THE RELATIONSHIP BETWEEN ENVIRONMENTAL MONITORING AND BIOLOGICAL MARKERS IN EXPOSURE ASSESSMENT

The poor quality of traditional assessments of exposure has encouraged epidemiologists to explore biological monitoring in studies of chronic diseases. Yet, despite theoretical advantages, biomarkers have not been widely used in such applications. This article compares the general utility of a biomarker with that of the measurement of exposure per se. Points are illustrated with a longitudinal study of boat workers in which levels of styrene in the breathing zone and in exhaled air were compared to sister chromatid exchanges (SCEs) in peripheral lymphocytes. First, the linear relationship is explored between personal exposure and the levels of a biomarker in the cohort. A good fit to the straight-line relationship reflected by a correlation coefficient which is close to 1,such as observed with styrene in exhaled air (r(2)=0.83), suggests linear kinetics, that the appropriate route of exposure was measured by personal monitoring, small interindividual differences, adequate sample sizes, and a specific biomarker. However, a small correlation coefficient, as observed between SCEs and styrene exposure (r(2)=0.11), indicates that either kinetics were nonlinear or that more complex issues were involved with one or more of these factors. Second, environmental and biologic measurements are compared for use as independent variables in establishing a straight-line relationship between exposure and the health effect, ii the ratio of the within-person to the between-person components of variance of ?he independent variable is large, then significant attenuation results when estimating the slope of the line. Since such attenuation can be reduced by making repeated measurements on each person in the cohort, the sample sizes required to reduce the bias to a fixed level can be used to compare the various measures of exposure. Using data from the styrene-exposed workers, it is shown that the slope being estimated would be within 10% of the correct slope parameter with 3 personal measurements of exposure compared to 4 samples of exhaled air (12 measurements) and 20 assays of SCEs. Thus, in this case, the measurement of airborne exposure would be more efficient than that of either exhaled air or SCEs for epidemiologic purposes.