Disclaimer: These guidelines were developed under contract using generally accepted secondary sources. The protocol used by the contractor for surveying these data sources was developed by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the Department of Energy (DOE). The information contained in these guidelines is intended for reference purposes only. None of the agencies have conducted a comprehensive check of the information and data contained in these sources. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The secondary sources used for supplements 111 and 1V were published before 1992 and 1993, respectively, and for the remainder of the guidelines the secondary sources used were published before September 1996. This information may be superseded by new developments in the field of industrial hygiene. Therefore readers are advised to determine whether new information is available.

OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR CHROMIUM (II) COMPOUNDS (as Cr)

INTRODUCTION

This guideline summarizes pertinent information about chromium (II) compounds for workers and employers as well as for physicians, industrial hygienists, and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available.

APPLICABILITY

The general guidelines contained in this document apply to all of the chromium (II) compounds. Examples of such compounds include chromium (II) chloride, chromium (II) dioxide, and chromium (II) oxalate. For illustrative purposes, the physical and chemical properties of several chromium (II) compounds are presented below.

SUBSTANCE IDENTIFICATION

Chromium (II) chloride

* Formula

CrCl(2)

* Structure

(For Structure, see paper copy)

* Synonyms

Chromium chloride, chromium dichloride, chromous chloride

* Identifiers

1. CAS No.: 10049-05-5

2. RTECS No.: GB5250000

3. Specific DOT number: None

4. Specific DOT label: None

* Appearance and odor

Chromium (II) chloride is a white solid in the form of deliquescent needles or a fused fibrous mass.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 122.9

2. Boiling point: Data not available.

3. Specific gravity at 25 degrees C (77 degrees F): 2.878

4. Vapor density: Data not available.

5. Melting point: 824 degrees C (1515.2 degrees F)

6. Vapor pressure: Data not available.

7. Solubility: Very soluble in water; insoluble in ether, or alcohol.

8. Evaporation rate: Data not available.

Chromium (II) dioxide

* Formula

CrO(2)

* Structure

Data not available.

* Synonyms

Chromium oxide, chromium dioxide, accrox c, accrox r

* Identifiers

1. CAS No.: 12018-01-8

2. RTECS No.: GB6400000

3. Specific DOT number: None

4. Specific DOT label: None

* Appearance and odor

Chromium (II) dioxide is a brownish to black, ferromagnetic, crystalline solid.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 84

2. Boiling point: Data not available.

3. Specific gravity (water = 1): 4.9

4. Vapor density: Data not available.

5. Melting point (minus oxygen): 300 degrees C (572 degrees F)

6. Vapor pressure: Data not available.

7. Solubility: Insoluble in water or organic solvents; soluble in nitric acid .

8. Evaporation rate: Data not available.

Chromium (II) oxalate

* Formula

CrC(2)O(4)þH(2)O

* Structure

Data not available.

* Synonyms

Chromous oxalate; ethanedioic acid, chromium (2+) salt (1:1); oxalic acid, chromium (2+) salt (1:1)

* Identifiers

1. CAS No.: 814-90-4

2. RTECS No.: Data not available.

3. Specific DOT number: None

4. Specific DOT label: None

* Appearance and odor

Chromium (II) oxalate is a yellow, crystalline powder.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 140 (anhydrous); 158 (hydrate)

2. Boiling point: Data not available.

3. Specific gravity (water = 1): 2.468

4. Vapor density: Data not available.

5. Melting/Freezing point: Data not available.

6. Vapor pressure: Data not available.

7. Solubility: Slightly soluble in cold water; soluble in hot water and dilute acids.

8. Evaporation rate: Data not available.

* Reactivity

1. Conditions contributing to instability: None reported for the example compounds listed above. Conditions contributing to instability will vary depending on the specific chromium (II) compound.

2. Incompatibilities: None reported for the example compounds listed above. Incompatibilities will vary depending on the specific chromium (II) compound.

3. Hazardous decomposition products: None reported for the example compounds listed above. The thermal degradation products will vary depending on the specific chromium (II) compound involved in the fire.

4. Special precautions: None reported.

* Flammability

The National Fire Protection Association has not assigned a flammability rating to any of the chromium (II) compounds listed in this document.

1. Flash point: Data not available.

2. Autoignition temperature: Data not available.

3. Flammable limits in air: Data not available.

4. Extinguishant: Use an extinguishant that is suitable for the materials involved in the surrounding fire.

Fires involving chromium (II) compounds should be fought upwind from the maximum distance possible. Isolate the hazard area and deny access to unnecessary personnel. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving chromium (II) compounds.

EXPOSURE LIMITS

* OSHA PEL

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for chromium (II) compounds (as Cr) is 0.5 milligrams per cubic meter (mg/m(3)) of air as an 8-hour time-weighted average (TWA) concentration [29 CFR 1910.1000, Table Z-1].

* NIOSH REL

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for chromium (II) compounds of 0.5 mg/m(3) as a TWA for up to a 10-hour workday and a 40-hour workweek [NIOSH 1992].

* ACGIH TLV

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned chromium (II) compounds a threshold limit value (TLV) of 0.5 mg/m(3) as an TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1991, p. 312]. Note: This limit is listed in the 1991 Documentation of the Threshold Limit Values and Biological Exposure Indices, 6th Ed., but is not specifically listed in the 1994-1995 Threshold Limit Values (for chemical substances and physical agents) and Biological Exposure Indices.

* Rationale for Limits

The NIOSH limit is based on the low-order toxicity of chromium (II) compounds [NIOSH 1992].

The ACGIH limit is based on the low-order of toxicity of chromium (II) compounds [ACGIH 1991, p. 313].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to chromium (II) compounds can occur through inhalation, ingestion, and eye or skin contact.

* Summary of toxicology

1. Effects on Animals: Chromium (II) compounds have caused respiratory system effects in experimental animals. Chromium (II) compounds are considered to have a relatively low-order of toxicity. The oral LD(50) in rats for chromium (II) chloride and chromium acetate hydrate are 1,870 and 11,260 mg/kg, respectively [NIOSH 1995; Sax and Lewis 1989]. Respiratory effects were noted in a chronic inhalation study on rats involving a concentration of 25 mg/m(3) of chromium (II) dioxide [NIOSH 1995]. Exposures in 6-hour intervals on an intermittent basis were given over a period of two years which resulted to changes in the lungs and respiration patterns of animals.

2. Effects on Humans: Chromium (II) compounds have been reported to cause asthma in exposed humans. The chromium (II) compounds are considered to have a lower-order of toxicity in humans as compared with hexavalent chromium. Although one some source indicated that contact with divalent chromium compounds may result in dermatitis ulcers of the skin, mucous membranes, and perforation of the nasal septum [NLM 1995], details of the studies were lacking, and the majority of sources did not concur with these findings. Some patients did have positive reactions to patch tests using divalent chromium, but overall, these compounds are considered to be much less potent sensitizing agents than the hexavalent chromium compounds [Hathaway et al. 1991]. One documented case of exposure-induced asthma has been reported following an exposure to chromium sulfate (details of exposure were not given) [Hathaway et al. 1991]. Four workers exposed to a concentration of about 0.26 mg/m(3) chromium during ferrochrome alloy production developed a nodular type of pulmonary disease and experienced impaired pulmonary function. Other dusts and fumes may have been involved with these exposures [Hathaway et al. 1991]. A number of animal and epidemiologic studies have been performed on these compounds, but the International Agency for Research on Cancer (IARC) has concluded that there is insufficient data to evaluate their carcinogenic potential [Hathaway et al. 1991].

* Signs and symptoms of exposure

1. Acute exposure: No signs or symptoms of acute exposure to chromium (II) compounds have been reported in humans.

2. Chronic exposure: Chronic exposure to chromium (II) compounds may result in asthma and the resulting respiratory system effects.

EMERGENCY MEDICAL PROCEDURES

* Emergency medical procedures: [NIOSH to supply]

5. Rescue: Remove an incapacitated worker from further exposure and implement appropriate emergency procedures (e.g., those listed on the Material Safety Data Sheet required by OSHA's Hazard Communication Standard [29 CFR 1910.1200]). All workers should be familiar with emergency procedures, the location and proper use of emergency equipment, and methods of protecting themselves during rescue operations.

EXPOSURE SOURCES AND CONTROL METHODS

The following operations may involve chromium (II) compounds and lead to worker exposures to these substances:

* The manufacture and transportation of chromium (II) compounds

* Use as catalysts, magnetic components in recording tapes, electroplating chemicals, astringents, antiseptics, fungicides, and wood preservatives [NLM 1995]

* Use in ceramics, pigment manufacture, in leather tanning, in the photographic industry, and in mordants [NLM 1995]

Methods that are effective in controlling worker exposures to chromium (II) compounds, depending on the feasibility of implementation, are as follows:

* Process enclosure
* Local exhaust ventilation
* General dilution ventilation
* Personal protective equipment

Workers responding to a release or potential release of a hazardous substance must be protected as required by paragraph (q) of OSHA's Hazardous Waste Operations and Emergency Response Standard [29 CFR 1910.120].

Good sources of information about control methods are as follows:

1. ACGIH [1992]. Industrial ventilation--a manual of recommended practice. 21st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

2. Burton DJ [1986]. Industrial ventilation--a self study companion. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

3. Alden JL, Kane JM [1982]. Design of industrial ventilation systems. New York, NY: Industrial Press, Inc.

4. Wadden RA, Scheff PA [1987]. Engineering design for control of workplace hazards. New York, NY: McGraw-Hill.

5. Plog BA [1988]. Fundamentals of industrial hygiene. Chicago, IL: National Safety Council.

MEDICAL SURVEILLANCE

OSHA is currently developing requirements for medical surveillance. When these requirements are promulgated, readers should refer to them for additional information and to determine whether employers whose employees are exposed to chromium (II) compounds are required to implement medical surveillance procedures.

* Medical Screening

Workers who may be exposed to chemical hazards should be monitored in a systematic program of medical surveillance that is intended to prevent occupational injury and disease. The program should include education of employers and workers about work-related hazards, early detection of adverse health effects, and referral of workers for diagnosis and treatment. The occurrence of disease or other work-related adverse health effects should prompt immediate evaluation of primary preventive measures (e.g., industrial hygiene monitoring, engineering controls, and personal protective equipment). A medical surveillance program is intended to supplement, not replace, such measures. To detect and control work-related health effects, medical evaluations should be performed (1) before job placement, (2) periodically during the term of employment, and (3) at the time of job transfer or termination.

* Preplacement medical evaluation

Before a worker is placed in a job with a potential for exposure to chromium (II) compounds, a licensed health care professional should evaluate and document the worker's baseline health status with thorough medical, environmental, and occupational histories, a physical examination, and physiologic and laboratory tests appropriate for the anticipated occupational risks. These should concentrate on the function and integrity of the respiratory system. Medical surveillance for respiratory disease should be conducted using the principles and methods recommended by the American Thoracic Society.

A preplacement medical evaluation is recommended to assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to chromium (II) compounds at or below the prescribed exposure limit. The health care professional should consider the probable frequency, intensity, and duration of exposure as well as the nature and degree of any applicable medical condition. Such conditions (which should not be regarded as absolute contraindications to job placement) include a history and other findings consistent with diseases of the respiratory system.

* Periodic medical evaluations

Occupational health interviews and physical examinations should be performed at regular intervals during the employment period, as mandated by any applicable Federal, State, or local standard. Where no standard exists and the hazard is minimal, evaluations should be conducted every 3 to 5 years or as frequently as recommended by an experienced occupational health physician. Additional examinations may be necessary if a worker develops symptoms attributable to chromium (II) compounds exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of chromium (II) compounds on the respiratory system. Current health status should be compared with the baseline health status of the individual worker or with expected values for a suitable reference population.

* Termination medical evaluations

The medical, environmental, and occupational history interviews, the physical examination, and selected physiologic or laboratory tests that were conducted at the time of placement should be repeated at the time of job transfer or termination to determine the worker's medical status at the end of his or her employment. Any changes in the worker's health status should be compared with those expected for a suitable reference population.

* Biological monitoring

Biological monitoring involves sampling and analyzing body tissues or fluids to provide an index of exposure to a toxic substance or metabolite. No biological monitoring test acceptable for routine use has yet been developed for chromium (II) compounds.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne chromium (II) compounds (as Cr) is made using a mixed cellulose ester filter (MCEF), 0.8 microns. Samples are collected at a maximum flow rate of 2 liters/minute until a minimum collection volume of 480 liters (maximum volume 960 liters) is reached. Analysis is conducted by flame atomic absorption spectroscopy (FAAS). This method (OSHA ID-121) is fully validated and is described in the OSHA Computerized Information System [OSHA 1994] and in NIOSH Method No. 7024 [NIOSH 1994]. OSHA has a second method (OSHA ID-125G) that relies on inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for analysis. This method is also fully validated.

PERSONAL HYGIENE PROCEDURES

If chromium (II) compounds contacts the skin, workers should immediately wash the affected areas with soap and water.

Clothing contaminated with chromium (II) compounds should be removed immediately, and provisions should be made for the safe removal of the chemical from the clothing. Persons laundering the clothes should be informed of the hazardous properties of chromium (II) compounds.

A worker who handles chromium (II) compounds should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, using toilet facilities, applying cosmetics, or taking medication.

Workers should not eat, drink, use tobacco products, apply cosmetics, or take medication in areas where chromium (II) compounds or a solution containing chromium (II) compounds is handled, processed, or stored.

STORAGE

Chromium (II) compounds should be stored in a cool, dry, well-ventilated area in tightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200]. Containers of chromium (II) compounds should be protected from physical damage and should be stored separately from incompatible chemicals.

SPILLS AND LEAKS

In the event of a spill or leak involving chromium (II) compounds, persons not wearing protective equipment and clothing should be restricted from contaminated areas until cleanup has been completed. The following steps should be undertaken following a spill or leak:

1. Do not touch the spilled material; stop the leak if it is possible to do so without risk.

2. Notify safety personnel.

3. For small dry spills, use a clean shovel and place the material into a clean, dry container; cover and remove the container from the spill area.

4. For small liquid spills, take up with sand or other noncombustible absorbent material and place into closed containers for later disposal.

5. For large liquid spills, build dikes far ahead of the spill to contain the chromium (II) compounds for later reclamation or disposal.

SPECIAL REQUIREMENTS

U.S. Environmental Protection Agency (EPA) requirements for emergency planning, reportable quantities of hazardous releases, community right-to-know, and hazardous waste management may change over time. Users are therefore advised to determine periodically whether new information is available. The EPA requirements may differ for specific chromium (II) compounds, therefore, for illustrative purposes an example compound (chromium (II) chloride) is used in the following section.

* Emergency planning requirements

Chromium (II) chloride is not subject to EPA emergency planning requirements under the Superfund Amendments and Reauthorization Act (SARA) (Title III) in 42 USC 11022.

* Reportable quantity requirements for hazardous releases

A hazardous substance release is defined by EPA as any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of contaminated containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required to notify the proper Federal, State, and local authorities [40 CFR 355.40].

The reportable quantity of chromium (II) chloride is 1,000 pounds. If an amount equal to or greater than this quantity is released within a 24-hour period in a manner that will expose persons outside the facility, employers are required to do the following:

- Notify the National Response Center immediately at (800) 424-8802 or at (202) 426-2675 in Washington, D.C. [40 CFR 302.6].

* Community right-to-know requirements

Employers are not required by EPA in 40 CFR Part 372.30 to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of chromium (II) chloride emitted or released from their facility annually.

* Hazardous waste management requirements

EPA considers a waste to be hazardous if it exhibits any of the following characteristics: ignitability, corrosivity, reactivity, or toxicity as defined in 40 CFR 261.21-261.24. Under the Resource Conservation and Recovery Act (RCRA) [40 USC 6901 et seq.], EPA has specifically listed many chemical wastes as hazardous. Although chromium (II) chloride is not specifically listed as a hazardous waste under RCRA, EPA requires employers to treat waste as hazardous if it exhibits any of the characteristics discussed above.

Providing detailed information about the removal and disposal of specific chemicals is beyond the scope of this guideline. The U.S. Department of Transportation, EPA, and State and local regulations should be followed to ensure that removal, transport, and disposal of this substance are conducted in accordance with existing regulations. To be certain that chemical waste disposal meets EPA regulatory requirements, employers should address any questions to the RCRA hotline at (703) 412-9810 (in the Washington, D.C. area) or toll-free at (800) 424-9346 (outside Washington, D.C.). In addition, relevant State and local authorities should be contacted for information on any requirements they may have for the waste removal and disposal of this substance.

RESPIRATORY PROTECTION

* Conditions for respirator use

Good industrial hygiene practice requires that engineering controls be used where feasible to reduce workplace concentrations of hazardous materials to the prescribed exposure limit. However, some situations may require the use of respirators to control exposure. Respirators must be worn if the ambient concentration of chromium (II) compounds exceeds prescribed exposure limits. Respirators may be used (1) before engineering controls have been installed, (2) during work operations such as maintenance or repair activities that involve unknown exposures, (3) during operations that require entry into tanks or closed vessels, and (4) during emergencies. Workers should only use respirators that have been approved by NIOSH and the Mine Safety and Health Administration (MSHA).

* Respiratory protection program

Employers should institute a complete respiratory protection program that, at a minimum, complies with the requirements of OSHA's Respiratory Protection Standard [29 CFR 1910.134]. Such a program must include respirator selection, an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, respirator fit testing, periodic workplace monitoring, and regular respirator maintenance, inspection, and cleaning. The implementation of an adequate respiratory protection program (including selection of the correct respirator) requires that a knowledgeable person be in charge of the program and that the program be evaluated regularly. For additional information on the selection and use of respirators and on the medical screening of respirator users, consult the latest edition of the NIOSH Respirator Decision Logic [NIOSH 1987b] and the NIOSH Guide to Industrial Respiratory Protection [NIOSH 1987a].

PERSONAL PROTECTIVE EQUIPMENT

Workers should use appropriate personal protective clothing and equipment that must be carefully selected, used, and maintained to be effective in preventing skin contact with chromium (II) compounds. The selection of the appropriate personal protective equipment (PPE) (e.g., gloves, sleeves, encapsulating suits) should be based on the extent of the worker's potential exposure to chromium (II) compounds. There are no published reports on the resistance of various materials to permeation by chromium (II) compounds.

To evaluate the use of PPE materials with chromium (II) compounds, users should consult the best available performance data and manufacturers' recommendations. Significant differences have been demonstrated in the chemical resistance of generically similar PPE materials (e.g., butyl) produced by different manufacturers. In addition, the chemical resistance of a mixture may be significantly different from that of any of its neat components.

Any chemical-resistant clothing that is used should be periodically evaluated to determine its effectiveness in preventing dermal contact. Safety showers and eye wash stations should be located close to operations that involve chromium (II) compounds.

Splash-proof chemical safety goggles or face shields (20 to 30 cm long, minimum) should be worn during any operation in which a solvent, caustic, or other toxic substance may be splashed into the eyes.

In addition to the possible need for wearing protective outer apparel (e.g., aprons, encapsulating suits), workers should wear work uniforms, coveralls, or similar full-body coverings that are laundered each day. Employers should provide lockers or other closed areas to store work and street clothing separately. Employers should collect work clothing at the end of each work shift and provide for its laundering. Laundry personnel should be informed about the potential hazards of handling contaminated clothing and instructed about measures to minimize their health risk.

Protective clothing should be kept free of oil and grease and should be inspected and maintained regularly to preserve its effectiveness.

Protective clothing may interfere with the body's heat dissipation, especially during hot weather or during work in hot or poorly ventilated work environments.

REFERENCES

ACGIH [1991]. Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ATS [1987]. Standardization of spirometry -- 1987 update. American Thoracic Society. Am Rev Respir Dis 136:1285-1296.

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

Hathaway GJ, Proctor NH, Hughes JP, and Fischman ML [1991]. Proctor and Hughes' chemical hazards of the workplace. 3rd ed. New York, NY: Van Nostrand Reinhold.

Lewis RJ, ed. [1993]. Hawley's condensed chemical dictionary. 12th ed. New York, NY: Van Nostrand Reinhold Company.

Lide DR [1993]. CRC handbook of chemistry and physics. 73rd ed. Boca Raton, FL: CRC Press, Inc.

Mickelsen RL, Hall RC [1987]. A breakthrough time comparison of nitrile and neoprene glove materials produced by different glove manufacturers. Am Ind Hyg Assoc J 48(11): 941-947.

Mickelsen RL, Hall RC, Chern RT, Myers JR [1991]. Evaluation of a simple weight-loss method for determining the permeation of organic liquids through rubber films. Am Ind Hyg Assoc J 52(10): 445-447.

NIOSH [1987a]. NIOSH guide to industrial respiratory protection. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-116.

NIOSH [1987b]. NIOSH respirator decision logic. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-108.

NIOSH [1992]. Recommendations for occupational safety and health: Compendium of policy documents and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92-100.

NIOSH [1994]. NIOSH manual of analytical methods. 4th ed. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-113.

NIOSH [1995]. Registry of toxic effects of chemical substances: Chromium (II) chloride, chromium (II) dioxide. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Technical Information Branch.

NLM [1995]. Hazardous substances data bank: Chromium (II) chloride, chromium (II) dioxide, chromium (II) oxalate. Bethesda, MD: National Library of Medicine.

OSHA [1994]. Computerized information system. Washington, DC: U.S. Department of Labor, Occupational Safety and Health Administration.

Sax NI, Lewis RJ [1989]. Dangerous properties of industrial materials. 7th ed. New York, NY: Van Nostrand Reinhold Company.

USC. United States code. Washington. DC: U.S. Government Printing Office.

Windholz M, ed. [1983]. Merck Index 10th ed. Rahway, NJ: Merck & Company.