Zinc and compounds

Overview

Zinc is mainly used as a protective coating for iron and steel (galvanising). It is further used for the production of zinc alloys (e.g. brass), rolled zinc, zinc dust (a pigment and a reducing agent), and zinc compounds (e.g. zinc oxide).

• Zinc oxide is the industrially most important zinc compound. It is used in rubber (vulcanising, pigment), photocopy paper, chemicals and paints. Other uses are in floor coverings, in glasses, enamels, fabrics, plastics, lubricants, in rayon manufacture, and in pharmaceuticals (powders and ointments for external application on burns, skin infections and for skin protection).
• Zinc acetate is used in wood preserving, as a mordant in dyeing, as a feed additive, as a food additive, as a component of adhesives, as a glaze for painting on porcelain, and as a reagent in testing for albumin, tannin, phosphate and blood. It is a pharmaceutical necessity for zinc eugenol dental cement for temporary fillings.
• Zinc carbonate is used as a fire-proofing filler for rubber and plastic compositions exposed to flame temperature, as a feed additive, as a pigment, in cosmetics and lotions, and in the manufacturing of zinc salts, porcelains, pottery, and rubber.
• Zinc chloride is used in fluxes (soldering and welding), for fire proofing, as a wood preservative, and in medicine (cauterising agent). It is used alone or with phenol and other antiseptics for preserving railway ties, and as a herbicide and foliar treatment on sidewalks, patios, and fence rows. It is used in the manufacturing of parchment paper, artificial silk, activated carbon, cold water glues, magnesia cements, cement for metals and for facing stone, dental cements, and golf balls. It is used as a mordant in printing and dyeing textiles, as electrolyte in dry cell batteries, as a corrosion inhibitor in water treatment, as an agent in the vulcanisation of rubber, and as a chemical intermediate for pesticides and micronutrients in agriculture. It is used in mercerising cotton, sizing and weighting fabrics, carbonising woollen goods, producing crepe and crimping fabrics, and preserving anatomical specimens. Zinc chloride is a primary ingredient in smoke bombs, as used by the military for screening purposes, crowd dispersal, and fire-fighting exercises.
• Zinc chromate is primarily used in paints for priming metals to resist corrosion. It is also used in varnishes and automotive paint pigments.
• Zinc cyanide is used in metal plating, in producing insecticides, electroplating, removing ammonia from producer gas, and gold extraction. It is also used as a chemical reagent, and in medicine and chemical analysis.
• Zinc fluoride is used in the fluorination of organic compounds, in the manufacturing of phosphors for fluorescent lights, in preserving wood, in electroplating baths, in galvanising steel, and making ceramics. It is also used as a termite repellent, in medication, and in glazes and enamels for porcelain.
• Zinc phosphide is used in rat and field mice poison, as a stomach poison for mosquito larvae and agricultural pests, and for control of crickets.
• Zinc potassium chromate is used as a rust inhibitor in metal paints and as an artist's colour.
• Zinc sulfate is used as a reagent in analytical chemistry and for paper bleaching, as a component of spinning bath in the manufacture of rayon, and as a chemical intermediary for the manufacture of carbamate fungicides, zinc metal, and other zinc compounds. It is used in skin fresheners, glue, textile dyeing and printing, and preservatives for wood and hides. It is also used as a fireproofing agent, a fertiliser ingredient, a feed supplement, a herbicide, a miticide, as a soil treatment on lawns, and in sewage against animal pathogenic bacteria. Zinc sulfate can be used as a supplement for humans, animals and plants with zinc deficiency.
• Zinc sulfide is used as a pigment for paints, oil cloths, linoleum, leather, and dental rubber, in white and opaque glass, plastics, dyeing, and in fungicides. It is used as a semiconductor, a photoconductor for solar cells, a pigment in paper, in infra-red thin film and transmitting devices, in detinning, and in optical filter coating. It is used as a phosphor in TV and X-ray screens, and in luminous dials of watches.

A range of organic zinc compounds exists (e.g. zinc soaps, Ziram, and Zineb) which are used as fungicides, antiseptics, water-repellents, lubricants, and for water-proofing textiles, papers, and concrete.

Substance details

Substance name: Zinc and compounds

CASR number: 7440-66-6

Molecular formula: Zn

Synonyms: Zinc dust, zinc powder, blue powder. Zinc acetate (CASR# 557-34-6), zinc carbonate (CASR# 3486-35-9), zinc chloride (CASR# 7646-85-7), zinc chromate (CASR# 13530-65-9), zinc cyanide (CASR# 557-21-1), zinc fluoride (CASR# 7783-49-5), zinc hydroxide (CASR# 20427-58-1), zinc oxide (CASR# 1314-13-2), zinc phosphide (CASR# 1314-84-7), zinc potassium chromate (CASR# 11103-86-9), zinc sulfate (CASR# 7733-02-0), and zinc sulfide (CASR# 1314-98-3).

Physical properties

Zinc is easily obtained from its ores. The main minerals are sulfides (sphalerite, wurtzite). Zinc is a bluish-white, lustrous metal. It is brittle at ambient temperatures but is malleable at 100 to 150°C. It can also be rolled at these temperatures. It is a reasonable conductor of electricity. Zinc forms many alloys. Brass, an alloy with copper, is an example.

Atomic Number: 30

Atomic Mass: 65.4

Melting Point: 420°C

Boling Point: 907°C

Specific Gravity: 7.14

The properties of zinc compounds vary greatly:

• Zinc acetate comes in the form of white granules. It is slightly efflorescent and has a faint vinegar odour. It decomposes at 200°C.
• Zinc carbonate comes as colourless crystals, or a white, crystalline powder. It is odourless and evolves carbon dioxide at 300°C.
• Zinc chloride comes in the form of hygroscopic white granules, white crystals, fused pieces, or rods. It is odourless but its white fume has an acrid odour. The melting point of pure zinc chloride is 275°C and its boiling point is 756°C. Its specific gravity is 2.9 and its vapour density is 4.7.
• Zinc chromate can be a yellow, fine powder or yellow prisms. It is odourless.
• Zinc cyanide is either a white powder, or colourless, rhombic crystals. It has the odour of bitter almonds. It decomposes at 800°C.
• Zinc fluoride can exist as colourless crystals, needles, or a white crystalline mass. It has a melting point of 872°C and a boiling point of 1502°C. Its specific gravity is 4.95.
• Zinc oxide is a white solid which turns yellow on heating. Its melting point is 1975°C and its specific gravity is 5.6.
• Zinc phosphide comes in the form of dark grey crystals, or a lustrous or dull powder. It has a faint phosphorus or garlic odour. Its melting point is greater than 420°C and it boils at 1100°C.
• Zinc potassium chromate is a yellow powder.
• Zinc sulfate comes in the form of colourless rhombic crystals, transparent prisms or small needles. It is efflorescent in dry air.
• Zinc sulfide comes in the form of colourless hexagonal crystals, or white/greyish-white or yellow powder.

Chemical properties

Zinc is insoluble in water but reacts readily with non-oxidising acids, forming zinc (II) and releasing hydrogen. It also dissolves in strong bases. It reacts readily when heated with oxygen to give zinc oxide. Direct reactions with halogens will also occur. Pure zinc in air forms a layer which protects the metal from corrosion. In dry air, this protective layer is an oxide layer and in wet air it is a carbonate-hydroxide layer.

Zinc ions found in aquatic environments are in the (II) oxidation state. It is rarely encountered as the free zinc (II) ion due to its strong tendency to form complexes with inorganic and organic compounds freely available in nature. Water solubility of zinc compounds varies, with zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, zinc chlorate and zinc perchlorate all readily soluble in water. Zinc oxide, zinc carbonate and zinc sulfide are practically insoluble in water. Properties of selected zinc compounds follow.

• Zinc acetate is soluble in water and alcohol. It crystallises from dilute acetic acid.
• Zinc carbonate is soluble in dilute acids, alkalies and in ammonium salt solutions. It is insoluble in water, ammonia, pyridine, alcohol and acetone.
• Zinc chloride is very soluble in water, and quite soluble in alcohol and acetone. It is also soluble in hydrochloric acid, glycerol and ether. It is insoluble in ammonia. It is very deliquescent. Its fumes are corrosive to metals.
• Zinc chromate is insoluble in cold water and acetone, and soluble in acid and ammonia. It is corrosive because of its oxidising potency.
• Zinc cyanide is insoluble in alcohol, and soluble in ammonium solutions, solutions of alkali cyanides and hydroxides.
• Zinc fluoride is soluble in water, and quite soluble in alcohol and acetone. It is also soluble in ammonium hydroxide, alkali, hydrochloric acid and nitric acid, slightly soluble in aqueous hydrofluoric acid, and insoluble in ammonia.
• Zinc hydroxide can be precipitated from zinc solutions by addition of bases. It dissolves in aqueous sodium hydroxide and concentrated ammonia.
• Zinc oxide is formed when burning zinc metal in air or by pyrolysis of zinc carbonate or zinc nitrate.
• Zinc phosphide is practically insoluble in alcohol and water, and slightly soluble in benzene. It is stable when dry. It reacts with acids and more slowly with water. It reacts violently with acids when heated (> 400 °C) to form phosphine gas.
• Zinc sulfate is soluble in water, methanol and glycerol. It is insoluble in alcohol. Insoluble sulfates are formed when zinc sulfate is combined with lead, barium, strontium, and calcium salts.
• Zinc sulfide is insoluble in water and alkalies, and soluble in dilute mineral acids.

Sources of emissions

Industry sources

Emissions to air, water and soil can occur at all stages of production and processing of zinc, particularly from mining and refining of zinc ores, and from galvanising plants. Sewage treatment plants and waste sites for industrial and household wastes can be sources of zinc levels harmful to the environment.

Note: Zinc minerals contain cadmium (CASR# 7440-43-9) as a common impurity which will be released when zinc is refined. Cadmium is a cancer-causing agent and thus much more harmful than zinc itself. Details about cadmium can be found elsewhere in the NPI.

Diffuse sources and industry sources included in diffuse emission data

Corrosion of galvanised structures can release zinc into soil and water. Uncontrolled release from application of fertilisers or herbicides may be possible.

Natural sources

Zinc is relatively abundant and natural levels of zinc are found in rocks, soil, air, waters, plants, animals, and humans. It is present in all foods.

Transport sources

Wear and tear of car tyres and fuel combustion can contribute to elevated levels of zinc in roadside dust.

Consumer products

Any product made from galvanised steel (such as cars, roofs, fences, etc.), dry cell batteries, ointments ('zinc cream' sunscreen), some vitamin/mineral dietary supplements, TV screens, watches, zinc soaps, car tyres (about 1.5 % zinc).

Environmental effects

The toxicity of zinc and many zinc compounds to plants and animals is generally low compared with the significance of zinc deficiency. Soils with an excessive zinc burden, e.g. in the vicinity of zinc smelters, can be toxic to plants. Soil pH is one factor that influences zinc availability to plants. Bioavailability increases with lower pH values, but wash-out is also more likely under more acidic conditions. The toxicity of zinc in water is influenced by water hardness and pH, with lower toxicity encountered in waters with higher water hardness and lower pH, and vice versa. Generally, zinc and its salts have high acute and chronic toxicity to aquatic life in polluted waters. Fish can accumulate zinc moderately. Insufficient data are available to evaluate or predict the short term and the long term effects of zinc and its compounds to plants, birds, or land animals.

Entering the environment

Zinc can be transported as particles released into the atmosphere or as dissolved compounds in natural waters.

Where it ends up

Some zinc is released into the environment by natural processes, but human activities like mining, steel production and burning of waste can make significant contributions. Zinc attaches to dust particles in the air which settle to the ground or are taken out of the air by rain. Zinc attaches to soil and sediment particles and most of the zinc will stay bound. Some zinc will move into the ground water and into lakes, streams, and rivers where it combines with other organic or inorganic matter. Zinc is likely to build up in fish and other organisms, but unlikely to build up in plants.

Environmental guidelines

Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992):

• Maximum of 5 microgram/L to 50 microgram/L (i.e. 0.000005 g/L to 0.00005 g/L), depending on water hardness, for fresh waters and
• 50 microgram/L (i.e. 0.00005 g/L) in marine waters respectively.

Description

Zinc is an essential trace element in the diet of all living organisms from bacteria to humans. Either too little zinc or too much zinc can be harmful, causing health problems. The severity of health effects will depend on how much zinc a person has been exposed to, for how long, the nature of the zinc compound(s), and current state of health. A human body (70 kg) contains about two grams of zinc. The recommended dietary allowance (RDA) for zinc is 15 milligrams a day for men, 12 milligrams a day for women, 10 milligrams a day for children and 5 milligrams a day for infants.

Not enough zinc in the diet can result in a loss of appetite, a decreased sense of taste and smell, slow wound healing and skin sores, or a damaged immune system. Young men who don't get enough zinc may have poorly developed sex organs and slow growth. If a pregnant woman doesn't get enough zinc, her babies may have growth retardation. Harmful health effects generally begin at levels in the 100 to 250 milligrams a day range. Eating large amounts of zinc, even for a short time, can cause stomach cramps, nausea, and vomiting. Taken longer, it can cause anaemia, pancreas damage, and lower levels of high density lipoprotein cholesterol (the 'good' form of cholesterol). Ingesting too much zinc may also interfere with the body's ability to absorb and use other essential minerals such as copper and iron. People with potentially high exposure to zinc include those who intentionally consume large doses of zinc as a dietary supplement, and patients who receive chronic treatment with drugs containing zinc salts (such as injectable insulin).

Zinc dust is irritating to the eyes, nose, and throat, and solid zinc compounds are irritating to the skin and eyes. Breathing large amounts of zinc dust can cause a cough with phlegm. Inhaling zinc dust or fumes can cause 'metal fume fever' which affects the lungs and body temperature. Long term effects of breathing high levels of zinc are unknown. Inhalation of zinc oxide fumes is common in occupational exposures and can produce serious injury to the respiratory system. Inhalation of zinc chloride fumes (smoke bombs) can result in coughing, chest pain, and respiratory tract irritation. Other symptoms include blueness of the skin (cyanosis), skin disease (dermatosis), skin inflammation (dermatitis), skin burns, ulceration of nasal passages, deficiency of calcium in the blood (hypocalcaemia), presence of blood traces in the urine (microhematuria), and pneumonitis. The fumes also affect eyes. Death can result from acute high dose inhalation of zinc chloride smoke. Zinc sulfate is astringent and corrosive to skin, and can cause dermatitis, boils, conjunctivitis, gastrointestinal disturbances, vomiting, cramps, renal damage, and inflammation of the pancreas through blood (haemorrhagic pancreatitis). Zinc sulfide is astringent and corrosive to skin, and if ingested with a high gastric acidity may decompose to hydrogen sulfide in the stomach, with subsequent systemic poisoning. In large doses, it can cause vomiting and diarrhoea.

Some zinc compounds are very harmful not because of zinc but because of other harmful constituents that make up the compounds. Examples include:

• zinc chromate (potential carcinogen, with many of the same health effects as chromium and chromates, including ulceration of the nasal septum, chronic rhinitis, respiratory irritations, conjunctivitis, skin ulcers, dizziness, intense thirst, abdominal pain, vomiting, shock, absence of urine (anuria), pharyngitis, dermatitis with fluid effusion (oedema) and ulceration, and death due to retention of urinary constituents (uraemia);
• zinc cyanide (with many of the same health effects as cyanide, including nausea, vomiting, confusion, vertigo, increased intake and depth of respiration (hyperpnoea), breathing difficulties (dyspnoea), headache, dizziness, dermatitis, weak and irregular pulse, blindness, damage to optic nerves and retina, sudden loss of consciousness, convulsions, and death from respiratory arrest);
• zinc fluoride (with many of the same health effects as fluoride, including severe gastritis, abdominal pain, vomiting, diarrhoea, shock, blueness of the skin (cyanosis), weak pulse, low blood pressure, drowsiness, liver injury, hyperactive reflexes, increase in radiographic density of bones (eventually causing anatomical abnormalities), and death from shock); and
• zinc phosphide (may evolve phosphine in the presence of moisture, which can cause intense nausea, abdominal pain, chills, tightness in the chest, breathing difficulties (dyspnoea), cough, shock from toxic heart muscle inflammation (myocarditis), jaundice from liver necrosis, severe gastrointestinal irritation, and fatal pulmonary oedema (fluid in the lungs).

Entering the body

Zinc can be inhaled or ingested.

Exposure

Zinc (in trace quantities) is essential for human health. Natural zinc levels are present in food and water, and small amounts are regularly ingested. Elevated zinc levels can be encountered when drinking contaminated water near mining and refinery sites, manufacturing or waste sites, or drinking contaminated water or a beverage that has been stored in metal containers or flows through pipes that have been coated with zinc to protect from rust. It may also happen when eating too many dietary supplements that contain zinc. Occupational exposure to higher than normal zinc levels may occur when breathing zinc dust or fumes at various industrial sites (such as smelters, galvanising facilities, etc.).

Workplace exposure standards

Safe Work Australia sets the workplace exposure standards for particulate matter through the workplace exposure standards for airborne contaminants. These standards are only appropriate for use in workplaces and are not limited to any specific industry or operation. Make sure you understand how to interpret the standards before you use them.

Zinc oxide (dust)

• Maximum eight hour time weighted average (TWA): 10 mg/m3

Zinc oxide (fume)

• Maximum eight hour time weighted average (TWA): 5 mg/m3
• Maximum short term exposure limit (STEL): 10 mg/m3

Zinc chloride (fume)

• Maximum eight hour time weighted average (TWA): 1 mg/m3
• Maximum short term exposure limit (STEL): 2 mg/m3

Zinc chromate (as Cr)

• Maximum eight hour time weighted average (TWA): 0.01 mg/m3