261 12 Reacti on and Transformation of Antibacterial Agents with Aqueous Chlorine underRelevantWater Treatment Conditions Ching-Hua Huang, Michael C. Dodd, and Amisha D. Shah 12.1 INTRODUCTION Each year large quantities of antibacterial agents (referred to as antibacterials here- after)areusedtotreatdiseasesandinfectionsinhumansandanimals.Applications ofantibacterialsinhumanmedicinecanultimatelyleadtosignicantdischargesof Contents 12.1 Introduction 261 12 .2 Background 263 12.2.1 Antibacterial Agents of Investigation 263 12.2.2 Chemical Oxidation by Aqueous Chlorine 267 12.2.3 PriorWorkontheReactionofPharmaceuticalswithChlorine 267 12.3 Materials and Methods 268 12.3.1 Chemica l Reagents 268 12.3.2 Sur fac e Water and Wastewater Samples 269 12.3.3 Reaction Setup and Monitoring 269 12.4 Results and Discussion 271 12.4.1 Reaction Kinetics and Modeling 271 12.4.2 Identication of Reactive Functional Groups 275 12.4.3 React ion Pat hways and Pr oduct s’ Biological Implications 276 12.4.4 Reaction in Real Water Matrices 283 12.5 Conclusion 285 References 285 © 2008 by Taylor & Francis Group, LLC 262 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems such compounds into surface waters, via excretion of the unmetabolized parent com- pounds into municipal sewage systems and subsequent passage through municipal wastewater treatment facilities. 1 In addition, antibacterials are utilized for a number ofagriculturalapplications,includinguseasgrowthpromotersandfeedefciency enhancers for livestock 2 and in aquaculture and fruit orchards. 3 It has been estimated that nearly 50% of the total antibacterial usage in the United States was for agricul- ture. 4 Signicant proportions of the administered antibacterials can be excreted from thedosedanimalswithlittlemetabolictransformation. 1,5 Anationwidereconnais- sancestudypublishedbytheU.S.GeologicalSurvey(USGS)in2002reportedthe presenceofawidevarietyofchemicalsincludingmanypharmaceuticalsandper - sonal-care products in U.S. streams. 6 Other similar ndings regarding the ubiquity of pharmaceuticals in the aquatic environment have also been reported in the United Statesandotherpartsoftheworld. 1,7–19 Among the pharmaceuticals, several widely appliedhuman-useandveterinaryantibacterialclasses,suchasuoroquinolone,sul- f o namide, tetracycline, macrolide, and so forth, have been repeatedly detected in concentrationsrangingfromlowng/Ltolowµg/L. 6–19 The presence of antibacterial residues in natural surface waters and wastewater efuentsmeritsconcernforanumberofreasons.First,thecontinuousexposureof wastewater-borne or environmental bacterial communities to mixtures of antibacterial residues may promote induction or dissemination of low-level resistant bacterial phe - n o types,whichhavesignicantindirectimplicationsforhumanhealth. 5,20,21 Second, studies have shown that, once present in bacterial populations, numerous resistance phenotypes are stable over many bacterial generations, even in the absence of selec - ti ve pressure from the antibacterial compounds themselves. 22–25 Furthermore, some antibacterials and their metabolites are reported to exhibit carcinogenic or genotoxic effects, which may be of direct signicance to human health. 26–28 To properly evaluate therisksposedbyantibacterialmicropollutants,andtoensureprovisionofsafepota- b l ewatersupplies,thebehaviorofantibacterialsduringrelevantwatertreatmentpro- c e sses should be critically evaluated. Chlorination is an important treatment process thatislikelytoaffectthefateofnumerousantibacterials,onaccountofitscommon useinwaterandwastewatertreatmentfordisinfectionpurposes,andbecausemany antibacterial compounds contain electron-rich functional groups that are susceptible to reaction with electrophilic chlorine. This chapter summarizes the authors’ recent contribution to developing a fun - damentalunderstandingoftheinteractionsoffourstructuralclasses(quinoxaline N,N’-dioxide, 29 uoroquinolone, 30 sulfonamide, 31 and pyrimidine 32 )ofantibacterials with aqueous chlorine under relevant water treatment conditions. In contrast to the previous publications in which each structural class was dealt with separately, this chapter discusses these four structural classes simultaneously, highlighting similar - i t y and difference in their interactions with aqueous chlorine. The investigations were undertaken to elucidate the chemical reactivity, reaction kinetics, products, and pathwaysbywhichantibacterialsaretransformedbyfreechlorine.Reactionkinetics weredeterminedoverawidepHrangeandevaluatedbyasecond-orderkineticmodel that incorporated the acid-base speciation of each reactant (i.e., oxidant and antibac - t e rial). Various structurally related compounds that resemble the hypothesized reac- t i ve and nonreactive moieties of the target antibacterials were examined to probe © 2008 by Taylor & Francis Group, LLC Reaction and Transformation of Antibacterial Agents with Aqueous Chlorine 263 reactive functional groups. Results obtained from kinetic experiments were supple- mented by product identication analyses by liquid chromatography/mass spectrom- et ry (LC/MS), gas chromatography/mass spectrometry (GC/MS), nuclear magnetic resonance spectroscopy ( 1 H-NMR), and other techniques to facilitate identication of reaction pathways and mechanisms. Additional experiments were conducted in real municipal wastewater and surface water matrices to assess the eld-applicabil - it y of observations obtained for reagent water systems in the laboratory. 12.2 BACKGROUND 12.2.1 A NTIBACTERIAL AGENTS OF INVESTIGATION Representative antibacterial agents from four structural classes—quinoxaline N,N’- dioxide, uoroquinolone, sulfonamide, and pyrimidine—were investigated (see Table 12.1 andT able 12.2 for the structures of investigated antibacterials and asso- ciated model compounds). Carbadox (CDX) and olaquindox (QDX) represent the quinoxaline N,N’-dioxide g roup of veterinary antibacterial agents, which are widely usedinswineproductionforpromotinggrowthandpreventingdysenteryandbacte- ri alenteritis.InrecentyearsCDXanditsmajormetabolitedesoxycarbadox(DCDX) have been shown to exhibit carcinogenic and genotoxic effects. 26–28 Such concerns ledtheEuropeanUniontobantheuseofCDXinanimalfeedsin1999 33 and Health CanadatoissueabanonCDXsalesin2001afterreportsofmisuseandaccidental contamination. 28 Ciprooxacin(CIP)andenrooxacin(ENR)belongtotheuoro- quinolone structural class, a group of synthetic, broad-spectrum antibacterial agents that interfere with bacterial DNA replication, 5 andareusedinamultitudeofhuman and veterinary applications. 2 CIPisoneofthemostfrequentlyprescribedhuman-use uoroquinolones in North America and Europe, 1 whereasENRwaspopularfordis- ease prevention and control in the U.S. poultry production industry until recently. 34 Sulfamethoxazole (SMX) is one of the most popular sulfonamide antibacterials used totreatdiseasesandinfectionsinhumans. 5 Sulfonamides, often referred to as sulfa drugs, are synthetic antibacterials widely used in human and veterinary medicines andasgrowthpromotersinfeedsforlivestock. 5 SMXiscommonlyprescribedin tandem with the synthetic pyrimidine antibacterial trimethoprim (TMP) under the name cotrimoxazole. 35 These two antibacterials function synergistically as inhibi- tors of bacterial folic acid synthesis. 5 Recent studies have reported frequent detection of uoroquinolones, sulfon- amides,andTMPintheaquaticenvironment.Reportedconcentrationsofvarious uoroquinolonesrangefrom~1to125µg/Linuntreatedhospitalsewage, 10,11 ~70 to500ng/Linsecondarywastewaterefuents, 7,14 –16 to~10to120ng/Linsurface waters. 6,14,15 SMX is the most frequently detected sulfonamide antibacterial at con- centrationsof70to150ng/Linsurfacewaters 6,12–14 and 200 to 2000 ng/L in second- ary wastewater efuents. 7,12–14,17 Occurrence of TMP was reported at several-hundred ng/L in secondary municipal wastewater efuents, 18,19 and at concentrations from approximately10toseveral-hundredng/Linsurfacewaters, 12,17 particularly those receiving substantial discharges of treated wastewater. 8 Concentrations of CDX in surfacewatersandwastewaterswerereportedintwostudiestobebelowthedetec- ti onlimitsof0.1µg/Land5ng/L,respectively. 6,17 © 2008 by Taylor & Francis Group, LLC 264 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems TABLE 12.1 Structures and Apparent Second-Order Rate Constants (k app )for Reactions of CIP, ENR, SMX, CDX, and Related Model Compounds with FAC at pH 7–7.2 and 25°C Compound k app (M -1 s -1 ) Compound k app (M –1 s –1 ) CDX N + N + N H NO O O – O – 1.3 × 10 4 CIP N OH O N HN O F 6.5 × 10 5 Desoxy-CDX N N N H NO O 2.3 × 10 3 ENR N F O OH O N N 5.3 × 10 2 ODX O H N OH N + N + O – O – ~0 FLU F O N OH O ~0 QDX N + O – N + O – ~0 SMX S NH O O N O NH 2 1.5 × 10 3 QXO N N + O – ~0 MMIB S NH O O N O ~0 QNO N + O – ~0 APMS S O O NH 2 1.1 × 10 2 DMI N O ~0 QDX = Quindoxin QXO = Quinoxaline N-oxide QNO = Quinoline N-oxide FLU = Flumequine MMIB = 4-Methyl-N-(5-methyl-isoxazol-3-yl)-benzenesulfonamide APMS = 4-aminophenyl methyl sulfone DMI = 3,5-dimethylisoxazole © 2008 by Taylor & Francis Group, LLC Reaction and Transformation of Antibacterial Agents with Aqueous Chlorine 265 As shown in Figure 12.1,eachoftheseantibacterialscontainsacidicorbasic functional groups in their structures that undergo proton exchange in aqueous sys- tems.CDXandDCDXeachcontainahydrazoneside-chain,inwhichanN-Hgroup can deprotonate with an estimated pK a of 9.6 for CDX (by Strock et al. using Che- maxon). 36 AsillustratedbyCIP,uoroquinolonesexhibitpH-dependentspeciation in cationic, neutral, zwitterionic, or anionic forms. Because the neutral and zwitter- ionic microspecies are often difcult to distinguish by simple potentiometric titra- tion techniques, macroscopic constants K a1 and K a2 are often used to describe the equilibrium between the cationic and neutral/zwitterionic forms and the equilibrium between the neutral/zwitterionic and anionic forms, respectively. Although the mac- roscopicconstantisnotforaparticularfunctionalgroup,literaturehaslinkedK a1 to the carboxylate group and K a2 to the piperazinyl N4 atom of uoroquinolones because of similar pK a values to those of monofunctional analogs. 37 Although not shown,ENR’spHspeciationpatternissimilartothatofCIPwithreportedpK a1 and pK a2 values at 6.1 and 7.7, respectively. 38 Sulfonamides contain two moieties con- nected by way of the characteristic sulfonamide linkage (-NH-S(O 2 )-); the aniline moiety in para-connectiontothesulfonylSiscommonamongalmostallsulfon- amides,andavarietyofdifferentstructuresmaybeconnectedtothesulfonamide N. 5 Sulfonamides exhibit two acid dissociation constants: one involving protonation TABLE 12.2 Structures and Apparent Second-Order Rate Constants (k app ) for Reactions of Trimethoprin (TMP) and Related Model Compounds with Free Available Chlorine (FAC) at 25°C Compound k app (M –1 s –1 ) TMP N N NH 2 NH 2 O O O 14.2 (pH 4) 48.1 (pH 7) 0.78 (pH 9) TMT O O O 59.8 (pH 4) 3.22 (pH 7) 0.24 (pH 9) DAMP N N NH 2 NH 2 0.46 (pH 4) 23.9 (pH 7) 0.77 (pH 9) TMT = 3,4,5-trimethoxytoluene DAMP = 2,4-diamino-5-methylpyrimidine © 2008 by Taylor & Francis Group, LLC 266 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems N + N + N H NO O O – O – N + N + N – NO O O – O – H N O OH O F N N S NH 3 + H N N O O O S NH 2 H N N O O O S NH 2 – N N O O O NH + NH 2 NH 2 O O O H + N N NH 2 NH 2 O O O H + N HN N O O – O F N H 2 N + N O O – O F N or Sulfamethoxazole (SMX) NH + NH 2 NH 2 O O O H + N N1 N3 Trimethoprim (TMP) H 2 N + N4 N O OH O F N N1 Ciprofloxacin (CIP) pK a Carbadox (CDX) 9.6 a pK a1 6.2 b 8.8 b pK a2 5.6 c pK a2 pK a1 1.7 c pK a1 3.2 d pK a2 7.1 e FIGURE 12.1 Structures and pH speciation of representative antibacterial agents. (a) Reference 36; (b)Reference37;(c)Reference39;(d)Reference 40;and(e)Reference41. © 2008 by Taylor & Francis Group, LLC Reaction and Transformation of Antibacterial Agents with Aqueous Chlorine 267 of the aniline N and the other corresponding to deprotonation of the sulfonamide N. 39 TMPcanundergoprotonationattheheterocyclicN1andN3nitrogenatoms contained within its 2,4-diamino-5-methylpyrimidinyl moiety, leading to positively charged species at circumneutral to lower pHs. 40,41 Aswillbediscussedinthischap- ter, variations in acid-base speciation of these antibacterial agents under environ- mentally relevant conditions strongly affect their reactivity with aqueous chlorine. 12.2.2 CHEMICAL OXIDATION BY AQUEOUS CHLORINE Aqueous chlorine (HOCl / OCl - )isanimportantdrinkingwaterdisinfectantandis used in both drinking water and wastewater treatment to achieve chemical oxida- ti on of undesirable taste-, odor-, and color-causing compounds and reduced inor- ganic species. 42,43 Aqueous chlorine is typically present either as hypochlorous acid (HOCl) or its dissociated form, hypochlorite ion (OCl – ),atpH>5(Equation12.1), andmayformmolecularCl 2(aq) atverylowpHorhighCl – concentrations (Equation 12.2) . The combination of these aqueous chlorine species (generally only HOCl + OCl - under typical water treatment conditions) is referred to as free available chlo- rine (FAC) hereafter in this chapter. HOCl OCl – +H + pK a =7.4–7.5(at25°C) 44,45 (12.1) Cl 2 +H 2 OHOCl+Cl – +H + K=5.1×10 –4 M 2 (at 25°C) 46 (12.2) In recent decades the electrophilic character of aqueous chlorine has drawn sub- stantial attention due to reactions with natural organic matter (NOM), leading to the formation of harmful chlorinated disinfection byproducts (DBPs) (e.g., trihalometh- an es [THMs] and haloacetic acids [HAAs]). 42 Substrates such as NOM are readily oxidized,sincetheyconsistoforganicmoleculeswithelectron-richsitesthatare susceptible toward electrophilic attack. The reaction mechanisms of aqueous chlo- ri newithNOMarecomplexandmayinvolveoxidationwithoxygentransferand substitutions or additions that lead to chlorinated byproducts. 42,47 The above reac- tionsmaythenbefollowedbyanumberofnonoxidationprocesses,suchaselimina- tion, hydrolysis, and rearrangement reactions, 42 further complicating the range of byproducts generated. Synthetic organic compounds such as antibacterials can be considered targets for transformation by aqueous chlorine. Since many antibacterials possess structural moietiesandfunctionalgroupsthatareelectronrich,suchasactivatedaromaticrings and amines (as seen in Figure 12.1), chemical t ransformation of these compounds duringchlorinetreatmentislikely.Therateandextentofsuchreactions,aswell as the byproducts formed, will be highly dependent on the antibacterials’ chemical properties, the applied chlorine dose, and water conditions such as pH, temperature, and concentrations and types of dissolved organic or inorganic species. 12.2.3 PRIOR WORK ON THE REACTION OF PHARMACEUTICALS WITH CHLORINE Prior studies indicate that a number of pharmaceuticals are highly susceptible toward chlorine oxidation and are readily transformed under various drinking water and wastewater conditions. Thus far, studies have either assessed particular groups of © 2008 by Taylor & Francis Group, LLC 268 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems pharmaceuticals that exhibit biological activity (e.g., endocrine disruptors, 48,49 C- blockers, 50 analgesics, 50 and antibiotics 51,52 ), or have focused on the detailed reactivity of individual compounds (e.g., 17 C-estradiol, 53 acetaminophen, 54 naproxen, 55 caf- feine, 56 and triclosan 57 ). In many of these studies, laboratory-scale experiments were conducted by assessing the removal of spiked pharmaceuticals by aqueous chlorine in synthetic water or waters taken from water treatment plants or natural rivers. One particular study examined a large number of pharmaceuticals in which degradation variedgreatly(<10to>90%)afteraninitialchlorinedoseof2.8to6.75mg/LasCl 2 , a24-hcontacttime,andasolutionpHof5.5. 58 Concentrations of pharmaceuticals in full-scaletreatmentplantsbeforeandafterchlorinationwerealsomonitoredinorder to evaluate the removal of these compounds by chlorine. 7 In many of these stud- ies, reaction kinetics were examined in synthetic waters to determine whether the selectedcompoundswerelikelytobecompletelydepletedduringcontacttimestypi - ca lofdrinkingwaterandwastewatertreatment.Inlimitedcases,byproductanalyses were conducted to assist in determining whether reaction products could potentially retain the biological activity of the corresponding parent compounds. 53 Compared to the broad range of pharmaceuticals detected in surface waters, drinking water supplies, and wastewaters, the number of pharmaceutical compounds that have been investigated in depth regarding the mechanisms and products of their transformation by chlorine is still quite limited. A fundamental understanding of the reactions of pharmaceuticals with chlorine is critical because it enables identication of reactive functional groups/structural moieties and creates the basis for predicting the fate of other emerging contaminants on the structural basis. For example, many of thetargetpharmaceuticalcompoundscontainaromaticfunctionalgroupswithelec - tr on-donating substituents (e.g., substituted phenols and aromatic ethers) 48,50,53,54,57 that are known to react readily with chlorine. 59 In a study addressing chlorination of natural hormones (17C-estradiol, estrone, estriol, and progesterone) and one synthetic hormone (17B-ethinylestradiol), a ll molecules with a phenolic group were rapidly oxidized (t 1/2 =6to8minatpH7,[chlorine] 0 =1mg/LasCl 2 ), whereas progesterone, whichlacksaphenolicgroup,remainedunchangedover30mininthepresenceof excess chlorine. 49 Another study addressing chlorination of analgesics found that all such compounds containing aromatic ether substituents were reactive toward excess chlorine, whereas those lacking such substituents (e.g., ibuprofen and ketoprofen) did notshowanysignicantlossesover5days. 50 Amine-containing compounds such as several C-blockershavealsobeenshown to be reactive toward chlorine. 51 In this chapter recent contributions by the authors toward elucidating the kinetics andtransformationpathwaysoffourstructuralclassesofantibacterials(quinoxaline N,N’-dioxide, uoroquinolone, sulfonamide, and pyrimidine) in reactions with free chlorine are discussed. 29–32 Signicantly, these studies on the reactions of antibacte- rialswithfreechlorineareamongtherstconductedinsuchdetail. 12.3 MATERIALS AND METHODS 12.3.1 C HEMICAL REAGENTS Theformsandcommercialsourcesofthetargetantibacterialsandstructurally related model compounds were described previsouly. 29–32 DCDX, quindoxin (QDX), © 2008 by Taylor & Francis Group, LLC Reaction and Transformation of Antibacterial Agents with Aqueous Chlorine 269 and quinoxaline N-oxide (QXO) were synthesized by methods described previ- ously. 60 All commercial chemical standards were of >97% purity and used without further purication. NaOCl was obtained from Fisher Scientic at ~7% by weight. Allotherreagentsused(e.g.,buffers,colorimetricagents,reductants,solvents,etc. from Fisher Scientic or Aldrich) were of at least reagent-grade purity. Stock solu - ti onsofantibacterialsandmodelcompoundswerepreparedat25to100mg/Lin reagent water (from a Barnstead or a Millipore water purication system) with 10 to 50%(v/v)methanol.FACstocksat0.1to1g/LasCl 2 were prepared by dilution of 7%NaOClsolutionsandstandardizediodometrically 61 or spectrophotometrically. 46 12.3.2 SURFACE WATER AND WASTEWATER SAMPLES Secondary wastewater efuent samples (collected after activated sludge processes and prior to disinfection) were obtained from pilot-scale or full-scale domestic waste- wat ertreatmentplantsinAtlantaandZurich.Surfacewatersampleswerecollected from the Chattahoochee River in Atlanta—near the intake of a regional drinking water treatment plant, and from Lake Zurich in Switzerland—at the intake of one of Zurich’s drinking water treatment plants. Samples were ltered through 0.45-µm lters,storedat4to6°C,andusedwithin2daysofcollection.Importantcharac - teristicsofthesesamplesweredeterminedbystandardmethodsorprovidedbythe facilities where samples were taken, as summarized in Table 12.3. 12.3.3 REACTION SETUP AND MONITORING Batch Reactions: For slower reactions, batch kinetic experiments were conducted in 25-mL amber glass vials at pH 3–11 under continuous stirring at 25°C. Reactions werebufferedusing10to50mMacetate(pH4to5.5),phosphate(pH6to8),or TABLE 12.3 Surface Water (SW) and Wastewater (WW) Sample Characteristics Sampling Site pH Alkalinity (mg/L, as CaCO 3 ) NH 3 (mg NH 3 -N/L) DOC* (mg/L as C) Atlanta WW 7.3 120 < 0.12 a 14.0 Zurich WW 1 8.3 143 0.013 5.6 Zurich WW 2 8.1 500 1.5 12.3 Atlanta SW 1 6.6 13 < 0.12 a 1.3 Atlanta SW 2 7.2 n.a. n.a. 2.8 Lake Zurich SW 1 8.4 126 0.0068 1.6 Lake Zurich SW2 8.1 135 0.019 1.7 a Minimum detectable concentration was ~ 120 µg/L NH3-N (~ 7 × 10-6 mol/L) n.a. = not available * DOC = dissolved organic carbon © 2008 by Taylor & Francis Group, LLC 270 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems tetraborate(pH9to11).Theinitialconcentrationoftestcompoundswastypically1 to 10 µM for kinetic studies. Reactions were initiated by adding excess (10×) molar amounts of FAC compared to the target compound. For SMX, 4-aminophenyl methyl sulfone (APMS), TMP, and 2,4-diamino-5-methylpyrimidine (DAMP), sample ali- quotswereperiodicallytakenandquenchedbya“soft”quenchingtechnique—using NH 3 as a reductant—to minimize potential reversal conversion of reaction interme- diates(e.g.,N-chlorinatedSMX)backtotheparentcompounds. 31 For the other com- pounds,samplealiquotswereperiodicallytakenandquenchedwithexcessNa 2 S 2 O 3 . Pseudo-rst-order rate constants, k obs ,werecalculatedfromlinear(0.95>r 2 >1) plots of ln([antibacterial]) vs. time. Experiments to monitor the reaction rates of anti- bacterials with chlorine in real water samples were conducted by similar procedures used to measure rate constants in reagent water matrix. In these cases, FAC was added at concentrations at least tenfold greater than the corresponding antibacterial concentrations. Competition Kinetics:ThereactionsofCDXandDCDXwithFACatpH>5and thereactionofCIPwithFACatpH4,5,6,10,and11weretoofasttomonitorby batchtechniques.Instead,twocompetitionkineticsmethodswereutilizedforthese measurements.InthemethodutilizedforCDXandDCDX,theantibacterialanda selected competitor (with known k app ) were added at equimolar concentrations to batch reactors at various pHs. Varying substoichiometric amounts of free chlorine were then added. Sample aliquots were taken after each reaction was completed and analyzed for the concentrations of remaining antibacterial and the competitor. Plot- ting the data according to the following linear relationship allows determination of the second-order rate constant of the antibacterial: ln [] [] , , competitor competitor T Tt app k 0 ¥ § ¦ ´ ¶ µ ccompetitor app antibacterial k s ln [antibacteri aal antibacterial ] [] , , T Tt 0 ¥ § ¦ ´ ¶ µ (12.3a) where [competitor] T,t and [antibacterial] T,t represent the remaining reactant concen- trationsafteraspecicsubstoichiometricdoseofFAChasbeenadded.4,6-Dichlo- roresorcinol, with known k app values reported in Rebenne et al., 62 wasselectedasthe competitorforCDX.OncetherateconstantforCDXwasdeterminedateachpH, CDX was used as the competitor for DCDX. In the method utilized for CIP, the antibacterial and the competitor 4,6-dichlo- roresorcinol were added to vials at varying molar ratios of competitor to antibacte- rialoverarangeofpHvalues.Axedsubstoichiometricdoseoffreechlorinewas thenaddedunderrapidmixingtoeachvial.Aftercompleteconsumptionoffree chlorine,1-mLsamplealiquotsweretransferredtoamber,borosilicatehigh-per- formance liquid chromatography (HPLC) vials, quenched with Na 2 S 2 O 3 to prevent reactions of the competitor with a N-chlorinated intermediate formed upon reac- tionofCIPwithfreechlorine,andstabilizedwith~0.1MH 3 PO 4 prior to analysis by HPLC with uorescence detection. Apparent second-order rate constants for the reactionofCIPwithFACatdifferentpHweredeterminedbymonitoringyields of a product (presumably 2,4,6-trichloresorcinol) formed upon chlorination of the © 2008 by Taylor & Francis Group, LLC [...]... omitted, and (ii) the kapp exhibits a well-defined bell-shaped pH profile (Figure 12. 2a) and reaches a maximum at the pH near the average of the pKas © 2008 by Taylor & Francis Group, LLC 274 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems of HOCl and CDX For SMX, the reaction of HOCl with the cationic form of SMX (SMX+) is neglected (i.e., Equation 12. 11) on the basis of two... present in the real water matrices The initial reaction of CIP with FAC in real water matrices was too rapid to follow directly However, the kinetics of its piperazine ring’s fragmentation could be evaluated indirectly by monitoring loss of the N-chlorinated intermediate of CIP (i.e., CIP-Ia1 in Scheme 12. 2) Model results confirmed the applicability of the kinetics measured in clean water systems to the. .. (Scheme 12. 3) might interrupt the charge interactions and hydrogen-bonding required for quinolone-DNA binding, this reaction may be relatively unimportant in real waters (due to the presence of scavengers for the R3N(4)Cl+ intermediate of ENR in natural waters) On the basis of these observations, one can infer that a majority of the transformation products likely to result from passage of fluoroquinolones... chlorine), further chlorination of N-chlorinated SMX is believed to lead to formation of a N,N-dichlorinated SMX intermediate, which subsequently decays via facile cleavage of the S-C bond to yield the N-chlorimine NCBQ (N-chloro-p-benzoquinoneimine), as well as AMI (3-amino-5-methylisoxazole) and SO2 The antibacterial activity of SMX is derived from its antagonistic competition with p-aminobenzoic acid for... reactive site and the quinoxaline N,N´-dioxide and quinoxaline moieties are relatively inert to chlorine The results that both CIP and ENR are reactive to chlorine; that the reactivity of CIP is about three orders of magnitude higher than that of ENR; and that FLU, which lacks the piperazine ring, does not react with chlorine clearly demonstrate the critical role of the piperazinyl N4 atom in the reaction... and MacCrehan, W.A Transformation of acetaminophen by chlorination produces the toxicants 1,4-benzoquinone and N-Acetyl-p-benzoquinone imine, Environ Sci Technol., 40, 516, 2006 55 Boyd, G.R., Zhang, S.Z., and Grimm, D.A Naproxen removal from water by chlorination and biofilm processes, Water Res., 39, 668, 2005 56 Gould, J.P and Richards, J.T The kinetics and products of the chlorination of caffeine... water samples (Figure 12. 3c) Details of these measurements and the corresponding model evaluation can be referred to Dodd et al.30 For real water experiments involving TMP, the FAC loss to matrix constituents over time was also modeled using first-order decay constants from two separate kinetic regimes in the drinking water and three separate kinetic regimes in the wastewater The equations describing... (12. 9) 3 (12. 10) 3 (12. 11) k12 k11 1 2 1 1 k13 k12 (12. 12) 1 3 1 2 k13 1 3 (12. 13) 2 ,hydrolysis The mathematic expressions of and values are discussed in the text For TMP: kH+ (in M–2s–1) represents the rate constant for the acid-catalyzed reaction between HOCl and TMP, kCl2(aq) (in M–1s–1) represents the apparent second-order rate constant for the bulk reaction of is the equilibrium constant for the. .. Rosselet, A., and Knusel, F Mode of action of quindoxin and substituted quinoxaline-di-N-oxides on escherichia-coli, Antimicrob Agents Ch., 13, 770, 1978 69 Abia, L et al Oxidation of aliphatic amines by aqueous chlorine, Tetrahedron, 54, 521, 1998 70 Morris, J.C Kinetics of reactions between aqueous chlorine and nitrogen compounds, in Principles and Applications of Water Chemistry, Faust, S.D and Hunter,... through water chlorination processes could remain biochemically active SMX: The reaction of SMX and FAC begins with an initial attack of HOCl on the anilinyl amino N of SMX (Scheme 12. 4) Under conditions where [FAC]0:[SMX]0 1 (i.e., excess chlorine), further . LLC 276 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems chlorineconditions,conrmingthatthe hydrazone side-chainisthereactivesiteand thequinoxaline N,N ´-dioxidea ndquinoxalinemoietiesarerelativelyinerttochlo- rine.TheresultsthatbothCIPandENRarereactivetochlorine;thatthereactivity ofCIPisaboutthreeordersofmagnitudehigherthanthatofENR;andthatFLU, whichlacksthepiperazinering,doesnotreactwithchlorineclearlydemonstratethe criticalroleofthe piperazinyl. = Quindoxin QXO = Quinoxaline N-oxide QNO = Quinoline N-oxide FLU = Flumequine MMIB = 4-Methyl-N-(5-methyl-isoxazol-3-yl)-benzenesulfonamide APMS = 4-aminophenyl methyl sulfone DMI = 3,5-dimethylisoxazole ©. Chattahoochee River in Atlanta—near the intake of a regional drinking water treatment plant, and from Lake Zurich in Switzerland—at the intake of one of Zurich’s drinking water treatment plants. Samples