Fate of Pharmaceuticals in the Environment and in Water Treatment Systems - Chapter 6 pptx

6 Sorption andDegradation of Selected Pharmaceuticals in Soil and Manure Nadia Carmosini and Linda S.. Sarmah et including the United States, the European Union, New Zealand, Kenya, Cana

6 Sorption and

Degradation of Selected Pharmaceuticals in

Soil and Manure

Nadia Carmosini and Linda S Lee

6.1 INTRODUCTION

Over the past two decades, the number of livestock and poultry farms in the United States has decreased by approximately half, while the number of animal units being

industrialized farms, termed “confined” or “concentrated animal feeding operations” (CAFOs), has resulted in concomitant increases in pharmaceutical use and manure generated per unit land area During their lifespan, roughly 60 to 80% of commercial livestock are treated with antibiotics as therapeutic, prophylactic, or growth

addition, hormones and their metabolites are produced and excreted naturally, with more than 50 tons of reproductive hormones being released annually by farm

every year represent an expansive source of pharmaceutical contamination

CAFOs typically store animal wastes in an outdoor lagoon, underground pit,

or litter storage facility For example, approximately 23% of swine operations in

Contents

6.1 Introduction 139

6.2 Assessing Contaminant Fate and Transport in Soil Environments 140

6.3 Antibiotics 142

6.3.1 Sorption by Soil 142

6.3.2 Degradation in Manure and Soil 155

6.4 Hormones 157

6.4.1 Sorption by Soil and Sediment 157

6.4.2 Degradation in Manure and Soil 159

6.5 Conclusion 160

References 161

the United States use lagoons; 57% use below-ground pits; and the remaining 20%

liquid, sludge, and solids that are periodically pumped out and injected or surfaceapplied to agricultural land as an economical disposal strategy that capitalizes on thewaste’s fertilizer value Most CAFOs pump down or dewater lagoons three to fourtimes annually (58%), while others dewater less that twice a year (16%) or never at all

in the liquid phase may dissipate as a result of anaerobic degradation and sorption toparticulates After land application, aerobic degradation and sorption to soils furtherreduce the persistence and mobility of pharmaceuticals in the environment In a sim-ilar manner, municipal wastewater treatment plants generate pharmaceutical-ladenbiosolids and wastewater effluents, which are disposed by land application and used

to meet irrigation demands in arid regions Recent surveys of organic contaminants

in wastewater effluents and biosolids have reported a suite of antibiotics and otherpharmaceuticals, albeit at concentrations substantially lower than those in livestock

Concern over potential negative impacts of biologically active pharmaceuticals

on nontarget organisms and ecosystem health has prompted many laboratory-scaleand a few field-scale assessments of their environmental fate Several reviews ofthis information have been published in the past 5 years, especially for veterinary

occur-rence, environmental fate, ecological impacts, and analytical techniques associated

and mechanisms for natural estrogens in wastewater treatment systems Sarmah et

including the United States, the European Union, New Zealand, Kenya, Canada,

occur-rence, excretion rates, and subsequent environmental fate, including sorption,

a review of the sorption and presence of veterinary antibiotics in soils, respectively

In this chapter we will emphasize the studies that have been particularly tal in gleaning information on the processes that determine the sorption behavior ofantibiotics, as well as present an overview of emerging research on the degradation

instrumen-of antibiotics and hormones in the environment

TRANSPORT IN SOIL ENVIRONMENTS

The potential for antibiotics and hormones to contaminate and adversely impact theenvironment is directly influenced by their mobility and persistence in animal wastesand soils As a result, many studies have examined the dissipation and partitioning ofthese contaminants in environmental matrices, such as soil, manure, organic matter,clays, metal oxides, and oxyhydroxides For the most part, either batch equilibrium

or column displacement techniques have been used The interpretation and tion of data from these experiments requires careful consideration of the experimen-tal design employed In batch equilibrium experiments, multiple concentrations of a

applica-Sorption and Degradation of Selected Pharmaceuticals in Soil and Manure 141

sorbate are equilibrated with a constant amount of sorbent in an electrolyte solution

to solution volume ratio and contaminant concentration range that ensure 50 ± 25%sorption of the applied compound when near-equilibrium conditions are attained.This degree of partitioning facilitates accurate quantification of sorbate concentra-

phases These concentrations are plotted against one another to construct a sorptionisotherm, which can be described with one of three commonly used equilibriumbased models: (1) Linear equation,K d = C s /C w , where K d(L/kg) is the linear distri-

bution coefficient; (2) Freundlich equation, C s = K f C w , where K f(mg1-NLNkg–1or

of isotherm nonlinearity; and (3) Langmuir equation, C s = C s,max K L C w /(1+K L C w),

maximum monolayer adsorption capacity (mg/kg or mmol/kg) Comparisons amongsorbents can be made independent of linearity using nonlinear model coefficients by

con-centration (C w ) that falls within the experimental range: K d = K f C w N–1

Direct quantification of the contaminant in both phases is critical for assessingpotentially reversible sorption and ensuring that the loss of the parent compoundfrom solution is due only to sorption If biotic and abiotic transformations, volatiliza-tion, sorption to labware, and other loss processes are significant and attributed tosorption, inflated estimates of sorption will be obtained Methods commonly used to

auto-claving, and filtration, or incorporating a dilute concentration of an antimicrobial,

When these steps are not taken, batch experiments can be used to assess biotictransformations in conjunction with sorption as long as concentrations of the parentcompound and metabolites in both sorbed and solution phases are determined To acertain extent, biotic transformations may occur even after systems have been steril-ized due to extracellular enzymes that remain active

In column displacement studies, the movement of a contaminant front or pulsethrough a packed or intact soil column is evaluated over time Information on thechemical’s partitioning between the soil and aqueous phases is derived from a plot ofthe outflow concentration vs time, called a breakthrough curve, which is compared

to the breakthrough curve for a nonsorbing, conservative tracer (e.g., Cl–, Br–) pared to batch experiments, column studies may more closely mimic the spatial andtemporal processes of a field scenario, particularly when intact soil cores are used.Contaminants moving through a soil profile may not persist in space and time for asufficiently long period of time to reach equilibrium; thus, observations under flowconditions can provide additional insights into the processes that affect a chemical’spersistence and mobility in soils However, most column studies are conducted undersaturated steady-state flow conditions, which are far not representative of verticaltransport through the vadose zone where unsaturated transient flow is the norm.Also, even column studies performed with intact cores often cannot reflect the effect

Com-of field-scale heterogeneity on fate and transport phenomena or adequately represent

One of the most challenging aspects of batch, column, and field-scale ments is the accurate quantification of low analyte concentrations in complex samplematrices Many spectroscopic techniques, such as ultraviolet-visible (UV-VIS), fluo-rescence, and mass spectrometry, are often plagued by positive or negative matrixeffects, necessitating the use of internal standards or matrix-matched standards.Finally, the use of sorption data in environmental fate models will only accuratelydescribe chemical partitioning in other systems with similar physicochemical prop-erties (e.g., pH, electrolyte concentration and composition, solute concentrationrange, sorbent composition) For example, the magnitude of sorption exhibited by apure clay sorbent may differ from that of the clay within a soil due to the presence

experi-of other sorption domains and the interactions between those domains (e.g., organicmatter coatings on clay surfaces)

6.3 ANTIBIOTICS

6 3.1 S ORPTION BY S OIL

To date, research on the fate of pharmaceuticals is dominated by work on veterinaryantibiotics in response to concerns that their extensive use in livestock production iscontributing to bioactive residues in the environment Although their physicochemi-cal properties are highly variable, most antibiotics are moderately water soluble and

functionalities are ionizable, resulting in compounds that exist as either neutral orcharged species (e.g., cations, anions, zwitterions) in proportions dependent on pHconditions While neutral molecules partition to solid phases via relatively weakvan der Waals and electron donor-acceptor interactions, charged species can interactwith charged sorbents (e.g., organic matter, clays, metal oxides, and oxyhydroxides)through stronger electrostatic mechanisms, such as cation-exchange, cation-bridg-

antibiotics discussed in this chapter

For antibiotics possessing a positive charge, cation exchange has emerged as animportant sorption mechanism In work conducted three decades before the present

clindamy-cin and tetracycline (TC) by montmorillonite clay over a broad pH range (1.5 to 11).X-ray diffraction analysis showed that the clay’s interlayer spacing increased underlow pH conditions where the antibiotics’ cationic species predominated In contrast,the spacing remained unchanged at high pH where clindamycin is neutral and TC

is predominantly anionic (+ or 0 ) Infrared radiation (IR) analyses also showedthat clindamycin decreased the intensity of the water absorption band, which wasattributed to the replacement of hydrated exchangeable cations in the clay’s inter-layer by clindamycin Under neutral to moderately alkaline conditions, IR spectralshifts indicated that sorption of the TC zwitterions (+ 0 and + ) occurred by cation

cat-ions and the antibiotic’s carbonyl group For the uncharged clindamycin molecule,

CH3 O

N

H Cl CH3

H

HO

S CH3 O

Lincosamide 424.98 7.6 a Human and veterinary therapeutic

O OH

OH

OH NH2

H3C

N

7.68 b 9.3 b

Human and veterinary therapeutic; Livestock growth promoter and prophylactic

OH

CH3

HO

CH3 H3C

NH2 H

7.32 b 9.11 b

Human and veterinary therapeutic; Livestock growth promoter and prophylactic; Fruit production; Aquaculture

(Continued)

OH

O O

N

Tetracycline 478.89 3.30 b

7.44 b 9.27 b

Human and veterinary therapeutic; Livestock growth promoter and prophylactic

O F

Fluoroquinolone 359.40 5.94 d

8.70 d

Veterinary therapeutic

O H

HO H3C

OH H

H

HH

H O

Ionophore 590.80 2.6 f Livestock growth promoter and prophylactic

TABLE 6.1.

(Continued)

Molecular Weight

H3C CH3

OH O

O O

O O O

O

N

OH HO

O

O O

HO

H3C

Macrolid 916.11 7.7 h Veterinary therapeutic; Livestock growth

promoter and prophylactic

CH3 CH3

H3C N

CH3

CH3 OH

O H3C

Macrolid 733.94 8.88 h Human and veterinary therapeutic; Livestock

growth promoter and prophylactic

(Continued)

CH3 CH3

HO

Pleuromutilin 493.74 9.51 g Veterinary therapeutic and prophylactic

(Continued)

Sorption and Degradation of Selected Pharmaceuticals in Soil and Manure 151

sorption was attributed to relatively weak physical processes (e.g., H-bonding, vander Waals forces) No sorption was observed for either antibiotic at high pH condi-tions (pH 11)

Recently, the importance of sorption by cation exchange has been documentedextensively in studies on tetracycline interactions with model clays, soils, and humic

pKavalues (≈3.3 to 9.3, seeTable 6.1) for tetracyclines results in large shifts in theproportion of the cation (+00), zwitterion (+ 0), and predominantly anionic spe-

described pH effects on oxytetracycline (OTC) sorption using a model that includedcation exchange plus surface complexation of the + 0 zwitterion species Previouswork on less complicated organic bases (e.g., quinoline and aromatic amines) has

species-spe-cific sorption coefficients normalized to pH-dependent CEC

that are weighted by the pH-dependent fraction of each species ( f +00 , f + 0 , f + ) as

OTC sorption by Na-saturated montmorillonite in 10 mM sodium bicarbonate

(3 500 L/equiv), indicating that the cation contributes the most to OTC sorptioneven under pH conditions where the zwitterion species predominates in solution To

mechanism involving positively charged protons on the montmorillonite surfaces

(FT)-IR analysis of Na-montmorillonite equilibrated with OTC at pH 5.0, whichshowed peak shifts consistent with coordination of the antibiotic’s carbonyl groupwith interlayer cations or hydrogen bonding with hydroxyl groups of water coordi-nated to interlayer cations

TC, and chlortetracycline (CTC) by eight soils varying in pH, type and amount ofclay, CEC, anion exchange capacity (AEC), and OC content The model fit the datawell across all soils (pH range of 3.8 to 7.49) except for a gibbsite-rich soil with high

agricul-tural soils

However, the CEC values reported and used in the correlation were measured at thesoils’ natural pH, which ranged from 3.6 to 7.5, and not the operational CEC values

range of interest for soils containing significant amounts of sorbents with variable orpH-dependent charge properties (e.g., kaolinitic clays, organic matter, metal oxides,

operational CEC would be higher than the reported CEC if the natural soil pH waslower than the buffered pH of 5.5 Alternately, for soils with pH values higher than5.5, the operational CEC would be lower than the reported CEC These discrepan-cies may have masked the true contribution of CEC to the sorption of OTC in theJones et al.26study

Additional experiments on electrolyte composition effects on the sorption of racyclines also support a cation exchange mechanism When cation exchange is acontrolling process, decreases in the concentration of competing inorganic cations

com-position, after accounting for induced pH-shifts, generally followed the trend: 0.001

N CaCl2> 0.01 N KCl > 0.01 N CaCl2 Ter Laak et al.23found that increases in ionicstrength decreased sorption of OTC in two agricultural soils with a more pronounced

Na-montmorillonite An increase in ionic strength from 0.01 M to 0.1 M by the

by serving as a cation bridge between negatively charged tetracycline molecules andclay surfaces Under alkaline conditions, OTC sorption coefficients for Ca-satu-rated montmorillonite were higher than either Na-saturated or untreated montmoril-

transform infrared spectroscopy indicated that the predominantly zwitterion TC 0) interacted with the metal oxides via the tricarbonylamide and carbonyl functionalgroups The formation of the surface complex subsequently resulted in the dissolu-tion of the metal-hydrous oxides and aqueous concentrations of 2:1 metal to TCcomplexes Other studies have shown that tetracyclines form complexes with diva-lent cations, such as Ca2+, Cu2+, Mn2+, Mg2+, and Zn2+at multiple chelating sites.31,32

(+-Since some animals are fed rations with high concentrations (g/kg range) of ganic cations for growth promotion (e.g., Cu2+and Zn2+),33–35elucidating the role ofcomplexing metals is particularly important in predicting the fate of antibiotics atCAFO-impacted sites

inor-Complexation with cations has also emerged as an important sorption anism for fluoroquinolone antibiotics, which consist of a bicyclic aromatic ring