Last reviewed 15 February 2012
Graham Birch of Argentic looks at the regulatory environment surrounding benzene and some of the developments in place to control exposure.
Benzene is a highly flammable solvent used in the production of drugs, plastics, synthetic rubber and dyes but it is also a Class 1 carcinogen. Repeated or high level exposure can cause blood and bone-related cancers, including leukaemia, as recorded by the International Agency for Research on Cancer (IARC).
Exposure may be by inhalation, ingestion, or skin absorption, and stringent workplace exposure limits are in place to ensure minimum risk of exposure to employees. These are regularly assessed and continue to be reduced, reflecting the potentially severe health consequences for employees and others alike.
Benzene is regularly present in crude oil, petrol and cigarette smoke. These, together with natural sources of benzene, including gas emissions from volcanoes and forest fires, contribute to the presence of benzene in the environment.
Current benzene detection methods are based on air monitoring by meter and laboratory analysis of gas tubes worn by at-risk personnel for personal exposure data. However, these methods do not measure actual presence of benzene in the individual, and do not take into account the potential for ingestion or skin absorption.
In the UK workplace, exposure to benzene is covered under the Control of Substances Hazardous to Health Regulations 2002 (COSHH 2002).
Under COSHH employers are required to:
assess risks to health and provide adequate control measures to prevent exposures
reduce, so far as is reasonably practicable, the amount of benzene breathed in, and keep this below the workplace exposure limit
determine the extent of exposure, normally by means of a monitoring programme
arrange for appropriate health checks to be made
ensure that all workplace control measures and personal protective equipment (PPE) are used and kept in good working order.
This assessment and the control measures devised must be made available to employees and anyone else who could be potentially exposed, either during routine operations, or as a result of accidental contact. Appropriate health and safety protective measures must be detailed, and companies must put in place healthcare checks designed to monitor and minimise exposure.
The EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals Regulation (REACH) that came into force in 2007 is a regulatory regime for the safe management of chemicals. REACH is co-ordinated from the European Chemicals Agency (ECHA) which became operational in 2008 and which manages the technical and administrative aspects of REACH.
Benzene has been registered with ECHA and is subject to specific restrictions concerning its manufacture and use. The Health and Safety Executive (HSE) is the REACH Competent Authority in the UK and has an advisory and enforcement role.
REACH adopted some of the older aspects of the chemical regulatory system in Europe, including the provision of Safety Data Sheets (SDS) which have been further adapted to take into account the new Classification, Labelling and Packaging Regulation 2008 (CLP).
Under the REACH requirement, the manufacturer or supplier must make an SDS available to the recipient of the substance or preparation free of charge. All SDSs must include relevant information within all 16 mandatory sections including toxicological information in section 11.
Under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR), an employer is required to report to the HSE if:
there is an acute illness needing medical treatment
a GP confirms chemical poisoning
there is an accidental release of any substance which may damage health.
It is required by the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment (Amendment) Regulations 2011 that the carriage of dangerous goods by road complies with the International Carriage of Dangerous Goods by Road agreement (ADR).
Benzene is transported under UN number 1114 (“BENZENE”) and has the Emergency Action Code 3WE.
In the code, the number 3 identifies that foam should be used in the case of fire or spillage, while W denotes the use of liquid tight chemical protective clothing with breathing apparatus. The E tells responders that people should be warned to stay indoors with all doors and windows closed while evacuation may need to be considered.
The Maritime Labour Convention Regulations 2006 (MLC) are a set of harmonised standards covering the health, safety and welfare of those working at sea. The UK is a signatory to the MLC, and UK law will be amended to incorporate necessary aspects of the regulations when fully ratified in the near future.
Benzene is widely transported as a cargo, and is also present at high concentrations in crude oil and bunker (fuel) oil, and thus there is considerable potential for exposure among UK maritime transport and port workers.
Developments in exposure assessment
An exposure to high levels of benzene in air, such as 10,000–20,000 parts per million (ppm), for only a few minutes can result in death. At somewhat lower levels of 700–3,000ppm, exposure can cause many symptoms which include drowsiness, dizziness, rapid heart rate, breathlessness, headaches, tremors, visual disturbances, confusion and then unconsciousness.
From a permissible workplace exposure limit of 200ppm in 1920, levels have reduced in stages following increasing research and awareness of the harmful effects of benzene. For instance, in 1946 the American Conference of Governmental Industrial Hygienists (ACGIH) recommendation was set at 100ppm which was soon reduced to 50ppm in 1947 and then to 35ppm in 1948.
The current limit in the UK and the EU is 1ppm per 8hrs time weighted average. A short-term exposure limit is not defined, although the UK Health Protection Agency has published interim acute exposure guidelines.
Historically, health checks for benzene workers have utilised blood tests, usually annually. These tests show changes in white cell count or other blood abnormalities which may indicate early stages of leukaemia. Normal preventive action is to transfer the employee to a position where no benzene exposure was possible.
Health technologists in the oil and chemical industries realised that there was a requirement for a test that could directly demonstrate biological exposure, prior to the development of any clinical conditions. Such tests could indicate a failure of protective equipment, systems, or processes, which could then be managed and corrected.
Initially assays were developed to identify benzene exposure by analysis of urine metabolites, primarily phenol. Phenol however, has several limitations, as a marker as it is produced by dietary, smoking, or other metabolic routes. The phenol assay is also insufficiently sensitive for measurement to today’s permitted levels.
Most persons in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid, S-phenylmercapturic acid (SPMA), phenol, catechol, hydroquinone and 1,2,4-trihydroxybenzene. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and may still be present for some days after exposure has ceased.
SPMA has been identified as the preferred basis for benzene screening purposes but until recently, SPMA analysis has been performed using gas chromatography-mass spectrometry (GCMS) or high performance liquid chromatography (HPLC) methods.
In recent years, chemists working in the oil industry have developed and implemented an immunoassay for SPMA in urine which allows accurate, rapid and more cost-effective measurement of benzene exposure.
SPMA sampling and bio-monitoring in practice
Each person has an individual background level of SPMA and this should be recorded initially, outside of their work environment. Sampling involves the collection of a small volume of urine which is placed in a preservative-treated vial. The vials are dispatched to the laboratory using robust packs that are compliant with transport regulations.
Once an individual’s background level is recorded, samples may then be taken before and after carrying out hazardous operations, with the second sample being taken within nine hours of task completion.
On analysis, a urine creatinine level is also recorded, to indicate sample dilution as a result of hydration level. Results are then presented as an SPMA to creatinine ratio.
Levels that indicate that permitted Time-weighted average (TWA) levels have been exceeded or approached, are highlighted and toxicological interpretation is provided.
Should a sample show a level of SPMA that indicates exposure to high benzene levels, then investigation and remedial actions would be carried out to remove or reduce the potential for exposure, and to ensure correct usage and functioning of PPE.
Additional testing of employees may also be performed on a random basis to demonstrate that exposure is not occurring due to accidental release. This testing should cover working, living or recreational areas where benzene vapours are not expected to be present.
As a result of the development of the SPMA immunoassay bio-monitoring system, employers now have available a simple, cost-effective, rapid and accurate means of risk minimisation. More frequent and extensive testing of personnel is now feasible, bringing direct benefits to employees in the form of reduced workplace health risk. In addition, employers may benefit from the decreased likelihood of workplace-related illness claims.
The use of regular bio-monitoring of personnel for benzene exposure enables:
workforce protection from the highly toxic carcinogenic effects of benzene
protection for employers by demonstrating best practice and regulatory compliance
reduction of personal injury claims as historical records can demonstrate exposure is unlikely
legal compliance through demonstrating that workplace exposure limits are not exceeded
re-assurance for employees by monitoring the routine working environment, or in cases of accidental release or contamination.
“Overview of Leukemia”. Merck Manual, Home Edition. rev. 2008
International Agency for Research on Cancer, Volumes 1 to 42, Supplement 7 which includes section on benzene
“Urinary t,t-muconic acid, S-phenylmercapturic acid and benzene as biomarkers of low benzene exposure”. Chemico-biological interactions, 153-54: 253–6. Fustinoni, S. et al. (2005).
Aston, JP., Ball, RL., Pople, JE., Jones, K. and Cocker, J. 2002 “Development and validation of a competitive immunoassay for urinary S-phenylmercapturic acid and its application in benzene biological monitoring”. Biomarkers, 7, 103–112.