Human Exposure Estimates of Methyl Tertiary Butyl Ether (MTBE)


EPA/600/A-94/255
HUMAN EXPOSURE ESTIMATES OF METHYL TERTIARY BUTYL ETHER (MTBE)
Alan H. Huber
Presentation and Abstract at
Conference on MTBE and Other Oxygenates;
A Research Update
Falls Church, VA, July 26-28, 1993
Sponsored by
U.S. Environmental Protection Agency,
American Petroleum Institute, and
Oxygenated Fuels Association

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HUMAN EXPOSURE ESTIMATES OP METHYL TERTIARY BUTYL ETHER (MTBS)
Alan H. Huber*
Atmospheric Sciences Modeling Division,
Air Resources Laboratory,
National Oceanic and Atmospheric Administration
Research Triangle Park, NC 27711
*0n assignment to the Atmospheric Research and Exposure Assessment
Laboratory, U.S. Environmental Protection Agency
Abstract
Data on ambient air quality and microenvironmental exposures
(e.g., during refueling, inside cars, in personal garages) are too
limited for a quantitative estimate of population exposures to
MTBE. At best, they can be used to estimate broad ranges of
potential exposures. Because of the interest in MTBE, the present
evaluation focuses on this compound, even though any potential
health effects might result from complex pollutant mixtures of
which MTBE is only one component. Furthermore, potential exposures
of only the general public, not occupationa1ly exposed groups, were
evaluated.
Figure 1 outlines the personal activities that have been
considered in developing an annual human exposure estimate.
Gasoline fill-up is divided into two parts to cover both the fill-
up (1.5 fill-ups per week) and the remaining time spent in the
station environment. The distribution of hours spent in each
microenvironment is based on reasonable interpretation of available
population activity studies. The greatest difficulty arose in
trying to distribute the balance of time spent in one's residence,
office or outdoors. In this example, meant to represent one
exposure scenario, the typical time one spends either at home or in
a work place is relatively large. Therefore, if there are elevated
concentrations in these microenvironments, they may become the
largest contributor to annual average human exposures.
There is a need to estimate both acute and chronic exposures
to elucidate health risks. A gasoline fill-up, although brief,
results in the highest acute exposures since human exposures are
greatest when one is near evaporative emissions. Thus, exposures
are greatest when handling gasoline. Figures 2-13 summarizes
available concentrations during fill-up, at gas stations, and in-
cabin during automobile commutes. New field measurements (Lioy et
al., 19 93; Johnson, 1993) were collected in New Brunswick, NJ (2
stations with full service and phase II vapor recovery),
Westchester County, NY (3 stations with self service and phase II
vapor recovery) and Fairfield County, CT (5 stations with self
service and no phase II vapor recovery). Ambient air quality was
measured in Fairbanks AK, Stamford CT, and Albany NY (Zweidinger,
1993) . Details on the study data should be obtained from the
authors' presentations and reports. The data analyses should be

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considered preliminary. The presentation below is provided to meet
an immediate need to present the range of MTBE concentrations in
the identified microenvironments and an annual exposure assessment
with some margin of safety.
International Technologies Corporation (IT) completed a set of
field measurements of MTBE concentrations in the personal breathing
zone during fill-up, at the pump island, and around the property
line of gas stations (Johnson, 1993) . This study was done in
coordination with the following EOHSI/RTI study (Lioy et. al.) at
the same ten gas stations. All concentrations for the IT study,
even those in the intermittent breathing zone, were a four-hour
continuous sample. Since the breathing zone collection was video
taped IT will try to adjust the breathing zone measurements to
reflect a personal exposure during the fill-up. Four-hour average
fence-line MTBE concentrations were found to range from 0.018-0.234
mg/m3 (0.005-0.065 ppm) . The highest fence-line MTBE concentrations
ranged from 0.36-0.5 mg/m3 (0.1-0.14 ppm). The highest 4-hour
average breathing zone and pump island MTBE concentrations ranged
from 0.7-9 mg/m3 (0.2-2.5 ppm). These breathing zone concentrations
are comparable to the 4-hour continuous sample occupational
concentrations in a recent NIOSH study (NIOSH, 1993). In the NIOSH
study, the mean breathing zone MTBE concentration for station
attendants was 2 mg/m3 (0.58 ppm) with the highest concentrations
exceeding 14.4 mg/m3 (4 ppm). As expected these breathing zone
concentrations are lower than reported by the Clayton Environmental
Consultant study (Clayton, 1991) which collected samples only
during the fill-up period. In the Clayton study mean MTBE
concentrations in the breathing zone for 12-13 percent MTBE were 13
mg/m3 (3.9 ppm) with vapor recovery and 30 mg/m3 (8.3 ppm) without
vapor recovery. The absolute range of the MTBE concentrations was
.* 0.32 to 137 mg/m3 (0.088-38 ppm).
A wide range of ambient air concentrations within the
breathing zone can be expected. Ambient air concentrations
measured at a gas station will be highly dependant upon the wind
speed and direction. In addition, breathing zone concentrations
can be dramatically influenced by how one stands relative to the
wind. A typical worst case MTBE concentration in the breathing
zone during fill-up would be 36 mg/m3 (10 ppm) for a few minutes.
However, an accidental spill of fuel while filling the tank can
dramatically increase the inhaled concentration.
Lioy et al. (1993) provides measurements of MTBE
concentrations inside an automobile during an approximate 30 min
commute and during a fill-up of the gas tank. A late-new model
" automobile (1992 Corsica) and an older-model automobile (1985
Caprice or 1986 Monte Carlo) were assigned to each commuter route.
The samples were collected in the front passenger side of the
automobile. The number of sampling runs (cases) per automobile *
ranged from 14-20 for the commute and 3-5 for the fill-up. The
driver's window was completely open during the fill-up. The
average time to complete a fill-up was about 2 min, while the total

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time at the gas station was approximately 5-10 min. Average in-
cabin concentrations of MTBE during the commute were found to range
from 0.018 to 0.275 mg/m3 (0.005-0.075 ppm). Average in-cabin
concentrations during the fill-up ranged from 0.03 6 to 1.8 mg/m3
(0.1-0.5 ppm). In addition to the measurements inside the
automobile, several measurements were collected on the person
refueling the gas tank. These concentrations were found to range
from 0.7-14 mg/m3 (0.2-4 ppm). The older model automobiles were
found to result in higher inside automobile concentrations which
probably reflect differences between the automobile design and
"wear".
Figures 14-20 summarize air concentrations collected in
Fairbanks AK, Stamford CT, and Albany NY (Zweidinger, 1993).
Alaska was not in the MTBE program during the February/March
collection. Albany was not part of the MTBE program.
Concentrations (except for garage/auto-shop) in Alaska are reduced
from 0.0072-0.14 mg/m3 (0.002-0.04 ppm) range to the 0.0036-0.054
mg/m3 (0.001-0.015 ppm) range after ending the MTBE program.
Concentration inside the house were higher than outside for some
cases indicating that there may be a source of MTBE indoors. It is
possible that the residential garage may have had a source of
evaporative emissions after parking the hot car in the garage or
from gasoline being stored in the garage. Figures 21-23 summarize
an EPA case study of measured evaporative emissions from an
automobile at rest after being run through the Federal Test
Protocol (FTP) cycle that was completed to provide an example
herein. Approximately 0.5 grams of MTBE was emitted during the 4-
hour test. These emissions were then used as the modeled source in
a 95 m3 garage attached to a residential house. This is believed
to provide a reasonable worst case demonstration of in-house
concentrations due to a hot car parked in a closed residential
garage at 75 deg F. A multizonal mass balance model CONTAM88
(Grot, 1991) was used to model indoor concentrations. Peak
concentrations were 2.3 mg/m3 (0.65 ppm) in the garage and 0.12
mg/m3 (0.035 ppm) in the residence.	One-hour averaged
concentrations in the garage ranged from 2.5-4.3 mg/m3 (0.7-1.2 ppm)
while concentration in the residence ranged from 0.072-0.32 mg/m3
(0.02-0.09 ppm). This is a worst-case situation since a newer car
or cold winter temperatures would likely have reduced evaporative
emission rates resulting in lower concentrations.
Figure 24 summarizes the range of concentrations for the
identified microenvironments. The components of an annual average
human exposure estimate are shown in Figure 25. The commute and
gasoline fill-up are clearly the most important microenvironment
unless one has significant evaporative emissions in the residential
garage. The annual estimate uses the Figure 25 values for the 4 mo
MTBE season and assumes that MTBE concentrations are 10 percent of
these values the remainder of the year. This assumption is based
on belief that the amount of MTBE in the ambient air is
proportional to the amount of MTBE in the fuel (1.5% versus 15%
should allow a margin of safety). It's difficult to estimate MTBE

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levels during the nonoxyfuels season since MTBE is used in premium
gasolines and to a lesser extent in some regular gasolines. These
exposure values result in an annual estimate of 0.03 mg/m3 (0.0084
ppm) using the low concentrations and 0.046 mg/m3 (0.013 ppm) using
the high concentrations in Figure 25. The above exposure scenario
was calculated to represent a reasonable worst case exposure
estimate for the working adult population after factoring-in the
margin of safety. Exposure for children is expected to be lower
because children do not pump gas and spend less time commuting in
heavy traffic.
Acknowledgements:
This presentation could not have been possible without the timely
effort of Ted Johnson (ITC), Paul Lioy and Cliff Weisel (EOSHI),
Kenneth Knapp (EPA) and Roy Zweidinger (EPA) to share their data
files as the data are preliminarily processed. The presented
analyses was prepared within several days preceding the conference
and was only possible with the assistance of Gary Evans (EPA) , John
Streicher (EPA), Mike Zelenka (EPA), Azzedine Lanzari (METI) and
Graham Glen (METI).
References:
Clayton Environmental Consultants (1991). Gasoline Vapor Exposure
Assessment for the American Petroleum Institute. Clayton Project
No. 31774.00, July 2, 1991.
Grot, R. A. (1991). User Manual NBSAVIS CONTAM88. Report NISTIR
4585, National Institute of Standards and Technology, Gaithersburg
MD.
Johnson, T. (1993) . Service Station Monitoring Study. (Abst. and
presentation) Conference on MTBE and Other Oxygenates, Falls
Church, VA, July 1993.
Lioy, P. J. , C. Weisel, E. Pellizzari, and J. Raymer (1993) .
Volatile Organic Compounds from Fuels Oxygenated with MTBE:
Concentration and Microenvironmental Exposures to MTBE in
Automobile Cabins. (Abst. and presentation) Conference on MTBE
and Other Oxygenates, Falls Church, VA, July 1993.
NIOSH (1993). HETA 88-304-2326 American Petroleum Institute,
Washington, DC.
Zweidinger, R. B. (1993) Air Quality Measurements in Fairbanks,
Stamford, and Albany. (Abst. and presentation) Conference on MTBE
and Other Oxygenates, Falls Church, VA, July 1993.

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PERSONAL ACTIVITIES
8760 hours/year

TIME (hours)
1. Gas Fill-up 1.5/wk @ 2min
2.6
other @ 10min
13.0
2. Commute/ In Vehicle iohr/week
520
3. Auto Shop 4/yr @ 15min
1
4. Public Garage 2/day @ lomin
60.83
5. Residential Garage 2 min/day
12.16
6. Residence 10hr/day +weekend
4160
7. Office 40hr/wk
2080
8. OTHER/PUBLIC BUILDINGS 17/wk
884
9. Outdoors 20hr/wk
1040
Figure 1

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CLAYTON FILL-UP STUDY
October - November, 1990
tmmm
E 10
S 9
<:
DC
LU
O
O 7
6
5
4
3
2
1
° 0
o u
38
Ft;-
mm
¦

mm
JS
wzk
WM
y^-4^

m
L7N/40 H/N/40 L/Y/34
mm

H/Y/6
H/N/42
Axis Legend: High or Low MTBE Fuel/ Yes or No Vapor Recovery/ Sample Size
MEAN
Figure 2

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Fill-up Stations Data
ITC
AM Samples

4 5
Station #
4 hr,, AM sample
¦	Pump
¦	Breath Zone
Figure 3

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Fill-up Stations Data
fence-line locations
rnpp
A JL
4 hr., PM Sample
0.1	=	
0.08
1=
g; 0.06
UJ
{? 0.04
0.02
12 3 4
Location's 1, 2, 3, & 4, combined
5 6 7 8 9 10
Station #
Figure 6

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0.16

0.14

0.12
E
CL
0.1
a.

HI
0.08
m

H
0.06
2

0.04

0.02
0
Fill-up Stations Data
fence-line locations
ITC
4 hr., AM Sample
-
£

4





5
A
5
4
5,	4	

	4	
+ + + -


5 6
Station #
10
Locations 1, 2, 3, & 4, combined
Figure 5

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Fill-up Stations Data
ITC
2.5
E
S- 1-5
O
LU
DQ ^
0.5


in
ill;
W/'X'A







1
s 1






PM Samples
4 hr., PM sample
mm
my/A

¥///#,
5 6
Station #
Figure 4
: • i
i

fell
ill
,

Breath Zone
7 8
10

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In-Cabin Concentrations During Refueling
1985 Caprice
0.14
E 0.12
5 0.08
mSSmi
0.02
Group 7; NJ during filiup
RTI
EOHSI
Figure 7

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In-Cabin Concentrations During Refueling
1986 Monte Carlo
0.3
0.25
E
CL
CL
LD
CD
h-
0.2
0.15
0.1
0.05
0
RTI
Figure 8
Groups 11 & 13, combined; CT during fillup (full- and self-serve, resp.)
EOHSI

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In-Cabin Concentrations During Refueling
1992 Corsica (W)
0.12
0.1
0.08
Q.
Q.
LU
DQ
H
0.06
0.04
0.02
0
Group 7; NJ during fillup
RTI
Figure 9
EOHSI
Mean

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In-Cabin Concentrations During Refueling
1992 Corsica (G)
0.12
0.1
0.08
Q.
Q.
LU
CO
h-
0.06
0.04
0.02
0
RTI
Figure 10
Groups 11 & 13, combined; CT during fillup (full- and self-serve, res p.)
EOHSI
Max
Mean
Min

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In-Cabin Commuting Concentrations
1985 Caprice
0.08
0.07
0.06
E 0.05
Ol
cl
m 0-04
CO
ii 0.03
0.02
0.01
0
-
14
-


-
St. Dev=0.0194

-

-

-
17
-

Std Dev=0.003S



Mean
EOHSI
Figure 11
RTI
Group 2

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In-Cabin Commuting Concentrations
1986 Monte Carlo
0.025
0.0225
0.02
0.0175
| 0.015
Q.
^ 0.0125
m
t 0.01
SE
0.0075
0.005
0.0025
0
Group 2

..18	


-	
Std. Dev=0.0043



20
-	

Std. Dev =0.0025






1 1
EOHSI	RTI
Figure 12

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In-Cabin Commuting Concentrations
1992 Corsica (W) & 1992 Corsica (G) - combined
0.035
0.03
0.025
E
§; 0.02
LU
® 0.015
0.01
0.005
0
Group 2
39
35
Std.Dev.=0.0034
Mean
Std. Dev.=0.0051
EOHSI	RTI
Figure 13

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ALASKA MTBE
December 17-22, 1992
AIRPORT
GAS ST.
HOUSE
POST O.
SCHOOL
j
0 0.01 0.02 0.03 0.04 0.05
CONCENTRATION (ppm)
Figure 14
Ambient 8-hour Sample
j—,—|—,—|—|—j—1—,—|—j—|—|—1—|—|—1—1—1—|—|—1—1—1—

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ALASKA MTBE
December 17-22. *992
HOUSE
POST O.
SCHOOL
Indoor 8-hour Sample
_i—)—|——i—i-
H	h
H	1	h
H	1-
0.01 0.02 0.03 0.04 0.05
CONCENTRATION (ppm)
Figure 15

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ALASKA MTBE
February & March 1993
AIRPORT
POST O.
SCHOOL
HOUSE
GAS ST.
0
Ambient 8-hour Sample
	1-
H	1	b
0.005	0.01	0.015
CONCENTRATIONS (ppm)
Figure 16a

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ALASKA MTBE
FEBRUARY & MARCH 1993
m ¦ m	m >¦¦¦¦
AIRPORT
POST O.
SCHOOL
HOUSE
GAS ST.
0
Ambient 8-hour Sample
H	1-
H	1	H
_j	1	1	^
0.05	0.1	0.15
CONCENTRATIONS (ppm)
Figure 16b

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ALASKA MTBE
February & March 1993
VEHICLE
POST O.
SCHOOL
HOUSE
l HI UI IHWWjPK
GARAGE
0
Indoor 8-hour Sample
Swamp

-+	h
H	1	1	h
H	h
0.05	0.1	0.15
CONCENTRATIONS (ppm)
Figure 17

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CONNECTICUT MTBE
April 13-14, 1993

Ambient 8-hour Sample
SCHOOL
¦ ill!

L.I. SOUND
I ; |

LIBRARY
Parking
Garage
GAS ST
hi iii!
MM



0
,
0.01 0.02 0.03 0.04 0.05
CONCENTRATION (ppm)
Figure 18

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CONNECTICUT MTBE
April 13-14, 1993

Indoor 8-hour Sample
OFFICE
See Figure 19b for better scale
•
Parking
Garage




0
1 1 . 1 | 1 . 1 1 | I 1 1 ' | I I T 1 " ' I T
0.1 0.2 0.3 0.4 .0.5
CONCENTRATION (ppm)
Figure 19a

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CONNECTICUT MTBE
April 13-14, 1993
OFFICE
Indoor 8-hour Sample
Parking
Garage
b		A.
H	1	b
H	1	h
_l	(	1	1-
0
0.005	0.01
CONCENTRATION (ppm)
0.015
Figure 19b

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NEW YORK MTBE
Albany
OTHER
GAS ST.
0
8-hour Sample
H	1	H	1	b	1	1-
H	1	(~
H	1		1	1	1	f-
0.01 0.02 0.03 0.04 0.05
CONCENTRATION (ppm)
Figure 20

-------
Lvaporative tmissions at /bl-
Following FTP Cycle
CO
E
o
k_
cr>
if)
if)
<
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0

T--
Vehicle: 1 986 Monte Carlo
Carburator Fuel System
Milage: 80,300
Fuel: Alaska I! (Sun)
MTBE content: 1 2.1%
RVP: 15.5 psi
Benzene q [g/minl = 0.0007*exp(-time/60)
-e-
Benzene Emission
20 40 60 80 100 120 140 160 180 200 220 240
TIME [minutes]
Figure 21

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MTBE Evaporative Emissions
Q = 1 2,9 Exp(-t/45) (mg/min)
CL
c
a
I 01 I ^
a
c
aj
a
c
O
O
LlI
00
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-•— Garage
o Kitchen
«— Living

J	i	L
J	.	L
'¦i.i.	L
01 23456789 10 11 12
Time (hr)
Figure 22

-------
Q
MTBE Evaporative Emissions
1 2.9 Exp(-t/45) (mg/min)
0.04
CL
Q_
C
o
"o
c
aj
a
c
o
CJ
LxJ
m
0.03
0.02
0.01
0.00
o°o
o
o
o
-\
o
o
0/
o Kitchen
¦a— Living
e®



_1	I	U
1 ¦ 1
' » 1
J	i	I	i	I	i	L
01 23456789 10 1112
Time (hr)
Figure 23

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MICROENVIRONMENT CONCENTRATIONS
1.	Gas Fill-up
2.	Commute/ In Vehicle
3.	Auto Shop
4.	Public Garage
5.	Residential Garage
6.	Residence
7.	Office
8.	School/ Public Buildings
9.	Outdoors
EPA ESTIMATE
Pump	1-10 ppm (36 mg/m3)
Other	0.1-1 ppm (3.6 mg/m3)
0.005-0.1 ppm (0.36 mg/m3)
0.1-0.5 ppm (1.8 mg/m3)
0.1-0.5 ppm (1.8 mg/m3)
High	0.1-1 ppm (3.6 mg/m3)
Low 0.001 -0.005 ppm (0.018 mg/m3)
High 0.005-0.01 ppm (0.036 mg/m3)
Low 0.001-0.005 ppm (0.018 mg/m3)
0.001-0.01 ppm (0.036 mg/m3)
0.001-0.01 ppm (0.036 mg/m3)
High	0.01-0.1 ppm (0.36 mg/m3)
Low 0.001-0.01 ppm (0.036 mg/m3)
Figure 24

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METHYL TERTIARY BUTYL ETHER EXPOSURE ESTIMATES
Activity
Occurrence
Time/Year (h)
Concentration
(mg/m3)
Exposure
(mg/m3 » h)
1. Gas fill-up
1.5/week @
2.6
36.0
93.6

2 min




Other @
13.0
3.6
46.8

10 min



2. Commute/in vehicle
10 h/week
520
0.36
187.2
3. Auto shop
4/year @
1.0
1.8
1.8

15 min



4. Public garage
2/day ®
60.83
1.8
109.5

10 min



5, Residential garage
2 min/day
12.16 high
3.6
43.8


low
0.018
0.22
6. Residence
10 h/day +
4,160 high
0.036
149.8

weekend
low
0.018
74.9
7. Office
40 h/week
2,080
0.036
74.9
8. School/public buildings
17 h/week
884
0.036
31.8
9. Outdoors
20 h/week
1,040 high
0.36
374.4


low
0.036
37.4
Figure 25

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TECHNICAL REPORT DATA
	
1. REPORT NO.
EPA/600/A-94/255
2 .
3.RECJ
4. TITLE AND SUBTITLE
Human Exposure of Methyl Tertiary Butyl Ether (MTBE)
5.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Alan H. Huber
8.PERFORMING ORGANIZATION REPORT
NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Atmospheric Research and Exposure Assessment Lab
HEFRD/HEMB
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Atmospheric Research and Exposure Assessment Lab
HEFRD/HEMB
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD
COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Data on ambient air quality and microenvironmental exposures (e.g., during
refueling, inside cards, in personal garages) are too limited for a quantitative
estimate of population exposures to MTBE. At best, they can be used to estimate
broad ranges of potential exposures. Because of the interest in MTBE, the present
evaluation focuses on this compound, even though any potential health effects might
result from complex pollutant mixtures of which MTBE is only one component.
Further more, potential exposures of only the general public, not occupationally
exposed groups, were evaluated.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED
TERMS
c.COSATI



18. DISTRIBUTION STATEMENT
Release to Public

19. SECURITY CLASS {This
Report)
Unclassified
21.NO. OF PAGES

20. SECURITY CLASS (This
Page)
Unclassified
22. PRICE

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