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WQA
Many municipal water supplies
have switched from chlorine to an alternative method of disinfection to reduce
the formation of trihalomethanes (THMs).
Chloramines do pose a risk for
hemodialysis patients and fish.
Nitrosamines can be generated
as byproducts from use of chloramines. They are strongly suspected of being
human carcinogens.
Contaminant
|
In Water As
|
Maximum Residual Disinfectant Level
|
Monochloramine
Dichloramine
Nitrogen Trichloride
|
NH2Cl
NHCl2
NCl3
|
MRDL* = 4.0 mg/L or ppm (measured as Cl2)
MRDLG** = 4.0 mg/L or ppm (measured as Cl2)
|
Sources of Contaminant
|
Municipal Treatment
|
|
Potential Health Effects
|
Can cause hemolytic anemia when present in dialysis
process water
|
|
Treatment Methods
Point-of-Entry (POE)
Point-of-Use (POU)
|
Activated Carbon
Catalytic Activated Carbon
|
|
*Maximum Residual Disinfectant Level (MRDL)
- The highest level of a disinfectant allowed in drinking water. There is
convincing evidence that addition of a disinfectant is necessary for control
of microbial contaminants.
**Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water disinfectant below
which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of
disinfectants to control microbial contaminants.)
|
Aqueous
chlorine reacts with certain organic materials present in water sources to form
trihalomethanes (THMs).
Long-term
exposure to these harmful byproducts of disinfection has been linked to an
increased risk of cancer and infant birth delivery problems.
It
is estimated that THMs in drinking water are responsible for as many as 2-17
percent of the bladder cancers diagnosed each year in the United States.
To
protect the public, the U.S. Environmental Protection Agency has established a
maximum contaminant level of 0.08 milligrams per liter (mg/L) for THMs.
To
conform to these regulations, many municipal water supplies have switched to an
alternative method of disinfection using chloramination; more than 1 in 5
Americans uses drinking water treated with chloramines.
Chloramination
involves the addition of anhydrous or aqueous ammonia (NH3) before or after the
addition of chlorine (HOCl) to produce monochloramine (NH2Cl).
This
reaction is as follows: NH3 + HOCl = NH2Cl + H2O Chloramines also form to a
lesser extent during conventional chlorine treatment when aqueous chlorine
reacts with natural organic nitrogen.
Monochloramine
is 200 times less effective as a disinfectant than chlorine, but is an
attractive alternative since it does not react as readily with organic materials
to form THMs.
Many
water utilities overcome the decreased efficiency of monochloramine by dosing
first with chlorine, then adding ammonia at a later stage of treatment.
Since
the initial application is of chlorine, this increases the initial biocidal
efficiency of the disinfection but also increases the risk of THM formation
during this initial treatment.
The
ammonia addition results in the residual chemical in the plumbing being
monochloramine, with longer lasting residual and reduced risk of THM formation
in the distribution system.
The
process of chloramination is both pH and concentration dependent.
Water
pH levels below 7.5 or chlorine to ammonia weight ratios exceeding 5:1 increase
the formation of dichloramine (NHCl2) and nitrogen trichloride (NCl3).
Dichloramine
and nitrogen trichloride are undesirable byproducts in that while they are more
effective disinfectants, they are less stable and cause greater “swimming
pool”- type taste and odor problems when they exceed concentrations of 0.80
mg/L and 0.02 mg/L (respectively).
Excessive
chlorine levels produce THMs, while excess ammonia increases the potential for
nitrification in the distribution system.
The
US EPA recognizes three analytical methods as acceptable for measuring residual
chloramines.
These
methods are:
• Amperometric Titration (Standard Method 4500-C1 D and ASTM Method
D 1253-86)
• DPD Ferrous Titrimetric (Standard Method 4500-C1 F)
• DPD Colorimetric (Standard Method 4500-C1 G)
The
average municipal water system maintains residual monochloramine concentrations
around 2 mg/L (range: 1.5 mg/L to 2.5 mg/L).
Chloramination
also has the added benefit of decreasing the formation of biofilms in water
supply systems since the residual levels of monochloramine remain relatively constant
throughout the system.
Although
the use of chloramination has recently increased, it has a long history of safe
and effective use in the United States.
The
City of Denver, Colorado has utilized chloramination since 1918.
An
extensive risk assessment by the EPA’s National Center for Environmental
Assessment (NCEA) utilized existing human and animal studies to conclude that
human health effect do not appear to be associated with levels of residual
chloramines typically found in drinking water.
However,
a Maximum Residual Disinfectant Level Goal (MRDLG) and Maximum Residual
Disinfectant Level (MRDL) of 4.0 mg/L was established by US EPA as the
enforceable maximum safety level for chloramines (measured as chlorine, Cl2)
for public water systems under the Safe Drinking Water Act, and the level below
which there is no known or expected risk to health.
Chloramines
do pose a risk for hemodialysis patients and fish. Chloramines easily enter the
bloodstream through dialysis membranes and the gills of fish.
Once
in the blood stream, chloramines denature hemoglobin and cause hemolytic
anemia.
Accidental
use of chloramine treated water for dialysis has been responsible for a number
of patients requiring transfusion to treat resultant hemolytic anemia, and was
a possible factor in an increased mortality (death) rate among the dialysis
center patients during the 5 months after the chloramine exposure when compared
to the 12 months before the chloramine exposure.
Nitrosamines
can be generated as byproducts from use of chloramines. They are strongly
suspected of being human carcinogens.
Nitrosamines
can come in contact with most of organs in the body in addition to crossing the
placenta.
Effects
such as cell damage and DNA mutations may occur and lead to cancer even at low
levels of exposure.
TREATMENT
METHODS
While
chloramines are not a drinking water health concern to humans generally, their
removal improves the taste and odor of drinking water.
Chloramines
are small, stable molecules with no net charge making them difficult to remove
by distillation, reverse osmosis, and ion exchange resins.
Due
to the reaction of aqueous chlorine with organic nitrogen, chloramines also
present a concern for municipal water systems utilizing chlorine as a method of
disinfection.
This
reaction is of concern because there is potential for harmful disinfection
byproducts to be produced from it.
The
most effective nonchemical method for removing chloramines is by activated
carbon (C).
Activated
carbon does not adsorb chloramines but rather removes them through its ability
to act as a catalyst for the chemical breakdown of chloramines to innocuous
chlorides in water.
This
catalytic reaction involves the formation of an oxide of carbon intermediate
(CO*).
This
reaction is as follows: NH2Cl + H2O + C* = NH3 + Cl- + H+ + CO* 2NH2Cl + CO*=
N2 + 2Cl- + 2H+ + H2O + C*
Fine
mesh sizes of activated carbon remove chloramines more efficiently since they
have greater surface areas and allow faster access to catalytic sites.
Also,
activated carbon that has been “acclimated” to achieve increased sites for
oxide of carbon intermediate (CO*) formation improves chloramine removal.
For
new activated carbon, initial dosing with chlorine to preoxidize the carbon may
result in more effective chloramine removal, as shown in the second reaction
above.
A
bed contact time of 10 minutes or greater can be required for complete
catalysis of chloramines with traditional activated carbons.
New
types of activated carbons have been developed with increased catalytic
activity that is especially effective at the removal of chloramines.
These
catalytic carbons may be marketed with a peroxide number (rate of hydrogen
peroxide decomposition) in addition to the traditional iodine adsorption
number.
The
chloramine removal capacity of activated carbon is dependent upon pH.
Catalytic
carbons have demonstrated increased chloramine removal efficiency at higher
pHs. Ammonia (NH3), chloride (Cl- ), and nitrogen gas (N2) are produced by the
catalysis of monochloramine.
The
removal of these catalytic byproducts can be achieved by additional treatment
with ion exchange resins or by reverse osmosis.
The
treatment methods listed herein are generally recognized as techniques that can
effectively reduce the listed contaminants sufficiently to meet or exceed the
relevant MCL.
However,
this list does not reflect the fact that point-of-use/point-of-entry (POU/POE)
devices and systems currently on the market may differ widely in their
effectiveness in treating specific contaminants, and performance may vary from
application to application.
Therefore,
selection of a particular device or system for health contaminant reduction
should be made only after careful investigation of its’ performance
capabilities based on results from competent equipment validation testing for
the specific contaminant to be reduced.
As
part of point-of-entry treatment system installation procedures, system
performance characteristics should be verified by tests conducted under
established test procedures and water analysis.
Thereafter,
the resulting water should be monitored periodically to verify continued
performance.
The
application of the water treatment equipment must be controlled diligently to
ensure that acceptable feed water conditions and equipment capacity are not
exceeded.
Visit
WQA.org to locate water professionals in your area. Note that Certified Water
Specialists have passed the water treatment education program with the Water
Quality Association and continue their education with recertification every 3
years.
REGULATIONS
In
the United States the EPA, under the authority of the Safe Drinking Water Act
(SDWA), has set the Maximum Residual Disinfectant Level (MRDL) for chloramines
(measured as Cl2) at 4.0 mg/L.
Disinfection
byproducts are also regulated under the SDWA, and the MCL for total THMs is
0.08 mg/L.
The
utility must take certain steps to correct the problem if the tap water exceeds
these limits and they must notify citizens of all violations of the standard.
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