WATER POLLUTION CONTROL RESEARCH SERIES • 16080 HTD 03/72
MERCURY POLLUTION
CONTROL IN STREAM
AND LAKE SEDIMENTS
U.S. ENVIRONMENTAL PROTECTION AGENCY
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters. They provide a central source of
information on the research, development, and demonstration
activities in the water research program of the Environmental.
Protection Agency, through inhouse research and grants and
contracts with Federal, State, and local agencies, research
institutions, and industrial organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications Branch
(Water), Research Information Division, R&M, Environmental
Protection Agency, Washington, D.C. 20A60.
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MERCURY POLLUTION CONTROL IN STREAM AND LAKE SEDIMENTS
by
JAMES D. SUGGS
DONALD H. PETERSEN
JAMES B. MIDDLEBROOK, JR.
ADVANCED TECHNOLOGY CENTER, INC.
P- 0. BOX 6lMt
DALLAS, TEXAS 75222
for the
OFFICE OF RESEARCH AND MONITORING
ENVIRONMENTAL PROTECTION AGENCY
PROJECT #16080 HTD
CONTRACT #68-01-0086
MARCH 1972
For sale by the Superintendent ol Documents, U.S. Government Printing Office, Washington, D.C. 20*02 - Price 60 cents
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EPA REVIEW NOTICE
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or
commercial products consitute endorsement or recommenda-
tion for use.
i i
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ABSTRACT
Organic fractions in sediments exhibit a strong tendency to sorb
inorganic mercury resulting in localized deposition near the con-
tamination source. High concentrations of mercury do not exist in
natural waters until the underlying sediments have reached their
sorption limits or until soluble organic forms have been generated.
Mercury getters based on elemental sulfur and thio-organic compounds
dispersed in recoverable matrices are capable of removing mercury
from both the water column and underlying sediments. Elemental sulfur
deployed as a coated meshwork was found to be the most effective
means of recovering inorganic mercury. The gettering action occurs
over a period of months with no apparent degradation in water quality.
Furthermore, the presence of elemental sulfur retards biological
methylation of mercury.
Long-term evaluation of mercury getter systems indicates that pH and
dissolved oxygen are important only to the extent that they affect
the concentration of desorbed mercury in the vicinity of the getter.
This report was submitted in fulfillment of Project Number 16080 HTD,
Contract 68-01-0086, under the sponsorship of the Environmental
Protection Agency.
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CONTENTS
SECTION PAGE
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 5
IV METHOD OF STUDY 7
V BEHAVIOR OF MERCURY IN WATER AND SEDIMENTS 11
VI DISCUSSION OF GETTER SYSTEMS 17
VII OTHER GETTER SYSTEMS 27
VIM DISPOSAL OF RECOVERED MERCURY GETTER SYSTEMS 29
IX ACKNOWLEDGMENTS 31
X REFERENCES 33
XI APPENDIX A 35
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FIGURES
Page
1. Mercury Equilibria Between Water and Sediments 12
2. Adsorption of Mercury Ion by Naturally Occurring 13
Sediments
3- Lifetime of Methyl Mercuric Chloride in Simulated 15
Natural Water Conditions
b. Getter Accumulation of Mercury 19
VI
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TABLES
Page
1. Accumulation of Metallic Mercury by Sulfur 21
2. Equilibrium Water Phase Mercury Concentration 22
Range Above Metallic Mercury Laden Sediments
3- Mercury Accumulation by Getters Dispersed in 2A
Polyvinyl Alcohol Gel
A. Gettering of Methyl Mercuric Chloride 26
VI I
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SECTION I
CONCLUSIONS
1. Sulfur coated cotton meshwork (net) will remove inorganic mercury
from contaminated water and sediments. The rate of removal is
proportional to the contamination level and the partition co-
efficient between the dissolved mercury and absorbed mercury. This
system is most effective in anaerobic sediments.
2. Polyvinyl alcohol gel containing sulfur or phenyl thiourea will
rapidly remove inorganic mercury from highly contaminated water and
sediments but is generally not applicable to sediment contamination
levels below about 25 to 50 ppm or where the getter must be deployed
for long time intervals.
3. Methyl mercuric chloride can be gettered by phenyl thiourea dis-
persed in polyvinyl alcohol gel.
4. Metallic mercury can be quickly and irreversibly removed by ele-
mental sulfur at a rate proportional to the surface area of the
getter.
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SECTION II
RECOMMENDATIONS
1. A sulfur coated cotton mesh should be constructed and deployed
at an early date to test its effectiveness under actual field
conditions.
2. The development of a stable coagulated polymer gel system as a
"methyl mercury" getter should be pursued in order to prepare a
recoverable mesh for field testing.
3. Consideration should be given to further study of the plating
out of mercury on cleaned plastic surfaces and the competitive
aspects of this with other short-term regenerable getter systems,
4. Further research should be conducted to determine the economic
feasibility of recovering mercury from the getter system once it
has been removed from the sediment.
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SECTION III
INTRODUCTION
Mercury contamination enters streams and lakes from a variety of sources.
It becomes sorbed onto the sediments where it resides in dynamic equilib-
rium with the dissolved species in the suprajacent water column. Aquatic
biota may then ingest mercury and become contaminated. As mercury accumu-
lates throughout the food web, it concentrates in higher life forms and
ultimately in man. Even if the discharge of mercury could be completely
halted, its presence in fluvial and estuarine sediments still poses a
potential threat of considerable magnitude. The reliance on natural dis-
persive mechanisms to dilute and eliminate mercury pollution is no longer
tenable as evidenced by high mercury levels in tuna and swordfish. Se-
lected species of edible fin and shell fish have been withdrawn from the
market causing economic hardship in many coastal areas dependent on fish-
ing for a livelihood. It is therefore evident that means must be found
to remove mercury from sediments without destroying the environment or
otherwise upsetting the ecological balance.
Under anaerobic conditions frequently found in stream and lake bed sedi-
ments, mercury in the presence of sulfur may be precipitated as mercuric
sulfide. This reaction was verified under laboratory conditions prior
to initiation of this project and found to be effective as a means of
removing mercury from contaminated waters.
The problem of mercury immobilization and removal was addressed by evalu-
ating a number of recoverable sulfur based getter systems. Examples of
these are: (1) elemental sulfur deployed as a coating on a recoverable
meshwork, and (2) thiourea type organic compounds dispersed in a recov-
erable matrix. In the course of these evaluations several improved
getter system combinations became obvious and these were also included
into the scope of this research.
During this project,only natural sediments and waters were used to pre-
pare test aquaria in order to simulate natural conditions as nearly as
possible. The choice was indeed fortunate because it was found that
the behavior of mercury in nature is more complicated than theory would
indicate. The difficulty arises because of the affinity of humic ma-
terials for mercury. This investigation further revealed that many high
molecular weight natural products absorb mercury. Consequently, this
project required more fundamental research than was originally planned
on techniques to desorb or break the humic mercury complexes and make
the metal available to the getter. The results presented herein are
based on approximately 2000 mercury analyses covering a wide variety of
getter combinations and environmental conditions.
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The getter systems were evaluated with respect to their ability to
remove metallic mercury, the mercuric ion and organometal1ic species
from both sand and silt-clay type sediments. Each getter was tested
under pH conditions ranging from pH 5 to 9- Oxygen content in the
aquaria was varied from aerobic to anaerobic.
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SECTION IV
METHOD OF STUDY
Laboratory Equipment
In order to insure against any extraneous mercury contamination during
this study, the entire laboratory was thoroughly cleaned prior to
initiation of any experimentation. All mercury thermometers and mer-
cury containing compounds were removed. The floor was cleaned with
Mercury X, a commercial mercury scavenger. Also, all sink drains were
removed and cleaned.
Only borosilicate glassware, polyethylene, and polypropylene bottles
were used during the course of this project. All containers were new
when the project was initiated. Each container, prior to use, was
cleaned with mercury-free materials by the following procedure:
1. Washed with hot soapy water.
2. Rinsed thoroughly with hot tap water.
3. Rinsed with distilled water.
k. Rinsed with 50% concentrated nitric acid.
5. Rinsed with distilled water.
Following Step 5 each bottle was sealed and placed in a closed cabinet
unti1 needed.
Test Aquaria
In order to rapidly determine which of the four proposed mercury getter
systems would offer the broadest range of applicability under varying
environmental conditions a series of tests were devised to provide a
quick look at each system.
For each of the four getter systems eighteen one liter polyethylene
aquaria were established. Each group consisted of three sets of six
aquaria each at pH 5, 7, and 9, respectively. Within each pH group there
were 2 samples under anaerobic conditions, 2 samples under aerobic
conditions, and two controls. Nine of the 18 were devoted to silt-clay
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type sediment and nine aquaria contained quartz sand. All experiments
were conducted at room temperature (21 to 23°C) .
Sed iments
Two sediment types were selected to simulate sediment conditions that
might be encountered in nature. First, a silt-clay type sediment was
collected from under approximately 2 feet of water at Lake Arlington,
Tarrant County, Texas. This material was wet sieved through a U.S.
Standard 200 mesh screen primarily to remove the coarser organic material
The fraction finer than Ik microns which was used for establishing the
test aquaria consisted predominantly of quartz with approximately 28%
calcium carbonate and 3% organic matter. Second, a medium grain, well
sorted, iron stained, quartz sand was collected along the south shore
line water level of Cedar Creek Lake, Henderson County, Texas. This
material contained neither carbonate nor organic fractions.
The original proposal stated that Ottawa sand would be used. However,
it was subsequently decided that it was unlikely that material of this
purity would be encountered in any contaminated natural environment.
Mercury determinations were performed on all sediment batches before
use in the aquaria.
Water
During the course of this project all mercury solutions used for
inoculating the test aquaria were made with water from Lake Arlington,
Tarrant County, Texas. Repeated analysis of Lake Arlington water re-
vealed a background mercury concentration of 0.004 ppm. Viable micro-
organisms were present in the water. Though valuable in the attempt to
simulate field conditions, these organisms did tend to complicate the
interpretation of the early data.
Proposed Getter Systems
The basic getter systems to be evaluated were fiber or steel meshworks
coated with:
a. elemental sulfur; or
b. paraffin doped with sulfur; or
c. parafin doped with a thio-organic such as thiourea; or
d. polyvinyl alcohol polymer gel, acidified, coagulated and
doped with elemental sulfur.
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In addition certain other combinations of these were investigated as
getter systems.
Analytical Procedure
Mercury analyses in this project were performed following a reduction-
aeration technique essentially the same as the Hatch and Ott (1968)
method. This technique consists of oxidizing the sample to form the
mercuric ion using excess potassium permanganate in a nitric acid-
sulfuric acid solution followed by reduction to the metallic state
by stannous chloride solution. The sample is connected to an aerator
which vaporizes theomercury and pumps these vapors through a UV absorp-
tion cell. A 2537 A line emitted by a mercury lamp is absorbed by the
vapor in proportion to the mercury concentration and the results are
read directly on the instrument meter. Only mercury-free reagents are
used in this process.
A Coleman Instrument Company Model MAS-50 mercury analyzer system was
used for in-house analysis. The instrument was calibrated with standard
solutions of known concentration prior to each day's use and the calibra-
tion was checked periodically during each day's use. A Perkin-Elmer
Model 303 atomic absorption unit was used for all sub-contract analyses.
Water analyses using the MAS-50 instrument are straightforward but the
instrument has a saturation limit of 9 micrograms of mercury in the sample
volume to be analyzed. The technique uses 100 ml of an aqueous sample
for analysis. Lower volumes of high mercury content solutions are
appropriately diluted to keep the meter reading on scale. Sediments
and other mercury-contain ing solids require vigorous digestion proce-
dures with strong oxidants. The more tightly-bound mercury samples
require higher concentrations of oxidants and longer digestion periods.
Incomplete digestion may result in erroneous readings. These may be
reflected by low readings where the incomplete digestipn has left the
mercury bound to its sorbent. Conversely, erroneously high readings
can be obtained from incompletely digested materials whose vapors
can also absorb 2537 A radiation such as oxides of sulfur and nitrogen.
Sediment analysis are accurate to within 10%, based on verification
by subcontracted analyses.
Digestion Procedure
Procedures for digesting mercury-contaminated sediments vary with
sediment type and organic content. High organic levels necessitate
the use of high acidity oxidizing agents. Basically, the procedure
is one of first using stronger oxidants to destroy any organic matter
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and then weaker oxidants to preserve the oxidized character of the diges-
tion products until the sample can be analyzed. All samples are care-
fully ground and normally a one gram sample is used for digestion. A
condenser is installed in the digestion flask and used throughout the
procedure with reagents being added through the condenser to eliminate
any mercury loss.
Procedure
(l) Slowly grind sediment sample in an agate mortar.
(2) Weigh out 1 gm sample and place in digestion flask.
(3) Add:
(a) 10 ml concentrated H^SO, ;
(b) 10 ml H202-
(4) Digest at 100°C for 20-30 minutes.
(5) Add:
(a) 10 drops of potassium permanganate (k%);
(b) 5 ml of 5% potassium persulfate solution.
(6) Continue digestion at 100°C for 1 hour.
(7) Cool, remove condenser and dilute entire sample to 250 ml
and make Hg determination.
The concentration of mercury present in sediment samples may be calcu-
lated by the following method:
(micrograms measured mercury) x (250 ml)
(grams sediment) x (nil analyzed sample)
Disposal of Mercury Contaminated Laboratory Wastes
All waste materials resulting from these experiments were considered as
toxic materials and were turned over to the LTV Aerospace Corporation
Safety Officer for disposal.
10
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SECTION V
BEHAVIOR OF MERCURY IN WATER AND SEDIMENTS
Three forms of mercury contamination were studied: 1. the free metal;
2. mercuric ion; and, 3- organometal1ic species. Of these, the organic
form constitutes the greatest hazard. A study of the behavior or each
mercury form in a simulated natural sediment-water environment was con-
ducted to aid in selecting the optimum getter system.
Bulk mercury metal dumped into the environment usually filters through
the porous sediments as far away from the sediment-water interface as
the soil conditions will allow. Once diffusion is beyond a few inches,
the metal is immobilized and out of the normal zone of biological activ-
ity. Metallic mercury has low solubility in water (less than 1 ppm as
Hg°) and, unless present in large quantities such as from placer gold
mining spills, it is not exposed and contributes little to the problem
of contaminated waters. However, colloidal mercury formed by reduction
of ionic species does contribute heavily to the problem of contaminated
sediments. Whenever oxidizing conditions are present, the free metal
can be converted to the more soluble ionic form which is free to migrate,
thus increasing the zone of contamination. The reduced metallic mercury
acts as a concentrated "in situ" source of more lethal mercury forms.
Behavior of the mercuric ion (Hg++) in natural waters is strongly de-
pendent upon the nature of the sediments and secondarily on pH, dissolved
oxygen content and redox conditions. Since Jernelov (1971) and Hem (1970)
have discussed these conditions, a detailed description is not considered
necessary here. Still, several points should be discussed as they relate
to both design and operational effectiveness of any mercury getter system.
High levels of mercuric ion contamination usually do not exist in natural
waters. The ion adsorbs to sediments and for any particular sediment
type, there is a family of water-sediment mercury equilibrium curves
whose break point varies with humic fraction and grain size (Figure 1).
In addition, the mercuric ion chemisorbs to humic materials to form
strong complexes; thus, there results a competitive natural gettering
action by the sediments (Figure 2). When these localized organic com-
plexes are broken, mercury will be released either as the mercuric ion
or as lower molecular weight, often soluble, humic fragments free to
redistribute the contamination. Jernelov (1969, 1970 has reported
that bacteria will convert the mercuric ion to methylated species but the
fate of the soluble complex forms is still open to question. Based on
these factors, it is obvious that environmental improvement can be
achieved by either removing all the mercury or by at least gettering
the mercuric ion from which the highly toxic methylated mercury species
are formed.
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100
o
\_
(U
10.0
1.00
Q.
Q.
0)
4-1
03
C
o
E 0.100
03
C
o
o
0.010
0.001
CLAY HUMUS •
38% SILICA— -it —
0.100
1.00 10.0
Mercury Content - Sediment (ppm)
100
FIGURE 1 MERCURY EQUILIBIUA BETWEEN WATER AND SEDIMENTS
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E
Q.
c
111
o
o
SAND —i
SILT-CLAY
8 10 12
Time (Days)
16
18
20
FIGURE 2 ADSORPTION OF MERCURY ION BY NATURALLY OCCURRING SEDIMENTS
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"
Two very different organo-mercury forms exist in nature. The first, a
localized humic fraction mercury complex, described above, acts as an
in situ" mercury source. Mercury release into the environment will
occur when the complex is oxidized or when metabolized by benthic
organisms. The second and more dangerous form is the low molecular
weight true organometal 1 i c form such as dimethyl mercury or phenyl
mercuric acetate.
The exact nature of the alkylated mercurial products resulting from
bacterial action on the mercuric ion in sediments is uncertain. Usually,
dimethyl mercury and methyl mercuric chloride are considered the primary
products. When humic materials are absent from sediments, methyl mer-
curic chloride moves freely. Even when the sediments contain several
percent humus, methyl mercuric chloride was found to have a half life
of 6-10 days in the suprajacent water column (Figure 3)- Similarly,
soluble mercury complexes resulting from breakdown of humic sediment
fractions, move freely in the water but the mercury is usually released
or exchanged to stronger bonding sediment adsorption sites. Obviously,
complete removal of organic mercury compounds would solve the contamina-
tion problem. Practically, prevention of their formation in the aquatic
environment would help to reduce the ecological impact of mercury con-
taminat ion .
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SAND—A —
SILT CLAY
12
21
FIGURE 3
15 18
Time (Days)
LIFETIME OF METHYL MERCURIC CHLORIDE IN SIMULATED NATURAL WATER CONDITIONS
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SECTION VI
DISCUSSION OF GETTER SYSTEMS
Mode of Operation
Mercury may be introduced into waterways both as soluble and as
particulate forms. Soluble mercury in the fluvial environment is
usually transformed to the particulate form by reduction to metallic
mercury, by precipitation as sulfides or oxides, by sorption onto
sediments, by complexation with nonviable particulate organics or
by assimilation by viable biota (Heide 1956, Dall'Aglio 1968, and Ross
1962). Fine-grained stream sediments remove a high percentage of any
slugs of mercury introduced into streams, often within a distance of
a few miles of the outfall. This depends, of course, upon stream
discharge, and the physical-chemical nature of the sediment. Such
contaminated sediments may then be transported downstream by currents
in a process that involves multiple cycles of deposition and erosion.
When a river flows into a standing body of water, the coarse size and
high specific gravity minerals quickly settle as a function of decreas-
ing inflow velocity. The finer size material, which has been found to
contain most of the mercury contamination, is carried in suspension or
as a colloidal form and is dispersed throughout the lake in response
to the prevailing circulation until it slowly settles to form the lake-
bed sediment surface. Any mercury accumulated in the sediments will be
reintroduced into the suprajacent water column through the natural
sediment-mercury-water equilibria (Figure 1). Higher mercury level
sediments induce greater mercury contamination in the overlying waters.
The mode of operation of each mercury getter system studied was found
to be the extraction of that portion of the mercury contamination which
was recycled into the covering water column. Getters covered by con-
taminated sediments perform better because there is less influence of
stream currents carrying the dissolved mercury away from the zone of
gettering activity. The pH and dissolved oxygen content of the water
appear to affect the gettering rate only to the extent that their
alteration might vary the concentration of desorbed mercury in the
vicinity of the getter.
Sulfur Mesh Getter Systems
Under anaerobic conditions often found in bottom sediments, dissolved
mercury precipitates as an insoluble sulfide by reacting with the sulfide
ion formed "in situ" (Hem, 1970). Advanced Technology Center, Inc. has
found that by using this same reaction on recoverable sulfur coated sub-
strates mercury can be removed from contaminated waters and sediments.
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Several different approaches to the deployment of elemental sulfur in
water and sediments were investigated. These included recoverable:
(1) high density sulfur pellets; (2) low density, high porosity sulfur
melts; (3) dispersions of sulfur in recoverable matrices; and (4) high-
surface area sulfur coated cotton mesh. High density pellets offered
the best handling characteristics but suffered a low surface area to
weight ratio. Sulfur melt preparations were effective but their friable
character resulted in high sulfur losses unless handling was done with
extreme care. Dispersions in polyvinyl alcohol were not stable. Coat-
ing a cotton mesh with sulfur proved the most successful approach both
from the standpoint of deployment and from the efficiency of mercury
remova1 .
Of the meshworks tested, only cotton was successfully coated. Sulfur
coatings on plastic and metallic materials exhibited poor bonding
properties and were not suitable for handling. Three methods of
coating the mesh were studied. First, attempts were made to coat with
a sulfur melt. This method was not successful as the sulfur wetted the
mesh with difficulty; the resulting coating was so fragile that considera-
ble sulfur was lost during handling. Quenching in order to achieve the
so called "rubbery sulfur" did not result in any significant improvement.
Coating the mesh with sulfur dispersed in melted paraffin wax gave a
coating that remained intact over the whole time period tested (5 months).
However, the sulfur-paraffin system proved less efficient than sulfur
alone. The most effective technique for coating was that of dipping
the meshwork in solutions of sulfur in volatile solvents. Carbon
disulfide containing kQ% sulfur was successfully used to give good
sulfur penetration of the cotton cord and allowed an attachment of
about 3 parts sulfur to 1 part cotton net by weight. The surface area
of the coated sulfur was estimated at about 0.1 rrr/g. No extensive effort
was made to increase the exposed reactive surface area.
Sulfur coated cotton mesh was tested for its effectiveness in gettering
both organic and inorganic mercury. Preliminary analytical results
indicated that sulfur deployed in this form is considerably more
effective as a getter of ionic mercury than was found in the original
screening test results using high density sulfur tablets. Part of the
improvement was traced to the gettering action of the cotton string.
As illustrated in Figure 4, the cotton string sorbs mercury more rapidly
than sulfur resulting in an anomalously high initial gettering rate.
However, the string soon reaches an early saturation point while sulfur
continues to getter mercury long after.
The data illustrated in Figure 4 were taken on a system of sulfur coated
cotton net deployed on a silt clay sediment with a simulated 200 ppm
mercury contamination level (as Hg++ from HgC^)- The sediment was
described in Section IV and in Figure 1. The coated net (75% sulfur)
has 3/4 inch square openings and weighed approximately 0.1 pound per
square foot. As the data show, the coated meshwork gettered about 0.05
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ex
Q-
(U
C3
C
o
c
0)
a
c
O
SULFUR - COTTON MESH
COTTON MESH
200 -
1000
FIGURE
Time (Days)
GETTER ACCUMULATION OF MERCURY
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gram of mercury per square foot after being deployed 3 months. This
is equivalent to approximately 2% of the mercury in a 2 inch thick
layer of sediment contaminated w'th 200 ppm mercuric ion. Covering
the getter with sediment improves the gettering rate in that it affects
the concentration of desorbed (dissolved) mercury in the reaction
sphere of the getter. For low levels of contamination an improvement
by a factor of two or more may be expected.
Experiments on the same sediment type but with only a 25 ppm mercury
level demonstrated a gettering rate approximately 100 times slower
than that for the 200 ppm sample. This is because the concentration
of desorbed (dissolved) mercury in the overlying water column is
approximately two orders of magnitude lower (Figure l). The non-linear
rate effect results because the two sediment contamination conditions
lie on different sides of the sorption-desorption equilibrium curve
breakpoint.
These data were for quiet aquaria. In any real test environment, t.ie
effect of stream current on the concentration of water borne mercury
will be an important consideration. However, it should be remembered
that mercury tends to collect in the low density humus fraction and
particularly on the "fines". Both fractions settle to form stream and
lake beds only in low energy, e.g., low stream current, locations.
In other words, the areas in which mercury will accumulate are those
which favor the mode of operation of this getter system.
The data on short term gettering of metallic mercury was even more
dramatic (Table 1). In only 3 days the sulfur accumulated 150 ppm
mercury. Unfortunately, no long term experiments were conducted.
Metallic mercury (Hg°) obviously is far more reactive and thus more
easily removed from the sediments than the ionic mercury. In addition
the oxidation of Hg° to the Hg++ was reduced 100-fold by the presence
of sulfur (Table 2).
In the reducing environment present in most organic laden sediments,
mercury is usually immobilized as either the free metal or as a complex
with the humus fraction. Based on the data presented here, this reducing
environment optimizes the mercury gettering action of elemental sulfur
coated onto a recoverable cotton net. Mercury metal, Hg°, reacts
faster with sulfur than either ionic or organic forms. In addition,
the presence of sulfur retards conversion of the mercury to other
more mobile and more lethal forms. It is expected that the gettering
rate of Hg° will be a function of sulfur surface area because the free
metal has limited solubility in water. Doubling the effective sulfur
reaction surface such as by using a smaller mesh or by increasing the
surface area should double the gettering rate. Unfortunately, ionic
mercury is a more complicated situation. Gettering the mercuric ion
from sediments is favored once the mercury level exceeds the limiting
20
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TABLE 1 - ACCUMULATION OF METALLIC MERCURY BY SULFUR
Concentration of Mercury in Getter (ppm)
N>
2
12
56
150
Gettering Time
6 hours
16 hours
48 hours
72 hours
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TABLE 2 - EQUILIBRIUM WATER PHASE MERCURY CONCENTRATION RANGE ABOVE
METALLIC MERCURY LADEN SEDIMENTS (ppm)
to
N>
Mercury Form
Hg°
<2
Sulfur Coated Cotton Mesh Present
0.01 - 0.03
below 0.03
No Getter Present
0.03 - 0.3
~0.3
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level as defined by the sediment physical and mineralogical nature.
Below that point, the horizontal asymptote of Figure 1, gettering
action for mercuric ion is quite slow. The humic fraction complex
is very strong and the desorption and diffusion of the mercuric
ion into the reaction sphere of the getter is slow. For this reason
no real precision is possible in the specification of getter efficiency
on sediments containing oxidized mercury; the mercury equilibrium between
sediment and overlying water column must be known.
Since most contaminated sediments are reducing in nature, it is recom-
mended that a sulfur coated cotton mesh be field tested in order to
fully evaluate its potential.
Polyvinyl Alcohol Gel Getter Systems
Optimization of the reaction rate of certain getters requires a pH
outside the normal range of natural waters. Although adjusting the
pH in streams and lakes might be achieved chemically, this would create
an ecological disaster as well as be quite impractical. Advanced
Technology Center, Inc. has developed an aqueous gel of adjustable
pH which might offer a unique solution to the problem of pH control.
The gel is formed from polyvinyl alcohol (PVA) crosslinked with borate
ion. By incorporating the getter into such a gel it is possible to
control the reaction environment and thus optimize the getter's effective-
ness. Of particular interest were acidified media containing elemental
sulfur as one example and a sulfide forming thio-organic compound as
another- The theoretical efficiency of such systems range up to a few
grams of gettered mercury per gram of dry getter. PVA-getter systems
of sulfur (PVA-S) and phenyl thiourea (PVA-PTU) were both found to
rapidly remove both organic and inorganic mercury from highly contamina-
ted water and sediments (Table 3)•
The getter-gel system is prepared by: 1. dissolving polyvinyl alcohol
in hot water; 2. blending the getter, e.g., sulfur, into the polyvinyl
alcohol solution; and 3- pouring the mixture into a borax solution acidi-
fied to pH 5 with hydrochloric acid where it then coagulates. By dipping
a cotton net first into the borax solution and then the PVA-getter mix-
ture, a meshwork coated with the PVA-getter system was obtained.
Generally, 1% solutions of Du Pont Elvanol 72-60,a fully hydrolyzed,
high molecular weight, polyvinyl alcohol were used. The getter, either
powdered sulfur or thfo-organic compound, was then dispersed in the PVA
solution. The dispersion of getter in PVA solution was then coagulated
with a 5% solution of either borax or ammonium pentaborate depending upon
the desired pH of.the gel. The use of borax as a gelling agent will pro-
duce a PVA-getter system having a pH of 10 which may be reduced to pH 5,
if desired, by the addition of selected amounts of mineral acids. Ammonium
23
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TABLE 3 - MERCURY ACCUMULATION BY GETTERS DISPERSED IN POLYVINYL ALCOHOL GEL
Sediment
Mercury Mercury Sediment Dispersed
Type Level (ppm) Description Getter
Mercury Uptake by Getter System
(ppm)
Deployment j
Time (Days) ~
HgCl2 32 Silt-Clay Sulfur ND*
10% Organic
Matter Phenyl Thiourea
HgCl2 14 Silt-Clay Sulfur
3% Organic
Matter Phenyl Thiourea
HgCl2 25 Silt-Clay Sulfur ND
3% Organic
Matter Phenyl Thiourea ND
HgCl- 200 Silt-Clay Sulfur 50
3% Organic
Matter Phenyl Thiourea 113
Hg° Bulk --- Sulfur 2
Mercury
Phenyl Thiourea 12
ND
0.4
ND
ND
0.5
ND
172
99
56
25
682
229
2
ND
ND
0.4
*ND - Not Detectable
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pentaborate when used as a gelling agent will produce a PVA-getter
system of pH 6.5 to 7.5.
As the early experimental work proceeded it became evident that
acidified gels were not stable. Furthermore, gels containing dis-
persed getters often dissolved in a matter of a few days. Alkaline
gels coated on cotton mesh survived longer and life times up to
several months were achieved in certain instances. In spite of the
instability, PVA gels are worthy of additional discussion and study.
As discussed earlier, for every sediment contamination level there
is a corresponding water-sediment mercury partition coefficient. PVA
gels containing getters exhibit a synergistic effect in that low molec-
ular weight polyvinyl alcohol fractions cause the equilibrium to shift
in a manner to desorb mercury from the sediment. Thus, the effective
concentration of mercury in the vicinity of the getter is increased
resulting in a subsequent improvement in gettering rate. A number of
PVA systems were tested but the majority of the study was devoted to
those containing either dispersed sulfur or phenyl thiourea. In
highly contaminated sediments and waters the PVA-phenyl thiourea get-
ter rapidly collects all forms of mercury while the PVA-sulfur activity
appears limited to inorganic mercury (Table k).
Of particular significance was the removal of methyl mercuric chloride,
one of the "methyl mercury" species formed in stream and lake sediments
by bacterial action. Because methylated mercury is a far greater
ecological hazard than its predecessor inorganic forms, the rapid
gettering of this species \s quite significant. Phenyl thiourea dis-
persed in polyvinyl alcohol was the only getter system found to be
effective for methyl mercuric chloride removal in the contamination
range studied. As Table k illustrates, the PVA-PTU gettered signifi-
cant amounts of mercury even within the first few hours of deployment.
Unfortunately, PVA-PTU gels were not sufficiently stable for long term
studies. The effective gettering of that toxic organometal1ic mercury
form warrants further study to develop a gel sufficiently stable to
be deployed for an extended period so that the system can be field
tested.
25
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TABLE k - GETTERING OF METHYL MERCURIC CHLORIDE (CH HgCl)
CH-jHgCl Level in
Overlying Water
Column (ppm)
10
1
10
10
10
Getter Description
Phenyl Thiourea Dispersed
in Poly vinyl Alcohol Gel
Phenyl Thiourea Dispersed
in Polyvinyl Alcohol Gel
Elemental Sulfur
Paraffin
Sulfur Dispersed in Paraffin
Accumulation of Mercury in Deployed
Getter (ppm)
Deployment
Time (days) 1
3
2
22
0.1
0.5
7
ND*
0.6
0.6
11
0.7
O.k
100
0.8
0.4
N>
*ND - Not Detectable
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SECTION VI I
OTHER GETTER SYSTEMS
During the course of this study, it became obvious that many natural
products act as mercury getters. In fact, many man-made polymeric
materials also exhibit a strong but usually short-lived mercury
gettering action. Previous descriptions have been devoted to the
more promising getters; this section covers other systems tested but
found unattractive for this applicaton.
Paraffin and Sulfur Dispersed in Paraffin
Laboratory studies at Advanced Technology Center, Inc., as well as
other reports of the affinity of hydrocarbons for certain forms of
mercury suggested that paraffin might be a particularly suitable get-
ter for methyl mercuric chloride. Some rapid gettering was observed
but long-term studies indicated that this was apparently a surface
phenomenon of limited value (Table 4). The paraffin-sulfur type getter
produced similar results for methyl mercuric chloride but more positive
gettering of inorganic mercury was observed. However, the mesh coated
just with sulfur was approximately 50 times more effective than the
paraffin-sulfur mixtures.
Sulfur Tablets
High density sulfur tablets were found to getter metallic mercury.
However, the reaction rate was proportional to surface area and the
sulfur coated cotton meshworks were more effective. Similar results
were observed in the gettering of mercuric ion. Approximately 1 micro-
gram of mercury per square centimeter of surface was gettered over a
120 day period. The sulfur tablets had little effect on methyl mer-
curic chloride contamination, gettering less than 0.1 microgram mercury
per square centimeter of exposed surface over a 120 day period.
Cotton and Paper
As previously mentioned, cotton meshwork was found to getter mercury.
Levels of several hundred ppm have been reached after a few days ex-
posure to high mercury contamination. However, the gettered mercury
is less tightly bound than that held by humic materials and is subject
to being resorbed by the sediments. Cotton mesh offers promise on a
short-term basis but is not theoretically capable of removing mercury
27
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to as low a level as can be achieved with mercury sulfide forming
getters. As expected, paper eel 1ulose performed similarly, however,
its mercury capacity was about one-half that of cotton mesh under
the same conditions.
Plastics
An interesting phenomenon observed in the laboratory was that mercury
will plate out on well-cleaned plastic items on a short term basis.
These include polyethylene and polypropylene laboratory ware normally
regarded as inert. The process appears to be adsorption to active
sites on the plastic surface. However, these sites desorb the mercury
within a few days and from then on appear to be inactive. For this
reason plating out is probably a better term than gettering. The total
quantity of mercury temporarily adsorbed by polyethylene and polypropylene
was usually less than 1 microgram mercury per square centimeter of surface.
Still, high surface area yarns may offer possibilities in certain situa-
tions where short-term reusable getters are desired.
Paraffi n-Thiourea
Thiourea dispersed in paraffin was also evaluated as a mercury getter.
Thiourea had a strong tendency to diffuse out of the paraffin and react
with the mercury away from the recoverable paraffin matrix. The sulfide
settled out on the sediment thus rendering it harmless but unrecoverable.
The results indicated that a less soluble thiourea derivative might be
applicable. The phenyl thiourea study already described confirmed that
conclus ion.
Polyvinyl Alcohol-Cystine
Cystine (C^Hj2^2^4S2)> a naturally occurring amino-acid containing a
reactive disulfide group, was dispersed in polyvinyl alcohol gel and
evaluated as a mercury getter. The gettering action exhibited by phenyl
thiourea was considerably greater than that of cystine.
Iron Oxides
Micro-crystalline iron oxides were evaluated for use as mercury getters,
however, no significant mercury reduction in the aqueous phase was
observed.
28
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SECTION VI I I
DISPOSAL OF RECOVERED MERCURY GETTER SYSTEMS
Subsequent to the recovery of the sulfur coated nets and gettered
mercury, means of safe storage and disposal must be found. For short-
term storage and transportation,steel barrels would be adequate. To
accomplish permanent disposal two alternatives are apparent: (l) the
material being in an essentially insoluble sulfide form could be buried
in a dry, preferably alkaline environment, or (2) because mercury sul-
fide is the principal ore of mercury it should be acceptable by some
mercury smelters, therefore, offering the possibility of partially
defraying the cost of mercury removal from stream and lake sediments.
The economics of disposal techniques are expected to vary with geographic
location,thus dollar estimates would need to be established on a regional
bas is.
29
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SECTION IX
ACKNOWLEDGMENTS
The support of this project by the Environmental Protection Agency
and the help provided by Dr. Curtis C. Harlin, Jr., and Dr. William
R. Duffer, the Project Officer, are gratefully acknowledged.
31
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SECTION X
REFERENCES
1. Dall'Aglio, M., 1968, the Abundance of Mercury in 300 Natural Water
Samples from Tuscany and Latium, in Ahrens, L.H., ed., Origin and
Distribution of Elements: New York, Pergamon Press, p. 1065-1081.
2. Hatch, W. R. and Ott, W. L., 1968, Determination of Sub-Microgram
Quantities of Mercury by Atomic Absorption Spectrophotometry:
Analytical Chemistry, Vol. 40, No. ]k, pp. 2085-208?.
3. Heide, F., Lerz, H. and Bohm, G., 1957, Lead and Mercury Content of
Water from the Saale River: Naturwissenshaften, Vol. kk, No. 16,
p. Ml-M»2.
k. Hem, J. D., 1970, Chemical Behavior of Mercury in Aqueous Media:
U.S. Geol. Survey Prof. Paper 713, pp. 19-24.
5- Jernelb'v, A., 1969, Conversion of Mercury Compounds. In Miller, M.W. ,
and Berg, G. C., eds. Chemical Fallout, p. 68-74.
6. Jernelb'v, A., 1971, Release of Methyl Mercury from Sediments with
Layers Containing Inorganic Mercury at Different Depths: Limnol.
and Oceanol. Vol. 15, p. 958-960.
7. Ross, R. G., and Stewart, D. K. R., 1962, Movement and Accumulation
of Mercury in Apple Trees and Soil: Canadian Jour. Plant Sci.,
Vol. 42, p. 280-285.
33
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SECTION XI
APPENDIX A
RESEARCH-DEMONSTRATION TEST PLAN
This research-demonstration test plan is designed to evaluate a sulfur
coated cotton mesh mercury getter system under field conditions and to
obtain the necessary research data to proceed from laboratory demon-
stration studies to a fully operational system suitable to broad scale
application. Advanced Technology Center, Inc. (ATC) recommends that
a site of approximately 1 acre (43,560 ft2) be selected in order to
fully evaluate all aspects of the system. While the areal extent of the
test site may be either increased or decreased, subject to the require-
ments of the Environmental Protection Agency, it should be noted that a
linear relationship in prices does not exist. Therefore, doubling the
test area will not double the cost nor would reducing the test area by
a half reduce the cost by half.
Site Selection
The geographic location and the physical parameters of the test site
are not critical factors in determining the effectiveness of the system,
however, they do affect costs. It is therefore recommended that both
site accessibility and water depth be given careful consideration. For
example, an easily accessible site having a water depth on the order of
a few feet would probably eliminate the necessity of net deployment and
recovery from a surface craft thus reducing cost without loss in test
data reliability. Deployment in deep waters would probably increase the
costs slightly. Ideally, the selected site would have a sediment con-
tamination level over 25 ppm Hg for rapid demonstration of gettering
rate and efficiency. The nature of the sediments is not critical so
long as the sediment is unobstructed for getter deployment. Many sites
of mercury contamination have been identified which should be applicable
as a field test site. Well-publicized zones of contamination are the
St. Clair and Detroit Rivers in Michigan, Lavaca Bay on the Gulf of
Mexico and Bellingham Bay in Puget Sound. Many other contamination
sites, as identified by the U.S. Geological Survey in Circular 6^3,
might also be considered in the selection of demonstration sites.
Site Evaluation
Following site selection, a sufficient number of both water and bottom
sediment samples to characterize the area should be obtained prior to
meshwork emplacement. ATC recommends that a grid network be established
35
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at the test site and sampled on 50-foot centers. Both water and
sediment samples should be obtained and analyzed to determine pH,
dissolved oxygen, organic content, both dissolved and total mercury,
and sulfide fraction. Depending on the site, sedimentation data
may also be necessary.
Getter System Emplacement and Recovery
The preparation of a sufficient quantity of sulfur coated cotton netting
to cover the test area will be accomplished by Advanced Technology Center,
Inc. ,personnel at a company facility and transported to the designated
test site.
For evaluation purposes ATC recommends the use of a Number 9 Medium Cotton
Netting, 1-1/2 inch stretch mesh (3/^ inch squares). To cover the test
site it is estimated that 1000 pounds of net will be required. Consider-
ing the coating ratio of 3 parts sulfur to 1 part netting, approximately
3000 pounds of sulfur will be required along with the necessary solvent
medium for coating.
Mode of emplacement is dependent upon site configuration. If a large
waterway and deep waters are encountered, a boat of approximately 20-30
feet length will be needed. In the event of a site location having suffi-
cient shore line accessibility the boat requirement may not exist. The
coated meshworkwill be deployed in 12-foot strips fastened together in
shallow water to assure full coverage. Deep water coverage will be assured
by net overlap when clipping adjacent strips is not practical.
The sulfur coated meshwork will remain in place for a period of six months.
The test site will be sampled monthly and the previously mentioned param-
eters measured. Net samples will also be obtained and tested for mercury
uptake and examined to determine if there has been any net deterioration
or microbiological growth. Following field evaluation of the getter
system the sulfur coated netting will be recovered and stored in adequate
containers prior to final disposal.
Alternative Evaluation Method
Many sites of mercury contamination exist in the United States. However,
two major non-technical problems are encountered in the selection of a
research field test site. First, there is almost always a problem of
multiple jurisdiction over any public waterway, e.g., County and State
Health and/or Water Quality and/or Water Development Boards. Even though
the ATC mercury gettering system is safe and will improve water and
sediment condition without any danger of water quality degradation, it
may still be impossible to acquire full permission to perform the field
36
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test. A second problem is that announcement of any mercury contamination
in any site new or already documented will certainly rekindle public
hysteria regardless of the test purpose and effectiveness. Therefore,
as an alternative to field test under "natural" conditions, it
is recommended that a simulated artificial reservoir having a surface
of several thousand square feet be constructed. The reservoir would
be fully lined in order to prevent contamination of ground water supplies
in the area. It is estimated that a depth of two feet would be sufficient.
A two-inch layer of sediments having a mercury contamination level of
25 ppm would be utilized to cover the bottom of the reservoir and a
sufficient volume of water added to give a fluid level of one foot. The
remaining one foot of reservoir capacity would serve as flood storage in
the event of unexpected rains. The entire reservoir area would be com-
pletely fenced and properly marked to prevent unauthorized access. The
sediments would be artificially doped with mercury to a level of 25 ppm.
Both water and sediment from an already identified mercury contamination
site would be used to inoculate the prepared reservoir with microbiota
which would be encountered in a "natural" site.
It is estimated that reservoir preparation costs would be offset by
reduced costs for site surveys, boat rentals, materials, and labor.
Thus, the total cost for this alternative would be approximately the
same as field test under "natural" conditions.
37
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OO
RESEARCH-DEMONSTRATION TEST PLAN
SCHEDULE
^^~~~~~~--^_^^ MONTHS AFTER
^~~~~~~—-~-_CON TRACT AWARD
TASK ^ ^^^
MAIbKIALb ALQU 1 b 1 T 1 ON
NET COATING
PRE DEPLOYMENT SITE SURVEY
NET DEPLOYMENT
SI TC MHM 1 THD 1 MT
1 1 t rlUlN 1 1 UK 1 Nb
NET RECOVERY & DISPOSAL
REVIEW BY EPA PROJECT OFFICER
PROJECT MAN DAYS
MONTHLY PROGRESS REPORTS
nMAI DCDHDT
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i
5
i
2
-•
•
20
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A
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
11 Report Mo.
3,
sion No.
w
4, Title
MERCURY, POLLUTION CONTROL IN STREAM AND LAKE SEDIMENTS
I S. JR.\- ort Date
\ S' "
I 9, ',
7. Author(s).
Suggs, J. D., Petersen, D. H., Middlebrook, J. B., Jr.
9. Organization
ADVANCED TECHNOLOGY CENTER, INC.
DALLAS, TEXAS
Report No'.,
10. Protect So.
16080 HTD 03/72
11. Contract/ Grant No.
,
'13. Type of Report and >'
, i " Period Covetttl
12. Sponsoring O.
16. Abstract
Organic fractions in sediments, exhibit a strong tendency to sorb inorganic
mercury resulting in localized deposition near the contamination source. High con-
centrations of mercury do not exist in natural waters until the underlying sediments
have reached their sorption limits or until soluble organic forms have been generated.
Mercury getters based on elemental sulfur and thio-organic compounds dispersed
in recoverable matrices are capable of removing mercury from both the water column and
underlying sediments. Elemental sulfur deployed as a coated meshwork was found to be
the most effective means of recovering inorganic mercury. The gettering action occurs
over a period of months with no apparent degradation in water quality. Furthermore,
the presence of elemental sulfur retards biological methylation of mercury.
Long-term evaluation of mercury getter systems indicates that pH and dissolved
oxygen are important only to the extent that they affect the concentration of desorbed
mercury in the vicinity of the getter.
This report was submitted in fulfi1Iment of Project Number 16080 HTD, Contract
68-01-0086, under the sponsorship of the Environmental Protection Agency.
(Suggs-ATC, \nc.)
17a. Descriptors
Mercury Getters*, Sediments*, Natural Mercury Sorbents, Methyl Mercuric Chloride,
Metal 1ic Mercury
17b. Identifiers
Mercury Pollution Control*
17c. COWRR Field i&Groa.a 05G
IS. Availability
I.
- (Report)
! 20, , Socutn/C/av*.
'
il.
Pages
Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Abstractor J- D- -Suggs,
institution Advanced Technology Center, Inc.
U. S. GOVERNMENT PRINTING OFFICE : 1972 _ b
(321 }
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