DETERMINATION OF HENRY'S LAW CONSTANTS OF

       SELECTED  PRIORITY POLLUTANTS
              H. Paul Warner
              Jesse M. Cohen
              John C.  Ireland
       Wastewater Research Division
Municipal Environmental  Research Laboratory
          Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
     OFFICE OF RESEARCH AND DEVELOPMENT
   U. S. ENVIRONMENTAL PROTECTION AGENCY
             CINCINNATI,  OHIO

               April 1980

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                                 SECTION 1

                               INTRODUCTION


     Millions of people living in this nation are concerned with the effect
their environment has on them.  The weight  of this concern has produced
legislation which will, it is hoped, protect them from the hazards of their
environment.  One result of this concern was the issuance of the Consent
Decree in 1976 which designates specific compounds considered to be poten-
tially toxic to various life forms.  This decree and other legislation
require that the U.S. Environmental Protection Agency (USEPA) act to answer
questions concerning the ultimate fate and  effect of these materials on
those life forms and to reduce, through effective regulation, the conse-
quences of unregulated dissemination of those compounds which are found to
be toxic.

     The responsibility given to the USEPA  provokes many questions.

     •    Of these compounds, are any present in concentrations
          sufficient to be toxic?

     •    If so, what are their origins?

     •    By what mechanism do they enter the environment?

     •    What are their health related effects on various life forms?  .

     •    How can they be controlled?

     •    Where should they be controlled?

A very complex multi-disciplinary effort is required to answer these questions.

     The USEPA through its Municipal Environmental Research Laboratory
(MERL) in Cincinnati, Ohio, is addressing some of these questions by
characterizing the ability of municipal wastewater treatment systems to
remove pollutants of health concern and by providing information relating
to the fate of these pollutants as they pass through these systems.

     Part of this effort involves the determination of Henry's Law constant
(H) for as many of the volatile priority organics as possible.  These values
for H will enhance the ability to predict the fate of volatile organics in
wastewater treatment systems.

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                                  -2-


                               SECTION 2

                        EXPERIMENTAL PROCEDURES


     The apparatus used in this study is that described by Mackay, et al.,
(1) with some modifications.   The major modification was an increase in
the liquid depth in the stripping vessel to assure system equilibrium for
all compounds studied.   Figure 1  is a diagram of the apparatus.  Nitrogen
from a high pressure cylinder was passed through a two-stage pressure
regulator and rotameter, and  then bubbled through water to saturate it and
prevent water evaporation from the stripping vessel.  The nitrogen was
then introduced into the bottom of the stripping vessel through a sintered
glass disc.  The liquid depth in the stripping vessel was 60 cm with a
liquid volume of 1 liter.  The vessel was water-jacketed and maintained at
25° +_ 0.05°C.  The exit gas was vented to a hood for safety and the flow
rate was measured by a soap bubble flow meter.

     The general procedure was to prepare a saturated solution of the test
compound by adding a quantity of the compound, sufficient to exceed its
solubility, to distilled deionized water and mixing overnight.  A portion
of this solution, the quantity of which was dictated by analytical pro-
cedure, was mixed with the temperature-stabilized deionized water from the
stripping vessel, the volume was adjusted to 1 liter, and the solution was
returned to the vessel for stripping.  The resulting test solution varied
from 10 ug/1 to 10 mg/1 of solute, depending on compound solubility and
analytical sensitivity.

     Distilled deionized water was used in all experiments.  Hydrocarbons
used were of the purest quality available and were used without further
purification.  In most cases, the purity was stated as > 99%.

     Several of the compounds with stated purities of >99% were significantly
less pure than indicated and some contained impurities of up to 50%.  These
impurities complicated the sample analysis, and in a few instances, required
the application of GC/MS analysis for identification of the test compound.

     As suggested by Mackay,  et al., (1), the system equilibrium should
not be significantly dependent upon gas-flow rates and thus varying the
rate should not significantly affect the experimentally-determined value
for H. Confirmation of this can be seen in Figure 2.  Varying the stripping
gas flow rate from 50 to 250 cc/min with benzene as the solute produced an
average value forH of 5.6 x 10~3 m^ atm/mol and a standard deviation of
+ 7.28%.  The average experimental value compared favorably with the calcu-
lated value of 5.5 x 10"-* ITH atm/mol.  A "standard" flow rate of 100 cc/min
was selected for the remainder of this study.  This rate was chosen because
it produced a good bubble pattern in the stripping vessel, and it allowed
adequate time for sampling.  Flow rates were checked before, during and
after completion of each run as dictated by elapsed time to assure constancy
of flow.

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                  Flow, cc/min

Figure 2. Flow rate vs Henry's law constant for
         volatilization of benzene

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                                    -5-


     To evaluate the reproducibility of this system at the selected gas
flow rate of 100 cc/min, repetitive runs were made using benzene as the
solute.  As can be seen in Table 1, no experimentally significant vari-
ation in the value for H was produced.


           TABLE  1.   REPRODUCIBILITY  OF  EXPERIMENTAL  PROCEDURE

     Run            H, m3 atm/mol x  10"3      Correlation Coefficient

     1                        5.41                     0.999

     2                        5.76                     0.999

     3                        5.34                     0.998

     4                        5.49                     0.998

     5                        5.62                     0.999

These results give a mean value for H of 5.52 x 10"3 m3 atm/mol and a
standard deviation of +_ 3%.


     In order to assure that equilibrium within the  stripping vessel was
being attained, one of the more volatile compounds,  benzene, was run
repetitively at varying liquid depths.  The results  in Table 2, show no
significant change in the experimental value for H was produced with
reductions  in liquid depth of up to  50%.


                  TABLE  2.   EFFECT OF LIQUID DEPTH ON H

     Liquid Depth, cm             H, m3 atm/mol x  10'3

           60                                5.50

           50                                5.73

           40                                5.69

           30                                5.85
Since system equilibrium was achieved with benzene at these depths,  it
was assumed that equilibrium would be achieved in systems with  less
volatile compounds.

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                                      -6-


     Samples for analysis were taken from the stripping vessel with a
glass syringe through a sample tap positioned at a depth of approximately
20 cm from the liquid surface.  The sampling frequency varied from minutes
to hours, depending upon the volatilization rate of the specific compound.
Varying the sampling depth during stripping did not result in variation in
concentration which confirmed that adequate mixing was accomplished by
the bubbles in the stripping vessel.  U-V spectroscopy and two gas chroma-
tography techniques; purge and trap, and solvent extraction, were employed
for analysis of the samples.

     A few of the compounds in this study were light-sensitive and the
stripping vessel was covered during the test.  Some of the compounds were
readily adsorbed on the glass surface of the stripping vessel.  To minimize
this effect, the stripping vessel surface was saturated with the compound,
i.e., the adsorption sites were saturated by exposing them to the test
compound repeatedly prior to each run.

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                                   -7-


                               SECTION 3

                         DISCUSSION AND RESULTS
     Even a casual inspection of the organics on the list of priority
pollutants will show that many of the low molecular weight chlorinated
hydrocarbons are volatile compounds.  It follows from this that loss of
these compounds from solution can be an important route of removal from
the aqueous flow, but this also indicates that the potential exists for
contamination of the air around a wastewater treatment plant.  Treatment
plants offer ample opportunity for volatilization from processes such as
the flows in the collection system, aerated grit chambers, settlers and
most especially from aeration basins where the driving force for desorp-
tion from solution is provided by the air or oxygen aeration.  Thus, it
is not surprising that volatilization from water bodies to the atmosphere
is generally recognized as a significant pathway for transfer of organics
from one environmental medium to another.

     The volatilization process from an aqueous solution is generally
accepted as consisting of diffusion of the solute from the bulk of the
water to the interface, followed by transfer across the interface and
finally diffusion from the interface to the bulk of the air phase.

     There have been many attempts in the literature to develop mathe-
matical models which would predict the rate of volatilization of a
compound from aqueous solution.  Most models incorporate parameters such
as Henry's Law constant, gas and liquid phase mass transfer coefficients
and, more recently, models have incorporated coefficients which account
for other parameters that affect the volatilization rate such as adsorp-
tion on solids and rate of biodegradation.

     An important coefficient in virtually all of the models is Henry's
Law constant (H).  This constant is an expression of the distribution of
a volatile solute at equilibrium between the liquid and vapor phases.
Unfortunately for many of the comompounds of environmental interest, the
value for H is not available.  When the necessary information on aqueous
solubility and vapor pressure is available, H can be calculated.  However,
published vapor pressure and solubility data are, in many cases, question-
able, and in some cases, either erroneous or non-existent.  Another
method for obtaining H was required to overcome this inability to obtain
or calculate a value for H from the literature.

     Mackay, et al., (1) described an apparatus for the determination of
Henry's Law constants for hydrophobic compounds with an accuracy of about
5%.    This device was employed in this study to provide values of H for
as many of the volatile priority pollutants as possible.  The method
involves measurement of the compound concentration in only the liquid
phase while being stripped isothermally from solution at a known gas
flow rate.  H can  readily be calculated from a plot of the natural log
of the concentration vs. time which should be linear with a slope of
-(HG/VRT).   Thus

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                                  -8-
          H  =    slope x VRT
                       G

where
     H  =  Henry's Law constant,  m3 atm/mol

     V  =  Volume of test solution, m^

     R  =  Gas constant, m^ atm/mol °K

     T  =  Temperature, °K

     G  =  Gas flow rate, m^/min


Henry's law constant was determined for 41 compounds.  The results of
these tests are presented in Table 3.  All experimental values for H
reported in the table are averages of 2 or more replicates.  Calculated
values for H were based on data from many published sources (1-11), and
can be calculated by
         H  =
                VP x MW
where
     H  =  Henry's law constant, m^ atm/mol

     VP  =  Vapor pressure of solute, atm

     MW  =  Molecular weight of solute, g/mol

     S  =  Solubility of solute,
     In all cases, except during the first few minutes when it is believed
that high solute concentrations overloaded the analytical detectors,
resultant curves were linear, with correlation coefficients (r) normally
greater than 0.980; see Figures 3 and 4.  In all but two of the compounds
studied a precision corresponding to a standard deviation of approximately
6% was achieved.

     As can be seen in Table 3, many of the calculated results correspond
closely to the experimental values, however, several deviate significantly
from these values and for some of the compounds, no values could be
calculated due to insufficient data.  Some deviation between experimental
and calculated values for H can be attributed to the use of the only
available data at temperatures different from the selected system tempera-
ture.  Other deviations are due to incorrect solubility and vapor pressure
information.  Literature values can vary over three orders of magnitude for
some compounds.  Some of the deviation can be attributed to experimental
error, however, questionable published data and confidence in the experi-
mental method dictates that H values determined experimentally are preferred
over calculated values.

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                         T = 298° K

                         V = 9.8 x 10-4 m3

                         G = 1.0 x 10-4 mVmin

                         r = 0.985
      0  10  20
             30  40  50  60  70  80   90 100

                Time, minutes
Figure 3. Typical plot for volatilization of

          trichloroethylene

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                  Time, minutes


 Figure 4. Typical plot for volatilization of benzene

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                        TABLE 3.  SUMMATION OF DATA FOR HENRY'S LAW CONSTANT  .
         Compound

Acenaphthene
Benzene
Carbon tetrachloride
Chlorobenzene
1,2,4-Trichlorobenzene
Hexachlorobenzene
1,2-Dichloroethane
1,1,1-Trichloroethane
Hexachloroethane
1,1-Dichloroethane
Chloroform
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
1,1-Dichloroethylene
1,2-trans-Dichloroethylene
1,2-Dichloropropane
1,3-Dichloropropylene
Ethyl benzene
Methylene chloride
Bromoform
Vapor
Pressure,
atm.x 10"J
_ _
125(3)
149(4)
15.5(4)
0.383(6)
- -
113*(4)
168* (4)
_ _
308(4)
260(6)
1.97(4)
2.48(6)
_ _
778(4)
263(4)
65.8(4)
32.9(5)
12.5(3)
599*(4)
7.37(4)
Temp.
°K
—
298
298
298
298
-
298
298
-
298
298
298
298
-
298
287
298
293
298
298
298
Solubility
g/m3
3.93(1)
1780(10)
800(2)
472(1).
30 7)
0.006(6)
8300(6)
5497*(4)
50(5)
5500(4)
9600(4)
145(4)
123(4)
79(4)
5000(6)
6300(2)
2700(4)
2700(5)
206(11)
16700(4)
3130*(5)
Temp.
°K
298
298
298
298
-
298
298
298
295
293
298
298
298
298
293
293
293
298
298
298
298
Molecular
Weight
g/mol
154.2
78.1
.153.8
112.6
181.5
284.8
99.0
133.4 .
236.7
99,0
119.2
147.0
147.0
147.0
97.0
96.9
113.0
111.0
106.2
34.9
252.8
  H,. m3 atm/mol  x 10"3
Calculated   Experimental
   5.48
   28.6
   3.70
   2.32
   1.35
   4.08
   5,54
   3.23
   2.00
   2.96

   15.1
   4.05
   2.75
   1.35
   6.44
   3.04
  0.595
0.241
 5.55
 30.2
 3.93
 1.42
 1.70
 1.10
 4.92
 9.85
 5.45
 3.39
 1.94
 2.63
 2.72
 15.0
 5.32
 2.82
 3.55
 6.44
 3.19
0.532

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                    TABLE 3.  (cont'd) SUMMATION OF DATA FOR HENRY'S LAW CONSTANT
         Compound
Bromodichloromethane
Trichlorof1uoromethane
Dibromochloromethane
Hexachlorobutadlene
Hexachlorocyc1opentad1ene
Nitrobenzene
4,6-Din1tro-o-cresol
Phenol
Acenaphthylene
Fluorene
Tetrachloroethy1ene
Toluene
Trichloroethylene
Aldrin
Dieldrin
Chlordane
Heptachlor
Heptachlor epoxlde
Arochlor 1254
Toxaphene

( ) Reference designation,
Vapor
Pressure.,
atm.x 10"J
M Ğ
833*(4)
65.8(5)
0.197 5)
0.107 4)
0.374 6)
._ •
- -
t
25.8*(4)
37.4(6)
97.8(6)
- -
Ğ•ğ Ğ•
Temp.
°JL
298
293
293
298
298

-

298
298
298
-
-
Solubility
g/m3
•V —
1100(4)
2(5)
0.805(5)
2000(6)

67000(6)
3.93(5)

1.98(5)
150(4)
535(9)
1100(4)
0.2(6)
0.186(6)
1.85(8)
0.056(6)
0.275(6)
0.012(5)
1.75(8)
Temp.
°K
_
298
293
298
298

298
298

298
298
298
298
293
298
298
298
298
298
298
Molecular
Weight
g/mol
163.8
137.4
168.8
260.8
272.7
123.1
198.1
94.1
152.2

116.2
165.8
92.1
131.5
364.9
380.9
409.8
373.4
389.3
328.4
413.9
H, m atm/mol x 10
Calculated Experimental
2.12
104 58.3
0.783
25.7 10.3
36.2 16.4
0.023 0.024
0.0014
0.0013
0.114

0.117
28.5 28.7
6.44 5.93
11.7 11.7
0.496
0.058
0.048
1.48
0.032
8.37
4.89
                                                                            ro
                                                                            i
* Data interpolated between two data points.  - Data unavailable.

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                                  -13-
                               REFERENCES

1.   Mackay,  D.,  Shiu.W.  Y. and Sutherland,  R.  P.,
     "Determination of Air-Water Henry's Law Constant  for  Hydrophobia
     Pollutants." Environ.  Sci. & Tech., K3, 333 (March  1979).

2.   Dilling, W.  L.,  "Interphase Transfer Processes.  II. Evaporation
     Rates of Chloro Methanes, Ethanes,  Ethylenes,  Propanes,  and
     Propylenes from Dilute Aqueous Solutions.   Comparison with
     Theoretical  Predictions." Environ.  Sci. & Tech.,  11,  405 (April 1977).

3.   Zwolinski, B. J., and  Wilhoit, R.  C.,  "Handbook  of  Vapor Pressures
     and Heats of Vaporization of Hydrocarbons and  Related Compounds,"
     API, 44-TRC Publications in Science and Engineering,  1971.

4.   Verschueren, K., "Handbook of Environmental Data on Organic Chemicals,"
     Van Nostrand Reinhold  Company, 1977.

5.   Water-Related Environmental Fate of 129 Priority Pollutants.  A
     Literature Search by Versar, Inc.,  for USEPA Office of Water Planning
     and Standards.  Contract No. 68-01-3852.   January-February 1979.
     Draft copies.

6.   ISHOW Data Base, University of Minnesota,  Duluth. April  1979.

7.   Spencer, W.  F.,  and  Farmer, W. J.,  "Assessment of the Vapor Behavior
     of Toxic Organic Chemicals," Contribution of Federal  Research, SEA,
     USDA and the University of California, Riverside, California.

8.   Weil, L., Dure,  G.,  and Quentin, K. E.,
     Z. Wasser -  Abwasser Forsch, 7(6),  169-185 (1974).

9.   Strier,  M.,  "Treatability of Organic Priority  Pollutants," Part C.
        USEPA Office of Quality Review,  June 1978.   Unpublished Manuscript.

10.   McAuliffe,  C.,  Jour.  Phys. Chem..  70, 1267 (1966).

11.  Identification of Organic Compounds in Effluents  from Industrial
     Sources.  USEPA Report, PB-241 641/OBA.

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                                  -14-
                            ACKNOWLEDGEMENTS
     This project could not have been completed without the able assistance
of Thomas A. Pressley, who, through 6C/MS,  verified some of our analytical
results.

     Special thanks are also due to Michael Jelus for his cooperation which
enabled a timely completion of the sample analyses.

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