Module 3: Toxicology - Section 3: Linking Chemical Exposures and Health Effects

TOX 3.7: Advantages and Disadvantages of Biological Monitoring

Advantages and disadvantages of biological monitoring

Although environmental measurements can be very useful in determining the sources of exposure and in identifying priorities for control measures, biological monitoring may offer several advantages for the following reasons:

• More direct indicator of risk to health since it measures the total absorbed dose of the substance.
• Takes into consideration absorption by routes other than lungs and is especially useful for substances absorbed through the skin or which enter the body by ingestion.
• Accounts for individual variations that influence uptake as well as non-occupational background exposure e.g. smoking, dietary habits.
• By integrating absorption from all exposure sources it can be used to gauge the overall effectiveness of workplace controls or where there is great dependence on personal protective equipment.

One of the major drawbacks of biological monitoring is that it detects uptake of hazardous substances after exposure has occurred. It also has little preventive value in monitoring workers with exposure to substances that exhibit their toxic effects at sites of first contact (e.g. primary lung irritants). Furthermore biological monitoring cannot always be used as an indicator of health risk unless the relationship between external exposure and internal dose is known.

Sampling Strategies For Biological Monitoring

Since the amount of the chemical substance or its metabolites in collected samples of blood or urine is very small, utmost care is required in sample collection to avoid contamination and, possibly, misleading results. The sampling strategy is determined by prior knowledge of the biological half-life of the substance in the biological fluid that is sampled. The shorter the biological half-life of a substance (e.g. benzene, arsenic), the more indicative it is of recent exposure.

For this reason, it is recommended that samples are taken at the end of the shift or the work week (i.e. when levels are expected to be at their highest). For substances with relatively long half-life (e.g. mercury, lead), the timing of the sample is less important. However, the timing for the collection of a chemical with a long biological half-life generally requires a period of exposure (e.g. six months) before biological monitoring will give meaningful results. If samples are not representative, or are not correctly collected or stored, the analytical results can be meaningless or misleading. Another issue to address is that corrections may be necessary e.g. creatinine levels when collecting urine samples to take in account overall kidney function.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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