A-600/1-75-002
arch 1975
Environmental Health Effects Research Series
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RESEARCH REPORTING SERIES
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EPA-600/1-75-002
March 1975
FORMATION OF HALOGENATED ORGANICS
BY CHLORINATION OF WATER SUPPLIES
A Review
by
J. CARRELL MORRIS
Gordon McKay
Contract No. P5-01-1805-J
Program Element 1CA046
Project Officer
Dr. Hend Gorchev
Office of Research and Development, Environmental Sciences
Environmental Protection Agency
Washington, D.C. 20460
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
LIP
U. S. .:. ..j:j;; AGENCY
EDISON, ...
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ABSTRACT
Available literature on the formation of halogenated organic compounds
during the chlorination of water supplies has been reviewed critically.
Types of organic compounds likely to be encountered in natural waters
have been surveyed and various known or prospective reactions of dilute
aqueous chlorine with these types of compounds have been discussed.
It is concluded that two principal types of chlorination reaction are
expected: (1) electrophilic aromatic chlorination as in the long-known
formation of chlorophenols; and (2) electrophilic chlorine addition to
activated double bonds like that of eno lace tone. Chloroform or other
haloforms may occur as end products of exhaustive chlorination in either
case. General substitution reactions of chlorine are unlikely however.
So carbon tetrachloride or fully chlorinated higher hydrocarbons are not
probably products of water chlorination.
Possible methods for minimizing the concentrations of halogenated organic
compounds in municipal supplies have been outlined. These include pre-
treatment methods, such as coagulation or preozonation to reduce amounts
of precursors to the halogenated compounds, and posttreatment methods,
such as carbon adsorption or aeration to remove halogenated compounds
after their formation.
Needed research has been described.
This report was submitted in fulfillment of Contract No. P5-01-1805-J
by J. Carrell Morris, Gordon McKay Professor of Sanitary Chemistry,
Harvard University, under the sponsorship of the Environmental Protec-
tion Agency. Work was completed as of February 1975.
ii
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CONTENTS
Page
Abstract ii
Conclusions 1
Recommendations 2
Introduction 3
Aqueous Chlorination Reactions 9
Organic Compounds in Water Supplies 19
Study of J. J. Rook 27
Work of Bellar, Lichtenberg and Kroner 29
Health Hazards in Water Chlorination 31
Recent Work of J. J. Rook 35
Possible Modifications in Treatment 38
Indicated Research Needs 41
References 43
iii
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CONCLUSIONS
The finding of product haloforms as a result of the chlorination of
relatively unpolluted surface water supplies poses a serious problem
for agencies producing domestic water supplies, for chlorination is the
almost universal procedure used to protect against the water-borne
transmission of infectious diseases. The problem lies not so much in
the production of the haloforms themselves as it does in the possibility
that other, unknown, highly toxic or carcinogenic compounds may also be
produced simultaneously.
A careful review and assessment of available literature relating to
the formation of chlorinated organic compounds under conditions pre-
vailing in natural waters leads to the conclusion that chlorination is
not indiscriminate, and so does not lead to the formation of all sorts
of chlorinated derivatives with any and all organic pollutants. Rather
it proceeds by a limited number of well-defined reactions on a few
specific types of organic structures.
The identifiable initial reactions are electrophilic aromatic substitu-
tion of positive chlorine and electrophilic addition of positive chlorine
to appropriately activated doulle bonds. The former reaction, which
produces malodorous chlorophenolic compounds in intermediate stages,
leads ultimately to oxidative ring rupture. The latter process leads to
chloroform (and other haloforms when bromide is present) as the end pro-
duct. . v
Direct substitution reactions of aqueous chlorine leading to the forma-
tion of exhaustively chlorinated hydrocarbons are unknown and unlikely.
The known mechanisms do not lead to such exhaustively chlorinated pro-
ducts as carbon tetrachloride or tetrachloroethylene.
Reduction in the concentration of chlorinated organic compounds in
finished municipal supplies can be achieved either by pretreatment methods
to remove organic precursors or by post-treatment with activated carbon.
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RECOMMENDATIONS
Because this contract was limited to the review and assessment of currently
available information, no experimentation was conducted to see whether
the judgments that have been reached are generally sound. The reports
on the formation of the haloforms have been initial findings; much addi-
tional research is needed to determine more fully conditions for the
occurrence of the phenomenon, its extent and the full range of products.
First efforts should be directed to a determination of the formation of
other chlorinated organics than the haloforms. Investigations to this
end should include stoichiometrlc and dynamic considerations. Effects
of chlorine dosage relative to organic matter, yields of chlorinated
organic materials relative to applied chlorine and to organic content,
and influence of time of reaction on the nature and yield of organic
materials all need prompt study.
Second, the effects of possible pretreatment steps on the extent of pro-
duction of chlorinated organic compounds should be investigated to deter-
mine which may be most useful in minimizing the problem. This study
should be correlated with more fundamental ones to discover the types of
materials and the structures responsible for the production of the chlor-
inated derivatives.
There should be no relaxation of the practice of water chlorination in
the meantime. Protection of the public health depends strongly on con-
tinuation and even intensification of water chlorination. Until there
is some positive indication that the formation of chlorinated organic
compounds during the disinfection of water supplies has hygienic signifi-
cance, there should be no attempt to make widespread modifications in
water treatment. Useful modifications should be developed, however, so
that they are promptly available if a need for change is shown.
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Introduction
In recent months concern about the presence and production of chlor-
inated organic compounds in water supplies has been greatly intensified
because of findings of numerous chlorinated organic compounds in drinking
water derived from the lower Mississippi River [47, 152, 31 ] and
because of the discovery by Rook ( 124) and later by Bellar, Lichtenberg
and Kroner ( 10 ) that chloroform and other halogenated methanes are formed
during the chlorination of water for disinfection. It should be noted that
these findings came as a result of the development of more sensitive and re-
fined analytical techniques and not because the occurrence or production of
the compounds is a recent situation.
There are four principal ways in which chlorinated organic compounds
may occur in water supplies: from non-point sources, from industrial dis-
charges, from chlorination of sewage or industrial wastewater and by the
chlorination of organic matter in the water supply. Different problems are
posed with each of these sources and different solutions may be required in
each instance. Accordingly, it is important that the categories be kept
distinct when consideration is given to the generality or seriousness of
the overall situation and when measures are being developed to deal with
them.
1. Non-point Sources. Chlorinated organic compounds may be intro-
duced into rainfall from atmospheric pollution or may be incorporated into
surface runoff to find their way into streams, lakes and rivers. Although
these sources have been incriminated in connection with health effects on
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aquatic life, they seem not to have led to sufficiently great concentra-
tions of known materials in drinking waters to have become a major direct
problem to human health. As is recognized, problems that may arise from
these sources of chlorinated organic compounds may be dealt with either by
restricting dissemination of the materials in the environment or by special
treatment to remove them.
The materials of importance in connection with non-point pollution
are pesticides, fungicides, weed killers and other agricultural chemicals
plus the polychlorinated biphenyls. The possibility that precursors of
hazardous chlorinated compounds may be introduced into water supplies in
this way to be converted ultimately into harmful products when the water
is chlorinated must not be overlooked, but no significant instance of such
an occurrence seems to have been observed until now.
The problem of chlorinated organic compounds that may be found in
water supplies as a result of contamination from non-point sources does not
fall within the scope of this report and will not be considered further. "
2. Industrial Discharges. The major source of chlorinated organic
compounds in water supplies is industrial discharge, both the intentional
discharge of wastewaters from manufacturing plants and accidental spillages
of chlorinated compounds that find their way eventually into water courses.
The variety of chlorinated organic compounds found in the Ohio and the lower
Mississippi Rivers (86, 10, 152 ) comes from such industrial discharges.
Similarly, the 50 chlorinated organic compounds reported to have been found
in Rhine water by Sondheimer ( 141) are considered to be almost wholly of
industrial origin.
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Finding of chlorinated organics in drinking waters derived from
sources such as the lower Mississippi and Rhine has bearing on the question
of the production of chlorinated organic compounds during water disinfection
by chlorination only to the extent that the types or concentrations of chlor-
inated compounds are shown to have been increased following this step in
water treatment.
Procedures for the alleviation of problems caused by the presence of
chlorinated organic compounds from this source are, first of all, enforced
regulation of industrial discharges and, secondly, supplementary treatment
of the water by adsorption on activated carbon or chemical oxidation to eli-
minate the offensive materials. Once again, detailed discussion of this
source of chlorinated organic compounds does not fall within the scope of
this report. It may be noted, however, that problems arising in this way
are limited to localities that use industrially polluted waters as their
source of drinking water and thus are not associated universally with basic
procedures of water treatment.
3. Sewage Chlorination. R.L. Jolley ( 83 ) has shown in a very im-
portant publication that the practice of chlorination of municipal wastewater
effluents for the purpose of disinfection results in the formation of numerous
chlorinated organic compounds, seventeen of which were identified. The yield
of these chlorinated organic compounds was not great, comprising in total
only about 1% of the chlorine dose.
This research has little direct bearing on questions of the formation
of chlorinated organic compounds during water chlorination except that it
points up the possibility of direct aqeuous chlorination of a wide range of
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organic compounds, some of which may also be encountered in water supplies.
The chlorination conditions for sewage effluents and for water supplies are
very different, however. In the former instance there is essentially imme-
diate complete formation of chloramine which then serves as the reactive
agent; in the latter instance it is normal to have present an excess of the
strongly oxidizing HOC1.
The seventeen compounds Identified by Jolley all contained only a
single chlorine atom. In general such minimally chlorinated compounds are
much more readily degraded biochemically than are the polychlorinated mate-
rials that have been found to be so perdurent in the environment. Accordingly,
it seems unlikely that any of these materials will persist in receiving waters
•
long enough to cause major problems at downstream water treatment plants or
that they will biologically accumulate in organisms to any great extent.
4. Water Chlorination. That the chlorination of water supplies pro-
duces chlorinated derivatives of organic compounds present is not a new dis-
covery. From almost the first years of the practice of water chlorination,
the formation of "chlorophenols" with their accompanying tastes and odors
has been a nagging problem for operators of water treatment plants. As early
as 1922, only a dozen years after the first sustained municipal chlorination
in this country, Donaldson ( 30 ), wrote: "Since the early days of chlori-
nation there has been recognized the probability of organic matter combining
'with chlorine and thus giving rise to disagreeable tastes."
The main concern in this and other early reports (18, 30, 36,
42, 53, 149 ) however, was the tastes and odors produced in the formation
of these chlorinated compounds. Provided tastes and odors were controlled
there was little systematic concern about other physiological effects of
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.chlorinated compounds in the distributed waters.
Along with the recent development of awareness of the physiological
hazards associated with many chlorinated compounds such as DDT, dieldrin,
polychlorinated biphenyls and vinyl chloride, there has come to be a general
opprobrium attached to any chlorinated organic compound. Accordingly, the
reports of the production of halogenated methanes in the chlorination even
of unpolluted water supplies have had a strong impact, -partly because of the
resulting distribution of the halogenated methanes themselves and partly be-
cause of the possibility that other more hazardous and as yet undetected
halogenated compounds are also being produced. Prospective hazards from
either of these sources call into question the whole process of water chlor-
ination by which the freedom of our drinking water from microbial contamina-
tion is assured.
Accordingly, it is essential that the total significance of these
reports be assessed as promptly as possible in order that the proper integrity
of our drinking water supplies be maintained to the highest degree. The total
range of chlorinated compounds formed during water chlorination and the condi-
tions of their formation are not presently known. In the absence of firm
experimental data it is necessary to estimate probable products and conditions
of formation from what is known about the general chemical behavior of aqueous
chlorine and the nature of the organic chemical compounds that may be found
in natural waters. Although such an estimation can only be a temporary stopgap
pending the acquisition, of firm experimental evidence, it may serve to indi-
cate the need for emergency measures during the interim period and may also
show the direction in which ultimate solutions should be sought.
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The subsequent sections of this report will deal first with the
types of reactions of aqeuous chlorine with various classes of organic
compounds. Then the types of organic compounds either known to be present
or likely to occur in natural waters will be described and their known or
probable interactions with available chlorine during water chlorination will
be surveyed. After a detailed evaluation of the findings of Rook and Bellar,
Lichtenberg and Kroner, the prospective health hazards associated with water
chlorination will be considered and assessed to the extent that our present
knowledge permits.
Next, possible modifications in treatment to minimize formation of
chlorinated organic compounds during the process of water chlorination will
be described. Finally recommendations will be made for research that needs
to be carried out to establish experimentally the significance and hazards
of the formation of chlorinated organic compounds in the disinfection of
water supplies by chlorination.
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Aqueous Chlorination Reactions
The central and most significant fact about aqueous chlorination
in the range of concentrations employed in water treatment is that elemental
chlorine, C12, is not involved. When chlorine is dispersed in water at pH
greater than five in concentrations up to 100 mg per liter or about 10
molar, the Cl? is hydrolyzed essentially instantaneously and completely
(better than 99.99%) to HOC1 and OC1~ ( 83, 91 ) in accordance with
the equations
C12 + HCO~ -»• HOC1 + Cl~ + C02 (1)
HOC1 * H+ + OC1~ (2)
So, it is necessary to consider the reactions of hypochlorite rather than
those of Cl_ in describing
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In each of these instances'formation of the chlorinated derivative is pre-
ceded by an ionization and formation of a carbanion to which the positive
chlorine of HOC1 becomes attached (96, 155).
(3) Oxidation, with reduction of the hypochlorite chlorine to chloride
as illustrated by the aldehydic oxidation
R - CHO + HOC1 + RCOOH + H+ + Cl~ (6)
(4) Substitution of chlorine for hydrogen on a nitrogen atom as shown
by the typical reaction
^ - 9 - R2 + HOC1 -»• RX - Ijl - R2 + H20 (7)
H Cl
Any of these reactions may be succeeded by additional reactions of
the same type or of the other types; there may also be, following elimination,
hydrolysis or migration reactions, depending on the structure or reactivity
of the initial products.
One type of reaction that is not to be expected is simple aliphatic
substitution as illustrated by the equation
CH3 - CH3 + HOC1 -»• CH3 - CH2C1 + H20 (8)
This type of reaction is nearly always a radical chain reaction, requiring
light, much thermal energy or an initiator and proceeding best in non-ionizing
environments.
The first three types of reaction convert the chlorine either to
chloride ion or to a covalently bound state in which the chlorine no longer
acts as an oxidizing agent toward iodide or other readily oxidized materials.
These reactions, therefore, represent the exertion of "chlorine demand",
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the conversion of active or available chlorine to a non-oxidizing form.
Chlorine demand always accompanies the formation of C-chlorinated organic
compounds; the chlorine demands of water supplies thus reflect in some
measure the potential for formation of chlorinated compounds during disin-
fection.
The yield of chlorinated compounds will vary of course with the nature
of the organic material. Jolley ( 83 ) for example, found that in the chlor-
ination of sewage effluent only about 1% of the applied.chlorine ended up
as chlorinated product.
In contrast the chlorine that reacts to substitute on nitrogen does
not lose its oxidizing capacity, although the vigor and potency of the oxi-
dizing action may be reduced. Subsequent reactions of the N-chlorinated
compounds, or chloramines, may also produce C-chlorinated compounds; so they,
too, are part of the active residual chlorine.
A. Reactions with Nitrogenous Substances. The last type of reaction, that
to form N-chlorinated compounds, will be discussed in detail first. Reaction
in accordance with Equation (7) occurs quite generally with all sorts of
nitrogenous compounds - amines, amides, amino acids, proteins and hetero-
cyclic compounds - and often proceeds rapidly, especially with the more
basic nitrogen atoms. The reaction with ammonia, for example, requires only
-4
about a minute at the milligram per liter (10 M) level at neutral pH.
When the nitrogenous reactant is a simple primary or secondary amine,
the N-chlorinated product is normally quite stable in dilute aqueous solution
and may persist for several days unless the chlorine is converted to chloride
by reaction with reducing materials or unless chlorination on carbon like
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that with hypochlorite occurs. These, latter types of reactions are presuma-
bly much slower than the corresponding hypochlorite reactions, but cannot be
ruled out completely.
When the nitrogenous material is a tertiary amine, so that no H atom
on N is available for replacement by Cl, an interesting oxidative cleavage
occurs with production of an N-chloro secondary amine and an aldehyde (24, 35 )
which may subsequently be oxidized by excess of hypochlorous acid. A typical
reaction sequence is
R.R2N - CH2 - R_ + 2 HOC1 •* RJEU NCI + R_CHO + H20 + H+ + Cl~ (9)
R3CHO + HOC1 -»• R_COOH + H+ + Cl~
a-Amino acids upon chlorination give first N-chlor derivations, but then,
in general, oxidativedeamtnation occurs giving an a-keto acid and ammonia chlor-
amine. With an excess of hypochlorous acid the keto acid, depending on its
structure, may be additionally oxidized and the nitrogen will go through the
breakpoint process. (28, 46, 78, 89 ). With alanine, for example, the initial
reactions are
H H
CH, - C - COOH + HOC1 •*• CH,C - COOH + H_0 (10)
3 , 3, 2
NH2 NHC1
H
CH, - C - COOH + HOC1 •* CH, - C - COOH + NH0C1
3 I 3 II 2
NHC1 0 + R+ + -
The chlorination of glycine is a special case. In addition to the oxida-
tive deamination to CHOCOOH and NHjCl, decarboxylation occurs yielding finally
CNC1 and O>2 as carbonaceous products (28, 90, 113, 166). No evidence for
formation of other C-chlorinated organic compounds as a result of these reac-
tions has been found, however.
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Heterocyclic ring compounds containing basic nitrogens, such as
pyrimidines, purines, pyrroles and indoles exhibit complex reactions with
aqueous chlorine. Pyrimidines, especially those with a 2- or 4- amino group,
react readily with aqueous chlorine, not only to form chloramines, but also
to give C-chlorinated derivatives, particularly the 5-chloro compounds.
(117, 120 ). Purines appear to be simultaneously oxidized and chlori-
nated (69, 83 ). Chlorination by mechanisms similar to aromatic substi-
tution seems to occur with pyrroles and indoles ( 83, 106 ). None of these
reactions has been investigated at the concentrations and conditions of water
chlorination, but clearly a possibility exists that aqueous chlorination of
these types of compounds, to the extent that they exist in raw water supplies,
is a source of chlorinated organic compounds.
Amides and imides react less rapidly with hypochlorite than amines,
V
so much so that some investigators have found no reaction at the concentrations
used in water treatment (126, 129,115). Rearrangements of these N-chloro-
amides may occur by a mechanism akin to the Hofmann reaction to give amine
plus COj, with subsequent chlorination of the amine in the presence of excess
hypochlorite. Rearrangements of aromatic N-chloroamides or N-chloranilides
may give rise to chlorine substitution on aromatic carbon. Presumably subse-
quent reactions of these chlorinated aromatic rings will resemble that of
the chlorinated phenols.
In summary, it appears that although there is extensive reaction of
hypochlorite with nitrogenous substances, there is little evidence for forma-
tion of stable C-chlorinated materials as a result of N^chlorination.
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B. Oxidation Reactions. Oxidation by aqeuous hypochlorite, like chlorine
substitution, does not occur readily with simple saturated aliphatic hydro-
carbon chains. Some point of attack is needed where some sort of substitution
or unsaturation is already present. Alcoholic, aldehydic, carbohydrate types
of materials, those for which hydrolysis to hydroxylated substances can take
place and compounds with sulfhydryl groups or other reduced sulfur linkages
are all classes of compounds subject to oxidation by aqueous hypochlorite.
Since no substitution of chlorine into the organic compounds occurs in this
type of oxidation, there is no need to explore the great number and variety
of such reactions in detail. Because oxidation reactions of aqueous hypo-
chlorite are common and extensive, however, it is highly probable that most
of the chlorine demand of natural waters results in production of chloride
ions rather than chlorinated organic compounds.
C. Addition to Olefinic Bonds. The standard reaction of hypochlorous acid with
olefinic double bonds is to produce chlorohydrins as shown in Equation 3
(25, 26, 83 ). The CHOH group in this type of addition product is then sub-
ject to additional oxidation and possible rupture of the carbon chain at this
linkage. In some instances a dichloro compound may be produced even though
HOC1 is the responsible agent, for the first step in the accepted mechanism is
an opening of the double bond with addition of Cl . The other end of the double
bond may then react with OH or Cl or possibly other anions in the aqueous
solution. So far as it is known there has been no investigation of possible
ultimate products in the presence of excess HOC1.
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D. Reactions with Aromatic Compounds. The typical first reaction of HOC1
with aromatic compounds is a substitution of Cl for H on the aromatic
ring, presumably by way of an additive intermediate. When the substrate
•
is the aromatic hydrocarbon itself, however, a strong acid must also be
present to give H2OC1 or Cl as the actual chlorinating agent. When the
aromatic ring is activated by an appropriate substituted group, the OH
group being a prime example, then substitution of Cl on the aromatic rings
will proceed readily even in neutral aqueous solution (91, 20, 96 ).
The traditional chlorination reaction of phenol proceeds readily
by way of ^-chlorophenol and £-chlorophenol formation through 2,4-dichloro-
phenol and 2,6-dichlorophenol to 2,4,6-trichlorophenol (19, 91,83). At
this point, however, dilute aqueous chlorination becomes much slower or
more difficult, so that oxidative rupture of the benzene ring becomes
dominant, yielding at first two-carbon residues and eventually C0_, ^0
and Cl (74, 91,78). A preferred pathway of oxidation appears to be through
hydrolytic oxidation and elimination of Cl from the 2 or 6 position to
give o-benzoquinone with subsequent ring rupture at the other positions.
Homologs and analogs of phenol, including cresols, hydroquinones,
anisole and 2-methoxy-4-methylphenol react similarly (8, 52,142). In
the last instance the two ring-carbon residues, oxalic acid and methyl-
fumaric acid were observed as products after ring rupture.
Aromatic aldehydes and acids, including benzole acid, salicyclic
acid, £-hydroxybenzoic acid, anisic acid, vanillic acid, vanillin, 2,4-
dihydroxybenzaldehyde, phenoxy-acetic acid and phthalic acid may also be
chlorinated in aqueous solution ( 68, 58 ). Reactions have not been
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studied with excess hypochlorite to determine whether ring rupture also
occurs with these compounds; it seems likely by analogy that it would
also occur in these instances, however.
Heterocyclic aromatic rings exhibit great variations in reactivity
toward chlorine substitution. Pyridine, for example, is much less reactive
than benzene and so does not chlorinate readily in aqueous solution. Pyrrole,
on the other hand, is activated, and so may be expected to give chlorinated
derivatives as phenol does (106, 46 ). Friend found that the amino
acid, proline, exhibited rapid chlorine demand after N-chlorination, per-
haps indicating a rupture of the 5-membered heterocyclic ring.
E. The Haloform Reaction. An aqueous chlorination reaction of particular
interest in connection with the treatment of water supplies is the halofonn
reaction, which occurs generally in alkaline aqueous solution with organic
0
compounds containing the acetyl group CH_-C- or with structures such as
CH_CHOH- that may be oxidized to the acetyl group. The three hydrogens
of the methyl group are successively replaced by chlorine or other halogen
and then the carbon bond to the carbonyl group is split giving rise to
a haloform and a carboxylic acid. The overall reactions may be written
CHLjCOR + 3HOC1 •»• CC13COR + 3H20 (11)
CC13COR + H20 -»• CHC13 + RCOOH (12)
The accepted mechanism for the reaction is an initial dissociation of
H to yield a carbanion which then adds positive halogen. Subsequent dis-
sociation and addition of positive halogen continue at the same carbon
until it is fully halogenated. Then nucleophilic base attack displaces the
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HOC1 •*• RCOCH2C1 + OH~ (14)
RCOCH2C1 -»• R
CCl- group, which combines with H to give chloroform ( ).
The complete sequence of mechanistic reactions is
0~
RCOCH3 -»• RC - CH2 + H (13)
RC - CH2 +
£ - CHC1 + H+ (15)
RC - CHC1 + HOC1 •*• RCCHC12 + OH~ (16)
RCOCHC12 + RC - CC12 + H+ (17)
RC = CC12 + HOC1 -»• RCOCC13 + OH~ (18)
RCOC13 + OH~ -»• RCOOH + CC13~ (19)
CC13~ + H+ * CHC13 ' (20)
The slowest step in this sequence of reactions is reaction 13, so
that once the beginning reaction is initiated, the ultimate formation of
chloroform is reached at the same rate as that at which the first reaction
occurs. It, therefore, makes no difference what the halogenating agent
is in reactions 14, 16, and 18; the reaction proceeds at the same overall
rate as the initial rate-determining step, reaction 13. This has been
observed experimentally.
It may be noted, however, that when mixed halogenating agents,
say HOC1 and HOBr, are present, then the relative amounts of RCOCHjCl
and RCOCH.Br obtained will be in proportion to the relative rates of
reactions 14a and 14b.
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RC = CH2 + HOC1 -> RCOCH2C1 + OH (14a)
RC = CH2 + HOBr ->• RCOCH2Br + OH (14b)
even though the overall rate is governed by reaction 13. Similar consid-
erations apply to the later stages of the reaction sequence, for reactions
15 and 17, though faster than reaction 13, are slow compared with their
succeeding reactions in each case.
Ethanol, acetaldehyde, methyl ketones and secondary alcohols with
the general formula CH-CHOHR are among the compounds or classes of com-
pounds that give the haloform reaction. So also may unsaturated compounds
with a structure CH-CH « CR..R,,, for, after addition of HOC1 to give
J J. 4.
CH-CHOH CRjIUCl, oxidation will give a methyl ketone. Possible sources
of haloforms are thus very extensive.
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Organic Compounds in Water Supplies
Natural waters, even when unpolluted, may contain a great number
of different organic materials. The extensive review of Vallentyne
( 161 ) described thousands of compounds of widely diverse types that
have been found in natural waters, but, even so, only a small fraction of
the total organic material present in a given natural water has been
fully characterized. Most researchers have restricted themselves to
detecting or determining the compounds belonging to a particular class
of compounds.
The total organic matter dissolved or colloidally dispersed in
typical unpolluted natural waters as determined by general methods for
total organic carbon or COD seems to fall in the range from one to a few
tens of milligrams per liter. Since analyses by carbon adsorption methods
generally indicate only a few tenths of milligram per liter, it is apparent
that these methods do not recover fully the organic materials in natural
waters, although they may be very effective for certain obnoxious classes
of compounds.
The major, almost the sole, source of organic matter in unpolluted
water supplies is plant material, either synthetic units, metabolic inter-
mediates, end products or decomposition residues of the biochemical activities
of members of the plant kingdom ranging from bacteria and algae to forest
trees. This unified source does not, however, place much restriction
on the number or variety of individual chemical components that may be
encountered. Not only the major structural and storage compounds with
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their antecedent or breakdown products need be considered, but also the
wide range of individual scents, flavors and other distinctive materials
that characterize separate forms of plant life.
Among just the broad classes of chemical compounds that have been
found to be present are: carbohydrates, proteins, lipids, nucleic acids,
terpenoids, carotenoids, chlorophylls, vitamins, carboxylic acids,
esters, amino acids, phenolic compounds, steroids and hurnic substances.
( 43, 161 ) In the following sections these and other classes of compounds
are surveyed with regard to their presence and concentration in water
supplies, but this can be done; in only a general way because of lack of
sufficient information.
A. Humic Substances. One of the most significant classes of compounds
contributing organic matter to water is the humic material which causes
the yellow to brown stain of surface waters. The humic substances arise
principally by extraction of the soluble fraction of wood tissues, by
dissolution or dispersion of decomposition products of decaying wood or
leaves and by leaching of soluble components from soil organic matter.
For the most part the material seems to have a molecular weight in the
4 5
10 - 10 range and to fall into the group of compounds designated
as fulvic acids (12, 13,21). Different waters, as might be expected,
exhibit different patterns of size distribution of molecular weights,
according to gel chromatographic studies (54, 55,56). Chemically the
humic material has been classified as aromatic polyhydroxymethoxycarboxylic acidj.
Operators of water treatment plants have observed repeatedly that
the chlorine demands of their upland surface supplies correlate closely
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with the depth of color of the supply (21, 135 ) indicating that a large
portion of the chlorine demand results from chemical reactions of hypo-
chlorite with the humic substances. Except for the suggestions by Rook
( 124 ) however, there has been little investigation of the nature
or the products of this interaction of hypochlorite with humic substances.
The known elements of structure give many possibilities for reaction,
some of which should yield the haloforms found by Rook.
B. Carboxylic Acids. Salts or esters of carboxylic acids comprise one
of the major groups of small molecular weight organic compounds found in
natural waters. Concentrations in the range of a milliequivalent per liter
have been found (108, 110) corresponding to several milligrams per liter
depending on the equivalent weight. Included in the total carboxylic
acid group are simple .aliphatic monocarboxylic acids, hydroxyacids and
dicarboxylic acids associated with the Krebs' cycle and aromatic carboxylic
acids such as benzoic and salicylic acids (109 HO) •
The simple aliphatic monocarboxylic acids, except for formic acid,
would not be expected to react with hypochlorite. Formic acid might be
oxidized to C02 and H.,0. The hydroxylated acids, mono-, di- and tricar-
boxy lie acids, are also subject to oxidation by hypochlorite, yielding
keto acids and possibly chlorine substitution products depending on the
structure. Decarboxylation and ultimate oxidation to CCL and H~0 are
also to be expected in some instances. The concentrations of the
hydroxylated acids should, however, be quite low, a few ppb. in most
situations because they are such active substances as biochemical metabolites.
The aromatic carboxylic acids will react with hypochlorite in the
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aromatic ring much as phenolic compounds do and should be otherwise non-
reactive. Their possible effects will, accordingly, be discussed along
with those of the phenols.
C. Sugars and Amino-Sugars. Many monosaccharides and oligosaccharides,
especially glucose, xylose, ribose and their condensation products, should
occur in natural waters because of their biochemical relationships.
Little has been done, however, to determine their nature or concentrations
(43, 161).
Simple reducing sugars are extensively oxidized by hypochlorite
(83, 129) but there is no evidence that any chlorinated derivatives are
produced. Ultimate potential oxidation to C0_ and H.O seems likely.
The amino sugars undergo N-chlorination like other amines and presum-
ably undergo oxidative deamination subsequently.
D. Amino Acids, Peptides. Proteins. Free amino acids and related com-
pounds have been found and partially characterized in some lake waters and
the ocean (94, 48 ) but, on the whole, relatively little attention has
been paid to these materials. The total amino-nitrogen content of unpol-
luted surface waters is usually several tenths of a milligram per liter,
but whether this is primarily proteid, amino acid or other nitrogenous
material is not known (43, 161 ).
Reactions of the amino acids with hypochlorite has been discussed
previously in some detail. N-chlorination followed by oxidative deamina-
tion is the general pattern to be expected. With some structures decar-
boxylation and subsequent complete oxidation may result eventually with
excess chlorine.
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Reaction of HOC1 with the peptide bond in peptides and proteins is
much slower than its reaction with the free amino group. So, with excess
free chlorine slow formation of N-chloropeptide bonds is expected. Such
N-chlorinated derivatives of amides are in many instances quite stable
and so available chlorine in these compounds may be very persistent. For-
mation of C-chlorinated derivatives is not known or expected generally.
E. Other Nitrogenous Compounds. In addition to the amino acids and pro-
teins other important types of nitrogenous organic compounds are pyrrole
and other porphyrin derivatives, formed in the breakdown of chlorophyll,
and pyrimidines and purines, associated with the synthesis and breakdown
of nucleic acids. No information is available on the occurrence of these
types of materials in natural waters.
Jolley (83, 50 ) found, however, that a number of chlorinated
pyrimidines and purines were formed during the chlorination of sewage
effluent. Among these were 5-chlorouracil, 5-chlorouridine, 8-chlorocaffeine,
6-chloroguanine and 8-chloroxanthine. It is possible that additional sub-
stitution or oxidation may occur with the excess hypochlorite available
in water chlorination rather than the chloramine prevalent in sewage
chlorination.
F. Phenolic Compounds. Phenolic compounds occur in unpolluted water
supplies as a result of the breakdown of lignins, tannins and other humic
substances ( 66, 161 ). Decomposing oak and beech leaves are felt to be
strong sources for aquatic phenolic materials. In addition to phenol
itself, various cresols, dihydric phenols, hydroxybenzoic acids, guaiacol '
and other similar substances may be present. One study of river water
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reported 37 different phenols, but many of these were of industrial
rather than plant origin.
Reactions of hypochlorousi acid with phenols have been described
in detail earlier. The usual first reaction is a ring chlorination in
the two or four position, followed by additional chlorination until
all the ortho and para positions are occupied. Then the ring is split and
full oxidation, eventually to CC>2 and H20, occurs ( 74, 91 ). Although
no worker has as yet noted any remaining chlorine substituted products,
it seems possible that some of the C-C1 linkages might be retained when
the phenol ring is broken to end up as some sort of chlorinated derivative.
Other aromatic derivatives—hydroxyaldehydes, hydroxy benzoic
acids and similar compounds—should react similarly. The same sorts of
reactions should obtain with naphthols and other fused ring systems; also
activated heterocyclic rings should behave similarly.
G. Terpenoids. Isoprenoids. Steroids. Carotenoids, Xanthophylls. Many
organic compounds found in plants are derived from the carbon skeleton of
isoprene. Among these are the terpenes and related alicyclic ring com-
pounds, sterols and other steroi.dal materials, carotenoids, some vitamins,
xanthophylls and numerous other coloring and flavoring materials. Most
of these predominantly hydrocarbon-like materials, often with double bonds
or ring structures, exist in simple molecular form within the plant cell
or structure and are excreted into water when the plant dies or is damaged.
Little is known of the occurrence of these materials in natural
waters or of their reactions with aqueous hypochlorous acid. However,
the unsaturation and ring structures that are often present plus the fre-
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quent key substitution of hydroxyl or other groups suggest that chlorination
reactions with compounds in this class of materials may be quite significant
and produce chlorinated derivatives of considerable importance. The
structure of isoprene itself, CH- - C(CH ) - CH - CH-, for example, is
such that it seems likely that chloroform or other chlorinated compounds
might be produced during its oxidation.
Research is needed with this class of materials.
H. Other Classes of Compounds. There are many other types of compounds
either known to occur or likely to be found in natural waters. Among
these are mercaptans and other sulfur-containing compounds, phosphate
esters, alkaloids, toxins and antibiotic substances. In general, the types
of reactions previously described will hold for reactions of the hydro-
carbon portions of these molecules and with oxidation or hydrolytic reac-
V
tions occurring with the non- carbonaceous groups.
Usually, also, these components will be such a small portion of
the total organic matter that their reactions will not make a major con-
tribution to any chlorinated organic compounds that may form. On the
other hand, the reaction pattern for a given class of organic compounds
can be so modified by the presence of activating or stabilizing atoms or
molecular groups that it is impossible to predict exactly when stable
chlorinated derivatives may be formed. At some time, surveys of the reac-
tion products formed when dilute aqueous solutions of abundant or significant
members of each of these classes of materials are allowed to react with
excess hypochlorous acid would be desirable.
I. Summary. Review of the likely chlorination reactions for the diverse
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classes of organic compounds that may be found in unpolluted drinking
water supplies indicates that three types of materials are prospective
sources of stable chlorinated organic compounds. These are: (1) Sub-
stances capable of undergoing the haloform reaction; (2) Phenols and related
aromatic compounds; (3) Pyrimidines and purines. For the second and probably
the third class of compounds, ring rupture and oxidation to non-chlorinated
products seems to occur before highly polychlorinated derivatives are
formed. In contrast, the highly chlorinated chloroform or other haloforms
are the end products of reaction with excess hypochlorite for the substances
in class (1).
Reactions of porphyrins and other pyrrole derivatives and reactions
of isoprenoid compounds need particular attention to see whether they are
potential precursors of chlorinated organic products.
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The Study of J. J. Rook
In July, 1974, J. J. Rook ( 124 ) reported the results of inves-
tigations on the drinking water supply for Rotterdam, Netherlands, in
which he found that chloroform and other trihalogenated methanes were
formed as a result of superchlorination of the water. Concentrations of
total halogenated methanes ranged from somewhat more than 10 yg per 1. to
about 100 yg per liter under differing conditions.
Additional experiments with unpolluted upland water and with extract
of peat gave strong evidence that it was the natural coloring materials
in the water that gave rise to the haloforms. Some idea of the yield
can be obtained from the fact that the peaty extract which contained 5
-4
to 8 mg. per liter of total organic carbon or about 5 x 10 atom per
liter gave rise to 2.0 ymol per liter of mixed haloforms, a yield of
0.4%.
Rook's results are reliable and his conclusions are well-established
and plausible. They must be accepted as valid and significant.
It is important to note also some negative aspects of Rook's work
in an assessment of its overall significance. No chlorinated derivatives
of hydrocarbons other than methane were found, implying that the formation
of chlorinated derivatives is restricted to the haloform reaction, or at
least that this is the major reaction path for the formation of chlorinated
organic compounds in water. The conclusion is not quite as firm as it
might be, for the headspace chromatographic method used detects only
volatile compounds, but at least some of the chlorinated ethanes should
have been detected if they had been produced in significant quantities.
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Even the carbon tetrachloride that was detected and cannot be accounted for
by the haloform reaction was found to be an impurity in the gaseous chlor-
ine used.
Consequently, the only stable chlorinated compounds known to be pro-
duced by chlorination, apart from the odorous chlorophenols that are
destroyed by free residual chlorination, are the halogenated methanes.
Other chlorinated organic compounds, like those found in the New Orleans
drinking water study, must have come from pollutional discharges and
not from the chlorination of the water.
Moreover, although chlorination of the water was found to produce
haloforms, it was also destroying detectable concentrations of organic
pollutant, possibly toxic in nature. Rook made the comment, "Comparison
of headspace fingerprints of water before and after breakpoint chlorination
indicated that the volatile micropollutants passed this treatment step
in diminished concentration." The volatile micropollutants had previously
been stated to include freons, chlorinated solvents, lower alkanes and
substituted benzenes and toluenes.
Rook also points out that the haloforms are significantly adsorbed
by activated carbon and also are removed by volatilization during flow in
open channels and by cascade aeration.
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The Work of Bellar. Lichtenberg and Kroner
Later in 1974 the results of a study similar to that of Rook
were published by Bellar, Lichtenberg and Kroner of the National Envi-
ronmental Research Center of the EPA in Cincinnati (10 ). These
authors found by headspace chromatography substantial concentrations of
haloforms to be present in a variety of finished drinking waters from
Ohio, Indiana and Alabama, in concentrations ranging from about 50 yg
per liter to almost 200 yg per liter. Drinking waters from nearby well-
water sources showed less than 10 yg per liter of haloforms.
Further investigation of one of the surface supplies showed that
the raw water contained less than 1.0 yg per liter of haloform and that
the haloform Increased t» more than 100 yg per liter after chlorination
of the water. Unfortunately, the compounds responsible for the formation
of the chloroform could not be identified, for the raw water was the Ohio
River, which had been polluted extensively upstream with a wide variety
of organic chemicals.
Bellar, Lichtenberg and Kroner showed that haloform formation
was slow in their water, requiring up to 24 hours for full development
with a single dose of free chlorine. This may be one reason for the
greater concentrations of haloforms found in this study as compared with
Rook's findings. Additionally, however, the concentrations of chlorine
used were generally greater.
The work of Bellar, Lichtenberg and Kroner is less thorough and
well-rounded that that of Rook. The one additional point it may add to
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Rook's work is the indication that other substances than the coloring
matter of water may produce haloforms. It accords with Rook in not finding
chlorinated organic compounds other than the haloforms although the stripping
procedure used was designed to detect compounds with boiling points up to
150°C.
Beliar, Lichtenberg and Kroner also attributed the production of
the haloforms to the haloform reaction, but suggested that they came from
ethyl alcohol, also detected in the water. They performed no follow-up
experiments, however, to show whether or not ethyl alcohol produces
chloroform when chlorinated under the conditions of water treatment.
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Health Hazards in Water Chlorination
Considerable interest in problems associated with the presence of
chlorinated organic compounds in drinking water was aroused in 1974 by
the publication of studies purporting to relate the occurrence of such
compounds with cancer rates in New Orleans (37, 162 ) and with the finding
of volatile chlorinated organics in the blood of patients at a New Orleans
hospital ( 31 ).
The evidence for a relation between cancer incidence and drinking
water quality in New Orleans is far from conclusive. Even if this relation-
ship were firm, there is no evidence to show that it is the chlorinated
organic compounds in the drinking water that are responsible for the rela-
tionship. (Presumably this class of compounds has received particular
notice because it includes chlorinated pesticides and vinyl chloride, and
because chlorinated compounds are detected with high sensitivity by gas
chromatography.) Beyond this there is no evidence that water chlorination
is responsible for any of the chlorinated organic compounds found at
New Orleans.
Apart from the chlorophenols, whose formation and subsequent destruc-
tion by aqueous hypochlorination are well documented, the only identified
chlorinated products from the hypochlorination of water supplies are chloro-
form, bromoform and the mixed chlorobromoforms. There remains a possibility
that non-volatile chlorinated organic compounds not detectable by the tech-
nique used are formed, but what meagre data there are on the products of
the hypochlorination of natural organic compounds suggests that highly
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chlorinated derivatives are not likely to form and that more moderately
chlorinated ones are generally subject to oxidative decomposition by excess
hypochlorite. The only waters in which an extensive variety of chlor-
inated organic compounds have been found have been those of rivers heavily
polluted by discharges from chemical industries.
Accordingly, the finding of numerous chlorinated organic compounds
in drinking waters derived from strongly polluted rivers is extraneous in
one major sense to the question of health hazards induced by water chlorina-
tion. On the other hand, there is a good probability that when waters
strongly polluted with chlorinated organic chemicals are subjected to free
residual chlorination, a sufficient fraction of these compounds will be
decomposed, as found by Rook, that the total concentration of chlorinated
organic compounds is considerably reduced. Then, whatever toxicological
or carcinogenic hazard is associated with the presence of chlorinated organic
chemicals will be lessened rather than accentuated by hypochlorination.
It seems possible that a partial solution to the problem of chlorinated
organic compounds in New Orleans drinking water is an intensification rather
than an abatement of hypochlorination. Obviously more complete chemical
studies are required in addition to toxicological ones, so that a total
balance of chlorinated organic substances and of other potentially
hazardous materials as they are affected by hypochlorination of the water
^
may be obtained.
With regard to the hypochlorination of otherwise unpolluted waters,
the only known health problem to be addressed is the toxic or carcinogenic
properties of the haloforms found to be produced in the hypochlorination
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process. Since no information on the toxicities or carcinogenic!ties
of bromodichloromethane, dibromochloromethane or bromoform could be
found, the problem is reduced at present to a consideration of the toxic
and carcinogenic properties of chloroform.
The acute toxic dose of chloroform to a number of test animals is
given as about 1800 mg. per kg. ( 95 ). It falls in the same class
of toxic substances as sesame oil and household sulfonated detergents in
this respect ( 95 ). Chronic toxic affects seem to begin with daily
doses in excess of 0.3 mg. per kg. body weight. At a dose rate of 0.4
mg. per kg. albino rats showed no effect, but guinea pigs exhibited increased
vitamin C in the adrenals. At a dose rate of 12.5 mg. per kg. the albino
rats showed disturbance of conditioned reflexes after four months( 95 ).
With a chloroform concentration of 0.1 mg. per liter and a consump-
tion of one liter per day, the intake rate of a 50 kg.'individual would
be .002 mg. per kg., about one two-hundredth of the minimum observed
chronic toxicity level.
Robeck has noted that the allowed limits for industrial air exposure
are about 1000 times as great as the expected water intake rate at the
maximum concentration levels found.
With regard to the carcinogenicity of chloroform the International
Agency for Cancer Research Monograph states that the carcinogenic potential
of chloroform has been inadequately investigated so that as of 1970 it
was not possible to extrapolate the carcinogenic risk of chloroform to
man.
Three feeding studies, two of them to mice, have been reported in
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the literature. In one of these, by Eschenbrenner and Miller ( 38, 39 )»
liver hepatomas were observed, but only if the doses of chloroform were
great enough to cause necrosis of the liver and death of a majority of
the mice within 150 days. No hepatoaas were observed with non-necrotizing
doses of chloroform.
Rudali ( 127 ) in the second mouse study, administered 0.1 ml
of 40% chloroform in oil twice a week. Three mice of 24 with an average
life span of 297 days developed hepatomas; however, there was no untreated
control group for comparison.
Hueper and Payne (72 ) fed rats 2% chloroform in their diets
for 13 months; no hepatomas were observed in the 40 test animals.
There are also two studies in which chloroform was administered by
subcutaneous injection, one with mice ( 123 ) and one with rabbits
(80 ). Results of both studies were negative with respect to car-
cinogenesis of chloroform.
The conclusion must be that although substances of established car-
cinogenic! ty may be carried by polluted water supplies and distributed in
drinking water, there is no evidence at present that the hypochlorination
of water supplies makes the drinking water carcinogenic.
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Recent Work of J. J. Rook
At a recent (Feb. 1975) meeting with Drs. Rook additional and
more recent findings of his work were discussed. There have been no major
new discoveries, but Drs. Rook was able to expand on some of the data and
conclusions in his paper. A drinking water supply derived from the Meuse
River and subsequently treated by a month or more of storage followed by
slow-sand filtration was chlorinated at 0.5, 1.0, 2.0-and 5.0 ppm aqueous
chlorine and subjected to head space analysis after an hour of contact.
Haloforms in concentrations up to perhaps 50 micrograms per liter were
found,,in spite of the fact that biological activity during storage and
slow sand filtration should have eliminated possible small molecule pre-
cursors like ethanol and acetone and in spite of the fact that the finished
color was only 5 units. Apparently even high quality waters may contain
biologically resistant natural organic matter, not as colored as the
fulvic acids, that will produce haloforms upon chlorination.
Some model reactions that Rook has studied include the production
of haloforms from alcohol and acetone. He has found that formation of
chloroform from these substances at water pH values and milligram per liter
concentrations is far too slow for these substances to be the source of
the haloforms in water chlorination.
No very extensive studies have been made on the effect of pH. A
few experiments were performed at the very low pH of 3.5 with some indication
of reduced yields of haloform, but there was no dramatic change. There
had been no studies of pH effects within the range 6 to 8.5 at the time
-35-
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of meeting, but these were planned for the near future.
Data on the possible formation of other halogen derivatives thaft
those of methane were scanty. Drs. Rook felt that some of his chromato-
graphs showed chlorinated ethane, but he was not certain of its source
and whether it was actually formed in the chlorination process. Larger
chlorinated molecules were not generally detectable with Rook's head-
space technique.
Rook had evaporated samples of some of his chlorinated waters and
had obtained positive analyses for organically bound halogen on some of
the residues in excess of amounts present in the unchlorinated waters. A
large part of the organically bound halogen was bromine, giving additional
indication of formation of these halogenated organic materials during water
chlorination.
Rook had no indication of any formation of CC1, in the process of
water chloriaation.
In his earlier studies Rook had found that a number of compounds
simulating portions of the proposed structures for humic substances, like
pyrogallol and dihydroxybenzenes, react with dilute hypochlorite to give
chloroform. More recent studies have not confirmed this; it now appears
that reaction of these substances at the part per million level is too
slow to account for the observed haloform formation.
One possibility is that meta rather than para or ortho dihydroxy
substitution is needed to provide the required rate of hypochlorination.
Since the haloform reaction depends eventually on a structure of the type
-C - C-, and this structure is found most readily in a compound like 1, 3,
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5<-trihydroxybencene, it is perhaps1 to structures of this sort that one
should look for precursors of the .halo£oras. Indeed, of the compounds
investigated by Rook, resorclnel, m-dlhydroxybenzene, seems to be the one
exhibiting the required rate of reaction at the part per million level.
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Possible Modifications in Treatment
The hygienic significance; of the formation of haloforms during
water chlorination is at present: largely unknown. Health hazards claimed
or foreseen for other chlorinated materials encountered as pollutants in
natural waters should not be transferred willy-nilly to the haloforms.
Should any health hazard be shown to be associated with haloforms
or other halogenated compounds formed in the process of water chlorination,
then suitable modifications in source or treatment of the water should be
sought to minimize or eliminate the occurrence of the hazardous materials
without degrading the hygienic quality of the water in other ways.
The obvious step is to eliminate chlorination. Such a move would,
however, mean a loss qf all the benefits to health provided by chlorination:
security from water-borne disease; maintenance of cleanliness and water
quality in the distribution system; and simplicity and reliability in
operation of the disinfection process. No other disinfecting agent, how-
ever powerful, provides all the advantages to health that chlorination
does.
Moreover, no substitute disinfectant to chlorine should be recom-
mended generally until it has been shown by studies as extensive and
rigorous as those with chlorine that the use of such a disinfectant is
more free from the production of noxious by-products than chlorination is.
If chlorination is to be retained, there are two approaches for
minimizing the occurrence of noxious by-products in the finished water.
One is to remove precursor material as much as possible before the water is
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chlorinated. The second is to remove the chlorinated by-products after
they have been formed.
The first approach means that prechlorination, which has been used
widely as a general preconditioning step for water treatment, must be
replaced by post chlorination after as much as possible of the organic
material has been removed in other ways. Techniques of this type may be
preferred when relatively unpolluted upland waters are being treated, for
intensive chlorination of long duration is not needed for adequate 'disin-
fection with such waters. Preliminary treatment steps for reduction in
concentration of precursor organic matter may be: (1) Storage for one to
several months; (2) Coagulation-filtration; (3) Ozonation; (4) KMnO,
treatment; or any combination of these.
The experience of Rook indicates that storage and coagulation, although
useful in reducing the concentrations of halofonus, cannot be expected to
eliminate them fully. Ozone is known to react only selectively with organic
material in water, but its effectiveness on humic substances and its known
reactivity towards double bonds may mean a very substantial reduction in
haloform precursors. Permanganate provides a more general oxidizing action
than ozone, but a less rapid and intense one. A combination of ozonation
with some permanganate treatment may provide the most substantial overall
reduction in organic matter.
The other approach, removal of haloforms and other formed chlorinated
compounds following their formation,appears preferable when the source
is a polluted one probably.containing a substantial concentration of chlor-
i
inated organic material before any treatment. Best treatment of such waters
-39-
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requires that some effort be made to remove the chlorinated substances
already present in the raw water and this treatment may then also be utilized
to take out haloforms produced during chlorination.
The most effective final treatment for removing chlorinated substances
is, in all probability, adsorption on activated carbon. Aeration techniques
can be used substantially to reduce haloform concentrations but is
ineffective for heavier, less volatile molecules. Rook has found that
powdered activated carbon has a good adsorptive affinity for haloforms.
When final adsorptive treatment is used for the removal of chlor-
inated substances, the initial prechlorination step should be intense, with
maintenance of substantial residual free chlorine. There are two reasons
for this recommendation. First,, the presence of excess free chlorine will
encourage the completion of the haloform reaction, yielding the relatively
innocuous haloforms themselves, rather than partially chlorinated inter-
mediates that may be both more hazardous and more difficult to remove.
Second, the strong oxidizing potential of residual free chlorine seems to
be effective in reducing the concentrations of some chlorinated organic
substances present in typical polluted waters by oxidizing them to carbon
dioxide and water.
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Indicated Research Needs
Until the recent paper by J. J. Rook, the problem of the formation
of chlorinated organic compounds during water chlorinatlon had been almost
completely ignored except for the reactions with phenolic materials. As
a result the need for knowledge to be obtained from research is great and
varied. Almost any accurate information related to the subject will be
useful at least in providing orientation.
There are, however, certain subjects for research that seem most
likely to provide an early assessment of the seriousness of the problem
posed by the formation of haloforms and possibly other chlorinated organic
substances during water chlorination.
A first priority should probably be determination of the extent of
formation of other chlorinated materials than the haloforms. This will
require somewhat more sophisticated techniques than simple head-space
analysis, but might usefully be accomplished with some sort of initial
low-pressure vapor-distillation concentrating process like that used by
Silvey in obtaining odorous concentrates from actinomycetes. If no other
significant compounds than the haloforms are found, the overall problem
cannot be considered at present a very serious one.
A second issue that it would be well to have clarified as soon
as possible is the yield of haloforms in relation to other parameters
measuring aspects of organic matter in water, such as T.O.C., color,
C.O.D. or permanganate value, CCE or CAE, etc. Only when some sort of cor-
relation with properties such as these is shown will it be possible to
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know what to aim for in the pretreatment of water to make it suitable
for chlorination.
Third, the effects of diverse pretreatment steps should be studied
with regard to the production, of haloforms or other chlorinated organic
substances. Obviously, such information is needed to assess the efficacy
and benefit of possible pretreatment processes.
There needs also to be a. study or series of studies, more fundamental
in nature, to determine the dynamics and mechanism of the formation of the
haloforms or other chlorinated organic substances. It seems clear that
the pertinent reactions, at lea.st in dilute aqueous media at the part per
million level, are relatively specialized ones and do not indicate a
generalized, random chlorine substitution. Also, the work of Bellar,
Lichtenburg and Kroner indicates that the haloform-producing reactions
are slow,and thus an understanding of the time dependence is important.
Perhaps a dechlorination after fifteen to thirty minutes of disinfection
would minimize formation of chlorinated derivatives. At the same time
there should be dynamic comparison of the exertion of chlorine demand
and the formation of haloforms. The relation between these will indicate
the role of intermediates in the overall process.
Finally, because the standard haloform reaction is a classic
example of a base-catalyzed organic reaction, there should be a detailed
investigation of effects of pH on both the stoichiometry and the dynamics
of formation of haloforms during water chlorination. This will serve not
only as a clue to understanding the chlorination process, but also as a
guide to best practice in minimizing extraneous chlorination.
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REFERENCES
1. Ackman, R. G. and Burgher, R. D. Quantitative Gas-Liquid Chroma-
tographic Estimation of Volatile Fatty Acids in Aqueous Media.
Anal. Chem. _35_, 647-652 (1963).
2. Allen, L. A., Blezard, N. and Wheatland, A. B. Formation of Cyanogen
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•h U.S GOVERNMENT PRINTING OFFICE 1975- 582-421/256
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/1-75-002
2.
3. RECIPIENT'S ACCESSIOI*NO.
tfste)
4. TITLE AND SUBTITLE
Formation of Halogenated Organics by Chlorination of
Water Supplies (A Review)
5. REPORT DATE
Mar. 26, 1975 (transmittal
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
J. Carrell Morris, Gordon McKay Professor
of Sanitary Chemistry, Harvard University
9. PERFORMING ORGANIZATION NAME AND ADDRESS
J. Carrell Morris
Pierce Hall 127
Oxford Street
Cambridge. MA 02138
10. PROGRAM ELEMENT NO.
1CA046 (PEMP)
11. CONTRACT/GRANT NO.
P5-01-1805-J
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
Environmental Protection Agency
Washington, DC
13. TYPE OF REPORT AND PERIOD COVERED
final. Nov. 1. 1974-Mar. 25. ]
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Available literature on the formation of halogenated organic compounds during
the chlorination of water supplies has been reviewed critically. Types of organic
compounds likely to be encountered in natural waters have been surveyed and various
known or prospective reactions of dilute aqueous chlorine with these types of com-
pounds have been discussed.
It is concluded that two principal types of chlorination reaction are expected:
(1) electrophilic aromatic chlorination as in the long-known formation of chlorophe-
nols; and (2) electrophilic chlorine addition to activated double bonds like "that of
eric-lace tone. Chloroform or other haloforms may occur as end products of exhaustive
chlorination in either case. General substitution reactions of chlorine are unlikely
however. So carbon tetrachloride or fully chlorinated higher hydrocarbons are not
probable products of water chlorination.
Possible methods for minimizing the concentrations of halogenated organic com-
pounds in municipal supplies have been outlined. These include pretreatment methods,
such as coagulation or preozonation to reduce amounts of precursors to the halogena-
ted compounds, and posttreatment methods, such as carbon adsorption or aeration to
remove halogenated compounds after their formation.
Needed research has been described.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Toxicity, Activated Carbon Treatment,
Chlorination*, Aeration, Catalysis,
Chemical Reactions, Coagulation, Water
Treatment, Water Supply
0620
0702
0703
1302
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (ThisReport/
21. NO. OF PAGES
20. SECURITY CLASS (This page)
22. PRICE
EPA Form 2220-1 (9-73)
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