Total Chlorine or Chloramine. In your water
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
HEALTH
EFFECTS
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
|
Residential Point-of-Use Point-of-Entry |
Activated Carbon Catalytic
Activated Carbon |
|
Municipal |
N/A |
|
Visit
WQA.org to search for products certified to NSF 42 for chloramine reduction. |
|
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.
REFERENCES/SOURCES
Bauer, R.C.
and V.L. Snoeyink, Journal Water Pollution Control Federation, 45:2290 (1973).
Safe Drinking Water Act Amendments of 1996. Public Law 104-182. (Aug. 6, 1996).
Tripple MA, Shusterman N, Bland LA, McCarthy MA,
Favero MS, Arduino MJ, Reid MH,
Jarvis WR;
Illness in hemodialysis patients after exposure to chloramine contaminated
dialysate; Hospital Infections Program, Center for Infectious Diseases,
Atlanta, Georgia 30333; ASAIO
Trans. 1991 Oct-Dec: 37 (4): 588-91.
U.S.
EPA.Drinking Water Criteria Document for Chloramines. ECAO-CIN-DOO2, (March,
1994).
U.S.
EPA. 1999. EPA Guidance Manual: Alternative Disinfectants and Oxidants.
EPA815R99014, (April 1999).
U.S.
EPA. 1998. National Primary Drinking Water Regulations: Disinfectant and
Disinfectant Byproducts Notice of Data Availability; Proposed Rule, Federal Register 63 (61): 15673-15692
U.S.
EPA, 2006. National Primary Drinking Water Regulations: Stage 2 Disinfectants
and Disinfection Byproducts Rule; Federal Register 71: 388-493
WHO
(2004). Monochloramine in Drinking Water. http://www.who.int/water_sanitation_health/dwq/chemicals/en/monochloramine.pdf
Xu Xu and Clifford Weisel (2005). Human respiratory
uptake of chlororform and haloketones during showering.
Journal of Exposure Analysis and Environmental
Epidemiology.
Xu
Xu and Clifford Weisel (2005). Dermal uptake of chloroform and haloketones
during bathing. Journal of Exposure Analysis and Environmental Epidemiology.
ACKNOWLEDGEMENT
|
WQA wishes to express
sincere appreciation for the unselfish contributions of the members of WQA who
contributed their time and expertise toward the completion of this bulletin.
The Water Quality Association
publishes this Technical Application Bulletin as a service to its members and
the interested public. Information contained herein is based upon the most
recent public data known as of the publication date and cannot take into
account relevant data published thereafter. The Water Quality Association makes
no recommendations for the selection of a treatment system, and expressly
disclaims any responsibility for the results of the use of any treatment method
or device to reduce or remove a particular contaminant.
This reference document is published by:
National
Headquarters & Laboratory
4151 Naperville Road • Lisle, Illinois 60532
Tel: 630 505 0160 • Fax: 630 505 9637
|
Contaminant |
In Water As |
Maximum
Residual Disinfectant Level |
|
Monochloramine Dichloramine Nitrogen
trichloride |
NH2Cl NHCl2 NCl3 |
US EPA: 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 Point-of-Use |
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.) |
||
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