Nitrobenzene

General information

Key Points Fire

Flammable Violently reacts with strong oxidants, acids and nitrogen oxides Emits toxic fumes of nitrogen oxides when heated to decomposition In the event of a fire involving nitrobenzene, use fine water and liquid tight chemical

protective clothing with breathing apparatus Health

Toxic by inhalation, ingestion and skin absorption Possibly carcinogenic in humans May cause reproductive toxicity The onset of symptoms may be delayed 1-4 hours after exposure to nitrobenzene Inhalation can cause irritation of the respiratory tract, nausea, headache, dizziness,

shortness of breath and in extreme cases could lead to coma and death Ingestion of nitrobenzene may cause gastrointestinal irritation with nausea, vomiting

and diarrhoea, as well as symptoms similar to those for inhalation Inhalation and ingestion may also cause vertigo and bluish colouration of the skin due

to a condition called methaemoglobinaemia, with drowsiness, high blood pressure, convulsions, anaemia, jaundice and kidney failure

Skin contact with nitrobenzene may result in mild skin irritation and eye contact may lead to mild eye irritation

Environment

Dangerous for the environment Inform Environment Agency of substantial incidents

Prepared by J C Wakefield CHAPD HQ, HPA

2008 Version 1

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Background

Nitrobenzene is a colourless or yellow oily liquid, with an odour of bitter almonds and is flammable following moderate heating. Nitrobenzene does not occur naturally and is therefore only produced synthetically for industrial applications. One of the major uses for nitrobenzene is for the production of aniline, which is a chemical intermediate used during the manufacture of polyurethane. Nitrobenzene is also used industrially in the manufacture of some pharmaceuticals, dyes and rubbers, as a constituent in some polishes and paint solvents and as a solvent in the refining of petroleum.

Exposure of the general public to nitrobenzene is extremely unlikely as it is not commonly used in the home in substantial quantities. The most common source of exposure to considerable amounts of nitrobenzene is in the workplace, either where it is produced, or during the production of other materials. Nitrobenzene is very toxic and irritant to humans who are exposed to it either by inhalation, ingestion or skin contact. Exposure to vapours or splashes of nitrobenzene will cause irritation of the skin, eyes and respiratory tract. The main effect of inhaling or ingesting nitrobenzene is a condition called methaemoglobinaemia, which affects the ability of the blood to carry oxygen. The effect of this includes headache, nausea, vomiting, weakness, dizziness, vertigo, bluish discolouration of the skin, rapid heart rate and breathlessness. These symptoms may be delayed for up 1 to 4 hours following exposure. In some cases,

nitrobenzene may cause jaundice (yellow discolouration of the skin), failure of the kidneys, coma and even death.

Contact of the skin or eyes with vapours or liquid nitrobenzene can cause irritation at the site of contact. Nitrobenzene can also be absorbed through the skin and contact with large quantities could result in adverse effects similar to those seen following inhalation or ingestion. Repeated exposure to nitrobenzene by any route may cause damage to the liver in addition to the effects resulting from a single exposure.

Children exposed to nitrobenzene are expected to show similar adverse health effects to those seen in exposed adults, although the effects are expected to be more severe, as children are particularly susceptible to the adverse effects of exposure to nitrobenzene. There is evidence to suggest that exposure to nitrobenzene during pregnancy, at concentrations that may harm the mother, may possibly cause adverse effects to the unborn child. Nitrobenzene has been classified as possibly having the ability to cause cancer in humans, by the International Agency for Research on Cancer.

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Production and Uses

Key Points

Nitrobenzene does not occur naturally in the environment It is produced industrially by reacting benzene with sulphuric acid, nitric acid and

water Nitrobenzene is used in the production of aniline, a chemical used to manufacture

polyurethane foams Nitrobenzene is also used to manufacture pharmaceuticals, rubbers, dyes, polishes

and paint solvents Nitrobenzene does not occur naturally in the environment. It is produced industrially by reacting benzene with sulphuric acid, nitric acid and water. One of the major uses for nitrobenzene is for the production of aniline, which is a chemical intermediate used during the manufacture of polyurethane foams. Nitrobenzene is also used industrially in the manufacture of some dyes, rubbers and pharmaceuticals (it is an important component in the production of paracetamol). Nitrobenzene is also used as a constituent in some polishes and paint solvents and as a solvent in the refining of petroleum. Historically nitrobenzene was used in perfumes and as a flavouring known as ‘artificial oil of bitter almonds’ due to its strong odour. This use of nitrobenzene has long been discontinued due to its toxicity.

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Frequently Asked Questions What is nitrobenzene? Nitrobenzene is a colourless or yellow oily liquid, with an odour of bitter almonds and is flammable following moderate heating. The main use of nitrobenzene is in the chemical synthesis of aniline, which is a chemical used in the manufacture of polyurethane foams. How does nitrobenzene get into the environment? Nitrobenzene does not occur naturally in the environment and as such is most likely to enter the environment from workplaces where it is manufactured or used. How will I be exposed to nitrobenzene? As nitrobenzene is only used industrially, it is unlikely that you will be exposed to significant amounts unless you work with it. Nitrobenzene will form a vapour at room temperature, and therefore anyone working with it is at risk of inhaling the vapours if adequate protective equipment is not used. People working with nitrobenzene are also at risk of getting splashes of it on their skin if they are not adequately protected. If there is nitrobenzene in the environment will I have any adverse health effects? The presence of nitrobenzene in the environment does not always lead to exposure. Clearly, in order for it to cause any adverse health effects you must come into contact with it. You may be exposed by breathing, eating, or drinking the substance or by skin contact. Following exposure to any chemical, the adverse health effects you may encounter depend on several factors, including the amount to which you are exposed (dose), the way you are exposed, the duration of exposure, the form of the chemical and if you were exposed to any other chemicals. Nitrobenzene is an irritant and exposure to vapours or splashes will cause irritation of the skin, eyes and respiratory tract. Nitrobenzene is toxic by inhalation, ingestion and skin contact. The main symptom of exposure to nitrobenzene is a condition called methaemoglobinaemia, which affects the ability of the blood to carry oxygen. This condition is associated with headache, nausea, vomiting, weakness, dizziness, vertigo, bluish discolouration of the skin, rapid heart rate and breathlessness. The symptoms may be delayed for up 1 to 4 hours following exposure. In some cases, nitrobenzene may cause jaundice (yellow discolouration of the skin), failure of the kidneys, coma and even death. Can nitrobenzene cause cancer? Nitrobenzene has been classified by the International Agency for Research on Cancer as possibly causing cancer in humans. Does nitrobenzene affect children or damage the unborn child? Children exposed to nitrobenzene are expected to show similar adverse health effects to those seen in exposed adults, although the effects are expected to be more severe, as children are particularly susceptible to the adverse effects of exposure to nitrobenzene. There is evidence to suggest that exposure to nitrobenzene during pregnancy, at concentrations that may harm the mother, may possibly cause adverse effects to the unborn child.

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What should I do if I am exposed to nitrobenzene? It is very unlikely that the general population will be exposed to a level of nitrobenzene high enough to cause adverse health effects. This document from the HPA Centre for Radiation, Chemical and Environmental Hazards reflects understanding and evaluation of the current scientific evidence as presented and referenced in this document.

Nitrobenzene

Incident management

Key Points Fire

Flammable Violently reacts with strong oxidants, acids and nitrogen oxides Emits toxic fumes of nitrogen oxides when heated to decomposition In the event of a fire involving nitrobenzene, use fine water and liquid tight chemical

protective clothing with breathing apparatus Health

Toxic by inhalation, ingestion and dermal absorption The onset of symptoms may be delayed 1-4 hours after exposure to nitrobenzene Inhalation can cause irritation of the respiratory tract, nausea, headache, dizziness,

shortness of breath and in extreme cases could lead to coma and death Ingestion of nitrobenzene may cause gastrointestinal irritation with nausea, vomiting

and diarrhoea, as well as symptoms similar to those for inhalation Inhalation and ingestion may also cause vertigo and cyanosis due to

methaemoglobinaemia with drowsiness, hypotension, convulsions, haemolytic anaemia, jaundice and renal failure

Dermal exposure to nitrobenzene may result in mild skin irritation and ocular exposure may lead to mild eye irritation

Environment

Dangerous for the environment Inform Environment Agency of substantial incidents

CRCE HQ, HPA

03/2012 Version 2

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Hazard Identification Standard (UK) Dangerous Goods Emergency Action Codes(a)

UN 1662 Nitrobenzene

EAC 2X

Use fine water spray. Wear liquid-tight chemical protective clothing in combination with breathing apparatus*. Spillages and decontamination run-off should be prevented from entering drains and watercourses.

APP -

Hazards Class 6.1 Toxic substance

Sub risks

-

HIN 60 Toxic or slightly toxic substance

UN – United Nations number; EAC – Emergency Action Code; APP – Additional Personal Protection; HIN - Hazard Identification Number * Liquid-tight chemical protective clothing (BS 8428) in combination with self-contained open circuit positive pressure compressed air breathing apparatus (BS EN 137).

a Dangerous Goods Emergency Action Code List 2011. National Chemical Emergency Centre (NCEC). The Stationary Office, London.

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Chemical Hazard Information and Packaging for Supply Classification(a)

Classification

Carc. cat 3 Category 3 carcinogen

Repr. Cat 3 Category 3 reproductive toxin

T Toxic

N Dangerous for the environment

Risk phrases

R23/24/25 Toxic by inhalation, in contact with skin and if swallowed

R40 Limited evidence of a carcinogenic effect

R48/23/24 Toxic: danger of serious damage to health by prolonged exposure through inhalation and in contact with skin

R51/53 Toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment

R62 Possible risk of impaired fertility

Safety phrases

S1/2 Keep locked up and out of the reach of children

S28 After contact with skin, wash immediately with plenty of ... (to be specified by the manufacturer)

S36/37 Wear suitable protective clothing and gloves

S45 In case of accident or if you feel unwell seek medical advice immediately (show the label where possible)

S61 Avoid release to the environment. Refer to special instructions/safety data sheet

a Annex VI to Regulation (EC) No 1272/2008 on Classification, Labelling and Packaging of Substances and Mixtures- Table 3.2. http://esis.jrc.ec.europa.eu/index.php?PGM=cla (accessed 03/2012)

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Globally Harmonised System of Classification and Labelling of Chemicals (GHS)(a)

Hazard Class and Category

Carc. 2 Carcinogenicity, category 2

Repr. 2 Toxic to reproduction, category 2

Acute Tox. 3 Acute toxicity (inhalation, dermal and oral), category 3

STOT RE 1 Specific target organ systemic toxicity following repeated exposure, category 1

Aquatic Chronic 2

Chronic hazard to the aquatic environment, category 2

Hazard Statement

H351 Suspected of causing cancer

H361f Suspected of damaging fertility

H331 Toxic if inhaled

H311 Toxic in contact with skin

H301 Toxic if swallowed

H372 Causes damage to organs through prolonged or repeated exposure

H411 Toxic to aquatic life with long lasting effects

Signal Words DANGER

Implemented in the EU on 20 January 2009.

a Annex VI to Regulation (EC) No 1272/2008 on Classification, Labelling and Packaging of Substances and Mixtures- Table 3.1. http://esis.jrc.ec.europa.eu/index.php?PGM=cla (accessed 03/2012)

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Physicochemical Properties

References(a,b,c)

a Nitrobenzene (HAZARDTEXT® Hazard Management). In: Klasco RK (Ed): TOMES® System, Thomson Micromedex, Greenwood Village, Colorado, USA. (electronic version). RightAnswer.com, Inc., Midland, MI, USA, Available at: http://www.rightanswerknowledge.com/data/dt/dt193.htm (accessed 01/2012). b The Merck Index (14th Edition). Entry 6588: Nitrobenzene, 2006. c The Dictionary of Substances and their Effects. Ed. S Gangolli. Second Edition, Volume 5, 1999.

CAS number 98-95-3

Molecular weight 123

Empirical formula C6H5NO2

Common synonyms Nitrobenzol

State at room temperature Liquid

Volatility Vapour pressure 0.3 mm Hg at 25°C

Specific gravity 1.2 at 20°C (water = 1)

Flammability Flammable, after moderate heating

Lower explosive limit 1.8%

Upper explosive limit 40.0%

Water solubility Low solubility in water, 1.8g L-1 at 25°C. Soluble in ethanol, acetone and benzene

Reactivity Reactive. Nitrobenzene reacts violently with strong oxidants, strong acids and nitrogen oxides, causing risk of fire and explosion

Reaction or degradation products

Releases toxic fumes of nitrogen oxides when heated to decomposition

Odour Bitter almonds

Structure

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Threshold Toxicity Values

EXPOSURE VIA INGESTION

g SIGNS AND SYMPTOMS REFERENCES

4.3 -11 Unconsciousness, cyanosis, circulatory collapse, rapid and shallow breathing and tachycardia

a

a International Programme on Chemical Safety, Environmental Health Criteria 230: Nitrobenzene, 2003.

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Published Emergency Response Guidelines Emergency Response Planning Guideline (ERPG) Values

Listed value

(ppm) Calculated value

(mg m-3) ERPG-1*

Data not available ERPG-2** ERPG-3***

* Maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hr without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odour. ** Maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hr without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action. *** Maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hr without experiencing or developing life-threatening health effects. Acute Exposure Guideline Levels (AEGLs) ppm 10 min 30 min 60 min 4 hr 8 hr AEGL-1†

Data not available AEGL-2†† AEGL-3††† † The level of the chemical in air at or above which the general population could experience notable discomfort. †† The level of the chemical in air at or above which there may be irreversible or other serious long-lasting effects or impaired ability to escape. ††† The level of the chemical in air at or above which the general population could experience life-threatening health effects or death.

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Exposure Standards, Guidelines or Regulations Occupational Standards

WEL(a)

http://www.hse.gov.uk/

LTEL (8 hour reference period): 0.2 ppm (1 mg m-3)

STEL(15 min reference period): No guideline value specified

Public Health Guidelines

DRINKING WATER QUALITY GUIDELINE

No guideline value specified

AIR QUALITY GUIDELINE No guideline value specified

SOIL GUIDELINE VALUE AND HEALTH CRITERIA VALUES

No guideline value specified

WEL – Workplace exposure limit; LTEL - Long-term exposure limit; STEL – Short-term exposure limit

a EH40/2005 Workplace Exposure Limits (second edition, published 2011). http://www.hse.gov.uk/pubns/priced/eh40.pdf (accessed 01/2012)

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Health Effects

Major Route of Exposure(a)

Toxic by inhalation, ingestion and dermal absorption Immediate signs or symptoms of acute exposure(a,b,c)

After ingestion, inhalation and skin exposure the onset of symptoms may be delayed 1-4 hours. Symptoms include headache, vertigo and cyanosis due to methaemoglobinaemia with drowsiness, shallow respiration, hypotension, convulsions, haemolytic anaemia, jaundice and renal failure.

Inhalation causes irritation of the respiratory tract. Exposure to large amounts of nitrobenzene can cause nausea, headache, dizziness, shortness of breath and in extreme cases coma and death

Ingestion causes gastrointestinal irritation with nausea, vomiting and diarrhoea. Ingestion of high levels of nitrobenzene can cause symptoms similar to those after inhalation

Dermal exposure can cause skin irritation Nitrobenzene can be irritating to the eyes causing an immediate stinging and burning

sensation with lacrimation

TOXBASE - http://www.toxbase.org (accessed 01/2012) a TOXBASE: Nitrobenzene, 2007. b TOXBASE: Nitrobenzene – features and management, 2007. c TOXBASE: Eye irritants, 2002.

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Decontamination and First Aid Important Notes

Ambulance staff, paramedics and emergency department staff treating chemically-contaminated casualties should be equipped with Department of Health approved, gas-tight (Respirex) decontamination suits based on EN466:1995, EN12941:1998 and prEN943-1:2001, where appropriate.

Decontamination should be performed using local protocols in designated areas such as a decontamination cubicle with adequate ventilation.

Dermal Exposure(a)

Remove patient from exposure. The patient should remove all clothing and personal effects. Double-bag soiled clothing and place in a sealed container clearly labelled as a

chemical hazard. Gently blot away any adherent liquid from the patient. Wash hair and all contaminated skin with copious amounts of water (preferably warm)

and soap for at least 10-15 minutes. Decontaminate open wounds first and avoid contamination of unexposed skin.

Pay special attention to skin folds, axillae, ears, fingernails, genital areas and feet. Ocular Exposure(b)

Remove patient from exposure. Remove contact lenses if present and immediately irrigate the affected eye

thoroughly with water or 0.9% saline for at least 10-15 minutes. Patients with corneal damage or those whose symptoms do not resolve rapidly

should be referred for urgent ophthalmological assessment. Inhalation(c)

Remove patient from exposure. Ensure a clear airway and adequate ventilation. Give oxygen to symptomatic patients. Apply other supportive measures as indicated by the patient’s clinical condition.

Ingestion(c)

Ensure a clear airway and adequate ventilation. Give oxygen to symptomatic patients. Apply other supportive measures as indicated by the patient’s clinical condition.

This document from the HPA Centre for Radiation, Chemical and Environmental Hazards reflects understanding and evaluation of the current scientific evidence as presented and referenced in this document.

TOXBASE - http://www.toxbase.org (accessed 01/2012) a TOXBASE: Nitrobenzene – features and management, 2007. b TOXBASE: Eye irritants, 2002. c TOXBASE: Nitrobenzene, 2007.

Nitrobenzene

Toxicological overview

Key Points

Kinetics and metabolism

Nitrobenzene is readily absorbed following inhalation, ingestion and dermal contact Dermal contact with nitrobenzene may give rise to systemic toxicity due to extensive

dermal absorption Nitrobenzene is slowly excreted in the urine and faeces either unchanged or as the

major metabolites p-aminophenol and p-nitrophenol Health effects of acute exposure

Acute exposure to nitrobenzene may cause methaemoglobinaemia, with symptoms including headache, nausea, dizziness, fatigue, shortness of breath, cyanosis and convulsions

The onset of methaemoglobinaemia may be delayed for 1 to 4 hours post exposure Severe acute exposure to nitrobenzene can cause jaundice, renal failure, coma and

may be fatal Dermal or ocular contact with nitrobenzene may cause mild irritation

Health effects of chronic exposure

Chronic exposure to nitrobenzene can cause methaemoglobinaemia similar to that seen following acute exposure

Chronic nitrobenzene exposure may give rise to headache, nausea, vertigo, confusion, hyperalgesia, haemolytic anaemia and toxic hepatitis

Nitrobenzene may cause adverse effects on male fertility due to testicular atrophy Nitrobenzene is considered to be a possible human carcinogen

Prepared by J C Wakefield CHAPD HQ, HPA

2008 Version 1

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Toxicological Overview

Summary of Health Effects Nitrobenzene is readily absorbed following inhalation, ingestion and dermal contact [1]. There is no human information available regarding oral ingestion of nitrobenzene, however, its absorption is expected to be extensive. Nitrobenzene can undergo extensive dermal absorption, therefore dermal contact with nitrobenzene may cause considerable systemic toxicity [1, 2]. The principal characteristic health effect following acute exposure to nitrobenzene is the development of methaemoglobinaemia, which can give rise to symptoms including headache, nausea, dizziness, drowsiness, shortness of breath, fatigue, cyanosis and convulsions [1, 3, 4]. The onset of methaemoglobinaemia may be delayed for 1 to 4 hours post exposure [4]. In some cases of acute nitrobenzene ingestion haemolytic anaemia may develop approximately 5 days post-exposure [1]. Serious acute exposure to nitrobenzene may result in jaundice, liver failure, renal failure, coma and can potentially be fatal [1-3, 5]. Dermal or ocular exposure to vapours or liquid splashes of nitrobenzene may cause mild irritation [4]. Long term occupational exposure to nitrobenzene is associated with similar adverse effects as those observed following a large single acute exposure, such as the development of methaemoglobinaemia [1, 3]. Some symptoms related to chronic nitrobenzene exposure may include headache, nausea, vertigo, confusion and hyperalgesia. Chronic exposure to nitrobenzene may also give rise to the development of haemolytic anaemia and toxic hepatitis [1, 5]. There is evidence from animal studies that nitrobenzene exposure may cause adverse effects on male fertility due to testicular atrophy [1, 3, 5]. Studies in female animals suggest that nitrobenzene does not cause embryotoxicity or teratogenicity at concentrations which do not cause significant maternal toxicity [1]. However, no studies were located regarding reproductive or developmental effects of nitrobenzene following chronic exposure in humans. The International Agency for Research on Cancer (IARC) have evaluated that there is insufficient evidence for the carcinogenicity of nitrobenzene in humans. However, there is sufficient evidence that nitrobenzene is carcinogenic in experimental animals. Therefore, based on the animal carcinogenicity data, nitrobenzene has been classified overall as possibly carcinogenic to humans (group 2B) [5].

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Kinetics and metabolism Nitrobenzene is readily absorbed following inhalation, ingestion and dermal contact [1]. Following a 6-hour inhalation exposure of human volunteers to nitrobenzene the pulmonary absorption was found to be extensive, with uptake in the range of 73-87%. No human studies have been located regarding oral exposure of humans to nitrobenzene, although based on the effects of accidental poisonings, oral absorption is expected to be rapid and extensive. Animal studies have shown significant absorption from the gastrointestinal tract following oral exposure to nitrobenzene [1, 3]. The dermal absorption of nitrobenzene has not been well studied, in either humans or experimental animals. However, there have been numerous incidences of human poisonings following dermal exposure to nitrobenzene, suggesting that dermal absorption is also of considerable importance [1, 2]. Studies involving oral administration of nitrobenzene to rabbits demonstrated distribution to the blood, liver, kidney and lung, and in rats, nitrobenzene was detected in all tissues, excluding stomach and intestines, particularly in kidney and intestinal fat and skeletal muscle. Following accidental nitrobenzene poisoning in humans, the highest concentration was found in the liver, brain, blood and stomach [1]. No studies were located regarding the distribution of nitrobenzene following inhalation or dermal exposure. There are few studies investigating the metabolism of nitrobenzene in humans. Guinea pigs administered nitrobenzene intraperitoneally showed the main metabolite was p-nitrophenol [1]. The main route of excretion of nitrobenzene is in the urine and to a lesser extent in the faeces. In rats administered nitrobenzene as a single oral dose, approximately 65% of the applied dose had been excreted in the urine and 15 % in the faeces by 5 days post-exposure either as metabolites or unchanged [1, 3]. In cases of human toxicity following either dermal or inhalation exposure to nitrobenzene, the major urinary metabolites identified were p-aminophenol and p-nitrophenol [3]. In a human volunteer study following the oral administration of 30 mg nitrobenzene the urinary excretion of p-nitrophenol was slow, with an initial elimination half-life of approximately 5 hours, followed by a secondary slow phase with an elimination half-life of over 20 hours [1]. The presence of p-aminophenol in urine has been used in biomonitoring studies as a marker of occupational exposure to nitrobenzene [1]. Following exposure to nitrobenzene vapours, any absorbed material was excreted in the urine as p-nitrophenol. Similarly, urinary excretion of p-nitrophenol was reported in individuals following inhalation of nitrobenzene [1].

Sources and route of human exposure The major source of exposure to nitrobenzene is from occupational exposure, since its principal use is in industrial processes, such as during the production of aniline [1, 3]. Nitrobenzene is unlikely to be present in significant quantities in domestic situations and does not occur naturally but can be formed at low levels by the reaction of benzene and nitrogen oxides in the atmosphere [1]. In the occupational context, in addition to controlling airborne levels to the occupational exposure standard it is also necessary to protect against skin absorption by the use of appropriate protective clothing [1, 2]. The major routes of occupational exposure to nitrobenzene are by inhalation of vapours or dermal absorption. Nitrobenzene is a considerable occupational exposure hazard as it readily forms a vapour at room temperature and also may undergo significant dermal

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absorption. Ingestion of nitrobenzene may also occur, as the relatively pleasant almond odour may not discourage individuals from drinking water contaminated with it [1, 3]. Nitrobenzene may be present in the environment close to industrial locations where it is manufactured or used. It has also been reported as being detectable near hazardous waste sites. However, the levels of nitrobenzene present in such locations would be expected to be many times lower than those observed during occupational exposure [1, 3].

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Health Effects of Acute / Single Exposure

Human Data

General toxicity

Nitrobenzene is toxic via inhalation, ingestion and dermal absorption. The principal adverse health effect following exposure to nitrobenzene is methaemoglobinaemia [1]. There are very few accounts of human fatalities following nitrobenzene exposure, due to prompt medical intervention in many case studies [3].

Inhalation

Acute inhalation of nitrobenzene can result in respiratory irritation, headache, nausea, dizziness, drowsiness, shortness of breath, fatigue, cyanosis and convulsions, due to methaemoglobinaemia [1, 3, 4]. The symptoms of methaemoglobinaemia may develop within 1 to 4 hours post-exposure [4]. Serious acute exposure to nitrobenzene may lead to jaundice, renal failure, unconsciousness and can possibly be fatal [1-3, 5]. However, there are few reports of acute inhalation exposure to nitrobenzene at levels sufficient to cause fatality [1]. In an early study based on toxic symptoms in factory workers, it was considered that exposure to 200 ppm would produce serious adverse effects after a 1 hour exposure, or 60 – 100 ppm for 6 hours [1].

Ingestion

There are numerous reports of poisoning from nitrobenzene in the first half of the 20th Century when it was widely available as a substitute for oil of bitter almond or as a dye in shoe polish. Acute oral ingestion of nitrobenzene results in gastric irritation, including nausea and vomiting, the onset of which may be delayed for up to 12 hours post exposure [1]. Methaemoglobinaemia will develop 1 to 4 hours post-exposure, indicated by cyanosis, the symptoms of which may be similar to those following inhalation [4]. Severe exposure to nitrobenzene by ingestion can also give rise to progressive drowsiness and coma which may prove fatal due to respiratory failure [1].

Dermal / ocular exposure

Dermal exposure to nitrobenzene either from splashes of liquid or contact from vapours may cause mild irritation [4]. Nitrobenzene will readily undergo dermal absorption and there have been numerous reports of nitrobenzene toxicity in humans, particularly infants, following skin contact [1, 3, 4]. Following dermal absorption of sufficient quantities of nitrobenzene the main adverse effect of nitrobenzene exposure is methaemoglobinaemia similar to that observed following inhalation and ingestion [1, 2].

Delayed effects following an acute exposure

The onset of methaemoglobinaemia from all routes of exposure may be delayed for 1 to 4 hours depending upon the severity of exposure [1, 3, 4]. In some cases following severe ingestion of nitrobenzene, haemolytic anaemia may develop around 5 days post exposure [1].

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Animal and In-Vitro Data

General toxicity The acute toxicity of nitrobenzene in experimental animals resembles that seen in humans, with the development of methaemoglobin being the characteristic adverse effect [1, 3, 5, 6].

Inhalation

There are only limited data on acute exposure to nitrobenzene via inhalation. Exposure of rats to an atmosphere saturated with nitrobenzene vapour for 3 hours resulted in no deaths over the 14 day observation period. However, exposure for 7 hours resulted in 25% of the exposed animals (3/12) dying. No information was available on the actual exposure levels [1].

Ingestion

The oral LD50 for nitrobenzene administered to rats is 600 mg kg-1 body weight [1, 3]. In a study in which female rats were orally administered 640 mg kg-1 nitrobenzene the percentage of methaemoglobin formed 30, 60 and 120 mins post-exposure were 11, 19 and 28%, respectively [1]. Histological changes in the liver and testes were noted at autopsy in rats 2 or 5 days after single doses of nitrobenzene at 200 mg kg-1 and above [1].

Dermal

The dermal LD50 of nitrobenzene in rats has been reported to be 2100 mg kg-1 body weight [1]. In this dermal LD50 study, the percentage of methaemoglobin formed following an LD50 dose, was found to be 16%, 25% and 35% at 30, 60 and 120 minutes, respectively. The dermal LD50 of nitrobenzene in rabbits was found to be 760 mg kg-1 body weight [1].

Skin and Eye Irritation

Nitrobenzene only produces slight and transient skin and eye irritation. The skin irritation potential of nitrobenzene was investigated in male rabbits using the Draize method and was found to produce only very slight erythema at 24 hours post exposure [1]. Studies investigating ocular irritation in male rabbits using the Draize method found nitrobenzene to produce slight irritation at 1 and 24 hours post-exposure, but had resolved completely at 48 hours [1].

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Health Effects of Chronic / Repeated Exposure

Human Data

Inhalation

Long term occupational exposure to nitrobenzene may be associated with similar symptoms as those observed following excessive levels of acute exposure. The most common adverse effect following occupational inhalation of nitrobenzene is the formation of methaemoglobinaemia [1, 3]. A worker exposed to nitrobenzene (no details available on exposure levels) for 17 months developed severe methaemoglobinaemia, with headache, nausea, vertigo, confusion and an increased sensitivity to pain (hyperalgesia) from pin-prick. The worker also had enlarged and tender spleen and liver and abnormal results from liver-function tests. The exposure and absorption of nitrobenzene were confirmed by the presence of p-nitrophenol and p-aminophenol in the urine [1]. Chronic exposure to nitrobenzene may also give rise to the development of haemolytic anaemia and toxic hepatitis [1, 5].

Dermal / Ocular

Very little information was identified relating to chronic occupational dermal exposure of nitrobenzene. However, as nitrobenzene will undergo rapid dermal absorption the symptoms are expected to be similar to those observed following chronic inhalation.

Genotoxicity

No studies were identified regarding genotoxic effects following chronic exposure to nitrobenzene in humans [1, 3]

Carcinogenicity

No data was located regarding the carcinogenicity of nitrobenzene in humans. The International Agency for Research on Cancer (IARC) has concluded that there is insufficient evidence for the carcinogenicity of nitrobenzene in humans. However, based on animal carcinogenicity data, nitrobenzene has been classified overall as possibly carcinogenic to humans (group 2B) [5].

Reproductive and developmental toxicity

No studies were located regarding reproductive or developmental effects of nitrobenzene in humans [1, 3].

Animal and In-Vitro Data

Inhalation

The toxicity of nitrobenzene following chronic inhalation was studied in two strains of rat (Fisher-344 and Sprague Dawley) and B6C3F1 mice, exposed to nitrobenzene at concentrations up to 125 ppm for 6 hours day-1, 5 days week-1 for 2 weeks. The Sprague-Dawley rats exposed to 125 ppm nitrobenzene showed severe adverse clinical signs including rapid shallow breathing and wheezing with 40% lethality at the fourth day of exposure. All of the mice exposed at the same concentration showed morbidity which

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necessitated the animals being sacrificed on the fourth day of exposure. However, the Fisher-344 rats tolerated this dose for 2 weeks and showed no adverse clinical signs, indicating marked strain differences in susceptibility to nitrobenzene [1]. The study also reported significant concentration-dependent increases in liver, spleen and kidney weights [1]. Rats exposed to nitrobenzene by inhalation at just 5 ppm (25.15 mg m-3) for 6 hours day-

1, 5 days week-1 for 90 days displayed symptoms of methaemoglobinaemia [3].

Ingestion

A study of Fisher-344 rats orally exposed to nitrobenzene at 125 mg kg-1 body weight day-1 for 28 days, showed decreased movement, pale skin, gait abnormalities and decreases in body weight or body weight gain. In this study, increases in the weights of the liver, spleen and kidneys were observed along with reductions in the weight of the thymus and the testis in the males. An increase in liver weights of males was also observed at a low dose of 5 mg kg-1 body weight day-1 [1]. In another study in Fisher-344 rats, nitrobenzene was administered (by gavage) for 13 weeks at doses of up to 150 mg kg-1. Some lethality occurred at the top dose. Clinical signs seen at 75 and 150 mg kg-1 body weight day-1 included ataxia, head tilt, lethargy, trembling, circling, dyspnoea as well as cyanosis of the extremities. Marked brain lesions were noted at autopsy [1]. A study in which B6C3F1 mice were administered nitrobenzene orally at up to 300 mg kg-1 body weight day-1 for 13 weeks showed signs of toxicity including ataxia, lethargy, ataxia, dyspnoea, convulsions, irritability and rapid head-bobbing movements, some lethality was noted at the highest dose [1].

Dermal

The effects of repeated skin painting of nitrobenzene have been investigated in a number of studies. In 14 day studies in B6C3F1 mice and Fisher-344 rats, similar effects were seen in both species. Dose levels in the range of 200 – 3200 mg kg-1 body weight day-1 were used. Dose levels of 1600 mg kg-1 body weight day-1 and above resulted in lethality. Clinical signs reported included ataxia, prostration and dyspnoea. Significant depression of weight gain was noted in mice at all dose levels. At autopsy there was histological evidence of damage to the brain, liver, spleen and testes, with mice being less affected than rats [1].

Genotoxicity

Nitrobenzene has been fairly extensively investigated for its genotoxic potential using both in-vitro and in-vivo studies. The data suggest that it is not a genotoxic carcinogen and does not possess any significant mutagenic effects in vivo [1]. Nitrobenzene has been investigated for its ability to produce mutations or DNA lesions in two well established assays. There are numerous reports of studies to investigate the potential of nitrobenzene to produce gene mutations in vitro in the Ames test using strains of Salmonella typhimurium, either in the presence or absence of metabolic activation with liver S9 fraction. Negative results were consistently obtained [1]. Nitrobenzene was also found to be negative for unscheduled DNA synthesis (UDS) when tested using primary hepatocytes cultured in vitro from either humans or rats [1]. The ability of nitrobenzene to induce chromosome damage has been investigated in vivo. Negative results were obtained in a micronucleus study using mice and the intraperitoneal route of exposure. Dose levels of up to 250 mg kg-1 body weight were used, with bone marrow harvested after 24 and 48 hours and examined for micronucleated polychromatic erythrocytes. Nitrobenzene has also been investigated in the in-vivo UDS test with rat liver cells. The compound was given orally at dose levels up to 500 mg kg-1. The study was limited by the use of a single harvest time, but there was no increase in UDS [1].

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Carcinogenicity

The carcinogenicity of nitrobenzene has been investigated in chronic bioassays using the inhalation route in rat and mice studies. In one study in rats an increase in the incidence of hepatocellular neoplasms, thyroid follicular-cell adenomas and adenocarcinomas and renal tubular-cell adenomas was seen in the treated males. In the treated females there was an increase in hepatocellular neoplasms and endometrial stromal polyps. In a second study in which only male rats were used, an increase in the incidence of hepatocellular neoplasm was seen [5]. In male mice exposed to nitrobenzene an increase in alveolar-bronchial neoplasms and thyroid follicular-cell adenomas was observed [5]. Overall, the IARC has concluded that there is sufficient evidence for the carcinogenicity of nitrobenzene in experimental animals [5].

Reproductive and developmental toxicity

Numerous studies have established that nitrobenzene is a testicular toxicant. The most sensitive end points were sperm count and motility, followed by progressive motility, viability, presence of abnormal sperm and finally fertility index [1]. In repeated dose studies (13 week) testicular atrophy was seen in mice at daily doses of 19 mg kg-1 body weight and above, and in rats at 150 mg kg-1 body weight and above. In a 2 generation reproductive toxicity study in rats using the inhalation route, 40 ppm (6 hours day-1, 5 days week-1) produced a marked decrease in fertility index, but was not seen at 20 ppm [1]. These studies suggest that nitrobenzene may cause reproductive toxicity in males due to testicular atrophy [1, 3, 5]. Studies investigating the developmental toxicity of nitrobenzene in rats and rabbits using the inhalation route have not observed fetotoxic, embryotoxic or teratogenic effects at concentrations associated with maternal toxicity [1].

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References [1] International Programme on Chemical Safety (IPCS) (2003). Nitrobenzene.

Environmental Health Criteria 230. WHO. Geneva.

[2] International Programme on Chemical Safety (IPCS) (1993). Nitrobenzene. International Chemical Safety Card: 0065. WHO. Geneva.

[3] Agency for Toxic Substances and Disease Registry (ATSDR) (1990). Toxicological Profile for Nitrobenzene. US department of Health and Human Services. Atlanta, US.

[4] National Poisons Information Service (NPIS) (2007). Nitrobenzene. TOXBASE®.

[5] International Agency for the Research on Cancer (IARC) (1996). Nitrobenzene. Vol 65. IARC. Lyon.

[6] Weisburger, E. K. and Hudson, V. W. (2001). Aromatic nitro and amino compounds, Chapter fifty-seven. John Wiley & Sons, Inc. New York, NY.

This document from the HPA Centre for Radiation, Chemical and Environmental Hazards reflects understanding and evaluation of the current scientific evidence as presented and referenced in this document.