Exposure assessment for epidemiology: characteristics of exposure.
Smith TJ; Hammond SK; Hallock M; Woskie SR
Appl Occup Environ Hyg 1991 Jun; 6(6):441-447
Various characteristics of occupational exposures were discussed in terms of epidemiological exposure assessments for industrial hygiene research. Composition and intensity of occupational exposures varied by type of job and workplace conditions, thus complicating retrospective assessment of long term exposures. Factors affecting exposure included source, transport, worker components and setting. Two models for estimating past exposures were discussed and illustrated with an ongoing study of hydrocarbon exposures in gasoline transport workers. The source receptor model estimated exposure over time as a function of source output composition and strength, transport processes, worker position relative to source, exposure controls at source or worker and subject's work activities. Historical changes could be analyzed in terms of materials, processes or work site configuration. The task specific time weighted average (TWA) model utilized limited monitoring data with job title and work location. This model provided statistical distributions of overall TWAs for job title exposure assignments and a method for historical estimates of full shift exposures based on changes in job exposures. The TWA model was especially useful for TWA exposure extrapolations from short term task data with potential high exposures. TWA distribution was not necessarily lognormal, even when individual task exposure levels were lognormally distributed. A simple mathematical model was used to identify types of cases where statistical distributions of full shift TWA exposures were lognormal or nonlognormal. Both models were useful for assessing potential errors in exposure estimation. The authors conclude that consideration of various exposure measures is important because less quantitative measures based on nature of operations and job activities can be useful in some cases for epidemiologic assessment of etiologic hypotheses.
NIOSH-Publication; NIOSH-Contract; Contract-91-38661; Humans; Industrial-hygiene; Epidemiology; Exposure-levels; Occupational-exposure; Health-hazards; Materials-transport; Statistical-analysis; Analytical-models
Applied Occupational and Environmental Hygiene