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70.6  Literature Cited

Billing, W.L., N.B. Tefertiller, and G.J.  Kallos.  1975.   Evaportion
  rates of methylene chloride, chloroform, 1,1,1,-trichloroethane,
  trichloroethylene, tetrachloroethylene,  and other chlorinated compounds
  in dilute aqueous solutions.  Environ. Sci. Technol. 9(9):833-838.

Dorfman, L.M. and G.E. Adams.  1973.  Reactivity of the hydroxyl radical
  in aqueous solution.  NSRDS-NBS-46.  NTIS:COM-73-50623.   Springfield, Va.

Dreisbach, R.R.  1952.  Pressure-volume-temperature relationships of
  organic compounds.  3rd Edition.  Handbook Publishers,  Inc., Cleveland,
  Ohio.  349p.

Durkin, P.R., P.H.  Howard, and J. Saxena.   1975.  Investigation of  selected
  potential environmental contaminants:  haloethers.  U.S. Environmental
  Protection Agency, Office of Toxic Substances, Washington, D.C.  168p.
  (EPA 560/2-75-006).

Jaffe, H.H. and M.  Orchin.  1962.  Theory and application of ultraviolet
  spectroscopy.  John Wiley and Sons, New York.  253p.

Kankaanpera, A.  1969.  Basicities of the oxygen atoms in symmetrical and
  unsymmetrical acetals.  Part II.  The base strengths and their relation
  to the rate coeffficients of the different partial fission reactions of
  acetal hydrolysis.  Acta Chem. Scand.  23(5):1728-1732.

Leo, A., C. Hansch and D. Elkins.  1971.  Partition coefficients and their
  uses.  Chem. Rev.  71:525-612.

Metcalf, R.L. and J.R. Sanborn.  1975.  Pesticides and environmental
  quality in Illinois.  111. Nat'l. Hist.  Survey Bull.  31:381-436.

Moriguchi,  I.  1975.  Quantitative structure-activity studies on parameters
  related to hydrophobicity.  Chem. Phara. Bull.  23:247-257.

Patai, S. (ed).  1967.  The chemistry of the ether linkage.  Interscience
  Publishers, New York.  785p.

Radding, S.B., D.H. Liu, H.L. Johnson, and T. Mill.  1977.  Review of the
  environmental fate of selected chemicals.  U.S. Environmental Protection
  Agency, Office of Toxic Substances, Washington, D.C.  147p.   (EPA
  560/5-77-003).
                                      70-6

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Shackelford,  W.M. and L.H.  Keith.  1976.   Frequency of organic compounds
  identified in water.  U.S. Environmental Protection Agency, (ERL,) ,
  Athens, Ga.   617p.  (EPA 600/4-76-062).

Webb, R.F., A.J. Duke, and L.S.A. Smith.   1962.   Acetals and oligoacetals,
  Part I.  Preparation and properties of reactive oligoformals.   J.  Chem.
  Soc. (Lond.)  4307-4319.
                                       70-7

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SECTION VII:  MONOCYCLIC AROMATICS
          Chapters 71-93

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                               71.  BENZENE


71.1  Statement of Probable Fate

    Based on the information found, it appears that the predominant process
for removal of benzene from the water column is volatilization to the atmos-
phere.  That portion of the benzene which volatilizes to the atmosphere is
probably depleted at a fairly rapid rate due to attack by hydroxyl radi-
cals.  It must be noted, however, that the solubility of benzene in water
is relatively high; consequently, persistence of some benzene in the water
column would be expected.  Although the role of benzene sorption onto sedi-
ments and suspended solids cannot be established based on the reviewed
literature, there is evidence of gradual biodegradation of benzene at low
concentrations by aquatic microorganisms.  The rate of benzene biodegrada-
tion is enhanced when other hydrocarbons are present.

71.2  Identification

    Benzene has been detected in finished drinking water (U.S. Environ-
mental Protection Agency 1975), in water and sediment samples from the
lower Tennessee River in ppb concentrations (Goodley and Gordon 1976) and
in the atmosphere (Howard and Durkin 1974).  The chemical structure of
benzene is shown below.

                                             Alternate Names

                                             Benzol
                                             Cyclohexatriene


     Benzene

     CAS NO. 71-43-2
     TSL NO. CY 14000

71.3  Physical Properties

    The general physical properties of benzene are as follows.

    Molecular weight                         78.12
    (Weast 1977)

    Melting point                            5.5°C
    (Weast 1977)
                                    71-1

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    Boiling point at 760 torr                80.1°C
    (Weast 1977)

    Vapor pressure at 25°C*                  95.2 torr
    (Mackay and Leinonen 1975)

    Solubility in water                      **

    Log octanol/water partition coefficient  ***
*Vapor pressure values found in the literature include 45.5 torr at 10°C
(Mackay and Leinonen 1975), 95.2 torr at 25°C (Mackay and Leinonen 1975;
Mackay and Wolkoff 1973), and 100 torr at 26.075°C (Howard and Durkin
1974).

**Several values for the solubility of benzene in water were found in the
literature.  Some of the reported values found in the literature include
1750 mg/1 at 10°C (Mackay and Leinonen 1975), 820 mg/1 at 22°C (Chiou_et
_al. 1977), 1780 mg/1 at 25°C (Mackay and Wolkoff 1973; Mackay and Leinonen
1975), and 1800 mg/1 at 25°C (Howard and Durkin 1974).

***The log octanol/water partition coefficient of benzene is reported to be
1.95 by Leo _et al. (1971) and 2.13 by Chiou _et _al. (1977).

71.4  Summary of_Fate Data

    71.4.1  Photolysis

         Since the ozone layer in the upper atmosphere effectively filters
out wavelengths of light less than 290 nm, and since the ultraviolet spec-
trum of benzene indicates that this compound does not absorb wavelengths of
light longer than 260 nm (Bryce-Smith and Gilbert 1976) direct: excitation
of benzene in the environment is unlikely unless a substantial wavelength
shift is caused by the media (Howard and Durkin 1974).  For instance, al-
though benzene does not absorb light directly in appreciable amounts at
wavelengths longer than 280 nm when dissolved in cyclohexane (Silverstein
and Bassler 1968) , slight shifts in wavelength absorption might be expected
in more representative environmental media such as water or the surface of
particulate organic matter (Howard and Durkin 1974).

    71.4.2  Oxidation

         No specific information pertaining to oxidation of benzene in the
aqueous environment under ambient conditions was found.  Howard and Durkin
(1974), however, report that catalysts, elevated temperature, elevated
pressure, or any of these conditions operating together may serve as ini-
tiators of benzene oxidation.  Based on this information, it can be
                                     71-2

-------
inferred that direct oxidation of benzene in environmental waters is un-
likely.

         Inasmuch as the main transport process that would account for re-
moval of benzene from water appears to be volatilization, the atmospheric
destruction of benzene probably is much more likely than any other fate
process.  These complex photochemical reactions have been studied in simu-
lated smog chambers (Altshuller et_ al. 1962; Laity _e_t _al. 1973) that
measured the rate of disappearance of the volatilized organic material.
The half-conversion time of m-xylene and 1,3,5-trimethylbenzene have been
reported to be somewhat less than four hours (Altshuller &t_ _al. 1962).
From this value and the table of relative reactivities given by Laity et
al. (1973), it can be inferred that the corresponding range for the half-
conversion time for benzene would be approximately 20 to 50 hours.  This
value for the estimated half-conversion time of benzene is in reasonable
agreement with the estimated half-life of benzene proposed by Darnall et
al. (1976) of 2.4 to 24 hours.  This half-life value is based on the
assumptions that benzene depletion is due solely to attack by hydroxyl radi-
cal (OH')) and that even high concentrations of ozone present in ambient
atmospheres will not contribute significantly to the photooxidation of
alkanes and aromatics, in general.  A second-order rate of reaction of ben-
zene with hydroxyl radicals of 0.85 x 10~9 i .mol'-'-sec"-'- has been ob-
tained by Darnall et al. (1976) by averaging rates from smog chamber data
by Hansen ^t al. (T9757 and Davis e£ al. (1975).  The temporal stability of
benzene under actual atmospheric conditions is, as yet, unknown.  Experi-
ments performed in laboratory irradiation chambers are usually conducted
for relatively short periods and cannot account for all of the meterologi-
cal variables within a natural airshed.

    71.4.3  Hydrolysis

         No specific information pertaining to the hydrolysis of benzene
under ambient conditions was found.  The hydrolysis of benzene is an un-
likely process under environmental conditions since nucleophilic attack of
the aromatic ring by water or hydroxide ion will be impeded by its negative
charge-density (Morrison and Boyd 1973).

    71.4.4  Volatilization

         The half-life with respect to volatilization from a water column
one meter thick has been estimated by Mackay and Leinonen (1975) to be 4.81
hours for benzene at 25°C; at 10°C the half-life with respect to volatili-
zation from the same depth of water has been estimated to be 5.03 hours.
Mackay and Leinonen (1975) point out that for benzene the rates and half-
lives of volatilization are insensitive to temperature and that tempera-
ture only affects the rate of volatilization significantly if the system
                                   71-3

-------
is vapor-phase controlled.   Some assumptions made in the estimation of
rates of volatilization and half-lives were as follows:   1)  the contaminant
concentration is in solution rather than in suspended,  colloidal, ionic,
complexed, or adsorbed form;  2) the vapor is in equilibrium  with the liquid
at the interface;  3) the water diffusion or mixing is sufficiently fast so
that the concentration at the interface approaches that of the bulk of the
water; and 4) the  rate of evaporation of water is negligibly affected by
the presence of the contaminants.

         Mackay and Leinonen (1975) point out that interpretation of the
significance of the evaporative rate of compounds such as benzene from en-
vironmental waters using values calculated with a one-meter  depth is de-
pendent upon the type of environmental situation encountered.  In situa-
tions where the water body is turbulent with frequent mixing between the
surface layer and  the bulk, as in a rapidly flowing shallow  river or during
white-capping on a lake or ocean, the evaporative rate would be more rapid
than for depths greater than one meter or in quiescent water, as evidenced
in a deep, slowly flowing river.

    71.4.5  Sorption

         Although no specific environmental sorption studies were found in
the reviewed literature, the values of the log octanol/water partition co-
efficient found for benzene (log P=1.95, Leo _et al. 1971; log P=2.13, Chiou
_e_t al. 1977) indicate that sorption processes may be significant for ben-
zene under conditions of constant exposure.  Presumably, benzene will be
adsorbed by sedimentary organic material; the extent to which this possible
adsorption will interfere with volatilization has not been considered.

    71.4.6  Bioaccumulation

         Neely et al. (1974) have shown that the bioaccumulation potential
of a compound is related to the log octanol/water partition coefficient
(log P) of the compound.  The log P values obtained'from the literature for
benzene of 1.95 (Leo _et al. 1971) and 2.13 (Chiou _et al. 1977) indicate
that the bioaccumulation potential of benzene by aquatic organisms at
pollutant concentrations anticipated in environmental waters would probably
be low.

    71.4.7  Biotransformation and Biodegradation

         Some species of soil bacteria have been demonstrated to be capable
of utilizing benzene as the sole source of carbon (Zobell 1950; Gibson
1976; Glaus and Walker 1964).  A study by Walker and Colwell (1975), how-
ever, showed that petroleum-degrading bacteria isolated from the oil-
polluted Colgate Creek of the Chesapeake Bay would only utilize benzene
                                     71-4

-------
when present in combination with dodecane, or with dodecane and naphtha-
lene.  This utilization was suggested by Walker and Colwell (1975) to most
likely occur as a result of co-oxidation or because of a lower concentra-
tion of benzene present than when petroleum-degrading bacteria were treated
with benzene alone.  Since measurable utilization of benzene at a 0.1%
concentration occurred for more than 30% (68 of 200) of the pure cultures
of hydrocarbon-utililizing bacteria, Walker and Colwell (1975) feel that
the latter explanation cannot be excluded.

         Gibson (1976) and Gibson et al. (1968) conducted experiments to
determine the metabolic pathway involved in the microbial, oxidative de-
gradation of benzene.  Although the microorganism used in these experi-
ments, Pseudomonas putida, could utilize benzene as the sole source of
carbon and energy for growth, toluene served as a better substrate, and
cells grown with toluene were used to investigate benzene metabolism.
Gibson (1976) found that the initial reactions in the bacterial oxidation
of aromatic hydrocarbons involved the formation of c is-dihydrodiols which
undergo further oxidation to yield catechols.  Gibson (1976) found that
mammals, on the other hand, oxidize benzene to arene oxides which are
hydrated to form trans-dihydrodiols prior to oxidation to yield catechols.

         For several reasons, the view that only a few genera of bacteria
such as Pseudomonas (Gibson 1976), and Achromobacter (Glaus and Walker
1964) can utilize benzene as a sole carbon source may not be valid.  The
usual enrichment procedures for isolating such bacteria tend to select only
those that grow rapidly.  Vigorous growth in pure culture is a great ad-
vantage in biochemical studies but may not encompass all of the more impor-
tant features of a natural habitat.  A specific compound may in fact be
readily metabolized in soil despite the failure to isolate single microbial
species capable of using that compound as a sole carbon source (National
Research Council 1977).  On the other hand, the isolation of single species
cabable of using a test compound as a sole carbon source must also be
viewed with caution.  An organism capable of using a test substrate as a
sole carbon source in pure culture may not be able to assimilate the com-
pound under natural conditions.  Generally, the concentration of substrate
used in pure culture studies is considerably higher than normally en-
countered in nature.  As a result, the enzymes essential for biodegradation
may not be induced under natural conditions.  Further, pure culture studies
rarely lead to useful degradation rate information (Howard and Durkin
1974).

         Helfgott e_t_ _aJL_. (1977) report the refractory index (often referred
to as the biorefractory index by other authors) of benzene to be 0.23
                                       71-5

-------
indicating that benzene is quite resistant to degradation.   The refractory
index of a compound as defined by Helfgott et al.  (1977)  is a parameter for
estimating the biodegradability and treatability of organic materials found
in and entering into the aquatic environment.  Values for the refractory
index normally range from 0.0 to 1.0.   Refractory materials are defined as
those materials having refractory index values (R.I.) of  less than 0.6.
According to Helfgott et^ al.  (1977) such refractory compounds are not
expected to degrade in an aerobic wastewater treatment system such as an
activated sludge process and  are expected to persist in natural water
systems such as aquifers, rivers, and  lakes.  They suggest  that the
aromatic symmetry and electron delocalization of benzene  are probably the
factors which impart persistence to this compound.  In a  study by Thorn and
Agg (1975) benzene is listed  as a synthetic organic chemical which should
be degradable by biological sewage treatment provided that  suitable
acclimatization can be achieved.

71.5  Data Summary

    Table 71-1 summarizes the aquatic  fate information found for benzene.
Volatilization appears to be  the major transport process  of benzene from
the water column to the atmosphere.  The atmospheric photooxidation of
volatilized benzene probably subordinates all other fate  processes.  The
reported rates of oxidation are atmospheric photooxidation rates based on
smog chamber data.  One half-life value and rate reported for the
atmospheric photooxidation of benzene  is based on the assumptions that ben-
zene depletion is due solely to attack by hydroxyl radicals and that even
high concentrations of ozone present in ambient atmospheres will not con-
tribute significantly to the photooxidation of alkanes and  aromatics, in
general.  Since benzene is relatively soluble in water, some benzene is ex-
pected to persist in the water column.  That portion of benzene which
persists in the water column would be  expected to eventually biodegrade at
a slow rate. The biodegradation of benzene would probably be enhanced by
the presence of other hydrocarbons.
                                    71-6

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71.6  Literature Cited

Altshuller, A.P., I.R. Cohen, S.F. Sleva, and S.L. Kopczynski.  1962.  Air
  pollution:  photooxidation of aromatic hydrocarbons.  Science
  138:442-443.

Bryce-Smith, D. and A. Gilbert.  1976.  The organic photochemistry of
  benzene - I.  Tetrahedron.  32:1309-1326.

Chiou, C.T., V.H. Freed, D.W. Schmedding, and R.L. Kohnert.  1977.
  Partition coefficients and bioaccumulation of selected organic chemicals.
  Environ. Sci. Technol. 11(5):475-478.

Glaus, D. and N. Walker.  1964.  The decomposition of toluene by soil
  bacteria.  J. Gen. Microbiol. 36:107-122.

Da mail, K.R, A.C. Lloyd, A.M. Winer, and J.N. Pitts, Jr.  1976.
  Reactivity scale for atmospheric hydrocarbons based on reaction with
  hydroxyl radical.  Environ. Sci. Technol. 10(7):692-696.

Davis, D.D., W. Bellinger, and S. Fischer.  1975.  Kinetics study of the
  reaction of the OH free radical with aromatic compounds.   I.  Absolute
  rate constants for reaction with benzene and toluene at 300°K.  J. Phys.
  Chem. 79:293-294.

Gibson, D.T., J.R. Koch, and R.E. Kallio.  1968.   Oxidative degradation of
  aromatic hydrocarbons by microorganisms.  I.  Enzymatic formation of
  catechol from benzene.  Biochemistry 7:2653-2662.

Gibson, D.T. 1976.  Initial reactions in the bacterial degradation of
  aromatic hydrocarbons.  Zbl. Bakt. Hyg. I. Abt. Orig. B.  162:157-168.

Goodley, P.C. and M. Gordon.  1976. Characterization of industrial organic
  compounds in water.  Trans. Kentucky Academy of Science 37(1-2):11-15.

Hansen, D.A. , R. Atkinson, and J.N. Pitts, Jr.  1975.  Rate constants for
  the reaction of OH radicals with a series of aromatic hydrocarbons. J.
  Phys. Chem.   79:1763-1766.

Helfgott, T.B., F.L. Hart, and R.G. Bedard.  1977.  An index of refractory
  organics.  U.S. Environmental Protection Agency, (Office of Research and
  Development), Ada, Oklahoma. 131p. EPA 600/2-77-174.

Howard, P.H. and P.R. Durkin.  1974.  Sources of  contamination, ambient
  levels, and fate of benzene in  the environment.  U.S. Environmental
  Protection Agency,  (Office of Toxic Substances), Washington, D.C. 65p.
  EPA 560/5-75-005.
                                     71-J

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Laity, J.L., I.G. Burstain, and B.R. Appel.  1973.  Photochemical smog and
  the atmospheric reactions of solvents.  Chap. 7, pp. 95-112. Solvents
  Theory and Practice.  R.W. less (ed.)  Advances in Chemistry Series 124.
  Am. Chem. Soc., Washington, D.C.

Leo, A., C. Hansch, and D. Elkins.  1971.  Partition coefficients and their
  uses.  Chem. Rev. 71:525-616.

Mackay, D. and A.W. Wolkoff.  1973.  Rate of evaporation of low-solubility
  contaminants from water bodies  to atmosphere.  Environ. Sci. Technol.
  7(7):611-614.

Mackay, D. and P.J. Leinonen.  1975.  Rate of evaporation of low-solubility
  contaminants from water bodies  to atmosphere.  Environ. Sci. Technol.
  9(13):1178-1180.

Morrison, R.T. and R.N. Boyd.  1973.  Organic chemistry.  3rd Edition.
  Allyn and Bacon, Inc., Boston.  1258p.

National Research Council,  1977.  Fates of pollutants.  Research and
  development needs.  National Academy of Sciences, Washington, D.C. 144p.

Neely, W.B., D.R. Branson, and G.E. Blau.  1974.  Partition coefficient to
  measure bioconcentration potential of organic chemicals in fish. Environ.
  Sci. Technol. 8:1113-1115.

Silverstein, R.M. and G.C. Sassier.  1968.  Spectrometric identification of
  organic compounds.  2nd Edition.  John Wiley and Sons, New York.  256 p.

Thorn, N.S. and A.R. Agg.  1975.   The breakdown of synthetic organic
  compounds in biological processes. Proc. Roy. Soc. Lond. B 189:347-357.

U.S. Environmental Protection Agency.  1975.  Preliminary assessment of
  suspected carcinogens in drinking water.  U.S. Environmental Protection
  Agency, (Office of Toxic Substances), Washington, D.C. 33p. EPA
  560/4-75-003.

Walker, J.D. and R.R. Colwell.  1975.  Degradation of hydrocarbons and
  mixed hydrocarbon substrate by  microorganisms from Chesapeake Bay.
  Prog. Water Technol. 7(3-4):783-791.

Weast, R.C. (ed). 1977.  Handbook of chemistry and physics.  58th Edition.
  CRC Press, Inc., Cleveland, Ohio.  2398p.

Zobell, C.E. 1950.  Assimilation  of hydrocarbons by microorganisms.
  Advances in Enzymology and Related Subjects of Biochemistry.  F.F. Nord
  (ed.) Volume 10:443-486.  Interscience Publishers, Inc. New York.
                                    71-9

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                            72.   CHLOROBENZENE


72.1  Statement of Probable Fate

    Based on the information found,  it is not  possible to determine the
predominant aquatic fate of chlorobenzene.  There is some experimental
evidence indicating that volatilized chlorobenzene will undergo atmospheric
photooxidation in the presence of nitric oxide.   The extent to which such
photooxidation will occur at chlorobenzene concentrations prevalent in the
atmospheric environment in the presence of nitric oxide, as well as other
free radical initiators, is unknown.  Information found concerning the
biodegradation potential of chlorobenzene indicates that this compound,
being very persistent, will probably eventually  biodegrade, but not at a
substantial rate unless the microorganisms present are already growing on
another hydrocarbon source.

    Chlorobenzene has a high affinity for lipophilic materials, and it also
is reported to have a relatively low solubility  at temperatures anticipated
to be prevalent in most ambient waters.  Consequently, sorption, bioaccumu-
lation, and volatilization are expected to be  competing processes.  The rate
at which each of these competing processes occur will determine which fate
is predominant for chlorobenzene in the aquatic  environment.  Should vol-
atilization occur at a more rapid rate than sorption or bioaccumulation,
then atmospheric processes would be expected to  regulate the fate of chloro-
benzene.  On the other hand, should sorption and bioaccumulation occur more
rapidly than volatilization, biodegradation of chlorobenzene by aquatic
microorganisms would be anticipated to regulate  the fate of this compound.

72.2  Identification

    Chlorobenzene has been detected in finished  drinking water, in ground
water, in uncontaminated upland water, in waters contaminated by either
industrial, municipal, or agricultural wastes  (U.S. Environmental Protec-
tion Agency 1975), and in the atmosphere (Ware and West 1977).  The
chemical structure of chlorobenzene is shown below.
                                             Alternate Names

                                             Monochlorobenzene
    Chlorobenzene                            Benzene Chloride

    CAS NO. 108-90-7
    TSL NO. CZ 01750
                                     72-1

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72.3  Physical Properties

    The general physical properties of chlorobenzene are given below.

    Molecular weight                         112.56
    (Verschueren 1977)

    Melting point                            -45°C
    (Verschueren 1977)

    Boiling point at 760 torr                132°C
    (Verschueren 1977)

    Vapor pressure at 20°C                   *

    Solubility in water                      **

    Log octanol/water partition coefficient  2.84
    (Leo et al. 1971;  Chiou et al. 1977)
*Values for the vapor pressure of chlorobenzene in water were reported to
be 8.8 torr at 20°C (Verschueren 1977) and were calculated to be 11.72 torr
at 20°C from the table of vapor pressures, critical temperatures and criti-
cal pressures of organic compounds in-Weast (1973).

**Values for the solubility of chlorobenzene in water were reported to be
500 mg/1 at 20°C (Verschueren 1977),  488 mg/1 at 25°C (Mardsen and Marr
1963), and 448 mg/1 at 30°C (Chiou _etal. 1977).

72.4  Summary of Fate Data

    72.4.1  Photolysis

         No specific information pertaining to the direct photolysis of
chlorobenzene in the aqueous or atmospheric environments under ambient con-
ditions was found.

    72.4.2  Oxidation

         No specific information pertaining to the oxidation of chloro-
benzene in the aqueous environment under ambient conditions was found.

         Billing e_t al. (1976) studied the photodecomposition rate of
chlorobenzene under simulated atmospheric conditions.  The reactor was a
waterjacketed Pyrex cylinder maintained at 27 + 1°C and 35% relative
                                     72-2

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humidity.  The ultraviolet light sources were two General Electric
275-Wreflector sunlamps, each of which had a short wavelength cutoff of 290
nm.  Chlorobenzene decomposed relatively slowly when compared to other
chlorinated compounds studied.  In the presence of nitric oxide, a probable
reaction initiator, chlorobenzene, at a concentration of 10 mg/1, underwent
43% reaction in 7.5 hours;  this corresponds to an estimated half-life of
8.7 hours.  No photodecomposition products were reported.  For comparison,
the estimated half-life of benzene proposed by Darnall et_ aL. (1976) was
2.4 to 24 hours.  Using the half-conversion time of m-xylene and
1,3,5-trimethylbenzene, which was reported to be somewhat less than four
hours (Altshuller ^t_ a_l. 1962), and the table of relative reactivities
given by Laity et_ al_. (1973), the corresponding range for the half-
conversion time for benzene was inferred to be approximately 20 to 50
hours.  Due to decreased susceptibility to electrophilic attack, chloro-
benzene would be anticipated to have a longer half-life than benzene under
similar conditions of exposure.  Because the experimental procedure of
Dilling et_ al. (1976) is different from the hypothetical conditions used
for the theoretical calculation of Darnall e_t_ a^L. (1976) the results cannot
be quantitatively compared.  However, they do show that chlorobenzene will
undergo photolysis over a defined range of times.  In addition, experiments
of the type carried out by Dilling e_t_ aJ. (1976) should, for accuracy, be
carried out for at least 2 or 3 half-times.

    72.4.3  Hydrolysis

         Chlorobenzene, being an aryl halide, will undergo nucleophilic
substitution only with extreme difficulty.  For example, Morrison and Boyd
(1973) report that chlorobenzene is converted into phenol by aqueous sodium
hydroxide only at temperatures over 300°C.  Consequently, hydrolysis of
chlorobenzene under environmental conditions would not be expected to
occur.

    72.4.4  Volatilization

         Available data on chlorobenzene indicate that this compound prob-
ably volatilizes from the water column to the atmosphere at a relatively
rapid rate.  Garrison and Hill (1972) reported that at 300 mg/1 of chloro-
benzene volatilized almost completely (less than 1 mg/1 chlorobenzene re-
mained) from aerated distilled water in less than four hours.  The same
concentration of chlorobenzene volatilized almost completely (less than 1
mg/1 chlorobenzene remained) from unaerated distilled water in less than 3
days.  No further details of this experiment were reported.  Assuming a
first order process and also assuming that volatilization is the only re-
moval process operating (i.e., no gas-stripping and negligible adsorption
onto container walls), the data of Garrison and Hill (1972) yield estimates
                                 72-3

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of about 0.5 hours and 9 hours for evaporative half-lives of chlorobenzene
in water under conditions of aeration and quiescence,  respectively.
Because of the limited data on experimental  conditions,  it is difficult to
interpret the effect of aeration on the rate of evaporation.   Furthermore,
because of the possibility of air-stripping  during aeration,  it is
concluded that the 0.5 hour value is not a valid evaporative  half-life for
chlorobenzene in agitated water.  The value  of 9 hours appears to  be valid
for the non-agitated case.

         According to Mackay and Wolkoff (1973) the rate of evaporation of
pollutants having a low solubility in water  can be quite rapid even though
these compounds often have a high molecular  weight and a low vapor
pressure, and should, on these bases, evaporate slowly.   Mackay and  Wolkoff
(1973) contend that these compounds often have high activity coefficients
in water which cause unexpectedly high partial vapor pressures at  equili-
brium and thus high rates of evaporation. Although chlorobenzene, which
has a reasonably low solubility in water of  488 mg/1 at  25°C (Mardsen and
Marr 1963), was not mentioned specifically,  other chlorinated hydrocarbons
having a low solubility in water were predicted to have  relatively rapid
rates of evaporation.  Presumably, chlorobenzene would have a rate of
evaporation similar to compounds having vapor pressure and solubility
values approximately equal to those values for chlorobenzene.

         The published values for the vapor  pressure (Weast 1973)  and
solubility (Mardsen and Marr 1963) of chlorobenzene in water at 25°C were
used to compute the Henry constant as being  approximately 3.56 x 10"^
atmos. m-Ymole. This constant for chlorobenzene may be compared to the
value of 3.51 x 10"3 atmos m3/mole predicted for Aroclor 1248 at 25°C
(Mackay and Leinonen 1975).  In the case of  Aroclor 1248, the half-life for
evaporation from a water column one meter thick was estimated by Mackay and
Leinonen (1975) to be 9.53 hours at 25°C. An estimate of the corresponding
half-life for evaporation of chlorobenzene under the same conditions would
presumably be of the same order, approximately 10 to 11  hours, or  close to
the value of about 9 hours discussed previously.

         The interpretation of the environmental significance of the rate
of evaporation of chlorobenzene based on calculations involving an assumed
depth of one meter is dependent upon the type of environmental situation
encountered.  In situations where the water  body is turbulent with frequent
mixing between the surface layer and the bulk, as in a rapidly flowing
shallow river, or during white-capping on a  lake or ocean, the rate of
evaporation would be more rapid than for depths greater than one meter or
in quiescent water, as exists in a deep, slowly flowing  river.
                                      72-4

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    72.4.5  Sorption

         Although no specific environmental sorption studies were found in
the literature, the values of the log octanol/water partition coefficient
found for chlorobenzene (log P = 2.84, Leo e_t_ al_. 1971;  Chiou _e_t_ _al_. 1977)
indicate that sorption processes may be substantial for chlorobenzene at
pollutant concentrations anticipated in environmental waters.  Presumably,
chlorobenzene will be adsorbed by sedimentary organic material;  the extent
to which this possible adsorption will interfere with volatilization has
not been considered.

    72.4.6  Bioaccumulation

         Chlorobenzene was studied for its bioaccumulation potential in a
model aquatic ecosystem developed by Lu and Metcalf (1975).  This aquatic
ecosystem was devised for studying relatively volatile organic compounds
and simulating direct discharge of chemical wastes.  A 3-liter flask
containing members of an aquatic food chain, including daphnia, mosquito
larvae, snails, mosquito fish, and green filamentous algae, was maintained
at 80°F with 12 hours daylight exposure.  Radiolabelled derivatives were
added to the flask in concentrations of 0.01 to 0.1 ppm.   After 48 hours,
the experiment was terminated.

         The contaminative efficacy of chlorobenzene was evaluated by de-
termining the quantitative distribution of the radioactivity in the
organisms, water, and air of the model aquatic ecosystem.  Chlorobenzene
was found to be a highly persistent compound, as demonstrated by the eco-
logical magnification (EM) values (often referred to as the bioconcentra-
tion or bioaccumulation factors by other authors) of 645 in fish, 1292 in
mosquito larva, 1313 in snail, 2789 in daphnia, and 4185 in alga.  Lu and
Metcalf (1975) define ecological magnification as the ratio of the con-
centration of the parent compound in an organism to the concentration in
the water.  Hydroxylation served as the predominant detoxification mecha-
nism of chlorobenzene by all of the organisms in the model aquatic food
chain except filamentous green alga, Oedogonium cardiacum.  Hydroxylation
of chlorobenzene to o- and p-chlorophenol and to 4-chlorocatechol was found
in mosquito larva and in water extracts.

         In addition to experimental evidence, there is empirical evidence
that chlorobenzene has a high potential for bioaccumulation in organisms.
Neely et al. (1974) and Lu and Metcalf (1975) have shown that the log
octanoTTwater partition coefficient (log P) correlates well with the
ability of a compound to accumulate in the lipids of tissues of living
organisms.  The log P value of 2.84 (Leo et al. 1971;  Chiou et al. 1977)
                                     72-5

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indicates that bioaccumulation of chlorobenzene by aquatic organisms at
pollutant concentrations anticipated in environmental waters will probably
occur.

    72.4.7  Biotransformation and Biodegradation

         Some species of soil bacteria have been demonstrated to be cap-
able of obtaining their energy and carbon requirements from chlorobenzene
(Matthews 1924).  A study by Gibson e_t_ _al_. (1968), however, indicated that
the microorganism Pseudomonas putida could oxidize chlorobenzene only when
it was already growing on an aromatic hydrocarbon source.  In this study,
cultures of Pseudomonas putida were initially grown on toluene as the sole
source of carbon for 15 hours and were subsequently grown on chlorobenzene
for up to 20 hours.  This oxidative degradation of chlorobenzene by
Pseudomonas putida resulted in the formation of 3-chlorocatechol (Gibson et
_al. 1968).

         In a study by Garrison and Hill (1972), chlorobenzene was exposed
to aerated mixed cultures of aerobic microorganisms to test their resis-
tance to microbial action.  Garrison and Hill (1972) reported that chloro-
benzene volatilized completely from these aerated cultures in less than one
day.  No other information on this particular study was given.

         In a report by Heukelekian and Rand (1955) BOD (Biochemical Oxygen
Demand) data on pure compounds were compiled and assembled into broad
groups on the basis of certain chemical similarities.  The BOD values were
expressed as grains per gram of chemical tested at 20°C.  Most of the data
reported have BOD values based on a 5-day incubation period, although there
were  some BOD values based on an incubation period of 10 days or based on
ultimate values.  From the reported data, it appears that the presence of a
chlorine atom on a benzene ring results in a BOD value lower than that of
benzene itself.  For comparison, the BOD of benzene was reported as 1.20
g/g after a 10-day incubation period whereas the BOD of chlorobenzene was
reported to be 0.03 g/g after a 5-day incubation period.  This decrease in
BOD value as a result of the presence of a chlorine atom on the benzene
ring  indicates an increased resistance to microbial attack.  Although the
difference in the incubation time for benzene and chlorobenzene could
account to some degree for the difference in BOD values for the two
compounds, Alexander and Lustigman (1966) also found that the presence of a
chlorine atom on the benzene ring retarded the rate of biodegradation.

         Lu and Metcalf (1975) reported values for the biodegradability
index of chlorobenzene ranging from 0.014 to 0.063 in organisms found in a
model aquatic ecosystem.  The biodegradability index is defined as the
ratio of polar products of degradation to the non-polar products.  A  low
value for the biodegradability index indicates that a compound resists
biodegradation.  Comparison of the biodegradability index of chlorobenzene
with  that of some more widely studied persistent pollutants such as DDT and
                                      72-6

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aldrin, give a better idea of the significance of these values.  Lu and
Metcalf (1975) reported a biodegradability index for DDT of 0.012 in
mosquito fish compared to a value of 0.015 for aldrin, and 0.014 for
chlorobenzene .

    72.4.8  Other Reactions

         In an investigation by Carlson et_ _a_l_. (1975), monosubstituted
aromatics were exposed to low concentrations of aqueous chlorine (7 x
10~^M) for 20 minutes at varying pH conditions to determine the extent of
chlorine incorporation into aromatic compounds.  Chlorine, being an elec-
trophile, was found to be more slowly incorporated into aromatic compounds
containing deactivating groups such as chloro, nitro, nitrile, and carbonyl
than into aromatic compounds containing activating groups such as hydroxyl,
ether, amine derivatives, or alkyl.  For comparison, when chlorobenzene, a
compound containing a ring-deactivating group, and phenol, a compound
containing a ring-activating group, were exposed at pH 3 to 7 x 10~^M
aqueous chlorine for 20 minutes, the chlorine uptake was 1.8 +_ 0.1% and
97.8 + 0.1%, respectively.  Chlorobenzene was not chlorinated at higher
pH. Since the typical range of pH found during the course of most water
treatment processes is 5 to 9, there is a low probability of forming higher
chlorinated benzenes from reactions of chlorine and chlorobenzene.

72.5  Data Summary

    There is not enough environmentally significant information on photo-
lysis, oxidation, or sorption processes to be able to predict the aquatic
fate of chlorobenzene.  Chlorobenzene has a high affinity for lipophilic
materials, and it is also reported to have a relatively low solubility at
temperatures expected to prevail in most ambient waters.  Consequently,
sorption, bio accumulation, and volatilization are expected to be competing
processes.  The rate at which each of these competing processes occur will
dictate which fate is predominant for chlorobenzene in the aquatic
environment.  These data are summarized in Table 72-1.
                                     72-7

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                                                   Table  72-1

                                   Summarv of Aauatic Fate of Chlorobenzene
Environmental
   Process

Photolysis

Oxidation
Hydrolysis
Volatilization
Sorption
Bioaccumulation
 Biotransformation/
   Biodegradation
           Summary
          Statement                       Rate

No information found.

No information was found concerning
the oxidation of Chlorobenzene
in ambient waters.  Experimental
evidence indicates that volatilized
Chlorobenzene will undergo atmos-
pheric photooxidation in the pre-
sence of nitric oxide.  The extent
to which photooxidation will occur
at Chlorobenzene concentrations
prevalent in the atmospheric en-
vironment in the presence of nitric
oxide or other initiators in unknown.

Chlorobenzene probably will not
hydrolyze in ambient waters due to
the extreme difficulty with which
aryl halides undergo nucleophilic
substitution.

This compound probably volatilizes
from the water column to the atmos-
phere at a relatively rapid rate.

The high log P value found for             -
Chlorobenzene indicates that sorp-
tion processes may \>e substantial
for Chlorobenzene at pollutant
concentrations anticipated in
environmental waters.

Experimental and empirical evidence
indicates that Chlorobenzene has an inter-
mediate potential for bioaccumulation in
the lipids of tissues of living organisms.

Information  found concerning  the           -
biodegradation potential of Chloro-
benzene  indicates that  this compound
will probably eventually biodegrade,
but not  at a substantial rate unless
the microorganisms present are already
growing  on another hydrocarbon source.
                                                                           Half-Life
  8.7 hours
Confidence
 of Data

   Low

   Low
   9 hours
1C or 11 hours
                                                                                                Medium
                                                                                                Medium
                                                                                                Low
                                                                                                Medium
                                                                                                Medium
 a.   There  is insufficient  information  in  the  reviewed literature to permit assessment of a most probable fate.
 b.   This half-life is the  estimated half-life based on the experimental results and conditions of Billing et_ &._
     (1976)  and  probably  does  not  reflect  the  photooxidation half-life of Chlorobenzene under environmental
     conditions.
 c.   This half-life is tha  estimated half-life based on the experimental results and conditions of Garrison and
     Hill  (1972)  in unaerated  distilled water.
 d.   This half-life is based on  the calculated Henry constant of Chlorobenzene which is of the same order as the
     Henry  constant predicted  for  Aroclor  1248 at  25°C by Mackay and Leinonen (1975).   Since the half-life for
     evaporation of Aroclor 1248 from a water  column one meter thick was estimated by Mackay and Leinonen (1975)
     to  be  9.53  hours  at  25 C,  the half-life for evaporation of Chlorobenzene under the same conditions was
     assumed to  be  only slightly longer.
                                                    72-8

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72.6  Literature Cited

Alexander, M. and B.K. Lustigman.  1966.  Effect of chemical structure on
  microbial degradation of substituted benzenes.  J. Agr. Food Chera.
  14(4):410-413.

Altshuller, A.P., I.R. Cohen, S.F. Sleva, and S.L. Kopcaynski.    1962.
  Air pollution: photooxidation of aromatic hydrocarbons.    Science
  138:442-443.

Carlson, R.M., R.E. Carlson, H.L. Kopperman, and R. Caple.  1975.  Facile
  incorporation of chlorine into aromatic systems during aqueous
  chlorination processes.  Environ. Sci. Technol.  9(7):674-675.

Chiou, C.T., V.H. Freed, D.W. Schmedding, and R.L. Kohnert.  1977.
  Partition coefficient and bioaccumulation of selected organic chemicals.
  Environ. Sci. Technol.  11(5) :475-478.

Darnall, K.R., A.C. Lloyd, A.M. Winer, and J.N. Pitts, Jr.  1976.
  Reactivity scale for atmospheric hydrocarbons based on reaction with
  hydroxyl radical.  Environ. Sci. Technol. 10(7):692-696.

Dilling, W.L., C.J. Bredeweg, and N.B. Tefertiller.  1976.  Simulated
  atmospheric photodecomposition rates of methylene chloride,
  1,1,1-trichloroethane, trichloroethylene, and other compounds.  Environ.
  Sci. Technol.  10(4):351-356.

Garrison, A.W. and D.W. Hill.  1972.  Organic pollutants from mill persist
  in downstream waters.  Am. Dyest. Rep. 21-25.

Gibson, D.T., J.R. Koch, C.L. Schuld, and R.E. Kallio.  1968.  Oxidative
  degradation of aromatic hydrocarbons by microorganisms.  II.  Metabolism
  of halogenated aromatic hydrocarbons.  Biochemistry 7(11):3795-3802.

Heukelekian, H. and M.C. Rand.  1955.  Biochemical oxygen demand of pure
  organic compounds.  Sewage and Industrial Wastes 27(9):1040-1053.

Laity, J.L., I.G. Burstain, and B.R. Appel.  1973.  Photochemical smog and
  the atmospheric reactions of solvents.  Chap. 7.  pp. 95-112.  Solvents
  Theory and Practice.  R.W. Tess (ed.)  Advances in Chemistry Series 124.
  Am. Chem. Soc., Washington, D.C.

Leo, A., C. Hansch, and D. Elkins.  1971.  Partition coefficients and
  their uses.  Chem. Rev. 71:525-616.

Lu,  P. and R.L. Metcalf.  1975.  Environmental fate and biodegradability of
  benzene derivatives as studied in a model aquatic ecosystem.   Environ.
  Health Perspect. 10:269-284.
                                    72-9

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Mackay, D. and A.W. Wolkoff.  1973.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
   7(7):611-614.

Mackay, D. and P.J. Leinonen.  1975.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  9(13):1178-1180.

Mardsen, C. and S. Marr.  1963.  Solvents guide.  Cleaver-Hume   Press
  Ltd., London.  239p.

Matthews, A.   1924.  Partial sterilization of soil by antiseptics.  J. Agr.
  Sci.  14:1-57.

Morrison, R.T. and R.N. Boyd.  1973.  Organic chemistry.  3rd Edition.
  Allyn and Bacon, Inc., Boston.   1258p.

Neely, W.B., D.R. Branson, and G.E. Blau.  1974.  Partition coefficient  to
  measure bioconcentration potential of organic chemicals in fish.
  Environ. Sci. Technol. 8:1113-1115.

U.S. Environmental Protection Agency.   1975.  Preliminary assessment  of
  suspected carcinogens in drinking water.  U.S. Environmental Protection
  Agency, Office of Toxic Substances, Washington, D.C.  33p.   (EPA
  560/4-75-003).

Verschueren, K.  1977.  Handbook of environmental data  on organic
  chemicals.   Van Nostrand/Reinhold Press, New York.  659p.

Ware,  S.A. and W.L. West.  1977.   Investigation of selected potential
  environmental contaminants:  halogenated benzenes.  U.S. Environmental
  Protection Agency, Office of Toxic Substances, Washington, D.C.   283p.
  EPA  560/2-77-004.

Weast, R.C.   1973.  (ed).  Handbook of  chemistry and physics.  54th
  Edition.  CRC Press,  Inc., Cleveland, Ohio.  2452p.
                                    72-10

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                73.   1,2-DICHLOROBENZENE  (o^DICHLOROBENZENE )


 73.1   Statement  of Probable  Fate

    Based  on the information found,  it is  not  possible  to  determine  the
 predominant aquatic  fate  of  1,2-dichlorobenzene.   There is some  evidence
 that  dichlorobenzenes  in  general  are reactive  toward  hydroxyl  radicals in
 air with a half-life of approximately three  days.   Products  and  further de-
 tails of such  photooxidation reactions,  however, were not  indicated.   In-
 formation  concerning the  biodegradation  potential  of  1,2-dichlorobenzene
 indicates  that  this  compound is very persistent and will probably, at  best,
 be biodegraded  very  slowly by microorganisms already  growing on  another
 hydrocarbon source.

     1,2-Dichlorobenzene has  a high affinity  for lipophilic materials and it
 is reported to  have  a  relatively  low vapor pressure and low  aqueous  solu-
 bility at  ambient temperatures.   Consequently, sorption, bioaccumulation,
 and volatilization are expected to be competing processes.   The  rate at
 which each of  these  competing processes  occur  will determine which fate is
 predominant for 1,2-dichlorobenzene  in the aquatic environment.  Should
 volatilization  occur at a more rapid rate  than sorption or bioaccumulation,
 then  atmospheric processes would  be  expected to regulate the fate of
• 1,2-dichlorobenzene.   On  the other hand, should sorption and bioaccumula-
 tion  occur more rapidly than volatilization, biodegradation  of 1,2-di-
 chlorobenzene  by aquatic  microorganisms  would  be anticipated to  regulate
 the fate of this compound.

 73.2   Identification

     1,2-Dichlorobenzene has  been  detected  in finished drinking water, in
 superchlorinated municipal wastewaters,  in ground  water (U.S.  Environmental
 Protection Agency 1975),  in  wastewater effluent (Glaze  and Henderson 1975),
 and in the atmosphere  (Ware  and West  1977).  The chemical structure of
 1,2-dichlorobenzene  is shown below.
                                             Alternate Names

                                             o-Dichlorobenzene
                                             Orthodichlorobenzene
     1,2-Dichlorobenzene                      Dowtherm E

     CAS NO. 95-50-1
     TSL NO. CZ 45000
                                     73-1

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73.3  Physical Properties

    The general physical properties  of 1,2-dichlorobenzene are given below.

    Molecular weight                        147.01
    (Weast 1977)

    Melting point                            -17.0°C
    (Weast 1977)

    Boiling point at 760 torr                180.5°C
    (Weast 1977)

    Vapor pressure at 25 °C                   1.5 torr*

    Solubility in water at 25°C              145 mg/1
    (Verschueren 1977)

    Log octanol/water partition coefficient  3.38
    (Leo et al. 1971)
*Values for the vapor pressure of 1,2-dichlorobenzene in water were re-
ported to be 1.5 torr at 25°C (Verschueren 1977)  and were calculated to be
1.45 torr from the table of vapor pressures,  critical temperatures and
critical pressures of organic compounds in Weast  (1973).

73.4  Summary of Fate Data

    73.4.1  Photolysis

         No specific information pertaining to the direct photolysis of
1,2-dichlorobenzene in the aquatic or atmospheric environments was found.

    73.4.2  Oxidation

         According to Ware and West (1977) 1,2-dichlorobenzene is resistant
to autooxidation by the peroxy radical (R02*) in  water.  No more de-
tails of this phenomenon were reported.  Dichlorobenzenes in general were
reported by Ware and West (1977) to be reactive toward hydroxyl radicals
(OH') in air with a half-life of approximately three days.  Products and
further details of such photooxidation reactions  were not indicated.
1,2-Dichlorobenzene specifically was reported by  Ware and West (1977) to be
resistant to autooxidation by ozone in air.
                                    73-2

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    73.4,3  Hydrolysis

         No specific information pertaining to the hydrolysis of 1,2-di-
chlorobenzene has been found.  Although Ware and West (1977) report that
the inductive electronegative effect of halogen substitutents on an aromat-
ic ring facilitates attack by nucleophiles such as OH~, Morrison and Boyd
(1973) report that aryl halides are characterized by very low re-
activity toward nucleophilic reagents such as OH~.

         As an example of the difficulty with which aryl halides undergo
nucleophilic substitution, the conditions necessary for the nucleophilic
substitution of hexachlorobenzene to a pentachlorophenyl derivative were re-
ported by Patai (1973) to be the presence of aqueous ammonia at a tempera-
ture of at least 250°C.  On this basis, 1,2-dichlorobenzene, being less
chlorinated and, consequently, less easily attacked by nucleophiles than
hexachlorobenzene, would not be expected to undergo hydrolysis at an
appreciable rate under environmental conditions.

    73.4.4  Volatilization

         Available data on 1,2-dichlorobenzene indicate that this compound
probably volatilizes from the water column to the atmosphere at a rela-
tively rapid rate.  Garrison and Hill (1972) reported that a 100 mg/1 con-
centration of 1,2-dichlorobenzene volatilized almost completely (less than
1 mg/1 of 1,2-dichlorobenzene remained) from aerated distilled water in
less than 4 hours.  The same concentration of 1,2-dichlorobenzene volatil-
ized almost completely (less than 1 mg/1 of 1,2-dichlorobenzene remained)
from unaerated distilled water in less than 3 days.  No further details of
this experiment were reported.  The data of Garrison and Hill (1972) can be
used to calculate approximate values for evaporative half-lives.  For the
aerated solution, the calculated half-life is less than 30 minutes;
however, since the aeration probably caused air-stripping of the 1,2-di-
chlorobenzene, this value is not representative of an evaporative half-life
under conditions of agitation.  The data for unaerated conditions,
apparently close to quiescence, correspond to a half-life of less than
about nine hours.

         According to Mackay and Wolkoff (1973) the rate of evaporation of
pollutants having a low solubility in water can be quite rapid even though
these compounds often have a high molecular weight and a low vapor
pressure, and should, on these bases, evaporate slowly.  Mackay and Wolkoff
(1973) contend that these compounds often have high activity coefficients
in water which cause unexpectedly high equilibrium partial vapor pressures
and thus high rates of evaporation.  Although 1,2-dichlorobenzene  was not
mentioned specifically, other chlorinated hydrocarbons having relatively
low solubility in water were predicted to have somewhat rapid rates of
evaporation.
                                       73-3

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         The published value for the vapor pressure (Verschueren 1977) and
solubility in water (Verschueren 1977) of 1,2-dichlorobenzene at 25°C were
used to compute the Henry constant as being approximately 1.99 x 10~3
atmos. m-Vmole which may be compared to the value of 1.55 x 10"^ atmos.
m-Vmole predicted for biphenyl at 25°C (Mackay and Leinonen 1975).  In
the case of biphenyl, the half-life for evaporation from a water column one
meter thick was estimated by Mackay and Leinonen (1975) to be 7.52 hours at
25°C.  An estimate of the corresponding half-life for evaporation of
1,2-dichlorobenzene under the same conditions would presumably be of the
same order,  at most, approximately 8 or 9 hours.  Mackay and Leinonen
(1975) point out that interpretation of the environmental significance of
the rate of evaporation of compounds such as 1,2-dichlorobenzene from en-
vironmental waters using values calculated at 1 meter depth is dependent
upon the type of environmental situation encountered.  In sitviations where
the water body is turbulent with frequent mixing between the surface layer
and the bulk, as in a rapidly flowing shallow river or during white-capping
on a lake or ocean, the rate of evaporation would be more rapid than for
depths greater than 1 meter or in quiescent water, as exists in a deep,
slowly flowing river.

    73.4.5  Sorption

         Although no specific environmental sorption studies were found in
the literature, the value of the log octanol/water partition coefficient
for 1,2-dichlorobenzene (log P = 3.38, Leo _e_t _al. 1971) indicates that
sorption processes may be substantial for 1,2-dichlorobenzene at pollutant
concentrations anticipated in environmental waters.  Presumably, 1,2-di-
chlorobenzene will be adsorbed by sedimentary organic material;  the extent
to which this possible adsorption will interfere with volatilization has
not been considered.

    73.4.6  Bioaccumulation

         Although no experimental evidence of the bioaccumulation potential
of 1,2-dichlorobenzene was found, there is indirect evidence that 1,2-di-
chlorobenzene has a high potential for bioaccumulation in aquatic organ-
isms.  Neely _e_t al. (1974) and Lu and Metcalf (1975) have shown that the
log octanol/water partition coefficient (log P) correlates well with the
ability of a compound to accumulate in the lipids of tissues of living
organisms.  Furthermore, the incorporation of chlorine into an organic
molecule increases its lipophilic character resulting in an increased
bioaccumulation potential (Kopperman _e_t_ _al_. 1976).  For comparison, chloro-
benzene, a compound containing only one chlorine atom, and 1,2-dichloro-
benzene, a compound having two chlorine atoms, have log P values of 2.84
(Leo _et _al. 1971;  Chiou _e_t al. 1977) and 3.38 (Leo _et _al. 1971), re-
spectively.  Since it has been established experimentally that chloro-
                                    73-4

-------
benzene bioaccumulates in aquatic organisms (Lu and Metcalf 1975), 1,2-di-
chlorobenzene,  would be expected to be bioaccumulated by aquatic organisms
at least as much as chlorobenzene.

    73.4.7  Biotransformation and Biodegradation

         According to Ware and West (1977), the more highly halogenated a
compound becomes, the more resistant it is to biodegradation.   Experimental
(Lu and Metcalf 1975) as well as empirical evidence (Leo et_ £l. 1971; Chiou
et_ a_l.  1977) has been found indicating that chlorobenzene is a persistent
chemical and is not readily biodegraded unless the microorganisms present
are already growing on another hydrocarbon source. Furthermore, Alexander
and Lustigman (1966) found that the presence of a chlorine atom on the ben-
zene ring retarded the rate of biodegradation.  On these bases, 1,2-di-
chlorobenzene,  being more highly chlorinated than chlorobenzene, would
presumably biodegrade at least as slowly as chlorobenzene under the same
conditions of exposure to microorganisms.

         Evidence that 1,2-dichlorobenzene is a persistent chemical is
presented in a study by Thorn and Agg (1975), which lists 1,2-dichloroben-
zene as a synthetic organic chemical which is unlikely to be removed during
biological sewage treatment even after prolonged exposure of the biota. In
contrast, Thorn and Agg (1975) list chlorobenzene, a compound with one less
chlorine atom than 1,2-dichlorobenzene, as a synthetic organic chemical
which should be degradable by biological sewage treatment provided that
suitable acclimatization can be achieved.  Based upon inference 1,2-di-
chlo.robenzene should be resistent to biodegradation; but in the absence of
solid experimental evidence, no definitive conclusion can be reached.

73.5  Data Summary

    There is not enough environmentally significant information on photoly-
sis, oxidation, sorption, or biodegradation processes to be able to predict
the aquatic fate of 1,2-dichlorobenzene.   1,2-Dichlorobenzene has a high
affinity for lipophilic materials and it is reported to have a relatively
low vapor pressure and low solubility at temperatures expected to prevail
in most ambient waters.  Consequently, sorption, bi©accumulation, and
volatilization are expected to be competing processes. The rate at which
each of these competing processes occur will dictate which fate is pre-
dominant for 1,2-dichlorobenzene in the aquatic environment.  These data
are summarized in Table 73-1.
                                     73-5

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                                                     Table  73-1

                            Summary  of  Aqtmtlc Fnle of 1,2-Dichlorobenzene
Environmental
   Process a
              .Summary
             SLatempDt
                                                                  Rate
                                                                                 Half-Life
                                                                           Conf ttlnncp
                                                                             of Data
Photolysis           No information found

Oxidation            1,2-Dichlorobenzene is reported to be
                     resistant to autooxidation by the peroxy
                     radical (ROs-) in water.   Dichlorobenzenes
                     were reported to be reactive toward hydroxyl
                     radicals (OH1) in air.

Hydrolysis           1,2-Dichlorobenzene will  probably not hydro-  -
                     lyze in ambient waters due to the extreme
                     difficulty with which aryl halides undergo
                     nucleophilic substitution.

Volatilization       This compound probably volatilizes from the
                     water column to the atmosphere at a relatively
                     rapid rate.

Sorption             The high log P value found for 1,2-dichloro-  -
                     benzene indicates that sorption processes
                     may be sustantial for this compound at pollu-
                     tant concentrations anticipated in environ-
                     mental waters.
                                                                           Low

                                                           ~3 daysb        Low
                                                                           Medium
                                                      ^8  or  9  hours    a   Medium
                                                      less than 9 hours
                                                                           Low
Bioaccumulation
Empirical evidence indicates that 1,2-di-
chlorobenzene will bioaccumulate in the
lipids of tissues of living organisms.
                                                                                                Low
Biotransformat ion/
  Biodegradation
Will biodegrade, at best,
rate.
                          at a very slow
                                                                           Low
a.   There is insufficient information in the reviewed literature to permit assessment
     of a most probable fate.

b.   This half-life is the reported half-life of dichlorobenzene toward hydroxyl radicals in air
     cited in Ware and West (1977).

c.   This half-life is based on the calculated Henry constant of 1,2-dichlorobenzene which is of
     the same order as the Henry constant predicted for biphenyl at 25°C by Mackay and Leinonen
     (1975) .   Since the half-life for evaporation of biphenyl from a water column one meter thick
     was estimated by Mackay and Leinonen to be 7.52 hours at 25°C, the half-life for evaporation
     of 1,2-dichlorobenzene under the same conditions was assumed to be of the same order, at most,
     approximately 8 or 9 hours.
 d.
     This half-life is the estimated half-life based on the experimental results and conditions of
     Garrison and Hill (1972) in unaerated distilled water.
                                                   73-6

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73.6  Literature Cited

Alexander, M. and B.K. Lustigman.  1966.  Effect of chemical structure on
  microbial degradation of substituted benzenes.  J. Agr. Food Chem.
  14(4):410-413.

Chiou, C.T.,  V.H. Freed, D.W. Schmedding, and R.L. Kohnert.  1977.
  Partition coefficient and bioaccumulation of selected organic chemicals.
  Environ. Sci. Technol.  11(5 ):475-478.

Garrison, A.W. and D.W. Hill.  1972.   Organic pollutants from mill persist
  in downstream waters.  Am. Dyest. Rep. 21-25.

Glaze, W.H. and J.E. Henderson.   1975.  Formation of organochlorine
  compounds from the chlorination of a municipal secondary effluent.   J.
  Water Poll. Cont. Fed.  47(10 ):2511-2515.

Kopperman, H.L., D.W. Kuehl, and G.E. Glass.  1976.  Chlorinated compounds
  found in waste treatment effluents and their capacity to bioaccumulate.
  Proceedings of the conference on the environmental impact of water
  chlorination.  Oak Ridge, Tennessee, October 22-24.  (Preprint only.)

Leo, A., C. Hansch, and D. Elkins.  1971.  Partition coefficients and their
  uses.  Chem. Rev. 71:525-616.

Lu, P. and R.L. Metcalf.  1975.   Environmental fate and biodegradability of
  benzene derivatives as studied in a model aquatic ecosystem.   Environ.
  Health Perspect.  10:269-284.

Mackay, D. and A.W. Wolkoff.  1973.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  7(7):611-614.

Mackay, D. and P.J. Leinonen.  1975.   Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  9(13):1178-1180.

Morrison, R.T. and R.N. Boyd.  1973.   Organic chemistry.  3rd Edition.
  Allyn and Bacon, Inc., Boston.  1258p.

Neely, W.B.,  D.R. Branson, and G.E. Blau.  1974.  Partition coefficient to
  measure bioconcentration potential of organic chemicals in fish.
  Environ. Sci. Technol. 8:1113-1115.

Patai, S.  (ed).  1973.  The chemistry of the carbon-halogen bond:  Part 2.
  John Wiley Interscience, New York.   1215p.
                                     73-7

-------
Thorn, N.S. and A.R. Agg.  1975.  The breakdown of synthetic organic
  compounds in biological processes.  Proc. Roy. Soc. Lond.  B 189:347-357.

U.S. Environmental Protection Agency.  1975.  Preliminary assessment of
  suspected carcinogens in drinking water.  U.S. Environmental Protection
  Agency, Office of Toxic Substances, Washington, D.C.  33p.  EPA
  560/4-75-003.

Verschueren, K.  1977.  Handbook of environmental data on organic
  chemicals.  Van Nostrand/Reinhold Press, New York.  659p.

Ware, S.A. and W.L. West.  1977.  Investigation of selected potential
  environmental contaminants:  halogenated benzenes.  U.S. Environmental
  Protection Agency, Office of Toxic Substances, Washington, D.C.  283p.
  EPA 560/2-77-004.

Weast, R.C. (ed).  1973.  Handbook of chemistry and physics.  54th Edition.
  CRC Press, Inc., Cleveland, Ohio.  2452p.

Weast, R.C. (ed).  1977.  Handbook of chemistry and physics.  58th Edition.
  CRC Press, Inc., Cleveland, Ohio.  2398p.
                                     73-8

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               74.  1.3-DICHLOROBENZENE (m-DICHLOROBENZENE )


74.1  Statement of Probable Fate

    Based on the information found, it is not possible to determine the
predominant aquatic fate of 1,3-dichlorobenzene.  The probable aquatic fate
of this compound can only be inferred from information available on its
more thoroughly studied structural isomers, 1,2- and 1,4-dichlorobenzene,
and from information available on dichlorobenzenes in general.  There is
some evidence that dichlorobenzenes are reactive toward hydroxyl radicals
in air with a half-life of approximately three days.  Products and further
details of such photooxidation reactions, however, were not indicated.
Information concerning the biodegradation potential of 1,3-dichlorobenzene
indicates that this compound is very persistent and will probably, at best,
be biodegraded only very slowly by microorganisms already growing on
another hydrocarbon source.

    1,3-Dichlorobenzene has a high affinity for lipophilic materials, a
relatively low vapor pressure, and low aqueous solubility at ambient
temperatures.  Consequently, sorption, bioaccumulation, and volatilization
are expected to be competing processes.  The rate at which each of these
competing processes occurs will determine which fate is predominant for
1,3-dichlorobenzene in the aquatic environment.  Should volatilization
occur at a more rapid rate than sorption or bioaccumulation, then
atmospheric processes would be expected to regulate the fate of 1,3-
dichlorobenzene.  On the other hand, should sorption and bioaccumulation
occur more rapidly than volatilization, biodegradation of 1,3-dichloro-
benzene by aquatic microorganisms would be anticipated to control the fate
of this compound.

74.2  Identification

    1,3-Dichlorobenzene has been detected in drinking water and ground
water (U.S. Environmental Protection Agency 1975).  The chemical structure
of 1,3-dichlorobenzene is shown below.
                  C\                         Alternate Names
    1,3-Dichlorobenzene                      m-Dichlorobenzene
                                             Metadichlorobenzene
    CAS NO. 541-73-1
    TSL NO. None Assigned
                                    74-1

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74.3  Physical Properties

    The general physical properties of 1,3-dichlorobenzene are given below.

    Molecular weight                         147.01
    (Weast 1977)

    Melting point                            -24.7°C
    (Weast 1977)

    Boiling point at 760 torr                173°C
    (Weast 1977)

    Vapor pressure at 25°C                   2.28 torr*
    (Weast 1973)

    Solubility in water at 25°C              123 mg/1
    (Verschueren 1977)

    Log octanol/water partition coefficient  3.38
    (Leo et al. 1971)
*This vapor pressure was calculated from the table of vapor pressures,
critical temperatures and critical pressures of organic compounds in Weast
(1973).

74.4  Summary of Fate Data

    74.4.1  Photolysis

         No specific information pertaining to the direct photolysis of
1,3-dichlorobenzene in the aquatic or atmospheric environments was found.

    74.4.2  Oxidation

         No specific information pertaining to the oxidation of 1,3-di-
chlorobenzene in ambient waters was found.

         Dichlorobenzenes in general were reported by Ware and West (1977)
to be reactive toward hydroxyl radicals (OH*) in air with a half-life of
approximately three days.  Products and further details of such photooxida-
tion reactions were not indicated.

    74.4.3  Hydrolysis

         No specific information pertaining to the hydrolysis of 1,3-di-
chlorobenzene in ambient waters was found.   Although Ware and West (1977)
report that the inductive electronegative effect of halogen substitu-
                                     74-2

-------
ents on the benzene ring facilitates attack by nucleophiles such as OH~~,
Morrison and Boyd (1973) report that aryl halides will undergo nucleophilic
substitution only with extreme difficulty.  For example, Patai (1973) re-
ported that the minimum conditions necessary for the nucleophilic substitu-
tion of hexachlorobenzene to a pentachlorophenyl derivative were the
presence of aqueous ammonia and a temperature of at least 250°C.  On these
bases, 1,3-dichlorobenzene, being less chlorinated and, consequently, less
easily attacked by nucleophiles than hexachlorobenzene, would not be anti-
cipated to undergo hydrolysis at an appreciable rate under environmental
conditions.

    74.4.4  Volatilization

         Garrison and Hill (1972) found that chlorobenzene, 1,2-dichloro-
benzene, 1,4-dichlorobenzene, and 1,2,4-trichlorobenzene volatilized almost
completely (less than one mg/1 of the compounds remained) from aerated
distilled water in less than four hours.  Initial concentrations of the
compounds were 300 mg/1, 100 mg/1, 300 mg/1, and 100 mg/1, respectively.
The same concentrations of the four chlorinated benzenes volatilized from
unaerated distilled water in less than three days.  1,2,4-Trichlorobenzene
disappeared from unaerated distilled water in less than two days.  Pre-
sumably, 1,3-dichlorobenzene under similar conditions would volatilize at a
similar rate.

         According to Mackay and Wolkoff (1973) the rate of evaporation of
pollutants having a low solubility in water can be quite rapid even though
these compounds often have a high molecular weight and a low vapor pres-
sure, and should, on these bases, evaporate slowly.  Mackay and Wolkoff
(1973) contend that these compounds often have high activity coefficients
in water which cause unexpectedly high equilibrium partial vapor pressures
and thus high rates of evaporation.  Although 1,3-dichlorobenzene, which
has a reasonably low vapor pressure of 2.28 torr (calculated from Weast
1973) and a low solubility in water of 123 mg/1 at 25°C (Verschueren 1977)
was not mentioned specifically, other chlorinated hydrocarbons having a low
solubility in water and a low vapor pressure were predicted to have rela-
tively rapid rates of evaporation.  Presumably, 1,3-dichlorobenzene would
have a rate of evaporation similar to these chlorinated compounds having
vapor pressure and solubility values approximately equal to those values
for 1,3-dichlorobenzene.

         The calculated value for the vapor pressure (Weast 1973) and the
published value for the solubility in water (Verschueren 1977) of 1,3-di-
chlorobenzene at 25°C were used to compute the Henry constant as being
approximately 3.58 x 10~3 atmos. ra-Vraole, which may be compared to the
value of 3.51 x 10"^ atmos. m-^/mole predicted for Aroclor 1248
                                    74-3

-------
at 25°C (Mackay and Leinonen 1975).  In the case of Aroclor 1248, the
half-life for evaporation from a water column one meter thick was estimated
by Mackay and Leinonen (1975) to be 9.53 hours at 25°C.  The corresponding
half-life for evaporation of 1,3-dichlorobenzene under the same conditions
would presumably be of the same order, at most, approximately 10 or 11
hours.   Mackay and Leinonen (1975) point out that interpretation of the en-
vironmental significance of the rate of evaporation of compounds such as
1,3-dichlorobenzene from environmental waters using values calculated at 1
meter depth is dependent upon the type of environmental situation en-
countered.  In situations where the water body is turbulent with frequent
mixing between the surface layer and the bulk, as in a rapidly flowing
shallow river or during white-capping on a lake or ocean, the rate of
evaporation would be more rapid than for depths greater than 1 meter or in
quiescent water, as evidenced in a deep, slowly flowing river.

    74.4.5  Sorption

         Although no specific environmental sorption studies were found in
the literature, the value of the log octanol/water partition coefficient
found for 1,3-dichlorobenzene (log P = 3.38, Leo et_jl. 1971) indicates
that sorption processes may be substantial for 1,3-dichlorobenzene at
pollutant concentrations anticipated in environmental waters.   Presumably,
1,3-dichlorobenzene will be adsorbed by sedimentary organic material;  the
extent to which this possible adsorption will interfere with volatilization
has not been considered.

    74.4.6  Bioaccumulation

         Although no experimental evidence of the bioaccumulation potential
of 1,3-dichlorobenzene was found, there is empirical evidence that 1,3-di-
chlorobenzene has a high potential for bioaccumulation in aquatic organ-
isms.  Neely et_ jJ.. (1974) and Lu and Metcalf (1975) have shown that the
log octanol/water partition coefficient (log P) correlates well with the
ability of a compound to accumulate in the lipids of tissues of living
organisms.  Furthermore, the incorporation of chlorine into an organic
molecule increases its lipophilic character resulting in an increased
bioaccumulation potential (Kopperman e_t_ _a_l. 1976).  For comparison,
chlorobenzene, a compound containing only one chlorine atom, and 1,3-di-
chlorobenzene, a compound having two chlorine atoms, have log P values of
2.84 (Leo et_ a_l. 1971;  Chiou et_ _al.  1977) and 3.38 (Leo et_ al. 1971), re-
spectively.  Since it has been established experimentally that chloro-
benzene bioaccumulates in aquatic organisms (Lu and Metcalf 1975), 1,3-di-
chlorobenzene would be expected to be bioaccumulated by aquatic organisms
at least as much as chlorobenzene.
                                     74-4

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    74.4.7  Biotrans format ion and Biodegradation

         According to Ware and West (1977), the more highly halogenated a-
compound becomes,  the more resistant it is to biodegradation.   Experimental
(Lu and Metcalf 1975) as well as empirical evidence (Leo et al.  1971; Chiou
et_ al_.  1977) has been found indicating that chlorobenzene is a persistent
chemical and is not readily biodegraded unless the microorganisms present
are already growing on another hydrocarbon source. Furthermore,  Alexander
and Lustigman (1966) found that the presence of a chlorine atom on the ben-
zene ring retarded the rate of biodegradation.  On these bases,  1,3-di-
chlorobenzene,  being more highly chlorinated than chlorobenzene, would
presumably biodegrade at least as slowly as chlorobenzene under the same
conditions of exposure to microorganisms.

         Evidence that 1,3-dichlorobenzene is a persistent chemical is
presented in a study by Thorn and Agg (1975), which lists 1,3-dichloro-
benzene as a synthetic organic chemical which is unlikely to be removed
during biological sewage treatment, even after prolonged exposure of the
biota.   In contrast, Thorn and Agg (1975) list chlorobenzene, a compound
with one less chlorine atom than 1,3-dichlorobenzene, as a synthetic
organic chemical which should be degradable by biological sewage treatment
provided that suitable acclimatization can be achieved.  Based upon
inference 1,3-dichlorobenzene should be resistant to biodegradation but in
the absence of solid experimental evidence, no definitive conclusions can
be reached or its biodegradability.

74.5  Data Summary

    There is not enough environmentally significant information on pho-
tolysis, oxidation, sorption, or biodegradation processes to be able to
predict the aquatic fate of 1,3-dichlorobenzene.  1,3-Dichlorobenzene has a
high affinity for lipophilic materials and is reported to have a relatively
low vapor pressure and low solubility at temperatures expected to prevail
in most ambient waters.  Consequently, sorption, bioaccumulation, and
volatilization are expected to be competing processes. The rate at which
each of these competing processes occur will dictate which fate is
predominant for 1 , 3-dichlorobenzene in the aquatic environment.   These data
are summarized in Table 74-1.
                                       74-5

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                                                   Table 74-1

                            Summary of Aquatic Fate of 1,3-Dichlorobenzene
Environmental               Summary
   Processa               Statement

Photolysis           No information found.

Oxidation            Dichlorobenzenes in
                     general were reported to
                     be reactive toward hydroxyl
                     radicals (OH-) in air.

Hydrolysis           1,3-Dichlorobenzene will
                     probably not hydrolyze
                     in ambient waters due
                     to the extreme difficulty
                     with which aryl  halides
                     undergo nucleophilic sub-
                     stitution.

Volatilization       This compound probably
                     volatilizes from the
                     water column to  the
                     atmosphere at a  relatively
                     rapid rate.

Sorption             The high log P value found
                     for 1,3-dichlorobenzene in-
                     dicates that sorption  pro-
                     cesses may be substantial
                     for this compound at pollutant
                     concentrations anticipated in
                     environmental waters.
                                                          Rate
                                                                     Half-Life
                                                                        daysn
                                                          Confidence
                                                            of Data
                                                                                     Medium
                                                                     MO  or  more
                                                                      hours0
                                                          Medium
                                                                                     Medium
      Bioaccumulation
                           Empirical evidence indicates
                           that 1,3-dichlorobenzene will
                           bioaccumulate in the lipids of
                           tissues of living organisms.
                                                                                     Medium
      Bio trans formation/
        Biodegradation
Will biodegrade, at best, at
a very slow rate.
                                                                                     Low
a.  There is insufficient  information in  the reviewed  literature  to  permit  assessment
    of a most probable fate.

b.  This half-life is the  reported half-life of  dichlorobenzenes  toward  hydroxyl  radicals in
    air cited in Ware and  West  (1977).

c.  This half-life is based  on  the calculated Henry constant  of 1,3-dichlorobenzene which is of
    the same order as the  Henry constant  predicted  for Aroclor  1248  at 25°C by  Mackay  and Leinonen
    (1975).   Since the half-life for-evaporation of Aroclor 1248  from a  water column one  meter thick
    was estimated by Mackay  and Leinonen  to  be 9.53 hours  at  25°C, the half-life  for evaporation of
    1,3-dichlorobenzene under  the same  conditions was  assumed to  be  of the  same order, or approxi-
    mately 10 or more hours.
                                                    74-6

-------
74.6  Literature Cited

Alexander, M. and B.K. Lustigman.  1966.  Effect of chemical structure on
  microbial degradation of substituted benzenes.  J. Agr. Food Chem.
   14(4):410-413.

Chiou, C.T.,  V.H. Freed, D.W. Schmedding, and R.L. Kohnert.  1977.
  Partition coefficient and bioaccunmlation of selected organic chemicals.
  Environ. Sci. Technol.  11(5):475-478.

Garrison, A.W. and D.W. Hill.  1972.  Organic pollutants from mill persist
  in downstream waters.  Am. Dyest. Rep. 21-25.

Kopperman, H.L., D.W. Kuehl, and G.E. Glass.  1976.  Chlorinated compounds
  found in waste treatment effluents and their capacity to bioaccumulate.
  Proceedings of the conference on the environmental impact of water
  chlorination.  Oak Ridge, Tennessee, October 22-24.  (Preprint only).

Leo, A., C. Hansch, and D. Elkins.  1971.  Partition coefficients and their
  uses.  Chem. Rev. 71:525-616.

Lu, P. and R.L. Metcalf.  1975.  Environmental fate and biodegradability of
  benzene derivatives as studied in a model aquatic ecosystem.   Environ.
 Health Perspect.  10:269-284.

Mackay, D. and A.W. Wolkoff.  1973.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  7(7):611-614.

Mackay, D. and P.J. Leinonen.  1975.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  9(13):1178-1180.

Morrison, R.T. and R.N. Boyd.  1973.  Organic chemistry.  3rd Edition.
  Allyn and Bacon, Inc., Boston.   1258p.

Neely, W.B.,  D.R. Branson, and G.E. Blau.  1974.  Partition coefficient to
  measure bioconcentration potential of organic chemicals in fish.
  Environ. Sci. Technol. 8:1113-1115.

Patai, S.  (ed).  1973.  The chemistry of the carbon-halogen bond:  Part 2.
  John Wiley Interscience, New York.  1215p.

Thorn, N.S. and A.R. Agg.  1975.  The breakdown of synthetic organic
  compounds in biological processes.  Proc. Roy. Soc. Lond. B 189:347-357.
                                     74-7

-------
U.S. Environmental Protection Agency.  1975.  Preliminary assessment of
  suspected carcinogens in drinking water.  U.S. Environmental Protection
  Agency, Office of Toxic Substances, Washington, B.C.  33p.  EPA
  560/4-75-003.

Verschueren, K.  1977.  Handbook of environmental data on organic
  chemicals.  Van Nostrand/Reinhold Press, New York.  659p.

Ware, S.A. and W.L. West.  1977.  Investigation of selected potential
  environmental contaminants:  halogenated benzenes.  U.S. Environmental
  Protection Agency, Office of Toxic Substances, Washington, D.C.  283p.
  EPA 560/2-77-004.

Weast, R.C. (ed).  1973.  Handbook of chemistry and physics.  54th Edition.
  CRC Press, Inc., Cleveland, Ohio.  2452p.

Weast, R.C. (ed).  1977.  Handbook of chemistry and physics.  58th Edition.
  CRC Press, Inc., Cleveland, Ohio.  2398p.
                                     74-8

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               75.  1,4-DICHLQRQBENZENE (_p_-DICHLOROBENZENE )


75.1  Statement of Probable Fate

    Based on the information found, it is not possible to determine the
predominant aquatic fate of 1,4-dichlorobenzene.  There is some evidence
that dichlorobenzenes in general are reactive toward hydroxyl radicals in
air with a half-life of approximately three days. Products and further de-
tails of such photooxidation reactions, however, were not indicated.  In-
formation concerning the biodegradation potential of 1,4-dichlorobenzene
indicates that this compound is very persistent and will probably, at best,
be biodegraded very slowly by microorganisms already growing on another
hydrocarbon source.

    1,4-Dichlorobenzene has a high affinity for lipophilic materials, have
a relatively low aqueous solubility and low vapor pressure at ambient
temperatures.  Consequently, sorption, bioaccumulation,  and volatilization
are expected to be competing processes. The rate at which each of these
competing processes occur will determine which fate is predominant for
1,4-dichlorobenzene in  the aquatic environment.  Should volatilization
occur at a more rapid rate than sorption or bioaccumulation, then atmo-
spheric processes would be expected to regulate the fate of 1,4-dichloro-
benzene.  On the other  hand, should sorption and bioaccumulation occur more
rapidly than volatilization, biodegradation of 1,4-dichlorobenzene by
aquatic microorganisms  would be anticipated to regulate  the fate of this
compound.

75.2  Identification

    1,4-Dichlorobenzene has been detected in drinking water, in superchlo-
rinated municipal wastewaters,  in ground water (U.S. Environmental Protec-
tion Agency 1975), in wastewater effluent (Glaze and Henderson 1975), and
in the atmosphere (Ware and West 1977).  The chemical structure of
1,4-dichlorobenzene is  shown below.
                                             Alternate Names

                                             p-Dichlorobenzene
                                             Paradichlorobenzene
              Cl
     1,4-Dichlorobenzene

     CAS NO.  106-46-7
     TSL NO.  CZ 45500
                                      75-1

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75.3  Physical Properties

    The general physical properties of 1,4-dichlorobenzene are given below.

    Molecular weight                        147.01
    (Weast 1977)

    Melting point                            53.1°C
    (Weast 1977)

    Boiling point at 760 torr                174°C
    (Weast 1977)

    Vapor pressure at 25°C                   *

    Solubility in water at 25°C              79 mg/1
    (Verschueren 1977)

    Log octanol/water partition              3.39
    coefficient (Leo et. al. 1971;
    Chiou et al. 1977)
*T,he value of the vapor pressure of 1,4-dichlorobenzene at 25°C was ob-
tained by interpolation from the values at 20°C (0.6 torr) and 30°C (1.8
torr) from Gray (1957). The value at 25°C was calculated to be 1.18 torr.
For further explanation, see Methods section.

75.4  Summary of Fate Data

    75.4.1  Photolysis

         No specific information pertaining to the direct photolysis of
1,4-dichlorobenzene in the aquatic or atmospheric environments was found.

    75.4.2  Oxidation

         According to Ware and West (1977) 1,4-dichlorobenzene is resistant
to autooxidation by the peroxy radical (RC>2') in water.  No more de-
tails of this phenomenon were reported.

         Dichlorobenzenes in general were reported by Ware and West (1977)
to be reactive toward hydroxyl radicals (OH*) in air with a half-life of
approximately three days.  Products and further details of such photooxida-
tion reactions were not indicated.  1,4-Dichlorobenzene, specifically, was
reported by Ware and West (1977) to be resistant to autooxidacion by ozone
in air.
                                     75-2

-------
    75.4.3  Hydrolysis

         No specific information pertaining to the hydrolysis of 1,4-di-
chlorobenzene has been found.  Although Ware and West (1977) report that
the inductive electronegative effect of halogen substituents activates the
ring making such compounds more easily attacked by nucleophiles such as
OH~, Morrison and Boyd (1973) report that aryl halides are characterized
by very low reactivity toward nucleophilic reagents such as OH~.  As an
example of the difficulty with which aryl halides undergo nucleophilic sub-
stitution, the conditions necessary for the nucleophilic substitution of
hexachlorobenzene to a pentachlorophenyl derivative were reported by Patai
(1973) to be the presence of aqueous ammonia at a temperature of at least
250°C.  On these bases,-1,4-dichlorobenzene, being less chlorinated and,
consequently, less easily attacked by nucleophiles than hexachlorobenzene,
would not be expected to undergo hydrolysis at an appreciable rate under
environmental conditions.

    75.4.4  Volatilization

         Available data on 1,4-dichlorobenzene indicate that this compound
probably volatilizes from the water column to the atmosphere at a rela-
tively rapid rate.  Garrison and Hill (1972) reported that a 300 mg/1
concentration of 1,4-dichlorobenzene volatilized almost completely (less
than 1 mg/1 of 1,4-dichlorobenzene remained) from  aerated distilled water
in less than 4 hours.  The same concentration of 1,4-dichlorobenzene
volatilized almost completely (less than 1 mg/1 of 1,4-dichlorobenzene re-
mained) from unaerated distilled water in less than 3 days.  No further de-
tails of this experiment were reported.  The data of Garrison and Hill
(1972) can be used to calculate approximate values for evaporative half-
lives.  For the aerated solution, the calculated half-life is less than 30
minutes;  however, since the aeration probably caused air-stripping of the
1,4-dichlorobenzene, this value is not recommended as an evaporative half-
life under conditions of agitation.  The data for unaerated conditions,
apparently close to quiescence, correspond to a half-life of less than
about nine hours.

         According to Mackay and Wolkoff (1973) the rate of evaporation of
pollutants having a low solubility in water can be quite rapid even though
these compounds often have a high molecular weight and a low vapor pres-
sure, and should, on these bases, evaporate slowly.  Mackay and Wolkoff
(1973) contend that these compounds often have high activity coefficients
in water which cause unexpectedly high equilibrium partial vapor pressures
and thus high rates of evaporation.  Although 1,4-dichlorobenzene, which
has a moderately low vapor pressure (1.18 torr) and a low solubility in
water of 79 mg/1 at 25°C (Verschueren 1977) was not mentioned specifically,
other chlorinated hydrocarbons having a low solubility in water were pre-
dicted to have relatively rapid rates of evaporation.  Presumably, 1,4-
                                     75-3

-------
dichlorobenzene would have a rate of evaporation similar to those chlor-
inated compounds having vapor pressure and solubility values approximately
equal to those values for 1,4-dichlorobenzene.

         The calculated value for the vapor pressure (Gray 1957) and
published value for the solubility in water (Verschueren 1977) of 1,4-di-
chlorobenzene were used to compute the Henry constant as being approxi-
mately 2.88 x 10~3 atmos. m-Vmole which may be compared to the value of
2.76 x 10~~3 atmos. m^/mole predicted for Aroclor 1254 at 25°C (Mackay
and Leinonen 1975).  In the case of Aroclor 1254, the half-life for
evaporation from a water column one meter thick was estimated by Mackay and
Leinonen (1975) to be 10.3 hours at 25°C.  An estimate of the corresponding
half-life for evaporation of 1,4-dichlorobenzene under the same conditions
would presumably be of the same order, approximately 11 or more hours.
Mackay and Leinonen (1975) point out that interpretation of the environ-
mental significance of the rate of evaporation of compounds such as 1,4-
dichlorobenzene from environmental waters using values calculated at 1
meter depth is dependent upon the type of environmental situation en-
countered.  In situations where the water body is turbulent with frequent
mixing between the surface layer and the bulk, as in a rapidly flowing
shallow river or during white-capping on a lake or ocean, the rate of
evaporation would be more rapid than for depths greater than 1 meter or in
quiescent water, as exists in a deep, slowly flowing river.

    75.4.5  Sorption

         Although no specific environmental sorption studies were found in
the literature, the value of the log octanol/water partition coefficient
for 1,4-dichlorobenzene (log P = 3.39, Leo _e_t a_l. 1971) indicates that
sorption processes may be substantial for 1,4-dichlorobenzene at pollutant
concentrations anticipated in environmental waters.  Presumably, 1,4-di-
chlorobenzene will be adsorbed by sedimentary organic material; the ex-
tent to which this possible adsorption will interfere with volatilization
has not been considered.

    75.4.6  Bioaccumulation

         Although no experimental evidence of the bioaccumulation potential
of 1,4-dichlorobenzene was found, there  is empirical evidence that 1,4-
dichlorobenzene has a high potential for bioaccumulation in aquatic organ-
isms.  Neely _e_t _al, (1974) and Lu and Metcalf (1975) have shown that the
log octanol/water partition coefficient  (log P) correlates well with the
ability of a compound to accumulate in the lipids of tissues of living
organisms.   Furthermore, the incorporation of chlorine into an organic
molecule increases its lipophilic character resulting in an increased
bioaccumulation potential (Kopperman et  al. 1976).  For comparison, chloro-
benzene, a compound containing only one  chlorine atom, and 1,4-dichloro-
                                    75-4

-------
benzene, a compound having two chlorine atoms, have log P values of 2.84
(Leo _et _al. 1971; Chiou ejt _al. 1977) and 3.39 (Leo _et _al. 1971), respec-
tively.  Since it has been established experimentally that chlorobenzene
bioaccumulates in aquatic organisms (Lu and Metcalf 1975), 1,4-dichloro-
benzene, would be expected to be bioaccumulated by aquatic organisms at
least as much as chlorobenzene.

    75.4.7  Biotransformation and Biodegradation

         According to Ware and West (1977), the more highly halogenated a
compound becomes, the more resistant it is to biodegradation.  Experimental
(Lu and Metcalf 1975) as well as empirical evidence (Leo et al. 1971; Chiou
_e_t jj. 1977) has been found indicating that chlorobenzene is a persistent
chemical and is not readily biodegraded unless the microorganisms present
are already growing on another hydrocarbon source.  Furthermore, Alexander
and Lustigman (1966) found that the presence of a chlorine atom on the ben-
zene ring retarded the rate of biodegradation.  On these bases, 1,4-di-
chlorobenzene, being more highly chlorinated than chlorobenzene, would
presumably biodegrade at least as slowly as chlorobenzene under the same
conditions of exposure to microorganisms.

         Evidence that 1,4-dichlorobenzene is a persistent chemical is
presented in a study by Thorn and Agg (1975) which lists 1,4-dichlorobenzene
as a synthetic organic chemical which is unlikely to be removed during
biological sewage treatment, e-ven after prolonged exposure of the biota.
In contrast, Thorn and Agg (1975) list chlorobenzene, a compound with one
less chlorine atom than 1,4-dichlorobenzene, as a synthetic organic
chemical which should be degradable by biological sewage treatment provided
that suitable acclimatization can be achieved.  Based upon inference
1,4-dichlorobenzene should be resistant to biodegradation but in the
absence of solid experimental evidence no definite conclusions can be
reached on its biodegradability.

75.5  Data Summary

    There is not enough environmentally significant information on photoly-
sis, oxidation, sorption, or biodegradation processes to be able to predict
the fate of 1,4-dichlorobenzene.  1,4-Dichlorobenzene has a high affinity
for lipophilic materials, yet it is reported to have a relatively low vapor
pressure and low solubility at temperatures expected to prevail in most
ambient waters.  Consequently, sorption, bioaccumulation, and volatiliza-
tion are expected to be competing processes. The rate at which each of
these competing processes occur will dictate which fate is predominant for
1,4-dichlorobenzene in the aquatic environment.  These data are summarized
in Table 75-1.
                                    75-5

-------
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75.6  Literature Cited

Alexander, M. and B.K. Lustigman.  1966.  Effect of chemical structure on
  microbial degradation of substituted benzenes.  J. Agr. Food Chem.
  14(4):410-413.

Chiou, C.T., V.H. Freed, D.W. Schmedding, and R.L. Kohnert.  1977.
  Partition coefficient and bioaccumulation of selected organic chemicals.
  Environ. Sci. Technol.  11(5) :475-478.

Garrison, A.W. and D.W. Hill.  1972.  Organic pollutants from mill persist
  in downstream waters.  Am. Dyes. Rep. 21-25.

Glaze, W.H. and J.E. Henderson.  1975.  Formation of organochlorine
  compounds from the chlorination of a municipal secondary effluent.   J.
  Water Poll. Cont. Fed.  47(10) :2511-2515.

Gray, D.E. (ed.).  1957.  American institute of physics handbook.
  McGraw-Hill, New York. 2052p.

Kopperman, H.L., D.W. Kuehl, and G.E. Glass.  1976.  Chlorinated compounds
  found in waste treatment effluents and their capacity to bioaccumulate.
  Proceedings of the conference on the environmental impact of water
  chlorination.  Oak Ridge, Tennessee, October 22-24.  (Preprint only).

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

Lu, P. and R.L. Metcalf.  1975.  Environmental fate and biodegradability of
  benzene derivatives as studied in a model aquatic ecosystem.   Environ.
  Health Perspect.  10:269-284.

Mackay, D. and A.W. Wolkoff.  1973.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  7(7):1178-1180.
Mackay, D. and P.J. Leinonen.  1975.  Rate of evaporation of low-solubility
  contaminants from water bodies to atmosphere.  Environ. Sci. Technol.
  9(13):1178-1180.

Morrison, R.T. and R.N. Boyd.  1973.  Organic chemistry.  3rd Edition.
  Allyn and Bacon, Inc., Boston.  1258p.

Neely, W.B., D.R. Branson, and G.E. Blau.  1974.  Partition coefficient to
  measure bioconcentration potential of organic chemicals in fish.
  Environ. Sci. Technol. 8:1113-1115.
                                    75-7

-------
Patai, S.  (ed).  1973.  The chemistry of the carbon-halogen bond:  part 2.
  John Wiley Interscience, New York.  1215p.

Thorn, N.S. and A.R.  Agg.  1975.  The breakdown of synthetic organic
  compounds in biological processes.  Proc.  Roy. Soc. Lond. B 189:347-357.

U.S. Environmental Protection Agency.  1975.   Preliminary assessment of
  suspected carcinogens in drinking water.  U.S. Environmental Protection
  Agency, Office of Toxic Substances, Washington, D.C.  33p.  EPA
  560/4-75-003.

Verschueren, K.  1977.  Handbook of environmental data on organic
  chemicals.  Van Nostrand/Reinhold Press, New York.  659p.

Ware, S.A. and W.L.  West.  1977.  Investigation of selected potential
  environmental contaminants:  halogenated benzenes.  U.S. Environmental
  Protection Agency, Office of Toxic Substances, Washington, D.C.  283p.
  EPA 560/2-77-004.

Weast, R.C. (ed).  1977.  Handbook of chemistry and physics,.  58th Edition.
  CRC Press Inc., Cleveland, Ohio.  2398p.
                                    75-8

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                        76.   1,2,4-TRICHLOROBENZENE
76.1  Statement of Probable Fate

    1,2,4-Trichlorobenzene has a high affinity for lipophilic materials and
is reported to exhibit a relatively high rate of volatilization from aque-
ous systems.   Consequently, sorption, bioaccumulation,  and volatilization
are anticipated to be competing processes.   The rates at which these com-
peting processes occur will determine which fate is predominant for 1,2,4-
trichlorobenzene in the aquatic environment, but the data found were
insufficient  to determine the most rapid process.   Should volatilization
occur at a more rapid rate than sorption or bioaccumulation,  then atmo-
spheric processes would be expected to regulate the fate of 1,2,4-tri-
chlorobenzene.  On the other hand, should sorption and  bioaccumulation
occur more rapidly than volatilization,  biodegradation  of 1,2,4-tri-
chlorobenzene by aquatic microorganisms  would be anticipated  to regulate
the fate of this compound.

76.2  Identification

    1,2,4-Trichlorobenzene has been detected in drinking water (U.S. En-
vironmental Protection Agency 1975), in  wastewater effluent (Glaze and
Henderson 1975), and in the atmosphere (Ware and West 1977).   The chemical
structure of  1,2,4-trichlorobenzene is shown below.
                                             Alternate Name
                                             unsym-Trichlorobenzene
    1,2,4-Trichlorobenzene

    CAS NO. 120-82-1
    TSL NO. DC 21000

76.3  Physical Properties

    The general physical properties of 1,2,4-trichlorobenzene are as
follows.
    Molecular weight
    (Weast 1977)

    Melting point
    (Weast 1977)
181.45
16.95°C
                                     76-1

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    Boiling point at 760 torr
    (Weast 1977)

    Vapor pressure at 25°C

    Solubility in water at 25°C
    (Dow 1978)
213.5°C


0.42 torr (calculated)

30 mg/1
    Log octanol/water partition coefficient  4.26
    (Calculated from Tute 1971;  See
    Methods section on Bioaccumulation)

76.4  Summary of Fate Data

    76.4.1  Photolysis

         No specific information pertaining to the direct photolysis of
1,2,4-trichlorobenzene in the aquatic or atmospheric environments was
fo und .

    76.4.2  Oxidation

         No specific information pertaining to the oxidation of 1,2,4-tri-
chlorobenzene in the aquatic environment was found.  1,2,4-Trichloroben-
zene, however, was reported by Simmons et al.  (1976) to  be susceptible to
attack by hydroxyl radicals in the atmosphere.  The rate of this react'ion
is  not known, but the half-life was estimated  by Simmons _e_t _a_l_. (1976) to
be  one to several days.

    76.4.3  Hydrolysis

         No specific information pertaining to the hydrolysis of 1,2,4-tri-
chlorobenzene in ambient waters was found.  Although Ware and West (1977)
report that the inductive electronegative effect of halogen substitutents
activates the ring making such compounds more easily attacked by nucle-
ophiles such as OH~, Morrison and Boyd (1973)  report that aryl halides
will undergo nucleophilic substitution only with extreme difficulty.  For
example, Patai (1973) reported that the minimum conditions necessary for
the nucleophilic subtitution of hexachlorobenzene to a pentachlorophenyl
derivative were the presence of aqueous ammonia and a temperature of 250°C.
On these bases, 1,2,4-trichlorobenzene, being less chlorinated and, con-
sequently, less easily attacked by nucleophiles than hexachlorobenzene,
would not be expected to undergo hydrolysis at an appreciable rate under
environmental conditions.

    76.4.4  Volatilization

         Available data on 1,2,4-trichlorobenzene indicate that this com-
pound probably volatilizes from the water column to the atmosphere at a
                                       76-2

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relatively rapid rate.  Ware and West (1977) cited information in which the
half-life for evaporation of 1,2,4-trichlorobenzene from water is 45
minutes at standard temperature and pressure.  Garrison and Hill (1972) re-
ported that at 100 mg/1 1,2,4-trichlorobenzene volatilized almost
completely (less than 1 mg/1 of 1,2,4-trichlorobenzene remained) from
aerated distilled water in less than 4 hours.  The same concentration of
1,2,4-trichlorobenzene volatilized almost completely (less than 1 mg/1 of
1,2,4-trichlorobenzene remained) from unaerated distilled water in less
than 2 days.   No further details of this experiment were reported.

         Assuming that volatilization as reported by Garrison and Hill
(1972) is a first order process, then the evaporative half-lives corres-
ponding to the above data are 36 minutes for the aerated condition and 7.2
hours for the unaerated (quiescent) condition.  The evaporation half-life
of 45 minutes cited by Ware and West (1977) is very close to the 36 minutes
resulting from aeration;  aeration is assumed to have involved some gas
stripping of  the 1,2,4-trichlorobenzene from the solution.

         In a separate experiment by Garrison and Hill (1972) an aqueous
solution of 1,2,4-trichlorobenzene (50 mg/1) was exposed to mixed cultures
of aerobic microorganisms and aerated.  Based on the graphical
representation of the data by Garrison and Hill (1972) and assuming a
negligible rate of biodegradation in comparison to volatilization (no
degradation products were found), the evaporative half-life for the
1,2,4-trichlorobenzene in this system appears to be on the order of 4 to 5
hours.  A measurable concentration of the compound was detected after nine
days of exposure.  In this experiment, the half-life with respect to
volatilization is reasonably close to the 7.2 hours cited above for the
quiescent condition in distilled water.  It is believed that this result
illustrates the effect of partitioning of 1,2,4-trichlorobenzene between
the water and suspended biological material.

         In summary, the rate of volatilization of 1,2,4-trichlorobenzene
from distilled water is relatively high, but, when suspended organic
materials are present, the partitioning between water and" suspended solids
can greatly reduce the volatilization rate.

    76.4.5  Sorption

         Although no specific environmental sorption studies were found in
the literature, the calculated value of the log octanol/water partition
coefficient found for 1,2,4-trichlorobenzene (log P = 4.26, Tute 1971)
indicates that sorption processes, may be substantial for this compound at
pollutant concentrations anticipated in environmental waters.  Presumably,
1,2,4-trichlorobenzene will be adsorbed by sedimentary organic material;
the extent to which this possible adsorption will interfere with
volatilization has not been studied.
                                    76-3

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    76.4.6  Bioaccumulation

         Macek _e_t _al. (1977) investigated the relative significance of
aqueous and dietary exposure of bluegill sunfish (Lepomis macrochirus) to
1,2,4-trichlorobenzene using an aquatic food chain which consisted of a
food organism, the water flea,  Daphnia magna, and a consumer organism, the
bluegill sunfish, Lepomis macrochirus.  Prior to initiation of the food
chain experiment, the duration of exposure required to "load" daphnids and
fish to an equilibrium concentration of radiolabelled 1,2,4-trichloroben-
zene was determined.  Two flow-through experimental units (A,B) were dosed
to maintain continuous aqueous exposure of bluegill sunfish to a concentra-
tion of 3.0 ug/1 of 1,2,4-trichlorobenzene.  Two other flow-through
experimental units (C,D) contained no aqueous concentrations of 1,2,4-tri-
chlorobenzene.  Fish in units B and C were fed daphnids allowed to reach
equilibrium concentrations of 1,2,4-trichlorobenzene, while fish in A and D
were fed uncontaminated daphnids.  As a result, fish in unit A experienced
only aqueous exposure to the chemical, fish in unit B experienced both
dietary and aqueous exposure, fish in unit C experienced only dietary
exposure, and fish in unit D experienced no exposure and served as a con-
trol group.  Quantitative measures of the accumulation of -^C-residues of
1,2,4-trichlorobenzene in bluegill sunfish were determined by removing five
fish from each experimental unit on day 1,3,7,10,14 and each succeeding 7
days during exposure and radiometrically analyzing each individual fish.

         Daphnids continuously exposed to a mean measured aqueous concen-
tration of 3.1 + 0.4 ug/1 of 1,2,4-trichlorobenzene had a mean measured
equilibrium 14-C residue body burden of 0.44 j- 0.16 mg/1.  Therefore, the
estimated equilibrium bioconcentration factor for daphnids is 142X.  Fish
continuously exposed to a mean measured aqueous concentration of 2.9 + 1.1
ug/1 of 1,2,4-trichlorobenzene had a mean measured equilibrium 14-C residue
body burden of 0.53 + 0.25 mg/1.  Consequently, the estimated equilibrium
bioconcentration factor for fish is 182X.  Macek _e_t al. (1977) define bio-
concentration as that process wher.eby chemical substances enter aquatic
organisms through gills or epithelial tissues directly from water.  Bio-
accumulation, on the other hand, is defined by Macek _e_t _al. (1977) as a
broader term referring to a process which includes bioconcentration as well
as any uptake of chemical residues from dietary sources.  The data from
investigating the bioaccumulation of 14-C 1,2,4-trichlorobenzene by blue-
gill sunfish from food and water yielded a mean equilibrium 14-C residue
body burden in sunfish of 0.57 +_ 0.5 mg/1 when exposed to 2.9 ug/1 of
1,2,4-trichlorobenzene and fed daphnids having a mean concentration of 0.44
mg/1 of 14-C residue.

         The drawback of the experiments of Macek et al. 1977 is that
either results are based upon total c-^-carbon analysis and hence do not
take into account metabolic by-products and bound residues.  If biodegrada-
tion does not occur, their bioconcentration factors will be maximal.  Under
the conditions of the experiment, however, bioconcentration factors very
likely will be lower.
                                    76-4

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          Macek et al. (1977) concluded that the contribution of the
dietary source of 1,2,4-trichlorobenzene to the ultimate equilibrium body
burden is probably insignificant compared to the aqueous source of this
chemical even if the  two sources are additive.   The lack of significant
contribution of dietary 1,2,4-trichlorobenzene  to the equilibrium 14-C
residue body burden of bluegill sunfish was confirmed by results of a study
where bluegill sunfish were held in uncontaminated water but fed daphnids
containing 0.44 mg/1  of 14-C residues as 1,2,4-trichlorobenzene.  The mean
14-C residue body burden in bluegill sunfish during dietary exposure to
approximately 3 yg/1  of 1,2,4-trichlorobenzene  was 0.03 + 0.01 mg/1.  This
value represents only about 5 percent of the 1,2,4-trichlorobenzene 14-C
residue body burden in bluegill sunfish exposed for a comparable period to
either aqueous or combined  aqueous and dietary  1,2,4-trichlorobenzene.
Macek et_ al. (1977) conclude that the percent of residue burden due to
dietary intake alone  of 1,2,4-trichlorobenzene  by bluegill sunfish fed
contaminated daphnids is less than the error associated with the ability to
estimate residues due to bioconcentration alone.

         Neely _et al. (1974) and Lu and Metcalf (1975) have shown that the
log octanol/water partition coefficient (log P) correlates well with the
ability of a compound to accumulate in the lipids of tissues of living
organisms.  Furthermore, the incorporation of chlorine into an organic
molecule increases its lipophilic character resulting in an increased po-
tential for bioaccumulation (Kopperman _et _al. 1976).  The rather high log P
value of 4.26 as calculated from the method of  Tute (1971) indicates that
the bioaccumulation potential of 1,2,4-trichlorobenzene by aquatic organ-
isms at pollutant concentrations anticipated in environmental waters would
probably be relatively high.  Based upon the minimal available evidence,
however, 1,2,4-trichlorobenzene appears not to  be bioaccumulated as ex-
tensively as chlorobenzene.  Whether this is a  function of insufficient
sampling or an exception to the connection between log P and bioaccumula-
tion cannot yet be determined.

    76.4.7  Biotransformation and Biodegradation

         Experimental evidence indicates that chlorobenzene, which is
structurally similar to 1,2,4-trichlorobenzene  but less highly chlorinated,
is not readily biodegraded unless the microorganisms present are already
utilizing another carbon source (Gibson et_ _al.  1968).  According to Ware
and West (1977), resistance to biodegradation generally increases as the
degree of halogenation of a compound increases, and Alexander and Lustigman
(1966) found that the presence of a chlorine atom on the benzene ring re-
tarded the rate of biodegradation.  From the above, it can be inferred that
1,2,4-trichlorobenzene, being more highly chlorinated than chlorobenzene,
would presumably be biodegraded less rapidly than chlorobenzene under the
same conditions of exposure to microorganisms.
                                       76-5

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          Ware and West (1977) report an experiment in which 1,2,4-tri-
chlorobenzene at a concentration of 50 mg/1 was exposed to preconditioned
treatment plant cultures.   1,2,4-Trichlorobenzene was very persistent as
evidenced by the slight decrease in concentration probably due primarily to
atmospheric loss after a 50-hour period. The microorganisms absorbed
approximately 40 percent of 1,2,4-trichlorobenzene but did not substan-
tially biodegrade the absorbed portion.

         Ware ana West (1977)  also report another experiment in which the
biodegradation of 1,2,4-trichlorobenzene was studied in order to assess the
extent and rate of degradation and the role of acclimatization.  When un-
acclimatized industrial wastewater microorganisms were used, 99 percent of
the 1,2,4-trichlorobenzene at  an initial concentration of 1.7 mg/1 dis-
appeared from the experimental mixture after 10 days.  The BOD (Biochemical
Oxygen Demand) value  after 10  days, however, indicated that only 55 percent
of the theoretical value was removed.  The 45 percent theoretical oxygen
demand remaining was  assumed to be due to incompletely oxidized metabolites
of 1,2,4-trichlorobenzene which were probably incorporated in the cell
wall.  The experiments found no apparent degradation as measured by BOD in
the first few days of monitoring.  Analysis, however, indicated a 14 per-
cent reduction in the concentration of 1,2,4-trichlorobenzene after 24
hours, a 36 percent reduction  at 72 hours, and a 43 percent reduction at 7
days.  At a concentration of 2.6 mg/1 the rate of degradation was appar-
ently lower for the first few days.  After seven days of exposure of the
microorganisms to a concentration of 2.6 mg/1 of 1,2,4-trichlorobenzene,
analysis indicated 28 percent  decrease in the concentration of 1,2,4-tri-
chlorobenzene.  This  is quite  different from the 43 percent decrease of
1,2,4-trichlorobenzene after seven days of exposure of the microorganisms
to a concentration of 1.7 mg/1 of this compound.  After ten days, however,
all of the 1,2,4-trichlorobenzene at the higher concentration had
disappeared from the  BOD bottles.

         Ware and West (1977)  reported another phase of the previous ex-
periment in which the formation rate of carbon-14 labeled C02 through
biodegradation of 1,2,4-trichlorobenzene by activated sludge was examined.
After 5 days, 13 percent of the  1,2,4-trichlorobenzene remained, while 56
percent was converted to carbon dioxide, 23 percent to polar metabolites,
and 7 percent was volatilized.  Approximately 80 percent of the 1,2,4-tri-
chlorobenzene was adsorbed on solids, accounting for the low volatility
from the system.  In summary,  biodegradation of 1,2,4-trichlorobenzene has
been demonstrated under conditions where microorganisms are acclimated and
another carbon source is utilized, as in the activated sludge process.
Under environmental conditions, biodegradation would be expected but at a
very much lower rate than in the waste treatment studies reported above.
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76.5  Data Summary

    Information found concerning photolysis, oxidation, or sorption pro-
cesses was insufficient to allow prediction of the aquatic fate of
1,2,4-trichlorobenzene.  1,2,4-Trichlorobenzene has a high affinity for
lipophilic materials and is  predicted to have a relatively low vapor
pressure and low solubility  at ambient temperatures.  Consequently,  sorp-
tion and bioaccumulation are expected to be competing with volatilization
in removing the compound from the water column. The rate at which each of
these competing processes occur will dictate which fate is predominant for
1,2,4-trichlorobenzene in ambient waters.  These data are summarized in
Table 76-1.
                                       76-7