Environ. Sci. Technol. 2003, 37, 2400-2409

Fate and Transport of 17β-Estradiol
in Soil-Water Systems
F R A N C I S X . M . C A S E Y , * ,†GERALD L. LARSEN,‡H E L D U R H A K K , ‡ A N D J I Ř IÄ Š I M U° NEK§
Department of Soil Science, North Dakota State University,
Fargo, North Dakota 58105, Animal Metabolism Unit,
Biosciences Research Laboratory, USDA-ARS, Fargo,
North Dakota 58105, and George E. Brown, Jr. Salinity
Laboratory, USDA-ARS, Riverside, California 92507

Over the past several years, there has been an increasein concern regarding reproductive hormones in theenvironment. To date, there exists limited research on thefate and transport of these chemicals in the environment.
In this study, a series of laboratory batch sorption and miscibledisplacement experiments were done using radiolabeled[14C]17β-estradiol. The 17β-estradiol concentrations that wereused were similar to those found in manures that are
applied to field soils. Equilibrium batch experiments indicatedhigh sorption affinity with correlations to mineral particle
size and organic matter content. The sorption affinity appeared
to be associated with the surface area and/or the cationexchange capacity of the soil. The miscible-displacement
breakthrough curves indicated chemical nonequilibriumtransport, and a single highly polar metabolite was present
in the column effluent along with sporadic and trace
detections of estriol. Sorbed to the soil within the column
were found 17β-estradiol, estrone, and trace and sporadic
detections of estriol. Two chemical nonequilibrium, miscibledisplacement models were used to describe the column
breakthrough curves; one without transformations and theother with transformations. Both models resulted inexcellent descriptions of the data, which indicated nonuniquesolutions and less confidence in the parameter estimates.
Nonetheless, the modeling and experimental results
implied that degradation/transformation occurred in thesorbed phase and was rapid. Also, both models indicatedthat sorption was fully kinetic.

Introduction
The presence of low levels of bioactive chemicals in theenvironment have become a concern to the United States,
other countries, and international organizations (e.g., World
Health Organization, United Nations). A congressional bill
(H.R. 1712) was submitted to the 106th U.S. Congress that
proposed to amend the Federal Water Pollution Act toauthorize an estrogenic substance screening program. Koplin
et al. (1) has recently completed an extensive reconnaissanceof surface waters in which 139 streams were sampled across
30 states in the United States. Reproductive hormones were
found in approximately 40% of the 139 streams sampled. A* Corresponding author phone: (701)231-8577; fax: (701)231-7861;
e-mail: francis.casey@ndsu.nodak.edu.
† North Dakota State University.
‡ USDA-ARS, Fargo.
§ USDA-ARS, Riverside.
2400 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003

great number of people and wildlife can be impacted byexposure to reproductive hormones, especially since they
can produce adverse effects at remarkably low concentrations(<1.0 ng L-1; 2-4). For example, 17β-estradiol has been foundto cause vitellogenin production in male fish at environmental
concentrations of 1.0 ng L-1 (2).
Possible exposure to estrogens may come from animal
manures that are applied to agricultural fields. Estrogens arenaturally produced and excreted by animals, and they arealso administered as growth promoters to help in efficiency
of feed utilization. When used as such, they are given as
benzoate and palmitate esters of estradiol, and the body willhydrolyze them to 17β-estradiol. On the eastern shore of
Maryland, it has been estimated that 200 000 t yr-1 of broiler
chicken manure is produced, which contains 30 ng g-1 (30ppb) of 17β-estradiol. This is equivalent to about 6 kg of
17β-estradiol being applied to fields when the manure isused as a fertilizer (5). In 1997, the entire U.S. poultry industry
produced over 10 billion kg of broiler litter, 90% of which
was applied to crop lands. In a worst case situation, thisamount of manure can potentially contain 270 kg of 17βestradiol, which, at a 1.0 ng L-1 concentration, has the capacity
to contaminate 270 km3 of water.
In an experiment where manure was applied to a field,
17β-estradiol was found in a nearby free flowing stream atconcentrations of 5 ng L-1 (5). In another experiment where
manure was applied to a field, the concentrations of 17βestradiol in surface runoff reached 150-2300 ng L-1 (6).
Recently, Renner (7) reported that hormone adulterated
runoff from cattle feedlots could be affecting local fish.
Furthermore, Nichols et al. (8), Shore et al. (9), and Peterson
et al. (10) have identified 17β-estradiol (highest concentrationof 37.6 ng L-1) in aquifers underlying areas where animal
wastes have been applied. Limited studies have been doneon the persistence (11-13) and sorption (14, 15) of estrogens
in soil and sediment, but little is known about the fate andtransport of these chemicals in the environment.
It is essential to understand the fate and transport
processes of estrogens in the environment in order to assess
their potential impacts on soils, surface water, and groundwater resources. The objectives of this research were to
identify the sorption, fate, and mobility of 17β-estradiol in
soil-water systems. These objectives would identify thegeneral effects of soil composition on these parameters byusing laboratory batch sorption and miscible-displacement
experiments. Also, 17β-estradiol was chosen for the following
reasons: (i) it is potent at low concentrations (<1.0 ng L-1)
and has the capability of impacting very large amounts ofsoil and water resources; (ii) it has the capability of producing
other potent metabolites; (iii) it is a prototype chemical for
all endocrine disruptors that interact through the estrogen
receptor; (iv) it is eliminated (i.e., excreted) by all studiedorganisms, from cattle and poultry to humans, and therefore
it has the potential to be widely distributed in the environment; and (v) little is known about how 17β-estradiol and its
metabolites behave in the environment.

Materials and Methods
The soils that were used were Bearden-silty clay loam,
Gardena-clay loam, Glyndon-sandy clay loam, LaDelle-silt
loam, and Sioux-loam (taxonomic descriptions provided inTable 1). All these soils, except the Glyndon, were obtained
from Ag-Vise Company (Northwood, ND) and were collected
in North Dakota and represent a variety of soil textures (Figure1). Additionally, a medium quartz sand (250-500 µm) andkaolinite and bentonite clays were used in the batch
10.1021/es026153z CCC: $25.00

 2003 American Chemical Society
Published on Web 04/25/2003

TABLE 1. Soil Fractions Used for Sorption and Miscible-Displacement Experiments, Their Official Soil Series Description, andOrganic Matter Content
soil series

taxonomic description

Bearden-silty clay loam
Gardena-clay loam
Glyndon-sandy clay loam
LaDelle-silt loam
Sioux-loam
bentonitekaolinitesandfine-silty, mixed, superactive, frigid Aeric Calciaquolls
coarse-silty, mixed, superactive, frigid Pachic Hapludollscoarse-silty, mixed, superactive, frigid Aeric Calciaquolls
fine-silty, mixed, superactive, frigid Cumulic Hapludolls
sandy-skeletal, mixed, frigid Entic Hapludolls

FIGURE 1. United States Department of Agriculture textural triangle
showing the mineral particle size distribution of the soils used inthis study.
experiments. All the soils were initially dried at 85 °C for 24
h and sieved. Major physical and chemical properties (Table
1) of each soil type were measured at the Soil and Water
Environmental Laboratory at North Dakota State University.
Specific surface area was measured using the ethylene glycol
monoethylene ether method (16).
Statistical analysis was done using SAS (17) to determine
the influence of certain soil properties on fate and transportmodel parameters from the batch and miscible-displacement
experiments. The statistical tests that were used were simple
correlations, stepwise standard least-squares analysis, andmultiple linear regression models. These models were also
used in an attempt to distinguish the effects of different soil
properties on 17β-estradiol fate and transport parameters.
Batch Sorption Experiments. Batch equilibrium sorption
studies were used to identify the sorption of 17β-estradiol toeach soil. Soil and water (0.0l M CaCl2) were added to 10-mL
vials in a ratio of 1.6 g:8 mL, respectively. The soil mass foreach batch experiment was identical except for the bentonite
clay, where only 0.16 g of solid was used because of theextreme swelling of this clay. The batch equilibrium experiments were done using various concentrations of 14Cradiolabeled 17β-estradiol (American Radiolabeled Chemicals, St. Louis, MO), where the radiolabeled carbon was
located in position 4 of the A-ring. The 14C-spiked 17βestradiol was added to triplicate vials to create solution
concentrations of 0.15, 0.015, and 0.0015 µg mL-1. These
concentrations were chosen because they were within therange of 17β-estradiol that has been found in manure applied
to agricultural fields (6). The soil-water slurries were agitatedby rotation of the vials top to bottom (360°/5 s).

organic matter
content (%)

specific surface(m2 g-1)

7.5
5.3
3.3
9.2
7.5
0.0
0.0
0.0

175
154
123
151
106
654
43

pH
6.4
6.4
7.9
7.8

After 48, 96, and 168 h, the bottles were centrifuged at
1700 rpm (380g for 20 min), and triplicate 100-µL aliquots
were removed and assayed for radioactivity by liquid
scintillation counting using a 1900 CA scintillation counter(Packard, Downers Grove, IL). Thin-layer chromatography(TLC) was used to determine if transformation occurred. The
TLC was done using silica gel plates (250 µm; Whatman Lab.
Div., Clinton, NJ) with the following solvent systems: (a)methylene chloride:hexane (1:1) and (b) tetrahydrofuran:
ethyl acetate:hexane (12.5:12.5:25). [System 2000 Imaging
Scanner (Bioscan, Inc., Washington, DC)]. Also, an assay for
total 14C sorbed to soil was done by combustion analysis ona Packard model 307 oxidizer (Downers Grove, IL). Using
these methods, the detection limit for 17β-estradiol was 1.5
ppb in terms of water (8 mL) and 7.5 ppb in terms of soil
(1.6 g).
After the bottles were centrifuged, the supernatant appeared to be clear, and it was assumed that the measured
14C was attributed entirely to the dissolved aqueous phase.
The relative centrifugal force was calculated much after theexperiments were completed, and it was found to be lower
than expected, 380g. The lower than expected centrifugal
force meant that the 14C measured in solution may haveincluded solutes attached to colloids. To identify whether
some of the measured 14C in the supernatant was attributed
to colloids, an additional batch experiment was performed.
This batch experiment was done using the same proceduredescribed earlier; however, after the centrifugation at 380g
for 20 min, another ultracentrifugation at 100000g for 1 h
was done. After the ultracentrifugation, the supernatant was
assayed for 14C again. If the 14C decreased in the final assay,then it was assumed that the loss was attributed to colloids
suspended in the solution after the first centrifugation.
Batch Sorption Model. Freundlich sorption isotherms
were used to describe the batch equilibrium experiments
and help identify the effects of various soil fractions on
sorption. In the Freundlich sorption isotherm, the concentration of solute adsorbed on the soil matrix (S; mg g-1) isrelated nonlinearly to the aqueous concentration in the soil
solution (C; mg L-3):

S ) KdC n(1)

where Kd (L g-1) is the Freundlich distribution coefficientand n is an empirical constant that controls the deviationfrom linearity (linear is n ) 1). A nonlinear, least-squares
approximation method (18) was used to obtain the best-fit
of eq 1 to the observed data by optimizing the unknown
parameters (i.e., Kd and n). Also, the coefficient of determination (r 2) was calculated to measure the goodness ofthe fit.
Miscible-Displacement Experiments. Each soil series(Table 1) was packed into individual columns, and bothchloride ion and 17β-estradiol were passed through eachcolumn. Table 2 provides the major physical properties ofeach column. The soils were evenly packed in glass columns
VOL. 37, NO. 11, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2401

TABLE 2. Soil Column Physical Properties
soil series

mass of dry soil(g)volumetric water content(cm3 cm-3)

pore water velocity(cm min-1)

pore volume(mL)

pulse input(relative PV)

Bearden-silty clay loam
Gardena-clay loam
Glyndon-sandy clay loam
LaDelle-silt loam
Sioux-loam
sand

760
699
1126
759
874
956

0.60
0.62
0.50
0.64
0.60
0.57

0.35
0.34
0.34
0.35
0.38
0.30

500
514
435
528
498
471

0.08
0.08
0.09
0.08
0.08
0.08

(diameter ) 8.4 cm, length ) 15.2 cm) with stainless steel
end caps. Sandwiched between the soil and the end caps
were several layer of cheesecloth and a 40 mesh stainlesssteel screen, which retained the soil in the column. Glass,
Teflon, and stainless steel were used in the construction tominimize adsorption to the experimental apparatus.
Each column was slowly wetted, from the bottom up,over a 24-h period using a weak salt solution (0.01 M CaCl2).
This was done to reduce the amount of entrapped air andto maintain soil structure. After the column was wetted, flow
was established from the top down using the same 0.01 M
CaCl2 salt solution. Once steady-state pore water velocity(v; cm min-1) was achieved, a pulse of chloride ion tracer(0.05 M CaCl2) was applied and eluted with the 0.01 M CaCl2
solution. The effluent was fraction collected every 2 min,and conductivity of each fraction was measured using a
conductivity meter (Oakton PC 300, Vernon Hills, IL). Table
2 provides the volumetric water content (θ; cm3 cm-3), porevolume (PV), and v of each column experiment. The v values
measured for each column resulted in residence times within
the columns that ranged between 40 and 44 min for the soils
and about 50 min for the sand.
Following the chloride ion breakthrough curve experiments, several relative pore volumes (RPVs) of the 0.01 M
CaCl2 solution were flushed through the soil column. Thena pulse of [14C]17β-estradiol (0.65 µCi, 0.2 mg) was applied
to the surface of the soil column in 40 mL of 0.01 M CaCl2(Table 2) and eluted with the 0.01 M CaCl2 solution for atleast 7-12 RPVs. The steady-state v was essentially constantfor both chloride ion and 17β-estradiol experiments (averagecoefficient of variability < 3%). The column effluent was
fraction collected every 2 min, and each fraction (ca. 20 mL)
was analyzed for 14C using the liquid scintillation method
described earlier for the batch experiment. Also, the TLC
analysis described earlier for the batch experiments was used
to determine the presence of metabolites in the column
effluent.
Additionally, at the end of the experiment, the distributionof resident 14C in the column was determined. The soil was
extruded from each column in 1-cm increments, dried, andassayed for 14C by the combustion analysis described earlier.
Solution extracts were then obtained from each 1-cm soil
increment by sequential elution with toluene, ethyl acetate,
and methanol in an accelerated solvent extractor (model
200; Dionex, Sunnyvale, CA). Analysis for metabolites wasthen done on these extracts using the TLC analysis described
for the batch experiments.
Miscible-Displacement Model. The computer program
HYDRUS-1D version 2.0 (19) was used to model the miscibledisplacement experiments. This program uses an inverse
modeling technique to fit the model solution to observed
data in order to estimate fate and transport parameters. The
inverse modeling approach uses a least-squares optimization
routine to obtain the best-fit model solution and does thisby iteratively changing model parameters until the best fit
is achieved. Also, the chloride ion and 17β-estradiol miscibledisplacement experiments were simultaneously analyzed
using the method developed by Casey and Šimůnek (20).
2402 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003

This simultaneous analysis of the two solutes leads to morereliable identification of underlying transport processes
because of added constraints to the inverse solution (20).
To describe the dynamic fate and transport, a two-site(21, 22), convective-dispersive model with transformation
and Freundlich kinetic sorption was considered. The HYDRUS-1D code assumes that solutes can exists in two phases(aqueous and sorbed) and that transformation processes canbe different in each phase. The following is the partial
differential equation that governs the nonequilibrium chemical transport for a homogeneous system during onedimensional, steady-state water flow:

∂ 2C
∂S
∂C
∂C
+ Fb ) θvλ 2 - θv
- µwθC - µSFbS
∂t
∂t
∂x
∂x

θ

(2)

where t is time (h), Fb is soil bulk density (g cm-3), λ (cm) is
the dispersivity, x is depth (cm), and µw and µS are first-orderdegradation/transformation rate constants (h-1) for the liquidand sorbed phases, respectively. For a stable nonsorbing
solute, such as the chloride ion tracer, S ) µw ) µS ) 0.
The HYDRUS-1D code may be used to simulate nonequilibrium interactions between aqueous (C) and sorbed(S) concentrations in the soil-water system. The equilibrium
sorption isotherm relating S and C is described by the
Freundlich isotherm (eq 1).
The concept of two-site sorption (21, 22) is implemented
in the HYDRUS-1D code to account for possible nonequilibrium adsorption-desorption reactions. In the two-site
model, sorption can occur instantaneously on labile exchangesites (i.e., type-1 sites signified by Se) or kinetically on theremaining exchange sites (i.e., type-2 sites signified by Sk).
The mass balance equations for the type-2 sites in thepresence of degradation/transformation is given by

S ) Se + Sk

(3)Se ) fKdC n

(4)

∂Sk
) ω[(1 - f )KdC n - Sk] - µSSk∂t(5)

where ω is the first-order kinetic sorption coefficient (h-1)
and f is the fraction of exchange sites that are in equilibriumwith the solution phase (-).
An alternative model was also considered that included
transformations or production of the various 17β-estradiol
metabolites. Recent studies have indicated that 17β-estradiol
undergoes rapid transformation in agricultural soils (11). Also,
our results from the TLC data indicated that transformation
occurred. The chemical nonequilibrium, convective-dispersive model that was considered includes transformationin both aqueous and dissolved phases and is governed by
the following partial differential equations:

FIGURE 2. Freundlich isotherms obtained from the equilibrium batch experiments from this study as compared with isotherm determined
for sediment (20).

∂S1∂ 2 C1∂C1∂C1+ Fb) θvλ 2 - θv
∂t
∂t
∂x
∂x
(µw + µ′w)θC1 - (µS + µ′S)FbS1 (6)

θ

θ

∂C2
∂C2
∂S2
∂ 2 C2+ Fb) θvλ 2 - θv
+ µ′wθC1 + µ′SFbS1 (7)
∂t
∂t
∂x
∂x

where µ′w and µ′S are first-order transformation rate constants providing mass connection between 17β-estradiol andits metabolites. The first solute species (C1 and S1) canrepresent 17β-estradiol that is transformed into a second,
mobile species (C2 and S2), which was unidentified by the
TLC analysis but found to have high polarity. The first species
17β-estradiol is also degraded/transformed (µw and µS) intoa third species (metabolite), which was identified as estrone.
However, estrone was not followed further by the model,
and it was assumed that it was strongly adsorbed to the soil.
Additionally, estriol was detected in the sorbed and aqueous
phases, but these detections were sporadic and insignificant;therefore, it also was not followed by the model. Linear
sorption (not Freundlich) was considered in this case becauseof the model’s complexity. Also, two-site sorption with labileand kinetic sorption sites was considered where the massbalance equations for the sorption sites are given by eqs
3-5.

Results and Discussion
Batch Experiments. Measurement of 17β-estradiol at such
low experimental concentrations was complicated by transformations and by possible colloidal suspensions. After 48
h, the batch experiments for 17β-estradiol appeared to be atequilibrium (i.e., there was little difference in supernatant
14C counts between 48 and 169 h). However, the TLC analysis
indicated that there were appreciable amounts of metabolite
present after 169 h. The parent compound, 17β-estradiol,
only accounted for approximately 50-70% of the 14C at the
169-h sample time. Additionally, the amount of 14C present
in the supernatant decreased by approximately 20% after
the ultracentrifugation experiment (100000g for 1 h), whichsuggested that some 14C was found on colloids suspended
in the supernatant. This result indicated the contributionthat colloid facilitated transport may have on the fate andtransport of 17β-estradiol.
During the first 48 h, the 17β-estradiol sorption rates
ranged from 0.002 µg g-1 h-1 for the sand to 0.112 µg g-1 h-1

TABLE 3. Freundlich Sorption Isotherm Parameters andCoefficient of Determination of Isotherm Fit
soil

Kd (L g-1)nr2

Bearden-silty clay loam
Gardena-clay loam
Glyndon-sandy clay loam
LaDelle-silt loam
Sioux-loam
bentonitekaolinite
sand

0.151
0.332
0.086
6.670
0.135
0.110
0.010
0.004

1.088
1.297
1.151
1.299
1.363
0.954
1.053
2.000

1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00

for the bentonite clay. These 17β-estradiol sorption rates
were similar to sorption rates from river and estuary
sediments (0.07-0.37 µg g-1 h-1 calculated at 1-5 h)measured by Lai et al. (15).
Freundlich Parameters. The Freundlich isotherm parameters (Table 3) were determined from the 48-h concentrations because of the larger amounts of metabolites foundat 168-h sample times. Also, the concentrations did not
exclude any possible contributions from colloids in suspension. Lai et al. (15) reported a Kd for 17β-estradiol of 0.036
L g-1 for the sediments, which fell within the lower range ofvalues found in this study (Table 3), but their n value (n )0.67) was lower than any found in this study (Table 3).
Although the parameters did not completely agree, theisotherms calculated from the Lai et al. (15) parameterscompared well with the isotherms in this study (Figure 2).
The difference between the isotherm parameters may be
attributed to several differences between studies, including
particle size distributions, organic matter content, andsuspended colloids. Additionally, Lai et al. (15) used an earlier
time, 1 h, to calculate isotherm parameters as comparedwith the time used in this study, 48 h. At 1 h, the 17β-estradiol
may not have reached an equilibrium sorption concentration,
which could result in lower Kd values. On the other hand,transformations may occur at longer times (as used in thisstudy), which may affect the sorption parameter estimates.
Except for the bentonite clay, all of the n values from thisstudy were >1.0 (Table 3), which indicated that sorption site
availability did not approach a limit as it did for the sedimentstudy (15). This meant that there was little competition for
exchange sites by estrogens.
Batch Sorption Correlations. Correlations between
Freundlich parameters and soil fractions were not madeVOL. 37, NO. 11, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2403

FIGURE 3. Correlations between sorbed estrogen (initial concentration was 0.0015 mg L-1 in 8 mL of water and 1.6 g of soil and shaken
for 48 h), particle sizes, and organic matter content from the batch experiments.
because the isotherms were nonlinear (i.e., n * 1). Insteadcorrelations of sorption to various soil fractions were
determined for the initial aqueous concentrations of 0.0015
mg L-1 in 8 mL of water and 1.6 g of soil and shaken for 48
h. A general correlation between sorption and particle size
was found (Figure 3). These correlations reflect a relation
between sorption and surface area where specific surface
area (Table 1) was highly correlated (r 2 ) 0.92) to sorption.
However, these correlations to particle size may also reflect
a sorption mechanism governed by interactions between
surface ion-exchange sites and charged or polar solutes. Lai
et al. (15) found estrogen sorption to iron oxides and suggest
an ion exchange mechanism where polar, phenolate estrogens bind to charged iron oxides. Cation exchange complexes
are associated with clay minerals and organic matter andcan result in the sorption of polar compounds, such as
phenolates. This sorption mechanism may partially explain
the difference in the sorption affinity between bentonite (highaffinity) and kaolinite (low affinity) clays as well as the soils
with the taxonomic designation of “superactive” (Table 1).
2404 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003

Kaolinite has a low specific surface area (Table 1) and a low
cation-exchange capacity (CEC) that typically ranges between
3 and 15 cmol kg-1. Bentonite has a high specific surface
area (Table 1) and is mainly composed of smectite, which
has a high CEC of 100-150 cmol kg-1. The “superactive”
taxonomic designation (Table 1) of the Bearden, Gardena,
Glyndon, and LaDelle soils denotes a high CEC, and all thesesoils have higher isotherms than the nonsuperactive Siouxsoil (Figure 2). These results indicate that clay minerals will
likely influence sorption, but further experiments are needed
to elucidate the binding mechanism of estrogens in naturalsoils.
Last, there appeared to be a strong correlation between
sorption and silt content (r 2 ) 0.92) (Figure 3); however, thiscorrelation was confounded because silt was also correlated
to the organic matter content (r 2 ) 0.68). The statistical model
used was unable to significantly distinguish the effects oforganic matter from the effects of silt content on sorption.
It would intuitively seem that the organic matter was thecause of this correlation and that the silt correlation was

FIGURE 4. 17β-Estradiol column breakthrough curves and corresponding model fits for each soil. The model schematic for the first model(eqs 2-5) and the second model (eqs 6 and 7) are provided in Figure 5. The Glyndon series soil shows the 17β-estradiol distribution within
the soil column because there was no effluent breakthrough. Also presented are chloride ion breakthrough curves that were simultaneously
modeled with the 17β-estradiol.
coincidental, because silt is relatively inert. Lai et al. (15) also
found a strong correlation between total organic carbon, but
only weak correlations with particle size distribution.
Miscible-Displacement Experiments. For all the soils,
very little or no (i.e., Glyndon-sandy clay loam) 14C was present
in the column effluent (Figure 4). Although 14C was not present

in the Glyndon column effluent, there was significant
redistribution throughout the column profile (Figure 4). The
mass balance of 14C (Table 4) recovered from within the
Glyndon soil column was -100%. The TLC analyses indicatedthat 17β-estradiol was not present in any of the effluents ofany soil columns, which suggested little or no aqueous orVOL. 37, NO. 11, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2405

TABLE 4. Miscible-Displacement Parameter Estimates for the First Model (Eqs 2-5; Figure 5) with 95% Confidence Interval(in Parentheses)asoil
Bearden-silty
clay loam
Gardena-clay
loam
Glyndon-sandy
clay loam
LaDelle-siltloam
Sioux-loam

λ(cm)
12.556(0.902)
10.339(0.942)3.615(0.514)9.062(1.465)61.997(1238.397)

f
0
0.008
(0.015)00.003(0.004)0.527(36.728)

Kd(L g-1)n

0.769(2.945)0.542(2.590)1.614(8.940)1.043(1.925)0.265(19.438)1.637(0.494)1.346(0.445)1.394(1.250)1.873(0.697)0.984(0.272)

µw
(h-1)

µS
(h-1)

0.001
(3.372)0.001(9.524)01.494(0.542)2.800(1.009)00.001(3.739)4.544(28225.544)

0.480(0.929)0.284(44.994)ω (h-1)

r2

mass
recoveryb
(%)

0.615
(0.802)0.526(1.002)
1.173(1.781)
0.152(0.134)0.664(47.231)

0.998

3.2

0.997

0.4

0.985

0.0
(99.6)
20.8

0.989
0.966

0.1
(75.8)a Also present are coefficients of determination of model fit and the mass recovery of 14C. b Mass recovery represents the amount of solute
recovered in the column effluent. Values inside parentheses in this column represent the mass recovered from within the soil.

colloidal transport of this highly sorbed chemical. Rather, anunidentified high-polarity metabolite was found in theeffluent along with sporadic and trace detections of estriol.
Bolton et al. (23) suggest a metabolic pathway where 17βestradiol is oxidized to estrone and then further to a morepolar semiquinone or quinone. Quinones and semiquinones
can cause oxidative damage to DNA and can be ionized (i.e.,
have a negative charge), which would make them watersoluble and very mobile in soil. An ionized compound could
possibly explain the early arrival of 14C in the column effluent(Figure 4), which appeared nearly at the same time as thechloride ion tracer. It was just as likely that other possible
metabolites may have also been present. Layton et al. (13)and Jurgens et al. (24) show transformation of 17β-estradiol,ultimately leading to mineralization/ring cleavage in activatedsludge and river water, respectively.
The TLC analyses of the soil extracts from within eachcolumn indicated that the majority of the sorbed 14C was
17β-estradiol and another metabolite of lower polarity, which
was identified as estrone. Estriol was also detected sporadically in trace amounts in the extracts. These general results
indicated that 17β-estradiol entered the soil column, readily
partitioned to the solid phase, and underwent rapid transformation to form at least three metabolites of different
polarity. The lower polarity estrone was adsorbed to the soil,
and the higher polarity metabolites were more mobile in thecolumn and more readily transported in the aqueous phase.
It was possible that some of the 14C was redistributed throughthe column by colloidal transport, especially for the highly
sorbed estrone and 17β-estradiol. However, none of the highly
sorbed compounds were present in the effluent, only thehigh polarity metabolite, which was likely transported in the
dissolved aqueous phase.
Miscible-Displacement Model Analysis. The breakthrough of 14C in the column effluents (Figure 4) displayedsigns of nonequilibrium transport, which was signified by
the long tails or late arrivals of solute. However, the chloride
ion tracer was transported through all soil columns as aconvective-dispersive process with no sorption or transformation (eq 2 when S ) µS ) µw ) 0). The nonequilibriumtransport of the 14C was thus determined to be a result ofchemical interactions (e.g., sorption processes, degradation)
because there were no strong indications of physical nonequilbrium (i.e., preferential flow) from the chloride ion
experiments. The dispersivity (λ) values presented in Table
4 represent a single value that was simultaneously optimized(20) for both chloride and 17β-estradiol experiments, whileassuming v was constant for both experiments. The λ was
the same for the two models that were considered, which
added constraints to the other parameter estimates andimproved the inverse model uniqueness.
2406 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003

The analysis of the breakthrough curves for the 17βestradiol was complicated by the fact that simultaneoustransformation and kinetic sorption occurred. The TLC
data analyses indicated the presence of three metabolites
but were unable to quantify their relative concentrations.
Therefore, no quantitative conclusions could be made about
the transformation of 17β-estradiol, which was only foundsorbed inside the column and not in the column effluent. It
was necessary to make an assumption regarding the transportof the 17β-estradiol and its metabolites and to consider
different types of models to interpret the data.
The two models that were considered were presented in
Figure 5. The first model (eqs 2-5) treated the total 14C asa single species that underwent transformation in the aqueousand sorbed phases. This meant that the identified sorption
or transformation rates were identical or represented alumped value for 17β-estradiol and its metabolites. The
second model (eqs 6 and 7) considered that the 17β-estradiol
entered the soil and was transformed into the unidentified
high-polarity metabolite in addition to estrone or estriol.
The transformation constants µw and µS were used for estrone,and µ′w and µ′S were used for the polar metabolite. The
parameters for the second model were estimated by simultaneously fitting (20) the measured concentrations of 17βestradiol and the polar metabolite in the column effluent,where 17β-estradiol concentrations (C1 in eqs 6 and 7) were
all set to zero and the polar metabolite concentrations(C2 in eqs 6 and 7) were set to the measured 14C. The second
model could not follow the fate of estrone or estriol, but it
could be assumed that they were strongly sorbed to the soil
shortly after transformation, which was consistent with the
TLC data.
Both the first and the second models had advantages anddisadvantages. The first model simultaneously tracked all
estrogen compounds, used Freundlich sorption, and had
fewer model parameters to estimate. Fewer parameters
increase the reliability of their estimates; however, theidentical transformation or sorption rates for 17β-estradiol
and its metabolites made this model physicochemically lesslikely. The second model was physicochemically more
realistic, but additional parameters were needed, only linear
sorption was considered, and transport of estrone and estriol
were not followed after transformation. Both models provided
excellent description of the data (indicated by r 2 values inTables 4 and 5). However, the lack of information about thetransformation process, metabolic products, and the highnumber of fitting parameters resulted in decreased confidence in parameter estimates and decreased uniqueness in
the inverse model solution. As a result, the confidence
intervals of the parameter estimates (Tables 4 and 5) often
spanned the entire spectrum. Additional information about

FIGURE 5. Schematics of the two miscible-displacement models that were used to describe the fate and transport of 17β-estradiol. The
arrows indicate mass transfer or transformations of the compounds in the parentheses. Double-headed arrows link compartments thatreach equilibrium instantaneously. Also C1, C2, S1, and S2 were defined in eqs 6 and 7.

TABLE 5. Parameter Estimates for the Second Model (Eqs 6 and 7; Figure 5) with 95% Confidence Interval (in Parentheses)
soil
Bearden-silty
clay loam
Gardena-clay
loam
LaDelle-siltloam
Sioux-loam

Kd,1(L g-1)

µw
(h-1)

µS
(h-1)

µ′w
(h-1)

µ′S
(h-1)

T1
(h-1)

Kd,2
(L g-1)

T2
(h-1)

0.180
(0.920)0.837(69.230)0.418(39.870)
1.209(3.000)0.000(0.270)4.069(5129.890)
0.001(0.000)0.001(0.000)0.418(0.270)1.221(15.310)0.001(0.600)0.299(1.130)5.687(3.080)4.949(5.170)34.547(264.560)
0.001(1.680)0.388(0.25)
0.281(10.61)
0.766(4.30)
0.026(0.20)

0.292(1.540)0.119(5.570)0.143(14.510)0.333(0.880)0.223(0.110)0.412(0.120)0.059(0.040)0.178(0.590)0.029(0.010)0.035(0.010)0.057(0.030)0.677(0.620)

the relative amounts of the various sorbed metabolites wasneeded to improve parameter confidence and uniqueness.
Nonetheless, the model solutions provided realistic parameter values that could be used to create a hypothesis for thefate and transport of 17β-estradiol and its metabolites.
The confidence in the modeling was especially low for
the Sioux-loam where the effluent concentrations were very
low. A complete breakthrough curve was not obtained during
the experiment, and measured concentrations were significantly scattered. Consequently, different initial estimates of
optimized parameters resulted in widely different estimates

r2
0.931
0.988
0.986
0.818

with similar values of the objective function. The optimized
parameters for this soil suffered from the largest degree of
uncertainty and will not be discussed further.
Sorption. Miscible-displacement sorption coefficientswere not held constant to the values obtained from the batch
experiments for several reasons. Transformations occurred
during the column studies and the metabolite sorption
coefficient would not be the same as the batch experiments.
Sorption parameters obtained from a column study will beaffected by rate-limited mass transfer because of advective
transport. Sorption parameters from batch experiments will
VOL. 37, NO. 11, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2407

not include this rate-limited mass transfer. It should be noted,that the batch sorption values were used as initial guesses
for the inverse parameter estimates. This helped to achievea minimum for the objective function.
The f values for both models were small or zero (Tables
4 and 5) and indicated that sorption was almost fully kinetic
with no instantaneous or labile sorption sites (i.e., type-1
sites). All the soil column breakthrough curves modeled withthe second model resulted in full kinetic sorption with notype-1 sorption sites, so f ) 0 in each case (Table 5). The only
case where labile sorption was significant was for the firstmodel for the Sioux-loam, where model confidence was verylow.
Equilibrium sorption estimated by the first and second
models compared well with the batch experiments and withother studies. The batch Fruendlich parameters (Table 3)
fell within the range of values estimated from the first model(Table 4). The linear 17β-estradiol Kd,1 values of the second
model (0.18-1.209 L g-1) compared well with the linearized(where n was forced to equal 1) batch experiment Kd values(0.010-0.322 L g-1). Also, the linearized 17β-estradiol Kdvalues from the first (0.137-0.661 L g-1) and second (0.1801.209 L g-1) models were slightly higher but comparable tothe linearized Kd value (0.070 L g-1) reported for sediments
by Lai et al. (15).
For the second model, the polar metabolite had a similar
or slightly lower Kd value as compared to the 17β-estradiol.
This indicated that sorption kinetics had a significant role inthe mobility of these compounds. The difference in thesorption kinetics was indicated by the difference between ω1and ω2 values for the second model (Table 5). The ω1 waslower than ω2 for all soils except the Sioux-loam, where theconfidence of the model analysis was low. Using batch kinetic
experiments with sediments, Lai et al. (15) shows that 17βestradiol has more rapid sorption than its metabolite, estriol.
The higher ω value of 17β-estradiol would result in a rapid
sorption process, which quickly binds it to the soil and makes
it less mobile. By separating the ω values between 17βestradiol (i.e., ω1) and its metabolite (i.e., ω2), the second
model was able to describe the solute tailing better than thefirst model (Figure 4). The first model lumped ω for both17β-estradiol and its metabolites, which resulted in a poorer
description of the solute tail. A better description of the data
would indicate a more realistic description of the fate andtransport processes.
Degradation/Transformations. The first model indicatedthat nearly all degradation/transformation occurred on thesorbed phase. The second model also indicated a sorbed
phase transformation for 17β-estradiol. Previous research(13) on the degradation of 17β-estradiol in biosolids ofwastewater treatment facilities provides evidence for sorbedphase transformations. This earlier research indicates theimportance of the amount of 17β-estradiol that remains in
the aqueous phase, and how it can decrease the effectivenessof removal by degradation. Furthermore, the sorbed-phasedegradation/transformation of 17β-estradiol was consistent
with the TLC results where 17β-estradiol, estrone, and trace
estriol were the only 14C found sorbed to the soil and themore oxidized polar metabolite was predominantly found in
the aqueous phase.
No efforts were made to isolate biodegradation in thisstudy (i.e., sterilization of the soil). Also, the degradation
rates may not have accurately reflected natural rates because
biodegradation may have been reduced due to the ovendrying process. Nonetheless, the µS values for the first andsecond models were similar to other studies, which measured
degradation in agricultural soils and biosolids. Previous
studies have shown that estrogens undergo rapid degradationin agricultural soils (11, 12) and by biosolids in wastewater
treatment facilities (13). The 17β-estradiol degradation rates
2408 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003

(0.06-0.12 h-1) reported for agricultural soils (11) fell in thelower range of µS values of the first model (0.284-2.800 h-1)
and were very similar to the µS and µ′S values (0 0.001-1.221h-1) of the second model. Degradation rates (0.252 ( 0.012h-1) reported for 17β-estradiol in biosolids (13) fell within
the range most similar to the µS values for the 17β-estradiolof the second model (Table 5). Any differences between µ
values from the current column experiments and thosereported by earlier studies can be explained by relative
uncertainty of the optimized parameter values and by several
experimental factors that affect 17β-estradiol degradation/transformation rates. These factors include temperature andwater content (11-13). The experiments done in this study
were conducted at or near saturation, while the study on
persistence in agricultural soils used unsaturated soils (0.13
cm3 cm-3). The column experiments of this study contained
more soil than the previous studies (11, 13). The greater
amount of soil would increase the amount of available
sorption sites where degradation may likely occur.
The results from the column experiments and recent
studies (11, 13) have indicated rapid degradation/transformation of 17β-estradiol. Colucci et al. (11) found that 17βestradiol is rapidly transformed into estrone and that estrone
persists in the soil for the duration of their experiment (3 d)without further degradation. Other studies have suggested
a metabolic oxidation sequence of 17β-estradiol, where
estrone and estriol are produced (25), and further transformations can occur to form semiquinones and quinones (23)or possibly result in steroid ring cleavage (13, 24). Thesestudies indicate a sequence of possible transformations thatare consistent with the identification of metabolites fromour miscible-displacement experiments. However, it was notpossible to definitively identify the high-polarity metabolite,
which could pose a greater risk (if found to be potent) tosurface and subsurface water because of its higher mobility.
Additionally, the long-term persistence of estrone in the soil
needs to be identified and may lead to impacts on soil andwater quality if it is repeatedly applied to the soil, as would
occur in a field setting. The preliminary findings from thisstudy nonetheless indicated that no intact 17β-estradiol or
identifiable estrogen metabolites could escape from these
agricultural soils. It may be concluded that 17β-estradiolenriched manure could be safely applied to these high organic
disturbed soils provided that no bypass flow (e.g., preferential
transport) or facilitated (e.g., colloid) transport results insignificant depth of transport. The disposal of 17β-estradiol
enriched manure would also be precluded in areas where
there is significant surface runoff where sorbed 17β-estradiol
can be transported in suspension.

Acknowledgments
The authors greatly appreciate the long hours dedicated tothis research by the following technical experts: Mrs. Barbara
K. Magelky and Mrs. Colleen M. Pfaff. The authors also
acknowledge the National Science Foundation for theirsupport of this research.

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Received for review September 12, 2002. Revised manuscript
received March 12, 2003. Accepted March 19, 2003.
ES026153Z

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