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| Module 1: Occupational Hygiene - Section 3: OH Standards |
| OH2.4: Biological Standards and Exposure to Mixtures of Hazardous Substances |
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| Module 1: Occupational Hygiene - Section 3: OH Standards |
| OH2.4: Biological Standards and Exposure to Mixtures of Hazardous Substances |
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One of the most useful means of assessing exposure to hazardous substances is the analysis of biological samples that are obtained from exposed workers. This analysis may provide an indication of body burden of the substance, amount circulating in blood, or amount excreted.
Biological exposure monitoring has some advantages over air sampling. For example, substances absorbed through the skin and GIT are accounted for over and above what is inhaled. Therefore a more integrated measure of exposure can be obtained.
Differences in stature, health status and work habits among workers may influence how much of the substance is absorbed and how the body metabolizes the absorbed substance. For example, women or children may be more susceptible to the effects of exposures in the external environment. Biological exposures may therefore be higher than for adult males for the same external exposures.
Biological Exposure Indices (BEI's) are reference values that are used in a similar way to exposure standards to indicate overexposures that could result in health effects. They are contained in Table 3 of the Regulations for Hazardous Chemical Substances. BEIs do not necessarily indicate an actual health risk, but indicate a need for corrective action.
Biological exposure monitoring is not intended to replace air monitoring, but is used to complement it. As such it can be used to substantiate air monitoring results, to evaluate effectiveness of personal protective equipment, or to evaluate potential for dermal exposure.
When two or more hazardous substances which act on the same organ system are present, their combined effect rather than the effects of either individually should be given primary consideration.
Examples of processes which are typically associated with two or more harmful airborne contaminants are welding, automobile repair, blasting, and certain foundry operations.
Additive Substances:
In the absence of information to the contrary, the effects of the different hazards should be considered additive. That is, if the sum of the following fractions exceeds one, then the threshold limit of the mixture should be considered as being exceeded.
Synergistic Substances:
The Synergistic effect of mixtures is an effect that is greater than the sum of individual effects. Synergistic action or potentiation may occur with some combinations of airborne contaminants. Potentiating agents are not necessarily harmful by themselves but only when present jointly with another agent.
Synergistic effects of substances are considerably less common but are more serious in their effec, requiring the strictest control.
Independent Substances:
Independent substances typically involve single exposures. Where there are multiple exposures and where synergistic are not considered likely, constituents can be regarded as acting independently in the sense of additively. So this is another term for Additive Substances above. Then it is sufficient to ensure compliance with each of exposure limits individually.
