Document zzMMEVq0K2dR9k7GjRmqBL9O0

j *i-<* .n ,,r.e .ower tropospnere ana weetts in the upper tropospnere 114. .'i>. any cloud seeding with Agl at some distant location and previous time could have enhanced the Ag aerosol concentrations. Because Cd is the most volatile element under study, its behavioral pattern mav result from fossil fuel combustion at some distant time and place. Seasonal differences, with associated causes, are most pronounced with Al and Mn. The increase in aerosol Pb appears to be related to the return of 2000 students (and associated autos) for the fall semester. Less explainable though are the reasons for the reduced Cd, Co, Tl, and Zn concentrations during the drier and dustier 1974 summer season, unless these elements, too, are at times from an thropogenic sources. Their sources may be difficult to doc ument. Acknowledgment The author is grateful to Michele Daniels, Michael Diechart, Kermit Kinsley, Marie Smith, and John W. Win chester for technical assistance and advice. Literature Cited (1) Stwempler, A. W., "Adsorption Characteristics of Silver, Lead. Cadmium. Zinc and Nickel on Borosilicate Glass, Polyeth ylene and Polypropylene Container Surface," Anal. Chem., 43, 2251--1 (1973). (2) NOAA, EDS-NCC. "Annual Climatological Summary for Chadron, Nebraska, 1973," Federal Building, Asheville, N.C- 23801. (3) Ibid.. 1974. (4) Nat. Air Pollut. Control Admin. Pub. No. AP-49, "Air Qualitv Criteria for Particulate Matter." 1969. tester, j. A , Brar. a. S,, N'eison. D. M.. Areawide Trace Metna- Concentrations Measured by Multielement Neutron Activation Analysis: A One Day Study in Northwest Indiana." J Atr p-, lut. Control Assoc.. 21, 363-70 (1971), (6) Kay, M. A., McKown. D. M.. Gray, D. H., Eichor, M. E. Vogt. J. R.. "Neutron Activation Analyse in Environmental Chem*/ try." .4m. Lab.. July, 1973. mw' (71 John. W., Kaifer, R,, Rahn, K., Wesolowski. J, J,, "Trace Ele- ment Concentrations in Aerosols from the San Francisco Bsv Area." Atmos. Environ.. 7, 107-18 (1973), y (8) Shum. Y. S.. Loveland, W. D., "Atmospheric Trace Element Concentrations Associated with Agricultural Field Burning in the Williamette Valley of Oregon," ibid.. 8,645-55 (1974). 19) Hoffman. G. L.. Duce, R. A., Zoller. W. H,, "Vanadium, Cap per, and Aluminum m the Lower Atmosphere between Califor nia and Hawaii." Environ. Sci. Techno!., 3, 1207-10 (1969). (10) Duce, R. A., Hoffman. G. L., Zoller. W. H,, "Atmospheric Trace Metals at Remote Northern and Southern Sites: Pollution or Natural?." Science, 187,59-61 (1975). (11) Zoller. W. H,, Gladney, E. S.. Duce, R. A., "Atmospheric Con- centrations and Sources of Trace Metals at the South Pol*" ibid.. 183, 193-200 (1974). (12) Mason. B.. "Principles of Geology," 3rd ed.. Wiley & Sons New York. N.Y., 1966. (13) Nat. Acad, of Sci., "Lead, Airborne Lead in Perspective." Washington. D.C.. 20418.1972. (14) Poet, S. E., Moore, H. E., Martell, E. A., "Lead 210. Bismuth 210. and Polonium 210 in the Atmosphere: Accurate Ratio Mea surement and Application to Aerosol Residence Time Determi nation," J. Geophys. Res., 77,6515-27 (1972), (15) Rasool, S. I., ed.. "Chemistry of the Lower Atmosphere." Ple num Press, New York. N.Y., 1973. Received for review September 9, 1974. Accepted August 20.1975 Work supported m part by the Chadron State College Research Institute. Performance of Charcoal Tubes in Determination of Vinyl Chloride John E. Cuddeback*, William R. Burg, and Shelton R. Birch1 Department of Environmental Health, University of Cincinnati, Cincinnati, Ohio 45267 The adsorption characteristics of airborne vinyl chloride on activated charcoal was examined for use as an analytical sampling device. Data are presented to show that charcoal has a limited yet useful capacity for adsorbing low levels of vinyl chloride. Breakthrough volumes, sampling rates, and storage characteristics are presented that indicate a 100-mg portion of activated charcoal in a sampling tube has a ca pacity of at least 65 ug of vinyl chloride with a twofold safe ty factor when sampling air containing 5 ppm of vinyl chlo ride. Analytical methodology is described that produced a 90% recovery of vinyl chloride even after two weeks of sam ple storage. The need for analysis of ambient air for low levels of vinyl chloride monomer iVCM) was recognized -January 22, 1974, It was on this day that it was made puDlic that three polymerization reactor cleaning personnel at the B. F. Goodrich Co. plant in Calvert City, Ky.. had died of a rare form of liver cancer. The results of this announcement was an immediate implication of VCM as a cancer suspect agent. The ensuing investigation if, 2) indicated the need for an accurate analytical method for low level work. 1 Present address. L'SAF Environmental Health Laboratory, Kelly AFB. Tex. The Environmental Protection Agency (EPA) and the National Institute of Occupational Safety and Health (NIOSH) were concerned with monitoring personal and en vironmental exposure to VCM. The EPA was concerned with airborne concentrations of VCM that were transport ed beyond the plant boundaries into the surrounding com munity and would be covered under the National Hazard ous Pollutant Standards. On the other hand, NIOSH re quired in-plant exposure data in order to advise the Occu pational Safety and Health Administration lOSHA) on safe working standards. After the announcement by B. F Goodrich Co. there was a flurry of measurement and standards-setting activity; the OSHA standard went from 500 ppm <3) to 50 ppm (4) to 1 ppm (5). As of this writing the EPA has yet to set an emission standard, however, a iarw amount of data has been obtained from the ambient air rhe vicinity of polyvinyl chloride plants (6). and this be the basis for future research. The general sampling method finally chosen bv the EPA and NIOSH was based on absorption of VCM on charco*i followed by desorption by CS? and gas chromatograph"-' analysis. The major difference in the methods ui the t*v agencies was the size of the sampling device and amount ocharcoal used; the EPA used an lS-in. tube with three 3-sections of charcoal (6) and NIOSH used a smaller tut* with about one inch of charcoal divided into two unequal sections (7, 8). The EPA is finalizing a method for air s*' 1U1 Environmental Science A Technology SL 068786 41 ay nt in 'P- or*nc on .>n- -ns. ve, ;uth lea-tiU' Pie- .Ji?r5 arch '.MQuV - a: - 3f i r' f 100 TjOe V VOCuum House Air 1 Xnorcooi Tube V i L^S ! ia5 ; - n C l*irqrnptc - i i ! grQDh Sampling Voive Figure 1- Dynamic dilution system tor charcoal tube testing and caltwation cl gas chromatograph r100 90 ) 30 i 70 r 60I 50|0- 3 $ 30- 20- rni j . i/ J Figure 2. Breakthroui J curves tor 25 ppm ,/ ' vinyl chloride: samplii // nr>Q?&V rates, +50 cc/mi 0-100 cc/min. ai X150 ec/mm iC 15 20 25 30 35 40 45 VOLUME SAMPLED (liters) i the ealth d enerned iport- COffl- izardH reOccu\) on B. F. Stan- m 500 ng the i large air in .s may e EPA \arcoal raphic ne two junt of inequal ir sam pling at this time (9). The charcoal-filled tubes have been extensively used by both of the agencies for field studies of VCM levels in air: however, there has not been a thorough description of the performance parameters and thus our laboratory undertook an examination of the charcoal tube absorption method for VCM. Experimental Apparatus and Procedures Calibration and Standards, Known concentrations of ''CM were obtained in the flow dilution system (Figure 11 with a gravimetrically calibrated permeation device made as described previously (10). A combination of two differ ent permeation devices and variation of dilution air provid ed a concentration range of 0.5-50 ppm VCM. Solution standards were also made by injecting known volumes of 1CM into volumetric flasks*containing measured quan tities of carbon disulfide. The flasks were sealed with a sili cone rubber septum before injecting the VCM. and adjust ment was made for atmospheric conditions assuming ideal ess behavior. Solution standards were made fresh daily as needed. Samples from the dynamic flow dilution system '''ere periodically checked against solution standards so (bat solution standards were not often needed and served only as a cross-check. Sampling Equipment. Samples were obtained by drawmg a metered stream of air through charcoal tubes ob tained trom the Mine Safety Appliance Co. The tubes were 'be small type used for personal monitoring (S) and were bom a single batch of charcoal. The sampling system is ^thematically shown in Figure 1. The regulated house vacu- Ur" astern was used to draw samples through the charcoal tubes thus providing a constant flow. Effluent from the Table I. Retention Data for Vinyl Chloride on Charcoal Tubes Vinyl chloride concn. ppm Sample rate. ml/min Mass VCM Retention (low rate. Retention time. ug/mtn volume, lJ mmJ Total mass. c 50 0.639 10.0 200 5 100 5 150 25 50 1.278 1.916 3.19 9.8 29.3 7.9 98 195 158 25 100 6.38 22.8 228 25 150 9.58 20.5 137 50 50 6.38 9.0 180 50 100 12.78 18.1 181 50 150 19.16 14.8 98.7 J At 10 . DreaKtnrough from front section of tube. 127.9 125.2 373.6 504 1456 1312 1285 2311 1891 charcoal tube was sampled by means of a stainless steel seven-port sampling valve with a calibrated (ID loop sys tem. the loop could be used for direct air sampling when the charcoal tube was not in line. Analytical Equipment. Analysis of flow system gases was performed directly using a Tracor MT 160 chromato graph equipped with a flame ionization detector. The oper ating conditions were as follows: column 6 ft X % in. stain less steel, column packing Poropak Q, column temperature 135C, inlet temperature 150*0. detector temperature 175C, carrier gas flow rate 30 cc/min of nitrogen. Peak areas were computed by means of a Disc Integrator. The detection limit for VCM was 1 ng. Sample Analysis. Analyses of air samples were made di rectly using the calibrated gas-sampling loop. Air was drawn through the sampling loop for 30 sec at 100 cc/min before injection to achieve reproducible results. The detec tion limit was less than 0.1 ppm VCM when using a 3.81-ml sample volume. A charcoal tube was placed in series with the sample loop and the effluent analyzed when determin ing sampling efficiencies. The charcoal tubes were analyzed for VCM by placing the charcoal in a 2-ml glass vial and sealing the vial with a silicone rubber septum. The vial was then cooled to dry ice temperatures for several minutes be fore injecting 0.5 ml of room temperature carbon disulfide through the septum. The vial was removed from the dry ice when the bubbling produced by the mixing of the carbon disulfide and charcoal ceased. The vial was allowed to stand at room temperature for 5 min before removing 5 *d of the solution from the sealed vial for injection into the chromatograph. ResuLts and Discussion Sample Capacity. Testing of the charcoal tubes was un dertaken to determine their capacity for vinyl chloride. In these tests only the front portion of the two-section char coal tube was used. Figure 2 illustrates a set of break through curves obtained when sampling from a 25-ppm VCM in dry air (less than 20% r.h.). The general sigmoid shape of the breakthrough curves remained the same for 5and 50*ppm samples. Data for three concentrations of vinyl chloride are presented in Table I. There is not a definite trend with sample concentration and breakthrough volume nor is there a firm trend with sampling rate and break through volume. It is apparent, however, that the 50-cc/ min sample rate had a 10% breakthrough volume that was lower than when sampling at higher flow rates in all cases. Table II gives packing data for the front section of char coal tubes from two manufacturers. As can be seen there is considerable variation both in total content and how effec- pausing n ir.e L^urcoai ruses mav explain idCK at consis tency between the 100- and 150-cc, mm sampie rates as noted in Table [, however, this does not explain the consis tently lower retention volume for the 50-cc/min flow rate. One further point should be made concerning the possible differences when used in the field with a reciprocating pis ton-type pump: The flow in the system used in our experi ments was a constant vacuum source and did not have the pulsed flow observed with the small personal pumps. The pumping system may radically alter the retention charac teristics and give more consistent results between the high flows and the low flows. The variability of charcoal in absorbing VCM can be readily seen in Table III which presents data on respirators as well as charcoal tubes. Respirator data were obtained by NIOSH (12) on commercially available charcoal scrubbers used in respirators. The major feature of interest is the dif ference in capacity of the charcoal in the three situations examined. Again the difference must be explained as a combination of flow rate and packing characteristics. The data obtained on the charcoal tubes were taken at a much lower relative humidity which may explain the appreciably greater capacity of the tubes. Recovery of VCM. Desorption of a substance from charcoal is dependent on variables such as compound to be desorbed, solvent, charcoal source, temperature, and sam ple age. Table IV presents the recovery data for charcoal tubes stored for up to two weeks. The recovery figures indi cate an average initial recovery of vinyl chloride of about 87.5% which diminishes somewhat with age, about 7% in one week. Additional storage beyond one week apparentlv has little effect on the higher concentration sample. How ever, if only the two variables, storage time and concentra tion, are considered, a 16% decrease m recovered vinyl chloride was noted for the low concentration samples after 14 days. During sample storage there was migration of the vinyl chloride from the front section to the back section of the tubes and this made analysis of both sections mandatory in order to determine total VCM. The tubes were stored at room temperature and the migration could have been mini mized by storing under refrigeration. This migration may explain the slight decrease in the average sample recovery upon storage if it is assumed that the charcoal retains a cer tain fraction of vinyl chloride. Thus, there is an added amount of charcoal that must be considered after migra tion. A straightforward linear approach indicates that the amount retained would "be 1.5 times greater than if ail of the vinyl chloride were on the front section--i.e., the total amount of charcoal would be 150 mg instead of 100 mg on front only. As shown in Table III, the average loss with no storage is 13% and increases to an average of 19% for 7 days and 24% for 14 days whereas a linear approximation would predict 19.5% average loss due to the additional charcoai. Migration was observed between the sections of the char coal tube and led to the examination of the effects of tem perature plus the possibility of losses by migration out of the tube to ambient air. To examine variations in migration with temperature and losses from the tubes, a senes of tubes were stored at 43. 22, and 4C, sealed by ordinary plastic caps supplied with the tubes or fused closed by means of a torch. Table V presents the data from 24 sam ples. There is one immediately apparent factor: storage at 4SC limits migration severely during the seven-day storage period. Even at the end of 15 days the migration of vinyl chloride between the two sections was appreciably hin dered. Thus, there is a definite effect of storage tempera ture on the migration of vinyl chloride throughout the tube: Table il. Packing Variations in Charcoal Tubes Supplier front section packed length, mm Front section Wt. of pecking, mg MSAJ 18.2 MSAJ 14.6 MSA Av 16.6 15.5 % rel. std. 10.9% deviation SKC6 * * * * 15.1 SKC SKC 15.2 14.1 SKC SKC SKC Av % rel. std. deviation 16.6 17.0 17.2 15.9 7.8% JMine Safety Appliance Co, &SKC, me. 103.1 92.8 103.2 99.7 6.0% 85.0 82.4 86.2 87.3 90.5 35.9 86.2 3,1% Wt 9/mm 5.66 6.36 6,22 6.08 6.1% 5.63 5.42 6.11 5.26 5.32 4.99 5.45 7.0% Table III. Ten Percent Breakthrough Capacity of Charcoal Absorbers Cartridges.11 sample capacity Canisters.6 sample capacity Charcoal tubes,sample capacity Air. 1 Ig charcoal VCM, mg/g charcoal Air, l/g charcoal VCM, mg/g charcoal Air, l/g charcoal VCM. mg/g charcoal 44.9 5.7 48.9 12.5 148 18.9 36.6 4.7 53.5 13.3 181 23.1 41.1 5.2 35.8 9.1 90 12.8 40.0 5.1 40.1 10.2 . ** ciow rate. 30 l/mn at 50 Opm and 50% fl. numidity (Re#. 12). " Flow rate. oQ l/mm at 100 ppm and 50% rel. numidity (Re#. 12). * Amounts of SQ-ioo, and 150 cc/min at less than 20% relative numiciity. Table IV. Partition of VCM Upon Storage Storage time. days Vmyl chloride sampled. Mg Vinyl chloride recovered. Recovered sample in front, % Recoversd sample in back section. % 0 2.55 85 100 Q 0 31.9 89 100 0 y 2.55 33 84 15 7 31.9 79 86 14 14 2.55 71 34 16 14 31.9 81 79 21 2 Average for six tuoes at eacn storage time exceot for .zero storage n wmcn case only one tuoe was usee. however, this migration did not affect the total recovery of the vinyl chloride. A multivariant analysis was performed on the data dis played . In Table V the four variables, storage temperature, time, quantity of VCM, and sealing method, were exam ined for effect on recovery of the VCM. The multivartant analysis included two additional variables not included is the result indicated in Table IV'--storage temperature and method of sealing the tubes. The hypothesis that each of the indicated variables had no effect was tested at the 0.01 level and in none of the cases was this hypothesis rejected. The effect of the above variables on partition of the VCM between the sections of the tubes was also tested and as might be expected, temperature had an effect on the parti tion: however, the storage time and quantity of VCM ab- 1170 Environmental Science 4 Technology SL 068788 Table V. Charcoal Tube Performance Under Various Conditions High concentration. 31.9 ug Capped lubes, C Fused tubes, C days 43 22 4 43 22 4 Recovery,% 91 71 87 69 79 79 7 Total recovered in 22 14 3 19 21 3 back section, % Recovery, % 78 98 85 60 81 85 15 Total recovered in 28 20 11 28 23 15 back section, % Low concentration. 2.6 ug Capped tubes, C Fused tubes. C 43 22 4 43 22 4 87 84 23 14 77 72 86 90 0 27 27 10 76 67 31 64 69 69 28 18 5 22 19 1 sorbed also affected the degree of partition. The only factor that did not influence the VCM partition was the method of sealing the tubes. Analytical Methodology. From the data presented above, it can be seen that the charcoal tubes must be refrig erated if any information is to be gained from a separate analysis of the rear section of the tube. The function of the additional section is to determine breakthrough of VCM during sampling. To achieve this additional bit of informa tion. it is necessary to refrigerate the tubes, preferably at dry' ice temperatures, in the interim between sampling and analysis. If the tubes have not been refrigerated during the interim, the analytical procedure should be modified and the tube sections should be analyzed as a combined sample. When the tube sections were combined, the recovery was enhanced considerably over separate analysis. Ten identi cal VCM samples were obtained, and the charcoal tubes stored at ambient temperature for two weeks. Five of the tubes were analyzed as a unit by combining the front and rear sections before analysis, and the remaining Five were analyzed separately. The average total recovery was 90.8% istd dev 5.5%) for the combined section analysis and 78.0% Istd dev 4.5%) for the tubes which had each section ana lyzed separately. Thus, there was a 14% decrease in recov ery when analyzing the tube sections separately and this could be significant at low concentrations. The sample losses upon immediate analysis of the char coal tubes, or when analyzing the combined sections of tubes stored for a period preceding analysis, amounted to approximately 10%. An examination of the head-space gas in sealed 2-ml vials containing standard solutions indicated that VCM was distributed between the gas phase and the carbon disulfide such that the head-space gas should not be neglected. Comparison of solutions of carbon disulfide orig inally containing 30.1 ng/ml of VCM and the head-space gas above the solution provided an approximate value for the Henry's law constant; the value determined was 8.1 atm. When we usp this val<J8 and apply Henry's law to the analysis procedure described previously, head-space gas losses would be expected to be on the order of 6% when the head space was 1.5 ml. The remaining losses of VCM can be attributed to irreversible absorption on the charcoal. The Henry's law constant can be used to show typical losses when making-up standards in a 25-ml volumetric flask are on the order of 1% which may be decreased by limiting the head space. Conclusions A small charcoal tube is adequate for sampling vinyl chloride if well-controlled conditions are maintained. From the data given above, the recommended sampling proce dure is as follows: sample rate, 100 cc/min; maximum sam ple volume, 5 1; and low-temperature storage, if break through is thought to be a problem. The conditions given above provide a safe limit under most circumstances such that variabilities in temperature and relative humidity will not pose a problem. The analysis of tube contents should be performed on the combined contents of the charcoal tube unless the tubes have been stored at --20C or less, in the interim between sampling and analysis and the headspace gas over the desorbing reagent, CS?, should be mini mized for highest recovery efficiencies. For accurate deter mination of recoveries, each charcoal tube batch should be examined by random selection of charcoal tubes from the same batch followed by a performance check using a dy namic flow system to absorb known concentrations on the charcoal. The dynamic system should be used to avoid sample losses that might occur when using a standard vinyl chloride solution in ethyl acetate as previously done (7) for other compounds. Recovery data should be determined over the same time interval as anticipated storage time. Thus, while the charcoal tube method appears adequate for concentrations of VCM on the order of 1-50 ppm or more, there should he great care taken when using the method for very low levels, such as might be found around the perimeter of a polyvinyl chloride plant. As the concen tration of VCM decreases, the scatter in the data and sam ple losses become a greater factor in analytical accuracy. Acknowledgment The authors wish to thank Jeanne Cooper Burg for ad vice on the statistical analysis. Literature Cited (1) Maltom, C,, "Preliminary report on carcinogenicity bio-assays of vinyl chloride," Presented at OSHA Hearing, February 15, 1974. (2) Tabershaw Cooper Associates. Inc., "Final report epidemiolog ical study of vinyl chloride workers," Presented to Manufactur ing Chemists Association, 1974. (31 Fed, Regist., 36. No. 105, Mav 29, p 10505, 1974. (4) Ibid.. 39, No. 67. April 5, p 12342, 1974. (5) Ibid.. No. 195, October 4, p 35890. 1974. 16) Environmental Protection Agency, "Preliminary assessment of environmental problems associated with vinyl chloride and polyvinyl chloride," 1974. (7) White. L. D., Taylor. D G., Mauer, P. A., Kupel. R. E., Am. Ind Hyg. Assoc. J , 31. 225 (1970). (8) U.S. Dept, of Health. Education, and Welfare. "NIOSH manu al of analytical methods." p 127-1. 1974. (9) Analytical Quality Control Newsletter, p 2, Environmental Protection Agency. No. 24. January 1975. (10) Saltzman. B. E., Burg, W. R.. Ramasuamy, G,, Environ Sci. Technoi. 5, 1121 (1971). (11) Cuddeback, J. E- Burg, W. R., Birch, S., Anal. Chem., 42,355 (1975). (12) U.S. Dept, of Health. Education and Welfare, "Evaluation of organic vapor respirator cartridges and canisters against vinyl chloride." HEW Publication No. 75*11 (NIOSH). 1974. Received for review April 7.1975 Accepted August 14, 1975. Work supported by U.S. Public Health Service Grant ES 00159 and by the Environmental Protection Agency under Research Grant R800869. SL 068789 v/nlnrrM 9 Number 13. December 1975 1171