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CASRN: 7758192

Update: May 2004

Current Massachusetts Regulatory Limit
MMCL = 1 mg/L. ORS has adopted the MCL published by the U.S. EPA in its Disinfectants and Disinfection Byproducts Rule (Federal Register, December 16, 1998 – Volume 63, Number 241). 

Federal Regulatory Limit
Under its Disinfectants and Disinfection Byproducts Rule (Federal Register, December 16, 1998 - Volume 63, Number 241), U.S. EPA set the MCLG for chlorite at 0.8 mg/L. The MCL was set at 1.0 mg/L based on feasibility. 1.0 mg/L is the lowest level considered practically achievable by typical systems using chlorine dioxide, from both treatment and monitoring perspectives. 

Basis for Criteria

Because chlorine dioxide is rapidly reduced to chlorite, U.S. EPA believes that data on chlorite are relevant to assessing the risks of chlorine dioxide. U.S. EPA has set an MCLG for chlorite of 0.8 mg/L based on the assumption that a 70 kg adult ingests 2 L/day of water. Since most exposure to chlorite is likely to come from ingestion of drinking water, a relative source contribution factor of 0.8 is applied to this value.

RfD oral = 0.03 mg/kg/day (U.S. EPA, 2000)
UF: 100 (10 = interspecies; 10 = intraspecies)
MF: 1
Confidence in RfD: Medium to High

The MCLG was derived using the following equation:
MCLG = 0.03 mg/kg/day x 70 kg/2 L/day x 0.8 = 0.8 mg/L

Critical Effects
Numerous animal studies have examined neurodevelopmental toxicity of chlorite. These studies consistently show a LOAEL of 14 mg/kg-day and NOAEL of 3 mg/kg-day for multiple neurodevelopmental endpoints (CMA, 1996; U.S. EPA, 2000). 

Cancer Assessment
Data are inadequate for assessment of human carcinogenic potential.

U.S. EPA believes that the available cancer epidemiological data provides important information that contributes towards the weight-of-evidence evaluation of the potential health risks associated with chlorinated drinking water. However, U.S. EPA does not believe at this time that the cancer studies are sufficient to establish a causal relationship between exposure to chlorinated drinking water and cancer. 

disinfectant byproduct

Analytical Information

Analytical Methods
U.S. EPA Methods 300.0 and 300.1

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at

Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:

Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at

RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

CMA (Chemical Manufacturers Association). 1996. Sodium chlorite: drinking water rat two-generation reproductive toxicity study. Quintiles Report Ref. CMA/17/96.

Federal Register. December 16, 1998. Part IV. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142. National Primary Drinking Water Regulations: Disinfectants and Disinfection Byproducts; Final Rule. (63 FR 69391).

U.S. EPA (U.S. Environmental Protection Agency). October 10, 2000. Integrated Risk Information System (IRIS). Washington, D.C.