0036 Hg Levels in Exhaust Air from Dental Vacuum Systems

M.E. STONE1, B.A. DEBBAN1, M.E. COHEN2, and J.C. KUEHNE1, 1Naval Institute for Dental and Biomedical Research, Great Lakes, IL, USA, 2Naval Institute for Dental and Biomedical Research, Skokie, IL, USA

Objective: This project surveyed Hg levels in air exhausted from dental vacuum systems (not HVAC systems). Methods: Hg vapor levels were measured utilizing three techniques: Ohio Lumex, Inc. RA-915+; which employs atomic absorption spectrometry (detection limit of 2 ng/cubic meter); Jerome 431-X which measures Hg vapor indirectly by changes in electrical resistance in a gold foil (detection limit of 1000 ng/cubic meter) and OSHA method ID-140 which uses calibrated air pumps (Airchek™ model 52, SKC, Inc.), Hg sorbent material (Hydrar™, SKC, Inc.), and atomic absorption spectrometry. Air velocity measurements and temperatures (measured at the center of exhaust ports) were determined with a thermal anemometer (Kurz Instruments™, Inc., model 2441). Flow rates were calculated by multiplying area of the exhaust port by the velocity. Three different dental clinics were sampled. Results: Hg levels from the three clinics with temperature and air flow data are presented below:

Clinic I (110 chairs)
Hg, (RA-915+) a 40,060 (n=19,sd=25,928)
Hg, (431-X) b 55,526 (n=19,sd=43,189)
Hg, (ID-140) c 50,000 (n=8,sd=35,000)
Temp (°F) 155.4 (n=26,sd=2.9)
Velocity, SFM 446 (n=26,sd=46)
Port Surface Area 0.92175 square feet
Flow, SCMM 11.6
ng Hg/min d 580,000
grams Hg/year e 305.1

Clinic II (30 chairs)
Hg, (RA-915+) a 79,511 (n=19,sd=25,628)
Hg, (431-X) b 70,952 (n=19,sd=11,147)
Hg, (ID-140) c 71,000 (n=8,sd=27,000)
Temp (°F) 133.3 (n=26,sd=7.8)
Velocity, SFM 2838 (n=26,sd=368)
Port Surface Area 0.02181 square feet
Flow, SCMM 1.8
ng Hg/min d 127,800
grams Hg/year e 67.2

Clinic III (2 chairs)
Hg, (RA-915+) a 58,368 (n=19,sd=16,136)
Hg, (431-X) b 36,895 (n=19,sd=7894)
Hg, (ID-140) c 33,000 (n=8,sd=10,000)
Temp (°F) 118.9 (n=26,sd=2.9)
Velocity, SFM 829 (n=26,sd=60)
Port Surface Area 0.02181 square feet
Flow, SCMM 0.5
ng Hg/min d 16,500
grams Hg/year e 8.7

aOhio Lumex Hg analyzer, bJerome 431-X Hg analyzer, cSKC calibrated pump and sorbent system; sampling done at 0.2 L/minute over 3 hours. Hg units are in ng/cubic meter, SFM is velocity in standard feet per minute, SCMM is flow in standard cubic meters per minute. Hg levels per minuted (ng Hg/minute) were calculated by multiplying Hg levels from the OSHA method by the flow in SCMM. Ambient Hg levels away from exhaust ports averaged approximately 30 ng/cubic meter. eAssumes continuous operation (worst case scenario).

Conclusions: The three methods used to measure Hg vapor provided similar estimates of Hg concentrations. Hg vapor release to the atmosphere from dental vacuums can be substantial and can exceed OSHA permissible exposure limits (Time Weighted Average of 50,000 ng/cubic meter). Hg binding sorbents may be useful in reducing Hg vapor released to the environment from dental vacuum systems.

This study was supported by the U.S. Navy and by the USEPA's GLNPO.

Russ did you post your study where you were going to take mercury readings all all sorts of different places?

Thought you said you were posting this when you got back (maybe I missed it)

thanks