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Zinc Compounds Toxicology

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

By Edouard Bastarache

Related Information

Links

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	Zinc Oxide A pure source of ZnO for ceramic glazes, it is 100% pure with no LOI.
Materials	Zinc Carbonate
Materials	Zinc Borate
Oxides	ZnO - Zinc Oxide

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