LAB Comp and LAS Performance

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LABSA characteristics

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  • 19

    Effect of LAB composition on LAS performance

    Chlorina1ionParaffin Chlomparaffin LAB (high 2-phenyllhigh dialkyhelralin)

    + Aiel} catalystbenzene

    Linear alkylbenzene sulfonate(LAS) continues 10 be the mostwidely used surfactant in theworld. Currently. on a global basis.more than four billion pounds of lin-ear alkylbenzene (LAB). the feedstockused 10 make LAS. are consumedannually. In addition. several newplants are under construction in theworld today.

    The popularity of LAS is simple toexplain: LAS has an exceptional cost-performance profile. and has provenhuman safety and environmentalacceptability. However. there is someuncenainty related to LAS in terms ofunderstanding how variations in struc-rure impact performance. There aretwo reasons for this confusion: (a) for-mulations have become more concen-trated. which effectively magnifiesdifferences in the formulatabilityamong commercial products. and (b)new technologies have been devel-oped to manufacture LAB which havea greater variation in composition.

    The purpose of this article is toclarify how commercial LABs canvary in composition. and how thesevariations affect the performance ofLAS.

    IntroductionThe LAB molecule consists of a linearparaffin chain attached to a benzenering (Figure I).

    Commercial LAB. however. con-sists of a blend of LAB molecules thatvary in terms of paraffin chainlength,

    DehydrogenalionParaffin I

    SURFACTANTS & DETERGENTS

    This article was prepared forINFORM by Michad F. Coxand Dewey L. Smith, CondeaVista Co.. 12024 Visla ParkeDr.. Austin. TX 78726. ........

    position of the benzene ring along theparaffin chain, and concentration of acoproduct called dialkyltetralin. Thesevariations in composition remain

    intact when LAB is sulfonated to formthe finished surfactant, LAS.

    The most important factor interms of LAB composition is averagemolecular weight. Increasing theaverage molecular weight increasessurface activity and solution viscosi-ty, but decreases water solubility andwater hardness tolerance. Theinverse is true when average motecu-

    tar weight is decreased. Optimalaverage molecular weight dependslargely on use conditions (such astemperature, water hardness, andconcentration).

    The second-most important factorin relating LAB composition to LASperformance is the concentration ofdialkyltetralin (OAT). OAT sulfonatesreadily and completely to formdialkyltetralin sulfonate (OATS).OATS aCIS as a surfactant. ahydrcrrope, and a viscosity modifier.Consequently, high OAT-containingLAB (with 6-10% OAT) is preferredfor LAS intended for liquid formula-tions because less (or no) additionalhydrotrope is required to achievedesired solubility and viscosity.Because OATS is nearly as surface-active as LAS itself, the presence ofOAT in LAB has little effect on LASperformance.

    The distribution of phenyl isomerscontained within a commercial LAB

    Figure 1. Linear alkylbenzene (one po .. l-ble Isomer ot dodecylbenzene)

    LAB (low 2-phenylllow diaJkyhetraJin)HFcalalyst

    Olefin (-,""',...,,...,.,..+ Solid alkylation

    benzene catalysl

    LAB (high 2-phenylllow dialkyltetralin)

    LAB (high 2-phenylllow dialkylteuaJin)

    Figure 2. Commereial processes tOl" LAB production

    INFORM. Vol. 8. no. I (January 199n

  • 20

    SURFACTANTS & DETERGENTS

    "'~~----;::::=:===;-] CII-Avg. LAS

    C1rAvg. LAS

    ... C13-Avg. LAS

    Coocenlnltion of LAS [Jog C (gIL)] (increases from lefllo right)

    Figure 3. Surface tension (at 2S"C, with 0.01 M N~O.,to buffer ionic strength).I.functlon of concentration for C,,-average LAS, C1z-lIVI!ntge LAS, and C13-eYeflIge LAS

    8000

    700l

    6000

    "5000'"l4000" 300l200l

    100l

    0II 12

    Average LAS carbon chainlenglh

    Figure 4. The effect 01 molecular weight on viscosity (25% LAS, 30C, shear rete ..5 e-1)

    also can influence solubility and vis-cosity, because it affects the way LASmolecules pack together in solution. Ahigher concentration of the 2- and 3-phenyl isomers generally improvesLAS solubility. Although the effect ofphenyl isomer distribution is smaller inmagnitude compared to the effect ofOATS, it can be significant. particular-ly when LAS concentration is high. orin the presence of high ionic strength.

    Although understanding the rela-tionship between LAB compositionand LAS performance is important inobtaining maximum cost-effective-ness. such understanding also is diffi-cult because several variables areinvolved. and the effect of these vari-ables depends on the conditions underwhich the LAS is being used.

    Why variations occurManufacture of LAB is accomplishedby connecting a paraffin chain 10 abenzene molecule. Chemically, this isachieved through the Friedel-Craftsalkylation of benzene withchloropar affins or olefins and analkylation catalyst. Although manypossible catalysts could be used, onlythree are used commercially: alu-minum chloride (AlCI). hydrofluoricacid (HF), and a newly patented solidalkylation catalyst (patent numberU.S. 5196574). Commercial routesused to manufacture LAB are illustrat-ed in Figure 2.

    Commercial LAB can vary interms of average molecular weight.DAT content, and phenyl isomer dis-tribution.

    -0

    Il

    Table 1Solubility (cloud polntl') 01 LASas a function of average carbonchalnlength (15% of LAS with1% sodIum sulfate)

    Cloud point("C)2.5

    20.563.4

    Cu-Avg. LASCtrAvg. LASCu-Avg. LAS

    " Teml"'",.ure which IO'I> ~Iu';""$ 01" LAS .urnckludy (. \ovI'er cloud poin empenlun: ~ \(I.

    hi&hn"..-.e KJ!ubili.y)

    Average molecular weightCommercial LAB is produced fromthe alkylation of benzene with variousblends of Cw c., CI2, Cn. and CI4linear chloroparaffins or olefins. Dif-ferent average molecular weightLABs are available. normally averag-ing in the 232 (CII) to 260 (Cn)molecular weight range. This specificmolecular weight range provides bothacceptable solubility and surfaceactivity.

    Increasing molecular weight above260 produces a LAS with better sur-face activity but very low water solu-bility. Decreasing molecular weightbelow 232 produces a very solubleLAS which has poor surface activity.The effect of LAB molecular weighton surface activity and water solubili-ty is shown in Figure 3 and Table I.

    LAS molecular weight also has asignificant influence on LAS solutionviscosity, as shown in Figure 4. This iswhy high molecular weight LAS slur-ries usually have high viscosities, andare more difficult to handle in com-parison to low molecular weight LASslurries.

    Optimal LAS molecular weight isdetermined by the conditions underwhich the LAS will be used. LASreacts with water hardness ions (calci-um and magnesium) to form insolublesalts. This interaction can effectivelyremove LAS from the wash liquor.lowering its concentration and effec-tiveness. Lower molecular weightLAS is much less sensitive to waterhardness than higher molecularweight LAS. and is therefore normal-ly used in formulations that do not

    INFORM, Vol. 8, no. 1 (January 199n

  • .-------------------------------------------------------------21

    contain ingredients which controlwater hardness (builders). This is whyCII LAS is typically used in unbuiltlaundry liquids and dish washing liq-uids.

    The effect of LAS molecularweight on detergency performance isillustrated in Figure 5. As shown. opti-mal detergency performance underlow water hardness (50 ppm) condi-tions is obtained with a higher molec-ular weight LAS. while a shorter car-bon chain length is best under highwater hardness conditions. Overallperformance decreases with increas-ing water hardness because waterhardness ions interact with soils andsolution components in addition 10LAS.

    The effect of LAS molecularweight on foam stability (dishwashingperformance) is shown in Figure 6.Again. optimal performance isobtained with a high molecular weightLAS under low water hardness ccndi-nons. and with a low molecularweight LAS under high water hard-ness conditions. Note that. contrary towhat is observed in detergency. over-all foam performance increases withincreasing water hardness becausewater hardness ions help stabilizeLAS at the air-water interface (helpstrengthen the foam). This is whymanufacturers sometimes add mugne-sium salts to dishwashing liquid for-mulations.

    Another factor related to molecularweight which can affect performanceis carbon chain distribution. Carbonchain distribution (the relative distri-bution of CI(). CII' C12 C13 and CI4homologs) affects LAS performanceproperties by determining averagemolecular weight. but it also canaffect performance if it changes therelative concentration of the lesserperforming (or better performing)homologs. For example. C\O LAS andCI4 LAS are good surfactants. but CI4LAS is not very soluble. and CIO LASis not very surface active. If the car-bon chain distribution were "peaked"so that average molecular weightremained the same but the ccncenca-tions of C\O LAS and Cl4 LAS weresignificantly reduced. then perter-mance would be enhanced because theconcentration of the better performing

    '"75

    s I--a1l~,70,'a

    ""il "~!!.",60! I-& I-g 55~~SO

    9

    Permanem press

    -,

    - - ..- --..

    _e-. 50 ppm water hardness-.... - 150 ppm water hardness--b- 300 ppm water hardness

    1\ 14

    homologs (CII CU, and Cn) wouldbe increased.

    In practice, varying the distributionof homologs requires more specializedparaffin feeds, which naturally wouldincrease manufacturing costs. Howev-er. variations do occur and should betaken into account when selecting anLAB.

    In summary. LAB (or LAS) molec-ular weight is by far the most impor-

    10

    l:I~

    12 13 I'LAS carbon chaintength

    75,-------------------,~"170'a

    j 65!!.

    160 t-~ I-K. _ 50 ppm water hardness-g 55 -I50ppmwotcrhardnc:ssJt 5OL- L- L- ~L-_-I>-~JL_pp_m__ w__"1'_h._ro_.,.__ __l

    9 10 II 12 13 14 15

    ~------..-------.-------~------~- _ ..- - - ... - - ..

    Conoo

    LAS carbon chainlcngth

    Agure S. Detergency performance 01 LAS homologa, ea meaaured by Vllta LabMethod 30391 (high 2phenyl/hlgh OATS-type LAS at SO,150, and 300 ppm waterhardneaa; 16% LASI3O% sodium trtpo/ypholphate (STPP)llo% 11Iieateformutatlon; 0.15% concentratlon, l00"F, .. bumfduataoltl

    ..

    tant factor to consider when formulat-ing with LAS. Other variations incomposition play significant but sec-ondary roles.

    OAT levelAlkylation normally results in a singleattachment between the paraffin chainand a benzene molecule. Sometimes,however. attachment can occur twiceto form OAT or dialkylindane. The

    tNfORM.Vol. 8. no. 1 (January 199n

  • 22

    SURFACTANTS & DETERGENTS

    ,~" 2-Phenyl J2 18" , 3-Phenyl 20

    ",

    4-Pheny\ 17 20,, 5-Phenyl"

    24,, 6-Phenyl " 18,, 7-Pheny\ I I,b

    13 14 "

    -0-.0 ppm water hardness__ - 50 ppm water hardness-/:r- 150 ppm water hardness

    Table 2Phenyl isomer distribution for "hIgh 2-phenyl" and "low 2-phenyl" ell aver-age LAB

    Phenyl Isomer High 2phenyl

    distribution

    Low 2-phen)"

    distribution

    zs

    ],20 ,e / -,

    ~ /0. /~ / ,,0 rs ,~ " .-E ,,00 .-0 , ,,~10 ,e .' ~-------e

    s, 10 " 12structure of these coproducts is shownin Figure 7.

    Levels of OAT and dialkylindaneare detennined primarily by the alkyl-arion process itself. The chloroparaf-fin/Aiel] process produces alkylatethat contains 6-8% OAT, while theolefin/HF. olefin/AleI3 andolefin/solid alkylation catalyst pro-cesses produce alkylate generally hav-ing less than 1% OAT. Levels ofindane in all processes are low. gener-ally below the ability to measurethem.

    OAT readily sulfonates to formOATS. A misconception is that OATSdoes not contribute to performance.OATS, however, is nearly as surface-active as LAS itself (Figure 8). Theonly difference between LAB andOAT is a second attachment betweenthe alkyl chain and the benzenemolecule. This second attachmentmakes the molecule more rigid. whichenhances its ability to affect solubilityand viscosity without significantlyreducing its surface activity.

    OATS acts as a "structure breaker."which improves water solubility andlowers viscosity (Figures 9. 10). Thisis why chioroparaffin/AlCI3 LAS ispreferred for liquid formulations: it iseasier to formulate, and less expensivein terms of hydrotrope COSI. becauseof the presence of OATS.

    Although OATS has a significamimpact on solubility and viscosity.its presence does nOI have a signifi-cant effect on performance becauseit is surface active (Figures 11 and12).

    us carbon chainlcngth

    Figure 6. Foam ltabillty (dllhwalhlng performance) of LAS homolog' (formulatIon ..24% LASi6% lauryl3-mole ether lutfalei'l% laury1 myristyl mono-elhanolamlde; at 0, 50,and 150 ppm walar hardnallj. Plales soiled with vegetable shortening; hand dlshwash-Ing lasl performed with 0.05% formulations USing Vista Lab Method 31192.

    oDialkyhndnnc(one of many possible isomers)

    Dialkyhetralin(one of many possible isomers)

    Figure 1. TWo possible coproduct structures

    es

    60

    E ss~~ 50:s.~-e~

    40

    ,~as30

    zs-3 _2.5

    ... C12 LAS COATS

    _1.5

    LogC (gIL)

    -I -'1.5

    Figure 8. Surface tension venus log (C) of C12 OATS and e12 LAS

    INFORM. Vol. 8. no. 1 (Jonuary 1997)

  • 23

    Table 3low 2-phenyl distribution of CII-and Cu' average LAB

    Phenyl isomer CII" CU'everage a,-erage

    2-Phenyl 18 I.3-Phenyl I. "4-Phenyl 20 "S-Phenyl 2' 226-Phenyl 18 237.Phenyl I "

    Phenyl isomer distributionDuring the alkylation process, thebenzene molecule can end up attached10 any carbon along the alkyl chain(with the exception of the terminalmethyl groups), Two possible isomersare illustrated in Figure 13.

    The "phenyl isomer distribution"refers to the relative concentration ofLAB molecules in which the benzenegroup is attached to the second carbonof the alkyl chain. the third carbon ofthe alkyl chain. the fourth carbon. andso forth. The phenyl isomer distribu-tion obtained during alkylation isdependent almost solely on the alkyla-tion catalyst. Alel3 and the propri-etary solid alkylation catalyst givewhat is normally called a "high 2phenyl" distribution, while HF gives a"low 2-phenyl" distribution, The "2-phenyl" designation is used simply todistinguish between the two majortypes of alkylute (Table 2).

    Phenyl isomer distribution isaffected by carbon chain distributionor average molecular weight. A highermolecular weight means that the aver-age chain length of the alkyl chain islonger, which means that more iso-mers are available. For example, a CIILAB molecule has five possible iso-mers (2-phenyl, 3-phenyl, a-phenyl, 5-phenyl, and 6-phenyl), while a CoLAB molecule has six possible iso-mers (2-phenyl. j-phenyl. a-phenyl. 5-phenyl. e-phenyt. and 't-pbenyl).Increasing the molecular weight there-fore results in a broader distributionsince more isomers are possible. Thisis illustrated in Table 3.

    5Or;:=:::::::;::=-=:::::;---~_A-. High 2phcnyllhigh

    DATSCI1 LAS...... _ High 2phenyl/low

    OATS CI1 LAS....... Low 2phcnylllow

    OATS CI1 LAS

    ~~~.~

    ----- -._10L_---' __ ---'__ ---'-__ --'--__ --'--_---l

    10 " 20LAS concentration ('lo.

    .,-..,...--. wIodIlOto_"'LAS ......-,. (a_-pc.-......,.....,_ ...........- ........,.)Figure 9. LASaolubillty:Ioud point) II. function of (:onc:enlnltion(2% salt Iddecf)

    7~h===~;=~==~----------~_A-. High 2.phenyllhigh

    OATS CI1 LAS......_ High 2-phenyl/low

    DATSCII LAS

    ....... Low 2phcnyl/lowDATSC11 LAS

    6000 i//

    3000 -

    ~L,-------W~------~3L,-------l~c-------.L,C------150LAS coocentllnion ('lo)

    Figure 10. VlSCOltty venul percenllge LAS(30"C. shear rate", 10 sec-1)

    Under practical use concentrations.when LAS is dissolved in water, mostof the LAS aggregates into micelles.and the remainder stays in solution asindividual molecules called

    Phenyl isomer distribution has littleeffect on performance (Figures I I,12) except with respect to water solu-bility and formulatability in liquidproducts.

    INFORM. VOl. 6. no. 1 (Jonuory 1997)

  • 24

    J

    SURFACTANTS & DETERGENTS

    Table 4CompoSition 0' commercial LAB

    Property AICIJ-calalyzed HF-catalyzed Solid-calalyxedalkylation alkylation alkylation

    Average carbonchain C11-C1) CII-C13 CI:,-CJ3

    Percentage 2-phenyJ 27-30 15-24 21-30

    Percentagedialkyllctrni inlindane 6-10"

  • 28

    SURFACTANTS 8. DETERGENTS

    Current environmental issues for surfactantsThe most complete and desirable pro-cess for determining the environmen-tal acceptability of commercially usedsurfactants is commonly referred to asrisk assessment. In this process. fieldmonitoring studies are done to deter-mine concentrations of a surfactant inenvironmental compartments of inter-est. such as wastewater treatmentplant effluents, surface waters, sedi-ments. or soils. It also is possible toestimme environmental concentrationsby applying models which predict thefate of chemicals in the environment.The measured or predicted field con-centrations then are compared withthe concentrations of the surfactantknown to be toxic to organisms Jivingin the affected environmental com-partrncnrs. If the measured concentra-tions are less than the toxic levels, amargin of safety exists, and the surfac-tant is considered to be environmen-tally acceptable at current use levels.

    Even though this approach is themost desirable process for determin-ing the environmental acceptability ofsurfucumts. it is expensive in terms oftime, manpower. and money. At times,evaluations have been made withoututilizing the whole risk assessmentprocess, thus resulting in misconcep-tions and erroneous conclusions thatpersist in the marketplace. These are:(a) claims that oleochemical-basedsurfactants are environmentallypreferable to petrochemical-based sur-Iactants: (b) claims thai surfactantswhich don't manifest anaerobicbiodegradation in certain tests wil1accumulate and harm the environ-ment: and (c) undue reliance on labo-ratory biodegradation screening testresults for estimating the environmen-tal fute of surfactants.

    Environmental acceptability of sur-IactantsOver the last several years. claimshave been made that oleochemical-based surfactants are environmentallypreferable to petrochemical-based sur-factnnts. For example, papers makingsuch claims were given at the 3rdCESIO International SurfactantsCongress in London, United King-

    TIre fol/owing article was written by AII~n M. Ni~/srnof Condra Visfa Co., 12024 Vista PaTh! Dr.. AlISlin,TX 78726.

    dom. in 1992. and at the 3rd WorldConference on Detergents in Mon-treux. Switzerland. in 1993 (1-3).

    These claims are based, in part,upon results from laboratory biodegra-darien test results in which differencesin biodegradation rates have beenobserved. Because of the significantbusiness and political implications ofsuch claims. two major studies toevaluate these claims were undertakenby the European surfactant industry(4.5) and the Dutch government (6).

    The first approach taken was toexamine the environmental impact ofproducing surfactants by doing a LifeCycle Inventory (LCI). An Lei con-sists of determining the amount ofenergy and raw materials consumed 10produce a surfactant and its feedstocksas well as quantitating the amounts ofatmospheric, waterborne, and solidwaste emissions intrinsic to these pro-cesses. This study was very thoroughin that all of the commercially impor-tant oleochemical- or petrochemical-based surfuctunts were analyzed (4.5).A summary of this massive study isshown in Table I. which depicts anoverview of the total resource require-ments and environmental releasesinvolved only in production of thesesurfactants (data are from Tables 2, 3,and 4 of Reference 5). An evaluationof the requirements and releasesoccurring during torrnutauon intodetergent products was not included inthis study. The surfactanrs are listed inthe left-hand margin. with a notationof whether they are derived frompetrochemicals (Pc). oleochemicals(Oc). or a combination of both. The

    information presented includesrequirements for raw materials. con-sumption of energy. and atmospheric.waterborne. and solid waste releases.All data are normalized to the produc-tion of 1000 kilograms of the surfnc-rant.

    These results show no clear differ-ences in the overall amounts of energyand raw materials consumed or emis-sions produced between the oleo-chemical- or petrochemical-based sur-factants. Since there is no agreementwithin the scientific community as tohow to rate the environmental impactof the emissions and consumptions, noimpact assessment was done. Howev-er, the overall conclusion from thestudy is that the potential impact fromproducing either oleochcmical- orpetrochemical-based surfactantsappears to be about the same. Thisconclusion is clearly stated in theabstract of the summary paper for thisstudy (5): "Based on the findings. nounequivocal technical rationale existsfor claiming overall environmentalsuperiority. neither for production ofindividual surfactants nor for the vari-ous options for sourcing from petro-chemical and oleochemicaVagricultur-al feedstocks and minerals. The valueof the study lies in allowing each man-ufacturer to assess opportunities forimproving the environmental profileof its surfactants and intermediates."

    The second approach, mandatedby the Dutch government (6) andsupported by the surfactant industry.particularly the Dutch Soap Associa-tion (NVZ). consisted of an exhaus-tive risk assessment for the four

    INFORM. Vol. 8. no. 1 (January 1997)

  • 29

    Table 1Overview of total resource requirements and environmental releases

    Surfactant" Requirements geteeses

    Raw materials Energy Atmospheric Waterborne Solid waste(kg/JOoo kg) consumption (kgllOOO kg) (kg/JOoo kg) (kg/lOoo kg)

    (GJflOOO kg)

    LAS p, 1040 61 1661 5 65

    AS Pc 1091 73 2604 7 81oe 2077 57 1684 26 75

    AE, p, 1310 73 2335 5 68oe 2167 67 2024 2. 96

    Sao. oe 2167 50 4451 .5 144SAS Pc 1013 52 1261 2 64

    AE, Pc 1448 83 2366 6 67oe, Pc 2401 73 2044 28 66

    AE, Pc 1570 7. 2281 6 64Oc,Pe 2264 72 2062 21 64

    AEII Oc,Pe 2064 82 2299 11 63APG oe 2060 63 2015 35 142a Pc. pelnxhrmical; Oc *oleochcmi

  • 30

    SURFACTANTS & DETERGENTS

    Table 3Removal of LAS from a German (Edewechterdamnl sludge-only landfill

    Age (years) LAS concentration(mglkg)9160861031701560245

    Deposition period

    19861983-19851979-19831975-19791972-1975

    0.51-33-7

    7-1111-14

    rent use levels.The above studies demonstrate the

    value of utilizing all the 1001s avail-able instead of relying solely on labo-ratory biodegradation tests to arrive atimponant conclusions concerning theenvironmental acceptability of surfac-rants.

    "For the research to the actualexposure in the aquatic environment.in a cooperation between NVZ. RLZA(National Institute of Surface Waterand Wastewater Management).RIVM, and the University of Amster-dam. a monitoring study was per-formed on the concentrations of thefour ingredients in influents and efflu-ents of seven sewage treatment plants.Subsequently, modeling was used tomake an estimate of the concentra-tions of the substances in surfacewaters. From this monitoring study, itbecomes clear that the removal of thesubstances in sewage treatment plantsis almost complete (99.1-99.8%). Asa consequence, the expected concen-trations in the surface waters (PEC)close to the plants are low, about afactor of 100 below MTR level.Therefore, it can be concluded fromthis risk assessment that the environ-mental risks for the use of these sub-stances in (luundry and cleaning)L&C products are acceptable by dis-posal to normal-functioning sewagetreatment plants. Assuming that thisis the case in The Netherlands, Iappraise the usage of these substancesas acceptable in every respect."

    All of the ecotoxlcologtcat datawere normalized to LAS: C11.6: AE:C\J.3 EO:S.2 AE5: Ct2.S E03.4 sincethese are representative of the com-mercial surfactants present in theaquatic environment in The Nether-lands (6).

    Other evaluations done by theEuropean Union for laundry detergentecolabel (7) and the British govern-ment (8) confirm the general conclu-sion thai currently used surfactarusincluding those derived either frompetrochemicals or oleochermcals arenot a threat to the environment at cur-

    Significance of 'anaerobic'biodegradabilityThere has been concern that surfac-tants will accumulate and persist ifbiodegradation is limited in anaerobicenvironments. This concern has result-ed in requirements for anaerobicbiodegradability in certain ecolabelprograms in Europe and Scandinavia(7,9). These are the result of anincomplete evaluation of existing dataas well as the fact that no overall riskassessment evaluation has been donefor chemicals in anaerobic environ-ments.

    Strictly anaerobic environments aremuch less prevalent in nature than aer-obic or microaerophilic environments,and they typically house a minor por-tion of the total volume of surfacmmsreleased to the environment. Anaero-bic habitats also playa transitory rolein the biodegradation of surfactantssince these reach the environment ascomponents of domestic and munici-pal wastewater and are extensivelyexposed to aerobic conditions before.during, and after wastewater treatment(10).

    The anaerobic biodegradation testmethod most commonly required inthe ecolabel programs is found in theEuropean Chemical Industry Ecologyand Toxicology Centre's(ECETOC's) Technical Report No.28 (11). This method consists ofplacing the surfactant in a sealed bot-

    tie with a nutrient medium andsewage sludge and then measuringthe gaseous products of anaerobicbiodegradation with time. Thismethod only simulates the environ-ment found in anaerobic digestorsused in wastewater treatment plantsin which sludge from the process isexposed to anaerobic digestion in aclosed tank. The ECETOC methoddoes not simulate what is happeningin other so-called anaerobic environ-ments such as landfills. sediments,and flooded soils. In these actualenvironmental compartments. expo-sure to oxygen occurs often by vari-ous mechanisms such as diffusion ofgaseous oxygen. exposure to waterwith dissolved oxygen. physical dis-ruption by air or water movements,and action of the biological popula-lion. More evidence that exposure tooxygen is occurring in these compart-ments is that aerobic and facultativeanaerobic as well as strictly anaero-bic bacteria can be cultured fromthese environments (12).

    The fate of LAS in so-called anaer-obic environments illustrates the erro-neous conclusions which can beformed if one only considers theresults from laboratory anaerobicbiodegradation tests such as the ECE-TOC No. 28 test method. The initialstep in biodegradation of LASrequires oxygen (13) so LAS fails theECETOC No. 28 lest; however, thereare examples which demonstrate thatLAS is nOI accumulating in "anaero-bic" environments such as sedimentsor landfills.

    Table 3 is a summary of LAS anal-ysis done in a German sludge-onlylandfill. This landfill is from 8-10meters deep and has been in operationsince 1972. It receives digested sludgefrom the Edewechterdamm wastewa-ter treatment plant, which treatswastewater from the city of Bremen.The samples were taken in PVC lin-ers. dried. pulverized, extracted, andanalyzed. Samples were taken at dif-ferent depths in order to analyzesludges of different ages. as noted inTable 3. It was possible to calculatethe approximate ages of the sludgesamples by evaluating the sludge

    INFORM,VOl.8, no. 1{January t99n

    (t;onlinu~donpog~32)

  • 32

    SURFACTANTS & DETERGENTS

    .1

    Ij

    --6- Me.. un:d ""ter (IIIVL)..... COk:uJ ...... lledi nl (111"1)

    ~ Meuured Kdi nl (jI.fl)

    Sampling location in ,,,....{tm)

    FIgure 1. Calculated and measured dlsappearal'lC8 of linear alkylbenzane sulfonate (LAS)In river water and aedlmenla

    (continued/rom page 30)

    deposition records of the wastewatertreatment plant. Over a 14-year peri-od, the concentration of LAS in thesludge decreased by >97% (14).

    Another striking example of thebiodegradation of LAS in a so-calledanaerobic environment is shown inFigure I. taken from the work of lar-son and colleagues (15). This studywas carried out downstream of theRapid City, South Dakota. USA,wastewater treatment plant which dis-charges into Rapid Creek. RapidCreek is a mountain stream whoseflow is regulated by the Pacrola Damsome 32 kilometers upstream ofRapid City. It flows 100 kilometersdownstream from Rapid City to theCheyenne River. The only discharge

    into Rapid Creek comes from theRapid City wastewater treatmentplant, a trickling filter plant. Monitor-ing sites were at 0.8, 12, 25. and 48kilometers downstream of the plant.During the fall sampling period, grabwater samples were collected frommidchannel and sediment samplesfrom nearshore locations. The datareported here came from a samplingexercise in which the samples werecollected in a time sequence based onflow velocity. so that a single volumeelement of water could be followeddownstream. The samples wereimmediately frozen. shipped to thelaboratory, extracted, and analyzed.The major point of this figure is thatthere is a large difference when acomparison is made between the con-centrations of LAS measured in the

    8r.odfORi So.>.p W""'''. Lid.Chn,cr. 011 4QL. En8bnd024+'-M'lIOO

    BRADFORDOri(!inal Rr;odford So..p Wor .... Inc.......,.., .....a,...;ck. RI 0".!89~USA(

  • 33

    Monitoring well

    ./ u!Laundromat24 wasters

    Algal-bacterial mat

    ./Laundromat pond

    Clay Organic flocClay

    Sandy vadose zone

    ,,~,

    Groundwater \.IIble--H---------------~--------------~~~~Groundwater flow

    ~~---;.....Agure 2. Sen-matlc dlagrlm showlng the maJOI'"environmental eonlpertmentl 01 the Summit lake Laundromat pond system

    ments. In the test (test set-up shownin Figure 4), 75 mL sediment slurrywas placed in a vessel with small-bore Teflon tubing distributedthrough it. The lest vessels were 150-mL glass serum bottles with greybutyl rubber septa. The amount ofaeration going to the sediment wasregulated by controlling the flow rateof oxygen through the tubing. Oxy-gen was introduced into the test ves-sels by diffusion through Teflon-typepolytetrafluroethylene (PTFE) tubingof various lengths. Each flask was fil-led with a 2-mL high-densitypolyethylene centrifuge tube contain-ing I.5 mL of 0.25 M KOH to trapany CO2 produced by the sedimentmicroorganisms. {l4C] - benzenering-labeled CI2 LAS was added at 5ppm (I x 106 dpm). In this experi-ment. the flow rate of oxygen wasreduced to the point that the rate ofoxygen consumption by the sedimentwas greater than the rate of oxygencoming into the system or. in otherwords. the environment would be

    called anaerobic even though oxygenwas still coming into it. Even in thisapparent anaerobic environment.LAS underwent complete biodegra-dation and mineralization (conversioninto CO2), The results are illustratedin Figure 5.

    Furthermore, additional studies bySalanitro and Diaz (20) have demon-strated that the concentrations of sur-factants required by the ECETOC No.28 test method are toxic to sludge anddo nor reflect the levels actually foundin anaerobic digester sludge.

    Based on the pattern of use. themajor environmental compartmentsexposed to surfactants are primarilyaerobic. Chronic exposure to anaero-bic conditions is limited and not like-ly to significantly impact environ-mental concentrations. To illustratethe importance of aerobic biodegra-dation in controlling the environmen-tal fate of surfactants, a mass balancefor LAS can be constructed for theUnited States. In the United States.75% of LAS is treated in municipal

    wastewater treatment systems andabout 25% in on-site treatment sys-tems such as septic tank systems. Ofthe fraction going 10 municipal treat-ment systems. -77% is removed bymineralization and 22% is sorbed tosludge which is disposed of via incin-eration. addition to soils. or landfills.LAS associated with sludge contin-ues to undergo extensive aerobicbiodegradation in surface soils and,as discussed earlier, will undergoslow but significant biodegradation inlandfills. Of the fraction going 10septic tanks, only 5% is mineralized.22% is sorbed to sludge, and theremaining 73% is discharged to sub-surface soils where extensive aerobicbiodegradation has been confirmed.The septic tank sludge is disposed ofin municipal treatment systems orapplied to soils where continued aer-obic biodegradation occurs. The netresult is that over 99% of the LASadded 10 the environment has beenremoved by aerobic mechanisms( 10).

    INFORM. Vol. 8. no. 1 (JonUOf)' 1997)

  • 34

    SURFACTANTS & DETERGENTS

    test compounds during the tests. Thesetradeoffs can lead to potential falsepositive or negative results.

    For example, surfactant concentra-tions in most standard biodegradationleSIS range from JO to 100 mgIL sothat simple analytical procedures forthe surfactants can be utilized. Unfor-tunately, these concentrations may betoxic to the natural bacterial popula-tions used in the tests. Many times Ihisis due 10 the fact thai the environmen-tal concentration of the surfactant maybe orders of magnitude lower that thetest concentrations. Larson and hiscolleague (21,22) demonstrated thiseffect with LAS in river die-away testsutilizing Ohio River water in whichthe natural concentration of LAS wasmeasured to be 50 ~gILbut tests weredone at 5, 10, 20, 40, and 80 mglL.Not surprisingly. no activity was notedat 20. 40. and 80 mgIL because of tox-icity. Biodegradation occurred at 5and JO mgIL but only after lag limesof al least four days. Only when therests were done at 50 Ilg/L didbiodegradation begin immediately(21.22).

    A second critical issue is the use of"acclimated" and "nonacclirnated'microorganisms in the tests. Asdescribed above. if microorganismsare exposed to certain levels of a sur-factant in the environment but testedat much higher concentrations in thetest method without being acclimatedto the higher concentration, negativeresults will likely be observed even ifit is biodegradable at environmentalconcentrations. However, many timesthe microorganisms can "acclimate"to the higher test concentrations anddemonstrate adequate biodegradationeven at the unrealistically high testconcentrations. An important exampleof this is encountered in doing the pre-sumptive test for LAS in the ASTMTest Method 0-2667-89. "StandardTest Method for Biodegradability ofAlkylbenzene Sulfonate" (23). Thismethod states that the test must bedone at 30 mglL. It has been docu-mented (24) that only in very concen-trated row sewage could 30 mgIL LASbe encountered in the environment. Itis very clear that when this method

    [continued on pag~36)

    '"o

    Agure a. Decrease In LAS concentrations as a lunction 01 depth In soli samples collectedbeneath the laundromat pond system

    +--0, +--0,Initial JlWlCof~I with N2to create anxrobic conditiom

    4111 NIUTOWbon:. ihin,,-all PTFE tubing

    4111 Stir bar

    150 mL seplum sealed serum bottle

    Figure 4. Oxygen diffusion lest vessel

    The risk assessment approachteaches us several facts about surfac-tarns. such as LAS, which may notpass a laboratory anaerobic test: (a)aerobic conditions dominate in theenvironment, and aerobic biodegra-dation accounts for >99% removalof LAS; (b) many environmentswhich were assumed to be anaerobicactually do have oxygen penetratingthem which allows for aerobicmetabolism to continue: and (c) thetrace quantities of LAS which maybe found in strict anaerobic environ-ments such as deep and undisturbed

    Undue reliance on screeningbiodegradation testsTo understand the significance ofresults from laboratory biodegradationtests. it is important to remember thaievery biodegradation test is a series oftradeoffs between an attempt to simu-late some environmental compartment(such as a surface water) and the prac-tical concerns of setting up the testand analyzing the disappearance of

    sediments are well below those lev-els having adverse ecotoxicotogicnlimpacts.

    INFORM. Vol. 8. no. I {January 199n

  • 36

    SURFACTANTS Be DETERGENTS20.000

    18.000 f-

    ~ 6,0000,000

    ~'000 -"""'"00 20

  • cate that the chemical will not persistin the environment. In those caseswhere a more accurate estimate ofenvironmental concentration isrequired to ensure that undue risk tothe environment does not occur. itmay be necessary to proceed to thenext level and do simulation tests. Anegative result will normally meanthat further work on biodegradabilityis not necessary and that persistencemay be assumed.

    Simulation tests are designed toprovide evidence of the rate ofbiodegradation under some environ-mentally relevant conditions. Thesetests are more expensive because theyusually entail extensive research andmay require \t4CJ_ radiolabeled testcompounds.

    Furthermore, even if the very bestsimulation possible is used. as a gen-eral rule the results from laboratorytests underestimate what happens innature (15.26).

    In summary. screening biodegra-dation tests underestimate thebiodegradation potential of manycompounds including surfactantsbecause of the use of unacclimatedmicrobial populations and unrealisti-cally high test concentrations. Fur-thermore. even if the best simula-tions of the environmental compart-ment of interest are done. these labo-ratory tests will almost alwaysunderestimate the biodegradationcapabilities of the real world. There-fore. the use of screening levelbiodegradation tests to make deci-sions concerning the environmentalfate of a surfactant will likely begrossly overconservanve and elimi-nate useful surfacrants from the mar-ketplace.

    Finally. it is evident that the rigidapproach to decision-making basedonly on laboratory test results is notthe best. The best approach is to mea-sure or estimate the levels of a surfac-tant in the environment and comparethat 10 the levels at which it causeseffects on biological occupants of theenvironmental compartment in ques-tion.

    AcknowledgmentsThis paper was presented at the 1stSeminar and Exposition on Surfac-

    tams. HOUSEHOLD '96. Brazil.Sao Paulo, Brazil, held June 24-25.1996.

    ReferencesI. Yamane. L Detergent Raw Mate-

    rials and Ecologies in Japan, Pro-ceedings of the 3rd CESIO Inter-national Surfoctoms Congress &Exhibitioll-A World Market, Ple-nary Lectures. A & B. London.United Kingdom. June 1-5. 1992.pp. 15-38.

    2. Hovetmann. P.. The Basis ofDetergents: Basic Oleochemicals.Proceedings of the 3rd WorldConference on Detergents: Glob-al Perspectives. edited by ArnoCahn. AOCS Press. Champaign.IL, 1994. pp. 117-122.

    3. Satsuke. T.. Methyl Ester Sul-fcnares: A Surfactant Based onNatural Fats, Ibid .. pp. 135-140.

    4. Tenside Surfactant Detergents32(2).-82-193 (1995).

    5. Stalmans M. H. Berenbold. J.L.Bema, L. Cavalli. A. Dillarstone.M. Franke. F. Hirsinger. D.Janzen. K. Kosswig. D. Postleth-waite. T. Reppert. C. Renta. D.Scharer. K.-P. Schick. W. Schul.H. Thomas. and R. Van Sioten,European Life-Cycle Inventoryfor Detergent Surfactant Produc-tion. Ibid.:84-109 (1995).

    6. Feijtel, T.C.J .. and E.1. van dePlassche. Environmental RiskCharacterization of 4 Major Sur-foctonts Used in TIle Netherlands,Report 679101-025. NationalInstitute of Public Health andEnvironmental Protection andDutch Soap Association. Septem-ber 1995.

    7. The Commission of the EuropeanCommunities. Commission Deci-sion of 25 July 1995. Establishingthe Ecological Criteria for theAward of the Community Ecolabelto Laundry Detergents. Officialloumal of the European Comma-nates. Sept. 13. 1995, pp. 14-30.

    8. United Kingdom Department ofthe Environment. 2nd Report ofthe Technical Comminee onDetergents and the En"ironmellf.1994, pp. 53-60.

    9. Nordic Environmental Labeling,Environmental Labeling of Deter-

    37

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  • 38

    DynamicPropertiesof InterfacesandAssociationStructuresV. Pillai and D.O. Shah, editors

    In recent years. dynamic structuresof amphiphites have generatedtremendous research activities dueto their wide ranging technologicalapplications. Therefore, this mono-graph should be of great interest toresearchers both in academia andindustry. The book also includes areview on "Dynamics of organizedassemblies of amphiphiles in solu-lion" by Dr. R. Zana. It containscurrent stare-of-the-an informationon fundamental aspects. properties.technological applications. andmethods to study dynamics of inter-faces and assoctenon structures. aswell as valuable references on allthese topics.

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    SURFACTANTS & DETERGENTS

    gents for Textiles. Detergents0613.1. Feb. 2. 1996.

    10. Birch. R.R., W.E. Gledhill, R.J.Larson, and A.M. Nielsen. Roleof Anaerobic Biodegradability inthe Environmental Acceptabilityof Detergent Materials. Proceed-ings of the 3rd CESIO Interna-tional Surfoaants Congress &r:hibitiOll-A \Vorld Markel. Ses-sions . F & LCA Seminar, Lon-don, United Kingdom, June 1-5,1992, pp. 26-33.

    II. European Chemical IndustryEcology and Toxicology Centre(ECETOC), Evaluation ofAnaerobic Biodegradation, Tech-nical Report No. 28. Brussels,June 1988.

    12. Pfennig, N., Formation of Oxy-gen and Microbial ProcessesEstablishing and MaintainingAnaerobic Environments, InStrategies of Microbial Life illExtreme Environments. edited byM. Shilo. Dahlem Konferenzen,Berlin, 1979, pp. 137-148.

    13. Schobert. P., Basic Principles ofLAS Biodegradation. TensideSurfactant Detergents 26(2):86-94 (1988).

    14. Marcomini. A . F. Cecchi, and A.Sfrisco, Analytical Extraction andEnvironmental Removal of Alkyl-benzene Sulphonates. Nonylphe-nol and NonylphenolMonoerhoxytate from DatedSludge-Only Landfills. Environ.Tech. 12:1047-1054(1991).

    15. Larson. R.J .. T.M. Rothgeb. R.J.Shimp, T.E. Ward. and R.M. Ven-tullo. Kinetics and Practical Sig-nificance of Biodegradation ofLinear Alkylbenzene Sulfonate inthe Environment. J. Am. OilChem. Soc. 70:645-657 (1993).

    16. Takada. H., R. Ishiwatari, andN. Ogura. Distribution of lin-ear Alkylbenzenes (LABs) andLinear Alkylbenzene Sul-phonates (LAS) in Tokyo BaySediments. Estuarine. Coastaland Shelf Science 35:141-156(1992).

    17. Larson. R.J .. T.W. Federle. R.J.Shimp. and R.M. Ventullo.Behavior of Linear AlkylbenzeneSulfonate (LAS) in Soil Infiltra-

    uon and Groundwater. TensideSurfactant Detergents 26(2),116-121(1989).

    18. Britton. L.N .. and A. M. Nielsen.Relevance of AnaerobicBiodegradability Testing to Envi-ronmental Fate. Abstract I02P.First SETAC World Congress,Ecotosicology and Environmen-tal Chemistry-A Global Per-spective. Lisbon. Portugal. March28-31. 1993.

    19. Heinze. J.. and L.N. Britton.Anaerobic Biodegradation: Envi-ronmental Relevance, Proceed-ings of the 3nl World Conferenceon Detergents: Global PerSIJeC-rives, edited by Arno Cahn.AOCS Press. Champaign, IL.1994. pp. 235-239.

    20. Satanuro. J.P .. and L.A. Diaz.Anaerobic Biodegradability Test-ing of Surfactants, Chemospilere30(5),813-830 (1995).

    21. Larson. R.J., Comparison ofBiodegradation Rates in labora-tory Screening. Studies withRates in Natural Waters, ResidueReviews 85: 159-171 (1983).

    22. Larson. R.J.. and R.L. Perry. Useof the Electrolytic Respirometerto Measure Biodegradation inNatural Waters. \Valer ResearchIH97-702 (1981).

    23. ASTM Designation: D 2667-89.Standard Test Method forBiodegradability of AlkylbenzeneSUlfonate. Annual Book of ASTMStandards, Vol. 11.05, ASTM.West Conshohocken. Pennsylva-nia.

    24. Painter. H.A., and T.F. Zabel.Review of the EnvironmentalSafety of LAS. WRc Report CO/659-M/I/EV 8658, The Euro-pean Centre of Studies on LinearAlkylbenzene and Derivatives(ECOSOL). 1988.

    25. OECD Guidelines for Testing ofChemicals. Section 3: Degrodo-non and Accumulation. Summaryof Consideration, Paris, May 12.1981. pp. \-5.

    26. Schroder. F.R.. Concentrarions ofAnionic Surfactants in ReceivingRiverine Water, Tenside Surfac-tallt Oetergents 32(6):492-497(1~5).