Exposure assessment for chemical and physical agents.

Exposure assessment to either chemical or physical agents, as applicable, is a necessary step for both etiologic diagnosis of occupational disease and health surveillance of workers. The assessment can be carried out by measurements of concentrations in air of the substance by either fixed or personal samplers. The former give an indication of the general environment, the latter, applied near the mouth of the worker, provide personalized information. Dermal exposure (deposition) and absorption occur in the occupational setting, but their measurement is so complex that there are no routine methods and no exposure limits established. Oral exposure is accidental or associated with poor hygienic practices, is very difficult to assess, and there are no occupational exposure limits of oral intake. Also accidental injuries caused by needles or other sharp objects that might be contaminated by chemicals occur but exposure assessment in this condition is almost impossible. Exposure is also assessed by biologic monitoring that entails measurements of the substance and/or of its metabolite(s) in accessible fluids, generally urine, blood, or expired air. Biochemical changes, e.g., enzyme inhibition, associated with exposure are also measured. The results of these measurements are compared with existing limit values in order to conclude on the safety of the working conditions. Since the limit values are derived with the application of conservative assumptions, there are no fine lines between health and disease. Therefore, in the clinical setting values below the limit can be generally regarded as safe. Values above the limits should be considered in conjunction with all other information to judge on the likelihood that the disease under investigation may have been caused by exposure to the substance.