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, DC  20460.


                 Leonard H.  Bongers and
                   Mohammed N. Khattak
          Research Insitute for Advanced Studies
                Martin Marietta Corporation
                    1450 South Rolling Road
                Baltimore,  Maryland 21227
                          for the

             Office of Research and Monitoring

                 Project Code #16080 HVA
                    Contract #68-01-0089
                        January 1972
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, B.C. 20402 - Price 55 cents

                     EPA Review Notice

This report has been reviewed by the Environmental Protection Agency
and approved for  publication.   Approval does not signify that the con-
tents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.

The release of toxic mercurials by mercury-enriched river sediments
was examined in the laboratory.   These tests indicated that about
1 \ig of methylmercury was released per m^ per day.  The release of
such toxic mercurials could be prevented by a layer of sand, 6 cm in
thickness,  applied over the mercury-enriched sediments.  Layers of
fine or coarse gravel (6  cm deep) were as effective as sand.   Thinner
layers of sand,  1.5 and 3 cm in thickness,  appeared to be unsatisfactory.
The cost of applying 3-inch layers of sand or gravel over contaminated
river sediments is estimated to be about $3000 to $4000 per acre.

The formation of methylmercury occurred in sediments with low and
high organic content, in  sediments with low and high cation exchange
capacity, and in aerobic and anaerobic sediments.

A convenient indicator of the potential toxicity of a contaminated sed-
iment is  the presence of metallic  mercury.  The slow release of metallic
mercury occurred in aerobic  sediments, but the release was much faster
in anaerobic sediments.   Using ascorbate as an artificial electron donor,
metallic  mercury could be released at high rates  from aerobic sediments
as well.  Ascorbate  appeared to be a helpful indicator of the presence
of divalent biologically accessible mercury.

Although the laboratory investigations proved the  soundness of the sand
blanket approach, its practical and economic feasibility must be deter-
mined in a combined field and laboratory analysis program.

This report is submitted in fulfillment of Project  16080 HVA,  Contract
#68-01-0089, under  the sponsorship of the Office  of Research and
Monitoring, Environmental Protection Agency.


Section                                                         page

  I          Conclusions                                          1

  II          Recommendations                                    3

  III         Introduction                                          5

  IV         Materials and Methods                                7

  V          Results and Discussion                              17

  VI         Economic Considerations                            37

  VII        Acknowledgments                                    41

  VIII       References                                          43



1     Schematic of closed system used for mercury analysis.      8

2     Calibration curve for absorption at 253. 7 nm for mercury   9
      concentrations between 0 and 0. 7 )j,g/sample.

3     Calibration curve for absorption at 253. 7 nm for mercury  10
      concentrations between 0 and 15 p,g/sample.

4     Calibration curve for absorption at 253. 7 nm for mercury  11
      concentrations between 0 and 25 ng/sample.

5     Schematic of flow-through system used to measure         12
      mercury vapor  released directly from sediments.

6     Schematic of laboratory incubation procedure.              14

7     Time course of mercury assimilation by guppies.          20

8     Methylmercury uptake by guppies as a function of con-     21

9     Effect of a protective cover 6 cm in depth on mercury      28
      accumulation by guppies.

10    Transformation pathways of mercury and its derivatives    30
      in aquatic environment.

11    Rate of Hg° evolution from aerobic sediments spiked      32
      with HgCl2.

12    Rate of Hg° evolution from anaerobic sediments spiked     34
      •with 50 |j,g of


No.                                                           Pag

1      Distribution of Hg between solid and liquid phase          17
       in 10 g  (dry weight) of sediment mixed with 1000 |j,g
       of Hg as HgCl2.

2      Distribution of Hg between solid and liquid phase          18
       in 10 g  (dry weight) of sediment mixed with 200 |Xg
       of Hg as CH3HgCl.

3      Effect of sand overburden on the mercury content         23
       (Hg) of surviving guppies  incubated for 3 weeks using
       Sediment I enriched with  HgCl2-

4      Effect of sand overburden on the mercury content         24
       (ug) of surviving guppies  incubated for 4 weeks using
       Sediment II enriched with HgCl;?.

5      Mercury content of sand and sediment above and below    24
       Hg-enriched layer.

6      Mercury content of the liquid phase at the end of a        25
       3 -week  incubation using Sediment I.

7      Effect of a 6 -cm overburden of sand or gravel on         26
       the mercury content (|j,g)  of surviving  guppies
       incubated for 3 weeks  in the presence  of Sediment
       II enriched with
8      Estimate of mercury content (p,g) in the liquid phases    29
       and acid extracts of mercury-enriched sediments in-
       cubated aerobically or anaerobically.

9      Estimated fixed /variable costs of distributing sand      38
       in an area south of Wyandotte.

10     Estimate of the cost involved in the  application of        39
       3 inches of sand to 2, 25, and 50 acres of sediment
       contaminated with mercury.

                          SECTION I


Laboratory simulation studies dealing with the release of toxic mercury
from river sediments enriched with mercuric chloride showed that:

1.  Approximately 1 p,g of  methylmercury  is released per m  of
sediment per day.

2.  Sand applied to a thickness of 6 cm will prevent the release of this
mercury during a 4-week laboratory incubation.  Thinner layers of sand
were unsatisfactory under  the experimental conditions.

3.  Other aggregates, such as fine and coarse gravel, applied to the same
thicknesss were as effective as sand.

4.  A field application would cost about $3000-$4000 per  acre.

5.  Ionic mercury introduced into a normal aerobic sediment to a con-
centration of about 200 ppm or less is rapidly complexed with sediment
entities or converted to mercuric sulfide.  The complexed form might
give rise  to a slow release of metallic mercury.

6.  Significant quantities of metallic  mercury might be released if
relatively small quantities of ionic mercury are introduced into an
anaerobic sediment.

7.  Ascorbate might be used to identify sediments containing bio-
logically accessible mercury deposits.

                          SECTION II


As a result of this research,  it is recommended that:

1. A field feasibility study be conducted in an area known to release
substantial amounts of toxic mercury (e.g. , Detroit River).

2. The chemical and physical nature of the sediments be defined in
sufficient detail to allow a projection from the test area to another
contaminated area.

3. Caged bioaccumulators (e.g., carp, pike,  or catfish) be used,  prior
to and after the  preventive sand or gravel overburdens are applied so
that their effectiveness can be determined.

4. Laboratory simulation tests be initiated to determine  the long-term
(> 1 year) effectiveness of the abatement procedures.

5. The nature of mercury present in sediments be  defined in much
greater detail and that the broader environmental hazard  of the contam-
inated sediments be determined.

6. The fate of mercuric  sulfide and the complexed mercuric ions in an
aerobic environment be determined.

                          SECTION III


Following the discovery in Sweden during  the late sixties of high levels of
mercury in fish and seed-eating birds, fish from suspected waters in
Canada and the United States were examined for mercury contamination.
The findings ledto the banning of fishing at many sites (Lake St.  Clair,
Ontario; Lake Erie, Detroit River) (1).   Mercury levels in fish of 5 mg/
kg and more were observed—a level well  in excess of the proposed
practical limit of 0. 05 mg Hg/kg for food  (2).

Detailed studies by Westoo (3) showed that mercury in fish, and probably
in other biological systems as well (4),  occurs predominantly as methyl-
mercury, a mercurial which was used as  a fungicide in agriculture (seed
dressing) and industry (pulp preservation).  Although contamination in
many cases was clearly related to the use of this fungicide, other organic
and inorganic compounds were implicated. Findings suggested  that the
toxic  products were formed from less toxic mercury compounds.

Over  the years, industrial and other activities  resulted in the release of
inorganic and organic mercurials in the aquatic environment.  Here,
these compounds are easily absorbed by surfaces of organic particulate
matter, clays, silt particles, planktonic organisms, and hydrated ferric
oxides.  Consequently,  mercury compounds tend to accumulate  in the
sediments of lakes and rivers,  where the  relatively harmless mercurials
can be transformed  into highly toxic and soluble methylmercury or into
the harmless and insoluble mercuric sulfides (8).

Little is known concerning the biochemical and chemical processes
associated with mercury in these sediments.  Intuitively,  it is assumed
that mild anaerobic  conditions would promote the formation of insoluble
sulfide.  Strong anaerobic environments -would  be undesirable because
these would promote the activity of methanogenic bacteria and,  from the
work  of Wood et al (5) and Jensen et al (6), this activity could enhance
methylation processes.  Strong aerobic sediment conditions also would
be undesirable,  because sulfides would be oxidized to sulfates,  allowing
the methylation of the inorganic mercury.   Methylation  of mercury also
may proceed by a non-enzymatic process  involving vitamin Bio(7).  This
means that waters with high bacterial counts and those  affected by
sewage discharges may promote these undesirable conversion processes.

Although much remains to be  learned concerning the magnitude  of these
processes,  it appears that the release of toxic  mercurials from contam-
inated sediments depends on biological processes occurring in these
sediments.  In order to control the exchange of mercury bet-ween the

sediments and the overlying water,  the biological processes occurring
in the contaminated sediments must be controlled.

Clearly, in  order to design efficient control methods, detailed knowledge
is needed concerning environmental conditions that enhance the formation
of mercuric sulfides and stimulate the release of toxic mercury.   Much
of this knowledge is  lacking, but programs are suggested (8) to test the
effectiveness of various control procedures.  Proposed field methods
aim at (a) increasing the pH of the water-sediment interface,   (b) intro-
ducing materials with stmng absorptive capacities, and (c) reducing
available oxygen and thereby promoting the development of hydrogen
sulfide and formation of insoluble mercuric sulfides.

The effect of an overburden of sand or gravel on  the release of toxic
mercurials from contaminated sediments is examined in this  report.
This overburden would reduce the availability of oxygen and thus promote
the conversion of mercury to  mercuric sulfide.  Natural sedimentation
could further bury the contaminated sediments reducing even more the
danger of exposure and subsequent release in the water.  This abate-
ment procedure appears economically and ecologically appealing.

The sand overburden required to control the release of toxic mercury
from mercury-enriched sediments was investigated, and the effective-
ness of sand  and fine and coarse gravel was compared.  The  cost in-
volved in a field application was estimated, and some preliminary
experiments were conducted to assess the immediate fate of inorganic
mercury added to aerobic and anaerobic sediments.

                          SECTION IV

                  MATERIALS AND METHODS

Inorganic mercury was determined according to the flameless atomic
absorption technique (FAAS) described by Hatch and Ott (9) employing
the procedure and reagents described by Perkin-Elmer Corp. (10) and
Kolb (11), respectively.  The mercury vapor was measured at 253. 7 nm. The
arrangement used is illustrated in Figure 1.  To measure  various con-
centration ranges, quartz-windowed absorption cells  having a light path
of 1,25,  Z. 50,  or 20 cm were used.  Figures 2, 3,  and 4 show the
relationship between absorbancy and mercury concentration and the
concentration ranges for which the three cells were employed.  Cali-
bration curves were prepared using a stock solution containing 0. 1354 g
of mercuric chloride (HgC^) dissolved in  IN H2SO4- To prepare
standard curves, the stock solution was diluted to the required values.
Resolution of 0. 01 |j,g of Hg was obtained with the 20-cm  cell. With 0. 1
M>g of Hg,  a precision of about - 3% was obtained.

Metallic mercury vapor,  present or formed in sediments was determined
with a flow-through  system developed for this purpose (Figure 5).  To
transport metallic mercury through the  measuring cell,  air or N£ was
used as a carrier gas; this gas was introduced into the sediment through
the fritted disk of medium porosity.  A gas flow of 100 to 150 cc  was
commonly used for 100 ml of a watery sediment containing some 30  g
dry weight of material.  This allowed continuous monitoring of evolved
metallic mercury.

Organic mercury in fish or in sediment  was determined,  where  possible,
by flameless atomic absorption spectroscopy (FAAS)  after conversion
into inorganic mercury by acid digestion (Figure 1).   Digestion was
carried out in 30-ml Kjeldahl flasks containing  a 2-ml mixture of con-
centrated H2SO4 and HNO3,  to which KMnO4 was added.  Routinely,
digestion was  complete after 20 to 30 min at about 100C.   Using methyl-
mercuric chloride (CH3HgCl) and HgCl£  as test  compounds, recoveries
of 85% to  100% were observed.  Lower digestion temperatures (50C to
70C) gave incomplete recovery with CH3HgCl (12).  This result was
attributed to incomplete digestion. Since methylmercury is the  dominant
form of mercury reported in fish (13) and because its C-Hg bond is
relatively strong, digestion procedures  developed for methylmercury
would apply to other mercurials as well.  Thin  layer  chromatography and
two types of resin (13,  28) were used to separate inorganic mercury from
organic mercurials.

Reagents;  Mercury compounds were obtained from the K and K  Company,
New York.  Organic mercurials contained  2 to  5% of inorganic mercury,

  to aspirator
Figure 1.  Schematic of closed system used for mercury analysis.

 §  750
 Z  600
                         Lp 20cm   range 0-0.7 ftgHg
              0.1     0.2     0.3     0.4     0.5

                        /igHg / SAMPLE
0.6    0.7
Figure 2.  Calibration curve for absorption at Z53.7 nm for mercury

          concentrations between 0 and 0.7 tig/sample.


 "-~   600


                        Lp 2.5cm    range 0-15
          0      2.5    5.0     7.5     10.0    12.5

                         /igHg / SAMPLE
Figure 3. Calibration curve for absorption at 253.7 nm for mercury

         concentrations between 0 and 15 p,g/sample.

 'E   750
                          Lpl.25cm   range 0-25/j.gHg

                                 / SAMPLE
Figure 4.  Calibration curve for absorption at 253.7 nm for mercury

          concentrations between 0 and 25 u,g/sample.

oust  f
   fritted  disc
Figure 5.  Schematic of flow-through system used to measure mercury
         vapor released directly from sediments.

as indicated by thin layer chromatography and NMR spectroscopy.
Dithizone was Baker's analyzed; diphenyl thiocarbazone was Fisher's
certified; and tetrahydroxy-p-benzoquinone was an Eastman Kodak
Company product.  Bismethylmercuric sulfide, (CH3Hg)2S,  was pre-
pared according to a procedure of Dadii et al (14) from methylmercuric
bromide and sodium sulfide in ethanol.  Male guppies were used as
accumulators of organic mercurials.  As will be seen later,  guppies
almost quantitatively removed organic mercurials of interest from
the water, but they did not accumulate inorganic mercury compounds,
even when such compounds were present at relatively high concentration.
Mercury observed in fish is assimilated as organic compounds.

Column preparation; Columns were prepared following the procedure
described by Jernelov (15) and as shown in Figure 6.  For all experiments
reported here, the mercury-rich sediment -was prepared by adding 16 mg
Hg  (as HgClz) to  160 ml  of watery sediment (the amount of Hg-enriched
sediment used in each cylinder).  This Hg-enriched sediment was spread
on a 10-cm sediment, relatively free of mercury,in a 10-cm diameter
column.   The enriched layer contained about 200 M-g of Hg/g of dry sed-
iment and was about 1 cm in thickness.  Subsequently,  sand or coarse
or fine gravel was spread over the enriched layers to the required
thickness, and tap water was added for a total volume of about 4 liters.
The depth of water layer was approximately 12 cm.  Six  guppies were
added to the control and to each experimental series.  The columns
were placed in an environmental chamber,  which was kept at 20C and
subjected to 12-hr light/dark intervals.  Illumination was provided by
fluorescent and incandescent light sources.  The light intensity was
approximately 0.3 mW cm~2 (400 to 700 nm).  The sand  used for these
experiments was  obtained from a local distributor and fractionated by
a standard sieve procedure before use.  The -30 +70 fraction (particle
sizes between 210 and 595 microns) wasusedfor all experiments.  The
fine gravel ranged from  3/16 to 1/4 inch in particle size. The size
distribution was between 3/4 and 1 inch for the coarse gravel.

Sediments:  The sediments used for the experiments described in this
report were obtained from the fresh water section of the  Patapsco River
in Maryland.  Two sediment "types" were used.  One sediment (collected
near Baltimore, Maryland, and referred to as Sediment  I) was relatively
rich in sulfur as determined according to the  methods of Vogel (16) and
Carius (17).  Both methods suggested  a sulfur content of about 1% in dry
sediment.  The cation exchange capacity (CEC) of this sediment  was about
10 milli-equivalents (me) per 100 g of sediment as determined by the
method of Toth and Ott (18).  The organic content of Sediment I was
approximately 7%.  This was determined by weight loss at 500C  for
2 hr.  The difference in weight  before and after ignition was  taken as


                      Hg-rich layer


Figure 6. Schematic of laboratory incubation procedure.

the organic fraction and expressed as a percentage of the total weight.
Similar measurements were made on Sediment II,  obtained from the
Patapsco River near Frederick,  Maryland.  The organic content of
Sediment II was about 10%, and the CEC was  19 me per 100 g of dry

Organic and inorganic Hg in sediment: To determine inorganic  Hg in
sediment,  an aliquot of known weight (~ 1 g) •was mixed with 2 ml of con-
centrated acid (H2SC>4 + HNC>3) with KMnC>4  added and kept at  room
temperature for 30 min.  Subsequently, the  sample was made up to 5 ml,
centrifuged at 5000 g,  and the Hg content of  the supernatant was analyzed.
To determine the total Hg content of a sediment, a similar procedure
was followed,  except that the mixture was digested for 20 min at 100C
(19, 20).   The organic content was taken  as  the difference between the
total Hg content of the sediment and the inorganic fraction.

                          SECTION V

                  RESULTS AND DISCUSSION

Retention of mercurials by sediments;  It is to be expected that both
HgCl^ and CH-jHgCl will, to a  given extent,  form complexes with sed-
iment entities.  The extent to which this occurs  depends on the affinity
of both salts for binding sites.  We assumed that the binding ability of a
sediment is reflected by the cation exchange capacity and organic content

An assessment of the ability of sediments to retain inorganic mercury
was made by mixing 1 mg of Hg as HgCl2 with a sediment  slurry con-
taining 10 g (dry weight) of Sediment I in about 40 ml volume.  After a
2-hr incubation period at room temperature,  the liquid fraction was
removed by vacuum filtration (Whatman 41), and the Hg content of the
leachate  was determined.  Subsequently,  the solid fraction was mixed
with diluted HC1, to a final concentration of about IN.   After  2 hr of
incubation, the leachate was removed, and the mercury content was
determined in the acid leachate.  The mercury content of the solid
fraction also was measured.  The observed results,  recorded in Table  1,
show  that a large majority of the  added  inorganic mercury was retained
by the solid sediment fraction.
                          Table  1

Distribution of Hg between solid and liquid phase in 10 g (dry weight) of
sediment mixed with 1000 M-g of Hg as HgCl2-

    Fraction                     M*gHg                   % Total

    Liquid (H2O)                 < 10                    < 1

    Liquid (IN HC1)              < 50                    < 5

    Solid                        800                     90

    % Recovery                                          90-95
Similar measurements were made with CH^HgCl.   The results, recorded
in Table 2,  show that methylmercury is not as readily absorbed as in-
organic mercury.  For example,  whereas water and acid extraction re-
moved only insignificant quantities of inorganic mercury from the

 absorbing complex, about two-thirds of the organic mercury was re-
 moved by this procedure.  The non-ionic nature of methylmercury
 might be responsible for the difference in behavior.  Thus,  once formed
 in the sediment layers,  methylmercury could be released to the over-
 lying water.
                             Table 2

 Distribution of Hg between solid and liquid phase in 10 g (dry weight) of
 sediment mixed with 200 M-g of Hg as CH^HgCl.
Fraction M*gHg
Liquid (H2O ) 58
Liquid (HC1) 80
Solid 50
% Recovery
% Total
Retention of inorganic mercury in the sediment also could occur through its
conversion to a sulfide (HgS).  In contrast, the release of methylmercury
would be enhanced by complexing with sulfur.  As will be discussed
later,  the formation of bismethylmercuric sulfide, (CH3Hg)2S, anorganic
mercurial which is even more toxic than methylmercury,  is likely to
occur under such conditions.  Because of its non-polar nature, the
release.of this compound would occur more readily than methylmercury.
A third organic mercurial that is readily  released from sediments is
the volatile dimethylmercury (Cr^HgCF^), which, according to Wood
and co-workers (5), is formed under alkaline conditions.

The nearly complete absorption of Hg   to the solid fraction is not
surprising, considering the affinity of the  divalent ions for absorption
sites  and the fact that the amounts used are small (about 0. 112 me/100 g
sediment) relative to the cation exchange  capacity of this sediment
(10 me/100 g).

Apparently,  methylmercury is less readily absorbed on the solid sed-
iment fraction.   The relatively low binding capacity of methylmercury is
indicative of the monovalent bond and the  non-ionic nature  of the salt.
Our results indicate that the interstitial liquid and the solid fraction of
the sediment should be  sampled to determine the extent of the  methylation

Uptake of organic and inorganic mercury by guppies; To determine
whether  the mercury present in guppies is of an organic or inorganic
origin, measurements were made of the extent and the rate of Hg up-
take by male guppies exposed to known quantities of either organic or
inorganic mercury.

In these  experiments, usually 8 to 10 guppies -were incubated at about
ZOC in 100 ml aged aquarium water spiked with about 25 [j,g Hg as
CH3HgCl,  (CH3Hg)2S, or HgClz-  At given time intervals, guppies were
removed from the incubator and analyzed  for Hg content by the procedures
described earlier.  Results of a typical series are  presented in Figure 7.

A rapid increase in the Hg content was observed in guppies exposed to
methylmercury  and bismethylmercuric sulfide.  Guppies exposed to the
inorganic mercury also showed increased Hg content, but the total
amounts  retained were much less and did  not increase significantly
with time.

At initial mercury  concentrations of 25p,g of methylmercury per 100 ml
of water, about  1 p,g of Hg accumulated per guppy (average weight was
100 mg).  Occasionally,  values of 2 to 3 |j,g per fish were observed.  At
the lower values, most guppies survived.

Mercury concentrations of 50 ng of methylmercury per  100 ml volume
also were tested; but, at these levels,  most of the animals died within
a 2-hr exposure.

To  test whether guppies quantitatively remove methylmercury from the
medium, 7 guppies were exposed  to 16. 5 |j,g Hg (as CH^HgCl) in 100 ml
water.  After 77 hr   the animals and the medium were  analyzed for Hg,
and only  0. 1  p,g  Hg was found in the medium,  and a total of  12. 5  (ig of Hg
was found in  the  animals, indicating a recovery of about 75%.

The concentration of  methylated mercurials used in the above experiments
is high relative  to values  most likely to be encountered  in contaminated
environments.   A more realistic  approach would use less than one-
hundredth of  that concentration and exposure times of weeks or months.
To  simulate a natural situation more realistically and to  obtain some
estimate of the lower threshold level at which guppies accumulate
organic mercurials,  the rate of accumulation was  determined as a
function  of mercury concentration.  To this end, guppies -were exposed
to concentrations of methylmercury varying between 3 |j,g to  15 |j,g per
liter.  After  36  hr  of exposure, the animals were sacrificed and
analyzed.  The results, illustrated in Figure 8,  show a near-linear
relationship between  mercury accumulation by the guppies and the
mercury content of the liquid.

30         60        90       120

      TIME  (min)
Figure 7.  Time course of mercury assimilation by guppies.

            3       6       9       12
               CH3HgCI (/ig/liter)
Figure 8.  Methylmercury uptake by guppies as a function of concentration.

These findings suggest that guppies will tolerate prolonged exposure
to relatively low concentrations of methylmercury and that they are
capable of concentrating organic mercurials even if present at reason-
ably low concentrations.  At the lower limit used in the above experiments,
a concentration factor of about 1000 was calculated, estimating a guppy's
volume at 0. 3 ml.  On the basis of these results,  the investigators are
confident that the methylmercury formed in the laboratory simulations
(described in the following sections) is accumulated by the fish.

Effect of  sand on the release of organic mercury:  The objective of this
series of experiments was to determine the extent of organic and inorganic
mercury  release from mercury-enriched  sediments covered by layers of
sand of varying thickness.  The procedure is based on Swedish observations
(22) that mercury-rich layers become inactive rapidly when covered with
2 to 10 cm of mercury-poor sediment. To evaluate the efficacy of this
"burying procedure, " a laboratory simulation was  carried out using sed-
iments enriched with mercuric chloride (200 M-g of  Hg/g of dry sediment)
and covered with layers of sand 0, 1.5, 3, and 6 cm in thickness.  (The
stratification is illustrated in Figure 6.)  Incubators were supplied with
at least 6 guppies each, and,  after a 4-week incubation,  the mercury
content was determined in the fish,  in the overlying water, in the  enriched
sediment layers, in the sand.and in the sediments beneath the enriched
layers,.  It was assumed that this type of  analysis would provide some
indication of the extent of the mercury's vertical transport through the
sediment and sand layers.

The data on mercury accumulation by guppies are recorded in  Tables  3
and 4.  On the basis of the observed data, it is  apparent that the for-
mation of methylmercury is low in those incubators supplied with a sand
cover  of 6 cm over the mercury-enriched layer.  Although the mercury
accumxilation by fish varied widely with sand covers of  1. 5 and 3 cm,  it
appears that this overburden is only partially effective in controlling
the release of methylmercury.

Experiments reported in Tables  3 and 4 were conducted with Sediment I
and Sediment II differing in organic content (7% vs 10%) and cation ex-
change capacity (10  me vs 19 me).   Considering prevailing experimental
conditions and the obtained results, it appears that these  sediment
parameters have little  effect on the release of toxic mercurials.

In all incubators with 1. 5 cm of sand,  and in a few with 3 cm, a build-up
of black material on top of the sand layers was observed.  This  material
•was due to the activity  of  sludge worms (Tubificidae) present in large
quantities of Sediment I (obtained 2 miles below a sewage outfall).  The
mercury content of the worms' rejects was measured; as expected, this

content was quite similar to that in the mercury-enriched layer of the
experimental series.  In the control  series, no mercury was detected.
Although a similar build-up •was not observed in incubators with 6 cm
of sand, the  results suggest that in areas where the sludge fauna carries
on its function actively,  additional coverage might be required.  Besides
the conveyance of mercury by sludge worms, vertical transfer apparently
•was limited,  since only  small amounts of mercury were detected in the
sand and sediment  above and below the enriched layer.  (See Table 5. )
Sediment II,  collected far from sewage outfalls, did not exhibit this
sludge worm activity.  Therefore, a shallower sand overburden would
control the release from a  sediment  typified by Sediment II.
                           Table 3

Effect of sand overburden on the mercury content (|j,g) of surviving
guppies incubated for 3 weeks using Sediment I enriched with
                                      Sand Overburden

      Additions            0 cm      1. 5 cm     3 cm        6 cm
          f  n            0.3       0.2        0.2          0.2
      HgCl2               No        2.5        2.5          0.5
      Enriched            survivors

      HgCl2               3.5       3.3        1.0          0.4

         Note:   Due to animal mortality,  only a few fish
                 were available for analyses at the end of
                 the 3-week incubation.  Results reported
                 here are based on the analysis of 2 fish
                 and are expressed as (j,g Hg/g fish.

                           Table 4

Effect of sand overburden on the mercury content (M-g) of surviving
guppies incubated for 4 weeks using Sediment II enriched with
0 cm
Sand Overburden
     1. 5 cm     3 cm
            6 cm
0. 1
0. 2
5. 0
2. 1
4. 3
0. 1
0. 1
0. 1
2. 1
0. 3
0. 1
0. 1
1. 0
0. 3
0. 1
0. 1
0. 1
0. 1
        Note:   Each value indicates an individual animal and is
                expressed in M-g of Hg/g of fish.
                           Table 5

Mercury content of sand and sediment above and below Hg-enriched
                  0 cm          1. 5 cm     3 cm        6 cm
(M.g Hg/g sand)

(5 cm beneath
enriched layer)
(M-g Hg/g sediment)
                0. 5
0. 1
1. 5
         Note:   For details, see Table 3.

The pH of the liquid phase also was measured and  analyzed for mercury
content. Although the initial pH value of the -water  in all incubators was
slightly acidic (6. 7 to 6. 9),  alkaline values were observed in all incubators
at the end of the  3-week incubation.  Considering the algal growth observed
in most incubators,  the rise in pH might be due to a significant decline in
the carbon dioxide content of the water.

As recorded in Table 6, algal  concentrations of incubators supplied with
0 and 1. 5 cm of sand were relatively high in comparison to values
observed with 3 and 6 cm of sand.   However, these values might be mis-
leading since, in the latter cases,  algal growth along the walls was
significant,  and representative sampling -was virtually impossible.
Although no attempts were made to determine the specific  distribution,
it appeared  from the color that blue-green algae were predominant in in-
cubators with 3 and  6 cm;  green varieties appeared to dominate in in-
cubators supplied with 0 and 1. 5 cm of sand.  It is  not known whether
sand constituents or differences in the rate of nutrient release from
the sediment is the principal cause of the phenomenon.
                            Table 6
Mercury content of the liquid phase at the end of a 3-week incubation
using Sediment I.
                   0 cm

               1. 5 cm     3 cm
                        6 cm
    Total Hg
    Total Hg
    (mg/liter )
. 5
         Note;  0.45 micron (Millipore) filter was used.
                The algal content was derived from  chlorophyll
                estimation.   To determine this content,  an 80%
                acetone extract was prepared and read at 663 nm.
                To convert chlorophyll  concentration to algal con-
                centration,  a content of 2% dry weight was  assumed.

Significant quantities of mercury were observed in the water (see
Table 6).   This  "suspended" mercury apparently was present on or
in the algal cells,  since  it could be removed almost completely from
the liquid phase by filtration over 0.45 micron filters (Millipore).  As
shown in Table 6,  at least 90% of  the mercury remained on the filter.
This fraction was  found to be inorganic in nature.

Comparison of sand and  fine and coarse gravel;  A layer of sand 6 cm
in thickness controlled the release of organic mercury to the overlying
water.  To examine tne usefulness of other aggregates, the  effectiveness
of fine gravel (5 to 6 mm) and coarse gravel (18 to 25 mm) was compared
with sand.   (This type of coarse gravel is used routinely in the preparation
of "popcorn" concrete.  Popcorn concrete was not tested because it was
felt that the addition of cement would significantly increase the pH and
thus invalidate the comparison with other aggregates. )  In this comparison,
6-cm layers of the two grades of gravel •were used instead of sand (see
Figure 6).   This series employed two experimental (+Hg) and one control
(-Hg) incubator.  Incubation time was 3 -weeks.

The results, recorded in Table 7, revealed that coarse and  fine gravel
are as effective as sand  in controlling the release of toxic mercury.  In
laboratory experiments,   the use of gravel required less precaution than
for sand,  but it remains to be seen whether this also holds true for
field application.
                           Table 7

Effect of a 6-cm overburden of sand or gravel on the mercury content
(p,g) °f surviving guppies incubated for 3 weeks in the  presence of
Sediment II  enriched with
Aggregate                 Sand             Fine gravel    Coarse gravel
Size distribution (mm)     0. 2 to 0. 6        5 to 6          19 to 25

No Hg added              0. 1  0. 2         0. 2  0. 3       0. 2   0. 3
                          0.2  0.2         0.3  0.2       0.3   0.3
HgC 2,                    0.2  0.2         0.2  0.2       0.3   0.3
Enriched                  0.2  0.2         0.2  0.2       0.3   0.3
      Note:  Content is based on values of individual
             animals and expressed in y,g Hg/g fish.

To demonstrate and summarize the effect of a 6-cm sand or gravel
overburden on mercury abatement,  all data observed in the presence
of a 6-cm cover (irrespective of sediment type and the nature of the
cover material) and in  the absence of a cover were pooled separately
and compared to the pooled control values.  Results,  illustrated in
Figure 9, show that a 6-cm cover surpresses the release of toxic
mercurials from contaminated sediments.  Comparisons  of the  cal-
culated means  and the standard deviations indicate the soundness of the
observed data.

Effect of anaerobioses  on release of toxic mercury; Wood and co-workers
(5) reported that anaerobically incubated extracts of methanogenic bacteria
stimulate the conversion of inorganic mercury into methylmercury.   If
a similar conversion occurs in sediments,  one would expect tne production
of methylmercury to be relatively high under strictly anaerobic  conditions.
This aspect -was examined by comparing methylmercury formation in an
anaerobic sediment (argon equilibrated) to an aerobic sediment  (air
equilibrated).   Containers similar in design to those used for aerobic
experiments were fitted with male and female ground joints and used as
anaerobic incubators.

After a one-month incubation, the liquid phases were removed from both
series, filtered over Whatman #40 filter paper,  adjusted  to pH 6. 5 with
HC1, and flushed with air to remove  volatile gases  (H2S,  CH4) and to
raise the level of dissolved oxygen.   Subsequently,  eight guppies were
added to  the liquid, and the mercury content of the guppies was  deter-
mined after two and five days of exposure.  To obtain a rough estimate of
the residual organic mercury in the sediment, part of the enriched layer
was removed from the  incubators and extracted with IN HC1.  It was
assumed that acid extraction would remove the loosely bound toxic
mercurials. After neutralization with NaOH, guppies were added to
the extract, incubated for a  day,  and, subsequently, analyzed as usual.

The results, recorded  in Table 8, showed that the concentration of toxic
mercury (i. e. , guppy assimilable) is higher in the anaerobic incubator
than in the aerobic incubator.  Considering the residual mercury content
of the sediment (as analyzed in the  IN HC1 extract),  it appears  that the
toxic mercury  is released to the liquid phase under anaerobic conditions,
but it is retained,  at least in part,  under aerobic conditions.

The investigators  cannot offer a reasonable explanation for the observed
difference.  Conceivably, the organic fraction constitutes a significant
part of the ion  exchange capacity of  this sediment, and anaerobiosis
could have adversely affected its capability to retain ions.  From  these
qualitative results  one would conclude that aerobic and  anaerobic

 w  2.0
         .15 ±.01 (erg)

                                      ( DATA FROM
                                      TABLES 3, 4 AND 7)
Figure 9.  Effect of protective cover 6 cm in depth on mercury
         accumulation by guppies.

conditions stimulate the formation of toxic mercury to about the same
extent,  but that strong anaerobic conditions enhance the  release of toxic
mercury from the sediment.
                          Table 8

Estimate of mercury content (|j,g) in the liquid phases and acid extracts
of mercury-enriched sediments incubated aerobically or anaerobically.

                          Aerobically      Anaerobically
                          incubated        incubated

         Wa tor
          ,                0.2 to 0.3        5 to 6

         Acid             1.4 to 1.8        0.5 to 0.6

             Note: Values represent the content of mercury per
                   incubator (4 liters) and are rough estimates

In a parallel experiment, mass spectrometric analysis was used to deter-
mine the formation of methane in the anaerobic incubator.  A gradual
increase in the methane concentration was observed.  The rate of in-
crease appeared to follow first-order kinetics, indicative of a logarithmic
cell reproduction.  At the end of a  one-month incubation,  about 900 ^mole
CH^ was formed per  100 g sediment.  In the  same period and calculated
on an equimolar basis,  approximately 0. 03 ^mole of methylmercury  was
formed.  Apparently, the rate of methylmercury formation is small
relative  to the rate of methane formation, suggesting that both products
are formed independently.

Effect of redox state  on release of  mercury;  Results discussed thus  far
are concerned with transformations of mercuric chloride into organic
mercurials.  From a toxicological point of view,  the latter are of
principal concern.  Transformations leading  to their formation are
depicted in Figure 10.

In the general scheme,  other inter conversions also must be considered,
both in connection with abatement procedures and the translocation of
mercury.  Although little is  known about the  importance  of reactions
leading to the formation of mercury complexes in a sediment, intuitively
one would assume that  inorganic and humic entities of the sediment play

      ^ Hg dimethylmercury

  CI-LHg monomethylmercury
                                   (CH,HgL S bismethylmercuric
                                      *   L       sulfide
Figure 10.  Transformation pathways of mercury and its derivatives in
           aquatic environment.

an important role in stabilizing mercury contaminated sediments.  This
aspect was examined previously (see Tables  1 and 2).  The formation
of the relatively insoluble mercuric sulfide (HgS) must be considered
as another stabilizing factor.  Its formation and its ultimate fate is
determined,  to a large extent, by the redox state of the sediment.

The measured redox state of sediments is largely a function of the micro-
bial activity,  the presence of oxygen, and the availability of degradable
organic substances.  Reducing conditions usually result if aeration is
relatively low, and these conditions promote the formation of insoluble
sulfides (25).  The extent to which this occurs depends upon the avail-
ability of sulfur.  If sulfur is limited and mercury is available in an
ionic form (Hg++),  reduction to metallic mercury (Hg°) will occur.
Since the redox  state  of  a sediment can be assessed by using simple
sensing probes, its value assumes significance principally because it
can be used in the field as a convenient indicator of the hazard posed
by a mercury-laden sediment.  Therefore, the investigators assessed
the effect of the redox state on the release of metallic  mercury by an
aerobic,  i. e. , high-redox potential,  sediment and by an anaerobic,  or
low-redox potential,  sediment.

The high-redox  potential  sediment was obtained by  drying material in
air overnight  at room temperature.  Subsequently, 30 g of this material
was added to 100 ml distilled water,  mixed thoroughly, and transferred
to the sediment  chamber  illustrated in  Figure 5.  The  Eh of the pre-
pared sediment  was about 450 mV (Orion 96-78-00).  Various amounts
of HgCl2 were added through the entrance port  (see Figure  5),  and the
release of Hg° was measured as a function of time.  The results are
illustrated in  Figure  11.

The amount of metallic mercury evolved from an aerobic sediment was
dependent on the relative amount of mercuric chloride added to it.  The
release pattern  observed upon addition of different  amounts of HgCl2 to
a constant amount of sediment (30  g), presented in  Figure  11, also was
observed when the sediment was increased and the  mercury content of
the liquid was held constant.

Figure 11 also shows that the rate of Hg° evolution increased gradually
upon addition  of HgCl2 until,  about an hour later, a steady state value
was attained.  To determine the rate of Hg° formation, the efflux was
scrubbed by the solution  of nitric acid  and sulfuric acid, and the
mercury content of the solution was determined by  the usual procedure.
It was found that approximately 1  ^g of Hg° was released per min by
30 g of sediment enriched with 100 mg  of HgCl2 and flushed with about
100 cc of air per min.

     320 -
30g (dry weight)
Aerobic Sediment
Suspended in
100ml distilled
                               (20mg HgCI2
                               (lOmg HgCl2)
10    20     30    40
                           TIME (min)
Figure 11.  Rate of Hg evolution from aerobic sediments spiked with

The release of metallic mercury from anaerobic sediments appeared to
follow different kinetics.   For example, the addition of 50 p-g of HgCl-,
to an anaerobic sediment (Eh = ~ 50 mV) resulted in an immediate re-
lease of substantial amounts of metallic mercury (Figure 12,  curve 1).
Subsequent addition of 50 pig each  increased the rate of Hg° evolution
until, after 4 additions,  the rate of release became constant at about
1 p,g of  Hg° per min (Figure 12, curve 4).

A comparison between the two sediments reveals other differences as
well. For example, whereas Hg°  evolution was at its  maximum at
200 fig of HgCl2 per 30 g of anaerobic sediment, about 500 times as
much HgCl2 was required for the production of a similar  amount of Hg°
from the aerobic sediment.  Although no effect was observed if HgCl2
was added to an aerobic  sediment,  a 200 ug dose of HgCl2 added to an
anaerobic  sediment produced a Hg° gush of a magnitude that was be-
yond the measuring range  of the apparatus.

From the above, it appears that at least two processes control the  re-
lease of metallic mercury in sediments.  The slow process, as seen
with the aerobic sediment,  could be a reflection of biological activity.
Tonomura et al (26, 27)  reported the "bio-conversion" of organic mercury
into metallic mercury carried out by mercury-resistant microorganisms.
However, it is not clear whether this  conversion was active or passive
in nature.  In sediments, a physico-chemical process  could be responsible
for the  conversion of Hg++ into metallic mercury. A slow release  of
electrons, due to a biological  process, could lead to the reduction  to
Hg°.  As will be discussed later, once the divalent ion is  complexed
•with a sediment entity or is converted into mercuric sulfide, it is much
less likely to be converted into the metallic form.

The fast process observed with anaerobic sediments undoubtedly is due
to a chemical reduction of HgCl2 according to Hg"1"1" + 2e—^Hg°.  In an
anaerobic sediment, a pool of  various reduced entities could provide
electrons for such a reduction. This point was investigated by using
ascorbate as an electron donor •with (a)  aerobic sediment, (b) anaerobic
sediment, and (c) water.  In all three cases,  metallic mercury was  pro-
duced from HgCl2 if ascorbate also was present.

In effect,  a stochiometric  relationship was observed between the mercury
gush and ascorbate addition  il HgCl2 was added immediately after the
addition of ascorbate.  However, if HgCl2 was thoroughly mixed with
the aerobic sediment and ascorbate added later,  no mercury gush
occurred,and normal release kinetics were observed.  It made no
difference whether  aerobic sediment or an artificial resin was used.
The latter (Chelex  100) retained Hg~l~+ (28) as firmly as  the sediment, and

 ±. 160
       30g (dry weight)
       Anaerobic Sediment
       Suspended in 100ml
       distilled water
                           TIME (min)
Figure 12.  Rate of Hg° evolution from anaerobic sediments spiked
           with 50 ug of HgCl2.

ascorbate was unable to reduce the divalent ion and release it in the
metallic form.

These observations strongly suggest that once the divalent ion is con-
verted into the  sulfide form or complexed with a sediment entity
(probably most of them are organic  in nature), the ion no longer is
readily reduced by natural electron  donors or artificial ones with a re-
ducing potential equal to that of ascorbate.  One is tempted to draw a
similar conclusion for enzymatic and non-enzymatic reductions.
                                                         UBBARX ua. ifJ»

                          SECTION VI


In the laboratory simulation program, the use of sand and gravel was
tested as a means of preventing the release of toxic mercury from
mercury-enriched bottom sediments.  This laboratory simulation led
to the conclusion that common sand and  fine or coarse gravel,  applied
to a thickness of about 2 to 3 inches, can virtually eliminate the release
of toxic mercurials from contaminated sediments.  In this section, the
approximate cost of applying this  abatement procedure in the field is

Trenton Channel of the  Detroit River near Wyandotte was selected as a
"representative" location.  The channel varies from approximately  1/8
mile to 1/4 mile in •width.  The landside depth is about 13 ft, the channel
depth is 28 ft, and the depth on the island side is 4 ft.  The area of
interest is a 200-ft-wide and one-mile-long band on the Michigan side
immediately below Wyandotte Chemical  Company. This  strip is known
to be heavily contaminated with mercury (1).

These  economic projections assume the use of the cheapest grade of sand
selling at about  $. 95  a yard (approximately  1. 5 ton).  (Gravel is not con-
sidered separately since  the cost  of application appears very similar to
that of sand. ) Considering typical trucking, loading,  and unloading
charges,  the price increases to $2. 25 a yard in  a scow at dockside.
Since the overland transportation  costs are  significant,  the possibility
of a waterborne source of supply--possibly from a nearby dredging
operation—was  explored.   The nearest large-scale sand mining oper-
ation is in Lake Erie and, although materials of various  grades are
shipped to the Detroit area, this source appeared not to be competitive
with pit sources in Michigan--at least in the cheap, low-grade,  sand

A number of application methods were considered, but a barge-mounted
system appeared to be the most adaptable  and economical.  This system
consists of a fixed-boom  clam shell, feeding a conveyor belt that
delivers the material to a swivel-type sand piler.  A clam shell -with a
2-1/2 to 3-yard bucket can load a conveyor at the rate of about 200 tons
per hour.  The swivel piler would be a 16-inch unit,  handling  about
200 tons per hour, allowing maximum use of the piler.  A swivel piler
can spread sand or other  small-lump aggregate  material over a 270°
arc.  Depending upon the  speed of the barge, swivel motion, and sedi-
mentation characteristics at the locale,  a fairly even layer of material
could be applied over the  mercury-laden sediments.

The distribution equipment would be assembled on a small equipment
barge at Wayndotte, towed to the  site, and anchored there.  A tug would
deliver sand-filled  800- to 1000-yard-capacity scows alongside the
barge-mounted  equipment as  a supply source.  Ideally, the tug would
tow enough material to the site during the early morning to allow
continual operation of the  spreading machinery during the daylight hours.

Table 9 presents estimates of the fixed and variable costs  associated
with this hypothetical  case.  The following assumptions were made:
(a) the site is near enough to  port for the tug to return empty sand scows
at night and to deliver loaded ones by early morning, (b) weather  conditions
are ideal,  (c) traffic at the site is negligible, and (d) no machinery down-
time is experienced.
                            Table 9

Estimated fixed/variable costs of distributing sand in an area south of

    Fixed Costs:

       Spreading Equipment System                         $20, 000. 00
       (i. e. ,  swivel piler, conveyor,  clam
       shell,  fixtures, hopper, etc. )

    Variable Costs;

       Sand,  dockside, per yard                                  2.25

       Tug boat and crew, per 12-hour day                    1, 900. 00

       Deck scow, 800-to 1000-yard capacity, per day            100.00

       Equipment barge,  per day                                 30. 00

       Labor, per day (2)                                       80.00

       Equipment maintenance, per day                          10. 00

Based on these considerations, the cost of applying 3 inches  of sand to
2-,  25™,  and 50-acre areas was estimated.  The results,  shown in
Table  10,  suggest that the overall cost of application •would increase
linearly as a function of  the size of the area treated.

                           Table 10

Estimate of the cost involved in the application of 3 inches of sand to
2, 25, and 50 acres of sediment contaminated with mercury.
                                      Number of Acres
                             2               25*50
    Fixed Costs ($):

    Variable Cost($):
20, 000
20,000          20,000
Tug rental
Scow rental
Number of days
Yards of sand
1, 670
1, 900
20, 800
24, 700
1, 300
1, 040
48, 360
47, 500
2, 500
2, 000
*  An area of this size is used as an example in the discussion.
The preliminary nature of this cost evaluation is recognized.   Such
factors as the local conditions of transportation,  the actual sediment
characteristics, the accessibility and topography of the site, water
currents and depth, prevailing weather conditions,  and the availability
of labor, materials,and hardware have an impact on the cost.  Such
factors,  which are site-dependent,  could not be fully evaluated at
this time.

                         SECTION VII


The authors wish to thank Dr.  Ed H. Parkison and Messrs. Donald R.
Talbot,  Werner F. Furth, Otto J.  Ollinger, and Thomas J. Quinn of
RIAS for their  contributions  to the work presented in this report.  The
many discussions  of the complexities associated with the mercury abate-
ment problem during the course of this work with Drs. George M. Cheniae,
Bessel Kok.and Kenneth L.  Zankel, also of RIAS, have been very helpful.
The discussions with Dr. Curtis C. Harlin,  Jr. ,  Project Officer, Robert S.
Kerr Water Research Center,  EPA, Ada, Oklahoma, have been partic-
ularly stimulating.

                         SECTION VIII


1.  Turney, G.W., "Mercury Pollution:  Michigan's Action Program, "
    J. Water Pollution Control Federation,  43,  7, pp  1427-1439 (1971).

2.  Ackefores,  H. , "Effects of Particular Pollutants; Mercury Pollution
    in Sweden with Special Reference to Conditions in the Water Habitat, "
    Proc.  Roy. Soc. London B,  177,  pp   365-387 (1971).

3.  Westoo, G. , "Methylmercury Compounds in Animal Foods, " Chemical
    Fallout, Charles C. Thomas,  Springfield, 111.,  pp   75-93  (1969).

4.  Berglund,  F. , and Berlin,  M. , "Risk of Methylmercury Cumulation
    in Man and Mammals, "  Chemical Fallout, pp  258-273 (1969).

5.  Wood,  J. M. ,  Kennedy,  F.S., and Rosen, C.G. , "Synthesis of
    Methylmercury Compounds by Extracts of a Methanogenic  Bacterium, "
    Nature,  (London) 220, pp 173, 174 (1968).

6.  Jensen,  S. , and Jernelov, A. , "Biological Methylation of Mercury
    in Aquatic Organisms," Nature,  (London),  223,  pp 753, 754 (1969).

7.  Bertilsson, L. , and Neujahr,  H. Y. ,   "Methylation of Mercury Com-
    pounds by Methylcobalamin, " Biochemistry,  10, 14,  pp 2805-2808

8.  Nelson,  N. , et al,  "Hazards  of Mercury, " Environmental  Research,
    4, pp 29-31 (1970).

9.  Hatch,  R. ,  and Ott, W. L. , "Determination  of Sub-Microgram
    Quantities of Mercury by Atomic Absorption Spectrophotometry, "
    Anal.  Chem. 40, pp 2085-2087 (1968).

10. Perkin-Elmer Corporation, "Mercury Analysis  System, " Operating
    Directions 303-2119, Norwalk, Connecticut, March  (1971).

11. Kalb,  G. W. ,  "The Determination of Mercury in Water and Sediment
    Samples by Flameless Atomic Absorption, " Atomic  Absorption
    Newsletter, 9, 4 pp 84-87 (1970).

12. Uthe,  J. F. , Armstrong, F. A. J. ,  and Stainton,  M. P. , "Mercury
    Determination in Fish Samples by Wet Digestion and Flameless
    Atomic Absorption Spectrophotometry, " J. Fisheries Res. Board
    Can.,  27,  pp 805 (1970).

13. Westoo, G. , "Determination of Methylmercury Compounds in Food
    Stuffs, " Acta.  Chem.  Scand. , 20,  pp 2131-2137 (1966).

14. Dadii,  M. , Grdenic,  D. ,  "Preparation of Bismethylmercury Sulfide, "
    Croat.  Chem.  Acta. ,  32,  pp 39 (1969).

15. Jernelov,  A. ,  "Release of Methylmercury from Sediments with Layers
    Containing Inorganic Mercury at Different Depths,"  Limol. Oceanog. ,
    15, pp 958-960 (1970).

16. Vogel,  A. I. , "Determination of Sulfur, " Quantitative Inorganic
    Analysis,  Wiley and Sons, N. Y. ,  pp 408-721 (1961).

17. Steyermark, A. , "Determination of Sulfur, " Quantitative Organic
    Micro Analysis,  Acad. Press. N. Y. , pp 277-290 (1968).

18. Toth, S. J. , and Ott,  A. N. ,  "Characterization of Bottom Sediments :
    Cation Exchange  Capacity and Exchangeable Cation Status, " Environ-
    mental  Sci. and Technology,  4, pp 945-939  (1970).

19. Gorgia,  A. ,  and  Monnier, D. , "Determination of Mercury (II) in the
    Presence of Organic Mercurials, " Anal. Chem. Acta. ,  54, pp 505-
    570 (1971).

20. Magos, I. , "Selective Atomic-Absorption Determination of Inorganic
    Mercury  and Methylmercury in Undigested Biological Samples, "
    Analyst. 96, pp 847-858 (1971).

21. Hugget,  R. J. ,  Bender, M. E. , and Slone, H. D. ,  "Mercury in
    Sediments from Three Virginia Estuaries, " Chesapeake Science,
    III, pp 280-282 (1971).

22. Jernelov, A. ,  "Conversion of Mercury Compounds, " Chemical
    Fallout, Charles C. Thomas,  Springfield, 111., pp 68-74 (1969).

23. Tatton, J. O'G. , and  Wagstaffe,  P.J.,  "Identification and Deter -
    mination of Organic Mercurial Fungicide Residues by Thin-Layer
    and Gas Chromatography,  " J. Chromatog. ,  44,  pp 284-289 (1969).

24. Chau,  Y. K. , and Saitoh,  H.  , "Determination of Submicrogram
    Quantities of Mercury in Lake Water, " Environmental Science and
    Technology,  4, 10, pp 839-841 (1970).

25. Stumm, W. , and Morgan,  J. J. ,  "Oxidation  and Reduction, " Aquatic
    Chemistry, Wiley-Intersc. ,  N. Y. ,  pp 300-379 (1970).

26. Tonomura,  K. ,  Maeda,  K. ,  Futai, F., Nakagami,  T. ,  and Yamada,
    M. ,  "Stimulative Vaporization of Phenyl Mercuric Acetate by
    Mercury-Resistant Bacteria, " Nature,  27,  pp 644-646 (1968).

27. Tonomura,  K. , and Kanzaki, F. , "The Reductive Decomposition
    of Organic Mercurials by Cell Free Extract of Mercury Resistant
    Pseudomonad, " Biochim. Biophys. Acta, 184, pp 227-229 (1969).

28. Law,  S. L. , "Methylmercury and Inorganic  Mercury Collection by
    a Selective Chelating Resin, " Science,  174, pp 285-286  (1971).

Ac cess; on Number

Subject field
Organization _ , _ ,•,,/•
Research Institute for
& Group
Advanced Studies (RIAS)
               Martin Marietta Corporation
               1450 South Rolling Road, Baltimore, Maryland 21227
               Sand and Gravel Overlay for
               Control  of Mercury in Sediments

Leonard H.
N. Khattak

Project Designad'on
EPA, Project Code #16080 HVA,
r.nmtrari- #68-01-0089
Descriptors (Starred First)

Mercury Abatement; Organic Mercury,  Methylmercury, Release of Mercury;
Mercuric Sulfide Formation; Fate of Mercury in Sediment Environment
     Identifiers (Starred First)
     Mercury pollution control, methylated mercurials
  The release of toxic mercurials by mercury-enriched river sediments was examined in
  the laboratory.   Tests showed a release of 1 ^g of methylmercury per m^, per day.
  Methylmercury occurred in sediments with low and with high organic  content, in sed-
  iments with low and high cation exchange capacity,  and  in aerobic and anaerobic
  sediments.  The release of toxic mercury could be prevented by a layer of sand, 6 cm
  in thickness,  applied over  the mercury-enriched sediments.  Layers  of fine or coarse
  gravel (6 cm deep) were as effective as sand.  Thinner  layers of sand, (1.5 and 3 cm)
  were  unsatisfactory.  The  cost of applying 3-inch layers of sand or  gravel was about
  $3000 to $4000 per acre.  A slow release of metallic  mercury occurred in aerobic
  sediments.  The release was much faster in anaerobic  sediments.  Using ascorbate as
  an artificial electron donor, metallic mercury could be released at  high rates from
  aerobic  sediments as  well.  Ascorbate appeared to be a useful indicator of divalent and
  biologically accessible mercury.  The laboratory investigations proved the soundness
  of the sand  blanket approach.  Its practical and economic feasibility must be determined
  in a combined field and laboratory analysis program.