Recent exposure to benzene can be determined by biological monitoring (also known as biomonitoring). This is the measurement of benzene or its unique metabolites in biological fluids e.g. in urine. Biomonitoring reflects the total uptake of benzene by inhalation, ingestion or absorption through the skin. Other methods for measuring exposure, for example air sampling, will not indicate actual exposure levels within an individual.
Health Effects of Benzene
Benzene is a highly flammable liquid which occurs naturally in crude oil and natural gas. Once processed it is found in fuel e.g. bunker oil and chemical applications e.g. pre-cursor, solvents.
- Acute occupational exposure to benzene may cause narcosis: headache, dizziness, drowsiness, confusion, tremors and loss of consciousness. Use of alcohol enhances the toxic effect.
- Benzene is a moderate eye irritant and a skin irritant.
Effects following chronic exposure
- Benzene is a well-established cause of cancer in humans. The International Agency for Research on Cancer has classified benzene as carcinogenic to humans (Group 1). Benzene causes acute myeloid leukaemia (acute non-lymphocytic leukaemia), and there is evidence that benzene may also cause acute and chronic lymphocytic leukaemia, non-Hodgkin’s lymphoma and multiple mye-loma.
- Chronic exposure to benzene can reduce the production of both red and white blood cells from bone marrow in humans, resulting in aplastic anaemia.
- Both B-cell proliferation and T-cell proliferation are reduced by benzene. Decreased host resistance to infection has been reported in several laboratory animals exposed to benzene.
- Chromosomal aberrations in human peripheral lymphocytes are associated with occupational exposure to benzene. Chromosomal aberrations, micro nuclei, sister chromatid exchange and sperm head abnormalities have been seen in laboratory species treated in vivo. Chromosomal aberrations and mutations were seen in human cells in vitro and in laboratory animal cells in some in vitro studies.
- Benzene is fetotoxic in mice and rabbits following maternal exposure by inhalation, causing a reduction in birth weight.
Due to the highly toxic nature of benzene, repeated exposure has been linked with the onset of blood
disorders such as leukaemia.
Employees in a number of major industries may be exposed to benzene, either in routine work situations or following its accidental release into the atmosphere.
Industries where benzene exposure is a potential hazard include:
- Oil, gas and chemical – production and transportation
- Coke and coal production
- Petroleum storage and distribution
- Oil refineries,
- Chemical plants
- Petroleum processing industries
- Gasoline station employees
- Steel industry
- Coke and smelting
- Fire fighters and emergency response organisations
- Rubber industry
- Printing industry
- Pesticide production
- Detergent production
- Solvent production
- Paint and varnish production
- Shoe manufacture
- Waste management, and
- Laboratory technicians
Urinary S-Phenyl Mercapturic Acid (S-PMA) testing
S-PMA is a metabolite of benzene and a positive result indicates exposure to benzene offering an highly sensitive and specific testing method to monitor total exposure to benzene. This state of-the art analysis method can test for benzene exposure using a small amount of urine and generates
important information on exposure, significantly adding value to conventional air-borne analyses as S-PMA indicates total benzene exposure from all sources, either through vapour inhalation, ingestion or absorption through the skin. It readily identifies benzene exposures at levels considerably lower
than previous regulatory guidelines, even for workers who are heavy smokers.
Benefits of S-PMA testing
Implementation of systematic Benzene Exposure Biomonitoring by S-PMA analysis has resulted in a number of benefits for petrochemical industries. These include:
- Measurement of total exposure: Tests measure exposure via inhalation, ingestion and skin absorption. The latter is unaccounted for in air borne monitoring, therefore underestimating total uptake.
- Evaluation of site safety practices: Confirmation of the efficacy of personal protective equipment and whether breathing apparatus, protective suits and gloves are functioning or are being used correctly.
- Provision of safety assurance for employees: Provides reassurance of safety to operatives performing potentially hazardous tasks, such as spill clean-up, by the timely reporting of benzene bio-monitoring results.
- Simple non-invasive urine sample collection provides minimal disruption to workflow.
- State-of-the-art technology: Provides results at or below current health standards, offers rapid result turnaround for employee confidence.
- Establishes good working practices: Confirms that a company is deploying ‘Best Health & Safety Working Practice’ and is supporting improvements in working practices.
- Enables data tracking: Provides data on work processes and identification of exposure trends.
International recognition of S-PMA as a benzene-specific biomarker
The American Conference of Governmental Industrial Hygienists (ACGIH) and the Deutsche Forschungsge-meinschaft (DFG) in Germany have published biological exposure indices for S-PMA as a marker of benzene exposure. The Health and Safety Laboratories (HSL) in the UK recognize and advocate using S-PMA as a biomarker of occupational exposure to benzene.
Recommended sampling program
- Routine sample: To ensure peak levels of S-PMA are not missed for routine testing, the recommendation is to collect urine samples to test for benzene exposure after the end of the shift.
- Post Incident sample: Following any exposure incident, a sample should be collected one hour post exposure and should be followed up, if possible, with further samples after 9-12 hours and 24 hours. These three samples will enable S-PMA concentrations to be charted and will assist in the interpretation of results.