Biological monitoring provides one means to assess exposure and health risk to workers. It entails measurement of the concentration of a chemical determinant in the biological media of those exposed and is an indicator of the uptake of a substance, expressed on the form of a Biological Limit Value (BLV).
Biological Monitoring Guidance Values are either based on:
▪ A relationship between biological concentrations and health effects;
▪ A relationship between biological concentrations and exposure at the level of the WEL or
▪ Data collected from a representative sample of workplaces correctly applying the principles of good occupational hygiene practice.
BMGVs are set where they are likely to be of practical value, suitable monitoring methods exist and there is sufcient data available.
In the United States, Biological Exposure Indices (BEIs) are an example of BLVs for assessing biological monitoring results. Similar standards exist in the UK in the form of Biological Monitoring Guidance Values (BMGV).
BEIs represent the levels of determinants that are most likely to be observed in specimens collected from healthy workers who have been exposed to chemicals to the same extent as workers with inhalation exposure at the Threshold Limit Value
(TLV).
The exceptions are the BEIs for chemicals for which the TLVs are based on protection against nonsystemic effects (e.g., irritation or respiratory impairment) where biological monitoring is desirable because of the potential for signicant absorption via an additional route of entry (usually the skin).
Biological monitoring indirectly reects the dose to a worker from exposure to the chemical of interest. The BEI generally indicates a concentration below which nearly all workers should not experience adverse health effects. The BEI determinant can be the chemical itself; one or more metabolites; or a characteristic, reversible biochemical change induced by the chemical. The BEIs are not intended for use as a measure of adverse effects or for diagnosis of occupational illness.
Biological monitoring can assist the occupational health professional to detect and determine absorption via the skin or gastrointestinal system. In addition to that by inhalation;
▪ Assess body burden;
▪ Reconstruct past exposure in the absence of other exposure measurements;
▪ Detect non occupational exposure among workers;
▪ Test the efcacy of personal protective equipment and engineering controls; and
▪ Monitor work practices.
Biological monitoring serves as a complement to exposure assessment by air sampling. The existence of a BEI does not indicate a need to conduct biological monitoring. Conducting, designing, and interpreting biological monitoring protocols and the application of the BEI requires professional experience in occupational health and reference to the current edition of the Documentation of the Threshold Limit Values and Biological Exposure Indices (ACGIH).
Section 4 of the ILO Code of Practice: Occupational Exposure to Airborne Substances Harmful to Health sets out the principle that:
‘Whenever valid biological monitoring methods are available, they should be used to complement monitoring of the working environment in order to increase protection of workers’ health.’
If a result exceeds the Biological Limit Value (BLV), it does not necessarily mean that ill-health will result; however it does indicate control measures may not be adequate and more could be achieved.
The advantage of BLVs is that they provide an accurate estimation of the actual exposure and therefore a denitive indication of whether control measures are effective.
Advantages
BLVs are set where they are likely to be of practical value, suitable monitoring methods exist and there is sufcient data available. The advantages of this approach are:
▪ It can be a very useful complementary technique to air monitoring when air sampling techniques alone may not give a reliable indication of exposure;
▪ It provides an accurate estimation of the actual exposure and therefore a denitive indication of whether control measures are effective.
▪ The overall exposure results are from all routes, i.e. inhalation, ingestion, absorption and injection; and
▪ The exposure does not need to have been observed, thus can be used where air monitoring is not practicable. It is also effective for monitoring intake of illegal substances.
Disadvantages
The disadvantages of biological monitoring, however, are:
▪ It can be expensive – requiring occupational health and laboratory resources.
▪ A number of external factors may affect the results:
▪ individual differences in metabolism;
▪ health status of the individual; and
▪ when the sample is taken.
▪ It is by nature a reactive form of monitoring i.e. if an excessive concentration of material is found within the worker’s body, it is too late – the harmful exposure has already occurred;
▪ It can be invasive and staff may be uncomfortable with giving samples; and
▪ Only a certain number of substances can be monitored in this way.
BLVs are not an alternative or replacement for airborne exposure limits. BLVs are generally non-statutory and any biological monitoring undertaken in association with a guidance value needs to be conducted on a voluntary basis (i.e. with the fully informed consent of all concerned).
Monitoring may need to be carried out at a specic time, e.g. immediately post-shift.
This is because some substances will be quickly metabolised. Alcohol for example, is metabolised at approximately one unit per hour; thus the testing needs to be undertaken as soon as possible.