15 Occurrence of N-Nitrosamines in the Workplace Some Recent Developments D. H . F I N E and D . P. R O U N B E H L E R New England Institute for Life Sciences, 125 Second Avenue, Waltham, MA 02254
The largest known human exposures to exogenous nitrosamines have been shown to occurinthe work place, p a r t i c u l a r l y in the rubber and leather tanning industries. Recent data for amines, nitrosating potential and nitrosamines will be presented i n the framework of assessing the extent of the various exposures. Excluding tobacco and tobacco smoke ( 1 , 2 , 3 ) , the largest known human exposure to N-nitrosamines i s i n the i n d u s t r i a l sector ( 4 ) . The area or process a i r samples containing the largest amount of nitrosamines are i n a t i r e factory, NMOR at the 250 yg/m l e v e l ( 5 ) , a leather tannery, NDMA at the 47 yg/m l e v e l ( 6 ) , and a rocket fuel factory, NDMA at the 36 yg/m l e v e l ( 7 ) . The highest actually measured personal (breathing zone) exposure was 25 yg/m of NMOR (time-weighted average) for a worker i n the feed m i l l and calender operation of a t i r e factory ( 5 ) . Recently, much of our work has concentrated on minimizing, or possibly eliminating, these extraordinarily high human expos ures to nitrosamines. This has been achieved by f i r s t - improv ing the analytical procedures so that r e l i a b l e data can be obtain ed, second - using the new data base to understand the broad scope of the problem and three - applying the new knowledge and under standing i n the work place so as to minimize the human exposure. Measurement of airborne nitrosamines i s complicated by the fact that nitrosamines are usually found to be present i n a vast sea of precursor amines and oxides of nitrogen. A proper understand ing of the problem, therefore, requires the simultaneous a r t i f a c t free measurement of nitrosamines, amines and oxides of nitrogen. The capability to carry out a l l three determinations on the same sample of a i r has only recently been developed. 3
3
3
3
Nitrosating Potential. The nitrosating potential of a sample i s defined as i t s capacity to nitrosate amines to produce N0097-6156/81/0174-0207$05.00/0 © 1981 American Chemical Society
208
N-NITROSO COMPOUNDS
nitrosamines. I t may be determined quantitatively by measuring the amount of an added marker amine which i s converted to the corresponding marker nitrosamine. In a i r , we determine nitrosat ing potential by passing a known volume of a i r over a ThermoSorb/A cartridge (8) to which had been added a known weight (approxi mately 10 mg) of thiomorpholine (or 2,6 dimethlmorpholine). The amount of the corresponding N-nitroso derivative, N-nitrosothio morpholine (or N-nitroso 2,6, dimethylmorpholine) found on the cartridge i s a measure of the nitrosating potential of the a i r sample. Nitrosating potential of the a i r sample may be c a l i brated to the nitrogen dioxide content of the sample by passing a i r containing a known amount of nitrogen dioxide through a cartridge containing the marker amine. A typical calibration, showing the amount of N-nitrosothiomorpholine produced per l i t e r of a i r , versus the square of the nitrogen dioxide concentration, i s shown i n Figure 1. Amines. A modified ThermoSorb/N cartridge (8), called ThermoSorb/A (Thermo Electron Corporation), i s used to c o l l e c t airborne amines. Instead of eluting with an organic solvent such as methanol/dichloromethane, the ThermoSorb/A cartridge i s eluted with 0.1N KOH. The eluate contains both the amine and the n i t r o s amine, and i s injected directly into a GC interfaced to an abso lute organic nitrogen detector, the TEA 610 (Thermo Electron Corporation). This new GC detector operates by completely com busting a l l organics with oxygen, to give carbon dioxide, water vapor, and n i t r i c oxide, NO (9). The NO content (and hence the amine content of the sample) i s determined by the intensity of the chemiluminescent reaction of the NO with ozone. Instead of an absolute GC-nitrogen detector, a GC detector with enhanced select i v i t y to nitrogen, such as the H a l l or AFID can be used instead, provided that non-nitrogen containing compounds do not co-elute with the compound of interest. Tire Factories. Airborne amine and nitrosamine data from a typical t i r e factory are shown i n Figures 2 and 3. Figure 2, a GC-TEA (N-mode) shows the presence of large concentrations of dimethylamine and morpholine, together with traces of trimethylamine, diethylamine and triethylamine, together with small amounts of several unidentified N-containing compounds. Figure 3, the equivalent GC-TEA chroma to gram of the same sample of a i r , shows that the only two nitrosamines which were detected were the N-nitroso derivatives of the two amines which were present are included i n Table I . In most cases, the airborne n i t r o s amine concentration was about 1% of the airborne amine concentra tion. I t i s perhaps surprising to note that although diethy1and triethylamine were found, N-nitrosodiethylamine was not detected. Due to a combination of company and union concern for worker safety, and p a r a l l e l involvement of the National Institute of
Figure 1. Calibration plot for nitrosation potential showing amount of N-nitrosothiomorpholine formed vs. the square of the nitrogen dioxide concentration. Standard conditions of 50%relative humidity, 25°C, and 1 LI min flow rate for 30 min were used.
s
N>
210
N-NITROSO COMPOUNDS
Figure 2. GC-TEA (N mode) chromatogram of a tire factory air sample. The column was a 5.5 m glass tube, 2mm. i.d., packed with Carbopak B(4% Carbowax 20 M, with 0.8% KOH on charcoal). Carrier gas flow rate was 15 mL/min. Column temperature was held at 40°C for 2 min, and then increased by 8°/min to 180°C. Peak identity 1-dimethylamine, 2-trimethylamine, 3-diethylamine, 4-triethylamine, and 5-morpholine.
FINE AND ROUNBEHLER
N-Nitrosamines
in the Workplace
21
NMOR
NDMA
Figure 3. Conventional GC-TEA (nitrosamine mode) chromatogram of the tire factory air sample shown in Figure 2 above. Two nitrosamines are shown to be present, N-nitrosodimethylamine and N-nitrosomorpholine.
212
JV-NITROSO COMPOUNDS
Table I Airborne Amine and Nitrosamine Concentrations i n a Tire Factory 3
MethylDMA TMA NDMA 2 130
5 27
0.12 1.5
Concentrations i n yg/m PropylEthyl NPA NNPA DEA TEA 10 9
N.D. N.D.
0 50
330 16
Mbrpholine NDEA
MOR
N.D. N.D.
20 0.7 2600 66
NMOR
Occupational Safety and Health, dramatic reductions i n airborne nitrosamine levels were achieved i n only 7 months (5). Figure 4 shows that at the beginning of the study, i n August, 1979, the highest area NMOR l e v e l found was 250 yg/m . Within two months, this had been reduced to 120 yg/m , just by venting. Two months l a t e r , a further reduction to 63 yg/m was achieved, mainly by the use of exhaust canopies. By February 1980, just seven months after the study was i n i t i a t e d , the highest detectable area NMOR l e v e l was only 14 yg/m - The l a t t e r reduction was achieved by discontinuing the use of diphenylnitrosamine, and using a phthalimide derivative instead (5). 3
3
3
3
Leather Industry. Using the capability of simultaneous meas urement of airborne nitrosation potential, amines and nitrosamines, a complete tanning operation was studied so as to ascertain the source of the NDMA. None of the bulk samples which were collected at the same time (see Table I I ) , contained NDMA ( s e n s i t i v i t y l i m i t 0.5 yg/ml), including the fresh dimethylamine sulfate (DMAS), the hide unhairing solution, and even water on the f l o o r near the unhairing operation. This negative finding demonstrates conclusive l y that the source of NDMA i s not an impurity i n the DMAS; nor i s NDMA being formed i n the unhairing solutions. Table I I Analyses of Bulk Samples from a Leather Tannery Sample Description Floor Water near unhairing
NDMA (yg/ml) N.D.*
DMA (yg/ml) 120
Fresh hide unhairing solution containing DMAS
N.D.
790
Hide unhairing solution - no DMAS added
N.D.
8
4-day old hide tmhairing solution containing DMAS
N.D.
630
40% solution of DMAS N.D. 120,000 * N.D. - None detected - detection l i m i t 0.5 yg/ml
15.
FINE AND ROUNBEHLER
N-Nitrosamines
in the Workplace
3001—
AUG
•79
OCT
'79
DEC
'79
FEB
'80
Figure 4. Highest area sample NMOR levels in a tire factory, showing the reduction achieved. The October 1979 reduction was attributed to venting, the December 1979 reduction to the installation of exhaust canopies, and the February 1980 reduction to use of a phthalimide derivative instead of diphenylnitrosamine (data from Ref. 5)
213
214
N-NITROSO COMPOUNDS
However, at the time the bulk samples were collected, NDMA was present i n the a i r at a l l test sites i n the tannery. The a i r borne data (see Table I I I ) , shows that dimethylamine (DMA) was always present. The amount of airborne NDMA was always approx imately equal to 1% of the amount of airborne DMA. The apparent lack of correlation of the NDMA levels with nitrosating capacity i s probably due to the r e l a t i v e l y small variation i n the measured NO levels. Table I I I Analyses of A i r Samples* Collected at a Tannery i n Milwaukee, August 1980 X
Sample Location
NO ppS
DMA μ g/m
NDMA μ g/m
NDMA/DMA
3
3
%
Unhairing vats
58
488
4.6
0.9
Center of unhairing
37
280
5
1.8
Fleshing machine
67
183
1.2
0.6
Head s p l i t t i n g
88
260
3.3
1.3
Bating area
80
280
3.6
1.3
*Each data point i s the mean of three samples taken on three different days A t o t a l of eight separate leather f a c i l i t i e s were surveyed for the presence of N-ni croso compounds and two of these were resurveyed. Four of the eight plants were found to have airborne NDMA at levels greater than 0.5 yg/m . Table IV summarizes the operations of each plant and the highest l e v e l of NDMA found at that plant. The use of DMAS i s associated with the presence of airborne NDMA. Even a f a c i l i t y which had recently discontinued the use of DMAS, and another which used DMAS on an experimental basis, contained airborne NDMA. There i s an apparent anomoly i n the tannery data. As can be seen from Table IV, DMAS, used to gently loosen hairs from the hides i s clearly needed to produce detectable NDMA levels. Yet the DMAS i t s e l f , and i t s aqueous solutions do not contain NDMA. Airborne NDMA i s associated with a much higher l e v e l of DMA, as well as an adequate airborne nitrosation capacity. Thus, i t must be concluded that the NDMA i s formed from DMA outside the solution - either i n the gas phase, or heterogeneously on sur faces. The major source of the DMA i s presumably the DMAS. The source of the nitrosating agent i s probably oxides of nitrogen, formed by the combustion of f o s s i l fuels i n gas powered f o r k - l i f t trucks, or i n open gas heaters. This could not be demonstrated unambiguously, since the tanneries which were
15.
FINE AND ROUNBEHLER
N-Nitrosamines
215
in the Workplace
v i s i t e d and which used DMAS, a l l had a plausible source of oxides of nitrogen (Table IV). Table IV Summary of NDMA Findings at Eight Leather Manufacturers Highest NDMA Description observation of NO Source DMAS Used Wg/m Tannery X 47 A l l operations f o r k - l i f t trucks Yes J
A l l operations
Yes
f o r k - l i f t trucks
11
A l l operations
No
f o r k - l i f t trucks
0
A l l operations
No
f o r k - l i f t trucks
0
Partial-wet
recently discontinued
f o r k - l i f t trucks
8
Partial-wet
used experimentally
open gas heaters
3
Partial-dry
No
f o r k - l i f t trucks
0.05
Partial-dry
No
None
0
Acknowledgement s We thank John Fajen for many valuable and illuminating d i s cussions. The work described here was supported, i n part, by the National Institute for Occupational Safety and Health (NIOSH) under Contract 210-77-0100. Any opinions, findings, conclusions and recommendations experessed are those of the authors and do not necessarily r e f l e c t the views of NIOSH. Literature Cited 1. Hoffman, D., Adams, J.D. Brunnemann, K.D., Hecht, S.S., Cancer Res., 1979, 39, 2505-2509 2. Hoffmann, D., Adams, J.D., Piade, J.J., Hecht, S.S., IARC Sci. Publ. 1981, 31, 507-616. 3. Brunnemann, K.D., Yu, L., Hoffmann, D., Cancer Res., 1977, 37, 3218-3222. 4. Fine, D.H., Oncology, 1980, 37, 199-202 5. McGlothlin, J.D., Wilcox, T.C. Fajen, J.M. and Edwards, G.S., "Chemical Hazards in the Workplace", American chemical Society Symposium Series #149, Washington, D.C.,1981; p.283
N-NITROSO COMPOUNDS
216
6. Rounbehler, D.P., Krull, I.S., Goff, U.E., Mills, K.M., Morrison, J., Edwards, G.S., Fine, D.H., Fajen, J.M., Carson G.A. and Reinhold, V., Fd. Cosmet. Toxicol., 1979, 17, 487491. 7. Fine, D.H., Rounbehler, D.P., Pellizzari, E.D., Bunch, J.E., Bereley, R.W., McCrae, J., Bursey, J.T., Sawicki, Ε., Krost, K. and DeMarrais, G.A., Bull. Environ. Contam. Toxicol., 1976, 15, 739-746. 8. Rounbehler, D.P., Reisch, J.W., Coombs, J.R. and Fine, D.H., Anal. Chem., 1980, 52, 273-276. 9. Fine, D.H., British Patent Number 1513007, issued 1978. Filed 1974. RECEIVED
September
16, 1981.
