mfety in the chemical loboratory
edited by MALCOLM M. RENFREW Univer~ityof idaho Moscow, Idaho 83843
Student Exposure to Mercury Vapors Joyce Weber California State University, Fresno, Fresno, CA 93740
Laboratory air quality-especially in organic courses where volatile solvents are routinely used-is an issue often raised in THIS JOURNAL (1-3). Elemental mercury has no odor or significant characteristics common t o these organic solvents. But mercury spills occur daily in high school and university laboratories as a result of broken thermometers; and we do know that mercury vapors can he hazardous t o human health. Since mereurv soilled on floors and counter- has a bad hdoit uf rolling into thr ncnreit mark, cullrrring all u i thr spilled mercury l a a n tmpussihle msk. Some inevitably remains. This poses a serious question: Does the level of mercury vapor given off by the residual material constitute a health hazard t o students and faculty working in the lahoratory? A ~rocedurewas develooed a t California Stat* Ilnrverrrty, Freinc. ICSI:FI recently tu munitor mercury vapors m r h r m i s p l a b oratories-several ofwhieh have heen in use 25 years. The purpose was to determine mercury vapor levels in relation to potential health hazards and to establish base line values far future monitoring programs. The Occuoational Safetv and Health Adrn:nil;trdtivr; (OSHA1 has ;rtahliJhcd a fedrrnl -alcly standard fur uurktrv :n manufarIurity facilitirj.This sew the nlaxirnum e x posure limit to mercury vapor a t 0.1 mg/m3 of air per eight-hour period, time-weighted average (TWA). The question of how a n eight-hour industrial standard applies to an
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is an inshuctional support technician and supervisor of stockrooms for the Chemistry Department, California State University. Fresno. She earned a BS in biology at CSUF in 1982 and an MS in health science at CSUF in 1985. Currently she is enrolled in the Certificate Praaram for Hazardous Materials Management at the University of California, Davis. Joyce Weber
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academic laboratory was subsequently addressed by Bayer (4). However, he focused his evaluations on toxic vapors produced from volatile organic chemicals used during a given class period and the subsequent effect of ventilation on the laboratory atmosphere. From this authar'sperspective, mercury spills present a slightly different problem in the classroom since most of the mercury vapor comes from "hidden" mercury present in cracks and crevices in the floorine and under covine. A concern of the cherniGry departmrnt a; CSUF has been thrpotrntiol health haaardofthia"hiddrn" nlercurv, which ir present at all timrk-not just when the classroom is in use. Another concern is whether or not the concentration increases with time. Since no base line data has ever been established, increasing Levels might pose future problems, especially in older classrooms and laboratories. Numerous studies have been conducted on mercury vapor levels in research laboratories ( 5 ) , clinical laboratories (6), and in dental schools (7). However, little monitoring has been done in the academic classroom. One study (8) was conducted previously in the Dallas region on indoor mercury vapor levels in two academic chemistry laboratories. In hoth laboratories, mercury levels were below the OSHA standard maximum. In the present study the mercury vapor was collected on Hopealite (a solid ahsorbent) via personnel sampling-pumps placed a t counter and floor levels. The volume of air sampled ranged from 0.9 m3 to 1.2 m3 collected over a 16-hour period. The mercury collected was desorbed off the Hopcalite with nitric acid and analyzed by atomic absorotion (AAL The cold vaoor method first m i z e d hy ~ a u h a n 0d t t 14, with modificar u m hy Lawrence (101was employed. The AA spectrophotometer was operated a t the spectral line of 253.7 nm wavelength. The combined collection and desorption efficiency of the Hopealite was 9890, and the detection limit was 0.2 ng mercury per milliliter of analytical solution. The facilities in which this study took place included two college science buildings,
the first occupied in 1956, the other in 1976. The older building contained six laboratories, which now house introductory chemistry courses. Before 1976, biochemical, organic, analytical, and physical chemistry were taught in these rooms. Courses taught in the 12 laboratories located in the newer building include organic, biochemical, analytical, and physical chemistry. Air-conditioning facilities in both buildings were one-waysystems; air was not re& culated back into the rooms, hut shunted outside. Since base Line values a t the worstcase level were soueht.. samnles were taken during the winter ireak when no students were [using the laboratorirs. All windows and d w r s were r l ~ a e d ,and rampling took place overnight when there was no traffic in or out of the rooms. One set of samples in each building was obtained when the airconditioning system was operational. A seeand set, taken in three of the rooms in the older building, was obtained when theventilation system was shut down during the winter break. Floor coverings were vinyl tile. Students occupied t h e laboratories 11 months each year. As one might suspect, mercury levels in the newer science building (0-496 ng/m3, Table 1)were consistently lower than those in the older science building (124-874 ng/ m3, Table 2). Levels varied considerably from counter to floor in hoth huildings. However, known spills or experimental procedure accounted for some of this variation. Room 251 in the new science building housed a mercury-containing polarograph a t the time of sampling; and room 262 was the scene of a spill of about 12 pounds of mercury on the floor two years prior to samdine. The older huildine (with its much older vent~latmn system^ also showed a w d e varrntmn from floor t o counter w t h no d ~ s tinct pattern of occurrence in either mercury levels or known mercury usage. The relationship between adequate ventilation in a room and vapor levels was evaluated by Spedding and Hamilton (11). Their results showed that four chanees of air oer hour would result in asteady stateof mercuI). w p c m 81 levels below the OSHA stan-
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dard. Since a normal laboratory ventilation system is designed to produce four t u 12 room air changes per hour (121, even minimal operating conditions would result in low exposure levels t o the student. Table 3 lists results of two sampling runs conducted under different ventilation conditions.
Table I.
Mercury Level (ng/m3, TWA) In Newer Sclence Bulldlng
Room Number
Counter
Fiwr
Organic 350 357 370 372
34 43
57 9
19
ND
7 NO
226 NO
132 14
496
NO
14
...
198 122
366
Biochemistry 344 351
Analytical 234 236
Instrument 251
inorganic 253
Physical Chemistry 262 266
ND
Mercury Levels (nglmJ, TWA) In Older Science Bulldlng
Table 2.
Room Number
Coumer
Floor
152 155 157 241 247 251
124 286 608 502 202 874
564 176 208 600 768
Table 3. Rwm Number 152 155 157
...
Mercury Levels (ng/m3, TWA) In Older Sclence Bulldlng* NO
Area
Ventilation
Ventilation
Counter Floor Counter Floor Counter Floor
124 564
476 476
266 176
1026 846
606 206
2028 2020
Although these two samples were eollectedin the older building (with its25-year-old ventilation system) the results are striking. Except for one floor sample, levels registered when the system was functioning were less than one third of the Levels recorded under no ventilation. It was concluded that an operational vm~ilationsystem has a rignifirant effect on the concentration of vaporb in clarsrwms. Furthermore, student traffic in and out of the rooms during a normal Laboratory period would probably dilute the vapor levels even more. The question of how much mercury has been spilled on our chemistry laboratory floors (end not adeauatelv retrieved) is difficult loanswer. However, we now know rhar rooms in the newer science building at CSUF contaminated with mercury from broken thermometers have much lower levels than those rooms that have been the scene of major spills, or that house mercurycontaining scientific equipment. The levels in these two latter rooms, new science 262 and 251, approximate the levels in the older science building. In conclusion, the current study reveals that mercury contamination of undergraduate chemistry laboratories presents minimal risk to the student. Comparing the OSHA standardof 0.1 mg/m3 withthe mercury levelsfound in these two science buildings indicates that the students and/or instructors a t CSUF are in minimal danger of suffering h e a l t h effects from m e r c u r y v a p o r s present--even if they are in a n academic laboratory eight hours per day. Even with scores of thermometers broken over the years, and minimal clean up, mercury vapor levels are below OSHA standards. That is not t o say that spill clean-up procedures should he neelected. But adeauate ventilatron systems apparently help rumpensaw fur "hidden nun-retrievable" mercury present in all chemistry laboratories.
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Acknowledgment The author thanks Dean Mitchell and Elizabeth Luckett for technical and editorial help. This study was done in partial fulfillment of requirements for the degree of Masters of Science a t California State University, Fresno.
Literature Clted 111 Hertlein,F.,IIIJ.Chem.Edue. 1379.5S,A199.
I21 Car1ton.T.S.J Chem. Educ. 1982,59,53L (8) Frcilcld, M.J.Chem. Educ. 1982.59.A351. (41 Bayer, R. E. J. Chrm.Educ. 1980.57.A287. (51 Goidwater, L. J.; KLeinfeld, M.; Berger, A. B. A.M.A. Amh. Ind. Health 1956.13.245. 161 Harrington, J. M. The l a n c e t 1374,7848.86. (71 Hosein, H. R.:~ o r d A. , B.: Smith, D.C. Ontario Dentiat 1980.57.7. 181 Foote, 8.S. Science 1912,177,513. (91 Hatch. W. R.;Mt, W. L.Anol. Cham. 1968,40,2085. 1101 Lamen-, K. E.; White M.;Pot*, R. A.;Bertrmd,R. D. A n d Chem. 1980,52,1391. I111 Spedding, D.J.; Hamiltan, R. B. Enuiron. RPS. 1982, 29, 30. I121 Bsyer, R. J. Chem. Edue. 1982.59, A385.
Volume 63
Number 9
September 1986
A225
