Mercury vapor levels in exhaust air from dental vacuum systems.

Objective: This study was undertaken to determine mercury (Hg) vapor levels in the air exhausted from dental vacuum systems.

Methodology: Hg vapor concentrations from the dental vacuum system exhaust ports of three dental clinics were measured utilizing the Jerome 431-X mercury vapor analyzer and the United States Occupational Safety and Health Administration's (OSHA) method ID-140 in units of ng Hg/m3. Air velocity measurements and temperatures were determined with a constant temperature thermal anemometer. Hg emissions per unit time were then calculated in ng Hg/min. Ambient Hg concentrations from a location approximately 1000 feet away from the closest clinic sampled in this study were measured with an Ohio Lumex Inc. RA-915+ Hg vapor analyzer.

Results: Mean Hg vapor concentrations analyzed with the Jerome 431-X were: 46,526, 72,211, and 36,895 ng/m3 for clinic I (110 chairs), clinic II (30 chairs) and clinic III (2 chairs), respectively. Mean Hg vapor concentrations utilizing OSHA method ID-140 were 45,316, 73,737, and 35,421 ng/m3, respectively. Air flow values were: 11.6, 1.8, and 0.5 standard m3/min, respectively. Hg emission data utilizing air flow measurements were calculated to be 532,684, 131,353, and 18,079 ng/min, respectively, (P<0.001). There was no statistical difference between the two methods used to measure Hg vapor concentrations. The mean Hg concentration in ambient air approximately 1000 feet from the nearest clinic sampled was 13.2 ng/m3.

Conclusion: The two different methods used to measure Hg vapor concentrations provided similar estimates of Hg concentrations from the exhaust air of three dental vacuum systems. Hg vapor release to the atmosphere from dental vacuums can be substantial and can exceed human exposure limits.