ES/RP 532
Page 1 of 19
Applied Environmental Toxicology
November 8, 2004
Lecture 19
Volatile Organic Compounds (VOCs) (BTEX; Chlorinated Solvents; MTBE)
I. General Comments About Sources
A. Obviously, the groups of compounds targeted for this lecture is too varied and too
numerous to cover adequately in one lecture. Thus, I will highlight some of the compounds
that have been comparatively more studied because of known health effects (usually from
high dose animal testing).
B. These groups of compounds in general arise from fuel use (for ex., gasoline--BETX,
benzene, ethylbenzene, toluene, xylene; a.k.a. monoaromatic hydrocarbons [HCs]),
industrial precursor for synthesis of polymers (for ex., styrene, dibutyl phthalates and
congeners [to be discussed in the lecture on plasticizers], some volatile organohalogens),
from water treatment processes and subsequent environmental reactions (some of the
halogenated VOCs), from natural sources (for ex. organohalogens including brominated
compounds like methyl bromide).
C. BETX has been problematic at LUST sites (Leaking Underground Storage Tanks),
especially at local gas stations.
D. A major source of VOCs in water is wastewater effluents and runoff from streets.
E. One unexpected source was discovered in the early 70’s; surface water undergoing
chlorination and being held unprotected from sunlight was found to contain numerous one
and two carbon halocarbons--thus photocatalytic synthesis in the presence of humic
materials can also produce halogenated VOCs. These groups of chemicals are called
trihalomethanes (THMs) because most of them have a total of three halogens as either
chlorine or bromine.
F. In an attempt to reduce air pollution in urban areas, specific localities in the U.S. were
required by the EPA to oxygenate gasoline supplies.
1. MTBE (methyl tertiary butyl ether) was the most widely used fuel oxygenate.
2. Now we know that MTBE has become a ubiquitous water contaminant in areas where it
was used.
G. Biosynthesis and emission, especially brominated compounds from oceans. VOCs such as
isoprene may also be emitted from vegetation. These groups are generally called biogenic
VOCs.
II. Environmental Chemistry
A. Physicochemical Properties
1. In the table below, you will note that most of the compounds of concern have low Koc’ s
and are quite volatile, as measured by both V.P. and KH.
Compound
WS
log Kow
log Koc
V.P.
KH . 3
(mg/L)
(mm Hg)
(atm m /mol)
benzene
1800
1.6 - 2.1
1.7 -2.0
76 - 118
5.5 x 10-3
ethylbenzene
161
3.15
2.2
9.53
8.4x10-3
toluene
490-515
2.7 - 2.8
2.1
22-40
6.7x10-3
xylene
152-200
3.0 - 3.2
2.1 -3.2
10
5 -7 x 10-3
hexachlorobenzene
0.0062
5.31
4-5
1.9x10-5
1.3x10-3
styrene
310
2.95
2.4-2.7
6.6
2.81x10-3
cresols (N)
23-30
1.95
1.3-1.7
0.13-0.31
8.7-16 x10-7
-5
dibutyl phthalate
11.2
4.72
2.2-3.8
1.4x10
4.6x10-7
methyl bromide
methyl chloride
17,500
6,480
ESRP532 Lecture 19.doc
1.2
0.9
2.1
1633
4310
6.2x10-3
2.4x10-2
Fall 2004
ES/RP 532
chloroform
carbon tetrachloride
formaldehyde (N)
trichloroethylene
tetrachloroethylene
vinyl chloride
acrolein
Benzene
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Applied Environmental Toxicology
8,000-9,300
800-1,160
550,000
1,100-1,470
150
2763
208,000
toluene
ethylbenzene
1.9 - 2.0
2.8
0.4
2.3 - 3.3
2.6 -2.9
1.4
-0.1
1.6
2.4-2.6
1.8-2.1
2.3 -2.6
<1
1.4
p-xylene
m-xylene
o-xylene
3- 7.2 x10-3
2.4- 3 x10-2
3.3x10-7
9-11 x 10-3
1.5x10-2
1.1x10-2
4.4x10-6
160-245
113
3883
58 -94
20
2660
265
Cl
Cl
OH
Cl
HO
Cl
Cl
Cl
OH
hexachlorobenzene
styrene
o-cresol
m-cresol
O
Cl
Cl
H3C
O
Br
Cl
Br
CH
Cl
bromodichloromethane
chloroform
H3C
O
Cl
Cl
O
Br
Br
CH
CH
Br
Br
Cl
dibromochloromethane
C
Cl
Cl
carbon tetrachloride
formaldehyde
Br
Cl
methylchloride
dibutyl phthalate
CH
Cl
methyl bromide
O
H2C
p-cresol
bromoform
Trihalomethanes (THMs)
Cl
Cl
Cl
Cl
Cl
Cl
trichloroethylene
Cl
Cl
vinyl chloride
O
acrolein
tetrachloroethylene
B. Fate of VOCs in water
1. General Observations: (based on Wakeham, S. G. et al. 1983. Distributions and fate of
volatile organic compounds in Narragansett Bay, Rhode Island. Can. J. Fish. Aquat.
Sci. 40:304-321).
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Applied Environmental Toxicology
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a. VOCs measured in water columns along a north-south transect in Narragansett Bay,
RI.
1. Gas chromatograms of water extracts indicated several hundred different VOCs
in the bay.
b. Volatilization apparently is a major removal process for all VOCs. Calculations
suggested water column residence times of 150-300 h with respect to volatilization.
c. Biodegradation was important for aromatic hydrocarbons (HCs) during summer;
HCs degraded in a few days;
d. Sorption onto particulate matter and eventual sedimentation was minor, except for
the higher molecular weight alkanes.
e. Observations about tetrachloroethylene (also known as perchloroethylene or Perc);
1. Concentrations decreased significantly along transect (i.e., gradient evident)
a. Note the relatively higher concentrations (in ppt or ng/L) at the Fields Point
(OT; F) sampling sites in the map below; these areas are outfalls for sewage
treatment facilities that discharge combined municipal, industrial, and storm
water effluents into the Providence River and upper Narragansett Bay.
b. Note that the sampling point (P) in the Providence River is just upstream of
the sewage plant outfalls.
c. Absolute concentrations in the lower Bay were greater in winter than
summer, but levels in the upper bay tended to be a little less variable.
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ES/RP 532
Applied Environmental Toxicology
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d. Note that in the shallower part of the bay (where depths are 4 m or less),
significant concentrations of VOCs were found near the bottom of the water
column. Thus, the water may be fairly well mixed.
f. Observations about toluene
1. Concentrations tend to be higher in winter than summer
2. Concentration gradient tended to be weak, suggesting either uniform inputs
around the bay or rapid removal near the sources so as to leave a uniform
distribution
3. Aromatic hydrocarbons could have multiple input sources all around the bay; for
example, runoff of petroleum derivatives (fuel, gasoline, oil, etc.) used in
transportation or at homes; perhaps spills
Perc and toluene concentration in Narragansett Bay. All residue concentrations expressed as ppt (ng/L)
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Applied Environmental Toxicology
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2. Wakeham et al (1983) conducted mesocosm experiments to determine the fate and
persistence of volatile organic compounds in coastal seawater. Environ. Sci. Technol.
17:611617.
a. Experimental setup:
1. Mesocosms (5.5 m high x 1.8 m diameter) were spiked with VOCs;
2. Mesocosms were outside; sampled different times of year;
3. One set of tanks was sterilized with HgCl2 .
b. Results:
1. Volatilization appeared to be the major process removing aromatic HCs,
chlorinated C2-HC’s, and chlorinated aromatic hydrocarbons during all seasons,
with biodegradation also important for aromatic hydrocarbons in summer.
2. Aliphatic hydrocarbons were quickly sorbed onto particulate matter and thus
removed from the volatile pool; biodegradation also affected alkanes.
Half-lives of Selected VOCs from the Wakeham Mesocosm Exp’t. The two summer experiments
represent sampling at two different times in summer, so the values for half-life are different
Compound
Winter T1/2 Summer T1/2
T1/2, summer, (Sterile) T1/2, summer, (Natural)
benzene
13
3.1
6.9
toluene
13
1.5
7.9
naphthalene
12
nd
11.3
0.8
tetrachloroethylene
12
14
12.1
12.0
dodecane
3.6
0.7
1.8
0.94
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Applied Environmental Toxicology
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C. Fate in Air
1. The Clean Air Act has tightened the regulations regarding ambient concentrations of a
host of “hazardous air pollutants” (HAPs); of course, VOCs make a large contribution
to total HAPs.
2. EPA ambient monitoring programs have yielded information on concentrations (median
and ranges in µg/m3 ) as well as expected atmospheric lifetimes (lifetime measurements
shown as days;
a. Categorized as <1 day, 1-5 days, and >5 days).
1. See table below (adopted from Kelly et al., 1994, Concentrations and
transformation of hazardous air pollutants, Environ. Sci. Technol. 28(8):378387).
b. Primary reaction influencing lifetime was interaction with OH radical.
Summaries of atmospheric concentrations and atmospheric lifetimes of selected VOCs
Ambient Concentration Measurements
# of Locations
Median or range Lifetime in Air
Compound
Sampled
# of Samples
(µg/m3 )
(days)
benzene
>140
>10,000
5.1
>5
ethylbenzene
93
8723
1.1
<1
toluene
131
9373
8.6
1-5
o-xylene
104
8542
2.2
<1
m-xylene
98
8431
4.2
<1
p-xylene
102
3597
4.3
<1 to 1-5
hexachlorobenzene
21
6117
0.6
<1
o-cresol
3
10
1.5
<1
m-cresol
2
3
nd
<1
p-cresol
11
62
0.20
<1
dibutylphthalate
3
>13
0.5-6.0 ng/m
<1
methyl bromide
48
1081
nd
>5
methyl chloride
37
1434
1.3
>5
chloroform
117
4368
0.2
>5
carbon tetrachloride
131
5739
0.8
>5
formaldehyde
58
1358
3.3
1-5
trichloroethylene
124
4267
0.4
>5
tetrachloroethylene
133
4893
1.7
>5
vinyl chloride
66
1864
nd
<1 to 1-5
acrolein
2
12
nd
<1
nd = not detected
D. Fate in Soil
1. Volatilization from soil is directly dependent on temperature and humidity (Shonnard
& Bell. 1993. ES&T 27:2909-2913.
a. Note in the results taken from Shonnard & Bell’s paper, sinusoidal fluctuations in
soil temperature cause sinusoidal variations in volatilization flux of benzene;
1. Beware that the x-axis is the reciprocal square root of time;
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ES/RP 532
Applied Environmental Toxicology
Page 7 of 19
6
Benzene Flux
(mg/cm 2 /min)
2
26
1/time
Temperature
oC
20
Elapsed Time in Experiment
b. Note that when the relative humidity in a soil-column dropped to near zero, flux also
dropped off (note the break in the flux curve between points 1 and 2; remember that
in the upper graph, time is the square root of the reciprocal)
2. BETX components are biodegradable under both aerobic and anaerobic conditions;
microbial cultures have been isolated which can degrade the compounds; major pathway
is via oxidative enzyme system (a.k.a. toluene dioxygenase)
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Applied Environmental Toxicology
OH
COOH
COOH
OH
Benzene
cis, cis-Muconic acid
Catechol
O2
CHO
COOH
OH
2-hydroxy-cis,cis-Muconic Semialdehyde
acetaldehyde + pyruvic acid
O2
O
COOH
COOH
beta-Ketoadipic Acid
succinic acid + acetyl-CoA
3. Leaching will occur because of the solubility of the compounds; if there is a spill or a
leak where large concentrations of compounds are present, soil water (and thus
groundwater) can easily be contaminated.
III. Toxicology (mainly concentrating on human exposures and effects of BENZENE as a known
hazard)
A. Toxic Effects
1. The major and most hazardous effect of benzene is probably its known carcinogenicity
(there seems to be sufficient human evidence); the site of action seems to be the bone
marrow, producing acute mylogenous leukemia (ALM) or the adult form of acute
leukemia.
2. Another effect of benzene is the potential to cause multiple myeloma (tumor of bone
marrow plasma cells, which are the antibody-producing cells derived from
lymphocytes).
3. A non-neoplastic effect is aplastic anemia; benzene affects the formation of red and
white blood cells and platelets
4. At levels of 100 ppm and significantly above, benzene can adversely affect the central
nervous system (drowsiness, lightheadedness, headache, delirium, vertigo, and narcosis
leading to loss of consciousness).
B. Metabolism & Toxicodynamics (Mammalian)
1. 43% of administered benzene dose was expired unmetabolized;
2. 1.5% exhaled as CO2 ;
3. 35% recovered as urinary metabolites;
a. 23% phenol
b. 4.8% hydroquinone
c. 2.2% catechol
d. 1-2% trans,trans-muconic acid
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Applied Environmental Toxicology
4. Metabolism to phenol and subsequent conjugations are detoxifications;
5. Metabolism of phenol to hydroquinone (and to p-benzoquinone) and of benzene to
muconic acid are two pathways that are currently thought to lead to the formation of
toxic metabolites.
a. Muconaldehyde causes bone marrow depression in mice
b. Benzoquinone is known to form DNA adducts
O
H
HOOC
C
C
C
COOH
C
H
O
O
p-Benzoquinone
trans, trans-Muconic Acid
OH
Oxepin
OH
OH
OH
+
Benzene
O
Phenol
OH
Hydroquinone
Catechol
Benzene oxide
Glucuronide + Sulfate Conjugates
S N
Acetyl Cysteine
C. A recent report suggests that benzene toxicity may be regulated by AhR signaling (Yoon et
al. 2002; Aryl hydrocarbon receptor mediates benzene-induced hematotoxicity.
Toxicological Sciences 70:150-156.)
1. This hypothesis stemmed from an experiment in which AhR knock-out mice were not
affected by benzene (300 ppm inhalational exposure; hematotoxicity as the toxicological
endpoint); AhR wildtype mice were adversely affected.
2. Metabolites of benzene (phenol and hydroquinone) given to AhR knock-out mice,
however, could cause characteristic physiological affects.
D. Risk Characterization
1. Estimated risk of 8 in 1 million for benzene-induced leukemia associated with breathing
1 µg/m3 (~0.4 ppb) of benzene for 70 years.
2. For drinking water, the level of benzene responsible for a one in 1 million lifetime risk
has been calculated by EPA to be 0.66 ppb.
E. Human Exposure to Benzene (and other VOCs)--a case of contaminants everywhere!!!
1. Chan et al. 1991. Driver exposure to volatile organic compounds, CO, ozone, and NO2 ,
under different driving conditions. ES&T 25:964-972.
Median In-Vehicle Concentrations of Seven Target Aromatic VOCs Measured at Urban and Interstate
Routes for Each Driving Period (concentrations as µg/m3 )
Urban
Interstate
Morning
Evening
Morning
Evening
Benzene
11.6
15.9
10.8
9.1
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ES/RP 532
Toluene
Ethylbenzene
m/p-Xylene
o-Xylene
1,3,5-trimethylbenzene
1,2,4-trimethylbenzene
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Applied Environmental Toxicology
19.0
9.5
33.3
12.8
5.0
17.3
75.8
13.9
46.0
17.1
7.1
24.1
38.5
7.4
25.7
9.5
3.7
13.0
30.7
6.0
20.6
7.8
3.5
11.0
Comparisons of in-vehicle concentrations of CO and selected VOCs between three ventilation conditions
(Raleigh, NC, 1988; Chan et al. 1991)
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Applied Environmental Toxicology
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Comparison of VOC measurements in in-vehicle, car exterior, sidewalk, and fixed site for selected VOCs
((Raleigh, NC, 1988; Chan et al. 1991)
2. McKone, T. E. 1987. Human exposure to volatile organic compounds in household
tap water: the indoor inhalation pathway. ES&T 21:1194-1201.
a. Note that chloroform has been a concern because of studies during the 1970’s that
showed it was a liver carcinogen in mice. Chloroform (CHCl3 ) is one type of
disinfection byproduct produced by chlorination of water and subsequent exposure
to sunlight. These types of disinfection byproducts are called trihalomethanes
(THMs). Other important species include bromodichloromethane (CHCl2 Br),
dibromochloromethane (CHClBr2 ), and bromoform (CHBr3 ).
1. However, further biochemically based mechanistic studies showed that at high
doses it caused hepatic cellular toxicity, which was accompanied by cellular
proliferation. (Larson et al. 1994. Induced cytotoxicity and cell proliferation in
the hepatocarcinogenicity of chloroform in female BC3F1 mice: comparison of
administration by gavage in corn oil vs. ad libitum in drinking water.
Fundamental and Applied Toxicology 22:90-102)
a. Thus, chloroform at normal environmental concentrations should present a
very small risk of hepatocarcinogenicity
b. Indeed, recently for the first time, the EPA proposed to consider a “nonzero” water standard for chloroform on the basis that it was a threshold
carcinogen! However, environmental advocacy groups cried foul, and the
EPA seems to have backed off its “courageous” stand.
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Applied Environmental Toxicology
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b. Other VOCs have also been found in potable water; for example trichloroethylene
(TCE), which is used as a degreasing and cleaning agent by industry and dry
cleaners.
1. TCE has been deemed carcinogenic by the EPA, although genotoxicity studies
are equivocal (some are positive, some are negative); similar results have been
observed in carcinogenicity assays (Fan, A. M., 1988, Trichloroethylene: water
contamination and health risk assessment. Reviews of Environ. Contam. &
Toxicol. 101:56-92.)
a. The safety criterion for TCE in water is 5 ppb; in urban areas of California, a
number of wells have been reported to have concentrations greater than 5
ppb.
b. The main concern, however, is with worker exposure.
c. McKone has modeled the concentration of VOCs in the air of households (in
general) as well as specifically in the shower. Note that in McKone’s model, he
assumed a 1 mg/L concentration of each VOC.
Average Air Concentrations Calculated for VOCs in Each of Three Household Compartments Using a Tap
Water Concentration of 1 mg/L. (The concentrations shown are in µg/L).
Shower Air
Bathroom Air Household Air 1 Household Air 2
Carbon tetrachloride
18
3.6
0.12
0.024
Chloroform
20
3.8
0.12
0.026
DBCP
93
1.8
0.80
0.020
EDB
19
3.8
0.12
0.025
PCE (Perc)
17
3.4
0.11
0.023
(=tetrachloroethylene)
TCE
18
3.5
0.11
0.024
(trichloroethylene)
For the shower, the period form 7 am to 8 am is modeled. For the bathroom, the period 7 am to 9 am is
modeled. For the household air 1, the period 7 am to 11 pm is modeled. For household air 2, the
period 11 pm to 7 am is modeled.
d. So what does it mean?
1. For TCE, the EPA and National Academy of Sciences (NAS) have set a lifetime
exposure water criteria for no more than a 1 x 10- 6 risk of excess cancer at 2.8
and 4.5 ppb, respectively.
2. Potable water should not be normally be contaminated with TCE at levels higher
than the standards; for example, in sampling programs conducted in California,
median levels were <2 ppb. However, some wells were very high and
approached 100 ppb.
3. Fan (1988) has presented a calculation of short term exposure (via showering or
dermal and inhalation and drinking) to TCE contaminated water;
a. A short term risk assessment (say for 3 months) is valuable because if a
water supply is unacceptably contaminated (for example because of a
leaking underground tank or spill), than the water could be treated or an
alternative supply used for a short time; meanwhile people may have been
using the water for a short while before the contamination was discovered.
b. Fan calculated that exposure to water with TCE at 3 ppm for 3 months (via
showering and bathing route), should not cause excess cancer at a risk of 1 x
10-6.
c. The level of exposure considered not to cause any adverse health effects and
provide a margin of safety of 1000-fold was 0.1 mg/kg/day;
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Applied Environmental Toxicology
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1. Note that the exposures calculated and presented by Fan based on water
containing 3 ppm TCE are generally lower than the health standard
(some are a little above).
TCE Occurrences from Random and Nonrandom Sample Sites Serving Large (>10,000 persons) and
Small (<10,000 persons) Ground Water Systems in an EPA (1984) National Survey
Type of
Type of
No. of
Occurrences Occurrences Median
Maximum
System
Samples
Samples
Number
%
(ppb)
(ppb)
Large
Random
186
21
11.4
1.0
78
Small
Random
280
9
3.2
0.88
40
Large
Nonrandom
158
38
24.1
1.5
130
Small
Nonrandom
321
23
7.2
1.2
29
Comparative Daily Doses (mg/kg bw) of TCE Received by Individuals of Various Body Weights Under
Various Exposure Conditions to Water Containing 3 ppm TCE
Body Weight
70 kg
22 kg
10 kg
Drinking (oral)
Showering
Dermal
Dermal + Inhalation
Inhalation
Bathing (3 mg/L)
Dermal (15 min)
Dermal (5 min)
0.086
0.204
0.064
0.083
0.099
0.1
0.129
0.154
0.051
0.24
0.08
0.3
0.08
F. Recent Concerns—Associations with adverse reproductive outcomes (e.g., spontaneous
abortion) due to trihalomethanes
1. Trihalomethanes (THMs) are disinfection byproducts produced from the chlorination of
drinking water, interaction of the chlorine with natural organic matter, and subsequent
photocatalytic synthesis of small molecular weight chlorine or bromine containing
volatile and semi-volatile hydrocarbons.
2. THMs include compounds like chloroform, bromoform, bromodichloromethane, and
chlorodibromomethane.
3. The EPA defined regulatory limit for THMs in drinking water is 100 ppb (100 µg/L).
4. Many water utilities have switched to chlorine dioxide or ozone as a disinfectant. Both
produce substantially less THMs (by up to three orders of magnitude according to
Richardson (1994, Today’s Chemist at Work, vol. 3 (3), p. 29-32). However, neither
disinfectant is stable and so chlorine or chloramine must be added to the water before it
is sent through the distribution system.
5. During 1998, THMs in drinking water were in the news (once again) because of
studies published by the CA Dept. of Health Services (CDH) (Swan et al., 1998,
Epidemiology 9:126-133; Waller et al., 1998, Epidemiology 9:134-140)
a. CDH researchers studied spontaneous abortions in CA women from three regions
having different water sources (I = mix of ground water and surface water; II =
primarily surface water; III = primarily ground water.
b. Within each region, respondents to a survey (5,342 useable subjects) were
segregated by consumption of bottled water vs. tap water and number of glasses
drunk each day.
c. The study was prospective, so pregnancy outcomes could be followed post
interviews.
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Applied Environmental Toxicology
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d. The study results showed the following:
Number of Women, Percentages within Each Region, and Percent with Spontaneous Abortion (SAB) in
California (Swan et al. 1998)
Region I
Region II
Region III
Variable
N
%
%
N
%
%
N
%
%
SAB
SAB
SAB
Consumption of Bottled Water
0
548
33.3 11.5
781
44.4
10.9
775
44.5
9.8
0.5-5.5
826
50.2 8.0
746
42.5
9.0
726
41.7
10.1
≥6
271
16.5 8.1
230
13.1
10.9
239
13.7
9.2
≥6 & no cold
184
11.2 6.5
149
8.5
12.8
137
7.9
11.0
tapwater
Consumption of Total Tapwater
0
565
34.3 8.7
457
26.0
9.4
441
25.3
10.4
0.5-5.5
879
53.4 8.5
1008 57.4
10.3
1000 57.4
10.0
≥6
200
12.2 13.0
291
16.6
10.3
300
17.2
8.3
≥6 & no
148
9.0
14.9
241
13.7
9.5
234
13.4
8.1
bottled water
Consumption of Cold Tapwater
0
771
46.8 8.4
619
35.2
9.7
535
30.7 11.4
0.5-5.5
753
45.7 8.9
955
54.4
10.4
981
56.4 9.5
≥6
120
7.3
15.0
182
10.4
9.9
225
12.9 7.6
≥6; no bottled
95
5.8
17.9
162
9.2
9.9
187
10.7 8.0
water
Spontaneous Abortion Rates and Odds Ratios by Water Type and Amount in Region I (Note that in
Region II and Region III, there was no trend in SAB with water source)
Bottled Water
Unadjusted Odds Ratio
Adjusted Odds Ratio
(95% CI)_
(95% CI)
0.5 – 5.5 vs. 0
0.66 (0.46-0.95)
0.68 (0.47-0.99)
≥6 vs. 0
0.68 (0.41-1.13)
0.60 (0.35-1.03)
≥6 and no cold tap vs 0 and
≥6 cold tap
Total Tapwater
0.5-5.5 vs. 0
0.98 (0.68-1.43)
1.03 (0.70-1.52)
≥6 vs. 0
1.57 (0.95-2.61)
1.66 (0.99-2.78)
≥6 and no cold tap vs 0 and
2.50 (1.11-5.64)
3.51 (1.43-8.63)
≥6 cold tap
Cold Tapwater
0.5-5.5 vs. 0
1.06 (0.74-1.52)
1.10 (0.76-1.59)
≥6 vs. 0
1.92 (1.09-3.36)
2.17 (1.22-3.87)
≥6 and no bottled vs 0 and
3.12 (1.42-6.86)
4.58 (1.97-10.64)
≥6 bottled
Odds ratio adjusted for age, prior spontaneous abortion, race, gestational age at interview, showering,
weight.
e. The abstract of the Swan et al. paper (tables illustrated above) concludes that the
study confirms the association between cold tapwater and spontaneous abortion, that
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was first seen in Region I in 1980. “If causal, the agent(s) is not ubiquitous but is
likely to have been present in Region I for some time.”
1. Note: Cold water was included as a separate variable because hypothetically,
letting the water sit should allow for volatilization of THMs.
f. Interestingly, in the discussion, Swan et al. state:
1. “Our prior studies suggested that the relation between spontaneous abortion
and tapwater was independent of chlorination by-products, since the strongest
associations were seen in the two studies conducted in areas served only by
unchlorinated groundwater.” (Referring to studies published in 1992).
2. Swan et al also state in their discussion: “Nevertheless, we believe that the
associations with cold tapwater and bottled water presented here, which are
specific to Region I, cannot be explained by exposure to chlorination byproducts, because the association is seen in the absence of high levels of these
chemicals.
3. The chemical concentrations (i.e., of the four main THMs) were analyzed in the
companion paper by Waller et al. 1998. From that study they concluded that the
risk was associated with specific chlorination by-products, namely ,
bromodichloromethane.
% SAB and O.R. for SAB among 5144 Women Exposed to Varying Levels of Total THMs in Residential
Drinking Water During The First Trimester of Pregnancy
Total THMs
Cold Tapwater % SAB
N
Unadjusted
Adjusted
(µg/L)
Glasses/Day
Odds Ratio
Odds Ratio
(95% C.I.)
(95% C.I.)
<75
N/A
9.1
3,672 1.0
1.0
≥75
N/A
11.4
950
1.3 (1.0-1.6)
1.2 (1.0-1.5)
<75
<5
9.2
3,105 1.0
1.0
≥75
<5
10.8
828
1.2 (0.9-1.5)
1.1 (0.9-1.4)
<75
≥5
8.5
565
1.0
1.0
≥75
≥5
15.7
121
2.0 (1.1-3.6)
2.0 (1.1-3.6)
Low Personal THM
N/A
4,988 1.0
1.0
exposure
High Personal THM N/A
121
1.8 (1.1-2.9)
1.8 (1.1-3.0)
Exposure
Region I
Low <75 µg/L
<5
8.9
1,614 1.0
1.0
High (≥75 µg/L) ≥5
24.1
29
3.2 (1.4-7.7)
4.3 (1.8-10.6)
Region II
Low <75 µg/L
<5
9.7
1,656 1.0
1.0
High (≥75 µg/L) ≥5
14.0
86
1.5 (0.8-2.8)
1.5 (0.8-2.9)
Region III
Low <75 µg/L
<5
9.8
1,718
High (≥75 µg/L) ≥5
0.0
6
N/A
N/A
O.R. for SAB Associated with High Personal Exposure to Individual THMs
THM
All Regions
All Regions * Region I
Chloroform
0.9 (0.5-1.6)
0.6 (0.3-1.2) 1.4 (0.5-4.1)
Bromoform
1.0 (0.5-2.0)
0.7 (0.2-2.1) 1.3 (0.4-4.5)
Bromodichloromethane
2.0 (1.2-3.5)
3.0 (1.4-6.6) 2.1 (0.9-4.5)
Chlorodibromomethane
1.3 (0.7-2.4)
0.8 (0.2-2.8) 1.3 (0.4-3.7)
ESRP532 Lecture 19.doc
Region II/III
0.8 (0.4-1.5)
1.0 (0.5-2.1)
2.3 (1.1-4.9)
1.4 (0.6-3.2)
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* Adjusted for all covariates (gestational age at interview, maternal age at interview, cigarette smoking,
history of pregnancy loss, race, employment during pregnancy plus all four individual THMs as covariates
simultaneously.
g. Note that a 1995 study by Savitz et al. (Environ. Health Perspectives 103:592-596)
found no association between level of water intake, THMs, and spontaneous
abortion.
h. A paper by Reif et al. (1996, Environ. Health Perspectives 104:1056-1061) made
this statement in discussing the reproductive and developmental effects of
disinfection by-products in drinking water:
1. “The epidemiologic evidence supporting associations between exposure to
water disinfection by-products and adverse pregnancy outcomes is sparse, and
positive findings should be interpreted cautiously.”
6. One pathway of loss not taken into consideration is the possibility of volatilization of
THMs upon allowing the water to stand. Research (Batterman et al. 2000, ES&T,
34:4418-4424) has shown that volatilization losses approached 75% when water was
boiled for brief period of time and reached 90% when boiled water was poured and
served. For typical adults, who drink nearly half of their water as hot beverages,
volatilization will reduce ingestion of THMs by a factor of 2.
Volatilization rate constants for total THM from water at different temperatures and water column
heights (Batterman et al. 2000)
Container
Water Column
Temperature
Rate Constant
Height (cm)
(°C )
k (h-1)
Tall glass
14.5
Average 4 –16
0.081
Tall glass
14.5
25
0.048
Tall glass
14.5
30
0.154
Tall glass—half full
6.2
25
0.065
Tall glass—half full
6.2
30
0.206
Wide-mouth
8.5
25
0.135
Wide-mouth
8.5
30
0.391
Coffee mug
6.2
Average 40 – 100
1.5
IV. The Saga of MTBE (methyl tertiary-butyl ether): Creating an Environmental
Contaminant While Trying to Fix Another Problem (Source: Hogue, 2000, Chemical &
Engineering News 78[13]:6).
CH3
CH3
O C
CH3
CH3
A. MTBE was originally added to gasoline as an octane enhancer compound to replace alkyl
lead compounds.
B. Under the 1990 mandate of the Clean Air Act to reduce ozone and thus smog formation,
MTBE was added as a fuel oxygenate, supposedly to make gasoline burn cleaner.
C. Until recently, only reformulated gasoline (i.e., with MTBE added to conventional gasoline)
could be sold in ~12 urban areas with smog problems. A number of states and cities
voluntarily chose to use reformulated gasoline.
1. About 87% of reformulated gasoline uses MTBE as an oxygenate.
a. MTBE is added to a concentration of up to 15% by weight, which creates a fuel with
about 2.7% oxygen by weight (Hanson 1999, Chem. Eng. News 77(42):49).
2. Thus, the annual use of MTBE was ~4.5 billion gallons.
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D. Nearly from the beginning of its use, MTBE was pegged with problems.
1. A number of consumers complained about ill health, including dizziness, nausea,
irritated nose and throat, coughing, disorientation and headaches.
a. However, controlled exposures in the lab did not cause an increase in putative
symptoms.
E. By 1996, however, MTBE was being found in drinking-water supplies because of leaking
underground gasoline pipelines and storage tanks.
1. As little as 15 ppb of MTBE can be tasted or smelled in water.
2. The USGS conducted a survey of ground water contamination by MTBE around the
U.S. (Squillace et al. 1996, Preliminary assessment of the occurrence and possible
sources of MTBE in groundwater in the United States, 1993-1994. Environ. Sci.
Technol. 30:1721-30.).
a. Note that about 109 million people live in areas where oxygenated fuels were
mandated for use.
b. About 27% of urban ground water samples had detections of MTBE at 0.2 ppb or
above.
1. About 1.3% of agricultural wells had MTBE detections.
Concentration of MTBE in shallow groundwater from urban land use study areas, 1993-1994
(Squillace et al. 1996)
F. MTBE has generally not been found in ground water with other components of BTEX.
1. Nevertheless, research suggests that MTBE is more likely associated with gas stations
using oxygenated fuels than using “conventional” fuel. (Lince et al. 2001. Effects of
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Applied Environmental Toxicology
gasoline formulation on methyl tert-butyl ether (MtBE) contamination in private wells
near gasoline stations. Environ. Sci. Technol. 35:1050-1053.)
Well Classification
(Independent variable
classified by fuel
type)
Combined (wells
representing all gas
stations)
Conventional gasoline
Number
of Wells
>1 µg/L-19 µg/L
≥20 µg/L -49 µg/L
≥50 µg/L
74
14 (19%)
5 (7%)
2 (3%)
40
6 (15%)
1 (3%)
1 (3%)
Reformulated
34
8 (24%)
4 (12%
1 (3%)
Gas/Oxyfuel (MTBE) *
Control wells (up
21
1 (5%)
0
0
gradient of gas stations
* RFG or reformulated gasoline will probably have MTBE (estimates of 84% use) but not all RFG
will necessarily have used MTBE.
G. It is not surprising that MTBE has been found in so many water wells; note its
physicochemical properties:
1. Water solubility: 23.2 – 54.5 g/L
2. Log Kow: 0.94 – 1.16
3. Vapor Pressure: 249 mm Hg
4. KH: 5.87 x 10-4 atm-m3 /mole
H. MTBE moves in the soil as a conservative tracer (little interaction with substrate).
I. MTBE has been found at ppt concentrations in the Sierra Mts., but it is noted for rapid
photodegradation that may reduce the deposition load (Schade, G. W., B. Dreyfus, and A. H.
Goldstein. 2002. Atmospheric methyl tertiary butyl ether (MtBE) at a rural mountain site in California.
J. Environ. Qual. 31:1088-1094.)
1. However, MTBE has been measured in urban and rural precipitation in Germany
(Achten, C. and A. Puttmann W. Kolb. 2001. Methyl tert-butyl ether (MTBE) in urban and rural
precipitation in Germany. Atmospheric Environment 35:6337-6345.)
a. MTBE is detected in precipitation when ambient temperatures are lower than about
10-15°C.
b. MTBE is detected in greater amounts in the first precipitation after a dry period than
after a wet period.
c. Urban runoff contains MTBE.
d. MTBE is detected in urban precipitation more often (86% of samples with detects)
than in rural precipitation (18% of samples with detects)
J. An interesting ecotoxicological phenomenon (Cho, E.-A., A. J. Bailer, and J. T. Oris. 2003.
Effect of methyl tert-butyl ether on the bioconcentration and photo induced toxicity of fluoranthene in
fathead minnow larvae (Pimephales promelas). Environ. Sci. Technol. 37:1306-1310.)
1. MTBE is also released directly into lakes from motorized water craft.
2. Between 20 and 30% of thee fuel that enters the combustion chamber is released in the
exhaust unburned, and between 3 and 10% of MTBE is released directly into water.
3. Watercraft exhaust is considered one of the most important sources of MTBE in
California lakes and reservoirs.
a. Residues range from <1 µg/L to a high of 88 µg/L.
1. Use of MTBE in watercraft fuel is now forbidden in the Lake Tahoe Basin.
4. Combustion of fuel in gasoline engines produces a complex mixture of PAHs.
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a. In the presence of natural or simulated sunlight, PAHs are acute toxic to aquatic
organisms at concentrations that are below the PAH aqueous solubility limits (i.e.,
PAHs are phototoxic).
b. Is there any interaction between MTBE and PAHs
5. Fathead minnows exposed to 20 µg/L fluoranthene (FA) in the presence (40 µg/L) or
absence of MTBE (Cho et al. 2003)
a. Bioconcentration of FA and depuration by fish was monitored
1. Bioconcentration of FA in the presence of MTBE increased up to 2.2 times over
exposures in the absence of MTBE.
2. Survivability, when in the presence of artificial sunlight, was decreased by the
presence of MTBE.
K. Whether MTBE is carcinogenic or not is up in the air; nevertheless EPA has essentially
ruled that MTBE is “history” as far as its use in gasoline is concerned.
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