ZINC COMPOUNDS

CAS Registry Number: Zinc: 7440-66-6; Zinc oxide: 1314-13-2

Molecular Formula: Zn; OZn

Elemental zinc is a bluish-white, lustrous metal which becomes covered with a white coating of basic carbonate on exposure to moist air, but is stable in dry air. The dust is flammable when exposed to heat or flame and may ignite spontaneously in air when dry (Sax, 1989). Zinc is insoluble in cold and hot water and soluble in acid, alkalies, and acetic acid. It burns in air with a bluish-green flame; is slowly attacked by sulfuric or hydrochloric acid, oxidizing agents or metal ions; and forms zincates with alkali hydroxides (Merck, 1989).

There are many zinc compounds, including zinc salts (zinc chloride, zinc oxide), and fumed zinc. Zinc oxide is a white or grayish powder which is odorless and noncombustible. It is almost insoluble in water and alcohol, but is soluble in dilute acetic or mineral acids and ammonia (Sax, 1987).

Physical Properties of Zinc and Zinc Oxide

Synonyms of zinc:Blue powder; zinc powder; C.I. 77945; emanay zinc dust; granular zinc; jasad; merrillite; pasco

Synonyms of zinc oxide: Chinese white; zinc white; flowers of zinc; philosopher's wool; C.I. 77947; C.I pigment white; akro-zinc bar 85; amalox; azo-33

ZincZinc oxide
Valence:2
Molecular Weight:65.37 81.38
Melting Point: 419.5 oC1975 oC
Vapor Pressure: 1 mm at 487 oC
Density/Specific Gravity:7.14 at 25 oC5.61 at 20/4 oC

(Merck, 1989; Sax, 1989)

Examples of Zinc Compounds

Zinc acetate, Zinc hydride, Zinc ammonium nitrite, Zinc nitrate, Zinc arsenate, Zinc oxide, Zinc chlorate, Zinc permanganate, Zinc chloride, Zinc phosphide, Zinc cyanide, Zinc sulfate, Zinc fluoride

SOURCES AND EMISSIONS

A. Sources

Zinc is used in alloys, galvanizing iron and other metals, electroplating, metal spraying, auto parts, electrical fuses, batteries, engravers' plates, cable wrappings, organ pipes, extracting gold, purifying fats for soaps, and railroad car linings (Merck, 1989).

Zinc (metallic zinc) is a very minor component of a fungicide product composed of mancozeb, cymoxanil, and manganese sulfate. It is registered for use (under an emergency exemption) on tomatoes and potatoes to control late blight (DPR, 1996).

Zinc Chloride is registered as an herbicide. It is used to control lichen and moss growing on the roofs of houses and other domestic dwellings, along walks, driveways, fences, and wherever moss grows (DPR, 1996).

Zinc phosphide is registered as a rodenticide for the control of mice, rats, gophers, squirrels, and other pestiferous rodents. Application sites include ornamental turf areas and golf courses, and in and around nurseries, farm structures, silos, and grain storage areas. Zinc phosphide may also be applied in orchards and other general agricultural areas where rodents are pests (DPR, 1996).

Ziram (Zinc dimethyl dithio carbamate) is registered as a fungicide. It is used for the prevention and control of agricultural plant diseases in grapes and tomatoes, and in nut orchards, stone fruit orchards, and pome fruit orchards. It may also be used to control plant diseases on a variety of ornamental plants including roses, azaleas, pines, carnations, bulb plants etc. (DPR, 1996).

The licensing and regulation of pesticides for sale and use in California are the responsibility of the Department of Pesticide Regulation (DPR). Information presented in this fact sheet regarding the permitted pesticidal uses of zinc, zinc chloride, zinc phosphide, and ziram has been collected from pesticide labels registered for use in California and from DPR's pesticide databases. This information reflects pesticide use and permitted uses in California as of October 15, 1996. For further information regarding the pesticidal use of these compounds, please contact the Pesticide Registration Branch of DPR (DPR, 1996).

Zinc has been detected or identified but not quantified in motor vehicle exhaust by the ARB (ARB, 1991). The primary stationary sources that have reported emissions of zinc in California are electric services, petroleum refining, crude petroleum and natural gas extraction (ARB, 1997b).

Zinc oxide is used in paints, ointments, cosmetics, cement, glass, automobile tires, fabricated rubber products, plumbing fixtures, glue, matches, tiles, ceramics and porcelains, feed additives, seed treatment, inks, zinc green, electrostatic copying paper and color photography, flame retardant, semiconductor manufacturing, and as an ultraviolet absorber in plastics (Merck, 1989; Sax, 1987).

The primary stationary sources that have reported emissions of zinc oxide in California are manufacturers of fabricated rubber products, manufacturers of fabricated metal heating and plumbing products (excluding electric), and manufacturers of inorganic chemicals (ARB, 1997b).

B. Emissions

The total emissions of zinc and zinc compounds from stationary sources in California are estimated to be at least 210,000 pounds per year, based on data reported under the Air Toxics "Hot Spots" Program (AB 2588) (ARB, 1997b).

C. Natural Occurrence

Zinc occurs naturally in smithsonite, sphalterite, wurtzite, zinc blende, zincite, willemite, franklinite and gahnite ores. The average concentration of zinc in the earth's crust is estimated to be 40 milligrams per kilogram (HSDB, 1993).

AMBIENT CONCENTRATIONS

Zinc and its species are routinely monitored by the statewide Air Resources Board air toxics network. The network's mean concentration of zinc (including its species) from January 1996 through December 1996 is estimated to be 51.4 nanograms per cubic meter (ng/m3) (ARB, 1997c).

INDOOR SOURCES AND CONCENTRATIONS

Sources of indoor airborne zinc identified by source apportionment methods include infiltration of outdoor air, smoking, cooking, and other indoor sources (Ozkaynak et al., 1996). The "other" indoor sources were unidentified, but may have included activities such as cleaning, dusting, vacuuming, and hobbies.

Zinc was measured in about 170 homes during the fall of 1990 in southern California. Indoor PM10 (particles less than 10 microns in diameter) concentrations of zinc ranged from 38 to 360 ng/m3 with an average of 90 ng/m3 during the daytime, and from 27 to 180 ng/m3 with an average of 63 ng/m3 during the nighttime. Outdoor zinc concentrations measured at these homes were less than indoor concentrations. Outdoor zinc concentrations (PM10) ranged from 28 to 160 ng/m3 with an average of 67 ng/m3 during the daytime, and from 22 to 170 ng/m3 with an average of 56 ng/m3 during the nighttime (Pellizzari et al., 1992).

Zinc concentrations (PM10) measured by personal exposure samplers in the daytime were much greater than the concentrations measured indoors or outdoors at these homes. Personal exposure to zinc concentrations ranged from 62 to 490 ug/m3 with an average of 152 ug/m3 during the daytime, and from 29 to 200 ug/m3 with an average of 70 ug/m3 during the nighttime (Pellizzari et al., 1992).

ATMOSPHERIC PERSISTENCE

Zinc compounds are expected to be particle-associated or in the aerosol form in the atmosphere, and hence subject to wet and dry deposition. The average half-life and lifetime for particles and particle-associated chemicals in the troposphere is estimated to be about 3.5 to 10 days and 5 to 15 days, respectively (Balkanski et al., 1993; Atkinson, 1995).

AB 2588 RISK ASSESSMENT INFORMATION

The Office of Environmental Health Hazard Assessment reviews risk assessments submitted under the Air Toxics "Hot Spots" Program (AB 2588). Of the risk assessments reviewed as of December 1996, for non-cancer health effects, zinc and zinc compounds contributed to the total hazard index in 37 of the approximately 89 risk assessments reporting a total chronic hazard index greater than 1. Zinc and zinc compounds also contributed to the total hazard index in 5 of the approximately 107 risk assessments reporting a total acute hazard index greater than 1 (OEHHA, 1996b).

HEALTH EFFECTS

Probable routes of human exposure to zinc are inhalation, ingestion, and dermal contact.

Non-Cancer: Zinc is an essential trace element which has a role in normal growth, taste, and sperm development. Acute inhalation exposure to high levels of zinc such as from welding and smelting of metallic zinc (forming zinc oxide) has resulted in "metal fume fever", with symptoms of headache, chills, fever, and muscle aches (HSDB, 1995). Damage to the mucous membranes of the respiratory tract and ulceration of the skin can result from exposure to zinc chloride, and irritation of the respiratory tract may lead to pneumonitis (Sittig, 1991).

A chronic non-cancer Reference Exposure Level (REL) of 35 micrograms per cubic meter is listed for zinc compounds in the California Air Pollution Control Officers Association Air Toxics "Hot Spots" Program, Revised 1992 Risk Assessment Guidelines. The United States Environmental Protection Agency (U.S. EPA) has established an oral Reference Dose of 0.3 milligrams per kilogram per day zinc based on red blood cell effects in human adult females. The U.S. EPA has not established a reference concentration (RfC) for zinc compounds (U.S. EPA, 1995a).

Cancer: The U.S. EPA has classified zinc and zinc compounds in Group D: Indicating inadequate evidence as to its carcinogenic potential (U.S. EPA, 1995a). The International Agency for Research on Cancer has not classified zinc as to its carcinogenic potential (IARC, 1987a).