I

Transport of Manure-Based Applied
Sulfadiazine and Its Main TransformaƟon
Products in Soil Columns

S

S

:A

M. Unold,* J. Šimůnek, R. Kasteel, J. Groeneweg, and H. Vereecken
Solute displacement experiments with the an bio c sulfadiazine (SDZ) and its main transforma on products in pig
manure were performed to inves gate the influence of manure on SDZ transport. Either pig manure containing
14C-sulfadiazine (4-amino-N-2-pyrimidinyl-benzenesulfonamide), and its main transforma on products 14C-4-OH-SDZ
and 14C-N-Ac-SDZ, or a 14C-SDZ solu on was incorporated in the first cen meter of undisturbed and repacked soilcolumns, which were then irrigated. Breakthrough curves (BTCs) of 14C, SDZ, 4-OH-SDZ, N-Ac-SDZ and 4-[2-iminopyrimidine-1(2H)-yl]-anilin were measured. The 14C distribu ons vs. depths were determined a er the conclusion of theleaching experiments. An applica on of SDZ together with manure resulted in lower peak values of the 14C BTCs anda slightly lower amount of eluted mass. In the experiments with manure, the 14C concentra ons in the uppermost
layers of the soil columns were higher, probably due to the filtra on of manure par cles onto which SDZ or its transforma on products were sorbed. The transforma on products showed a rela vely high leaching poten al similar to
SDZ. Cotransport with organic par cles seemed to be of minor relevance for the eluted amounts of solutes. All BTCs
were modeled using a numerical model that considered degrada on chains from N-Ac-SDZ into SDZ and from SDZ into
4-OH-SDZ, as well as one reversible and one irreversible kine c sorp on site for each solute. The applied model fi ed
the BTCs of SDZ and its transforma on products reasonably well. The fi ng process revealed a high mobility of both
SDZ and its transforma on products. While N-Ac-SDZ degrada on into SDZ was fast and no extended tailing of N-AcSDZ was observed, the transport behavior of 4-OH-SDZ was similar to that of SDZ.
A
: BTC, breakthrough curve; CDE, convection–dispersion equation; HPLC, high performance liquid chromatography; SDZ,
sulfadiazine; TOC, total organic carbon.

I, several studies have shown the widespread occurrence of sulfonamide antibiotics in surface waters(Christian et al., 2003; Managaki et al., 2007), groundwaters(Sacher et al., 2001; Hamscher et al., 2005; Focazio et al., 2008)
and soils (Höper et al., 2002; Boxall, 2004; Hamscher et al.,2005). The major risk of introducing these substances into theenvironment is the development and spread of resistant pathogens (Kemper, 2008), especially since the probability of thesechemicals reaching the food chain via drinking water (Batt etal., 2006; Ye et al., 2007) or root uptake by plants (Dolliver etal., 2007) is high.
The main diﬀerence in how antibiotics and other organic
contaminants, such as pesticides, are introduced into theenvironment is the way of their application. While pesticides
are intentionally spread over the ﬁeld, antibiotics are mostly

introduced unintentionally with the application of manure(Jørgensen and Halling-Sørensen, 2000). The application of thesulfonamide antibiotic SDZ with manure into the root zone,
which is a common practice in Germany, may inﬂuence soil
structure and other conditions aﬀecting solute transport in thesoil proﬁle. The eﬀects of manure application on soil aggregation
have been studied by many, including Wortmann and Shapiro(2008). These researchers found that manure application resulted
in the formation of macroaggregates. They concluded that the riskof surface runoﬀ may be greatest shortly after application because
macroaggregates have had no time to develop.
Suspended colloidal material, as found in manure, can facilitate the transport of pollutants in soils. Molecules of organic
substances can sorb to small particles (McGechan and Lewis,2002) and travel along with them at usually rapid, unretarded
velocities. Colloid-facilitated transport has been shown, forexample, to accelerate the transport of pesticides, phosphates,
and heavy metals (Hesketh et al., 2001; de Jonge et al., 2004;
Pang and Šimůnek, 2006). McGechan and Lewis (2002) indicated in their review that macropores are the main pathways forcolloidal transport since such larger particles are otherwise eﬀectively retained by physical ﬁltration processes (Jarvis et al., 1999;
Kretzschmar, 1994).
Due to speciation, sorption of sulfonamide antibiotics to soils(Kurwadkar et al., 2007) and organic material (Kahle and Stamm,2007) is strongly dependent on pH. Due to high amounts of
NH4 present in manure, the soil water pH can increase by 1.5
units after the application of manure (Kay et al., 2005a), which
may lead to a signiﬁcantly lower sorption of SDZ.

M. Unold, R. Kasteel, J. Groeneweg, and H. Vereecken, Agrosphere
Ins tute, ICG 4, Forschungszentrum Jülich GmbH, Leo Brandt Str., 52425
Jülich, Germany; J. Šimůnek, Dep. of Environmental Sciences, Univ. of
California, Riverside, CA. Received 14 Aug. 2008. *Corresponding author(m.unold@fz-juelich.de).
Vadose Zone J. 8:677–689
doi:10.2136/vzj2008.0122© Soil Science Society of America
677 S. Segoe Rd. Madison, WI 53711 USA.
All rights reserved. No part of this periodical may be reproduced or transmi edin any form or by any means, electronic or mechanical, including photocopying,recording, or any informa on storage and retrieval system, without permission
in wri ng from the publisher.

www.vadosezonejournal.org · Vol. 8, No. 3, August 2009677

Several studies focused on the sorption and transport of antibiotics in the presence of manure (Boxall et al., 2002; Kay et al.,2004, 2005a; Kreuzig and Höltge, 2005; Blackwell et al., 2007;
Stoob et al., 2007). Antibiotics of the sulfonamide group seemto have a stronger tendency for leaching and overland ﬂow thanother antibiotics, such as tetracyclines and tylosin. Blackwell etal. (2007) and Kay et al. (2005b) demonstrated this tendency
for sulfachloropyridazine in ﬁeld and lysimeter studies. Kay
et al. (2005a) found no inﬂuence of manure on the transportof the tetracycline antibiotic oxytetracycline. In batch studies,
Kreuzig and Höltge (2005) observed a tendency of SDZ to forma nonextractable fraction, which remained in the manure matrix.
Additionally, the extractable fraction of SDZ in a soil was much
lower when SDZ was applied together with manure. In contrast,
Thiele-Bruhn and Aust (2004) and Boxall et al. (2002) founddecreased sorption of SDZ and other sulfonamide antibiotics inthe presence of manure, probably due to the use of diﬀerent soils
and manures in their experiments.
Kreuzig et al. (2005) and Heise et al. (2006) reported that
sulfonamides quickly form nonextractable residues in soils. Bialkand Pedersen (2008) showed that the sulfonamide antibiotic sulfapyridine can be covalently bound to the model humic substanceprotocatechuic acid, which is one explanation for the observed
irreversible sorption behavior of sulfonamides. While degradationof sulfonamides has often been observed (Sukul et al., 2008b;
Wang, 2006), their mineralization has been found to be relatively
low (Loftin et al., 2008; Schmidt et al., 2008).
Various studies have shown that manure from SDZadministered animals contains the parent compound SDZ as
well as several transformation products. Lamshöft et al. (2007)
studied excretion patterns from pigs that were administeredwith 14C-SDZ. They detected about 96% of the applied 14C
excreted in manure and identiﬁed ﬁve transformation products
in addition to SDZ. While 4-N-acetyl-SDZ (N-Ac-SDZ) and
4-hydroxy-SDZ (4-OH-SDZ) were found in relatively large concentrations, formyl-SDZ and acetyl-hydroxyl-SDZ were present
only in trace amounts.
The occurrence of these transformation products cannot be
regarded as the result of a degradation process that makes theparent compound harmless, since it is known, for example, thatthe metabolite 4-OH-SDZ can still be microbially active (Nouws
et al., 1989) and that N-Ac-SDZ can retransform into the active
parent compound SDZ (Berger et al., 1986). There are indications that transformations not only occur during metabolizationin animals, but also in soils (Burkhardt et al., 2005; Wehrhan,
2006; Wehrhan et al., 2007) and aqueous solutions (Sukul etal., 2008b).
Up to now, little has been known about the occurrence andfate of transformation products in the environment. This may
be due to a lack of reference substances (Díaz-Cruz and Barceló,
2006). Their relevance in environmental assessments was shown
by Hilton and Thomas (2003), who detected relatively high concentrations of the acetyl form of the antibiotic sulfamethoxazole
in eﬄuent and surface waters, whereas the concentration of theparent compound was lower than the detection limit.
Various types of models are available to simulate the transportof antibiotics. These models need to consider various physical processes involved in the transport of antibiotics, as well as
chemical processes, including kinetic and equilibrium sorption
www.vadosezonejournal.org · Vol. 8, No. 3, August 2009and degradation. The process of degradation is usually simulated
in transport models as a ﬁrst-order process. Examples of model
applications that considered ﬁrst-order degradation are, for example, Casey and Šimůnek (2001) and Schaerlaekens et al. (1999)
for the transport of trichloroethylene, Casey et al. (2003, 2004,
2005), Das et al. (2004), and Fan et al. (2007) for the transport ofhormones, and Papiernik et al. (2007) for the transport of an herbicide. Das et al. (2004), for example, used a bicontinuum modelwith ﬁrst-order degradation to describe the transport of estradiol
and testosterone, as well as their daughter products. Similarly,
Casey et al. (2003, 2004, 2005) included ﬁrst-order degradation
to describe the transport of estradiol and testosterone and theirdaughter products. Similar ﬁrst-order reaction pathways are also
often used to describe the simultaneous transport of N species(Hanson et al., 2006), radionuclides (van Genuchten, 1985), or
organic explosives (Šimůnek et al., 2006).
The main objectives of this study were to investigate (i)the eﬀects of pig manure on the fate and transport of SDZ in
soil columns and (ii) the transport in soil columns of two SDZtransformation products present in applied manure. To achievethese objectives, solute displacement experiments were performed
using both repacked and undisturbed soil columns involving
two soils. Pig manure containing 14C-SDZ, 14C-4-OH-SDZ,
and 14C-N-Ac-SDZ was incorporated into the top of the soilcolumns. A 14C-SDZ solution was additionally incorporated
into one repacked column of each soil. Breakthrough curves
and 14C distributions vs. depth were analyzed using a transportmodel that considered convective–dispersive transport withone kinetic reversible and one kinetic irreversible sorption site.
Transformation and sorption rates for the diﬀerent solutes were
determined using an inverse parameter optimization procedure
based on the Levenberg–Marquardt algorithm.

Materials and Methods
Experimental Setup
To study the eﬀects of manure on the transport of SDZ
and its transformation products, we conducted experiments on
undisturbed and repacked columns of two soils. Soil samples forboth the repacked and undisturbed soil columns were collectedfrom the upper 30 cm of two ﬁelds with soil types that are typical for agricultural land use in Northrhine-Westpfalia, Germany.
A silt loam soil (an Alﬁsol or Orthic Luvisol) was collected froma ﬁeld near Jülich-Merzenhausen (denoted below as Soil M),
while a loamy sand soil (an Inceptisol or Gleyic Cambisol) was
sampled from a ﬁeld near Kaldenkirchen (denoted below as Soil
K). Selected soil properties are shown in Table 1.
For the repacked soil columns, the soils were sieved (2 mm)
and air dried. During the packing procedure, layers of about
0.5-cm thickness were added to the columns and compacted byweakly pressing with a pestle. Columns constructed of polyvinyl
chloride (PVC) with an inner diameter of 8 cm and heights of
10 cm were used for all experiments. The excellent solute mass
recoveries in most experiments suggested that we could neglect
SDZ sorption onto the PVC material.
Undisturbed soil columns were collected using PVC columns and a metal adaptor with a sharp front attached at one
end to facilitate entry into the soil. No roots were visible in thesoil, so only ﬁne roots may have existed in the soil columns. The
678

T
1. Selected physical and chemical proper es of the Kaldenkirchen soil (K) and the Merzenhausen soil (M).
Property
Clay (<0.002 mm), mass %†Silt (0.002–0.064 mm), mass %†Sand (0.064–2.0 mm), mass %†pH (0.01 mol L−1 CaCl2)‡
Total organic C, mass %†Ca on exchange capacity, cmolc kg−1§

Soil K
4.9
26.7
68.5
6.8
1.07
7.8

Evaporation losses were determined by weighing two water-ﬁlled
tubes at regular time steps.
Before and after the SDZ-transport experiments, we used
Cl− as a non-reactive tracer to characterize the physical transport mechanisms in the soil columns. For this purpose, pulsesof 0.05 mol L−1 CaCl2 solution were applied to the columns
for 1 h (corresponding pore volumes are listed in Table 3). The
Cl− concentration in the outﬂow samples was measured using anelectrical conductivity sensor included in the experimental setup.
The correlation between electrical conductivity and Cl− concentration was determined by establishing a calibration curve using
samples of known Cl− concentration.
For determining the BTCs of SDZ and its transformation
products, either 15.07 g of pig manure containing 14C-SDZ or
15.07 g of a 0.01 mol L−1 CaCl2 solution with the same amountof SDZ was incorporated into the top 1 cm of the soil columns.
Manure or the SDZ solution was ﬁrst mixed with the air-driedsoil of the particular soil type and then added to the top of thesoil columns from which the original soil had been removed.
When the leaching experiments were ﬁnished, the soil columns were cut into slices of 0.5- or 1-cm thickness to measure
14C concentrations in the column proﬁles by combusting aliquots of each slice in an oxidizer (Robox 192, Zinsser Analytik
GmbH, Frankfurt, Germany), following the approach describedin Unold et al. (2009). This method allows 14C concentrations
in soils to be measured without applying any extraction procedures, which were reported to have low eﬃciencies and variations
between fresh (<71%) and aged (<46%) SDZ residues (Förster
et al., 2009). Thus only the total amount of radioactivity wasmeasured in the soil. For each slice, three 0.5-g replicates of ovendried (105°C), ground, and homogenized soil were combusted
in an oxidizer. After combustion, the evolving gas was washedinto a scintillation cocktail (Oxysolve C-400, Zinsser Analytics,
Frankfurt, Germany), in which the labeled CO2 was trapped andthen analyzed by liquid scintillation counting (LSC). Blanks wererun before and after the samples to check for background andcross-contamination. The eﬃciency of the combustion process(>95%) was ascertained by combusting samples spiked with aknown amount of the model compound 14C-anilazine prior toand after analyzing the samples.
All experiments were performed in a laboratory without
sunlight to prevent photodegradation. Samples were exposed
only brieﬂy to artiﬁcial light during sample collection and preparation. Biodegradation was not impeded. Samples were stored
in a refrigerator until measurements were conducted withinapproximately 2 or 3 wk. We assumed that concentrations ofSoil M
15.4
78.7
5.9
7.4
1.24
11.4

† Data were measured at the Ins tut für Nutzpflanzenwissenscha en und
Ressourcenschutz of the University of Bonn.
‡ Average pH values in soil column eﬄuents for the columns with manure.
§ Data taken from Förster et al. (2009).

repacked and undisturbed soil columns were mounted on porous
glass plates having a high conductivity and an air-entry value>100 mbar. Overall, seven experiments were performed. The
experimental conditions for each setup are shown in Table 2.
While either manure or the SDZ solution was applied to therepacked soil columns, only manure was incorporated into theundisturbed soil columns. The soil columns were slowly saturated
from the bottom with 0.01 mol L−1 CaCl2 for approximately 2
d before displacement experiments started. The same solution
was also used as a background solution. A thin layer of coarse
quartz sand was placed on top of the columns to protect thebare soil surface from the impact of the irrigation water. Six soilcolumns were irrigated at a constant ﬂow rate of about 0.19 cm
h−1. An additional experiment was performed using a second
undisturbed column containing Soil K to which manure wasapplied. In this case, the same amount of irrigated water per hour
was applied at a higher ﬂow rate for 5 min, followed by 55 minof redistribution.
All soil column experiments were run with software-controlled equipment. Irrigation of the soil columns started a few
days before the leaching experiments. The irrigation rate wasrecorded by weighing the storage bottle of the irrigation solution.
Suction was applied at the bottom of the soil columns. Suctions
within the range of 4 to 41 mbar were chosen separately for eachsoil column to establish a constant pressure head (water content)in the soil columns for a given ﬂow rate. This meant that gravity
was the primary factor driving water ﬂow. The suctions inside of
the columns were followed using two tensiometers installed 2.5
and 7.5 cm below the soil columns’ surfaces. Fifteen millilitersof the outﬂow was collected in test tubes for each sample. Water
lost due to evaporation, which was approximately 2.19 × 10−6
L h−1, was included in calculations of the solute concentrations
to correct the measured concentrations for evaporation losses.
T

2. Experimental condi ons for diﬀerent soil column experiments.
Soil column†

KrepMAN
KrepSOL
KundMAN
KundMANi
MrepMAN
MrepSOL
MundMAN

Soil

Packing

Sulfadiazine applica on

Irriga on

K
K
K
K
M
M
M

repackedrepackedundisturbed
undisturbed
repackedrepackedundisturbed

manuresolu onmanuremanuremanuresolu onmanureconstant
constant
constant
intermi ent
constant
constant
constant

Bulk densityg cm−3
1.42
1.37
1.49
1.40
1.34
1.27
1.88

Flow velocity
cm h−1
0.18
0.19
0.20
0.18
0.19
0.19
0.19

Applied suc on
mbar
23
41
10
10
30
29
4

† The first le er represents soil type (either K or M), columns were either repacked (rep) or undisturbed (und), and either manure (MAN) or a stock solu on(SOL) was incorporated into the column; subscript i denotes intermi ent infiltra on.
www.vadosezonejournal.org · Vol. 8, No. 3, August 2009679

T
3. Transport parameters for the conserva ve tracer Cl−: V is the pore-watervelocity, D is the dispersion coeﬃcient, R2 is a measure of the rela ve magnitude of
the total sum of squares associated with the fi ed equa on, λ is dispersivity, and θ iswater content.

injection volume was 0.25 cm3 for each sample. A
gradient with an increased amount of methanol
was used for peak separation, starting with 100%water for 6 min. The methanol fraction increased
Soil
Pore
linearly to 27% during the ﬁrst 23 min, then to
V
D
R2
λ
θ
column†volumes37%
within the next 3 min, and to 47% during
cm2 h−1cm
cm3 cm−3
cm h−1the following 2 min. The methanol part reached
KrepMAN
0.56 (± 0.02)‡
0.41 (± 0.04)
17.9
0.97
0.74
0.32
its maximum of 57% after 30 min. Sulfadiazine,
KrepSOL
0.78 (± 0.03)
0.42 (± 0.10)
12.7
0.94
0.54
0.25
N-Ac-SDZ, and 4-OH-SDZ could be detected
KundMAN
0.54 (± 0.01)
0.85 (± 0.04)
16.4
0.99
1.57
0.37
KundMANi
0.53 (± 0.01)
0.45 (± 0.02)
18.7
0.99
0.84
0.34
using this HPLC method. The substances were
MrepMAN
0.44 (± 0.01)
0.25 (± 0.02)
22.7
0.99
0.57
0.43
identiﬁed according to their retention times comMrepSOL
0.54 (± 0.01
0.29 (± 0.02)
18.5
0.99
0.54
0.36
pared with standards of SDZ and N-Ac-SDZ. The
MundMAN
0.46 (± 0.01)
0.71 (± 0.02)
0.99
1.54
0.42
21.7
retention time of 4-OH-SDZ was known from† The first le er represents soil type (either K or M), columns were either repacked (rep) or
previous experiments. Retention times of SDZ,
undisturbed (und), and either manure (MAN) or a stock solu on (SOL) was incorporated
N-Ac-SDZ,
and 4-OH-SDZ were approximately
into the column; subscript i denotes intermi ent infiltra on.
‡ Values in parentheses indicate 95% confidence intervals.
16.70, 20.18, and 15.60 min. The detection limitof the radio HPLC was about 3 μg L−1 mass equivalents of SDZ. For two manure extractions that wethe transformation products did not change during this time due
conducted, 7.6 and 8.3% of the radioactivity could not be assigned
to the low-temperature environment.
to a peak, probably due to sorption onto organic material.
The content of total organic C (TOC) in selected samples
Sulfadiazine and its main transformation products in thewas measured using a TOC 5050A analyzer (Shimazdu, Duisburg,
outﬂow samples were also separated using radio HPLC. Using
Germany). Samples for this purpose were frozen before TOC
the measurement protocol described above, four peaks could bemeasurements.
distinguished in the chromatograms. In addition to SDZ and thetwo main transformation products, we also detected 4-[2-imiAnalysis of Sulfadiazine and Transforma on Products
nopyrimidine-1(2H)-yl]-anilin with a known retention time from
The pig manure containing 14C-labeled sulfonamides usedprevious experiments of approximately 6.2 min.
in our studies was obtained from a feeding experiment conducted
The same measurement technique applied in previous experiat Bayer AG Monheim where 14C-SDZ with single labeling ofments (Unold et al., 2009) was also used here to detect SDZ andthe pyrimidine ring and 12C-SDZ were administered to pigs in
its transformation products in samples with concentrations below
a ratio of 1:19. The speciﬁc radioactivity of SDZ in manure was
the detection limit of the HPLC radio detector. Outﬂow from
0.44 MBq mg−1. After dosing, manure was collected, mixed, andthe HPLC was collected during the retention times of SDZ andstored at 4°C in darkness. The total 14C concentration of theits transformation products, as well as within these time frames,
manure was 270 mg L−1 in mass equivalents of SDZ.
for background correction. Solutes in three replicate samples wereCarbon-14-SDZ was provided by Bayer HealthCare AG
quantiﬁed with LSC using a counting time of 15 min, for which(Wuppertal, Germany) as a powder with a purity of 99% and athe samples were mixed with 10 cm3 of the scintillation cocktail
speciﬁc radioactivity of 8.88 MBq mg−1. The application solu(Insta-Gel Plus, Canberra Packard GmbH, Dreieich, Germany).
tion for the experiments without manure was prepared by adding
The detection limit of the LSC detector was 0.4 Bq, which correappropriate amounts of 14C- and 12C-SDZ (Sigma Aldrich,sponds to 0.045 ng mass equivalents of SDZ dissolved in an aliquot
Germany) to a 0.01 mol L−1 CaCl2 solution. Since the pH valueof the outﬂow sample. Non-zero concentrations were assigned toof the manure was approximately 8, the SDZ application solutions
a solute when the measured radioactivity was >1.2 Bq, which was
were buﬀered to this pH value by adding low amounts of 0.01 mol
three times the detection limit of LSC. Otherwise its contribution
L−1 NaOH. Since the added amounts of Na were very low, its
was set to zero. Using this method, the transformation productspresence should not have substantially aﬀected the results.
could be quantiﬁed with the help of the speciﬁc radioactivity of 14C
The method of Lamshöft et al. (2007) was used to deterdown to a concentration of 0.5 μg L−1 mass equivalents of SDZ in
3mine the transformation products in the manure. Brieﬂy, 4 cm
the outﬂow samples. A background correction of the HPLC meaof McIlvaine buﬀer (1 mol L−1 citric acid/1 mol L−1 Na2HPO4,
surements was done and the method was validated by measuring a
18.15 cm3/81.85 cm3; adjusted to pH 7) was added to centricalibration curve. Triplicate measurements of total radioactivity infuging vials containing 1 g of homogenized manure. The extracts
the samples were performed with LSC after mixing an aliquot of
were shaken for 30 s with a vortex mixer, treated for 15 min in an
0.5 cm3 with 10 cm3 of the scintillation cocktail.
ultrasonic bath, and centrifuged for 0.5 h (514 × g) in an Allegra
Selected samples were ﬁltered (Centricon 10, Millipore,
6 KR centrifuge (Beckmann Coulter, Palo Alto, CA). This proceBillerica, MA) and total 14C was measured before and after ﬁldure produced clear supernatants, which were transferred into hightration. Since there was no diﬀerence in the measurements, we
performance liquid chromatography (HPLC) vials and analyzed
concluded that solutes in the outﬂow samples were not attachedwith radio HPLC (LB 509 detector, Berthold Technologies, Bad
to colloidal particles.
Wildbad, Germany). Our HPLC system included a reversed-phase
Theory of Solute Transportcolumn (Phenomenex Synergi Fusion RP 80, 250 by 4.6 mm),3
which was eluted with a mixture of water (490 cm ) and methanol
The steady-state transport experiments on unsaturated(10 cm3), buﬀered with 0.5 cm3 of a 25% H3PO4 solution. The
repacked and undisturbed soil columns were analyzed as onewww.vadosezonejournal.org · Vol. 8, No. 3, August 2009680

dimensional transport problems, assuming constant watercontents and ﬂuxes throughout the soil columns. Solute transport
is commonly described using the convection–dispersion equation(CDE), which for conservative, nonreacting tracers during steadystate ﬂow conditions can be expressed as
∂C
∂C
∂ 2C
= −V
+D
∂t
∂z
∂z 2

[1]

where t is time [T], V is the average pore-water velocity [L T−1],
C is the solute concentration in the liquid phase [M L−3], D
is the dispersion coeﬃcient [L2 T−1], and z is depth [L]. The
parameters V and D for the Cl− BTCs were estimated using
a nonlinear parameter estimation procedure based on theLevenberg–Marquardt algorithm. We used the CXTFIT code
(Toride et al., 1999), which analytically solves the CDE for appropriate boundary conditions. The estimated transport parameters(i.e., V and D) and the experimentally determined Darcian ﬂux,
q [L T−1], were then used to evaluate the volumetric water content, θ = q/V [L3 L−3], and the longitudinal dispersivity, λ = D/V.
These parameters were assumed to fully characterize the physicaltransport process and were ﬁxed in subsequent transport simulations of reactive SDZ and its transformation products using a
modiﬁed version 4.03 of HYDRUS-1D (Šimůnek et al., 2008).
Based on a previous study with SDZ BTCs (Unold et al.,2009), a model concept with one reversible and one irreversible
kinetic sorption site was used to analyze the BTCs of SDZ and
its transformation products. The model concept (Fig. 1) for theexperiments was developed to account for all known processes.
We included the transformation of N-Ac-SDZ into SDZ according to information from the literature (Berger et al., 1986). The
irreversible sorption site was omitted for N-Ac-SDZ according
to Förster et al. (2009), who found no signiﬁcant sequestration of the N-Ac-SDZ metabolite in soils. Covalent coupling
to organic material as described by Bialk and Pedersen (2008)is also unlikely for N-Ac-SDZ since the free aniline moiety is
not available. A transformation from SDZ into 4-OH-SDZ wasincluded in the model according to our experimental results using
SDZ solutions.
Using the above model concept, the transport equation foreach solute with the transformation chain can now be written as∂ C k ρ ∂ S k ,k
+
=
∂t
θ ∂t
∂Ck
∂ 2C k−V+D−μ irr,kC k −μ deg,kC k + μ deg,k−1C k−1∂z∂z 2
k = 1, 2, 3

F . 1. Conceptual model for the transport of sulfadiazine (SDZ) andits transforma on products in the experiments with manure.

where Kf,k [M1−β solute L3β M−1 soil] is the Freundlich coefﬁcient, βk (dimensionless) is the Freundlich exponent, and αk[T−1] is a ﬁrst-order sorption rate coeﬃcient.
While a ﬂux-type boundary condition with zero concentration for all compounds was used as the upper boundary condition,
the lower boundary condition was a zero-concentration gradientin the numerical solutions. Liquid-phase initial concentrationsof SDZ and its transformation products in the uppermost centimeter of the soil proﬁle were calculated using the initial total
mass of solutes (Table 4) and water contents of the particular soilcolumns. In the experiments with the SDZ solution, all of themass was initially contributed to SDZ since no transformation
products were present in the input solution. For the fully kinetic
model, all solid-phase concentrations were initially set to zero.
While BTCs were available for each particular solute, only
total 14C measurements (i.e., the sum of all three solutes in boththe liquid and the solid phases) were available for the various
solutes in the soil columns at the end of the experiments. The
HYDRUS-1D code was therefore modiﬁed to add the sorbed(both reversible and irreversible) and liquid concentrations of all
three solutes in a particular degradation chain.
Concentrations of the transformation products were lower
than those of SDZ. To obtain adequate ﬁts for all BTCs during
the simultaneous ﬁtting process, the data points of N-Ac-SDZ,
4-OH-SDZ, and the total concentration proﬁle were weighed
relative to SDZ according to

[2]

w=

where ρ is the soil bulk density [M L−3], Sk,k is the sorbed soluteconcentration at the kinetic sorption site [M M−1], the subscript
k indicates the kth solute, μirr [T−1] is a ﬁrst-order coeﬃcient thatis used to mimic irreversible sorption (Baek et al., 2003), andμdeg,k [T−1] is a ﬁrst-order rate constant that accounts for the
degradation of the kth solute into the solute k + 1.
The sorbed concentration at the kinetic sorption sites of the
fully kinetic model was calculated as∂ S k,k= α k K f ,kC k βk − S k,k
∂t

(

)

www.vadosezonejournal.org · Vol. 8, No. 3, August 2009

∑ ni=SDZ
1 C i ,SDZ

nBTC deg ,Profile
nSDZ

nBTC

∑ i =1 deg,ProfileC i ,BTC deg ,Profile[4]

where n accounts for the number of data points of the BTCs orconcentration proﬁles of SDZ and its transformation products(BTCdeg), and Ci are measured concentrations at the ith time
for a particular BTC expressed in mass equivalents of SDZ pervolume of solution (or per volume of soil for the concentration proﬁle).
The goodness of ﬁt for particular solutes and BTCs was
expressed using the mean absolute error:

[3]

681

T
4. Mass frac ons of 14C in the breakthrough curves (BTCs) and the soil profile and mass frac ons (in %)of the parent compound sulfadiazine (SDZ) and its transforma on products in the BTCs.

repacked soil columns,
indicating more heteroRadioac vity Radioac vity
Total mass
4-[2-iminopyrimidinegeneity in the original
Column†SDZ
Acetyl-SDZ OH-SDZ
in BTC
in soil profile
recovery1(2H)-yl]-anilin
soil material.
————————————————————————————— % —————————————————————————————
Since Cl − BTCs
Manure1
67.7‡
14.9‡
17.4‡
ND§
from both repacked andManure2¶
82.4‡
8.7‡
8.8‡
ND
undisturbed
soil colKrepMAN
70.3
32.3
102.6
76.0
9.7
17.3
ND
umns could be described
KrepSOL
76.0
19.0
95.0
75.9
ND
7.8
16.1
KundMAN
70.9
30.5
101.4
78.0
9.9
15.2
ND
well using the CDE for
74.2
28.3
102.5
80.7
8.9
12.5
ND
KundMANiconservative tracers, we
MrepMAN
75.3
29.0
104.3
74.0
7.7
18.5
ND
concluded that physiMrepSOL
86.0
6.4
92.4
90.0
ND
1
12.0
cal nonequilibrium
MundMAN
62.0
37.8
99.8
91.0
7.4
4.8
0.9
processes, such as pref† The first le er represents soil type (either K or M), columns were either repacked (rep) or undisturbed (und), and either
erential flow, did notmanure (MAN) or a stock solu on (SOL) was incorporated into the column; subscript i denotes intermi ent infiltra on.
influence solute trans‡ The amount of 14C which could not be associated with a peak was distributed among SDZ and the transforma on products.
§ ND indicates that the transforma on product could not be detected.
port in our columns.
¶ Manure 2 was applied to soil columns MundMAN.
The Cl− BTC for the soilcolumn subject to transient water ﬂow (i.e., intermittent irrigation) could also be
1[5]
MAE = ∑ f i − y idescribed well using the CDE. Intermittent irrigation was
nused to generate higher water contents and higher ﬂuxes towhere n is the number of data points on a particular BTC, and fi
induce macropore ﬂow, which apparently did not happen.
and yi are predicted and measured values, respectively.
Carbon-14 Breakthrough Curves
Except for several BTCs of N-Ac-SDZ and 4-OH-SDZ,
and Concentra on Profiles
most BTCs showed extensive tailing on a logarithmic scale, aphenomenon that was also observed in two previous studies
Figure 3 presents 14C BTCs and proﬁles in the soil columns(Wehrhan et al., 2007; Unold et al., 2009). In these two studies,for all column experiments. The amounts of 14C that were eluted
the numerical models were ﬁtted to logarithmically transformed
or that remained in the soil columns, as well as the sums of both,
outﬂow 14C concentrations to better capture the long tailing.
are summarized in Table 4. Solute mass recoveries were, in mostFitting of logarithmically transformed data had the advantage
cases, between 95 and 105%. Although the manure was stirredof adding additional weight to, and thus properly describing,
before its application, the applied radioactivity in the experilow concentration values, while at the same time decreasing thements with manure may diﬀer due to inhomogeneities in theweight on, and hence probably describing less well, the concentrasubstrate. This explains why some mass recoveries are >100%.
tion of the peaks. A disadvantage of ﬁtting log-transformed data is
Recovery rates for the experiments with the SDZ solution werethat the model may also capture less well the overall leached mass.
Therefore in this study the observed data were ﬁtted without thelogarithmic transformation.

Results and Discussion
Chloride Breakthrough Curves
Chloride BTCs (Fig. 2) were measured on soil columns
before and after the incorporation of pig manure or the SDZ
stock solution (except for the repacked column of Soil K treatedwith the SDZ solution, KrepSOL, for which only the “before”
BTC was measured). Time is expressed in Fig. 2 as dimensionless pore volumes, i.e., the time needed to replace all the waterin the soil column. Although most measured Cl− BTCs werevery similar before and after the SDZ experiments, some BTCs
diﬀered slightly. There was no visible trend in Cl− BTCs thatwould indicate that incorporation of manure or the stock solution aﬀected the soil structure. Transport parameters obtainedby ﬁtting the Cl− BTCs after the incorporation of manure wereused to model the BTCs of SDZ and its transformation products, except for soil column KrepSOL, for which the “after”
BTC was not available. Fitted transport parameters for the Cl−
BTCs are summarized in Table 3. The dispersivity of two of thethree undisturbed soil columns was higher than those of thewww.vadosezonejournal.org · Vol. 8, No. 3, August 2009

F . 2. Selected Cl− breakthrough curves for soil columns (a) KundMAN and (b) MundMAN measured before and a er incorpora ng
pig manure.
682

<100%. The missing amount can be assigned to the proﬁledata, since mass errors in BTCs are less likely because moredata points were available and more precise experimental
techniques had been used.
Peaks in the 14C BTCs for the loamy sand (Soil K)
appeared after approximately 1.3 pore volumes, which was
about 0.6 pore volume later than in the silt loam (Soil M).
There are several factors indicating more extensive sorption in Soil M. Due to the larger clay content of Soil M,
a larger speciﬁc surface area of the mineral phase can be
expected, which is also reﬂected in the cation exchange
capacity. Additionally, the fraction of TOC was higher inthis soil. One possible explanation for the faster observed
transport is the amphoteric character of SDZ, which causesa pH-dependent sorption of sulfonamides (Kurwadkar et al.,2007; Gao and Pedersen, 2005). The average pH value inthe outﬂow samples from Soil M was higher than from Soilcurves for (a) Soil K and (c) Soil M, as wellK, as was shown for the repacked soil columns with manure F . 3. Carbon-14 breakthroughas distribu ons of 14C in the soil column profiles for (b) Soil K and (d) Soil
(Table 1). This leads to the presence of relatively more of the M. The 14C concentra ons are given in mass equivalents of sulfadiazine.
less sorbing anionic SDZ species in Soil M (89%) than inSoil K (68%). Calculations of the species distribution weredone according to Schwarzenbach et al. (2003). Another factor
on the pore size distribution of the porous medium was shown bythat may cause the diﬀerence in apparent transport velocities
Bradford et al. (2006). They determined concentration proﬁles ofbetween the soils is the kinetic component of SDZ sorption.
manure particles in sandy soil columns and similarly found thatAll BTCs were characterized by a fast initial increase inmost manure particles were retained in the uppermost layer.
concentration at the beginning and extended tailing after the
The presence of manure may also inﬂuence sorption behavior
peak concentration was reached. In general, the peak height wasin other ways. Sukul et al. (2008a) found in batch experiments
inﬂuenced by the dispersivity of the soil columns. Undisturbed
an increased sorption of SDZ onto soils of diﬀerent origins whensoil columns of both soils with manure added (KundMAN andmanure was present. Kreuzig and Höltge (2005) also found in
MundMAN) with dispersivities of around 1.5 cm had about 2 μgbatch experiments a higher tendency of SDZ to form nonextractcm−3 lower peak concentrations than the repacked soil columns
able residues in the presence of manure with 7-d-old SDZ. In(7.75 μg cm−3), with dispersivities ranging from 0.54 to 0.84 cm.
their lysimeter studies in which an SDZ test slurry was incorSimilar 14C peak concentrations were observed for the undisporated into undisturbed proﬁles, Kreuzig and Höltge (2005)
turbed soil column with intermittent irrigation and the repacked
observed similar concentration proﬁles as in our soil columns.
soil column with constant irrigation (Soil K), indicating that a
Distinct diﬀerences were observed in the 14C concentrasimilar dispersivity was more important than the modality of irrition proﬁles between the sand and loam columns. The observed
gation. Of the two columns receiving the SDZ solution, the 14C
amount of 14C in the ﬁrst centimeter of the loam soil (Soil M)−3peak in Soil K (13.8 μg cm ) was lower than the corresponding
was higher than in the sand soil (Soil K). There are two expla14C peak of Soil M (17.4 μg cm−3), although both had similar
nations for this phenomenon. On the one hand, this ﬁnding
dispersivities. While Soil K showed similar amounts of 14C (71%)
corresponds with the results of Schmidt et al. (2008), who studeluted from both the undisturbed and repacked columns with
ied the formation of nonextractable residues of manure-based
14C-SDZ to the same two soils. For short contact times, the nonmanure, the amounts were diﬀerent for the repacked (75%) andundisturbed (62%) soil columns of the silt loam (Table 4).
extractable part was higher in a silt loam (Soil M) (69%) than in
Compared with the experiments with the SDZ solution,a loamy sand (Soil K) (54%). On the other hand, smaller pore
lower 14C peaks and slightly lower eluted amounts of 14C weresizes could have led to enhanced ﬁltration in this soil.
observed for the soil columns spiked with manure. These lower
The 14C concentrations gradually decreased with depth ineluted amounts in the experiments with manure can be explained
the experiments with manure on Soil M. The 14C concentrations
14
14
using the C-concentration proﬁles. Although the highest C conin the soil proﬁles were more or less constant below the ﬁrst
centrations were found in the ﬁrst centimeter of all soil columns,
centimeter in the experiments with Soil K and in the repacked
these surface layer concentrations were much higher for the columns
column of Soil M treated with the SDZ solution (MrepSOL),
with manure. We hypothesize that this accumulation of 14C in thealthough in the Soil K columns with manure a slight increase inuppermost centimeter of the soil columns with manure was caused
concentrations was observed below a depth of about 4 cm.
by the sorption of SDZ and its transformation products to colBreakthrough Curves of Sulfadiazine
loidal particles in the manure. These particles then may have been
and Its Transforma on Products
unable to move through the soil because of straining in small pores.
This assumption was supported by the fact that, during the HPLC
Both experimental and simulated BTCs of SDZ and its
measurements of the manure extracts, approximately 8% of thetransformation products 4-OH-SDZ, N-Ac-SDZ, and 4-[2-imiradioactivity could not be related to a peak, probably due to adsorpnopyrimidine-1(2H)-yl]-anilin are presented in Fig. 4 and 5.
tion to organic material. Filtration of manure particles dependent
Although no transformation products were present in the input
www.vadosezonejournal.org · Vol. 8, No. 3, August 2009683

F . 4. Breakthrough curves of sulfadiazine (SDZ) and its transforma on products 4-OH-SDZ and
4-[2-iminopyrimidine-1(2H)-yl]-anilin, as well as 14C-concentra on profiles for the experimentswith the SDZ solu on for the (a) and (b) KrepSOL experiments and (c) and (d) MrepSOL experiments. Simula ons using a model with one reversible kine c and one irreversible sorp on site arealso presented. Concentra ons are given in mass equivalents of SDZ. Run 1: models were fi ed tobreakthrough curves (BTCs) of SDZ and 4-OH-SDZ; Run 2: models were fi ed to BTCs of SDZ and
4-[2-iminopyrimidine-1(2H)-yl]-anilin; Run 3: models were fi ed to BTCs of SDZ and the sum ofboth transforma on products as well as to the 14C data in the profile.

F . 5. Breakthrough curves of sulfadiazine (SDZ), 4-OH-SDZ, and N-Ac-SDZ in repacked and undisturbed
soil columns of Soils K and M for the experiments with manure, as well as simula ons using a modelwith one reversible kine c and one irreversible sorp on site: (a) KrepMAN, (b) MrepMAN, (c) KundMAN, and (d) MundMAN experiments. Concentra ons are given in mass equivalents of SDZ.

Breakthrough Curve of theOrganic Material

solution of the experiments with the SDZ solution (KrepSOL
and MrepSOL), both 4-OH-SDZ and 4-[2-iminopyrimidine1(2H)-yl]-anilin were detected in the outflow from thesecolumns (Fig. 4).
Mass fractions of particular transformation products forall soil columns are listed in Table 4. For the experiments with
www.vadosezonejournal.org · Vol. 8, No. 3, August 2009

the SDZ solution, the mass fraction of SDZ was largest comparedwith its transformation products
in all soil columns. The 4-[2-iminopyrimidine-1(2H)-yl]-anilin was
the main transformation product,
followed by 4-OH-SDZ, which
provided only a minor contribution.
The transformation from SDZ into
4-[2-iminopyrimidine-1(2H)-yl]-anilin and 4-OH-SDZ was higher in SoilK than in Soil M.
The 4-[2-iminopyrimidine-1(2H)yl]-anilin was detected in the outﬂow
of the columns with the SDZ solution
and also in the manure experiment on
the undisturbed Soil M (MundMAN),but at very low concentrations. Sukul
et al. (2008b) identified this compound to be the major photoproductof SDZ, but they observed it also as
a product of biodegradation. We canassume that 4-[2-iminopyrimidine1(2H)-yl]-anilin was formed in the soilcolumn, since our experiments wereconducted in the dark. So far we haveno explanation why we detected thistransformation product in the experiments with the SDZ solution and notin the experiments with manure.
In the soil columns with manure(Fig. 5), SDZ, 4-OH-SDZ, and N-AcSDZ were detected in the outﬂow aswell as in the manure at the time of
application. Mass fractions of the twotransformation products in the outﬂow samples diﬀered with time. While
N-Ac-SDZ was characterized by a fastdissipation, the mass fraction of 4-OHSDZ was stable or increased. According
to these results, we can expect a constant release of low 4-OH-SDZ
concentrations from soils in the longterm, similarly as for SDZ. Note thatmanure incorporated in the undisturbed Soil M column (MundMAN)
had lower mass fractions of 4-OHSDZ and N-Ac-SDZ, probably due toadvanced aging. The lower fraction of
applied transformation products was
also reﬂected in their lower fractionsin the column eﬄuents (Table 4).

Figure 6 shows BTCs of 14C concentrations, the electricalconductivity, pH, and the TOC for soil column KundMAN. The
TOC reﬂects the amount of organic substances in the outﬂow
samples. Changes in pH were relatively small, ranging from 6.6684

to 7.0. This indicates fast dilution of the slurry, which had ahigher pH of 8. The peak of the electrical conductivity appeareda short time before the peak in 14C, probably reﬂecting the breakthrough of the main anion in the manure (i.e., Cl−). The peak in
TOC also appeared shortly before the peak in 14C, at the sametime as the peak in the electrical conductivity. This indicates thatthe main part of SDZ was not transported together with the dissolved organic material (i.e., facilitated transport). We could notobserve any diﬀerences in 14C concentrations between ﬁlteredand unﬁltered outﬂow samples. These ﬁndings are consistent withobservations by Thiele-Bruhn and Aust (2004), who did not ﬁnd
any sulfonamide losses in their batch experiments during solidphase extraction with the supernatants. Solid-phase extraction
is supposed to remove the dissolved organic material (pig slurry
and soil organic matter) together with the adsorbed substances.
We therefore conclude that although transport facilitated by dissolved organic C may not be completely ruled out, this process
does not seem to be a major transport mechanism involved in
the leaching of SDZ and its transformation products. The outﬂow TOC concentrations, however, did not reach zero during
the experiments (Fig. 6), thus suggesting a continuous release oforganic material. While this supports the hypothesis that the 14C
accumulation in the ﬁrst centimeter of the soil columns is causedby the ﬁltration of organic material, in the long term the releaseof organic material, possibly together with bound SDZ residues,
may still be possible.

F . 6. Breakthrough curves of 14C, electrical conduc vity, and totalorganic C (TOC) measured in the soil column KundMAN a er the
manure applica on.

degradation into a particular transformation product was compensated by an increase in irreversible SDZ sorption. Irreversible
sorption of the transformation products was ﬁxed to zero since
the rate of their formation (degradation of SDZ) would haveotherwise been inﬂuenced by this process. In the third run, concentrations of the two transformation products were summed
up and the resulting BTC was ﬁtted together with the BTC of
SDZ and the 14C concentration proﬁle data. The degradationcoeﬃcient in this case refers to the sum of 4-OH-SDZ and
4-[2-iminopyrimidine-1(2H)-yl]-anilin degradation. For alltransformation products that showed very low concentrations in
the SDZ-solution experiments, we ﬁxed the kinetic sorption rate
coeﬃcient, α, at the very high value of 10 h−1, thus assumingthat sorption was basically an equilibrium process. This was done
to reduce the number of optimized parameters and to increase
the reliability of the optimized sorption parameters, which had
in some cases large conﬁdence intervals. Values of the Freundlich
exponents for SDZ and its transformation products were closely
correlated with the Kf values and therefore were ﬁxed in optimization model runs to values that were needed to describe thetailing of the BTCs.
The model could describe the BTCs of SDZ and 4-OHSDZ reasonably well, except for the observed increase in the
4-OH-SDZ concentration after 10 pore volumes. There is a clear
diﬀerence between the two soils in terms of the Freundlich sorption coeﬃcients for SDZ (Table 5). While the Freundlich sorption
coeﬃcients for the silt loam are lower than for the loamy sand,the Freundlich exponents are in a similar range. This indicates alower sorption capacity for the silt loam and reﬂects the earlier
breakthrough in this soil. On the other hand, the lower kinetic
sorption rate reﬂects the slightly faster transport in Soil M.
Optimized Freundlich parameters for 4-OH-SDZ in the
loamy sand produced an isotherm with a much lower sorption
capacity than for SDZ. No sorption parameters were ﬁtted forthis transformation product for the silt loam because of very low
observed concentrations. Sorption capacities for 4-[2-iminopyrimidine-1(2H)-yl]-anilin were in a similar range in both soils andfor Soil K the sorption capacity for 4-[2-iminopyrimidine-1(2H)yl]-anilin was lower than for 4-OH-SDZ. Breakthrough curve
tailing of 4-[2-iminopyrimidine-1(2H)-yl]-anilin in both soils

Modeling Results
Similarly to Unold et al. (2009), we selected a transportmodel with one kinetic reversible and one kinetic irreversible
sorption site. Sorption on the reversible site was described assuming a first-order process and Freundlich-type sorption. The
conceptual model could describe most curves quite well (see Fig.
4 and 5). The long tailing is characteristic for chemical nonequilibrium processes and nonlinear sorption. The tailing could not
be described solely by assuming a fully kinetic process, however.
It was also necessary to consider nonlinearity of the sorption process by using low values of the Freundlich exponent, β. Initial
estimates of the Freundlich parameters were selected in a way
so that the tailing was described well. This was accomplished bychoosing a Freundlich exponent <0.44, similar to the ﬁndings ofthe previous studies of Wehrhan et al. (2007) and Unold et al.
(2009). In the experiments of Kurwadkar et al. (2007), a linear
sorption isotherm was able to describe the sorption data of sulfonamides for concentrations up to approximately 0.5 mg L−1.
Concentrations of both the applied solution and the manure weremuch higher (272 mg L−1) in our study. Because of the muchwider concentration range in our study, we can assume strong
nonlinear sorption behavior.

Experiments with the Sulfadiazine Solu on
The modeling process for each experiment with the SDZ
solution was split into three parts, since it was not possible with
HYDRUS-1D to simultaneously ﬁt degradation from SDZ into
4-OH-SDZ and 4-[2-iminopyrimidine-1(2H)-yl]-anilin. In theﬁrst run, the BTCs of SDZ and 4-OH-SDZ were ﬁtted without considering the proﬁle data. In the second model run, thesame was done for 4-[2-iminopyrimidine-1(2H)-yl]-anilin. The
proﬁle data were not included in these optimization runs sincewww.vadosezonejournal.org · Vol. 8, No. 3, August 2009685

T
5. Fi ng parameters for the breakthrough curves (BTCs) of sulfadiazine (SDZ), 4-OH-SDZ, and 4-[2-imino-pyrimidine-1(2H)-yl]-anilin
for the experiments with the SDZ solu on (SOL) in repacked columns (rep) of Soils K and M. Run 1: parameters were fi ed to the BTC dataof SDZ and 4-OH-SDZ; Run 2: parameters were fi ed to the BTC data of SDZ and 4-[2-imino-pyrimidine-1(2H)-yl]-anilin; Run 3: parameters
were fi ed to the BTC data of SDZ, the 14C-profile data, and the sum of the BTCs of both transforma on products.
Parameter†
SDZ
Kf1, μg1−β cm3β g−1
β1
μ irr1, h−1
μ deg1, h−1
α1, h−1
MAE
Transforma on products
Kf2, μg1−β cm3β g−1
β2
μ irr2, h−1
α 2, h−1
MAE
MAEprofile
Eluted, %R2

KrepSOL

MrepSOL

Run 1

Run 2

Run 3

Run 1

Run 2

Run 3

1.18 (± 0.03)
0.38§
0.035 (± 0.004)
0.0036 (± 0.0002)
10‡
0.13

1.20 (± 0.04)
0.38‡
0.026 (± 0.002)
0.012 (± 0.0006)
10‡
0.16

0.52 (± 0.03)
0.44§
0.010 (± 0.002)
0.0016 (± 0.0001)
0.50 (± 0.09)
0.028

0.55 (± 0.04)
0.44‡
0.0044 (± 0.002)
0.0061 (± 0.0002)
0.43 (± 0.07)
0.086

4-OH-SDZ

4-[2-imino-pyrimidine1(2H)-yl]-anilin

1.29 (± 0.07)
0.38‡
0.018 (± 0.003)
0.011 (± 0.001)
0.74 (± 0.3)
0.23
Sum of bothtransforma on
products

4-OH-SDZ

4-[2-imino-pyrimidine1(2H)-yl]-anilin

0.50 (± 0.1)
0.44‡
0.006 (± 0.001)
0.0076 (± 0.002)
0.55 (± 0.4)
0.078
Sum of bothtransforma on
products

0.098 (± 0.008)
0.53§
0‡
10‡
0.023
0.79
59.4
1

0.044 (± 0.03)
0.27§
0‡
10‡
0.09
0.35
65.0
0.99

0.12 (± 0.003)
0.50§
0‡
10‡
0.12
0.21
72.3
0.98

0‡
0‡
0‡
0‡
0.035
0.51
75.4
0.99

0.052 (± 0.009)
0.72§
0‡
10‡
0.036
0.19
80.9
1

0.36 (± 0.05)
0.72§
0‡
10‡
0.032
0.25
0.77
0.98

† Kfj, Freundlich coeﬃcient for solute j; β j, Freundlich exponent for solute j; μ irrj, irreversible sorp on rate for solute j; μ degj, transforma on rate of solute j;
α j, kine c sorp on rate of solute j; MAE, mean absolute error; Eluted, mass eluted out of the soil column.
‡ Parameter was fixed.
§ Parameter was fixed at a value determined in a previous model run.

could not be described with the model, although the Freundlich
exponent was in a range low enough to describe the tailing of
SDZ and 4-OH-SDZ in the experiments with manure.
In the ﬁrst model run to optimize the BTC parameters of
4-OH-SDZ and SDZ, the proﬁle data were considerably overestimated for both soils since the amount of SDZ that degraded toform 4-[2-iminopyrimidine-1(2H)-yl]-anilin was added to irreversible sorption. While the same tendency was observed for Soil
K for the model run that optimized the BTC parameters of SDZ
and 4-[2-iminopyrimidine-1(2H)-yl]-anilin, this run described
the proﬁle data best for Soil M. The reason is that the eﬀectof 4-OH-SDZ formation on irreversible sorption was negligible.
Since the third model run included the proﬁle data (Fig. 4), thisrun was expected to provide the best ﬁts. While this was true
for Soil K, we overestimated data points in deeper layers of Soil
M. Increased irreversible sorption to reduce the misﬁts between
observed and simulated values in the top layer was the reason
for this overestimation. This eﬀect was smaller for Soil K, where
the diﬀerence between concentrations in the top and deeper soil
layers was smaller. Average concentrations in the soil proﬁles were
captured reasonably well by the model, although the sorption
process was probably not correctly understood. This became obvious from the opposite trends between the data and the model inthe uppermost layers.
Compared with previous experiments with SDZ solutions(Unold et al., 2009), optimized values of the kinetic sorption rate
coeﬃcient, α, were higher, indicating that kinetic sorption was
faster when SDZ was incorporated directly into the soil. In several
cases, sorption was even close to equilibrium. Therefore, some
BTCs could be ﬁtted reasonably well by assuming equilibrium

www.vadosezonejournal.org · Vol. 8, No. 3, August 2009

reversible sorption, but in such cases the initial increase in the
BTCs was predicted less well.

Experiments with Manure
For each experiment with manure, the BTCs of SDZ and
its transformation products were ﬁtted simultaneously together
with the concentration proﬁle data below the uppermost 1 cm.
Concentrations in the top 1 cm were signiﬁcantly higher than in
the rest of the soil proﬁle. We hypothesized that the high sorbed
concentrations in the uppermost soil column layers were theresult of interactions between the organic material of the slurry
and the soil structure. We did not attempt to model these processes. Therefore, the two uppermost data points in the proﬁleswere not included in the objective function and hence we did not
expect that the high sorbed concentrations in the top of the soilcolumns would be reproduced by the model.
The Freundlich exponents for SDZ were ﬁxed to values optimized to experimental data with the SDZ solution to avoid large
parameter correlations with the Freundlich distribution coeﬃcients. The kinetic sorption rate coeﬃcients for the transformation
products were again ﬁxed to 10 h−1 to decrease the number ofparameters and to increase parameter reliability. Since most BTCs
of N-Ac-SDZ did not show much tailing, its Freundlich exponent
was ﬁxed to one, thus assuming linear sorption in all soil columns except for the repacked Soil M column treated with manure(MrepMAN). In preliminary model runs, the tailing of 4-OHSDZ concentrations was not captured well since it was describedby only a few data points. Therefore, we increased the weights
on the tailing concentrations compared with the data points inthe peak according to Eq. [4]. For Soil K, the Freundlich exponent was ﬁtted for the repacked soil column with the manure686

application and ﬁxed for the undisturbed soil columns. For Soil
M, this parameter was ﬁtted for each soil column separately, sinceno extended tailing for the 4-OH-SDZ BTC was observed for theundisturbed column treated with manure (MundMAN).
The relatively low transformation rates from SDZ into
4-OH-SDZ as estimated from the experimental data with the
SDZ solution were used to model the experiments with manure.
A possible transformation reaction from 4-OH-SDZ into anotherproduct was not included in the model, since no additional product was detected in the outﬂow samples. The model with optimized
parameters produced reasonable descriptions of the transport ofSDZ and its two transformation products for the experimentswith manure. Four examples are presented in Fig. 5.
Similarly as for the experiments with the SDZ solution,
the SDZ sorption capacity for the experiments with manure
was lower for Soil M than for Soil K, but the diﬀerence wassmaller. The same tendency in Kf values as for SDZ was foundfor N-Ac-SDZ, and partly also for 4-OH-SDZ, for which thesoil column MrepMAN had a similar Freundlich coeﬃcient as
the soil column KrepMAN. For 4-OH-SDZ, ﬁtted Freundlich
exponents were similar as for SDZ but the Freundlich coeﬃcientswere lower, indicating a lower sorption capacity for 4-OH-SDZ.
On the other hand, the irreversible sorption rate was higher for
4-OH-SDZ and thus the overall sorption may be similar. Sincelinear sorption was found for N-Ac-SDZ in most soil columns,
the sorption capacity was lower than for SDZ only when theconcentration was <8 μg cm−3. In our experiments, both higher
and lower concentrations were present.
Fitted Freundlich coeﬃcients for SDZ in the experimentswith manure were higher than for the experiments with the

SDZ solution for both soils, reﬂecting the slightly higher sorbed
amounts in the experiments with manure. For Soil K, the kinetic
eﬀect was more distinct for the experiments with manure than for
the experiments with the SDZ solution (Table 6). There was noclear diﬀerence in the kinetic sorption rates α in the experimentswith manure between the two soils.
The 14C-concentration proﬁles were described quite well inthe deeper soil layers below the depth of application, where theyreached more or less constant values (Fig. 7). Simulations forcases where no proﬁle data were included in the objective function led to similar results (data not shown).
Eluted solute masses were described quite well with thenumerical model, which over- or underestimated the maxima by
only about 5%. Since the mass in the uppermost layer of the soilcolumns of the experiments with manure was not included in the
optimization, the model compensated for this missing mass byslightly overestimating concentrations below the 1-cm depth orby predicting higher eluted masses (KundMAN and KundMANi).
Because of the complex nature of the invoked transport model, it
was diﬃcult to ﬁnd unique solutions; however, the BTCs could
not be described with parameter combinations out of the rangeof the ﬁtted ones.
Optimized parameters for the Freundlich isotherm characterize the sorption equilibrium state and thus can only becompared with sorption parameters from batch experiments
determined when equilibrium is reached. This was the case forthe batch experiments of Kurwadkar et al. (2007) and Sukul
et al. (2008a). In both studies, the Freundlich exponents forsulfonamides were higher than in our study. In the study of
Sukul et al. (2008a), they were even >1. An explanation forT
6. Fi ng parameters for the breakthrough curves (BTCs) of sulfadiazine (SDZ), 4-OH-SDZ, and N-Ac-SDZ for the experiments withmanure (MAN) on columns of Soil K or M that were either repacked (rep) or undisturbed (und); subscript i denotes intermi ent infiltra on.
Parameter†
N-Ac-SDZ

KrepMAN

KundMAN

KundMANi

MrepMAN

MundMANKf1, μg1-β cm3β g−1
β1
μ deg1, h−1
α1, h−1
MAE
SDZ

0.30 (±0.02)
1‡
0.063 (±0.006)
10‡
0.05

0.37 (±0.03)
1‡
0.067 (±0.007)
10‡
0.03

0.35 (±0.05)
1‡
0.053 (±0.008)
10†
0.05

0.16 (±0.02)
0.70§
0.054 (±0.008)
10‡
0.09

0.25 (±0.02)
1‡
0.040 (±0.005)
10‡
0.02

Kf2, μg1-β cm3β g−1
β1
μ irr1, h−1
μ deg1, h−1
α 2, h−1
MAE
4-OH-SDZ

1.49 (±0.05)
0.38‡
0.012 (±0.002)
0.0036‡
0.57 (±0.07)
0.19

1.58 (±0.1)
0.38‡
0.0054 (±0.002)
0.0036‡0.36 (±0.1)
0.151.53 (±0.1)
0.38‡
0.0061 (±0.002)
0.0036‡0.68 (±0.2)
0.311.18 (±0.1)
0.44‡0.0078 (±0.003)
0.0016‡0.13 (±0.02)
0.33

1.03 (±0.06)
0.44‡
0.017 (±0.004)
0.0016‡0.51 (±0.2)
0.13

Kf1, μg1-β cm3β g−1
β1
μ irr1, h−1
α 3, h−1
MAE
Profile MAE
R2Eluted, %0.39 (±0.04)
0.44§ (±0.03)
0.040 (±0.005)
10‡
0.07
0.84
0.98
72.3

0.52 (±0.06)
0.44‡
0.035 (±0.007)
10‡
0.09
0.73
0.97
75.1

0.50 (±0.007)
0.44‡
0.033 (±0.007)
10‡
0.09
0.78
0.97
74.2

0.19 (±0.04)
0.41§
0.036 (±0.006)
10‡
0.13
1.43
0.95
75.3

0.41 (±0.04)
1§
0.090 (±0.009)
10‡
0.03
1.30
0.99
63.7

† Kfj, Freundlich coeﬃcient for solute j; β j, Freundlich exponent for solute j; μ irrj, irreversible sorp on rate for solute j; μ degj, transforma on rate of solute j;
α j, kine c sorp on rate of solute j; MAE, mean absolute error; Eluted, mass eluted out of the soil column.
‡ Parameter was fixed.
§ Parameter was fixed at a value determined in a previous model run.
www.vadosezonejournal.org · Vol. 8, No. 3, August 2009687

ments; Thorsten Büttner, Stefan Masjosthusman, Kavita Mayekar andMaja Stiefelhagen for their assistance in the laboratory; and Jürgen
Höltkemeier and Ansgar Weuthen for building the experimental setup.

References
Baek, D.S., S.B. Kim, and D.J. Kim. 2003. Irreversible sorption of benzene insandy aquifer materials. Hydrol. Proc. 17:1239–1251.
Batt, A., S. Kim, I.B. Bruce, and D.S. Aga. 2006. Determination of antibiotics
within various wastewater treatment plants and the impact of their discharges on surrounding surface waters. Abstr. ENVR 151. In ACS Natl.
Meeting, 231st, Atlanta, GA. 26–30 Mar. 2006. Am. Chem. Soc., Washington, DC.
Berger, K., B. Petersen, and H.B. Pfaue. 1986. Persistenz von Gülle-Arzneistoffen in der Nahrungskette. Arch. Lebensmittelhyg. 37:99–102.
Bialk, H.M., and J.A. Pedersen. 2008. NMR investigation of enzymatic coupling of sulfonamide antimicrobials with humic substances. Environ. Sci.
Technol. 42:106–112.
Blackwell, P.A., P. Kay, and A.B.A. Boxall. 2007. The dissipation and transport ofveterinary antibiotics in a sandy loam soil. Chemosphere 67:292–299.
Boxall, A.B.A. 2004. The environmental side eﬀects of medication: How are human and veterinary medicines in soils and water bodies aﬀecting humanand environmental health? EMBO Rep. 5:1110–1116.
Boxall, A.B.A., P. Blackwell, R. Cavallo, P. Kay, and J. Tolls. 2002. The sorption
and transport of a sulphonamide antibiotic in soil systems. Toxicol. Lett.
131:19–28.
Bradford, S., Y.F. Tadassa, and Y. Pachepsky. 2006. Transport of Giardia and manure suspensions in saturated porous media. J. Environ. Qual. 35:749–757.
Burkhardt, M., C. Stamm, C. Waul, H. Singer, and S. Muller. 2005. Surface
runoﬀ and transport of sulfonamide antibiotics and tracers on manured
grassland. J. Environ. Qual. 34:1363–1371.
Casey, F.X.M., H. Hakk, J. Šimůnek, and G.L. Larsen. 2004. Fate and transportof testosterone in agricultural soils. Environ. Sci. Technol. 38:790–798.
Casey, F.X.M., G.L. Larsen, H. Hakk, and J. Šimůnek. 2003. Fate and transportof 17beta-estradiol in soil–water systems. Environ. Sci. Technol. 37:2400–
2409.
Casey, F.X.M., and J. Šimůnek. 2001. Inverse analyses of transport of chlorinated hydrocarbons subject to sequential transformation reactions. J. Environ.
Qual. 30:1354–1360.
Casey, F.X.M., J. Šimůnek, J. Lee, G.L. Larsen, and H. Hakk. 2005. Sorption,
mobility, and transformation of estrogenic hormones in natural soil. J. Environ. Qual. 34:1372–1379.
Christian, T., R.J. Schneider, H.A. Farber, D. Skutlarek, M.T. Meyer, and H.E.
Goldbach. 2003. Determination of antibiotic residues in manure, soil, andsurface waters. Acta Hydrochim. Hydrobiol. 31:36–44.
Das, B.S., L.S. Lee, P.S.C. Rao, and R.P. Hultgren. 2004. Sorption and degradation of steroid hormones in soils during transport: Column studies andmodel evaluation. Environ. Sci. Technol. 38:1460–1470.
de Jonge, L., C. Kjaergaard, and P. Moldrup. 2004. Colloids and colloid-facilitated transport of contaminants in soils: An introduction. Vadose Zone
J. 3:321–325.
Díaz-Cruz, M., and D. Barceló. 2006. Determination of antimicrobial residues
and metabolites in the aquatic environment by liquid chromatography
tandem mass spectrometry. Anal. Bioanal. Chem. 386:973–985.
Dolliver, H., K. Kumar, and S. Gupta. 2007. Sulfamethazine uptake by plantsfrom manure-amended soil. J. Environ. Qual. 36:1224–1230.
Fan, Z.S., F.X.M. Casey, H. Hakk, and G.L. Larsen. 2007. Discerning and modeling the fate and transport of testosterone in undisturbed soil. J. Environ.
Qual. 36:864–873.
Focazio, M.J., D.W. Kolpin, K.K. Barnes, E.T. Furlong, M.T. Meyer, S.D.
Zaugg, L.B. Barber, and M.E. Thurman. 2008. A national reconnaissancefor pharmaceuticals and other organic wastewater contaminants in the
United States: II. Untreated drinking water resources. Sci. Total Environ.
402:201–216.
Förster, M., V. Laabs, M. Lamshöft, J. Groeneweg, S. Zühlke, M. Spiteller,
M. Krauss, M. Kaupenjohann, and W. Amelung. 2009. Sequestrationof manure-applied sulfadiazine residues in soils. Environ. Sci. Technol.
43:1824–1830.
Gao, J., and J.A. Pedersen. 2005. Adsorption of sulphonamide antimicrobial
agents to clay minerals. Environ. Sci. Technol. 39:9509–9516.
Hamscher, G., H.T. Pawelzick, H. Hoper, and H. Nau. 2005. Diﬀerent behavior

F . 7. Carbon-14 distribu ons in soil columns KrepMAN and MrepMAN and simula ons using a model with one reversible and one
irreversible kine c sorp on site. The 14C concentra ons are given
in mass equivalents of sulfadiazine.

the lower exponents ﬁtted to our transport experiments is thata kinetic process leading to extended tailing may partly mask
strong sorption nonlinearity. To compare our results with theresults reported in these two studies, we calculated the sorption
capacity for a liquid concentration of 1 μg cm−3 and compared
it with the highest and lowest reported values. The Freundlich
sorption capacities in the batch studies were higher than in ourstudy, probably because in batch sorption experiments the process of irreversible sorption is not considered separately.

Conclusions
The application of pig manure containing SDZ and its transformation products to soil columns led to an accumulation of
total 14C in the uppermost soil layers and resulted in lower peakvalues of the 14C BTCs compared with experiments with a pure
SDZ solution. For the assumed experimental conditions, SDZ
as well as its transformation products showed a high potential
for leaching. Co-transport with dissolved organic matter did notseem to be a major transport mechanism for the solutes.
The conceptual model with degradation and one kinetic andone irreversible sorption site provided a good description for most
BTCs of SDZ and its transformation products 4-[2-iminopyrimidine-1(2H)-yl]-anilin, N-Ac-SDZ, and 4-OH-SDZ. The
14C concentrations remaining in the soil columns could not be
predicted correctly for the experiments with the SDZ solution,
which suggests a sorption process that is not well understood.
Transport parameters ﬁtted to BTCs of individual species (SDZ
and its transformation products) revealed a lower sorption capacity for the transformation products than for SDZ in the low
concentration ranges. The N-Ac-SDZ was rapidly transformed
and did not show any patterns useful for characterizing SDZ
transport, such as an extended tailing of the BTCs or irreversible
sorption. The transport behavior of 4-OH-SDZ seemed to be
similar to that of SDZ. The model also revealed a higher sorption
capacity for SDZ in the presence of manure.
A
We acknowledge the German Research Foundation (DFG) for theirﬁnancial support (FOR566), Bayer HealthCare (Wuppertal, Germany)for providing the 14C-labeled sulfadiazine, BayerCropScience AG for
the performance of the SDZ feeding experiment, and the Division of
Soil Science of INRES at the University of Bonn for the measurementsof soil texture. We thank Stephan Köppchen for the HPLC measure-www.vadosezonejournal.org · Vol. 8, No. 3, August 2009688

of tetracyclines and sulfonamides in sandy soils after repeated fertilization
with liquid manure. Environ. Toxicol. Chem. 24:861–868.
Hanson, B.R., J. Šimůnek, and J.W. Hopmans. 2006. Evaluation of urea–ammonium-nitrate fertigation with drip irrigation using numerical modeling.
Agric. Water Manage. 86:102–113.
Heise, J., S. Höltge, S. Schrader, and R. Kreuzig. 2006. Chemical and biological characterization of non-extractable residues in soil. Chemosphere65:2352–2357.
Hesketh, N., P.C. Brookes, and T.M. Addiscott. 2001. Eﬀect of suspended soilmaterial and pig slurry on the facilitated transport of pesticides, phosphateand bromide in sandy soil. Eur. J. Soil Sci. 52:287–296.
Hilton, M.J., and K.V. Thomas. 2003. Determination of selected human pharmaceutical compounds in eﬄuent and surface water samples by high-performance liquid chromatography–electrospray tandem mass spectrometry.
J. Chromatogr. A 1015:129–141.
Höper, H., J. Kues, H. Nau, and G. Hamscher. 2002. Eintrag und Verbleib vonTierarzneimitteln in Böden. Bodenschutz 4:141–148.
Jarvis, N.J., K.G. Villholth, and B. Ulen. 1999. Modelling particle mobilizationand leaching in macroporous soil. Eur. J. Soil Sci. 50:621–632.
Jørgensen, S.E., and B. Halling-Sørensen. 2000. Drugs in the environment.
Chemosphere 40:691–699.
Kahle, M., and C. Stamm. 2007. Sorption of the veterinary antimicrobial sulfathiazole to organic materials of diﬀerent origin. Environ. Sci. Technol.
41:132–138.
Kay, P., P.A. Blackwell, and A.B.A. Boxall. 2004. Fate of veterinary antibiotics in amacroporous tile drained clay soil. Environ. Toxicol. Chem. 23:1136–1144.
Kay, P., P.A. Blackwell, and A.B.A. Boxall. 2005a. Column studies to investigate
the fate of veterinary antibiotics in clay soils following slurry application
to agricultural land. Chemosphere 60:497–507.
Kay, P., P.A. Blackwell, and A.B.A. Boxall. 2005b. A lysimeter experiment toinvestigate the leaching of veterinary antibiotics through a clay soil andcomparison with ﬁeld data. Environ. Pollut. 134:333–341.
Kemper, N. 2008. Veterinary antibiotics in the aquatic and terrestrial environment. Ecol. Indic. 8:1–13.
Kretzschmar, R. 1994. Filter eﬃciency of three saprolites for natural clay andiron oxide colloids. Environ. Sci. Technol. 28:1907–1915.
Kreuzig, R., and S. Höltge. 2005. Investigations on the fate of sulfadiazine inmanured soil: Laboratory experiments and test plot studies. Environ. Toxicol. Chem. 24:771–776.
Kreuzig, R., S. Höltge, J. Brunotte, N. Berenzen, J. Wogram, and R. Schulz.
2005. Test-plot studies on runoﬀ of sulfonamides from manured soils after
sprinkler irrigation. Environ. Toxicol. Chem. 24:777–781.
Kurwadkar, S.T., C.D. Adams, M.T. Meyer, and D.W. Kolpin. 2007. Eﬀects
of sorbate speciation on sorption of selected sulfonamides in three loamy
soils. J. Agric. Food Chem. 55:1370–1376.
Lamshöft, M., P. Sukul, S. Zuhlke, and M. Spiteller. 2007. Metabolism of 14Clabelled and non-labelled sulfadiazine after administration to pigs. Anal.
Bioanal. Chem. 388:1733–1745.
Loftin, K.A., C.D. Adams, M.T. Meyer, and R. Surampalli. 2008. Eﬀects ofionic strength, temperature, and pH on degradation of selected antibiotics.
J. Environ. Qual. 37:378–386.
Managaki, S., A. Murata, H. Takada, B.C. Tuyen, and N.H. Chiem. 2007. Distribution of macrolides, sulfonamides, and trimethoprim in tropical waters: Ubiquitous occurrence of veterinary antibiotics in the Mekong Delta.
Environ. Sci. Technol. 41:8004–8010.
McGechan, M.B., and D.R. Lewis. 2002. Transport of particulate and colloidsorbed contaminants through soil. Part 1: General principles. Biosyst. Eng.
83:255–273.
Nouws, J.F.M., D. Mevius, T.B. Vree, and M. Degen. 1989. Pharmacokinetics
and renal clearance of sulfadimidine, sulfamerazine and sulfadiazine andtheir N4-acetyl and hydroxy metabolites in pigs. Vet. Q. 11:78–86.
Pang, L., and J. Šimůnek. 2006. Evaluation of bacteria-facilitated cadmium transport in gravel columns using the HYDRUS colloid-facilitated solute transport model. Water Resour. Res. 42:W12S10,
doi:10.1029/2006WR004896.
Papiernik, S.K., S.R. Yates, W.C. Koskinen, and B. Barber. 2007. Processes affecting the dissipation of the herbicide isoxaﬂutole and its diketonitrile metabolite in agricultural soils under ﬁeld conditions. J. Agric. Food Chem.
55:8630–8639.
Sacher, F., F.T. Lange, H.-J. Brauch, and I. Blankenhorn. 2001. Pharmaceuticals

www.vadosezonejournal.org · Vol. 8, No. 3, August 2009

in groundwaters: Analytical methods and results of a monitoring programin Baden-Würtemberg, Germany. J. Chromatogr. A 938:199–210.
Schaerlaekens, J., D. Mallants, J. Šimůnek, M.Th. van Genuchten, and J. Feyen.
1999. Numerical simulation of transport and sequential biodegradationof chlorinated aliphatic hydrocarbons using CHAIN_2D. Hydrol. Proc.
13:2847–2859.
Schmidt, B., J. Ebert, M. Lamshoft, B. Thiede, R. Schumacher-Buﬀel, R. Ji,
P.F.X. Corvini, and A. Schaeﬀer. 2008. Fate in soil of 14C-sulfadiazine
residues contained in the manure of young pigs treated with a veterinary
antibiotic. J. Environ. Sci. Health B 43:8–20.
Schwarzenbach, R.P., P.M. Geschwend, and D.M. Imboden. 2003. Environmental organic chemistry. 2nd ed. John Wiley & Sons, New York.
Šimůnek, J., D. Jacques, M.Th. van Genuchten, and D. Mallants. 2006. Multicomponent geochemical transport modeling using HYDRUS-1D andHP1. J. Am. Water Resour. Assoc. 42:1537–1547.
Šimůnek, J., H. Sejna, M. Saito, M. Sakai, and M.T. van Genuchten. 2008.
The HYDRUS-1D software package for simulating the one-dimensional
movement of water, heat, and multiple solutes in variably-saturated media.
Version 4.0. Dep. of Environ. Sci., Univ. of California, Riverside.
Stoob, K., H.P. Singer, S.R. Mueller, R.P. Schwarzenbach, and C.H. Stamm.
2007. Dissipation and transport of veterinary sulfonamide antibiotics after
manure application to grassland in a small catchment. Environ. Sci. Technol. 41:7349–7355.
Sukul, P., M. Lamshoft, S. Zuhlke, and M. Spiteller. 2008a. Sorption and desorption of sulfadiazine in soil and soil–manure systems. Chemosphere73:1344–1350.
Sukul, P., M. Lamshoft, S. Zuhlke, and M. Spiteller. 2008b. Photolysis of 14Csulfadiazine in water and manure. Chemosphere 71:717–725.
Thiele-Bruhn, S., and M.O. Aust. 2004. Eﬀects of pig slurry on the sorption of
sulfonamide antibiotics in soil. Arch. Environ. Contam. Toxicol. 47:31–39.
Toride, T., F.J. Leij, and M.T. van Genuchten. 1999. The CXTFIT code for estimating transport parameters from laboratory or ﬁeld tracer experiments.
Version 2.1. Res. Rep. 137. U.S. Salinity Lab., Riverside, CA.
Unold, M., R. Kasteel, J. Groeneweg, and H. Vereecken. 2009. Transport andtransformation of sulfadiazine in soil columns packed with a silt loam anda loamy sand. J. Contam. Hydrol. 103:38–47.
van Genuchten, M.Th. 1985. Convective–dispersive transport of solutes involved
in sequential ﬁrst-order decay reactions. Comput. Geosci. 11:129–147.
Wang, Q. 2006. Sulfadimethoxine degradation kinetics in manure as aﬀectedby initial concentration, moisture, and temperature. J. Environ. Qual.
35:2162–2169.
Wehrhan, A. 2006. Fate of veterinary pharmaceuticals in soil: An experimental
and numerical study on the mobility, sorption and transformation of sulfadiazine. Ph.D. diss. Environ. Vol. 66. Forschungszentrum Jülich GmbH,
Jülich, Germany.
Wehrhan, A., R. Kasteel, J. Šimůnek, J. Groeneweg, and H. Vereecken. 2007.
Transport of sulfadiazine in soil columns: Experiments and modelling approaches. J. Contam. Hydrol. 89:107–135.
Wortmann, C.S., and C.A. Shapiro. 2008. The eﬀects of manure application on
soil aggregation. Nutr. Cycling Agroecosyst. 80:173–180.
Ye, Z.Q., H.S. Weinberg, and M.T. Meyer. 2007. Trace analysis of trimethoprim and sulfonamide, macrolide, quinolone, and tetracycline antibiotics
in chlorinated drinking water using liquid chromatography electrospraytandem mass spectrometry. Anal. Chem. 79:1135–1144.

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