EPA/AA/CTAB/PA/81-15
Technical Report
Nitrosamines and Other Hazardous Emissions
From Engine Crankcases
by
Thomas M. Baines
June, 1981
Notice
Technical Reports do not necessarily represent final EPA decisions or
positions. They are intended to present technical analysis of issues using
data which are currently available. The purpose in the release of such
reports is to facilitate the exchange of technical information and to inform
the public of technical developments which may form the basis for a final
EPA decision, position or regulatory action.
Control Technology Assessment and Characterization Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, Michigan 48105
-------
-2-
Nitrosamines and other Hazardous
Emissions from Engine Crankcases
I. Background
Under most operating conditions, the crankcases of automotive engines emit a
stream of effluent composed of gases and particulate matter. Most of the
gaseous portion of this effluent stream originates at the imperfect seal of
the piston against the cylinder wall. This "blowby" originates in the com-
bustion chamber and, after "blowing by" the piston rings, enters the crank-
case and is then vented. A large part of the particulate matter in the
crankcase effluent stream appears to originate in the crankcase.
The crankcases of all gasoline fueled engines were subjected to regulatory
control in 1968. This regulation prohibited any crankcase emissions from
gasoline fueled light duty engines and resulted in the use of total recircu-
lation of these emissions through the engine. Since that time, crankcase
emissions have been prohibited from light duty gasoline engines and are
currently prohibited by CFR 86.081-8 (c) (reference No. 1)*. For light
duty gasoline trucks, crankcase emissions are prohibited by CFR 86.081-9
(c) (reference 1), and for heavy duty gasoline engines by CFR 86.080-10(c)
(reference 1). At the time the first gasoline engine emissions control
regulations were promulgated, it was determined that Diesel crankcase emis-
sions did not need to be so regulated because of their low HC, CO, and NOx
content. For many years most light duty Diesels have used crankcase emis-
sions recirculation. Recently, however, some light duty Diesel manu-
facturers have eliminated crankcase controls. Until recently, almost no
heavy duty Diesel engines employed crankcase controls, but rather discharged
the effluent into the atmosphere. This situation will change in 1984 when
CFR 86.084 - 11 (c) (reference 1) takes effect. This will require crank-
case effluent control on heavy duty naturally aspirated Diesel engines but
not on turbocharged or Roots supercharged Diesel engines. Therefore, most
bus engines would be permitted to exhaust their crankcase effluent into the
atomosphere. In fact, since most heavy duty Diesel engines are expected to
be turbocharged, most of these engines will also have no mandated crankcase
control. The gas phase portion of the crankcase stream contains pollutants
such as HC, CO, NOx, aldehydes and other gases. These exist at levels of
0.005 to 4.1 percent of the corresponding exhaust emissions (e.g., crankcase
emission levels of HC are about 0.2 to 4.1 percent of the HC exhaust emis-
sion levels) (2). The gas phase also contains nitrosamines, a very strong
carcinogen(S). These are emitted at levels up to 268.8 ug/hour (3).
* Number in parenthesis identifies the reference, a list of which is
found at the end of the paper.
-------
-3-
The particulate portion of the Diesel crankcase effluent stream consists
primarily of heavy hydrocarbons. About 88% to 98% of this material is
solvent-soluble organic matter with the remainder being carbonaceous
particulate and a small amount of sulfate. Analysis of this particulate
indicates that the soluble portion is largely a lubricating oil-type of
material which leads one to conclude that it could be entrained lubricating
oil mist material (3). Fresh lubricating oil appears to be biologically
benign (4), but used lubricating oils have been known to be a carcinogen
since 1935 (5). More recent work has shown used lubricating oils to be
mutagenic, also (4, 6).
II. Nitrosamine Emissions
Nitrosamines are a group of compounds that take the general form of RoN =
NO (7). Lijinsky (8) has described them as follows:
"Among carcinogens the N-nitroso compounds are the most broadly
acting and among the most potent. They comprise the directly
acting nitrosamides and the systematically acting nitrosamines,
which require enzymic activation for their carcinogenic
action. More than a hundred N-nitroso compounds have been
tested for carcinogenic activity and most of them have induced
tumors in rats; a much smaller number has been tested in
hamsters, mice or guinea pigs and, again, most of those tested
have been carcinogenic."
In recent testing of Diesel crankcase emissions, nitrosamines were found to be
present in all of the samples taken (3). The nitrosamine levels appeared to
be a function of the lubricating oil used (brand and age), the engine and its
associated crankcase NOx flow rate, engine operating cycle, and possibly other
factors not addressed by the experimental design.
The major influence on Diesel crankcase nitrosamine emissions appears to be
the lubricating oil. All engine lubricating oils contain an additive package
designed to help the oil function better in high pressure areas, to suspend
foreign matter, to widen the viscosity range and to prevent rapid
deterioration by oxidants and acids. Many of these additives contain amines
and other nitrogen-containing compounds. The research described in references
3 and 9 indicated that the interaction between these nitrogen-containing oil
additive compounds and the crankcase NOx and elevated temperatures resulted in
the formation of nitrosamines.
Reference (3) indicated that there are large differences in the amount of
nitrosamines that result from the use of various oils. In order to quantify
this effect, a bench procedure was developed to determine the nitrosation
potential associated with a given oil. This yielded much interesting data.
For example, base oil (before the additive package is added) has no ability to
form nitrosamines under this procedure. However, 84% of the 62 samples of
fresh oil that were analyzed for their nitrosation potential yielded
dimethylnitrosamine (NDMA). Of the 60 fresh oils that were analyzed for their
nitrosation potential, 38% yielded n-nitrosomorpholene (NMOR). (Few of these
oil samples had detectable levels of nitrosamines before artificial
nitrosation.)
-------
-4-
The nitrosation potential for NDMA of fresh oils ranged from a low of 0.6 ppb
to a high of 202 ppb; a range of 337 fold, dividing the highest by the
lowest. Thus, there is a large difference in the ability of different brands
of oils to form nitrosamines. There is also a difference in nitrosation
potential of a given brand of oil. For example, Amoco 300 SAE 30 from the
Whiting refinery has a much higher nitrosation potential than the Amoco 300
SAE 30 from the Houston refinery because of different levels of additive
required at the two refineries.
Given that there is a wide difference in the ability of different oils to form
nitrosamines, it would follow that the nitrosamine emissions from a given
engine's crankcase would vary as a function of the oil. This, as it turns
out, was the case in the experimentation described in reference 3. A single
heavy duty Diesel engine (Mack ETAY(B) 673A) was tested with four different
oils representing a range of different nitrosation potentials as measured by
the bench procedure. The results are presented in Table 1 and they showed a
very clear correlation (r=0.97) between nitrosation potential and nitrosamine
emissions.
Table 1
Table of NDMA in Nitrosated Oil Vs. Average
NDMA in Crankcase Emissions For Mack
ETAY(B) 673A HD Diesel Engine
NDMA in Average* NDMA
Oil Nitrosated Oil (ppb) Emission Rate (ug/hr)
Shell Rotella T (SAE30) 1 4
Amoco 300 (SAE30) 25 36
Mobil Delvac 1200 (SAE30) 88 96
Mobil Delvac Super (15W40) 200 144
* Average of two measurements per mode. The seven modal averages are
then composited using distributed weighting factors based on 13 mode
weighting factors.
The measurements for the data presented in Table 1 were taken after one hour
of preconditioning on the fresh oil so that experimental consistency could
be maintained. Therefore, the results are valid only for the fresh oil
case. Nevertheless, there appears to be some influence due to the age of
the oil on the nitrosation potential of the oil and the associated nitrosa-
mine emissions. Some heavy duty Diesel engine manufacturers supplied oils
for nitrosamine and nitrosation testing from in-use engines. These samples
included a fresh sample and samples taken at various in-use intervals. Un-
-------
-5-
fortunately, most of the oils chosen had low fresh oil nitrosation
potentials. The results showed that of the eight used-oil series tested,
all but two of them had declining (or no detectable) nitrosation potential
levels. On the other hand, some extended mileage samples taken from the
various vehicles showed significant levels of nitrosamines. Therefore, it
must be concluded that the ability of an oil to form nitrosamines probably
decreases with time of use. The rate at which this decrease occurs has not
been quantified. This change in the ability of the oil to form nitrosamines
may be related to the consumption or deterioration of the additive package.
The type of engine also has an effect on the nitrosamine levels emitted.
Reference 3 describes the results of nitrosamine emissions measurements
taken from three different engines operated on one type of oil. These
results are presented in Table 2. References 3 and 9 conclude that the
engine variables primarily responsible for the variation in nitrosamine
levels shown in Table 2 are 1) crankcase flow 'rate of NO and N02, and
2) volume flow rate of crankcase gases which influences residence time of
NOx with the nitrosatable amines.
Table 2
Table of Nitrosamine Emission Rates of Four \
Different Engines Operated on Mobile Delvac Super (15W40)A
\
NDMA Emission Rate, ug/hr
Weighted^
Engine Peak Composite
Mack ETAY (B) 673A 268.8 135.4
DDAD 6V-71 N 52.2 11.0
Caterpillar 3406 71.2 35.8
Mercedes 240D* 18.4 13.8
* Light Duty Vehicle. Data in "Weighted Composite" Column are Geometric
Average of 2 Steady State Modes.
@ 7 mode composite - see footnote, Table 1
The impact that these emission levels has on ambient air nitrosamine levels
is not a straight forward issue to analyze. Such an analysis is complicated
by lack of a crankcase emissions dispersion model. However, some data can
be discussed in this regard.
-------
-6-
Very little monitoring of roadside nitrosamines has been performed. The
limited amount of monitoring performed to date has shown levels in the range
of 1 jug/m-*. For example, Gordon (10) sampled air along roadways in the
Los Angeles basin and found levels up to 1.1 jug/m^. He found no evidence
for any specific point emission sources for the nitrosamines. He found peak
levels at about 8 am and 6 pm. He feels that there is a high likelihood
that the source is mobile source related (11).
Shapley reports levels of NDMA of 0.8 jig/m on the Cross-Bronx Expressway
in New York City (12) and infers that this is probably mobile source related
but could not identify a specific mobile source for this finding.
Pellizzari (13) reported 0.1 ppb of diethylnitrosamine as well as DMNA in
the Eisenhower Tunnel in Colorado. This is also probably mobile source
related since the tunnel is an area away from industry and since it is a
motor vehicle tunnel.
As far as sources of this nitrosamine are concerned, few such sources are
confirmed except for crankcases. Some data was reported by Urban, et al..
(14) which were in the form of mass spectroscopy results at the same
retention time as NDMA. These were taken from various vehicles equipped
without catalysts and with oxidation catalysts. The data are considered to
be inconclusive evidence of nitrosamine presence in gasoline fueled vehicle
exhaust. GM has also presented data that can be considered to be
inconclusive with respect to the identification of nitrosamines in gasoline
fueled vehicle exhaust (15).
Cadle et al.. (16) report results of work done in search for amines (nitros-
amine precursors), under the theory that such amines may react with nitrous
acid in the atmosphere to form nitrosamines. Their conclusion is that "it
is unlikely that any of the standard gasoline cars on the road today are
emitting significant quantities of amines" and therefore little liklihood of
gasoline fueled cars contributing significantly to the nitrosamine levels
reported. Also, Hurn et al.. (17) could not detect amines in the exhaust of
noncatalyst cars. Consequently, it appears one could conclude that there is
little data that show that exhaust from gasoline fueled engines (light or
heavy duty) contributes to roadside nitrosamine levels.
Currently, there are only two confirmed sources of mobile source nitrosa-
mines and one strong indication of mobile source nitrosamines. The con-
firmed sources are crankcase emissions from Diesel engines and vehicle
interior emissions (18, 19). The strong indication of nitrosamines in ex-
haust is reported in reference 3. While performing engine sampling for
crankcase nitrosamines, raw exhaust emissions were sampled from one of the
heavy duty Diesel engines. The results of this showed emission rates of
about 13.6jug/min. The method used was one that was qualified for crankcase
emissions (i.e., a high NOx environment) but not specifically for raw engine
exhaust. Therefore, the results should be considered as strongly indicative
of the presence of NDMA, but not as confirmed evidence. Very recent work
-------
-7-
being performed at Southwest Research Institute (20) has shown no exhaust
nitrosamines from a light duty Diesel engine (Fiat, naturally aspirated)
using a qualified methodology. How this result impacts the heavy duty
Diesel engine result is not known.
How do these confirmed sources of NDMA contribute to the NDMA levels found
along roadways? This is a question which is not very easy to answer. The
data indicate that crankcase emissions contain NDMA at concentrations up to
28 ug/m3 (3). Roadway concentrations up to 1.1 ug/m3 have been
detected. What portion of the roadside level is contributed by crankcase
emissions? No really adequate dispersion model currently exists to compute
this. One way to approximate this might be to ratio the numbers that were
used in the support documentation for the Heavy Duty Particulate rulemaking
(21). Such an approach yields a NDMA concentration of 19 x 10"^-^ g/m-^
from crankcases; a small fraction of the 1.1 x 10~6 g/m3 NDMA observed
along roadways.
If the same method (21) were to be used for the tentative Diesel exhaust
NDMA emission factor, the result would be 112 x 10 ~12g/m3, again a
small fraction of the observed roadway concentrations.
Another approach would be to look at the relative hazard assoicated with the
levels of nitrosamines observed along roadways. Assume a roadway
concentration of 1.1 ug/m3 of NDMA (of which the crankcase emissions would
contribute a part) and also postulate a hypothetical commuter spending 2
hours per day breathing such air (which can be a relatively conservative
assumption). At a 10 liters/min respiration rate and an assumed total
pulmonary adsorption of the NDMA, this person would intake
(1.1 ug/m3) (10 1/min) (0.001 m3/!) (2 hr)(60min/hr) = 1.3 ug NDMA.
This is about equivalent to the nitrosamine level of one can of beer or
several strips of bacon (22). Obviously, the amount of nitrosamine intake
would increase with increasing exposure. Also, this exposure would also add
to any exposure from the interior of the automobile. Using the EPA risk
assessment model (23)which is used for drinking water risk assessment, this
would translate into an cancer incidence of 0.36 per 100,000 populaton per
year. Assuming 150 million Americans are so exposed, the number of annual
cancer incidents attributable to roadside DMNA concentrations of 1.1 ug/m3
would be 546. However, as Fine points out (23):
"The animal data base for the low dose response study is based
on the 1963 study of Druckrey. Very recent work in England has
found that NDMA causes increased tumor incidence in rats at a
level of 0.035 - 0.130 ug/1, which is 10 to 30 times less than
the earlier Druckrey study. If the latest British data had been
used to calculate the risk assessment, the number of incidents
would have been increased 10 to 30 fold."
-------
-8-
If one assumes a 20 fold increase in incidents due to more up to date potency
data, this would result in 10,920 incidents of cancer per year due to roadside
nitrosamines. If one were to assume only 1.5 million persons (0.68% of the
total U.S. population) were exposed to the 1.1 jag/nH levels, the number of
of cancer incidents would then be 109 per year.
The other confirmed source of nitrosamines is automobile interiors. The work
by Fine et al.. (18, 22) has shown levels in new automobiles as high as 0.83
ug/m^. The work done recently by Smith (19) for EPA (ECTD) found a maximum
level of 0.63 .ug/m-*. This level decreases with vehicle operation to about
one fifth of the at-rest concentration, or 0.13 ug/m^ when applied to his
maximum concentration. Using the same assumptions as above, a hypothetical
commuter traveling for 2 hours per day (with 10 min/day at the at-rest
concentration) would be exposed to 0.21 ug of NDMA. Using the up to date
potency data for NDMA and assuming only 0.68% of the population is so exposed,
21 additional incidents per year of cancer would occur.
The crankcase emissions from a light duty Diesel; engine were sampled and a
nitrosamine (NDMA) emission rate of 18.4 ug/hr (9.2 >ug/m^) was determined
for a 50 mph steady state condition. Therefore, light duty Diesel crankcase
emissions will also contribute to roadside nitrosamine emissions if they are
emitted into the atmosphere. Currently, most such vehicles have crankcase gas
recirculation systems. However, some are being equipped with road draft tubes
to vent the crankcase to atmosphere.
No nitrosamine measurements have been taken of .gasoline crankcase exhaust
because of regulations prohibiting crankcase venting to atmosphere (1).
However, from the available evidence (3), it can be concluded that such
engines would probably contribute even more nitrosamines to ambient levels
because oils designed for use in gasoline engines usually contain more of the
amine containing compounds. This is verified by bench nitrosation of used
gasoline-fueled-engine oils which usually show positive levels of nitrosamines.
III. Particulate
The effluent stream from Diesel engine crankcases is composed of particulate
matter as well as gases. Table 3 gives some particulate data from several
engines. The particulate emissions are primarily composed of soluble organic
matter, and the indications are that it is mostly of a lubricating oil nature
(2). Therefore, most of the particulate may be entrained lubricating oil.
Table 3
Table of Particulate and BaP Rates for
Three Heavy Duty Diesel Engines (2)
Particulate* Percent BaP, Weight % BaP
Engine Mass Rate, g/hr Solubles ug/hr in Particulate
DDAD 6V-71 0.80 88.2 25.0 0.0031
DDAD 6V-71 2.44 98.1 76.8 0.0032
Cummins NTC-350 1.01 93.0 10.2 0.00094
* 7 mode composite
-------
-9-
Also, the data in Table 3 show that the particulate contains benzo-a-pyrene,
which is emitted at a rate of from 10 to 77 jiig/hr.
Again, it would be useful to know what hazard, if any, these particulate
emissions represent. The benzo-a-pyrene is well known to be a carcinogen,
one that does require metabolic activation. Used lubricating oil itself has
been known since 1935 to be a carcinogen. Twort et al.. (5) has reported
used lubricating oils as being carcinogenic as determined by mouse skin
painting. They observed that used oils are more carcinogenic than fresh
oils. More recent work done by Wang et al..(4) has shown that unused motor
oil samples were not mutagenic but that motor oil from a CFR single cyclinder
engine became mutagenic after 43 hours of running. All mutagenic measures
were made by the Ames test, strain TA98. Payne et al. . (6) has also
reported the mutagenic nature of used crankcase oils, both neat and
fractionated. Payne also reports (24) that mutagens (some of them possibly
very potent) are found in nitrosated samples of petroleum. Finally, there is
some indication that used lubricating oil can contain some polychlorinated
biphenyls (PCBs) which are known to be carcinogenic.
IV. Summary and Conclusions
The emissions from heavy duty Diesel crankcases contain a number of hazardous
compounds. Research has discovered some of them and it may be possible that
there are some that have not yet been quantified. Nitrosamines (a potent
carcinogen in animals and probably also in humans) are emitted from engines
using fresh oil. These emissions seem to be a function of the type of oil
used and some engine parameters such as crankcase flow rate of NOx
compounds. There is some evidence that the emission rate of nitrosamines may
decrease with time, but this has not been thoroughly investigated. It is
currently difficult to convert the nitrosamine emission rates into roadside
concentrations due to lack of a model tailored especially for that purpose.
The observed roadside concentrations are quite significant and could possibly
contribute to several hundred cases of cancer per year. The only confirmed
sources of this nitrosamines are Diesel crankcases and automobile interiors.
Diesel exhaust is also a possible source. Spark ignition engines are
probably not a source of either nitrosamines or nitrosamine precursors (ie. ,
amines). Other exposure scenarios for nitrosamines should be analyzed, such
as tunnels, garages, bus terminals, etc. The role of crankcase emissions
should be analyzed when evaluating epidimiological data taken from such
confined areas. The highest priority seems to be acquiring some more
roadside nitrosamine measurments to confirm the limited data available. Work
is also needed to determine the atmospheric fate and reactions of nitrosamine
(e.g. would nitrosamines emitted by roadsides have a long atmospheric life
and widely diffuse into the urban air?).
-------
-10-
Th e particulate emissions from Diesel crankcases contain what appears to be
mostly entrained lubricating oil. Used lubricating oil has been shown to
contain carcinogenic compounds such as benzo-a-pyrene. It has also been
shown to be carcinogenic when tested in skin painting experiments. It has
also been shown to be mutagenic, both neat and fractionated. Therefore, it
can be concluded that the particulate portion of the crankcase effluent
stream may start out after an oil change at a level containing few
carcinogenic compounds but the level of these compounds increases with time.
In summary, crankcases emit a variety of hazardous chemicals and evaluation
of the costs and benefits of the control of these emissions should be
seriously considered.
-------
-11-
References
1) Code of Federal Regulations, 40 Protection of Environment, Parts 81 to
99, Revised as of July 1, 1980.
2) Hare, Charles T., Montalvo, Daniel A., "Diesel Crankcase Emissions
Characterization", Final Report prepared for Task No. 4 EPA Contract No.
68-03-2196, May, 1977. '
3) Fine, David H., Goff, E. Ulku, "Nitrosamine Analysis of Diesel Crankcase
Emissions", Final Report prepared for EPA Contract No. 68-03-2719, EPA
460/3-81-001.
4) Wang, Yi Y., Rappoport, Stephen M., Sawyer, Robert F., Talcott, Ronald
E., and Wei, Eddie T. , "Direct Acting Mutagens In Automobile Exhaust", in
Cancer Letters, Vol. 5, pp. 39-47, 1978.
5) Twort, C.C., Twort, J.M. , "Induction of Cancer by Cracked Diesel Mineral
Oils," The Lancet, 2, pp. 1226-1228, Nov. 30, 1935.
6) Payne, Jerry F., Martins, Isabel, and Rahimtula, Anver, "Crankcase Oils:
Are They A Major Mutagenic Burden In the Aquatic Enviroment?", Science,
Vol. 200, pp. 329-330, April 21, 1978.
7) Anselme, Jean-Pierre, "The Organic Chemistry of N-Nitrosamines: A Brief
Review", in N-Nitrosamines, Jean-Pierre Anselme, ed., American Chemical
Society, 1979.
8) Lijinsky, William, "N-Nitrosamines as Environmental Carcinogens", in
N-Nitrosamines, Jean-Pierre Anselme, ed., American Chemical Society, 1979.
9) Goff, Ulku, E., Coombs, James R., Fine, David H. and Baines, Thomas M. ,
"Nitrosamine Emissions from Diesel Engine Crankcases", SAE 801374,
Baltimore, MD, October, 1980.
10) Gordon, Robert J., "Survey for Airborne Nitrosamines", Final Report for
CARB Contract No. A6-096-30, June, 1979.
11) Personal communicatons with Robert J. Gordon.
12) Shapely, D., Science, 191, 268(1976).
13) Pellezzari, E.D., EPA Report 600/7-77-055 for EPA, ORD, ESRL, 1977.
14) Urban, Charles M., Garbe, Robert J., "Regulated and Unregulated Exhaust
Emissions from Malfunctioning Automobiles", SAE 790696, Dearborn, MI.,
June 11-15, 1979.
-------
-12-
15) General Motors Advanced Emission Control System Development Progress,
submitted to the Environmental Protection Agency, Dec. 15, 1976, pp VIII
- 24.
16) Cadle, Stephen H., Mulawa, Patricia A., "Low Moelcular Weight Aliphatic
Amines in Exhaust from Catalyst-Equipped Cars", Environmental Science &
Technology, Vol. 14, No. 6, June, 1980.
17) Hum, R.W., Allsup, J.R. , Cox, F., EPA Report 650/2-75-014 for EPA, ORD
(RTF, N.C), 1975.
18) Rounbehler, D.P., Reisch, J., Fine, D.H., "Nitrosamines in New Motor
Cars", Food and Cosmetic Toxicology, Vol. 18, pp. 147 to 151, 1980.
19) Smith, Lawrence R., "Nitrosamines in Vehicle Interiors", Draft Final
Report for EPA Contract No. 68-03-2588, May 1981.
20) Personal conversation with Mr. Charles Hare, Southwest Research
Institute, June 4, 1981.
21) Heiser, Daniel P., "An Investigation of Future Ambient Diesel Particulate
Levels Occurring in Large-Scale Urban Areas", EPA Technical Report No.
EPA-AA SDSB 79-30, November, 1979.
From TableAl, the Heavy Duty Diesel Truck (HDT-D) emission factor is 2.0
g/mi and the HDT-D VMT represents 25% of the total VMT. Combining these,
the HDT-D represents 40% of the total weighted emission factor used.
This weighted emission factor was used to compute ambient particulate
concentrations from Diesel HD truck. Taking the ratio of the HDT-D
portion of the total resultant ambient concentration to the HDT-D
emission factor and then multiplying by the HDT-D nitrosamine emission
factor, the ambient nitrosamine concentration is computed. The exhaust
nitrosamine emission factor is used in the same manner to compute the
exhaust contribution to ambient nitrosamine concentrations.
22) Fine, D.H., Reisch, J., Rounbehler, D.P., "Nitrosamines in New
Automobiles," in N-Nitroso-Compounds: Analysis, Formation and
Occurrence, E.A. Walker, M. Castegnaro, L. Griciute, M. Borzsonyi, Lyon
(IARC Scientific Publications No. 31), 1980.
23) Letter from David H. Fine to Thomas M. Baines, December 14, 1979.
24) Letter from Dr. Jerry F. Payne (Research & Resource Services, Fisheries
and Oceans, Government of Canada) to Laurie Gallagher (EPA), August 13,
1980.
------- |