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SILVEX (2,4,5-TP) ((2,4,5-Trichlorophenoxy)Propionic Acid)
CASRN: 93721

Update: March 1996

Current Massachusetts Regulatory Limit
MMCL = 0.05 mg/L. ORS has adopted the MCL published by the U.S. EPA.

Federal Regulatory Limit
The MCL for silvex is equal to its MCLG of 0.05 mg/L.

Basis for Criteria
The MCLG is derived based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of drinking water. A relative source contribution factor of 20% is incorporated into the final value.

RfD: 7 x 10-3 mg/kg/day
UF: 100 (10 = intraspecies; 10 = interspecies) MF: 1

Critical Effects
The RfD is based on a two-year dog feeding study from which a NOAEL of 0.75 mg/kg/day in the diet was reported (Mullison, 1966; Gehring and Betso, 1978). Histopathological changes in the liver were noted at higher doses.

Cancer Assessment: D
Human data are not available and the available animal cancer bioassay studies are considered to be inadequate. Thus, U.S. EPA has determined that silvex is non-classifiable as to human carcinogenicity.

Phenoxy Pesticide

Analytical Information
: 0.005 mg/L

Analytical Methods
U.S. EPA 515.1; Electron capture/GC

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.

Federal Register. November 13, 1985. Part IV. Environmental Protection Agency. 40 CFR Part 141. National Primary Drinking Water Regulations: Synthetic Organic Chemicals, Inorganic Chemicals and Microorganisms; Proposed Rule. (50 FR 46936).

Federal Register. May 22, 1989. Part II. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary and Secondary Drinking Water Regulations; Proposed Rule. (54 FR 22062).

Federal Register. January 30, 1991. Part II. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary Drinking Water Regulations; Final Rule. (56 FR 3526).

Gehring, P.J. and J.E. Betso. 1978. Phenoxy acids: Effects and fate in mammals. In: Chlorinated Phenoxy Acids and Their Dioxins. v. 27c. Ramuel Ed. Ecol. Bill. Stockholm. P. 122-133.

Mullison, W.R. 1966. Some toxicological aspects to silvex. In: 19th Ann. Meet., Southern Weed Science Society. Raleigh, NC. p. 420-435.