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STYRENE
CASRN: 100425

Update: March 1996

Current Massachusetts Regulatory Limit
MMCL: 0.1 mg/L. ORS has adopted the MCL published by the U.S. EPA 56 FR 3526 (1/30/91).

Federal Regulatory Limit
The MCL for styrene is equal to its MCLG of 0.1 mg/L. A secondary MCL of 0.01 mg/L has been proposed (45 FR 22062; 56 FR 3526).

Basis for Criteria
The MCLG is based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of drinking water. The MCLG incorporates a relative source contribution factor of 20% and a 10-fold uncertainty factor to account for potential carcinogenicity.

RfD: 2 x 10-1 mg/kg/day
UF: 1000 (10 = interspecies; 10 = intraspecies; 10 = subchronic to chronic)
MF: 1

Critical Effects
The RfD for styrene is based on a subchronic study by Quast et al., (1979) where beagle dogs were exposed to styrene by gavage at 0, 200, 400 or 600 mg/kg/d in peanut oil 7 days per week for up to 561 days. The effects included red blood cell and liver effects. A NOAEL of 200 mg/kg/d was determined from this study.

Cancer Assessment: The current cancer status of styrene is currently under review by U.S. EPA and the Scientific Advisory Board (SAB). For more information - refer to discussion in May 1989 Fed. Reg. Vol. 54, No. 97 and January 30, 1991 Fed. Reg. Vol. 56, No. 20.

U.S. EPA presented arguments to the SAB that styrene should be designated a B2 carcinogen whereas the SAB maintained that the weight of evidence for styrene only supports a group C classification under the U.S. EPA's classification system. The evidence for styrene is based on upon several positive animal studies via inhalation that are limited due to poor survival of the animals. There is currently no adequately conducted drinking water study for styrene.

Class
VOC

Analytical Information
PQL
: 0.005 mg/L

Analytical Methods
U.S. EPA Methods 503.1, 524.2

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 http://www.epa.gov/safewater/methods/methods.html.

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 http://www.epa.gov/waterscience/drinking/standards/dwstandards.pdf.

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 http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

References
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).

Quast, J.F., C. A. Humiston, R.Y. Kalmins, et. al. 1979. Results of a toxicity study of monomeric styrene administered to beagle dogs by oral intubation for 19 months. Toxicology Research Laboratory, Health and Environmental Sciences, Dow Chemical Co., Midland, MI. Final Report.