Benzene – Priority Existing Chemical (PEC) Report No. 21

© Commonwealth of Australia 2001

ISBN 0 642-51896-3

Preface

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This assessment was carried out under the National Industrial Chemicals Notification and Assessment Scheme (NICNAS). This Scheme was established by the Industrial Chemicals (Notification and Assessment) Act 1989 (the Act), which came into operation on 17 July 1990.

The principal aim of NICNAS is to aid in the protection of people at work, the public and the environment from the harmful effects of industrial chemicals.

NICNAS assessments are carried out in conjunction with Environment Australia (EA) and the Therapeutic Goods Administration (TGA), which carry out the environmental and public health assessments, respectively.

NICNAS has two major programs: the assessment of the health and environmental effects of new industrial chemicals prior to importation or manufacture; and the other focussing on the assessment of chemicals already in use in Australia in response to specific concerns about their health/or environmental effects.

There is an established mechanism within NICNAS for prioritising and assessing the many thousands of existing chemicals in use in Australia. Chemicals selected for assessment are referred to as Priority Existing Chemicals.

This Priority Existing Chemical report has been prepared by the Director (Chemicals Notification and Assessment) in accordance with the Act. Under the Act manufacturers and importers of Priority Existing Chemicals are required to apply for assessment. Applicants for assessment are given a draft copy of the report and 28 days to advise the Director of any errors. Following the correction of any errors, the Director provides applicants and other interested parties with a copy of the draft assessment report for consideration. This is a period of public comment lasting for 28 days during which requests for variation of the report may be made. Where variations are requested the Director’s decision concerning each request is made available to each respondent and to other interested parties (for a further period of 28 days). Notices in relation to public comment and decisions made appear in the Commonwealth Chemical Gazette.

In accordance with the Act, publication of this report revokes the declaration of this chemical as a Priority Existing Chemical, therefore manufacturers and importers wishing to introduce this chemical in the future need not apply for assessment. However, manufacturers and importers need to be aware of their duty to provide any new information to NICNAS, as required under section 64 of the Act.

Copies of this and other Priority Existing Chemical reports are available from NICNAS either by using the prescribed application form at the back of this report, the website www.nicnas.gov.au or ordering directly from the following address:

• GPO Box 58
• Sydney
• NSW 2001
• AUSTRALIA

Overview

Benzene (CAS No. 71-43-2) was declared a Priority Existing Chemical on 7 April 1998 in response to occupational and public health concerns.

Benzene occurs naturally in fossil fuels and is produced incidentally in the course of natural processes and human activities that involve the combustion of organic matter such as wood, coal and petroleum products. The main industrial use of benzene is as a starting material for the synthesis of other chemicals. Most benzene feedstock is imported, but some is manufactured at an Australian steelworks as a by-product of coal coking. Large quantities of benzene are produced during the refining of petroleum and retained as a component of petrol. Petrol vehicle emissions are the predominant source of benzene in the environment.

Benzene is volatile and water-soluble and is considered biodegradable. Its major release is to the atmosphere, where it will break down in a matter of weeks. Direct release to the aquatic compartment is expected to be minor and significant removal will occur from volatilisation. Benzene release to soil is likely to be marginal. Concentrations in aquatic systems are expected to be far lower than of concern and a low aquatic risk is predicted. Due to the low expected exposure, a low environmental risk to terrestrial organisms is predicted. The short atmospheric lifetime of benzene indicates concentrations will not occur at levels harmful to the atmosphere. While widespread transport within the troposphere is possible, the chemical is not expected to reach the stratosphere and therefore would not have an influence on global warming or ozone depletion.

In animals and humans, benzene is absorbed by all routes of exposure, although dermal absorption is limited by its rapid evaporation from the skin. It is metabolised in the liver and several other organs, including the bone marrow. The parent molecule is eliminated with exhaled air. The metabolites are excreted in the urine.

In animals, benzene is not highly acutely toxic. Chronic exposure can result in central nervous system depression, immunosuppression, bone marrow depression, degenerative lesions of the gonads, foetal growth retardation, damage to genetic material and solid tumours in several organs.

In humans, acute exposure to high concentrations of benzene vapours can result in irritation of the skin, eyes and respiratory system and in central nervous system depression. Chronic exposure can result in bone marrow depression and leukaemia, particularly acute myeloid leukaemia, and possibly an increased risk of non-Hodgkin’s lymphoma and multiple myeloma. Structural and numerical chromosome aberrations have been detected in peripheral blood cells of workers exposed to high levels of benzene. For bone marrow depression, the lowest observed adverse effect level in humans is 7.6 parts per million (ppm), based on minimal blood count changes in otherwise healthy workers. No threshold has been established for the genotoxic and carcinogenic effects of benzene. Epidemiological evidence indicates that the risk of leukaemia increases with exposure and is significantly elevated at cumulative exposures above 50 ppm-years, corresponding to an 8-hour time-weighted average exposure above 1.25 ppm over a working life of 40 years.

Chronic benzene toxicity has been attributed to the formation of reactive metabolites that appear to exert their toxic effect in combination, with no one metabolite accounting for all of the observed effects.

Benzene is currently listed in the NOHSC List of Designated Hazardous Substances with the following classification: ‘Flammable’, ‘Carcinogen, Category 1’ and ‘Toxic: Danger of serious damage to health by prolonged exposure through inhalation, in contact with skin and if swallowed’. Category 1 carcinogens are those substances known to be carcinogenic to humans. Based on the assessment of health effects, this report has concluded that benzene also meets the NOHSC Approved Criteria for Classifying Hazardous Substances for classification as a skin, eye and respiratory system irritant and as a mutagenic substance in Category 3.

The public is exposed to benzene through the inhalation of indoor, in-vehicle and outdoor air contaminated with the chemical through releases that predominantly derive from vehicle exhaust, petrol evaporation and tobacco smoke. The 24-hour average lifetime exposure in the Australian urban population is estimated at 5.2 parts per billion (ppb). It is one-fifth higher in passive smokers exposed to tobacco smoke at home, at work and in their cars (6.1 ppb) and almost three times as high (15.2 ppb) in the average smoker.

Benzene-induced bone marrow depression is not expected to present a significant public health risk. Based upon low-dose extrapolation of relevant quantitative risk estimates and the above-mentioned exposure estimate, the excess lifetime risk of benzene-induced leukaemia in the Australian urban population is estimated to be in the order of one case per 10,000 with increased risk in sensitive subpopulations or at higher exposure levels. However, the estimated excess risk is based on substantial uncertainties in the exposure assessment which should be validated through collection of monitoring data.

As benzene is an established human carcinogen for which no safe level of exposure has been established, it is recommended that any increase in public exposure be avoided and that measures be taken to reduce exposure where this is practicable. The establishment of a national ambient air benzene level would facilitate these objectives.

Occupational exposure to benzene is predominantly by the inhalation route. It occurs primarily in the petroleum, steel, chemical and associated industries and in laboratories using the chemical for research or analysis. Occupational exposure to benzene can also result from the contamination of workplace environments with petrol vapours, engine exhaust or tobacco smoke, for example, in vehicle mechanics, professional drivers and hospitality workers. It is estimated that current long-term occupational exposures to benzene are less than or equal to 0.7 ppm in the steel and associated industries and during maintenance of phenol plants; less than 0.1 ppm in the upstream petroleum industry (oil and gas production); less than 0.5 ppm in the chemical industry and in laboratory workers; less than 0.2 ppm in vehicle mechanics; less than 0.7 ppm in the downstream petroleum industry (refining, distribution and marketing of petroleum products); and less than 0.05 ppm in people who work in roadside or in-vehicle environments contaminated with vehicle exhaust or in indoor environments contaminated with tobacco smoke.

The occupational risk characterisation found no cause for concern about acute health effects or bone marrow depression, given the control measures which are already in place in Australian workplaces. However, there is cause for concern about the risk for leukaemia in all workers with repeated occupational exposure to benzene. There is no known threshold for the carcinogenic effects of benzene, but because the risk for leukaemia increases with exposure, it can be reduced by controlling exposure to the highest practicable standard.

With regard to occupational health and safety, it is recommended that the national exposure standard for benzene be revised. It is recommended that an eight-hour time-weighted average of 0.5 ppm be adopted. It is further recommended that the current hazard classification be amended to include classification as ‘Irritating to eyes, respiratory system and skin’ (risk phrase R36/37/38) and as a mutagenic substance in Category 3 (risk phrase R40: ‘Possible risks of irreversible effects, Mutagen Category 3’). Occupational exposures to benzene should be minimised by improving workplace control measures and by using the best available technology.

This report has identified the need to reduce public exposure to air benzene levels as much as practicable. Public health recommendations include measures to reduce indoor benzene levels, such as proper sealing of attached garages and minimising environmental tobacco smoke. In order to better characterise the risk to the public from benzene exposure, personal and ambient air monitoring is recommended and a national ambient air standard should be set.

1. Introduction

1.1 Declaration

The chemical benzene (CAS No. 71-43-2) was declared a Priority Existing Chemical for full assessment under the Industrial Chemicals (Notification and Assessment) Act 1989 on 7 April 1998. It was nominated by the public because of concerns about its human health effects and the adequacy of the current Australian occupational exposure standard.

1.2 Objectives

The objectives of this assessment were to:

• characterise the properties of benzene;
• determine the uses of benzene in Australia;
• determine the extent of occupational, public and environmental exposure to benzene;
• characterise the intrinsic capacity of benzene to cause adverse effects on persons or the environment;
• characterise the risks to humans and the environment resulting from exposure to benzene; and
• determine the extent to which any risk is capable of being reduced.

1.3 Sources of information

Consistent with the objectives, this report presents a summary and critical evaluation of relevant information relating to the potential health and environmental hazards from exposure to benzene. Relevant scientific data were submitted by the applicants listed in Section 3, obtained from published papers identified in a comprehensive literature search of several online databases up to December 2000, or retrieved from other sources such as the reports and resource documents prepared for the health surveillance program of the Australian Institute of Petroleum (AIP) and the Illawarra leukaemia cluster investigation. Due to the availability of several peer-reviewed overseas assessment reports, not all primary sources of data were evaluated. However, relevant studies published since the cited reviews were assessed on an individual basis.

The characterisation of health and environmental risks in Australia was based upon information on use patterns, product specifications, occupational exposure and emissions to the environment made available by applicants and relevant State authorities. Information to assist in the assessment was also obtained through site visits and telephone interviews. The site visits included two petroleum refineries, two petrol terminals, a steelworks, a coal tar distillery, a bulk liquid storage facility and three chemical plants.

1.4 Peer review

During all stages of preparation, the report has been subject to internal peer review by NICNAS, Environment Australia (EA) and the Therapeutic Goods Administration (TGA). Selected parts of the report were also peer reviewed by Professor Tom Beer, CSIRO Atmospheric Research (Sections 8 and 15); Dr Stephen Corbett, New South Wales Department of Health (Section 11); Dr Andrea Hinwood, Department of Environmental Protection, Western Australia (Sections 9, 11 and 13); and Professor Martyn T. Smith, University of California (Sections 9 and 12).

2. Background

2.1 Introduction

Benzene is a naturally occurring, hazardous, volatile organic compound which is ubiquitous in the environment. It is formed from biomass under the impact of heat, pressure and geological time. As such, it is present in fossil fuels which may release it to air when unearthed and, in particular, when heated to combustion. Benzene is also a product of natural processes and human activities that involve the instantaneous thermal degradation of organic matter. These sources of entry include bush fires, crop residue and forest management burning, petroleum refining, petrol combustion, wood and charcoal fires, fumes from heated cooking oils, tobacco smoke, incense, and waste incineration. In addition, benzene enters the environment in emissions and waste streams from industrial processes and waste disposal facilities.

2.2 International perspective

Benzene was first isolated in 1825 and gradually became widely used as a solvent and starting material for the synthesis of a number of organic chemicals (Folkins, 1984). Benzene also became recognised as a valuable constituent of petrol because of its antiknock properties and ability to increase the octane rating of automotive fuels.

Until World War II, benzene was isolated from light oil, which is a by-product of the carbonisation of coal to produce gas for heating or coke for the blast furnaces of the steel industry. Beginning in the 1930s, new catalytic and thermal processes for the production of aromatic hydrocarbons from crude oil were discovered and commercialised in the petroleum industry. With the advent of natural gas in the 1960s, worldwide coal gas production started to diminish. Simultaneously, the introduction of modern steel processing methods decreased coke production and made it attractive to burn the light oil as fuel rather than segregate it into benzene and other products. In consequence, the petroleum industry is now the predominant source of benzene.

In recent years, the use of benzene-containing solvents has been practically eliminated because of the toxicity of the chemical. Current worldwide consumption of benzene is 30-35 million metric tonnes (t) per annum, primarily as chemical feedstock in the production of large-scale intermediates such as ethyl benzene, cumene and cyclohexane (Chemistry & Industry News, 1996). This figure does not include benzene produced by the petroleum industry and retained as a petrol component.

Commercial low-grade qualities are sometimes referred to as benzol. Benzene is not to be confused with benzine, which is a mixture of several low-boiling hydrocarbons obtained in the distillation of petroleum.

2.3 Australian perspective

Developments in Australia have followed the general pattern outlined above, albeit with a delay of 1-2 decades. The recovery of benzene from coal gas is now limited to the steelworks at Port Kembla in New South Wales and Whyalla in South Australia.

There are eight petroleum refineries in Australia: two in Brisbane and Sydney and one in Adelaide, Geelong, Melbourne and Perth. Since the 1970s, close to 100% of local demand for petrol has been met from crude which is low in aromatic fractions (Tresider, 1998). As such, all Australian petroleum refineries have processes in place to increase the content of aromatic hydrocarbons including benzene in their petrol blendstock. Petroleum-derived benzene feedstock for the chemical industry is not produced in Australia.

As of 1986, new petrol-driven cars had to be fitted with catalytic converters and use unleaded fuel. An Australian Standard for petrol for motor vehicles was established in 1990 and limited the benzene content to a maximum of 5% v/v (Standards Australia, 1990). In 1998, the average benzene content in Australian petrol was 2.9, 2.6 and 3.3% v/v in leaded petrol (LP), unleaded petrol (ULP) and premium unleaded petrol (PULP) respectively (AIP, 1998b). The Fuel Quality Standards Act 2000 enables the Commonwealth to make mandatory national quality standards for fuel supplied in Australia. Among others, these will include a maximum content of benzene in petrol of 1% v/v from January 1 2006. Meanwhile, Western Australia and Queensland have introduced regulations limiting the benzene content in petrol to 1% and 3.5% respectively (EA, 2000b).

In 1980, AIP contracted The University of Melbourne to set up an epidemiological health surveillance program called Health Watch. The program covers about 95% of the industry’s 18,000 employees in refineries, natural gas plants, distribution terminals and production sites. It consists of a prospective cohort study of all-cause mortality and cancer incidence, in addition to a case-control study of lympho-haematopoietic cancers and benzene exposure established in 1988 (Glass et al., 1998, 2000; Health Watch, 1998).

Air pollution became a major concern in the 1990s and prompted environment and health authorities from the Commonwealth, States and Territories to initiate several research projects into ambient air quality. Early results of this research resulted in the inclusion of benzene in the National Pollutant Inventory (NPI), which was established by the National Environment Protection Council (NEPC) in 1998. The NPI currently comprises 36 chemicals of health and environmental concern which must be reported to EA if the quantity used or handled per site exceeds a threshold limit, which for benzene is 10 t per year (EA, 1999b). More recently, the Australian and New Zealand Environment and Conservation Council contracted the Victorian Environment Protection Authority (EPA) to assess the available air level data and derive a risk-based rank order of hazardous air pollutants according to their priorities for further research (EPA Victoria, 1999). Based on a scoring system as well as on professional judgement, benzene came first among 15 chemicals recommended for general urban air monitoring. Benzene is also the subject of a publication in the series of National Environmental Health Forum Monographs, which are intended to provide plain language information about important, topical environmental health matters (Wadge & Salisbury, 1997). Current EA initiatives such as the Fuel Quality Review and Living Cities – Air Toxics Program both address a number of environmental aspects relating to benzene (EA, 2000a, 2000b).

Public concern about exposure to benzene reached a peak in 1996, when a cluster of leukaemia cases was identified in people living in the suburbs adjacent to the coke ovens and coal gas by-product plant at the Port Kembla steelworks. A committee reporting to the New South Wales Department of Health was set up to investigate the matter. It concluded that based on the available data, it was not possible to ascribe the cluster to a particular exposure (including benzene). The investigation produced several useful publications relating to benzene and the risk of leukaemia (ILISC, 1997; Westley-Wise et al, 1999).

2.4 Assessments by other national or international bodies

Although there have been restrictions on the manufacture, handling, storage and use of benzene in Australia since 1978, this report represents the first comprehensive risk assessment by a national agency.

Benzene has been assessed by several overseas or international bodies involved in the review or evaluation of data pertaining to the health and/or environmental hazards posed by chemicals. Of these, the most noteworthy are:

• The Advisory Committee to the German Chemical Society on Existing Chemicals of Environmental Relevance (GDCh, 1988);
• The Agency for Toxic Substances and Disease Registry under the US Department of Health and Human Services (ATSDR, 1997);
• The Commission of the European Communities (EC, 1989, 2000);
• Environment and Health Canada (Government of Canada, 1993);
• The International Agency for Research on Cancer (IARC, 1982a, 1987);
• The International Programme on Chemical Safety (IPCS, 1993);
• The UK Department of the Environment (DoE, 1994);
• The US Environmental Protection Agency (USEPA, 1985, 1998a, 1998c); and
• The OECD SIDS International Assessment Report (draft) (OECD, 2000).

3. Applicants

Following the declaration of benzene as a Priority Existing Chemical, 21 companies or organisations applied for assessment of the chemical. The applicants supplied information on the properties, import and manufacturing quantities and uses of benzene and, in some cases, on occupational exposures and releases to the environment. In accordance with the Industrial Chemicals (Notification and Assessment) Act 1989, NICNAS provided the applicants with a draft copy of the report for comments during the corrections/variation phase of the assessment. The applicants were as follows:

Alltech Associates (Australia) Pty Ltd

PO Box 6005

Baulkham Hills NSW 2153

Australian Institute of Petroleum 

GPO Box 279

Canberra ACT 2601

Australian Council of Trade Unions

393 Swanston Street

Melbourne VIC 3000

Australian Manufactures Workers Union 

3/440 Elizabeth Street

Melbourne VIC 3000

Bio-Scientific Pty Ltd 

PO Box 78 

Gymea NSW 2227

BP Australia Holding Limited

360 Elizabeth St

Melbourne VIC 3000

Caltex Petroleum Australia Pty Ltd 

19-29 Martin Pl 

Sydney NSW 2000

Crown Scientific Pty Ltd

Private Mail Bag 4

Moorebank NSW 2170

Huntsman Chemical Company Australia Pty Ltd 

PO Box 62 

West Footscray VIC 3012

ICN Biomedicals Australasia 

PO Box 187 

Seven Hills NSW 2147

Whyalla Steelworks (OneSteel Manufacturing)

PO Box 21 

Whyalla SA 5600

Koppers Coal Tar Products Pty Ltd

PO Box 23

Mayfield NSW 2304

Merck Pty Ltd 

207 Colchester Rd 

Kilsyth VIC 3137

Mobil Oil Australia Pty Ltd 

417 St Kilda Rd 

Melbourne VIC 3004

BHP Steel – Flat Products

PO Box 1854

Wollongong NSW 2505

Qenos Pty Ltd

Private Bag 3 

Altona VIC 3018

Selby-Biolab

Private Bag 24 

Mulgrave North VIC 3170

Sigma-Aldrich Pty Ltd 

PO Box 970 

Castle Hill NSW 2154

Terminals Pty Ltd 

PO Box 268 

Footscray VIC 3011

3M Australia Pty Ltd

PO Box 144

St Marys NSW 2760

Trafigura Fuels Australia Pty Ltd

Unit 2, 47 Epping Rd 

North Ryde NSW 2113

4. Chemical Identity and Composition

4.1 Chemical name (IUPAC)

Benzene

4.2 Registry numbers

Benzene is listed on the Australian Inventory of Chemical Substances (AICS) as benzene.

CAS number – 71-43-2

EINECS number – 200-753-7

UN number – 1144

4.3 Other names

Annulene

Benzol(e)

Bicarburet of hydrogen

Carbon oil

Coal naphtha

Cyclohexatriene

Mineral naphtha

Motor benzol

Phenyl hydride

Pyrobenzol(e)

4.4 Molecular formula

C6H6

4.5 Structural formula

4.6 Molecular weight

78.11

4.7 Composition of commercial grade product

Several different grades of benzene are commercially available. The principal impurities are toluene, xylenes and other hydrocarbons with boiling points similar to that of benzene. The higher the grade, the lower the content of thiophene (thiofuran) and other sulfur compounds, which foul many catalysts used in reactions of benzene (Fruscella, 1992). The specifications for two typical import grades and the benzene/toluene/xylenes (BTX) mixture produced at the Port Kembla steelworks are shown in Table 4.1.

Table 4.1: Raw material specifications for some commercially available benzene grades

Test	Pure benzene	Crude benzene	BTX
Benzene (% v/v)	>99	>=95	>=80
C9 & higher (% v/v)	-	<1.5	<1.6
Carbon disulfide (ppm)	-	<50	<4000
H2S & SO2	None	-	-
Non-aromatic C5-C6 (% v/v)	<0.15	<0.7	<1.5
Styrene (% v/v)	-	-	<1.8
Thiophene (ppm)	<1	<6000	<6000
Toluene (% v/v)	-	-	<12.5
Total sulfur (ppm)	-	-	<6000
Xylenes & styrene (% v/v)	-	-	<3.8

Abbreviations and Acronyms

ACGIH – American Conference of Governmental Industrial Hygienists

ADG – Australian Dangerous Goods

AIP – Australian Institute of Petroleum

ALC – absolute lymphocyte count

ALL – acute lymphatic leukaemia

AML – acute myeloid leukaemia

ANLL – acute non-lymphocytic leukaemia

atm – atmosphere

Avgas – light aircraft gasoline

BCF – bioconcentration factor

BP – benzene poisoning

BTX – benzene/toluene/xylenes

BW – body weight

C – centigrade

CAS – Chemical Abstracts Service

CFU-E – colony forming units of erythrocyte progenitor cells

CFU-M – colony forming units of granulocyte/macrophage progenitor cells

CI – confidence interval

CLL – chronic lymphatic leukaemia

cm – centimetre

cm² – square centimetre

cm³ – cubic centimetre

CMA – Chemical Manufacturers Association

CML – chronic myeloid leukaemia

CNS – central nervous system

CSF – colony stimulating factor

CYP – mcytochrome-P450

DNA – deoxyribonucleic acid

EA – Environment Australia

EC₅₀ – median effective concentration

EINECS – European Inventory of Existing Chemical Substances

EPA – Environment Protection Authority

ETS – environmental tobacco smoke

g – gram

GC – gas chromatography

GC-MS – gas chromatography-mass spectrometry

GD – gestation day

GLP – Good Laboratory Practices

GM-CSF – granulocyte/macrophage colony stimulating factor

GSH – glutathione

GST – glutathione-S-transferase

h – hour

ha – hectare

Hb – haemoglobin

Hct – haematocrit

IARC – International Agency for Research on Cancer

IL-1 – interleukin-1

IPCS – International Programme on Chemical Safety

IUCLID – International Uniform Chemical Information Database

IUPAC – International Union for Pure and Applied Chemistry

K – Kelvin

kg – kilogram

K_m – Michaelis-Menten constant

km – kilometre

km² – square kilometre

K_oc – sorption coefficient

kPa – kilopascal

kt – kilotonne

L – litre

LC – lymphocyte

LC₅₀ – median lethal concentration

LD₅₀ – median lethal dose

LOAEL – lowest observed adverse effect level

LP – leaded petrol

LPG – liquid pressurised gas

m³ – cubic meter

MCV – mean corpuscular volume

MDS – myelodysplastic syndrome

mg – milligram

mL – millilitre

ML – megalitre

mM – millimolar

MM – multiple myeloma

MN – micronucleus

mol – mole

MSDS – material safety data sheet

NADPH – nicotinamide adenine dinucleotide phosphate

NEPC – National Environment Protection Council

NEPM – National Environment Protection Measures

ng – nanogram

NHIS – National Health Interview Survey

NHL – non-Hodgkin’s lymphoma

NICNAS – National Industrial Chemicals Notification and Assessment Scheme

NIOSH – National Institute of Occupational Safety and Health

nm – nanometre

nmol – nanomole

nM – nanomolar

NOAEL – no observed adverse effect level

NOEC – no observed effect concentration

NOHSC – National Occupational Health and Safety Commission

NPI – National Pollutant Inventory

NQO1 – NAD(P)H:quinone oxidoreductase

NSAID – non-steroidal anti-inflammatory drug

OECD – Organisation for Economic Co-Operation and Development

OR – odds ratio

OSHA – Occupational Safety and Health Administration

PAH – polycyclic aromatic hydrocarbon

PGE₂ – prostaglandin E2

PKC – protein kinase C

Plt – blood platelet

PNEC – predicted no-effect concentration

P_o/w – octanol/water partition coefficient

POP – persistent organic pollutant

ppb – parts per billion

PPE – personal protective equipment

ppm – parts per million

PULP – premium unleaded petrol

RBC – red blood cell (erythrocyte)

RNA – ribonucleic acid

RR – relative risk

s – second

SAb – spontaneous abortion

s-AML – secondary acute myeloid leukaemia

SC – subcutaneous

SCE – sister chromatid exchange

SGA – small-for-gestational age

SIR – standardised incidence rate

SMA – State marketing area

SMR – standardised mortality rate

STP – sewage treatment plant

SUSDP – Standard for the Uniform Scheduling of Drugs and Poisons

t – tonne

TGD – Technical Guidance Document

TWA – time-weighted average

TWA₈ – 8-h time-weighted average

ULP – unleaded petrol

UN – United Nations

USEPA – United States Environmental Protection Agency

UTL_95%,95% – upper tolerance limit of a distribution’s 95th percentile

v/v – volume/volume

VOC – volatile organic chemical

w/w – weight/weight

WBC – white blood cell (leukocyte)

WHO – World Health Organization

y – year

µg – microgram

µL – microlitre

µM – micromolar

µmol – micromole

8-OHdG – 8-hydroxydeoxyguanosine