Setting Occupational Exposure Limits for Chemical Allergens--Understanding the Challenges

Abstract

Chemical allergens represent a significant health burden in the workplace. Exposures to such chemicals can cause the onset of a diverse group of adverse health effects triggered by immune-mediated responses. Common responses associated with workplace exposures to low molecular weight (LMW) chemical allergens range from allergic contact dermatitis to life-threatening cases of asthma. Establishing occupational exposure limits (OELs) for chemical allergens presents numerous difficulties for occupational hygiene professionals. Few OELs have been developed for LMW allergens because of the unique biological mechanisms that govern the immune-mediated responses. The purpose of this article is to explore the primary challenges confronting the establishment of OELs for LMW allergens. Specific topics include: (1) understanding the biology of LMW chemical allergies as it applies to setting OELs; (2) selecting the appropriate immune-mediated response (i.e., sensitization versus elicitation); (3) characterizing the dose (concentration)-response relationship of immune-mediated responses; (4) determining the impact of temporal exposure patterns (i.e., cumulative versus acute exposures); and (5) understanding the role of individual susceptibility and exposure route. Additional information is presented on the importance of using alternative exposure recommendations and risk management practices, including medical surveillance, to aid in protecting workers from exposures to LMW allergens when OELs cannot be established.

Keywords: allergens; asthma; chemicals; exposure; occupational; sensitization.

Figure 1. Illustration of the development of allergic sensitization and diseases associated with chemical allergens. Illustration of a simplified description of the onset of allergic sensitization and diseases associated with chemical allergens. In the first phase, sensitization of a naïve individual occurs following an initial encounter with a chemical allergen that results in an adaptive immune response that primes the immune system for future exposures. This is a subclinical phase that is symptomless. Subsequent exposures to the chemical allergen trigger the clinical phase, referred to as elicitation, which manifests as allergic hypersensitivity reactions such as asthma, rhinitis, and allergic contact dermatitis.

Figure 2. Consideration in assessing the health risks of potential chemical allergens. HB = hazard band; OEL = occupational exposure limit; WOE = weight of evidence.Theflowchart illustrates key consideration during the risk assessment of potential chemical allergens. On the basis of the risk assessment paradigm, the outlined process relies on a weight of evidence approach to critically evaluate available data. Included within the flowchart are options within each of the primary steps: hazard characterization, dose-response analysis, exposure assessment, risk characterization, and risk management and communication. These options allow for the evaluation of data, determining appropriate level of recommendation developed (i.e., hazard notation vs. occupational exposure limit), type of exposure assessment, and control technique.