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Chlorine Dioxide Disinfection in the Use of
Individual Water Purification Devices
Technical Information Paper #31-007-0306
PURPOSE
This information paper provides an in-depth review of chlorine dioxide as a disinfectant in
potable water supplies. This paper is intended to assist the reader in evaluating the disinfection
capabilities of Individual Water Purification Devices (IWPDs) using chlorine dioxide to kill or
inactivate disease-causing bacteria, viruses, and protozoan cysts.
REFERENCES
Appendix A contains a list of references.
INTRODUCTION
Background
Understanding the disinfection capabilities of chlorine dioxide to kill or inactivate disease-
causing microorganisms is important in protecting soldiers, who are considering using this
technology, from acute health threats posed by these microorganisms. Soldiers deployed beyond
traditional field drinking water supplies must have access to microbiologically safe water. Using
IWPDs is one way to provide microbiologically safe water in these situations. These IWPDs
must protect the Soldier from acute microbial health threats. The U.S. Environmental Protection
Agency (EPA) Guide Standard and Protocol for Testing Microbiological Water Purifiers
(reference 1) provides performance standards by which an IWPD using chlorine dioxide can be
evaluated. The perfonnance standards are a minimum 6-log reduction/inactivation of bacteria,
4-log reduction/inactivation of viruses, and 3-log reduction/inactivation of protozoan cysts.
Chlorine dioxide-using IWPDs meeting these standards are considered effective against disease
causing bacteria, viruses, and protozoan cysts. Some IWPD manufacturers test their devices
using this protocol. This is the best way to evaluate the IWPDs disinfection capabilities. In the
absence of that testing data, this infonnation paper can be used to gain an understanding of
chlorine dioxide disinfection capabilities and help determine if an IWPD using chlorine dioxide
could successfully meet the EPA Guide’s minimum performance standards.
General
Chlorine dioxide (CIO2) was discovered in 1811 (reference 2). It’s widely used in numerous
industries including wood pulp processes, wastewater treatment, and food processing. Water
treatment plants in the United States first used chlorine dioxide in the 1940s for taste and odor
control (reference 3). In addition to taste and odor control, many drinking water systems
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1. REPORT DATE
MAR 2006
2. REPORT TYPE
technical
3. DATES COVERED
00-10-2005 to 00-03-2006
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
U.S. Army Center for Health Promotion and Preventive Medicine
(USACHPPM),5158 Blackhawk Road, APG,MD, 21010
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Chlorine Dioxide Disinfection in the Use of Individual Water Purification 5b GRANT NUMBER
Devices -
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
Steven Clarke; William Bettin 31-007-0306
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
U.S. Army Center for Health Promotion and Preventive Medicine report number
(USACHPPM),5158 Blackhawk Road, APG,MD, 21010 TIP 31-007-0306
9. SPONSORING/MONITORING AGENCY NAME(S ) AND ADDRESS(ES ) 10. SPONSOR/MONITOR' S ACRONYM(S)
11. SPONSOR/MONITOR'S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES
14. ABSTRACT
Soldiers deployed beyond traditional field drinking water supplies must have access to microbiologically
safe water. Using Individual Water Purification Devices (IWPDs) is one way to provide microbiologically
safe water in these situations. These IWPDs must protect the Soldier from acute microbial health threats.
Understanding the disinfection capabilities of chlorine dioxide to kill or inactivate disease-causing
microorganisms is important in protecting soldiers, who are considering using this technology, from acute
health threats posed by these microorganisms. This information paper provides an in-depth review of
chlorine dioxide as a disinfectant in potable water supplies. This paper is intended to assist the reader in
evaluating the disinfection capabilities of IWPDs using chlorine dioxide to kill or inactivate disease-causing
bacteria, viruses, and protozoan cysts.
15. SUBJECT TERMS
water; drinking water; water treatment; purification; chlorine dioxide; disinfection; military; IWP
(individual water purifier); pathogen removal
16. SECURITY CLASSIFICATION OF:
a. REPORT
unclassified
b. ABSTRACT
unclassified
c. THIS PAGE
unclassified
17. LIMITATION OF
18. NUMBER
ABSTRACT
OF PAGES
14
RESPONSIBLE PERSON
Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
TIP #31-007-0306
throughout the world today use chlorine dioxide for disinfection, control of organic disinfection
byproducts (e.g., trihalomethanes), and oxidation of iron and manganese. Currently, there are
only a few Commercial-Off-The-Shelf (COTS) IWPDs using chlorine dioxide for disinfection.
CHLORINE DIOXIDE CHEMISTRY IN WATER
General
Chlorine dioxide exists as an undissociated gas dissolved in water at a near neutral pH range (pH
6-9) (reference 4). Because chlorine dioxide exists as a gas it is vulnerable to volatilization; it
can be easily removed from water by turbulent aeration, and is destroyed by ultraviolet light
when exposed to sunlight (reference 5). Chlorine dioxide is stable in dilute solution in a closed
container in the absence of light (reference 5). One of the advantages of using chlorine dioxide
over chlorine for disinfection is the decreased formation of organic disinfection byproducts
(DBPs), such as trihalomethanes (reference 3). However, chlorine dioxide is an oxidant and
reactions with organic matter form inorganic DBPs including primarily chlorite ion (CIO2’) and
to a lesser extent chlorate ion (CIO3'). Chloride (CT) is also formed to a lesser extent. The
reaction of chlorine dioxide in water at pH 6-8 containing organic matter is suggested to be
(reference 6):
C102 + e' -»• C102'
CIO2" + H+ <-» HClOo (chlorous acid)
4HC102 -*■ 2C102 + H+ + CT + HCIO3 + H20
Chlorine dioxide reacts rapidly. In drinking water, where typical dosages are 0.07 - 2.0 mg/L,
chlorite is the predominant reaction product with approximately 50-70% of chlorine dioxide
converted to chlorite, and 30% converted to chlorate and chloride (reference 3). Manufacturer
recommended dosages for IWPD use may be similar to those used in water systems or may be
much higher. Chlorine dioxide IWPD manufacturers recommend dosages from 0.7-4 mg/L for
most waters and up to 7.5 mg/L when treating cold and/or cloudy waters (references 7 and 8).
Generation
Chlorine Dioxide Generation for Water Systems
Chlorine dioxide can’t be stored commercially or compressed since it is explosive under
pressure. Therefore, it must be generated on-site (reference 5). Although there are emerging
technologies for chlorine dioxide generation, the two most common methods are (references 2
and 5):
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(1) sodium chlorite - acid generation
5NaC102 + 4HC1 <-► 4C102 + 5NaCl +2H20
(2) sodium chlorite - chlorine generation
NaC102 + Cl2 2C102 + 2NaCl
Chlorine Dioxide Generation for IWPDs
Chlorine dioxide must also be generated on-site on a much smaller scale or provided in dilute
chlorine dioxide solutions for IWPD use. Currently, generating chlorine dioxide on-site for use
as an IWPD uses buffered sodium chlorite, generally referred to as “stabilized chlorine dioxide”
(references 9 and 10). The sodium chlorite must be “activated” by adding an acid, usually
phosphoric or citric acid, resulting in the formation of chlorine dioxide in a reaction similar to
the sodium chlorite - acid generation reaction used by water systems (shown earlier). There are
health concerns associated with the use of “stabilized chlorine dioxide.” “Stabilized chlorine
dioxide” can potentially result in little formation of chlorine dioxide, thereby reducing
disinfection capability, and can also potentially result in high concentrations of chlorite, which
may cause adverse health effects when ingested and also has no disinfection capability
(references 3 and 1 1). Dilute solutions of chlorine dioxide are also used as IWPDs. These
solutions lose chlorine dioxide over time, but can be stable for several months and possibly
longer. One study showed dilute chlorine dioxide concentrations (approximately 35 mg/L)
exhibited variable losses based on the type of container used for storage (reference 12). For
example, a 35 mg/L chlorine dioxide solution stored in a high-density Polyethylene
Terephthalate (PETE) container for 45 days resulted in a 3% loss of chlorine dioxide (34 mg/L).
In contrast, the same study stored chlorine dioxide in a clear glass container for 3 1 days which
resulted in a 12% gain of chlorine dioxide (39 mg/L) possibly due to continuing formation of
chlorine dioxide from chlorite. Another study showed a 6.2% overall gain in chlorine dioxide
concentration after 252 days of storage in a PETE container (reference 12).
DISINFECTION CAPABILITIES
General
Chlorine dioxide is an effective disinfectant against bacteria, viruses, and many cysts including
the capability to disinfect Cryptosporidium with realistic (typical to slightly higher water system)
dosages (reference 3). A comparison of CTs required for a 2-log inactivation for E. Coli
bacteria, Poliovirus 1, and Giardia cysts showed Giardia cysts were 2-5 times more resistant
than Poliovirus 1 and 16-22 times more resistant than E. Coli bacteria (reference 13). The CT is
the product of disinfectant concentration (C in mg/L) and contact time (T in min). The CT
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product is a useful way for comparing alternative disinfectants and the resistance of various
pathogens (reference 28). Poliovirus was 4-11 times more resistant than
E. Coli bacteria (reference 13). Cryptosporidium oocysts are the most resistant, being 8-16 times
more resistant than Giardia cysts (reference 5). Chlorine dioxide’s general disinfection
capability with respect to microorganisms can be illustrated in the following way from most
effective to least effective:
bacteria > viruses > Giardia cysts > Cryptosporidium oocysts
Chlorine dioxide is similar to other chemical disinfectants in that its disinfection capability
decreases with decreasing temperature, its disinfection capability generally decreases with
increasing turbidity, and its disinfection capability is affected by pH (references 3, 4 and 13).
Since chlorine dioxide exists as an undissociated gas in water, volatilization and loss of chlorine
dioxide and subsequent disinfecting capability is a concern (reference 3). Because chlorine
dioxide is an oxidant it will react with organic matter in the water forming primarily chlorite and
to a lesser extent chlorate and chloride. Both chlorite and chlorate show no disinfection
capabilities and may cause adverse health effects in children, infants, and fetuses (reference 11).
Drinking water systems using chlorine dioxide for disinfection are not generally able to provide
adequate disinfection per regulations in raw water with high organic carbon (i.e., organic matter)
when adding chlorine dioxide in the raw water. This is because the chlorine dioxide is used up
by reacting with organic matter, being reduced to primarily chlorite and leaving no chlorine
dioxide residual (reference 3). This can be a concern for IWPDs when treating raw, unfiltered
water supplies. Higher dosages may be necessary to react with organic matter and provide
disinfection.
Environmental Effects on Disinfection Capability
Effect of pH on Disinfection Capability
Compared to chlorine, chlorine dioxide is a more effective disinfectant across a broader pH
range (roughly between 5 and 10) than free chlorine (reference 3). Several studies have shown
the effect of pH on chlorine dioxide disinfection capability, with most results indicating
disinfection capability generally increases with increasing pH (reference 14). Numerous studies
with viruses (e.g., poliovirus, hepatitis A virus) showed CTs required for a 2-log virus
inactivation were 13-20 times higher at a pH of approximately 6 compared to a pH of 9 and 10
(references 13 and 15). Another study showed CTs up to 90-100 times higher were required for
a 4-log virus inactivation at a pH of 6 compared to a pH of 10 (reference 16). Although these
studies showed much higher CTs necessary at lower pHs, CTs were still low at the lower pHs
(ranging from approximately 3-13 mg-min/L). This indicates chlorine dioxide is a highly
effective disinfectant over a broad pH range. In contrast to the previous studies, a study on
chlorine dioxide disinfection capability against Cryptosporidium oocysts indicated pH does not
appear to have a significant effect on Cryptosporidium inactivation (reference 17). The degree
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of pH effect may be dependent on the targeted organism and in general chlorine dioxide shows
an increase in disinfection capability with increasing pH. Chlorine dioxide would likely be
effective over the pH range (pH 6-9) for natural, untreated water sources likely to be encountered
when using IWPDs.
Effect of Temperature on Disinfection Capability
Like most chemical disinfectants, chlorine dioxide disinfection capability decreases with
decreasing temperatures (reference 5). Cold water temperatures slow disinfection and must be
compensated for by longer contact times or higher dosages to achieve comparable disinfection at
warmer water temperatures (reference 18). A two to three-fold increase in inactivation rates per
10° C water temperature increase seems a generally accepted rule (reference 18). When
considering chlorine dioxide, the U.S. environmental Protection Agency (EPA) developed CT
tables for the Surface Water Treatment Rule (SWTR) by assuming a twofold decrease in CT for
every 10° increase (reference 19). Research shows a 2-log inactivation of E. Coli required four
times higher CT at 5° C compared to 20° C (reference 13). A study using Naegleria cysts
showed at 5° C a CT twice as high than at 20° C was required to provide a 2-log inactivation
(reference 5). Using a two-fold CT increase for every 10° decrease in water temperature is a
good estimate to use when determining CT requirements for chlorine dioxide disinfection
capability.
Effect of Turbidity on Disinfection Capability
Turbidity also has an effect on chlorine dioxide disinfection capability. Turbidity in the form of
particulate matter, aggregated or clumped microorganisms, and dissolved organic matter can
reduce the effectiveness of chlorine dioxide. One study determined that bentonite clay added to
produce turbidity levels up to 2.3 nephelometric turbidity units (NTUs) had no adverse effect on
chlorine dioxide disinfection of poliovirus. However, at turbidity levels of 3.2 and 14.1 NTU,
poliovirus inactivation was noticeably decreased (references 13 and 20). The study suggested
that bentonite appeared to offer protection or shield the viruses from chlorine dioxide
disinfection. Another study using bentonite reduced chlorine dioxide disinfection capability
against Naegleria cysts by 11% at turbidities less than or equal to 5 NTU and 25% at turbidities
between 5 and 17 NTUs (reference 5). Clumped or aggregated microorganisms are also shown
to be more resistant to chlorine dioxide disinfection (reference 5). In the presence of organic
matter chlorine dioxide rapidly oxidizes the organic matter and is converted to primarily chlorite,
and to a lesser extent chlorate and chloride ion (reference 3). This results in loss of chlorine
dioxide residual and an increase in chlorite ion leading to reduced disinfection capability.
Turbidity does have an effect on chlorine dioxide disinfection capability. Chlorine dioxide
disinfection capability decreases in more turbid waters since microorganisms are protected by
solid particles in water, protected by aggregation or clumping, and protected by loss of chlorine
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dioxide residual from oxidation of organic matter. Higher chlorine dioxide dosages may be
necessary when using IWPDs to overcome organic matter oxidation and still provide disinfection
when treating raw, unfdtered water supplies.
Bactericidal Capability
Chlorine dioxide is an effective bactericide. Research on chlorine dioxide bactericidal capability
shows bacteria are less resistant than viruses and cysts (reference 13). Studies using E. Coli
showed 2-log inactivation occurred very quickly in demand-free waters (i.e., no organic matter
present) with CT’s all less than 1.0 mg-min/L, ranging from 0.25 - 0.48 mg-min/L, at the
coldest water temperatures (5° C) and lowest pH levels (6.5 - 7.0) (i.e., worst case conditions,
references 13, 21). Another study estimated CTs of 1 or less at 5° C necessary for a 4-log
E. Coli inactivation (reference 22). Chlorine dioxide should easily achieve a 6-log bacteria
inactivation at low temperatures and low pHs if chlorine dioxide is used for disinfection of more
resistant viruses and cysts. Highly turbid water may require higher CT (i.e., longer contact time
and/or higher dose).
Virucidal Capability
Chlorine dioxide is an effective virucide. Research shows viruses are more resistant than
bacteria but less resistant than cysts (reference 13). Similar to bactericidal capability, viruses are
rapidly inactivated (reference 13). Experiments conducted under worst case conditions (5° C
water temperature in the 6-7 pH range) resulted in CT’s of 5.5 mg-min/L for a 2-log Poliovirus
1 inactivation and 12.6 mg-min/L for a 4-log Hepatitis A virus inactivation (references 13 and
16). The SWTR provides the following CT values for 4-log virus inactivation at various water
temperatures with pH 6-9 (reference 19):
Table 1. EPA Surface Water Treatment Rule (SWTR) Required CT Values
for 4-Log Inactivation of Viruses
by Chlorine Dioxide for pH 6-9
Temperature (deg C)
<=1 _ 5 _ 10 _ 15 _ 20 _ 25
50.1 33.4 25.1 16.7 12.5 8.4
The data used to develop Table 1 were based on experiments conducted in low turbidity waters
under otherwise worst case conditions, 5° C water temperature and pH 6. These CT values are
based on low turbidity waters since it is assumed water systems provide disinfection after
filtration, as the last treatment step prior to distribution. Higher turbidity waters may require
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higher CT to achieve the same log inactivation. Separate CT values for different pHs were not
developed since chlorine dioxide is generally a more effective disinfectant at higher pHs.
Therefore, these CT values are more conservative at the higher pHs (reference 19). A safety
factor of 2 was applied to the data to determine CT values in Table 1 (reference 19). The CT
values at temperatures other than 5° C in the Table were detennined by using a two-fold increase
in CT for every 10° C decrease (reference 19). Even at cold water temperatures, low pHs, and
low turbidity waters, CTs appear realistic and achievable. Based on a typical chlorine dioxide
dosage of 2.0 mg/L for a water system, contact times of 4-25 minutes are necessary to achieve
CT values in Table 1. A chlorine dioxide dose of 0.8 mg/L [EPA’s Maximum Residual
Disinfectant Level (MRDL) for chlorine dioxide] results in contact times of 1 1-63 minutes which
are still reasonable for IWPD use. Highly turbid water may require higher CT (i.e., longer
contact time and/or higher dose).
Cysticidal Capability
Giardia Cysts
Chlorine dioxide is effective against Giardia cysts. One study showed CTs ranging from
1.7-17.6 mg-min/L necessary for 2-log Giardia muris cyst inactivation (reference 23). The
SWTR provides the following CT values for 3-log inactivation of Giardia cysts at various water
temperatures with pH 6-9 (reference 19):
Table 2. EPA SWTR Required CT Values for 3-Log Inactivation of Giardia Cysts
by Chlorine Dioxide for pH 6-9
Temperature (deg C)
<=1 _ 5 _ 10 _ 15 _ 20 _ 25
63 26 23 19 15 11
Data used to develop Table 2 were based on experiments conducted in low turbidity waters at
pH 7 and water temperatures ranging from 1 - 25° C for 2-log Giardia cyst inactivation
(reference 19). Determining 3-log inactivation at all temperatures listed in Table 2 required
extrapolation using first order kinetics and applying a safety factor of 1.5 (reference 19). Based
on Table 2 it appears chlorine dioxide is effective against Giardia cysts at realistic and
achievable CT values. Based on a typical chlorine dioxide dosage of 2.0 mg/L for a water
system, contact times of 6 - 32 minutes, depending on temperature, are necessary to achieve the
CT values in Table 2. These contact times are also reasonable for IWPDs. A chlorine dioxide
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dose of 0.8 mg/L (EPA’s MRDL for chlorine dioxide) results in contact times of 14 - 79 minutes
which are still reasonable for IWPD use. Highly turbid water may require higher CT (i.e., longer
contact time and/or higher dose).
Cryptosporidium Oocysts
Chlorine dioxide appears effective against Cryptosporidium oocysts at CT values achievable by
water systems. Studies show 3-log Cryptosporidium inactivation varied from a CT of 70 mg-
min/L to 400 mg-min/L under various water quality conditions (reference 5). Cryptosporidium
is more resistant than Giardia cysts; up to 8-16 times more resistant (reference 5). Similar to
bacteria, viruses, and other cysts, chlorine dioxide, in general, is more effective against
Cryptosporidium oocysts at higher pHs and higher temperatures (reference 5). However, there is
data suggesting pH has a negligible effect on inactivation of Cryptosporidium (reference 17).
Pursuant to the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), the EPA
proposed chlorine dioxide CT tables for various log inactivations of Cryptosporidium (reference
24) based on studies conducted using low turbidity waters. The proposed CT values for 3-log
Cryptosporidium inactivation are shown in Table 3. These doses are conservative and were
developed using a safety margin to account for variability and uncertainty in the experimental
data (reference 24).
Table 3. EPA Proposed CT Values for 3-Log Inactivation of Cryptosporidium Oocysts
by Chlorine Dioxide for pH 6-9
Temperature (deg C)
1 _ 5 _ H) _ 15 _ 20 _ 25
1830 1286 830 536 347 226
Based on a typical chlorine dioxide dosage of 2.0 mg/L for a water system, contact times of
115-915 minutes (2-15 hours), depending on temperature, are necessary to achieve the CT
values in Table 3. For water systems, these CT values are realistic and achievable at warmer
water temperatures. Higher than typical chlorine dioxide dosages would be necessary for a water
system to achieve the proposed CTs in colder waters (i.e., less than 10° C). Based on this Table,
use of an IWPD would be practical in only wanner waters (i.e., above 10° C). Highly turbid
water may require even higher CT values (i.e., longer contact time and/or higher dose). Chlorine
dioxide is effective against Cryptosporidium oocysts in wanner, low turbidity waters.
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CHLORINE DIOXIDE TOXICITY
Health Effects of Chlorine Dioxide and Chlorite
Chlorine dioxide and its byproducts, chlorite and chlorate ion can result in adverse health effects
when consumed at large enough quantities. The EPA regulates chlorine dioxide and chlorite ion
in drinking water for systems using chlorine dioxide for disinfection. The EPA established a
MRDL of 0.8 mg/L for chlorine dioxide and a maximum contaminant level (MCL) of 1.0 mg/L
for chlorite (reference 25). The most common adverse health effects of chlorine dioxide and
chlorite ion are oxidizing effects seen in the blood, either as methemoglobinemia or hemolytic
anemia (reference 3). Children, infants, and fetuses, a more susceptible subpopulation may
experience adverse neurotoxic effects (reference 26). When a regulated water system using
chlorine dioxide is out of compliance with the chlorine dioxide MRDL or chlorite MCL, the EPA
considers this to have a significant potential to have serious adverse health effects as a result of
short-term exposure (reference 27). However, the short-term adverse health effects are limited to
children, infants, and fetuses. It is these groups that may be susceptible to adverse nervous
system effects from short-term exposure (reference 27). Health effect data for healthy adults
appear to indicate that short-term exposure does not result in adverse health effects. Several
clinical studies assessing the acute and subchronic effects of chlorine dioxide, chlorite, and
chlorate have been conducted (reference 3). Healthy adults consuming 2.5 mg daily of either
chlorine dioxide, chlorite, or chlorate for 12 weeks showed no clinically significant adverse
health effects (reference 3). Another study had healthy adults consuming 0.1 to 24 mg/L
concentrations of either chlorine dioxide, chlorite, or chlorate daily for 3 weeks, again resulting
in no clinically significant adverse health effects. Based on this information, it is not likely that
healthy adults consuming water containing chlorine dioxide concentrations recommended by
IWPD manufacturers (0.7 - 7.5 mg/L) for a short duration (e.g. ,<3 weeks) would experience
any adverse health effects from ingestion of chlorine dioxide, chlorite, or chlorate. However,
adverse health effects could occur if higher chlorine dioxide dosages are used for treating highly
turbid and/or colder water to kill Cryptosporidium. To avoid potential adverse health effects,
longer contact times should be used in place of higher chlorine dioxide dosages, provided
sufficient chlorine dioxide remains after oxidizing organic matter.
Health Concerns of Stabilized Chlorine Dioxide
The use of “stabilized chlorine dioxide” products for IWPD use may expose the user to
significant chlorite concentrations. The “activation” of stabilized chlorine dioxide (i.e., sodium
chlorite) with an acid can result in high levels of chlorite remaining after activation and relatively
low chlorine dioxide concentrations compared to typical chlorine dioxide generating systems
(reference 3). Use of these products may result in the direct application of several hundred mg/L
of chlorite to the water, much higher than typical drinking water chlorite levels (reference 3).
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CONCLUSIONS
Chlorine dioxide as an IWPD can be effective against bacteria, viruses, Giardia cysts, and to a
limited extent, Cryptosporidium oocysts. Very high CT values are estimated for a 3-log
Cryptosporidium inactivation in colder waters, requiring very high chlorine dioxide dosages
and/or very long contact times. Colder temperatures, lower pHs, and higher turbidity all tend to
have an adverse effect on disinfection capability. Health concerns of ingesting chlorine dioxide
and chlorite ion are likely minimal for healthy adults over a short-term duration (e.g. ,<3 weeks)
for IWPD manufacturer-recommended chlorine dioxide dosages of 0.7 - 7.5 mg/L. However,
adverse health effects could occur if higher chlorine dioxide dosages are used for treating highly
turbid and/or colder water to kill Cryptosporidium. To avoid potential adverse health effects,
longer contact times should be used in place of higher chlorine dioxide dosages, provided
sufficient chlorine dioxide remains after oxidizing organic matter. IWPDs using “stabilized
chlorine dioxide” may result in exposure to high levels of chlorite. Table 4 provides a summary
of chlorine dioxide’s disinfection capabilities.
Table 4. Chlorine Dioxide Disinfection Capabilities
Parameter
Chlorine Dioxide Disinfection
General Disinfection
Capability
Cysts most resistant. Achieving cyst inactivation will
ensure adequate bacteria and virus inactivation.
Disinfection capability generally follows:
Bacteria > viruses > Giardia > Cryptosporidium
Bacteria
Effective at reasonable CT values for IWPD use
Viruses
Effective at reasonable CT values for IWPD use. Use EPA
SWTR CT table for recommended CT values (Table 1).
Giardia Cysts
Effective at reasonable CT values for IWPD use. Use EPA
SWTR CT table for recommended CT values (Table 2).
Cryptosporidium Oocysts
Effective at high CT values. Use Table 3 as guide for CT
values. If possible, use longer contact times instead of
higher dosages to achieve adequate CT values.
Effect of Temperature
Colder water temperatures require higher CT values. Use a
two-fold increase in CT for every 10° C decrease. Use
longer contact time instead of higher dosages to achieve
higher CT values.
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Effect of pH
Effective over typical pH levels for raw, untreated natural
waters. Disinfection capability generally increases with
increasing pH.
Effect of Turbidity
Higher turbidity generally reduces disinfection capability.
Use longer contact time instead of higher dosages in more
turbid waters to achieve CT values. Higher dosages may be
necessary to ensure chlorine dioxide remains after oxidation
of organic matter.
Health Effects
Chlorine dioxide and chlorite are potential health concerns.
IWPD manufacturer-recommended dosages are not likely
to cause adverse health effects for healthy adults. Exposure
to much higher chlorite concentrations may occur when
using stabilized chlorine dioxide products.
PREPARED BY: Steven H. Clarke, Environmental Engineer
DATED: March 2006
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APPENDIX A
REFERENCES
1. U.S. Environmental Protection Agency (EPA), Registration Division Office of Pesticide
Program, Criteria and Standards Division Office of Drinking Water, 1987. Guide Standard and
Protocol for Testing Microbiological Water Purifiers. Washington, D.C.
2. Aieta, E.M., & Berg, J.D., 1986. A Review of Chlorine Dioxide in Drinking Water
Treatment. Journal of the American Water Works Association (AWWA), 78(6), 62-72.
3. Gates, D., 1998. The Chlorine Dioxide Handbook Water Disinfection Series. AWWA,
Denver, CO.
4. EPA Office of Research and Development, 2001. Controlling Disinfection By-Products and
Microbial Contaminants in Drinking Water. (EPA/600/R-01/1 10). Washington, D.C.
5. EPA Office of Water, 1999. Alternative Disinfectants and Oxidants Guidance Manual.
(EPA 815-R-99-014). Washington, D.C.
6. Myhrstad, J.A. & Samdal, J.E., 1969. Behavior and Determination of Chlorine Dioxide.
Journal of the AWWA, 61(4), 205-208.
7. Disinfection Technology, Inc. Directions for Use. XINIX AquaCare Water Disinfectant.
La Jolla, CA.
8. Katadyn Products, Inc. Directions for Use. Micropur MP 1 Emergency Drinking Water
Tablets. Minneapolis, MN.
9. Olsen, N., et. al. The Use of Chlorine Dioxide in Potato Storage. (Bulletin 825). University
of Idaho, College of Agriculture.
10. Technical Advisory Committee on Safe Drinking Water, 2004. Environmental Public
Health Field Manual for Private, Public and Communal Drinking Water Systems in Alberta,
2nd ed. Canada Institute of Public Health Inspectors (Alberta Branch).
11. Noss, C.I., & Olivieri, V.P., 1985. Disinfecting Capabilities of Oxychlorine Compounds.
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13. National Academy of Sciences, 1980. Drinking Water and Health Vol. 2. National
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Research, 37, 2773-2783.
18. Auerbach, P.S., 1995. Wilderness Medicine Management of Wilderness and Environmental
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Branch, 1991. Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources. Washington, D.C.
20. Scarpino, P.V., Cronier, S., Zink, M.L., & Brigano, F.A.O., 1977. Effect of Particulates on
Disinfection of Enteroviruses and Coliform Bacteria in Water by Chlorine Dioxide. Water-
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Chlorine Dioxide as a Bactericide. Applied Microbiology, 13(5), 776-780.
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26. Federal Register, 1997. National Primary Drinking Water Regulations: Disinfectants and
Disinfection By-products; Notice of Data Availability; Proposed Rule. 62(212), 59387-59484.
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28. Crittenden, J.C. et. al., 2005. Water Treatment: Principles and Design Second Edition.
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