering plants (7
- 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
- The major environmental
exposure hazard for humans is with fish
- Anthropogenic production of
dioxin has decreased a lot during the past two
- Current herbicide
manufacturing processes are designed to remove dioxin
- 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
- The biologic half-life in
humans has been measured to be in the range of 5 to 8
- 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
- -eye and respiratory
- -skin rash,
- A process accident in
1949 was followed by :
- -acute skin, eye, and
respiratory tract irritation,
- -headache, dizzines, and
- These symptoms subsided
within 1-2 weeks and were followed by
- -severe muscle pain in the
extremities, thorax, and shoulders,
- -fatigue, nervousness, and
- -complaints of decreased
- -intolerance to
- Workers also exhibited
- -delayed prothrombin
- -increased total serum lipid
- A follow-up study 30 years
later found persistance of chloracne in 55% of the
- B-Chronic intoxication
- Essentials of diagnosis
- -soft tissue
- - non-Hodgkin's
- 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
- In others, workers
- -weight loss,
- 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
- 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.
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 ftus.
- A variety of immunologic
effects have been seen in animals.
- Dioxin produces adverse
developmental and reproductive effects in fish, birds,
- 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
- 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
- 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
- NIOSH REL (Dioxin) : Reduce
to lowest feasible level.
- 1-Abnormalities reported
most consistently are :
- -elevated liver
- -prolonged prothrombin
- -elevated cholesterol and
- 2-Urinary porphyrins may be
- 3- 2,3,7,8-TCDD may be
measured in :
- -serum (body
- -blood lipids
- -adipose tissue
- -breast milk.
- Known causes of an acneiform
eruption in the workplace include :
- -petroleum cutting
- -coal tar,
- -chlorinated aromatic
- With systemic complaints,
such as weight loss, headache, myalgias, and
irritability, other underlying medical illnesses
should be ruled out before attributing the disorder to
- Not knowing the exact
exposure of ceramicists to the different congeners and
isomers (different levels of toxicity) identified in
kaolins and ball clays, it is very difficult to
discuss this problem properly.
- The US firm Battelle Corp.
has recently conducted a study among the personel of
the Ohio State Ceramics Department, the report is at
the stage of analysis by EPAs experts and should
be available soon to elucidate this
- 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 with
low or no dioxin-containing clays could be recommended
for those more worried while awaiting more
- 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
- Edouard Bastarache M .D.
(Occupational & Environmental
- Author of "Substitutions
for Raw Ceramic Materials"
- 1-Occupational Medicine,
Carl Zenz, last edition.
- 2-Sax's Dangerous
Properties of Industrial Materials, last edition
- 3-Occupational &
Environmental Medicine, Ladoue J., last
- 4- Clinical Environmental
Health and Toxic Exposures, Sullivan & Krieger,
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
- 7-Ceramics Monthly,
January 2001, page 8.
- 8-R&H Hall Technical
Bulletin Issue No.1~2000, Dr. Mark McGee, Technical
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