Variability in airborne and biological measures of exposure to mercury in the chloralkali industry: implications for epidemiologic studies.

Abstract

Exposure assessment is a critical component of epidemiologic studies, and more sophisticated approaches require that variation in exposure be considered. We examined the intra- and interindividual sources of variation in exposure to mercury vapor as measured in air, blood, and urine among four groups of workers during 1990-1997 at a Swedish chloralkali plant. Consistent with the underlying kinetics of mercury in the body, the variability of biological measures was dampened considerably relative to the variation in airborne levels. Owing to the effects of intraindividual variation, estimating workers' exposures from a few measurements can attenuate measures of effect. To examine such effects on studies relating long-term exposure to a continuous health outcome, we evaluated the utility of each exposure measure by comparing the necessary sample sizes required for accurate estimation of a slope coefficient obtained from a regression analysis. No single measure outperformed the others for all groups of workers. However, when workers were evaluated together, creatinine-corrected urinary mercury better discriminated workers' exposures than airborne or blood mercury levels. Thus, pilot studies should be conducted to examine variability in both air and biomonitoring data because quantitative information about the relative magnitude of the intra- and interindividual sources of variation feeds directly into our efforts to design an optimal sampling strategy when evaluating health risks associated with occupational or environmental contaminants.ImagesFigure 1

Personal light-at-night exposures and components of variability in two common shift work industries: uses and implications for future research

“…This was examined in the current study by collecting repeated measurements from 49% of participants. Low within-worker variability (range 2.3-11.4% of total variance) was observed for all LAN exposure metrics; differing from other occupational studies that have demonstrated high withinworker variability for exposures such as magnetic fields (28) and mercury (29). This is likely due to the relative stability of LAN, where exposures are less affected by specific work tasks or activities compared to other types of occupational exposures.…”

Evaluation of mercury in urine as an indicator of exposure to low levels of mercury vapor.

“…2) Subjects of studies should have chronic exposure to airborne mercury (i.e., at least 6 months based on the time for mercury in urine to reach steady state with exposure to mercury vapor) (ACGIH 2000). 3) Air measurements should be collected over most of a day [preferably averaged over several days to ameliorate high reported variation in day-to-day exposures of workers (Symanski et al 2000)] and should be expressed as a time-weighted average (TWA). 4) Urine data should be expressed as an average of multiple spot samples per individual or as an average of urinary data from several individuals.…”

“…Log transformation greatly reduced the nonhomogeneity of variance (Figure 2). A recent regression analysis of variation in airborne and biologic mercury concentrations in workers also used log-transformed data (Symanski et al 2000).…”

Evaluating measurement error in estimates of worker exposure assessed in parallel by personal and biological monitoring

“…Studies to assess measurement error in monitoring data have been carried out on workers exposed to styrene in the reinforced plastics industry [Rappaport et al, 1995;Symanski et al, 2001;Liljelind et al, 2003], mercury in the chloralkali industry [Symanski et al, 2000], and dust in the carbon black manufacturing industry [van Tongeren et al, 1997], the construction industry [Tjoe et al, 2004], and sawmills [Teschke et al, 2004]. Taken together, these studies indicate that attenuation effects of imperfectly measured exposure can be quite substantial.…”

“…Taken together, these studies indicate that attenuation effects of imperfectly measured exposure can be quite substantial. Few studies, however, have had the requisite data to make comparisons between different methods of assessing exposure [Rappaport et al, 1995;Symanski et al, 2000;Symanski et al, 2001;Liljelind et al, 2003;Lin et al, 2005], and none employed a study design to insure that the same workers were monitored over common periods using multiple sampling methods. Thus, we carried out a study to quantify measurement error in multiple measures of exposure collected in parallel on groups of workers exposed to different contaminants from a broad cross-section of industries.…”