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    IPCS INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
    Health and Safety Guide No. 101

    HYDROQUINONE
    HEALTH AND SAFETY GUIDE






    UNITED NATIONS ENVIRONMENT PROGRAMME

    INTERNATIONAL LABOUR ORGANISATION

    WORLD HEALTH ORGANIZATION




    WORLD HEALTH ORGANIZATION, GENEVA 1996

    This is a companion volume to Environmental Health Criteria 157:
    Hydroquinone

    Published by the World Health Organization for the International
    Programme on Chemical Safety (a collaborative programme of the United
    Nations Environment Programme, the International Labour Organisation,
    and the World Health Organization)

    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization

    WHO Library Cataloguing in Publication Data

    Health and safety guide for hydroquinone

         (Health and safety guide ; no. 101)

         1.Hydroquinones - adverse effects  2.Dermatologic agents
         3.Environmental exposure  4.  I.Series

         ISBN 92 4 151101 X          (NLM Classification: QD 341.P5)
         ISSN 0259-7268

    The World Health Organization welcomes requests for permission to
    reproduce or translate its publications, in part or in full. 
    Applications and enquiries should be addressed to the Office of
    Publications, World Health Organization, Geneva, Switzerland, which
    will be glad to provide the latest information on any changes made to
    the text, plans for new editions, and reprints and translations
    already available.

    (c) World Health Organization 1996

    Publications of the World Health Organization enjoy copyright
    protection in accordance with the provisions of Protocol 2 of the
    Universal Copyright Convention.  All rights reserved.

    The designations employed and the presentation of the material in this
    publication do not imply the expression of any opinion whatsoever on
    the part of the Secretariat of the World Health Organization
    concerning the legal status of any country, territory, city or area or
    of its authorities, or concerning the delimitation of its frontiers or
    boundaries.

    The mention of specific companies or of certain manufacturers'
    products does not imply that they are endorsed or recommended by the
    World Health Organization in preference to others of a similar nature
    that are not mentioned.  Errors and omissions excepted, the names of
    proprietary products are distinguished by initial capital letters.

    CONTENTS

    INTRODUCTION

    1. PRODUCT IDENTITY AND USES

         1.1. Identity
         1.2. Physical and chemical properties
         1.3. Analytical methods
         1.4. Production and uses

    2. SUMMARY AND EVALUATION

         2.1. Environmental transport, distribution, and
               transformation
         2.2. Environmental levels and human exposure
         2.3. Kinetics and metabolism
         2.4. Effects on laboratory mammals and  in vitro test systems
         2.5. Effects on humans
         2.6. Effects on other organisms in the laboratory and field

    3. CONCLUSIONS AND RECOMMENDATIONS

         3.1. Conclusions
         3.2. Recommendations

    4. HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY
         ACTION

         4.1. Human health hazards, prevention and protection, first
               aid
               4.1.1. Advice to physicians
               4.1.2. Health surveillance advice
         4.2. Explosion and fire hazards
               4.2.1. Explosion hazards
               4.2.2. Fire hazards
         4.3. Storage
         4.4. Transport
         4.5. Spillage
         4.6. Disposal

    5. HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION

    6. SUMMARY OF CHEMICAL SAFETY INFORMATION

    7. CURRENT REGULATIONS, GUIDELINES, AND STANDARDS

         7.1. Previous evaluations by international bodies
         7.2. Exposure limit values
         7.3. Specific restrictions
         7.4. Labelling, packaging, and transport

    BIBLIOGRAPHY
    

    INTRODUCTION

    The Environmental Health Criteria (EHC) monographs produced by the
    International Programme on Chemical Safety include an assessment of
    the effects on the environment and on human health of exposure to a
    chemical or combination of chemicals, or physical or biological
    agents. They also provide guidelines for setting exposure limits.

    The purpose of a Health and Safety Guide is to facilitate the
    application of these guidelines in national chemical safety
    programmes. The first three sections of a Health and Safety Guide
    highlight the relevant technical information in the corresponding EHC.
    Section 4 includes advice on preventive and protective measures and
    emergency action; health workers should be thoroughly familiar with
    the medical information to ensure that they can act efficiently in an
    emergency. Within the Guide is a Summary of Chemical Safety
    Information which should be readily available, and should be clearly
    explained, to all who could come into contact with the chemical. The
    section on regulatory information has been extracted from the legal
    file of the International Register of Potentially Toxic Chemicals
    (IRPTC) and from other United Nations sources.

    The target readership includes occupational health services, those in
    ministries, governmental agencies, industry, and trade unions who are
    involved in the safe use of chemicals and the avoidance of
    environmental health hazards, and those wanting more information on
    this topic. An attempt has been made to use only terms that will be
    familiar to the intended user. However, sections 1 and 2 inevitably
    contain some technical terms. A bibliography has been included for
    readers who require further background information.

    Revision of the information in this Guide will take place in due
    course, and the eventual aim is to use standardized terminology.
    Comments on any difficulties encountered in using the Guide would be
    very helpful and should be addressed to:

    The Director
    International Programme on Chemical Safety
    World Health Organization
    1211 Geneva 27
    Switzerland

    THE INFORMATION IN THIS GUIDE SHOULD BE CONSIDERED AS A STARTING POINT
    TO A COMPREHENSIVE HEALTH AND SAFETY PROGRAMME

    1.  PRODUCT IDENTITY AND USES

    1.1  Identity

    Common name:             hydroquinone

    Molecular formula:       C6H4(OH)2

    Chemical structure:

                             CHEMICAL STRUCTURE 1

    CAS chemical name:       1,4-benzenediol

    Trade names:             Black and White Bleaching Cream, Diak S,
                             Eldopoque, Eldoquin, Tecquinol, Tenox HQ

    Synonyms:                1,4-benzenediol;  p-benzenediol;
                             benzohydroquinone; benzoquinol;
                             1,4-dihydroxybenzene;  p-dihydroxybenzene;
                              p-dioxobenzene;  p-dioxybenzene; 
                             hydroquinol; hydroquinole;
                             alpha-hydroquinone;  p-hydroquinone;
                              p-hydroxyphenol; quinol; -quinol

    CAS registry
    number:                  123-31-9

    RTECS register
    number:                  MX 3500000

    1.2  Physical and Chemical Properties

    Hydroquinone is a white crystalline substance when pure and is highly
    soluble in water. Hydroquinone is combustible when preheated. It is a
    reducing agent that is reversibly oxidized to semiquinone and quinone.

    Other properties of hydroquinone are given in Table 1.

    Conversion factors (at 25C and normal atmospheric pressure)

         1 ppm = 4.5 mg/m3

         1 mg/m3 = 0.222 ppm

    Table 1.  Properties of hydroquinone
                                                                        

    Physical state                long needles

    Colour                        white (analytical grade)

    Odour                         odourless

    Melting point                 173-174C

    Boiling point                 287C

    Flash point                   165C (closed cup)

    Autoignition temperature      515C

    Flammability                  combustible when preheated

    Explosion limits              slight when exposed to heat; reactive at
                                    high temperature or pressure

    Vapour pressure               2.410-3 Pa (1.810-5 mmHg) at 25C

    Specific gravity              1.3 at 15C

    Vapour density                3.81

    Log  n-octanol/water
      partition coefficient       0.59

    Solubility in water (25C)    70 g/litre

    Solubility in organic
      solvents (w/w at 25C)

        ethyl alcohol             57%
        acetone                   20%
        methyl isobutyl ketone    27%
        2-ethylhexanol            12%
        ethyl acetate             22%
                                                                        

    1.3  Analytical Methods

    Hydroquinone in the air is sampled either by trapping in solvent or on
    a mixed-cellulose-ester membrane filter.

    Analysis of hydroquinone is carried out by titrimetric, colorimetric,
    spectrophotometric, or, most commonly, chromatographic techniques.

    1.4  Production and Uses

    Hydroquinone is produced industrially in several countries. In 1979,
    the total world capacity for production exceeded 40 000 tonnes, while
    in 1992 it was approximately 35 000 tonnes. Hydroquinone is
    extensively used as a reducing agent, as a photographic developer, as
    an antioxidant for many oxidizable products, as a stabilizer or
    polymerizing inhibitor for certain materials that polymerize in the
    presence of free radicals, and as a chemical intermediate for the
    production of antioxidants, antiozonants, agro-chemicals, and
    polymers. It is a skin-lightening agent and is used in cosmetics, hair
    dyes, and medical preparations.

    2.  SUMMARY AND EVALUATION

    2.1  Environmental Transport, Distribution, and Transformation

    Hydroquinone occurs in the environment as a result of man-made
    processes, as well as in natural products from plants and animals.

    Because of its physical and chemical properties, hydroquinone will be
    distributed mainly to the water compartment when released into the
    environment. It degrades as a result of both photochemical and
    biological processes; consequently, it does not persist in the
    environment. Bioaccumulation has not been observed.

    2.2  Environmental Levels and Human Exposure

    No data on hydroquinone concentrations in air, soil, or water have
    been found. However, hydroquinone has been measured in mainstream
    smoke from non-filter cigarettes in amounts varying from 110 to 300 g
    per cigarette, and also in sidestream smoke. Hydroquinone has been
    found in plant-derived food products (e.g., wheat germ), in brewed
    coffee, and in teas prepared from the leaves of some berries, where
    the concentration sometimes exceeds 1%.

    Amateur photographers can be exposed to hydroquinone dermally or by
    inhalation. However, data on exposure levels are not available. Dermal
    exposure may also result from the use of cosmetic and medical products
    containing hydroquinone, such as skin lighteners. The European
    Economic Community (EEC) countries have restricted its use in
    cosmetics to 2% or less. In the USA, the Food and Drug Administration
    has proposed concentrations between 1.5 and 2% in skin lighteners.
    Concentrations up to 4% may be found in prescription drugs. In some
    countries, even higher concentrations may be found in skin lighteners.

    Few industrial hygiene monitoring data are available for hydroquinone.
    Average concentrations in air during the manufacturing and processing
    of hydroquinone have been reported to be in the range of 0.13 to
    0.79 mg/m3.  Occupational air exposure limits (time-weighted
    average) in different countries range from 0.5 to 2 mg/m3

    2.3  Kinetics and Metabolism

    Hydroquinone is rapidly and extensively absorbed from the gut and
    trachea of animals. Absorption via the skin is slower but may be more
    rapid with vehicles such as alcohols. Hydroquinone distributes rapidly
    and widely among tissues. It is metabolized to  p-benzoquinone and
    other oxidized products, and is detoxified by conjugation to
    monoglucuronide, monosulfate, and mercapturic derivatives. The
    excretion of hydroquinone and its metabolites is rapid, and occurs
    primarily via the urine.

    Hydroquinone and its derivatives react with different biological
    components, such as macromolecules and low relative molecular mass
    molecules, and have effects on cellular metabolism.

    2.4  Effects on Laboratory Mammals and In Vitro Test Systems

    Oral LD50 values for several animal species range between 300 and
    1300 mg/kg body weight. However, LD50 values for the cat range from
    42 to 86 mg/kg body weight. Acute high-level exposure to hydroquinone
    causes severe effects on the central nervous system (CNS) including
    hyperexcitability, tremor, convulsions, coma, and death. At sublethal
    doses, these effects are reversible. The dermal LD50 value has been
    estimated to be > 3800 mg/kg in rodents. Inhalation LC50 values are
    not available.

    A formulation containing 2% hydroquinone in a single-insult patch test
    on rabbits resulted in an irritation score of 1.22 (on a scale of 0
    to 4). Daily topical applications for three weeks of 2 or 5%
    hydroquinone in an oil-water emulsion on the depilated skin of black
    guinea-pigs caused depigmentation, inflammatory changes, and
    thickening of the epidermis. The depigmentation was more marked at
    higher concentrations, and female guinea-pigs were more sensitive than
    males.

    Sensitization tests on guinea-pigs have shown weak to strong
    reactions, depending on the methods or vehicles used. The strongest
    reactions were obtained with the guinea-pig maximization test. A
    cross-sensitization of almost 100% between hydroquinone and
     p-methoxyphenol was also seen in guinea-pigs, but only restricted
    evidence of cross-reactions to  p-phenylenediamine, sulfanilic acid
    and  p-benzoquinone was obtained.

    A 6-week, oral toxicity study on male F-344 rats resulted in
    nephropathy and renal cell proliferation. Thirteen-week oral gavage
    studies on F-344 rats and B6C3F1 mice resulted in nephrotoxicity in
    rats at 100 and 200 mg/kg, and tremors and convulsions in rats at
    200 mg/kg; reduced body weight gain was seen in both rats and mice.
    Dosing at 400 mg/kg was lethal in rats. In mice dosed for 13 weeks at
    400 mg/kg, tremors, convulsions, and lesions in the gastric epithelium
    were reported. Thirteen-week hydroquinone exposure of Sprague-Dawley
    rats resulted in decreased body weight gain and CNS signs at
    200 mg/kg. CNS signs were also observed at a dose level of 64 mg/kg
    body weight, but not at 20 mg/kg.

    Hydroquinone injected subcutaneously reduced fertility in male rats,
    and prolonged the estrus cycle in female rats. However, the effects on
    male rats were not found in oral studies (a dominant lethality study
    and a two-generation study). In a developmental study in rats, oral
    doses of 300 mg/kg body weight caused slight maternal toxicity and
    reduced fetal body weight. In rabbits, the no-observed-effect level
    (NOEL) for maternal toxicity was 25 mg/kg per day, and it was 75 mg/kg

    per day for developmental toxicity. In a two-generation reproduction
    study on rats, hydroquinone caused no reproductive effects at oral
    doses of up to 150 mg/kg body weight per day. The no-observed-adverse-
    effect level (NOAEL) for parental toxicity was determined to be
    15 mg/kg per day; for reproductive effects through two generations, it
    was 150 mg/kg per day.

    Hydroquinone induces micronuclei  in vivo and  in vitro. Structural
    and numerical chromosome aberrations have been observed  in vitro and
    after intraperitoneal administration  in vivo. Furthermore, the
    induction of gene mutations, sister-chromatid exchange, and DNA damage
    has been demonstrated  in vitro. Intraperitoneal injection of
    hydroquinone caused chromosomal aberrations in male mouse germ cells
    of the same order of magnitude as in mouse bone marrow cells.
    Induction of germ-cell mutations could not be established in a
    dominant lethal test on male rats dosed orally.

    In a two-year study, oral administration of hydroquinone caused a
    dose-related incidence of renal tubular cell adenomas in male F-344/N
    rats. The incidence was statistically significant in the high-dose
    group. In high-dose males, renal tubular cell hyperplasia was also
    found. In female rats, a dose-related increased incidence of
    mononuclear cell leukaemia occurred. Female B6C3F1 mice developed a
    significantly increased incidence of hepatocellular adenomas. In
    another study, hydroquinone (at a dietary level of 0.8%) produced a
    significantly increased incidence of epithelial hyperplasia of the
    renal papilla and a significant increase in renal tubular hyperplasia
    and adenomas in male rats. No increased incidence of mononuclear cell
    leukaemia was observed in female rats. In mice, the incidence of
    squamous cell hyperplasia of the forestomach epithelium was
    significantly increased in both sexes. In male mice, there was a
    significantly increased incidence of hepatocellular adenomas and also
    of renal tubular hyperplasia. A few renal cell adenomas were observed.

     In vivo (intraperitoneal injection) and  in vitro studies on mice
    demonstrated that hydroquinone has a cytotoxic effect by reducing the
    bone marrow and spleen cellularity and also an immunosuppressive
    potential by inhibiting the maturation of B-lymphocytes and the
    natural killer cell activity. Results also indicate that bone marrow
    macrophages may be the primary target for hydroquinone myelotoxicity.
    Myelotoxic effects were not observed in a long-term bioassay on
    rodents.

    In a 90-day study on rats using a functional-observational battery,
    dose levels of 64 and 200 mg hydroquinone/kg produced tremors, and a
    level of 200 mg/kg produced a depression in general activity. The
    results of neuropathological examinations were negative.

    2.5  Effects on Humans

    Cases of intoxication have been reported after oral ingestion of
    hydroquinone alone or of photographic developing agents containing
    hydroquinone. The major signs of poisoning included dark urine,
    vomiting, abdominal pain, tachycardia, tremors, convulsions, and coma.
    Deaths have been reported after ingestion of photographic developing
    agents containing hydroquinone. In a controlled oral study on human
    volunteers, ingestion of 300-500 mg hydroquinone daily for 3-5 months
    did not produce any observable pathological changes in the blood and
    urine.

    Dermal applications of hydroquinone at concentrations in different
    bases of less than 3% caused negligible effects in male volunteers
    from different human races. However, there are case reports suggesting
    that skin lightening creams containing 2% hydroquinone have produced
    leukoderma, as well as ochronosis. Hydroquinone (1% aqueous solution
    or 5% cream) has caused irritation (erythema or staining). Allergic
    contact dermatitis due to hydroquinone has been diagnosed.

    Combined exposure to airborne concentrations of hydroquinone and
    quinone causes eye irritation, sensitivity to light, injury of the
    corneal epithelium, corneal ulcers, and visual disturbances. There
    have been cases of appreciable loss of vision. Irritation has occurred
    at exposure levels of 2.25 mg/m3 or more. Long-term exposure causes
    staining of the conjunctiva and cornea, and also opacity. Slowly
    developing inflammation and discoloration of the cornea and
    conjunctiva have resulted after daily hydroquinone exposure, for at
    least two years, to levels of 0.05-14.4 mg/m3; serious cases have
    not occurred until after five or more years. One report described
    cases of corneal damage occurring several years after the exposure to
    hydroquinone had stopped.

    There are no adequate epidemiological data to assess the
    carcinogenicity of hydroquinone in humans.

    2.6  Effects on Other Organisms in the Laboratory and Field

    The ecotoxicological behaviour of hydroquinone has to be related to
    its physical and chemical properties, which induce sensitivity to
    light, pH, and dissolved oxygen. Its ecotoxicity, which is generally
    high (e.g., < 1 mg/litre for aquatic organisms), varies from species
    to species.

    Algae, yeasts, fungi, and plants are less sensitive to hydroquinone
    than the other organisms generally used for toxicity testing. However,
    within the same taxonomic group, the sensitivity of different species
    to hydroquinone may vary by a factor of 1000.

    3.  CONCLUSIONS AND RECOMMENDATIONS

    3.1  Conclusions

    The general population may be exposed to hydroquinone through
    consuming plant-derived foods that contain this chemical as a natural
    component, through smoking (active or passive), or through using
    cosmetics and skin-lightening creams. Amateur photographers who
    develop film manually may be exposed through skin contact and
    inhalation.

    Ingestion of large quantities may produce vomiting, convulsions, and
    coma. Repeated skin contact can lead to depigmentation, allergic
    contact dermatitis, and sensitization. Long-term occupational exposure
    to airborne hydroquinone can result in eye irritation, sensitivity to
    light, and visual disturbance.

    Hydroquinone is highly toxic for most organisms in the environment,
    though the toxicity varies considerably from species to species.
    However, the substance is readily degraded and does not persist in the
    environment.

    3.2  Recommendations

    a) In view of the widespread inappropriate use of skin-lightening
    creams, it is recommended that over-the-counter sales of creams
    containing hydroquinone be restricted. Health education programmes
    should be developed to discourage the use of hydroquinone-containing
    creams for whole-body skin lightening.

    b) Sufficient time should be allowed for the degradation of
    hydroquinone in wastewater effluent before it reaches the recipient
    water.

    4.  HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY ACTION

    4.1  Human Health Hazards, Prevention and Protection, First Aid

    The human health effects associated with certain types of exposure to
    hydroquinone, together with preventive and protective measures and
    first-aid recommendations, are listed in the Summary of Chemical
    Safety Information (section 6).

    Repeated or prolonged contact with skin may cause dermatitis and skin
    sensitization. The substance may have effects on the eye and skin,
    resulting in discoloration of the conjunctiva and cornea, loss of
    vision, skin depigmentation, and discoloration of nails and hair.

    4.1.1  Advice to physicians

    At room temperature and in the presence of moisture, hydroquinone
    oxidizes to quinone, which causes much worse eye irritation than
    hydroquinone itself; there is a consequent risk of conjunctivitis and
    corneal erosion. Lung oedema symptoms usually develop several hours
    after severe inhalation exposure and are aggravated by physical
    exertion; rest and hospitalization are essential. As first aid,
    administration of corticosteroid spray should be considered.

    In cases of dermatitis due to hydroquinone, removal from exposure will
    quickly clear up the symptoms.

    4.1.2  Health surveillance advice

    Depending on the extent of exposure, regular medical check-ups are
    advisable. Careful examination of the eyes, including visual acuity
    and slit lamp examinations, should be carried out in pre-employment
    and periodic examinations. The skin should also be examined.

    4.2  Explosion and Fire Hazards

    4.2.1  Explosion hazards

    A hydroquinone dust cloud may explode if ignited in an enclosed area.
    It is important to prevent dispersion of dust and to use a closed
    system and dust explosion-proof electrical equipment and lighting.

    4.2.2  Fire hazards

    Hydroquinone is combustible when preheated, and forms toxic gases. It
    reacts with oxidizing agents, and a violent reaction occurs with
    sodium hydroxide.

    Solid hydroquinone should be handled in such a way that particles do
    not become airborne. In areas where it is used, there should be no
    open flames and no smoking. In the event of a fire, extinguishers

    containing dry chemical, alcohol-resistant foam, water, or carbon
    dioxide should be used. Water used to control fires should be
    contained, or diked, for subsequent disposal.

    4.3  Storage

    Hydroquinone should be stored in light-proof, tightly closed
    containers in a cool, dark place, away from heat and oxidizing agents.
    It should be labelled as corrosive.

    4.4  Transport

    Containers should be in good condition and labelled appropriately.
    Transporters should comply with national and international
    requirements regarding the transport of hazardous material.

    4.5  Spillage

    Rubber gloves and boots should be worn while clearing up the spillage.
    The spilled substance should be swept into metal or glass fibre
    containers and removed to a safe place. If available, a P2 respirator
    should also be worn. Any remaining hydroquinone should be flushed away
    with water, but it is important to prevent run-off entering water-
    courses.

    4.6  Disposal

    The recommendation of the International Register of Potentially Toxic
    Chemicals (IRPTC) Expert Consultation (May 1985) was:

         "Incineration (1000C, 2 seconds minimum), then scrub to remove
         harmful combustion products".

    The peer-review conclusions from this IRPTC Expert Consultation were:

         "Oxidation produces quinone. Small amounts only: dilute to
         100 mg/litre and discharge to sewer".

    5.  HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION

    Because of its physical and chemical properties, hydroquinone will be
    distributed mainly to the water compartment when released into the
    environment. It is, in general, highly toxic for organisms in the
    environment, though the sensitivity of different species within the
    same taxonomic group varies greatly. However, hydroquinone degrades as
    a result of both photochemical and biological processes; consequently,
    it does not persist in the environment. Bioaccumulation has not been
    observed.

    Contamination of the environment can be avoided by the use of suitable
    methods of storage, transport, handling, and waste disposal (see
    sections 4.3, 4.4, and 4.6). Sufficient time should be allowed for
    hydroquinone in wastewater effluent, e.g., from photographic
    processing, to degrade before it reaches the recipient water. In the
    case of spillage, the clean-up methods described in section 4.5 should
    be used.

    6.  SUMMARY OF CHEMICAL SAFETY INFORMATION

     This summary should be easily available to all health workers
     concerned with, and users of, hydroquinone. It should be displayed
     at, or near, entrances to areas where there is potential exposure to
     hydroquinone, and on processing equipment and containers. The
     summary should be translated into the appropriate language(s). All
     persons potentially exposed to the chemical should also have the
     instructions in the summary clearly explained.

     Space is available for insertion of the National Occupational
     Exposure Limit, the address and telephone number of the National
     Poison Control Centre, and local trade names.


        HYDROQUINONE

    1,4-benzenediol

    C6H4(OH)2
                                                                                                                                              
    PHYSICAL PROPERTIES                                                                  OTHER CHARACTERISTICS
                                                                                                                                              
    Relative molecular mass                      110.11                                  Light tan, light grey, or colourless crystals;
    Melting point (C)                           173-174                                 the vapour mixes readily with air;
    Boiling point (C)                           287                                     can enter the body by inhalation or ingestion or,
    Flash point (closed cup) (C)                165                                     to a a limited extent, through the skin;
    Autoignition temperature (C)                515                                     corrosive to the eyes, skin, and respiratory tract;
    Relative density (15C)                      1.332                                   prolonged exposure to fumes, dust, or vapour can
    Relative vapour density                      3.81                                    cause lung disorders
    Vapour pressure (Pa) (25C)                  2.4  10-3
    Solubility in water (g/litre, 25C)          70
    Log P  n-octanol/water                        0.59
                                                                                                                                              
    HAZARDS/SYMPTOMS                             PREVENTION AND PROTECTION               FIRST AID
                                                                                                                                              
    EYES: Corrosive; redness, pain,              Wear safety goggles or face             Rinse with plenty of water for at least
    blurred vision                               shield                                  15 min (remove contact lenses);
                                                                                         obtain medical attention immediately

    SKIN: Corrosive; redness, pain,              Avoid skin contact; wear                Remove contaminated clothing immediately;
    serious burns, allergic dermatitis,          protective clothing and gloves          wash skin with soap and plenty of water;
    sensitization                                                                        obtain medical attention

    INHALATION: Corrosive;                       Apply local exhaust or breathing        Remove victim to fresh air and place in half-
    coughing, breathing difficulties,            protection; avoid inhalation of         sitting position; obtain medical attention
    headache, dizziness, nausea,                 vapour, particularly when               immediately
    diarrhoea                                    liberated at high temperature
                                                                                                                                              

    HYDROQUINONE (cont'd)
                                                                                                                                              
    HAZARDS/SYMPTOMS                             PREVENTION AND PROTECTION               FIRST AID
                                                                                                                                              
    INGESTION: Corrosive; blue skin,             Do not eat, drink, chew, or smoke       Rinse mouth; give water to drink (ONLY IN
    confusion, dizziness, headache,              during work; keep out of reach of       CONSCIOUS PERSONS!); obtain medical
    vomiting, unconsciousness,                   children                                advice immediately
    haemolytic anaemia, liver effects

    ENVIRONMENT: Presents a risk                 Contamination of water and soil
    for aquatic and soil organisms               should be avoided by proper methods
                                                 of storage, transport, and waste
                                                 disposal
                                                                                                                                              
    SPILLAGE                                     STORAGE                                 FIRE AND EXPLOSION
                                                                                                                                              
    Wear rubber gloves and boots;                Store in a cool, dark place in          Solid hydroquinone is combustible and dust
    clean up spilled substance and place         light-proof, tightly-closed             explosions are possible; in case of fire, keep
    in metal or glass fibre containers;          containers                              containers cool with water spray; evacuate
    flush away any remainder with                                                        personnel to a safe area; use powder; water,
    water (additional individual                                                         alcohol-resistant foam, or carbon dioxide to
    protection: P2 respirator)                                                           extinguish fire
                                                                                                                                              
    WASTE DISPOSAL                               LABELLING
                                                                                                                                              
    Incinerate (1000C, 2 seconds                National occupational exposure limit:
    minimum) then scrub to remove
    harmful combustion products;                 United Nations No. 2662
    sufficient time should be allowed
    for hydroquinone in wastewater               Hazard Class 6.1
    effluent to degrade before reaching
    recipient water                              Packing Class III

                                                 National Poison Control Centre:

                                                 Local trade names:
                                                                                                                                              
        7.  CURRENT REGULATIONS, GUIDELINES, AND STANDARDS

    The information given in this section has been extracted from the
    International Register of Potentially Toxic Chemicals (IRPTC) legal
    file. A full reference to the original national document from which
    the information was extracted can be obtained from IRPTC. When no
    effective date appears in the IRPTC legal file, the year of the
    reference from which the data are taken is indicated by (r).

    The reader should be aware that regulatory decisions about chemicals,
    taken in a certain country, can only be fully understood in the
    framework of the legislation of that country. Furthermore, the
    regulations and guidelines of all countries are subject to change and
    should always be verified with appropriate regulatory authorities
    before application.

    7.1  Previous Evaluations by International Bodies

    In 1977, the International Agency for Research on Cancer (IARC)
    Working Group concluded that the available data on hydroquinone did
    not allow an evaluation of its carcinogenicity.

    Hydroquinone was evaluated by a Nordic Expert Group for Documentation
    of Occupational Exposure Limits in 1989. It was recommended that its
    genotoxic effects should be given attention and also its possible
    effects on the immune system, bone marrow, skin, and mucous membranes.

    7.2  Exposure Limit Values

    Some exposure limit values are given in the following table.

    7.3  Specific Restrictions

    In the European Economic Community countries, hydroquinone is
    restricted for use in cosmetics to 2% or less. The US Food and Drug
    Administration has issued a Notice of Proposed Rule-making for the use
    of hydroquinone as a skin lightener in over-the-counter drugs at
    concentrations below 1.5-2.0%.

    7.4  Labelling, Packaging, and Transport

    The United Nations Committee of Experts on the Transport of Dangerous
    Goods classifies hydroquinone as a toxic substance (Hazard Class 6.1),
    and, with regard to packing, as a substance presenting minor danger
    (Packing Group III).


        Exposure Limit Values
                                                                                                                               
    Medium    Specification    Country/               Exposure limit description                      Value          Effective
                               organization                                                                            date
                                                                                                                               

    AIR       Occupational     Argentina              Maximum permissible concentration (MPC)                          1991
                                                      - Time-weighted average (TWA)                   2 mg/m3

                               Canada                 Threshold limit value (TLV)                                      1990
                                                      - Time-weighted average (TWA)                   2 mg/m3

                               Germany                Maximum worksite concentration (MAK)                             1992(r)
                                                      - Time-weighted average (TWA)                   2 mg/m3
                                                      - Short-term exposure limit (STEL)              4 mg/m3
                                                        (5-min)

                               Russian                Maximum allowable concentration (MAC)                            1989
                                 Federation           - Ceiling value (aerosol)                       1 mg/m3

                               Sweden                 Hygienic limit value (HLV)                                       1991
                                                      - Time-weighted average (TWA)                   0.5 mg/m3
                                                      - Short-term exposure limit (STEL)              1.5 mg/m3
                                                        (15-min)

                               United Kingdom         Occupational exposure standard (OES)                             1992
                                                      - Time-weighted average (TWA)                   2 mg/m3
                                                      - Short-term exposure limit (STEL)              4 mg/m3
                                                        (10-min TWA)

                               USA (ACGIH)            - Threshold limit value (TLV)                                    1989
                                                      - Time-weighted average (TWA)                   2 mg/m3

                               USA (NIOSH)            Recommended exposure limit (REL)                                 1990(r)
                                                      - Ceiling value                                 2 mg/m3

                                                                                                                               

    Exposure Limit Values (cont'd)
                                                                                                                               
    Medium    Specification    Country/               Exposure limit description                      Value          Effective
                               organization                                                                            date
                                                                                                                               

    AIR       Occupational     USA (OSHA)             Permissible exposure limit (PEL)                                 1990(r)
                                                      - Time-weighted average (TWA)                   2 mg/m3

    AIR       Ambient          Russian                Preliminary safety level (PSL)                  0.02 mg/m3       1983
                                 Federation

    WATER     Surface          Russian                Maximum allowable concentration                                  1989
                                 Federation           (MAC)                                           0.2 mg/litre
                                                                                                                               
        European Economic Community legislation requires labelling as a
    harmful substance using the symbol Xn.

    FIGURE 1

    The following label statements are required:

         R 20/22        Harmful by inhalation and if swallowed

         S 2            Keep out of reach of children

         S 24/25        Avoid contact with skin and eyes

         S 39           Wear eye/face protection

    BIBLIOGRAPHY

    ACGIH (1986)  Documentation of the threshold limit values and
     biological exposure indices. Cincinnati, American Conference of
    Governmental Industrial Hygienists.

    ACGIH (1989)  Threshold limit values and biological exposure indices
     for 1989-1990. Cincinnati, American Conference of Governmental
    Industrial Hygienists.

    CEC/IPCS (1991)  International Chemical Safety Card 166: Hydroquinone.
    Luxembourg, Commission of the European Communities.

    CLAYTON, G.D. & CLAYTON, F.E. (1981)  Patty's industrial hygiene and
     toxicology. Vol. 2B. New York, John Wiley & Sons.

    DUTCH CHEMICAL INDUSTRY ASSOCIATION (1991)  Chemical safety sheets.
    Kluwer Academic Publishers, Samson Chemical Publishers, Dutch
    Institute for the Working Environment, Dutch Chemical Industry
    Association.

    GOSSELIN, R.E., HODGE, H.C., SMITH, R.P., & GLEASON, M.N. (1976)
     Clinical toxicology of commercial products. 4th ed. Baltimore,
    Maryland, The Williams and Wilkins Company.

    IPCS (1994)  Environmental Health Criteria 157: Hydroquinone. Geneva,
    World Health Organization.

    IRPTC (1992-1993)  Legal file. Geneva, International Register of
    Potentially Toxic Chemicals.

    SAX, N.I. (1984)  Dangerous properties of industrial materials. New
    York, Van Nostrand Reinhold Company.

    US NIOSH (1976)  A guide to industrial respiratory protection. 3 Vol.
    Cincinnati, Ohio, US National Institute for Occupational Safety and
    Health. Occupational Safety and Health Administration.

    US NIOSH/OSHA (1981)  Occupational health guidelines for chemical
     hazards. 3 Vol. Washington, DC, US Department of Health and Human
    Services, US Department of Labour (Publication No. DHHS (NIOSH)
    01-123).

    US NIOSH/OSHA (1985)  Pocket guide to chemical hazards. Washington
    DC, US National Institute for Occupational Safety and Health,
    Occupational Safety and Health Administration (Publication
    No. 85.114).
    


    See Also:
       Toxicological Abbreviations
       Hydroquinone (EHC 157, 1994)
       Hydroquinone (ICSC)
       Hydroquinone  (SIDS)
       Hydroquinone (IARC Summary & Evaluation, Volume 71, 1999)