Epidemiologic assessment of measures used to indicate low-level exposure to mercury vapor (Hg)

Mercury (Hg) concentrations in individual spot urine samples collected over consecutive 1-d periods were compared with Hg concentrations measured in combined 24-h urine samples from 69 practicing dental professionals with low exposure to Hg vapor (Hg) in order to validate the use of spot urine samples as an indicator of Hg exposure. The level of Hg in air as an exposure measure was also evaluated by comparing air concentrations of Hg in dental offices with both spot and 24-h urine Hg levels. The results showed: (1) There was little diurnal variation (approximately 9%) in urinary Hg values; (2) a strong correlation (R2 = .85) exists between the Hg concentration in the first morning void and that in a complete 24-h urine sample; (3) adjustment of urinary Hg levels for creatinine concentrations did not improve this correlation; (4) there was no added value in the speciation of total urinary Hg into the inorganic Hg fraction; and (5) concentrations of Hg in air did not significantly correlate with measures of Hg in urine at this low Hg exposure level. We conclude from this study that first morning void urine samples may be used to derive reasonably valid estimates of Hg concentrations found in the total amount of urine collected over a 24-h period. Thus, due to its comparability, ease of collection, and lower cost, the first morning urine void may be used in place of a sample collected over a full 24 h to facilitate Hg exposure assessments in epidemiologic studies that use urinary Hg levels as a measure of low-level Hg exposure.