Biological monitoring is the measurement of a substance or its metabolites in body fluids such as urine or blood. It provides a complementary approach to air monitoring for estimating exposure to workplace contaminants.
Biological monitoring provides a better indication than air monitoring of the bodies uptake of the chemical. It provides information on the addition of non-workplace exposures, respiratory protection practices, absorption through other routes such as the skin and hand to mouth absorption and the effectiveness of elimination practices.
Biological monitoring has been widely used to monitor the uptake for accumulative toxins; for example lead, mercury and organophosphates.
It is important to observe the timing of the sample collection. The level of a substance will vary with the time elapsed since last exposure and the BEI (Biological Exposure Index) for some substances is only applicable if the recommended timing of sample collection is closely adhered to.
If there has been continual exposure over the working day, the following potential sample periods have been used.
Prior to next shift: Following a period of 16 hours with no exposure (Suitable for substance ‘promptly’ but not rapidly eliminated.)
End of shift: The last 2 hours immediately following the end of the working day (Suitable for substance ‘rapidly’, whose measured levels could have fallen substantially if sampling was delayed until just prior to the next shift)
End of work week: After at least four days with exposure. (Suitable for substances eliminated more slowly and thus incompletely over 24 hours, causing some accumulation with the highest levels observed on the final day)