Personal exposure to hazardous substances can be measured using two methods. Workplace air monitoring, and biological monitoring. Workplace air monitoring is utilised where an inhalation risk is present. However, this method of measurement does not provide information about other exposure routes. Including, skin absorption and ingestion.
The Benefits of Biological Monitoring
The British Occupational Hygiene Society (BOHS) describes biological monitoring or biological testing as a way in which we can determine how much of a particular contaminant has been taken up by the body from various routes of entry, including inhalation.
This approach can be highly advantageous as it not only provides additional information where there is a respiratory hazard, but it can be used where the main route of exposure isn't inhalation. Further benefits of utilising this method of sampling are:
It can highlight deficiencies in the wearing of personal protective equipment (respiratory protective equipment, protective gloves or gauntlets, chemical resistant clothing).
It provides evidence as part of a medical assessment.
Biological monitoring can be undertaken by retrieving a sample of either breath, blood or urine of which is then examined as a biological specimen from exposed workers. Through the measurement of appropriate determinants, exposures can be identified and further quantified. Common examples of what specimens are obtained to measure exposures are:
Blood - Lead and Mercury
Urine - Cadmium and Methylene bis-orthochloroaniline
Hair and Nails - Arsenic
Breast Milk and Body Fats - Pesticides and Polychlorinated Biphenyls
Expired Air - Carbon Monoxide and Organic Solvents
These types of biological monitoring are known as Direct Biological Monitoring, used to assess the internal dose of the chemical in question with the aim of ensuring the exposure does not reach levels that can cause adverse effects.
Biological Effect Monitoring is another type of monitoring strategy which allows for the assessor to identify early and reversible biochemical changes resulting from exposures. For example, Zinc Protophorphyin will increase in the blood following exposure to Lead because Lead inhibits the biosynthesis of Heme.
Another example is detecting Cholinesterase activity in red blood cells and plasma which would be undertaken to analyse effects following exposure to organophosphate based pesticides which depress cholinesterase activities.
Biological effect monitoring is not health surveillance, through which individuals with early signs of adverse health effects are identified.
Exposure can be measured in a number of ways. A chemical may be excreted from the body without being metabolised and therefore can be measured directly in from the specimen. On the other hand, the chemical may be metabolised through oxidation, reduction, hydrolysis or a combination of these often followed by a biochemical reaction in the body. Therefore, it is critical that a choice of exposure indicator and specific timing requirements should be followed to maximise the sample retrieval effectiveness.
Substances will have a biological half-life, which is the time required form half the substance to be removed by the body by either physical or chemical processing. Substances have a varied half-life. A competent occupational hygienist should emphasise the importance of timing and undertake the appropriate sampling strategy in line with sample requirements set in the occupational hygiene standards. Guidance of these timings are listed in ACGIH (2007).
In the UK, the Heath and Safety Executive (HSE) has established a system of biological monitoring guidance values (BMGVs) as an aid in the interpretation of the biological monitoring data.
These BMGVs are set where they are likely to be of practical value, according to the BOHS. Whereby, suitable monitoring methods exist and there are sufficient data available.
BMGVs can be found in EH40/2005 as consolidated with amendments. This is a useful document produced by the HSE which shows workplace exposure limits set by the HSE.
A free copy can be downloaded here: https://www.hse.gov.uk/pubns/books/eh40.htm
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