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Environ. Sci. Technol. 2003, 37, 2400-2409
Fate and Transport of 17â-Estradiol
great number of people and wildlife can be impacted byexposure to reproductive hormones, especially since they in Soil-Water Systems
can produce adverse effects at remarkably low concentrations(<1.0 ng L-1; 2-4). For example, 17â-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 are Department of Soil Science, North Dakota State University, naturally produced and excreted by animals, and they are Fargo, North Dakota 58105, Animal Metabolism Unit, also administered as growth promoters to help in efficiency Biosciences Research Laboratory, USDA-ARS, Fargo, of feed utilization. When used as such, they are given as North Dakota 58105, and George E. Brown, Jr. Salinity benzoate and palmitate esters of estradiol, and the body will Laboratory, USDA-ARS, Riverside, California 92507 hydrolyze them to 17â-estradiol. On the eastern shore ofMaryland, it has been estimated that 200 000 t yr-1 of broilerchicken manure is produced, which contains 30 ng g-1 (30ppb) of 17â-estradiol. This is equivalent to about 6 kg of Over the past several years, there has been an increase 17â-estradiol being applied to fields when the manure is in concern regarding reproductive hormones in the used as a fertilizer (5). In 1997, the entire U.S. poultry industry environment. To date, there exists limited research on the produced over 10 billion kg of broiler litter, 90% of which fate and transport of these chemicals in the environment.
was applied to crop lands. In a worst case situation, this In this study, a series of laboratory batch sorption and miscible- amount of manure can potentially contain 270 kg of 17â- displacement experiments were done using radiolabeled estradiol, which, at a 1.0 ng L-1 concentration, has the capacity [14C]17â-estradiol. The 17â-estradiol concentrations that were to contaminate 270 km3 of water.
used were similar to those found in manures that are In an experiment where manure was applied to a field, applied to field soils. Equilibrium batch experiments indicated 17â-estradiol was found in a nearby free flowing stream at high sorption affinity with correlations to mineral particle concentrations of 5 ng L-1 (5). In another experiment wheremanure was applied to a field, the concentrations of 17â- size and organic matter content. The sorption affinity appeared estradiol in surface runoff reached 150-2300 ng L-1 (6).
to be associated with the surface area and/or the cation- Recently, Renner (7) reported that hormone adulterated exchange capacity of the soil. The miscible-displacement runoff from cattle feedlots could be affecting local fish.
breakthrough curves indicated chemical nonequilibrium Furthermore, Nichols et al. (8), Shore et al. (9), and Peterson transport, and a single highly polar metabolite was present et al. (10) have identified 17â-estradiol (highest concentration in the column effluent along with sporadic and trace of 37.6 ng L-1) in aquifers underlying areas where animal detections of estriol. Sorbed to the soil within the column wastes have been applied. Limited studies have been done were found 17â-estradiol, estrone, and trace and sporadic on the persistence (11-13) and sorption (14, 15) of estrogens detections of estriol. Two chemical nonequilibrium, miscible- in soil and sediment, but little is known about the fate and displacement models were used to describe the column transport of these chemicals in the environment.
It is essential to understand the fate and transport breakthrough curves; one without transformations and the processes of estrogens in the environment in order to assess other with transformations. Both models resulted in their potential impacts on soils, surface water, and ground- excellent descriptions of the data, which indicated nonunique water resources. The objectives of this research were to solutions and less confidence in the parameter estimates.
identify the sorption, fate, and mobility of 17â-estradiol in Nonetheless, the modeling and experimental results soil-water systems. These objectives would identify the implied that degradation/transformation occurred in the general effects of soil composition on these parameters by sorbed phase and was rapid. Also, both models indicated using laboratory batch sorption and miscible-displacement that sorption was fully kinetic.
experiments. Also, 17â-estradiol was chosen for the followingreasons: (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 The presence of low levels of bioactive chemicals in the all endocrine disruptors that interact through the estrogen environment have become a concern to the United States, receptor; (iv) it is eliminated (i.e., excreted) by all studied other countries, and international organizations (e.g., World organisms, from cattle and poultry to humans, and therefore Health Organization, United Nations). A congressional bill it has the potential to be widely distributed in the environ- (H.R. 1712) was submitted to the 106th U.S. Congress that ment; and (v) little is known about how 17â-estradiol and its proposed to amend the Federal Water Pollution Act to metabolites behave in the environment.
authorize an estrogenic substance screening program. Koplinet al. (1) has recently completed an extensive reconnaissance Materials and Methods
of surface waters in which 139 streams were sampled across The soils that were used were Bearden-silty clay loam, 30 states in the United States. Reproductive hormones were Gardena-clay loam, Glyndon-sandy clay loam, LaDelle-silt found in approximately 40% of the 139 streams sampled. A loam, and Sioux-loam (taxonomic descriptions provided inTable 1). All these soils, except the Glyndon, were obtained * Corresponding author phone: (701)231-8577; fax: (701)231-7861; from Ag-Vise Company (Northwood, ND) and were collected in North Dakota and represent a variety of soil textures (Figure North Dakota State University.
‡ USDA-ARS, Fargo.
1). Additionally, a medium quartz sand (250-500 µm) and § USDA-ARS, Riverside.
kaolinite and bentonite clays were used in the batch 2400 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003
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, and
Organic Matter Content
soil series
content (%)
Bearden-silty clay loam fine-silty, mixed, superactive, frigid Aeric Calciaquolls Gardena-clay loam coarse-silty, mixed, superactive, frigid Pachic Hapludolls Glyndon-sandy clay loam coarse-silty, mixed, superactive, frigid Aeric Calciaquolls LaDelle-silt loam fine-silty, mixed, superactive, frigid Cumulic Hapludolls sandy-skeletal, mixed, frigid Entic Hapludolls After 48, 96, and 168 h, the bottles were centrifuged at 1700 rpm (380g for 20 min), and triplicate 100-µL aliquotswere removed and assayed for radioactivity by liquidscintillation counting using a 1900 CA scintillation counter(Packard, Downers Grove, IL). Thin-layer chromatography(TLC) was used to determine if transformation occurred. TheTLC 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 ImagingScanner (Bioscan, Inc., Washington, DC)]. Also, an assay fortotal 14C sorbed to soil was done by combustion analysis ona Packard model 307 oxidizer (Downers Grove, IL). Usingthese methods, the detection limit for 17â-estradiol was 1.5ppb in terms of water (8 mL) and 7.5 ppb in terms of soil(1.6 g).
After the bottles were centrifuged, the supernatant ap- peared to be clear, and it was assumed that the measured14C 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 lowerthan expected, 380g. The lower than expected centrifugal FIGURE 1. United States Department of Agriculture textural triangle
force meant that the 14C measured in solution may have showing the mineral particle size distribution of the soils used in
included solutes attached to colloids. To identify whether this study.
some of the measured 14C in the supernatant was attributed experiments. All the soils were initially dried at 85 °C for 24 to colloids, an additional batch experiment was performed.
h and sieved. Major physical and chemical properties (Table This batch experiment was done using the same procedure 1) of each soil type were measured at the Soil and Water described earlier; however, after the centrifugation at 380g Environmental Laboratory at North Dakota State University.
for 20 min, another ultracentrifugation at 100000g for 1 h Specific surface area was measured using the ethylene glycol was done. After the ultracentrifugation, the supernatant was monoethylene ether method (16).
assayed for 14C again. If the 14C decreased in the final assay, Statistical analysis was done using SAS (17) to determine then it was assumed that the loss was attributed to colloids the influence of certain soil properties on fate and transport suspended in the solution after the first centrifugation.
model parameters from the batch and miscible-displacement Batch Sorption Model. Freundlich sorption isotherms
experiments. The statistical tests that were used were simple were used to describe the batch equilibrium experiments correlations, stepwise standard least-squares analysis, and and help identify the effects of various soil fractions on multiple linear regression models. These models were also sorption. In the Freundlich sorption isotherm, the concen- used in an attempt to distinguish the effects of different soil tration of solute adsorbed on the soil matrix (S; mg g-1) is properties on 17â-estradiol fate and transport parameters.
related nonlinearly to the aqueous concentration in the soil Batch Sorption Experiments. Batch equilibrium sorption
solution (C; mg L-3): studies were used to identify the sorption of 17â-estradiol toeach soil. Soil and water (0.0l M CaCl2) were added to 10-mL S ) K C n vials in a ratio of 1.6 g:8 mL, respectively. The soil mass foreach batch experiment was identical except for the bentonite where Kd (L g-1) is the Freundlich distribution coefficient clay, where only 0.16 g of solid was used because of the and n is an empirical constant that controls the deviation extreme swelling of this clay. The batch equilibrium experi- from linearity (linear is n ) 1). A nonlinear, least-squares ments were done using various concentrations of 14C- approximation method (18) was used to obtain the best-fit radiolabeled 17â-estradiol (American Radiolabeled Chemi- of eq 1 to the observed data by optimizing the unknown cals, St. Louis, MO), where the radiolabeled carbon was parameters (i.e., Kd and n). Also, the coefficient of determi- located in position 4 of the A-ring. The 14C-spiked 17â- nation (r 2) was calculated to measure the goodness of estradiol was added to triplicate vials to create solution concentrations of 0.15, 0.015, and 0.0015 µg mL-1. These Miscible-Displacement Experiments. Each soil series
concentrations were chosen because they were within the (Table 1) was packed into individual columns, and both range of 17â-estradiol that has been found in manure applied chloride ion and 17â-estradiol were passed through each to agricultural fields (6). The soil-water slurries were agitated column. Table 2 provides the major physical properties of by rotation of the vials top to bottom (360°/5 s).
each 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
mass of dry soil
volumetric water content
pore water velocity
pore volume
pulse input
soil series
Bearden-silty clay loam Gardena-clay loam Glyndon-sandy clay loam LaDelle-silt loam (diameter ) 8.4 cm, length ) 15.2 cm) with stainless steel This simultaneous analysis of the two solutes leads to more end caps. Sandwiched between the soil and the end caps reliable identification of underlying transport processes were several layer of cheesecloth and a 40 mesh stainless because of added constraints to the inverse solution (20).
steel screen, which retained the soil in the column. Glass, To describe the dynamic fate and transport, a two-site Teflon, and stainless steel were used in the construction to (21, 22), convective-dispersive model with transformation minimize adsorption to the experimental apparatus.
and Freundlich kinetic sorption was considered. The HY- Each column was slowly wetted, from the bottom up, DRUS-1D code assumes that solutes can exists in two phases over a 24-h period using a weak salt solution (0.01 M CaCl2).
(aqueous and sorbed) and that transformation processes can This was done to reduce the amount of entrapped air and be different in each phase. The following is the partial to maintain soil structure. After the column was wetted, flow differential equation that governs the nonequilibrium chemi- was established from the top down using the same 0.01 M cal transport for a homogeneous system during one- CaCl2 salt solution. Once steady-state pore water velocity dimensional, steady-state water flow: (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 CaCl2solution. The effluent was fraction collected every 2 min, and conductivity of each fraction was measured using a wθC - µS b conductivity meter (Oakton PC 300, Vernon Hills, IL). Table2 provides the volumetric water content (θ; cm3 cm-3), pore where t is time (h), Fb is soil bulk density (g cm-3), λ (cm) is volume (PV), and v of each column experiment. The v values the dispersivity, x is depth (cm), and µw and µS are first-order measured for each column resulted in residence times within degradation/transformation rate constants (h-1) for the liquid the columns that ranged between 40 and 44 min for the soils and sorbed phases, respectively. For a stable nonsorbing and about 50 min for the sand.
solute, such as the chloride ion tracer, S ) µ ) Following the chloride ion breakthrough curve experi- The HYDRUS-1D code may be used to simulate non- ments, several relative pore volumes (RPVs) of the 0.01 M equilibrium interactions between aqueous (C) and sorbed CaCl2 solution were flushed through the soil column. Then (S) concentrations in the soil-water system. The equilibrium a pulse of [14C]17â-estradiol (0.65 µCi, 0.2 mg) was applied sorption isotherm relating S and C is described by the to the surface of the soil column in 40 mL of 0.01 M CaCl2 Freundlich isotherm (eq 1).
(Table 2) and eluted with the 0.01 M CaCl2 solution for atleast 7-12 RPVs. The steady-state v was essentially constant The concept of two-site sorption (21, 22) is implemented for both chloride ion and 17â-estradiol experiments (average in the HYDRUS-1D code to account for possible nonequi- coefficient of variability < 3%). The column effluent was librium adsorption-desorption reactions. In the two-site fraction collected every 2 min, and each fraction (ca. 20 mL) model, sorption can occur instantaneously on labile exchange was analyzed for 14C using the liquid scintillation method sites (i.e., type-1 sites signified by Se) or kinetically on the described earlier for the batch experiment. Also, the TLC remaining exchange sites (i.e., type-2 sites signified by Sk).
analysis described earlier for the batch experiments was used The mass balance equations for the type-2 sites in the to determine the presence of metabolites in the column presence of degradation/transformation is given by Additionally, at the end of the experiment, the distribution S ) Se + Sk of resident 14C in the column was determined. The soil wasextruded from each column in 1-cm increments, dried, andassayed for 14C by the combustion analysis described earlier.
Se ) fK C n Solution extracts were then obtained from each 1-cm soilincrement by sequential elution with toluene, ethyl acetate, and methanol in an accelerated solvent extractor (model ) ω[(1 - f )K C n - Sk] - µ Sk 200; Dionex, Sunnyvale, CA). Analysis for metabolites wasthen done on these extracts using the TLC analysis describedfor the batch experiments.
where ω is the first-order kinetic sorption coefficient (h-1) Miscible-Displacement Model. The computer program
and f is the fraction of exchange sites that are in equilibrium HYDRUS-1D version 2.0 (19) was used to model the miscible- with the solution phase (-).
displacement experiments. This program uses an inverse An alternative model was also considered that included modeling technique to fit the model solution to observed transformations or production of the various 17â-estradiol data in order to estimate fate and transport parameters. The metabolites. Recent studies have indicated that 17â-estradiol inverse modeling approach uses a least-squares optimization undergoes rapid transformation in agricultural soils (11). Also, routine to obtain the best-fit model solution and does this our results from the TLC data indicated that transformation by iteratively changing model parameters until the best fit occurred. The chemical nonequilibrium, convective-dis- is achieved. Also, the chloride ion and 17â-estradiol miscible- persive model that was considered includes transformation displacement experiments were simultaneously analyzed in both aqueous and dissolved phases and is governed by using the method developed by Casey and Sˇimu ˚ nek (20).
the following partial differential equations: 2402 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003
FIGURE 2. Freundlich isotherms obtained from the equilibrium batch experiments from this study as compared with isotherm determined
for sediment (20).
TABLE 3. Freundlich Sorption Isotherm Parameters and
Coefficient of Determination of Isotherm Fit
µ′S b 1 Kd (L g-1)
Bearden-silty clay loam + µ′F S (7) Gardena-clay loam Glyndon-sandy clay loam LaDelle-silt loam where µ′ and µ′ are first-order transformation rate con- stants providing mass connection between 17â-estradiol and its metabolites. The first solute species (C1 and S1) can represent 17â-estradiol that is transformed into a second, mobile species (C2 and S2), which was unidentified by theTLC analysis but found to have high polarity. The first species for the bentonite clay. These 17â-estradiol sorption rates 17â-estradiol is also degraded/transformed (µw and µS) into were similar to sorption rates from river and estuary a third species (metabolite), which was identified as estrone.
sediments (0.07-0.37 µg g-1 h-1 calculated at 1-5 h) However, estrone was not followed further by the model, measured by Lai et al. (15).
and it was assumed that it was strongly adsorbed to the soil.
Freundlich Parameters. The Freundlich isotherm pa-
Additionally, estriol was detected in the sorbed and aqueous rameters (Table 3) were determined from the 48-h concen- phases, but these detections were sporadic and insignificant; trations because of the larger amounts of metabolites found therefore, it also was not followed by the model. Linear at 168-h sample times. Also, the concentrations did not sorption (not Freundlich) was considered in this case because exclude any possible contributions from colloids in suspen- of the model's complexity. Also, two-site sorption with labile sion. Lai et al. (15) reported a Kd for 17â-estradiol of 0.036 and kinetic sorption sites was considered where the mass L g-1 for the sediments, which fell within the lower range of balance equations for the sorption sites are given by eqs values 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, the Results and Discussion
isotherms calculated from the Lai et al. (15) parameters Batch Experiments. Measurement of 17â-estradiol at such
compared well with the isotherms in this study (Figure 2).
low experimental concentrations was complicated by trans- The difference between the isotherm parameters may be formations and by possible colloidal suspensions. After 48 attributed to several differences between studies, including h, the batch experiments for 17â-estradiol appeared to be at particle size distributions, organic matter content, and equilibrium (i.e., there was little difference in supernatant suspended colloids. Additionally, Lai et al. (15) used an earlier 14C counts between 48 and 169 h). However, the TLC analysis time, 1 h, to calculate isotherm parameters as compared indicated that there were appreciable amounts of metabolite with the time used in this study, 48 h. At 1 h, the 17â-estradiol present after 169 h. The parent compound, 17â-estradiol, may not have reached an equilibrium sorption concentration, only accounted for approximately 50-70% of the 14C at the which could result in lower Kd values. On the other hand, 169-h sample time. Additionally, the amount of 14C present transformations may occur at longer times (as used in this in the supernatant decreased by approximately 20% after study), which may affect the sorption parameter estimates.
the ultracentrifugation experiment (100000g for 1 h), which Except for the bentonite clay, all of the n values from this suggested that some 14C was found on colloids suspended study were >1.0 (Table 3), which indicated that sorption site in the supernatant. This result indicated the contribution availability did not approach a limit as it did for the sediment that colloid facilitated transport may have on the fate and study (15). This meant that there was little competition for transport of 17â-estradiol.
exchange sites by estrogens.
During the first 48 h, the 17â-estradiol sorption rates Batch Sorption Correlations. Correlations between
ranged from 0.002 µg g-1 h-1 for the sand to 0.112 µg g-1 h-1 Freundlich parameters and soil fractions were not made VOL. 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). Instead Kaolinite has a low specific surface area (Table 1) and a low correlations of sorption to various soil fractions were cation-exchange capacity (CEC) that typically ranges between determined for the initial aqueous concentrations of 0.0015 3 and 15 cmol kg-1. Bentonite has a high specific surface mg L-1 in 8 mL of water and 1.6 g of soil and shaken for 48 area (Table 1) and is mainly composed of smectite, which h. A general correlation between sorption and particle size has a high CEC of 100-150 cmol kg-1. The "superactive" was found (Figure 3). These correlations reflect a relation taxonomic designation (Table 1) of the Bearden, Gardena, between sorption and surface area where specific surface Glyndon, and LaDelle soils denotes a high CEC, and all these area (Table 1) was highly correlated (r 2 ) 0.92) to sorption.
soils have higher isotherms than the nonsuperactive Sioux However, these correlations to particle size may also reflect soil (Figure 2). These results indicate that clay minerals will a sorption mechanism governed by interactions between likely influence sorption, but further experiments are needed surface ion-exchange sites and charged or polar solutes. Lai to elucidate the binding mechanism of estrogens in natural et al. (15) found estrogen sorption to iron oxides and suggest an ion exchange mechanism where polar, phenolate estro- Last, there appeared to be a strong correlation between gens bind to charged iron oxides. Cation exchange complexes sorption and silt content (r 2 ) 0.92) (Figure 3); however, this are associated with clay minerals and organic matter and correlation was confounded because silt was also correlated can result in the sorption of polar compounds, such as to the organic matter content (r 2 ) 0.68). The statistical model phenolates. This sorption mechanism may partially explain used was unable to significantly distinguish the effects of the difference in the sorption affinity between bentonite (high organic matter from the effects of silt content on sorption.
affinity) and kaolinite (low affinity) clays as well as the soils It would intuitively seem that the organic matter was the with the taxonomic designation of "superactive" (Table 1).
cause of this correlation and that the silt correlation was 2404 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003
FIGURE 4. 17â-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 17â-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 17â-estradiol.
coincidental, because silt is relatively inert. Lai et al. (15) also in the Glyndon column effluent, there was significant found a strong correlation between total organic carbon, but redistribution throughout the column profile (Figure 4). The only weak correlations with particle size distribution.
mass balance of 14C (Table 4) recovered from within the Miscible-Displacement Experiments. For all the soils,
Glyndon soil column was -100%. The TLC analyses indicated very little or no (i.e., Glyndon-sandy clay loam) 14C was present that 17â-estradiol was not present in any of the effluents of in the column effluent (Figure 4). Although 14C was not present any soil columns, which suggested little or no aqueous or VOL. 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)a
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, an The analysis of the breakthrough curves for the 17â- unidentified high-polarity metabolite was found in the estradiol was complicated by the fact that simultaneous effluent along with sporadic and trace detections of estriol.
transformation and kinetic sorption occurred. The TLC Bolton et al. (23) suggest a metabolic pathway where 17â- data analyses indicated the presence of three metabolites estradiol is oxidized to estrone and then further to a more but were unable to quantify their relative concentrations.
polar semiquinone or quinone. Quinones and semiquinones Therefore, no quantitative conclusions could be made about can cause oxidative damage to DNA and can be ionized (i.e., the transformation of 17â-estradiol, which was only found have a negative charge), which would make them water- sorbed inside the column and not in the column effluent. It soluble and very mobile in soil. An ionized compound could was necessary to make an assumption regarding the transport possibly explain the early arrival of 14C in the column effluent of the 17â-estradiol and its metabolites and to consider (Figure 4), which appeared nearly at the same time as the different types of models to interpret the data.
chloride ion tracer. It was just as likely that other possible The two models that were considered were presented in metabolites may have also been present. Layton et al. (13) Figure 5. The first model (eqs 2-5) treated the total 14C as and Jurgens et al. (24) show transformation of 17â-estradiol, a single species that underwent transformation in the aqueous ultimately leading to mineralization/ring cleavage in activated and sorbed phases. This meant that the identified sorption sludge and river water, respectively.
or transformation rates were identical or represented a The TLC analyses of the soil extracts from within each lumped value for 17â-estradiol and its metabolites. The column indicated that the majority of the sorbed 14C was second model (eqs 6 and 7) considered that the 17â-estradiol 17â-estradiol and another metabolite of lower polarity, which entered the soil and was transformed into the unidentified was identified as estrone. Estriol was also detected sporadi- high-polarity metabolite in addition to estrone or estriol.
cally in trace amounts in the extracts. These general results The transformation constants µw and µS were used for estrone, indicated that 17â-estradiol entered the soil column, readily and µ′ and µ′ were used for the polar metabolite. The partitioned to the solid phase, and underwent rapid trans- parameters for the second model were estimated by simul- formation to form at least three metabolites of different taneously fitting (20) the measured concentrations of 17â- polarity. The lower polarity estrone was adsorbed to the soil, estradiol and the polar metabolite in the column effluent, and the higher polarity metabolites were more mobile in the where 17â-estradiol concentrations (C1 in eqs 6 and 7) were column and more readily transported in the aqueous phase.
all set to zero and the polar metabolite concentrations It was possible that some of the 14C was redistributed through (C2 in eqs 6 and 7) were set to the measured 14C. The second the column by colloidal transport, especially for the highly model could not follow the fate of estrone or estriol, but it sorbed estrone and 17â-estradiol. However, none of the highly could be assumed that they were strongly sorbed to the soil sorbed compounds were present in the effluent, only the shortly after transformation, which was consistent with the high polarity metabolite, which was likely transported in the dissolved aqueous phase.
Both the first and the second models had advantages and Miscible-Displacement Model Analysis. The break-
disadvantages. The first model simultaneously tracked all through of 14C in the column effluents (Figure 4) displayed estrogen compounds, used Freundlich sorption, and had signs of nonequilibrium transport, which was signified by fewer model parameters to estimate. Fewer parameters the long tails or late arrivals of solute. However, the chloride increase the reliability of their estimates; however, the ion tracer was transported through all soil columns as a identical transformation or sorption rates for 17â-estradiol convective-dispersive process with no sorption or trans- and its metabolites made this model physicochemically less formation (eq 2 when S ) µ ) 0). The nonequilibrium likely. The second model was physicochemically more transport of the 14C was thus determined to be a result of realistic, but additional parameters were needed, only linear chemical interactions (e.g., sorption processes, degradation) sorption was considered, and transport of estrone and estriol because there were no strong indications of physical non- were not followed after transformation. Both models provided equilbrium (i.e., preferential flow) from the chloride ion excellent description of the data (indicated by r 2 values in experiments. The dispersivity (λ) values presented in Table Tables 4 and 5). However, the lack of information about the 4 represent a single value that was simultaneously optimized transformation process, metabolic products, and the high (20) for both chloride and 17â-estradiol experiments, while number of fitting parameters resulted in decreased confi- assuming v was constant for both experiments. The λ was dence in parameter estimates and decreased uniqueness in the same for the two models that were considered, which the inverse model solution. As a result, the confidence added constraints to the other parameter estimates and intervals of the parameter estimates (Tables 4 and 5) often improved the inverse model uniqueness.
spanned the entire spectrum. Additional information about 2406 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 11, 2003
FIGURE 5. Schematics of the two miscible-displacement models that were used to describe the fate and transport of 17â-estradiol. The
arrows indicate mass transfer or transformations of the compounds in the parentheses. Double-headed arrows link compartments that
reach 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)
the relative amounts of the various sorbed metabolites was with similar values of the objective function. The optimized needed to improve parameter confidence and uniqueness.
parameters for this soil suffered from the largest degree of Nonetheless, the model solutions provided realistic param- uncertainty and will not be discussed further.
eter values that could be used to create a hypothesis for the Sorption. Miscible-displacement sorption coefficients
fate and transport of 17â-estradiol and its metabolites.
were not held constant to the values obtained from the batch The confidence in the modeling was especially low for experiments for several reasons. Transformations occurred the Sioux-loam where the effluent concentrations were very during the column studies and the metabolite sorption low. A complete breakthrough curve was not obtained during coefficient would not be the same as the batch experiments.
the experiment, and measured concentrations were signifi- Sorption parameters obtained from a column study will be cantly scattered. Consequently, different initial estimates of affected by rate-limited mass transfer because of advective optimized parameters resulted in widely different estimates 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, (0.06-0.12 h-1) reported for agricultural soils (11) fell in the that the batch sorption values were used as initial guesses lower range of µS values of the first model (0.284-2.800 h-1) for the inverse parameter estimates. This helped to achieve and were very similar to the µS and µ′ values (0 0.001-1.221 a minimum for the objective function.
h-1) of the second model. Degradation rates (0.252 ( 0.012 The f values for both models were small or zero (Tables h-1) reported for 17â-estradiol in biosolids (13) fell within 4 and 5) and indicated that sorption was almost fully kinetic the range most similar to the µS values for the 17â-estradiol with no instantaneous or labile sorption sites (i.e., type-1 of the second model (Table 5). Any differences between µ sites). All the soil column breakthrough curves modeled with values from the current column experiments and those the second model resulted in full kinetic sorption with no reported by earlier studies can be explained by relative type-1 sorption sites, so f ) 0 in each case (Table 5). The only uncertainty of the optimized parameter values and by several case where labile sorption was significant was for the first experimental factors that affect 17â-estradiol degradation/ model for the Sioux-loam, where model confidence was very transformation rates. These factors include temperature and water content (11-13). The experiments done in this study Equilibrium sorption estimated by the first and second were conducted at or near saturation, while the study on models compared well with the batch experiments and with persistence in agricultural soils used unsaturated soils (0.13 other studies. The batch Fruendlich parameters (Table 3) cm3 cm-3). The column experiments of this study contained fell within the range of values estimated from the first model more soil than the previous studies (11, 13). The greater (Table 4). The linear 17â-estradiol K amount of soil would increase the amount of available d,1 values of the second model (0.18-1.209 L g-1) compared well with the linearized sorption sites where degradation may likely occur.
(where n was forced to equal 1) batch experiment Kd values The results from the column experiments and recent (0.010-0.322 L g-1). Also, the linearized 17â-estradiol Kd studies (11, 13) have indicated rapid degradation/transfor- values from the first (0.137-0.661 L g-1) and second (0.180- mation of 17â-estradiol. Colucci et al. (11) found that 17â- 1.209 L g-1) models were slightly higher but comparable to estradiol is rapidly transformed into estrone and that estrone the linearized Kd value (0.070 L g-1) reported for sediments persists in the soil for the duration of their experiment (3 d) by Lai et al. (15).
without further degradation. Other studies have suggested For the second model, the polar metabolite had a similar a metabolic oxidation sequence of 17â-estradiol, where or slightly lower Kd value as compared to the 17â-estradiol.
estrone and estriol are produced (25), and further transfor- This indicated that sorption kinetics had a significant role in mations can occur to form semiquinones and quinones (23) the mobility of these compounds. The difference in the or possibly result in steroid ring cleavage (13, 24). These sorption kinetics was indicated by the difference between ω1 studies indicate a sequence of possible transformations that and ω2 values for the second model (Table 5). The ω1 was are consistent with the identification of metabolites from lower than ω2 for all soils except the Sioux-loam, where the our miscible-displacement experiments. However, it was not confidence of the model analysis was low. Using batch kinetic possible to definitively identify the high-polarity metabolite, experiments with sediments, Lai et al. (15) shows that 17â- which could pose a greater risk (if found to be potent) to estradiol has more rapid sorption than its metabolite, estriol.
surface and subsurface water because of its higher mobility.
The higher ω value of 17â-estradiol would result in a rapid Additionally, the long-term persistence of estrone in the soil sorption process, which quickly binds it to the soil and makes needs to be identified and may lead to impacts on soil and it less mobile. By separating the ω values between 17â- water quality if it is repeatedly applied to the soil, as would estradiol (i.e., ω1) and its metabolite (i.e., ω2), the second occur in a field setting. The preliminary findings from this model was able to describe the solute tailing better than the study nonetheless indicated that no intact 17â-estradiol or first model (Figure 4). The first model lumped ω for both identifiable estrogen metabolites could escape from these 17â-estradiol and its metabolites, which resulted in a poorer agricultural soils. It may be concluded that 17â-estradiol- description of the solute tail. A better description of the data enriched manure could be safely applied to these high organic would indicate a more realistic description of the fate and disturbed soils provided that no bypass flow (e.g., preferential transport) or facilitated (e.g., colloid) transport results in Degradation/Transformations. The first model indicated
significant depth of transport. The disposal of 17â-estradiol that nearly all degradation/transformation occurred on the enriched manure would also be precluded in areas where sorbed phase. The second model also indicated a sorbed there is significant surface runoff where sorbed 17â-estradiol phase transformation for 17â-estradiol. Previous research can be transported in suspension.
(13) on the degradation of 17â-estradiol in biosolids ofwastewater treatment facilities provides evidence for sorbed- phase transformations. This earlier research indicates the The authors greatly appreciate the long hours dedicated to importance of the amount of 17â-estradiol that remains in this research by the following technical experts: Mrs. Barbara the aqueous phase, and how it can decrease the effectiveness K. Magelky and Mrs. Colleen M. Pfaff. The authors also of removal by degradation. Furthermore, the sorbed-phase acknowledge the National Science Foundation for their degradation/transformation of 17â-estradiol was consistent support of this research.
with the TLC results where 17â-estradiol, estrone, and traceestriol were the only 14C found sorbed to the soil and themore oxidized polar metabolite was predominantly found in the aqueous phase.
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