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

TOX 3.8: Interpreting Biological Monitoring Results

Interpreting biological monitoring results

Biological monitoring results are compared to Biological Exposure Indices (BEIs), which are reference values intended as guidelines for the evaluation of potential health hazards and are primarily indices of exposure. They do not indicate the presence of health effects from exposure to workplace chemicals. While biological monitoring may be used for a limited number of hazardous substances, the existence of a BEI does not indicate a need to conduct biological monitoring unless it is warranted from the findings of the risk assessment and/or air monitoring. For substances associated with acute toxic effects e.g. acids, alkalis, asphyxiants, routine biological monitoring may not be appropriate unless it used to determine the cause of an accidental poisoning incident. With mixed exposures, exposure assessment is usually based on the concentrations of each of the constituent substances, unless effects are known to be additive or synergistic. In some instances, where routine monitoring indicates that the relative concentration of chemicals is constant, selection of a key marker, which may be one of the constituents, can be used. Exposure to the marker is then controlled to a level such that exposures to all components will be controlled.

The results of biological monitoring may be interpreted at an individual or group level by considering their statistical distribution. Greater significance should be given to the variations in an individual's level from period to period than to differences between individuals within a group. At a group level, if all the observed values are significantly below the BEI, the working conditions may be assumed to be satisfactory. If the majority (to be defined at the outset) of the results are above the BEI, the cause of the excessive values must be investigated and action taken to reduce exposure. The Department of Labour must also be notified when such incidents denote high exposure.

Ethical considerations

To prevent results from being used in a discriminatory manner, ethical considerations (informed consent, confidentiality) are required in the application of biological monitoring in the workplace. Since monitoring is undertaken to provide an indication of the level of absorption of a workplace hazardous substance, group data should be made available to people who will investigate and, when necessary, improve the work environment. For this reason, it is important that worker participation is on a voluntary basis and informed written consent is obtained before individual quantitative results are released to the employer.

Worker notification programmes

A biological monitoring programme must be well planned and part of a larger programme which includes environmental monitoring. Participating workers must understand its requirements and objectives, and be informed of how the results will be handled. Appropriate feedback to the individual, employer and enforcement agency is a necessity. Under the MHSA requirements, the results of biological monitoring must be clearly stated in the exit certificate issued to the worker on termination of employment.

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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