Zinc Compounds
By Edouard Bastarache
Sources and Production :
Zinc is a bluish-white soft metal. It is
always divalent.
When heated to temperatures higher than
500 C, zinc volatilizes into small zinc oxide particles that
rapidly flocculate as they cool, forming fumes.
The principal ores of zinc are
sphalerite and wurtzite. Zinc constitute approximately 0.02% of
the earth's crust and is distributed widely. It is a relatively
poor conductor of electricity and heat.
Sites, Industries, and
Businesses Associated with Exposure :
Zinc ore is processed by crushing and
then concentrating to 50%-60% metal by flotation. This concentrate
is roasted to remove sulfur by either smelting or electrolytic
refining. Smelted zinc contains impurities of other metals
:
-lead,
-copper,
-cadmium.
It is suitable for :
-galvanizing,
-spraying,
-annealing,
-painting.
Electrolytic refining produces
high-grade zinc (in excess of 99.99% pure) suitable for alloys and
die casting. Chile, Canada, Australia, and Russia are the
principal producers.
Metallic zinc is used principally in
galvanizing iron and steel to prevent corrosion and oxidation.
Zinc metal is also die-cast for :
-automotive components,
-electrical equipement,
-tools,
-hardware,
-toys,
-fancy tools.
Zinc alloys include combinations with
:
-lead,
-cadmium,
-iron,
-tin,
-copper,
-aluminium,
-magnesium,
-titanium.
Exposure of metallic zinc or zinc fumes
to an oxidizing atmosphere converts zinc to the oxidized form,
zinc oxide (ZnO)
Some of the occupations involving
exposure to zinc and zinc compounds are alloy makers, embalmers,
petroleum refinery workers, welders and solderers.
Common Zinc Compounds
and their Uses :
|
Compounds
|
Uses
|
|
Zinc acetate
|
Wood preserving, mordant,
glazes, reagent.
|
|
Zinc carbonate
|
Pigment, feed additive,
manufacture of porcelains, pottery, rubber.
|
|
Zinc chloride
|
Deodorant, disinfectant, wood
preservative, fireproofing, soldering flux, cement,
mordant, petroleum refining, textile treatment,
vulcanizing rubber, solvent for cellulose, manufacture of
activated carbon, paper, glues, and dye.
|
- Zinc chromate (VI), "
hydroxide (zinc yellow, buttercup yellow)
|
- Pigment in paint, oil,
varnish, linoleum, rubber.
|
|
Zinc cyanide
|
Electroplating, removing NH2
from gas.
|
|
Zinc fluoride
|
Fluoridation of organic
compounds, glazes, enamels, wood preserving,
electroplating; manufacture of phosphors for fluorescent
lights.
|
|
Zinc oxide (flowers of zinc,
zinc white, philosopher's wool)
|
Pigments, cements, glass, tires,
glue, matches, white ink, reagent, photocopy paper, flame
retardant, semiconductor, fungicide, cosmetics, dental
cements.
|
|
Zinc phosphide
|
Rodenticide
|
|
Zinc silicate
|
Television screens, neon
lights.
|
|
Zinc stearate
|
Tablet and rubber manufacture;
cosmetic and pharmaceutical powders; ointments,
waterproofing, releasing agent in the manufacture of
plastics.
|
|
Zinc sulfate (zinc vitriol,
white vitriol)
|
Mordant, wood preserving, paper
bleaching, reagent, manufacture of Zn salts,
electrodeposition of Zn.
|
|
Zinc sulfide (zinc
blende)
|
Pigment (manufacture of luminous
dials, X-ray and television screen).
|
Clinical Toxicology
:
I-Routes of Exposure :
The most common route of exposure to
zinc is that of diet.
Inhalation of zinc fumes and dust occurs
in some of the aforementionned industrial settings.
Absorption occurs across broken
epithelium when zinc oxide is applied to treat burns and
wounds.
II- Absorption, Metabolism, and
Elimination :
A-Absorption :
Absorption of zinc occurs throughout the
intestine but mainly in the jejunum and involves zinc-protein
complexes such as metallothionein. Absorption ranges from 25% to
90% after zinc oral administration in humans and is influenced by
dietary factors and probably regulated by the needs.
After oral administration of Zn,
measurable zinc levels may be found in the blood within 15 to 20
minutes, with peak levels in 2 to 4 hours; plasma and serum levels
are higher than in whole blood.
B-Metabolism :
Significant concentrations occur in the
pancreas, prostate, kidney, liver, muscles, and retina.
As many as 300 enzymes require the
presence of zinc for optimal function.
Zinc interacts with proteins to regulate
DNA and RNA synthesis and to modulate neurotransmission.
It is required for growth hormone, helps
to maintain cell membrane structural integrity, and retain
antioxidant properties by inducing metallothionein
production.
C-Elimination :
Zinc's biological half-life exceeds 300
days. A total of 70% to 80% of ingested zinc is excreted in the
feces via bile and pancreatic secretions, which are enhanced by
dietary protein of plant origin.
Urinary and sweat excretion together may
account for up to 25%. Breast milk also contains significant
concentrations of zinc.
The zinc concentration in lymphocytes
may reflect body burden.
III-Signs, Symptoms, and Syndromes
:
In the industry, the toxicity of zinc is
mainly the result of exposure to freshly made zinc oxide
responsible for metal fume fever. In the metallurgy of zinc, the
hazards of intoxication depend mainly on the concommitant presence
of other metals such as arsenic, cadmium, manganese, lead. The
presence of arsenic in zinc is a source of exposure to arsine each
time it is in contact with strong acids.
A-Acute toxicity :
Acute symptoms of oral zinc poisonning
are primarely gastrointestinal. Symptoms include nausea, vomiting,
abdominal pain, diarrhea, hematemesis. Fever is also reported.
With supportive care, zinc toxicity usually is self-limited, and
resolution of symptoms occurs in a matter of hours or days.
1-Skin :
a- Zinc chloride :
Owing to its caustic action, zinc
chloride can cause ulcerations and dermatitis of the exposed
skin.
b-Zinc pyrithione :
A common constituent of shampoos, it may
cause dermatitis with positive patch testing.
c-Zinc dielthyldithiocarbamate :
Present in rubber prosthetic sleeves, it
may also cause dermatitis.
d-Zinc oxide :
Its dust may give rise to papular,
pustular exzema by blocking sebaceous glands with positive patch
testing.
2-Eye :
Zinc chloride and zinc sulfate can cause
significant eye injuries.
Redness and persistent discomfort occur
after exposure to concentrated solutions of either salts.
Within 6 days, a discrete stromal
opacity of the cornea develops, along with irregularity of the
overlying epithelium.
Lens opacities, iritis, and glaucoma may
occur after splashing of concentrated (50%) zinc chloride
solution.
3-Respiratory System :
Most zinc salts irritate mucous
membranes of the upper respiratory tract after inhalation.
a-Zinc chloride :
Inhalation of zinc chloride may cause
:
-cough,
-dyspnea,
-adult respiratory distress syndrome,
death, resulting from delayed pulmonary vascular fibrosis.
Ten deaths and 25 cases of non-fatal
injury occurred among 70 persons exposed to high chloride
concentrations of zinc chloride released from smoke generators. Of
the 10 fatalities, a few died immediately or within a few hours
with pulmonay edema, whereas those who survived longer developed
bronchopneumonia.
On dissolution of zinc chloride, both
hydrochloric acid and zinc oxychloride are formed, contributing to
the corrosive action.
b-Zinc oxide :
Inhalation of freshly produced zinc
oxide can produce metal fume fever.
4-Gastrointestinal System
:
Gastrointestinal effects occur after
ingestion of zinc chloride and zinc phosphide, or from drinking
acidic beverages from galvanized containers. These effects include
:
-abdominal pain,
-nausea,
-vomiting,
-diarrhea,
-hematemesis.
Zinc chloride has been found to cause
oesophagitis and mucosal burns of the stomach.
The toxicity of zinc phosphide is
probably due to the release of phosphine, which occurs on contact
with water and is accelerated by an acidic environment.
Intraveinous zinc poisonning causes
:
-nausea,
-vomiting,
-jaundice.
5-Renal System :
a-Zinc chloride :
Ingestion of zinc chloride can be
followed by hematuria.
Inhalation of zinc chloride smoke caused
acute tubular necrosis, probably due to hypoxia, in soldiers after
fatal adult respiratory distress syndrome.
b-Zinc sulfate :
Iatrogenic intravenous
overadministration of zinc sulfate can cause oliguria and renal
failure.
6-Neurologic System :
Lethargy follows ingestion of zinc
chloride and elemental zinc. Symptoms are reversible with
treatment.
7-Hematologic System :
Chronic ingestion of high doses of
supplemental zinc gives rise to sideroblastic anemia and
leukopenia induced by copper deficiency which reverse , with or
without copper replacement, after cessation of zinc supplements.
Leukocytosis can occur in zinc metal fume fever.
B-Chronic and Long-Term Effects
:
Other than producing corneal and lens
opacities after ocular zinc salt injury and anemia from
zinc-induced copper deficiency, zinc toxicity does not result in
any known chronic effects.
C-Metal Fume Fever :
Exposure to freshly generated zinc oxide
fumes, usually from welding on galvanized iron/steel, leads
to metal
fume fever causing :
-sweet metallic taste,
-dry cough,
-shortness of breath,
-myalgias,
-fever,
-chills
-leucocytosis;
beginning 4 to 12 hours after exposure.
Symptoms may last from 1-3 to 24-48
hours.
No long-term sequelae have been
observed.
Other causes of metal fume fever
are :
1-Antimony,
2-Arsenic
3-Beryllium,
4-Cadmium,
5-Cobalt,
6-Copper,
7-Iron,
8-Lead,
9-Manganese,
10-Magnesium,
11-Mercury,
12-Nickel,
13-Tin
D-Immunologic Reactions :
One case of asthma has been described in
a metal galvanoplasty worker attributed to zinc because he tested
positive to a zinc sulfate challenge test ( a 6 minute exposure to
an aerosol containing 10 mg/l of the product).
One case of hypersensivity pneumonia has
been reported ( cough, dyspnea, lymphocytosis in the the
broncho-alveolar lavage liquid), attibuted to exposure to zinc
oxide fumes.
E-Teratogenicity and Carcinogenicity
:
Zinc toxicity appears not to be
teratogenic, altough zinc deficiency is.
In general, exposure to zinc chloride
does not increase mutation frequencies
in bacterial or mammalian test
systems.
Zinc chromate is a confirmed human
carcinogen owing to hexavalent chromium.
However, no evidence substantiates zinc
carcinogenicity in humans.
IV-Management of Toxicity
:
A- Clinical Examination :
1- Ingestion :
*Zinc chloride :
Evaluating patients with acute onset of
:
-nausea,
-vomiting,
-abdominal pain
after ingestion of solder flux, moss
killer or disinfectants should lead clinicians to suspect zinc
chloride poisonning.
*Elemental zinc :
Drinking acidic beverages from
galvanized containers is a potential source of elemental zinc
toxicity.
Examination of the upper
gastrointestinal tract should be conducted for mucosal burns and
bleeding if hematemesis or guaic-positive stools are encountered
or if symptoms include abdominal or chest pain.
Urine output must be monitored.
2-Inhalation :
When inhalation of zinc chloride or zinc
phosphide is suspected, careful examination of the lungs and upper
respiratory tract is warranted.
Special consideration should be given to
delayed-onset pulmonary edema, which may not develop until several
days after acute inhalation of zinc chloride smoke.
3-Anemia :
In patients with anemia and normal iron
stores, chronic abuse of zinc-containing multivitamins or zinc
supplements should be considered.
B-Laboratory Diagnosis :
1-Zinc chloride :
After acute zinc chloride ingestion,
abnormal laboratory values have included elevations in
-serum zinc,
-glucose,
-amylase,
-lipase,
-alkaline phosphatase.
2-Zinc oxide( metal fume fever)
:
Elevations in :
-serum zinc,
-white blood cells,
-lactate deshydrogenase,
may be encountered.
Pulmonary function may be diminished,
and patchy infiltrates on radiography may be seen during the
episode. All findings return to normal during recovery.
Most workers develop an immunity to
these attacks, but it is quickly lost; attacks tend to be more
severe on the first day of the workweek.
3-Zinc-induced copper deficiency
anemia :
In this condition, the following
parameters are depressed :
-serum copper,
-ceruloplasmin,
-hemoglobin,
-hematocrit,
-red cell indices,
-reticulocyte count.
Serum zinc may be either normal or
elevated. Serum iron and total iron-binding capacity are
normal.
Ringed sideroblasts are seen on
peripheral blood smears.
C-Treatment :
Treatment for acute zinc toxicity is
supportive.
1-Zinc or zinc salts ingestion
:
Treatment should be directed toward
control of :
-nausea,
-vomiting,
-diarrhea.
In the case of substantial ingestion of
zinc tablets,
-induced emesis,
-gastric lavage,
-or activated charcoal
may be useful.
In the case of zinc phosphide, water
should not be given with ipeca or gastric lavage, and activated
charcoal should be mixed sorbitol instead of water to minimize the
liberation of phosphine.
Fluid and electrolyte imbalances must be
corrected.
Upper gastrointestinal mucosal burns
should be treated with H2 receptor antagonists, sucralfate, or
antiacids.
Calcium
disodium-ethylene-diaminetetraacetic acid (EDTA) and dimercaprol
have been successsful in lowering serum zinc levels.
2-Zinc chloride inhalation :
Supportive care is also
indicated:
-ventilatory support with end-expiratory
pressure,
-antibiotics,
-steroids,
-maintenance of cardiac output.
3-Zinc oxide inhalation :
The development of metal fume fever
requires nonspecific treatment after the patient has been removed
from exposure.
4-Zinc-induced copper deficiency
:
This condition requires discontinuation
of supplemental zinc and therapy with oral or intraveinous copper
if neceesary.
D-Biological Monitoring :
For workers repeatedly exposed to zinc
or zinc salts. Preplacement and periodic examinations should
include :
-a baseline history,
-a physical examination,
-a complete blood count,
-spirometry.
There is no Biologic Exposure Index
(BEI) for zinc.
Serum and plasma zinc concentrations are
near 1 µg/ml.
Blood zinc concentration is fivefold
higher than that in plasma, owing to zinc concentration in
erythrocytes.
Urinary zinc excretion in humans not
occupationally exposed is approximately 0.5 mg/24-hour urine
collection.
Occupational exposure to zinc can
produce a plasma concentration of 1.4 µg/ml, and urinary
concentrations of 800 µg/ g. of creatinine.
Occupational and Environmental
Regulations :
The recommended daily allowance for zinc
is 15 mg per day for men, 12 mg for women, 10 mg per day for
children, and 5 mg per day for infants.
The US EPA recommends no more than than
5 ppm in drinking water.
Quebec has exposure limits for zinc
chloride fumes, zinc chromates (CAS# 13530-65-9;
11103-86-9; 37300-23-5), zinc dusts and
fumes, and zinc stearate.
Quebec's Exposure
Limits
|
NAME
|
VEMP
|
VECD
|
- NOTES
|
- Zinc, chloride
(fumes)
- (CAS# 7646-85-7)
|
1 mg/m³
|
-
|
-
|
|
Zinc, chromates (CAS#13530-65-9,
11103-86-9, 37300-23-5), expressed as Cr.
|
0.01 mg/m³
|
-
|
C1, RP, EM
|
- Zinc, oxide (CAS#
1314-13-2)
- Fumes
- Dusts
|
-
- 5 mg/m³
- 10 mg/m³
|
-
- 10 mg/m³
-
|
-
-
- Pt.
|
- Zinc, stearate
- (CAS# 557-05-1)
|
- 10 mg/m³
|
-
|
-
|
VEMP = Valeur d'Exposition Moyenne
Pondérée (TWA).
VECD = Valeur d'Exposition de Courte
Durée (STEL).
C1 = Confirmed carcinogen in
humans.
EM = Substance that should be kept at
the lowest practicable level
RP = Substance whose recirculation is
prohibited in accordance with the law
Pt. = Total dust.
Exposure Controls :
Workplace zinc oxide fumes should be
maintained at less than 5 mg/m³ by engineering controls, such
as appropriate exhaust ventilation. Zinc oxide dust should be
maintained at less than 10 mg/m³ (total dust).
Use of personal protective devices
(respirators) should be limited to short exposures that occur
during performance of unusual jobs.
Monitoring should be carried out any
time for changes in work process or procedure that may cause an
increase in zinc fumes or dusts.
Environmental Fate and Transport
:
Zinc is found in the earth's crust at
approximately 40 mg/kg. In ambient air, the zinc concentration is
normally well below 1µg/m³, and in water 1 to 10
µg/L.
The principal anthropogenic sources are
mining and refining, primarely from blasting, crushing, and wet
flotation. Significant soil contamination is found only near point
sources.
References :
1-Occupational Medicine,Carl Zenz,
last edition.
2-Clinical Environmental Health and
Toxic Exposures, Sullivan & Krieger; last edition.
3-Sax's Dangerous Properties of
Industrial Materials, Lewis C., last edition.
4-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R.R. last
edition.
5-Chemical Hazards of the Workplace,
Proctor & Hughes, 4th edition
Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
Out Bound Links
In Bound Links
- (Materials - General)
Zinc Oxide - ZnO - Pure Source Of Zinc
ZnO, Zincite
- (Materials - General)
Zinc Borate - 2ZnO.3B2O3.3.5H2O
- (Materials - General)
Zinc Carbonate - ZnCO3
Smithsonite, zinc spar
| 
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