Final Report
SOIL AS A SINK FOR ATMOSPHERIC
CARBON MONOXIDE
Prepared for:
COORDINATING RESEARCH COUNCIL
NEW YORK, NEW YORK
CONTRACT CAPA-4-68 (1-69)
and
THE ENVIRONMENTAL PROTECTION AGENCY
DURHAM, NORTH CAROLINA
STANFORD RESEARCH INSTITUTE
Menlo Park, California 94025 • U.S.A.
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STANFORD RESEARCH INSTITUTE
Menlo Park, California 94025 • U.S.A.
Final Report
October 1971
SOIL AS A SINK FOR ATMOSPHERIC
CARBON MONOXIDE
By: R. B. INGERSOLL
Prepared for:
COORDINATING RESEARCH COUNCIL
NEW YORK, NEW YORK
CONTRACT CAPA-4-68 (1-69)
and
THE ENVIRONMENTAL PROTECTION AGENCY
DURHAM, NORTH CAROLINA
SRI Project SCU-8799
Approved by:
W. A. SKINNER, Executive Director
Life Sciences Division
Copy No.
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CONTENTS
LIST OF ILLUSTRATIONS
iv
LIST OF TABLES
III
v
I
1
INTRODUCTION
II
BACKGROUND
3
SUMMARY AND CONCLUS IONS
7
IV
METHODS AND MATERIALS
9
Test Systems
Plastic Atmospheric Chambers
Flasks
Clean Benches
Gas Analysis Apparatus
9
. .
9
11
11
12
Test Materials
12
Soil s .
Higher Plants
Microorganisms
12
12
12
Soil Treatments
13
Steam Sterilization
Antibiotic and Saline Treatments
Anaerobic Treatment
Inoculation of Sterile Soil
Temperature Treatment
Light-Dark Treatment
Isotope Fractionation Technique
Preliminary Isotope Studies
Prolonged Exposure to CO
13
13
14
14
14
14
15
15
16
V
RESULTS
17
Higher Plants
17
Potting Soil and Natural Soil
17
Effects of Soil Treatments
22
ii
-------
Soil Microorganisms
31
Influence of CO on Soil Microbial Population
32
Tracing CO Uptake with 14C
33
VI
DISCUSSION
35
LITERATURE CITED
38
iii
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
ILLUSTRATIONS
Influence of Soil Volume in PAC on
Carbon Monoxide Uptake. . . . . .
. . . . .
. . . . . .
Reduction of CO in Test Atmosphere with Time
by 2.8 kg of Potting Soil . . . . . . . . . . . .
Uptake of CO by Soil in PACs and in situ
. . . .
. . . .
--
CO Uptake by Steam-Sterilized vs.. Nonsterile Soil
Effects of Antibiotic, Saline and Anaerobic Treatments
on Rate of CO Depletion over Potting Soil. . . . . . .
Effect of Soil Saturation with An Antibotic Solution
(1000 ppm Cycloheximide, 510 ppm Streptomycin,
870 ppm Erythromycin) on the Rate of CO Depletion
CO Uptake Capacity of 2.8 kg of Autoclaved Potting
Soil with Time Following Inoculation with 1 g of
Non s t e r i 1 e So i 1 ..... . . . . . . . . . . . . . . .
Influence of Light on CO Uptake by Soil
........
Isotopic Fractionation of CO During Uptake by Soil
iv
10
19
20
23
24
25
26
29
30
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Table I
Table II
Table III
Table IV
Table V
Table VI
Table VII
Table VIII
TABLES
Higher Plants Tested in Aseptic Culture
for Capability to Remove CO from Atmosphere
. . . . .
Rate of Removal of CO from Test Atmospheres
at 25°C by Various Soils . . . . . . .
. . . .
Rate of CO Removal over 100 g of Potting Soil
at Different Temperatures. . . . . . .
. . . .
Carbon Monoxide Evolution by Autoclaved Soil
. . . .
Soil Fungi Active in CO Uptake
........
Effect of Prolonged Exposure to CO on CO Uptake
by S oi 1 . . . . . . . . . . . . . . . . .
Influence of Prolonged Exposure to CO
on Soil Microflora . . . . . . . . .
. . . .
. . . .
Uptake of 14C-Carbon Monoxide by Soil.
.......
v
18
21
27
28
31
32
33
34
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I
INTRODUCTION
The increasing emission of carbon monoxide (CO) through the burning
of fossil fuels, notably gasoline by motor vehicles, has caused serious
concern among public health officials and representatives of the auto-
motive and petroleum industries.
It has been estimated that over
200 million metric tons of CO per year are liberated into the earth's
atmosphere due to man's activities alone (18). Yet, ambient concentrations
do not appear to have changed appreciably as a result, in spite Qf calcu-
lations (14) showing that at this rate of liberation, the ambient CO level
should double within 4-5 years.
The fate of CO liberated into the atmo-
sphere therefore has aroused scientific curiosity and become medically
significant. The biological effects of abnormally high levels of CO in
the atmosphere have been intensively studied (4), and research is con-
tinuing in this area to more specifically define the effects of CO
concentrations encountered under various road traffic situations.
A series of research contracts was awarded to Stanford Research
Institute by the Coordinating Research Council and the National Air
Pollution Control Administration (later transferred to the Environmental
Protection Agency) to provide insight into the fate of atmospheric CO.
The objective was to investigate the biosphere as a possible sink for
atmospheric CO.
Research conducted under the initial contract by
Mrs. Elaine Levy (14) showed that nonsterile soil depleted CO from test
atmospheres, whereas steam-sterilized soil did not, suggesting a role for
soil or soil microorganisms as a sink.
Tests regarding uptake of CO by
certain large marine algae were inconclusive.
The research described in this report was conducted under a second
contract, and was designed as an extension of Mrs. Levy's work.
were to:
Objectives
1
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Measure CO uptake by soils from different locations.
Determine whether CO uptake by the soil was mediated by a physical
or biological mechanism.
Determine which organisms, if any, were responsible for CO uptake.
Determine the role of higher plants as a CO sink.
Determine effects of selected environmental conditions on CO uptake
by soil.
an
Some of the results of this research have been published (8) and
additional paper is in preparation.
2
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II
BACKGROUND
Concentrations of CO in the ambient atmosphere appear seldom to
exceed 1 part per million (ppm).
Swinnerton et ale (22) recorded
concentrations over the Atlantic Ocean between Chesapeake Bay and Puerto
Rico that ranged between 0.075 and 0.44 ppm.
Within the Potomac River-
Chesapeake Bay area, concentrations decreased with increasing distance
from urban areas, but increased over the large ocean mass.
Robinson and
Robbins (19) found values over the Pacific Ocean ranging from 0.04 ppm
at latitude of 50° S to 0.2 ppm at 40° N.
The higher values for the
northern hemisphere were attributed to air pollution sources in this
hemisphere. Concentrations of CO at ground level at Point Barrow, Alaska,
averaged 0.09 ppm through an ll-day sampling period in September (2).
Seiler and Junge (20), in a study of the global tropospheric distribution
of CO, found the average for the northern hemisphere to be 0.1-0.15 ppm.
Robbins et al. (18) measured 0.3-0.9 ppm of CO at ground level in Green-
land, 0.8 ppm at one spot on the north coast of California, 0.03-0.3 ppm
at Crater Lake, Oregon, and concentrations up to 0.8 ppm at Patrick
Point, California.
They considered the average ambient concentration of
CO in the Northern Hemisphere to be approximately 0.05 ppm.
Both man-made and natural sources contribute to ambient CO levels.
Because the largest single source of anthropogenic CO is the automobile,
CO levels over large urban centers always exceed those found in remote
regions and can be observed to rise and fall with the intensity of motor
vehicle traffic.
During a recent study in Los Angeles, the CO level at
one station along the Harbor Freeway measured 3 ppm at 4:00 a.m., when
traffic intensity was the lowest, and 15 ppm at 8:30 a.m. during the
morning rush hour
(25).
Similar patterns are evident in any large
metropolitan area.
During prolonged periods of air stagnation, CO levels
in Los Angeles have exceeded 30 ppm for an 8-hour period.
In London,
CO concentrations at street level on a calm day have reached 360 ppm.
3
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Robbins et al. (18) have estimated that the worldwide production of
CO by man exceeds 200 million metric tons each year.
According to
Jaffe (9), over 90% of the CO liberated by man in the United States is
due to the burning of gasoline by motor vehicles.
There are also numer-
ous natural sources of CO.
The extent to which these may contribute to
the total ambient picture is not yet understood, but evidence is accumu-
lating that indicates that CO produced in ocean waters is a prime con-
tributor to ambient levels.
Swinnerton et al. (22) observed that CO
content in Atlantic ocean waters was greater than that in the Potomac
River and Chesapeake Bay.
Moreover, equilibrium for CO between the sea
water and the atmosphere was not observed, in that the net gas transport
was from the sea to the air.
Seiler and Junge (20) found CO concentrations
in surface waters of the Atlantic to be 10-40 times higher than would be
expected for equilibrium values calculated on the basis of atmospheric
concentrations.
Swinnerton et al. (23) also found the Atlantic waters to
be supersaturated with CO, and recognized the ocean as a significant
natural source that may produce an amount equivalent to 5% of that liberated
by man.
In further studies (29), a bacteria-free culture of the ultra-
diatom Chaetoceros galvestonensis produced over 5 times as much CO as the
illuminated sterile controls although CO production in sea water could
also be mediated by a photochemical reaction involving only dissolved
organic carbon under sterile conditions.
Some CO production was also
observed in the dark, however.
Production of CO by other marine species
such as brown algae (3,16) and the vertically migrating siphonophore,
Nanomia bijuga (17), has also been noted. Formation of CO by cucumber
seedlings growing in the dark under 5% 02-95% A atmosphere was noticed by
Siegel et al. (21).
Euphorbia clandestina produced 200 mg of CO during
a 3-month test period within a 16-liter experimental atmosphere containing
initially 0.09% O2, 0.24% CO2, 1.4% argon, and N2 to give P = 0.1 atm.
CO was also produced at reduced O2 levels by germinating seeds of rye,
pea, cucumber, turnip, and lettuce, but not by seeds of corn, bean, and
tomato.
Catabolism of haem-like compounds is known to result in CO production
within living or autolyzing systems (4).
Likewise, Wilks (28) showed
4
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that macerated tissues of several green plants, most notably alfalfa
leaves, evolved CO.
Westlake et al. (27) found that the degradation of
flavonoids such as rutin by certain fungi, including Aspergillus spp.
and Penicillium spp., resulted in CO formation.
Hence the process of
death and decay in Nature can be suspected of being a prime natural
source of CO.
The residence time of CO in the atmosphere has been variously
estimated.
(6,15,26).
The most recent calculations range from 0.1 to 0.3 year
This relatively short residence time is circumstantial evi-
dence that one or more sinks for CO exist.
Jaffe (9) has suggested
several possible sinks, including various elements of the biosphere and
atmospheric reactions.
Seiler and Junge (20), noting the rapid decrease
of CO above the tropopause, considered the stratosphere as a major sink
for CO due to its oxidation there by OH, H202 and H02 radicals. A
steady-state model of the lower atmosphere constructed by Levy (15) pre-
dicted concentrations of hydroxyl and hydroperoxyl radicals sufficient
to limit CO residence time in the atmosphere to 0.2 years.
Laboratory
experiments by Dimitriades and Whisman (6) simulated lower atmospheric
conditions in a 50-liter reaction flask, under which CO was oxidized to
CO2 at an approximate rate of 0.05% per hour, equivalent to a natural
residence time of approximately 0.3 years.
Conversely, evidence also
exists that the atmosphere is a natural source of CO as well as a sink.
Swinnerton et al. (24) have found that raindrops may show up a 200-fold
supersaturation with CO in respect to attendant atmosphere, and postulate
that the source of CO in this instance is in rain-forming clouds.
They
suggest, as a plausible CO-formation mechanism, the photo-oxidation of
dissolved organic matter in the rain water or the dissociation of CO2
by electric discharges in storm clouds.
That certain elements of the biosphere are involved in turnover of
CO has been known for some years.
Anaerobic methane bacteria are known
to oxidize CO to CO2 in the absence of H2' or to reduce CO directly to
methane in the presence of H2
(12).
Cell-free extracts of Desulfovibrio
desulfuricans also oxidize CO to CO2 in the presence of sulfite (30).
In the 1930s, Jones and Scott (10) reported that certain bacteria present
5
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in sealed coal mines were capable of removing CO from the mine atmosphere.
Kistner (11) found evidence that the oxidation of CO by the bacterium
Hydrogenomonas carboxydovorans was mediated via an adaptive enzyme system,
and that the ability to transform CO could be lost following a 24-hour
period of culture on organic media lacking a CO atmosphere.
In regard to higher plants, Krall and Tolbert (13) found that cut
barley leaves took up CO at a low rate, but that the mechanism was
definitely light-dependent and resulted in production of photosynthetic
cycle intermediates and serine. Daly (5) observed an increase in the
respiration of wild plum leaf tissue subjected to CO atmospheres in the
dark.
Hill (7) was unable to demonstrate CO uptake by alfalfa.
The above literature, although indicative that carbon monoxide is
undoubtedly involved in various biological mechanisms and atmospheric
reactions that may influence its concentration and residence time in the
atmosphere, does not make clear the role of the biosphere in reducing
atmospheric CO.
Quantitative data are needed before the biosphere can be
considered as a natural sink for carbon monoxide.
This report presents
data relating to the action of the soil and soil microorganisms in removing
carbon monoxide from experimental atmospheres.
6
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III
SUMMARY AND CONCLUSIONS
This report describes studies conducted to determine if soils and
vegetation could serve as a sink for atmospheric carbon monoxide.
This
was accomplished by exposing various soils and plant samples to experi-
mental atmospheres containing carbon monoxide.
The results show:
1.
Higher plants tested had no detectable capacity for decreasing
carbon monoxide levels in the atmosphere surrounding them.
2.
Soils from a wide range of ecotypes depleted carbon monoxide
from atmospheres above them at rates averaging 8.44 mg/hr/m2 of
soil surface.
This rate indicates that soils could be a major
sink for atmospheric carbon monoxide.
3.
The depletion of carbon monoxide by soils was sensitive to
temperature, with a maximum depletion rate at 30°C and a Ql0 of
3-6. Soils sterilized by steam, antibiotics (mixture of
cycloheximide, streptomycin, and erythromycin) or salt lost the
capacity.
However, steam-sterilized soil reinoculated with a
small amount of nonsterile soil slowly regained the capacity.
Anaerobic conditions totally inhibited the process and there
was a slight specificity for a depletion of the lighter isotopes
of carbon monoxide.
All these facts lead to the conclusion that
the process was biological in nature.
4.
Constant and prolonged exposure of soil to carbon monoxide
reduced the soil's microflora population and also reduced the
soil's capacity to deplete carbon monoxide from the atmosphere.
5.
Among the bacteria and fungi isolated from soils, 14 fungi
(4 strains of Penicillium digitatum, ~. restrictum, 2 strains
of Aspergillus fumigatus, A. niger, ~. fisheri, ~. cervinus,
2 strains of Haplosporangium parvum, Mucor hiemalis, Mortierella
7
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vesiculata) were found to possess the capacity in pure culture
to deplete carbon monoxide from atmospheres above them.
6.
Preliminary experiments with C14-labeled carbon monoxide
indicated that soils oxidize carbon monoxide to carbon dioxide.
8
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IV
METHODS AND MATERIALS
Test Systems
Plastic Atmospheric Chambers
Plastic atmospheric chambers (PACs) containing soil and experimental
atmospheres constituted the major test system.
Each chamber had a volume
of 11 liters when closed and sealed.
Ports in the top and ends of the
PACs provided for the introduction of the test atmosphere and its circu-
lation and sampling during the tests.
Circulation of the test atmosphere
was accomplished by a peristaltic pump.
The PACs were tested for leaks
prior to use.
When necessary, the PACs were sterilized by submerging them in 10%
hypochlorite solution for 10 minutes.
They were then air-dried on the
"clean" benches.
Two liters of air-dried soil, an amount found to give
near optimum uptake of CO (Fig. 1), was placed into the PAC and brought
to 10-20% moisture with sterile deionized water. Test soil was incubated
in the PAC for 2 weeks at room temperature prior to testing.
The PACs
were also used to aseptically grow seedlings of higher plants for testing,
Prior to testing, the lids of the PAC were sealed and the PAC was
connected to the peristaltic pump.
The test atmosphere was then intro-
duced into the PAC by purging with 100 ppm CO in balance air at 2 cfm
for 5-10 minutes.
The system was then closed and a l-ml gas sample was
immediately withdrawn via a gas-tight syringe and analyzed for CO con-
tent, providing the "zero time" reading for the test.
Additional samples
were withdrawn periodically to determine the rate at which CO was being
depleted from the test atmosphere.
In the field, PACs were positioned upside down over the soil and
then pressed into the soil to a depth of 2.5 inches (a depth that
achieved approximately the same soil:atmosphere ratio as that in the PACs
in the lab).
Soil was then pressed down against the outside edge of the
9
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140
40
SOl L!PAC
. 2.9 kg
o 1.6 kg
. 0.8 kg
o 0.4 kg
.. 0.2 kg
120
100
E
c.
c. 80
......
o
o
U
...J
<{
::J
o
U) 60
w
a:
20
o
0 4 8 12 16 20 24 28 32 36
TIME - hour
FIGURE 1 INFLUENCE OF SOl L VOLUME IN PAC ON CO UPTAKE
-------
PAC.
The procedure for gassing and sampling was the same as for PACs
in the lab except that no peristaltic pump was attached in the field
experiment.
Flasks
For studies requiring numerous replicates or exact temperature
regulation, small 2S0- and SOO-ml filter flasks were used to contain
the test material.
The flasks were stoppered with rubber stoppers
fitted for gassing and sampling.
flasks.
The atmosphere was not circulated in
Microorganisms isolated from soils were tested in 2S0-ml filter
flasks for their CO uptake capacity in pure culture.
The microorganisms
were grown on 10 g of vermiculite moistened with potato dextrose broth
(20 ml for bacteria, 30 ml for fungi).
The inoculated flasks were
incubated 2 weeks prior to testing to allow sufficient growth to occur.
The flasks were then flushed with 100 ppm CO in balance air and sealed;
a l-ml initial sample was taken for analysis.
After 4 hours, a final
sample was taken and analyzed.
During the test period, the flasks were
maintained in an incubator water bath at 2SoC.
Clean Benches
Two "clean" benches were built to provide a relatively sterile
environment for a number of the experiments.
The benches were enclosed
on three sides and the top.
A vertical laminar flow of purified air at
100 cfm was maintained across the top of the benches. The air was
purified by passing it through an absolute filter (99.97% efficient for
0.3-~ particles). Lighting was provided by twelve 40-w cool-white
fluorescent tubes mounted 30 inches above the working surface.
A l2-hour
diurnal light cycle was maintained.
The inside walls of the clean bench
were periodically surface-sterilized using a 10% hypochlorite solution.
The benches were maintained in a separate air-conditioned room to
minimize contamination and drafts and to help regulate the temperature.
Nutrient agar plates left open on the benches for 30 minutes picked up
no contamination.
11
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Gas Analysis Apparatus
The analytical technique for the measurement of CO involved its
catalytic reduction to methane followed by flame-ionization detection
of the methane, as used and described by E. Levy (14).
Test Materials
Soils
-
The potting soil used in the majority of these studies was a mixture
of sandy loam (95%) and Canadian sphagnum peat moss (5%). Natural soils
were collected at selected locations in California, Florida, and Hawaii.
The gross duff surface cover was removed from the soil surface prior to
collection.
These soils were air-dried at 80°F, stored in sealed con-
tainers, and held for testing.
For tests, soil aliquots were adjusted
to the required moisture level and incubated for 2 weeks at room tempera-
ture prior to treatment and testing.
Higher Plants
The plant species tested were grown from seed obtained from com-
mercial sources in the case of trees, crops and ornamentals, from the
Rancho Santa Ana Botanical Gardens, Pomona, California, for the desert
plants, and from field collections for the common weeds.
To attain
aseptic plants, the seeds were surface-sterilized in a 10% hypochlorite
solution for 6 minutes, rinsed with sterile distilled water four times,
air-dried on the "clean" bench, and planted in steam-sterilized potting
soil in the PACs.
From 100 to 500 seeds, depending on the species, were
planted in each PAC to provide a dense stand of seedlings.
The seedlings
were raised in the PACs on the "clean" benches with a 12-hour light cycle
Microorganisms
All of the microorganisms tested in this study were isolated from
the soils collected in California. Two weeks prior to isolation, soil
samples were brought to 10% moisture with sterile deionized water and
incubated at room temperature.
Fifty grams of this incubated soil was
then blended with 450 ml of 1/4-strength sterile Ringer's solution.
This
soil solution was allowed to settle for 30 minutes; l-ml aliquots were
12
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then withdrawn in triplicate for serial dilution in sterile soil extract
to 10-4, 10-5, 10-6, and 10-7 dilution liters.
A I-ml aliquot of each
of the dilutions was plated on 10 different nutrient agars (Czopek's Dox +
Actidione, Littman-Oxgall, Topping's Medium, Taylor's Soil Extract
Medium, Wort, Heart Infusion, Lockhead's Soil Extract Medium, W L Differen-
tial Medium, Basal-Amino Acid-Vitamin Tryptophan Medium (BAVT), and Algae
Simple Salts Medium.
Each dilution was replicated on each medium three
times.
After 3-5 days of incubation at 29°C, the various forms of growth
present on the plates were segregated on the basis of colony characteristics
and isolated on the same medium.
For comparisons, the individual isolates
were all transferred to a common medium (BAVT agar) and the organisms were
grouped according to gross morphological characteristics.
Soil Treatments
Steam Sterilization
Two liters of air-dried soil was placed into 8 x 16 x 2-inch Pyrex
dishes enclosed in paper bags, and then autoclaved for at least 30 minutes
at 121°C and 15 psi. After being cooled, the soil was dumped into a
sterilized PAC, moistened to 10% moisture with sterile deionized water,
and tested for its CO uptake capacity-
Antibiotic and Saline Treatments
Potting
treated with
soil samples (200 g) were placed in 500-ml filter flasks and
50 ml each of erythromycin (500 ppm), cycloheximide (500 ppm),
(500 ppm) or 10% saline (NaCl) solution. The flasks were
streptomycin
allowed to incubate 4 days prior to testing.
In further experiments, a 2-liter (air-dried) sample of potting
soil was thoroughly mixed by agitation inside a plastic bag with 150 ml
of a solution containing 1000 ppm cycloheximide, 510 ppm streptomycin and
870 ppm erythromycin.
The soil was then placed into a PAC, allowed to
air-dry on the "clean" bench, again drenched with 150 ml of the antibiotic
solution, allowed to dry again, drenched with 150 ml, and tested for its
CO uptake capacity.
13
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Anaerobic Treatment
Potting soil (100 g) was moistened to 10% and incubated for one week
in a 250-ml filter flask. The soil was then incubated for another week
under an N2 atmosphere, which was renewed daily to ensure anaerobic
conditions.
Ability of the soil to remove CO from the atmosphere was
then determined using a test atmosphere composed of 70 ppm CO in N2 at
250C.
Inoculation of Sterile Soil
Two liters of steam-sterilized potting soil was placed in a sterile
PAC on the "clean" bench, adjusted to 10% moisture content with sterile
deionized water; and inoculated with 1 g of nonsterile potting soil.
The soil in this PAC was tested daily for its CO uptake capacity for a
period of 35 days.
Temperature Treatment
Samples (100 g each) of potting, soil were placed into 250 vacuum
filter flasks, with 6 replicates per treatment.
The soils were brought
to 10% moisture and allowed to incubate at room temperature for one
week.
The flasks were then placed in a water bath in a reach-in incubator.
The test temperature was maintained by both the water bath and incubator
at + lOCo
The flasks were allowed to equilibrate for 30 minutes.
They
were then gassed, and one flask was sampled in rotation every 10 minutes
or longer, depending on the rate of CO uptake.
In several of the tests
at different temperatures, flasks containing steam-sterilized soil pre-
pared as above were added as controls.
Light-Dark Treatment
Potting soil (200 g, air-dried) was placed into six 500-ml filter
flasks, brought to 10% moisture, and incubated for one week. Three of
the flasks were then wrapped in tin foil to darken them.
The flasks
were placed into a water bath in a reach-in incubator (both holding a
temperature of 25 ~ lOC).
The lights in the incubator produced approxi-
mately 2700 foot-candles of light.
The flasks were gassed with 100 ppm
CO in balanced air and tested for their uptake capacity.
14
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Isotope Fractionation Technique
Yosemite Valley soil (2 liters, air-dried) was placed in a PAC,
brought to 15% moisture, and incubated 2 weeks at room temperature.
The
PAC was equipped with extra ports to provide for transfer of atmosphere
samples into vacuum bottles and for balloons, which inflated within the
PAC as large samples were withdrawn by the vacuum bottles. Samples
(0.5 to 1 liter) of the atmosphere in the PAC were taken at 1000 ppm
CO (initial concentration), 500 ppm CO (50% concentration), 200 ppm
(20% concentration), 100 ppm CO (initial concentration), and 50 ppm CO
(50% concentration). The sample bottles were then sent to Mr. Charles
Stevens at Argonne Laboratories for mass spectral analysis of the CO.
Preliminary Isotope Studies
Yosemite Valley soil was ground in a ball-mill to ensure a uniform
texture for sampling. The soil was brought to 15% moisture and incubated
for two weeks at room temperature. Samples (30 g) of this soil were
placed into 125-ml filter flasks.
The flasks were wrapped with tin foil
to darken them and placed in a water bath at 25°C. Carbon monoxide-14C
(sp. act. 4.5 mCi/mM) was injected into the flasks to bring the starting
concentration to approximately 100 ppm CO.
A sterile flask with no
soil was used as a control. After varying periods of exposure to
isotopically labeled CO (30, 60, 100 and 300 minutes), when the concen-
tration of CO as measured by GLC was 66 ppm, 35 ppm, 0 ppm, and 0 ppm,
respectively, the atmosphere of the flask was analyzed.
The control
flask without soil was used for the zero time-lOO ppm CO reading.
For
analysis, the entire atmosphere of the flask was expelled using air as
a carrier. The expelled gas was passed through a bubbler containing 8 ml
of 1 M hyamin hydroxide in methanol to collect the CO2, The gases were
then passed through a column of hopcalite to convert the remaining CO to
CO2 and through another bubbler with 8 ml of hyamine hydroxide to collect
the CO2 from the CO.
Samples of the hyamine hydroxide (0.8 ml) and soil samples from the
flasks (0.3 g) were placed into scintillation vials with 15 ml of the
counting cocktail (Aqual-Sol, New England Nuclear).
The radioactivity
15
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of each vial was determined on a Beckman LS 100 liquid scintillation
counter.
Prolonged Exposure to CO
Soil from Lake Arrowhead was brought to 15% moisture and incubated
for 2 weeks at room temperature.
Then 50-g samples were placed into
eight 250-ml filter flasks.
Two of the flasks were sacrificed immediately,
and the microorganisms in that soil were isolated according to the
previously described technique. The remaining flasks were placed in a
water bath at 25°C, and premoistened sterile air (passed through a Milli-
pore filter) was continuously flushed through three of the flasks at
~ 0.5 cfm.
The other three flasks had premoistened sterile air plus
50 ppm CO flushed through them at ~.5 cfm.
The CO uptake capacity of
the flasks was determined at 0, 5, 12, 34 and 41 days of exposure.
The
flasks continuously gassed with air were flushed with 50 ppm CO in air
for 8 minutes at 6 cfm, and were then sealed and monitored.
The flasks
gassed with CO in air were sealed anp monitored.
Immediately on cessa-
tion of monitoring, the flasks were returned to the continuous gassing
regime.
At the end of the prolonged exposure (41 days), samples of soil
from the CO-exposed flask and the air control flask were analyzed for
their microbial populations.
16
-------
v
RESULTS
Higher Plants
Previous experiments on the uptake of CO by higher plants (14) were
inconclusive because the uptake may have been entirely due to the non-
sterile soil used as a support medium,
In this experiment, steam-
sterilized soil was used to grow the surface-sterilized seed in a sterile
environment,
Due to limitations on space imposed by the sterilization
procedures, only a few species could be tested (Table I).
was made to test species of a wide variety of plant types,
An attempt
However, a
number of species (e.g., Phaseolus vulgaris) were not adaptable to the
sterilization procedures,
None of the plants tested showed the slightest
capacity for CO uptake during a standard test period of 3-4 hours, or
even for a 24-hour test period.
Potting Soil and Natural Soil
As a result of previous experimentation (14), it was suspected that
soil might serve as a sink for atmospheric CO,
To test this hypothesis,
potting soil was exposed to 100 ppm CO at 2SoC in the PACs,
This ex-
periment was repeated numerous times, with virtually identical results.
Figure 2 shows the results of one typical experiment.
As can be seen,
the depletion rate of CO in the PAC is nearly linear for the test period
of 3 hours,
The rate of uptake calculated from this figure is 5.54 mg
CO/hr/m2,
Studies with concentrations of CO up to 1,000 ppm were also
characterized by a linear rate of approximately 6 mg CO/hr/m2.
Control
PACs containing no soil showed no detectable decrease in concentrations
during a 4-hour period.
The relationship of the laboratory soil-PAC experiments to soil in
its natural state was studied by a field experiment.
The uptake of CO
by soil in the PACs in the lab was very similar to the uptake by soil
in situ in the field covered by a PAC (Figure 3).
The similarity of
--
17
-------
Table I
HIGHER PLANTS TESTED IN ASEPTIC CULTURE
FOR CAPABILITY TO REMOVE CO FROM ATMOSPHERE
Classification
Species
Coniferous trees
Pinus radiata
Monterey Pine
Knobcone Pine
Pinus attenuata
Deciduous trees
Cassia phyllodinea
Cassia leptocarpa
Common weeds
Amaranthus albus
Pigweed
Curly dock
Rumex crispus
Sorghum halepense
Johnson grass
Crops and ornamentals
Zea mays
Hordeum vulgare
Field corn
Barley
Cotton
Gossypium hirsutum
Cucumis sativus
Cucumber
Kalanchoe blossfeldiana
Dwarf Tom Thumb
Desert plants
Salvia columbariae
Baeria chrysostoma
Coreopsis bigelovii
the rates indicates that the lab results could be used as an approxima-
tion of results on soils in the natural state.
The slightly lower rate
of uptake by the soil in situ could be due to a lower temperature in the
--
field.
Very similar results were obtained from soil contained in a
plastic bag and buried in situ for one month prior to testing.
--
The
p}astic bag was used to ~nsure a complete seal for the PAC over the soil.
To determine if the uptake of CO by soil was similar for different
types of soil, a number of soil samples collected at different sites in
California, Hawaii, and Florida were tested (Table II).
These soils
are listed in their order of decreasing activity.
Each soil was tested
at least twice and the tests were averaged to calculate uptake rates
18
-------
OJ
:1.
I 800
o
u
FIGURE 2
1600
1200
.
400
o
o
60
120
180
240
TIME - minutes
REDUCTION OF CO IN TEST ATMOSPHERE WITH TIME BY 2.8 kg
OF POTTING SOIL
19
-------
100
80
K 60
c.
o
U
....J
-------
Table II
RATE OF REMOVAL OF CO FROM TEST ATMOSPHERES AT 250C BY VARIOUS SOILS
Sand: b
a CO Uptake
Location of Soil Vegetation pH Sil t :Clay % Organic (mg/hr/m2)
Eureka-Arcata Coast redwoods 5.7 53:34:13 25.1 16.99
H. Cowell St. Pk. Oak 5.3 73:12:15 11.2 15.92
H. Cowell St. Pk. Coast redwoods 5.7 57:26:17 13.6 14.39
Lake Arrowheadc Ponderosa pine 6.2 65:24:11 17.4 13.89
Redding Grass-legume 5.1 53:32:15 21.0 11 . 94
pasture
Riversidec Grapefruitd 6.6 75:14:11 4.3 11. 48
Yosemite Valley Grass meadow 5.05 49:42:9 20.6 10.52
Kauai, Hawaii Forest 4.74 58:18:24 22.8 9.90
San Bernardino c None 7.2 55: 30:' 15 2.2
6.89
Freeway
Mojave Desert Chaparral 7.9 79:6:15 2.4 6.46
Woodland d '6.6 33:32:35 2.1
Oak stubble 6.23
Riverside (desert)c Chaparral 7.35 85:4:11 1.0 4.31
Yosemite Wall White fir 5.1 65:18:17 5.7 3.48
d
Corcoran Cotton (fallow) 7.1 57:22:21 2.8 3.48
d 53:26:21
Hanford Almond 6.95 3.5 2.82
d
Boynton Beach, Weeds (fallow) 6.0 86:0:14 1.4 2.65
Florida
Oahu, Hawaii 4.93 40:26:34 15.3 2.16
a.
All soils were collected in California unless otherwise noted.
Average rate at end of test period; 2-3 determinations.
b.
c.
Locations where high levels of air pollution occur due to combustion
of fossil fuels and photochemical smog.
Land under cultivation or with recent history of cultivation.
d.
21
-------
for each.
Generally, soils high in organic content and low in pH were
found to have the highest rates of CO uptake.
Two exceptions to this
trend were observed.
Soil from Riverside grapefruit orchard was rela-
tively low in organic content but ranked high in CO uptake capacity.
The soil from Oahu, which was low in pH and high in organic content,
ranked low in CO uptake capacity.
No correlation was observed between
the ranking of the soil and its prior history of exposure to high levels
of natural atmospheric CO.
Effects of Soil Treatments
The depletion of CO over soil could be due to physical processes
such as adsorption onto the surface of soil particles, or to biological
processes such as oxidation by soil microorganisms.
To determine which
of these processes was active in CO uptake, a series of experiments were
conducted.
The first group of these experiments attempted to eliminate
the biological capacity of soils so that any physical property that was
active could be measured.
Soil that was steam-sterilized by autoclaving showed no capacity for
CO uptake (Figure 4).
Because autoclaving is a rather drastic treatment
that could possibly affect the physical properties of soil as well as
sterilize it, other attempts were made to steri~ize soil using anti-
biotics and salt (Figures 5 and 6).
Treatment of soil individually with
erythromycin, cycloheximide or streptomycin had only partial effects on
the uptake of CO, generally reducing the uptake rate by 50% (Figure 5).
A 10% saline solution, however, was 100% effective in eliminating the CO
uptake capacity of soil (Figure 5). Part of the inactivity of antibiotics
could be due to a lack of total treatment of the soil particles because
of problems of wettability.
When soil was repeatedly drenched with a
combination of cycloheximide, streptomycin, and erythromycin, its CO
uptake capacity was completely eliminated (Figure 6). Further, it was
found that soil held under anaerobic conditions (nitrogen) also had no
capacity for CO uptake (Figure 5).
Steam-sterilized soil inoculated with a minute amount of nonsterile
soil gradually regained a capacity for CO uptake (Figure 7), presumably
22
-------
100
80
E
&: 60
t>:J
UJ
o
()
..J
«
::J
o
~ 40
a:
20
o
o
\
\
\
\
\
\
\.
\
\
\
\
\
\
\
\
\
.
.......
.......
.........
.......
.......
'...
60
120
. Autoclaved
. Non-autoclaved
180
240
300
360
420
TIME - minutes
FIGURE 4
CO UPTAKE BY STEAM-STERILIZED VERSUS NONSTERILE SOIL
-------
120
- ~------........
-------A.- - '"
-- --. -- ----6-
. Nontreated control
o Erythromycin, 500 ppm
. Cycloheximide, 500 ppm
o Streptomycin, 500 ppm
...
80
E
a. !':. !':.
a.
o
u 60
...J
«
~ :J
CI
~ ii5
w
a::
40
20
o
o
... Saline - 10 percent
!':. Anaerobic
60
120
180
240
300
360
TIME - minutes
FIGURE 5
EFFECTS OF ANTIBIOTIC, SALINE, AND ANAEROBIC TREATMENTS ON RATE
OF CO DEPLETION OVER POTTING SOIL
-------
FIGURE 6
160
. Treated with antibiotics
. Not treated
120
E
a.
a.
.
---_JL_-------------
.
o
u 80
...J
o
(IJ
w
a:
40
o
80
120
160
40
TIME - minutes
EFFECT OF SOIL SATURATION WITH AN ANTIBIOTIC SOLUTION
(1000 ppm Cycloheximide, 510 ppm Streptomycin, 870 ppm
Erythromycin) ON RATE OF CO DEPLETION
25
-------
N
E
~ 3
c>
E
I
I:\J
(j)
w
~
«
I-
a..
::> 2
o
u
5
4
.
o
o
.
.
.
.
.
.
.
.
.
10
20
DAYS
30
40
FIGURE 7
CO UPTAKE CAPACITY OF 2.8 kg OF AUTOClAVED POTTING SOil WITH
TIME FOllOWING INOCULATION WITH 1 g OF NONSTERllE SOil
-------
as the soil population of microorganisms was re-established.
One month
after inoculation, the uptake rate was as great as that of nonsterile
control soil.
These experiments suggested rather strongly that aerobic soil micro-
organisms were responsible for CO uptake.
Therefore, the next series of
experiments were conducted to further define the biological phenomenon.
The CO uptake rate of soil was found to be very sensitive to tem-
perature changes (Table III).
A maximum uptake rate was found at 30°C,
with almost no uptake at the extremes of 10 and 50°C.
The temperature
coefficient (Ql0) of this process ranged from 3 to 6 between the tem-
peratures of 15 and 30°C.
High Ql0S and optimum rates between 20 and
40°C are very characteristic of biological processes.
On the other hand,
physical processes would increase continuously as temperatures increased
and have a Ql0 in the range of 1-1.4.
Table III
RATE OF CO REMOVAL OVER 100 g
OF POTTING SOIL AT DIFFERENT TEMPERATURES
~~
Temperature CO Uptake Rate Test Period
(OC) (mg/hr/m2) (hr)
10 0.30 24
15 0.38 6
20 1.25 5
25 2.38 3
30 3.46 2
35 2.44 2.3
40 1.89 4
45 1.17 4.5
50 0.20 19
i~
Average rate at end of test period.
27
-------
The initial experiments with steam-sterilized soil (Figure 4) in-
dicated that treated soils showed a slight evolution of CO. This phe-
nomenon became more pronounced at higher temperatures (Table IV). At
50oC, the rate of CO evolution, 136 ~g CO/kg soil/hr, was nearly as
great as the uptake of CO would be at its maximum by that much soil.
This phenomenon could be observed even when the steam-sterilized soil
was stored in an open-air container prior to being tested at a higher
temperature.
Table IV
CO EVOLUTION BY AUTOCLAVED SOIL
Incubation
Temperature
(DC)
20
40
CO Evolution Rate ~~
(~g CO/kg sOil/hr)
Dark Light
3.3
50
36
136
46
~~
Based on the average of three
replicates.
Light had very little effect on the uptake or evolution of CO by
soil (Figure 8 and Table IV). The small differences between light and
dark were probably due to the 0.50C higher temperature in the flasks in
the light.
Mass spectral analysis of the isotopes of CO remaining at various
times during CO depletion by soil shows that there is some isotopic
fractionation (Figure 9). Both C12 and 016 containing CO molecules were
removed in preference to those containing C13 and 018.
This is a con-
sistent trend for biological processes that oxidize organic compounds.
However, this is not an absolute proof of biological activity for, in
general, the lighter isotopes are more reactive. The differences be-
tween samples designated I and II are due to the fact that these samples
were drawn from different gas tanks.
28
-------
100
. Light
. Dark
80
E
8: 60
o
U
..J
«
::>
o
en
w 40
II:
20
o
o
50
100
150
200
TIME - minutes
FIGURE 8
INFLUENCE OF LIGHT ON CO UPTAKE BY SOIL
29
-------
10
o
-10
~...J
:1E
oc
UJ
c.. -20
10
~o
00--
~o
<1
-30
-40
-50
-60
FIGURE 9
Ii 00.
-50
I50.
NOTES:
-40
o II-C02
o 200
II-C02
500
. II200
. II500
AIR C02.
(2)
o II-CO
2'000
1. PDB = 0
2. Oxygen converted to C02 with I205 for analysis.
I == Test run number
500 == concentration of CO at time of testing.
-30
.6.C'3/C'2 PER MIL'
-20
-10
ISOTOPIC FRACTIONATION OF CO DURING CO UPTAKE BY SOIL
(Provided by C. M. Stevens)
30
o
-------
Soil Microorganisms
Since the uptake of CO by soil was shown in the preceding experi-
ments to be biological, a search for the specific microorganisms involved
was conducted. Isolates were made from the Lake Arrowhead soil (40
bacteria and 35 fungi), the Yosemite Valley soil (50 bacteria and 24
fungi), and the Riverside desert soil (48 bacteria and 24 fungi). The
fungi active in CO uptake are listed in Table V.
The uptake rates
listed for these fungi were calculated from the rate over the first
Table V
SOIL FUNGI ACTIVE IN CO UPTAKE
CO Uptake Rate2
Species Strain No; (f.Lg CO/hr/m2)
Aspergillus fumi ga tu s 1 1.824
Aspergillus fumigatus 2 1.000
Aspergillus niger 1.838
Aspergillus fischeri 1.054
Aspergillus cervinus 1.000
Haplosporangium parv1im 1 1.027
Haplosporangium parvum 2 1.684
Mortierella vesiculata 0.568
Mucor hiemalis 2.351
Penicillium digitatum 1 2.292
Penicillium digitatum 2 1.714
Penicillium digitatum 3 2.373
Penicillium digitatum 4 1.768
Penicillium restrictum 0.959
1
Morphologically different types of the same species,
2
Calculated from the first test of the second sub-
culture of the organism.
31
-------
4-hour exposure period. The figures should not be taken as absolute,
however, for it was very difficult to standardize the experiment. The
organisms all grew at different rates and it was found during retesting
that in pure culture, all of these fungi--over a period of 2-3 months
and during 3-4 subcultures--Iost all capacity for CO uptake.
Although
no bacteria that could take up CO were found, this does not preclude the
possibility that some soil bacteria may be active.
The isolation pro-
cedure used isolated only a fraction of the soil bacteria, and the test-
ing conditions were not optimum for the growth of a number of bacteria.
Influence of CO on Soil Microbial Population
Soil samples were continuously exposed to atmospheres with and
without 50 ppm CO for an extended period (41 days), and the influence on
the soil population of microorganisms was studied.
The prolonged ex-
posure to CO greatly reduced the capacity of the soil for CO uptake.
After 41 days of exposure (Table VI), the soil had only one-fourth the
uptake capacity of unexposed soil.
The prolonged exposure had little
influence on the soil fungal population.
However, both the number of
species as well as the total number of bacteria were apparently reduced
by the exposure (Table VII).
Table VI
EFFECT OF PROLONGED EXPOSURE
TO CO ON CO UPTAKE BY SOIL
Days of Exposure
Rate of CO depletionl (mg/hr/m2)
Exposed to CO-free air Exposed to 50 ppm CO in air
o
5
6.65 7.16
6.57 4.54
5.35 4.11
7.13 2.37
6.45 1.46
12
35
41
1
Rates calculated on an average of two replicates.
32
-------
Table VII
INFLUENCE OF PROLONGED EXPOSURE
TO CO ON SOIL MICROFLORA
Treatment
Bacteria
Number
of Varieties
Isolated
Fungi
Prolonged exposure
to 50 ppm CO
36
Total ~.
No./g soil
2 X 105
Number
of Varieties
Isolated
79
Total ~.
No./g soil
3.6 X 105
Control kept under
CO-free air
53
3.2 X 107
72
2.8 X 105
~.
Average of two replicates.
Tracing CO Uptake with 14C
Studies on the pathway of CO in the uptake process by soil, using
14C-Iabeled carbon monoxide (Table VIII), indicate that CO is oxidized
to CO2 and not bound in the soil. The results were highly variable,
probably due to the low recovery rates and the low efficiency and non-
specificity of hyamine hydroxide for absorbing CO2,
The results do
definitely indicate that as the CO decreases, as measured by GLC, radio-
activity was still picked up from the gaseous phase by the hyamine
hydroxide and no radioactivity was detected in the soil.
Only after
most of the CO was oxidized, did the label become fixed in the soil.
This delayed uptake could be due to CO2 fixation by the soil micro-
organisms.
33
-------
Table VII
INFLUENCE OF PROLONpED EXPOSURE
TO CO ON SOIL MICROFLORA
Treatment
Bacteria
Number
of Varieties
Isolated
Fungi
Prolonged exposure
to 50 ppm CO
36
Total ~~
No./g soil
2 X 105
Number
of Varieties
Isolated
79
Total ~~
No./g soil
3.6 X 105
Control kept under
CO-free air
53
3.2 X 107
72
2.8 X 105
~~
Average of two replicates.
Tracing CO Uptake with 14C
Studies on the pathway of CO in the uptake process by soil, using
14C-Iabeled carbon monoxide (Table VIII), indicate that CO is oxidized
to CO2 and not bound in the soil.
The results were highly variable,
probably due to the low recovery rates and the low efficiency and non-
specificity of hyamine hydroxide for absorbing CO2,
The results do
definitely indicate that as the CO decreases, as measured by GLC, radio-
activity was still picked up from the gaseous phase by the hyamine
hydroxide and no radioactivity was detected in the soil.
Only after
most of the CO was oxidized, did the label become fixed in the soil.
This delayed uptake could be due to CO2 fixation by the soil micro-
organisms.
33
-------
Table VIII
UPTAKE OF 14C-CARBON MONOXIDE BY SOIL
Radioactivity (cpm) 1
Time of Exposure Residual CO Percent
Sample Replicate (min) (ppm) CO2 CO Soil Total Recovery
Control A 240 81 19,564 20,851 40,415 9.35
B 240 81 18,580 19,806 38,386 8.88
Test A 30 66 129,301 18,844 0 149,145 31.58
B 30 66 131,285 19,312 0 150,597 31. 89
A 60 35 33,152 27,004 105 61,206 14.31
B 60 35 30,243 25,688 48 58,411 13.19
UJ
~
A 100 0 270,696 31,895 225 302,816 68.66
B 100 0 275,983 30,512 300 306,795 69.56
A 300 0 28,569 17,030 270 45,869 9.81
B 300 0 30,777 19,749 210 50,736 10.85
1
Counting efficiency 90-93% figures corrected for dilution and background (50 cpm).
-------
VI
DISCUSSION
The rate of disappearance of CO from the atmosphere over soils of
different ecotypes ranged from 2.16 to 16.99 mg/hr/m2. The average rate
of CO uptake from these soils was 8.44 mg/hr/m2, which is equivalent
to 191.1 metric tons/year/square mile.
If it is assumed that this average
rate is representative of the average capacity of temperate zone soils,
then the total capacity of the soil surface of the conterminal United
States (2,977,128 square miles) is estimated to be 569 million metric
tons of CO per year.
I
man-made CO released annually in the United States and is 3 times that
released worldwide. This rapid uptake rate is considerably greater than
values reported for photochemical atmospheric reactions (6). Soil could
This value is 5.5 times the estimated amount of
be the large sink for CO that is implied by the relatively short resi-
dence time (less than one year) estimated in recent studies of the
problem (19,26).
The above estimate of soil capacity was based on a limited number
of laboratory observations and a large number of assumptions, and is
thus only a crude approximation.
A more accurate measurement could and
should be obtained by an extensive field survey backed by a laboratory
study of the relative significance of the field variables.
Recent
studies (24,29) indicate that there are a number of significant natural
sources
of CO.
Those studies, together with the findings reported here,
indicate that a CO turnover cycle surely existed prior to man's recent
contributions.
More refined knowledge of this cycle would allow for a
more precise definition of the fate of the 200 million metric tons of
CO produced annually by man.
This information would also provide a
basis for estimating what influence the ever-larger amounts of CO pro-
duced by man have on the natural cycle.
A more detailed study of soil
as a sink is also justified by a recent study by Abeles et al. (1),
which indicates that soil may be a sink for other atmospheric pollutants.
35
-------
They found that soil took up ethylene, sulfur dioxide, and nitrogen
dioxide at rates roughly equivalent to the rate reported here for CO.
There is now sufficient evidence to state that CO uptake by soil
is a biological process and that a number of soil fungi contribute
significantly to the process.
Although no bacteria were found to be
significantly active in CO uptake, previous studies (10-12,30) have
demonstrated that certain soil bacteria do have this capacity.
Failure
to find any in this case may be due to inadequacies in the isolation
and/or testing techniques, or the CO uptake rates of the active bacteria
may simply be too low to be of any significance.
Although the isotope tracer studies involving CO were rudimentary,
it would appear that the fungi may not incorporate CO into protein but,
instead, may oxidize it to carbon dioxide. The oxidation of CO by micro-
organisms has been previously described (12,30). Since CO is a potent
metabolic inhibitor, such an oxidative capacity could serve as a defense
mechanism.
It may even be that the ,CO never enters the cells of these
organisms but is oxidized at the cell surface by membrane-bound enzymes.
It would seem that agricultural lands, due to cultural practices,
would have a texture and fertility that would provide for optimum
microbial growth and, hence, maximum rates of CO uptake.
However, the
few agricultural soils that were tested generally ranked low in relative
CO uptake capacity.
The balance of microorganisms could be upset by
agricultural practices, or the use of fungicides and other agricultural
chemicals could suppress the growth of the active microorganisms and
thus account for lower uptake activity.
The lack of CO uptake by any of the higher plants tested agrees
with the findings of Hill (7) for a field of alfalfa. Although these
negative results do not rule out the possibility that some species of
plants could take up CO, at present it appears unlikely that plants
contribute significantly as sinks for CO.
However, it does appear
likely that plants could influence the properties of soil by altering
the soil microflora, by changing the porosity of soil, and/or by
influencing the gas-diffusion patterns above the soil.
36
-------
The practical effect of the uptake of CO by soil on lowering local
atmospheric CO levels in areas of high air pollution may be limited due
to the high atmosphere:soil surface ratio.
It would appear more likely
that the significance of soil as a CO sink is greater on a regional or
global basis than on a local basis.
No correlation was found between a soil's CO uptake rate and the
general level of air pollutants in the respective areas in which the soil
was collected.
Also it was found that prolonged exposures to CO reduced
the soil's capacity for uptake.
Possibly, soils in areas of high and
prolonged levels of atmospheric pollution (e.g., Los Angeles Basin) are
being poisoned and are gradually losing their capacity for uptake.
On
the other hand, perhaps the prolonged exposures may be providing a selec-
tive pressure for the evolution of a better CO-oxidizing organism.
37
-------
LITERATURE CITED
1.
Abeles, F.B., L. E. Craker, L. E. Forrence and G. R. Leather.
Fate of air pollutants: Removal of ethylene, sulfur dioxide,
and nitrogen dioxide by soil. Science 173, 914-916 (1971).
2.
Cavanaugh, L. A., C. F. Schadt and E. Robinson.
hydrocarbon and carbon monoxide measurements at
Alaska. Environ. Sci. Tech. ~, 251-257 (1969).
Atmospheric
Point Barrow,
3.
Chapman, D. J., and R. D. Tucker. Occurrence
of carbon monoxide in some brown algae. Can.
1438-1442 (1966).
and production
J. Botany 44,
4.
Coburn, R. F. (Ed.). Biological effects of carbon monoxide.
Ann. N.Y. Acad. Sci. 174, 1-430 (1970).
5.
Daly, J. M. Stimulation of respiration by carbon monoxide.
Arch. Biochem. Biophys. 51, 24-29 (1954).
6.
Dimitriades, B., and M. Whisman. Carbon monoxide in lower at-
mosphere reactions. Environ. Sci. Tech. ~, 219-222 (1971).
7.
Hill, A. C. Vegetation: A sink for atmospheric pollutants.
Proc. APCA 64th Annual Meeting, Atlantic City, June 1971.
8.
Inman, R. E., R. B. Ingersoll and Elaine A. Levy. Soil: A
natural sink for carbon monoxide. Science 172, 1229-1231 (1971).
9.
Jaffe, L. S. Ambient carbon monoxide and its fate in the at-
mosphere. J. Air Pollution Control Assoc. 18, 534-540 (1968).
10.
G. S. Scott. Carbon monoxide in underground
role of bacteria in its elimination. Ind. Eng.
(1939).
Jones, C. W., and
atmospheres. The
Chern. 31, 775-778
11.
Kistner, A. Conditions determining the oxidation of carbon
monoxide and of hydrogen by Hydrogenomonas carboxydovorans.
Proc. Koninkl. Ned. Akad. Wetenschap. 57, 186-195 (1954).
12.
Kluyver, A. J., and Ch. G.
of carbon monoxide by pure
biochem. 14, 57-70 (1947).
T. P. Schueller. On the fermentation
cultures of methane bacteria. Arch.
38
-------
13.
Krall, A. R., and N. E. Tolbert. A comparison of the light de-
pendent metabolism of carbon monoxide by barley leaves with that
of formaldehyde, formate, and carbon dioxide. Plant Physiol. 32
321-325 (1957). -'
14.
Levy, Elaine A. The biosphere as a possible sink for carbon
monoxide emitted to the atmosphere. Final Report, Project PSU-7888,
Stanford Research Institute, Menlo Park, California, 1970.
15.
Levy II, H. Normal atmosphere: Large radical and formaldehyde
concentrations predicted. Science 173, 141-143 (1971).
16.
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