Assessing the Environmental Partitioning of
          Organic Acid Compounds
                    by
              Chad T.  Jafvert
     Environmental research Laboratory
   U.S. Environmental Protection Agency
          .Athens-, Georgia 30613
             .Submitted as an
       Environmental Research Bxdef

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Background




      The  ultimate disposition of organic compounds in the environment is




influenced tremendously by their tendency to partition,  or "adsorb" to




sediment  particles or other distinct environmental components or phases.  To




date,  the majority of sorption research for organic chemicals has focused on




describing partitioning processes of neutral compounds,  such as the




polycyclicaromatic hydrocarbons, polychlorinated biphenyls,  and dioxins.  Many




environmentally relevant organic compounds,  however,  contain acid or base




functional groups.  Compounds containing acid functional groups include the




chlorinated phenoxyalkyl acid herbicides,  such as 2,4-D  and 2,4,5-T;  chloro-




and nitro- phenols,  such as pentachlorophenol (PCP);  and sulfonated compounds,




such as azo and anthraquinone acid dyes, and linear alkylbenzenesulfonate




(LAS)  surfactants.  Organic bases of significance include the nitrogen




heterocycles,  such as quinoline, and aromatic amines,  such as benzidine.




      This Research Brief focuses on the partitioning of  organic acid compounds




in octanol-water and in sediment-water systems.  The jnain emphasis is  to




characterize the adsorption processes of these compounds "mechanistically,"  to




permit the development n~F -tpmni rfai-fry^ 4jrt-nac-3trrg-^u^t-jwi.i.y T^J a*~i*?T?*5:h'JiTT;  in




lignt of  the differences in adsorption reactions among neutral,  cationic,  and




anxonic-organic compounds,  a "briBf theoretical description -is ^iven as t.o -why




these compounds partition as they do in the  environment.   For example,  why do




certain environmental components,  such as  fish lipid,  or the organic  material




in soils  and sediments preferentially adsorb neutral  compounds over charged




species?   An explanation is given based on thermodynamic considerations,  and




various assumptions  and requirements necessary to quantify these partitioning




processes  are examined.

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Equilibrium Partitioning




      If no  kinetic limitations  exist,  the  tendency  to partition,  expressed as




an equilibrium adsorption coefficient  (Kd),  is directly  related  to  the




standard  free  energy of adsorption,  AG°ds,  as expressed  by  Equation 1.  (See




 [1,2]  for a more thorough discussion).







            AG°dg  =  -  RT In Kd                             (D




To characterize the adsorption  of organic  compounds to environmental matrices,




such  as soils,  sediments, and biota, this  "standard free energy"  of adsorption




must  be factored into adsorption components (i.e. soil organic carbon).




Adsorption  to  each of these components,  in turn, results from additive  effects




or" ^arioxts  adsorption interactions or  "energies" .   According to Stern  [see




1,2],  in  the most basic form these energies can be  separated into an intrinsic




chemical  energy, term (AG°^em) and an electrostatic  energy term CAG°^) .





          AGads  -   AGchem  +   <1                        (2)



      For  neutral organic compounds,  the  total energy of  adsorption  contains no




electrostatic  component,  and hence,  is equal to the intrinsic chemical




adsorptiozi  energy (AG^famn) -  -Sox moderately large .{imoleinilar ragygfofc >• J.OQ}




no-npolar  compounds,  this adsorption energy is dominated  by   hydrophobia




forces,.  Hence -partitioning occurs "out" of hydrophilic -phases such -as -water




to more hydrophobic phases.   Water solubility (corrected for crystal energy




of solids), octanol-water partitioning,  connectivity indices, chromatographic




retention times,  and estimated  molecular surface areas,  all  have  been used to




index  chemical  activity (or  free energy  changes) of hydrophobic  compounds  for




estimating  partitioning to media such  as soil organic carbon and  fish lipid.




     Because the  intrinsic  chemical  adsorption energy (AG^^) for  organic




compounds,  as  a rule, results from hydrophobic interactions, ;this term  for




both cationic  and anionic organic  compounds  is less than for neutral compounds

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of similar  structure.   For  these charged species, however, the primary change


in the  overall  adsorption energy may result from electrostatic contributions


to adsorption  (AC0^) .   This  electrostatic contribution can be positive or


negative, and is  equal  to the product of the compound's valence  (z) , Faraday's


constant  (F) , and the surface potential (V>) .  Most natural soils and sediments


contain mineral and organic surfaces that possess negatively charged


functional  groups.   Therefore,  the overall sign of AG^ is ultimately


determined  by the charge of the adsorbing ion.


      For  adsorption of  cationic organic compounds (z —Hi) , the overall sign


of AG°^ is  negative, and electrostatic interactions can promote adsorption


beyond  what is  predicted for  a  similar neutral compound based purely on


hydrophobic interactions.   Examples of this in the literature include the


adsorption  of benzidine (4,4-diaminobiphenyl, pK& = 4.3)  [3] and quinoline


(pKa  —  4.94)  [4]  onto sediments or aquifer material.  The adsorption of these


compounds to  natural surfaces is highly pH dependent because of their


relatively  low  pK& values.  At  pH values where the cationic form of these


compounds predominates,  adsorption can be two orders of magnitude greater than


rtbe hydrophohic adsorption  «f ±he corresponding TKentral species^  This .type of


.reaction is generally referred  to as ligand (or cation) exchange, and modeling


this :process relies on  understanding the adsorption behavior of other

                              • Q       _|_0
exchangeable  ions,  such as  Ca  and Mg  .  Also, adsorption can occur to


various subcomponents of soils  and sediments, such as the organic matrix and


various mineral components.   To effectively describe these processes, model


algorithms  must be  somewhat complex.  Modeling the adsorption of organic


cations may best be accomplished by incorporating adsorption algorithms into


"electrostatic" or  ligand exchange adsorption models, similar to those used to


estimate metals adsorption.

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      For the adsorption of anionic organic  compounds  (z  = -1),  the overall




 sign on AG°-^ is positive,  and electrostatic interactions act  to attenuate




 adsorption.   Hence,  adsorption to natural sediments by the  anionic form of an




 organic acid is generally less than adsorption of the corresponding neutral




 species.  Because no specific electrostatic interactions occur  to  promote




 adsorption,  the partitioning process must result  from the existence of a




 significant chemical adsorption energy term.   This situation  results in




 adsorption occurring predominantly through  hydrophobic interactions,




 attenuated by electrostatic forces.   Indeed,  in limited  cases  [5,6],  the




 adsorption of anionic organic compounds has been  normalized to  the organic




 carbon content of the sediments and soils.   In another study  [7],  adsorption




 oi? IAS -surfactants was shown to increase with surfactant alkyl  chain length




 through the surfactant series investigated, indicating that hydrophobicity




 contributes to the total energy of adsorption.




      In quantitatively assessing these partitioning reactions,  separating the




 hydrophobic component of partitioning from  the  electrostatic component is




 essentially impossible.   As with neutral organic  compounds, however,  model




 systems can be used  to assess :and possibly  quantitatively describe sorption




-processes.   Model systems include some of the same "systems" or parameters




-used-to assess partitioning of neutral compounds,  such as solubility or




 octanol-water distribution.   Indeed,  many of the  same factors that influence




 the  transfer of organic  acids between octanol and water  (or affect the




 apparent water solubility)  influence the transfer of these  compounds between




 the  components of the more  heterogeneous system of sediment-water  [8-10].




 These  similar factors include the degree of dissociation and the




 hydrophobicity and electrostatic influences of  both sorbent and sorbate.




     As  a result of  these similarities,  the distribution of several organic




 acids between octanol and water phases has  been examined as a function of

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aqueous phase  salt  concentration  (for KCl, NaCl, LiCl, MgCl2, and CaCl2) and




aqueous phase  pH  [9].   Compounds  that have moderately low  (< 5) pKa values




were chosen.   From  these  experiments, equilibrium partition coefficients of




the neutral and charged forms,  as well as several pK& values have been




calculated.  The  sediment-water distribution of selected organic acids also




has been  investigated  as  a  function of aqueous phase ionic composition and pH




[10].  Experimental results and model development for each system is briefly




reviewed.




Octanol-Water  Partitioning




     The  distribution  of  organic  acids between water and octanol in the




presence  of monovalent inorganic  cations can be described by -Reactions 1




through 6 of Figure 1.  The reactions in Figure 1 are formulated in terms of




KCl as the monovalent  salt,  although NaCl and LiCl also have been used.  The




mass action equations-for these reactions, along with the material balance and




electroneutrality constraints,  comprise the chemical equilibrium model.




     Reaction  1 describes acid  dissociation in the aqueous phase.  Reaction 2




describes transfer  of  the neutral species (HA) to the octanol phase.  This




:reactian  is the Tsasis  of linear _±ree energy TElaSonsnips xelating 3CQC (the




sediment  or soil  equilibrium partition coefficient^ normalized for organic




carbon content) and KOW (the octanol-water partition coefficient) for sorption




of nonpolar organic compounds [11,12].  For any ionizable compound, this




mechanism is important  when a significant fraction of the total compound




exists in the  neutral  form.  Reactions 3 and 4 represent transfer of the free




and ion-paired inorganic  species, respectively, to the octanol phase.  For




both KCl  and NaCl,  an aqueous phase concentration of 0.2 M (with no organic




compounds present)  will result  in approximately 40 /zM total salt partitioning




into the  octanol phase.  Reactions 5 and 6 describe the transfer of the free

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and ion-paired organic  species,  respectively,  and the  inorganic  counter-ion to

the octanol  phase.    The  transfer  of the  organic  ion,  as  a  free  species or as

an ion-pair,  is highly  dependent upon the counter-ion.  Also,  as the  aqueous

phase  inorganic salt concentration is increased,  the transfer  of the  organic

ion as an ion-pair  is favored.

     To illustrate  these  effects,  the overall  distribution  ratio (D),  of total

compound in  the octanol phase to total in the  aqueous  phase, can be

calculated:
      D  =  U^Jo + [A JQ -t- IJl A JQ;                         (3)
                 ([HA]W + [A']w)

where,  M+ represents the monovalent  electrolyte K+, Na+, or Li+.   For

experiments-performed at sufficiently high pH  (e.g., 12), [HA] is an

insignificant species in either phase,  and the overall distribution results

from  Reactions 5 and 6 of .Figure 1.   Using the calculated partition

coefficients  K^x and K^px for the inorganic  species KC1, NaCl, or LiCl,  and

the measured  coefficients K^,  and K^  for the  organic compounds

pentachlorophenol (PCP),  4-chloro-a-(4-chlorophenyl)-benzeneacetic  acid  (DDA),

and 2a4,,5-±richloxopiieiiDxyaEet±c acid .^2f^3-T)^ vs can ofarain the  overall

distribution  of these compounds (Figure 2) as  a function of aqueous phase salt

-concentration,.   For comparison,  the concentration of the organic species IA"]W

was fixed at  10 /iM,  and the pH value  was set at 12.  For the salts  NaCl  and

KC1,  little difference in the  calculated distribution is seen, whereas

partitioning  into the octanol  obviously is favored for the LiCl system.  Also,

the importance  of the hydrophobicity  of these  compounds is apparent.  The

magnitude of  partitioning into the octanol for the organic anions follows the

sequence  PCP  >  DDA > 2,4,5-T for all  three salt systems.  This is the same

ordering  as the octanol-water  distribution coefficients of the corresponding

neutral species (KQW).   Indeed,  for ten organic compounds investigated,

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 including various carboxylic acids and phenols,  the calculated partition




 coefficients for formation of the ion-pair in the octanol phase (Kj_p)




 correlates extremely well to KQW values [9].




      Results of four experiments in which pH  was varied at constant ionic




 strength ([K+]w = 0.1 M) are presented in Figure 3.   The curves were




 calculated using the partition coefficients given in Figure 3  for the  organic




 compounds arid calculated values for the coefficients Kix and Kipx,  for KC1.




 At low pH values (approximately pH 1 to 2) , the  neutral species is  dominant  in




 both phases, and the value of log D is Independent of pH.   At  intermediate pH




 values (approximately 4 to 6), the neutral species is dominant in the  octanol




 phase and the am'onic species becomes dominant in the aqueous  phase, and the




 distribution ratio becomes pH dependent.   At  high pH (above pH 9),  the anion




 predominates in both phases, and the distribution ratio is again independent




 of pH, but dependent on ionic strength, as previously discussed.




      The significance of each component of this  equilibrium system  can be more




 clearly seen in a log[ concentration] versus pH diagram as presented in Figure




 4 for 4,6-dinitro-o-cresol (DNOC).  All lines in this figure are calculated




;:from ihe .six stpfnThrxom constants 3for ISHDC and 1HH,  the :tcrtal jnass of 13HDC




 and KC1 in the system, and the volumes of each phase.   The difference  Between




 ±he concentration of T5NOC in the octanol  at low  pH and the concentration in




 the water at high pH is due to the difference in the volumes of the two




 phases.




 Sediment-Water Partitioning




       As in octanol-water partitioning,  the distribution of organic acids




 between sediment and water is highly dependent upon the degree of chemical




 dissociation.   To assess the effects of pH (and  hence,  dissociation) on




 sediment-water distribution,  initial experiments have been performed using a

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pH-stat.   The  pH-stat can be used to  titrate  and maintain a sediment slurry to

a  given or set pH value.   Over the course  of  an experiment,  a  slurry can be

sampled and the pH then can be lowered to  a new set-point sequentially,

resulting in a "titration curve".   Considerable changes  in sediment

characteristics result from such a titration.   This  approach,  however, allows

factoring of the overall chemical distribution into  discrete coefficients for

the  neutral species (Kd)  and the anionic species (K^) .   These constants may

be defined operationally as,
          Kd =     sed                                       (4)
               [HA]W
                                                             (5)
                [A'Jw

with,
                 [HA]W

where,  [HAjsed (mo I/kg)  and {HA]W (M)  are  the Tieutral species concentrations

in  sediment and aqueous  phase,  respectively, and  [A~]secj and  [A"]w are the

anionic species sediment and .aqueous pfaa««»
Because' only total  concentration in each phase can le determined analytically,

mass "balance equations  fox each phase  and for the total system are needed,


          [HA]aq =  [HA]W +  [A']w                              (7)


          [HA]S =  [HA]sed +  [A']sed                           (8)


          [HA]t =  [HA]aq +   (m/v)[HA]s                        (9)


where,  (m/v) is the sediment mass (kg) to aqueous volume  (L) ratio.

Combination  of Equations 4 through  9 results in an expression for the fraction

of total compound in the aqueous phase,

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      f   =  [HA]W+ [A-]w  _  (K
                  [HA]t        (Ka + {H+} + (Kd{H+) + KdiKa)(m/v))






 Results of initial studies on several organic acid compounds, using a silty




 sediment from the Ohio River (EPA sediment 11) suggests a definite pH




 dependence on Kd^ [10] .  In accord with electrostatic considerations described




 previously, some type of pH dependence on the adsorption of the anion may seem




 unequivocal, resulting from changes in the surface charge or degree of




 protonation of the organic carbon matrix.  For the compounds studied on EPA




 sediment 11 to date, Kd^ can be expressed as,






   log Kdi = ai(pH) + log Ki                                 (11)






 where, the average pH dependence or -slope (0^) is equal to 0,30, and JC^ is -the




 "intrinsic" chemical adsorption term (given in Table 1 for each compound).




 Only one sediment system was examined,  however, and clearly more evidence is




 needed to confirm this general pH dependence.  In total,  5 parameters  are used




 in Equations IB and 11.  One constant.,  jkKg,  is intrinsic  ±o the adsorbate; two




 constants,  T£d and K^, describe "the interactions "between adsorbate and




 radsorbent;  one constant,  a^ : is contained in Kd^ (along with Kj) and is




-""intrinsic '"to the adsorbent; and pH (or {H+}) is the independent variable.




      The experimental data for four compounds are shown in Figure 5, along




 with model  results using the  constants  given in Table 1.   For PCP, DBA and 2-




 (2,4,5-trichlorophenoxy)-propionic acid (silvex) ,  organic carbon-normalized




 partition coefficients for the neutral  species (Koc) are, within a factor of




 two,  equal  to the KQW.   The KQC for DNOC is  significantly greater than its




 K   ,  likely resulting from polar interactions with the sediment by, the nitro-




 groups on DNOC.   A similar trend exists for  the anionic species.






                                        10

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     Partitioning in octanol-water  and sediment-water  systems  by organic




compounds  that contain a single,  relatively strong  (2  < pKa <  5)  acidic




functional group has been examined.   Clearly,  a  significant conclusion of this




work is  that,  at pH values found  in most  natural environments  (i.e.,  5 to 9),




Petitioning can occur by both the  neutral  and ionic forms of  these  and




similar  compounds.   Therefore,  to determine a  priori chemical  distribution in




the  environment,  partitioning must  be factored into measurable or predictable




quantities for each adsorbing species,  as has  been  attempted here.   The




adsorption of neutral organic compounds is  the simplest case,  wherein the




-adsorption energy is largely determined by  hydrophobic interactions.




Octanol-water distribution (KQW) , in turn,  has been used as a  measure of




chemical hydrophobicity.   Octanol-water distribution for organic  anions  is




more complex,  and is a function of  both chemical hydrophobicity and  inorganic




ion  composition.   For the partitioning to sediments, an "ionic"  or




electrostatic effect also is observed for organic ions.  This  effect  is  most




obvious  as a result of varying the  pH of  sediment systems, and may result from




changes  ±n ^surface 4»xopextxB3 (i_,e^.; xhaxge)..  '33iese and joiffaer Effects ±faat




determine  the adsorption of organic .anions  to  natural  materials must be




examined further.
                                       11

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 .References

 1.   Stumn,  W and J.J.  Morgan.   1981.   Aquatic Chemistry,  An Introduction
 Emphasizing Chemical Equilibria in Natural Waters,  2nd Ed.   John Wiley and
 Sons,  New York.

 2.   Morel,  F.M.M.  1983.  Principles  of Aquatic Chemistry  John Wiley and
 Sons,  New York.

 3.   Zierath D.L., J.J. Hassett, W.L.  Banwart,  S.G.  Wood,  and J.C.  Means.
 1980.   Sorption of benzidine by sediments and soils.  Soil Science.  129:277-
 281.

 4.   ZacharaJ.M., C.C. Ainsworth,  L.J. Felice,  and C.T. Resch.   1986.
 Quinoline sorption to subsurface materials:   Role  of  pH and retention of the
 organic cation.   Environ. Sci.  Technol., 20:620-627-

 5.   Nkedi-Kizza, P., P.S.C. Rao, and  J.W. Johnson.  1983.   Adsorption of
 diuron and 2,4,5-T on soil particle size separates. J.  Environ.  Qual.
 12:195-197.

 6.   Ogram,  A, V., R.E. Jessups, L.T.  On, and P.S.C. Rao.  1985.   Effects  of
 sorption vn biological degradation rates of (2,4-dichloropherrency)  ace-tic  acid
 in soils.  Appl. Environ. Microbiol.   49:582-587.

 7.   Hand, V.C.,  G.K. Williams.  1987.   Structure-activity  relationships for
 sorption of linear alkylbenzenesulfonates,  -Environ. £c±. Technol., 21:370-
 373.              	

 8.   Westall, J.C., C.  Leuenberger, amd R.P.  Schwarzenbach.  1985.   Influence  of
 pH and ionic strength on the aqueous-nonaqueous distribution of chlorinated
 phenols.   Environ. Sci. Technol.,  19:193-198.

 9.   Jafvert, C.T., J.C. Westall, E. Grieder, and R.P.  Schwarzenbach.  1989.
JJistribution of hydropnobie ianogenic organic compounds between octanol and
-water*  "organic  adds. To 3>E submitted-ior publication,

10.  Jafvert, C.T. 1989,  Sorption of organic acid compounds to sediments:
inital model development.  Summitted  for publication.

 11.  Leo, A.; Hansch,  C.; Elkins,  D.   1971.   Partition coefficients and  their
uses.   Chemical  Reviews. 71:525-616.

12.  Lyman, W,J~;  Loreti, C,¥.   Prediction of Soil  and Sediment Sorption
for Organic Compounds. Final Draft Report to Office of Water, U.S.  EPA,
Washington  D.C., 1986.
                                        12

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Table 1.  Constants Used in Modeling the Adsorption of Organic Acid Compounds
          to Sediment 11.


 Compound       (m/v)a          pKab          log Kd        log Kj_
PCP
DDA
DNOC
Silvex
0.05
0.08
0.10
0.10
4.85
3.66
4.46
3.07
3.0
2.45
1.93
1.87
3.33
2.31
2.83
2.03
.f Sediment mass to water volume ratio (kg/L)
bReference  [9].
                                       13

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          Reactions of HA                       Expression

          1.  [HA]W - [H+]w +  [A-]w                 Ka

          2.  [HA]W - [HA]Q                         Kow


          Reactions in KC1, NaCl, and LiCl salt systems.

          3.  [K+]w+ [Cl-]w= [K+]0 +  [C1-]Q       Kix

          4.  [K+]w+ [Cl-]w = [K+C1-]0             Kipx

          5-.  IK+]W + [A-]w =  [K+]0 + [A']0         K±

          6.  IK+]W + [A']w =  [K+A']0               Kip

          7.  ir'-i^-H IOH-]W = IK+]O -H  IOH-]O

          8.  [K+]w + [OH']W = [K+OH-]Q
Figure 1.  Equilibrium Reactions of Monovalent Organic Acids
           in Octanol-Water.  Adapted from reference  [8].  HA
           represents a neutral organic molecule and A"
           represents the corresponding mono-valent organic anioiu
           Terms subscripted with "w" or "o" represent aqueous
           phase or octanol phase concentrations, repectively.
                                       14

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               2.5-
              2.0-
              1.5-
                                                   PCP, LiCI
                                                   PCP, NaCI
                                                   PCP, KC!
                                                   DDA,  LiCI
         O
          cr>
          O
1.0-
DDA, NaCI
DDA, KCI
             0.5-
                                                - 2,4.5-T, LiCI
             0.0-
                                    2,4,5-T, NaCI
                                   .2.4,5-T, KCI
               0.04   0.08    0.12   0.16   0.20    0.24

            Total K,  Na,  or LI (M) In Aqueous Phase
Figure  2.  The octanol-water distribution of 2,4,5-T,  DDA, and PCP,
          using the calculated partition coefficients from experimental
          data, and setting [A"]w at 10 /iM and the pH at 12.
                                    15

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                                                            log(K)
         6.0-J
         4.CH
   o'    2.0-1
         O.CH
       -2.0-
                              • PCP
                              n DDA
                              «• 2,4,5-T
                              A DNOC
5.07
4.64
3.31
2.14
-4.85
-3.66
-2,83
-4.46
-2.13
-3.60
-3.76
-3.92
 Kip
2.67
1.84
0.60
0.016
JDLD
                                      iBLt) '  ' ia!b '  ' 1DJD '   12.0    14.D
                                           PH
Figure 3.
The octanol-water distribution of four compounds as a function of
aqueous phase pH.   Symbols are data points,  and lines are
calculated by minimizing  residuals on KQW and Ka.   In experiments,
the aqueous phase contained 0.1 M KCl, and HC1 or KOH for pH
adjustment.  The total mass of compound per tube in each experiment
was constant.
                                      16

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 Q)
 O
 c
 O
o
       -2.0-
J    -4.0H
      -8.0H
  (o) Total  Measured In
     Octanol Phase
                                                    (•) Total Measured In
                                                       Water Phase
                                              in Octanol
                                       IHAH-A- H- A-K+]O
Total m Water
[HA +
                                 .-4JD

                                Aqueous  Phase  pH
 \
B.O
                                             1DJ)
       4   pC - PH diagram of DNOC species partitioning between octanol and
        •   H^er as a  function of pH>   symbols are data points  and lines are
           model fit.   Solid lines are for concentrations in the octanol
           phase,  and  dashed lines are for concentrations in the aqueous
           phase'   The volumes of each aqueous phase - 10 ml, volume of
           octanol - 2.5 ml, total mass of DNOC in each tube -  1.25x10'
           moles.   The aqueous phase contains 0.1 M KC1, and HC1 or KOH for
           pH adjustment.
                                      17

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       UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                      WASHINGTON, D.C. 20460
                                                     OFFICE OF
                                              RESEARCH AND DEVELOPMENT
SUBJECT:
FROM:
TO:
Transmittal of an ORD Research Brief Entitled Assessing
the Environmental Partitioning of Organic Acid
Compounds (Del iverable ,-§149A)
 ourtney Riordan
Director, Of f ice MDT Envi ronmental  Processes  and
    Effects Research (RD-682)

Sylvia Lowrance
Director, Office of Solid Waste (OS-300)
     The attached  research brief  is being delivered to your
office  in response to the Agency's need for information about
those processes that determine fate and resultant potential
exposures to organic chemicals that may enter natural surface and
ground-water systems from disposal sites.

     The objective of the work reported here was to examine
partitioning of organic acids in  octanol-water and sediment-water
systems.  The main emphasis was to characterize adsorption
processes of these compounds  "mechanistically" to permit
development of quantitative structure-activity relationships.

     A  significant conclusion of  the work is that, at pH values
found in most natural environments (i.e., 5 to 9), partitioning
can occur by both  neutral and ionic forms of the tested
compounds.   Therefore, to determine a priori chemical
distribution in the environment,  partitioning must be factored
into measurable or predictable quantities for each adsorbing
species.  Effects  of pH and other variables that determine
adsorption  of organic ions to natural materials will be examined
and quantified in  continuing  research.

     This document is product of  the Land Disposal Assessment and
Evaluation  of Other Management Systems research program at the
Environmental Research Laboratory, Athens, GA.  The results  of
this study  have been prepared as  a research brief in order to
provide interim results in a  timely manner and in a form useful
to your office.  Thus, this report has been reviewed within  ERL-
Athens  but  has not been subjected to the Agency's peer review

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process;  it should not, therefore, be distributed to, or used by,
non-Agency persons.   Further along in the research program,  when
more variables have  been investigated and quantified, and the
structure-activity relationships are better understood,  a peer
reviewed, thoroughly scientifically defensible journal article or
report will be written.  Dr. Zubair Saleem of your
Characterization and Assessment Division is familiar with the
project.

cc:   Chris Zarba (WH-585)
     Elizabeth Bryan (TS-798)
     Patrick Holden  (H-7509)

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