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CYANIDE (as free cyanide)
CASRN: 57125

Update: May 2004

Current Massachusetts Regulatory Limit
MMCL = 0.2 mg/L. ORS has adopted the MCL published by the U.S. EPA (55 FR 30370; 7/25/91).

Federal Regulatory Limit
The MCL is equal to the MCLG of 0.2 mg/L.

Basis for Criteria

The MCLG is based on the potential for adverse health effects as demonstrated in rat studies. The MCLG assumes that a 70 kg adult ingests 2 L/day of water and incorporates a relative source contribution factor of 0.2.

RfD: 2 x 10-2 mg/kg/day (RfD for hydrogen cyanide)
UF: 100 (10 = intraspecies; 10 = interspecies)
MF: 5 Confidence in RfD: medium

A modifying factor of 5 is used to account for the apparent tolerance to cyanide when it is ingested with food rather than in water.

Critical Effects
In a two-year study, cyanide was administered to rats in feed that had been fumigated with HCN. No treatment related effects on growth rate, no gross signs of toxicity, and no histopathologic lesions were seen (Howard and Hanzal, 1955). In another rat study, decreased weight gain and thyroxin levels as well as myelin degeneration in rats was noted at 30 mg/kg/day (Philbrick et al., 1979). Other chronic studies identified either used the subcutaneous route or had higher effect levels. The Howard and Hanzal and the Philbrick rat studies were used to identify a LOAEL of 30 mg/kg/d and a NOAEL of 10.8 mg/kg/day. The RfD (of 0.022 mg/kg/day) was derived based on the NOAEL of 10.8 mg/kg/day.

Cancer Assessment: 
Data are Inadequate for the Assessment of Human Carcinogenic Potential/D

There are not enough available data upon which to classify the carcinogen potential of cyanide.

inorganic; nitrile

Analytical Information
Analytical Methods
335.2; distillation titrimetric
335.3; distillation, automated
spectrometric others

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 US EPA Drinking Water Analytical Methods .

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 US EPA Current Drinking Water Health Advisories .

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.

Howard, J.W., and Hanzal, R.F. 1955. Chronic toxicity for rats of food treated with hydrogen cyanide. Agric. Food Chem. 3:325-329.

Philbrick, D.J., Hopkins, J.B., Hill, D.C., Alexander, J.C. and Thomson, J.C. 1979. Effects of prolonged cyanide and thiocyanate feeding in rats. J. Toxicol. Environ. Health. 5: 579-592.