This product is
unstable under the following conditions : when heated it
decomposes at 400 degrees Celsius and emits lead monoxide, carbon
monoxide and carbon dioxide.
In the relevant
literature, we have not found any information relating to thermal
breakdown products for the following lead frits: lead bisilicate,
lead sesquisilicate and lead-boro-silicate.
On the other hand
lead silicate, PbO.SiO2, emits toxic lead fumes when heated to
This product is
unstable under the following conditions : when heated to
decomposition (more than 500 degrees Celsius), there is release of
oxygene and emission of toxic lead fumes.
This product is
unstable under the following conditions : when heated between 300
to 400 degrees Celsius, it is converted to lead tetroxide.
Inorganic lead is
absorbed only by the respiratory and digestive tracts, except for
metallic lead, which can penetrate the skin in a negligible
absorption of lead depends on the size of particles; a small
proportion of particles of size greater than 0,5 µm is
retained at the pulmonary level. The retention of particles having
a diameter smaller than 0,5 µm is inversely proportional to
absorption also depends on respiratory frequency.
3- The pulmonary
deposition rate of lead present in the air is approximately 30 to
4- Lead which
penetrates deeply into the lungs is almost completely absorbed.
The rest of lead particles which are found in the higher parts of
the respiratory tract, are directed towards the gastro-intestinal
system where they are ingested.
5-Lead does not
accumulate in the respiratory tract.
B-Gastrointestinal absorption :
1-Gastrointestinal absorption of lead varies
according to the physiological state of the individual (fast, age)
and the type of lead compound ingested. Thus, the rate of
absorption may vary in the fasting adult from 5-15 % to 60-80 %.
It is approximately 30 to 50 % in the child.
influenced by the size of the ingested particles (the smallest
being better absorbed).
lead, which takes place in the duodenal region of the small
intestine, seems to occur by a saturable mechanism.
from the route of absorption, absorpbed lead passes into the blood
circulation where more than 90 % finds itself bound to
erythrocytes (it is fixed especially inside the cell rather than
on the membrane). The remainder diffuses into the serum.
undertaken in man indicate that absorbed lead is distributed
primarily in 3 compartments: the first compartment is blood, the
second is made up of soft tissues (central and peripheral nervous
systems, liver, kidneys and muscles) and the third one is composed
of bone tissue.
researchers have proposed refinements to this kinetic model, it
has thus been proposed to subdivide the blood compartment into 4
in order to better take into account lead kinetics in the plasma
and in the erythrocytes. It is also proposed to subdivide the bone
compartment into 2 in order to better reflect the speed of
turnover and bone tissue metabolism.
model was proposed taking into account the soft tissues with which
the exchanges are fast and those with which they are slow.
Lead is not
metabolized in the body.
1- Ingested lead
that is not absorbed is directly excreted in the feces.
2-Nearly 80 % of
the absorbed lead is eliminated by the urinary tract,
approximately 16 % is eliminated via the bile and the remainder is
eliminated in the saliva, sweat, hair and nails.There are
significant inter-individual variations in the capacity of lead
1-In the adult,
blood lead half-life is approximately 1 month.
in soft tissues (such as central and peripheral nervous systems,
the liver, kidneys and muscles) is approximately 40 to 60 days.
in the bone compartment is approximately 20 to 30 years
4-The whole body
lead half-life depends on the body burden, which itself is related
to the duration of exposure of workers.
toxicokinetics and toxicological effects can be affected by
interactions with certain essential elements and nutriments:
administration of calcium and phosphorus, at concentrations which
can be found in an average meal, decreases lead gastrointestinal
absorption by a factor of 6 in fasting adults.
B-It would also
seem that the daily intake of food fibers, thiamin and iron lowers
blood lead level (BLL) in exposed workers.
is reduced by a calcium or zinc intake, probably by a competitive
mechanism at the intestinal level.
is enhanced by the intake of food high in fat.
intoxication is rare in the work environment.
The inhalation of
significant lead amounts can cause digestive disorders (vomiting,
epigastric and abdominal pain, diarrhoea and black stools), renal
disorders, hemolytic anemia, neurological disorders
(encephalopathy, intracranial hypertension, convulsive coma).
A-The effects of
lead intoxication in man are the same whatever the route of entry
into the body. They are generally described in terms of internal
dose (amounts of lead in the blood ) rather than in terms of
ambient level of
(mg/m³ or ppm).
B-One of the
first symptoms of lead exposure is the appearance of digestive
This results in
colics (intense abdominal pains, nausea, vomiting), constipation,
anorexia and a loss of weight.
muscular pains in the extremities are also reported.
D- A blue
coloured line has been observed on the gingival tissues of people
exposed to significant lead concentrations.
certain blood effects. It induces anemia (caused by a reduction in
the lifespan of red cells and by a fall of the synthesis of heme
by enzymatic inhibition). It also involves an increased production
of abnormal erythrocytes.
effects on the nervous system thus being able to cause
encephalopathy and peripheral neuropathy.
symptoms of encephalopathy can appear in the weeks following
initial exposure to lead; these are irritability, lassitude, loss
of appetite, reduction in the attention,headaches, jerked
movements of the eyes, hallucinations, a deterioration of the
cognitive functions (reduction in the performance in certain
psychometric tests like, for example, eye-hand coordination,
skills of verbal reasoning, memory, etc).
worsen, sometimes abruptly, and one can observe delirium,
convulsions, paralysis, coma and death. Peripheral neuropathy can
result in muscular tremors, weakness of the upper limbs and
paraesthesias of the lower limbs (pins and needles, tingling).
to lead present an increased risk of chronic nephrotoxicity.
The lead levels
which can cause such an effect seem to be a function of the
duration of exposure. A review of several studies seems to
indicate that lead can cause nephropathy at blood lead levels as
low as 1,93 µmol/l.
effects are reversible whereas others are not. A recent study
suggests that the exposure to low lead levels can cause renal
problems in middle-age and old age men.
suggest that there is a weak positive correlation between blood
lead level (BLL) and an increase in blood pressure. However, it is
currently premature to draw conclusions on this subject.
I-There is some
evidence that high lead doses could be responsible for cardiac
lesions and disturbances in the electrocardiogram.
some studies, lead could weaken the immune system.
Biological Monitoring :
parameter, biological index of exposure and time of blood sampling
according to different organizations, (time of blood sampling is
discretionary); the ACGIH proposes 1,45 µmol/L (level aiming
at minimizing or preventing the effects being able to result in a
persistent functional damage);
the WHO and
Lauwerys propose 1,93 µmol/L (maximum tolerable blood lead
level); the level in non-exposed individuals is < 0,50
protoporphyrins (ZPP) :
The time of blood
sampling must be at least one month after the beginning of
exposure. Lauwerys proposes 0,67 µmol/L in order to prevent
certain health effects. The level for non-exposed individuals is
< 0,32 µmol/L.
Exposure Indicators :
aminolevulinic acid : an indicator of toxic effect; this test is
less sensitive than the measurement of ZPP.
be considered for interpretation :
- these values
apply only to exposures to metallic lead or inorganic salts.
absorption by the digestive tract;
2-a BLL of about
2,42 µmol/L is expected in workers who are exposed, day after
day, to lead air levels of 0,15 mg/m³ ;
anemia, iron deficiency (increased ZPP);
protoporphyria (increased ZPP); increased carboxyhemoglobin, if
the analysis of ZPP is carried out by hematofluorometry (method
used by the IRSST, Quebec), it involves an undervaluation of the
concentration of ZPP.
between lead blood concentrations and their toxic effects :
lead level (µmol/l)
lead level of a nonexposed person
0,97 à 2,90
in the concentration of erythrocyte protoporphyrins
in the urinary concentration of coproporphyrin
2,41 à 2,90
encephalopathy in the child
encephalopathy in the adult
2,90 à 3,86
3,38 à 4,80
3,86 à 4,80
3,86 à 14,5
factor for blood lead level :
0,004826 = µmol/l
suffering from a neurological dysfonction;
suffering from a renal disease;
certain genetic diseases, such as thalassemia, glucose-6 phosphate
dehydrogenase deficiency, porphyrias, an excessive activity of the
Limit for dusts
and fumes, expressed as Pb (lead).
Main measures are
involving a hazard of lead exposure should not be dispersed in the
factory, but on the contrary, put together.
aspiration systems at the place of generation of lead dusts, fumes
cleanliness of workstations :
with water to avoid accumulation of lead dust.
To allow for
adequate personal hygiene: sinks, showers, different lockers for
work and town clothes, refectory away from workstations.
evaluation of lead concentration in the air :
It must be done
at the workstation. Since in the industrial settings, the main
route of entry is the respiratory tract, the mesurement of lead in
the air allows to estimate the exposure hazard.
protection apparatus should be worn if the concentration in the
work environment is greater than the VEMP (0,15 filter
Masks: they must
be regularly cleaned and filters replaced.
hygiene: nobody should smoke nor eat in workshops. One must also
incite workers to wash their hands regularly and to use
shower/baths after each working day. Working clothes will not be
medical examination :
suffering from anemia, kidney diseases; pregnant or breast-feeding
women, should be kept away from lead exposure. According to Cramer
(1966), alcoholism would make workers more sensitive to the toxic
action of lead.
It is necessary
to seek and recognize the signs of lead impregnation and the first
symptoms and clinical signs of lead poisoning, and to prescribe
the biological tests cited above such as BLL and ZPP.
In the case of
chronic intoxication, tests for kidney function can also be
In the USA, the
Action Level (AL) is .03 mg/m3 of air. The general industry
standard requires that all employees exposed to or above the AL
for more than 30 days per year take part in a medical surveillance
program provided by the employer, regardless of whether
respiratory protection is used. Routine measurements of BLL and
ZPP supplement the information provided by air lead measurements
to guide prevention efforts.
industry standard :
a- A medical
examination must be undergone by all the candidates for employment
where an exposure to lead higher than the AL during more than 30
days per year is encountered. This examination must comprise a
clinical evaluation and laboratory tests.
Evaluation :General and lead-specific history and physical
examination with special attention to hematological, neurological,
(central and peripheral ), pulmonary, cardiovascular,
gastrointestinal, musculoskeletal, renal, and reproductive
systems.Medical clearance to wear respirator, if used, applies to
Testing: it must include BLL, ZPP, blood count with blood smear,
urea and plasma creatinine , complete urinalysis. A sperm analysis
or pregnancy test could be made if requested by the employee, and
any other test the physician deems necessary.
will be necessary to repeat BLL and ZPP measurements every 6
b- When the last
BLL was = or > 1.93 µmol/L. but lower than the threshold
recommended to carry out Medical Removal Protection.
Evaluation: complete evaluation as described above, annually.
Testing : complete lab panel if not done within last 12 months
(see above). Repeat BLL and ZPP every two (2) months until two (2)
consecutive BLLs are < 1.93 µmol/L.
c- When a single
BLL is = or > 2.896 µmol/L. or when the average of the
last three (3) BLLs, or of all the BLLs of the previous six (6)
months are = or > than 2.413 µmol/L. (whichever covers a
longer time period), Medical Removal Protection becomes mandatory.
Evaluation: as soon as the Medical Removal Protection is
initiated. See the clinical evaluation described above.
Testing: Complete lab panel (see above). Repeat BLL and ZPP at
least monthly until two (2) consecutive BLLs are =or< 1.93
d- When an
employee reports signs or symptoms of lead toxiciy, desires advice
about effects of lead exposure (on reproductive system, child
bearing, etc.), has increased risk of material impairment to
health due to lead exposure, or has difficulty breathing with
Evaluation: as soon as possible (see above).
Testing: as deemed appropriate by the physician based on
individual case needs.
Industry Standard :
It will not be
discussed here because it is irrelevant.
Removal Protection :
must recommend to the employer that an employee be removed from
lead exposure and enter a Medical Removal Protection program if
any of the following conditions are met.
Industry Standard :
BLL=or> 2.896 µmol/L, or
b-An average of
the last three (3) BLLs or of all BBLs over the previous 6 months
(whichever covers a longer period of time) is=or>2.413
has a « detected medical condition » that places him or
her at increased risk of « material impairment to health
». The physician is given the discretion to make such a
determination on an individual case basis.
physician detects symptoms and/or clinical signs usually
associated with lead poisoning even if the BLL is lower than the
standards cited above, or when the employee is pregnant.
employee is withdrawn from work, Laboratory Testing (Biological
Monitoring) must be done at least once per month.
f-When the BLL is
twice consecutively = or < 1.93 µmol/L. the physician may
recommend the return to work provided that the employer has taken
proper steps to control lead exposure and that the symptoms/
clinical signs of the intoxication have disappeared.
Removal Protection a physician may recommend that an employee, if
physically able, returns to work in a place where there is no lead
exposure, or in a place where lead exposure is below the AL
(Action Level) which is below .03 mg/m3.
Industry Standard :
It will not be
discussed here because it is irrelevant.
It consists of
a gastric lavage
with a solution precipitating lead in the form of insoluble
sulphate, for example :
sulphate aa 40g,
- water ad 1
- daily injection
of calcium EDTA, in association with BAL in the child;
- need to treat
shock, especially by the parenteral rehydration.
(ethylenediaminetetraacetic acid) is a chelating agent capable of
fixing lead, calcium and other cations to form a non-ionized
complex. To avoid hypocalcemy, a salt of calcium or disodium
should be given. Lead (but also other metals: zinc, copper, iron)
will replace calcium. The soluble complex lead-EDTA is quickly
excreted by the kidneys (glomerular filtration).
Since EDTA is
toxic to the kidneys, especially to the glomerular basal membrane,
its administration should be done with prudence in the presence of
renal ailments. Renal function should be monitored during
treatment. The maximum amount to be given should not exceed
last 5 days and if urinary lead remains high, it can be repeated
after a period of rest of at least 4 to 5 days.
(diethylenetriaminepentaacetic acid trisodium salt, monocalcic)
seems slightly more effective than EDTA.
(dimercaptosuccinic acid) given orally in gradually increasing
amounts has been recommended. Its administration is more effective
than EDTA when the presence of lead in the digestive tract can be
chelation therapy with EDTA and DMSA has been recommended in the
case of significant intoxication.
5-In the case of
lead encephalopathy in the child, it seems that the combined
administration of BAL and EDTA is preferable to EDTA alone.
Finally, let us
remember that the preventive administration of a chelating agent
is to be prohibited. Only the control of the work environment
represents the method of adequate prevention. A drug cannot
replace industrial hygiene measures.
It is of various
a-in lead colicky
abdominal pain: antispasmodic drugs;
convulsions by barbiturates,
intracranial hypertension by the intravenous administration of a
In the case of
renal impairment, peritoneal dialysis allows a significant and
fast elimination of lead, avoiding kidney poisonous chelating
of Lead Impregnation :
In the case of
lead impregnation, hazard control is a must (prevention measures,
job change) and possibly, an EDTA treatment in the adult, 4g/day
by mouth, during 5 to 10 days. By mouth, dimercaptosuccinic acid
(DMSA) seems more active than EDTA.
Repertoire Toxicologique, 2002
Industrielle et Intoxications Professionnelles, Lauwerys R. last
3-Potterycrafts-MSDS, United Kingdom, april
Dangerous Properties of Industrial Materials, Lewis C., last
Surveillance of the Lead Exposed Worker, Current Guidelines,
Hipkins K.L. et al, AACHN Journal, July 1998.
Environmental Health and Toxic Exposures, Sullivan J.B and Krieger
G.R., last edition.
Is Mexican Terra-cotta pottery lead-glazed? Yes.
This piece was bought in Sinaloa in 2020. The merchant said it was made in Puebla. The lead test procedure involves leaving white vinegar in the piece overnight, pouring some of that into a test tube, dipping a cotton swab into a reagent solution and then stirring the vinegar. The color indicates lead content. As you can see, it has turned black, indicating heavy concentration of lead. This pottery is a tradition in Mexican culture and is used for food and liquid surfaces everywhere. There are manufacturers trying to make stoneware that retains the traditional appearance, but few people use it. Further refiring tests demonstrated that these are fired around 1700-1750F, a temperature sufficient to melt pure lead bisilicate into a glossy transparent but the body is still very soft and porous.
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.
Lead in Ceramic Glazes Lead is a melter in ceramic glazes and performs exceptionally well. However recent findings show it to be even more environmentally pervasive and toxic at low levels than originally thought