SEPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens, GA 30613-7799
Research and Development EPA/600/M-90/004 July 1990
ENVIRONMENTAL
RESEARCH BRIEF
Sorption of Heavy Metals by Intact Microorganisms, Cell Walls, and Clay-
Wall Composites
M. D. Mullen1, T.J Beveridge2, F. G. Ferris2, D. C. Wolf3, and G. W. Bailey4
Abstract
Sorption of Ag + , Cd2', Cu2*. and La?~ from solution by
four bacteria, Bacillus cereus, B. subtilis, Escherichia coli,
and Pseudomonas aeruginosa, and two fungi, Aspergillus
mger and Mucor rouxii, was examined. Metal sorption was
assessed using Freundlich adsorption isotherms to
partitioning of these metals between the solution and
microbial biomass phases. Precipitation of Ag and La by the
bacteria precluded the use of the Freundlich isotherm for
these metals. Freundlich K values for bacterial sorption of
Cd and Cu ranged from 0.389 to 1.067 and 2.188 to 4.150,
respectively. The affinity series for bacterial sorption of
these metals decreased in the order Ag > La > Cu > Cd.
Mean K values for fungal metal sorption were 2.235, 0.098,
0.818, and 4.290 for Ag, Cd, Cu, and La, respectively. The
fungal affinity series was La > Ag > Cu > Cd.
To further define toxic heavy metal sorption by bacterial
surfaces, walls from representative gram-negative (E. coli)
(E) and gram-positive (B. subtilis} (B) bacteria were isolated
and purified, and compared to smectite (S) and kaolinite (K)
Department of Agriculture and Natural Resources. University of
Tennessee-Martin, Martin. TN 38238
Department of Microbiology, CBS, University of Guelph.Guelph,
Canada NIG 2W1
Department of Agronomy, University of Arkansas. Fayetteville. AR
72701
Environmental Research Laboratory. U.S. Environmental Protection
Agency,Athens. GA 30613-7799
with regards to metal binding capacity. Metal binding
decreased in the order B>E>S>Kfora group of
metals consisting of Ag, Cu. Ni. Cd, Pb, Zn, and Cr. High
levels of metal immobilization tn B and E were the result of
surface-associated heavy metal precipitates. Adsorption
isotherms were constructed for wall-clay interactions and
clearly showed that there were strong interactions between
each clay and each wall type to form composite aggregates.
The composites utilized a variable proportion of the innate
reactive sites available to heavy metal ions and resulted in
lower concentrations of immobilized metals
Binding capacity was in the order B + S > B + K >
E + S > E + K and it was apparent that the biological
constituents dominated the immobilization process.
Experiments were designed to remobilize three bound
metals (Ag, Cu and Cr) and relied on several parameters -
pH fluctuation, metal chelation by outside agents (EDTA),
metal complexation by natural organic acids (fulvic acid),
competition for binding sites by non-toxic metal ions (Ca2 + ),
and enzyme hydrolysis of the wall fabric (lysozyme). The
results of these experiments suggested that there was no
easily observed trend for remobilization; each particulate
component, each composite, and each metal had a distinct
influence on the ease of heavy metal remobifization.
Increased knowledge of the metal sorption capacity of
microbial cells and their cell walls should enable us to better
predict the fate of metals introduced into the environment,
and may also be of value for enhanced utilization of
microbial cells in renovation and metal recovery from
municipal and industrial wastewaters.
-------
Background
Adsorption-desorption processes regulate the fxtent of
binding that exists betyveen a given solid surface and a
chemical species in solution. Adsorption refers to a'process
whereby solutes such as metal ions adhere tola solid
surface such as that presented by microbial cells. In the
environment, mineral and organic surfaces in soils and
sediments are the principal sites of metal ion adsorption.
One important organic surface category that has riot been
extensively studied is that possessed by microorganisms.
The cell surfaces of bacteria and fungi have chemical
properties that could play important roles in the adsorption
and mass partitioning of ,metal ions. , To conduqt a risk
assessment of potential heavy metal contamination of
terrestrial and aquatic ecosystems, it is necessary to
quantitate the magnitude of metal adsorption to biological
surfaces. \
The information available, on metal adsorption by
microbial surfaces is rather limited, and most of it has been
published in the last 20 years. Bacteria behave as colloidal
particles in aqueous systems and have a pH-dependent net
negative surface charge1. Metal binding studies of Bacterial
cell walls have demonstrated that these surfaces are
capable of removing appreciable quantities of a variety of
metals 2- 3. Isolated cell walls of the gram-positive bacteria
B. subtilis and B. licheniformis bound "larger quantities than
cell envelopes of th'e gram-negative bacterium E.\ coli 2.
Metal ion uptake by the fungus Rhizopus arrhiziis was
found to be'directly related to the Ionic radii of some ten
metals tested, and it was concluded that adsorption of the
metals occurred at sites in and on the cell that contained
phosphate and carboxylate groups 4.
Information on partitioning of heavy metals in tejrestrial
and aquatic ecosystems is not complete. Increased
knowledge of heavy metal partition coefficients between
aqueous solutions and solid surfaces will enable us to more
accurately predict heavy metal behavior in the environment
and, thus, more carefully assess potential toxic heav^ metal
exposure. Specifically, this information will aid Jin the
development of risk assessment models. It will aid in our
understanding of the mobility and fate of metals in both
surface and groundwaters. Land application of municipal
sewage sludge and disposal of heavy metal-containing
hazardous wastes are also areas where information
regarding metal partition coefficients Is crucial An
additional area where heavy metal adsorption to bacteria
and other biomass is particularly important is [in the
understanding of metal partitioning in municipal and
industrial wastewater treatment facilities and their evaluation
relative to metal removal efficiency. I
Laboratory Procedures j
Intact Microbial Cell Studies \
Bacterial cells of B. cereus strain ATCC 117|78 P
aeruginosa strain ATCC 14886, B. subtilis 168 and £ coli
K-12 strain AB264 were maintained and cultured as
previously described s. The fungi examined were A\ niger
ATCC 34467 and M. rouxii ATCC 24905. Fungal celte were
harvested by vacuum filtration and washed with 3 volumes
of cold, 10 mM Ca(N03)2 solution. Portions of moist'fungal
biomass were weighed, placed in 10-mL polypropylene
tubes, and 8 ml. of Ca(NO3)2 were added. The cells were "
stored at 5°C for approximately 2 h prior to use. Mpisture
determinations were done on six subsamples to determine
the dry weight added to the tubes.
Nitrate salts of Ag*, Cd2*, Cu2*, and La3* were used.
All metal solutions were made in "pH 4, 10TnM Ca(N03)2
solutions to minimize precipitation of metals and differences
in ionic strength across metal concentrations. Initial metal
concentrations for the bacterial experiments were: 1 0 1
0.01, and 0.001 mM Cd2 + ; 1, 0.1, 0.01 and 0.005 mM Cu2 + ;
and 10, 1, 0.1, and 0.01 mM for Ag + and La3*. Equilibrium
concentrations of both Ag and La were typically below
detection limits at initial concentrations of 0.01 mM or less.
For fungal sorption experiments, initial concentrations of all
metals were 1, 0.1, 0,01, and 0.005 mM.
Bacterial metal sorption was determined by
equilibrating cells in the metal solutions at a concentration of
2 to 3 mg dry wt mL-1. The cell suspensions for all
microorganisms were equilibrated for 2 h at 5 °C on a
rotating shaker. Timed equilibration experiments indicated
that metal sorption was relatively constant within the 2 h
time. After equilibration, bacterial cells were removed from
solution by centnfugation and fungal cells were removed by
filtration through 0.45-nm membrane filters. Concentrations
of metal in solution were determined by inductively coupled
argon plasma spectroscopy. Sorption is defined as the
removal of metal from solution by microorganisms ,by one or
more processes, such as adsorption, precipitation, or
uptake. Where applicable, sorption isotherms were
evaluated using the logarithmic form of the Freundlich
adsorption equation.
logS = logK + nlogC
(1)
where S is the metal sorbed in iimol g dry wt-1, C is the
equilibrium solution concentration in nmol L-i, and K and n
are constants 6. isotherms were constructed using the
methods outlined by Dao et al.7
Isolated Bacterial Wall, Clay, and Wall-Clay
Composite Studies
Walls from B. subtilis 168 and from E. coli K-12 strain
AB264 were isolated and purified according to Walker et al.s
Na-smectite (montmorillonite, SWY-1 Crook County, WY)
and Na-kaolinite (KGA-1, Washington County, GA) were
obtained from the Source Clays Repository of the Clay
Minerals Society.
Adsorption isotherms of the wall-clay composites were
determined by reacting 1 mg mL-1 of clays in distilled water
with 0, 0.05, 0.1, 0.2, 0:4, 0.6, 0.8 or 1.0 mg dry weight mg
mL-1 of walls at circumneutral pH for 10 min at 22°C. The
experiments relied on the natural buffering capacity of the
particulate material. Centnfugation at 12000 x g for 30 min
into a 60% (w/v) sucrose cushion separated unabsorbed
walls from the clay and the clay-wall composite and allowed
adsorption efficiency to be estimated.
Sorption of Ag, Cu, Ni, Cd, Zn, Pb and Cr nitrate salts
was accomplished in 5 mM metal solutions at a clay, wall or
clay-wall concentration of 1. mg dry weight mL-1 for 10 min
at 22°C. The particulates were washed five times in
distilled water to remove unbound metal. The metals were
analyzed by atomic absorption spectrophotometry. In
addition, location of metal concentration was monitored by
transmission electron microscopy and energy dispersive X-
-------
ray speetroscopy.
in Walker et al.s
More experimental details can be found
Remobilization Experiments
Ag ~, Cu," or Cr" loaded B. subtilis and E. coli walls,
clays, and wall-clay composites (as outlined in section 2)
were used in this study. Fulvic acid (10 to 120 mg L-1),
Ca2+ (0 to 160 mg L-1), EDTA (0 to 500 M), H+ (pH 3 to
9). and lysozyme (40 to 160 mg L-1) were used as
remobilization agents and were interacted with the heavy
metal-loaded particulates for 48 h at 22°C. Particulates were
separated from the fluid phase by centrifugation (18000 x g
for 30 min) and the supernatant was analyzed for
remobilized metal. The amount of cell wall hydrolysis by
lysozyme was estimated by the acid ninhydrin test 9.
Results and Discussion
Intact Microbial Cell Studies
Constants for sorption of Cd and Cu from solution by
the four bacteria are given in Table 1. B. subtilis was the
least efficient bacterium for sorption of Cd and B. cereus
was the least efficient for Cu sorption, with K values of 0.147
and 2.188, respectively. £ coli and B. subtilis were the
most efficient for Cd and Cu sorption with K values of 1.067
and 4.150, respectively. The slopes of the isotherms were
all less than one and were generally different among
bacteria within metals. Because the slopes were not equal,
the differences in affinities for the metals by the bacteria
predicted by K at an equilibrium concentration of 1 iiM may
not hold at higher concentrations. For example, P.
aeruginosa removed the most Cd and Cu from solution
when the initial concentration was 1 mM. Figure 1 presents
the actual Cd sorption isotherms for B. cereus and P.
aeruginosa.
Bacterial sorption of Ag and La did not conform to the
Freundlich equation because of precipitation of these metals
by the bacteria. On average, 99% of the total Ag+ and
89% of the total La3+ were removed from the 0.1 mM
solutions by the bacteria. Electron microscopy and energy
dispersive X-ray analysis indicated that Ag precipitation was
likely a reductive process with the formation of colloidal Ag
aggregates, whereas La precipitates were crystalline and
probably La-oxides or -hydroxides 5. The affinity series for
bacterial sorption of these metals decreased in the order Ag
> La > Cu > Cd.
Freundlich constants for sorption of all four metals by
the filamentous fungi are given in Table 2. The isotherms
adequately described the removal of the metals by the
fungi, although some precipitation of Ag may still be
occurring as Ag sorption was much greater than La sorption
(188.3 versus 48.6 nmol g-1 at an initial concentration of 1
mM). Based on K values, M. rouxii was more efficient at Ag
and La sorption, whereas A. niger removed the most Cd and
Cu from solution. Because of the differences in isotherm
slopes, however, A. niger was more efficient than M. rouxii
for sorption of Ag and La from 1-mM solutions. The K
values indicated that fungal affinity for these metals
decreased in the order La > Ag > Cu > Cd. Although not
statistically comparable, the bacteria in this study generally
Figure 1. Freundlich isotherms for cadmium sorption by B.
cereus and P. aeruginosa. The dotted lines represent 95%
confidence intervals about the isotherms. Reproduced from
Applied and Environmental Microbiology 55: (in press), 1989 by
permission of the American Society for Microbiology and the
authors.
100.0
f
•a
(D
_a
O
10.0
1.0
0.1
0.1 1-0 10.0 100.0
Equilibrium Concentration (\iM)
1000.0
Table 1. Freundlich isotherms for sorption of Cd2+ and Cu2+ by bacteria3
Metal Bacterium
log K ± SE
n± SE
Cd
Cu
B.cereus
B. subtilis
E. coli
P. aeruginosa
B. cereus
B. subtilis
E. coli
P. aeruginosa
-0.673+ 0.083
-0.833 ±0.027
0.028 ±0.066
-0.410 + 0.043
0.340 ±0.064
0.61 8 ±0.032
0.411 +0.049
0.399 + 0.140
0.657 ±0.043
0.857 + 0.014
0.497 + 0.033
0.770 + 0.023
0.482 + 0.036
0.521 ±0.019
0.574 + 0.029
0.677 ±0.091
0.212
0.147
1.067
0.389
2.188
4.150
2.576
2.506
0.962
0.998
0.966
0.992
0.952
0.988
0.977
0.860
a Log K is the intercept and n is the slope of the regression line. The constant K
represents the amount of metal sorbed in umol g-1 at an equilibrium concentration
of 1 uM (logC=0).
Reproduced from Applied and Environmental Microbiology 55: (in press), 1989 by
permission of the American Society for Microbiology and the authors.
-------
appeared to bind more metal than the fungi on a iimol g
wt-1 basis.
dry
The disparity between predicted efficiencies of different
microorganisms at low and high concentrations for a given
metal may be indicative of differences in total binding sites
per gram dry weight and/or affinities of individual binding
sites on the bacteria for the metals. For example, B. subtilis
may have sites with a higher affinity for Cu than does; P.
aeruginosa, with P. aeruginosa having more total sites
available on a dry weight basis. This may explain! P.
aeruginosa binding more Cu at high concentrations and B.
sublilis binding more at low concentrations.
These data indicate that microorganism-metal
interactions may be amenable to equilibrium modelijng,
particularly when precipitation of metal is not a major factor.
Such modeling may allow for the eventual inclusionj of
biological surfaces in equilibrium solution chemistry codes,
(or example MINTEQ. '
Isolated Bacterial Wall, Clay, and Wall-Clay
Composite Studies I
Of all bacterial structures, cell walls are the most
resilient and are virtually indestructible unless either
degraded by specific enzymes (muramidases) lor
hydrolyzed by extreme pH conditions. 1° Frequently, once a
bacterial cell dies, uncontrolled autolysis ensues, the cell
lyses, and the wall is degraded into small fragments, YLet,
the very wall enzymes that are responsible for this
phenomenon are easily inactivated by dilute heavy metals,
such as Fe, Cu, Cr and Ag, within the cell's aqueous
environment Because bacteria are ubiquitous to natiiral
soils, sediments, and groundwater systems, it is very
possible that they can affect the migration of toxic he^vy
metals throughout these natural environments; indeed, these
metals may actually increase the residence time of bactej-ial
walls within waters, soils and sediments thereby making
them a major force in the determination of toxic metal
mobility. For this reason, it was important to study exactly
how representative bacterial wall types modified hea'vy
metal migration patterns in simple soil simulations, such las
clay suspensions in the laboratory. j
The metallic ion adsorption capacity of soils is control-
led by aluminosilicate clay minerals, metal oxides/-
hydroxides and organic matter. For this reason, our
Table 2. Freundlich constants for metal sorption by filamentous
fungi" I
Molal Fungus K n r2 I
Ag
Cd
Cu
La
A. niger
M. rouxii
A. niger
M. rouxii
A. niger
M. rouxii
A. niger
M. rouxii
1.096
3.373
0.156
0.039
0.889
0.746
2.877
5.702
0.892
0.641
0.679
0.875
0.495
0.551
0.426
0.314
0.953I
0.806
0.861
i
0.994
0.921
0.963
0.971 ! •
0.968
8 The constant K represents the amount of metal sorbed in jimo! g-1 [at
an equilibrium concentration of 1 yM and n is the slope of the log i
transformed isotherm.
simulation experiments used two clays, smectite
(montmorillonite) and kaolinite, that at circumneutral pH
carry a net negative charge and function as cation
exchangers. Cell walls of B. subtilis (representative of a
gram-positive bacterium) and £ coli (representative of a
gram-negative bacterium) were used as the biological
component of the system. At neutral pH, the metal ion
sorption capacity of these walls is dominated by ionized
carboxyl and phosphoryl groups.2 Previous experimentation
has shown that these walls can immobilize large quantities
of soluble metaf cations and act as nucleation sites for the
production of various minerals.2
Before laboratory simulations using clay-bacterial wall
composites could be performed, it was necessary to
establish the heavy metal sorption capacity of each of the
single components (Table 3); it was already apparent that
the order of reactivity was B. subtilis (B) > £ coli (E) >
smectite (S) > kaolinite (K). Further experimentation
revealed that each of the clays also was capable of binding
to the bacterial walls, presumably through polynuclear
aluminohydroxide bridging, 11 to make organo-clay
composites.8 Kinetic analysis of these adsorption isotherms
revealed that saturation occurred at approximately a 1:1
stoichiometry of clay-to-wall masses (Figure 2). Metal
immobilization experiments revealed that a proportion of the
reactive sites of each component (wall and clay) were
apparently used in composite production and, consequently,
were not available for metal binding yielding a reduced
capacity for heavy metal immobilization (see calculated
versus observed binding values in Table 4 and following
discussion). Yet, it was apparent that the biological
components of the clay-wall composites continued to
dominate the system (Table 5). The order of reactivity for
the composites was B + S>B + K>E + S>E + K.
This study was conducted to determine the net effect of
clay sorption on the metal binding capacity of bacterial
walls. The results indicated that metal binding was
substantially reduced in wall-clay aggregates, a reduction
Table 3. Metal bound by native Bacillus subtilis walls, Escherichia
coli envelopes, kaol;inite and smectite.3
nMole Metal Bound/Gram Dry Weight
Metal
Wall
Envelope
Kaolinite
Smectite
Ag
Cu
Ni
Cd
Pb
Zn
Cr
423 ±15
530±13
654 ±25
683 + 19
543 ± 1 1
973 ±13
435 + 37
176+ 3
172+ 9
190+ 3
221 ± 6
254+ 5
529 + 32
102+ 2
0.46 ±0.02
5 ± 0.03
4 +0.2
6 ±0.2
3 + 0.2
37 ±1
8 ±0.5
43 ±0.3
197±4
173 + 10
1 +0.02
118 + 6
65 ±2
39 ±5
a Each component was suspended for 10 min. at 22° C in a 5 mM metal
nitrate solution and washed 5 times by centrifugation to remove
unbound metal. Metals were analyzed by atomic absorption
spectrophotometry. The data represents the average of 3-5
determinations for each sample + standard error.
Reproduced from Applied and Environmental Microbiology 55: (in press),
,1989 by permission of the American Society for Microbiology and the
authors.
-------
attributed to a physical blocking of negatively charged sites
in the cell walls and envelopes by the sorbed clay particles.
The contribution of the clays to heavy metal binding was
small in comparison to that of the organic constituents of
these composites (Table 5). These results suggest that
small remnants of bacterial walls in soils or sediments,
adsorbed to clay particles, would substantially increase the
metal binding capacity of the soil., An important question
Figure 2. Adsorption of Bacillus subtilis walls (A) and
Escherichia coli envelopes (B) to smectite (*) and
kaolinite (o) clays. Reproduced from Applied and
Environmental Microbiology 55: (in press), 1989 by
permission of the American Society for Microbiology
and the authors.
1.25
1.00
CB
€
O
0.75
= 0.50
g
O)
0.25
0.5 1.0 1.5
mg walls reacted/mL
2.0
1.25
•§ 1.00
O>
-Q
O
0.75
§ 0.50
CD
O>
0.25
0.5 1.0 1.5
mg envelopes reacted/mL
2.0
which should be addressed in future research regards the
stability and immobility of metals bound by wall-clay
complexes compared to metals bound to the walls or clays
alone.
Remobilization Experiments
Once toxic heavy metals have been concentrated by
walls, clays, and composites in a natural environmental
setting, they would be subject to a range of chemical and
enzymatic agents that could leach the particulates of their
bound metal. For instance, low pH frequently has the
capability of remobilizing metal precipitates.12 To test this
reaction, four different pHs (pH 9, 7, 5 and 3) were used on
our single and multicomponent systems (Figure 3); Ag was
remobilized best, whereas Cr was little affected.
It is also possible that competing, non-toxic, naturally
occurring counter-ions such as Ca2 + could prove effective
at displacing bound heavy metals. In this instance,,
laboratory tests showed that Cu was remobilized best
(Figure 4) followed by Ag and Cr. Fulvic acid, a natural
complexing agent, proved to be not as effective at
remobilization as Ca2 + (cf. Figure 4 and 5), whereas EDTA,
which has a high binding constant for these metals and
which forms true chemical chelates, had a profound effect
on Cu but not on Ag or Cr (data not shown).
Lysozyme is a muramidase that cleaves the covalent
bonds holding the glycan chains of a major bacterial wall
constituent, peptidoglycan, together10 and, consequently,
should solubilize the wall fabric away from the bound metal.
Interestingly, there was a highly variable response to this
enzyme and Cr was barely remoblized at all. Previous work
suggested that heavy metal ions can inactivate native
muramidases (autolysins) within the wall13, and it is possible
that a variable proportion of the lysozyme used in our study
was denatured by the heavy metals liberated during initial
wall digestion. We currently are conducting studies to
confirm this hypothesis.
Summary and Future Research
It is clear from the studies outlined in this report that
microorganisms and their surfaces can have a profound
effect on the immobilization of toxic heavy metals in
aqueous solution. Furthermore, they are capable of
chemically interacting with aluminosilicate minerals to
produce composites in which the microbial component
dominates the aggregate binding of metals. Frequently, the
remobilization of these bound metals is difficult and does
not follow a set pattern. Clearly, microbial complexation
with metals in soils, sediments, and pore waters is important
and must be taken into account when modeling the
transport patterns and ultimate fate of toxic heavy metals in
natural systems.
Future research should include the evaluation of other
environmentally relevant metals and microorganisms, and
their physiological processes related to metal dynamics.
For example, microorganisms produce extracellular
compounds that assist in Fe transport14, and these
compounds also may act as complexing agents for a full
range of metals.15 The role of microbial metal complexing
agents in metal transport is poorly understood and requires
careful assessment if we are to develop complete
mathematical models that accurately predict metal
movement in the soil, surface, and ground water.
-------
Table 4. Comparison of the metal binding capacities of clay-wall and clay-envelope mixtures with predicted values as
calculated from Table 3 '
Metals
Wall* Smectite
pMole Metal Bound/Gram Dry Weight
Wall + Kaolinite Envelope + Smectite
Envelope + Kaolinite
Calculated3
Ag
Cu
Ni
Cd
Pb
Zn
Cr
233 ±
364 ±
414 ±
342 ±
331 ±
519 ±
237 ±
8
3
18
10
8
7
21
Observed13
115 ± 2
263 ± 4
148 ± 2
689 ± 13
148 ± 5
464 ± 15
122 ± 22
Calculated | Observed
212± 8 107 ±
268 ± 7
329± 13
181 ±
176 ±
345 ± 10 299 ±
273 ± 6
505 ± 7
222 ± 19
271 ±
367 ±
122 ±
2
10
0.3
8
5
7
16
Calculated
110 ± 8
364 ± 9
414 ± 18
342 ± 10
331 ± 9
519 ± 8
237 ± 21
Observed
19 ±
100 ±
37 ±
141 ±
134 ±
92 ±
19 ±
0.2
2
2
5
6
6
1
Calculated
87 ± 2
89 ± 6
97 ± 2
114 ± 3
129 ± 3
283 ±17
55 ±13
Observed
30 ± 2
49+2
28 ± 0.6
57 ± 1
27 ± 2
82 ± 2
28 ± 4
I
a Calculated from average uptake for each component of the mixture in Table 3.
b The same metal binding conditions as outlined in Table 3 were used and the data represents averages from 3-5 determinations ±
standard error.
Reproduced from Applied and Environmental Microbiology 55: (in press), 1989 by permission of the American Society for
Microbiology and the authors.
Table 5. Metal Proportion (%) associated with the cellular
constituents in the clay-wall/envelope |
components" |
Metal
Ag
Cu
Ni
Cd
Pb
Zn
Cr
Wall-
Kaolinite
100
99
99
99
99
99
99
Wall-
Smectite
91
73
79
100
82
94
92
Envelope-
Kaolinite
100
97
98
97
99
99
93
Envejope-
Smeptite
80
4J7
5(2
100
68
89
^
"Calculated from the data in Table 3.
Reproduced from Applied and Environmental Microbiology 5J5: (in
press), 1989 by permission of the American Society for l
Microbiology and the authors.
55: (in
-------
Figure 3. Effect of decreasing pH on the remobilization of bound metal. B = B. subtilis walls, E = E. coli envelopes, S =
smectite, and K = kaolinite. The pHs are arranged in groups of four and, from left to right, are pH = 9,7, 5 and
3.
Ag
100
50
-a
o
N
S
o n
1
1
tl
I
-
!.-:,
j
~
1
-
-
r
,— i
7
j-
i
CD
Q_
100
Cr
50
IL
-CL
n
_n
S K B + K
Decreasing pH
(pH .9, 7, 5, 3)
B + S E + K E + S
-------
Figure 4. Effect of increasing Ca concentrations on the remobilization of Cu. The Ca concentrations are arranged in
groups of four and are Ca = 0,40, 80, and 160 mg I/1.
100
I
§ 50
Cu
S K B + K B + S
Increasing Ca concentrations
(0, 40, 80, 160 mg/L)
E + K E + S
Figure 5. Effect of fulvic acid on Cu remobilization. Ipulvic acid concentrations = 10, 30, 60, and 120 mg I/1.
100
Cu
13 50
CD
I
CU
Q.
S K B-t-K B + S
Increasing fulvic acid concentrations
(10, 30, 60, 120 mg/L)
E+K E + S
-------
Acknowledgments
This research was funded through EPA
Cooperative. Agreements CR813605-01-1 and
CR813609-01-2. The technical assistance of S.G.
Walker, L. Smith and C.A. Flemming is acknowledged.
References
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