TECHNICAL REPORT DATA

(Please read Instructions on the reverse before completing)

REPORT NO. 2.
EPA-600/3-78-054

3, RECIPIENT'S ACCESSIONNO,

TITLE AND SUBTITLE

FACTORS INFLUENCING THE VOLATILIZATION OF MERCURY
FROM SOIL

rs

5. REPORT DATE
May 1978

6. PERFORMING ORGANIZATION CODE

x

, AUTHOR(S)

Robert D. Rogers and James C. McFarlane

8. PERFORMING ORGANIZATION REPORT NO,

9

PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development

U.S. Environmental Protection Agency

Las Vegas, NV 89114

10. PROGRAM ELEMENT NO.
1AAG02

77, CONTRACT/GRANT NO.

12, SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV 89114

13. TYPE OF REPORT AND PERIOD COVERED
‘ Final

14, SPONSORING AGENCY CODE

EPA/600/07

15. SUPPLEMENTARY NOTES

16. ABSTRACT

nitrate ceased within 1 week after application.
of the applied mercury was lost from a silty clay-lo
from a loamy sand soil.

by microorganisms.

Mercury volatilization from soils amended to 1 ppm mercury with mercuric
During the first week, 20%
am soil and 43% was lost
Volatilization of Hg from the loamy sand soil re-
sulted in a concurrent decrease in ammonium nitrate-extractable mercury.
Other work with sterile soil indicates that the volatilization was mediated

Inorganic chemistry
volatilization

7. KEY WORDS AND DOCUMENT ANALYSIS
a. OESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS |c. COSAT! Field/Group
Mercury o7B
Radioactivity 08M
Soil chemistry 143
18B

18. DISTRIBUTION STATEMENT

19, SECURITY CLASS (This Report)

UNCLASSIFIED 20
RELEASE TO THE PUBLIC 20. SECURITY CLASS (This page) 22. PRICE
UNCLASSIFIED

21. NO. OF PAGES

EPA Form 2220-1 (9-73)


Clayey soil amended to 10 ppm Hg as Hg(NO3)2 volatilized 31% of this
Hg during the test period (Figure 6). The bulk of this loss was during the
first 3 days with an initial loss rate of 1,500 ng/h. During the first
24 hours of incubation, a small amount (4.5% of the total) of the Hg was
found to be 1N NH,NO3-extractable.

Steam-sterilized clay lost only 2% of the applied 20 ug Hg (Figure 7).
No 1N NH,NO3- extractable Hg was found.

DISCUSSION

The data from this study show that Hg was lost from soils amended with
Hg(NO3)2. In every case, except one (Figure 3), almost 100% of the volatili-
zation of applied Hg occurred within the first week. There was a considerable
difference between the sand and clay. In general, the volatilization from
clay was faster to start but less of the Hg was lost overall. Increasing
the Hg concentration from 1 ppm to 10 ppm increased the loss of Hg from the
sand by a factor of 11 and the clay by 15 times (Figures 3 and 6).

F 1500
: F 1400
© Volatile Hg
- 1300
NHsNOs- Soluble
. = 1200
° ‘ (IM Non-Soluble

rm 1100

1000

Volatile Hg (ng/h)

Soll Hg (ug)

. T T q T T iy T q im q q T v qT
10 20 30 40 50 60 70 80 90 100 110 120 130 140

Time (h)

Figure 6. Rate of Hg volatilization and Hg remaining in clayey soil
amended to 10 ppm Hg. The soil Hg (ug) axis is nonzero.


FOREWORD

Protection of the environment requires effective regulatory actions
which are based on sound technical and scientific information. This informa-
tion must include the quantitative description and linking of pollutant
sources, transport mechanisms, interactions, and resulting effects on man
and his environment. Because of the complexities involved, assessment
of specific pollutants in the environment requires a total systems approach
which transcends the media of air, water, and land. The Environmental Moni-
toring and Support Laboratory-Las Vegas contributes to the formation and
enhancement of a sound monitoring data base for exposure assessment through
programs designed to:

* develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment

* demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of
the Agency's operating programs

A study was conducted to determine some of the factors responsible for
the volatilization of mercury from soils amended with mercury. It was dis-
covered that the amount of mercury lost from the soil could be correlated
with the amount of mercury in the soil that is solubilized by ammonium
nitrate. In addition it was found that the volatilization was mediated
by microorganisms. The conclusions can be beneficial in designing experi-
ments dealing with mercury compounds and soils and also in the interpretation
of data gathered by other investigators. Users who should find the report
of value include the Office of Air Programs, Office of Toxic Substances,
laboratories within the Office of Research and Development, other Federal
agencies, University and industrial research staffs.

1 Sage Ste ~

Director
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada

1ii


over 150 ug of the initial 200 ug of Hg remained after volatilization had
almost ceased. With the sandy soil, even after 170 hours (not shown in
Figure 3), Hg was being evolved at a rate of 260 ng Hg/h. If evolution
were to continue at this rate for 2 more weeks, 95% of the applied Hg
would be volatilized. This would bring the remaining Hg to about the

Same concentration as that found in the sand amended with 10 ug of Hg after
it ceased volatilization (11 ug).

REFERENCES

1. Alberts, 5. 3., J. EL Schindler, R. W. Miller, and D. &. Nutter, Jr.
Elemental Mercury Evolution Mediated by Humic Acid. Science 184:895-897,
1974,

2. Avotins, P., and E. A. Jenne. The Time Stability of Dissolved Mercury

in Water Samples II. Chemical Stabilization. J. Environ. Qual. 4:
515-519, 1975, .

3. Ben-Bassat, D., and A. M. Mayer. Volatilization of Mercury by Algae.

Physiol. Plant. 33:128-132, 1975.

4, Follett, R. H., and WwW. L. Lindsay. Changes in DTPA-extractable Zinc,
Iron, Manganese, and Copper in Soils Following Fertilization.. soil
Sci. Soc. Amer. Proc. 35:600-602, 1971.

5. Furukawa, K., and K. Tonomura. Enzyme System Involved in the Decomposi-
tion of Phenyl Mercuric Acetate by Mercury-resistant Pseudomonas.

Agr. Biol. Chem. 35:604-610, 1971.

6. Hitchcock, A. E., and P. W. Zimmerman. Toxic Effects of Vapors of
Mercury and of Compounds of Mercury on Plants. ann. N.Y. Acad. Sci.
65:474-497. al

7. Holm, H. W., and M. F. Cox. Transformation of Elemental Mercury by
Bacteria. Appl. Microbiol. 29:491-494, 1975.

8, Izaki, K. Enzymatic Reduction of Mercurous Ions in Escherichia colt
Bearing R Factor. J. Bacteriol. 131:696-698, 1977.

9. Jenne, E. A., and P. Avotins. The Time Stability of Dissolved Mercury

in Water Samples. I. Literature Review. J. Environ. Qual. 4:427-430,
1975.

10. Kimura, Y., and V. L. Miller. The Degradation of Organomercury Fungi-
cides in Soil. Agri. and Food Chem. 12:253-257, 1964.

ll. Krenkel, P. A. Mercury: Environmental Considerations. Part II.
Critical Reviews in Environ. Control 4:251-339, 1974.

12


After an experiment, the counts per minute (cpm) which had been con-
tinously recorded on graph paper were converted to a more meaningful form by
applying appropriate corrections for decay, specific activity, efficiency
and unit conversion. The slope of the line was then determined at l-hour
intervals and the results presented as the Hg volatility rate (nanograms per
hours, ng/h).

Soils amended with Hg were subjected to different extracting agents
after 24 hours of incubation in order to determine one suitable for use.
These solutions included H20, 1N NH,NO3, and DTPA (Follett and Lindsay,
1971). Each extraction was for 18 hours and included vigorous agitation on
a rotary shaker. The soil mixture was then centrifuged and the supernatant
was passed through a Whatman number 1 filter paper. The resulting clear
extract was used for the 7°°Hg determination. Table 2 gives the amount of
the applied Hg which was extracted from each of the soils. In all subse-
quent experiments 1N NHyNO3 was used for the extractions.

Experiments were designed so that volatile mercury was determined from
one set of replicates and the extractable and soil-bound mercury from another
set. By combining these results a budget could be reconstructed. Agreement
was generally good between the amount of mercury lost via volatilization as
determined by integrating the loss-rate curve and the amount determined by
subtracting the amount remaining as soil-bound and extractable from the
original amount of the amendment. However, there was one exception where
there was a discrepancy of 18% between these two methods of determining loss.

Because of greater precision the results of the direct analysis of the
volatile mercury are presented as the most reliable measure of the amount
lost via this route. The amount of mercury in the 1N NHyNO3-wash solution
and the amount remaining in the soil after extraction were determined by
counting the gamma activity on a sodium iodide scintillation crystal using
a multi-channel analyzer. For convenience in interpretation, the data are
presented so that the volatility rate is superimposed over the data depict-
ing the soluble and nonsoluble Hg. This was done to allow visualization of
how changes in loss rate were correlated with amounts of mercury residual
in the soil as soluble and nonsoluble compounds.

TABLE 2. PERCENT MERCURY EXTRACTED FROM SOIL WITH
VARIOUS EXTRACTANTS AFTER _24-HOUR INCUBATION

% Recovered % Recovered
Extractant from Sand from Clay
H20 8.5 0.6
1N_NHANO3 20.5 0.6
DTPA 8.2 0.6



CONCLUSIONS

Mercury (Hg) when applied to soil in a soluble form was initially very
rapidly volatilized from the soil. The rate of volatilization decreased
with time until it approached zero even though the soil still contained 50°
to 80% of the applied Hg. Increasing the concentration of soil Hg increased
the period of maximum volatility.

Volatilization is the result of microbial action. The rate is deter-
mined by the availability of Hg to the microbes. This in turn is determined
by many factors including soil texture and organic matter content.

RECOMMENDATIONS FOR FUTURE RESEARCH

Clarification of how Hg is bound in soil is needed. Also, information
on the volatility of various species of Hg is needed to understand the com-
plexities of Hg contamination of soil. It is likewise important to determine
the microorganisms involved in these reactions in order to understand and
predict mercury movement and its potential threat to food contamination.

INTRODUCTION

Interest in the environmental cycling of Hg has turned to the trans-
formation of Hg into forms other than organics. It is known that Hg
applied to the soil in many chemical forms can be lost as volatiles (Alberts
et al., 1974; Kimura and Miller, 1964; Hitchcock and Zimmerman, 1957).
However, no definitive study on the volatility rate, chemical species. formed,
and binding of mercury in soil has been reported. What mediates the volatili-
zation of Hg from soil systems is not well understood. Kimura and Miller
(1964) noted that autoclaved soils showed a decreased loss of Hg vapor,
thus indicating a biological interaction. Specific microorganisms have been
isolated from lake and river sediments (Izaki, 1977; Holm and Cox, 1975;
Avotins and Jenne, 1975; Summers and Silver, 1972; Tonomura, Maeda, and
Futai, 1968) which reduce ionic Hg to elemental Hg. These same microbes
can be found in aerobic soil; therefore, it is reasonable to assume that
there can be biological reduction and volatilization of Hg from natural and
agricultural soils. The duration and rates of Hg volatilization after
application are not available. In addition, the solubility of Hg in the
soil solution as related to the volatility has not been determined.


ABSTRACT

Mercury volatilization from soils amended to 1 ppm mercury with mercuric
nitrate ceased within 1 week after application. During the first week, 20%
of the applied mercury was lost from a silty clay-loam soil and 43% was lost
from a loamy sand soil. Volatilization of Hg from the loamy sand soil re-
sulted in a concurrent decrease in ammonium nitrate-extractable mercury.
Other work with sterile soil indicates that the volatilization was:mediated
by microorganisms.

iv


12.

13.

14.

15.

16.

17.

18.

19.

Rogers, R. D. Abiological Methylation of Mercury in Soil. J. Environ.
Qual. 6:463-467, 1977.

Rogers, R. D. Methylation of Mercury in Agricultural Soils. J. Environ.
Qual. 5:454-458, 1976.

Strohal, P., and D. Huljev. Investigation of Mercury-pollutant Interac-
tion with Humic Acids by Means of Radiotracers. In Nuclear Techniques
in Environmental Pollution. International Atomic Energy Agency,

Vienna, 1971, p. 439.

Summers, A. O., and L. I. Sugarman. Cell-free Mercury (II)-reducing
Activity in a Plasmid-bearing strain of Escherichia coli. J. Bacteriol.
119: 242-249.

Summers, A. O., and S. Silver. Mercury Resistance in a Plasmid-Bearing
Strain of Escherichia coli. J. Bacteriol. 112:1228-1236, 1972.

Tonomura, K., K. Furukawa, and M. Yamada. Mercury Transformation in
the Environment. II. Microbial Conversion of Mercury Compounds.
pp. 115-133. In F. Matsumura (ed) Environmental Toxicology of
Pesticides. Academic Press, NY, 1972.

Tonomura, K., K. Maeda, and F. Futai. Studies on the Action of
Mercury-Resistant Microorganism on Mercurial. II. The Vaporization
of Mercurials Stimulated by Mercury Resistant Bacterium. J. Ferment.
Technol. 46:685-692, 1968.

Trost, P. B., and R. £. Bisque. Differentiation of Vaporous and Ionic
Mercury in Soils. Geochem. Exlor. 11:276-279, 1971.

Yr U.S. GOVERNMENT PRINTING OFFICE! 1978=785-028/1218 9-1

13


evaporation was replaced as necessary. The bottles were closed with rubber
stoppers containing connections for inlet and outlet air lines. All bottles
were flushed during the study at a rate of 20 cubic centimeters per minute
(cc/min) with water-saturated, compressed air.

Air flushed from the bottles being used for the volatility experiments
was passed through a. charcoal collector located inside a side-hole scintil-
lation crystal. Flexible tubing used to connect the bottle to the collector
had a polyethylene liner. The charcoal collector was made from a 10-ml
volumetric pipette cut to length, with the bulb being filled with charcoal
pulverized to a 16 mesh.

Air from bottles whose contents were to be used in the extraction por-
tion of this study was passed through charcoal traps connected to the outlet
tubes of the rubber stopper. These traps were used as a safety measure and
not to determine volatile Hg. It was not necessary to change them during
the course of the study.

Each of the two side-hole scintillation crystals was connected to a
single-channel analyzer and the output was recorded on a strip chart recorder.
In this way a continuous record was obtained of the amount of volatilization
in terms of 203ng disintegrations as cpm. The charcoal collectors were
changed 2: to 4 times a day during the first 72 hours of each experiment to
insure that the cpm rate did not go off scale. The bottles were maintained
at 25° Cc in water baths. Figure 1 is a representation of the experimental
set up.

Lead Shield

Air Flow At.0.1 LPH

Vaive At 10 PSI
Al Li ‘Charcoal Filter
ir Line
L
ff,
. 1] | Scintillation
5 ‘Lead Shiota Crystal
she P.M. Tube
4 Cont. Temp.
Water Bath
H20
Bottle Containing Soll Sample

Compressed Air

Count f
Rate > Strip
| \
Meter [— Chart
Recorder

Pigure 1. Representation of the experimental setup for determining the
rate of Hg volatilization.

3


United States Environmen tal Monitorin 9 EPA-600/3-78-054
Environmental Protection and Support Laboratory May 1978
Agency P.O. Box 15027

Las Vegas NV 89114

Research and Development

SEPA Ecological
Research Series

Factors Influencing
the Volatilization
of Mercury from
Soil

DY SS


Sandy soil was also amended with Hg(NO3)2 at a concentration of 10 hg
Hg/g soil (10 ppm Hg). During the 6-day incubation period, approximately
50% of the applied Hg was lost in the vapor form (Figure 3). There was a
lag time of some 20 hours before the onset of rapid volatilization, but in
this case no distinct volatilization peak was noted, rather the maximum
rate of between 700 and 900 ng Hg/h persisted for some 50 hours before

=) Volatile Hg
NH.4NO3- Soluble

M111 Non- Soluble -

17554

150 4

125 44

Soll Hg (ug)
Volatile Hg (ng/h)

100

INT

T T
10 20 30 40 50 60 70 80 90 100 110 120 130 140

Time (h)

Figure 3. Rate of Hg volatilization and Hg remaining in sandy soil amended
to 10 ppm Hg. The soil'Hg (Wg) axis is nonzero.

gradually decreasing. Even at the end of the test there was a substantial
rate of volatile Hg loss. A decrease in the 1N NH,NO3~soluble Hg was noted
after 12 hours and continued throughout the study (e.g., at 144 hours only
16% of the applied Hg was still soluble versus 50% at the start).

Steam-autoclaved sandy soil amended with Hg(NO3)2 at a concentration
of 20 Ug Hg/20 g soil (I ppm) had a total volatile loss of only 10% of the
applied Hg after 144 hours (Figure 4). There was no initial lag in vola-
tilization as with the non-sterile sandtrials. The rate of Hg loss decreas-
ed rapidly during the first 16 hours and then remained about constant through-
out the duration of the test. The decrease in. 1N NH,NO3-soluble Hg during _
the test period was negligible.

The pattern of Hg loss from the clayey soil was quite different from
that of the sandy soil. Clayey soil amended to a concentration of 1 ppm
Hg as Hg(NO3)2 lost a total of 20% of the applied Hg during the 144-hour
examination period (Figure 5). Of this amount, 80% of the volatile loss
occurred within the first 36 hours. Since there was no 1N NH,NO3-extractable
Hg from this soil, the loss of Hg was from the non-extractable fraction.
In addition there was no lag period between Hg applications and peak Hg
volatilization rate with any of the treatments of this soil.

6


RESULTS

Various combinations of soil type, Hg concentration, and sterile and
natural soils were investigated. Replicates of experimental trials yield-
ed similar results but varied slightly in summation of the mercury budgets.
Yet all replicates yave similar rates, thus representative curves will be
presented instead of the entire data collected. When sandy soils were
amended with 20 yg Hg/20 g soil (1 ppm Hg), 43% of the applied mercury was
lost within the first 6 days. The data presented in Figure 2 show that
volatilization increased reaching a peak rate: at about 40 hours after the
Hg was added. The rate of decreasing 1N NH4NO3~soluble and nonsoluble
mercury content was greatest when the volatility rate was at its maximum.
Soluble Hg decreased from 30% of the amount initially applied to about 2%
at the termination of these tests. The volatility rate decreased to a
minimum by about 100 hours after’ which there appeared to be a steady state
established. Some volatility continued at a rate which appeared to be in
equilibrium with the amount of soluble Hg.

+ 220
=] Volatile Hg L 200
NH4NOs-Soluble | 180
(TJ Non-sotuble L 160 =
—
a
+ 140 &
&
a
bi200060
204 -_ @
ae rm |S
lew Cocco S
Ss Pato y 80 >
2 1S-Pooooooooo dpe.
~ 700060000000 t 60
eg aeeaes 2am
EZ saresshe S08
= OO + 40
° Wo
7) 104 a
F 20
75: ;
‘

t i T T TT T r
10 20 30 40 50 60 70 80 90 100 110 120 130 140,

Time (h)

Figure 2. Rate of Hg volatilization and Hg remaining in sandy soil amended
to l ppm Bg. The soil Hg (ug} axis is nonzero.


A study was conducted to investigate the volatilization of Hg from
amended soils, the rate of loss, the chemical and biological availability
of Hg in soil, and whether such volatility is of a biological origin.

MATERIALS AND METHODS

Two soils, a loamy sand and a silty clay-loam, were used for this study.
They were collected from the upper 10 centimeters (cm) of the Ap horizon
(plow layer) in an agricultural area of southern Nevada. The moist soil
was processed through a 2-millimeter (mm) sieve and stored at room tempera-
ture in plastic bags. Some physical and chemical properties of the soils
are listed in Table 1. Sterilized soil was prepared by steam autoclaving
200-gram (g) quantities at 121° C for 4 hours. After 3 days the samples
were reautoclaved. To insure that the soils were indeed sterile, 0.1 g
of each soil was spread over the surface of nutrient agar in a petri dish.
These samples were then incubated for 1 week. No growth was seen on the
inoculated dishes.

TABLE 1. PHYSICAL AND CHEMICAL PROPERTIES OF SOIL

Cation
Soil Exchange

(Texture Clay Organic Capacity
Classification) Series Sand % Carbon _meg/100g__pH

Sand Bluepoint - a member of 79.8 3.5 0.53 4.3 9.0
(Loamy Sand) the mixed thermic family

of Typic Torripsamment

Clay Overton - a member of 14.7 34.4 3.44 29.0 7.8
(Silty Clay the fine montmorillonitic
Loam) calcareous thermic family

of Mollic Haplaquepts

Mercuric nitrate [Hg(NO3))] was used to amend the soil. To each portion
of soil (20 g), 20 micrograms (jig) of Hg was added and stirred. This resulted
in a concentration of 1 part per million (ppm) Hg. Radioactive mercury
{203g (NO3)9] was mixed with the stable Hg(NO3)2 before the soil addition.
Those soils from which volatile Hg was to be determined received 40 nano-
curies (nCi) of 203hg and the soils used for extraction purposes received
4 ncCi of 203ug. The mixed solution was such that 2 milliliters (ml) of
solution contained the desired amount of both stable and radioactive Hg.

The Hg solution was added to 20 g of soil contained in 250-ml polyethylene
bottles. After addition, distilled water was added to bring the soil
Moisture to 50% of the soil moisture-holding capacity. The bottles with
their contents were weighed daily and the amount of water lost through


DISCLAIMER

This report has been reviewed by the Environmental Monitoring and
Support Laboratory--Las Vegas, U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.

ii


[==] Volatile Hg
(0) Non-Soluble

Volatile Hg (ng/h)

10 20 30 40 50 60 70 80 90 100 110 120 130 140

Soil Hg (ug)

Time (h)

Figure 7. Rate of Hg volatilization and Hg remaining in sterile clayey
soil. The soil Hg (Ug) axis is nonzero.

Autoclaving the soils had a pronounced effect on the amount of Hg
lost over the duration of these tests (144 hours, Figures 4 and 7). In
the case of the sandy soil, this reduction was from 8.6 lig Hg to 2 ug Hg
and a change of 4 wg Hg to 0.4 ug Hg for the clay. To insure that the Hg
loss was initiated biologically, both soils were inoculated with 1 g of
each of their respective nonsterile soils after 160 hours of incubation.
No effect was noted with the clayey soil but within 8 hours the inoculated
sandy soil started volatilizing Hg at a high rate (Figure 8). The volatiliza-

2a0
220-4
200_|
~
Ew
a
£04
2 wo
2 i
=
Zw
3 4
>
eo
eo
«4
2

i
10 20 30 40 50 60 70 80 $0 100 120 130 140 150 160 170 180 190 200 210 220

Time (h)

Figure 8. Rate of Hg volatilization from sterile sandy soil. Arrow
indicates when soil was inoculated with 1 g of nonsterile
soil.


fraction (Figures 2 to 4). However, since the volatilization of Hg decreased
to near zero when the extractable Hg was exhausted, it is speculated that,
in the case of the sand, Hg was lost only from the soluble fraction and the
easily exchangeable fraction of the nonsoluble Hg. Data from studies on
the volatile loss of Hg from water also link volatility with Hg availability.
It has been shown that, as the concentration of complexing agents such as
chlorine and bromine increase, the amount of Hg volatilized decreases because
of a decrease in microbially available Hg (Jenne and Avotins, 1975). In
other work with nonsterile solutions, it was shown that the amount of Hg
volatilized from the solution depends on the amount of Hg which has become
unavailable for microbial action due to combination with organic matter
(Avotins and Jenne, 1975). The same authors reported that volatilization
had almost ceased after 96 hours. ‘These data are comparable with the find-
ings from the sandy soil as far as the effect of Hg-complexing material,
biological interactions on Hg volatilization, and the time required for

the volatilization of the biologically available Hg. Note that during

the time course of the sterile sand study, the extractable Hg content
remained unchanged (Figure 4). Results from this study also support the
hypothesis that the decrease in Hg volatility with time is caused by a

loss of available Hg and not because the Hg is becoming more tightly bound
with time.

While the volatilization of Hg from the clayey soil is also obviously
a biological phenomenon (Figure 5 and 7), the Hg being volatilized was not
correlated with a 1N NH,NO3-extractable source. Even though the Hg was not
1N NHyNO3-extractable, some 20 to 31% of it was biologically available
(Figures 5 and 6). This would indicate that the Hg was initially in a form
available to microbes but not in solution or easily removed from the soil
exchange sites. How the Hg is being bound is not known but it has been
shown that Hg is tightly complexed on organic matter and cannot be replaced
with another ion except Hg (Strohal and Huljev, 1971). Since the clayey
soil was higher in organic matter than the sandy soil, the soil organic
matter could also be a viable factor in Hg retention by the clayey soil.
The same could also be true for the inorganic exchange sites. Because the
experiments were not designed to isolate clay or organic matter as factors
affecting volatilizations, it is not possible from these data to emphasize
which has the greater effect. It is possible that the amount of observed
Hg volatility is not a true indication of the total Hg vapor occurring in
the soil. This is because both clay and organic matter can sorb vapor-
phase Hg (Krenkel, 1974; Trost and Bisque, 1971).

The data from both the sandy and clayey soils show that the amount of
Hg volatilized from a soil is not an indication of the total amount of Hg
contained by the soil. Conversely, knowing the total amount of Hg con-
tained by a soil will not give an indication of potential losses due to
volatilization. But, with more information from different soils some
idea on how Hg is being bound by soils could be obtained from determining
what portion of the total soil Hg is being volatilized.

The increase in volatility in response to the increase in Hg concentra-
tion (Figures 3 and 6) indicates that the organisms responsible for volatili~
zation are capable of processing large quantities of Hg. It was apparent

11


EPA-600/3-78-054
May 1978

FACTORS INFLUENCING THE VOLATILIZATION OF MERCURY FROM SOIL

By
Robert D. Rogers and James C. McFarlane
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114

U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114


RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

Environmental Health Effects Research

Environmental Protection Technology

Ecological Research

Environmental Monitoring

Socioeconomic Environmental Studies

Scientific and Technical Assessment Reports (STAR)
Interagency Energy-Environment Research and Development
“Special” Reports

Miscellaneous Reports

This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.

CONDON wONMW =

This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.


Volatile Hg
NHsNOs3-Soluble

(1 Non-Soluble

+ 120
=
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3 Beesasesuasscess cease sess sesasasasaSaoaS zr
bad 13989883888 e8e8c tea ee0a9e95 99999896 909099 te BO
189393939899080095285%58 395982 aS0882 09090; o
2 8385 888esacegesalccasese oss ots sosoaazeoas 2
= + 40 3
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8 $s
20

10 20 30 40 50 60 70 80 80 100 110 120 130 140

Time (h)
Rate of Hg volatilization and Hg remaining in sterilized sandy

Figure 4.
soil amended to 1 ppm Hg. The soil hg (Ug) axis is nonzero.

be 200

— 180

(=) Volatile Hg ri“

MIM Non-Soluble [| '°

Volatile Hg (ng/h)

7.5 4

| f 40

6 t rrr t tt tt
10 20 30 40 50 60 70 80 90 100 110 120 130 140

Soll Hg (ug)

Time (h)

Figure 5. Rate of Hg volatilization and Hg remaining in clayey soil
amended to 1 ppm Hg. The soil Hg (Wg) axis and the volatile

Hg (ng/h) axis are nonzero.

7


tion from the sandy soil reached a peak 22 hours after inoculation. Total
Hg loss after 214 total elapsed hours was 31%. Since the pool of 1N NH,NO3-
extractable Hg had not been reduced in the sandy soil during the period of
sterile incubation (Figure 4), it is speculated that this fraction was being
yolatilized. There was apparently no Hg available for volatilization in

the clayey soil.

These data clearly indicate that Hg loss from these soils was mediated
by a biological system, although this may not be the case for all soils
since it has been shown that humic acid solutions can mediate the loss of
ionic mercury (Hgt*) as elemental Hg (Alberts et al., 1974). Workers in
the area of aquatic Hg cycling have shown in recent years that there are
several microorganisms which can cause the volatilization of Hg. These
microbes include Eseherichia coli, staphyloceus aureus, and several species
of Pseudomonas (Summers and Sugarman, 1974). Mercury loss from cultures of
Pseudomonas amended with Hgtt was found to be elemental Hg (Tonomura,
Furukawa, and Yamada, 1972). Some algae are also capable of causing the
volatilization of Hg from solutions amended with HgCl2 (Ben-Bassat and
Mayer, 1975). The consensus is that these organisms cause Hg loss by the
reduction of Hgt* to elemental Hg which is then lost because of its elevated
vapor pressure (Tonomura, Maeda, and Futai, 1968; Izaki, 1977). It should
be noted that while the pathways for volatile Hg in these soils are biologi-~
cal, the transformation of Hg*t into methyl Hg is abiological (Rogers, 1977,
1976). Methylmercury also has an elevated vapor pressure and, when formed
one molecule at a time, it too is suspected of being volatile.

In the clayey soil the volatility rate continuously decreased while
in the sandy soil the rate remained relatively stable for a few hours,
followed by a significant increase. Since the enzyme system responsible
for volatilization has been shown to be inducible (Furukawa and Tonomura,
1971) it may be that such an induction wa~ responsible for the increases
observed in the sandy soils (Figures 2 and 3). The lack of a similar
pattern in the clayey soils may indicate the lack of a similar inducible
enzyme system or more probably, the removal of mercury from microbe avail~
ability. The presence of only a small 1N NHyNO3~extractable fraction in
the 10-ppm treatment (Figure 5) and no detectable 1N_NH,NO3-soluble frac-
tion in the l-ppm treatment (Figure 4) of the clayey soils may also repre-

sent the lack of availability.

The number of soil microbes at the time of gesting were ely x 10°/s soil
6 i the clayey and sandy soils, respec
numbers 10 eet ange significantly after 30 hours of incubation. Species
of organisms were not ascertained. The initial volatility rates opserve
in the clayey and sandy soils were in approximate relationship to the _
ratio of the numbers of microbes. However, insufficient data were collec
ed to ascertain if this was a cause-effect relationship.

In all cases (except sand with 10 ppm Hg) the rate of Hg volatilization
decreased to near zero long before all the applied Hg was used (80 to 71%
remaining in clay and 50 to 57% remaining in sand). In the sandy soil the
decrease in volatility correlated with a decrease in the amount 1N NHyN03~
extractable Hg and to a lesser extent with a decrease in the nonsoluble

10