139
6
Sorption and
Degradation of Selected
Pharmaceuticals in
Soil and Manure
Nadia Carmosini and Linda S. Lee
6.1 INTRODUCTION
Overthepasttwodecades,thenumberoflivestockandpoultryfarmsintheUnited
States has decreased by approximately half, while the number of animal units being
raised has increased by about 10%.
1
Thisshifttowardfewerbutincreasinglylarger
industrialized farms, termed “conned” or “concentrated animal feeding operations”
(CAFOs), has resulted in concomitant increases in pharmaceutical use and manure
generatedperunitlandarea.Duringtheirlifespan,roughly60to80%ofcommercial
livestockaretreatedwithantibioticsastherapeutic,prophylactic,orgrowthpromot-
ing agents,
2
andmuchoftheingesteddoseisexcretedunchangedorasactivemetab-
olites.
3
Hormones are also used for growth promotion and reproductive control. In
addition,hormonesandtheirmetabolitesareproducedandexcretednaturally,with
more than 50 tons of reproductive hormones being released annually by farm ani-
mals in the United States.
4
Asaresult,the130billionpoundsofmanureproduced
everyyearrepresentanexpansivesourceofpharmaceuticalcontamination.
CAFOstypicallystoreanimalwastesinanoutdoorlagoon,undergroundpit,
or litter storage facility. For example, approximately 23% of swine operations in

armanner,municipalwastewatertreatmentplantsgeneratepharmaceutical-laden
biosolidsandwastewaterefuents,whicharedisposedbylandapplicationandused
tomeetirrigationdemandsinaridregions.Recentsurveysoforganiccontaminants
in wastewater efuents and biosolids have reported a suite of antibiotics and other
pharmaceuticals, albeit at concentrations substantially lower than those in livestock
andpoultrymanures(lessthanμg/kgvs.mg/kglevels).
6,7
Concern over potential negative impacts of biologically active pharmaceuticals
on nontarget organisms and ecosystem health has prompted many laboratory-scale
andafeweld-scaleassessmentsoftheirenvironmentalfate.Severalreviewsof
thisinformationhavebeenpublishedinthepast5years,especiallyforveterinary
pharmaceuticals.Mostrecently,Leeetal.
8
summarizedwhatisknownontheoccur-
rence, environmental fate, ecological impacts, and analytical techniques associated
with veterinary antibiotics and hormones. Khanal et al.
9
reviewed the removal rates
andmechanismsfornaturalestrogensinwastewatertreatmentsystems.Sarmahet
al.
10
compiled data on veterinary antibiotic use and sales trends for several countries,
including the United States, the European Union, New Zealand, Kenya, Canada,
Japan,China,andRussia.Kumaretal.
11
summarized veterinary antibiotic occur-
rence, excretion rates, and subsequent environmental fate, including sorption, degra-
dat
ion, and transport. Preceding these reviews, Tolls
12

sorption of the applied compound when near-equilibrium conditions are attained.
This degree of partitioning facilitates accurate quantication of sorbate concentra
-
t
i
onsinboththesolid(C
s
, mg/kg or mmol/kg) and aqueous (C
w
,mg/Lormmol/L)
phases. These concentrations are plotted against one another to construct a sorption
isotherm, which can be described with one of three commonly used equilibrium
based models: (1) Linear equation,
K
d
= C
s
/C
w
,whereK
d
(L/kg) is the linear distri-
bution coefcient; (2) Freundlich equation, C
s
= K
f
C
w
N
,whereK

(L/mgorL/mmol)istheLangmuirafnitycoefcientandC
s,max
is the
maximum monolayer adsorption capacity (mg/kg or mmol/kg). Comparisons among
sorbentscanbemadeindependentoflinearityusingnonlinearmodelcoefcientsby
estimating a concentration-specic sorption coefcient (
K
d
*
) at an equilibrium con-
centration (C
w
) that falls within the experimental range: K
d
*
= K
f
C
w
N–1
.
Direct quantication of the contaminant in both phases is critical for assessing
potentiallyreversiblesorptionandensuringthatthelossoftheparentcompound
from solution is due only to sorption. If biotic and abiotic transformations, volatiliza
-
t
i
on,sorptiontolabware,andotherlossprocessesaresignicantandattributedto
sorption, inated estimates of sorption will be obtained. Methods commonly used to
inhibit biodegradation include sterilization of the sorbent by

saturatedsteady-stateowconditions,whicharefarnotrepresentativeofvertical
transportthroughthevadosezonewhereunsaturatedtransientowisthenorm.
Also,evencolumnstudiesperformedwithintactcoresoftencannotreecttheeffect
of eld-scale heterogeneity on fate and transport phenomena or adequately represent
the magnitude of macropore ow at the eld scale.
16
© 2008 by Taylor & Francis Group, LLC
142 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems
Oneofthemostchallengingaspectsofbatch,column,andeld-scaleexperi-
ments is the accurate quantication of low analyte concentrations in complex sample
matrices.Manyspectroscopictechniques,suchasultraviolet-visible(UV-VIS),uo-
re
scence, and mass spectrometry, are often plagued by positive or negative matrix
effects, necessitating the use of internal standards or matrix-matched standards.
Finally, the use of sorption data in environmental fate models will only accurately
describe chemical partitioning in other systems with similar physicochemical prop
-
er
ties (e.g., pH, electrolyte concentration and composition, solute concentration
range,sorbentcomposition).Forexample,themagnitudeofsorptionexhibitedbya
pureclaysorbentmaydifferfromthatoftheclaywithinasoilduetothepresence
of other sorption domains and the interactions between those domains (e.g., organic
matter coatings on clay surfaces).
6.3 ANTIBIOTICS
6.3.1 SORPTION BY SOIL
Todate,researchonthefateofpharmaceuticalsisdominatedbyworkonveterinary
antibioticsinresponsetoconcernsthattheirextensiveuseinlivestockproductionis
contributing to bioactive residues in the environment. Although their physicochemi-
cal
properties are highly variable, most antibiotics are moderately water soluble and

is predominantly anionic (+ or 0 ). Infrared radiation (IR) analyses also showed
that clindamycin decreased the intensity of the water absorption band, which was
attributed to the replacement of hydrated exchangeable cations in the clay’s inter
-
layerbyclindamycin.Underneutraltomoderatelyalkalineconditions,IRspectral
shifts indicated that sorption of the TC zwitterions (+ 0 and + ) occurred by cation
exchange as well as by the formation of a complex between the interlayer Ca
2+
cat-
ions and the antibiotic’s carbonyl group. For the uncharged clindamycin molecule,
© 2008 by Taylor & Francis Group, LLC
Sorption and Degradation of Selected Pharmaceuticals in Soil and Manure 143
TABLE 6.1
Properties of Selected Antibiotics
Antibiotic Class
Molecular
Weight
(g mol
–1
) pKa Usage
Clindamycin
CH
3
O
N
H
N
Cl
CH
3

b
7.68
b
9.3
b
Human and veterinary therapeutic; Livestock
growth promoter and prophylactic
Oxytetracycline
OH OH
OH
OH
N
H
OH
CH
3
HO
CH
3
H
3
C
OOO
NH
2
H
Tetracycline 460.44 3.27
b
7.32
b

OH
OO
N
Tetracycline 478.89 3.30
b
7.44
b
9.27
b
Human and veterinary therapeutic; Livestock
growth promoter and prophylactic
Ciprooxacin
HN
F
N
N
O
OH
O
Fluoroquinolone 331.35 5.90
c
8.89
c
Human therapeutic
Enrooxacin
H
3
C
N
NN

C
Quinolone 261.23 6.9
e
Veterinary therapeutic; Aquaculture
Saraoxacin
O
O
N
N
F
HN
F
OH
Fluoroquinolone 385.37 4.1
e
6.8
e
Veterinary therapeutic; Aquaculture
(Continued)
© 2008 by Taylor & Francis Group, LLC
146 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems
Monensin
HO
O
O
O
O
O
O
O

Ionophore 670.88 4.2
f
Livestock growth promoter and prophylactic
Lasalocid
H
3
C
OH OH
H
OH
O
O
O
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
H
3
C
OH
H

3
CH
3
CH
3
CH
3
OH
H
3
C
H
3
C
CH
3
OH O
O
O
O
O
OH
Ionophore 751.01 4.45
g
Livestock growth promoter and prophylactic
Tylosin
H
3
C
CH

O
O
N
OH
HO
O
O
O
HO
H
3
C
Macrolid 916.11 7.7
h
Veterinary therapeutic; Livestock growth
promoter and prophylactic
Erythromycin
HO
H
3
C
CH
3
H
3
C
CH
3
CH
3

C
Macrolid 733.94 8.88
h
Human and veterinary therapeutic; Livestock
growth promoter and prophylactic
(Continued)
© 2008 by Taylor & Francis Group, LLC
148 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems
Roxithromycin
H
3
C
H
3
C
CH
3
CH
3
H
3
C
CH
3
CH
3
CH
3
CH
3

g
Human therapeutic
Carbadox
O
–
O
–
N
+
N
O
O
CH
3
H
N
N
+
Quinoxaline 262.22 <0i9.61
i
Livestock growth promoter and prophylactic
Olaquindox
O
–
CH
3
O
–
O
OH

CH
3
CH
3
Sulfonamide 278.32 2.28
j
7.42
j
Human therapeutic; Livestock growth
promoter and prophylactic
Sulfamethoxazole
H
3
C
N
H
N
S
NH
2
O
O
O
Sulfonamide 253.27 1.85
j
5.29
j
Human and veterinary therapeutic
Sulfapyridine
N

CH
3
H
3
C
OHO
Pleuromutilin 493.74 9.51
g
Veterinary therapeutic and prophylactic
(Continued)
© 2008 by Taylor & Francis Group, LLC
150 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems
Triclosan
Cl
OH
O
Cl
Cl
Na 289.54 7.99
l
Commercial disinfectant
Chlorophene
Cl
OH
Na 218.68 9.96
l
Commercial disinfectant
a
Ref 17
b

) pKa Usage
© 2008 by Taylor & Francis Group, LLC
Sorption and Degradation of Selected Pharmaceuticals in Soil and Manure 151
sorption was attributed to relatively weak physical processes (e.g., H-bonding, van
der Waals forces). No sorption was observed for either antibiotic at high pH condi
-
ti
ons (pH 11).
Recently, the importance of sorption by cation exchange has been documented
extensivelyinstudiesontetracyclineinteractionswithmodelclays,soils,andhumic
materials under varying pH and ionic strength conditions.
18–23
Therangeofthethree
pK
a
values(≈3.3to9.3,seeTable 6.1) for tetracyclines results in large shifts in the
proportion of the cation (+00), zwitterion (+ 0), and predominantly anionic spe
-
ci
es(+ )overtheenvironmentallyrelevantpHrange.Figueroaetal.
18
effectively
described pH effects on oxytetracycline (OTC) sorption using a model that included
cation exchange plus surface complexation of the + 0 zwitterion species. Previous
work on less complicated organic bases (e.g., quinoline and aromatic amines) has
shown that when cation exchange dominates contaminant binding to a sorbent,
K
d
or K
d

explain the sorption of the +–0 zwitterion, Figueroa et al.
18
proposed a complexation
mechanism involving positively charged protons on the montmorillonite surfaces.
TheproposedhypothesisissupportedbyKulshresthaetal.’s
19
Fourier transformed
(FT)-IR analysis of Na-montmorillonite equilibrated with OTC at pH 5.0, which
showed peak shifts consistent with coordination of the antibiotic’s carbonyl group
with interlayer cations or hydrogen bonding with hydroxyl groups of water coordi
-
n
at
ed to interlayer cations.
Sassman and Lee
22
employed the same model to describe the sorption of OTC,
TC,andchlortetracycline(CTC)byeightsoilsvaryinginpH,typeandamountof
clay, CEC, anion exchange capacity (AEC), and OC content. The model t the data
wellacrossallsoils(pHrangeof3.8to7.49)exceptforagibbsite-richsoilwithhigh
AE
C. Values for
were one to two orders of magnitude greater than val-
ues(e.g.,6.43×10
6
and1.46×10
5
L/equiv, respectively, for OTC in 0.01 N CaCl
2
).

lower than the buffered pH of 5.5. Alternately, for soils with pH values higher than
5.5, the operational CEC would be lower than the reported CEC. These discrepan-
ci
esmayhavemaskedthetruecontributionofCECtothesorptionofOTCinthe
Jonesetal.
26
study.
Additionalexperimentsonelectrolytecompositioneffectsonthesorptionoftet-
ra
cyclines also support a cation exchange mechanism. When cation exchange is a
controlling process, decreases in the concentration of competing inorganic cations
(e.g., 0.01 to 0.001 N CaCl
2
)orareductionintheselectivityoftheinorganiccat-
ion (e.g., substituting K
+
for Ca
2+
) are expected to increase solute sorption. Indeed,
Sassman and Lee
22
observed that reductions in CTC sorption with electrolyte com-
position, after accounting for induced pH-shifts, generally followed the trend: 0.001
N CaCl
2
> 0.01 N KCl > 0.01 N CaCl
2
.TerLaaketal.
23
found that increases in ionic

kg
–1
L
N
and 0.95 for Al-hydrous oxides and 59.1 mol
1–N
kg
–1
L
N
and 0.85 for Fe-hydrous
oxides,respectively,measuredatanionicstrengthof0.01MandpH5.4.
30
(Units
for K
f
wereerroneouslyreportedtobeunitlessbyGuandKarthikeyan.
30
)Fourier
transform infrared spectroscopy indicated that the predominantly zwitterion TC (+-
0) interacted with the metal oxides via the tricarbonylamide and carbonyl functional
groups.Theformationofthesurfacecomplexsubsequentlyresultedinthedissolu-
ti
on of the metal-hydrous oxides and aqueous concentrations of 2:1 metal to TC
complexes. Other studies have shown that tetracyclines form complexes with diva-
le
nt cations, such as Ca
2+
,Cu
2+

oxacin (CIP) (pK
a1
=6.16,pK
a2
=8.62)toAl-andFe-hydrousoxides.CIPisan
important third-generation uoroquinolone reserved for human use, and it is also the
primary metabolite of enrooxacin, a veterinary antibiotic that differs structurally
fromCIPbyasingleethylgroup.SorptionofCIPbyFe-hydrousoxideincreased
from pH 4 (
K
d
≈400L/kg),wherethecompoundexistspredominantlyasacation,to
amaximumatpH7(K
d
≈2000L/kg),whereitispredominantlyazwitterion.Further
increases to pH 10 reduced sorption as a result of increasingly repulsive interactions
betweenthenegativelychargedantibioticandsorbate.Thesametrendwasobserved
for CIP sorption to Al-hydrous oxide; however, the maximum
K
d
waslessthan400
L/kg.AnalysisbyFT-IRindicatedthiswasattributabletodifferencesinthetypesof
antibiotic-metal complexes formed. CIP and Fe formed a strong bidentate complex
between the metal and the deprotonated
C-
keto a
cid. In contrast, CIP formed only a
monodentate complex between the deprotonated carboxylate group and an Al atom.
Ea
rlierworkbyNowaraetal.

values
decreasedto2980L/kgwiththeadditionofCa
2+
,suggestingthatCa
2+
competed
with OTC for cation exchange sites on the humic acid. However, sorption coef-
c
i
entsforTCbyElliottsoilhumicacid(23mmolCa
2+
/kg DOC) were increased
from approximately 4000 L/kg OC to 5000 L/kg DOC by Ca
2+
amendments (8333
mmol Ca
2+
/kg DOC).
21
Holten Lützhøft et al.
42
measured K
DOC
values in the same range for the binding
of uoroquinolones by Aldrich humic acid (3000 to 200,000 L/kg DOC). Sorption
ofumequinandoxolinicacidincreasedmarkedlybetweenpH3and6butremained
constant with further increases in pH. Anticipated electrostatic repulsion between
thenegativelychargedantibioticandthehumicaciddidnotreducesorptionaspH
increased. These results suggest a cation bridging mechanism since umequin and
oxolinic acid posses a single ioniza

-
in
gly, the carboxyl and ether O atoms in the molecules can chelate environmentally
relevant cations (e.g., Na
+
,K
+
,Ca
2+
,Mg
2+
),whichmayincreasetheapparenthydro-
phobicityofthemoleculesandpossiblyaltertheirsorptionandmobilitybyreduc-
i
n
gtheirnetcharge.Elucidatinginteractionswithdivalentmetals,especiallythose
frequently incorporated in animal feeds, will be necessary for understanding the fate
of these antimicrobials in the environment.
Hydrophobic partitioning also appears to contribute to sorption by soils of tylo
-
sin, a basic macrolid antibiotic (pK
a
=7.7),andtwoofitsmetabolites,tylosin-D
and tylosin A-aldol.
15
Sorption isotherms measured for six soils were nonlinear
with Freundlich model N v
alues o
f 0.42 to 0.80. Comparisons among soils made by
examining K

exchange of the antibiotic and improved recovery to 98% from 26 to 50% attained
with methanol alone.
Hydrophobicforceshavealsobeenshowntoplayaroleinthesorptionofcarba
-
d
o
x,aquinoxalineantibioticaddedtothefeedofstarterpigsintheUnitedStatesto
prevent dysentery and improve feed efciency. Strock et al.
44
investigated the sorp-
tion of carbadox and its N-oxide reduced metabolites (N4 oxide, N1 oxides, and bis-
desoxycarbadox) by several soils, a sediment, and homoionic smectite and kaolinite
clays. Both carbadox and bis-desoxycarbadox have been identied as potential
mutagens,
45
prompting the need for information on the environmental fate of these
novel aromatic N-oxide compounds. Sorption appeared well correlated to soil OC
content(e.g.,log
K
oc
=3.98±0.18forCBX).However,sorptionwasenhancedby
thepresenceofK
+
relative to Ca
2+
, competitive sorption by the metabolites was
observed, and sorption by clay minerals was large (e.g., log K
d
≈ 5 for montmoril-
lonite)andinverselycorrelatedtosurfacechangedensity.Intheabsenceofaclay

-
sition and essentially linear with approximated K
d
valuesinthe10to16L/kgrange.
At pH <5, sorption of sulfonamides increased with decreasing pH and decreased
with increasing ionic strength, which are characteristic trends of sorption by the pro
-
ton
atedanilinicamine.AtpH>7,sorptiondecreasedtonearzerowithincreasingpH
as the fraction of the anionic species increased. The magnitude of sorption and the
pH effect were dependent on clay charge density. Similar trends in sorption (K
+0
>
K
00
>K
0–
)andwithpHhavebeenreportedforthesorptionofsulfathiazoletocom-
post, manure, and humic acid.
47
Sorption of a suite of sulfonamides by whole soils
andsoilfractionsexhibitedarangeofsorptionnonlinearity(N =0.75to1
.21) and
correlations to OC appeared dependent on the composition of organic matter indicat-
in
g the occurrence of some site-specic interactions.
48,49
In model systems, Bialk et
al.
50

using a two-compartment, rst-order model.
52
Addition of NaN
3
(50 g/L), intended
to eliminate biodegradation, increased these times to 90 h and 500 h, respectively.
In contrast, aerating the systems in either the presence or absence of NaN
3
reduced
the 90% disappearance times for the open and covered lagoons to 12 h and ≤32 h,
© 2008 by Taylor & Francis Group, LLC
156 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems
respectively,inamannerthatfollowedarst-orderdegradationmodel.Theauthors
attributed that the dissipation of tylosin primarily to irreversible sorption to solids
and aeration induced increases in pH, which enhanced base-catalyzed reactions. In
another study on tylosin, calculated rst-order half-lives in aerobic cattle, chicken,
and swine manure slurries ranged from 6.2 to 7.6 d.
53
New studies have reported on the dissipation of various antibiotics in soils.
Sassmana
ndL
ee
43
investigatedthedegradationofmonensinandlasalocidin
60
Co
irr adiated a
nd n
onsterilelaboratorysoilmicrocosmswithandwithoutmanure
amendment. In nonsterile soils, less than 25% of either ionophore remained after

highreductionpotential(1.23V)andcanplayanimportantroleinthetransforma
-
tion of organic compounds. Departure from pseudo-rst-order kinetics was reported
in each study, likely due to changes to the MnO
2
surfacepropertiesoverthecourse
of the experiments.
59
To facilitate comparisons of reaction kinetics and calculations
of reaction order, Zhang and Huang
56–58
used initial rates during the rst few hours
where pseudo-rst-order kinetics were approximated. Except for umequine for
which no transformation was observed, all tested uoroquinolones degraded in the
presence of MnO
2
at pH 6 with initial reaction rate constants (k
init
)rangingfrom
0.54 h
–1
to 1.11 h
–1
.
57
Triclosan and chlorophene degraded in reagent water (pH 5)
with k
init
values of 1.74 h
–1

the MnO
2
surface.Oxidationoftheorganiccompoundrequirestheformationofa
© 2008 by Taylor & Francis Group, LLC
Sorption and Degradation of Selected Pharmaceuticals in Soil and Manure 157
precursor complex with the surface of the MnO
2
, and the ability to form this complex
will vary among the different pH-dependent species of the ionizable compounds.
57,58
Differences in transformation rates among related compounds of a particular anti-
ba
cterial class were attributed to specic functional groups and described in detail
bytheauthors.Inrelatedwork,Bialketal.
50
found that selected sulfonamides also
underwent signicant transformation (20 to 65%) in the presence of MnO
2
.Inaddi-
tion, the presence of certain model substituted phenols, intended to simulate humic
materials, enhanced transformation rates by promoting covalent cross-coupling of
the sulfonamides to the model phenols. Goethite has also been shown to oxidatively
transformuoroquinolones,albeitatratesapproximatelythreeordersofmagnitude
lowerthanMnO
2
,reectingthelowerredoxpotential(0.63V)ofthemineral.
60
6.4 HORMONES
6.4.1 SORPTION BY SOIL AND SEDIMENT
The occurrence of natural and synthetic estrogens and androgens in surface waters

metabolites in several Midwestern soils. Concentrations of the parent compounds
and metabolites were measured directly in the aqueous and soil phases to generate
sorption isotherms that, in general, t the linear model well. Near equilibrium condi-
t
i
onsinthebatchreactorswereachievedwithinafewhours.AveragelogK
oc
values
for 17C-estradiol (
E2), 17B-ethynylestradiol (EE2), and testosterone were 3.34, 2.99,
and 3.34, with standard deviations of ≤0.18 log units. Log K
oc
values in the same
range(2.77to3.69)werealsoobtainedbyDasetal.
67
and by Casey et al.
68,69
Recent
work by Khan et al.
70
on the widely used livestock growth promoter 17C-trenbolone
acetate and its primary metabolites, 17B-trenbolone a
nd trendione, shows that these
compounds sorb in a manner similar to natural steroid hormones. Average log K
oc
values for 17C-trenbolone (3.10 ± 0.28) and trendione (3.42 ± 0.26) were consistent
with reported aqueous solubilities and log K
ow
values, indicating that soil OC is a
primarysorptiondomain.

lacksanionizablephenolicfunctionalgroup,followedasimilarsorptionpattern
as EE2 and E1, further negating the electrostatic interaction hypothesis. In each
of these cases, sorption to the minerals was estimated by difference rather than by
direct quantication of the sorbed concentration. Thus, loss of mass from solution
mayhaveresultedfromsurface-catalyzedtransformationsorinstabilityinalkaline
conditions rather than sorption.
The presence of DOC can result in lower-than-expected sorption of hormones
duetotheassociationofthehormonesasfollows:
where
istheapparentsorptioncoefcientinthepresenceofDOCand[DOC]isthe
concentrationofDOC(kg/L).HighlogK
DOC
values for the binding of E2, EE2, and
E3(4.13to4.86)havebeenreportedforcommercialhumicandfulvicacidsandfrom
sediment-derived DOC.
74,75
Interestingly, log K
DOC
values were greater than log K
oc
values and were not correlated to log K
ow
,whichdiffersfromthetrendsobserved
for other more strongly hydrophobic compounds.
76
Yamamoto et al.
74
proposed that
hydrogenbondingandinteractionsbetweenπ-electronsofestrogeniccompounds
andtheDOCaugmentedsorptionbeyondwhatwouldbepredictedfromsimple

duringstorageandafterlandapplication.Hakketal.
79
measured decreases in water-
solubleestrogenicactivity(83to13ngestradiolequivalents/g)andandrogenicactiv-
it
y(115to11ngtestosteroneequivalents/g)inpoultrymanurecompostpilesover
a 139-d period. Dissipation followed rst-order kinetics with loss rate constants of
0.01 d
–1
and 0.015 d
–1
, respectively. Water-extractable hormones were still detectable
after 4.6 months of composting.
Colucci et al.
78
and Colucci and Topp
80
reported somewhat longer dissipation rate
constantsforE2(0.07to3.12d
–1
)andEE2(0.1to0.37d
–1
)inmoistagriculturalsoil
microcosms.Theseratescorrespondtohalf-livesbetween0.5dand7.7d.Transfor-
mat
ionofE2toE1occurredinbothautoclavedandnonsterilesoil,whereasEE2
persisted in sterilized soil. In nonsterile soils, both E2 and E1 formed nonextractable
residuesinafewdays(56to91%),andmineralizationtoCO
2
was minimal (15%)

4
+
restored degradation. Esti-
matedsorptionmass-transferconstantscalculatedduringowwereatleastanorder
of magnitude higher than the degradation rate constants. This indicates that although
sorption by soils of the hormones and metabolites was substantial (4 to 142 L/kg),
degradation was not impeded by sorption, and near-equilibrium conditions could
beassumedwithinashorttimeperiod,whichisconsistentwithotherbatchexperi
-
ments.
66,68,71
Schiffer et al.
81
also used saturated columns to monitor the transforma-
tion of 17C-trenbolone t
o17B-trenbolone.ConversionwashigherinasurfaceAp
horizonsoil(1.6%OC)comparedtoasubsurfaceBthorizonsoil(0.6%OC),which
may be attributed to potentially greater microbial activity inherent with higher OC
soilsandisinagreementwithobservationsbyDasetal.
67
Likewise, Khan et al.
(unpublisheddata)observedfasterdegradationinahigherOCsoilfortrenbolone
compared to a sandy soil. They also noted no differences between the two isomers
andthatdegradationwasfasteratlowerappliedhormoneconcentrationsof1mg/kg
soil(half-livesof<0.5d)comparedto10mg/kg(half-livesupto2.5d).Theprimary
metabolitetrendioneexhibitedlongerhalf-livesof3dto2weeks.
Two studies have measured dissipation and mineralization rates in soils amended
with different types of animal litter.
82,83
Lucas and Jones

owpaths.Inanintactsoilcoreexperimentwithapulseapplicationofradiola
-
be
lled E2 and testosterone, Sangsupan et al.
84
foundthatasmuchas27%and42%,
respectively,oftheappliedhormonesleachedout.Inveofthesixsoilcolumns,
peak hormone
and Cl
-
breakthrough concentrations occurred simultaneously, indi-
cating movement through preferential ow paths. Schiffer et al.
81
also found that
smallamountsof17C-trenbolone a
nd melengestrol acetate leached through packed
soil columns within one pore volume, and subsequent breakthrough occurred earlier
than predicted from sorption isotherm data.
6.5 CONCLUSION
As the world’s human population grows and global afuence increases, the demand
forfoodanimalscanbeexpectedtorise.Currentusagedataindicatethatantibiotics
and hormones are likely to play a major role in meeting this demand, particularly as
developing countries modernize their livestock and poultry industries to meet food
requirements.
10
Asaresult,thepressureonagriculturallandstoaccommodatemore
animalandhumanwastescanbeexpectedtoincreaseconcomitantly.
Atthistimetherearesignicantgapsinourunderstandingofthefateandenvi-
ro
nmental impacts of the large quantities of pharmaceutical residues present in the

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