The document summarizes research on the biodegradation kinetics of three nitrogen-substituted naphthalenes (1-aminonaphthalene, 2-aminonaphthalene, and 1-amino-2-methylnaphthalene) under aerobic conditions in flooded soil. The researchers found that mineralization of the compounds proceeded in two phases - an initial fast phase followed by a slower second phase. Sorption of the compounds onto the soil followed hyperbolic isotherms described by the Langmuir model. Initial mineralization rates obeyed Michaelis-Menten kinetics and were directly proportional to aqueous concentrations, reaching a maximum at 100 μg/g soil slurry. The second phase mineralization rates were

1. ~ Pergamon 0043-1354(93)E0039-U
War. Res. Vol. 28, No. 8, pp. 1827-1833, 1994
Elsevier Science Ltd. Printed in Great Britain
BEHAVIOR OF NITROGEN-SUBSTITUTED
NAPHTHALENES IN FLOODED SOIL--PART II. EFFECT
OF BIOAVAILABILITY ON BIODEGRATION KINETICS
BILAL AL-BASHIR[, JALAL HAWARI2., RI~JEAN SAMSON2 and ROLAND LEDUC3
IDepartment of CivilEngineeringand Applied Mechanics,McGillUniversity,Montreal, Quebec,Canada
H3A 2K6, 2Environmental Engineering Group, Biotechnology Research Institute, National Research
Council Canada, Montreal, Quebec,Canada H4P 2R2 and 3Departmentof CivilEngineering,University
of Sherbrooke, Sherbrooke, Quebec, Canada JIK 2RI
(First received February 1993; accepted in revised form November 1993)
Abstract--Mineralization of l-aminonaphthalene, 2-aminonaphthalene and I-amino-2-methyl-naph-
thalene under aerobic conditions in flooded soilwas found to proceed with a biphasic pattern, an initial
fast phase followed by a slower second one. Also the sorption isotherms of these substrates were found
to be hyperbolic and were bestdescribedby the Langmuir model. When initial mineralization rates were
expressed in terms of initial aqueous-phase concentrations, they gave rise to simple hyperbolic kinetics
that obeyed Michaelis-Menten model for enzyme-catalysedreactions. These initial mineralization rates
were found to be directly proportional to the substrate aqueous concentration reaching their maxima at
about 100#g g-t (aminonaphthalene/soil slurry). Whereas the second phase mineralization rates were
found to be first order with respect to the adsorbed fraction of the substrate and showed no sign of
saturation, thus indicating that biodegradation is controlled by the rate of desorption.
Key words--aminonaphthalene, mineralization, sorption, bioavailability, Michaelis-Menten, first-order
kinetics.
INTRODUCTION
Biodegradation kinetics of pollutants in the soil
environment provides a basis for a better
understanding of their fate, persistence and potential
threat to living organisms. Several studies have
shown that bioavailability plays a crucial role in
determining the biodegradation of various organic
contaminants and several models have been devel-
oped to understand biodegradation kinetics. Scow
et al. (1986) have reported that the mineralization of
the aromatic amine, aniline, in soil is biphasic and is
attributed to several factors, i.e., the presence of two
states of the substrate bioavailability, the involve-
ment of different populations of organisms, or the
accumulation of intermediate metabolites. Conse-
quently, a two-compartment model has been devel-
oped (Scow et al. 1986) to describe the biphasic
phenomena encountered in the mineralization of
aniline.
Others (Steen et al. 1980) have modified a second-
order model, applicable to biodegradation of
pollutants in natural waters, by incorporating a
partition coefficient in it. The model assumes that
adsorption affects biodegradation solely by decreas-
ing concentration of the pollutants in the aqueous
*Author to whom all correspondence should be addressed.
phase, i.e. only the aqueous fraction is bioavailable
and the adsorbed fraction is totally unavailable. Also,
Hamaker (1972) proposed a biodegradation model
based on simple hyperbolic kinetics and on the
assumption that soil contains both active and inactive
biological sites. Accordingly, the rate of degradation
is proportional to the amount of contaminant
adsorbed on the active sites and adsorption on active
and inactive sites is proportional to the concentration
of the soluble substrate.
Mihelcic and Luthy (1991) have reported that
mineralizationof naphthalene in a soil-water suspen-
sion under denitrifying conditions is dependent on
solute partitioning between soil and water. They
described the overall change of soluble naphthalene
in the aqueous phase by developing a model which
combines Michaelis-Menten kinetics with those of
sorption/desorption in soil. The model assumes that
the soluble and the sorbed substrate were in
equilibrium throughout the course of the experiment
and suggests that complete mineralization of the
adsorbed fraction is attainable. The latter two as-
sumptions deal with a specific case in which desorp-
tion is instantaneous and shows no hysteresis, i.e.
desorption is first order with respect to aqueous
concentration, and does not take into consideration
the limiting case when desorption turns zero order
with respect to aqueous concentration.
1827

2. I828 BILALAL-BASHIRel al.
These previous studies indicate that there is a need
to further investigate the extent to which bioavailabil-
it5, affects biodegradation kinetics. Furthermore,
studies on the behavior of amino-substituted PAHs
are seriously lacking in the literature. In the preceding
paper (Al-Bashir et al. 1994), the mineralization of
three aminonaphthalenes, i.e., 1-aminonaphthalene,
2-aminonaphthalene and I-amino-2-methyl-naph-
thalene, was found to be biphasic and it was
suggested that bioavailability considerations were
responsible for such behavior. It is the purpose of this
study to investigate the kinetics of mineralization of
these compounds and to examine the mechanisms
and the extent to which bioavailability affects their
kinetics.
MATERIALS AND METHODS
The aminonaphthalenes, l-amino-[l-J4C]-naphthalene
and 2-amino-[8-14C]-naphthalene were prepared from a
mixture of their corresponding radiolabelled and unmarked
naphthols (Sigma Chemical Co., St. Louis, Mo, U.S.A.)
using the Bucherer reaction (Vogel, 1978). The compounds
had a specific activity of 32,874 and 36,283 dpmmg -l,
respectively, and a final purity of 99 _+%. [8-14C]-l-amino-2-
methytnaphthalene was prepared by reducing [8-~4C]-l-ni-
tro-2-methylnaphthatene using Urushibara catalysts (Hata,
1971) which, in turn, was prepared by direct nitration of
[8>4C]-2-methylnaphthalene. For more details on the
synthesis of these compounds see A1-Bashir et al. (1994).
The soil sample was obtained from Jarry Park, Montreal,
Quebec and was characterized as clayey loam with soil
organic matter~ organic carbon, pH and cation exchange
capacity as 3.96%, 1.60%, 7.27 and 19.94me/lOOg soil,
respectively.
Varying initial concentrations of each compound were
investigated. For 1-aminonaphthalene, these were, 5, 10, 20,
30, 40, 50, 100 and 150 Hg l-aminonaphthalene g ~of soil
slurry. The initial concentrations for 2-aminonaphthalene
were 5, 15, 30, 50, 100 and 150~gg ~and for l-amino-2-
methylnaphthalene were 10, 20, 35, 50, 100 and 200,ug g- ~.
The amino-compounds were added as a methanol stock
solution and the total volume of methanol added was
constant at 200t~I per vial.
Batch equilibrated adsorption experiments were con-
ducted for autoclaved slurry samples at pH 6.5 following the
procedure described previously (AI Bashir et al., 1990).
Biodegradation was carried out in 100-ml glass vials con-
taining 30 g soil slurry (30% w/w soil/water) and housing a
KOH trap. The aqueous phase was a mineral growth
medium prepared by the method of Thomas et al. (1986).
Biodegradation was carried out under pure oxygen and the
pH was kept between 6.5 and 7.0 using HC1 (1 N). Pure
oxygen was also replenished every sampling session. For
each concentration, six replicates were prepared of which
three were analysed regularly for ~4CO2in the alkali trap
without acidification, two were sacrificed by acidification to
make corrections for any CO, in the soluble form and the
sixth one acted as control by receiving 500 pg/g HgCI> The
evolved ~4CO2was captured in KOH traps comprising of
10-ml glass tubes that shared the same head space with the
slurry. Radioactivity in the alkali was measured using a
scintillation counter (Packard Tri-Carb #4530, Downers,
ILL, U.S.A.). On few occasions, duplicate samples of 2-ml
slurry were taken from the biologically-active vials. These
were centrifuged at 15,600 × g for 10min (Centrifuge 5414,
Eppendorff, Hamburg). The supernatant was then analysed
for radioactivity.
RESULTS
The effect of initial N-substituted naphthalene
concentration on the mineralization of l-aminonaph-
thalene, 2-aminonaphthalene and I-amino-2-methyl-
naphthalene is shown in Fig. 1. Concentrations
reported in the legend of Fig. 1 represent total initial
concentration of /~g of compound per g of soil
slurry. At relatively low concentrations, no lag period
was observed for any of the studied compounds.
However, a lag period became more pronounced for
both 1- and 2-aminonaphthalene at 150#gg ~ and
for l-amino-2-methyl-naphthalene at 200~gg
(Fig. 1). This is manifested in the lapse of 1-2 weeks
between the spiking of the soil samples with the
contaminants and the onset of an active biodegrada-
tion process. After the lag phase, mineralization of
each of the studied aminonaphthalene compounds
showed a two-phase process; an initial rapid phase
followed by a second one with a diminished rate
(Fig. 1). The diminished mineralization rates,
observed for the second phase, are attributed to the
partial unavailability of the contaminants to
microbial uptake (Al-Bashir et al., 1994). Figure 1,
also, shows that amounts mineralized (yg contami-
nant g ~ slurry) increased with increasing initial
concentration in slurry (/lg of contaminant g ~ soil
slurry) but the latter decreased when expressed as a
20
16
12
0
m 16..=
0
16
12
l l l i
a. 1-aminonaphthalene~
~- ~ " / S i control
x./~ -- +- Slag/g
~."" ~ 10 ~g/g
. j ~ ----eP ZO ,ug/g
- , ~ f ' ~ ~ --*- so.Q/g
: ~ ~ ~ ---e- 1O0/~j/~
= r ~ : ~ - - % ~ , ~ s o ~g/,r
b. Z-aminonaphthalene
• control
5 ~g/g
~ 1S~g/g
~ 30/Jg/g
- ~ SO.ug/g
100/~g/g
• ~. J.. ,'.t. x lSO/~g/g
c, 1 -amino-2 -methyinaphthalene
• control
i I0/Jglg
--'o--'20 jug/g
+ 35/~g/g
• SO/~/fl
-'-'~ 1O0/.Jg/g
• = ' ~. 200ua/a
0 50 IOO 150 ZOO Z50
Time (days)
Fig. 1. Mineralization of (a) I-aminonaphthalene, (b) 2-
aminonaphthalene and (c) I-amino-2-methyl-naphthalene
at various initial concentrations in flooded soil.

3. Nitrogen-substituted naphthalenes in flooded soil--part I1 1829
O.Z
0.15
0.1
0.05
i O
0.15
I Od
• 0.05
0
0.15
, , ~ ' "=,
, ,
Y T
i l i I i I i
0.05 -imlno-2~
o
0 40 80 lZO 1SO ZOO
Initial concentration in slurry (/~/g)
Fig. 2. Initial mineralization rates as a function of total
concentration in slurry of (a) l-aminonaphthalene, (b)
2-aminonaphthalene and (c) l-amino-2-methylnaphthalene.
percent of the total amounts added. Furthermore, the
initial mineralization rates for the three aminonaph-
thalenes (/Jg contaminant g-' slurry day-') increased
with increasing initial total concentration in the
slurry and reached their maxima at about 100/zgg -~
as shown in Fig. 2. In this figure and subsequent ones,
an error bar indicates the standard deviation of three
measurements. These errors are independent from
each other as opposed to the dependent errors
incorporated in the cumulative observations of Fig. 1
(Callas and Gehr, 1989).
Initial-phase mineralization
As Fig. 3 indicates the adsorption of the studied
compounds gave rise to hyperbolic isotherms that
were best described by the Langmuir model:
q = KLCM/(I + KLC) (I)
where q is the sorbate concentration (gg g-~ soil) in
the solid phase and c is solute concentration
(/~gml-') in the liquid phase, KL is the Langmuir
affinity parameters (ml/~g-~ ) and M is the adsorption
maximal (#gml-J). To find q in equation (1), the
mass of contamination in the solid phase is calculated
by subtracting the mass in aqueous phase from the
total mass added initially and this in turn is divided
by the weight of soil in the soil slurry. In Fig. 3, an
error bar represents the standard deviation of three
measurements of the aqueous phase concentration.
Table 1 reports estimates of KLand M for the three
aminonaphthalenes. These estimates were obtained
using the Lineweaver-Burk method for the linear
transformation of the Langmuir model (Kinniburgh,
1986). Accordingly, a plot of l/q versus 1/c yields a
straight line such that KL=intercept/slope and
M = l/intercept. Table 1 reports the r-values for the
linear fits and the 90% confidence intervals for the
estimated parameters. The confidence intervals of
the two functions: (1) the inverse of slope and (2) the
intercept over the slope, were obtained following
the procedure outlined by Ang and Tang (1975).
When initial-phase mineralization rates are
expressed as a function of contaminant aqueous-
phase concentrations, they yield hyperbolic curves
(Fig. 4) that fit Michaelis-Menten kinetics:
V = (RmaxC)/(K m + C) (2)
where, v, is mineralization rate (g g ml-J day-t), c, is
solute concentration (#g ml-') in the liquid phase,
Rm= is the maximum attainable rate (/zg ml-' day-' )
and K,, is the half-saturation constant (/zgml-').
Michaelis-Menton model assumes a reversible for-
mation of a catalyst-substrate complex followed by a
first order decomposition of the complex to a
product. At relatively low substrate concentrations
mineralization is first order with respect to the
substrate concentration, i.e., v = (Rm,~/Km)c. While
at very high concentrations, all of the catalyst is
presumably complexed, and the mineralization rate
thus reduces to v = R.... i.e., zero order kinetics with
respect to substrate concentration (Fig. 4).
The linear transformation of the
Michaelis-Menten equation using Lineweaver and
Burk method gives (Piszkiewicz, 1977):
1/v = (Km/RmaxC) - 1/Rma x (3)
When l/v for each substrate, i.e., l-aminonaph-
thalene, 2-aminonaphthalene, and I-amino-2-methyl-
naphthalene, is plotted against its respective l/c for
initial mineralization rates, a linear relationship is
700
600
500
o
.~ 400
300
200
1O0oo
0
0
r , . . . . ~ • ' + ' ' r • ' + ' ' '
~ n o - 2 - m e t h y l -
naphthalene
, , i , i i , , i r , , , , , , , I , ,
10 ZO 30 40 SO SO 70
Concentration in liquid (/Jg/rnl)
Fig. 3. Partitioning of (a) l-aminonaphthalene, (b) 2-
aminonaphthalene and (c) l-amino-2-methyinaphthalene
between the solid and the aqueous-phases of the soil-water
suspension.
WR 2S/S--K

4. 1830 BILAL AL-BASHIR et al.
Table 1. Estimation of adsorption and mineralization kinetic parameters of the studied amino-PAHs
Langmuir parameters*
Michaelis-Menten First-order
kinetics parameterst kinetics parameters:~
K~ Rm~. k,(day) I
Compound KL M r (/~g/ml) (#g/ml.day) r x 10 4 r
I-aminonaphthalene 0.16_+0.06 765 + II0 0.998 4.0+2.1 0.42_+0.21 0.973 6,1 +_0.2 0,998
2-aminonaphtbalene 0,16 + 0.03 355 + 49 0.997 1.90+ 0.19 0.13 + 0.01 0,996 5.7 + 0.6 0.988
I-amino-2-methyl-naphthalene 0.33 + 0.15 1053_+441 0,997 1.10+ 0.11 0.14 + 0.06 0,992 2.9 + 0.2 0,996
*KL is Langmuir partition coefficient (ml/#g), M is adsorption maximum (ug/g), r, is the correlation coefficient. "['Rma~ is maximum
mineralization rate attainable with increasing concentration [from equation (2)], K~ is the half-saturation constant [from equation (2)].
.~k. is the uptake coefficient from equation (3). The ( _+) error establishes the 90% confidence interval
obtained with correlation coefficients, r, reaching
0.973, 0.996 and 0.992, respectively. Table 1 sum-
marizes the parameters Rmax and Km for all studied
aminonaphthalenes and their corresponding 90%
confidence intervals.
Not all of the compounds originally present in
the aqueous phase were mineralized during the
initial phase, especially those at concentrations
leading to maximum mineralization rates. Pre-
sumably, part of the soluble fraction of the
aminonaphthalene underwent further irreversible
adsorption (i.e., chemisorption) onto the soil, e.g.,
humic materials. To confirm this observation, the
concentration of the contaminant in the aqueous
phase was determined and was found to be negli-
gible. Bollag et al. (1983), Parris (1980) and Hsu and
Bartha (1974) have all reported that aromatic
amines and their enzymatic metabolic products
.8
F:
m
0.30 • 1 . i . i • i , i .
020? ]
0.10
0.00
0.20
0.10
0.00
0.20
0.10
a. t-ami~naphthatene
, l = l , i i l l l =
b. 2.aminonaphthalene
I l l l l l i l l
c. 1-amino-2-methyl-
naphthalene
0.00 I I I I I I I I
0 5 10 15 20 25 30
Concentration in the aqueous-phase (/Jg/ml)
Fig. 4. Initial mineralization rates as a function of concen-
tration in the aqueous-phase of (a) l-aminonaphthalene, (b)
2-aminonaphthalene and (c) l-amino-2-methylnaphthalene.
cross-link to humic substances in the soil through
chemical bonding.
Second-phase mineralization
The second-phase mineralization rates remained
fairly constant during the experiment (Fig. 1),
increasing linearly with the contaminant concen-
tration in the soil part of the slurry and showing no
sign of saturation (Fig. 5). The relationship between
the mineralization rate and concentration in the
solid phase can be expressed mathematically as:
v = k.q (4)
where ku is the substrate uptake coefficient from the
solid-phase (day-') and q is the substrate concen-
tration in the solid-phase (#gg-~). Equation (4)
represents first order kinetics in which the rate is
"K
a9
0.3
0.2
0.1
0.2
0.1
0.2
' i , i • i . i i
i i i i i , i i
b. 2<mlno~ap~halene
/i i t i i
e. 1-tm~no.2-molhy~lhllkmg
0
0 100 200 300 400 500 600
Concentration in the solid-phase "q" (pg/g)
Fig. 5. Second-phase mineralization rates as a function of
concentration in the solid-phase of (a) l-aminonaphthalene,
(b) 2-aminonaphthalene and (c) l-amino-2-methyl-
napthalene.

5. Nitrogen-substituted naphthalenes in flooded soil--part II 1831
directly proportional to the first power of substrate
concentration in the solid phase. Plots of v against q
for I-aminonaphthalene, 2-aminonaphthalene and
1-amino-2-methyl-naphthalene give straight-line
relationships with correlation coefficients, r, reaching
0.998, 0.988 and 0.996, respectively. Values of k~ and
their 90% confidence intervals are reported in
Table 1.
General case: competitive adsorption
ks
SA---~P+A +U
/z[S+A +U k6
SU
(5)
DISCUSSION
The biphasic curves observed in the mineralization
of the aminonapbthalenes, i.e., l-aminonaphthalene,
2-aminonaphthalenes and l-amino-2-methylnaph-
thalene, indicate a kinetic change. The initial
phase of the mineralization curve is characterized by
a readily available fraction of the contaminant
which is in reversible equilibrium with the soluble
substrate and which biodegrades following
Michaelis-Menten reaction kinetics. Upon the
depletion of the readily available fraction, the
biodegradation process enters its second phase in
which the desorption of the contaminant from the
solid-phase becomes the rate-limiting step and the
biological reaction is transformed into first-order
kinetics.
In utilizing Michaelis-Menten kinetics to describe
initial-phase mineralization rates, it is assumed that
the catalyst concentration (the biomass concen-
tration) remains constant with respect to the con-
taminant concentration. This is a reasonable
assumption given the fact that mineralization rates
were measured at short and equal periods of time
from the onset of the biodegradation experiments.
Also the initial amounts of aminonaphthalenes con-
stituted only a small fraction of the total organic
matter available to the microbial population in the
form of naturally occurring organic carbon and
added methanol. Therefore, it is reasonable to ne-
glect any difference in microbial growth prompted
by variations in initial concentrations of the studied
compounds.
In past kinetic studies, the presence of two
different states of substrate bioavailability has been
attributed to several reasons including, partitioning
of the contaminant between soluble and sorbed
forms (Steen et al., 1980, Mihelcic and Luthy, 1991),
association of the substrate with active and inactive
biological soil sites (Hamaker, 1972) and substrate
partitioning between the soil labile and non-labile
phases (Guerin and Boyd, 1990). In the present
study, the catalyst suggested by the Michaelis-
Menten model could refer either to microorganisms
(enzymes) acting as the liquid/soil interface, to
biologically active sites on soil surfaces or to labile
matter associated with soil. Accordingly, the biologi-
cal system under consideration can be described by
reactions 5-7:
Initial-phase: Michaelis-Menten kinetics
k I kj
S + A ~ SA -"~ P + A (6)
ks
Second-phase: first-order kinetics
k6 k3
SU--* SA --* P + A + U (7)
where S is a quantitative measure of the amount of
the substrate, A represents the biologically-available
sites which stand for the catalyst, U refers to the
biologically-unavailable sites of the soil, SA and SU
are the complexed forms of the substrate with
available and unavailable sites, respectively, P is the
reaction product and kl-k6 are reaction constants.
The overall reaction 5 describes the substrate, S,
partitioning between the biologically-available and
unavailable sites. The substrate undergoes competi-
tive adsorption between these two sites, where kt/k2
is a measure of the affinity of the substrate to the
biologically-available phase and k4/k5 is a measure of
the affinity of the substrate to the biologically-
unavailable phase. Initially, when the substrate
availability is not limiting which is a special case of
reaction 5, the biological reaction is described by
reaction 6 and follows Michaelis-Menten kinetics.
However, when the substrate in the bioavailable
fraction is depleted, the biological reaction is reduced
to reaction 7, another special case of reaction 5. In
this case, the rate of desorption of the substrate from
the biologically-unavailable to the biologically-
available phase constitutes the rate-limiting step.
Here, the substrate becomes available to microorgan-
isms as a result of desorption and the reaction
proceeds only in the forward direction.
The previous discussion has dealt separately with
each single compound and no attempt was made to
investigate the effect of substitution on the mineraliz-
ation kinetics. However, the following mathematical
derivation seeks to do so. Under equilibrium
conditions, the Michaelis-Menten reaction yields
k, [S][A ] = (k2+ k3)[sa ] (8)
where [] indicate concentration of the respective
species. Rearranging equation (8) yields
[S ][A ]/[SA ] = (k2+ k 3)/kl = g m (9)
where K~, as previously defined in equation (2), is the
Michaelis half-saturation constant.
According to equation (9), K~ represents the
constant for the momentarily equilibrium (termed as

6. 1832 BILALAL-BASHIRet al.
pseudo-equilibrium) between the associated and
dissociated forms of S and A. It is pseudo equilibrium
because as mineralizationproceeds, the equilibriumis
continually disturbed.
Maximum reaction rate (Rmax) occurs when all the
catalyst is present in the SA-complex form, in which
case the maximum reaction rate can be expressed as
Rmax = k3[A]total (10)
where [A ],ot,~is the total concentration of A that is
available for complexing the substrate. Substitution
equation (10) back into (9) yields
g m = (k 2 q- Rmax/[A]total)/kl (1 l)
Since the same soil type was used for the different
compounds, then it is reasonable to assume that
[A ],o,,tis constant across the three compounds. Also,
it is important to emphasize here that while the
available substrate is gradually being utilized by the
microorganisms, a series of equilibrium states occur
momentarily with their corresponding kj and k2-
values [equation (6)]. However, it has been found that
aminonaphthalenes exhibit significant hysteresis (see
AI-Bashir et al., 1994), therefore, as mineralization
proceeds, kz gradually becomes negligible while k~
remains constant. Given the above, then equation
(11) can be reduced to
Km=CtRm,x/k j (12)
where • = I[A ]total-
For an initial equilibrium state prior to the onset
of the mineralization process, the corresponding
sorption equilibrium constant (K~q)is given by
Kcq = k I/k2.o (13)
where kz.0 is the initial conditions desorption rate.
From equation (13), we have
k, = flKeq (14)
where fl = k2.0. Substitution equation (14) back into
(12) yields
Km=Y(Rmax/Keq ) (15)
where 7 =~/fl. According to equation (15), Km is
directly proportional to Rmax and is inversely
proportional to the initial conditions equilibrium
constant Koq. However, the initial equilibrium
constant for adsorption was obtained for both avail-
able and unavailablesites and it is reported in Table 1
as values of KL for the three aminonaphthalenes.
Using experimental data for the three aminonaph-
thalenes compounds, a plot of Km against Rmax/KL
gives a linear relationship with a high correlation
coefficient, r equals to 0.994 (Fig. 6). Therefore, the
plot suggests that KLand Kmcorrelate and that in this
specific case, KLis directly proportional to K~ for the
biologically-available sites. In other words, the
affinity to the biologically-availablesites (k~/k2) rela-
tive to the unavailableones (k4/ks) remained constant
across the three amino-compounds. However, the
oc
T I
2 3 4
K
m
Fig. 6. Relationship between Michaelis Menton mineraliz-
ation constants and biological affinity parameters for the
three studied aminonaphthalenes.
correlation coefficient obtained in Fig. 6 is only
indicative of a particular trend and does not fully
reflect the accuracy of the estimated parameters.
In conclusion, for a better understanding of the
biodegradation kinetics of recalcitrant organic
contaminants in the soil environment, it is necessary
to investigate the range of limitingfactors influencing
the biodegradation process. This will help distinguish
between three kinds of recalcitrance: first, the
inherent properties of the contaminant, i.e., k3 is
limiting, second, catalyst limitations, i.e., kj is limit-
ing and finally the substrate bioavailability, i.e., k6 is
limiting. Recalcitrance of aminonaphthalenes in the
soil environment is attributed to their ability to form
complexes with soil matter which, to a large extent
renders them biologically unavailable. Further work
is needed to investigate the effect of soil organic
content, cation exchange capacity and soil-to-water
ratio on initial and second phase mineralization rates
and total amounts mineralized. This has important
implications for mediation of contaminated soil and
ground water.
Acknowledgements--The authors greatly acknowledge Dr
Attila Demeter and Dr Tibor Cseh for their helpin synthe-
sizing the radiolabetled compounds and Ms Chantale
Beaulieu for her technical assistance.
This research paper is registeredas NRC Number 33860.
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Effectof soil/contaminantinteractionson the biodegrada-
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Behavior of nitrogen-substituted naphthalenes in flood
soil--Part 1. Sorption/desorption and biodegradation.
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